Revision as of 03:09, 5 August 2012

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

• WP:RD/S

Main page: Help searching Misplaced Pages

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

How do I answer a question?

Main page: Misplaced Pages:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

• Teahouse
• Help desk
• Village pump
• Help manual

August 1

Blood relations

i was marry with my mothers elder brothers daughter <request for medical advice removed> are we first cousins or second cousins? — Preceding unsigned comment added by Nalaka88 (talk • contribs) 06:40, 1 August 2012 (UTC)

We cannot give medical advice, so it would be best for you to seek guidance from a medical professional. Evanh2008 06:43, 1 August 2012 (UTC)

Please see our medical disclaimer. BigNate37_(T) 06:48, 1 August 2012 (UTC)

We can answer the non-medical question. Your father in law also being your uncle makes you and your wife first cousins. See Cousin#Basic_definitions. 203.27.72.5 (talk) 08:31, 1 August 2012 (UTC)

While we can't give medical advice, I can give you a link to Cousin marriage#Biological aspects. If you wish to know how that information relates to you, then you'll need to speak to a doctor or genetic counsellor. --Tango (talk) 11:47, 1 August 2012 (UTC)

This is far more a political or cultural issue than a medical one. A small detail not mentioned in the cousin marriage article is that in the traditionally more widely favored cross cousin arrangement, which this exemplifies, one greatgrandfather contributes his X to a daughter and his Y to a son, the third generation (opposite sexes of either variety) then marry; in this case no part of the greatgrandfather's X can meet up with itself in the fourth generation. (Of course, recessive sex-linked traits only matter to women anyway) Wnt (talk) 14:23, 1 August 2012 (UTC)

Chromosomes don't stay together. See chromosomal crossover. Also, you are ignoring all the non-sex chromosomes. --Tango (talk) 23:01, 1 August 2012 (UTC)

Vitamin C in raw meat

Where does the vitamin C in raw meat come from? Madifrop (talk) 15:43, 1 August 2012 (UTC)

From the animal's food of course. Roger (talk) 15:48, 1 August 2012 (UTC)

(ec) Most animals can produce vitamin C in their bodies (see Vitamin C), and of course animals can also gain vitamin C from their food, as we humans do. - Lindert (talk) 15:49, 1 August 2012 (UTC)

The ability to synthesize Vitamin C, a rather simple compound with a similar chemical structure to glucose, was lost in the ancestry of the haplorrhines, the primate group including the monkeys, apes, and tarsiers. This was possible because these animals received enough ascorbic acid in their diets (from fruits like figs), that they did not need to synthesize it, so losing the gene for the enzyme that catalysed its synthesis was no handicap. μηδείς (talk) 03:03, 2 August 2012 (UTC)

Shovel-shaped incisors

Why were Shovel-shaped incisors developed in humans and why are they prevalent in the Mongoloid races? What do people with non Shovel-shaped incisors have instead? Reticuli88 (talk) 15:57, 1 August 2012 (UTC)

According to , the crown shapes of maxillary central incisors in Caucasians is ovoid, square, or triangular. StuRat (talk) 21:58, 1 August 2012 (UTC)

See Sinodonty and Sundadonty. Dental patterns in humans go from generalized to specialized. "Proto-Sundadonty" is believed to be the ancestral dental pattern of all late Pleistocene human populations. Isolated populations that underwent the least amount of genetic drift like the Ainu, the prehistoric Jomon, modern Papua New Guineans, and Australian Aborigines still resemble Proto-Sundadonts closely. Dental patterns of South Asians, Indochinese, Austronesians, southern Chinese, Arctic Native Americans (Aleut, Inuit, etc.), and some other Native Americans are predominantly the less generalized Sundadont dental pattern (which do not exhibit shoveled incisors). Not sure about modern European, western and central Asian, and African dental patterns, but I think they are also generalized and resemble Sundadonty. On the other hand, East Asians, Northeast Siberians, and the rest of the Native Americans who underwent the most amount of genetic drift from the original human migrants out of Africa are predominantly the more derived Sinodonts. There is no whys about it, though.-- OBSIDIAN†SOUL 23:47, 1 August 2012 (UTC)

Extracting multiple regression lines from a single data set

I was inspired by the discussion here on how to extract nonlinear order from chaos in seemingly random time series such as the logistic map by using something called a "(Poincare) return map" (a little different from the Poincare map described here on Misplaced Pages). I used the same idea to look at the time series variables of my Drosophila, where I had tracked things like velocity, acceleration, angular velocity, etc.

I've shown two examples of the return maps I have gotten for all my Drosophila populations (more or less in the same form) to the right, though the acceleration plots and the velocity plots are from different populations. These are just examples of the plots I'm getting-- all the velocity and acceleration plots have the same basic form as these plots, although slopes and spread/distribution might differ.

I created the return maps by plotting f(t+1) on the y-axis versus f(t) on the x-axis, where f is either velocity or acceleration as appropriate. (The time difference between time t and t+1 is 1/15 of a second, i.e. time-series measurements are sampled at 15 Hz.) It reveals intriguing semidiscrete stochastic decision-making on the part of Drosophila, but how do I even statistically analyse the multiple trendlines, especially so I can detect differences between genetically-different populations? My normal approach (line/curve fitting) is useless here. I think extracting things like slopes, angle difference (maybe as a function of probability), spread from the trendlines but I wouldn't know how to begin. Can someone introduce me to "multiple trendline" analysis methods? (How would you pick out the main sequence from a Hertzsprung-Russell diagram for example?) Nothing gold can stay (talk) 21:28, 1 August 2012 (UTC)

"It reveals intriguing semidiscrete stochastic decision-making on the part of Drosophila..." ... or, it reveals aliasing due to quantization noise. You're sampling a continuous trajectory; your resolution in time is band-limited by your video frame-rate; and your samples in space are band-limited by your camera's optical/digital resolution (number of millimeters per pixel). You're aliasing like crazy in three dimensions! (x,y, and t). All data derived from the measurements should be carefully processed to avoid creating spurious signals. But, if you're certain that you believe these charts, and simply want to fit equations to the scatter-plots, you should start by reading Statistical classification. There are many different types of classifier algorithms; these types of mathematical algorithms can be used to distinguish one "blob" from another "blob" in a scatter-plot or a point-cloud. Once you separate the data into separate "blobs," (rather, "once you classify the data into disjoint sets"), you can fit a linear equation, or any other sort of statistical parameterization, for each set. Nimur (talk) 21:40, 1 August 2012 (UTC)

However I observe the discretization only happens at fast speeds or fast accelerations, where the fly moves or accelerates a lot between frames. If it was due to quantization noise, you would expect the quantization to increase as speed or acceleration decreased. If the fly is moving or accelerating quickly, there is a greater spectrum of values that it could "land" on. My spatial resolution is roughly ~6.3 pixels per mm and temporal resolution at 15 Hz, thus my velocity resolution is at least 2.4 mm/s and acceleration resolution at least 36 mm/s^2. Nothing gold can stay (talk) 22:19, 1 August 2012 (UTC)

...You're not making a very convincing case. You've computed the derivative numerically, correct? Are you familiar with the noise problem introduced by applying the finite difference operator to approximate the derivative? In other words, solving for velocity v(t) by computing the difference in position x(t+1) - x(t) is a very great way to amplify noise and amplify the error in your measurement. You don't think it's a strange coincidence that the data seems clustered around a line with slope of 1/2, 1, and 2? What you're proposing is that statistically, a fly who is buzzing around at 42.5mm/s for 1/15 of a second is very likely to decide that during the next 1/15 second, it should fly at 21.25 mm/s. This doesn't strike you as a procedural error? Nimur (talk) 23:52, 1 August 2012 (UTC)

I have a good reason to suspect my tracking problem superlocalises so the resolution is in fact better than 2.4 mm/s. I don't think it's that likely to jump from 42.5 to 21.25 mm/s because the biggest steps would be in 2.4 mm/s, if not smaller. I do note that separation increases as a function of speed/acceleration. Also, I would think error in measurement in one frame is unlikely to propagate to another because the video samples at every frame and doesn't do any sort of dead reckoning. Correct me if I'm wrong? Nothing gold can stay (talk) 00:08, 2 August 2012 (UTC)

(Also, for both aesthetic and scientific reasons, may I suggest that you use squared axes when plotting velocity-vs-velocity, or any other case when you create a scatter-plot of dimensionally-identical quantities? It helps make the interpretation easier. If you used MATLAB to create the plots, use axis equal. Nimur (talk) 21:51, 1 August 2012 (UTC)

As far as writing a program to handle the top graph, it should only compute distance from each line to those points closer to that line than the other two. You would have to specify that it needs to look for 3 lines, though. You could expect such a program to take far longer to run than if you manually separated the data into 3 blobs. StuRat (talk) 22:05, 1 August 2012 (UTC)

Okay, but how would it find the lines once I've specified the number of lines? Nothing gold can stay (talk) 22:32, 1 August 2012 (UTC)

It would initially place all the lines, say, along the X axis, then use a hill-climbing method to change the angle and elevation of each line, until it found the best location for each. If you could specify an initial guess for the placement of each line, that would certainly speed things up. If you can provide a CSV file with the data in that top graph, I could take a shot at writing a program for it. StuRat (talk) 22:49, 1 August 2012 (UTC)

Thanks a lot for your offer! :) I'll see if I can package it online. Maybe I'll upload it to my university web page. Nothing gold can stay (talk) 00:08, 2 August 2012 (UTC)

(update) Okay, I have my csv files at http://people.virginia.edu/~jrs5fg/returnvelo.csv and http://people.virginia.edu/~jrs5fg/returnaccel.csv; they both correspond to the same raw experimental data set. Basically, there are two columns in each file, the first being f(t) and the second being f(t+1). Nothing gold can stay (talk) 03:58, 2 August 2012 (UTC)

StuRat, that will only work if you're planning to fit the data to a strictly convex model. "Hill climbing" algorithms also have a nasty tendency of finding numerical instabilities and local minima. Do you know the characteristics of this data-set inside and out? Are you an expert in the field of trajectory modeling in drosophila? If so, why don't you offer up some reliable sources for best practices and techniques? And if you aren't... that's why we don't offer to conduct research. I think our O.P. ought to get in touch with their P.I. for a little more guidance and direction. Nimur (talk) 23:43, 1 August 2012 (UTC)

Geez, what's with the vitriol ? I just offered to curve fit a graph, and it shouldn't matter what the data is. It's up to the researcher to decide what it means, not the curve fitting program, or programmer. Hill-climbing doesn't always work, but, looking at the top graph, hill climbing should work fairly well here, and is likely the only option that could fit this amount of data with three lines in a reasonable time frame. The only problem I see is where the data overlaps, but I don't see any solution for that problem. I'd restrict the curve fitting to the point where the data diverges. StuRat (talk) 23:56, 1 August 2012 (UTC)

The No Original Research policy applies to Misplaced Pages articles. This is not an article, it's a Ref Desk question. What on earth is wrong with an answer that contains original research, significant research even, as well as just a simple calculation or graph, if the provider of the articles is happy to do provide it? Doing so may mean that the poster gets no official credit, but that's his problem. The NOR policy is appropriate to WP articles, as they comprise an encyclopedia (=collection of known facts), but here the sole criteria should be does it help the OP? As with any sort of answer on Ref Desk, it is up to the OP to assess the merits of any OR provided Wickwack120.145.176.119 (talk) 00:52, 2 August 2012 (UTC)

I'm exhausting all available options here-- I've contacted other people in my department but they are away teaching at a mountain lake this summer, so I'm trying other options. Also my PI says I have to seek outside help to solve my problem, because he doesn't know the techniques to solve this problem himself. Nothing gold can stay (talk) 00:08, 2 August 2012 (UTC)

Just curious, do drosophila have three different modes of locomotion, like a horse has a trot, gallop, etc. ? StuRat (talk) 00:14, 2 August 2012 (UTC)

I don't think so...? (I haven't heard of it, at least...) From other papers I've seen where they looked at behavior through return maps, discrete locomotion behaviors (trot, gallop, etc.) would correspond to spherical'ish clusters on a return map, not lines. i.e. at f(t) there would be discrete clusters a, b, c ... (corresponding to the different velocity modes), and at f(t+1) a, b, c, and the return map would simply imply switching between discrete modes. This is opposed to the lines bx +c... also if measured velocity was in fact discretised, wouldn't the return map break up into such clusters? Instead, the lines are fairly continuous. Nothing gold can stay (talk) 00:30, 2 August 2012 (UTC)

Did you choose 1/15th of a second because that's the time frame that makes the lines have slopes of .5, 1 and 2, or did it just work out that way the first time you plugged in the data? It just seems incredibly suspicious to me. I showed your graph to my own lab's tracking expert, and he simply refused to believe the lines are real. Someguy1221 (talk) 00:36, 2 August 2012 (UTC)

It's 1/15 second because it seems to be the maximum sampling rate from VirtualDub (I can't seem to change it, I think my camera is capable of 1/29.97). Also I believe the slopes are closer to 0.4, 1 and 2.5....what's so suspicious about the lines? Again the structure of the return map suggests possible velocity is continuous, not discrete, just that change in velocity can follow three modes, and once the fly has "chosen" a mode, there is wide continuum within that mode in which to choose. Also, why is everyone ignoring the acceleration graph? Acceleration ranges from -500 to 500 mm/s^2 (and the resolution would be at least 36 mm/s^2). When a fly is at 0 mm/s, its pdf for the next frame ranges from 0 to 500 mm/s^2-- once such a positive acceleration is chosen in that frame, a negative acceleration is likely in the frame after that, proportional to the positive acceleration "chosen". And once a negative acceleration is chosen, there is a tendency to return to zero acceleration in the next next frame. Thus, a fly's acceleration plot wanders all over from -500 to 500 mm/s^2 over time, in a seemingly random fashion. If the plots suffered from quantization error I would expect the acceleration return map (as well as the velocity return map) to look a lot different, breaking up into clusters rather than lines. Can someone check my logic? Nothing gold can stay (talk) 00:45, 2 August 2012 (UTC)

A note on using both return maps together

Suppose a fly is at 30 mm/s at t=1. It has a good chance of decreasing around 10 mm/s in the next (1/15) second. Then its acceleration will be (v2 - v1) * 15 fps = -300 mm/s^2 at t=2. But according to the acceleration return map it's likely that acceleration will now go to zero in the next frame +/- 50 mm/s^2 (velocity would increase or decrease 3 mm/s max) at t=3, so we can deduce that velocity will most likely remain around 10 (+/- 3) mm/s at t=3.

