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April 16

all sky surveys

Does anyone know what the best (in terms of resolution and magnitude it goes down to) all sky survey in the visible spectrum that doesn't have any copyright restrictions?©Geni (talk) 04:45, 16 April 2014 (UTC)[reply]

Is reality ultimately digital or analog? Can another particle pass through the intervening space while an electron is performing a quantum leap?

When I was young I remember reading or hearing somewhere that you can divide a line up an infinite amount of times. Therefore, when physically moving from point A to point B it's just an illusion. As you're not really moving through the intervening space since it can be divided up an infinite amount of times. I'm pretty sure there's something I'm not understanding there or a flaw in the logic, but ever since then I've still always wondered, is there an ultimate limit to how many times the space between two points can be divided up? Is reality ultimately digital or analog?

I've since learned about the planck length, but recently also learned something else that has now been confusing me: quantum leaps, and that the electron does not move through the intervening space when it leaps from orbital to orbital. My other question then is, is it possible for another particle to pass through the intervening space between electron orbitals? Especially, just as a quantum leap is occurring.. let's say a quark (or whatever) happens to fly through the picture.. is it also subject to 'quantum leaping'? Or can it move through the intervening space while an electron can't? I'm sure I'm missing something or not understanding something about wave/particle duality here, but I'm just a layman. Glad there's some really intelligent folks here that can explain some things or at least point me towards the right articles. Thanks, 70.71.247.169 (talk) 12:28, 16 April 2014 (UTC)[reply]

Electrons are not little balls that move in circles around another little ball. That's not what an atom is. Your question presupposes this to be the case; that an electrons moving between energy levels somehow changes "tracks" or moves without crossing the intervening "space". Electrons don't work like that, and the question shows a fundamental misunderstanding of how electrons work. One cannot even answer the initial question regarding whether another particle can "pass" through the "space" during a "quantum leap". Electrons don't change locations. Per the uncertainty principle electrons are not even localizable enough to say where one is, and if you don't know where it is you don't know where it moves to. No, electrons change the amount of energy they have, and the change between amounts of energy is confined to certain values. That's what a "quantum leap" is. It isn't a physical change of location. Any electron has a non-zero chance of being at any location in the known universe; though within certain probability limits we can define areas outside of the nucleus of an atom where any particular electron is likely to be (see orbital). --Jayron32 12:48, 16 April 2014 (UTC)[reply]

I would start with Zeno's Paradoxes, which is almost certainly what confused you as a child. From a mathematical point of view, this is addressed in calculus and infinitesimals: from a philosophical point of view, I'm sure you could find a variety of interesting discussions and arguments that I am ill-equipped to advise on. 86.146.28.229 (talk) 12:56, 16 April 2014 (UTC)[reply]

As far as not being able to move anywhere because that requires going through an infinite number of intermediate locations, the flaw in that logic is that as you divide the space up you also divide the time it takes to pass through that space. So, you can think of it as taking zero time to pass through each infinitely small space. But then you might still think zero time multiplied by an infinite number of positions gives us either zero or infinite time, so that seems wrong, too. However, these are limits we are dealing with, not actual numbers. For example, if we had the expression x/x, and we wanted to evaluate that as x approaches infinity, we could break it down to just x, which approaches infinity, multiplied by 1/x, which approaches zero. So, this seems to be the same case of zero times infinity. However, for any value of x, no matter how small or large, we can obviously see that x/x is just 1. StuRat (talk) 13:08, 16 April 2014 (UTC)[reply]

For many values of x, at least, that holds true. Mathematicians means something pretty intense when they say "for any value of x." There exists at least one x for which L'Hôpital's rule can not be applied to the limit of x/x as x goes to zero; that would be an indeterminate form. The limit might not exist; or, the method to find the limit might be more difficult. Nimur (talk) 14:59, 16 April 2014 (UTC)[reply]

"Digital" and "analog" are probably the wrong conceptual models to frame the original question. Those are adjectives we apply to machines we build; if we design a transistor-circuit to usefully operate in a specific way, so that its outputs are thresholded, we call it "digital," and so on.

A more useful set of adjectives to describe our formal models of "reality" are the words "continuous" and "discrete". Both of these concepts are mathematical models of the world. They are ideas constructed by humans as part of our effort to understand the physical world, (using idealized abstraction). Mathematicians can prove amazing properties about discrete or continuous systems by carefully describing their assumptions and proceeding logically to derive complicated results. But those mathematical facts apply to an idealized world, as denoted by axioms set up by the mathematician! When we study the physical world - as observational scientists or engineers - we usually have the luxury of choosing any model that works to suit our needs. When we zoom to very microscopic scales, we find that some quantities are always discrete, while others vary continuously. As an example: it is useful to model space as a continuous variable. It is convenient to study the position of a particle as a discrete value. In some cases, physical constraints quantize a potentially continuous value so that it is only measured to have a small number of discrete values. When we discover such a property - like angular momentum - and note that it is always quantized, then we have discovered a simple fact about the nature of our universe.

But, even the most enthusiastic physicist would be hard-pressed to say that quantization of certain physical properties demonstrates that "reality is quantized." All we have shown is that certain physical properties behave that way. "Reality" is too poorly defined for us to use inductive logic on it. Nimur (talk) 15:12, 16 April 2014 (UTC)[reply]

The most pertinent articles I can find on Wikipedia about this topic are Digital physics and Fredkin finite nature hypothesis. But see also Bekenstein bound and Margolus–Levitin theorem. On at least some of the digital physics stuff, it starts getting far enough away from mainstream physics that even calling it "highly controversial" is being kind. Red Act (talk) 18:06, 16 April 2014 (UTC)[reply]

Also see Quantum spacetime (or Spacetime#Quantized spacetime for context), the discussion of discrete spacetime in Pregeometry (physics), and Causal sets. Red Act (talk) 20:12, 16 April 2014 (UTC)[reply]

It’s a question that has intrigued me as well. We call our computers digital because the calculations they make are by discrete numbers, not by physical traits such as weight, mass or temperature. But when we examine the microchip more closely, we see that it too is dependent on analog parameters. There must be natural mechanisms that impel the photons, and the chip will heat up if the channels are too small, and so on. But what about when we really get to the most basic substrate of reality? Is it digital or analog? Popper and other logicians have argued that if fundamental reality was digital, or nomino-deductive, then we could prove empirical observations as being necessary in the way that a triangle necessarily has 3 sides. In the physical world, we cannot prove any empirical observation like that. Snow might be seen as always white, but we cannot prove that it always was and always will be white.

In a fundamental way, these kinds of questions are being asked by researchers at the Large Hadron Collider. Can we ever really get a digital picture of reality that provides us with mathematical certainty in the way 1 + 1 = 2 does? What would that kind of reality look like? I don’t think it could even be imagined, and even in sci fi fantasy, there is no fake reality like that which we could look at and say, “Well, it might be a bit like this...”

Final reality, if there IS such a thing ( quite a few philosophers and scientists think there is no end to the layers of reality, and thus no bedrock to it), but if there IS such a final reality, it might be something unimaginably different to EITHER digital or analog. It might be something that our brains, rooted in space and time, simply cannot visualise or conceptualise. After all, how bizarre are the findings of Quantum Physics even now? The real truth might be a lot weirder than a particle being in two places at once, and a wave or a particle according to how it is being measured. Myles325a (talk) 09:14, 17 April 2014 (UTC)[reply]

Plant identification request.

So that I can label this for commons, any suggestions on what it is?Sfan00 IMG (talk) 12:54, 16 April 2014 (UTC)[reply]

That's not much to go on. Is it a shrub? Where in the world was the photo taken? Any description of the environment it was in, or how large it was? Extra info would help. SemanticMantis (talk) 15:39, 16 April 2014 (UTC)[reply]

Posssibly Canada , based on the Uploaders other contributions.. ? Sfan00 IMG (talk) 18:44, 16 April 2014 (UTC)[reply]

Really hard to say, but my best guess (don't use this for labeling tho) is that this is some sort of maple bud. Maples have these tripartate buds, kinda like a fleur-de-lys, see these pics. This looks like after the bud starts to put out shoots. --Jayron32 01:20, 17 April 2014 (UTC)[reply]

I can identify buds and I can identify leaves, but identifying the transitional stage is beyond me I'm afraid. I think maple is a fairly safe bet though. THE MAPLES OF NORTH AMERICA suggests that there are about 13 or so maple species that are native to North America. Alansplodge (talk) 17:15, 17 April 2014 (UTC)[reply]

Something's bugging me...

Namely the identification of these insects. Some I haven't even a clue what family they're in, let alone the genus or species... These were all taken in Umbulharjo, Cangkringan, Sleman, Indonesia.

