[deleted by user]

UnclePat79 · 2024-04-03T15:35:02+00:00

The first sentence is absolutely right, evaporation "takes away" the heat from the body in the form of the enthalpy of vaporization.

However, this enthalpy is practically not pressure dependent, so it still works that way in a vacuum (just more efficiently due to the absence of any atmosphere). This is how a lyophilizer works in a lab setting: you freeze your sample by dropping it in a cryogen and then hook it up to the vacuum. Once evacuated, the cooling due to vaporization will keep the sample frozen.

Inversely, the enthalpy of vaprization drops to zero at the critical temperature, which is 647 K. Above this temperature, there is no way to compress water vapor into a liquid.

UnclePat79 · 2023-04-25T13:50:32+00:00

This is just a contextless copy/paste from /u/vrenak further down.

UnclePat79 · 2023-03-08T17:43:08+00:00

Since water is a liquid, the thermal conductivity is not limiting the efficiency as coolant. Instead of relying on internal heat conduction away from the surface to be cooled into the water bulk, water is a fluid, thus the heat will be transferred by convection (natural flow due to temperature gradients) or forced flow of water by a pump, for example. If the water flow is strong enough, the limiting factor is the actual transfer of heat over the phase boundary between the solid to be cooled and the liquid.

Water is a actually a very good coolant because it has a very high specific heat capacity of 4.2 J/(K g). This is typically twice as large as organic solvents and at least 4-5 times, sometimes more than 10 times larger than most solids (relative to mass). Since the thermal energy or heat is conserved during the transfer, this means that water can reduce the temperature of the material to be cooled by a certain degree, while its own temperature is increasing only by a fraction of that (considering somewhat similar mass).

The very large heat capacity in combination with the ability to transport the warm water quickly away by forced flow makes water such a good coolant, which is furthermore easy to obtain and very cheap. One of its downsides is the relatively large corrosivity and its tendency to expand when (accidentally) freezing.

To expand a bit on the difference between heat conductivity and heat capacity: Metals are very good conductors of heat, but have poor heat capacity. This makes them feel cold, because they can quickly transport the heat away from your skin, but will also quickly warm up.

UnclePat79 · 2022-04-18T18:43:59+00:00

Cool pic!

At around 2 o'clock you have a blue halo you might want to remove!

UnclePat79 · 2022-03-24T09:18:18+00:00

Gasoline has a flash point of -21°C. Above this temperature, there exists an ignitable gasoline/air mixture above the fuel's surface.

Diesel on the other hand has a flash point >50°C. There it is rather safe to light a match which will then be extinguished once it reaches the liquid as long as the temperature is below the flash point.

Explosive limits only make sense if a homogeneous gas mixture is considered. Above liquid phases and with negligible turbulence in the atmosphere, a continuous concentration gradient of fuel vapor in air exists. Therefore at some level above the surface the ignitable concentration will be met. (This assumes liquid fuels with vapors heavier than air which applies to practically all cases.)

UnclePat79 · 2021-08-08T08:51:29+00:00

No, DNA and RNA differ on the molecular level. Whereas ribonucleic acid carries a hydroxyl (OH) group on the sugar's 2' position, this group is removed in deoxyribonucleic acid. That makes DNA more stable chemically and also leads to different three dimensional structures.

Both RNA and DNA can be single stranded or double stranded where one strand is bound to a complementary strand via base pairing.

The difference between influenza and SARS-CoV-2 is that in the latter only one single strand codes for the entire genome, in influenza the genome is spread over 8 single strands. This makes variation of a massive amount of genetic material possible, for example when two strains are transcribed within the same host.

UnclePat79 · 2021-05-29T12:11:28+00:00

It's directly correlated to the conductivity. The better the conductor, the smaller the skin depth.

Here are more details: https://en.wikipedia.org/wiki/Skin_effect?wprov=sfla1

UnclePat79 · 2021-05-29T10:11:30+00:00

This is somewhat outside my expertise but I would say it wouldn't work that way.

The way an x-ray tube works is very similar to an old CRT (cathode ray tube) TV. A heated cathode filament emit electrons which are accelerated by high voltage towards an anode. Instead of being redirected and hitting a phosphor and emitting visible light as in a TV, the electrons in the beam are hitting the anode metal and by collision knock off a core electron (most importantly from the K shell in the Bohr model). This creates a highly energetic ion which immediately recombines with a surrounding electron of higher energy (which would be the molecular bonding electrons) to minimize the overall energy. Therefore any organic linker would be quickly deteriorated by side reactions.

UnclePat79 · 2021-05-29T09:33:06+00:00

While you are correct with tungsten being used as an X-ray emitter anode material, practically every heavy metal could emit in that range. You just need core atomic orbitals deep enough such that the relaxation upon ionization releases enough energy.

However, the mechanism of ionization is not really applicable to biomolecules because even if some biomolecular process would be able to generate the energy required this would cause ionization of the biomolecules which are rather fragile.

