Wikipedia:Reference desk/Archives/Science/2015 March 18

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March 18

wilmshurst machine application!

i want to make generator by using wilmshurst machine. Wlimshurst machine uses the static energy but we don't know how to storage the static electrocity. I know the leyden jar but is there anything I can alternate? And Wilmshurst makes the high voltage and little current, but I want to boost the current so I can use for any charger. Please help me — Preceding unsigned comment added by 1.211.74.81 (talk) 02:55, 18 March 2015 (UTC)

What's a Wilmshurst machine? --Jayron32 03:35, 18 March 2015 (UTC)

Wimshurst machine. The rest of the question is non trivial. I suspect you could charge a capacitor which you could then discharge into something else, that would be far from "easy", you could just use a dynamo to do the same thing but much simpler. I understand if the "challange" of it is to use a wilmshurst machine instead, but if no one else has done it before you (cursory google search doesn't show anything obvious), you have some real "figuring it out" ahead of you. Vespine (talk) 03:56, 18 March 2015 (UTC)

Polar Clock - article needed

I came across some fancy android app about Polar Clock. It’s a clock with concentric circles which shows second, minute, hour, date and month. See this Google images search result for better understanding of what I mean. Seems that there are also wrist watches based on this. Searching for it in Wikipedia I came across something of same name at http://en.wikipedia.org/wiki/Charles_Wheatstone#Measuring_time. I am not sure if both of these are same, or are based on similar principles. Maybe Wikipedia should have an article on both of these. 14.141.141.26 (talk) 06:41, 18 March 2015 (UTC)

Sphere spin problem

Suppose I drop a rough but perfectly rigid sphere on a rough horizontal plane and the sphere is spinning about a vertical axis. If it is rotating clockwise when viewed from above, does it spin clockwise or anticlockwise after the bounce? I can imagine it doing either. Is there a rotational equivalent of Newton's experimental law of restitution? Thanks, Robinh (talk) 07:28, 18 March 2015 (UTC)

The bounce affects only the linear motion, so the rotation will not, in an ideal bounce, be affected at all. In practice, there will be some deformation, and therefore a small torque about the spin axis during the time in contact, so there will be a slight slowing of the spin.

The rotational equivalent of a "bounce" would be the situation where opposite projections on the sphere come into contact with rigid stops. In theory, given perfect elasticity between the projections and the stops, the resulting couple will reverse the direction of spin. This perfect reversal would be difficult to achieve in practice, and a couple of springs at the stops would probably be better at absorbing the rotational energy and reversing it, just as in the case of the vertical bounce. Newton's law of restitution applies to the forces at the stops (equal and opposite), and hence to the rotational motion. Dbfirs 08:30, 18 March 2015 (UTC)

(OP) thanks Dbfirs. I've just tried it with a football and depending on the details of the surface (carpet, grass, concrete) the spin can be zero, clockwise, or anticlockwise. So the answer is "it depends", I guess. So I'm going to need a coefficient to describe this. Best wishes, Robinh (talk) 21:47, 18 March 2015 (UTC)

Yes, you can get some very interesting effects with a football which is far from the rigid sphere that you specified. I'd be surprised if you can reverse a fast spin with a bounce because I can't see where a large couple could be produced, but certainly carpet and grass can produce non-symmetrical forces during the deformation of the football as it bounces. No simple coefficient can describe the rotational changes because they depend on irregularities in the surface. Of course, if the football has some forward motion as it bounces, then forward spin and back spin and side spin will affect how it rebounds because of the extra frictional forces as it deforms. Dbfirs 22:15, 18 March 2015 (UTC)

• Reminder: if you're going to talk about footballs, please clarify which sport is called football where you live. The shapes are rather different. --65.94.50.15 (talk) 03:33, 19 March 2015 (UTC)

• I think we were both assuming the round-ball game here, but the shapes used for Rugby football and American football behave even more strangely when bounced.

(thanks!) agreed, except for the bit about "no simple coefficient". Sure, it might not be possible to get anything exact, but I don't see why something along the lines of equations 1 and 2 of http://arxiv.org/pdf/cond-mat/9708093v3.pdf , but specific to the relative angular velocities of the surfaces at the contact point couldn't be useful as an approximation. I guess I was asking whether there is a name for such a coefficient. Best wishes, Robinh (talk) 23:14, 18 March 2015 (UTC)

Yes, the coefficient of tangential friction determines the tangential force that has a moment about the centre of mass of the sphere, and this moment (integrated over the time of contact) determines the change in angular momentum of the sphere. This applies to your football with a forward motion, or to two colliding footballs, but not to your original perfectly rigid sphere since, in that idealised case, no force has a moment about the spin axis. Dbfirs 00:18, 19 March 2015 (UTC)