The one with the very long antennae
The fly on the flower, Tachinidae
The grasshopper in the dirt
The grasshopper on the leaf
The grasshopper on the stalk
The one which looks like a bee and a fly

Any ideas? — Crisco 1492 (talk) 15:52, 16 April 2014 (UTC)[reply]

"The one which looks like a bee and a fly" is probably a hoverfly (family Syrphidae), but as there are 6000 species to choose from that may not be much help... AndrewWTaylor (talk) 17:23, 16 April 2014 (UTC)[reply]

We don't have an article, but the bluish green grasshopper may be a "Chameleon Grasshopper". Found a few pics in Google Images that may work for that, see this. --Jayron32 17:40, 16 April 2014 (UTC)[reply]

I don't have anything relevant to add. I never thought I would say this, but that grasshopper is gorgeous! Justin15w (talk) 22:02, 16 April 2014 (UTC)[reply]

Kosciuscola tristis or similar? Yes, it is quite a gorgeous creature. Aularches miliaris is also a beaut. — Crisco 1492 (talk) 00:53, 17 April 2014 (UTC)[reply]

Kosciuscola tristis or another Kosciuscola, perhaps (strangely the genus isn't even mentioned on Wikipedia yet)? There are five species, and I think I saw a source (didn't keep the link) that said all of them have the ability to change color. — Crisco 1492 (talk) 00:53, 17 April 2014 (UTC)[reply]

The "one the the very long antennae" is a cricket, possibly a tree cricket. Mikenorton (talk) 06:49, 17 April 2014 (UTC)[reply]

That looks to be a reasonable guess (although this one was out at 11 a.m., which isn't quite "nocturnal"... however, we may have disturbed it by tromping through the woods) — Crisco 1492 (talk) 08:16, 17 April 2014 (UTC)[reply]

Reason for Worthing exponent of metal electrical resistivity

Reference manuals for engineering often give constants ρ_T1 and α for use in an algebraic modification of Mitchell's formula for resistivity:

ρ_T2 = ρ_T1[1 + α(T₂ - T₁)]

where ρ_T2 is the resistivity at temperature T₂ and ρ_T1 is the resistivity at temperture T₁. However this formula is a rough approximation usually good enough where T₁ is around 300 K and T₂ is around 300 to 400K. For all metals above the scattering point (typically << 300 K) and below the melting temperature or Curie temperature for ferromagnetic metals, Worthing's formula is accurate within a few percent and often much better:-

ρ_T = ρ_T1K T^P

where ρT is the resistivity at any temperature T, ρ_T1K is the notional resistivity at 1 Kelvin (not to be confused with the actual intrinsic resistivity at 1 K) and P is an exponent characteristic of the particular metal. For many metals, P is around 1.2, which means that the slope dρ/dT increases slightly with increasing temperature. For ferromagnetic metals, P is around 1.7, so the curvature of dρ/dT is very pronounced. For some metals, e.g., palladium, Tantalum, P is around 0.8, which means that dρ/dT decreases with temperature. What is the reason for P being in three groups, P ~ 1.2, P ~ 1.7, and especially P ~ 0.8? 124.178.128.203 (talk) 16:33, 16 April 2014 (UTC)[reply]

I can't answer directly, but it seems similar to why most substances expand when heated, but there are exceptions, like with water, which expands when it freezes. There I believe the reason is that the structure of ice crystals contains more empty space. StuRat (talk) 16:40, 16 April 2014 (UTC)[reply]

No. Some metals are face centered cubic (eg Nickel, P = 1.747), some body centered cubic (eg tungsten, P = 1.205, or Iron, P = 1.768), and some are hexagonal (eg Cobalt, P = 1.687). Palladium is face centerred cubic and has P = 0.803 yet Tantalum is body centred and has P = 0.820. No correlation. 124.178.128.203 (talk) 16:50, 16 April 2014 (UTC)[reply]

Do any phase changes take places over the temperature ranges in question ? StuRat (talk) 17:09, 16 April 2014 (UTC)[reply]

In the case of iron (Fe), a phase change occurs at 1183 K (from body centred to face centred), but the Curie point is below this at 1043 K. The resistivity curve follows Worthing's formula accurately (better than +,- 1%) with P = 1.768 up to the Curie point then continues with P close to unity up to and past 1183 K. There may be an inflection point at 1183 K but it is difficult to detect in measured data. ( A paper by V E Zinovev & others in the Soviet Journal of Physics in 1972 claimed a slight step at about 1200 K but to my knowlege this hasn't been replicated. It may have been due to unidentified impurities, or more likely an instrument connection problem - only one test on one sample was done) , In fact, in engineering, we usually take the resistivity curve above the Curie point as a straight line. If phase changes have any significant effect, surely one would expect a point of inflection at the phase change temperature, not a smooth curve. Palladium resistivity is very curved with P = 0.803 and is fcc right up to melting. 124.178.128.203 (talk) 17:24, 16 April 2014 (UTC)[reply]

You're assuming the phase change takes place instantly throughout the sample. I'd expect some overlap of the two phases around the phase transition temperature, with the resulting resistivity being somewhere between those of each phase. This would be predicted to produce a smoother curve. StuRat (talk) 12:45, 17 April 2014 (UTC)[reply]

Again, no. Definately not. Resistivity is by definition a steady state property. One does not measure it while changing the temperature - one measures it at in a series of constant temperatures, waiting as long as is necessary for the sample to come to thermal equilibrium at each step. On either side of the transition temperature, one of the two phases is unstable and will not sustain. Under these conditions, the phase must be the same thoughout the sample - we are talking about sensibly pure metals and supercooling, quenching, and the like phenomena do not apply. 121.221.225.6 (talk) 13:25, 17 April 2014 (UTC)[reply]

Longevity documents

What other documents, aside from birth certificate and passport, I may need to submit in case of longevity (assuming that the Gerontology Research Group and the Guinness World Records would still exist)?--93.174.25.12 (talk) 18:11, 16 April 2014 (UTC)[reply]

Unless you are very old such documents are likely archived. Historians also use birth announcements in newspapers and religious (baptismal, Bris) records. Good luck. μηδείς (talk) 21:54, 16 April 2014 (UTC)[reply]

Since your passport was most likely obtained using your birth certificate, the birth certificate is the only document needed. Unlike your passport, your birth certificate is a vital record.--Shantavira|^{feed me} 08:53, 17 April 2014 (UTC)[reply]

I suspect you would need to produce evidence that it is you all your life. Let me explain what I mean here - I mean that the person claiming the longevity is not your son or daughter masquerading as you! --TammyMoet (talk) 09:28, 17 April 2014 (UTC)[reply]

List of the verified oldest people states that a supercentenarian would need at least three documents, so I wonder which is the third. 93.174.25.12 (talk) 17:14, 17 April 2014 (UTC)[reply]

April 17

How cold would a room temperature superconductor feel?

The more conductive something is the colder it feels right? So would a room temperature superconductor (assuming the room is colder than you are) feel super cold or is there some lower boundary to this? On a sort of related thought, if you were in a very cold room, say -50° F and you touched a superconductor, would it draw the heat out of you so fast it would look ghoulishly cartoonish how fast you turned to ice?--108.46.109.33 (talk) 00:26, 17 April 2014 (UTC)[reply]

No matter how fast the object conducts heat internally, you still can't lose it any faster than it can flow out of whatever part of your body is touching the object. --Trovatore (talk) 00:32, 17 April 2014 (UTC)[reply]

...in other words, even if you had an infinitely thermally-conductive heat sink chilled to within a whisper of absolute zero, and you decided to be a dumbass and poke it with your finger, your hand (and body) wouldn't instantly freeze solid. The first small fractions of an inch of your finger would freeze quite quickly, but the freezing rate would fall off (rapidly!) as the freezing progressed up your finger. Heat from your hand would have to be slowly conducted down the entire length of your frozen finger, in a process that would probably take hours just to get to your wrist.

That said, it is worth bearing in mind that all known superconductors, while having no apparent resistance to the flow of electrical current, still possess a finite thermal conductivity. Moreover, their thermal conductivities typically aren't much different from what they are in their slightly-warmer non-superconducting states. Infinitely thermally conductive materials remain, sadly, in the realm of science fiction. TenOfAllTrades(talk) 02:49, 17 April 2014 (UTC)[reply]

Superconductivity only applies to electrical conductivity. Thermal conductivity does not necessarily increase below the critical temperature. [1] discusses the thermal conductivity in magnesium diboride. Around the critical temperature, the thermal conductivity drops from ~250 mW/cm-K to nearly 0. In YBCO [2], the thermal conductivity does increase, but only by about a factor of 2. At its highest point, it's still only comparable to bronze or stainless steel. [3], [4], [5] are the best explanations I can find that don't require a PhD in solid-state physics to understand.

Liquid helium below the lambda point acts similar to a super thermal conductor (the value is still finite, but is a couple orders of magnitude higher than just about every other known material). But any thermal conductor is still going to tend toward equilibrium with its surroundings. It won't conduct heat in from a hot object faster than it can conduct it out into a cold object. And it will be limited by the thermal conductivity or heat transfer coefficient of the substances in contact with it. So, basically, it's going to feel like whatever it's in contact with, though it would probably be dependent on the size of the piece. A large piece with a large surface area will be able to conduct into more of the contacting material than a small piece, so it will conduct faster. If it's in a room chilled to -50, it will take heat out of your finger and transport it into whatever it's sitting on, warming that up. But it won't chill itself to below -50. Mr.Z-man 03:38, 17 April 2014 (UTC)[reply]

This is an interesting topic that gets far too little attention. First, the association with thermal conductivity in metals is apparently the Wiedemann–Franz law, based on the idea that electrons mediate both in that environment. It would obviously be extremely useful to invent better thermal conductors, for basic purposes like building antennas to radiate waste heat from power plants without heating rivers, cooling computers without fans, etc. But does any genuine zero-resistance thermal conductor exist? Do we know if one even could exist? Is there a theory that would say it should have a critical temperature? Is there something Cooper pairs could do to facilitate it? I should admit, I have no idea about it. Our article gives the impression that there isn't much theory about the whole field of thermal conductivity, and that seems like a really expensive deficit to have. Wnt (talk) 21:37, 18 April 2014 (UTC)[reply]

Severe colorblindness

How do normal people understand what monochromats can see, and/or how do monochromats communicate their vision in an manner understandable to normal people? I'm somewhat colorblind, but I can understand my condition because other colors come through fine: I can easily produce correct color descriptions for anything that doesn't involve red or green somehow. However, if you're stuck with just one color, how can you understand your situation in normal people's terms? If I had no color vision, I wouldn't be able to grasp the concept of color, so I wouldn't know what I was missing or how to explain that I was missing it. Alternatively, imagine that all you've ever seen was a single-color computer monitor, such as File:IBM PC 5150.jpg. Since your eyes have never seen anything except "black" and "green", how are you supposed to form a concept of "white" or "blue", or indeed how can you conceive of anything that's not black or green? Surely this has an answer that's not too hard, but I can't imagine what it is. Nyttend (talk) 00:59, 17 April 2014 (UTC)[reply]