But now that acceleration is close to zero, it will most likely choose acceleration values anywhere from 0 to 500 mm/s^2, so it would prefer one of the two modes (increasing or maintaining velocity) but not the decreasing velocity mode, such that velocity will be anywhere from 7 to 43 mm/s at t=4, but not below that, even though the velocity return map would allow for values between 0 to 7 mm/s otherwise. At t=5, it is likely the fly will decelerate (according to the acceleration return map, because it just accelerated) proportional to the acceleration chosen-- this locks out the increasing-velocity mode -- but because v can be anywhere from 7 to 43 mm/s (roughly) and acceleration anywhere from 0 to 500 mm/s^2 at t=5, we can't deduce much about t=6. (The acceleration return map cuts off because of how I cropped it but the lines reach +/- 500 mm/s^2.)

Of course, if v=30 mm/s at t=1, it's v could also be 30 or 60 mm/s at t=2 (with less probability), going into loops that will be broken by drift. Walkthrough: If velocity stays the same (at 30 mm/s) at t=2, acceleration is zero at t=2, so it will likely accelerate at t=3, in which case the velocity return map indicates ~60 mm/s^2, in which case acceleration will be roughly +450 mm/s^2 at t=3. But then acceleration will likely be -450 mm/s^2 at t=4 (note it does not have a good chance of accelerating or staying at the same velocity, which you would expect if the discretization was due to quantization error) so it will go back to 30 mm/s^2 at t=4. But this implies (according to the acceleration return map) that acceleration is zero at t=5, i.e. at t=5 v is 30 mm/s^2 with acceleration at t=6 being anywhere from 0 to 500 mm/s^2, but with a bias to accelerate it at +450 mm/s^2 towards 60 mm/s at t=6 for the cycle to begin again. (Stochastic drift, or chance of being an outlier, allows the fly to escape this cycle.) But, if v = 60 mm/s at t=2, then a = ~+450 mm/s^2 at t=2, which means a ~= -450 mm/s^2 and v ~= 30 mm/s at t=3, a ~= 0 mm/s^2 and v ~= ~30 mm/s at t=4 and v = 60 mm/s and a = 450 mm/s^2 at t=5 -- another short-term loop which will be broken by drift.

This is just for v = 30 mm/s at t=1 -- I haven't even gone through the deduction process for other values yet. If the discrete divergence of modes were simply due to quantization, these implied cycles wouldn't exist and you would see more than one preferred "next acceleration" for a given current acceleration at time t. (t+1 acceleration varies the most when acceleration is zero at time t.) Using the info from both plots, we can see sometimes one can "eliminate" one or two other modes from consideration in deciding behavior at the next step. I don't think I would be able to deduce this much information if the discrete modes were due simply to quantization error. Again, I think I would get clusters rather than continuous lines. Nothing gold can stay (talk) 01:48, 2 August 2012 (UTC)

I find it intriguing that no other contributor (at the science desk!) except Nimur points out that this data doesn't make sense (biologically) and looks like a clear example of measurement and/or processing artifacts. What do you suggest as interpretation of your data? Drosophila has somehow only three modes of acceleration? And nobody noticed before? Do you have some kind of control experiment? That tests that your equipment and your analysis pipeline is really able to measure what you want? I would bet that a control experiment with some light point in random motion (or some other insect/small animal, which could be easier to arrange) captured the same way would give the exact same "split" of data points. And I think this is the way to proceed, if you ever want to publish this data in some form. Is there something comparable already published in your field? Or did you set up the method yourself? It would perhaps be helpful to look how others have setup their measurement and analysis. Sorry for my harsh tone, but I really think the RefDesk Science could do better in such a central question as measuring artifacts, so I find it important to bring my point across. --TheMaster17 (talk) 09:11, 2 August 2012 (UTC)

Another important point concerning your expectation of cycles because of quantization is that you are dealing here with quantization in every single measured variable (x,y and t). It is not trivial to extrapolate what kind of artifacts you get when quantization errors have an effect on each other and on your derived values, such as v and a here. Circles are definitive not the shapes I would expect. --TheMaster17 (talk) 09:16, 2 August 2012 (UTC)

Do you know how return maps work? It is not that hard to conjecture what happens because the effect of noise and discretization on return maps has been studied. Please not that velocity or acceleration is not confined to discrete points. You seem to make this mistake a lot. At each point t, there seems to be 3 choices (sometimes less-- possibly two or one , due to the patterns implied, which likely wouldn't happen with discretization), but each choice has a certain element of drift and randomness in it, and the output velocity or acceleration is dependent on this choice and the previous velocity or acceleration. Even if there were no stochastic noise at all, very chaotic behavior can arise from very determined behavior -- see the logistic map, in which determined equations make a function wander all over the place. People haven't also answered my question at why discretization would separate modes most at fast accelerations and speeds, rather than slow ones. Nothing gold can stay (talk) 11:30, 2 August 2012 (UTC)

But do let me conduct the control experiment. But my goal is not to study this sort of thing, it's simply to find an assay that will differentiate genotypes or drugs. But few people seem to have answered my statistical questions.... Nothing gold can stay (talk) 11:25, 2 August 2012 (UTC)

It is surprising, but we shouldn't reject data out-of hand just because it's not what we expected. For example, the observation that the expansion of the universe is accelerating seemed very odd, at the time, but has since been verified by many others. Perhaps, using a car analogy, they tend to "floor it", "maintain cruising speed", or "slam on the brakes", rarely picking any acceleration in between. While I wouldn't have expected this, it's not exactly shocking. And, if it can be verified by others, this is an interesting observation worth publishing. StuRat (talk) 09:18, 2 August 2012 (UTC)

You are totally right, and I never proposed to just discard the data. But the OP really needs to address some questions if he wants to get a firm interpretation. And coming to your example, exactly for the same reasons the expansion of the universe was only accepted as fact after it was confirmed around the world by different measurements in different groups: to quote Laplace, "The weight of evidence for an extraordinary claim must be proportioned to its strangeness." And I really cannot imagine that this simple setup with camera was never tried by others. I remember, for example, a study about movements of some social insects (ants, bees or termites probably) which plotted routes of them inside the nest, which would probably use a similar setup. Concerning your "it's not exactly shocking" statement, I must admit that I would find it rather shocking when a complex animal like drosophila would only ever have three kinds of acceleration. Even plots of bacteria and other single celled organisms moving through or over medium show a diverse range of speeds and acceleration depending on a broad range of factors, and not just three discrete modes. This is why I wouldn't believe the data just as they are now. With appropriate controls this could change, of course. --TheMaster17 (talk) 09:55, 2 August 2012 (UTC)

Maybe this behavior is limited to drosophila. If so, it would be interesting to isolate the genes which cause it. StuRat (talk) 10:22, 2 August 2012 (UTC)

Dude, possible accelerations are not discrete, they vary continuously. However style of acceleration seems to be discretely dependent on t and the previous acceleration, but the freedom in which to vary is large (for example when previous acceleration (t=1) is zero, acceleration chosen is likely to be anything positive thus ensuring that when t=3, acceleration is likely to be anything negative), plus there is the stochastic randomness in which a fly chooses to "break" the trend or slowly drift away from it. One test to see if this is an artifact of data processing is to freely vary the time lag interval (i.e. t and t+2, etc.) I bet you that at t+5 the correlation would probably disappear. (Let me check this.) From what I see, groups have applied return maps to animal behavior, but generally things like "interval time between rats pressing levers" etc rather than motion. I don't think this is an extraordinary finding. Of course, my PI doesn't think this a thing worth pursuing until it can separate the effects of different drugs or genotypes.

Also, there are very few papers on Drosophila walking-tracking (there are a lot on a fly with clipped wings being held by a force gauge to measure pseudoflight) -- I have consulted other papers doing tracking studies, but they never looked at return maps. Nothing gold can stay (talk) 11:06, 2 August 2012 (UTC)

I can read the plots, that is why I said "discrete modes", not "discrete accelerations". But what you are proposing in your interpretation is that there are only three classes of points in your a and v plots for t and t+1. Why should this be real? What could be the biological cause of this? And I cannot really follow your narrative in your previous explanation. Why should a(t=3) be negative? If the fly is continuously moving (because it accelerated between t=1 and t=3), I would expect it to be around 0 sometime after this, after the animal has picked up velocity and is moving at its preferred speed (depending on the context). What you are proposing is really that the animals are jumping, in steps of 15th of a second, between accelerating and deaccelerating (sometimes no acceleration at all) continuously? This would be really wasteful. Another thing that comes to mind: Did you check that the alignment of your camera pixels does not influence the quantization of the position? You could, for example, get preferential different results for v (and therefore a) if the animal is running along a neat line of pixels, or in diagonal, because the quantization error differs systematically between the two cases. --TheMaster17 (talk) 12:03, 2 August 2012 (UTC)

But there are surely papers of walk-tracking for other insects. Did they ever describe something similar? I would see no reason why drosophila should be different in walking pattern than say, for example, an ant or a bug. And if it is really different, you would still need extraordinary proof for this extraordinary claim (and probably have a hypothesis why it is special). Before you really dive into this, I think you have to check your data and setup. Nothing feels as bad, in my opinion, as to realize after half a year that you hunted an artifact the whole time. Happened to me, too. --TheMaster17 (talk) 12:10, 2 August 2012 (UTC)

And let's not forget the important point that Nimur already mentioned: Using your (already quantized and therefore having a measurement error) x,y differences to compute numerically the first derivative v and then the second derivative a is not the way to go, because you will invariably inflate errors. There really is no reason why the fly should only be able to chose certain classes of velocities and accelerations at t+1 depending on its speed and acceleration at t. A fly has a longer memory than 1/15th of a second, and both speed and acceleration should form a continuum and not split into three classes at high values. --TheMaster17 (talk) 13:02, 2 August 2012 (UTC)

"There really is no reason why the fly should only be able to chose certain classes of velocities and accelerations at t+1 depending on its speed and acceleration at t.". I can easily imagine a cause -- something like a central pattern generator -- different neurons are taking over movement at different points at time. I am going to sample at different points to see how the patterns change.

"This would be really wasteful." Sustained movement is often a cycle. Have you thought about how you run? You accelerate sharply, cruise for a bit, then decelerate. Is that wasteful? The same thing goes with wing flapping.

"But there are surely papers of walk-tracking for other insects." There are not very many using return maps. Drosophila is an important model organism.

I do not expect deviation from other insects. I have used my data to investigate other things like velocity-curvature relationship, and Drosophila appears to be close to the 2/3 power law described for velocity-(radius of curvature) throughout nature, from eye saccades to hand movement. Nothing gold can stay (talk) 14:37, 2 August 2012 (UTC)

Processing data

I took the velocity data you supplied and made my first attempt at dividing it into 3 "blobs". However, as I noted before, we have a problem where the three blobs overlap. It's not a severe problem for the central blob, since presumably an approximately equal number of data points are lost (or gained) at both edges. However, a clear skewing effect is seen at the lower and upper blobs. So, we should drop the data in the region where the overlap occurs. I'll leave it to you to decide how much to drop, but it looks to me like data in the 40 unit range from the origin has this problem. Once you let me know how much data you'd like to drop, I can then provide you with CSV files for the 3 blobs, and you can then run those through your favorite curve fitting application. StuRat (talk) 08:17, 2 August 2012 (UTC)

Wow thanks! Could you provide me with the script perhaps? I have many data plots like this, so it's not the csv file I need. Also, is there a way to weight a probability mapping for points that seem to be "shared" by either blob-- perhaps a point in the middle would have a 50% weighting for one blob and 50% for the other. (Or perhaps a probability function can be used to decide which blob a point should belong to.) Can this technique be applied to the acceleration graph? Acceleration does seem more cleanly separated after all. Nothing gold can stay (talk) 11:11, 2 August 2012 (UTC)

I could assign a probability if we knew the distribution ahead of time, but we don't. For example, if I just said a point midway between two lines has a 50% chance of being in either, I'd likely be wrong. So, I really don't think we can get any useful data out of the place where all three blobs overlap. StuRat (talk) 17:48, 2 August 2012 (UTC)

You would find less statistical skewing if you used an actual classifier algorithm, like I described in my very first post. But, since you're already taking great liberties with data-processing, why not just throw out any subset portion of the data that is statistically destroyed by an intermediate processing step! But seriously, if you're actually planning to pursue this as a topic of research, you've got to identify your methodological error first. Not after you spend a week analyzing invalid results. You're flying at 60 mm/sec down the wrong road here. "Science" is about understanding your data, and its natural causes, not about running an elaborate post-processing algorithm to a point-cloud. Though, if you announce to the world that you've discovered something huge based on a statistical anomaly, only to recant six months later because all you discovered is that you don't know how to operate and interpret your own experimental equipment, you'd be in good company. I've got a recommendation: Proakis and Manilakis, because I think you're missing some fundamentals of elementary signal-processing techniques. And once you've mastered regular signal processing, here's an even more advanced book, available for free online: Statistical Signal Processing. I'd also recommend that you review how your trajectories are generated from your raw data. I'd also look at your raw data. StuRat has called my responses vitriolic, and I apologize. I am not trying to discourage your work; but from over here, what it looks like is that somebody handed you a copy of MATLAB and told you to "use it" to process fly trajectories. They may as well put you in front of a Cray. It is also a very powerful number-crunching machine, but you don't know how to use it. The computer will spit results out, and StuRat can even write a program to color-code them, but... that doesn't mean anything. Nimur (talk) 15:41, 2 August 2012 (UTC)

I agree that the preliminary data needs to be checked for systemic error, but this doesn't necessarily need to be done prior to curve-fitting. Indeed, curve fitting may help to detect some types of systemic error. It could also be used to request better equipment or a colleague's assistance (in the same lab or another), to verify the results. StuRat (talk) 19:29, 2 August 2012 (UTC)

The author of the program I'm using got back to me, and apparently my program does some sort of superlocalising. "Ctrax calculates the position and orientation of flies by fitting ellipses to connected groups of foreground pixels using the spatial moments of each connected component. The precision of this calculation is limited by the bit depth and spatial resolution of the source images, but the relationship isn't straightforward." Nothing gold can stay (talk) 22:31, 2 August 2012 (UTC)

Biological explanation ?

