21

Technology / Re: Is there commercially available gas centrifuge to filter out SO2?

« on: 16/04/2020 03:35:49 »

Even in  a sealed container with no temperature gradient, you won't get a useful degree of separation.

What do you think will happen if I put a mixture of Helium, Nitrogen, and SO2 with equal volume and pressure inside a 10 meters vertical pipe. Will we get the same composition between top and bottom part?

That will depend on the temperature, pressure, and gravity.

But assuming that you mean Earth gravity (9.8 m•s^–2), 1 atm, and 300 K (27 °C), then the difference in gravitational potential energy between having 1 mole of He at the very top of the 10 m tube and 1 mole of SO₂ at the very bottom, and having 1 mole of He at the very bottom of the 10 m tube and 1 mole of SO₂ at the very top is 9.8•10•(0.064–0.04) = 5.88 J/mol. This could be viewed as the maximal enthalpy of gravitational un-mixing in a 10 m column (being favorable by 5.88 J/mol, so ΔH > –5.88 J/mol).

But there is also an entropic cost. http://hyperphysics.phy-astr.gsu.edu/hbase/Therm/entropgas.html
The change of entropy of an ideal monoatomic gas with change in volume is (ideal gas is a good model for He, not so great for SO₂, but doesn't really matter here... the errors will cancel):

ΔS = N•k*ln(V_f/V_i)

so if we had 1 mole of each gas being restricted to 1/2 the volume of the tube (from having had the whole tube), then for each mole of gas we would have:
ΔS = N•k*ln(1/2) = –5.76 J•K^–1•mol^–1
and therefore ΔS = –11.52 J•K^–1•mol^–1 (because we are restricting two moles of gas, the He and the SO₂)

thus at 300 K:

ΔG_un-mixing = –5.88 J•mol^–1 – (300 K)(–11.52 J•K^–1•mol^–1 ) = +3450 J/mol

(recall that ΔG must be negative for a process to be spontaneous)

22

COVID-19 / Re: What test were Chinese officials applying to the forehead to diagnose Covid?

« on: 14/04/2020 16:08:18 »

I think they were infrared thermometers looking for people with fevers. A cheap and quick test that identifies people in need of more testing (many causes of fever), or at least greater extent of isolation/restriction based on being more likely to be infected/infectious.

23

Physics, Astronomy & Cosmology / Re: What difference does this make to our understanding of infinity?

« on: 14/04/2020 15:36:45 »

A nice way of showing this 1-1 correspondence of the uncountably infinite reals between 0 and 1 (or any finite distance) and all the reals is to imagine an arc (semicircle) connecting the two endpoints. Every point on that arc corresponds to a point on the line beneath it (we can define every point on the semicircle uniquely using only the x coordinate, so if the diameter of the circle is 1, this is the continuum from 0 to 1. Every point on this arc also has a slope (slope of the tangent line), and it contains all real numbers, from arbitrarily large negative slopes to arbitrarily large positive slopes. Therefore there is a 1:1 correspondence between the continuum from –∞ to +∞ and the continuum between 0 and 1.

Screen Shot 2020-04-14 at 10.42.13 AM.png (15.17 kB . 394x306 - viewed 2766 times)
In other words: if you think there are more slopes than x values in the setup described above, choose any real slope, and I will find you the only x value that gives it. Likewise, if for some bizarre reason you think that there should be more x values than slopes, I challenge you to find an x value in the domain that does not uniquely correspond to a slope.

24

COVID-19 / Re: Is Lockdown Cost Effective?

« on: 14/04/2020 02:59:27 »

This gif uses data for USA specifically, but is likely reasonably extended to most industrialized nations. It is a fascinating and horrifying graphical progression:

https://public.flourish.studio/visualisation/1727839/

It indicates that in the order of a few weeks, deaths directly attributable to COVID-19 has eclipsed even heart disease as the leading cause of death (who knows how many otherwise preventable deaths will result from the flooding of hospitals and the exhaustion of physical and human resources associated with outbreaks).

That said, the value of human life is not infinite. The United States Department of Transportation defines the value of a statistical human life as about $10,000,000. So the difference between 100,000 deaths (locked down) vs 2,000,000 deaths (not locked down) is on the order of (1.9x10⁶)(10⁷) = $1.9x10¹³

Add to that lost wages assuming that everybody was still working, and it looks like without the lockdowns ~80% of people would contract the disease, of which about 50% would have no symptoms. So if 40% of the US working population were out sick for 2 weeks, with US median pay, that's about $1800x1.56x10⁸x0.4 = $1.1x10¹¹. Not so big compared to all the dying, but also not great.