At a fundamental level you are asking a very deep philosophical question, for which there is no easy answer. Similar to what does a blind person dream? I think qualia is the most relevant article. In the end, your perception is your perception and there is no way to be 100% certain what other people perceive. Lots of more or less colorblind people don't find out that they are colorblind because unless it makes an impact to how you perceive traffic lights, which is quite rare, everyone thinks the situation is normal. Vespine (talk) 07:00, 17 April 2014 (UTC)[reply]

As for your first question, we polychromats (is that a word?) have experience with night vision (no color) not to mention BW photography. — At one point in Ed Wood, an actress asks a cameraman, "Which dress do you like better, the red one or the green one?" "Which is which? I'm colorblind." We the audience are colorblind too, because the movie was shot in BW, but suspend our awareness of that fact until this bit of dialogue brings it up! —Tamfang (talk) 08:49, 17 April 2014 (UTC)[reply]

Within a particular environment, it's usually possible to associate a particular shade of grey with a colour, but this doesn't transfer reliably between environments. Measurements have shown that individuals "see" colours very differently, but we have been socialised very early in life to interpret the differing signals in a way that fits in with the colour names that others use. In your example of a green monitor, an individual would soon learn that very bright green was called "white" by others, but the concept of "blue" would be tricky or impossible to explain. Even people with "normal" colour vision often can't agree on the blue/green borderline, and an individual interpretation often depends on the background, and on what the eye has previously been looking at. Colour perception has a large element of social learning which overlays the nerve signals transmitted to the brain from individual cones. I assume that you've read the article on Colour vision. Dbfirs 09:02, 17 April 2014 (UTC)[reply]

It's worth considering that there are people who are tetrachromats. The woman known as "subject cDa29" is currently the only 'verified' human tetrochromat - but it's certain that there are many more. These people see more colors than we mere trichromats with "normal" vision. Then there are many species of freshwater shrimp who see things in as many as 12 different colors. So we should not kid ourselves that our vision is "full color" - that's very far from the truth. It's true to say that all humans are "color blind" to some degree.

A monochromat can get some appreciation for color by viewing the world through color filters. So, for example, if you cannot normally distinguish red and green - then you can view the world through a red or a green filter and note which objects get dimmer in the red filter and which get dimmer in the green filter. This would allow you to determine whether something is red or green - but (of course) you can no more understand what people with normal human vision are seeing than normal people can grasp what a tetrachromat or a freshwater shrimp can see. I have used infra-red vision devices that let me see hot things as bright and cold things as dark. This lets me distinguish infra-red light - but my perception of it is just the shades of grey that the device's display produced for me.

But how do we know that our own personal feeling of what "blue" is matches what someone else's feeling of "blue" is? We can't share that experience directly - so we can only guess that other people's brains are interpreting the color in the same way that we are. In that sense, it may not even be a meaningful question to ask how people with normal human vision see color. SteveBaker (talk) 18:50, 17 April 2014 (UTC)[reply]

I actually wasn't asking about personal feeling: I've wondered about that for a long time, but I've long assumed that it was unknowable. For that reason, Steve, I was only interested in how ophthalmologists could study the presence and absence of color-related sensations, and thus I really appreciate the point about the color filters: I've never before imagined anything that would convey any color-related information whatsoever to a person who couldn't see that color. Of course I understand that the monochromat can't experience the color itself, just as I can't really experience the difference between big increases and big decreases in File:GDP Real Growth.svg (8-10% decrease is identical to >10% increase, as I see it), but I was interested in finding any way in which a monochromat could experience any effect of color whatsoever. As noted above, it's somewhat related to blindness, but very different in that most of us got our colorblindness from Mom and Grandpa (it was congenital), but many blind people lost their sight in adulthood, so they can remember times when they could see; vaguely comparable to the biblical account of the blind man of Bethsaida (he could say that the people looked like trees because he'd seen trees), while we congenital types are like the congenitally blind man who obviously wouldn't have known what a tree or a person looked like. Nyttend (talk) 01:16, 18 April 2014 (UTC)[reply]

See:Neil Harbisson - he is a monochromat who has had a device implanted in his skull called an eyeborg that allows him to '"hear'" colour. As for the reply that says "Lots of more or less colorblind people don't find out that they are colorblind because unless it makes an impact to how you perceive traffic lights, which is quite rare" - what a load of nonsense! I have a red green colour deficiency - which occurs in about 8% of the male population - and I found out, like most people, when I took the ishihara test as a child. The only difference it makes to my perception of traffic lights is that the red light looks a little dimmer that the green and amber lights - something I would probably never have noticed if I wasn't looking for it. Mostly I have problems with distinguishing red hues mixed in with other colours when the overall lighting is not very bright. Ophthalmologists use a number of tests to study colour vision such as the Farnsworth-Munsell 100 hue test. Also, colorblindness can be inherited or acquired. Richerman (talk) 10:04, 18 April 2014 (UTC)[reply]

Thanks for the Farnsworth test, but again, it measures someone's reaction (if I understand rightly; the article is not well written), just like the Ishihara test: if you're monochromatic, all you get from it is a lack of sensation. Harbisson's interesting, but he obviously had a sense of what color was, even though he couldn't experience it; I was imagining someone who had no real idea of color in the first place. Nyttend (talk) 12:13, 18 April 2014 (UTC)[reply]

Decomposition of Urea

I've heard that the odor of urine is a result of urea decomposing back into ammonia. Does this mean that after shedding one of its nitrogen atoms, the molecule is methanolamine? What does the methanolamine (or whatever the correct decomposition product is) decompose into? — Preceding unsigned comment added by 70.171.10.159 (talk) 04:06, 17 April 2014 (UTC)[reply]

Actually, I believe the initial decomposition product is carbamic acid, which also smells bad and decomposes into ammonia and carbon dioxide. Methanolamine is a different molecule which would require some serious rearrangement to be produced from decomposition of urea! 24.5.122.13 (talk) 04:23, 17 April 2014 (UTC)[reply]

WP:WHAAOE wins again. Ammonia volatilization from urea. And it has diagrams and chemical equations and everything. --Jayron32 13:05, 17 April 2014 (UTC)[reply]

Degraded DNA – But is there hope for recreating the genome?

I often hear that strands of ancient DNA found in some fossil or frozen carcass is split and degraded, but I then wonder about how difficult it would be to put together a copy of the original code of the whole genome in question. So yes, what we recover from an ancient carcass may be badly degraded, but then, there would have been millions of copies of it, one genome per cell. So surely, if we can get millions of those cells together, extract their DNA and put them in a bath, then we can watch as they join together. And that’s just the cells from one carcass. We should be able to extract the DNA from every such carcass of a particular extinct organism that we can find, and then put them all together. Ideally, if there is a complete set of the genes out there, spread out or buried in different places, in one body or in many, then we should be able to reconstruct it, just as we can reconstruct a book that has had millions of copies originally, but now only postage size scraps exist.

And on top of that, we can deduce much about what missing genetic material might be by comparing the organism’s genome with the genetic material we can gather from organisms that flank it in evolutionary terms. Perhaps soon we might be able to make deductions from the phenome (bone structure and so on) to the genome, and write the code in reverse! Am I being a pessimist here in supposing that many extinct species will be resurrected when our facility for DNA manipulation gets a little stronger? Maybe the Dinosaurs are too far gone, but many extinct species have only been gone for a few hundred years, some only decades. Many mega fauna extinctions are associated with the spread of hunter-gatherers, and since Homo Sapiens has only been spreading thus from 20 to 40 thousand years, we should come across many well-preserved fossils which have DNA which is only thousands of years old, not millions.

Certainly, I would love to live to see the Tasmanian Tiger, The Elephant Bird and the Moa, and the Woolly Mammoths once again striding the plains. Myles325a (talk) 09:51, 17 April 2014 (UTC)[reply]

Much of what you say is correct. In fact, current methods of DNA sequencing actually work by splitting the DNA up into relatively short fragments, sequencing those fragments, and then using overlap data to join the partial sequences together. However, the phrase "watch as they join together" indicates a serious misunderstanding. DNA fragments do not join together of their own accord. It is possible to synthesize long strands of DNA, and as a matter of fact there was very recently a report of artificially synthesizing an entire functional chromosome (for yeast), but it's a very laborious process. In short, what you are proposing is beyond the current state of the art -- but not all that far beyond it. Looie496 (talk) 11:40, 17 April 2014 (UTC)[reply]

OP Myles325a back live. Thanks Looie, I was being whimsical when I described the scenario of dumping a lot of DNA into a tub and "watching it all put itself together". This was shorthand for whatever painstaking processes are actually used. But I WAS aware of the "shotgun" method of putting a lot of DNA fragments together and getting them to link up. I still am a optimist about what we can do with DNA restructuring, especially as we become more and more proficient with manipulating its structure. But I AM an amateur, and may be disenchanted by more sober minds with more expertise than I have. Myles325a (talk) 11:54, 17 April 2014 (UTC)[reply]

I think you meant to ask if we are being too optimistic, not pessimistic, in your original post. And no, you aren't, it all seems possible to me, with the note above that instead of literally joining all the different pieces of DNA together, you'd determine the genome on computer, then use that to synthesize a full DNA strand. Distinguishing the animal DNA fragments from bacteria DNA might also be a challenge.

There's also the Jurassic Park scenario that we might be able to patch missing DNA with that from current species, although we would want to use similar DNA, not frog DNA, as they used there. Probably more than 99% of mammoth DNA is in common with elephant DNA, for example, so a small missing fragment could likely be patched in with only a tiny chance it would differ from the mammoth's own DNA. But if you did end up with different DNA, then hopefully it would still be compatible, and you'd end up with a hybrid, like a liger.

However, there's still one other thing we need to do, as having an animal's DNA alone doesn't allow you to clone it. You also need a similar female animal into whose ovum you can insert the DNA. That ovum is then implanted back into that female (or another) to grow until birth. If the current species is smaller than the extinct one, such as an elephant being smaller than a mammoth, then natural birth might not work, and you might need to do a C-section instead. The surrogate mother also might not be able to carry it full-term (and note that the length of pregnancy might vary by species).