Presumably max acceleration and braking takes more energy than more gradual velocity changes. If this turns out to be real, one possible explanation for having 3 discrete acceleration modes might be preemptive predator evasion. Other flies randomly change direction when flying, whether they detect a predator or not. Perhaps these guys also randomly change acceleration, which certainly would make it difficult to catch them in flight. StuRat (talk) 19:35, 2 August 2012 (UTC)

Flies often do path-finding saccades, because they are constantly trying to explore new territory as well as revisit old ones to make sure they haven't missed anything. The velocity-curvature relationship roughly follows the 2/3 power law. I found that the pattern continues (but gets more noisy) comparing f(t+2) against f(t), f(t+5), and at f(t+10) you can still see the separate arms but they are very fat and short. (Going to upload pictures.) So apparently velocity and acceleration in one frame have a longer-term memory of a dozen or more frames back, which makes sense, because I am sampling at an arbitrary frrequency. Also a reason why I argue against noise is that angular velocity's return map does not break up into discrete lines -- it's a semi-random map with a weak/moderate f(t+1) = -f(t) signal. Nothing gold can stay (talk) 21:45, 2 August 2012 (UTC)

I see that Nimur posted once in the meantime, trying to point you to relevant sources to understand your sampling problem. I just want to give you a simple thought experiment to help you grasp the basic problem of quantization and numerical derivatives: Imagine a point-like fly that is moving in x-direction (skipping y for simplicity) with a velocity of 3 mm/s. Your temporal resolution is 1 s, and your camera+software has "bins" of 5 mm into which it sorts the position of the fly. The point-fly starts at t=0 s at x=0 mm. At t=1 s, it is at x=3 mm, fitting into the first bin. t=2 s, real position is x=6 mm, second bin. t=3 s, real position x=9 mm, still second bin. t=4 s, real position x=12 mm, third bin. If you now look only at the bins, as this is the output you get from the software, you would think the fly stopped between t=2 s and t=3 s, giving you a classical quantization error. Although, in reality, the fly had constant speed and an acceleration of zero, you would, with your method, calculate non-zero acceleration and changing speeds just because of the way your detection algorithm works. Granted, this example is very simplified, but I just wanted to give you a start for thinking. In your real dataset, you have quantization of every measurement (x,y,t), plus unknown interactions with the software that computes the detected position from the pixel-positions (as I mentioned: does it make a difference if a fly runs diagonal to the pixel grid? Did I understand correctly that the sampling rate of your software is different than the sampling rate of your camera?), followed by the calculation of numerical derivatives from the already error-prone measurements. All those error sources could amplify each other, and without systematic testing for that it is impossible to give a proper interpretation of what is real and what is noise. --TheMaster17 (talk) 07:41, 3 August 2012 (UTC)

No the sampling rate of my software is whatever the sampling rate of the video is. Also the spatial resolution of 5 mm in your example is pretty bad (my spatial resolution is at least 0.2mm, superlocalising brings this down to 0.1 mm or 0.05mm although this is a complicated relationship). Also note that my data doesn't have obvious bins. The spatial resolution appears to be pretty high, if you actually looked at my data. Have you looked at the spatial resolution on the axes? Nothing gold can stay (talk) 15:03, 3 August 2012 (UTC)

The spatial resolution of your axes tells you nothing about the real resolution of your data. It may be a hint, but this depends entirely on the software and formatting you use. And as I said, my example is extremely simplified. But you can put arbitrarily small values into my example and would still get numerical pseudo-signals if you don't apply some sort of filter to compensate for the quantization. The numbers are therefore irrelevant, I just wanted to demonstrate the principle. And the principle holds, regardless of the way you bin your data (and that is what you are doing in every real world scenario: breaking up continuous variables into discrete parts). --TheMaster17 (talk) 08:16, 4 August 2012 (UTC)

Could your tracking software pick up a small steel ball? I have seen videos of Drosophila tracking experiments in which a small steel ball was added to the arena, and a motorized magnet located beneath the arena moved the ball along a defined trajectory. You could run your analysis software on recordings of such a ball as a control. This could be something as simple as strapping the magnet to a motor that makes it spin in a circle. Someguy1221 (talk) 07:52, 3 August 2012 (UTC)

Perhaps some of the people involved with mosquito flight track analysis and the Track3D system at Wageningen University and Research Centre might by useful contacts. See . Sean.hoyland - talk 16:52, 3 August 2012 (UTC)

This sound like a good idea to get a grasp of the limitations (and abilities) of your setup. You could vary speed, acceleration and trajectory of the ball somewhat, and see how this influences the graphs you are producing. --TheMaster17 (talk) 08:19, 4 August 2012 (UTC)

Also, this may be of interest, Valente D, Golani I, Mitra PP (2007) Analysis of the Trajectory of Drosophila melanogaster in a Circular Open Field Arena. PLoS ONE 2(10): e1083. doi:10.1371/journal.pone.0001083. Sean.hoyland - talk 18:46, 4 August 2012 (UTC)

This is not only of interest, this is the solution. The authors of the paper that Sean.hoyland has cited state explicitly that the trajectory of the fly has to be smoothed before calculating the numerical derivative if you want a meaningful value. And they even mention another method of getting the derivative in the methods. I really recommend that you try to reproduce their method before interpreting anything about your v and a values (which are probably products of your noisy position data). --TheMaster17 (talk) 20:40, 4 August 2012 (UTC)

August 2

No electricity for you!

According to a news article discussing the recent massive blackouts in India, , 1/3 of India's 1,200,000,000 never have access to a supply of grid electricity at all, under the best of circumstances, even for part of each day. It's hard to imagine viewing a house for sale in the US or the UK and hearing that there is no electric line close enough to supply it with electricity. How long ago were electric lines extended to more than 2/3 of the population of the US, the UK, France, and Germany ? Was it 100 years ago, 50 years ago, or what? Do the nonelectric 400 million Indians use Kerosene lamps, candles, or what, once the sun goes down? Edison (talk) 01:13, 2 August 2012 (UTC)

This is one of my favorite graphs. The US hit the 2/3 mark a little over 80 years ago, and we hit the 100% mark about 50 years ago. This graph is by households, and I can't rule out that that the average number of household members might be different for wired and unwired homes. Someguy1221 (talk) 01:27, 2 August 2012 (UTC)

A substantial number of that 1/3 don't even have houses. They live in camps, train stations, or wherever they can find a bit of shelter. Looie496 (talk) 01:41, 2 August 2012 (UTC)

But aren't the train stations electrified? 203.27.72.5 (talk) 02:51, 2 August 2012 (UTC)

I suspect in the more rural areas they may not be, and even if they are the lights etc are likely turned off when no train is expected. Nil Einne (talk) 05:22, 2 August 2012 (UTC)

How many homeless in India? Literally no shelter, not even a public shelter, a derelict automobile, or an improvised shack? Sleeping on the ground, in the open? In some countries many people live in hovels, but tap into electric lines and steal current. The key thing would be having mains run somewhere near the house/shack. Edison (talk) 03:03, 2 August 2012 (UTC)

Theft of electricity is a common problem in India (our article appears to be solely on the situation in India), but I think much more among those who already have or could have electricity . For those in situations you mention, they are unlikely to be able to convince corrupt officials to turn a blind eye, plus if someone's shack in the middle of no where has electricity it's a bit of a dead giveaway. Not to mention they may not have the skills or tools to do it, or the equipement to do anything useful with the eletricity. (And if they did have the tools and skill, they'd probably be better of just stealing the wire to sell provided they can avoid vigilantes .) Nil Einne (talk) 06:08, 2 August 2012 (UTC)

Agree with Someguy. In the US, the 2/3 mark was reached by about 1927, and electrification was essentially universal by 1952. Can't say about India, but the house I grew up in in Pennsylvania was not electrified until 1972 because of a combination of remoteness and local political bickering (whereas my grandparents' home in the nearby city was electrified from when it was built in 1920). Lighting and refrigeration were powered by propane gas, supplemented with kerosene lamps, with candles for dinner. The level of comfort, though, far exceeded that that you will find in rural India, even in those areas that are electrified. Clotheswashing was probably the only chore that was significantly more time consuming than in a contemporary electrified household. So comparing when the US and India reached the 2/3 mark is like comparing apples and oranges. It does not mean the levels of comfort and convenience were comparable at that point. Dominus Vobisdu (talk) 02:00, 2 August 2012 (UTC)

Another factor you need to take into account is home generation. In Australia, large amounts of the population outside of metropolitan areas of the large cities were not covered by grid electricity until the 1960's. But what people had was gasoline or kerosene - powered home and/or farm generators. So they had all modern electric lihting and appliances, it's just that they were powered from their own generators and not from a power station. In many small rural communities in those days, often a local business such as a gas-station would provide electricity to nearby houses and other buildings in the village centre. I imagine a similar thing happened in rural USA and many other countries with a significant dispersed largely farming based population. And some people had gasoline powered washing machines. Wickwack120.145.176.119 (talk) 03:08, 2 August 2012 (UTC)

I think kerosene lamps are the most popular source of lighting besides electricity in Indai by far for households. (Despite what may lead one to think, propane doesn't seem to be a significantly lighting source.) From the last two results, the percentage of households without lighting is fairly small although given the population of India, still around 1.1-1.2 million households depending on which source you use (not sure what percentage of the population this is). BTW, with reference to some of the answers above, according to the census data at least, the number of houseless households (according to the definition they use) is relatively small, although given the population of India still affecting close to 2 million people as of the 2001 census . I expect the number is an underestimate (the PDF mentions it may be an overestimate but also mentions how they only visited certain areas and how they may have difficulties getting cooperation). Perhaps more importantly, just because you have access to kerosene lighting doesn't mean you use it regularly. In fact some of the other sources also note that just because you are nominally connected to the electric grid doesn't mean you have a reliable or even particularly usable supply, even discounting things like the recent blackouts. Nil Einne (talk) 05:58, 2 August 2012 (UTC)

In the UK, nearly all houses were connected to the "National Grid" by the 1960s. The nearest mains electricity to where I live was five miles away until 1961. A few houses had their own generators, but most of us used paraffin or bottled gas for lighting. One house near where I live was not connected until about ten years ago, and there are still just a few isolated properties in the UK without a connection to the "grid", but they are rare. Dbfirs 07:10, 2 August 2012 (UTC)

It's a technical quibble, mostly, but the national grid and mains electricity aren't the same thing. "Mains" just means you get electricity from a shared community power supply; "national grid" means there's a high-voltage connection between that community power and the UK's overall generating capacity. In the islands of Scotland, plenty of people have mains electricity but aren't on the grid - e.g. people on Orkney are on both, but on Shetland the power grid is isolated from the national grid. Eigg only recently got mains electricity (meaning householders didn't have to generate their own) but still isn't on the grid. -- Finlay McWalterჷTalk 00:26, 3 August 2012 (UTC)

Thanks for the correction. I'd forgotten about some of the Scottish islands. I think all the English and Welsh islands are connected to the National Grid, or at least the ones with significant population. Dbfirs 07:59, 3 August 2012 (UTC)

Why Does the Annual Mortality Rate Rapidly Increase Between Ages 113 and 114?

A 113-year old person has about a 50% chance of surviving to age 114 on his/her 113th birthday, but a 114-year old person has about a 30% chance of surviving to age 115 on his/her 114th birthday. How come? Futurist110 (talk) 02:46, 2 August 2012 (UTC)

I want to point out that the annual mortality rate stays roughly constant at ages 110-113, yet rapidly increases for ages 114 and 115. Look at the Gerontology Research Group's supercentenarian tables and you'll see what I mean. Futurist110 (talk) 02:49, 2 August 2012 (UTC)

From :

Human mortality after age 110 is at at a constant level of λ = 0.7. This implies an annual probability of death of q_x = 0.5. This result confirms the previous analysis by Robine et al. (2005). Correspondingly, life expectancy after age 110 is about 1.4 years. Beyond the age of 114, data become too sparse to allow us to make reliable statements. (emphasis added)

There just aren't enough people who live to 114 in order to get good statistics on their mortality rate. Dragons flight (talk) 03:23, 2 August 2012 (UTC)

We had a similar question a couple months ago. You may be interested in some of the answers to it. Evanh2008 03:26, 2 August 2012 (UTC)

When researching my answer for that question, I came across a wide variety of sources that gave wildly different estimates for the death-rate-vs-age curve. I recall once finding, although I can't remember where, a review that compared different methods of calculating that curve. Based on which source you went by, you could make the curve come out as a positive, negative, flat, or some exotic non-monotonic function, and the values themselves varied significantly, but all probably in the vicinity of 70% at those ages. The numbers of data points to go on at those ages is really just too small for good statistics, if you want to incorporate years worth of mortality data, you have to keep in mind that the lifespan average is a moving target, complicating things significantly. You can only trust a lifespan histogram for a cohort that is 100% dead. Someguy1221 (talk) 04:58, 2 August 2012 (UTC)

Mortality rates (or at least the ones that I'm using) are all for dead people only. And for the record, it's interesting that as the 115+ year old people ever sample got larger over the last 10 years, the mortality rate at age 114 and 115 actually increased a lot, from about 50-55% in 2000 to about 70% right now. Futurist110 (talk) 05:58, 2 August 2012 (UTC)

There are enormous numbers of different mortality tables created by different people for different purposes based on different populations and datasets. To talk about the mortality rate is meaningless. Please link to the mortality table you are talking about. Normally, mortality tables are pretty much just guesses after around age 90. They use real data until there isn't enough to draw meaningful conclusions (which, depending on your dataset and methodology will be somewhere between about 90 and 110 - definitely well before 113), and then you just pick an arbitrary age as the maximum possible lifespan and pick some smooth curve to get you up to 100% by then. You shouldn't take any mortality figures too seriously after about age 90. They are based on too little data. --Tango (talk) 17:41, 2 August 2012 (UTC)

http://www.grg.org/Adams/B2.HTM - Here is the table that I was talking about. The mortality rates are very easy to calculate from it. Futurist110 (talk) 19:48, 2 August 2012 (UTC)

That's not a useful data set for this kind of work. It is collated from various sources with no way of knowing it if is complete or unbiased. It spans more than 20 years, during which time mortality rates have changed enormously. It spans multiple countries, which have widely varying mortality rates. It is also far too small. Your 30% figure is, with 95% confidence, assuming a simple binomial model, anywhere between 21% and 37%. Your 50% is actually anywhere between 33% and 61%. So, you see, they could actually be exactly the same and it would still be consistent with your data. Your dataset is too small to give enough make the confidence intervals small enough that they don't overlap. That means you can't draw any conclusions. --Tango (talk) 01:14, 3 August 2012 (UTC)

