Science desk
< April 8	<< Mar \| April \| May >>	April 10 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

April 9

Plutonium and its electrical conductivity

Why does the electrical conductivity of plutonium, in the temperature range of 100 to 400 K, rise with increasing temperature?

This phenomenon is called a "negative temperature coefficient (of resistance)", but no article on Wikipedia I can find explains why this happens, though that link includes some examples. It appears there is more than one reason this can happen. This source lists some possibilities in its introduction. Someguy1221 (talk) 01:00, 9 April 2017 (UTC)[reply]

It may be like a semi-conductor - the concentration of charge carries increase with temperature in this range. Ruslik_Zero 08:32, 9 April 2017 (UTC)[reply]

"Plutonium Condensed-Matter Physics: A survey of theory and experiment" by A. Michael Boring and James L. Smith, Los Alamos Science Vol.26 2000 p.121 dismisses the Kondo effect as a good explanation and notes that it is a characteristic phenomenon of correlated electron materials, but does not offer an explanation as far as I can see. The phenomenon is even stronger in UBe₁₃, so this may be another avenue of approach.--Wikimedes (talk) 19:11, 10 April 2017 (UTC)[reply]

The effects of caffeine and alcohol

Caffeine is a stimulant. Alcohol is a depressant. If a cup of green tea and a cup of alcohol (wine, champagne, beer) are drunk at the same time, then what kind of effect do both have on the body? If a person is mentally depressed, then can he drink some caffeine? Can alcohol be drunk to calm a person with mania? 50.4.236.254 (talk) 02:09, 9 April 2017 (UTC)[reply]

Alcohol can be a stimulant or a depressant, depending on the dosage. Note that these terms don't refer to mental depression or mania, but rather physical stimulation and depression, such as heart rate, blood pressure, etc. There's some overlap between them, but they are not identical. StuRat (talk) 02:17, 9 April 2017 (UTC)[reply]

Alcoholic drinks have more rapid short-term effects, especially when the drink is carbonated, because alcohol readily passes through cell membranes into the bloodstream and brain. Its immediate effects are decreased anxiety and motor skill, hence the prohibitions on driving. The effects may proceed to euphoria and intoxication. Blooteuth (talk) 11:59, 9 April 2017 (UTC)[reply]

As I have seen it put, if you combine alcohol and caffeine, what you get is a wide awake drunk. At a biological level, the mechanisms of action of alcohol and caffeine are quite different. Some of their high-level effects cancel to some degree, but many do not. Basically the same things apply to the other combinations mentioned in the question. Looie496 (talk) 14:35, 9 April 2017 (UTC)[reply]

Are nuts made of cells?

Looking to improve Nut (fruit) with the answer to this question: Are the nuts that we eat made of plant cells, with cell walls and everything, or are they just piles of nutrients hoarded for nearby cells to use? This has inexplicably started to concern me every time I chomp down on one. 8) -- Beland (talk) 10:03, 9 April 2017 (UTC)[reply]

The nut is a seed so it must contain living cells if it is to germinate. I would assume that most of the nutrients are stored inside cells rather than between them, but perhaps an expert can confirm this? Dbfirs 10:55, 9 April 2017 (UTC)[reply]

Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent (not opening at maturity) seed, such as an acorn or hazelnut. Blooteuth (talk) 11:34, 9 April 2017 (UTC)[reply]

Every part of a plant starts as a living cell. Some cells (see Sclerenchyma develop very think and solid cell walls, and the inside of the cell dies - these form the fibres in wood and the shells of nuts. Depending on the age of the nut, some of the living cells from the kernel may also have died, and the fats they stored may have leaked out. The nut you eat probably has a mixture of living cells, dead cells, and some nutrients which have leaked out of cells. Wymspen (talk) 11:38, 9 April 2017 (UTC)[reply]

The biology here turns out to be pretty odd. See endosperm, which describes the cellular nature of the bulk of many seeds. Note the endosperm is a different organism than the embryo. Then there is the specific case of coconut water - see here for a cute bit about it. I should look it up properly when I get the chance. I'm reading things about nuclei floating around in a liquid cell - well, syncytium - if I take that right ... my mind boggles. A cell is a very broad concept. ;) Wnt (talk) 20:44, 11 April 2017 (UTC)[reply]

I'm not sure I agree with that last statement. Our cell article states "A cell is the smallest unit of life that can replicate independently..." That seems a pretty tight definition to me. DrChrissy ^(talk) 22:21, 11 April 2017 (UTC)[reply]