OTOH a perfectly rigid sphere wouldn't bounce on a perfectly rigid plane either. Maybe it would shatter. I guess "perfectly rigid" isn't quite as, er, rigid an assumption as we might like! Robinh (talk) 00:53, 19 March 2015 (UTC)

water displacement ballast propereties

How fast will an object rise in water if it displaces more water than its weight. Also does the speed accelerate if it displace 10 time its weight. object is 55 gallon drum with tapered nose. it is released from 100 ft. below the surface. The water is salt water common in any ocean. Also what is the terminal velocity? — Preceding unsigned comment added by 71.10.122.228 (talk) 02:11, 20 March 2015 (UTC) Please give answer in feet per second. — Preceding unsigned comment added by 71.10.122.228 (talk) 09:00, 18 March 2015 (UTC)

The speed will accelerate, self-evidently, as the object is released under water from zero speed, and if it is then moving, it had to accelerate to get there. It will accelerate until it reaches terminal velocity in the water, or until it reaches neutral buoyancy, whichever is first. It's speed at any given point in time cannot be determined by a single number from the information you've given, but will depend on a number of factors, including the depth the object is released from, the density of the object in question, its shape, the drag it creates in the water, etc. You've not given nearly enough information to even start to solve the problem. this page discusses some of the complexity and gives you the equations necessary to make the calculations you want to make. --Jayron32 12:42, 18 March 2015 (UTC)

Agreed. Also note that it's not as simple as the object accelerating at a constant speed until it reaches terminal velocity in water. The density of water varies at different depths, so the drag will vary with that as well as with the speed. And, once the surface of the water is breached, the buoyancy will change as the object rises, and thus displaces less water. If it leaves the water completely, then it would presumably slow and drop back down to the surface, unless the object is also lighter than air. StuRat (talk) 04:49, 19 March 2015 (UTC)

Physical representation of a memorized image

Was there any research about the possibility of physical representation (either via displaying on screen or even by printing) of a memorized image through head-attached electrodes or some other mediating device? AFAIK, current devices are able to at least pinpoint an area in the brain working when a particular memory is recalled (and the majority of people can retain a photographic memorized visualization of a given image). Brandmeister^talk 10:03, 18 March 2015 (UTC)

Have a look at this for example [1]. With better training for the person and using a larger part of the brain it might be possible to get something better, but for instance for me if the image isn't just purely visual you might get 3D or some other kind of relationship structure without a viewpoint though it would be interesting to automatically turn it into a 2D picture with colors for feelings for instance. Dmcq (talk) 11:56, 18 March 2015 (UTC)

That's interesting, but not really a memorized image. Rather, that's the brain processing an incoming image. Images really aren't stored as bitmaps in the brain, but more as concepts. For example, if there was a person sitting in a chair, the "person" and "chair" concepts would be stored, with some attributes stored for each like the age, gender, and other descriptions of the person, or the name, if known, and the type of chair. Other info stored in a pic would be lost, like the position of freckles on the person's face, unless that was somehow significant (if they had a particularly large freckle, for example). And some random writing in the background might not be stored either, again unless significant. StuRat (talk) 05:00, 19 March 2015 (UTC)

Condom protection against hiv

Why are condoms only 85 percent effective at preventing hiv/AIDS when used consistently and correctly if it's almost impossible for the virus to pass through a condom? — Preceding unsigned comment added by Roger adams49 (talk • contribs) 10:41, 18 March 2015 (UTC)

Who says they are? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:20, 18 March 2015 (UTC)

Well, our own article says that, for one. And the source for that comment verifies it. Dismas|^(talk) 11:42, 18 March 2015 (UTC)

Our article did but I removed it. I can't see where the source supports the claim, perhaps provide a quote? It mentions correct and consistent usage in several places in relation to other STIs and in general, but only mentions consistent usage for HIV. Nil Einne (talk) 12:05, 18 March 2015 (UTC)

It's at the top of page 14. Dismas|^(talk) 12:08, 18 March 2015 (UTC)

Where? That only mentions "Condom usage was classified into the following three categories: always (100% use), sometimes, and never" and "Among participants who reported always using condoms" and "consistent condom use decreased". As I said, I don't see anywhere correct usage is mentioned in the HIV section. Only consistent usage. Correct and consistent is mentioned in a few other places, but not in relation to HIV. Our article mentioned corrrect and consistent until I removed it [2], as did the OP, but I can't see where the source supports the claim of correct usage. Nil Einne (talk) 12:11, 18 March 2015 (UTC)

(EC) I take it you are referring to our condom article? If so, the claim the 85% was referring to correct and consistent usage wasn't actually in the source as far as I can tell, so I removed it [3].

