1

Physiology & Medicine / why is my skin so sensitive when I have a fever?

« on: 17/05/2022 23:20:59 »

I've come down with a fever (probably influenza, not covid... but tests are pending).

One thing I have noticed over the years, is that when I have a fever, my skin becomes very sensitive to friction. Like if I dry off with a towel, or change my clothing, even the softest and plushest materials feel like sandpaper scraping across my skin. There is no visible irritation (like redness or puffiness—no rash or welt or anything like that), and the sensation ceases almost instantaneously when the friction stops. But it is noticeable enough that I pat myself dry with towels rather than the typical rubbing motions, and I have a strong aversion to getting dressed/undressed.

Is this a known effect?

Is it common?

Is there a known (or likely) mechanism?

Is there anything I can do to limit it while recovering?

Thanks!

2

Chemistry / Re: Are there solvents that do not evaporate quickly?

« on: 17/05/2022 23:13:13 »

If you want diffusion kinetics to be like those in water, I recommend against a sol, gel, or solid.

The ionic liquid won't evaporate in any significant way for thousands of years at 40°C.

3

Chemistry / Re: Are there solvents that do not evaporate quickly?

« on: 17/05/2022 13:18:22 »

Do you want it to evaporate, but slowly?

In this case, something like dimethylformamide (DMF) might work. According to wikipedia (https://en.wikipedia.org/wiki/Dimethylformamide), at 20 °C, it has a vapor pressure of 516 Pa and a viscosity of 0.92 mPa•s. (compare to water, with a vapor pressure of 2300 Pa and a viscosity of 1.00 mPa•s)

If you don't want it to evaporate at all, perhaps an ionic liquid like ethylammonium nitrate could work. It is more viscous (28 mPa•s), but has essentially zero vapor pressure.

4

General Science / Re: Is it safe to transport hydrogen gas compressed into a water tank?

« on: 17/05/2022 02:46:44 »

Water doesn't get compressed

not really (Water is compressible—not much, but enough. Also, I'm not sure why you would say this, as it means that there is less room for added gas—a more compressible liquid would "make room" for the added gas as the pressure increases...)

you can inject any amount of gas into the water tank, as long as it can hold that pressure.

not really (at some point the pressure is high enough that it will liquify, and then there is less compressibility)

The reason to use water is to make hydrogen less dangerous during transportation

How? I can't think of any benefit from adding water. It just means that higher pressures will be needed to store the same amount of hydrogen (which is more dangerous), and more mass being carried (requiring more energy). If the hydrogen catches fire, the water won't do anything to stop it...

5

Chemistry / Re: How well understood is the Chemistry of the trans-uranic elements?

« on: 16/05/2022 20:47:23 »

Thanks @chiralSPO .

you're welcome!

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Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 16/05/2022 20:45:41 »

I can't help wondering about the original question.
"Is there a limit to how hot things can get?".
I wonder if the answer is "As hot as they were".

 (about 14 billion years ago)

I believe this is correct.

7

Chemistry / Re: How well understood is the Chemistry of the trans-uranic elements?

« on: 16/05/2022 17:16:37 »

Is it possible to slow the decay down by other methods?    A few years ago, school-level physics would have stated that nuclear reactions are unlike chemical reactions -  nuclear decay is a random process and the decay rates are un-affected by environmental conditions like pressure and temperature.  The general explanation being that the nucleus is dominated by the effects of nuclear forces (the strong and weak force) and effectively independent from whatever else is going on outside the nucleus.   It was a good explanation but like the semolina pudding they served at school lunchtime, it was just so wrong.
   This belief was seriously adjusted in my life time when a type of nuclear change called electron capture was studied.     (  https://en.wikipedia.org/wiki/Electron_capture  ).   In electron capture it is possible to adjust the nuclear reaction rates just by ionising the atom  (for example the nuclear change  ⁷₄Be⁺  →  ⁷₃Li⁺   proceeds more slowly than ⁷₄Be  →   ⁷₃Li   ).   You can get a smaller (but statistically significant) difference just by bonding the atom to certain things.

    I've not seen any information about it - but it begs the question that you might be able to adjust the rates of other nuclear changes.   For example, alpha emission may be reduced if the unstable nucleus can be surrounded with ligands that are positively charged and create a potential barrier against the emission of another positively charged particle.     Maybe just putting the unstable nuceii under pressure is enough to slow the decay (since the appearance of more particles tends to increase pressure PV = nRT   etc).    I don't know and It's important to point out that this is just speculation:   I have a personal belief that nuclear reactions are much more like chemical reactions than we had first imagined (just in terms of their reaction kinetics, obviously chemistry goes on outside the nucleus but nuclear change doesn't).

Neutrinos can also influence the rate of reverse electron capture (https://iopscience.iop.org/article/10.1086/305343/fulltext/34468.text.html)

And, obviously, nuclear fission chain reactions such as those crucial (critical?!? sorry...) to atomic bombs, show that nuclear decay can be influenced by the environment.