Ah, the miracle of the confidence interval. --TheMaster17 (talk) 08:54, 3 August 2012 (UTC)

Actually, I think that all or almost all of these cases with the exception of the Japanese ones have been verified by the Gerontology Research Group and its correspondents. As for Japan, their koseki system is very efficient, and thus the GRG does not usually consider it necessary to double-check Japanese cases. Thus, we know for a fact that all or almost all of these cases are accurate and reliable. As for what you said about confidence intervals, that is very interesting. Let me look more into that. Futurist110 (talk) 22:00, 3 August 2012 (UTC)

Earthing

What is the simple way to check whether the earth wire of a house electrical circuit is properly grounded? Thank you.175.157.5.252 (talk) 03:17, 2 August 2012 (UTC)

Call a competent electrician and ask them to check it out. Nil Einne (talk) 05:20, 2 August 2012 (UTC)

I tried looking this up online, only to deduce that doing it properly is not simple at all. Someguy1221 (talk) 05:26, 2 August 2012 (UTC)

The OP geolocates to Sri Lanka. I'm not at all certain, but Sri Lanka should be a country that uses the Multiple Earth Neutral System (MEN), or a close variant. In this system, the house earthing system has two main parts: An earth stake buried in the soil, and a connection to the street distribution nuetral wire. The house earth stake is of prescribed length, and it is generally sufficent to make a visual inspection. If the stake has no significant corrosion, and the wire connected to it is sound and the method of connection is sound (ie a pip clamp in good condition), then assuming the original installer did the right thing, that's all that's realy needed. The earth stake at each house does not ON ITS OWN do much - the system relies on all earth stakes at each premises fed from the street distribution having all their earth stakes connected in parallel by the power company's nuetral wire. All the earth stakes in parallel provide a low impedance to sink fualt currents even though an indiviual eartb stake caould not do so. If the neutral connection from the power company's strett wires to the house nuetral is deffective, then the house will have no power. If you know how to use a multimeter, check between your nuetral bar (in meter box) or the nuetral or earth pin of any wall outlet and the earth stake, on the earth stake below where the wire connectes to it. Check first for voltage - there should be well under a volt. If there is no voltage, then check resistance - it should be less than one ohm. These checks do not 100% guarantee everything is fine - beyond that you need a trained electrician. However they cover alll common deficiencies in an MEN system in a reasonably built up area. If you live in a new, undeveloped area or are isolated in a remote location, there's a bit more to it. Kiet121.215.2.150 (talk) 05:55, 2 August 2012 (UTC)

Determining that you have a ground is relatively simple, but determining that it's a proper ground is not. For example, you might currently only have a ground because a puddle of water is making the connection, which obviously isn't a proper ground, as you will no longer be grounded once that puddle disappears. StuRat (talk) 08:27, 2 August 2012 (UTC)

With the MEN system, that isn't generally a factor. A visual inspection, and grasping the stake and attempting to wriggle it is sufficient, assuming the installation was done in accordance with standards, as the electrical resistance to the "great body of earth" of an individual earth stake is unimportant. If an earth stake is so badly corroded that a puddle makes any significant difference, you'll almost always notice it on inspection. The most common defect is the wire is broken or the wire is no longer connected to the earth stake due to accidental damage or a defective clamp - all of which is easily spotted on visual inpection. In unusual situations such as remote area single-wire-earth-return feeds, there's more to it, but I did include a disclaimer. Keit120.145.189.101 (talk) 10:28, 2 August 2012 (UTC)

The suggestion to "wiggle the stake" is utter nonsense except to note that the wire is not connected to the ground rod. Such a practice could result in you holding a wire broken off by the action from the ground rod, with lethal high voltage on it, flowing through your body to ground. A utility I worked for would drive ground rods at transformer sites in 5 foot or so incremental lengths, with each stake screwed into the previously driven one. I would use a "ground megger" to measure the resistance of the new ground to several remote grounds. Sometimes it required 30 feet of ground rod to get to a required low impedance in soil underlaid by sand. A puddle at the surface would have scant effect on the portion 10 or more feet down, Several rods might be driven several meters apart and connected in parallel by large cables. One approach was to drive multiple grounds and use solution of a system of equations to determine ground impedance. Another approach was to use a remote ground. as a reference.Requirements might be less severe at a residence. Local codes will specify how low the impedance must be.and how many amperes of fault current the ground rod or system must sink without melting, possible thousands of amps for some time until fuses or breakers operate. In some US locations, codes might allow a clamped connection to a cold water pipe connected to a municipal water system by sturdy metal pipe, with a suitable jumper bypassing the water meter. It is not a job for the uninformed novice. Electrical shock hazard or structural fire might be the punishment for a mistake. The local ground has as one job the prevention of dangerous high voltage on all the conductors in a building if the transformer has a fault and primary voltage arcs to the low voltage secondary. Edison (talk) 05:14, 3 August 2012 (UTC)

Actually, Edison, it is YOU that wrote utter nonsense. Let's go thru this carefully: Firstly, the OP specifically asked about a HOUSE installation - not a substation, not a power station, not even a street transformer - just a house. My answer above is valid for a house, and is not intended for substations etc. Secondly, he geolocates to Sri Lanka. If he was in UK, Australia, Germany, etc, my answer would have been "go find a qualified electrician." But in Sri Lanka, he could be well off and in a quality city dwelling, or he could be in more third world conditions, and he may need to be both more interested and more resourceful. An lastly, and most importantly:-

I'll say this one more time, in capitals, so read it carefully: IN THE MEN SYSTEM (which these days is most of the World. USA may be different) INDIVIDUAL DWELLING EARTH STAKES INDIVIDUALLY DO NOT DO MUCH. THE SYSTEM OPERATION AND SAFETY COMES FROM A MULTITUDE OF SUCH EARTHS CONNECTED IN PARALLEL by the supply authority's neutral wire. You can (though it is illegal) cut any ONE of them without making any noticable difference. You are NOT at risk of shock if you disloge the wire from the electrode, any more than you would be if you disloged it accidentally, as I have done with a lawnmower. Electrical saftey standards must cover this sort of situation - in fact any system that allowed safety to be compromised by a single point of failure is just not on. You are however, generally expected by the terms of the supply contact you have with the electricity supplier to put any damged or corroded wire and/or elctrode right promptly - otherwise you could end up with most of the earths in the area damaged, and then there would be a problem. Household earths are not normally specified by performance, they are specified in terms of a mandatory stake/electrode length (typically 1.5 meters). A typical house earth may well be several hundred ohms resistance. If there is an appliance fault, the bulk of the fault current DOES NOT go to earth via your own earth stake. It returns to the transformer via the supply authority's nuetral wire, with only small amounts of current entering and leaving earth via individual stakes on the way.

It is thus perfectly ok to check the validity of the clamp that connects the wire to the eath stake by attempting to wriggle it. If it moves it's not up to scratch and needs fixing. It is possible that the buried part of a stake has corroded away. But if you grasp it and try to move it, and you can't then it's fine (resistance is not what makes it legal - only its depth). If you can feel it move at the top , then it needs fixing. Visual inspection and "wriggle" testing is what an electrican will do. An earth megger and similar instruments is not what the OP will have, and it has no relavence, as the requirement is a buried depth, not a specified resistance.

Keit60.230.203.89 (talk) 12:44, 3 August 2012 (UTC)

If you are testing grounds relative to other grounds, how is it determined that the first ground is working? Someguy1221 (talk) 07:54, 3 August 2012 (UTC)

This has absolutely NO relavence to teh OP's question, however: Special instruments are available, for which the internal operation is a bit complex to explain here, at least without diagrams and assuming a sound knowlege of meshed electrical circuit mathematics. Essentially, what they do is use selected earth stakes chosen as potential reference access points, and force a current though the earth stake under test, monitored by a sensing coil clamp around the electrode or its' connecting wire. The instruments do an internal calculation to find the resistance to "great body of earth" of the electrode under test. As long as the resistance of the reference electrodes is less than a certain amount, the resistance of reference electrodes does not affect the result. Earth electrodes near each other and near to other structures (eg metal pipes) share current paths through the soil to the great body of earth - this is manifested in what electrical engineers call "common resistance" - a resistance common to nearby stakes/electodes and added to the unique "component" resistance each electrode. In other words, 2 nearby electrodes form what is equivalent to "Y"-shaped circuit to great body of earth. I hope this is clear, as the subject is actually of some complexity, and the accurate measurement of earth systems is actually something that requires specialist knowlege of engineers. Whole textbooks have been written on this subject alone.

I point out that the words "ground" and "grounded" is USA terminology, but has spread around do to the wide availability of US textbooks and magazines. This is unfortunate, as the meaning of these words depends on context, and can be a source of confusion. The correct terminology for most of the English-speaking world is earth, meaning the great body of earth, earthed, meaning effectively connected to the great body of earth, earth stake or earth electrode, meaning the means of connecting to the great body of earth. Keit120.145.181.139 (talk) 11:15, 3 August 2012 (UTC)

Supplementary question from editor Edison moved to a new question Explain electricity consumer earthing by Keit. I moved it because an answer requires coverage of several related topics and would most likely not help the OP for this question. The OP is of course free to read the new question and its' answer(s). Keit60.230.207.82 (talk) 04:01, 5 August 2012 (UTC)

spina bifida case

Big Bang of nothing

Was the initial condition of the Universe an infinitely tiny bit of totally empty space? Since the initial mass of the Universe would be zero, dividing zero mass by zero volume does not give a singularity.

Then cosmic inflation hits and this empty space is blown up at vast speeds. This is all fine and dandy until a virtual meson pops up. This virtual meson is then torn apart before it can pop out. In order to avoid two bare quarks, each of the quarks gets paired up with another quark, giving a universe of two mesons. Each of these two mesons is then torn up, giving four mesons. Then eight, then sixteen, etc.

Exponential meson production continues until the Universe has enough mass/energy to reach a flat state and this stops inflation. The mesons then decay through the weak force, which applies its bias towards matter over antimatter. Would the result fit the observed Universe? Hcobb (talk) 13:14, 2 August 2012 (UTC)

I'm not an expert cosmologist, but as far as I understand the current theory, the standard models of the big bang start at infinite (or at least very high) densities, not at density zero. Energy already existed during cosmic inflation and was "stretched flat" by it - this explains the largely flat, isotropic and homogeneous appearance of the cosmos. If matter/energy was created during inflation, there is no good reason for this flatness. --Stephan Schulz (talk) 13:25, 2 August 2012 (UTC)

For most of the inflationary epoch, the universe is almost empty except for the scalar field (the inflaton), which is similar to the modern-day dark energy and the Higgs field—it has mass/energy but it's not matter in the conventional sense. Eventually the inflaton field decays, and that's the origin of all of the matter in the present-day universe. Any ordinary matter from before inflation is diluted to the point of irrelevancy. There is interest in looking for magnetic monopoles as relics of the pre-inflationary universe, but there's no theoretical reason to suppose there's even one of them in the present-day observable universe. -- BenRG (talk) 19:45, 2 August 2012 (UTC)

One outstanding question in cosmology is whether the early universe was isotropic and homogeneous. For example, consider reading this section, anisotropy in the observed cosmic microwave background. To the best of my understanding, the universe we see today appears very isotropic and inhomogeneous: it is still unknown if today's universe evolved from a similar isotropic, inhomogeneous initial condition. Nimur (talk) 15:10, 2 August 2012 (UTC)

If you mean the universe of 13.7 billion years ago, there's no question that it was extremely isotropic and homogeneous. The present-day universe is still very much so at large scales (~1 billion light years), but it's neither homogeneous nor isotropic at smaller scales. This is a result of magnification of slight inhomogeneities in the early universe by ordinary gravitational attraction. This process is well understood (though not by me). If you mean the universe before inflation, nobody has any idea. According to the inflationary model, the observed fluctuations in the CMB come from quantum fluctuations during inflation. They have nothing to do with the pre-inflationary universe. -- BenRG (talk) 19:45, 2 August 2012 (UTC)

Stephen Hawking insists that there was nothing prior to the big bang.

If our big bang article is correct, the concensous among scientists currently is to asume that the universe started of as a singularity with very very very high tempretures and pressure. The whole thing is very very complicated (I haven't been able to digest it completely yet) and coupled with the fact that the article provides a lot of info on this I feel that I don't need to repeat all of it here.Aliafroz1901 (talk) 16:10, 2 August 2012 (UTC)

Singularities are maths way of telling you you've made a mistake. I'm not sure any scientists actually think the universe had infinite density at time t=0 - what would that even mean? The singularity just tells us that it doesn't make sense to extrapolate all the way back to t=0 like that. Our understanding of physics starts a tiny fraction of a second after the "Big Bang", at which point the density was extremely high, but finite - we don't know what actually happened before that. It may well be that nothing interesting happened at t=0, it's just the time you happen to get to if you incorrectly extrapolate back. --Tango (talk) 17:51, 2 August 2012 (UTC)

Given the evidence, it's safe to say that it all happened in the Big Inning. ←Baseball Bugs carrots→ 00:21, 3 August 2012 (UTC)

The inflaton field does not need to decay. Just mix with virtual particles and Quantum chromodynamics will suck the energy out of the inflation field into a uniform meson soup. It's Hawking radiation on steroids because as soon as any mesons are created they'll exponentially multiply like rabbits. No new physics is needed, just an empty tiny bit of space suffering from a Negative Space Wedgie. Hcobb (talk) 00:37, 3 August 2012 (UTC)

Tango I never said that the universe had infinit pressure, what I said was that it may have had extremely great pressure. And you are correct We don't know what was there at T=0, I know that and I was not presenting unchalengeable facts, only presenting the sciontific concensous on the matter.Aliafroz1901 (talk) 10:46, 3 August 2012 (UTC)

... and, of course, in some models, there never was a time t = 0, as Tango implied above. Dbfirs 11:22, 3 August 2012 (UTC)

"and, of course, in some models, there never was a time t = 0" some models doesn't mene all thereies, and If the above linked big bang article is correct the big bang only tooke a few seconds to complete so most thereies would include a time T=0. — Preceding unsigned comment added by Aliafroz1901 (talk • contribs) 16:32, 3 August 2012 (UTC)

... It all depends on what you think time is! Using conventional modern "time", the earliest we know about is the Planck epoch. Dbfirs 06:13, 4 August 2012 (UTC)

How do antibodies kill antigens/pathogens?