Other sources also don't mention correct usage e.g. [4] says condoms "provide protection of about 80 to 85% against HIV" with 100% consistent usage. But it also makes clear it's not talking about perfect use, it includes usual rates of breakage, slippage etc.

Note that the wording in the second source is perhaps a litte confusing unless you read the later clarification "In other words for every 100 cases of HIV infection that would happen without condom use, about 15 (range: seven to 24) would happen when condoms are used consistently." Our article which I presume you read says the same thing but in less words. The 85% is the reduction compared to no condom usage.

The seroconversion rate is "0.9 per 100 person-years with condom". This [5] gives "1.14 per 100 person-years". In either case, this seems to be referring to cases involving "discordant couples (i.e. couples in which one of the partners is HIV-positive and the other free from HIV)". That source also provides a few reasons why the 85% or actually 80% for their case reduction compared to no condom usage may not be entirely correct.

BTW, once again may I suggest you read the sources in our article if you are confused about the details? Also if you do have to ask here, do link to whatever you referring to so people know what it is.

Nil Einne (talk) 12:04, 18 March 2015 (UTC)

BTW, I'm not entirely certain how correct usage is defined (I have an idea but lazy to confirm it). However I suspect correct usage doesn't prevent breakage and slippage. In fact the NIH report also includes several mentions of "correct use without breakage or slippage", which I take to mean the without bit is in addition. (These are generally mentioned when the authors are trying to explain for certain STIs this still won't prevent some transmission since unprotected areas of skin will also transmit the STI.) Nil Einne (talk) 12:32, 18 March 2015 (UTC)

Why do young birds reach full size quicker than mammals?

It's not always the case, but it seems that a lot of birds tend to be roughly the same size and shape as their parents by the time they are able to safely leave the nest, although they may still behave like 'babies' and be dependent on their parents for months (even years in the case of parrots) afterwards. Mammals, OTOH seem to have pronounced 'childhoods', where they're clearly much smaller and of a different body shape to their parents. Why does this happen? --Kurt Shaped Box (talk) 13:48, 18 March 2015 (UTC)

Very good question. As you acknowledge, quick maturation of birds is not a general rule, but it does seem to be a trend. Consider that a mouse will be roughly full size and reach sexual maturity in a few months max [6]. Consider that an ostrich only weighs about 100 lbs after their first year, and can take up to 3 years to reach maturity in captivity [7].

The general topic here is known as Life history theory in evolution/ecology. Several factors will affect a species' life history traits. If you have a lot of babies, you can't invest much time in caring for each one, and many will die. If you have only a few babies, the will get more resources from parents, but the total fecundity is lower. This is known as a "tradeoff", and when specifically thinking in terms of clutch size, this is known as r-k selection.

Age to maturity is not the same as clutch size, but there are similar tradeoffs. Also age to maturity is not the same age to max weight, but for many species they are closely related. Here's a paper that discusses how predators can affect age to maturity in prey [8], and here's one that relates age to maturity to life span [9].

As you know, some birds are very long lived, and they have a lot of variety in clutch sizes as well. The one fairly general pressure on flighted birds is that non-flying juveniles are extremely vulnerable, so that puts a strong selective pressure on fledging as fast as possible. That part is the basic intuition, but I can't easily find a ref that clearly states that. Here's a paper that discusses body size and time to maturity (from viruses to whales!) [10]. If we think only about flying birds, then they have strong restrictions on max weight, and that will also lead to faster times to maturity.

Here's a study of how time of fledging and weight at fledging affect one bird species [11], and here is a more general survey of growth rates in birds [12], which says "It is concluded that most species grow at some physiologically maximum rate."

So, this question taps in to a large amount of evolutionary theory, and you can get lost down that rabbit hole, but the basic idea I think comes down to the fact that no bird can hatch ready to fly, but some mammals can pop out ready for running and pronking - [13] (~4:30 or so for the good part). Hope that helps, SemanticMantis (talk) 14:18, 18 March 2015 (UTC)

(nb. many of the scientific articles I linked are behind paywalls, if anyone would like a copy for WP purpose they can contact me or ask at WP:REX SemanticMantis (talk) 14:25, 18 March 2015 (UTC))

Note that juvenile birds often appear larger than their parents, for a couple reasons, both ultimately due to them not flying yet:

1) Since they don't fly yet, they can pack on the pounds, which would be a disadvantage when flying, but a distinct advantage when just staying in the nest.