That said, because of the great energies typically involved in nuclear reactions, I don't think that most changes in pressures and temperatures that could be highly influential for chemical reactions would do much for nuclear ones. But the stability of neutrons in neutron stars is significantly greater than for lonely neutrons—and I think it might be due to the insane pressures within a neutron star that favor single neutrons over proton/electron pairs (and neutrinos!).

I think the case of electron capture in ⁷₄Be⁺ vs ⁷₄Be can be explained by looking at how much electron density is within the cross-section of the electron capture of the nucleus. However, I am not so sure that adding positive ligands around an atom would significantly reduce α decay. The electric field at the "surface" of the nucleus will be almost entirely dominated by the protons within the nucleus For example, a ²¹⁰Po nucleus, which typically undergoes α-decay with a half-life of about 140 days, has 84 protons in a sphere with a radius on the order of a few femtometers—adding a handful of singly (or doubly) positively charged ligands at a radius of 150 picometers (almost 1 million times as far away) likely won't change much. In terms of the electric potential at the nucleus, I think this will be a similar story, but might have a greater effect (but, I would expect it to be the opposite of your prediction—more positive ligands leads to a more positive potential at the nucleus, making it more favorable for the nuclear charge to decrease).

8

Physics, Astronomy & Cosmology / Re: shape change with no energy transfer?

« on: 16/05/2022 13:53:35 »

some crystals grow fastest at their edges (like bismuth), or along a single axis (like rutile).

It shouldn't be surprising that oversimplified models predict oversimplified outcomes.

Depending on the exact conditions, water will form all kinds of shapes (including spheres).

see here: https://www.its.caltech.edu/~atomic/snowcrystals/class/class-old.htm

9

Physiology & Medicine / Re: What would a strict diet of cabbage and cheese do to the human body?

« on: 14/05/2022 21:59:30 »

There are many types of cheese, with significant differences in nutritional components (fats, proteins, salt, calcium, live cultures, etc.) Does the diet include all types of cheese, or is it limited to only one variety (and if so, which?)?

10

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 12/05/2022 15:14:52 »

excellent questions!

I don't believe that there is any hard limit (that we know of) on the maximum possible temperature. In general, big bang energy tends to dissipate rather than concentrate, so a reasonable first approximation of the maximum temperature would be the temperature in the earliest moments of the big bang. According to this source (https://lco.global/spacebook/cosmology/early-universe/), in the first second, temperatures were on the order of 10³² Kelvin.

As a society, we are still learning about the earliest moments of the universe, so this may be subject to change.

Also, temperature can be difficult to define in extreme situations, especially if it only involves a few particles. So be aware that any discussion of "temperature" in particle collider experiments, is probably some sort of "effective temperature."

Humans are primarily made of (and dependent on) liquid water. This puts pretty significant restrictions on the range of temperatures and pressures that we can survive at. However, this apparent "specialness" is likely explained by the anthropic principle. Having arisen on the surface of the Earth, it makes sense that our existence is tuned to those conditions. I would not be terribly surprised if there were some form of plasma-based "life" that could have arisen in stars. They might not even be recognizable as alive to us (and we to them).

Finally, one thing to note is that, in some sense, negative temperatures are possible. The most common example given is lasers. https://en.wikipedia.org/wiki/Negative_temperature

11

General Science / Re: Is 2 really prime? If so, why isn't 1?

« on: 01/05/2022 18:02:44 »

Indeed. I was careless. I meant to divide each n-gon into m equal portions by connecting vertices to the center.

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General Science / Re: Is 2 really prime? If so, why isn't 1?

« on: 01/05/2022 15:08:23 »

Thanks for introducing me to larger sets (groups?) of "prime" things.

I had one more thought of a geometrical reasoning for defining the odd primes as a reasonable set:

"prime numbers" can be defined as regular polygons with n sides that can only be divided into n identical portions by connecting vertices to the center. Non-primes have more than one way to connect verteces to the center to form congruent subsections.


Screen Shot 2022-05-01 at 9.58.01 AM.png (92.41 kB . 1112x912 - viewed 553 times)

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General Science / Re: How to reduce cast iron melting point

« on: 30/04/2022 17:49:52 »

Sb is antimony.

According to the engineering toolbox (https://www.engineeringtoolbox.com/iron-alloys-melting-points-d_1436.html)

It's about 94% Sb, 6% Fe (so that's essentially Sb with some small contamination of Fe...

Also, from what I can find, the melting point of pure Sb is lower that reported by the engineering toolbox (and alancalverd), which doesn't make much sense to me.

14

General Science / Re: Is 2 really prime? If so, why isn't 1?

« on: 29/04/2022 19:19:50 »

Thanks, Eternal Student! That does make sense to me that the classification should be useful somehow. The phrase "odd primes" seems a clever way to make that distinction.

I came across another wrinkle: what about –1? It has exactly two factors, and can only be the product of 1 and itself (1×–1 or –1×1).

I think the answer here (and this is supported by the geometric interpretation), is that primes must be positive, or only positive factors can be considered. Otherwise –1 would be the only prime number as all others would have two pairs of ± factors (ie 7 could be decomposed into 1×7 and –1×–7, and all other positive primes would similarly have two positive and two negative factors, while –5 could be decomposed into 1×–5 and –1×5, and all other negative primes would similarly have two pairs of one positive/one negative factor).