Now, as for letting an extinct species loose to survive in nature, that doesn't seem wise to me, as we don't quite know how they would fit into our current ecosystem. Would mammoths knock down trees and attack people, for example ? It's probably a better plan to restrict them to nature preserves.

Also note that creating a single breeding pair by reconstructing male and female genomes and individuals alone won't itself recreate the entire species. There's the lack of genetic diversity to consider, and also they may not choose to breed. So, we might have to keep the species going by cloning, and prevent inbreeding, until we can recreate enough individuals to have a viable breeding population.

There also might be lost info on how to behave, as they may have been taught that by their parents in nature. Thus, your baby mammoths may end up behaving like elephants, if raised by elephants. (Of course, some behavior is genetic, not learned, and thus wolves raised as dogs still retain wolf behaviors.)

The extinct species' lack of immunity to current diseases could be a problem, too. The baby mammoth, for example, might not be immune to common elephant diseases. If this turns out to be an issue, we might need to do a bubble boy scenario, where the mammoth is kept in total isolation.

Extinct large predators might pose an additional problem. Current large predators seem to be genetically programmed to avoid hunting humans (with a few exceptions), since, if their ancestors had done so, they would have been wiped out by humans. However, a species that went extinct may have lacked such an instinct, either because they died out before they came in contact with humans, or perhaps they did come in contact with humans but failed to evolve the "stay away from humans" instinct quickly enough to survive. So, such large predators could pose more of a risk if they escape. StuRat (talk) 12:13, 17 April 2014 (UTC)[reply]

FYI cloning/recreating Mammoths may be imminent. Here's some news blurbs, you can google around for more info [6], [7]. The mammoth genome project has been "completed", more info straight from the source here [8]. SemanticMantis (talk) 14:35, 17 April 2014 (UTC)[reply]

Ah, "imminent" is a bit of a stretch. You cannot currently create a genome of that size, whether by modifying an existing genome inside a cell, or by synthesizing one de novo. Craig Venter's genome replacement method is probably the best hope, but it is currently operating on genomes a few orders of magnitude too small to recreate a mammoth cell. Someguy1221 (talk) 08:19, 18 April 2014 (UTC)[reply]

As another answer to the original question, the problem with sequencing fragmented genomes is not just that some sections are not represented in available collections, but also that some sections are so full of repetitive DNA that we could not tell what goes where even if the entire genome was represented. The solution to this problem in the sequencing of extant organisms has been to use various methods for making full or partial sequences of long fragments. Imagine you are trying to piece together a painting from cut up scraps, but the painting was mostly just the same image repeated many times. You could accurately reconstruct some small chunks, but on the whole, you'd have no idea which scraps went where, even if you had all of them at your disposal. If you had a scrap that was longer than the others, and in fact spanned the entire length of the painting, that could help serve as a guide to put your partially reconstructed chunks together into a complete painting. If an ancient DNA source has decayed to the point that no fragments over a few hundred bases long survive, you're just shit out of luck. Someguy1221 (talk) 08:31, 18 April 2014 (UTC)[reply]

Perhaps you can use a similar existing animal, like an elephant, when cloning a mammoth, to get the outline for where everything generally goes. And if you end up with a few mistakes, it may not matter, especially if the mistakes are in the junk DNA. Even in functional DNA segments, while a single error could be fatal, it isn't likely to be. Maybe that section controls something like eye color, for example, that doesn't much matter. StuRat (talk) 18:39, 18 April 2014 (UTC)[reply]

Repopulating the planet with more than biblical accuracy

If we suddenly found out that there was going to be a terrible catastrophe and the earth was going to be destroyed very soon, and by a surprising coincidence we also found a planet that was identical to earth in every way except there was no animal life on it, and we had some means of transporting animals and humans to the new planet, but couldn't take everything, what is the minimum amount of each species we'd have to take in order to have a good chance at survival? Like, if we just took 2 of everything like in Noha's ark then some of them would get eaten straight away and the others would starve or have incest offspring which would be genetically bad. Horatio Snickers (talk) 19:06, 17 April 2014 (UTC)[reply]

Minimum viable population gives some ideas. 75.41.109.190 (talk) 19:14, 17 April 2014 (UTC)[reply]

Also, Population bottleneck. The article mentions that all European bison are descended from 12 individuals. Apparently there are now almost 5000 of them and the population is increasing. By the way, Noah's ark contained 7 animals of some kinds, and 2 of others (in addition to 8 humans). - Lindert (talk) 20:38, 17 April 2014 (UTC)[reply]

To be fair, that depends on which source you're reading. Evan ^{(talk|contribs)} 02:29, 18 April 2014 (UTC)[reply]

Founder effect also has some food for thought.OttawaAC (talk) 05:23, 18 April 2014 (UTC)[reply]

Very interesting question, and good links above!

I respect the value of counterfactual conditions, and you're touching on many important issues in population biology. But, if taken literally, something that is "identical to earth in every way except there was no animal life on it" -- is basically logically impossible, based on our current understanding of evolution and ecology. For example, the adaptive radiation of flowering plants on Earth was tightly coupled to the mutualisms between plants and insect pollination syndromes. Simply put, without animals, a similar planet would not have anywhere near the diversity of plant life that we see on Earth, because our flora is intimately linked to our fauna. All the plants we know with animal-specific defenses would have no reason to exist O.o SemanticMantis (talk) 02:34, 18 April 2014 (UTC)[reply]

And thus there would be no point in taking animals that are strongly specialized in their diet. How many animals that leaves is another interesting question. —Tamfang (talk) 06:16, 18 April 2014 (UTC)[reply]

In fiction perhaps it might be explained away with another catastrophic event that happened on planet Earth II very shortly (days?) before it was discovered. Something that wiped out the entire animal population without affecting any of the other kingdoms. Erm .. perhaps. ---Sluzzelin talk 06:26, 18 April 2014 (UTC)[reply]

If we keep God in the picture, then whatever He said we needed is correct. As mentioned above, there is a bit of Deus ex Machina to have flora without fauna. If God overcame that problem, genetic diversity and population is a cakewalk. --DHeyward (talk) 09:15, 19 April 2014 (UTC)[reply]

Sulpher content in foods

Why is the sulfer content not listed when i search the nutrtional value of foods? I have also been searching for a comprehensive chart with thie sulfer content in particular and can not find it. So i thought to search each individual food and its not listed ther either. I would love to find it or to see it added! Thank you 96.50.231.89 (talk) 19:39, 17 April 2014 (UTC)[reply]

Well, I'm not aware that sulfur, per se, is thought of as a discrete "nutrient". There are single elements that are thought of like that, but they tend to be metals or near-metals (calcium, magnesium, then trace nutrients like copper and selenium). Are you concerned that you might be getting too little (or too much) sulfur in general? I have never actually heard of that.

Now, sulfur-containing amino acids, like say methionine or taurine, that's another story. I wouldn't expect those to be on the actual nutritional label as that's a little too detailed, but you can probably find their incidence in foods if you search. --Trovatore (talk) 20:24, 17 April 2014 (UTC)[reply]

The vast majority of sulfur (sulphur) in one's diet is consumed in the form of sulfur-containing amino acids (principally methionine and cysteine) which are part of all dietary proteins. Specific recommendations for dietary sulfur are not generally provided, as sulfur needs – in a form that the body can use – are almost always readily met by consuming the recommended amounts of total dietary protein.

Note that methionine is one of the essential amino acids, and that individuals on vegetarian/vegan diets do need to pay attention to their protein mix. Elemental sulfur in the diet (as the pure material or as part of most other compounds) cannot substitute for the required essential amino acids, as the human body is unable to synthesize methionine from scratch. TenOfAllTrades(talk) 13:51, 18 April 2014 (UTC)[reply]

"Vast majority" is an overstatement -- we also consume substantial amounts of sulfur in other forms. This chart gives a table of sulfur content for many foods. We also have an article about low-sulfur diets that contains some relevant information. Looie496 (talk) 14:32, 18 April 2014 (UTC)[reply]

April 18

Negative pH of acid mine drainage

Given that the molarity of hydrogen ions in pure sulfuric acid is not much less than the negative of the common log of 18 (the molarity of pure sulfuric acid), how can an aqueous solution (i.e. acid mine drainage) exceed that hydrogen ion concentration with a pH as low as -3.6? I know there's also iron oxidation contributing, but surely it can't be as important as the sulfuric acid present.--Jasper Deng (talk) 06:57, 18 April 2014 (UTC)[reply]

The paper traces back to [9]. The sulfate concentration is up to 760 g/L, but sulfuric acid has density 1.84, so it isn't all sulfuric acid (which only has pH -3 according to our article ... which is still lower than -log 18...). There are up to 200 g/L of other minerals present. Someone will have to get the paper to see what they are. Fundamentally, note that pH is not p[H], and that at low pH things get ... strange. According to our article the Nernst equation breaks down. But the bottom line is that you have to know exactly what you're measuring and not assume it means anything else when you're in that territory. Wnt (talk) 21:27, 18 April 2014 (UTC)[reply]

I got access to it via JSTOR, but it didn't elaborate too much on how those results were obtained. It did however consider the invalidity of the Nernst equation under those conditions and the need for a different definition of pH.

As I learned it, there was no distinction made between pH and p[H], but I never had to deal with solutions this acidic (i.e. it was a basic chemistry class).--Jasper Deng (talk) 04:48, 20 April 2014 (UTC)[reply]

Why is subculturing called passaging?

I've heard the word passaging pronounced with English and with French pronunciation rules. Is French the origin? And we just tack on English endings 'ed' and 'ing'?

