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  • richardmitnick 11:22 am on September 23, 2016 Permalink | Reply
    Tags: , Fermions, Physics, ,   

    From Research at Princeton: “Unconventional quasiparticles predicted in conventional crystals” 

    Princeton University
    Princeton University

    July 22, 2016 [Just appeared in social media.]
    No writer credit found

    Two electronic states known as Fermi arcs, localized on the surface of a material, stem out of the projection of a 3-fold degenerate bulk new fermion. This new fermion is a cousin of the Weyl fermion discovered last year in another class of topological semimetals. The new fermion has a spin-1, a reflection of the 3- fold degeneracy, unlike the spin-½ that the recently discovered Weyl fermions have. No image credit.

    An international team of researchers has predicted the existence of several previously unknown types of quantum particles in materials. The particles — which belong to the class of particles known as fermions — can be distinguished by several intrinsic properties, such as their responses to applied magnetic and electric fields. In several cases, fermions in the interior of the material show their presence on the surface via the appearance of electron states called Fermi arcs, which link the different types of fermion states in the material’s bulk.

    The research, published online this week in the journal Science, was conducted by a team at Princeton University in collaboration with researchers at the Donostia International Physics Center (DIPC) in Spain and the Max Planck Institute for Chemical Physics of Solids in Germany. The investigators propose that many of the materials hosting the new types of fermions are “protected metals,” which are metals that do not allow, in most circumstances, an insulating state to develop. This research represents the newest avenue in the physics of “topological materials,” an area of science that has already fundamentally changed the way researchers see and interpret states of matter.

    The team at Princeton included Barry Bradlyn and Jennifer Cano, both associate research scholars at the Princeton Center for Theoretical Science; Zhijun Wang, a postdoctoral research associate in the Department of Physics, Robert Cava, the Russell Wellman Moore Professor of Chemistry; and B. Andrei Bernevig, associate professor of physics. The research team also included Maia Vergniory, a postdoctoral research fellow at DIPC, and Claudia Felser, a professor of physics and chemistry and director of the Max Planck Institute for Chemical Physics of Solids.

    For the past century, gapless fermions, which are quantum particles with no energy gap between their highest filled and lowest unfilled states, were thought to come in three varieties: Dirac, Majorana and Weyl. Condensed matter physics, which pioneers the study of quantum phases of matter, has become fertile ground for the discovery of these fermions in different materials through experiments conducted in crystals. These experiments enable researchers to explore exotic particles using relatively inexpensive laboratory equipment rather than large particle accelerators.

    In the past four years, all three varieties of gapless fermions have been theoretically predicted and experimentally observed in different types of crystalline materials grown in laboratories around the world. The Weyl fermion was thought to be last of the group of predicted quasiparticles in nature. Research published earlier this year in the journal Nature (Wang et al., doi:10.1038/nature17410) has shown, however, that this is not the case, with the discovery of a bulk insulator which hosts an exotic surface fermion.

    In the current paper, the team predicted and classified the possible exotic fermions that can appear in the bulk of materials. The energy of these fermions can be characterized as a function of their momentum into so-called energy bands, or branches. Unlike the Weyl and Dirac fermions, which, roughly speaking, exhibit an energy spectrum with 2- and 4-fold branches of allowed energy states, the new fermions can exhibit 3-, 6- and 8-fold branches. The 3-, 6-, or 8-fold branches meet up at points – called degeneracy points – in the Brillouin zone, which is the parameter space where the fermion momentum takes its values.

    “Symmetries are essential to keep the fermions well-defined, as well as to uncover their physical properties,” Bradlyn said. “Locally, by inspecting the physics close to the degeneracy points, one can think of them as new particles, but this is only part of the story,” he said.

    Cano added, “The new fermions know about the global topology of the material. Crucially, they connect to other points in the Brillouin zone in nontrivial ways.”

    During the search for materials exhibiting the new fermions, the team uncovered a fundamentally new and systematic way of finding metals in nature. Until now, searching for metals involved performing detailed calculations of the electronic states of matter.

    “The presence of the new fermions allows for a much easier way to determine whether a given system is a protected metal or not, in some cases without the need to do a detailed calculation,” Wang said.

    Verginory added, “One can just count the number of electrons of a crystal, and figure out, based on symmetry, if a new fermion exists within observable range.”

    The researchers suggest that this is because the new fermions require multiple electronic states to meet in energy: The 8-branch fermion requires the presence of 8 electronic states. As such, a system with only 4 electrons can only occupy half of those states and cannot be insulating, thereby creating a protected metal.

    “The interplay between symmetry, topology and material science hinted by the presence of the new fermions is likely to play a more fundamental role in our future understanding of topological materials – both semimetals and insulators,” Cava said.

    Felser added, “We all envision a future for quantum physical chemistry where one can write down the formula of a material, look at both the symmetries of the crystal lattice and at the valence orbitals of each element, and, without a calculation, be able to tell whether the material is a topological insulator or a protected metal.”

    See the full article here .

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  • richardmitnick 10:57 am on September 23, 2016 Permalink | Reply
    Tags: , , , , , Physics, Vox,   

    From Yale via Vox: “Why physicists really, really want to find a new subatomic particle” 

    Yale University bloc

    Yale University



    Sep 21, 2016
    Brian Resnick

    The latest search for a new particle has fizzled. Scientists are excited, and a bit scared.

    Particle physicists are begging nature to reveal the secrets of the universe. The universe isn’t talking back. FABRICE COFFRINI/AFP/Getty Images

    Particle physicists are rather philosophical when describing their work.

    “Whatever we find out, that is what nature chose,” Kyle Cranmer, a physics professor at New York University, tells me. It’s a good attitude to have when your field yields great disappointments.

    For months, evidence was mounting that the Large Hadron Collider, the biggest and most powerful particle accelerator in the world, had found something extraordinary: a new subatomic particle, which would be a discovery surpassing even the LHC’s discovery of the Higgs boson in 2012, and perhaps the most significant advance since Einstein’s theory of relativity.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    And yet, nature had other plans.

    In August, the European Organization for Nuclear Research (CERN) reported that the evidence for the new particle had run thin. What looked like a promising “bump” in the data, indicating the presence of a particle with a unique mass, was just noise.

    But to Cranmer — who has analyzed LHC data in his work — the news did not equate failure. “You have to keep that in mind,” he says. “Because it can feel that way. It wasn’t there to be discovered. It’s like being mad that someone didn’t find an island when someone is sailing in the middle of the ocean.”

    What’s more, the LHC’s journey is far from over. The machine is expected to run for another 20 or so years. There will be more islands to look for.

    “We’re either going to discover a bunch of new particles or we will not,” Cranmer says. “If we find new particles, we can study them, and then we have a foothold to make progress. And if we don’t, then [we’ll be] staring at a flat wall in front figuring out how to climb it.”

