I am not sure if this is how it is a correct representation. I believe a common approach is to do a short history of quantum in the first year, and then do a from the ground up approach in the second and third year. Depending on who teaches it, this is either starting from a particle in a box or the approach stated here. The historical story is useful, because it tells a little bit of the why.
I don't think the actual proposed superconductivity mechanism is the relevant part of this paper. It is much easier to prove that this is superconducting than to prove why. And in a sense it is a bit less relevant. Although developing a working theory for room temperature is also probably worth a Nobel prize, so I am willing to bet some theorists are also running to their blackboards as we speak.
> I don't think the actual proposed superconductivity mechanism is the relevant part of this paper.
Plus even if the proposed-mechanism is incorrect and even if the effect is not strong enough for practical engineering... There's value in a "real" (if weak) superconductor which is both easy to fabricate and easy to run tests on.
It could become a starting-point for dozens of other tweaked formulations, enabling all sorts of not-so-expensive experiments and fresh data about how different parameters lead to different electromagnetic outcomes.
Yeah. BCS was proposed a half century after the first conventional superconductor was discovered, and even today we don't have a convincing mechanism for "regular" high-Tc superconductors. But if it superconducts, it superconducts, and research into the how is useful but not a blocker to using it.
That depends. If it super conducts, but it isn't useful in the real world, then we will be waiting for theory to - hopefully - give us some insight into how to improve things to useful.
This only can carry a small amount of current. I'm not sure how to figure out what small means (numbers are given in the article if you know how to use them!), but if the losses using regular wire are less than the energy needed to make this stuff then it isn't useful.
This is made out of lead. Even if it is useful for transmission, the difficulty of working safely with lead in a factory may mean it is impractical. Or it make leach lead into the real world making it not safe to deploy.
There are probably other ways this can turn into a "it works but isn't practical" thing that would force us to wait for theory (or luck!) to point to something better. What I wrote above is what I can think of in a couple minutes. Only time will tell though, I hope it works out.
> If it super conducts, but it isn't useful in the real world, then we will be waiting for theory to - hopefully - give us some insight into how to improve things to useful. This only can carry a small amount of current.
Thank you for this.
> This is made out of lead. Even if it is useful for transmission, the difficulty of working safely with lead in a factory may mean it is impractical.
Have you been to a hardware store lately? A huge amount of pipe fittings for gas and non-potable water are made from lead. Factories don’t find it hard to work with lead. It might be inadvisable but it’s not hard.
We can argue about the "working safely" part, but in terms of "does this make it impractical?" the answer seems to be no under the current global regulatory environment.
Nah. We have a reasonable understanding of fluids. It's just that the two things we say as simple explanations (the plane pushes air downwards causing an equal and opposite reaction to push the plane up; faster flow on top of the wing "sucks the plane upwards") are both only partial truths.
Sometimes you get arguments between partisans for each of these two simplified explanations, but really both are bogus.
I’ve never understood how this battle could possibly persist, considering that planes can fly upside-down. The fact that Bernoulli’s Principle creates a low-pressure zone on the top of the aerofoil just gives you laminar flow at higher angles of attack.
It really isn’t that mysterious, unless you insist that only a single physical law is allowed to come into play.
> You can build a pretty good mental model of flight with either simplified mechanism, but you end up underestimating performance by a fair bit.
I've never hear of a good mental model built on Bernoulli's Principle. They are either:
- Wrong
- Give no intuition
The key question is /why/ air moves faster on one side, and once you get away from the misconception of same time, I've never heard an intuitive argument.
Redirecting air down:
- makes complete sense
- can be demonstrated by sticking your hand out the window of a car
- works with flat airfoils (sails, kites, etc.), and explains those well too
And the shape of the wing comes in from wanting the leading edge parallel to incoming airflow, and the other edge parallel to outgoing airflow. On a sail, I can adjust the shape. On a steel wing, I can't much, so I make a shape which works across different angles of attack.
All of the other mechanisms, you can gradually work in from there to get accurate models. Toss in air moving to the low-pressure area, and having momentum, and you get why helicopters are less efficient than planes, as well as vortex shedding. It all builds up.