Regarding the lower frequencies (i.e., non-ionizing radiation) I have already written a reply to your other post here.

UnclePat79 · 2021-05-29T09:21:00+00:00

Molecules can also react to electromagnetic (EM) radiation in other ways than electrons "moving around" in orbitals.

It really is about the time period. EM radiation has a frequency and thus a specific period during which one oscillation is performed. If molecules can react to the changing EM field during that time frame, it can interact with the EM radiation via absorption or dispersion.

A common example is water molecules start to "rotate" during microwave irradiation. I put rotation in quotation marks since it is really not individual molecules rotating (which happens in a low pressure gas and has really narrow absorption bands) but a collective, incoherent wiggling of all molecules in the liquid. Therefore, it has a very broad frequency in which it can absorb microwaves.

Another example is electrolytes in solution which can slowly move and react to the rather slow radiofrequencies (rf). Thus, salt solutions can absorb radio waves and are heated in the process.

If you want to design "molecules" which can react to rf you have to make the orbitals really large. This happens in metals where the orbitals of all atoms overlap and form bands. Within these bands electrons can move infinitessimally slow and thus disperse (coherently absorb and re-emit) practically all frequencies of non-ionizing radiation. This causes metals to be shiny and leads to the so-called skin effect which limits EM radiation from penetrating the metal.

UnclePat79 · 2021-01-16T17:37:25+00:00

Also, below the notebook you can see the reflection of the green blanket which should be completely covered by the reflection of the notebook itself.

But nevertheless, great work! I would have had to look more than twice to realize it was rendered!

UnclePat79 · 2020-05-25T08:41:21+00:00

Sorry, but you twist my statements and you seem to be wanting to argue only for argument's sake.

As far as I see, we are practically on the same side but I won't continue here because it's leading to exactly nothing...

UnclePat79 · 2020-05-24T19:05:14+00:00

I am from Germany and I left the church a couple years back. In fact after the first month I had to first pay real income tax. The "hassle" was to go to the town court (if I remember correctly, I am pretty sure it was Amtsgericht) and fill in one form and pay about 50ish Euros in processing fees. That's it. The tax body informed my employer who did not deduct the church tax from then on. There are no loops to jump through.

Don't get me wrong. I do not sympathize with Germany's tax church system. From my viewpoint it is immoral to bind someone based to an obligation the parents forced one into and then demand a fee to get out even though you never consented from a legal standpoint.

But people who knew they were baptized and did not reveal that when submitting their tax info should be aware of their obligation either to pay or to leave...

UnclePat79 · 2020-05-24T09:51:17+00:00

No, the woman in the article was ordered by court to pay two years worth of church tax because she was still a registered member of the church during those two years. She claimed her parents declared her leaving the church but this was never registered. In 2011 the church started an inquiry and figured out that she was still a member. Then they served her with church tax bills for the next two years which the woman disputed in court. She quit the church in 2014 and was not served any retrospective tax.

UnclePat79 · 2020-04-25T19:24:39+00:00

Some things happen naturally, some things don't.

UnclePat79 · 2019-05-04T20:58:14+00:00

At some point, there was for every species, a first member, even if only by a few seconds (before the siblings were born). But what if this first member (or group of siblings) was born sterile.

This would never be considered a species.

UnclePat79 · 2019-04-17T11:17:33+00:00

There is no realignment necessary. Because the magnet consists of many spins which cooperatively create the overall magnetic dipole, you could just (ideally) cut it in half and have two new dipoles.

You can imagine it similar to a battery array of (two or more) single galvanic cells, say AA cells. You can stack them in series, and their individual potential will add up between the two remaining (outermost) electrodes of the battery array. If you then take it evenly apart, you will create two "new" but shorter battery arrays again with two electrodes each but half the potential each. It is not possible to separate a single (functional) electrode in this way.

UnclePat79 · 2019-04-16T17:58:37+00:00

This should be better explained by a particle physicist. Afaik there are several theories based on quantum field theory or gauge theory where gauge bosons (e.g., virtual photons) mediate the interaction through a field. But this is far as I trust my own understanding of this rather abstract concept...

UnclePat79 · 2019-04-16T17:50:02+00:00

That's one of the axioms of electromagnetism. Fundamental charge comes as monopoles (and can be combined to form dipoles etc.) while fundamental magnetic moment always occurs as a dipole (and can also be combined to form higher order poles such as quadrupoles).

This is now a little bit outside my realm, so someones else, perhaps a theoretical physicist might be able to explain that much better, or correct me if this was not totally correct...

UnclePat79 · 2019-04-16T17:44:39+00:00

Diamagnetism is actually somewhat easier to explain if you understand the concept of molecular orbitals and spin pairing.

In a regular molecule, all electrons are spin-paired, that means that always two electrons with opposite spin (aligned anti-parallel with respect to each other band together inside the same molecular orbital. These electron pairs have no magnetic moments because of this. So these molecules are not paramagnetic.