    This is a dramatic moment, one that could provoke “a crisis at the edge of physics,” according to a New York Times op-ed. Because if the superlative LHC can’t find answers, it will cast doubt that answers can be found experimentally.

    From here, there are two broad scenarios that could play out, both of which will vastly increase our understanding of nature. One scenario will open up physics to a new world of understanding about the universe; the other could end particle physics as we know it.

    The physicists themselves can’t control the outcome. They’re waiting for nature to tell them the answers.

    Why do we care about new subatomic particles anyway?

    A graphic showing traces of collision of particles at the Compact Muon Solenoid (CMS) experience is pictured with a slow speed experience at Universe of Particles exhibition of the the European Organization for Nuclear Research (CERN) on December 13, 2011, in Geneva. FABRICE COFFRINI/AFP/GettyImages

    The LHC works by smashing together atoms at incredibly high velocities. These particles fuse and can form any number of particles that were around in the universe from the Big Bang onward.

    When the Higgs boson was confirmed in 2012, it was a cause for celebration and unease.

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN ATLAS Higgs Event
    CERN ATLAS Higgs Event

    The Higgs was the last piece of a puzzle called the standard model, which is a theory that connects all the known components of nature (except gravity) together in a balanced, mathematical equation.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth

    The Higgs was the final piece that had been theorized to exist but never seen.

    After the Higgs discovery, the scientists at the LHC turned their hopes in a new direction. They hoped the accelerator could begin to find particles that had never been theorized nor ever seen. It was like going from a treasure hunt with a map to chartering a new ocean.

    They want to find these new subatomic particles because even though the standard model is now complete, it still can’t answer a lot of lingering questions about the universe. Let’s go through the two scenarios step by step.

    Scenario 1: There are more subatomic particles! Exciting!

    If the LHC finds new subatomic particles, it lend evidence to a theory known as supersymmetry. Supersymmetry posits that all the particles in the standard model must have a shadow “super partner” that spins in a slightly different direction.

    Standard model of Supersymmetry DESY
    Standard model of Supersymmetry DESY

    Scientists have never seen one of these supersymmetrical particles, but they’re keen to. Supersymmetry could neatly solve some of the biggest problems vexing physicists right now.

    Such as:

    1) No one knows what dark matter is

    One of these particles could be what scientists call “dark matter,” which is theorized to make up 27 percent of the universe. But we’ve never seen dark matter, and that leaves a huge gaping hole in our understanding of the how the universe formed and exists today.

    “It could be that one particle is responsible for dark matter,” Cranmer explains. Simple enough.

    2) The Higgs boson is much too light

    The Higgs discovery was an incredible triumph, but it also contained a mystery to solve. The boson — at 126 GeV (giga electron volts) — was much lighter than the standard model and the math of quantum mechanics suggests it should be.

    Why is that a problem? Because it’s a wrinkle to be ironed out in our understanding of the universe. It suggests the standard model can’t explain everything. And physicists want to know everything.

    “Either nature is sort of ugly, which is entirely conceivable, and we just have to live with the fact that the Higgs boson mass is light and we don’t know why,” Ray Brock, a Michigan State University physicist who has worked on the LHC, says, “or nature is trying to tell us something.”

    It could be that a yet-to-be-discovered subatomic particle interacts with the Higgs, making it lighter than it ought to be.

    3) The standard model doesn’t unify the forces of the universe

    There are four major forces that make the universe tick: the strong nuclear force (which holds atoms together), the weak nuclear force (what makes Geiger counters tick), electromagnetism (you’re using it right now, reading this article on an electronic screen), and gravity (don’t look down.)

    Scientists aren’t content with the four forces. They, for decades, have been trying to prove that the universe works more elegantly, that, deep down, all these forces are just manifestations of one great force that permeates the universe.

    Physicists call this unification, and the standard model doesn’t provide it.

    “If we find supersymmetry at the LHC, it is a huge boost to the dream that three of the fundamental forces we have [all of them except gravity] are all going to unify,” Cranmer says.

    4) Supersymmetry would lead to more particle hunting

    If scientists find one new particle, supersymmetry means they’ll find many more. That’s exciting. “It’s not going to be just one new particle that we discovered, and yay!” Cranmer says. “We’re going to be finding new forces, or learn something really deep about the nature of space and time. Whatever it is, it’s going to be huge.”

    Scenario 2: There are no new subatomic particles. Less exciting! But still interesting. And troubling.

    The LHC is going to run for around another 20 years, at least. There’s a lot of time left to find new particles, even if there is no supersymmetry. “This is what always blows my mind,” Brock says. “We’ve only taken about 5 percent of the total planned data that the LHC is going to deliver until the middle 2020s.”

    But the accelerator also might not find anything. If the new particles aren’t there to find, the LHC won’t find them. (Hence, the notion that physicists are looking for “what nature chose.”)

    But again, this doesn’t represent a failure. It will actually yield new insights about the universe.

    “It would be a profound discovery to find that we’re not going to see anything else,” Cranmer says.

    1) For one, it would suggest that supersymmetry isn’t the answer

    If supersymmetry is dead, then theoretical physicists will have to go back to the drawing board to figure out how to solve the mysteries left open by the standard model.

    “If we’re all coming up empty, we would have to question our fundamental assumptions,” Sarah Demers, a Yale physicist, tells me. “Which is something we’re trying to do all the time, but that would really force us.”

    2) The answers exist, but they exist in a different universe

    If the LHC can’t find answers to questions like “why is the Higgs so light?” scientists might grow to accept a more out-of-the-box idea: the multiverse.

    That’s the idea where there are tons of universes all existing parallel to one another. It could be that “in most of [the universes], the Higgs boson is really heavy, and in only in very unusual universes [like our own] is the Higgs boson so light that life can form,” Cranmer says.

    Basically: On the scale of our single universe, it might not make sense for the Higgs to be light. But if you put it together with all the other possible universes, the math might check out.

    There’s a problem with this theory, however: If heavier Higgs bosons exist in different universes, there’s no possible way to observe them. They’re in different universes!

    “Which is why a lot of people hate it, because they consider it to be anti-science,” Cranmer says. “It might be impossible to test.”

    3) The new subatomic particles do exist, but the LHC isn’t powerful enough to find them

    In 20 years, if the LHC doesn’t find any new particles, there might be a simple reason: These particles are too heavy for the LHC to detect.

    This is basic E=mc2 Einstein: The more energy in the particle accelerator, the heavier the particles it can create. The LHC is the most powerful particle accelerator in the history of man, but even it has its limits.

    So what will physicists do? Build an even bigger, even smashier particle collider? That’s an option. There are currently preliminary plans in China for a collider double the size of the LHC.

    Building a bigger collider might be a harder sell for international funding agencies. The LHC was funded in part because of the quest to confirm the Higgs. Will governments really spend billions on a machine that may not yield epic insights?