How do antibodies kill antigens and pathogens? Does the antibody kill the pathogen/antigen directly, or does immune cells kill the marked pathogen/antigen, or both, and if the antibodies kill the pathogen/antigen directly, how does that work? — Preceding unsigned comment added by 187.126.186.208 (talk) 14:10, 2 August 2012 (UTC)

See the Misplaced Pages article titled Antibody which explains all of that, and a lot more. --Jayron32 16:17, 2 August 2012 (UTC)

I found the following in the above article

"An antibody (Ab), also known as an immunoglobulin (Ig), is a large Y-shaped protein produced by B-cells that is used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, called an antigen. Each tip of the "Y" of an antibody contains a paratope (a structure analogous to a lock) that is specific for one particular epitope (similarly analogous to a key) on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize its target directly (for example, by blocking a part of a microbe that is essential for its invasion and survival). The production of antibodies is the main function of the humoral immune system.

Antibodies are produced by a type of white blood cell called a plasma cell. Antibodies can occur in two physical forms, a soluble form that is secreted from the cell, and a membrane-bound form that is attached to the surface of a B cell and is referred to as the B cell receptor (BCR). The BCR is only found on the surface of B cells and facilitates the activation of these cells and their subsequent differentiation into either antibody factories called plasma cells, or memory B cells that will survive in the body and remember that same antigen so the B cells can respond faster upon future exposure. In most cases, interaction of the B cell with a T helper cell is necessary to produce full activation of the B cell and, therefore, antibody generation following antigen binding. Soluble antibodies are released into the blood and tissue fluids, as well as many secretions to continue to survey for invading microorganisms."

So the answer to your first questionn seemes to be that both antibodies and immune cells kill antigens. and for the second it semes to be that antibodies kill pathogens via several methods with one of them being blocking an issential part of a microbe.Aliafroz1901 (talk) 16:49, 2 August 2012 (UTC)

Weight increments on a digital scale

I have always been curious and puzzled by this. Can someone please explain this to me? I have consistently noticed that digital weight machines (for weighing the human body) always seem to present the person's weight in increments of 0.2 pounds. So, the person weighing himself might get results of, say, 170.0 or 170.2 or 170.4 pounds, and so forth. But, the scale will never list weights such as 170.1 or 170.3 or 170.5 pounds. Why is this? I assume it has something to do with accuracy, precision, and rounding, etc. But, still, can't the machine (scale) "round" to the 0.1 pound increment, just as easily as its programmers selecting to round it to the 0.2 pound increment? This befuddles me. Any input? Again, I am referring to digital scales that measure the human body (e.g., a person trying to lose weight). I am not referring to the smaller types of scales that might measure fruit or food (in ounces or grams) or such. Thank you! Joseph A. Spadaro (talk) 16:51, 2 August 2012 (UTC)

A digital scale typically has an electronic sensor that converts weight to a voltage. This analog voltage is then converted in an analog to digital convertor (ADC) to a digital number. The ADC outputs a number with a fixed step size, each step representing a voltage difference of, in this case, 0.2 pounds. The ADC has a fixed and limited number of output values, so the scale cannot detect changes smaller than the step size of the ADC. To display these changes, the scale would need a more sensitive, more expensive ADC. It is also possible that manufacturers prefer to use the same ADC in scales that use pounds as they use in metric scales, which have often a step size of 0.1 kg, which is roughly 0.2 pounds. - Lindert (talk) 17:13, 2 August 2012 (UTC)

I've noticed that digital scales also have programming to make it look like you weigh exactly the same thing unless there's some large difference. This keeps it from giving a slightly different weight if you step off and right back on, and thus makes it seem more precise than it really is. I'm surprised they don't randomly sometimes add 0.1 to the weight (and then remember that), to make them look more accurate as well. (Heck, they could evenly randomly add several digits, to really make it look accurate, but that would cost more in display digits.) StuRat (talk) 17:43, 2 August 2012 (UTC)

Never confuse resolution with accuracy. Most digital scales for body weight are designed to weigh to a maximum weight of 130 kg or 300 Lb, with a display resolution of of 0.2 kg or 0.2 Lb. That's a resolution of 0.2/130 => 0.15% (in metric mode) or 0.2/300 => 0.07% (USA mode). The accuracy won't be anywhere near as good as that - 2% accuracy would be a good achievement with standard electronic circuitry. So while the display can resolve to within 0.1 kg or 0.1 Lb in terms of available digits, when weighing a 100 kg (220 Lb) man, you can only trust it to within 2 kg (4.4 Lb).

So why do they display to within 0.2 and not 0.1? ADC's (as mentioned by Lindert above) are made in standard resolutions: 8-bit, 10-bit, 12-bit, 16-bit, and 24-bit. The more bits, the greater the cost. If a scales manufactuer chooses to buy 8-bit ADC's, and decides to set the maximum weight at 300 Lb, the resolution will be 300/2 = 1.17 Lb. That's good enough weighing a 300 Lb man (it exceeds the system accuracy) , but what if Mother wants to weigh her 20 Lb child? The resolution is then 1/20 ~ 5% - not too good. So, most manufacturers wil choose a 10-bit ADC. Then the resolution will be 300 /2 = 0.3 Lb. Most electronic engineers, though, know a simple circuit trick to get another bit of resolution without the expense of a 12-bit ADC. So the system resolution is 11 bits i.e., 0.15Lb. Since to display this will require the cost of an extra digit, a quick bit of programming of the internal micro-computer will round it to 0.2. This can also save a few cents on the cost of a transistor etc to drive the display to resolve to 0.1.

The reason for the disply stability mentioned by StuRat is an issue with digital readouts well known to electronic engineers known as "Least significant bit uncertainty". In digital systems fed by an analog (ie continously variable) inputs such as force measuring strain gauges, small random variation in the input value and noise in electronic circuitry can, if the measured vaule is close to toggling the last digit, cause the last digit to rapidly flip between two adjacent values. Electronic engineers are used to this, but it can make non-technical people think the device is faulty or not trustworthy. So what we do is add hysteresis - the weight must increase at least twice the display resolution before the display is updated. Most bathroom scales wait until the weight is stable for a few seconds before settling on a value though.

Keit121.215.24.203 (talk) 23:58, 2 August 2012 (UTC)

I think they go beyond that, though. They don't want anyone to weigh themself twice in a row and get a different reading the second time, so require quite a large change from last time before they will register a change. Ironically, this improves the apparent precision while actually reducing the accuracy. You can trick it into giving you a real 2nd reading by adding a known weight, like 10 lbs, and then subtracting that. StuRat (talk) 04:16, 3 August 2012 (UTC)

That could add more error than you think it's eliminating unless you've ensured that your 10lb weight is exactly 10lbs. I highly doubt it is common practice for digital scale designers to include hysteresis, as consumer goods' sales are unaffected by small differences in post-purchase observed quality, perceived or otherwise. It is possible to see instrumentation report an identical voltage several measurements in a row, and there may even be some hysteresis effected by the circuitry, but to suggest it is intentional is unsubstantiated. BigNate37_(T) 05:27, 3 August 2012 (UTC)

It's definitely the case on my scale. I can eat a big meal, without using the bathroom, and it still reports the same weight as before. They don't want people returning the scales when they see how imprecise they are. With this system, they likely fool the people until after the return period ends. StuRat (talk) 05:32, 3 August 2012 (UTC)

Have you tried weighing yourself, and then reweighing yourself holding some weight that's say something like 5 pounds just to see if the scales still report the same thing? You could also weigh yourself repeatedly and each time increase the weight you're holding until you should be reading quite a substantial amount more. I, for one, doubt that any scales are designed in that way. 101.172.127.247 (talk) 08:13, 3 August 2012 (UTC)

What StuRat is describing is a symptom of possible mechanical binding, or a possible fault in the electronics. As a professional electronics engineer I am very familiar with the use of hysteresis in the manner I described. As I said above, many scales wait until the reading is stable for at least 1 or 2 seconds and then feeze it. It may be that Stu's scales work this way, and are programed to detect a large change as time to unfreeze the display - I have not seen any like that. The various scales I've seen either don't freeze the display, or if they do, they stay frozen until you get off completely. It is sufficient to "cover" +,- 1 digit to solve the least significant bit ambiguity. In pactice a design engineer may choose to make it cover 2 digits in order to ensure that production variation in parts and parts aging in use is not going to be an issue, but I would not expect more than that. I've tested my scales by taking 1 reading with just a large drum of carefully measured water (20 kg), then adding 0.2 kg, and the reading went up as expected, but both readings were about 3% low. Keit120.145.181.139 (talk) 11:32, 3 August 2012 (UTC)

I've heard of fake repeatability, by storing and repeating the last weight if it's close, being a common 'feature' in cheap scales see e.g. . These primarily refer to bathroom scales but I've also heard of it occuring in some kitchen type scales. As mentioned and some of the other links, most scales only seem to store the last value, so rather then doing StuRat's complicated suggestion, just start the scale then add some other weight, allow it to stablise and take it off is usually enough to avoid the (IMO) cheating circuit if you want to determine real repeatibility of the scale or just get a new result from some intentional change. Another form of (IMO) cheater circuit, particularly common in cheap kitcen scales of the brandless made in China variety yet ironically very annoying when you're actually using them for their intended purpose appears to be what you're (Keit) referring to, i.e. drift rejection; where if the weight slowly changes it assumes it's drift and does not change. So if you add stuff too slowly it can seriously reduce the accuracy from what the scale is capable of because it takes a while for the scale to accept it's being changed . (P.S. Whether these are useful features to the consumer or silly cheating obviously depends on one's POV, I've made my views clear but I understand not everyone will agree.) Nil Einne (talk) 20:42, 3 August 2012 (UTC)

Thanks, Nil, I knew I wasn't imagining it. Keit, you're lucky if you've never encountered this "feature" before. My strongest objection to this practice is that you can't tell if a scale uses this method or not, until you buy it. Nothing on the label tells you, and they aren't likely to let you try out the scales first (at the stores where I shop, at any rate). You could try reading online reviews, but those unfamiliar with this deception might say the scale is extremely accurate, since they step off and back on and get the exact same weight. StuRat (talk) 23:32, 3 August 2012 (UTC)

Thanks to all for the valuable insight and input. It does, indeed, make sense now that I have read the above replies. I can now understand why the manufacturers choose the scales to display weight to 0.2 rather than 0.1 pounds. Thanks again. Much appreciated! Joseph A. Spadaro (talk) 22:57, 4 August 2012 (UTC)

Can a singularity spin?

I was watching a video by creationist Kent Hovind and he was bashing the Big Bang Theory, and one of his claims that the BBT is false is his assertion that the singularity was spinning before it "exploded" (I know it didn't explode, but rapidly expanded). He contends that due to the conservation of angular momentum, all of the galaxies must be spinning in the same direction, but he points out that some of them are spinning in opposite directions. Two questions, can a singularity spin, and if so, was the singularity that spawned the universe, spinning before it expanded during the Big Bang? 148.168.40.4 (talk) 17:55, 2 August 2012 (UTC)

The cosmos has no net angular momentum (to within experimental precision). The spins of individual galaxies come from random local perturbations in the highly uniform initial state. They point randomly in all directions.

Singularities don't really have any properties. They exist in theories and are a sign that there's something wrong with the theory (for example, the ultraviolet catastrophe is a singularity in classical physics which was solved by quantum mechanics). The big bang singularity should disappear in a better cosmological theory, perhaps based on cosmic inflation. However, a cosmos with an overall spin is possible in general relativity, so the lack of overall angular momentum does need to be explained. It is a prediction of inflationary cosmology. -- BenRG (talk) 18:35, 2 August 2012 (UTC)

I suspect that Mr. Hovind is confusing the origin of the solar system (which did start with a spinning mass of dust) and the universe. I don't think cosmologists say the early universe was spinning. thx1138 (talk) 19:11, 2 August 2012 (UTC)

It's not even clear to me what "spinning" in respect to the universe would mean. Spinning compared to what? The Universe, which emerged out of the mathematical singularity, is all that is. What would be the frame of reference to say "it was spinning"? --TheMaster17 (talk) 08:51, 3 August 2012 (UTC)

That's a difficult question. Spin is not necessarily dependant on a frame of reference. Consider two masses in deep space connected be a string. If they are spinning, the string will be pulled taut. If they aren't, it won't. Whether the string is taut or not is not a frame dependant observation. --Tango (talk) 11:38, 3 August 2012 (UTC)

Yeah, I was wondering about this frame-independence of rotation, too, after I wrote my comment. But how would this appear from inside the universe? You would need a centripetal force (for example gravity) to hold the spinning "thing" together, wouldn't you? And wouldn't that mean there had to be a "center of rotation" somewhere (and in total, a physical difference between directions: spinward, anti-spinward and perpendicular), for which we have no indication (because the observable universe is isomorphic)? But I admit I'm out of my field with this topic, my lessons regarding relativity are mere distant memories. --TheMaster17 (talk) 12:28, 3 August 2012 (UTC)

It's not really my field, either... I don't think you need a centre of rotation, but you do need an orientation. So the universe could be homogeneous but it couldn't be isotropic. As you say, that isn't consistent with our observations. --Tango (talk) 17:29, 3 August 2012 (UTC)

You can have rotating black holes, so I don't see why the initial universe couldn't also have spin. The evidence suggests it didn't, though. --Tango (talk) 11:38, 3 August 2012 (UTC)

What evidence suggests the universe is not or had not been spinning? μηδείς (talk) 06:33, 4 August 2012 (UTC)

See my short discussion with Tango above. If the universe today would be spinning, not all directions in the universe would be the same. You would expect measurable differences between spinward and anti-spinward, for example. All observations at the moment point to an isotropic universe (meaning all directions are the same). But I'm not sure how exactly spinning would manifest, and in what measurements. We need someone with more physics background to answer this in detail. --TheMaster17 (talk) 08:03, 4 August 2012 (UTC)

Unexplored Areas

Are there unexplored land areas left on earth? Reticuli88 (talk) 18:47, 2 August 2012 (UTC)

I'd imagine that the majority of Antarctica's surface area has never known a human footprint. Though humans may have looked out of the window of a plane at it. --Kurt Shaped Box (talk) 18:54, 2 August 2012 (UTC)

