1

Chemistry / How can I find the optimum ΔH and ΔS for passive T control?

« on: 24/05/2022 18:32:34 »

This question is inspired by thinking about passive temperature control.
Please, don’t sidetrack this discussion with comments about alternative technologies, or putting on a sweater, or the pros/cons of a certain temperature, or anything about climate change. I want to keep the discussion focused on the chemistry/physics/engineering/math of optimizing a system as described in the next post (the remainder of this post is all background info pertaining to how I got to the question at hand—feel free to skip ahead)

A significant portion of our society’s energy usage goes towards heating and cooling our homes and places of business. There are many ways of passively controlling temperature inside building including insulation and reflective vs light-absorbing exteriors etc. But I want to focus this thread on materials/systems that have a mediating influence on temperature by virtue of their heat capacity (I believe “thermal mass” is the term used by architects).

Some substances have an extremely high heat capacity per unit volume. For example, liquid water; coming in at about 4.2 kJ•L^–1 •K^–1, with some minor variation across its liquid range. But this pales in comparison to the incredible latent heat of a phase change.

For example, t-butanol melts/freezes at 298 K (25 °C, or 77 °F), and has a latent heat of fusion of about 116 kJ•L^–1 •K^–1. Any room at equilibrium with a bottle of t-butanol would have a significant “thermal mass” crossing 298 K (25 °C, or 77 °F). A sufficiently large bottle of liquid t-butanol, with sufficiently fast heat exchange to the room would effectively prevent the room from dropping below 25 °C. Likewise, if the t-butanol were solid, the room could be held below this temperature. If you want a different temperature, you can pick a different substance, which will have a different melting point (and different latent heat of fusion)

The problem with this approach (ignoring issues specific to the substance of choice), is that it only works for a single temperature (very narrow temperature range). It probably wouldn’t be economically feasible to have such a large reservoir of this substance with heat exchangers etc. necessary to keep a room (or building) at a single temperature. And if the temperature at any point drifted far from the melting point, then the thermal mass of the substance would be very small compared to the latent heat of fusion.

One possible solution (no pun intended) would be to have a few different reservoirs containing different substances, with different critical temperatures. For example dmso melts at 19 °C (66 °F). So one could imagine a room that is kept between 19 °C and 25 °C with one reservoir of t-butanol and one of dmso. Or one could imagine using only one solvent, but with two (or more) reservoirs with different amounts of solute, resulting in slightly different melting points (by virtue of colligative properties).

2

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!

3

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 5348 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?

4

Just Chat! / scientific homophones (english)

« on: 17/01/2022 16:25:38 »

Phosphenes are visual artifacts, while phosphines are chemical compounds in which a phosphorus atom is bonded to three organic (or H) substituents and has a lone pair.

Humans are people, while humins are organic compounds found in the soil.

Can anybody identify other pairs of homophones between a scientific jargon term and a "normal" word, or jargon from different fields?

5

The Environment / MOVED: Why can't water vapor be the driver of today's climate change?

« on: 26/12/2021 22:08:45 »

As expected, this thread has shown itself to be unworthy of staying in the main boards. It can now be found in That CAN'T be True, here: https://www.thenakedscientists.com/forum/index.php?topic=83465.0

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Technology / What are some low-tech ways to address climate change?

« on: 02/11/2021 16:54:18 »

NOTE: this thread will assume that anthropogenic climate change real, as it is generally accepted by the scientific community—any attempts to shift discussion towards questioning accepted science will be removed.

Since it seems that there is not yet enough political or economic will to shift to renewable energy sources or make major societal changes (like population control, limiting meat-based agriculture/diet, not clear-cutting our forests, different approach to transportation, less materialism etc.), I am hoping to identify methods that are economically viable to be undertaken by individuals and small communities/organizations that can have significant impacts in the near term.

Feel free to propose solutions or discuss others' proposals. I'll start:

1) A significant percent of the global energy budget is producing low-grade heat for residential and commercial buildings during the winter months. Insulation is the first step.