If it's from the same root as the horsey sense (to move sideways) then it's from French passager, from Italian passeggiare and normally retains the French pronunciation, as for dressage, though, strangely, neither Wiktionary nor the OED record this fact. Dbfirs 20:59, 19 April 2014 (UTC)[reply]

Morphological diversity within a species

Although morphology may not be the best way to classify different species, it can be one practical way. However, even if two species may look very similar, they cannot mate with each other due to geographical isolation, temporal isolation, behavioral isolation, etc. Humans, on the other hand, seem to be the only exception. Humans can look widely different from one another and can potentially all mate with each other, and they are extremely mobile. They can travel from place to place, establish whole communities, and mate with the locals. Is there any other species that is so morphologically diverse as humans, or is this just one trait that makes humans more special and unique? 140.254.226.206 (talk) 14:19, 18 April 2014 (UTC)[reply]

Dogs are much more diverse. -- Finlay McWalterᚠTalk 14:21, 18 April 2014 (UTC)[reply]

For example, you might get an 8 pound Maltese and an 85 pound Alaskan Malamute; you won't find a tenfold mass differential between folks in one group of humans or another. -- Finlay McWalterᚠTalk 14:25, 18 April 2014 (UTC)[reply]

I think it would be best if the Alaskan Malamute is the female and the Maltese is male. The puppies need room to grow. 140.254.226.206 (talk) 14:39, 18 April 2014 (UTC)[reply]

Better give the Maltese a stepladder. :-) StuRat (talk) 21:17, 18 April 2014 (UTC) [reply]

See out-group homogeneity. We think that humans are different from each other because we are humans, and spent a lifetime trying to identify differences between people (both for good and evil purposes). You probably can't tell monkeys apart, but if you could ask a monkey whether he can tell his mommy apart from his daddy, he'll throw a rotten banana at you. Similarly a monkey might have a hard time distinguishing a black man from a white man, especially if both are fully clothed, and certainly won't understand why groups of seemingly indistinguishable people are trying to exterminate each other (Germans and Jews, Hutus and Tutsis, Turks and Armenians, etc). --Bowlhover (talk) 15:18, 18 April 2014 (UTC)[reply]

Yes, I used to be in charge of a breeding colony of Rhesus macaques and, to those of us who worked with them every day, they were all different to look at and quite easy to identify. Richerman (talk) 22:56, 18 April 2014 (UTC)[reply]

Humans only look different to us because we have evolved a lot of facial recognition to tell people apart. In part it has to do with our highly social nature, we are one of only a few eusocial mammals. To some hypothetical sentient alien, we'd all look pretty much the same. But sheep faces look very different to other sheep, and wasps look very different to other wasps, even though they all look pretty much the same to us [10] Paper_wasp#Facial_recognition. We are rather unique in our ability to mate with someone born on the other side of the planet. Finlay's dog example is pretty good for diversity, but of course dog breeds as we know them wouldn't exist without all the artificial selection we've put them through. See Sexual_dimorphism for other examples of extreme morphological diversity in non-human animals. (Post-EC:Bowlhover has a good point about outgroup homogeneity, this is in line with the biological examples I've given) (n.b. our article doesn't mention humans as eusocial animals, but E.O. Wilson considers humans to be eusocial, and as one of the most experienced experts in the field, I trust his judgment :)SemanticMantis (talk) 15:19, 18 April 2014 (UTC)[reply]

Calling human eusocial seems like a stretch to me -- true, there's a big mystery about homosexuality in mammals, and maybe you could think of it as a non-reproductive caste; or maybe you could argue that some others avoid reproducing for economic or religious reasons and play a similar role, but by and large, humans fail this criterion. In general the rearing of others' offspring seems more than a bit hit and miss. Of course it's just semantics and you can define a term however you like, and biology doesn't know theory. But recognizing facial features seems like a skill suitable for adversaries and competitors, and is often used for this purpose in modern society. Wnt (talk) 21:13, 18 April 2014 (UTC)[reply]

My main point is that we are highly social, and highly social animals tend to be better at distinguishing individuals of that species. As you say, it also involves adversaries, competitors (and friends, mates, kin, etc). As for the terminology, I sadly didn't get to ask Wilson how he was thinking about non-reproductive members of humanity, but I bet he'd have an interesting answer :) My own interpretation is that any child that helps rear its siblings, and and ~16-30 yr old that doesn't have children, are both types of humans that help us fit the definition. Also, it would just sound weird to say that humans are "semi-social"! SemanticMantis (talk) 13:39, 19 April 2014 (UTC)[reply]

Well, the social nature of modern humans seems largely forced by recent and rapid changes in the environment. I haven't done proper reading on the topic, but IIRC a few of the loci suspected of involvement with autism are also associated with the gregarious phase of locusts. In chimps one of the important genes is present in some individuals and absent in others [11]. So I'm suspicious that if you go back a few tens of thousands of years, that something related to we call autism might have had a fairly high prevalence in the population. I suspect we should even consider the possibility that aspects of the modern environment might provide a different background with epigenetic effects that could cause it to become common again. Admittedly that is a very speculative scenario, but I just mean to illustrate that historically speaking we don't know that humans were really all that social, or would be in more natural environments. Wnt (talk) 14:59, 19 April 2014 (UTC)[reply]

Our social behaviors are absolutely under environmental control. I personally think the theory that human civilizations were born from harsh conditions to be quite compelling, e.g. [12]. If life is easy and food grows on trees, why cooperate? But if water is scarce and agriculture is hard, cooperative societies have a strong advantage. But we're rather off-topic now, so I'll just leave it there :) SemanticMantis (talk) 15:10, 19 April 2014 (UTC)[reply]

Correlation for appearance of fruit and vegetables and their quality (redefine quality more than once if you think that helps)

Is there any reason why a particular shade/saturation of colour of, for example, lemons or limes would be of better quality for their zest or juice? I suppose better quality would be highest concentration of components of value including acids, vitamins, oils. Is there any rational reason to go for the regular lemons which look a bit nicer than the anaemic SmartPrice ones? ----Seans Potato Business 15:27, 18 April 2014 (UTC)[reply]

If you're happy with the taste of the uglier cheap ones then go with them. Fruits and vegetables sell better when they look prettier, and can be sold at a higher price. I usually take advantadge of this during tomato season - you can pick up a bushel of Roma "seconds" for the price of a half-peck of the pretty ones, but the sauce comes out just as tasty either way. Katie R (talk) 15:48, 18 April 2014 (UTC)[reply]

If we define "better quality" as "better tasting," then I think there are several factors to consider: 1. Produce that is ripe tastes better than under/over ripe produce -- this is usually judged by appearance (color) and touch. 2. Some produce appears more attractive in color and size due to chemical treatments or genetic modification, but in this case the appearance is artificially achieved and doesn't correlate to the state of ripeness of the produce. 3. Perceptions of taste are affected by sight -- if a piece of produce appears unattractive then you may not think it tastes good, but perhaps you would find it tasty in a blind taste test. 4. Taste is subjective. Some people may prefer a bland or one-dimensionally sweet version of a piece of fruit versus a "fruitier" more complex-tasting version. Unfortunately I can't find citations for the above. It is sort of "conventional wisdom." You could do an experiment and buy one each of the lemons and do a taste test to see if you prefer one over the other.--Dreamahighway (talk) 16:23, 18 April 2014 (UTC)[reply]

Taking a more biological track, note that all our domesticated fruits are based off of wild ancestors that used color, flavor, and nutrition to attract seed dispersers, so, there is a long trend of visually striking food that also tends to taste better. However, under modern breeding, color and shelf-stability often take precedence over actual flavor. Compare the beautiful but bland tomatoes you see on the shelf to a weird looking but delicious heirloom. This is a pop-sci account of a recent finding specifically about good-looking but lame tomatoes [13]. Compare the good looks and early fruiting of e.g. Early Girl to the dark and delicious Cherokee purple. SemanticMantis (talk) 17:01, 18 April 2014 (UTC)[reply]

Yes, we are genetically programmed to prefer fruits and vegetables that are good for us, such as colorful ones with lots of phytonutrients. However, marketing guys then use our own biology against us, and add dye or otherwise get unhealthy food to look healthy (like the bag of yellow oranges in a red mesh bag that makes them look orange and ripe).

Then there's the fact that "perfect" fruit or veggies often require the use of artificial fertilizers and pesticides, either of which may be harmful to humans and/or the environment. StuRat (talk) 17:29, 18 April 2014 (UTC)[reply]

Statically determinate structure

1 - Are there any easy ways to determine whether a structure is statically determinate? I always miss whether it is and end up doing a stiffness analysis unnecessarily.
2 - In a stiffness matrix, how do you identify the free nodes. I thought all nodes that arent fixed are free nodes but I was told roller and pin supports are also treated as fixed nodes, if they're not nodes which are being analysed, which doesn't make sense to me. 3 - Am I correct in assuming that where there is a force on a member such a axial, shear or a moment, the row on the stiffness matrix, representing that force, becomes 0?

Clover345 (talk) 16:29, 18 April 2014 (UTC)[reply]

Regarding your first question: Have you looked at our Statically indeterminate article? Basically if you have more unknowns than equations, it is indeterminate.--146.163.159.12 (talk) 17:53, 18 April 2014 (UTC)--Dreamahighway (talk) 17:54, 18 April 2014 (UTC)[reply]

thanks but I meant by just looking at it, without writing down any equations. Clover345 (talk) 18:05, 18 April 2014 (UTC)[reply]

See also Underdetermined_system. Unless you've done so many of these problems that you've developed a strong intuition, you have to do at least a quick check on how many constraints and how many unknowns there are. SemanticMantis (talk) 15:02, 19 April 2014 (UTC)[reply]

Storing food at temperature fluctuating between -20 and -40 better or worse than constant -20?