As a corollary, Bernoulli tells you where air moves faster, but that follows from lift. Not the other way around. At least in any model which fits the human brain.
Why are you benchmarking models to human intuition? If you apply the same reasoning to quantum mechanics you'll have a bad time.
I'm sure models can accurately compute how much of the wing lift comes from the suction effect on the top of the wing versus the push on the bottom of the wing.
> The key question is /why/ air moves faster on one side, and once you get away from the misconception of same time, I've never heard an intuitive argument.
Since the air follows a curved surface instead of straight ahead, you could perhaps apply your intuition for centrifugal force. Momentum sort of pulls the air away from the surface.
Counterpoint: A wing with the opposite curvature would work too, just much less efficiently. Your explanation has an element of truth, but an element of untruth. It'd take more analysis to tease them apart.
In the Vsauce video "Do Chairs Exist?" (I highly recommend it!), Michael talks about the concept of vagueness and how defining boundaries can lead to paradoxes. While it was primarily dealing with an ontological perspective, the linguistic perspective of a particular line has always stood out to me. Perhaps it makes a bit more sense in context of the full 40-minute video, but it is:
>"Composites are causally redundant. Believing in chairs is like believing that, while yes, the burning gas from my stove completely describes why the water in a pot boils, there’s ALSO a magical invisible substance called boil-o that comes out of my stove that does the same thing as the flame at the same time, and if there was no boil-o, the flame would warm the water just the same, but there IS boil-o... Chairs are no more real than boil-o. Composites over-determine what happens in the world."
Like your example with lift and fluid dynamics, simple explanations like "plane pushes air downwards" or "faster flow sucks the plane upwards" might be insufficient, but they're at least useful to the layman. It also reminds me of how Richard Feynman answered the question, "What is the feeling between 2 attracted magnets?" by explaining that it would be impossible to give a complete answer. Feynman pointed out that when you ask why two magnets attract each other, there are different levels of understanding depending on your background knowledge. For someone with no knowledge of physics, the simple explanation would be the existence of a magnetic force causing the attraction. However, delving deeper into the question raises complexities that can be challenging to explain.
Feynman highlighted the difficulty of answering "why" questions in general. Explaining magnetic attraction in terms of something else that we are more familiar with, like rubber bands, would be misleading and circular, as it ultimately comes down to electrical and magnetic forces. He acknowledged that some aspects of the natural world may need to be accepted as fundamental elements without a more profound explanation.
This is echoed in the Vsauce video, where defining boundaries and attempting to explain everything can lead to paradoxes and vagueness. The concept of "boil-o" illustrates how composites, like chairs, can over-determine what happens in the world and our own perception, making their actual explanation even more elusive.
We 100% know why airplanes of every shape and size stay aloft, and can calculate lift/drag extremely accurately based on the geometry of the plane and the airflow, in both steady state and much worse conditions. We have great approximations for steady state that make perfect sense and simplify the situation greatly and make it more understandable without simulation, even if they gloss over some details.
Where are you getting this terrible information that we don't know how flight works? Have you ever talked to literally anyone who has worked in aeronautical engineering, or even studied the basics of fluid dynamics?
> This is made out of lead. Even if it is useful for transmission, the difficulty of working safely with lead in a factory may mean it is impractical. Or it make leach lead into the real world making it not safe to deploy.
Lead is still routinely used in many applications today, either in metallic form, from ICE car batteries, to fishing or hunting gear, or as chemical compound in different kinds of glass. And the same can be said about other heavy metals like Cadmium or Mercury. Industries also routinely work with much more nasty things than lead, so it really doesn't sound like a show-stopper.
In particular, lead is still extremely common in radiation shielding, possibly because the drop in demand for other applications made it so cheap. Lead-lined drywall is the default approach for setting up a radiography, fluoroscopy or CT suite.
As a young fella, I carried a lot of that lead-lined drywall, it's (obviously) really heavy, and expensive so you got yelled at a lot if you damaged the edges, couldn't just trim it off like normal drywall.
> possibly because the drop in demand for other applications made it so cheap
Maybe a little bit. But I think it is more that it is a material with heavy atomic nuclei and high density, and thus effective at blocking radiation. And it is also relatively cheap.