After that though, we need better ways to heat our homes and businesses. While heat pumps, solar heaters are better than gas-, oil- or coal-powered heaters (which essentially directly converting valuable fuel or electricity into waste heat), wind-powered heaters may well be the way to go. Essentially, the mechanical energy of the rotor can be converted directly into heat either by using a Joule heater (like a water brake) or an induction heater (spinning a magnet around near a conductive material to produce eddy currents)

I found this:
https://solar.lowtechmagazine.com/2019/02/heat-your-house-with-a-water-brake-windmill.html

2) We might be able to send some energy back out to space more efficiently.
Just simple mirrors or white paint over dark surfaces that get direct sun would be useful. This could be especially important in tropical regions where sunlight is most intense, in polar and high-altitude regions that have lost ice/snow cover, revealing dark rock/water/etc.

Also, to increase the rate of energy loss from the ground during the night time, wind, hydro, or thermoelectric power could extract usable energy out of the surrounding environment and be used to power LEDs or lasers that can be used to emit visible light into space. (obviously the cost to power ratio of these devices would be significant, but they also serve a purpose that is otherwise not being done.

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General Science / What preposition does one use for a mirror image?

« on: 18/10/2021 21:01:09 »

This is both a question of grammar/convention and a question of accurate scientific usage. Feel free to comment/discuss once you have voted!

8

General Science / Which of the platonic solids is MOST special?

« on: 22/09/2021 19:21:39 »

Not really science, and definitely not important, but...

I was recently thinking about how the ancient Greeks had associated each of the platonic solids with an element (tetrahedron for fire, octahedron for water, cuber for earth, icosahedron for air, and dodecahedron for "quintessence"

Supposedly the existence/identity of the dodecahedron was at one point secret/sacred??

My question is: based on the mathematical properties of these shapes (I am coming at this more from group theory), shouldn't the tetrahedron be the odd shape out?

My case (most of these points are very much inter-related):
1) The cube and the octahedron are a pair (you can inscribe a cube in an octahedron such that each of the 8 vertices of the cube is in the center of one of the 8 faces of the octahedron, and you can inscribe an octahedron in a cube such that each of the 6 vertices of the octahedron is in the center of one of the 6 faces of the cube. Similarly the dodecahedron (with 12 faces and 20 vertices) and icosahedron (with 20 faces and 12 vertices) are a pair. The shapes within each pair is very closely related: they belong to the same point groups (and thus are isomorphic).

The tetrahedron, with 4 vertices and 4 faces is its own partner (you can inscribe a tetrahedron in another larger one).


DWRDUG6VQAIjX1J.jpeg (106.56 kB . 933x1200 - viewed 6029 times)

2) The tetrahedron is the only platonic solid that lacks a center of inversion. (when a tetrahedron lies on one face, there is a vertex directed straight up, making the shape useful for caltrops (ouch!))

3) The tetrahedron is the only platonic solid that lacks a hexagonal projection (it can’t make a hexagonal shadow). Best it can do is a square.

4) The tetrahedron is the only platonic solid for which the number of faces (and vertices) is a perfect square.

5) It is pleasing (which the Greeks cared about, I think) to arrange the four elements in a tetrahedral array. (how meta)

Screen Shot 2021-09-22 at 2.14.31 PM.png (29.7 kB . 432x406 - viewed 5423 times)

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Chemistry / How does one detect fake/diluted honey?

« on: 16/08/2021 18:58:24 »

You couldn't use the stuff we normally call "sugar" to make fake honey; it's sucrose and honey is largely glucose and fructose.

Depends how it’s done. When there is a poor nectar flow - we are about to enter one - beekeepers feed sucrose solution to tide the bees over. The bees will invert the sucrose, but you end up with a diluted flavour so you can’t (or rather shouldn’t) extract it for sale.
We also use an invert syrup with same glucose/fructose mix as honey so the bees don’t waste energy converting it, but same problem of saleability. Unscrupulous people could add the invert directly and I think this has been detected in imported honey.