It's hard to know what "would" have happened without lockdowns, but we can see example after example of places that "should" have locked down earlier (from a casualty perspective). But if we really want an "economical" strategy. Aggressive testing and tracking will be able to ensure that populations with low enough infection rates can return to business "as usual" while those with problematic infection rates can shelter in place for a few weeks at a time. (the more people self-isolate, the less time is required to strangle the infection: if only 10% of people isolate, there's no point at all)

25

Cells, Microbes & Viruses / Re: Are 85 Covid-19 deaths ON AVERAGE a day per 60 milllion a reason to PANIC?

« on: 02/04/2020 04:00:05 »

with respect to the original question:
https://public.flourish.studio/visualisation/1727839/

26

Physics, Astronomy & Cosmology / Re: Neutrinos travelling faster than light?

« on: 24/03/2020 03:02:55 »

Hi Halc.  That explains that then!  It's a typical knee jerk reaction from a newbie like myself when he thinks, hey something DOES travel faster than light! I guess that if the article was aimed at a non scientist like myself then it would have said the neutrinos get to Earth earlier than the light 'because ...'.

You too can travel faster than the speed of light, quite easily actually.

https://abcnews.go.com/Technology/story?id=99111&page=1

I would expect that, unless otherwise specified, "the speed of light" is typically meant to mean "the speed of light in a vacuum" ie the constant, c.

Yes, light can get slowed down by interactions with matter. It doesn't even have to be particularly special matter for significant differences (even liquid water can slow light down to about 75% of c)

27

New Theories / Re: Could the Covid 19 virus be used as a type of germ warfare?

« on: 18/03/2020 15:04:34 »

Given the unusual relationship between age and severity, one could be forgiven for wondering whether it had been designed by a millenial or genZ for generational warfare.

But paranoid thinking will not help the situation.

A recent analysis of its genome highly suggests natural evolutionary origins...

https://www.nature.com/articles/s41591-020-0820-9.pdf

28

Chemistry / Re: What is the difference between Phosphate and Phosphorous ?

« on: 11/03/2020 18:42:17 »

"phosphorus" refers to the element (atomic # 15) specifically. This can be used as reference to an atom of phosphorus in another compound, or as elemental phosphorus (there are a few different ways that P atoms can bond with each other, including diatomic P₂ molecules, which are like N₂, tetrahedral P₄ molecules "white phosphorus," a 1-D polymerized form consisting of vertex-sharing tetrahedra "red phosphorus," 2-D networks "black phosphorus" etc. etc.)

Phosphate refers to a phosphorus atom bound to 4 oxygen atoms. The phosphate anion PO₄^3– is the simplest form, and generally is what is meant by phosphate. But there are also phosphate esters (like trimethyl phosphate, (H₃CO)₃PO, and different protonation states of phosphate/phosphoric acid, like H₃PO₄, H₂PO₄^–, and HPO₄^2–.

Depending on the context, "total phosphate" may be used to describe a mixture of different compounds and/or ions containing the PO₄ subunit, regardless of what is (or isn't) bound to it. Also, there are polymeric forms of phosphates, like pyrophosphate, and metaphosphate (orthophosphate, in this case is used to specify that monomer).

29

Physics, Astronomy & Cosmology / Re: Neutrinos travelling faster than light?

« on: 10/03/2020 13:56:56 »

Just to reiterate what Halc said (and hopefully add something):

Neutrinos don't travel faster in a vacuum than light does through a vacuum, but they do usually travel at near-light speed because they have so little mass. The key is that most neutrinos can pass right through long expanses of dense matter without any interactions (they can interact through the weak force, so some will get absorbed or scattered)--so neutrinos effectively don't care what medium they are traveling through. Light, on the other hand, interacts quite strongly with matter through electromagnetic forces (so the dense ionic plasma of a star is really going to interact with light). Light will likely get absorbed and re-emitted or scattered billions of billions times before leaving the star.

According to this reference, light at the core of our sun has a mean free path of about 1cm, meaning it likely takes thousands of years (on average) to reach the surface: https://image.gsfc.nasa.gov/poetry/ask/a11354.html

In contrast, this website claims to calculate the mean free path of a neutrino through starlike medium is on the order of 100 lightyears! (I cannot confirm their calculations, but it looks reasonable): http://burro.case.edu/Academics/Astr221/StarPhys/neutrinos.html

30

Plant Sciences, Zoology & Evolution / Re: Insects and lizards, convergent evolution?