    “Maybe we were blessed as a field that we always had a target or two to shoot for. We don’t have that anymore,” says Markus Klute, an MIT physicist stationed at CERN in Europe. “It’s easier to explain to the funding agencies specifically that there’s a specific endpoint.”

    The LHC will keep running for the foreseeable future. But it could prove a harder task to make the case to build a new collider.

    Either way, these are exciting times for physics

    Dean Mouhtaropoulos/Getty Images

    “I think we have had a tendency to be prematurely depressed,” Demers says. “It’s never a step backward to learn something new,” even if the news is negative. “Ruling out ideas teaches us an incredible amount.”

    And she says that even if the LHC can never find another particle, it can still produce meaningful insights. Already, her colleagues are using it to help determine why there’s so much more matter than antimatter in the universe. And she reminds me the LHC can still teach us more about the mysterious Higgs. We will be able to measure it to a more precise degree.

    Brock, the MSU physicist, notes that since the 1960s, physicists have been chasing the standard model. Now they don’t quite know what they’re chasing. But they know it will change the world.

    “I can’t honestly say in all those 40 years, I’ve been exploring,” Brock says. “I’ve been testing the standard model. The Higgs boson was the last missing piece. Now, we have to explore.”

    See the full article here .

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    Yale University Campus

    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

  • richardmitnick 10:28 am on September 23, 2016 Permalink | Reply
    Tags: , , , Physics, , PTOLEMY laboratory, Tritium   

    From PPPL: “Intern helped get robotic arm on PPPL’s PTOLEMY experiment up and running” 


    September 22, 2016
    Jeanne Jackson DeVoe

    PPPL intern Mark Thom with a device containing a robotic arm that will be used with PPPL’s PTOLEMY experiment, behind him. (Photo by Elle Starkman/PPPL Office of Communications)

    Deep in a laboratory tucked away in the basement of the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), intern Mark Thom punched commands into a computer as two other students checked a chamber where a silver robotic arm extended from a small port.

    The arm will allow scientists studying neutrinos that originated at the beginning of the universe to load a tiny amount of nuclear material into the device while still maintaining a vacuum in the PTOLEMY laboratory.

    Thom, along with high school interns Xaymara Rivera and Willma Arias de la Rosa, worked closely with Princeton University physicist Chris Tully and PPPL engineers to get the robotic arm moving again. The crucial device will load tritium, a radioactive isotope of hydrogen, into PTOLEMY, the Princeton Tritium Observatory for Light, Early Universe Massive Neutrino Yield.

    Tritium can capture Big Bang neutrinos and release them with electrons in radioactive decay. The neutrinos can provide a tiny boost of energy to the electrons, which PTOLEMY is designed to precisely measure in the darkest, coldest conditions possible. It is funded by the Mark Simons Foundation and the John Templeton Foundation.

    “For me it was just amazing that I actually got onto that project,” Thom said. “It’s exactly the kind of thing I thought I would like to do, being an engineer working on a high-energy physics project.”

    The robotic arm, together with the portable container and the computer program to operate it, were recycled from another experiment when Thom and fellow interns Rivera and Arias de la Rosa began the project. Thom was responsible for making the arm operational and altering it so it would fit PTOLEMY.

    Handling delicate materials

    Tully said the device can safely handle very delicate radioactive materials from DOE’s Savannah River National Laboratory. Without the device, scientists would have to shut down PTOLEMY completely twice a day to change the tritium sample, he said. Maintaining a vacuum in PTOLEMY is also necessary for the extremely sensitive sensors that measure the energy spectrum of the electrons emitted from the tritium to function properly.

    To make the robotic arm function again, Thom had to analyze why the coding was failing, which meant learning the code for the machine. He had to learn an unfamiliar program and then rewrite it to redirect the arm to handle tritium samples, without having worked on a device of that kind before, Tully said.

    The students encountered a setback when the arm stopped working. At first, they thought the device would need a new motor, which would cost $20,000. It turned out that the culprit was a circuit that would cost just a few dollars to replace. While Tully fixed the computer, Thom took the arm apart and researched how to install magnetic shielding around the motors and sketched a design for that shielding, Tully said. “Mark was quite amazing,” he said. “I was very impressed with him.”

    Thom also designed a cover for one of the ports that would need to be sealed for the robotic arm to work. Rivera and Arias de la Rosa helped him operate and test the robotic arm and wrote procedures for running it. Thom and the other interns also worked with PPPL engineers Charles Gentile and Mike Mardenfeld, along with senior mechanical technician Andy Carpe and lead technician Jim Taylor.

    Gentile, who supervised Thom and other engineering interns, said Thom was one of the best interns he has seen in 25 years of supervising more than 200 interns. “He’s an excellent mechanical engineer,” Gentile said. “He was a hard worker and he came up with innovative solutions to problems.”

    The arm connects to PTOLEMY through two ports equipped with valves. One valve connects to the experiment. The other connects to a loading chamber where scientists can insert a tiny sample of tritium on a graphene base.

    Researchers would create a vacuum in the loading chamber and attach it to the vacuum chamber of PTOLEMY. The robotic arm could then collect the tritium and graphene sample and deposit it into PTOLEMY. Researchers would next retract the arm and close the valve connecting it to PTOLEMY.

    Following parents’ footsteps

    Thom, who is in his final year of master’s degree work at Howard University, is from Trinidad. The son of two engineers, he considered becoming a physician and briefly flirted with the idea of being an actor or music producer before choosing to follow in his parents’ footsteps.

    Thom studied engineering as an undergraduate at Howard. He learned about the internship when Andrea Moten, PPPL acting director of human resources, and engineer Atiba Brereton met him at National Laboratory Day at Howard University in February. The two passed Thom’s resume along to Gentile as a candidate for the engineering apprenticeship program.

    The graduate student recently celebrated his one-year anniversary with his wife, Sydney, who is also an engineer and is currently teaching at a Kipp DC Middle School in Washington, D.C. Thom commuted to Washington every weekend on Friday nights to see her and then headed back to New Jersey on Monday mornings. “It was challenging at first,” he said. “But after a while I got accustomed to it and I actually began to appreciate those drives because it gave me some time to think.”

    Thom said he enjoyed the laid-back atmosphere at PPPL. He was surprised when Gentile told him he was overdressed on his first day. But he most enjoyed talking to researchers about their work. “I met some really cool people – a bunch of physicists whom I was able to have certain conversations with, just talking about abstract theories. That’s the kind of conversation I enjoy,” Thom said. “Being able to interact with people like that in that atmosphere was really enjoyable.”

    The internship gave him a better idea of possible careers as he prepares to graduate, Thom said. “I had a limited view of the engineering world prior to going into this work,” he said. “But now I have a better idea of the kind of environment I’d like to be in, so it gives me idea of what I should do to prepare for that environment.”

    See the full article here .