But you could use golden syrup- which is a partially inverted sugar (and thus is much more similar to honey).

Honey police will get you 
Golden syrup contains high amount of 5-hydroxy methyl furfural (HMF). Honey is tested for HMF as it is a sign that the honey has been overheated in processing and adding golden syrup would push it above the legal limit.
Most amateur beekeepers don’t heat their honey in order to keep it as natural as possible.

Testing for fakes is interesting enough as a piece of analytical chemistry, but more than a little off topic.

That would be a very interesting topic. Particularly if you know a simple test to identify sucrose in honey.

Does polarimetry count as simple? I would expect that even a rudimentary polarimeter should be able to identify if significant amounts of sucrose had been added to a fructose/glucose mix…

https://en.wikipedia.org/wiki/Specific_rotation

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Physics, Astronomy & Cosmology / Could K-40 be a useful radioactive fuel for interstellar missions?

« on: 01/08/2021 17:32:02 »

(I opted not to tack these disorganized musings on to the existing thread regarding plutonium oxide fuel...)

Could ⁴⁰K be a useful radioactive fuel for interstellar missions?

Potassium is widely distributed and highly abundant in the Earth’s crust (as well as throughout the inner solar system, I would bet). ⁴⁰K is a very minor component of all potassium (about 0.012 % per Wikipedia), but it has a half-life of about 1.25x10⁹ years, so it should be widely available. This also means that it can provide stable power output for a very long time. And because its atomic mass is so low, it has a very significant energy density. (there are 3 possible decay pathways, each with its own energy and probability, and I don't have all the numbers I need to calculate it, but I feel like it could be a lot of energy density, even if the power density is fairly low)

As I understand it, most commercially produced potassium metal is actually produced as a gas and then condensed and solidified (it is distilled out of high temp reactions of potassium salts with molten sodium or molten aluminum).

So we have the infrastructure for large-scale distillation of potassium, would it not be feasible to also use distillation (or other gas-phase techniques like centrifugation, chromatography, etc) to enrich the  ⁴⁰K from natural abundance of 0.012 % to something more like 5 %? (obviously the greater the enrichment, the higher the power density, but I don’t know what would be ideal for use as fuel, and what would be practical limitations on enrichment)
 
(prep mass spec is also an option, like the Manhattan project, but even though it allows use of stable K⁺ ions, I still suspect it would be the more difficult option)

The fact that one of the decomposition products is Ar might pose some engineering challenges, but could also potentially be put to use?

11

Physics, Astronomy & Cosmology / How can we distinguish viscosity from camera speed?

« on: 26/07/2021 15:43:10 »

 Imagine filming a viscous fluid, like honey. Sometimes time lapses of veery viscous fluids moving can look like normal speed of less viscous liquids, and increased playback speed of less viscous liquids can look like normal speed of more viscous ones. But it's not perfect. What kinds of motions or observations would allow one to unambiguously tell whether the honey was hotter (less viscous), or the playback speed was increased?

i.e. if there is a droplet free falling that is obvious, because the acceleration is constant.

12

Physics, Astronomy & Cosmology / Does the cosmological principle dictate isotropy?

« on: 25/06/2021 15:44:13 »

As I understand it, the main idea underlying the cosmological principle is that no part of the universe is "special"

That seems a reasonable axiom, but where I have difficulty is that this appears to be widely interpreted as implying that the universe must be isotropic on some grand scale.

It seems more reasonable to me to extend the cosmological principle to say that no location in the universe is "special" and no scale in the universe is "special."

We observe structure in the universe at every scale. The structure isn't identical, or even necessarily analogous (don't worry, I'm not going to compare atoms to solar systems  ), and the forces that dictate the organization are different at different scales (?? < strong force < electroweak < gravity < ??). But there is always some sort of structure, some sort of organization, and at any given location, there is localized anisotropy.