Of course, most of the surface is hidden under ice, and likely won't be explored until we manage to melt off the ice cap. StuRat (talk) 04:18, 3 August 2012 (UTC)

There are almost certainly caves that have never had a person in them either. New land may appear when ice melts off it, or when molten rock solidifies. There are also likely to be some small; islands that humans have never visited. A related question that was here before was: what is the last land to be discovered? Graeme Bartlett (talk) 23:43, 2 August 2012 (UTC)

Thinking back to the last time I remember a somewhat similar question to the OPs being asked here, there was talk of unclimbed mountains - e.g. Gangkhar Puensum. --Kurt Shaped Box (talk) 00:16, 3 August 2012 (UTC)

While the ocean depths are not lands per se, http://xkcd.com/1040/ is relevant here. Bear in mind as a webcomic it takes gratuities liberties with the truth; for instance, David Bowie never walked the Abyssal Plain (though I believe Freddy Mercury has). BigNate37_(T) 05:31, 3 August 2012 (UTC)

Either the author of XKCD needs to write larger or scan at higher res, because I can't read most of that. Can you ? StuRat (talk) 23:37, 3 August 2012 (UTC)

Click the image to be directed to http://xkcd.com/1040/large/, which I am able to read with relative ease. BigNate37_(T) 23:47, 3 August 2012 (UTC)

Thanks. StuRat (talk) 03:40, 4 August 2012 (UTC)

It's "liberties with the truth". Truth needs no tips. Clarityfiend (talk) 19:56, 3 August 2012 (UTC)

Just because I'm wrong doesn't mean you have to tell everyone! BigNate37_(T) 23:47, 3 August 2012 (UTC)

It depends what you mean by unexplored. There are 67 uncontacted tribes in Brazil, and even within 100 miles of Sydney, new discoveries are being made in the dense rainforest.--Shantavira| 07:28, 3 August 2012 (UTC)

North Sentinel Island has not had many visitors. --Daniel 23:41, 3 August 2012 (UTC)

There are vast stretches of southwest Tasmania inaccessible due to horizontal scrub. There are mountain ranges in Canada which have likely not yet been climbed. 207.224.43.139 (talk) 06:22, 4 August 2012 (UTC)

Unconscious mind

Regarding the unconscious mind:

• What evidence is there to prove that it exists?
• Does the evidence point to either nonconscious processes or actual hidden thoughts?
• Is there anyway to access the unconscious mind?

--Melab±1 ☎ 19:10, 2 August 2012 (UTC)

Unfortunately this comes down to definitions. Neither "unconscious" nor "mind" have a specific universally accepted meaning, so the answer to the first question comes down to which definition you prefer. Some people, for example, don't think that the word "mind" should be applied to anything that is not consciously experienced, so to them, "unconscious mind" is an oxymoron. The best thing would be for you to read our article on the unconscious mind and come back with any questions it leaves unanswered. Looie496 (talk) 19:27, 2 August 2012 (UTC)

(edit conflict) It depends on what you mean by these terms, which are not defined the same way by different people. If you mean "are there processes in our nervous system which we are unaware and over which we don't have any conscious control", the answer is absolutely: the Autonomic nervous system governs a range of bodily functions. If you mean the "Freudian" concept of the Unconscious mind or of subconscious, the answer is that it is a lot less likely that such models accurately represent how the mind works. Concepts like "repressed memories" and the like are very controversial and poorly accepted among actual neuroscientists. People that study the "human mind" as a "soft science" (i.e. psyschology/psychiatry etc.) are more likely to work with such models of the human mind, but those that study the actual functions of the nervous system (neurologists/neuroscientists/neurobiologists) don't find them very useful. --Jayron32 19:29, 2 August 2012 (UTC)

I don't know all about that id and ego stuff but it is quite clear to me that thinking goes on without my being aware of it. I've done things like for instance stopping the car and only figuring out why it was the right thing to do a couple of seconds afterwards. Dmcq (talk) 21:50, 2 August 2012 (UTC)

There are things like reflex, training, and instinct which affect behavior, but I'm not sure what is sturcturally different than conscious behavior. Awareness is not the same thing as consciousness. --Jayron32 03:10, 3 August 2012 (UTC)

I don't know all the definitions but I in all probability have accessed the unconscious mind. At times I have walked from my room to the dineing room without realiseing what I am doing. At other acasions I have gone into the bathroom, come out and forgotten all about it then have my parents remind me that I have been to the bathroom, then remember it, then think that it was all a dreem. The latter tipicly takes place when I am half asleep.Aliafroz1901 (talk) 11:27, 3 August 2012 (UTC)

We are rarely consciously aware of what we are going to say, until we say it. If we had to consciously deliberate every word we were going to produce before we produced it, we could only do so by thinking in words about what word we were going to use, leading to an infinite regress. Hence most of what we say spontaneously is produced by the subconscious, with us only becoming conscious of what we are saying when we vocalize it. This is why we have the phenomenon of there being something on the tip of our tongues; a thought of whose struggle to make it into consciousness we are quite aware. μηδείς (talk) 16:55, 3 August 2012 (UTC)

I mainly don't think in words so I don't have that problem :) But yes I don't normally think about the actual words I'm going to say. Dmcq (talk) 18:45, 3 August 2012 (UTC)

It's one of, probably the, main trick to writing. Don't try to edit yourself as you write. Let the words flow. Then go back and consciously edit as a separate second step. If, while doing the first "free-flow" draft, you get stuck, write FIX (or the word you know should be replaced with a better one) in capital letters and keep going. If you try to edit while you write you give your subconscious a complex, and end up with the writer's version of a stutter. This has got to be the number one problem of people whom I teach writing to. μηδείς (talk) 05:28, 4 August 2012 (UTC)

Race and obesity

Why are white and black women more likely to be obese, while obesity is much rarer among women of other races? --108.206.7.65 (talk) 20:35, 2 August 2012 (UTC)

White and black women where? Such a broad statement is unlikely to be true, so your premise is highly flawed. Certain socio-economic groups in certain countries have a gretaer propensity for obesity, so if you define which groups in which countries you seek information on, it would be very helpful. The data is very different if one is looking at Zimbabwe or the U.S. or Australia, for example. --Jayron32 20:45, 2 August 2012 (UTC)

In America. I've noticed that white and black women seem to have much higher rates of obesity than Asians, Indians, etc. --108.206.7.65 (talk) 21:27, 2 August 2012 (UTC)

Obesity is also very high e.g. among Palestinian women (31.5%, ), who are neither white nor black, but Arab. I would say obesity is much more correlated with culture (including subculture) and with unemployment than with race. - Lindert (talk) 21:30, 2 August 2012 (UTC)

Palestinians are white, or at least defined as white by the U.S. census bureau. In regards to the original question, I saw a lot of fat Latina women here in the U.S., and I think that nowadays there is generally greater obesity among poorer people. More black and Latino people tend to be poor nowadays, so that is probably why there is a greater % of obesity among them. A lot of white people are also poor, if you go by total numbers. As for why poor people tend to be more obese, it's because they are often unable to afford healthier food or do not have the time to cook it, and thus buy and eat much more cheap fast food than higher-income people do. Futurist110 (talk) 21:42, 2 August 2012 (UTC)

The OP might be interested in our article on Steatopygia as it seems somewhat relevant here. Dismas| 22:13, 3 August 2012 (UTC)

A related question

Why is it that black and white women's appearances can range anywhere from very pretty to very ugly, but women from other races are almost always attractive? --108.206.7.65 (talk) 21:29, 2 August 2012 (UTC)

That is purely subjective and varies from person to person. Apperently you are of that opinion, and therefore it is only you who can answer why you feel that way. Noone can answer it for you. - Lindert (talk) 21:34, 2 August 2012 (UTC)

I agree with Lindert on this. I, for instance, have way different tastes than you do. Almost all of the women that I find sexually attractive are white and/or light-skinned. As yourself what qualities you find attractive in women and you'll probably be able to answer your own question afterwards. Futurist110 (talk) 21:39, 2 August 2012 (UTC)

The OP asked a similarly loaded question a few days ago, and being from Missouri, I guess he has to be shown. ←Baseball Bugs carrots→ 00:16, 3 August 2012 (UTC)

I think that OP's opinion are right. I have seen more obesity in white people around 45 to 50 years old than caucessian and Asians. GiantBluePanda (talk) 23:51, 3 August 2012 (UTC)

Um, how does your explaination explain why you believe the OP's opinion that 'black and white women's appearances can range anywhere from very pretty to very ugly, but women from other races are almost always attractive' (which is the subtopic you're replying under) is 'right' ? Nil Einne (talk) 17:26, 4 August 2012 (UTC)

Baby bird identification

Can someone identify these birds? The caption is "min egen bild" with a marker identifying it as Swedish; the user has no other uploads, and the filename is not particularly helpful. Nyttend (talk) 22:11, 2 August 2012 (UTC)

Birds are not really my thing, but I get whip-poor-will vibes looking at them, or perhaps some other brand of nightjar. Looie496 (talk) 00:10, 3 August 2012 (UTC)

The WP:BIRDS guys might be the ones to ask about this. They have regular 'birds for identification' discussions on their talk page. I don't think that any of them regularly contribute to the refdesks, but I'm sure that they'd be able to come up with a concrete answer, or at least narrow it down to a genus, if it happens to be one where the young of many species look very similar... --Kurt Shaped Box (talk) 00:25, 3 August 2012 (UTC)

Copied over there. Thanks for the pointer. Nyttend (talk) 01:32, 3 August 2012 (UTC)

Look like baby European Robins. Definitely not nightjars of any sort (though I can see why you'd get those "vibes"), as those species don't build nests; they lay their eggs directly on the ground. MeegsC (talk) 03:21, 3 August 2012 (UTC)

what physically changes between the ages of 18 to 22 -- fourth years look older than first years, but is it senescence?

I look at the photos of my friends (now 22) when they were first years (at 18), and they look so young! I am sad that we have lost our juvenile features and we seem "less cute" than before. But puberty ends between 16-18 doesn't it? What biological processes are occurring specifically? I don't think its the same type of aging that occurs later -- for example, I think our collagen remains taut, we don't develop wrinkles (yet), but what is changing? Nothing gold can stay (talk) 23:33, 2 August 2012 (UTC)

The biggest, most noticeable, effects of puberty tend to finish by around age 18 in boys and 16 in girls, but it doesn't stop completely until quite a bit older, particularly in men. Chest hair, for instance, is often still developing by age 22. --Tango (talk) 01:34, 3 August 2012 (UTC)

It could just be normal mature aging, as noted at senescence above, but some people continue to grow and develop through puberty into their early 20s. One somewhat famous example: David Robinson (basketball) grew three inches between the ages of 18-22, while many people stop growing in height well before then; for example I reached my adult height at 13. There is a lot of variation. There are also significant effects of things like diet and exercise. I went through a lot of changes at that age, crappy college food and a lack of activity added significant weight which had a general effect on my facial features and body shape. --Jayron32 03:07, 3 August 2012 (UTC)edit: spelling error corrected --Jayron32 04:07, 3 August 2012 (UTC)

"Man people" ? :-) StuRat (talk) 04:05, 3 August 2012 (UTC)

I think it depends on sex as well. When I was studying human developmental psychology some 30 years ago, I was told that the male physique continued to develop and mature until the mid-20s, whereas the female body reached maturity some years earlier. There then followed a period of relatively little change until the mid-30s when the ageing process started to have undesirable effects. In the years since, these dates may well have changed (50 is the new 30?) but the general principle still holds good. --TammyMoet (talk) 08:05, 3 August 2012 (UTC)

My female friends definitely seem to "mature" between the age of 18 and 22. My male friends seem to age less, actually. Nothing gold can stay (talk) 15:22, 3 August 2012 (UTC)

I haven't the slightest idea of a relevant article in general, but many things cause aging during that period: taking up alcohol and cigarettes, late nights and lack of sleep, excess sun exposure, poor eating habits, stress, and even sexual activity can affect the freshness of young skin. μηδείς (talk) 16:43, 3 August 2012 (UTC)

August 3

Magnitude 10 earthquake by combination of faults

I heard on a Discovery Channel program that a magnitude 10 earthquake could occur if the Cascadia subduction zone, the San Andreas Fault, and the Aleutian Trench all simultaneously ruptured. Is this possible? If so, how likely?--Jasper Deng (talk) 04:08, 3 August 2012 (UTC)

It's mentioned in the Cascadia article you linked to. 10-14% for magnitude 9 or higher in the next 50 years. Hot Stop 04:14, 3 August 2012 (UTC)

As likely as anything else, which means not likely at all. No earthquake in recorded history has been measured or estimated to have a magnitude greater than 10. 9.5 is the highest I can find at either Lists of earthquakes or Historical earthquakes. Sadly, the Discovery Channel (and other supposedly educational channels like the History Channel and TLC) have gone down the drain over the past decade or so. When they do run a "science" show, which is rare, they tend towards the sensationalistic, like impending asteroid impacts or supervolcanos, or stuff like that. I suppose this is what happens when geologists get really drunk at parties. Could it happen? I suppose. Could it happen this week? I wouldn't hold your breath... --Jayron32 04:14, 3 August 2012 (UTC)

Such a quake could possibly be a once-in-ten-milleniums in frequency/probability; I don't hold my breath for any megathrust earthquakes anyway.