Would storing food at a fluctuating temperature between -40 and -20 cause it to degenerate in a way that it wouldn't at a constant -20? ----Seans Potato Business 17:32, 18 April 2014 (UTC)[reply]

Celsius, Fahrenheit, or Kelvin? HiLo48 (talk) 17:56, 18 April 2014 (UTC)[reply]

It is fairly obvious that it's not Kelvin, unless you're in the habit of storing your food below absolute zero. (+)H₃N-Protein\Chemist-CO₂(-) 18:00, 18 April 2014 (UTC)[reply]

Given your username, Sean, I have to ask - does the food in question consist of potatoes? --Demiurge1000 (talk) 18:03, 18 April 2014 (UTC)[reply]

Potatoes are not involved at any level beyond that at which they exist in the mean average content of a Western European domestic freezer. ----Seans Potato Business 20:04, 18 April 2014 (UTC)[reply]

For what it's worth -40C is exactly the same temperature as -40F. So for the sake of simplicity, you could just read the question as "What happens if you raise/lower the temperature of food without going above the melting temperature of water?" in which case degrees C versus degrees F is pretty much irrelevant.(+)H₃N-Protein\Chemist-CO₂(-) 18:06, 18 April 2014 (UTC)[reply]

Well, you have two competing processes which will degrade food. There are chemical reactions, which occur less at lower temperatures, so from that POV a colder average is better. Then there's the thermal expansion and contraction cycles a varying temperature will cause. Since the temp stays below freezing, the expansion and contraction will be minimal. Still, with enough cycles, you might eventually get cracks propagating in hard foods (and most food is hard at those temps). So, I'm not sure which is better, it all depends on the relative scales of the two types of food degradation. StuRat (talk) 18:34, 18 April 2014 (UTC)[reply]

I've not noticed any real difference in the taste of caribou meat that has been harvested in the fall and stored outside over the winter. Nor have I heard of anyone getting sick from eating it in the spring. However, this is more a gradual change from −20 °C (−4 °F) to −40 °C (−40 °F) and back rather than rapid changes. See Cambridge Bay#Climate for where I am referring to. CBWeather, Talk, Seal meat for supper? 00:49, 19 April 2014 (UTC)[reply]

I take it the polar bears are all hibernating then ? Otherwise that temptation would presumably be too much for them. StuRat (talk) 00:52, 19 April 2014 (UTC) [reply]

No bears (polar) around here and as yet few grizzly. Loose dogs and foxes would be the culprits but who stores their food on the ground. Just get them up out of the way. CBWeather, Talk, Seal meat for supper? 02:37, 19 April 2014 (UTC)[reply]

Too bad that won't work against our squirrels. No bird feeder is safe around here. StuRat (talk) 02:56, 19 April 2014 (UTC) [reply]

Frozen food loses nutrients gradually anyway, frozen vegetables after 6 months or so, and frozen meat a few months after that. But as long as it stays frozen, it's still safe to cook and eat the food. I can't think of where anyone would get a chance to try storing food at -40F / C, other than the far north. OttawaAC (talk) 02:04, 19 April 2014 (UTC)[reply]

Source on frozen food losing nutrients? 86.128.79.70 (talk) 04:26, 19 April 2014 (UTC)[reply]

Frozen food#Effect on nutrients. Further reading has revealed that my food storage notions are based on FDA food storage guidelines that are themselves based on a perceived deterioration in quality, not nutrient levels. OttawaAC (talk) 13:49, 19 April 2014 (UTC)[reply]

StuRat, you could add another degradation mechanism: dehydration. Something stored at a constant temperature is more likely to have fewer (temporary) temperature differentials, which could lead to food losing moisture while another part of the freezer is colder than the food, which will not necessarily be reversed. This could be exacerbated by regular cycling of the temperature. Of course, this process does not need any cycling, only a temperature differential. For example, if the food is warmed by conduction from the shelf it rests on, and the heat is removed by a refrigerating element on inside the wall of the freezer compartment, there could be a continual migration of moisture sublimating from the food to the colder cooling element. —Quondum 04:43, 19 April 2014 (UTC)[reply]

Yes, that's the classic freezer burn, but good containers can reduce that. StuRat (talk) 23:20, 19 April 2014 (UTC)[reply]

Wigner effect and graphite density

In graphite-moderated nuclear reactors, can the Wigner effect be mitigated by producing graphite with more vacancy defects than other types (which would therefore be less dense), so that most of the displacements caused by each neutron amount to migrations of the existing vacancies rather than the creation of new Frenkel defects? Neon Merlin 18:02, 18 April 2014 (UTC)[reply]

April 19

What flowers are these?

the pink and white ones --78.148.106.196 (talk) 09:23, 19 April 2014 (UTC)[reply]

Could they be all white flowers which have been given red dye, at the stem ? StuRat (talk) 10:12, 19 April 2014 (UTC)[reply]

They are carnations, or Dianthus caryophyllus to give them their full name, and some of them look like that naturally. --TammyMoet (talk) 12:47, 19 April 2014 (UTC)[reply]

Yes, no dye used. They have been bred to look like this. (Red and white are natural colours for Dianthus, but this combination does not occur in the wild.) Dbfirs 06:40, 20 April 2014 (UTC)[reply]

Theme park rides

Are theme park rides designed by civil or mechanical engineers or both? Clover345 (talk) 09:50, 19 April 2014 (UTC)[reply]

That would be mostly mechanical engineering, but often some civil engineering (and several other disciplines) would be involved. If you read those articles they are fairly clear (though I was surprised to see a picture of the International Space Station in the lead of the civil engineering article).--Shantavira|^{feed me} 10:47, 19 April 2014 (UTC)[reply]

Really? I thought most of it would be structural and geotechnical engineering. I can understand the mechanical elements if it being mechanical engineering but what about the track structure, support structure, foundation, ride station etc. Clover345 (talk) 13:24, 19 April 2014 (UTC)[reply]

Why not perform a case-study? Let's take a look at a project orchestrated by Walt Disney Imagineering from two aspects: the portions of the project under the creative direction of the Disney group; and the portions of the project that are inevitably contracted to other companies.

Wikipedia has thorough articles on about every major theme park attraction: for example, the latest mouse ride.

You can also see what type of people Disney hires: the Disney Imagineering Professional Internships careers page has a lot of openings for (...you guessed it...) software, graphics design, business and marketing. There are some openings for the more hard-core engineering disciplines, but those are pretty rare. A recent humor-article on Cracked, 6 Things Nobody Tells You About Working at Disney World, focused on the in-park internships, and provides an interesting insight into the types of work a Disney corporate intern or employee can expect. Once in a while, you might even find something as technical as Animatronics Intern.

So, if Disney has decided to focus on the creative side, somebody else must be engineering and constructing the projects. Possibly the most famous cases are the Monorails at the Disney resorts. Famously, ALWEG engineered and built the first monorail in 1959; and in the 1960s they were replaced by MBB. Disney also operates a cruise line; but as the animation and film industry has little overlap with the operation of a large marine vessel, they subcontract the operation to BAE Systems. I specifically recall the Disney World Skyway at the Florida park; that item was built by Von Roll Holding, an industrial conglomerate that's mostly owned by Bombardier Inc.. Its construction and operational history is plagued by drama, and it has always inspired me to research the conglomerates who build my ski-lifts. (My favorite resort has a huge poster of the commando-looking engineers from Doppelmayr construction firm moving massive construction equipment over cliffs in the Sierra Nevada mountains - you can see some historic photos in their brochure series, Die Welt der Seilbahnen). The recurring theme you might see is that Disney subcontracts the heavy-lifting to major engineering and aerospace conglomerates - groups like BAE and Bechtel and Lockheed. In return, Disney Corporation helps out the defense industry reciprocally by camouflaging aerospace and defense factories so they look like theme parks from the air. But in all seriousness, if you're the sort of person who is attentive to detail, the next time you walk around a Disney-branded theme-park, you might start spotting the not-so-subtle corporate logos of a lot of other companies - particularly, the aerospace and defense supergiants - plastered on the sides of all the mechanical parts of the ride. Most kids are too busy paying attention to the cartoon characters to spot that stuff.

But the reality is, very few corporations have the expertise in the sorts of specialized engineering that a theme-park ride actually requires. Structurally, it requires moving around massive quantities of heavy material and equipment and setting up construction-facilities in remote swampland. This is the sort of thing that military logistics contractors and oil companies excel at: mobilizing the manpower and engineering to construct massive single-purpose projects; over-engineering complex-systems to provide simplicity, safety, and (best-effort)-idiot-proofing.

These corporations hire civil engineers, mechanical engineers, aerospace engineers, a wide variety of technicians and experts, and they directly hire (and subcontract) for a large volume of unskilled labor. If you want to work on such a project, you have a better chance applying to, say, Boeing or Schlumberger, than Disney; but you still have to be really talented and lucky and competitive to get assigned to a really cool theme-park project.

Meanwhile, Disney Corporation handles the branding and the marketing, and the "theming" of the park.

If you study major theme parks operated on behalf of other conglomerates, you will probably find the same trends.

Nimur (talk) 17:07, 19 April 2014 (UTC)[reply]

thanks for the detailed answer. Wouldn't most parks employ a small engineering team though, maybe within their project management group? Clover345 (talk) 17:41, 19 April 2014 (UTC)[reply]

I think most theme parks, even the ones owned by companies that do nothing but operate theme parks like Cedar Fair, don't design and build their own rides. Individual parks probably don't have enough new construction on a regular basis to justify a full-time engineering department to design them. But there are several companies that do specialize in theme park rides like Mondial, Bolliger & Mabillard, and Intamin.

As for the original question, I imagine it would depend on the type of ride. For something relatively simple like a conventional roller coaster or river rafting ride, I imagine it would probably be about equal between the mechanical and structural designs. But for more exotic rides like roller coasters launched with linear induction motors and things like this, the mechanical design is probably a little more involved. Mr.Z-man 17:42, 19 April 2014 (UTC)[reply]

Innovationin engineering and design

Do you think all engineering disciplines have just as much scope for innovation as each other? Clover345 (talk) 16:35, 19 April 2014 (UTC)[reply]

I think it's reasonable to accept that as a starting position and instead put the onus on arguing that they don't. — Lomn 16:50, 19 April 2014 (UTC)[reply]

I don't think "innovation" is well-defined or easily-compared, either. It is nearly impossible to provide a total ordering amongst various innovations, so we can't say whether one accomplishment was more innovative than another.

