A team of University of Arkansas physicists has successfully developed a circuit capable of capturing graphene's thermal motion and converting it into an electrical current

"An energy-harvesting circuit based on graphene could be incorporated into a chip to provide clean, limitless, low-voltage power for small devices or sensors," said Paul Thibado, professor of physics and lead researcher in the discovery.

The findings, published in the journal Physical Review E, are proof of a theory the physicists developed at the U of A three years ago that freestanding graphene—a single layer of carbon atoms—ripples and buckles in a way that holds promise for energy harvesting.

The idea of harvesting energy from graphene is controversial because it refutes physicist Richard Feynman's well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado's team found that at room temperature the thermal motion of graphene does in fact induce an alternating current (AC) in a circuit, an achievement thought to be impossible.

Discover the story of Lord Kelvin, whom no trial will absolve of having declared in 1900 the death of physics ... even though he never did.

Even by the standards of quantum physicists, strange metals are just plain odd. The materials are related to high-temperature superconductors and have surprising connections to the properties of black holes. Electrons in strange metals dissipate energy as fast as they're allowed to under the laws of quantum mechanics, and the electrical resistivity of a strange metal, unlike that of ordinary metals, is proportional to the temperature. ///

Lord Kelvin thought that everything has already been discovered; then came xx from New Zeeland and Roentgen and the Cities to blow up that idea...

If the universe is created by an infinite God, will we ever get to the end of discovering the depths of his creation?

Isotopes produced in the original Manhattan Project reactors seeded decades of research and even a few Nobel Prizes. //

On July 16 this year, on what marks the 75th anniversary of the first nuclear bomb test, a patient may go to the doctor for a heart scan. A student may open her textbook to study the complex chemical pathways green plants use to turn carbon dioxide in the air into sugar. A curious grandmother may spit into a vial for a genetic ancestry test and an avid angler may wake up to a beautiful morning and decide to fish at one of his favorite lakes.

If any of these people were asked to think about this selection of activities from their days, it would likely strike them as totally unrelated to the rising of a mushroom cloud above the New Mexico desert three-quarters of a century ago. But each item from the list has been touched by that event.

The device that was detonated at dawn on that fateful day unleashed the energy of around 20,000 tons of TNT from a plutonium core roughly the size of a baseball. It obliterated the steel tower on which it stood, melted the sandy soil below into a greenish glass -- and launched the atomic age. //

The scan, the textbook, the genetic test and the favorite lakeside retreat represent elements of the Manhattan Project’s forgotten legacy. They are connected through a type of atom called an isotope, which was deployed in scientific labs and hospitals before World War II, but whose overwhelming prevalence in the decades after the war was enabled and pushed by the government apparatus that was a direct heir of the effort to build the bomb.

“Generally when both ordinary people and scholars have thought about the legacy of the Manhattan Project, we thought about the way in which physics and engineering were put to military use,” said Angela Creager, a science historian at Princeton University whose book “Life Atomic” chronicles the history of isotopes in the decades after WWII. “Part of what I discovered was that atomic energy had just as much of a legacy in some of the fields that we think of as peaceable as it did in military uses. … A lot of the postwar advances in biology and medicine that have really been taken for granted owe a lot to the materials and policies that were part of the Cold War U.S.”

It's not as crazy as it sounds. //

In the March 1988 issue of Popular Mechanics, sci-fi author Isaac Asimov proposed building a particle accelerator on the moon.
A physicist recently revisited the idea in a paper published to the preprint website arXiv.org.
The moon, it turns out, might actually be a perfect place to put one. //

Asimov envisioned the year 2028. Humans—or Lunarians, as he called them—are thriving on the moon. They've erected a massive radio telescope on the moon’s far side and have built research stations, factories, and celestial observatories, all powered by nuclear and solar energy.

The moon, Asimov mused, is the ideal scientific laboratory, one that could help us unravel the mysteries of particle physics. "Turning to the heavens, special detectors would analyze rays from astrophysical sources, and moon-based particle accelerators would give new insight into the nature of matter," he wrote.

In the periodic table of elements there is one golden rule for carbon, oxygen and other light elements: Under high pressures, they have similar structures to heavier elements in the same group of elements. But nitrogen always seemed unwilling to toe the line. However, high-pressure chemistry researchers of the University of Bayreuth have disproved this special status. Out of nitrogen, they created a crystalline structure which, under normal conditions, occurs in black phosphorus and arsenic. The structure contains two-dimensional atomic layers, and is therefore of great interest for high-tech electronics. The scientists have presented this "black nitrogen" in Physical Review Letters.