That definition doesn't really work in a lot of cases. For example, most neurons can't replicate, but they are cells. More to the point here, there's the matter of what "replication" is. There are polyploid cells in the liver that will go 2n, 4n, 8n, 16n ... the cells get bigger, but they never form new nuclei. In this case we have the syncytium that forms new nuclei, but not new cell membranes until eventually somehow the nuclei congeal into the coconut meat around the edge. (a bit more about that here; in the coconut water, layers of cytoplasm congeal as "vesicles" around groups of nuclei? this just confuses me so far) I mean, technically my thought is that given there's no membrane between nuclei, the whole watery mass inside the coconut has to be counted as one very multinucleated cell. (this view is supported here) That is ... assuming there is a cell membrane at the edge of the coconut cavity, and not just some kind of extracellular tissue, which I still didn't get around to looking up. If there's no cell membrane even at the outside, is that even cellular tissue? Anyway, it's a broad concept however you look at it. ;) Wnt (talk) 23:08, 11 April 2017 (UTC)[reply]

Hmmmmm...I see what you mean. I had a quick look at injured nerves web-pages and they repair, rather than replicate. I take your point - thanks for the input. DrChrissy ^(talk) 23:30, 11 April 2017 (UTC)[reply]

I found this paper demonstrating a clear cellular structure in the coconut meat, after the nuclei form cells. This demonstrates that in general, endosperm at least can be made of fairly typical looking cells ... whatever the developmental process that took it to that point. Wnt (talk) 00:01, 12 April 2017 (UTC)[reply]

Will the human population reduce in numbers because of global climate change?

We don't answer requests for opinions, predictions, or debate. 50.4.236.254 (talk) 22:18, 9 April 2017 (UTC)[reply]

The following discussion has been closed. Please do not modify it.

If the polar ice melts completely and floods and buries the coastal cities, along with the disastrous natural occurrences (earthquakes, tornados, hurricanes, fires, volcanos), then will the human population decline in number? 50.4.236.254 (talk) 12:36, 9 April 2017 (UTC)[reply]

Probably not, because these changes will occur over decades or even centuries, giving most people enough time to move inland. The ultimate Q is how this will affect the planet's ability to grow food. While some land will be lost to flooding/contamination with salt water, other land, like that currently covered in permafrost, will open up to farming. In many cases this land currently lacks much soil, but that will develop in time, from plants and then trees that will grow there. Of course, over such long time frames other technologies, like hydroponics, may become more widespread. StuRat (talk) 18:33, 9 April 2017 (UTC)[reply]

Due to the speculative nature of the question, the answer is definitely "Maybe." ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:43, 9 April 2017 (UTC)[reply]

According to this site, the world population growth is currently over 22 million per year, so you would have to drown that many every year to stop population growth, by that method. This is not going to happen, so we need to look at effects on the food supply, instead. StuRat (talk) 19:05, 9 April 2017 (UTC)[reply]

It will decline in number long before that. Our civilization depends on agriculture, international trade is very important. The 2008 financial crisis demonstrates that there are weaknesses in the way we manage the system. Even if there are no fundamental problems with the production of goods, the system can crash. That's like an air-crash in clear weather due to only pilot error. I don't want to be in such a plane, certainly not if the plane were to enter an area of heavy turbulence. It then doesn't matter that the plane is designed to handle the turbulence well, that's not relevant if the pilot is too incompetent.

So, a relatively minor event is all that's needed to destroy our civilization. Consider e.g. a prolonged drought that would force China and India to import the food that they normally grow themselves. They have more than enough financial reserves to buy the food for the, say, 2.5 billion people for many years in a row, but this would mean that the US and the EU would have to export all that food leading to shortages. That's not going to happen, they'll impose an export ban. This will then cause the global trade system to collapse. If you can't buy what you need on the market if you have enough money, then that's the end of the market. So, the global economic system will collapse, the only way that this could be prevented is if there were a World government, a single authority that could manage the situation. Count Iblis (talk) 19:35, 9 April 2017 (UTC)[reply]

I agree that the rate of increase in population is unlikely to continue at the present rate, and that a major disaster will probably have an effect on the birthrate as well as on the population, but I think you are being over-pessimistic about the likelihood of a collapse in global trade and the necessity for a world government. Dbfirs 20:06, 9 April 2017 (UTC)[reply]

The need for a world government may be more to avoid a nuclear war (or biological war, antimatter war, or whatever other nasties we come up with). StuRat (talk) 20:47, 9 April 2017 (UTC)[reply]

@StuRat @Baseball Bugs @Count Iblis @Dbfirs Is it hard to understand "We don't answer requests for opinions, predictions or debate."? Blooteuth (talk) 21:04, 9 April 2017 (UTC)[reply]

Maybe you missed where I said "Maybe." ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:17, 9 April 2017 (UTC)[reply]

Wikipedia has articles that would be good starting points for this sort of investigation.

Effects of global warming
Effects of global warming on humans
The entire category Category : Effects of Global Warming

These articles defy simple summary, but they may lead you to the answer you're looking for. ApLundell (talk) 18:34, 10 April 2017 (UTC)[reply]