However, it seems logical. If the subduction zones could each generate 9.5 earthquakes, and the San Andreas Fault a 9.1, then this could produce something like 9.8. If it so happened that another adjacent subduction zone like the one off eastern Russia also joined in, this would easily break 10. The chances of this is extremely unlikely, but not impossible.--Jasper Deng (talk) 04:19, 3 August 2012 (UTC)

Basic answer: nobody knows. The general opinion was that the Japanese tsunami quake was extremely unlikely -- until it happened. The dynamics of large earthquakes are still quite poorly understood, and we only have about 100-150 years of good worldwide data on their frequency, so events that occur less often than that could easily be misunderestimated (as GWB might have put it.) Looie496 (talk) 04:27, 3 August 2012 (UTC)

General opinion was spot on. The Japanese tsunami quake was extremely unlikely. Just because it's actually happened, the chances of it recurring haven't suddenly increased (aftershocks from the original quake aside). -- ♬ Jack of Oz ♬ 11:36, 3 August 2012 (UTC)

Indeed. It is a common misconception that unlikely things happening is evidence that they weren't unlikely after all. You can't draw conclusions from a single data point like that. --Tango (talk) 11:42, 3 August 2012 (UTC)

But we have had quite a few earthquakes of magnitude larger than 9 in the last 100 years. Count Iblis (talk) 15:42, 3 August 2012 (UTC)

I've been following the literature on this, and it's pretty clear that many geologists have seen the Japanese quake as a wake-up call indicating that many probability estimates need revision. This overview from Science (available online here at the moment) may be helpful. Looie496 (talk) 16:59, 3 August 2012 (UTC)

* The problem comes with earthquakes with a long recurrence interval, like the Japanese earthquake and the 2004 Indian Ocean earthquake. We do have some idea about the biggest sections of subduction zones that are likely to rupture, which is about 1600 km as I recall, which is the length that ruptured in the 2004 earthquake. Magnitude is just the logarithm of the product of rupture surface area and displacement, so if we know the biggest area and the biggest displacement, we can work out the biggest magnitude possible. Using data from many large earthquakes it is possible to say that a M 10 earthquake would require a rupture of 1 million square kilometres . The width is relatively fixed depending on the dip of the megathrust and the depth of the top and base of the seismically coupled zone, with a likely maximum of 150 km. However, if we take 200 km, we need a fault length of 5000 km, something like the whole Peru-Chile plate boundary rupturing at once, for which there is no evidence at all. Large earthquakes are often made up of sub-events and they may change in type. The 2002 Denali earthquake started on a small thrust fault, before switching to the strike-slip Denali fault and then splitting off that onto the Totschunda fault, yet another strike-slip fault, so it can happen. Note however, that all these faults physically intersect each other, which the Aleutian Trench and the San Andreas Fault do not (unless you throw in the Queen Charlotte Fault as well). Also, all your separate faults have to be in the same part of their seismic cycle and be close to rupture, which becomes increasingly unlikely as more fault segments are involved. Mikenorton (talk) 22:18, 3 August 2012 (UTC)

Deicing equipment / heaters

Is there any disadvantage to running deicing heaters, whether it's the pitot tube or the other deicers, even if it's not needed? I'm talking about onboard systems too, not deicing on the ground. Shadowjams (talk) 06:06, 3 August 2012 (UTC)

1) I imagine it lowers fuel efficiency somewhat, depending on how they generate the electricity to run them.

2) Running that much electricity through wires has to increase the risk of fire, explosion, and electrocution, if the wires are damaged, but this risk should be minimal in a properly maintained airplane.

3) Running them on a hot day while sitting on the ground might actually cause overheating damage. StuRat (talk) 06:13, 3 August 2012 (UTC)

Anybody with cites or definitive knowledge have any ideas? Shadowjams (talk) 06:38, 3 August 2012 (UTC)

I'm about to board an international flight, and I'm seated in the first row. I'll see if I can quickly ask the pilot :) 101.172.127.242 (talk) 09:27, 3 August 2012 (UTC)

OK, the pilot was happy to answer my questions and took about 15 minutes to talk to me about various things. He said that the Airbus A-320 we were flying in was fitted with a deicing unit for the engines, a deicing using for the leading edge of the wing called "wing air" and small electric heating elements on the pitot tubes. The wing air and engine deicing work by taking a bleed of hot pressurised air from the turbines and directing it to the wing surface or the part of the engine that needs heating. Both of these lead to a performance penalty because they take pressure away from the turbines. The engine deicers are disabled by interlocks when not in the air and the wing air causes an extra take off distance equivalent to about 700kg of extra weight if it's activated on the ground. The power used to deice the pitot tubes is negligible, and that unit is activated automatically during the necessary parts of the flight envelope. 112.215.36.173 (talk) 14:06, 3 August 2012 (UTC)

I'm guessing this wasn't in the US, where knocking on the cabin door might get you tackled and arrested by a TSA agent. StuRat (talk) 23:19, 3 August 2012 (UTC)

Wow, cool. Thank you! I didn't know pilots actually took time to talk to passengers anymore! Shadowjams (talk) 22:57, 3 August 2012 (UTC)

Can we mark this Q resolved ? StuRat (talk) 23:22, 3 August 2012 (UTC)

Ask for help to identify the fungus.

See the link attachment for the Image. Thanks. SYSS Mouse (talk) 15:35, 3 August 2012 (UTC)

Location please? Likely to be the young fruiting bodies of any of the bright yellow species of shelf fungi under the genus Laetiporus. If from N. America, likely to be Laetiporus sulphureus.-- OBSIDIAN†SOUL 15:55, 3 August 2012 (UTC)

Oh dear. I think I saw Steve eat that once. (It goes without saying, but don't eat it.) BigNate37_(T) 16:01, 3 August 2012 (UTC)

It was not specified. It is from a forum post (The forum is in Chinese thus not linked) but the user who posted it is from Eastern Canada. EDIT: Also, the same fugus one week later. SYSS Mouse (talk) 16:35, 3 August 2012 (UTC)

Definitely Laetiporus then. They're quite distinctive. See this guide. That said, again, don't eat it! :P We're not exactly mushroom experts here, heh.-- OBSIDIAN†SOUL 17:25, 3 August 2012 (UTC)

Thank You. SYSS Mouse (talk) 03:51, 4 August 2012 (UTC)

Nutrition in Human Breast Milk

I'll freely admit that this question is purely inspired by the Song of Ice and Fire series--

A character in said series is about 8 years old and still subsists primarily on his mother's milk. I'm just wondering if the nutritional needs of a human beyond baby-hood (wherever one draws that line, 8 years old is clearly not a baby) can be met purely through breastmilk. Protein/fat I can see--but does the milk contain enough of the vitamins and minerals?

Puh-lease do not respond with "it's just a book" I'm not asking about the book, that's merely the impetus for the question.199.94.68.91 (talk) 18:46, 3 August 2012 (UTC)

Doing a Google search for the phrase "nutrition data human breast milk" turned up this page as the second result (after the Misplaced Pages article on human breast milk). That page contains all of the data on the nutrient content (including micronutrients such as vitamins and minerals). Finding the recommended daily intake for these nutrients for an 8 year old should also be easy to find. By cross referencing those two data sets, you can see where breast milk is both adequate and inadequate for nutritional needs. --Jayron32 19:00, 3 August 2012 (UTC)

I asked a question a long time back about how babies can get complete nutrition from milk, which seems to be deficient in several key nutrients. The answer, as I recall, is that babies are born with with excesses of those nutrients, and they switch to solid foods before they run out of this stockpile. In your case, you said "primarily", so the supplemental foods they get might supply the missing nutrients. If, however, a child was fed nothing but milk (human or otherwise) for 8 years, then I'd expect severe malnutrition. StuRat (talk) 23:15, 3 August 2012 (UTC)

Add to that the fact that the majority of humans become lactose intolerant at around 2 to 7 years of age. They will have limited to no nutritional benefits from drinking milk after that. Though the very recent evolution and growing dominance of lactase persistence is circumventing this somewhat.-- OBSIDIAN†SOUL 03:26, 4 August 2012 (UTC)

It's very recent by evolutionary standards - it's still about 10,000 years ago. I'm not sure what the overall prevalence of lactase persistence is, but in people of European descent (which I think best describes the character in question, although I haven't actually read the book) it is by far the majority as the article you linked to says. --Tango (talk) 18:04, 4 August 2012 (UTC)

Haven't read the book nor follow the series either. :P So I was assuming the OP meant all humans. -- OBSIDIAN†SOUL 00:55, 5 August 2012 (UTC)

Is there some reason why there is no link here to human breast milk? Or is the OR of various posters supposed to be more relevant on the wikipedia reference desk? μηδείς (talk) 22:16, 4 August 2012 (UTC)

Because it doesn't contain the answer?-- OBSIDIAN†SOUL 00:55, 5 August 2012 (UTC)

Filial Imprinting

Hello. Is filial imprinting related in any way, shape, or form to evolution? If so, how? Thanks in advance. --Mayfare (talk) 19:25, 3 August 2012 (UTC)

Anything that influences survival is related to evolution. Since filial imprinting enhances the survival of the young (by helping them stay protected), it is related to evolution. Of course "related to evolution" is an extremely vague term -- if you have something more specific in mind, please clarify. Looie496 (talk) 20:55, 3 August 2012 (UTC)

Filial imprinting can augment and override evolutionary instincts by allowing offspring to mimic learned behaviors appropriate for specific environmental conditions. 207.224.43.139 (talk) 05:56, 4 August 2012 (UTC)

HF solid-liquid transition: densities

Does anyone know if solid HF expands (like regular substances do) or contracts (like does very similar water, both have hydrogen bonds and so) upon melting? Has this been measured (I've done a search, returns nothing)? Are there values?--R8R Gtrs (talk) 19:33, 3 August 2012 (UTC)

What search returns nothing? Googling the obvious keywords suggests this depends on pressure because of different possible crystal structures. 207.224.43.139 (talk) 05:55, 4 August 2012 (UTC)

August 4

Farts

Not trolling—is it possible to fart in your sleep? 71.146.0.138 (talk) 01:26, 4 August 2012 (UTC)

I would assume so based on the various TV shows with characters farting in their sleep. Futurist110 (talk) 01:48, 4 August 2012 (UTC)

Does this count as original research? Yes. I've been told I do it all the time. Mingmingla (talk) 01:50, 4 August 2012 (UTC)

Thanks. 71.146.0.138 (talk) 03:49, 4 August 2012 (UTC)

Flatulence is caused by the buildup of gases in your gastrointestinal tract, usually as byproducts of secondary digestion by your gut flora. Their movement down your intestines is also controlled by the peristaltic movement of involuntary smooth muscles, which does not depend on you being conscious. So yes.-- OBSIDIAN†SOUL 03:40, 4 August 2012 (UTC)

Thanks. 71.146.0.138 (talk) 03:49, 4 August 2012 (UTC)

Thanks. 71.146.0.138 (talk) 03:49, 4 August 2012 (UTC)

The most common thing to wake me on long car trips where I am not driving is the rush of air as the windows are rolled down in panic. My grandmother's favorite story was of the woman from the next county over who, when looking for the pepper at the church kitchen while cooking pierogies on a Sunday, instead of asking, Gde póper déla? with a fixed Polonic penultimate accent asked Gde popér(-)dela? with a free Ukrainian oxytonic accent. μηδείς (talk) 05:13, 4 August 2012 (UTC)

As a non-speaker of Polish or Ukrainian (aplogies for this lamentable deficit) I'd be quite interested in understanding this semantic joke, any chance of a translation? Richard Avery (talk) 06:49, 4 August 2012 (UTC)

Certainly. The past tense of East Slavic verbs is formed by the past participle, which is declined for gender and number, with an implied form of "to be" which is usually deleted. (English retains the archaic perfect forms "Christ is risen" and "The time is come" which are parallel, except that East Slavic drops the "is" as implied. French has Elle est venue, "she is (has) come", with the feminine past participle of venir, "to come") The past participle of delati "to do, to put" for women is delala, shortened by haplology to dela. (One generally adds -la to the verb stem to form the Slavic feminine past participle.) "She put the pepper on the table" is Wona de(la)la poper na stol. The verb perdeti, "to fart", (perd-, following Grimm's Law, is cognate to the English; the root is PIE) like many verbs, takes the prefix po- to imply a single, completed action, as opposed to a continuing action: poperdeti, "to make a fart" whose feminine past participle is popérdela. Hence, the only difference between "Where did she put the pepper?" Gde póper déla and "Where did she fart?" Gde popérdela? in my grandmother's dialect is one of where the stress falls. Her friend's dialect, however, had a different stress pattern, where poper was stressed on the final syllable, as opposed to most of the ladies at the church who pronounced the word póper with initial stress. Hence their humorous reaction to her innocent question. μηδείς (talk) 07:26, 4 August 2012 (UTC)

:-) Thankyou. Richard Avery (talk) 14:10, 4 August 2012 (UTC)

Race and Running Speed?

This is a serious scientific question. I'm not trying to be offensive or racist. I've noticed that there are a lot of black people in professional (such as Olympic) running events. I have two questions:

1. Is the % of black people in professional running events disproportional to their % of the population? 2. If this is disproportional and a favorable proportion to black people, do black people have a genetic ability to run faster?

Thank you. Futurist110 (talk) 01:55, 4 August 2012 (UTC)

East Africans in particular, right? —Tamfang (talk) 02:46, 4 August 2012 (UTC)

Well, skin colour isn't going to make any difference at all. And different groups of people from many parts of the world have black skin. I doubt if the OP was thinking of Australian Aboriginals, Polynesians and south east Asians when he wrote that question. Some groups of people seem to have a higher proportion of members who can sprint faster than many (West Africans), or run longer distances better than others (East Africans), but one has to take social, geographic and economic factors into account too. If you live in a poor country, you're more likely to choose running as a sport than swimming or equestrian. If you live at high altitude, you can have an advantage in endurance sports. HiLo48 (talk) 03:04, 4 August 2012 (UTC)

See Kalenjin_people#Athletic_prowess. Members of the Kalenjin tribe of Kenya win about 40% of marathons world-wide. μηδείς (talk) 04:56, 4 August 2012 (UTC)

By black, I meant the U.S. census definition of black, meaning of Sub-Saharan African descent. Futurist110 (talk) 06:29, 4 August 2012 (UTC)

And HiLo pointed out that having black skin itself is irrelevant to running, it's probably only a chance marker (for US Americans...) for a certain genetic, cultural, geographic and economic background that is relevant. Black skin is as relevant to running as is white skin to building high skyscrapers. The two things simply have nothing to do with each other causally, they are only associated by common economic, cultural and educational traits (that for example favor "white" architects to build many skyscrapers). --TheMaster17 (talk) 07:48, 4 August 2012 (UTC)

So you're saying it has to do more with lifestyle and exercise and that it has nothing to do with race? Gotcha. Futurist110 (talk) 07:56, 4 August 2012 (UTC)

HiLo: Sources please. And scientific ones for this Science desk, not social commentary. Rmhermen (talk) 14:07, 4 August 2012 (UTC)

Sources for what? If we demanded sources for everything posted here this would be a very different place. I'm not trying to deceive anyone. I just can't be bothered hunting down sources right now. Ignore my comments if they don't fit your belief structure. HiLo48 (talk) 18:11, 4 August 2012 (UTC)

There was a BBC Horizon documentary about this issue quite some time ago about the long distance runners from Kenya and Ethiopia. The conclusion was that the most relevant factor here was that these runners have longer legs in relation to the rest of their body (or certain parts of their legs are longer), and that means that for the same effort they will go faster. It is basically the same reason that explains why bipedal motion is more efficient than walking on 4 legs. A human can outrun a horse on the long run, hunter gatherers in Africa run for hours persuing antilopes eventually catching up with them...