In my experience, "innovative" people need to be generalists who have the ability to quickly become the best specialist on the team. That means you have to be able to become the best at every branch of engineering. Today's problem might be software; tomorrow, it might be glue that isn't sticky enough; and in two weeks, it might be a budget shortfall. Innovation is being able to come up with a new solution that is better than the existing solution, no matter what today's problem is. As my co-worker jokes - "we're software engineers, which is why we have so many oscilloscopes." Nimur (talk) 17:18, 19 April 2014 (UTC)[reply]

I would think that in some engineering fields, it's innovate or fail, like consumer electronics, while other engineering fields are far more conservative, like civil engineering, since a new bridge design which collapses because it wasn't completely understood will cause massive lawsuits. See Tacoma Narrows Bridge (1940).

Airplane design is a field where you might think innovation would be needed, but innovations in that field often cause crashes, due to unknown forces and processes, like supersonic flight (turbulence and sonic booms), rectangular windows (force concentration and metal fatigue), composite materials (delamination), and lithium batteries (flammability). Of course, some innovation is needed, but everything needs to be thoroughly tested before it goes into production there, so being conservative makes sense in aeronautics. An exception might be for unmanned vehicles, where accidents are less likely to cause deaths. StuRat (talk) 19:57, 19 April 2014 (UTC)[reply]

So would you say there's more innovation in engineering research than in engineering practice? And what about computer science? Is there innovation in that? Clover345 (talk) 16:26, 20 April 2014 (UTC)[reply]

Yes to both, although some areas, like consumer electronics, have a lot of innovation in practice, as well. Some areas of computer science are pretty well set, like database design, while others, like microchip design, are very innovative fields. StuRat (talk) 16:38, 20 April 2014 (UTC)[reply]

LED bulbs and inteference

Do LED lamps produce interference they way CFCs do? The article doesn't say anything about it, so I assume that they don't. Bubba73 ^{You talkin' to me?} 18:49, 19 April 2014 (UTC)[reply]

CFCs usually refer to an unrelated chemical. Are you sure you don't mean CFL, as in compact fluorescent lamp ? Nimur (talk) 19:20, 19 April 2014 (UTC)[reply]

Yes, I meant CFL. Bubba73 ^{You talkin' to me?} 20:02, 19 April 2014 (UTC)[reply]

So, who you got winning the Grey Cup this year? --Jayron32 22:28, 19 April 2014 (UTC)[reply]

Yes, LED bulbs can produce electromagnetic interference. The references I have found (here, here, and here, to start) suggest that this comes from the power circuits driving the LEDs, rather than from the LEDs themselves. There seems to be some wide variance in EMI produced by LED bulbs depending on the type and the manufacturer. - Eron^Talk 19:06, 19 April 2014 (UTC)[reply]

I'm getting terrible interference on my electric guitar. Most of the bulbs in our house are CFLs. Some are incandescent and some are LEDs. I'm replacing CFLs by LEDs as they go bad. Bubba73 ^{You talkin' to me?} 20:17, 19 April 2014 (UTC)[reply]

You may be getting that interference over the power line, not RF through the air. I experimented with a strat with single-coil pickups, walking around with it hooked up to an iPod via iRig (so there's no ground loop or other mains connection at all) and I can only get an audible buzz when the pickup is < 10cm from the CF bulb's base. With most light fittings, I can't get the pickups close enough to the source of noise for any buzz to be evident. Instead of the expensive business of changing out the bulbs, you might like to first look at eliminating ground loops and, if that's not enough, install a power conditioner in front of the amp. -- Finlay McWalterᚠTalk 10:41, 20 April 2014 (UTC)[reply]

Power factor ?

CFL's seem to create some type of weird problem with the power factor or some such thing, which I've observed when I put them on the same circuit with a regular fluorescent light, all triggered by a motion detector. The lights wouldn't start until I added an incandescent bulb to the circuit, too. I wonder if LED lights also have this problem, or if they would work like an incandescent and smooth everything out ? StuRat (talk) 19:51, 19 April 2014 (UTC)[reply]

The motion detector is probably trying to bleed through a small current through the CFL to operate itself, so it may need a lower resistance item in the circuit to work. Graeme Bartlett (talk) 20:40, 19 April 2014 (UTC)[reply]

So do CFLs have high resistance, until they turn on, then drop to low resistance ? And would LEDs exhibit this behavior, too, or behave like incandescents ? StuRat (talk) 21:18, 19 April 2014 (UTC)[reply]

If I'm not mistaken, CFLs do have a high resistance at first because enough power has to be put into them to get the gas inside to fluoresce. Once the gas is fluorescing, then the resistance goes down. That is one of the problems (only one?) in getting CFLs to dim. LEDs can and do dim depending on the power that they are supplied, so I would expect them to allow a certain amount of power through without any observable light. Dismas|^(talk) 03:01, 20 April 2014 (UTC)[reply]

Interesting. So dimmable CFLs should work then, too ? StuRat (talk) 03:05, 20 April 2014 (UTC)[reply]

Yottabytes stored in all servers worldwide?

Does of you have any reliable information on how many bytes of data (ranging from text to movies) are stored in all the servers worldwide? One server alone in Utah is said to be able to store 1 yottabyte of data. 112.198.90.173 (talk) 21:20, 19 April 2014 (UTC)[reply]

Wired handwavily estimated that NSA's Utah Data Center could "handle yottabytes" (where "handle" does mean "store"), but Forbes estimated (with slightly less guessing, but still lots and lots) that it could store "3 and 12 exabytes", much less than a yottabyte. -- Finlay McWalterᚠTalk 21:44, 19 April 2014 (UTC)[reply]

"Handle" might mean "process". So, they might well process 1 yottabyte of data in a year, but only decide 3 and 12 exabytes of it is worth storing. StuRat (talk) 00:51, 20 April 2014 (UTC)[reply]

Grr, I meant to write "Handle" does not mean "store". -- Finlay McWalterᚠTalk 08:36, 20 April 2014 (UTC)[reply]

But are there any data how many bytes of data of humankind ranging from private data to govern databases are currently stored in the servers of the world, meaning the sum of all data produced by humankind since inception of data gathering? 112.198.90.161 (talk) 07:05, 20 April 2014 (UTC)[reply]

Our articles on Exabyte and Zettabyte have better information than Yottabyte. Dbfirs 07:17, 20 April 2014 (UTC)[reply]

No. Companies tend to keep that kind of thing secret. We can place some limits based on the number of hard drives sold. That suggests a few tens of Exabytes at most.©Geni (talk) 10:13, 20 April 2014 (UTC)[reply]

Replacing harmful flora with innocuous flora as a cure

You have probably already heard of people with colitis being treated by cleansing their intestinal tract and then deliberately repopulating it with a collection of different organisms, usually obtained from a healthy individual. It made me wonder about other ailments that arise from a disturbance in flora. For instance there's a suggested relationship between certain species of Malassezia (a yeast) and dandruff and seborrhoeic dermatitis and related skin disorders. Would it not be a good idea to try to cleanse the skin and then supplant those yeasts with less problematic ones? The same with acne, too. When I was a spotty kid, I got some sort of infection in the corner of my mouth which was easily treated with an antibiotic cream and didn't come back. The cream also reduced my spots but they came back after discontinuation of that cream. Maybe if I'd replaced the bacteria with a type that didn't have any involvement in acne, I'd have been "cured". I'm reckoning there are other afflictions that could be handled similarly but can't think of any at the moment. Do my suggestions make sense or is there a flaw I'm not seeing? I guess obtaining the alternative flora in appropriate ratios might be difficult. I know those "good bacteria" yoghurts are a crock because they don't represent the variety of bacteria in a healthy intestinal tract. --129.215.47.59 (talk) 22:52, 19 April 2014 (UTC)[reply]

The difference is that you can control which organism enter your intestines more easily than the bacteria which contact your skin. But, in areas where the person can control what goes in and out, your suggestion does make sense. For example, vaginal yeast infections could be controlled by introducing "good" organisms. (Douching seems to be the cause of many yeast infections, because it removes those good organisms.) StuRat (talk) 23:18, 19 April 2014 (UTC)[reply]

For reference, the OP seems to be hinting at gut flora and perhaps fecal transplants. Also probably the human microbiome. Last sentence seems a bit WP:SOAP, but we do have articles on yogurt and Fermentation_(food). That will be a good start with references, I'll think more and come back later :) SemanticMantis (talk) 23:28, 19 April 2014 (UTC)[reply]

The last sentence might be incorrect but was based in the fact that there are hundreds of species of bacteria in the healthy gut and there are less than 20 in probiotic yoghurt. Finding sources for how many different yoghurts contain is proving difficult. I've only found two sources so far. "It has three times the amount of probiotics that are in yogurt. This is because of the fact that in order to ferment a milk with kefir, 10 to 20 different types of probiotic bacteria and yeasts should be mixed" "A popular brand called Lifeway has 12 species or cultures." 129.215.47.59 (talk) 01:18, 20 April 2014 (UTC)[reply]

It's possible that only a few are often lost from the intestines, and in need or replenishment. StuRat (talk) 03:03, 20 April 2014 (UTC)[reply]

The reason your acne came back was because it's etiology is more complex than a simple bacterial infection (it is caused initially by hormonal changes) and the treatment didn't last long enough. It usually takes a number of months to clear it up. see [14]. Richerman (talk) 09:55, 20 April 2014 (UTC)[reply]

April 20

If it's called cardiac arrest when the heart suddenly stops...

