exchemist
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Posts posted by exchemist
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15 minutes ago, StanislavDolgopolov said:
Yes, the electrons in a local well are no longer usual conduction electrons. They form a new band - band of local states, which is usually much narrower than the conduction band.
Well then, if they are localised in the valence band they won't participate in superconducting behaviour, will they?
I'm not a solid state physicist but my understanding is conduction requires a continuum of delocalised states, so that there is no energy gap to be jumped when an electron is given a bit of extra energy.
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11 minutes ago, StanislavDolgopolov said:
Yes, I would discuss the topic with community, since it seems to be important for general understanding of superconductivity.
The conduction electrons are extended throughout the crystal before they fall into a local state. Inside the local state two electrons must be a singlet pair.
But if they fall into a localised state (presumably of lower energy if they "fall" into it) they cease to be conduction electrons, surely? In effect they go into the valence band, don't they?
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5 hours ago, StanislavDolgopolov said:
Crystals may contain electronic real-space-eigenstates as ground states, which are spatially much larger than one unit cell, such as impurity states, standing waves at Brillouin zone edges, Anderson localization, etc. Every eigenstate is usually occupied by two conduction electrons with opposite spins, forming a singlet pair. Notably: if the eigenstate is limited in real space, then the excitation energy of each singlet electron is not necessarily negligible, so below a certain temperature the singlet pair can be lasting. Isn't this a long-debated pairing mechanism in superconductors ?
For these to be “conduction electrons”, wouldn’t the state have to extend throughout the crystal? But would they then be treated as paired?
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12 hours ago, Photon Guy said:
Like it or not space exploration is going the way of the private sector. As it's been mentioned in this thread there's companies such as SpaceX and Bellend One and no doubt in the future there will be more private space companies still. That's how its always happened with travel and exploration throughout history, it starts out as something that is government funded and then goes the way of the private sector and more and more people are able to do it.
There is an article in today's Financial Times, saying that the European space industry is also going down the route of commercial competition. So yes, this is a natural progression, once a technology has been sufficiently mastered and once commercial exploitation opportunities open up in the field in question. It was not so long ago that nuclear power was all in state hands. But now, it no longer is.
But the private sector needs a return on investment that justifies the level of risk in the enterprise. Where there is little or no commercial return, and/or the risks are high, private enterprise will not get involved. Private enterprise may also be denied access to a sector if there is no prospect of effective competition (anti-monopoly legislation). So these are the areas where governments have to step in.
I am honestly not sure I understand what point you want to make, apart from having some kind of animus against NASA.
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4 hours ago, sethoflagos said:
Have you considered investing in this bold new venture?
If this becomes its unofficial name I shall be highly gratified.
It does resemble its creator, rather: Bezos should avoid roll-neck sweaters at all costs.😄
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2 hours ago, Ramil said:
PCC reagent was first developed by Corey group in 1975. You can refer to this paper to see the details regarding its introduction.
In regards to my background, I had to solve many Chemistry Olympiad problems back in high-school and I have seen this reagent overwhelmingly frequent. It seems it is used widely.
Hope it helps.
It does, thanks. Looks as if my organic chemistry tutor might just have been becoming aware of this around the time I sat finals.🙂
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6 hours ago, Ramil said:
Yes, CrO3Cl- is part of pyridinium chlorochromate (PCC) which is less reactive than other commonly used chromium-based reagents (such as Na2Cr2O7 with H2SO4) and is used in oxidation of primary alcohols to aldehydes (instead of to carboxylic acids)
Do you know when this reagent was introduced to the organic synthesis arsenal? I learned my organic synthesis back in the 1970s and I don't have a record of this one in my undergraduate book (ROC Norman) from that era, though it does of course have the dichromate method you mention. I see from Wiki this chlorochromate route was discovered "by accident" but there does not seem to be any information about when and how this came about. I wonder if it is more recent than my old books.
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13 minutes ago, chenbeier said:
My question is what is CrO3Cl-, I know CrO2Cl2 and CrO42- or Cr2O7 2-.
Or is it a mixture of NaCl and CrO3?
Probably from this: https://en.wikipedia.org/wiki/Pyridinium_chlorochromate
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On 2/2/2024 at 2:18 PM, Gian said:
I've just heard Richard Dawkins saying that one individual (a zillion years ago) had 2 children. One is the ancestor of baboons, the other the ancestor of humans.
Would all the subsequent evolution of the 2 species have to be descended from literally that one single creature? Or could it have been several such creatures, even hundreds, who all had 2 such children each?
Cheerz
GIAN🙂XXX
Yes you must have misunderstood, I think. It is populations of organisms that evolve, collectively, rather than single individuals spawning a whole new species. If it were the latter it could only happen by extreme in-breeding, which we know doesn't work out well.