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    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University. PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

  • richardmitnick 8:24 am on September 23, 2016 Permalink | Reply
    Tags: , Physics, , Sonic tractor beam   

    From Science Alert: “This sonic tractor beam costs less than $10 to make” 


    Science Alert

    23 SEP 2016

    P Fischer/Nature

    Welcome to the future.

    Researchers have managed to create a sonic tractor beam that can push and pull objects using nothing but sound waves – and they did it for less than $10.

    Similar to the tractor beams that drag spacecrafts on Star Trek – but on a much smaller scale – the new device uses acoustic waves to move matter through air or water in precise patterns, without having to touch them.

    This isn’t the first time researchers have used sound waves to manipulate matter, but it is the first time it’s been done so simply – and for less than the price of a lunch.

    Developed by engineers at the Max Planck Institute for Intelligent Systems in Germany, the tractor beam is made from just three parts (although it does require a 3D printer, too). All you need is a 3D-printed plastic disk, a thin brass plate, and the kind of speaker you’d find in a watch alarm.

    “We were genuinely surprised that nobody had ever thought of this before,” one of the researchers, Kai Melde, told William Herkewitz from Popular Mechanics.

    So how does it work? The basic idea behind any tractor beam is a wave that can transfer force to an object across a distance, and in the past, researchers have done this with both light and sound.

    Last year, a team of researchers created the first one-sided acoustic tractor beam by carefully tuning 64 small speakers so that they could move tiny polystyrene balls around – imagine it like the speakers painting an invisible hologram in the air with sound waves.

    Although that worked, it was extremely inefficient and expensive, so the team from Germany decided to simplify things.

    Instead of creating the acoustic pattern with multiple speakers, what if they just used a single speaker, and covered it with a patterned, 3D-printed plastic filter?

    “It worked even better than we hoped,” Melde told Popular Mechanics.

    In fact, using their 3D-printed plastic, which was fixed to the speaker with the brass plate, they were able to create even more detailed hologram patterns than a mix of speakers – you’d need an array of 20,000 speakers to create the same amount of resolution.

    You can see the device in action below, moving a little boat through water, and levitating water droplets:

    For now, there are still many limitations to the device: the speaker only sends the hologram in one direction, and can’t be angled, which means it can move objects around according to the desired pattern, but can’t suddenly decide to move them to the side once they’re in the air. That would require a new 3D-printed plastic disc to be created.

    And in its current form, the tractor beam only works in two dimensions, by moving an object around on a flat plane, instead of pulling it in and pushing it away.

    But the hope is that with further development, this kind of technology could one day be used like pair of acoustic tweezers, to manipulate sensitive and hard-to-reach substances in medicine and physics. Just imagine being able to direct your sound waves at a patient’s kidney stone to break it apart, or move it someone else.

    “There’s a great deal of interest in using our invention to easily generate ultrasound fields with complex shapes for localised medical diagnostics and treatments,” lead researcher Peer Fischer told Colin Jeffrey from New Atlas. “I am sure that there are a lot of [other] areas that could be considered.”

    The fact that we now know how to make at least simple versions of these tractor beams so cheaply is a great starting point.

    If you have access to a 3D printer, you should definitely try this one at home – you never know, you might even come up with a better design.

    The results have been published in Nature.

    See the full article here .

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  • richardmitnick 11:13 am on September 22, 2016 Permalink | Reply
    Tags: , Physics, , SLAC’s X-ray Laser Glimpses How Electrons Dance with Atomic Nuclei in Materials   

    From SLAC: “SLAC’s X-ray Laser Glimpses How Electrons Dance with Atomic Nuclei in Materials” 

    SLAC Lab

    September 22, 2016

    Studies Could Help Design and Control Materials with Intriguing Properties, Including Novel Electronics, Solar Cells and Superconductors

    SLAC’s LCLS X-ray laser reveals the ultrafast “dance” between a material’s electrons and vibrations that accounts for many important properties of materials.
    An illustration shows how laser light excites electrons (white spheres) in a solid material, creating vibrations in its lattice of atomic nuclei (black and blue spheres). SLAC’s LCLS X-ray laser reveals the ultrafast “dance” between electrons and vibrations that accounts for many important properties of materials. (SLAC National Accelerator Laboratory)


    From hard to malleable, from transparent to opaque, from channeling electricity to blocking it: Materials come in all types. A number of their intriguing properties originate in the way a material’s electrons “dance” with its lattice of atomic nuclei, which is also in constant motion due to vibrations known as phonons.

    This coupling between electrons and phonons determines how efficiently solar cells convert sunlight into electricity. It also plays key roles in superconductors that transfer electricity without losses, topological insulators that conduct electricity only on their surfaces, materials that drastically change their electrical resistance when exposed to a magnetic field, and more.

    At the Department of Energy’s SLAC National Accelerator Laboratory, scientists can study these coupled motions in unprecedented detail with the world’s most powerful X-ray laser, the Linac Coherent Light Source (LCLS). LCLS is a DOE Office of Science User Facility.

    “It has been a long-standing goal to understand, initiate and control these unusual behaviors,” says LCLS Director Mike Dunne. “With LCLS we are now able to see what happens in these materials and to model complex electron-phonon interactions. This ability is central to the lab’s mission of developing new materials for next-generation electronics and energy solutions.”

    LCLS works like an extraordinary strobe light: Its ultrabright X-rays take snapshots of materials with atomic resolution and capture motions as fast as a few femtoseconds, or millionths of a billionth of a second. For comparison, one femtosecond is to a second what seven minutes is to the age of the universe.

    Two recent studies made use of these capabilities to study electron-phonon interactions in lead telluride, a material that excels at converting heat into electricity, and chromium, which at low temperatures has peculiar properties similar to those of high-temperature superconductors.

    Turning Heat into Electricity and Vice Versa

    Lead telluride, a compound of the chemical elements lead and tellurium, is of interest because it is a good thermoelectric: It generates an electrical voltage when two opposite sides of the material have different temperatures.

    “This property is used to power NASA space missions like the Mars rover Curiosity and to convert waste heat into electricity in high-end cars,” says Mariano Trigo, a staff scientist at the Stanford PULSE Institute and the Stanford Institute for Materials and Energy Sciences (SIMES), both joint institutes of Stanford University and SLAC. “The effect also works in the opposite direction: An electrical voltage applied across the material creates a temperature difference, which can be exploited in thermoelectric cooling devices.”

    Mason Jiang, a recent graduate student at Stanford, PULSE and SIMES, says, “Lead telluride is exceptionally good at this. It has two important qualities: It’s a bad thermal conductor, so it keeps heat from flowing from one side to the other, and it’s also a good electrical conductor, so it can turn the temperature difference into an electric current. The coupling between lattice vibrations, caused by heat, and electron motions is therefore very important in this system. With our study at LCLS, we wanted to understand what’s naturally going on in this material.”

