61

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

62

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.

63

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?

64

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.

65

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.

66

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

67

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...

68

Plant Sciences, Zoology & Evolution / Re: Can a water buffalo inhale/exhale as it's snout, nose and mouth are underwater?

« on: 04/08/2020 19:32:22 »

I don't see any reason a buffalo couldn't exhale while submerged.

As for inhaling, yeah... if the creature wants to inhale air, it had better not have its whole face submerged.

As far as how this relates to filmmaking... if they are filming real water buffalo... presumably the creatures are alive and breathing. And if it is animated... why get so excited about such a minor detail? I'm sure the gravity and aerodynamics are also poorly rendered...

69

Chemistry / Re: How to reduce aluminum melting point?

« on: 04/08/2020 13:41:33 »

This may be of interest: https://www.engineeringtoolbox.com/aluminum-alloys-melting-points-d_1432.html

70

Physics, Astronomy & Cosmology / Re: Are proton/hydroxide membranes permeable to hydrogen/oxygen/water?

« on: 04/08/2020 13:39:41 »

Dude, you've been asking questions on the same general topic for over a year (I think a few years by now). Do some research! Take a course or a webinar or something. This site is not an encyclopedia!

71

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.

72

New Theories / Re: Can heat affect Earth's rotation?

« on: 01/08/2020 16:54:22 »

so it must eventually stop spinning.

Just as soon as it gets hold of something to which it can impart angular momentum.
Tricky for something  in a near vacuum.
Might need to wait until the Sun goes red giant.

Well, the moon is taking some... but tidally locked to the moon is also not "stopped"

gnoring second-order effects such as thermal winds, the source of kinetic energy is the rotational energy of the planet, so it must eventually stop spinning.

And there was me thinking that the Sun powered the wind.

I'm with Bored on this one. Thermal effects (wind) are only secondary to the rotation of the earth if your frame of reference is not tethered to the earth. If you wanna argue that the atmosphere is moving with the earth at several thousand kph, that windmill had better be inbound from outer space!

73

Geology, Palaeontology & Archaeology / Re: How to turn powdered rock into hard, solid rock?

« on: 22/07/2020 12:51:12 »

In addition to using cement as a binder,  you might consider using a glue or resin. (some experimentation required. to find ratios and setting time etc.)

74

Physics, Astronomy & Cosmology / Re: Why does nuclear charge screen off totally?

« on: 16/07/2020 18:55:32 »

As Bored chemist says, the charge from the nucleus is equal and opposite to that of the electron cloud.

Because the electrons are only separated from the nucleus by an Ångstrom or so (10^–10 meters), any particle that is more than 100 times this distance (10 nm) away essentially feels no difference in the electrostatic attraction from one and the attraction of the other (essentially same magnitude of force, and same direction, except one is attractive and one is repulsive).

There is some net force possible for particles that are very close. For example, London dispersion forces, which can be thought of as mutual distortions of the electron clouds in close neutral molecules.

75

General Science / Re: Can increases in molecular aurorae (methane etc) indicate climate change?

« on: 14/07/2020 16:27:04 »

It's an interesting question.

Strictly speaking, I think we can only hope to directly see changes in atmospheric composition using this approach,  rather than actually observing climate change. The atmospheric composition naturally plays a role in the climate (and vice versa), but we must be careful not to conflate the two.

Additionally, I wonder how sensitive this technique could be. Methane and carbon dioxide make up extremely small percentages of our atmosphere, so quantifying changes in these could be difficult from a technical perspective. We already have pretty accurate and precise ways to measure these species here on earth, and anywhere else we can send a probe. However, the possibility that this could be used to monitor other planets is (as far as I can tell) worthy of additional consideration.

76

Chemistry / Re: Are there reagents, enzymes, or toxins that bond proteins together?

« on: 07/07/2020 18:51:06 »

disulfide bonds are a good way to stick cystine-rich proteins together. first reduce them all to SH termination, then you might be able to oxidize them in a high enough concentration to have cross-linking between proteins. You might also use a bis-thiol linker.

77

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 939 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 943 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) ??

78

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!)

79

Chemistry / Re: How fast do buffers work?

« on: 28/06/2020 16:28:48 »

I think the source of confusion here is that the diffusion of "H⁺" in water is special. An aqueous solution with a pH of 6 has a concentration of "H⁺" of 10^–6 M. But this is really the concentration of "excess" H⁺. Because water is H₂O, the concentration of H atoms is about 110 M (more than 8 orders of magnitude higher than suggested by the pH). (note that this higher concentration doesn't change the thermodynamics or stoichiometry of acid-base reactions, but as far as kinetics are concerned, the reactions are hastened because it doesn't really matter where the H⁺ comes from--they are all equivalent.) In contrast, if there were an aqueous solution of Fe²⁺ that was only 10^–6 M, that is all the Fe in the solution.

80

Chemistry / Re: How fast do buffers work?

« on: 28/06/2020 01:42:00 »

Out of curiosity, why would you think that an intermolecular chemical reaction could be faster than diffusion?