What if there was a lake on the Moon? What would it be like to swim in it? Presuming that it is sheltered in a regular atmosphere, in some giant dome or something. -- Kim Holder

This would be so cool.

In fact, I honestly think it's cool enough that it gives us a pretty good reason to go to the Moon in the first place. At the very least, it's better than the one Kennedy gave.

Floating would feel about the same on the Moon as on Earth, since how high in the water you float depends only on your body's density compared to the water's, not the strength of gravity.

Swimming underwater would also feel pretty similar. The inertia of the water is the main source of drag when swimming, and inertia is a property of matter[1] independent of gravity. The top speed of a submerged swimmer would be about the same on the Moon as here—about 2 meters/second.

Everything else would be different and way cooler. The waves would be bigger, the splash fights more intense, and swimmers would be able to jump out of the water like dolphins. //

but the bottom line is that a normal swimmer on the Moon could probably launch themselves a full meter out of the water, and Michael Phelps may well be able to manage 2 or 3. //

But it gets even better. A 2012 paper in PLoS ONE, titled Humans Running in Place on Water at Simulated Reduced Gravity, concluded that while humans can't run on the surface of water on Earth,[5] they might just barely be able to do so on the Moon. (I highly recommend reading their paper, if only for the hilarious experimental setup illustration on page 2.)

The bright parts around the black hole are the accretion disk, which is in reality just a flat disk in the equatorial plane similar to the rings of Saturn, but is distorted visually by gravitational lensing. You can see a page here that gives some code for creating images using ray-tracing of light rays in curved spacetime, which offers a more schematic diagram of the visual appearance of a disk around a black hole (with a checkerboard pattern on it for clarity):

[image]

In this Q&A with Kip Thorne, he gives some background on how they created the images, indicating that they used a more sophisticated technique than ray-tracing:

I had been seen many years ago an image of an accretion disk with gravitational lensing that Jean-Pierre Luminet in France had made. I had sort of forgotten about it, but when I first saw the gravitationally lensed accretion disk that you actually see in the movie, it was a mixture of amazement on one hand and recognition that “Yes I do remember seeing something like that, years ago.” And a bit of awe and excitement that this team at Double Negative had just taken the equations I had given them — they don’t just use ray tracing, they propagate ray bundles or light beams — they’d used light beam propagation equations, laid down their own accretion disk based on artistic models based on astrophysicist’s stuff, and come back to me with a full-blown image of the sort you see in the movie. I was really impressed and gratified that they pulled it off and was so pleased with how it looked.

They didn't simulate all the optical effects that would be seen though--the physicist mentioned above, Jean-Pierre Luminet, comments in a facebook post here that the Interstellar image doesn't include "the strong Doppler and gravitational spectral shifts induced by the rotation of the disk at relativistic speed", and that after commenting about this he got a message from Kip Thorne saying that "The doppler shift was left out of the images, because (as you showed long ago) it makes the disk highly asymmetric, and much harder for a mass audience to grasp."

A happy accident in the laboratory has led to a breakthrough discovery that not only solved a problem that stood for more than half a century, but has major implications for the development of quantum computers and sensors.In a study published today in Nature, a team of engineers at UNSW Sydney has done what a celebrated scientist first suggested in 1961 was possible, but has eluded everyone since: controlling the nucleus of a single atom using only electric fields.

As with other nuclear fusion technology, the difficulty is in building a machine that can reliably initiate the reaction and harness the energy it produces.

(PhysOrg.com) -- Scientists have known for generations that hot water can sometimes freeze faster than cold, an effect known as the Mpemba effect, but until now have not understood why. Several theories have been proposed, but one scientist believes he has the answer. //

In his experiments, Brownridge took two water samples at the same temperature and placed them in a freezer. He found that one would usually freeze before the other, presumably because of a slightly different mix of impurities. He then removed the samples from the freezer, warmed one to room temperature and the other to 80°C and then froze them again. The results were that if the difference in freezing point was at least 5°C, the one with the highest freezing point always froze before the other if it was heated to 80°C and then re-frozen.

Brownridge said the hot water cools faster because of the bigger difference in temperature between the water and the freezer, and this helps it reach its freezing point before the cold water reaches its natural freezing point, which is at least 5°C lower. He also said all the conditions must be controlled, such as the location of the samples in the freezer, and the type of container, which he said other researchers had not done.

