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Plant Sciences, Zoology & Evolution / Re: Have animal reactions to mirrors and windows been studied?

« on: Today at 04:19:41 »

Well, this cat certainly appears to perceive motion in this static picture:

Perhaps just like we do:

rotsnake.jpg (613.75 kB . 1024x768 - viewed 76 times)

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Question of the Week / Re: QotW - 22.05.23 - Where does the potential energy of a spring go in acid?

« on: 23/05/2022 15:12:22 »

Good question!

The compressed spring will probably decompress as it corrodes. So, for the most part, the answer is, "wherever energy goes when a compressed spring is released without any load on it." The mechanical energy is dissipated, with some of it turning into sound, some into heat, and possibly some other minor components.

However, this doesn't answer the core question here (at least not directly). Some of the spring must have dissolved from the "compressed state". What happened to that energy?

So, the act of compressing spring increases the potential energy of the spring. Because energy is conserved, there must be a way to account for it. So there are a few possibilities:

• Either dissolving the compressed spring results in a solution with the excess energy stored in it somehow (probably as heat, so it would be warmer than a solution otherwise identically prepared from the uncompressed spring.)

• Or, the solutions resulting from dissolving the spring in either state are identical, and the energy was released (again, probably as heat).

• Or, there is a range of intermediate cases, in which some of the energy goes into the solution, and some is released.

So that's the pure thermodynamic approach. But how can we explain it in a more concrete way?

On an atomic level, the energy stored in the spring can be thought of as strain on many different bonds between atoms—the bonds are either too short (compressed) or too long (extended) compared to the optimal bond length. Either way, this means that the bonds between atoms will be easier to break. Because dissolving the spring in acid requires breaking the bonds, it will take less energy to do this part for the "energized" spring, leaving more energy for motion of the resulting ions (heat).

A similar approach can be taken for thinking about springs that are in the same state of compression, but different temperatures (or one that is molten, and one that is solid).

3

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).

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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

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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 1432 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?

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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?

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

« on: 28/02/2022 01:17:25 »

Trans-uranic elements are much harder to study (due to their radioactivity, rarity, and cost), but the chemistry of actinide elements (including trans-uranics) is an active field of study.

https://pubs.acs.org/doi/10.1021/acs.inorgchem.8b03603

These f-block elements don't have chemistry similar to carbon, but many of them do have quite complex chemistries. They can have many different oxidation states, and can be used in compounds that serve as catalysts (Fox, A.R.; Bart, S.C.; Meyer, K.*; Cummins, C.C.*, Towards Uranium Catalysis, Nature, 2008, 455, 341 - 349), fluorescent compounds (https://pubs.rsc.org/en/content/articlelanding/2006/cp/b607486c), and thereputics (https://www.lanl.gov/discover/publications/actinide-research-quarterly/pdfs/arq-2019-01.pdf)

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Physics, Astronomy & Cosmology / Re: Can sand/salt permanently molecules absorb resonate frequency?

« on: 22/02/2022 15:31:33 »

The patterns formed on Chladni plates are a result of the properties of the plates themselves, and has nothing to do with the sand/salt/sugar/dust/etc. placed on top for visualization purposes. The grains that are arranged into the pattern are "agnostic" of why they are in the particular place that they are in.

The plate vibrates in such a way that parts of the plate have significant displacement, and other parts hardly move at all (the "nodes"). Grains that happen to be on parts of the plate that are moving get tossed up and land on another part of the plate, while grains that happen to be on the nodes where the plate is hardly moving get to stay put. This means that after a brief period, almost all of the grains end up on the parts of the plate that are hardly moving. The pattern that the nodes make is a function of the frequency of the vibration and the size/shape of the plate.

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Physics, Astronomy & Cosmology / Re: Has the distance between the sun & earth changed?

« on: 23/01/2022 23:42:32 »

Im the one that asked the question; and thank you for posting this Origin.

I would like to know if this distance is a big cause of Climate change.

I see from posts that the distance does change, though is there an on going change that is climbing (a distance change or orbit change), and not staying nominal?

It can have an effect to some extent, and there are some cyclical changes in earth's orbit (see more here: https://www.fs.usda.gov/ccrc/education/climate-primer/natural-climate-cycles)

But the current (fast) changes in the climate are driven primarily by greenhouse gases (mostly carbon dioxide and methane).