I believe that most of the lead used today is a by-product or co-product of mining other more valuable metals like Zinc and silver. Lead is quite abundant in the Earth's crust and found in easy to access deposits.
I think >80% of the current industrial use of lead is for batteries. It's probably still in the top ten most mined metals by dollar value and definitely by mass.
The mineral containing Zinc is called Sphalerite, which is based on a greek etymology for "deciever" because it commonly occurs with Galena (which has Lead and Silver) and looks similar.
75% of aluminium supply is from recycling aluminium products.
The economy sort of has a "working capital" quantum of aluminium which also grows steadily from aluminium mining.
Lots of metals have very different and complex supply structures and thus completely different $$$ / volume curves for their supply.
Understanding the $$$ / volume curve of commodities is not something that is commonly considered when people try and predict the future. Mining a billion tonnes of Aluminium from an asteroid for example and safely landing it on Earth can never be profitable because the $$$ / volume curve for Aluminium is $0.00 at billion tonne volume.
Engine blocks too. If you go to a scrap yard though you’ll be pretty amazed at all of the stuff they’ve got collected and sorted. Metal recycling (compared to, say, electronics recycling or plastic recycling) has a very clear economic model and financial incentives. If you’re demolishing a building or scrapping old machinery it will cost significantly less to recycle the metal (because you get paid decently by the pound) than to take it to a landfill (where you pay by the pound instead).
TIL! Aluminium is an extremely useful metal, but I would never have thought it would be used for jewelry - I mean, it's not enough for the metal to be expensive, it also has to look and feel desirable, which soft and dull Aluminium definitely doesn't. If you have ever held Aluminium cutlery in your hand, it just feels cheap compared to stainless steel (not to mention silver).
Today it isn't used for jewelry. 200 years ago it was - not so much to wear, but to show off that you were rich enough to afford it. Only royalty could afford things made out of aluminum.
Unfortunately, most companies seem to have little compunction about exposing workers, consumers, or the environment to toxic materials. The use of lead is not in any way a blocker, for better or worse.
The strongest type of claim is when an a priori claim is called absurd, someone goes to make observations to disprove it and comes back convinced of your theory.
You might also say it's the only type of claim science recognizes. Though, whatever or how strong a claim is, the question is how important is what is proven and will it lead to real superconductive materials.
Do we know whether the mechanism was proposed before or after observing the results? If they found the material because of the theory, then I think it's very relevant.
Somewhat similar compounds are superconductors, so it's possible that a wrong theory gave them a lucky hint to modify an old superconductor into the new superconductor.
Lee and Kim first discovered the material in 1999 and have spent 20 years doing other things in between getting help to figure out how to isolate LK-99 and reproduce the correct grain structure.
They eventually got a world class physical chemist, Kwon.
There is now a huge bust up within the team, hence the muddled race to publish and claim credit.
Ahh that makes sense. I was wondering what was going on with the two papers and thought it might be something like that too. Thanks for the extra details.
I’m not entirely sure that’s true. A posit in the paper is this is a novel super conducting mechanism and as such if the mechanism is true it’s totally unexplored. That leaves open a huge field of new research. That’s certainly a relevant part of the paper. Super conductivity at room temperature is an amazing breakthrough alone, but if it was with a clever tweak with an existing well established technique that would be the end of the story. The fact it’s an entirely new technique opens a world unexplored and indicates a pathway to even more amazing discoveries to be had (and funding for entire generations of physicists).
Ding ding ding! We still don't know how bikes work, we have a pretty good but incomplete model for lift on airplanes, and no one has the faintest why Tylenol works.
We should figure that out! But we can definitely keep using all the applications until then. (Except for Tylenol, we keep learning how bad that stuff is)
EDIT: It won't let me post more, so here's the answers to responses.
There's no a priori reason conservation of momentum would apply; for that matter in 0-angle-of-attack aviation it doesn't.
Maybe to put it differently, the "Newtonian" model of flight comes out of assuming CoM applies, which we know isn't universally true.
