exchemist

According to my recollection from the lubricants industry this phenomenon applies to sliding surfaces, rather than just a static contact. It leads to what is known as adhesive wear (as opposed to abrasive or corrosive wear). With sliding surfaces, microscopic asperities come into contact, causing very high pressures and temperatures at the contact zone which leads to microscopic welding of the surfaces at these points. As the sliding continues, these microscopically welded areas are torn asunder. Often this does not occur at the point where the weld formed, so that material is torn out of one or both surfaces. It is often the practice to use dissimilar metals in bearings, chosen so that the welds are weaker than the parent metals. This encourages the adhesions to break without tearing lumps out and thus preserving the surface. (One example is in worm gears, where the worm is usually steel and the gear wheel is bronze. Worm gears have an extremely high rate of sliding relative to rotation, so the issue can be quite acute in such gears.) The purpose of lubricants of course is to keep the surfaces apart and prevent this from happening. It is common practice to add anti-wear or extreme pressure agents - often sulphur/phosphorus containing organic molecules - to lubricants where the nature of the motion does not ensure a constant pressurised film of lubricant to do this, another classic example being the cam followers in an engine. The anti-wear agents decompose under local temperature, adsorb on the surface and form a protective but weak layer, that easily breaks without damaging the parent surface. However one does also get "cold welding" of clean flat metal surfaces brought into static contact. This occurs especially with surfaces exposed under vacuum, so that no oxide layer has a chance to form: https://en.wikipedia.org/wiki/Cold_welding.

Not if all our grandparents had it, surely?

All the features you list are common to a vast range of creatures, so would not be part of this 1-4% you are enquiring about. So we share DNA all of these, even though we are not directly descended from any of them. It is often said we share 50% of our DNA with a banana, even. But my understanding is the 1-4% relates to DNA features found in homo sapiens neanderthalensis but NOT found in homo sapiens sapiens of African origin. As for where it comes from, one needs to keep in mind that H sapiens sapiens and H sapiens neanderthalensis appear to have interbred. So they are not fully separate species. Therefore, if, like me, you are of N European ancestry, it is likely you have some ancestors who were Neanderthals, rather in the way that I have one Welsh great-grandmother.

Thanks, that's helpful. What occurs to me about the graph is that they have chosen a scale and a range that makes the effect look as small as possible. We are in reality concerned with the range from 280ppm (the level at the end of the c.19th) to ~400ppm +/- 50 for scenarios in the recent past, today and the near future. So be useful, the graph should be scaled to show the effects within that range. On that basis it would be clearer that, even assuming the chart is correct, which I can't verify, the effect of an increase from 400-450ppm would be about 50% of the increase from 350-400ppm. So less rapid, sure, but still very substantial, and nowhere close to reaching some sort of asymptote of course.

On another forum a climate change denier posted this graph: At first glance it looks like no more than the expected exponential reduction in intensity with concentration of the absorber predicted by the Beer-Lambert law. Has anyone come across this being used as a counterargument to climate change science, is the implication true that further increases should have a proportionately lesser effect and what relevance does that have to the models used to predict climate change?

Re your first, apparently yes. Re your second, no, but that has nothing to do with anything physical.

As this is the person who once tried to convince members of another forum that you can be strangled by your own thymus gland in cold weather, nothing is off the table. 😄

I thought it was copper chromite that was commonly used as a decarboxylation catalyst.

I note the introduction of a new topic, in an irrelevant manner. This is a tediously familiar pattern.

I don't think you need to be that extreme. I have washed items with strong colours at 40C for years, with absolutely no trouble. But I would certainly not try 60C, at least not in a mixed wash. That's for whites and cream-coloured things (I have some sheets and towels that colour) only - plus those notorious maroon towels, which I have to do on their own, or with red items - I have some red polo shirts. (Towels really do need 60C or they can get smelly after a bit.)

No, you know me better than that.😆

And here comes the next item, in the drip-feed of crap to keep the roundabout of pointless dialogue spinning: dinosaurs.

As does the deliberately erratic spelling, color and colour in the same sentence, phisics (really?) etc. Timewaster.

Do you mean this? 1mm every 5secs would be 1.2cm/minute, so it would take 25mins for your feet to advance 1ft along the bath, by which time I’d have thought the water would be getting cold. But I suspect the phenomenon may involve some unnoticed feedback between the apparent weight of your legs and your muscles, i.e. not a pure physics problem. You may subconsciously relax progressively as your feet move and more of the weight is supported by the water. But it’s a speculation. It could also be some kind of slick-slip due to the movement of the skin, I suppose.

Haha, like “Motor Daddy and the Motor Boat” on sciforums, perhaps. That too became a standing joke.

Was that one of Theorist’s?

Aha, thanks very much. So would it be fair to say QFT is the mathematical underpinning of QED? I suppose it also plays the same role in QCD, doesn't it?

Yes you need not just QM but QFT, or QED (as a mere chemist, I remain a bit hazy about the distinction).

Zero point energy, at least, is fairly easy to grasp. All you need is the idea that in QM there is a ground state, in other worlds a lowest energy state that a given system can occupy, and that, in this state (depending on what kind it is), it may be that some residual energy remains present. The electron in the ground state of the hydrogen atom, for instance, still has some potential and kinetic energy. That is zero point energy, i.e. energy that remains in the atom. The same is true for the vibrational ground state of a molecule in which 2 or more atoms are joined by chemical bonds, which vibrate thermally. They still move a bit, even at absolute zero, because there is residual energy in the vibrational ground state. (In molecular rotation, on the other hand, the ground state has no residual kinetic energy, so there is no zero point energy of rotation, i.e. molecules do stop spinning at absolute zero.) What people find harder is the concept of a zero point energy of the vacuum. That will require more reading.

Nowadays that is a rather out of date view. A lot of misconceptions have arisen, historically, due to the choice of words made when originally formulating QM. They spoke - and we still speak - of "observable" properties and "observers", "observation" collapsing the wave function and so forth. Some people thought that "observation" implied a conscious entity to do the observing. But a moment's reflection shows you that can't make sense. Does anyone seriously contend that the reading on the dial changes when the observing experimenter goes off to get a cup of coffee? And what if the experiment is "observed" by the laboratory cat? Or a passing wasp? It's bonkers. The modern view is that it is interaction with another quantum system that collapses the wave function. So that can be part of a measuring device, whether or not anyone is looking at the measurement. Those people nowadays that maintain a role for consciousness in QM tend to be quantum woo charlatans like Deepak Chopra.

Yes it seems the fat of grass-fed animals contains some ALA.

Buoyant in what medium? Or do you just mean lighter than air at sea level pressure?

Who is wrong?

On the contrary.😉

I haven't played these synthetic games since university, nearly 50 years ago now, but it seems to me a start can perhaps be made by recognising the class of of molecule you have on the left. It's a particular kind of aldehyde, which undergoes particular reactions. Have you identified what it is?