    In their experiment, the researchers excited electrons in a lead telluride sample with a brief pulse of infrared laser light, and then used LCLS’s X-rays to determine how this burst of energy stimulated lattice vibrations.

    This illustration shows the arrangement of lead and tellurium atoms in lead telluride, an excellent thermoelectric that efficiently converts heat into electricity and vice versa. In its normal state (left), lead telluride’s structure is distorted and has a relatively large degree of lattice vibrations (blurring). When scientists hit the sample with a laser pulse, the structure became more ordered (right). The results elucidate how electrons couple with these distortions – an interaction that is crucial for lead telluride’s thermoelectric properties. (SLAC National Accelerator Laboratory)

    “Lead telluride sits at the precipice of a coupled electronic and structural transformation,” says principal investigator David Reis from PULSE, SIMES and Stanford. “It has a tendency to distort without fully transforming – an instability that is thought to play an important role in its thermoelectric behavior. With our method we can study the forces involved and literally watch them change in response to the infrared laser pulse.”

    The scientists found that the light pulse excites particular electronic states that are responsible for this instability through electron-phonon coupling. The excited electrons stabilize the material by weakening certain long-range forces that were previously associated with the material’s low thermal conductivity.

    “The light pulse actually walks the material back from the brink of instability, making it a worse thermoelectric,” Reis says. “This implies that the reverse is also true – that stronger long-range forces lead to better thermoelectric behavior.”

    The researchers hope their results, published July 22 in Nature Communications, will help them find other thermoelectric materials that are more abundant and less toxic than lead telluride.

    Controlling Materials by Stimulating Charged Waves

    The second study looked at charge density waves – alternating areas of high and low electron density across the nuclear lattice – that occur in materials that abruptly change their behavior at a certain threshold. This includes transitions from insulator to conductor, normal conductor to superconductor, and from one magnetic state to another.

    These waves don’t actually travel through the material; they are stationary, like icy waves near the shoreline of a frozen lake.

    “Charge density waves have been observed in a number of interesting materials, and establishing their connection to material properties is a very hot research topic,” says Andrej Singer, a postdoctoral fellow in Oleg Shpyrko’s lab at the University of California, San Diego. “We’ve now shown that there is a way to enhance charge density waves in crystals of chromium using laser light, and this method could potentially also be used to tweak the properties of other materials.”

    This could mean, for example, that scientists might be able to switch a material from a normal conductor to a superconductor with a single flash of light. Singer and his colleagues reported their results on July 25 in Physical Review Letters.

    This movie shows how a laser pulse hitting a chromium crystal causes charge density waves – alternating areas of high and low electron density within the crystal – to oscillate in height, or amplitude. The signal seen here is made by X-ray laser pulses scattering off the crystal. The timescale of the oscillations is shown in picoseconds, or trillionths of a second. (A. Singer/University of California, San Diego)

    The research team used the chemical element chromium as a simple model system to study charge density waves, which form when the crystal is cooled to about minus 280 degrees Fahrenheit. They stimulated the chilled crystal with pulses of optical laser light and then used LCLS X-ray pulses to observe how this stimulation changed the amplitude, or height, of the charge density waves.

    “We found that the amplitude increased by up to 30 percent immediately after the laser pulse,” Singer says. “The amplitude then oscillated, becoming smaller and larger over a period of 450 femtoseconds, and it kept going when we kept hitting the sample with laser pulses. LCLS provides unique opportunities to study such process because it allows us to take ultrafast movies of the related structural changes in the lattice.”

    Based on their results, the researchers suggested a mechanism for the amplitude enhancement: The light pulse interrupts the electron-phonon interactions in the material, causing the lattice to vibrate. Shortly after the pulse, these interactions form again, which boosts the amplitude of the vibrations, like a pendulum that swings farther out when it receives an extra push.

    A Bright Future for Studies of the Electron-Phonon Dance

    Studies like these have a high priority in solid-state physics and materials science because they could pave the way for new materials and provide new ways to control material properties.

    With its 120 ultrabright X-ray pulses per second, LCLS reveals the electron-phonon dance with unprecedented detail. More breakthroughs in the field are on the horizon with LCLS-II – a next-generation X-ray laser under construction at SLAC that will fire up to a million X-ray flashes per second and will be 10,000 times brighter than LCLS.

    “LCLS-II will drastically increase our chances of capturing these processes,” Dunne says. “Since it will also reveal subtle electron-phonon signals with much higher resolution, we’ll be able to study these interactions in much greater detail than we can now.”

    Other research institutions involved in the studies were University College Cork, Ireland; Imperial College London, UK; Duke University; Oak Ridge National Laboratory; RIKEN Spring-8 Center, Japan; University of Tokyo, Japan; University of Michigan; and University of Kiel, Germany. Funding sources included DOE Office of Science; Science Foundation Ireland; Volkswagen Foundation, Germany; and Federal Ministry of Education and Research, Germany. Preliminary X-ray studies on lead telluride were performed at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), a DOE Office of Science User Facility, and at the Spring-8 Angstrom Compact Free-electron Laser (SACLA), Japan.

    This movie introduces LCLS-II, a future light source at SLAC. It will generate over 8,000 times more light pulses per second than today’s most powerful X-ray laser, LCLS, and produce an almost continuous X-ray beam that on average will be 10,000 times brighter. (SLAC National Accelerator Laboratory)

    Citations: M.P. Jiang et al., Nature Communications, 22 July 2016 (10.1038/ncomms12291); A. Singer et al., Physical Review Letters, 25 July 2016 (10.1103/PhysRevLett.117.056401).

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  • richardmitnick 8:27 am on September 16, 2016 Permalink | Reply
    Tags: , Laboratory researchers find Earth composed of different materials than primitive meteorites, , Physics   

    From LLNL: “Laboratory researchers find Earth composed of different materials than primitive meteorites” 

    Lawrence Livermore National Laboratory

    Sep. 15, 2016
    Anne M Stark

    An independent compound chondrule consisting of barred olivine and porphyritic olivine section in the meteorite NWA 2372 CK4. Image courtesy of John Kashuba.

    Scientists from Lawrence Livermore National Laboratory (LLNL) have found that, contrary to popular belief, the Earth is not comprised of the same material found in primitive meteorites (also known as chondrites).

    This is based on the determination that the abundance of several neodymium (Nd) isotopes are different in the Earth and in chondritic meteorites.

    A long-standing theory assumes that the chemical and isotopic composition of most elements in the bulk silicate Earth is the same as primitive meteorites.

    However, 10 years ago it was discovered that rocks on the surface of the Earth had a higher abundance of 142Nd than primitive meteorites, leading to a hypothesis that Earth had either a hidden reservoir of Nd in its mantle or inherited more of the parent isotope 146smarium (Sm), which subsequently decayed to 142Nd.

