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Physiology & Medicine / Re: Where are the major 5 senses inside a human brain?

« on: 10/09/2020 16:40:30 »

Clearly there are some ways of messing with how time is perceived (adrenaline and hallucinogens such as LSD being obvious examples of chemicals that can influence time perception), but I don't know if a person can be made to experience a day in an hour...

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Physiology & Medicine / Re: Where are the major 5 senses inside a human brain?

« on: 10/09/2020 16:37:56 »

It's hard to say precisely *where* a sense is located. But there are specific regions of the brain that are associated with processing the various senses at different levels.

Vision is processed first in the eye itself, and then signals are sent via the optic nerve to the visual cortex in the occipital lobe:
https://en.wikipedia.org/wiki/Optic_nerve
https://en.wikipedia.org/wiki/Visual_cortex
https://en.wikipedia.org/wiki/Occipital_lobe#Function
(one could imagine hacking in at any point in this process)

For touch, you might be interested in the cortical homunculus:
https://en.wikipedia.org/wiki/Cortical_homunculus

There are also structures known for processing sound, smell, and other senses.

As far as putting our own signals in, I think there is some work that has been done using implanted electrodes (fairly crude), as well as use of microwaves, which can apparently cause people to perceive sounds.
https://onlinelibrary.wiley.com/doi/pdf/10.1002/bem.10163

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Physics, Astronomy & Cosmology / Re: Does spacetime bend only locally around objects?

« on: 20/08/2020 15:30:17 »

Great answer from Colin2B!

I will also add: we can detect gravitational waves from stellar (black hole and neutron star) collisions from billions of light years away!! It takes the most sensitive instruments on the planet to detect the motions of the most massive bodies in the universe—but it clearly demonstrates that massive bodies can distort space (space-time) across cosmic distances.

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COVID-19 / Re: Could asymptomatic people have invisible organ damage?

« on: 04/08/2020 19:37:57 »

My understanding is that this may be possible. "asymptomatic" unfortunately doesn't strictly mean "no symptoms of the disease occurred," it means "no symptoms of the disease were recognized."

It took many weeks before people realized that "asymptomatic" individuals could be diagnosed by looking for loss of smell/taste, or "covid toes." (new symptoms were discovered)

There are anecdotes of individuals who are (otherwise) "asymptomatic," but developed blot clots, which then caused stroke. So I would imagine that there could be cases of individuals who are infected, don't present the "standard" fever/cough/malaise but could still sustain significant damage to liver or kidneys or what have you...

There is still so much we don't understand about this disease...

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Physics, Astronomy & Cosmology / Re: How Do We Know Absolute Zero Is The Temperature It Is If It's Unattainable ?

« on: 02/08/2020 13:17:33 »

Extrapolation!

If you put a gas in a sealed piston (which will keep the internal pressure constant by allowing the volume to change), and start cooling it down (and/or heating it up) you will notice that the volume varies with temperature. After collection of much data it will become apparent that the volume is proportional to temperature, but only if you use a really odd temperature scale, that has a zero point at –273.15 °C.

There are other ways to get there, but I believe that historically, this is how it came about.

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Question of the Week / Re: QotW - 20.06.29 - Why does instant coffee dissolve so well?

« on: 30/06/2020 03:56:00 »

I have a question as to how coffee granules dissolve so well compared to soup-in-a-pack, for example. The difference is amazing, coffee dissolves with minimal or no stirring!

There are a few factors involved:

The inherent solubility of thee compounds in instant coffee is relatively high (compared to the amounts of stuff). Soup mixes will contain significant amounts of fats and other lipophilic/hydrophobic compounds (which melt and float in the soup, rather than dissolving).

The instant coffee grounds have quite a bit of exposed surface area, and I would guess that there might even have been a significant investment in engineering the particles to dissolve just so.  (if you could invest $5M once to figure out how to make your coffee dissolve 20% faster than your competitors' for only a 0.2% increase in production cost, it could well be worth it!)

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Chemistry / Re: Why don't electrons crash into the nucleus?

« on: 02/06/2020 15:52:35 »

It is entirely reasonable to say that an electron in an atomic orbital *has* fallen all the way to the central nucleus. It just so happens that electrons are effectively fluffy, and spread out over a volume 100,000 times larger that that occupied by the nucleus. Similar to how the atmosphere on Earth has fallen all the way down to the ground, but still measurably extends more than 100 km from the surface.

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Geology, Palaeontology & Archaeology / Re: Can Google Earth provide detailed images of caves in the Grand Canyon?

« on: 25/05/2020 02:06:33 »

The National Parks Service has virtual tours of many of the parks, including the Grand Canyon, which may be useful: https://www.nps.gov/grca/learn/photosmultimedia/virtualtour.htm

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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)

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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.

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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 2014 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.

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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)

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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/

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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)

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COVID-19 / 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

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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).

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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

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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).

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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.

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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.