« on: 09/03/2020 14:33:48 »

My understanding is that some of this (similarities between lizards and insects) is convergent evolution, and some is due to shared primordial ancestry.

Lizards, being vertebrates, are evolutionarily descended from fish. Fish already had heads with eyes and mouths, internal skeletons, and appendages for locomotion. Fins are not so great on land, but provided a starting point for evolution of legs.

Insects, being arthropods, are evolutionarily descended from marine arthropods. (I am imagining shrimp-like critters).

Both split off from what would eventually become mollusks, and as such have some genetic and structural similarities (like bilateral symmetry, and digestive tracts).

31

Physics, Astronomy & Cosmology / Re: How to determine thermodynamically favourable electrochemical reactions?

« on: 23/02/2020 20:09:03 »

the electrons have to go somewhere, so you will need to pair a reaction that consumes electrons with one that produces them.

You can see if the pair are thermodynamically favorable by adding their electromotive forces (the reduction potential of the reaction that is consuming electrons minus the reduction potential of the half reaction that is producing them) if the number is >0 the reaction is thermodynamically favorable.

For example:

Zn --> Zn²⁺ + 2 e^– (–0.763 V for the reverse reaction)
Ni²⁺ + 2 e^– --> Ni  (–0.280 V)

taking electrons from Zn and giving them to Ni²⁺ will be favorable by 0.483 V, the reverse reaction would be uphill by the same amount.

Note that to add and subtract these voltages, they must be compared to the same reference (NHE, RHE, SHE, Ag/AgCl, Hg/HgO, etc. etc.) and the conditions have to be the same (same temp, pressure, pH, electrolyte etc. etc. etc.) if the conditions are different, then Nernst equation must be used as well.

32

Physics, Astronomy & Cosmology / Re: How do the oceans ignore centrifugal force?

« on: 13/02/2020 15:00:21 »

How much centrifuge force would it take to displace 1g of mass of water carefully placed onto a disk shape that was about to be spun?

A centrifuge force is actually a linear force as I suspect you must already know .  In fluid dynamics , water has little to no way of 'gripping'' a surface . 

It was explained earlier that the centrifuge force of the earth has sufficient magnitude to alter the shape of the earth. 

Am I to believe that this force isn't enough to bulge all the water ?

Why would some water bulge and the above and under remain in location when as mentioned it has no ''grip'' ?

The spinning dish analogy fails to reproduce what we observe precisely because the earth has a gripping force that the dish/water doesn't: gravity.

A simple tweak to the analogy can work though. Put the water in a large conical dish and spin it--the water will experience a force away from the axis of rotation, but it has to flow uphill to move outwards. There will be an equilibrium established between those two opposing forces, and the equilibrium will be set by the angle of the cone (slope of the side of the dish, ie how far up does it have to go up to go 1 cm out?) and the rate of the rotation (assuming gravity is fixed). If the dish is spun quickly enough all the water would fly up and out, but for any sufficiently slow spinning, the equilibrium will allow all of the water to remain in the dish.

33

General Science / Re: What are the future scopes of nanoscience?

« on: 01/02/2020 13:38:48 »

A far as I know, Nanotech is pushing four main fields forward (or these fields are advancing nanotech--take your pick)

1) Electronics devices.
Circuit components are now essentially nanoscale, and the ability to fit more and more transistors on a chip is driving the tech to go smaller and smaller. There are also experimental technologies aimed at using fluorescent nanoparticles in
LEDs.

2) Catalysis
Nanoparticles (NPs) can be excellent heterogeneous catalysts if they are made of the right materials. In large part this is due to the surface area to volume ratio being maximized as the particles get smaller. Also, the smaller the NP, the less similar to the bulk material. Researchers are developing ways to control the shape, size, composition, and atomic structure.

3) Drug delivery
Actually, pharmaceutical companies care a lot about not only the composition of their drugs, but also the formulations. Many look into the absorption profile as a function of the size of the crystals of the drug. Nanoparticulate drugs dissolve quickly, and can deliver drugs faster than doses using larger crystals.

4)
Rockets and explosives
Many rocket motor compositions still involve mixtures of solids, which then must react. Again, due to the surface are to volume ratio, smaller particles are going to allow much much better mixing (think about mixing dark and light gravel together vs dark and light sand, vs dark and light flour...)