    Using higher precision isotope measurements, the team found that differences in 142Nd between Earth and chondrites (non-metallic meteorites) reflected nucleosynthetic processes and not the presence of a hidden reservoir in the Earth or excess 146Sm.

    “The research has tremendous implications for our fundamental understanding of the Earth, not only for determining its bulk composition, heat content and structure, but also for constraining the modes and timescales of its geodynamical evolution,” said Lars Borg, LLNL chemist and co-author of a paper appearing in the Sept. 15 edition of Nature.

    The team suggests that the Earth formed from material that was slightly more enriched in Nd produced by the a slow neutron capture process during the creation of asymmetric giant branch (AGB) stars.

    The team’s ultimate goal was to determine whether the magnitude of radiogenic (produced by radioactive decay) Nd correlated with Nd produced in nucleosynthetic environments such as supernova or AGB stars.They used large sample sizes (about 2 grams) to obtain higher precision Nd and Sm isotope data for a comprehensive set of meteorites including 18 chondrites, the ungrouped primitive achondrite NWA 5363 and a Calcium-Aluminum-rich inclusion (CAI) from the Allende meteorite (the largest carbonaceous chondrite ever found on Earth).

    “This research may provide a new means for assessing processes that affected solid material in the disk, as well as for identifying genetic relationships among planetary bodies,” Borg said. “It calls into question a fundamental tenant of geochemistry that the composition of the Earth is precisely represented by the composition of primitive meteorites.”

    Other scientists include collaborators from the University of Chicago and Westfalische Wilhelms-Universitat Munster in Germany.

    Neodymium is a powerful magnetic element used in compact electric motors. A Toyota Prius uses 1 kg in its electric motor magnets. Although neodymium is classifed as a rare earth element, it is fairly common, no rarer than cobalt, nickel and copper and is widely distributed in the Earth’s crust.

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  • richardmitnick 10:12 am on September 12, 2016 Permalink | Reply
    Tags: , Five particles that don’t exist – yet could change our world, , Physics   

    From New Scientist: “Five particles that don’t exist – yet could change our world” 


    New Scientist

    7 September 2016
    Andrea Taroni

    Fabrice Coffrini/AFP/Getty Images

    Move over, electron. Step aside, Higgs boson. The fundamental particles that make up physics’ standard model get a lot of air time. But there is another breed of particle, just as important, that is often overlooked. That’s understandable, for in a sense “quasiparticles” do not exist at all, though they have a lot in common with regular particles and are essential for understanding the world (see Lessons in reality from particles that don’t exist). They only pop up within the confines of solid materials, but their unique properties could revolutionise modern technology…

    Phonons: Electric cowboys

    Smashing protons in CERN’s Large Hadron Collider led to the discovery of the Higgs boson. It couldn’t have happened without phonons.

    At normal temperatures, phonons are collective oscillations of atoms that shuttle heat around solids. But at very low temperatures, these quasiparticles act as cowboys that corral electrons into herds that move as one with almost zero resistance. This is how low-temperature superconductivity arises, and the huge electromagnetic fields superconducting magnets create are what curves protons round the LHC’s circular racetrack. Such magnets are also used in MRI scanners, where they force oxygen atoms in tissues into a dance that emits traceable radio signals.

    Phonons are also key to the workings of fledgling thermoelectric materials. These convert heat into electricity, with the long-held dream of allowing a car’s waste engine heat to power its electrics.

    Magnons: Sultans of spin

    Imagine a computer that, when you flipped the on switch, came on at exactly the point you’d left it. That’s the promise of magnons, quasiparticles that emerge from waves of flipping spin, a quantum-mechanical property of atoms that is the origin of magnetism.

    In standard PCs and smartphones, working memory is stored as units of charge, which dissipates when the device is switched off. With magnons, stored information would not dissipate until the magnetic field was changed, regardless of power supply.

    Spintronics, as this idea is called, would have other advantages. It uses less power, so chips can be pushed closer together without overheating — a problem that is plaguing further miniaturisation of transistor chips. Magnons can also be prompted to organise by electromagnetic waves, so computers could become entirely wireless.

    Excitons: Plants’ secret weapon

    Earth receives more energy from the sun in an hour than the entire human population uses in a year. Plants have perfected the art of capturing that juice – thanks to excitons.

    Inside a plant’s leaves are light-harvesting proteins. Their electrons absorb photons, and the energy kick pings them out of position, creating a “hole”. The electron and hole then link up to form an exciton, which can be transported around the plant’s photosynthetic machinery. When they get to where they’re needed, the electron and hole recombine, releasing energy that is used to split water into hydrogen and oxygen, a key stage in making sugars from sunlight.

    This reaction ultimately supports all life on Earth, and we’d love to mimic it in solar cells. In 2013, researchers at the Massachusetts Institute of Technology found a way to directly image excitons, a significant step to making that happen.

    Majoranas: Quantum heroes

    If you ever want a true multi-tasker, go for a quantum computer. These as-yet imperfectly realised machines use delicate, indeterminate quantum states to weigh up lots of solutions to a problem all at once, as long as no disturbance from the environment breaks the quantum spell.

    Majorana quasiparticles could make quantum computing more robust, supplying “qubits” for quantum number-crunching. A sort of massless electron, Majoranas come in pairs, with each particle acting as a half of the whole. That means you have two copies of all the information they contain, so in theory Majorana qubits should be far less vulnerable to external noise. But these qubits exist in the midst of a huge background of other electronic effects, and isolating the Majorana information is tricky, says Attila Geresdi, who studies these systems at QuTech in Delft, the Netherlands.

    Weyl fermions: Ambidextrous electrons

    Weyl fermions are like a shy cousin of the electron. Predicted mathematically almost 80 years ago, they have two key properties: they have no mass, which means they can move very fast, and they come in mirror images of each other, like right and left hands.

    This handedness, or chirality, means Weyls are resistant to interference from sources that don’t match their handedness. This in turn means they are difficult to scatter, and streams of the two types of Weyl fermion can potentially flow close to each other without interfering. Some think these properties could make them the basis for highly sophisticated computer processing well beyond spintronics (see “Sultans of spin”, above). But since materials that host Weyl fermions were only created recently, it is early days in the field of “Weyltronics”.

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  • richardmitnick 8:30 am on September 7, 2016 Permalink | Reply
    Tags: , , , , Physics   

    From MIT: “Sponge creates steam using ambient sunlight” 

    MIT News
    MIT News
    MIT Widget

    August 22, 2016
    Jennifer Chu | MIT News Office

    MIT graduate student George Ni holds a bubble-wrapped, sponge-like device that soaks up natural sunlight and heats water to boiling temperatures, generating steam through its pores.
    Photo: Jeremy Cho

    Bubble wrap, combined with a selective absorber, keeps heat from escaping the surface of the sponge. Photo: George Ni

    How do you boil water? Eschewing the traditional kettle and flame, MIT engineers have invented a bubble-wrapped, sponge-like device that soaks up natural sunlight and heats water to boiling temperatures, generating steam through its pores.

