1

Chemistry / Re: Can a match be set alight without a strike?

« on: 06/12/2018 00:06:29 »

indeed, an ir laser would offer an easy and quite effective way to light the matches (without many of the risks of using volatile and corrosive compounds.)

given that this appears to be a religious ritual, i don't see any reason why they would feel compelled to be open about the scientific mechanism.

2

Chemistry / Re: Can a match be set alight without a strike?

« on: 04/12/2018 18:45:56 »

I can imagine a few substances that have a significant enough vapor pressure, and are reactive enough that they could start to heat the match head and trigger them...

It will depend strongly on what type of matches they are--"strike anywhere" matches can often be starteed with concentrated sulfuric acid (not volatile), so perhaps a similarly strong acid that is more volatile could be used (like TFA, but I don't want to think about what getting a TFA-laden gel on my skin would do...)

My suspicion is that it is either a volatile acid or fuel (or both), which would start reacting with the potassium chlorate in the match head.

3

Physiology & Medicine / Re: Can you receive radio signals with your body?

« on: 04/12/2018 16:41:09 »

It may also be possible that you do somehow have an antenna picking up AM radio and converting it to sound waves... But I don't know what the requirements are for that...

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Physiology & Medicine / Re: Can you receive radio signals with your body?

« on: 04/12/2018 16:32:22 »

The most boring explanations are usually the right ones:

It is quite possible that this was in fact part of a dream--I myself have had dreams on multiple occasions from which I awoke because I thought a bee had crawled in my ear, or something similar--and then upon waking was not sure whether the insect was real or dreamed. As I was waking up I was certain I still heard a buzzing sound, but once fully roused, there was no sign of any insect... (and I once tore my apartment apart looking for a cat that I was sure had sneaked into my open bedroom window--I had caught a glimpse of it entering just as I woke up--presumably because I heard it... but after a few hour of searching I eventually decided that my senses had deceived me, and there was no actual cat)

It is possible that you did hear an actual radio, most likely from a passing car or truck with the radio on too loud--by the time you were fully conscious, it had disappeared, but just as it passed, it was loud enough to rouse you.

It is possible that this was an auditory hallucination (nothing to worry about if it happens very rarely, especially if just at night, when waking up, but worth following up with a Dr. if it happens often, or increases in frequency).

It could also be tinnitus or an ear infection--something that is not an actual sound, but not hallucinated or dreamed either--the describing the sound as "muffled" and then "beeping like morse code" sounds to me like it could be caused by an ear infection (and I'm NOT a medical doctor). I have had intermittent ringing in my ear (with a noticeable ear ache) that did sound quite a bit like morse code, and the sound of the fluid moving around in my ear sometimes sounded like the crackle of an old radio.

It is possible, but highly unlikely (depending on who your friends are), that someone is pranking you, either playing actual sounds, or using more advanced technologies to generate sounds in your head (it is possible, but not well studied, so unless your friends are former KGB agents, you have nothing to worry about).

5

Chemistry / Re: A doublet peak for a solvent residue peak NMR?

« on: 29/11/2018 18:29:03 »

Residual CHCl₃ should only be a singlet (with very small ¹³C satellites, unless it is enriched in ¹³C, in which case it might show up as a doublet... It could also be another peak in there... do you have benzene (shows up at about 7.35 in CDCl₃), or other aromatic compounds in there?

What was the apparent coupling constant (in Hz)?

6

General Science / Re: How small is a smoke particle?

« on: 25/11/2018 22:02:11 »

Wood smoke 0.4 - 0.7 mm
Cigarette smoke, varies quite a bit but generally 0.2 - 0.8 m

Those both sound big...   I've never heard of 0.2 m smoke particles before! Perhaps some typos involved??

7

Chemistry / Re: When would you use d-DMSO over CDCl3 for H NMR?

« on: 25/11/2018 22:00:03 »

Oh, another thing to consider: the residual protiated solvent peak of chloroform shows up at 7.26 ppm, and dmso shows up at 2.5 ppm, so sometimes the choice can be made based on which part of the spectrum you need to look at.

8

Chemistry / Re: When would you use d-DMSO over CDCl3 for H NMR?

« on: 25/11/2018 21:57:58 »

DMSO is a much better solvent that chloroform (much more polar and more polarizable than chloroform, and a potent hydrogen bond acceptor to boot)--there aren't many molecular substances that aren't soluble in DMSO, at least enough to get a decent NMR (it's ok for some polymers and some salts as well).