I am reminded of turbulence, which produces eddies and swirls anywhere from the micron-scale to the galactic scale.

So can we be shocked every time there is evidence that the observable universe has anisotropy?

13

Chemistry / What would you want to see done with NaK?

« on: 27/04/2021 02:38:11 »

I needed a few grams of some metallic sodium and potassium for my research, but due to the logistics and expense of shipping, it doesn't really make sense to buy less than about 50 grams at a time. So fast forward a little while, and now I have some excess potassium that I need to quench before it goes bad (it can slowly react with oxygen to form a layer of potassium superoxide, which is a very potent oxidizer, and can form explosive mixtures with the mineral oil the potassium is typically stored under).

So I am considering combining the sodium and potassium metals to make the eutectic alloy, which is a liquid at room temperature.It is a beautiful shiny metal like mercury, but tarnishes very quickly if exposed to traces of O₂, H₂O, or CO₂, and will spontaneously combust in the air within seconds to minutes, depending on the humidity and temperature. (don't worry folks, I am trained to work with this stuff, and have a lab equipped with the protective equipment needed to handle the stuff!)

Other than the obvious thing of blowing it up by reacting it with water (which I don't particularly want to do), is there anything that ya'll would particularly like to see a few ounces of shiny liquid metal do on video? Non-destructive and destructive (to just the alloy itself) suggestions will be entertained. I have some ideas myself, but figured I would crowd source a bit before actually making the stuff.

Here are some vids about the stuff that I think are good, but I think I can do better (except for the fountain--I can't do that!!)
fountain:

making NaK:

(not sure I agree about handling the metals bare-handed, I would probably sweat...)
another synthesis of NaK:

14

General Science / Are there humorous textbooks?

« on: 30/11/2020 20:47:28 »

Every once and a while I will see an author throw in one or two "witty" comments into their otherwise dry textbooks. I have also seen spoof textbooks that are brimming with jokes and ridiculously false statements.

Are there any examples of textbooks (college level) that present factually correct information in a cohesive way, but using a humorous (college level; crass, taboo, cynical etc.) approach in how the material is presented or how questions are framed?

For example, instead of a statistics book using coins flips and dice (or even gambling) for explaining things, imagine learning about probabilities like:

"Chad has two girlfriends, and neither knows of the other. If Alice comes over to spend the night on average twice per week, and Bertha comes over on average one night a week (each being a random, independent event), how long can Chad expect to keep up the ruse?"

(hopefully funnier than that, but you get the idea)

15

Just Chat! / wtf usa?

« on: 06/11/2020 17:10:16 »

why must my country (USA) be so bad at everything?!?

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COVID-19 / Why are daily new cases so periodic?

« on: 30/06/2020 04:28:35 »

Screen Shot 2020-06-29 at 11.10.30 PM.png (89.32 kB . 1226x622 - viewed 3857 times)

This data (screen grabbed from the New York Times just now) clearly shows a periodic (possibly sinusoidal) variation in new cases reported each day. The period appears to be is exactly 7 days (1 week). With maxima coming on consecutive Fridays (with the occasional Thursday).

I see a few possible explanations:
1) This is an artifact caused by weekly patterns in data reporting (file the report by the end of the week.)
2) This is an artifact caused by when it is easiest for most people to get the tests.
3) This is real and represents a weekly pattern in when people get sick (maybe folks go out Saturday night, get infected then, and then feel bad enough to get tested 6 or maybe 5 days later.
4) This is real and represents ripple effects of more people get infected when there are more infectious people around, and because of the induction period there are actually bulges that propagate at a period of about 1 week.
5) something else?

Looking at the deaths graph offers more insight:

Screen Shot 2020-06-29 at 11.15.34 PM.png (113.1 kB . 1264x678 - viewed 3848 times)
1) is challenged by the fact that the reported deaths, although also following a weekly periodic undulation, peak on Wednesdays. (presumably there would be similar reporting biases)
2) is also not supported by the deaths graph (people don't tend to only die when it is convenient)
3) could be supported, if the length of time from showing symptoms to death is fairly consistent (and not supported if it varies widely)
4) see above
5) ??

