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Physics, Astronomy & Cosmology / Re: What are the origins of planet Jupiter?

« on: 26/10/2020 15:29:45 »

Jupiter isn't only made of gasses, though hydrogen and helium are its primary components.

Luckily, there is no need for heavier elements to condense into stellar and planetary bodies. (otherwise we would be stuck with the primordial composition of the universe). Having rocky and icy and metallic substances certainly speeds the process along (both by being dense, and by radiating energy more effectively than hydrogen and helium alone, allowing the heat of planetary or stellar formation to leave as EM radiation rather than just heating up the collapsing cloud and making it expand again), but all matter has mass, and if you get enough mass in a small enough space, it will hold itself together gravitationally.

My understanding is that Jupiter formed from the same cloud of dust and gas that the sun and the rest of the planets formed from.

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General Science / Re: The amount of daylight in summer and winter?..

« on: 20/10/2020 16:54:15 »

There isn't the same amount *locally*.

But the Earth gets essentially the same amount of insolation from the sun, no matter the season (modest eccentricity of our orbit means there is some variation over the course of the year which will systematically mean that during one "season" the Earth is closer than in other seasons, but my understanding is that there are even longer cycles for which that bias shifts around the year too).

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Chemistry / Re: Explain the order of nucleophilicity F->Cl->Br->I-?

« on: 12/10/2020 19:41:56 »

An important aspect to note is that nucleophilicity is typically used to indicate relative rates of reactions (ie a *kinetic* comparison) vs indicating the relative stability of the products and reactants (ie a *thermodynamic* comparison, like ΔG or pK_a or K_eq)

It's good to think about solvent effects, but even in polar aprotic solvetns, iodide is a better nucleophile (and leaving group) than bromide, which is in turn a better nucleophile (and leaving group) than chloride (fluoride is terrible as a nucleophile, and as leaving group for S_N1 and S_N2 reactions, though it is ok as a leaving group for S_NAr reactions and in acyl or phosphoryl fluorides).

The key here is polarizability. During the course of an S_N2 reaction, electrons have to be able to get from the non-bonding orbitals on the nucleophile into the σ* orbital of the C–LG bond. The more electrons there are, and the larger the orbitals they are in, the easier it is for the electrons to move to the right place. (this also. applies to the leaving groups, for which the C–LG bond must polarize during the course of the reaction).

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Chemistry / Re: Can Sulphites be removed from wine other than by adding hydrogen peroxide?

« on: 02/10/2020 15:17:27 »

sulfites (sulphites) are unlikely to volatilize--you can get rid of them by oxidation, but why do you want to? They are protecting the wine by essentially serving as sacrificial reducing agents (oxygen in the air will react with sulfite before it oxidizes components of the wine)

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Physiology & Medicine / Re: Is "urologist" a good name for penis doctors?

« on: 23/09/2020 18:32:28 »

I was not aware--but that makes more sense!

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Physiology & Medicine / Re: Is "urologist" a good name for penis doctors?

« on: 23/09/2020 18:15:03 »

Yeah, I too have wondered why such an unspecific name was chosen (I think I know why...) The word urologist implies (to me) that they specialize in subjects related to urine, or urethras or ureters... but both men and women have these.

Phallologist would make more sense (and is more fun to say)

Of course there's always Dickter 

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Plant Sciences, Zoology & Evolution / Re: Do individual birds have identical plumage every year?

« on: 22/09/2020 20:34:35 »

Well... there is often a difference between juvenile and adult patterns (examples like emperor penguins, cardinals, and swans spring to mind)

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Physics, Astronomy & Cosmology / Re: Does taking hydrogen from water for energy deplete water supplies?

« on: 18/09/2020 15:07:49 »

one would only need to split about fifteen thousand liters of water

15 tons of hydrogen gas takes a lot of space - unless you expend a lot of energy compressing it.

'Twas me who said this!

And yes, I agree whole heartedly. I think that rechargeable zinc-oxygen batteries (fuel cells) are the way to go (at least for stationary storage of huge amounts of energy.) While splitting water to make hydrogen and oxygen provides fuel with a favorable specific energy (up to about 142 MJ per kg of hydrogen, assuming its being re-converted to liquid water by reaction with oxygen), its energy density is not great (is only about 0.01 MJ per L of uncompressed hydrogen; up to 8.5 MJ/L if liquified).

In comparison splitting zinc oxide provides zinc metal, which has only modest specific energy (5.3 MJ/kg, assuming it's being reconverted to zinc oxide). But with an energy density of 38 MJ per/L of zinc, that's a much smaller footprint (and easier storage). If the oxygen is coming from the air, you can have a very compact fuel cell. But if the oxygen must be high purity, or is being stored, much of that improved energy density is lost, because of the volume of the oxygen gas.