So... we're not yet really making nanotech machines with moving parts--though there is some progress there. Honestly, the most impressive nanotech that I am aware of, that is most like scifi... is biology! Many of our enzymes are nanotech, and we get things like this:
https://www.reddit.com/r/educationalgifs/comments/7x9zmi/kinesin_protein_moving_a_molecule_around_a_cell/

34

Physics, Astronomy & Cosmology / Re: Can planets form without a star?

« on: 17/01/2020 08:45:15 »

I don't see any reason planets couldn't form under these conditions.

There are plenty of brown dwarf "failed stars" that are essentially large gas giant planets that never quite got big enough to ignite and turn into stars.

There are thought to be many starless "orphan" planets, but they are essentially impossible to detect with current methods (most of which detect the planets indirectly through measurements of their host stars). But even if the universe is teeming with orphan planets, it is still unknown what proportion of them were born in interstellar space, and what proportion were born near stars, and then tossed out through interaction with some more massive bodies.

35

General Science / Re: Are man-made things the nemesis of nature?

« on: 26/12/2019 16:44:48 »

The distinction between natural and unnatural is rather... artificial 

People are naturally occurring, and all that we do is part of our nature... so everything is natural (why is a skyscraper any less natural than a termite mound, or a beaver dam, or a wasp's nest?)

That said, the OP points out that there is an apparent oppositional relationship between our economic goals and a stable environment/ecosystem.

From my perspective, I think this has more to do with how our economic system is structured than the money itself: we don't typically ascribe much value to resources until they have been extracted for use, and don't recognize the value of services rendered by nonhuman, non-industrial systems, and even in cases where that value is recognized, there is no mechanism to integrate it into our economic systems.

For example, imagine a mangrove forrest that protects a coast from erosion, prevents seawater from contaminating freshwater, and provides a breeding ground and nursery for ocean-dwelling fish. Landowners don't pay the mangroves for keeping their properties from falling into the sea. Residents don't pay the mangroves for keeping their water potable. Fishermen don't pay the mangroves (or the sea, for that matter) for providing them with fish.

If a developer comes along and offers to buy the mangrove-filled real estate for a paltry $200000, with plans to build a marina, what mechanisms are in place to protect the millions of dollars of real estate and millions per year of fishing revenue?

https://www.sciencedirect.com/science/article/pii/S2212041612000046

36

Physics, Astronomy & Cosmology / Re: Can Atoms Touch Each Other?

« on: 18/12/2019 18:01:55 »

well... atoms don't have hands, but there are several reasonable definitions of touch that would include two atoms "touching."

There are also some definitions that would have requirements that one (or two) atoms couldn't possibly satisfy.

37

General Science / Re: why are omega fatty acids called Omega?

« on: 08/12/2019 03:26:19 »

typically, the omega will be followed by a number (like 3, or 5)

omega (ω) is the last letter of thee Greek alphabet, and is used in chemistry to denote the end of a long chain. an ω-3 unsaturated fatty acid is one that has a C=C bond three bonds in from the last carbon of the chain.

https://en.wikipedia.org/wiki/Omega-3_fatty_acid

38

The Environment / Re: How much heat is generated from methane from burning vs. the greenhouse effect?

« on: 02/12/2019 18:06:22 »

Long story short: it is better to burn it.

Burning 1000 kg of methane releases about 5×10¹⁰ J. But methane that is released into the atmosphere ends up "burning" anyway (converting methane and oxygen to carbon dioxide and water), in the upper atmosphere, releasing the same amount of energy, just over a longer timescale, and higher up in the atmosphere. The different location and timescale of the conversion of methane and oxygen to carbon dioxide and water may introduce a small difference in how much of that energy goes into heating the air near the surface, but this also ends up being minuscule compared to the amount of energy that can be trapped by adding 1000 kg of methane to the atmosphere.

Before degrading into carbon dioxide, methane is much more potent as a greenhouse gas. Over the course of 100 years, 1000 kg of methane "traps" about 30 times as much energy as 1000 kg of carbon dioxide.