    The design, which the researchers call a “solar vapor generator,” requires no expensive mirrors or lenses to concentrate the sunlight, but instead relies on a combination of relatively low-tech materials to capture ambient sunlight and concentrate it as heat. The heat is then directed toward the pores of the sponge, which draw water up and release it as steam.

    From their experiments — including one in which they simply placed the solar sponge on the roof of MIT’s Building 3 — the researchers found the structure heated water to its boiling temperature of 100 degrees Celsius, even on relatively cool, overcast days. The sponge also converted 20 percent of the incoming sunlight to steam.

    The low-tech design may provide inexpensive alternatives for applications ranging from desalination and residential water heating, to wastewater treatment and medical tool sterilization.

    The team has published its results today in the journal Nature Energy. The research was led by George Ni, an MIT graduate student; and Gang Chen, the Carl Richard Soderberg Professor in Power Engineering and the head of the Department of Mechanical Engineering; in collaboration with TieJun Zhang and his group members Hongxia Li and Weilin Yang from the Department of Mechanical and Materials Engineering at the Masdar Institute of Science and Technology, in the United Arab Emirates.

    Building up the sun

    The researchers’ current design builds on a solar-absorbing structure they developed in 2014 — a similar floating, sponge-like material made of graphite and carbon foam, that was able to boil water to 100 C and convert 85 percent of the incoming sunlight to steam.

    To generate steam at such efficient levels, the researchers had to expose the structure to simulated sunlight that was 10 times the intensity of sunlight in normal, ambient conditions.

    “It was relatively low optical concentration,” Chen says. “But I kept asking myself, ‘Can we basically boil water on a rooftop, in normal conditions, without optically concentrating the sunlight? That was the basic premise.”

    In ambient sunlight, the researchers found that, while the black graphite structure absorbed sunlight well, it also tended to radiate heat back out into the environment. To minimize the amount of heat lost, the team looked for materials that would better trap solar energy.

    A bubbly solution

    In their new design, the researchers settled on a spectrally-selective absorber — a thin, blue, metallic-like film that is commonly used in solar water heaters and possesses unique absorptive properties. The material absorbs radiation in the visible range of the electromagnetic spectrum, but it does not radiate in the infrared range, meaning that it both absorbs sunlight and traps heat, minimizing heat loss.

    The researchers obtained a thin sheet of copper, chosen for its heat-conducting abilities and coated with the spectrally-selective absorber. They then mounted the structure on a thermally-insulating piece of floating foam. However, they found that even though the structure did not radiate much heat back out to the environment, heat was still escaping through convection, in which moving air molecules such as wind would naturally cool the surface.

    A solution to this problem came from an unlikely source: Chen’s 16-year-old daughter, who at the time was working on a science fair project in which she constructed a makeshift greenhouse from simple materials, including bubble wrap.

    “She was able to heat it to 160 degrees Fahrenheit, in winter!” Chen says. “It was very effective.”

    Chen proposed the packing material to Ni, as a cost-effective way to prevent heat loss by convection. This approach would let sunlight in through the material’s transparent wrapping, while trapping air in its insulating bubbles.

    “I was very skeptical of the idea at first,” Ni recalls. “I thought it was not a high-performance material. But we tried the clearer bubble wrap with bigger bubbles for more air trapping effect, and it turns out, it works. Now because of this bubble wrap, we don’t need mirrors to concentrate the sun.”

    The bubble wrap, combined with the selective absorber, kept heat from escaping the surface of the sponge. Once the heat was trapped, the copper layer conducted the heat toward a single hole, or channel, that the researchers had drilled through the structure. When they placed the sponge in water, they found that water crept up the channel, where it was heated to 100 C, then turned to steam.

    Tao Deng, professor of material sciences and engineering at Shanghai Jiao Tong University, says the group’s use of low-cost materials will make the device more affordable for a wide range of applications.

    “This device offers a totally new design paradigm for solar steam generation,” says Deng, who was not involved in the study. “It eliminates the need of the expensive optical concentrator, which is a key advantage in bringing down the cost of the solar steam generation system. Certainly the clever use of bubble wrap and commercially available selective absorber also helps suppress the convection and radiation heat loss, both of which not only improve the solar harvesting efficiency but also further lower the system cost. “

    Chen and Ni say that solar absorbers based on this general design could be used as large sheets to desalinate small bodies of water, or to treat wastewater. Ni says other solar-based technologies that rely on optical-concentrating technologies typically are designed to last 10 to 20 years, though they require expensive parts and maintenance. This new, low-tech design, he says, could operate for one to two years before needing to be replaced.

    “Even so, the cost is pretty competitive,” Ni says. “It’s kind of a different approach, where before, people were doing high-tech and long-term [solar absorbers]. We’re doing low-tech and short-term.”

    “What fascinates us is the innovative idea behind this inexpensive device, where we have creatively designed this device based on basic understanding of capillarity and solar thermal radiation,” says Zhang. “Meanwhile, we are excited to continue probing the complicated physics of solar vapor generation and to discover new knowledge for the scientific community.”

    This research was funded, in part, by a cooperative agreement between the Masdar Institute of Science and Technology and MIT; and by the Solid-State Solar Thermal Energy Conversion Center, an Energy Frontier Research Center funded by U.S. Department of Energy.

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  • richardmitnick 7:36 am on September 7, 2016 Permalink | Reply
    Tags: , , Optical Solitons, Physics   

    From Caltech: “New Breed of Optical Soliton Wave Discovered” 

    Caltech Logo



    Robert Perkins
    (626) 395-1862

    These optical microcavities are where solitons are created. The solitary waves circle around the microscopic disks at the speed of light.
    Credit: Qi-Fan Yang/Caltech

    Applied scientists led by Caltech’s Kerry Vahala have discovered a new type of optical soliton wave that travels in the wake of other soliton waves, hitching a ride on and feeding off of the energy of the other wave.

    Solitons are localized waves that act like particles: as they travel across space, they hold their shape and form rather than dispersing as other waves do. They were first discovered in 1834 when Scottish engineer John Scott Russell noted an unusual wave that formed after the sudden stop of a barge in the Union Canal that runs between Falkirk and Edinburgh. Russell tracked the resulting wave for one or two miles, and noted that it preserved its shape as it traveled, until he ultimately lost sight of it.

    He dubbed his discovery a “wave of translation.” By the end of the century, the phenomenon had been described mathematically, ultimately giving birth to the concept of the soliton wave. Under normal conditions, waves tend to dissipate as they travel through space. Toss a stone into a pond, and the ripples will slowly die down as they spread out away from the point of impact. Solitons, on the other hand, do not.