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Physics, Astronomy & Cosmology / Re: Does taking hydrogen from water for energy deplete water supplies?

« on: 17/09/2020 21:53:24 »

You aree correct that splitting water into hydrogen and oxygen would use up water and produce oxygen (in addition to the hydrogen that would presumably be stored). But for that hydrogen to ever be useful as a fuel, it would need to be recombined with that oxygen, reforming the water. If you lose containment of the hydrogen, some of it might escape into space, preventing recombination with oxygen to form water. But no business is likely to waste their resources doing that.

Storing energy by splitting water does require some amount of water (and high purity water at that!), but compared to present-day grid-scale technological solutions (pumped hydro) electrolysis is very efficient in terms of water needs.

Pumped hydro is used today for storing large amounts of energy: You need a reservoir at the top of a mountain, and one at the bottom. To "charge" it with energy for later, one must simply use that energy to pump the water up to the top reservoir. Then, when the energy is required, you leet the water flow back down, and through a hydroelectric turbine. This has about a 90% round-trip efficiency (ie you get back 90% of the energy you put in), which is good; but to store 1 MWh of energy (3.6×10⁹ J), one would need to pump a million liters of water up to an altitude of 360 meters (double the change in height to halve the volume of water or vice versa).

On the other hand, one could electrolyze the water using the energy that needs to be stored, generating hydrogen and oxygen, and then release the usable energy by recombining the oxygen and hydrogen using a fuel cell (about 70% round trip efficiency) or by combustion (about 20% round trip efficiency). So the efficiency is not great, but there is a much smaller water requirement: to store 1 MWh of energy (3.6×10⁹ J), one would only need to split about fifteen thousand liters of water (less than 1/60 the volume needed with the 360 meter tall pumped hydro system).

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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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Chemistry / Re: How to determine the right buffer concentration?

« on: 08/09/2020 21:05:33 »

What pH do you need to maintain, and how narrow of a range do you need to maintain? And how similar is the pH to the pKa of your buffer? And how far away is the acid pKa?

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General Science / Re: Are there Wheels in Nature?

« on: 01/09/2020 14:08:58 »

What about beating tail (flagellum) of sperm?

Doesn't the flagellum rotate, relative to the head of the sperm?

The flagellum doesn't need a blood supply or nerve connections...

In my mind that's more like a propellor...

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Physics, Astronomy & Cosmology / Re: What is the 3D shape with the maximum surface area?

« on: 26/08/2020 19:14:36 »

It's quite easy to find the surface area of a cylinder:

the top and bottom circle are the same, each having area: where r is the radius of the cylinder

and the outside is just where h is the height of the cylinder

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Physics, Astronomy & Cosmology / Re: Would we exist if Dark Matter was physical?

« on: 20/08/2020 20:21:56 »

No spelling errors. It just doesn't make much sense scientifically (logically) to ask a question like, "what if dark matter weren't dark matter?"

Dark matter, by its very being and definition, does not interact with light. If it did, it wouldn't be dark matter.

My previous post was an admittedly snarky way of pointing that out.

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Physics, Astronomy & Cosmology / Re: Would we exist if Dark Matter was physical?

« on: 20/08/2020 19:49:25 »

Fine, what if dark matter was opaque?

What if dark matter had herpes? Should I get tested?

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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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General Science / Re: Cheese shelf life, why?

« on: 19/08/2020 14:20:58 »

Wow, look a plagiarist! Whether bot or human, I suspect dobolgatfr might not have anything to add to this thread...

In the off chance that dobolgatfr is a real person struggling to figure out how to use the "quote" functionality, I hope they do not take offense at my swift judgement. Future posts will help me to calibrate that judgement.

When the block is cut for retail, this highly nutritious material is exposed to oxygen and all the bugs and yeasts floating about in your kitchen, so what was once a slow maturing process is now a playground for anything and everything that eats cheese.

When the block is cut for retail, this highly nutritious material is exposed to oxygen and all the bugs and yeasts floating about in your kitchen, so what was once a slow maturing process is now a playground for anything and everything that eats cheese.

19

Chemistry / Re: What Chemical Could This Be?

« on: 12/08/2020 13:42:38 »

If we allow for the balls shown to be different elements, and assume that hydrogen atoms are implied, there are very many options for what this could be (as evan_au points out, it is unlikely to represent a stable compound otherwise).

My mind goes immediately to triisopropylphosphine: https://en.wikipedia.org/wiki/Triisopropylphosphine

It looks like there are red marks around the structure, but I can't tell with this resolution what they say. Could be a schematic of an object or building. Hard to say

20

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...