Thoughts?

15

General Science / Is 2 really prime? If so, why isn't 1?

« on: 28/04/2022 16:41:40 »

Got in a spirited debate the other evening (no pun intended), about whether the numbers 1 and 2 are prime.

The definition, as I know it from schooling, is that a prime number is "any number that is only divisible by itself and 1." ie if you can divide the number by any whole number that is not itself or 1, there must be a remainder or fractional component.

This can also be through of geometrically: if you have n things (let's say dots), then the only "rectangular" array of those n dots must be 1×n or n×1.

For example, in the image below, we can see that 3 dots can only be arranged in a rectangular array of 1×3 or 3×1. If we try making a 2×2, there is an incomplete edge. On the other hand, 4 is not prime because 2×2 works.

Screen Shot 2022-04-28 at 11.29.38 AM.png (85.49 kB . 990x1302 - viewed 1155 times)

1 is often left out from the primes because it has only one factor, itself (or 1). So it cannot be formed from an array of 1 by itself. Maybe this is a straw man argument (if so, please put me right). But this seems specious. A 1×1 array is still an array.

It seems to me that 2 should be treated the same as 1 because there isn't a choice among proportions of rectangular arrays. Only 1×1 for 1. Only 1×2 or 2×1 for 2. Only 1×3 or 3×1 for 3. etc. And really, there is no geometrical difference between a Only 1×2 and a 2×1 rectangle. The orientation is arbitrary (these aren't matrices).

Only when we get to non-prime numbers is there a choice of multiple types of rectangular arrays. One can arrange 4 dots as 1×4 (4×1) or 2×2. One can arrange 24 dots as 1×24 (24×1) or 2×12 (12×2) or 3×8 (8×3) or 4×6 (6×4).

There are many options for how to arrange 3 or more dots (only some of which. are rectangular arrays). There is only one option for 2 dots, and only 1 option for 1 dot.

So the real question I have is: if we count 2 as prime, should we not also count 1? Or, does the reason we don't count 1 also extend to 2?

16

Chemistry / Re: What chemicals can lower the melting point of aluminum oxide?

« on: 25/04/2022 18:03:00 »

Yes, lead oxide is definitely poisonous (and volatile!) I would highly recommend against using it.

Perhaps you could try a different approach to making synthetic corundums—growing crystals out of solution instead of from a flux or melt.

At room temperature, aluminum oxide has very high solubility in highly alkaline aqueous solution (forming aluminate ions), and can be precipitated out again with a decrease in the pH. Slowly changing the temperature and/or pH of the solution may allow growth of aluminum oxide crystals.

Hydrothermal synthesis of sapphires is a known alternative to synthesis from molten aluminum compounds.

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That CAN'T be true! / Re: Does the IVO thruster violate Newton's third law?

« on: 21/04/2022 17:43:12 »

A brief google search brings these up:
https://www.globenewswire.com/news-release/2022/03/24/2409190/0/en/IVO-Ltd-Introduces-the-World-s-First-Pure-Electric-Thruster-for-Satellites.html
https://www.ahedc.com/newsroom/ivo-ltd/

It looks like a scam or a mistake to me!

Either a "part-time Baptist pastor/part time electronics hobbyist" has completely revolutionized physics, or he hasn't and is just claiming to have done so...

18

Just Chat! / Re: A Short puzzle with dogs.

« on: 12/04/2022 16:47:55 »

Are these dogs point particles that must be co-localized at the endpoint, or do they have some nonzero radius that is less than the "1" specified as the side length?

19

Chemistry / Re: Will a water and diesel mix decompose at 500 degrees Celsius?

« on: 07/04/2022 11:53:56 »

Building a rocket to Mars. Having fantasy to beat Elon Musk at it!

water only:I have to eliminate water if it reacts with steel. What if at 500 deg C for 1 sec.

diesel only: seems normal boiling point low - 380 deg C. If could be heated to 500 deg C for few seconds, any major decomposition. Would it still be combustible diesel?

If you're hoping to go to mars using diesel as fuel, you'll need to bring your own oxygen too! Just heating the fuel without the oxygen won't get you very far...

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Chemistry / Re: Will a water and diesel mix decompose at 500 degrees Celsius?

« on: 06/04/2022 15:37:18 »

Can we heat water/diesel to 500 deg C in a strong closed steel chamber(oxygen free or fully filled with water/diesel) without decomposition to constituent elements.

Well, it won't turn entirely into the constituent elements, but it probably won't be the same as what you started with either. Products will depend on how long the reaction is held at 500°C (2 seconds probably won't look much different, but 2 years will be very different), what type of steel is used (mild steel will likely react with the water at this temperature, and other grades of steel might have transition metals that would catalyze different types of reactions, like Cr, Ni, Co, Mn, Mo etc.), what the ratio of water to diesel is, and what kind of diesel it is (any diesel is a mixture of many compounds, but what exactly the compounds are might have a significant effect on which reactions occur)