The effect now known as the Mpemba effect was first noted in the 4th century BC by Aristotle, and many scientists have noted the same phenomenon in the centuries since Aristotle’s time. It was dubbed the Mpemba effect in the 1960s when schoolboy Erasto Mpemba from Tanzania claimed in his science class that ice cream would freeze faster if it was heated first before being put in the freezer. The laughter ended only when a school inspector tried the experiment himself and vindicated him.

More information: Mpemba effect - Wiki article;
James D. Brownridge web page;
Mpemba Effect scientific paper, March 2010, by James D. Brownridge;
via Newscientist

© 2010 PhysOrg.com

The aerodynamic lift on the wing of an airplane (airfoil) is generally explained by the argument that the faster speed of the air along the top of the wing leads to reduced air pressure there and hence produces a lift (Bernoulli's Law). Using this argument, one should also expect a lift for a symmetric wing profile as shown in Fig.1.
Symmetric wing profile Fig.1
However, if one considers the problem from a microscopic point of view, one comes to a different conclusion: upward and downward forces should exactly cancel for a symmetric wing profile. This is easy to see if one simplifies the situation and replaces the curved wing surface by two plane sections (Fig.2)
Schematic illustration of symmetric wing profile Fig.2
If the wing is stationary, the pressure on all parts of the wing is identical, i.e. there is no lift. If the wing is moving in the indicated direction and assuming an inviscid gas, the front half of the upper wing surface experiences an increased pressure because of the increased speed and number of air molecules hitting it (due to the orientation of the surface, this creates a downward force). On the other hand, the rear half experiences a reduced pressure because the of the reduced speed and number of air molecules hitting it (creating a lift) (for a more detailed theoretical analysis of this see the page regarding aerodynamic drag and lift). Overall, there is consequently no lift, but only an anti-clockwise torque. It is obvious that an overall lift is only achieved if the rear section of the wing has a larger area than the front section, i.e. one would get the maximum lift for the following profile (Fig.3)

John Carrier leads the MIT Sloan Executive Education program Implementing Industry 4.0: Leading Change in Manufacturing and Operations. He also teaches in the F1 Extreme Innovation series, a collaboration between Formula One and MIT Sloan Executive Education. A native Detroiter who sees the world through a lens of systems thinking, Carrier recently watched the film (twice) with process improvement in mind. Here are three business lessons that “Ford v. Ferrari” demonstrates with historical accuracy and a touch of Hollywood flair.

Lesson 1: Don’t adopt new tech until you know what problem you are trying to solve

To test the aerodynamics of the GT40 prototype, the original Ford engineers put a large, heavy computer with attached sensors into the car. The Shelby team ripped out the computer and instead taped strings over the surface of the car, then observed the exterior of the car to see how air traveled over and around the vehicle. "Often the best model of the system is the system itself," Carrier says.

Another takeaway from this example is that the strings make the issue observable,

Unlike a computer printout, the streamers provided direct and immediate visual measurement of the entire system. Indeed, the very presence of the computer in the car distorted the performance of the system, as it significantly increased the weight of the car.

Lesson 2: Flatten your decision-making.

In the movie, Ford’s decision on the Shelby program went through the classic “15 middle managers,” visualized by a red folder circulating the Ford’s Dearborn, Michigan, headquarters, known as the Glass House. The red folder is the perfect analogy for the “hidden factory” of middle management. (A “hidden factory” is any activity or set of activities that reduce the quality or efficiency of operations but are not initially known to managers or others seeking to improve the process.)

Shelby eventually shortens the feedback loop by insisting he report directly to Henry Ford II.

“Paraphrasing a conversation I once had with Jay Forrester, the father of system dynamics, the purpose of middle management seems to be to turn the message 180 degrees while adding a time delay — the absolutely optimal way to destroy the performance of any system,” Carrier says.

Lesson 3: Learn from others.

In the Daytona race, Shelby bet his company to the Ford Motor Company on his driver, Ken Miles, winning — even against another Ford team in the race. Meanwhile, the Shelby team observed that the second Ford team in the next pit bay was having much faster pit stops. Shelby discovered they were utilizing NASCAR pit crew members.

“The lesson here is simple,” Carrier explains. “Look outside your own team, company, and/or industry for better ways of doing what you’re doing.”

Spoiler alert: In the case of Ford, all their hard work and lessons learned paid off. The GT40 MK II defeated Ferrari at Le Mans in 1966, capturing first, second, and third places. And they won again the following year.

How strong is your knot?

With help from spaghetti and color-changing fibers, a new mathematical model predicts a knot’s stability.