17

General Science / Who can find a more poorly behaved function?

« on: 26/06/2020 19:01:16 »

f(x) = lim    x^a     or just f(x) = x^∞
         a→∞

for –1 < x < 1, f(x) = 0
for x = 1, f(x) = 1
for 1 < x, f(x) = ∞ (unbounded, strictly positive)
for x = –1 f(x) = no f*n clue! (it's neither positive nor negative)
for x < –1 f(x) = no f*n clue! (it's completely divergent, neither positive nor negative)
I'm not sure if x

I'm sure ya'll can come up with some other poorly behaved functions

PS: I remember sin(1/x) is also a baddie when trying to get close to 0, but I think the above is worse.

18

Physics, Astronomy & Cosmology / Is Wolfram's new hypergraph approach to a TOE valid?

« on: 17/04/2020 21:10:12 »

https://writings.stephenwolfram.com/2020/04/finally-we-may-have-a-path-to-the-fundamental-theory-of-physics-and-its-beautiful/

If you don't care about the personal aspect, scroll down to "How it works" in. the link above.

I have only worked my way through about half of this, but I am quite intrigued...


0409img5.png (410.3 kB . 1236x868 - viewed 5439 times)

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COVID-19 / How badly do hospitals dealing with COVID19 need O2?

« on: 15/03/2020 19:30:01 »

I recently read an article that said that oxygen generators are in short supply in some places.
( http://www.cidrap.umn.edu/news-perspective/2020/03/global-covid-19-cases-pass-100000-mark )

Is this going to be a worry in most places as they become inundated with patients, or is it really just some particularly isolated locations?

How bad does it have to get for a hospital in the US to accept non-medically rated oxygen generators (provided the oxygen produced can be proven to be of sufficient purity/safety)?

My lab studies electrochemical oxygen generation. I know it's not as energy efficient as pressure swing oxygen concentrators, but we can generate arbitrarily large volumes of oxygen per second with minimal capital expenditure (and no moving parts!) compared to what I see medical oxygen concentrators going for...

Inspired by academic biochemical labs that have risen to the occasion and offered their expertise in running tests, I wonder, "is there anything a lowly chemist can do?" Or should I just start selling off our solvents as disinfectant?

20

Physiology & Medicine / How bad can stats reporting be in mainstream media?

« on: 24/02/2020 20:56:33 »

CNN (I know... I bring it upon myself... it is one of many news outlets I get my info from) had an interesting article online today, concerning the usage rates of seniors (65+) using cannabis. (https://www.cnn.com/2020/02/24/health/weed-marijuana-seniors-wellness/index.html )

But the discussion of the statistics was SOOO BAD, I have to vent here!
In one excerpt:

In 2006, only 0.4% of seniors over 65 reported using marijuana products in the past year, they said. The newly published study found that by 2015, the number had doubled to 2.4%. By 2018, it had doubled again, with 4.2% of seniors over 65 using weed.

2.4% is not twice 0.4% (that's a sixfold increase), and 4.2% is not twice 2.4% (1.75x is not terribly far from 2x, butt still...)

But simple arithmetic issues are only some of it.

They go on to say (a few paragraphs later)

One of the most disturbing findings, he said, was an increase in cannabis use among older adults who also use alcohol. In 2015, only 2.9% of seniors reported both alcohol and cannabis use (although the data cannot say if they use simultaneously). By 2018 it had jumped to 6.3%.

Huh? If only 2.4% of seniors reported using marijuana in 2015, how did 2.9% use marijuana and alcohol? And again, if 4.2% of seniors reported using marijuana in 2018, how did 6.3% use marijuana and alcohol?

Presumably they are discussing different datasets or different studies or different definitions of "use" or something.... but come on! This is the most basic aspect of reporting science... no wonder people don't trust science!

(sorry for the rant)