2) They can also have juvenile feathers, not designed for flight, but rather to keep them warm. Instead of the slick flight feathers, these juvenile feathers tend to be rather fluffy, and hence make them look bigger than they are. StuRat (talk) 17:28, 18 March 2015 (UTC)

• The needs of flight and migration are crucial. Waterfowl have huge clutches due to their very high infant mortality, with small chicks leaving the nest upon hatching. There's a minimum muscle mass necessary for flight, and it is an advantage to reach that quickly. Also, birds that migrate seasonally simply have no choice but to reach adult mass before the advent of the first migration. See also altricial versus precocial species. μηδείς (talk) 17:44, 18 March 2015 (UTC)

• "Huge" ? Isn't it around a half dozen ? StuRat (talk) 05:02, 19 March 2015 (UTC):

No. Merely checking the most obvious example that sprang to mind, Mallard, one finds "The clutch is 8–13 eggs", which from my half-remembered ornithological interests in former years I recall as being fairly typical for British ducks. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:28, 19 March 2015 (UTC)

Yep, and wood duck can go up to 16 eggs per clutch [14]. Of course "Huge" is very relative - both those ducks have small clutches compared to the mola mola, which can release ~ 300 million eggs at once. Further illustrations of r-k selection :) SemanticMantis (talk) 14:59, 19 March 2015 (UTC)

Thanks for all the answers so far, folks. I have just been thinking today - does anyone know of a flying bird species that is fully capable of flight before it reaches adult size/shape (ornamental plumage excluded)? Because I don't. AFAIK, you never see young birds that're something like 2/3 the size of their parents on the wing, despite what cartoons may tell us. --Kurt Shaped Box (talk) 16:30, 19 March 2015 (UTC)

I make no apologies for the use of the word huge! Lol. The "fowl" or Galloanserae (relatives of the chickens, ducks, and their ancient, separate lineage) are characterized by large clutches and precocial chicks. They don't feed their offspring, the offspring imprint on the mother, and follow her on the day they are born to begin feeding at a location she leads them to. The Neoaves which includes all birds that are not ratites (like the Ostrich and Kiwi) and are not land or water fowl tend to have much smaller clutches, songbirds often have four, and raptors and seabirds one or two, the second often not surviving. But the birds are fed in the nest until they grow large enough to fly and fend for themselves. μηδείς (talk) 17:06, 19 March 2015 (UTC)

In a bird context, I think it's fair to say 16 eggs is a huge clutch. Most waterfowl will indeed have larger clutches than e.g. passerines, for the reasons you mentioned. I looked around a bit, and couldn't find any other wild bird with a larger clutch size than the wood duck (domestic fowl are another matter entirely). SemanticMantis (talk) 18:10, 19 March 2015 (UTC)

This book chapter has a table of fledging times for grassland birds (Table 4.3 [15]), they range from 8.7 to 10 day means. Now that doesn't really tell us what you want to know, which is "percent of adult weight (or volume, length etc.) at time of fledging" - but it does make you wonder if a sparrow can really reach e.g. 90% max weight after just 8 days. I think you're right that in general most birds will reach a large percentage of their adult weight before they can fly, but also I think it would be hard to tell if a newly fledged sparrow only weighed 66% as much as their parents... Anyway, I think this is beyond our abilities to answer rigorously without a large amount of sorting through the scientific literature. AFAIK we have no actual ornithologist regular participants here. But, you can contact the ornithologists at one of the world's best labs here [16]. Note that they do not guarantee a response at all, and it might take a long time. One other thing you could do is bypass the front door and find a grad student who is studying something about bird nesting, incubation, or fledging, and ask them directly. Most grad students I've known would be flattered that you found them and asked. The Cornell lab directory [17] has a few grad students, research assistants, and postdocs that you could email, or you could look for a similar ornithology group based at a university in your area. SemanticMantis (talk) 18:07, 19 March 2015 (UTC)

I can tell you that a fledging sparrow is indeed lighter than and adult. We had a nest once in a birdhouse, and the last chick did not leave with the other chicks. After two days, I went to the nest, and found the chick's leg had been caught by a string in the nesting material. The chick was trapped and the leg was dead, so I amputated it at the ankle. It probably weighed about half of the adult mass of a house finch, which I used to catch by hand when they flew into my window frame through a slit in the screen, but could not escape.

We took he chick to an animal sanctuary in a shoebox. The little bugger flew off once we cracked the lid of the box to show the caretaker. (She said not to worry, there was plenty of water and there were feeders behind the shelter.) I suspect the bird had lost weight due to starvation and dehydration over two days. It was the length of an adult, but not of the same mass. In any case, it had no trouble flying and perching. μηδείς (talk) 18:27, 19 March 2015 (UTC)

Earth's magnetic field

From North Magnetic Pole:

The North Magnetic Pole is the point on the surface of Earth's Northern Hemisphere at which the planet's magnetic field points vertically downwards (in other words, if a magnetic compass needle is allowed to rotate about a horizontal axis, it will point straight down). There is only one location where this occurs, ...