Calculating precisely how much energy gets trapped in not straightforward, and depends on many assumptions (for example adding 1000 kg of methane to an atmosphere with 400 ppm carbon dioxide will not necessarily have the same effect as adding to an atmosphere with 600 ppm carbon dioxide). But as a rough approximation, having increased atmospheric carbon dioxide concentrations from 300 ppm to 400 ppm required about 5×10¹⁴ kg of carbon dioxide being released into the atmosphere. This is predicted to change the temperature by about 1.5 °C over the next century, which would require on the order of 10²⁵ J (based on the heat capacity of the atmosphere and oceans--as worked out in the 3rd reference below). This works out to about 2×10¹⁰ J/kg or 2×10¹³ J for 1000 kg of carbon dioxide, so this would be on the order of 6×10¹⁴ . (10000x as much as burning--and probably 1000000x as much as the difference between burning on purpose and slow oxidation in the upper atmosphere)

https://en.wikipedia.org/wiki/Global_warming_potential
https://www.epa.gov/ghgemissions/understanding-global-warming-potentials
https://scholarsandrogues.com/2013/05/09/csfe-heat-capacity-air-ocean/

39

General Science / Re: Herb and marijuana anxiety

« on: 17/11/2019 18:45:03 »

Hey guys... chill out. 

Cannabis has unfortunately not been studied very well under rigorous scientific conditions. Much of this is because it has historically been very difficult to get permission to study in human subjects, and approval often comes with stipulations that limit the sample sizes, or what the source of the test materials is (for a long time, in the US, studies needed to get their cannabis from the DEA... not exactly an uninterested party--there are actually instances in which researchers acquired official permission from their university, hospital, IRB, and local, state, and federal law enforcement agencies, only to be told that there was no cannabis for them to conduct their studies with (oh well). Many of the organizations in the USA, that researchers must satisfy in order to get permission or funding to run controlled tests involving cannabis have specific directives not to facilitate research that shows anything other than harm. It remains schedule 1 here because there is "no proof of medical utility" while researchers are banned from conducting studies looking specifically for benefits. (see more here: https://www.ncbi.nlm.nih.gov/books/NBK425757/ and here: https://www.rollingstone.com/culture/culture-features/why-is-it-so-hard-to-study-pot-124767/)

This means that most studies done in the US are specifically looking for harm, are often looking at longitudinal or epidemiological studies (which have sooo many confounding factors), and it is difficult to publish null results, so altogether, we are left with a significant bias in the literature.

Luckily, there has been some research done in Israel (https://cannabinoids.huji.ac.il/), among other places, with some promising results. I am skeptical of many of the medicinal cannabis claims (also often made by interested parties, and then hyped by those who wish to believe and those who profit by having others believe). But it would seem that there is serious research that is getting underway.

As far as recreational use goes, cannabis poses some very real, but relatively mild health risks.

For instance, many users (especially those who started using early in life) do use it habitually. It is not physically addictive (unlike drugs like alcohol and benzodiazepines, which have potentially lethal withdrawal symptoms, or drugs like opioids, nicotine, and amphetamines which can have significant physiological distress caused by withdrawal. Even drugs like caffeine have a greater physiological withdrawal effect.)

Smoked cannabis carries with it many of the dangers of inhaling any burning plant matter. And apparently vaporized extracts may be even more dangerous (it may be that this has more to do with lack of regulation, and greedy @$$holes willing to dilute their products to make a buck without any care for the consumers, or there could be some as-yet unknown reason why vapors are more harmful than smoke...)

The connection to psychosis is somewhat troubling, but I have yet to see studies showing a causative link conclusively, or providing any sort of insight into how this could happen mechanistically. High dosages of THC (in the absence of CBD, or with only traces of it) can certainly precipitate acute psychosis. But this is temporary. I'm sure there are cases of people frequently who get so high that they have episodes routinely, but I don't see this accounting for the supposed long-term risks.

My opinion is that the risks and benefits both need to be studies much more rigorously. But that in the meantime, cannabis be allowed as a legal product for both medical and recreation use, so long as the industry is heavily regulated, taxed enough to pay for costs to society (as should be done with alcohol and tobacco), and is kept away from children. So much more harm has been done to society by the war on cannabis than by the drug itself.

(wow, that turned into quite the rant! sorry)

40

Chemistry / Re: Why does egg white turn from translucent to white when whipped?

« on: 01/11/2019 14:02:45 »

I think it's the same reason that snow is white while ice is translucent/transparent.

Light will scatter at every interface of two environments with different refractive indices. When the egg white is undisturbed, there is only the one surface. One it begins to fill with little air bubbles, there are many surfaces, each with its own reflections, refractions and dispersions--so no images can make it through, and it just appears as diffuse white light.

(note that cream does not need to be whipped to become white--it is already an emulsion of two liquids with different refractive indices)