Jennifer Chu | MIT News Office
January 2, 2020

In sailing, rock climbing, construction, and any activity requiring the securing of ropes, certain knots are known to be stronger than others. Any seasoned sailor knows, for instance, that one type of knot will secure a sheet to a headsail, while another is better for hitching a boat to a piling.

But what exactly makes one knot more stable than another has not been well-understood, until now.

MIT mathematicians and engineers have developed a mathematical model that predicts how stable a knot is, based on several key properties, including the number of crossings involved and the direction in which the rope segments twist as the knot is pulled tight.

“These subtle differences between knots critically determine whether a knot is strong or not,” says Jörn Dunkel, associate professor of mathematics at MIT. “With this model, you should be able to look at two knots that are almost identical, and be able to say which is the better one.”

“Empirical knowledge refined over centuries has crystallized out what the best knots are,” adds Mathias Kolle, the Rockwell International Career Development Associate Professor at MIT. “ And now the model shows why.”

Pressure’s color

In 2018, Kolle’s group engineered stretchable fibers that change color in response to strain or pressure. The researchers showed that when they pulled on a fiber, its hue changed from one color of the rainbow to another, particularly in areas that experienced the greatest stress or pressure. //

In comparing the diagrams of knots of various strengths, the researchers were able to identify general “counting rules,” or characteristics that determine a knot’s stability. Basically, a knot is stronger if it has more strand crossings, as well as more “twist fluctuations” — changes in the direction of rotation from one strand segment to another.

For instance, if a fiber segment is rotated to the left at one crossing and rotated to the right at a neighboring crossing as a knot is pulled tight, this creates a twist fluctuation and thus opposing friction, which adds stability to a knot. If, however, the segment is rotated in the same direction at two neighboring crossing, there is no twist fluctuation, and the strand is more likely to rotate and slip, producing a weaker knot.

They also found that a knot can be made stronger if it has more “circulations,” which they define as a region in a knot where two parallel strands loop against each other in opposite directions, like a circular flow.

By taking into account these simple counting rules, the team was able to explain why a reef knot, for instance, is stronger than a granny knot. While the two are almost identical, the reef knot has a higher number of twist fluctuations, making it a more stable configuration. Likewise, the zeppelin knot, because of its slightly higher circulations and twist fluctuations, is stronger, though possibly harder to untie, than the Alpine butterfly — a knot that is commonly used in climbing.

After almost 350 years, physicists have just arrived at a statistical solution for Newton's three-body problem – that is, the problem of figuring out how three similar objects or bodies are going to travel in space in a way that fits in with the laws of motion and gravity. //

The researchers behind the latest study describe the three-body problem as "arguably the oldest open question in astrophysics", and while they haven't completely cracked the case, they've gotten closer than most by finding a statistical formula that fits this open question in certain scenarios.
In particular, they looked at a couple of centuries of previous research that puts forward the following idea: in unstable, chaotic three-body systems, one of those bodies eventually gets expelled, leaving behind a stable binary relationship between the two that are left. //

The three laws of motion laid down by Isaac Newton in 1687 are these: that objects remain in a state of inertia unless acted upon by force, that the relationship between acceleration and applied force is force equals mass times acceleration (F=ma), and that for every action there is an equal and opposite reaction.

So far so brilliant, as far as the basic physics of the Universe are concerned. But Newton ran into difficulties applying his rules to the Earth, Moon and Sun – the original three bodies. It actually became much harder to track three bodies with these mathematical rules.
While scientists have found fixes for special cases, a general formula for the three-body problem has proved elusive. It's like trying to apply a mathematical template to the butterfly effect – it's just too chaotic to track.

Atomic clocks are used around the world to precisely tell time. Each "tick" of the clock depends on atomic vibrations and their effects on surrounding electromagnetic fields. Standard atomic clocks in use today, based on the atom cesium, tell time by "counting" radio frequencies. These clocks can measure time to a precision of one second per every hundreds of millions of years. Newer atomic clocks that measure optical frequencies of light are even more precise, and may eventually replace the radio-based ones.

Now, researchers at Caltech and the Jet Propulsion Laboratory (JPL), which is managed by Caltech for NASA, have come up with a new design for an optical atomic clock that holds promise to be the most accurate and precise yet (accuracy refers to the ability of the clock to correctly pin down the time, and precision refers to its ability to tell time in fine detail). Nicknamed the "tweezer clock," it employs technology in which so-called laser tweezers are used to manipulate individual atoms.

Weird electron-positrons from decaying beryllium and helium hint at new boson. //

A new paper, by the same scientists that published the beryllium results. This time, they measured electron-positron emissions from excited helium. Same experiment, different atom, but the same 17MeV boson was found.