Is "There is only one location where this occurs" a physical certainty, or is it just based on the fact that only one pole has ever been observed, to the accuracy with which such measurements have been made? I obviously understand that a simple bar magent has only one north pole, but images of the magnetic field around, for example, the Sun, appear to show a tangle incorporating numerous smaller local poles. Could such a thing happen, in a less intense way, on Earth? 109.153.227.129 (talk) 14:25, 18 March 2015 (UTC)

See Dynamo theory for starters. SemanticMantis (talk) 14:30, 18 March 2015 (UTC)

I should explain in slightly more detail what I am envisaging. I am not envisaging a hitherto undetected pole in the middle of the Pacific Ocean, or anything like that; I am wondering whether within a few miles or tens of miles of "the" magnetic pole, the angle of the field lines could fluctuate around 90 degrees, such that several (or numerous) poles could exist within the vicinity. 109.153.227.129 (talk) 14:40, 18 March 2015 (UTC)

The International Geomagnetic Reference Field is the most widely respected model of Earth's non-ideal magnetic field. It is updated every few years based on high-accuracy, high-resolution measurements. This field is used by navigators, researchers, and other people who have stake in accurate measurement of the imperfect deviations from a simple dipole.

A pure dipole field would have exactly one point satisfying the OP's conditions. In actual fact, the Earth is very dipole-like. It would be a difficult numerical problem, however, to show whether the IGRF model predicts any other purely-vertical field lines pointing toward the Earth's barycenter (or, normal to the Earth's surface, a different but equally-interesting problem that would require very high-resolution topography data, like the SRTM dataset). The limitation, of course, is the resolution of the model. It is very plausible that as you get incredibly close to the "dipole" pole that minuscule deviations at very tiny length scales - say, meters or even millimeters - might satisfy the conditions. These types of details →are really just mathematical curiousities: in practice, we don't have models that make meaningful predictions of Earth's geomagnetic field with resolutions in the millimeter-scale.

Nimur (talk) 15:38, 18 March 2015 (UTC)

Full disclosure: I know many expert researchers who use the Dipole model of the Earth's magnetic field - and not the IGRF - because in their applications, the numerical differences are so small as to be negligible.

I even know aviators who even ignore the magnetic declination (the error between true north and the direction that the compass points) - either because they fly using GPS, or because they fly in Chicago, or because they fly in windy parts of California and just don't concern themselves with a constant course error of only 14-degrees while navigating visually. These guys would be lost, though, if they ever got chased into the clouds by the Luftwaffe.

And remember, as AOPA Magazine reminds you in Wind Directions: True or Magnetic?: surface winds reported by METAR are true direction; surface winds reported by ATIS are magnetic direction: unless the ATIS is digital, in which case they are true direction; winds aloft are true direction, unless they come from a PIREP, in which case you have to guess...

This might give you some perspective on how nearly perfect our simple magnetic field models are.

Nimur (talk) 15:54, 18 March 2015 (UTC)

IGRF is a 13th degree spherical harmonic solution, which implies the natural feature size in that model is still hundreds of kilometers. If there were multiple points of vertical inclination separated by even 100 km you wouldn't expect IGRF to reconstruct that faithfully. (For scale, the magnetic North pole is presently about 400 km from true North). Hence the global field models probably aren't the best tool for looking for duplicate poles. That said, I don't think a scientific expedition in the Arctic would miss a duplicate pole feature if the separation was anywhere as large as 100 km. Dragons flight (talk) 18:02, 18 March 2015 (UTC)

I generally agree that the resolution is quite low... but that's the best resolution available!

I found this posting in Dispatches from Antarctica, published as part of the official Department of Defense Science Blog, in which Lt. Col. Ed Vaughan wrote:

“ What are isogonic lines and how do they influence magnetic compass readings? Most modern airplanes have both magnetic compasses and gyroscopic compasses of some sort. Given the relationship between the Geographic South Pole and the Magnetic South Pole, and especially the density of isogonic lines in the region, which describes the rate of change of magnetic variation, magnetic compasses are next to useless here for flying. ”

In other words, if I may paraphrase... people who specifically study this problem and work near the poles just ignore the local magnetic field variations!

Here's a really cool data-book, published by the Government of Austrialia's Geosciences program: Isogonic Map of Austrailia (1965). The isogonic lines on the map just stop at the 41st parallel of latitude! A more recent map, in digital form, is available from NOAA: Historical Magnetic Declination. These charts are computed from IGRF, and it is the exact same source-data that official navigation charts are made from... I don't think anything higher resolution exists! If you zoom really close into the magnetic poles, you'll see rendering artifacts - in fact, some of the polygonal lines cross each other. Those would be places where the IGRF provides an inaccurate model compared to ground-truth, and those are the spots where you might expect to find it difficult to disentangle "duplicate poles." Some of these artifacts are surely rendering artifacts exacerbated by the choice of map projection and the specific method used to draw these lines programmatically; but others may be actually representative of model effects.