EDITING: of course it always "applies" in the sense that there is a definable system in which total momentum will be unchanged, the point being that there is no guarantee that's a system in which the plane gets lift greater than its weight
A symmetrical airfoil at zero angle of attack doesn't generate lift because it doesn't turn the fluid. A non symmetrical airfoil will generate lift even at zero AOA because air has viscosity and the lack of symmetry causes it to turn around the shape. When you bend fluid flow, COM comes into play.
I'm assuming they mean the balance mechanism, and specifically what allows us to balance. How much is it the rider shifting their weight, how much is micro steering adjusts as we move forward, how much is the gyroscopic forces of the wheels, how much of it has to do with the angle of the handle bars to the wheel verse the center of weight.
That said, I'm guessing this one is well understood by experts, but more complex than someone would assume at first glance, and many who have some understanding likely have an incorrect or at least incomplete understanding of how balancing works.
You are correct, a lot of forces are canceling out on the long term(instead of instantaneously) it can easily be manipulated into increasing periods of unbalance in one direction until a point is reached then a separate mechanism is used to force it to a balanced state. Conservation of energy is always in effect. Gyroscope effects that bike wheels can be added with other separate gyroscopes. Thus, a self righting bike. The effect called precession is understood well enough.
How a human is able to manipulate it is simply by using the force of gravity from shifting their weight(moving the center of gravity). However, the movement of the center of gravity has to be perpendicular to the wheels axle. The steeper the angle of attack the wheel has to the ground, there will need to be an exponential increase in distance to move the center of gravity. Once the wheel is parallel to the ground, there will be an undefined distance needed to move the center of gravity.
The smart phone is the culmination of understanding a million facts about materials sciences (applied and theoretical), some of which were obvious, some of which were non-obvious. Starting from a transistor you could see from across the room down to ones you can't even see with a magnifying glass.
It's the reason I got a degree in physics, if you have good professors - discussions like this cause you to break down the problem quite quickly in your head in a working model. Think force diagrams, but with a ton more math backing it up.
I actually find the ice skate a better example than a bike. We have all the physics solved for bikes, it's a complicated system but so is everything in motion. Hence we assume a spherical cow for the sake of the problem.
But ice skates... Now that's a funky one. Why do ice skates works? Ice skates aren't sharp bladed, they actually have flats. Ice is not slippery, it's when something is on ice in between our shoes and the ice that cause it to be slippery. Some people think it's the localized pressure of the blade that causes ice to locally melt. Hard to really wrap your head around. But it works :)
>We have all the physics solved for bikes, it's a complicated system but so is everything in motion. Hence we assume a spherical cow for the sake of the problem.
This depends upon the question one is trying to answer. If one is trying to create a bicycle that can self balance, that involves considering different factors compared to trying to determine why certain injuries result in a person losing the ability to balance on a bicycle while others do not. Is the focus the bicycle or the human?
e.g. What keeps bicycles balanced with or without a rider is still an active area of research, and even the seemingly basic idea that, for a bicycle to be self-stable, it needs to turn the handlebars into the fall, has not yet been proven.
You can write out the equations of motion for a bicycle that will very accurately predict the dynamics. You can put these equations into a numerical simulation and predict motion very accurately. You can change the parameters of the model and do simulations with high confidence. Just because there isn't some neat little equation that says exactly what each parameter change is going to do (without doing the simulation) doesn't mean that we don't understand bicycle physics. It's a silly line of reasoning. Those articles are hyperbolic.
There are things we can characterize to any desired degree of accuracy but that e don't get cute little equations out of... and some of those things are so simple they've been staring you in the face since middle school and you just didn't ever notice their absence from your formula sheets.
This is not the exact same situation being described but it's a similar thing. Being able to put a complex system into a computer and arbitrarily manipulate it still doesn't mean we can extract some simple explanation.
On the other end of the scale, see all the AIs coming out. They're 100% computer artifacts with theoretically no mystery in them whatsoever... but they're just tables of billions of opaque numbers and doing anything with the numbers beyond just running them is amazingly difficult.