Major disadvantages of DMSO with respect to chloroform: dmso is much less volatile than chloroform (it is very easy to remove chloroform from a sample by distilling it off at low pressure--once dissolved in dmso, there are very few ways to recover a sample), dmso has a very high freezing point (19 °C vs –64 °C for chloroform, so no low-temp VT studies), dmso will absorb moisture from the atmosphere while chloroform will not, substances dissolved in dmso can pass through the skin quite easily, so one must be EXTREMELY careful about handling toxic substances in dmso, and finally, cost (dmso is about 15% more expensive, which isn't crazy, but adds up).

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General Science / Re: How small is a smoke particle?

« on: 23/11/2018 19:35:27 »

Smoke particles range from molecule size (polycyclic aromatic hydrocarbons, which can be as small as about 1 nm across; https://en.wikipedia.org/wiki/Pyrene) up to very large particles. Often people care about how much particulate mater below 2.5 µm across (PM_2.5) is in the air: https://airnow.gov/index.cfm?action=aqibasics.particle

This 2.5 µm limit puts them much larger than viruses (more like bacteria), but I don't know what the distribution of smoke particle sizes is.

10

Chemistry / Re: Why would you need to acidify to pH 2 during an experiment?

« on: 23/11/2018 19:28:42 »

The desired product is a carboxylic acid. At pH values more basic than pH of 3, a significant fraction of the product will be deprotonated, as the carboxylate ion, which is likely to be quite soluble in water. By moving the pH down to 2, one can limit the fraction that exists as the carboxylate to less than one part per thousand, increasing the yield, and precipitating the insoluble acid from water.

11

Physics, Astronomy & Cosmology / Re: What units is radiation measured in?

« on: 23/11/2018 19:22:55 »

My favorite unit is the banana equivalent dose (BED) https://en.wikipedia.org/wiki/Banana_equivalent_dose

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That CAN'T be true! / Re: Is yuno44907 really banned?

« on: 18/11/2018 22:04:07 »

thank you.

I will attempt to avoid any/all of the above sins.

Yes, please

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That CAN'T be true! / Re: Is yuno44907 really banned?

« on: 18/11/2018 02:46:18 »

This former user took the art of trolling to a whole new level compared to what we usually see: A mix of apparent science denialism, religious proselytizing, hate speech, ad hominem attacks, links to sketchy websites... all within book-length posts. Honestly, it's better not to know.

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Physics, Astronomy & Cosmology / Re: Do aliens exist in other galaxies? Have they come to visit earth?

« on: 18/11/2018 02:37:16 »

This is my view.

Since life first formed on earth there have probably been millions of different forms of life, from bacteria to plants, from ants to humans.  And yet only one species (us) has achieved this level of intelligence.  So I think our level of intelligence is  rare thing.  I believe there is probably other life on other planets, but I think the chances of find life with our level of intelligence is highly unlikely

For the sake of argument, I'm going to disagree with you here (in a friendly way).

We really can't make predictions on how common life is with any idea of our certainty--because we only know of life on our one world, i.e. we have a dataset of 1. We can't know how stringent the requirements are for life, beyond knowing that our star is not unusual, and the composition of our planet is not unusual, and it appears that life, in the form of simple prokaryotes first appeared about 1 billion years after the Earth cooled enough to have a crust and oceans. This suggests that life may be common, but again, we don't have any good way of putting error bars on that.

On the other hand, we know that intelligence is evolutionarily advantageous to multiple types of species that have evolved on Earth. As far as we know, we are the most intelligent life on Earth to date, but even that is not certain, and we know of multiple examples of independent evolution of highly intelligent species: in addition to humans, several species of primates, birds, and even octopuses are known to fashion and use tools in the wild, and there are many more species still that have complex languages and social structures. It would appears that (at least on Earth) intelligence is a natural consequence of the evolution of multicellular organisms. Now, based on the evolutionary history of the life on Earth, I am willing to grant that perhaps life on most planets stalls out at single-celled organisms.

It took about 10⁹ years for the first prokaryotes to appear after the Earth cooled. It took about another 10⁹ years for the first eukaryotes to appear. And then it appears to have taken another 2x10⁹ years for the first true multicellular organisms to appear. After that, intelligent life arose within 2x10⁸  years...

15

Physics, Astronomy & Cosmology / Re: Do aliens exist in other galaxies? Have they come to visit earth?

« on: 15/11/2018 12:37:06 »

I will second Alan on this one.