Nimur (talk) 19:51, 18 March 2015 (UTC)

When the poles flip they don't just turn upside down, the magna's circulation breaks up and forms new cells. The dipole is the net effect of all those cells, hence the new field may be stronger or weaker than the original. i hazard a guess that during the chaotic bit between stable solutions there would be more than one area where the field lines were vertical. Greglocock (talk) 21:30, 18 March 2015 (UTC)

Dip needle

I am not sure anyone answered the OP's questions. The article to look at is Magnetic dip. At the North Magnetic Pole it is straight down 90 degrees from level and it is close to level (0 degrees) near the equator. I suppose there could be more then one place near the North Magnetic Pole where this happens, just because of iron deposits messing with the compass. Keep in mind the North Magnetic Pole moves around. Here is a picture of a dip needle to measure this sort of thing. Richard-of-Earth (talk) 09:28, 19 March 2015 (UTC)

The trouble is that no great maps of isoclinic lines - lines of constant geomagnetic inclination - not many people need that. You can create your own map from the same model or from the dataset. However, there are plenty of maps of the isogonic lines - and you can approximately infer the inclination by assuming the simplification that isoclines run parallel to the gradient of isogonic lines. The same problem exists as above: no dataset or model provides sufficient spatial resolution near the poles, which are the region of interest here. Nimur (talk) 13:19, 19 March 2015 (UTC)

• Thanks for the replies. 109.153.236.190 (talk) 12:12, 20 March 2015 (UTC)

Automated cell counting on microscope slides

Is there anything that I can buy to automate counting of cells across an entire microscope slide? It's not practical to do it manually 194.66.246.62 (talk) 16:48, 18 March 2015 (UTC)

I imagine counting the total number of objects could be automated, but recognizing which objects are cells and which are other things could be rather tricky. As far as doing it manually, why not use a smaller sample you can count, and then extrapolate to estimate the total ? StuRat (talk) 17:21, 18 March 2015 (UTC)

I might be missing something but why do you want to count across the 'entire' slide? What is to stop you using a hemocytometer and doing the math?--Aspro (talk) 17:29, 18 March 2015 (UTC)

This is commonly done with the free software ImageJ. It would require you to photograph each slide, with a decent camera and decent light. People in my old lab used it to count pollen, but little blobs are little blobs as far as image processing software is concerned... it can distinguish dust specks from cells, and also distinguish hairs or leaves from pollen. This google scholar search for /count imageJ/ [18] will show you many papers that use that software to count cells and other things. With a little more searching, you might even find a paper that hosts the specific code they used in an online repository. SemanticMantis (talk) 17:42, 18 March 2015 (UTC)

See also Fiji_(software) SemanticMantis (talk) 17:44, 18 March 2015 (UTC)

.....which is just ImageJ (Fiji Is Just ImageJ), sorry couldn't resist.. OP, you'll have to tell us a bit more about exactly what you want to do. There are hardware and software solutions for these kinds of problems. Fgf10 (talk) 21:49, 18 March 2015 (UTC)

Sun's radiation

As time passes, is the sun radiating less heat and light, more, or is it constant? --Llaanngg (talk) 18:30, 18 March 2015 (UTC)

Estimated evolution of the Sun. The red line shows changes in luminosity.

Solar luminosity, Stellar evolution, Faint young sun paradox. Stellar evolution models estimate that 4 billion years ago the sun would have been only about 70% as bright as it is today, and that it will continue brightening at a rate of about 1% per 100 million years for the next several billion years. Dragons flight (talk) 19:06, 18 March 2015 (UTC)

Main sequence stars, as noted, very gradually increase in luminosity as long as they stay in the main sequence. At some time in the distant future, the Earth will become too hot for human habitation, and we will all have to move to Mars unless in the meantime we develop a technology for moving planets themselves. Robert McClenon (talk) 21:16, 18 March 2015 (UTC)

Question about genealogy/evolution

I hope this question is not taken as racist, because this is only because of scientific curiosity.

If a European white couple were to move to central Africa and have a baby, the baby would turn out white as well, right? But if their bloodline stayed in central Africa for many generations and only interacted with other bloodlines of European descent, surely their babies couldn't stay white forever?