As a bit of an aside, most people don't know how bicycle wheels work. There's a whole section in https://en.wikipedia.org/wiki/The_Bicycle_Wheel that talks about how they actually work. It's not tension at the top, it's compression on the bottom.
what do you mean it's not tension at the top? did you misspeak? bicycle spokes are solely under tensile forces. they can't support compressive forces at all. i'm a hobbyist wheel builder and a once upon a time professional bicycle mechanic during hs & college.
if you want to test this take nearly all the pretension out of your spokes and sit on your bike. feel which ones are taught and which ones are completely loose. or just go to walmart. those bikes hardly have any pretension in their wheels.
This dialogue is reminiscent of rec.bycycles.tech arguments with Jobst, ca 1993.
A bike wheel is a linear elastic system, that can be thought of as a superposition of a uniformly set of tensioned spokes as one state, and a set of spokes in compression in the loaded zone (bottom of the wheel) as the other state. So long as the superposition of the two states obeys the limiting conditions (i.e. spokes in tension) they can be analysed separately.
The size of the loaded zone is related to the relative stiffness of the spokes (axial) and the rim (bending), and can be calculated using beam on elastic foundation methods. For typical rim/spoke combinations, this is approximately 4 spokes.
Outside of the loaded zone, spoke tensions essentially don’t change.
Pretty sure he did, but I don't have r.b.t. archives. He was definitely a proponent of them, preferred a specific brand/style, and would have easily been able to do the experiment.
Well. I wish we could sit in front of a bicycle wheel and discuss it. Because I have a feeling we are shooting arrows at different targets. As a mountain biker I'm more interested in what happens when an extreme amount of load is applied to the wheel, not the model with assumptions applied. Definitely a difficult concept to discuss with only text. Anyways.. glad to have a good discussion with you about bicycle wheels. Don't find many people like you. :)
I think I would have been a mechanical engineer if I were born 20 years earlier or 20 years later. Software was just new and shiny enough and it let me build things with my mind, at a time when I believed I was clumsy (I actually have always had excellent fine motor skills, it's macro motor control I lagged behind in). One of my better friends in college was an ME. Learned all sorts of things about metal fatigue and oddly enough picosecond lasers from him.
I don't know if I found Lego or Lego found me, but I definitely think in terms of shapes. I was past my midlife crisis before I realized that I don't have a large working memory (smaller than average in fact) it's just that I've been doing mind palaces without pictures since I was very small. When I'm thinking of large computer systems I'm essentially thinking of them as physics problems.
I really should figure out space to have a bike again. I never rode when I lived in Seattle (Seattle drivers are nuts) but I don't live there anymore and I need to catch up on 20 years of tech.
I think you're both in violent agreement using different terms.
You're looking at the macro "It's all in tension" (superposition of two states) and hinkley is looking at the "bottom is a compressive change" (dynamic portion of the load).
What I'm not clear of is if you think that the upper spokes change tension between the unloaded case and the plain gravity load case (force on hub down, ground on rim up at the bottom), or if you expect the top half spokes to increase and the bottom half to decrease in tension. I think this is what hinkley thinks you think.
That was indeed my interpretation of that half of the conversation. That they were claiming that the axle is suspended (tension increases with downforce) by the spokes above the midline of the circle, which is what Brandt vehemently contended was false.
That book I linked has another name, “the wheel building bible”. Jobst Brandt earned an obituary in Bicycling magazine including quotes from his friend Tom Ritchey (one of the original mountain bike makers). Jobst was a bike fanatic and a mechanical engineer.
Bike spokes are not loose, they’re under substantial tension. Bolts, I just learned a couple weeks ago, work in the opposite way. A tightened bolt compresses the two pieces of metal together, and when you tug on them, the bolt doesn’t stretch more. The tension instead first cancels out some of the compressive force on the two pieces of metal, before the bolt ever feels more load.
Conversely, all the spokes on the wheel are under tension. When you put the wheel on a surface and push down, the compression cancels out some of the tension on the bottom of the wheel. Cancel out all of the tension, and the wheel turns into a potato chip if you don’t reload it exactly, perfectly on axis. IIRC, none of the prior models or theories for how a spoked wheel works could adequately explain how potato chipping happens. His does.