The new result is pretty strong evidence. If the experiment has some kind of systematic error in it, then we would expect that the “new” particle would change mass between helium and beryllium. It doesn’t, though; the results are very consistent between experiments. That means that if it is an error, it is an unfortunately flukey one.

more scientists would be happier to accept the result if it fit their expectations. An axion with a mass as small as a few MeV? Sure thing. A giant WIMP with a mass of many GeV? Ok. But, a boson that is lighter than a proton and kind of middle of the road? Why haven’t we seen that before?

There may also be, I think, a certain amount of unconscious snobbery in the background. The experimental results haven’t come from any of the big labs. And now the big labs are going to be putting planned experiments on hold to see if a result that they won’t get credit for stands up. If they find the boson, then, great, they’ve won plaudits for someone else. But, if that gun doesn’t smoke, there will be a long and painful search for what makes the original experiment different from the rest.

A spacecraft has finally gotten close enough to the sun to gather clues about some lingering questions. //

It sounds counterintuitive, but it’s actually harder to reach the sun than it is to leave the solar system altogether. //

“To get to Mars, you only need to increase slightly your orbital speed. If you need to get to the sun, you basically have to completely slow down your current momentum,” //

No existing rocket technology is powerful enough to cancel out the Earth’s motion like that, so the Parker probe is getting an assist from other planets. The spacecraft has been flying way out to Venus and looping around, trimming its orbit each time to shed some of the Earth’s momentum and bring itself closer to the center of the solar system.

The Dean of Westminster, John Hall accompanied by Hawking's first wife Jane Hawking and son and daughter Tim and Lucy Hawking, presides over the interment of the ashes
Tributes have been paid to renowned physicist Prof Stephen Hawking in a Westminster Abbey memorial service.

British actor Benedict Cumberbatch, who played Hawking in a BBC drama, and astronaut Tim Peake were among those giving readings at the ceremony.

Prof Hawking died in March, aged 76, after a long battle with motor neurone disease.

His ashes are being buried alongside other great scientists like Charles Darwin and Isaac Newton. //

To mark the occasion, the European Space Agency beamed Prof Hawking's words towards the nearest black hole to Earth. The transmission, which was sent from a big radio dish in Spain, was backed by an original score from composer Vangelis. //

Stephen Hawking said that science would take us on a path to "the mind of God". By that he meant that we would know everything that God would know, with the caveat, "if there were a God, which there isn't. I'm an atheist."

On the face of it, the religious ceremony at Westminster Abbey was at odds with Prof Hawking's personal views. But hearing the choral works of Wagner, Mahler, Stravinsky, Elgar - and, of course, Holst's The Planets - filling the vast halls of the Gothic Abbey, one's mind was lifted beyond Earthly matters towards the ethereal. And that is what he did through his work - unravelling the mysteries of the Universe.

The neutrino could be the weirdest subatomic particle; though abundant, it requires some of the most sensitive detectors to observe. Scientists have been working for decades to figure out whether neutrinos have mass and if so, what that mass is. The Karlsruhe Tritium Neutrino (KATRIN) experiment in Germany has now revealed its first result constraining the maximum limit of that mass. //

The KATRIN experiment begins with 25 grams of a kind of radioactive hydrogen gas, called tritium, stored in a 30-foot container held at cryogenic temperatures—cold enough such that even neon gas is a liquid. These tritium atoms undergo a kind of radioactive decay called beta decay, where one of their neutrons turns into a proton, spitting out an electron and an electron-antineutrino in the process (which would have the same mass as the electron neutrino). These decay products go into a house-sized detector called a spectrometer that measures the energy of the electrons. The electron and neutrino each carry away some of the energy of the reaction, but how much they take away can vary. Scientists must look at the spectrum of all the different electron energies, focusing particularly on the electrons that have taken away the maximum energy, whose neutrinos would in turn have taken away the minimum energy. Analysis of the shape of the resulting graphs reveals the maximum mass of any of the neutrino mass states. //

The mere fact that oscillation exists sets a lowest possible average mass of the three mass states, less than 0.1 electron volts (eV). After a month of operating and 18 years of planning and construction, KATRIN has now predicted an upper limit of any of the three mass states at 1.1 eV, where an electron weighs around 500,000 eV and a proton weighs nearly a billion.

KATRIN scientists announced the results at the 2019 Topics in Astroparticle and Underground Physics conference in Toyama, Japan, last Friday.