For the sprint the type of muscles tissue you have is important, apparantly people of West African ancestory have the right stuff. Social effects can't be of much relevance here, because of the huge gap between the best white 100 meter personal best and the average best season's best time over the last decade. Only one white athlete has ever run faster than 10 seconds and none of the athletes from East Africa or Asia, see 10-second barrier:

"Nearly all the sprinters who have beaten the 10-second barrier are of West African descent. Namibian (formerly South-West Africa) Frankie Fredericks became the first man of non-West African heritage to achieve the feat in 1991 and in 2003 Australia's Patrick Johnson (who has Irish and Indigenous Australian heritage) became the first sub-10-second runner without an African background. Frenchman Christophe Lemaitre became the first white European under ten seconds in 2010 (although Poland's Marian Woronin had unofficially surpassed the barrier with a time of 9.992 seconds in 1984). In 2011, Zimbabwean Ngonidzashe Makusha became the 76th man to break the barrier, yet only the fourth man not of West African descent. No sprinter of predominantly Asian or East African descent has officially achieved this feat."

Count Iblis (talk) 15:46, 4 August 2012 (UTC)

Keep in mind as well that you are talking also about the very bleeding edge of the bell curves, here. The bell curves for all populations in terms of running performance are going to look nearly identical; where they vary are going to be maybe tiny, almost imperceivable shifts in the median, and tiny, tiny differences on the far fringes. The Olympics and whatnot are pitting the far fringe of one country against the far fringe of another. The tiniest of differences in genetics, training, and so forth make the differences in such situations. The lesson here isn't that the population genetics don't matter for these sports — they do seem to — but that you shouldn't read racing performance (or sports in general) as telling you too much about population genetics. It is not likely the case that your average Ethiopian is genetically a better long-distance runner than, say, your average Swede, but over a large population of Ethiopians and Swedes, your handful of gifted Ethiopians will be better at this sport than your handful of gifted Swedes. (It is also obviously the case that the countries that spend more time and more money on searching out talent end up with more of it. There is likely no genetic reason that Americans, Russians, and Chinese dominate gymnastics and Africans do not — finding and cultivating gymnastic talent is just a much bigger deal in the former countries, so they are able to find those who reside at the end of the bell curves and devote enough resources to them that they go to the Olympics as opposed to doing other things with their lives.) --Mr.98 (talk) 17:48, 4 August 2012 (UTC)

In terms of long distance running again certain people from East Africa have a slight advantage - hence the dominance of Ethiopeans, Somalis and Kenyans in these competitions - they tend to have longer heel bones calcaneus than most other people. This difference gives then a slight leverage advantage to the transfer of power frome their achilles tendon's to the ball of the foot - in long distance races this small advantage adds up to result in a disproportionate number of marathon champions. (The same leverage advantage comes into play with Maasai men's traditional jumping dances.) Roger (talk) 18:26, 4 August 2012 (UTC)

I missed where Futurist attributed running speed to skin color. Has anyone ever heard of the Kalenjin people, who win 40% of marathons world wide? I wonder what percentage of the world population the Kalenjin are? Something near 40%? Nothing statistically improbable going on there.... μηδείς (talk) 21:22, 4 August 2012 (UTC)

See second paragraph of first post. HiLo48 (talk) 00:14, 5 August 2012 (UTC)

I guess I missed the part where anyone here claimed that the genetic and social opportunity were equally distributed. Fighting strawmen with strawmen is a waste of everyone's time. --Mr.98 (talk) 21:34, 4 August 2012 (UTC)

So your point is that the Kalenjin are pampered rich brats? This is the wikipedia reference desk. If you think this place is about arguing you are mistaken. Provide links and refs, not ideological OR and ad hominem. μηδείς (talk) 22:19, 4 August 2012 (UTC)

Are you just trolling? Because you don't seem to be addressing anything I — or anyone else here — has actually written. --Mr.98 (talk) 02:03, 5 August 2012 (UTC)

Neurology and music

Is there any neurological basis to the moods associated with different types of musical scales, or is it entirely cultural? --108.206.7.65 (talk) 01:59, 4 August 2012 (UTC)

See Cognitive neuroscience of music.—Wavelength (talk) 02:36, 4 August 2012 (UTC)

That article doesn't discuss my question specifically. --108.206.7.65 (talk) 17:37, 4 August 2012 (UTC)

Can you perhaps elaborate a bit on what prompted the question ? Do you think there are different moods associated with different types of musical scales and if so what are they, for example ? Sean.hoyland - talk 17:51, 4 August 2012 (UTC)

It certainly must have a cultural dimension, as listening to squealing Chinese music must be more pleasant for them, or they would have executing all of the musicians long ago. StuRat (talk) 03:36, 4 August 2012 (UTC)

Hydrotriiodic acid

Since hydroiodic acid contains the iodide ion, I don't see why combination with elemental iodine should not produce the triiodide ion as with iodide salts.--Jasper Deng (talk) 04:10, 4 August 2012 (UTC)

http://pubs.acs.org/doi/abs/10.1021/j100810a041 207.224.43.139 (talk) 05:48, 4 August 2012 (UTC)

Involuntary Change of Sexuality?

I know the one's sexuality is not a choice, but is it possible in extreme cases for one's sexuality to (somewhat) change over time due to factors out of this individual's control? For instance, could it be possible for a bisexual gay who initially strongly preferred women when it came to sexual attractiveness to strongly prefer men later on? Personally, I was always straight, but the characteristics and types of women that I found attractive have changed over the years. My question is if it is scientifically possible for such a change in one's view of sexual attractiveness to be much more extreme over the years, as in my example above? Futurist110 (talk) 07:35, 4 August 2012 (UTC)

That's a minefield of a topic. See Sexual orientation for a brief and extremely simplified overview; and the Kinsey Reports and the Klein Sexual Orientation Grid for two studies which have attempted to find out. But the answer is yes from the results of the Klein Grid and from personal observation.

The why, however, is problematic. It may be prison sexuality, latent bisexuality (in the traditional sense or the innate bisexuality sense), situational sexual behavior, coming out or finally accepting repressed homosexuality, self-enforced conscious rejection or adoption of an orientation (however ineffective that may be), experimentation, peer pressure, the result of personal trauma, positive or negative reinforcement over long periods, dissonance between gender and very strong emotional attraction (affectional orientation), hormonal, genetic, cultural, etc. Add to that the questions surrounding gender and sexual identity, and the religious and cultural conventions that attempt to control or classify them, and you end up with only one conclusion:

Sex is complicated.-- OBSIDIAN†SOUL 09:51, 4 August 2012 (UTC)

Tom Robinson (singer) describes himself as "a gay man, who happens to have fallen in love with a woman". Go figure. --TammyMoet (talk) 12:28, 4 August 2012 (UTC)

I am not sure about the issue of control (who would say their sweet tooth is voluntary?) but I can attest that my polarity, for lack of a better word, has varied over the years. Before I knew what sex was I had crushes on males and females. From puberty to 18 I was primarily homosexual. From 18 to 24 primarily heterosexual in action, and homosexual in dreams. (My boyfriends and girlfriends have always known I was bisexual.) Then the reverse. Then back again after some time. I must say, the most shocking development was when I dreamt of having sex with Britney Spears. (And this was even after the South Park episode.) She is not at all my type physically or musically. But it was a dream, and I don't blame myself for acts of my subconscious. (And it was fun!) I can offer no explanation. But I recommend everyone try both ways lest they never know what they are missing. μηδείς (talk) 21:19, 4 August 2012 (UTC)

Getting wet

It is raining. The rain is coming at me at 45 deg. I have no raincoat. Will I be dryer when I get home if I run through the rain or if I walk? --89.243.128.176 (talk) 14:04, 4 August 2012 (UTC)

If it's coming towards you, then running will result in less water falling on you. If its hitting your back, walk at the same speed as the rain is moving horizontally.--Gilderien Chat|List of good deeds 14:05, 4 August 2012 (UTC)

I agree with the first part, and in the second part, that strategy will indeed minimize the rain hitting you from the side, but it depends on the vertical velocity of the rain whether that is more important than minimizing the time rain is hitting you from above, which you would get from running as fast as possible. - Lindert (talk) 14:19, 4 August 2012 (UTC)

There was actually a recently released study on this in the European Journal of Physics. (See news coverage , , and freely available research article ). The short answer is that you'll be drier in almost all cases if you run instead of walk, although there are exceptions. -- 71.35.119.233 (talk) 18:14, 4 August 2012 (UTC)

Is it just me or has this all ignored the fact that if you run home, you spend less time in the rain? Yes, you may make complicated alterations to the raindrop-per-second rate and those are interesting deductions. But as long as rain is subject to gravity, you're going to be dryer for having spent less time in it. BigNate37_(T) 18:48, 4 August 2012 (UTC)

Indeed. I expect everyone knows from personal experience that you can avoid getting as wet by running home. If you have to be outside for a fixed period of time, then all of this might make a difference, but if you can get home in half the time, you'll be drier. It's important not to over-think problems! --Tango (talk) 19:09, 4 August 2012 (UTC)

In a first approximation, speed doesn't matter. You have a certain density of raindrops in the air, and if you cover a certain distance, you will sweep out a certain volume (cross section times the distance covered), and that volume contains a certain amount of water. Count Iblis (talk) 19:37, 4 August 2012 (UTC)

We're not ancient Greeks - we don't ignore empirical evidence in favour of pure reason. We've all been caught out in the rain and know what happens. If you run, you don't get as wet. If your reason doesn't fit with the empirical evidence, they your reason is wrong. Now, it is possible that I'm simply wrong as I get just as wet either way - there is a natural human tendency to overestimate the amount of control we have over our lives. The way to find out isn't with maths, though. It's with people running and walking in the rain and seeing what happens. --Tango (talk) 20:38, 4 August 2012 (UTC)

Actually I think Count Iblis's approach is the best way of visualizing this problem, but you need to think of it in the rest frame of the raindrops, not the rest frame of the street. If the raindrops are falling at a 45° angle downward and to the right, then with respect to their rest frame, you, the street, and the shelter you're trying to reach are all moving at a 45° angle upward and to the left:

                  .........._........
                   ........|\.........
                    .........\.........
                     .........\.........
                      ..........#........
                       .........#.........
                        ........#..........

The ### is you, the dots are (stationary) raindrops, and the dotless areas on either side are shelters. You want to sweep the # figure in any upward/sideways direction, minimizing the number of dots you intersect. If you "stand still", you're moving up and to the left and intersecting more and more drops without bound, so that's bad. If you want to reach the shelter on the left, it appears that the most efficient way of doing it is to go directly to the left, which corresponds to running as fast as possible. If you want the reach the shelter on the right, the most efficient way appears to be straight up: since you're 1/3 as wide as you are tall, you intersect about 1/3 as many raindrops that way than if you went horizontally. This corresponds to running at the horizontal speed of the rain. But if the rain were falling more vertically, the shelter edges in this picture would be closer to vertical and going straight up wouldn't look so attractive any more. Once the slope of the sides exceeds 3, you're better off running as fast as possible. This approach still works if you add a third dimension and replace the rectangle with a more accurate human shape. -- BenRG (talk) 21:28, 4 August 2012 (UTC)

I asked a slightly more complicated version of this question here at the math desk: How wet will the windshield get? μηδείς (talk) 18:59, 4 August 2012 (UTC)

It is also important not to underthink the question. A tall skinny person moving at a certain speed with his body inclined at a certain angle will only get the top of his head wet, while at a faster speed he will run into the rain in front of him. The cross section, angle of attack, and relevant speeds all matter. See the link above for the definition of the variables in the formula ρ·s·A·(u·sin(Θ)/v+cos(Θ)) μηδείς (talk) 19:32, 4 August 2012 (UTC)

Time to bring in the Ultimate Authority: Mythbusters. They tested it and found you get wetter by running (at least for the way they set it up). Clarityfiend (talk) 00:34, 5 August 2012 (UTC)

• They seem to have done only one trial per configuration, and there are no error bars.
• The theoretical model predicts that when the rain is vertical the amount you absorb should be very similar whether you walk or run, but when walking a much larger fraction of it falls on your head. Their coveralls had no hoods.
• Running might splash more water from the ground onto your legs.

They seemed to have no theoretical understanding of the thing they were studying, and they made no attempt to isolate possible causes of their surprising result. Yet they pronounced the myth busted. Very poor science. -- BenRG (talk) 02:07, 5 August 2012 (UTC)

How many strings make up a quark?

I don't know if this question has a meaningful answer, but I'll throw it out there anyway. ScienceApe (talk) 16:21, 4 August 2012 (UTC)

String theory was originally a theory of strongly interacting quarks, in which a quark was the end of a string (thus explaining why single quarks never appear in isolation).

In superstring theory as a theory of quantum gravity, I think a quark would be "one string". Quarks are complicated even in the standard model, though, so take this with a grain of salt. -- BenRG (talk) 16:30, 4 August 2012 (UTC)

August 5

botox and spoiled food

1. Charles Janeway (2001). Immunobiology (5th ed.). Garland Publishing. ISBN 0-8153-3642-X. (electronic full text via NCBI Bookshelf).
2. Litman GW, Rast JP, Shamblott MJ, Haire RN, Hulst M, Roess W, Litman RT, Hinds-Frey KR, Zilch A, Amemiya CT (January 1993). "Phylogenetic diversification of immunoglobulin genes and the antibody repertoire". Mol. Biol. Evol. 10 (1): 60–72. PMID 8450761.
3. Pier GB, Lyczak JB, Wetzler LM (2004). Immunology, Infection, and Immunity. ASM Press. ISBN 1-55581-246-5.
4. Borghesi L, Milcarek C (2006). "From B cell to plasma cell: regulation of V(D)J recombination and antibody secretion". Immunol. Res. 36 (1–3): 27–32. doi:10.1385/IR:36:1:27. PMID 17337763.
5. Parker D (1993). "T cell-dependent B cell activation". Annu Rev Immunol. 11 (1): 331–360. doi:10.1146/annurev.iy.11.040193.001555. PMID 8476565.

• Pages automatically checked for accidental language links
• Misplaced Pages resources for researchers
• Misplaced Pages help forums