I used his book to build half a dozen wheels or so and the information it contained to fix many more.
i own the book.. and also The Art of Wheelbuilding - Gerd Schraner
of course in a properly built wheel usually all the spoke are under tension...
i was just demonstrating the fact that the spokes on the upper half of the wheel are supporting the hub and are under greater tension than the bottom ones, the spokes on the bottom half of the wheel should remain in tension, but only through the fact that they are already under tension applied during the building of the wheel.
the fact that the wheel works by tension of the spokes becomes obviously apparent when you start to remove the pretension and then the spokes will feel loose on the bottom half. of course you'd never want to ride a wheel like that because it will quickly become out of true.. just like a walmart wheel.
I think one of us needs to reread that book, because he emphatically denies that tension at the top of the wheel increases. It’s tension at the bottom that decreases.
> of course in a properly built wheel usually all the spoke are under tension...
No, a properly built wheel all of the spokes are always under enough tension you can bounce a penny off them. Always.
no. you're assuming the rim has no deflection which is untrue. if you build a rim out of schedule 80 steel pipe then yea. but 300-400-500g rims on high performance bikes do not act like that. the spokes are constantly loading and unloading tension as they bash through rocks and over jumps. the point is that the pretension on the wheel needs to be high enough the spokes do not loosen too much under these forces. if they do in fact loosen too much the nipples will begin to loosen and unwind and the wheel will become out of balance.
If you’re talking about twisted spokes unwinding, you don’t have to reach zero load for that to happen. You just need to reduce the load enough so the rotational force overcomes friction. Tension will also try to unwind a screw as well. But the thread pitch on spokes is very fine, which lessens that force. If you build spokes like wood screws we would have problems and that has nothing to do with reaching 0 newtons.
You can release a lot of those tensions by squeezing the spokes mid build. Just don’t wait until they’re too tight to do it. I had a pulse in my rear wheel that probably came from doing that wrong the first time. Unless it was a factory defect, I must have overtensioned and warped a brand new Mavic aero rim ever so slightly. Expensive lesson, but it could have been worse.
I wonder if those have less or more breakin issues compared to spokes. With a spoke you have to reset the angle of the bend to the shortest distance between the hub and the rim. But with cables they have to settle in along their entire length.
Doesn’t change the answer. They’re still compressing. They’re just pretensioned.
There's a lot more creep early on, which is compensated for by a staged tensioning over the course of a few days. They may require the spoke holes in the hub to be radiused, which can be a warranty issue between you and the hub manufacturer. Windup is controlled by a flat on the small bit of spoke used for threads.
They're ok (i.e., made it through Tour Divide with no issues), done well they're certainly better than badly done steel spokes, but it's not clear if the best builds are better than the best steel builds.
There are two situations when you can push on a string. One is when it’s frozen, and the other when it’s tensioned. How do you unload a bow string? You push it off the notches.
bro. you're wrong. just build a bicycle wheel some time. it becomes very obvious how they work as you take it through the various stages of tensioning.
Why do you think someone would talk about Brandt’s work if they hadn’t used it?
I’ve built more than half a dozen bicycle wheels. My set, my spare that my brother road (into the ground - my first set and practically the only problematic ones, but he road over bumps without getting out of the saddle), a set my dad commissioned from me, and a pair that he had me build for a friend. All by age 17.
I then worked as a mechanic for two summers of college. I was never the fastest, but if we had a customer we could not afford to disappoint, I or the senior mechanic got the job because my repairs did not come back.
I saved three or four wheels that would have been scrap by unwinding the spokes halfway and building it back up again like a wheel build. Only added an extra ten or fifteen minutes but it works a charm. When a good customer comes in on Wednesday before an out of town bike ride you can’t afford to fuck it up. I think I only built a couple professionally, and usually singles. That’s a lot of labor and few will pay.
The world is full of papers that are wrong. Including maybe the one this whole thread is about. It’s okay, it happens. Science doesn’t find right or wrong, though a lot of people think so. It finds more wrong and less wrong.