We can see the effects of the cycles, as well as the recent trends (the practically vertical line at the far right) by looking at atmospheric carbon dioxide concentrations found in ice cores, the record of which goes back almost a million years (https://keelingcurve.ucsd.edu/)

co2_800k.png (110.13 kB . 1000x600 - viewed 2248 times)

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Physics, Astronomy & Cosmology / Re: Whats a branch of physics with high potential that has unjustified disinterest

« on: 10/01/2022 22:11:01 »

I may be biased (as a chemist), but I would recommend physical chemistry. It has all the mathematical rigor and knowledge of "standard" physics, but it's also much more easily explored experimentally than high energy physics, astrophysics, cosmology etc.

Physical chemistry (or chemical physics, or materials science, depending on what you're looking at) involves a lot of quantum mechanics (because it largely deals with collections of photons, electrons, atomic nuclei, and how they interact with each other). It also involves relativity, when considering very heavy atoms (like gold or uranium), in which electrons that get close to the nucleus have enough kinetic energy that reletivistic considerations must be taken.

Bridging the gap between physics and chemistry means that it is very useful, and often overlooked by purist physicists and chemists alike. But physical chemistry is critically important for "sexy" topics like (among other things):
• quantum computing (and regular computing)
• LEDs (and OLEDs)
• Photovoltaics
• Drug design
• Protein folding
• Sensing
• Spectroscopy
• Making new dyes (for aesthetics, cellular imaging, light emission, light harvesting)

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General Science / Re: Is this a feasible system for recycling CO2?

« on: 02/01/2022 18:57:56 »

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Physics, Astronomy & Cosmology / Re: How can we see ultraviolet light in Balmer series?

« on: 02/01/2022 17:59:12 »

I think it is also important to note that the Balmer series (and Lyman, and Paschen etc.) are for atomic hydrogen, not molecular hydrogen (H vs H₂). H is not stable at standard temperatures and pressures, but is stable at temperatures where electronically excited H atoms are thermally accessible.

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Physics, Astronomy & Cosmology / Re: How can we see ultraviolet light in Balmer series?

« on: 28/12/2021 16:19:30 »

In the image provided, notice that the leftmost lines appear less intense than those on the right but still appear (to the eye, and on the screen) to be the same hue. The emissions are not actually less intense (if anything, they should be more intense, depending on how the atoms are being excited...) It's just that our eyes (and/or whatever camera was used to capture the image shown) are significantly less sensitive there.


human_cone_action_spectra.gif (7.91 kB . 766x369 - viewed 3298 times)
https://www.unm.edu/~toolson/human_cone_response.htm

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Chemistry / Re: Why does HNO3 exist but HPO3 does not?

« on: 29/11/2021 21:17:22 »

One can think of it as a hydration/dehydration equilibrium:
H₂O + HXO₃ H₃XO₄

There are two reasons that the equilibrium favors the left-hand side when X = N, but the right-hand side when X = P, As, (or Sb, I believe):

1) (the simple answer, pointed out by Bored chemist) nitrogen is the smallest of the bunch (covalent radius of N = 75 pm, P = 106 pm, and As = 119 pm), so it is simply harder to fit the extra oxygen on there.

2) (the complex answer) the 2p orbitals on nitrogen and oxygen have fairly similar energies** (–13.1 and –15.9 eV vs vacuum, respectively) as well as very similar sizes (as noted in point 1), as well as shorter σ bonds (also due to point 1). This means that the p orbitals on neighboring O and N atoms can form very strong π interactions, and that the electrons in the π bonding and π anti-bonding orbitals would both be shared fairly equally.

In contrast, the valence of the phosphorus atom is a 3p orbital, with a much higher energy** (–10.2 eV; again comparing to –15.9 eV for O), and extends much farther away from the nucleus (but not towards a neighboring atom).

Screen Shot 2021-11-29 at 4.15.13 PM.png (42.56 kB . 794x624 - viewed 2689 times)

This means that in HNO₃ the nitrogen atom has much more electron density compared to the P atom in HPO₃ (the N is less electrophilic than the P, making the N less likely to accept electron density from another O), while the oxygen atoms bound to N have less electron density than those bound to P (the P-bound O atoms are more basic than N-bound, making them more likely to gain H⁺) and much stronger N=O bonds than P=O bonds (so it is easier to break the double bonds).


Screen Shot 2021-11-29 at 8.08.24 PM.png (45.63 kB . 546x680 - viewed 2653 times)

* https://www.schoolmykids.com/learn/interactive-periodic-table/covalent-radius-of-all-the-elements
** https://www.colby.edu/chemistry/PChem/notes/AOIE.pdf

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Geology, Palaeontology & Archaeology / Re: How to genetically classify a weathering mineral?