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32 minutes ago, Swudu Susuwu said:
Human eyes use ganglion neurons to compress data from raw photons and output simple shapes/motions that go to V1 cortex.
V1 cortex processes those and compresses to data as objects and motions of objects that go to V2 cortex.
A few thousand neurons should allow to put compressed visual data to human's cortices
[spammy looking link removed]
https://link.springer.com/article/10.1007/s00424-007-0242-2
What point of discussion do you wish to raise? Or are you just spamming?
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5 hours ago, Photon Guy said:
Speaking of Elon Musk, I would like to point out that Howard Wolowitz got to meet him, lucky guy.
Who?
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1 hour ago, StringJunky said:
Ok. On lobbying: A chap with just nine shares in Tesla has just knocked Musk off his financial perch by having a judge anull his 50-odd billion pay packet. Appeals are on, of course, but I thought "That's interesting". It was ultimately financed by "no win, no fee" legal help.
You have to balance that with the cost to the tax payer at research level. How much of that research is taken on by pharmaceutical companies vs not used? This article relates to research access but it mentions the total spend:
Taxpayers spend $140 billion funding science each year — but can't access many of the results
I think with Big Pharma the problem is the Cinderella areas. They can make billions out of cancer but some of these 3rd world conditions barely get a look in because there's no money in it for them. We obviously need both approaches.
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31 minutes ago, StringJunky said:
One of the most common defences by Big Pharma for price gouging is that it will affect innovation. Not much of a leg to stand on, it seems to me. People on your level should be more vocal and tell them to stop misleading the public and naive politicians.
I think Big Pharma will be speaking of innovation in the sense of product development rather than ab initio research. Product development is extremely costly - and high risk.
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1 hour ago, Photon Guy said:
Yes and there's also Blue Origin by Jeff Bezos. Both Space X and Blue Origin mainly provides spacecraft to NASA though, which means its tax dollars that pay for their spacecraft. I've yet to hear about Space X or Blue Origin doing any space exploration of their own.
Greed might be a motivator but being greedy will work against you in the long run and a smart company will know that. Greed always ends up with you having less and we even have children's stories that teach that lesson. We also see that throughout history, just look at the automobile industry. Many people nowadays including myself prefer Japanese and German cars over American cars because they're made to last, unlike many American cars which are always breaking down and I speak from my own experience. In the late 90s I drove a Ford and it was complete junk. The problem is American car companies got greedy and just wanted to produce and sell as many cars as they could regardless of the quality. That's why I wouldn't a Ford today with a ten foot pole, and Im talking about a Ford made in this day and age not one made in the old days, 1970s and earlier, when Ford did make good vehicles.
And like it or not space exploration is going in the direction of being privately funded. We've got companies such as Space X and Blue Origin. In the future going into space might be as simple as getting on a plane, or getting on a bus, or even getting in a car. In a future where spacecraft are as common and as readily available as automobiles I couldn't imagine the space industry not being run by private companies.
If people want to stop archaeology or paleontology or any kind of study because of religious reasons than that's an even stronger case for such studies to be taken on by private companies because if such studies are paid for entirely by government funding then those who are against such stuff will vote against it. And if you're concerned about monetary motivations well let's face it, researching costs money and that money has got to come from somewhere. If such research is entirely government funded and you want more funding you've got one of two options, either cut back on other stuff or raise taxes, take your pick.
If you want to do the kind of research that the fictional John Hammond did, where are you going to get the funding?
What about Starlink, then? https://en.wikipedia.org/wiki/Starlink
But I’m now confused as to what you are arguing for. It’s clear that private enterprise can do a good job of research when there is an identifiable commercial goal. But it is equally clear that other, more fundamental, types of research are also needed for science to progress. Governments have always realised this, which is why state-funded research programmes continue to be supported.
None of this is new.
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14 minutes ago, Photon Guy said:
Well by the same token I think a good moon rock or mars rock would be a very valuable commercial property yet we don't see much if any commercial demand for the space program. NASA is entirely government funded and we don't have any private space companies that go into space. If we can create a demand for paleontology with fossils perhaps we can create a demand for the space industry. The problem with something being government funded is that if we are to increase funding the only ways we can do that is if we were to cut back on other stuff that's government funded or by raising taxes, neither of those are popular choices.
Have you not heard of Elon Musk’s Space X? https://www.spacex.com
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3 hours ago, Photon Guy said:
I don't see any folder on this forum for paleontology so I thought this would be the best place on this forum to post this. Dinosaurs are fascinating but Im wondering how paleontologists get the funding to do their research. I don't really see much of a demand for such research so most research would not be consumer funded I take it, and to the best of my knowledge the government does not fund such research so Im wondering where the funding comes from.
The government, at least in the UK, does fund a certain amount of research done by organisations such as universities and the Natural History Museum.