My daughter did her research in this field while an undergrad, and explained to me that photosynthesis is not yet well understood. Some of the theories of the mechanism are discussed here: https://physicsworld.com/a/is-photosynthesis-quantum-ish/
>I don't think the actual proposed superconductivity mechanism is the relevant part of this paper. It is much easier to prove that this is superconducting than to prove why.
As another commenter has pointed out, the proposal of a new mechanism seems to be extraordinary and novel, and could lead to an explosion of new research, so it does indeed seem to be "relevant" on its merits.
I also don't see this as a case of the "why" being left unexplained. In the history of superconducting it has indeed been the case that new cocktails have led to superconductivity without the underlying why being understood. But the commenter that you're responding to quotes part of the paper that shows an awfully specific mechanism.
I understand the sense in which there can be a "why" that remains to be explained in certain circumstances, even when you have a mechanism. Who do monarch butterflies have the black and orange pattern on their wings? There's a cause and effect answer but there's also a "why" answer. But with superconductivity, the mechanism is the why, unless I'm misunderstanding here. If other forms of superconductivity rely on other mechanisms, there isn't going to be a general why connecting this case to the other cases, but nor is there anything left unexplained just by explaining the "why" of this case by explaining it's extraordinary mechanism.
The national Dutch funding agency that effectively funds all research in the Netherlands requires this. Buy considers it sufficient for you to publish in a closed journal and then deposit a copy in an open repository. The French also have a similar system I believe.
To be clear, there is some dissipation with magnons, just a lot less than Joule heating. But exciting a magnon will heat up your sample, because magnons don't live forever and decay after some time. That energy has to go somewhere.
To be fair, this is really field dependent. In the sciences this is (mostly) true, but in the humanities your output for your PhD is sometimes just your thesis. The problem is fundamentally that the PhD traject is geared towards an academic career, but there are not enough academic positions for all those PhD students, so they end up in industry. And there their skills don't really translate that well, as OP also says.
>The problem is fundamentally that the PhD traject is geared towards an academic career, but there are not enough academic positions for all those PhD students, so they end up in industry. And there their skills don't really translate that well, as OP also says.
This is a gigantic problem and thank you for highlighting it. Imagine you're in the United States and you have a PhD but you're not a citizen here and you just invested a ton of time and effort but you have to go back home all because there's not a position in your field. It's absolutely nonsensical to think about how the United States justs pisses away talent.
This works wonders, especially for collaborative documents (which a thesis should be, a collaboration between you and your supervisor/other people). A first "vomit" draft allows you to at least discuss the concepts, and it forces you to align the thoughts in your head. It is how I have written all my papers/thesis, and I cannot recommended it enough!
Why is no one considering that this PhD student is wrong and that his supervisor does in fact know what they are doing? Starting in a new field is hard, and it takes years to get a broad view of the field in order to understand what directions to take. As a PhD student you are not expected to be able to do this: this is why you have a supervisor who has enough experience. Maybe the supervisor does have a clear vision as to where to take the research, and the student does not yet see this?
Because what you are saying is the default situation in research. Students don't speak up, because they are taught to keep their heads down whether they are right or wrong. The default assumption is that the supervisors know what they are doing, but this student has shared his experience that this is not always the case. Maybe you should start considering that maybe supervisors are wrong sometimes too?
Cyclists are protected by law, such that even if an accident is the fault of the cyclist, the car driver is still 50% liable. This in combination with the infrastructure, which separates cyclists and cars as much as possible, makes the Netherlands very safe for cyclists.
Note that younger children still usually wear a helmet, since they are more likely to have an accident on their own (i.e. falling over).
I live in a small city and have cycled to school since I was 6 years old. At first with a parent, but from about 9 years old I would cycle by myself. I have never seen anyone wear a helmet in that time.
Just to add: he has always said that after the Olympics he is retiring (at age 25). He has not confirmed it as far as I know, but he has hinted at it in interviews and also in this document. He basically took the long distances in speed skating by storm, and is now doing a massive mic drop.
He has said in interviews after winning his two gold medal that he's going to try to stop, but since he tried that two times before, there's a 20% chance he'll be back.
He also said he doesn't know what he's going to do the next few years, but that there are a few ultra runs he still wants to do.