« on: 16/11/2021 22:26:12 »

I would say this is a question of "taxonomy" not "genetics" (rocks don't have genes)

I think the OP is right that minerals as a result of weathering would be an exogenic classification, but I am not sure... I think the best member to answer this would be @Bass

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The Environment / Re: Is Rising CO2 level a Problem?

« on: 15/11/2021 14:38:47 »

Climate change aside, there is another *major* problem with increasing CO₂ in the atmosphere. It is literally and figuratively changing the bedrock of our marine ecosystems!

As it dissolves in ocean water, it causes a shift in this equilibrium:

CO_2(aq) + H₂O(aq) + CaCO_3(s) Ca²⁺_(aq) + 2 HCO₃^–_(aq)

While this looks innocuous enough, here is the catch: CaCO_3(s) is the primary component of sea shells, and coral reefs. More CO₂ released into the environment means that animals at the bottom of the food chain have weaker shells, and less healthy coral reefs, which then translates to major disruptions to the ecosystems that depend on the reefs.

https://ocean.si.edu/ocean-life/invertebrates/ocean-acidification

As with climate change, the problem isn't necessarily how much CO₂ there is at any given time (over the course of geological history, it has been much higher and much lower than it is today). The problem is how quickly things are changing. Sea creatures need time to evolve shells with slightly different compositions, or attain new behaviors to adapt to their new reality. Ecosystems need time to adjust to new status quo. And it is a good time to remind everybody that many of these systems are susceptible to positive feedback loops: small but sudden disruptions in an ecosystem can lead to odd boom-bust cycles that then really mess everything up.

(imagine that the oysters' shells become weaker, making it initially easier for otters to eat them. The population of otters will grow quickly while the oyster population shrinks. At a certain point, the oyster population cannot sustain itself, and crashes. Then the otter population crashes. If this were a "normal" predator-prey equilibrium, a brief disturbance would cause some oscillation in populations for a while before settling back down on the original equilibrium. But if the "balance point" is continuously changing because the environment is changing during the oscillation, then both species could go extinct in a matter of decades!)

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Physics, Astronomy & Cosmology / Re: Energy loss in electrolysis

« on: 11/11/2021 05:35:06 »

Often it depends on how patient you are. If you want to move or exchange lot of energy very quickly, you have to pay for it (energetically). Energy efficiency for splitting water into hydrogen and oxygen can be done with >90% efficiency using precious metal catalysts and low current densities. But once the currents involved are large enough that it is limited by the resistance of the solution, then you can basically view it as a resistor in the cell, producing heat with a power of current times overpotential (applied potential minus the thermodynamic potential). Energy efficiencies of <70% are acceptable if the energy/time is more important than energy/cost.

You didn't specify whether the recombination is electrochemical or not, or how you would like your energy.

If you want heat, I can get you a virtually 100% efficient source as any power you like up to a few thousand degrees °C. (ie a hydrogen oxygen flame, anywhere from a 50 W jewler's torch to a 2,000,000,000 W space shuttle engine).

If you want that energy in the form of DC electricity, you can use an acidic proton exchange membrane-based fuel cell to get 50–60% of your energy back from combining hydrogen and oxygen. (the rest goes to heat)

If you want AC, then either you burn it and drive a turbine, or convert DC to AC and take yet another conversion hit.

If you want light energy...

18

General Science / Re: Can Medicine solve Global Warming?

« on: 10/11/2021 15:10:54 »

It would be interesting to compare the carbon footprints of recreational drugs vs other forms of recreation and consumption.

IMHO a dozen milligrams (or so) of THC* and a plate a falafel is more enjoyable than a glass of bordeaux* and a filet mignon.


*which is legal for. recreational use for those 21 years and older in many parts of my country.

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

« on: 08/11/2021 20:38:57 »

Regarding livestock, the ingested/exhaled carbon is going to balance out perfectly. That is, until we find a way to convert fossil fuels directly into feed, and then we will have to count animal exhaust too.

One aspect, however, is that much of the nitrogen needed for agriculture (the footprint of which is dominated by livestock and production of feed for livestock) is fixed through highly energy intensive methods. The Haber Bosch process accounts for roughly 1 % of global energy demand (and associated emissions). So, this is a big deal. We wouldn't need nearly as much nitrogen if we were eating the crops directly, but since we are feeding it animals, we need much, much more plants (and therefore more fertilizer).

Again, the problem isn't the animals themselves. Rather, it is that we have found a way to intervene in natural processes to speed them up, using fossil fuels.

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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.