I mean, something must have happened in human history that caused different skin colours to develop in the first place. Will the surroundings eventually affect the babies' skin colours? I understand this would take millennia at the least. JIP | Talk 20:12, 18 March 2015 (UTC)

See Lamarckism for some interesting reading. Human_skin_color#Genetics_of_skin_color_variation may also help you in your research. --Jayron32 20:17, 18 March 2015 (UTC)

JIP's claim that light-skinned people could eventually have dark-skinned descendents doesn't depend on Lamarckism, I don't think. I'll simplify the scenario and assume that a few light-skinned Europeans start a clan in Africa, which has no other people. After the population has grown, there will be some natural variation in skin tone, and it may indeed be the case that fair skinned descendents have less offspring than their darker cousins, leading to a selective pressure for darker skin, and perhaps even gene fixation. I'm not saying this would definitely be the case, just that it could be, without appealing to (mostly wrong) Lamarckian concepts. SemanticMantis (talk) 20:52, 18 March 2015 (UTC)

If a fair-skinned European (or northeast Asian) couple were to have a baby in Africa, of course the baby would have their genes for skin color, yes. Dark skin is an adaptation to the African tropical sun, and fair skin is an adaptation to the mid-latitude sun of Europe or eastern Asia. Presumably there would be some selective pressure for darker skin in Africa. As the OP noted, any re-darkening would be on a time scale of millennia. I agree that the question isn't about Lamarckian evolution, but about Darwinian evolution. I think that the question is more or less answered as yes, that there would be a very slow selective pressure toward darker skin. (In the short run of one-and-one-half centuries, all that happens to Anglo-Celtic Australians is that they, unlike aboriginal Australians, get skin cancer.) Robert McClenon (talk) 21:14, 18 March 2015 (UTC)

I think the answer is possibly but not necesarily! Many evolutionary processes appear not to be easily "reversible". For example, it seems that it didn't take fish very long to evolve air breathing lungs, once they started down the land dwelling road, BUT no animal in histrory has ever gone BACK to water breathing gills (or any organ), even thugh several animals went back to the water long ago and have made other extraoirdinary adaptations for aquatic life. Vespine (talk) 21:59, 18 March 2015 (UTC)

Just to correct the "didn't take very long" bit, the first fish appeared during the Ordovician period, 480,000,000 years ago or so. The first fish-amphibian hybrids crawled onto land during the Devonian, about 120,000,000 years later. That's a pretty long time. But, you are correct, in the intervening 365,000,000 years, none of the animals that went back to the ocean evolved gills back again. Evolution is not likely a reversible process. Also, it seems unlikely that modern humans face the evolutionary pressures that humans did thousands of years ago. --Jayron32 23:18, 18 March 2015 (UTC)

Gaining or losing lungs or gills is quite a major change, and would require all the intermediate stages to be useful. In contrast, everyone (apart from albinos) have some melanine in their skin, and evolving a darker or lighter skin would just be a matter of changing how much is produced, an so presumably much easier. Also, bear in mind there's no such thing as a "pure" race, so this transplanted "white" population may well have had some recent "black" ancestors, and still have their genes in the genepool. As the genes get shuffled over the generations, some of their children might inheret more "black" genes - and if this is enough to provide an evolutionary advantage, then that lineage will produce more and healthier descendents, and the population as a whole will become darker. 62.172.108.24 (talk) 16:32, 19 March 2015 (UTC)

The reason dark skin developed in tropical areas is that the greater amount of sunlight there makes sunburn and skin cancer more likely, unless the UV light is blocked by greater amounts of melanin. However, we now have sunscreen, protective clothing, etc., so this can take the place of melanin. Actually, sunscreen, etc., seems like it might be a superior solution, because dark skin can also lead to overheating, which is a real problem in Africa. Thus, it may no longer be advantageous to have dark skin in Africa. StuRat (talk) 05:10, 19 March 2015 (UTC)

It should be noted that dark skin did not develop as an adaptation for pale skinned humans. They were already dark skinned, and already in Africa. Humans who moved to other areas developed lighter skin, not the other way around. See Recent African origin of modern humans. --Jayron32 14:49, 19 March 2015 (UTC)

True, but whether there has been much redarkening is I think still somewhat unclear. Our Human skin colour seems to suggest there hasn't. "Investigations into dark skinned populations in South Asia and Melanesia indicate that skin pigmentation in these populations is due to the preservation of this ancestral state and not due to new variations on a previously lightened population." Our dark skin, however says "According to Nina Jablonski, darkly pigmented modern populations in South India and Sri Lanka are an example of this, having redarkened after their ancestors migrated down from areas much farther north." One thing that is clear I think is that some populations have a darker average than surrounding and this is likely a later adaptation (i.e. there definitely has been some darkening). It is perhaps also worth mentioning that dark skin is an adaptation in itself, just one that began earlier in human evolution, around the time we lost body hair. Nil Einne (talk) 01:44, 20 March 2015 (UTC)