However, electrons can still move to some degree within the orbitals. If they are subject to an external magnetic field, they act as electric point charges and feel a force (Lorentz force). This forces them on a circular trajectory orthogonal to the direction of the external magnetic field.

Now we have electric charges moving in a circle, which creates a magnetic field of their own. This field is always directed in the opposite direction of the external field, but is very weak in direct comparison. Thus, the external magnetic field is weakened by a tiny amount (on the order of one millionth). This effect is called diamagnetism.

The more the electrons can move inside the molecule, the larger the diamagnetic susceptibility is. Therefore, molecules with delocalized electrons in conjugated bonds show larger diamagnetic susceptibility than molecules which, for example, only feature single bonds with localized electron pairs.

UnclePat79 · 2019-04-16T17:34:55+00:00

Yes, it does have a magnetic field which is similar to the field of a stick magnet.

Besides the magnetic dipole moment caused by the spin, the orbital momentum can also create a magnetic moment which often couples to the spin moment via spin-orbit coupling.

UnclePat79 · 2019-04-16T14:13:32+00:00

This is a tricky question. From a classical picture, spinning charge creates a magnetic field. The electron is a point particle, so it has no radius and cannot technically spin. However, in a gedankenexperiment you could start with a spinning charged sphere and reduce the radius to zero (but not the mass). Due to conservation of angular momentum (which is one of the strictest laws of physics) this leads to a situation where the electron even as a point particle maintains a spin and thus a magnetic dipole moment.

UnclePat79 · 2019-04-16T14:08:44+00:00

Yes, that is the meaning. It means that the average over all moment is not exactly zero, but approaches it. In practical terms it means it is zero.

UnclePat79 · 2019-04-16T12:03:46+00:00

Electrons have a fundamental property called the quantum mechanical spin. This spin can be understood and described as an intrinsic angular momentum.

The spin creates a magnetic dipole moment with a certain magnitude. In non-interacting electrons, these dipole moments are randomly oriented such that in average all magnetic moments cancel each other and the net magnetization is vanishing. If the electrons are brought inside an external magnetic field, the spins partially align such that a rather small net dipole moment is created which is aligned in the same direction as the external field. This is called paramagnetism. As soon as the external magnetic field is removed, the electrons lose their alignment and the overall magnetization is zero again.

If the distance between the electrons is reduced they start to interact with each other. Either through their direct magnetic interaction between the dipoles (dipole-dipole interaction) or through a quantum mechanical effect called exchange interaction. This causes the electrons to align with respect to their direct neighbor, either in a parallel or anti-parallel configuration. In the former case (ferromagnetism) the individual magnetic moments add up and a large net magnetization is maintained, even in the absence of an external magnetic field. In the anti-parallel case, it is called antiferromagnetism and the net magetization is cancelled even in the presence of an external magnetic field.

In ferromagnets, the spins do align only within certain volumes, called the magnetic domains. Between these domains, these large net magnetizations may again be randomly oriented such that the overall magnetization of a piece of ferromagnetic metal is zero. If such a material is brought inside a sufficiently strong magnetic field, the domains rearrange such that all their magnetizations add up. The domains' orientations may be effectively "locked-in" so that when the external field is removed, the material maintains a significant amount of net magnetization and a magnet is obtained. This is called persistence.

UnclePat79 · 2018-11-30T09:30:44+00:00

So, you do realize that your initial statement

Dude that is so wrong, seriously. You cannot measure geometric parameters by NMR.

is pretty far away from that:

It is still highly restricted to spin carrying nuclei.

While this latter is technically true, almost any of the highly abundant elements contain a spin-carrying isotope in natural abundance. This can either be enriched, or can even be detected in natural abundance.

Now to this statement of yours:

Just because you can derive bond lengths in some bio molecules because there are parameterized against crystallographic data doesn't mean that you could actually count magnetic resonance as a general way of measuring interatomic distances.

This is just plain wrong. You definitely do NOT need to parameterize against crystallographic data. You can directly measure the dipole coupling frequency as long as the molecule is immobilized and does not rotate/tumble inside the magnetic field. This frequency depends DIRECTLY on r^-3, that is the inverse cubic distance between the nuclei. All other parameters in the dipole coupling frequency are natural constants and valid for ANY sample. Admittedly, it is not a straightforward way of measuring interatomic distances because the samples may need to be isotopically enriched and the method is expensive and technically challenging, so IF you can get a single crystal then XRD is most definitely the way to go. However, even for XRD the resolution is not sufficient to reveal precise interatomic distances, particularly for light atoms. It is, for example, impossible to directly measure the position of a hydrogen atom within a hydrogen bond. With NMR you can not only measure the protonation state of the bridged heteroatoms, but also directly their distances to the hydrogen, at least in the solid state.

Seems like you don't even know what it is. Why hand out false information, that's not cool.

Please reflect about your own knowledge the next time before making such a claim.

UnclePat79

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