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2 hours ago, GrahamF said:
Let's say there was a way to make a duplicate of yourself. Assume it's a perfect copy that is identical to you in every way, except that the copy is legally your slave/servant. It's easy enough to go through the process knowing you would have someone who always does your bidding, but it might be easy to forget that your copy is also you, with the same experiences and memories. The other you had expected to get a servant, only to realize that you had become the servant.
A truly narcissistic personality would react very badly to this situation. To properly plan for the event you have to prepare yourself to not just be the master, but also the servant. Because both futures face you at the same time, requiring you to be able to anticipate both as they will happen simultaneously to you.
The Man Who Haunted Himself?
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1 hour ago, swansont said:
Yes, as I mentioned; Doppler broadening and collisional broadening are two of the prominent ones.
Energy is conserved, and if you have a polyatomic molecule or your gas has collisions, there's a ready reservoir for both energy and momentum conservation. I don't know if anyone has looked at a single neutral atom absorbing and emitting photons in an isolated situation, trying to see if e.g. a red-detuned photon was absorbed and resulted in a red-detuned emission, because how would you do that?
Yes. My understanding is that collisional broadening, or pressure broadening, is also due to the uncertainty principle as the collisions shorten the lifetime of the excited state.
But it's an interesting question @sethoflagos poses. The expectation values of energy e.g. of an ensemble, are conserved of course, but whether that is strictly so for an individual pair of absorption and re-emission events by the same atom I feel less confident.
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8 hours ago, sethoflagos said:
Of course. Blasted autocorrect.
Aha! So it's bounded by the uncertainty principle. That makes sense. Thank you!
I think there is also broadening due to the Doppler effects of random atomic motion, at least in gases.
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5 hours ago, John Cuthber said:
" how can be advertised at more intensity than the sales of automobiles with a $50k sticker each ?"
How often does the typical user buy
(1) Viagra(2) A car
?
The big cost of bringing a drug to market is all the testing.
Having sold many pills at $40 they have paid for that.
Now they only have to cover their costs, so the price has dropped
It's interesting to look at the variation of price between manufacturers.
https://bnf.nice.org.uk/drugs/sildenafil/medicinal-forms/
And now, it's just a commodity like bread.
It gets advertised so people buy a particular brand.I understand Pfizer's patents on Viagra in Europe also expired some time ago. So anyone can make it, without paying for a licence to do so.
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39 minutes ago, Phi for All said:
I think they're referring to the Alcubierre metric, which doesn't actually move space but rather creates a configurable energy density field that can "push" something massive, assuming you can create a negative energy density somehow.
Yeah....assuming you can create -ve energy density somehow........
Which is a bit like switching off gravity, if I'm not mistaken. 😀
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32 minutes ago, Photon Guy said:
Not by conventional means but there are theoretical ways of breaking the lightspeed barrier, such as if you were somehow able to move space itself and "ride" it, much like a surfer riding a wave.
But there is no theoretical way to move space itself. It's a bit like saying we could all fly if we could switch gravity off. Which is sort of true, except that we can't switch gravity off.
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3 hours ago, Falkor said:
Ok so apparently this is tied with solonoids apparently. What’s weird is I am getting very huge spikes in electricity. I tried this with some water in a glass and this weird wave kept flowing back and forth through the water it kept multiplying and I was just getting huge results with my oscilloscope that I fried the circuitry. I was also doing some math and this 2 to 3 number keeps appearing it also seems to be tied in with some fractal patterning going on. I must be really stupid because there is something happening here. If I am reading the literature correctly this phenomenon is basically some quantum effect that is tied in with general relativity and quantum mechanics. This dual nature is extremely bothersome. What’s worse is my water system I have designed is extremely efficient. I’m getting huge numbers I have never seen before just from adding these vibrations to the liquid. It can’t possibly be that what’s moving is not the object but space itself? That just can’t be, but this issue with paper having a poisson ratio of less than zero is making me believe that there is some knot action going on and that mass creates a fractal pattern that propagates through space time which leads to general relativity and can be quantized as qbits? I must be really stupid because I’m missing something here
Oh you sound very familiar now.
Bye.
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14 hours ago, Falkor said:
I hope you are all are doing well. I am engineer that is doing some home experiments on electrical signals through topological surfaces and was wondering if you guys know of any resources I could look at to get a better understanding. I personally find it useful to have a textbook that I can reference when working on new subjects. Thank you for your time
In electronics, what's the difference between a topological surface and a.......surface?
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Can real-space-eigenstates of conduction electrons in crystal cause formation of electronic singlet pairs?
in Quantum Theory
Posted
Well no, in general valence band electrons can't tunnel. The barriers are too high and too thick. You would need very special circumstances for tunnelling to be possible, I think.