Given that there are >100000000000 galaxies, each with >100000000000 stars, and it appears that, at least in our galaxy, most stars have at least one planet: I think it is very unlikely that there is not life in another galaxy.

However, to have travelled to Earth from another galaxy would require one of three options:
1) Several million years of travel time at close to the speed of light (Andromeda, the closest galaxy, is 2.5 million light years away)

2) Longer than the age of the universe, as we know it, traveling at the speed of our fastest out-going spaceship (a measly 17 kilometers per second, meaning it would take about 750 times longer to get to Andromeda as there has been time since the big bang)

3) Or perhaps there is some very advanced technology that somehow allows faster than light travel--let's even assume that it is instantaneous.

Option 2 seems least likely since they would have needed to leave their galaxy to come to ours before the existence of their galaxy, our galaxy, them or us.

Option 1 is most likely to me, but has the major problem of: how could they possibly have thought of Earth as an interesting target millions of years ago? Presumably if there is life in another galaxy, then life is fairly common (on an intergalactic scale), so why Earth--even if we think humans are special, we still didn't exist, and certainly didn't have a civilization worth visiting (we probably still don't).

Option 3 has two issues, even setting aside that we have no idea how faster than light speed could be acheived, or if it is even possible. The first is: even if they can get here instantaneously, and even if Earth is "worth" visiting (see above) how do they know to come here? It still would take millions of years for information to reach them from Earth, so they would have had to decide to come based on what they saw millions of years ago (plus I don't know how one could observe mastodon from millions of light years away). And finally... if these aliens can travel between galaxies in a heartbeat--what the f**k are they doing rearranging rocks on the surface of the Earth?

16

Chemistry / Re: Why would beetroot juice cause a slowly growing stain on a touchscreen?

« on: 13/11/2018 13:47:48 »

It looks to me like the beet juice has gotten between the screen protector and the actual phone screen, and then is effectively seeping by capillary action. I am surprised that the rate is on the order of several mm per day--I would have expected it to be either much faster or much slower--but it is what it is.

I think the major takeaway is that the compounds responsible for the color are so intensely colored that even a very, very thin layer is showing up to be extremely dark. It also looks like there may even be some separation of the different compounds, akin to thin-layer chromatography (https://en.wikipedia.org/wiki/Thin-layer_chromatography)

Very cool, and very unfortunate at the same time. (though I suspect that if the screen protector is removed, a damp kimwipe should be able to remove the offending stain.)

17

Chemistry / Re: What is the chemistry of silicon?

« on: 12/11/2018 17:10:43 »

Elemental silicon reacts with oxygen (at high temp, or with high surface area), fluorine, concentrated solutions of KOH or NaOH, and when finely divided, mixed with active metals such as lithium or magnesium and heated, it will form metal silicides (other metal silicides can also be formed, with more forcing conditions, or more roundabout methods).

18

Physics, Astronomy & Cosmology / Re: What is needed to create new atoms in the Universe?

« on: 07/11/2018 16:31:49 »

I also don't understand how could it be that the velocity at the outer edge of the accretion disc is 80% of Light speed while at the inner edge it is only 30% of Light speed.

My reading of this thread is that it has been suggested that the 80% c figure was the speed of particles in the polar jet, not the outer edge of the accretion disk.

The polar jets are emitted at up to 80% of c,

19

Physics, Astronomy & Cosmology / Re: Could Oumuamua be a light sail?

« on: 07/11/2018 15:30:27 »

a statistical significance of 30 sigma (that's very high)

But the statistical significance was not sufficient to confidently distinguish acceleration between forces proportional to 1/r or 1/r²...

True. They are certain that there was a non-gravitational acceleration, and that it was strongest when closer to the sun. But they did not have enough data (and/or precision) to distinguish the r^–1 from r^–2 relationships. I can't think of any force that goes as r^–1, and many that go as r^–2...

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Physics, Astronomy & Cosmology / Could Oumuamua be a light sail?

« on: 06/11/2018 15:05:15 »

Remember Oumuamua? (that interstellar thing that whizzed by us in 2017?) They're not saying it's aliens... (please be aliens! ...maybe?) but they are saying it is consistent with a light sail. (and "they" includes the chair of the astronomy department at Harvard)
https://arxiv.org/pdf/1810.11490.pdf

Part of the evidence is a previously published result that shows non-gravitational acceleration away from the sun with a statistical significance of 30 sigma (that's very high)
https://www.nature.com/articles/s41586-018-0254-4