Mammals in general seem to have either black or pink skin (with a few exceptions, like a mandrill). The black would be with lots of melanin, while the pink skin seems to lack melanin and any other pigments, such as carotin, so you see the red color of the blood through the translucent white skin. Primates, living mainly in tropical areas, seem to have mostly developed black skin. Then, when humans evolved from earlier primates, this characteristic remained, until humans moved out of tropical areas and the lack of sunlight meant vitamin D could no longer be synthesized in sufficient quantities with that much melanin blocking it. StuRat (talk) 06:54, 21 March 2015 (UTC)

• JIP's scenario would only work if the babies born with slightly darker skin tended to produce more children, while the lighter skinned babies produced fewer (by dying or being sick, etc.) If they all wore sunscreen and there was no differential reproduction there'd be no evolution toward dark skinnededness. μηδείς (talk) 16:55, 19 March 2015 (UTC)

Sewing machine oil vs turpentine substitute

My sewing machine instruction manual advises the application of kerosene to the oiling points after the machine has been idle for "some time" in cases where it does not "run smoothly". After applying kerosene to the oiling points the machine is to be a run quickly for one minute after which the oiling points are wiped off and oil applied. How does kerosene compare chemically to sewing machine oil? Wiping the oiling points will not remove all of the kerosene. Will the rest evaporate? Does the sewing machine oil turn rancid over time like cooking oil? --Seans Potato Business 21:27, 18 March 2015 (UTC)

Kerosene is a better solvent, so it will help to dissolve any gum from dried out oil. But, it is not a very good lubricant, so it will wear out your machine more quickly than oil.Any residual kero will dilute your oil a bit, if you are worried by this oil it, run it, wipe it clean, oil it again. Kero will evaporate very slowly, but any gum dissolved in it will then redepositGreglocock (talk) 21:38, 18 March 2015 (UTC)

Yes kerosene will evaporate. Think though, that the term 'polymerization' is more fitting than 'rancid' as the latter refers to taste. In resent years, cheaper lubricating oils have been used which in time polymerize (i.e., thicken). More tradition (and expensive) lubricants like 'porpoise jaw oil' lasted for years and didn't leave deposits. These days it is hard to find. However, a good clock maker may be able to get you some (by clock maker, I mean a proper horologist, not a purveyor of modern plastic round things controlled by a quartz oscillator). --Aspro (talk) 22:38, 18 March 2015 (UTC)

For the latter part, see rancidification and I think Hydroxylation. My WP:OR and previous reading suggests that mineral oils are far more stable than animal oils, and that plant oils (most cooking oils) go rancid/break down the fastest, at least generally speaking. I'm not sure what type of oil is sold as "sewing machine oil" (Lubricant#Base_oil_groups?), but I suspect it will not go rancid before it wears away, and the kerosene will help remove any residues. SemanticMantis (talk) 23:15, 18 March 2015 (UTC)

? I intermatted above that 'rancid' is not a good term. Stability, is the oils ability to resist cross-linking (get gummy). Mineral oil fractions can do this too. The origin of the lubricant does not matter as much as the the characteristics of the monocular chain. Nye Lubricants - 170 years of History--Aspro (talk) 00:02, 19 March 2015 (UTC)

Sure, you said that stuff, but you didn't include any refs or even wikilinks. I pointed out rancidification because OP asked about it, and it tells us "Akin to rancidification, oxidative degradation also occurs in other hydrocarbons, e.g. lubricating oils, fuels, and mechanical cutting fluids" - and that's what led me to hydroxylation. I admit I can't follow the details of the chemistry, but it seems that the degradation of plant oils and mineral oils is at least somewhat analogous. SemanticMantis (talk) 14:52, 19 March 2015 (UTC)

OK. Polymerization.--Aspro (talk) 20:02, 19 March 2015 (UTC)

My understanding is that the chemistry is pretty simple really. Drying oils from unsaturated fats that have often multiple double bonds that allow them to undergo reactions quite readily, whereas those that do not react are saturated hydrocarbons. With enough double bonds, oils can "dry" i.e. react with oxygen so quickly that they cause spontaneous combustion. It is very useful for one's sense of paranoia to understand this difference so you don't have to look at every oily piece of cloth the same way, but can... prioritize. Wnt (talk) 23:45, 19 March 2015 (UTC)

• Hello, the kero would be used to remove the "gum" or "varnish" (for all the names given as stated above) sewing machine oil is a mineral oil, however just like petorleum fuels used in engines, it eventually deposits some gum onto working parts if they have not moved for some time, or become overheated, this is why you are meant to lubricate with new oil often. as a sidenote, but related, One of the most common problems with small gas engines is that the fuel goes "stale", and leaves varnish on the jets of the carburetor etc. therefore new fuel is the first remedy.Read-write-services (talk) 22:50, 19 March 2015 (UTC)