    In addition to water waves, solitons can occur as light waves. Vahala’s team studies light solitons by having them recirculate indefinitely in micrometer-scale circular circuits called optical microcavities. Solitons have applications in the creation of highly accurate optical clocks, and can be used in microwave oscillators that are used for navigation and radar systems, among other things.

    But despite decades of study, a soliton has never been observed behaving in a dependent—almost parasitic—manner.

    “This new soliton rides along with another soliton—essentially, in the other soliton’s wake. It also syphons energy off of the other soliton so that it is self-sustaining. It can eventually grow larger than its host,” says Vahala, Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics and executive officer for applied physics and materials science in the Division of Engineering and Applied Science.

    Vahala likens these newly discovered solitons to pilot fish, carnivorous tropical fish that swim next to a shark so they can pick up scraps from the shark’s meals. And by swimming in the shark’s wake, the pilot fish reduce the drag of water on their own body, so they can travel with less effort.

    Vahala is the corresponding author of a paper in the journal Nature Physics announcing and describing the new type of soliton, dubbed the “Stokes soliton.” (The name “Stokes” was chosen for technical reasons having to do with how the soliton syphons energy from the host.) The new soliton was first observed by Caltech graduate students Qi-Fan Yang and Xu Yi. Because of the soliton’s ability to closely match the position and shape of the original soliton, Yang’s and Yi’s initial reaction to the wave was to suspect that laboratory instrumentation was malfunctioning.

    “We confirmed that the signal was not an artifact of the instrumentation by observing the signal on two spectrometers. We then knew it was real and had to figure out why a new soliton would spontaneously appear like this,” Yang says.

    The microcavities that Vahala and his team use include a laser input that provides the solitons with energy. This energy cannot be directly absorbed by the Stokes soliton—the “pilot fish.” Instead, the energy is consumed by the “shark” soliton. But then, Vahala and his team found, the energy is pulled away by the pilot fish soliton, which grows in size while the other soliton shrinks.

    “Once we understood the environment required to sustain the new soliton, it actually became possible to design the microcavities to guarantee their formation and even their properties like wavelength—effectively, color,” Yi says. Yi and Yang collaborated with graduate student Ki Youl Yang on the research.

    The research was funded by the Defense Advanced Research Projects Agency under the PULSE Program; NASA; the Kavli Nanoscience Institute; and the Institute for Quantum Information and Matter, a National Science Foundation Physics Frontiers Center supported by the Gordon and Betty Moore Foundation.

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  • richardmitnick 11:39 am on September 2, 2016 Permalink | Reply
    Tags: , , , , Physics, Sterling Chemistry Lab reopens as a catalyst for cutting-edge science,   

    From Yale: “Sterling Chemistry Lab reopens as a catalyst for cutting-edge science” 

    Yale University bloc

    Yale University

    August 31, 2016

    Jim Shelton

    President Salovey addresses the crowd at the SCL ribbon-cutting event. (Photo by Michael Marsland)

    From its gleaming, glass-enclosed teaching labs to the powerful mechanical hubs located in the basement and penthouse, the new Sterling Chemistry Lab (SCL) has all the right elements to be a citadel of science for the next century.

    The 93-year-old building has been transformed from the inside out, and Yale officials celebrated with a grand reopening on Aug. 30. Hundreds of students, faculty, and staff gathered to tour SCL’s new teaching labs, hear more about the building’s history and envision scientific discoveries yet to come.

    “The center of gravity of this campus is shifting north,” Yale President Peter Salovey said at the ribbon cutting, noting the construction of Yale’s newest residential colleges nearby and the resurgence of investment in Science Hill.

    “We are at a moment here at Yale when we will take the excellent science, research, and education we do on campus, especially Science Hill, and move it to a truly outstanding level,” Salovey said. “We should want nothing less for students and for faculty.”

    For the new SCL, that effort required two years of cranes, jackhammers, power saws, and occasional corridor closings. The exterior of the iconic building, designed by architect Williams Adams Delano in a Collegiate Gothic style, remains unchanged. CannonDesign is the architect for the renovation, with HBRA Architects designing the central public corridor areas, and Dimeo Construction guiding the work. SCL renovations encompass 159,000 square feet, of which 31,600 is additional space, and the building will be seeking LEED Gold certification.

    The renovation includes new teaching labs for chemistry, such as this one, as well as labs for physics and biology. (Photo by Michael Marsland)

    “Science is and must be a top priority for Yale,” said Provost Benjamin Polak. “If we think about what great universities will do in the 21st century, they’re going to advance knowledge by their discoveries, they’re going to change the world, and they’re going to move minds. That means science, and Yale has to be part of that — has to lead at that.”

    A trio of teaching labs is central to that goal at the new SCL, both physically and symbolically. Biology teaching labs are located on the second floor, with flexibility allowing for adaptability to a variety of experiments and teaching needs; chemistry teaching labs are on the third floor, with individual venting hoods for each student conducting an experiment and dedicated spaces for teaching general, organic, advanced, and physical chemistry. Physics teaching labs are on the second floor, built with enhanced flexibility for experiments of different durations and sizes.

    “This really is an occasion of coming together,” said Dean of the Faculty of Arts and Sciences (FAS) Tamar Gendler, noting that the renovation merges research and teaching, brings together students and faculty, and involves multiple disciplines. It also combines past and present, knits together different areas of the campus, and blends the abstract with the concrete, Gendler said.

    Scott Miller, the Irénée du Pont Professor of Chemistry, divisional director of sciences for FAS, and former chair of the Department of Chemistry, took note of the many scientific discoveries that have taken place at SCL since 1923. He mentioned Lars Onsager’s work on thermodynamics for irreversible systems; the pioneering chemical biology research of Stuart Schreiber; and emeritus professor Jerome Berson’s research on reactive intermediates.

    “Laboratories are sacred places,” Miller said. “Laboratories are the places where we try very hard to connect observation to explanation; where we try to make things on the basis of our theories and then when we can’t make them the way we’d like to we have to revise our theories. Laboratories are the places where we connect ‘mind to hand.’ These are truly profound things.”

    In order to create teaching labs for today’s students, the SCL renovation involved a major overhaul of the building’s mechanical systems. Prior to renovation, many of the individual labs in SCL required separate services to handle venting, electricity, and other needs. Now there is a centralized system to handle the flow of power, water, and ventilation throughout the building. In addition, SCL has new replacement skylights and windows, switched from steam heat to hot-water baseboards, upgraded its sprinkler system, installed a bigger service elevator, completed masonry work, and conducted structural upgrades.

    The renovation addresses aesthetic needs, as well. Expansive, well-lit corridors connect the labs with communal areas and a landscaped courtyard, for example. Also, the use of glass walls to frame the labs is intended to inspire a more connected, collaborative spirit among students and faculty.

    “I can’t wait to come back in the coming weeks and see students at these benches and classes being taught,” Salovey said.

    See the full article here .

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