...what's it called when the brain suddenly stops? Ac05number1 (talk) 02:37, 20 April 2014 (UTC)[reply]

Brain death. Dismas|^(talk) 02:54, 20 April 2014 (UTC)[reply]

Even in total brain death, parts of the brain, like the brain stem, may remain active. StuRat (talk) 02:59, 20 April 2014 (UTC)[reply]

That's not correct. See brain death#Medical criteria. Looie496 (talk) 13:26, 20 April 2014 (UTC)[reply]

I don't think it stops suddenly. The heart doesn't usually completely stop all at once either, just parts of it stop or pump out of sequence. StuRat (talk) 02:57, 20 April 2014 (UTC)[reply]

In some contexts, where a "cardiac arrest" is called a "heart attack", a Stroke is sometimes called a "brain attack". --Jayron32 03:06, 20 April 2014 (UTC)[reply]

Why does the term "cerebral arrest" not exist? -- Jack of Oz ^{[pleasantries]} 07:34, 20 April 2014 (UTC)[reply]

There's no accounting for the quirks of English. But consider this: The term "arrest" means to stop.[15] It occurs to me that the term "arrest" in any context usually refers to a sudden or swift action - like it's either beating or it isn't. In the case of the heart, if it stops beating it's pretty obvious just from listening to the chest. The brain doesn't "beat" like the heart does. It requires medical equipment to detect its activity, or lack thereof. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:46, 20 April 2014 (UTC)[reply]

Cerebral arrests are the Thought Police's job. —Tamfang (talk) 08:44, 20 April 2014 (UTC)[reply]

Cool. I'm sometimes tempted to make a citizen's cerebral arrest. Of course, in my particular case, it would be a cerebral citizen's arrest. :) -- Jack of Oz ^{[pleasantries]} 09:02, 20 April 2014 (UTC) [reply]

"Cardiac arrest" means that the heart suddenly stops pumping blood, but in almost every case the individual muscle fibers continue to contract for a while. What happens is that they lose their global synchrony, resulting in fibrillation. The most directly analogous phenomenon in the brain is an epileptic seizure. Those are rarely fatal, though, because they eventually end and don't cause the heart to stop. Breathing may stop for a while, but it usually resumes after the seizure ends. Looie496 (talk) 13:21, 20 April 2014 (UTC)[reply]

The end of LADEE

From IB Times: "Before LADEE crashed into the lunar surface, the spacecraft reached speeds of 3,600 miles per hour, and it most likely broke apart before impact."

What could cause LADEE to break up before impact? Bubba73 ^{You talkin' to me?} 05:24, 20 April 2014 (UTC)[reply]

I can think of two reasons why a plunging satellite might break up, but neither seems strong enough on the Moon to have that effect:

1) Hitting the atmosphere. The Moon has a very thin atmosphere, so even at 3600 mph, this doesn't seem likely to cause it to break up, to me, even considering that the satellite isn't designed to withstand re-entry.

2) Tidal effects. Here the near side of the object is pulled more than the far side. This caused Comet Shoemaker–Levy 9 to break up before it hit Jupiter. But, the Moon's gravity is far less than Jupiter's, so this seems unlikely. StuRat (talk) 07:18, 20 April 2014 (UTC)[reply]

Yes, but it had been orbiting only about 1 mile above the surface for a while, without breaking up. Bubba73 ^{You talkin' to me?} 08:20, 20 April 2014 (UTC)[reply]

I think it's just an error by the IB Times. The NASA press release says it broke up "during impact". -- BenRG (talk) 08:05, 20 April 2014 (UTC)[reply]

Probably. Bubba73 ^{You talkin' to me?} 08:20, 20 April 2014 (UTC)[reply]

What strain/breed of Columbia livia/Columbia livia domestica is the common white dove?

I have a problem with the so-called white doves (it's Easter day, after all... happy Easter to everyone!). This article says the most common strain of white doves is the Stielbacht, a breed or strain that does not apperar in this list. Should it be added or is it something different from a proper breed?--Carnby (talk) 10:04, 20 April 2014 (UTC)[reply]

Nodal loads on shear and moment diagrams

How do you represent nodal loads on shear and moment diagrams. As far as I know, these diagrams, always start and end at 0. So if for example, a simply supported beam has a uniform load on it but also a nodal load on 1 support. How do you factor this in? If I simply draw the uniform load on the diagrams and then put in the nodal load, the diagrams wouldn't end at 0 and hence the beam wouldn't be in equilibrium. Clover345 (talk) 14:35, 20 April 2014 (UTC)[reply]

Do I need to perform a HIV test?

For more than a year, I have been having my hair cut at a nearby barber shop (around 10+ times). The barber always cuts my chin when shaving, maybe because my beard is hard. He used his fingers cleaning the blood, and I did not notice it until recently. I have 2 flus, 1 at the time being, and 1 long ago I cannot remember. 3 months ago I had a muscle pain in my left leg which lasted for nearly 2 months. I felt extreme pain when I stretched my leg or performed a high kick. Currently it has not fully gone, but is negligible. I am 25, healthy. I don't care much about the flus, but the leg pain was really unusual.

Although I got cut many times, I know the risk is very small. The number of HIV infected people going to the same barber shop is small, the number of people getting cut is small, the chance between 2 bleeding people is small. But I am still worry about my unusual leg pain. Are there many causes for such pain? I do not really want to take a HIV test because of the discriminations. People here consider only those with social issues (drug, have sex with prostitutes, etc...) are vulnerable to the disease and need such kind of test. -- 222.252.79.24 (talk) 14:39, 20 April 2014 (UTC)[reply]

We cannot give you medical advice or diagnosis. See your doctor (and change your barber).--Shantavira|^{feed me} 14:49, 20 April 2014 (UTC)[reply]

For the benefit of other respondents, the IP geolocates to Vietnam (technically Hanoi, but I have doubts Vietnamese geolocation is that accurate). Nil Einne (talk) 16:25, 20 April 2014 (UTC)[reply]

222.252.79.24 - Be careful when looking for these kinds of things on the Internet; many people answer confidently without knowing what they're talking about and it's very easy to get bad information. Most doctors will not give definitive answers to these kinds of questions over the internet, nevermind us non-doctors, so as already stated we cannot give medical advice here. If you've not seen them already, there's an article on HIV/AIDS tagged as "good article" (high quality) as well as on Misconceptions about HIV/AIDS. The US government has a website for HIV/AIDS information that might be useful (aids.gov) and the AIDS Healthcare Foundation also operates in Vietnam, offering various services including testing. But it would be best to just call your local doctor who would be best able to point you in the right directions and answer questions you have. --— Rhododendrites ^talk | 17:55, 20 April 2014 (UTC)[reply]

Acacia motteana and Acacia podalyriifolia

I have read that Acacia motteana and Acacia podalyriifolia are two names for the same species. Do you know if it's true?--Carnby (talk) 14:54, 20 April 2014 (UTC)[reply]

Revision strategy

How do you revise for physics exams? Past papers and example questions? Do you have to time yourself? I find it too hard to time unless I've done every type of question possible which isn't always feasible as there's too many possible types. 90.205.212.104 (talk) 16:20, 20 April 2014 (UTC)[reply]

Your tutor will be able to guide you better than we can. Every course has a syllabus, and you will be asked questions on what you have covered from the syllabus. Your tutor will tell you whether there will be multiple choice questions on the paper, and how to complete the paper if there is. He/she will also be able to provide you with past papers. You only need to revise what is on the syllabus. --TammyMoet (talk) 18:59, 20 April 2014 (UTC)[reply]

microscopy

compare the limit resolution of air and oil — Preceding unsigned comment added by 115.240.159.50 (talk) 17:07, 20 April 2014 (UTC)[reply]

Location of the big bang and size of the universe

The observable universe is centred on Earth and it's unknown how big the universe is with some saying that it's infinite. I have a couple of questions, though I imagine you guys will have to correct me on a lot.

I see in the news every so often that new and improved telescopes have revealed how the very early universe took shape after the big bang. Does that mean in the observable universe we can see or almost see the location of the big bang and the very first galaxies?

The universe was only 630 million years old when GRB 090423 exploded and it took 13 billion years for that light to reach us. Similar to the above question, since we know GRB's location and how long is ago it exploded (relevant because everything is moving away from the big bang), doesn't that give us some clue as to the size of the universe and the location of the big bang? And would the location of the big bang be the centre of the universe, roughly, as everything in the universes exploded outwards from that location? Thanks, 92.16.58.122 (talk) 18:15, 20 April 2014 (UTC)[reply]

I know that the universe was just a small ball then it got much larger when the big bang occurred, like a balloon, so my question of location is whether the small ball expanded uniformly and so our knowledge of the early galaxies mean we know where the centre is and the length of time it took for that light to reach us mean we can guess the size of the universe. 92.16.58.122 (talk) 18:35, 20 April 2014 (UTC)[reply]

The usual analogy used for the young is to image the universe as the surface of a balloon. Draw a load of galaxies on a deflated balloon, then inflate it. The galaxies move further apart, but none of them are the centre. There is no location where the big bang started. The big bang wasn't an explosion of matter into space: it is the beginning of time and space as we know it, and space expands like the surface of a balloon.

This is exactly the right question for you to ask, to find out more about the big bang. So, well done. 86.146.28.229 (talk) 19:12, 20 April 2014 (UTC)[reply]

@@ Line 501: / Line 501: @@
 I know that the universe was just a small ball then it got much larger when the big bang occurred, like a balloon, so my question of location is whether the small ball expanded uniformly and so our knowledge of the early galaxies mean we know where the centre is and the length of time it took for that light to reach us mean we can guess the size of the universe. [[Special:Contributions/92.16.58.122|92.16.58.122]] ([[User talk:92.16.58.122|talk]]) 18:35, 20 April 2014 (UTC)
+:The usual analogy used for the young is to image the universe as the ''surface'' of a balloon. Draw a load of galaxies on a deflated balloon, then inflate it. The galaxies move further apart, but none of them are the centre. There is no location where the big bang started. The big bang wasn't an explosion of matter into space: it is the beginning of time and space as we know it, and space expands like the surface of a balloon.
+:This is exactly the right question for you to ask, to find out more about [[the big bang]]. So, well done. [[Special:Contributions/86.146.28.229|86.146.28.229]] ([[User talk:86.146.28.229|talk]]) 19:12, 20 April 2014 (UTC)