BLOGS

The ore pass at the Sanford Underground Research Facility in South Dakota. (Courtesy of Sanford Underground Research Facility, CC BY-NC-ND 4.0.)

Topics: Applied Physics, Modern Physics, Particle Physics, Theoretical Physics

The Deep Underground Neutrino Experiment (DUNE) will be the world’s largest cryogenic particle detector. Its aim is to study the most elusive of particles: neutrinos. Teams from around the world are developing and constructing detector components that they will ship to the Sanford Underground Research Facility, commonly called Sanford Lab, in the Black Hills of South Dakota. There the detector components will be lowered more than a kilometer underground through a narrow shaft to the caverns, where they will be assembled and operated while being sheltered from the cosmic rays that constantly rain down on Earth’s surface.

For at least two decades, the detector will be exposed to the highest-intensity neutrino beam on the planet. The beam will be generated 1300 km away by a megawatt-class proton accelerator and beamline under development at Fermilab in Batavia, Illinois. A smaller detector just downstream of the beamline will measure the neutrinos at the start of their journey, thereby enabling the experiment’s precision and scientific reach.

Building a ship in a bottle for neutrino science, Anne Heavey, FERMILAB, Physics Today

The effective mass of the electrons can be derived from the curvature around the maxima of the ARPES measurement data (image, detail). (Courtesy: HZB)

Topics: Alternate Energy, Applied Physics, Battery, Chemistry, Civilization, Climate Change

A longstanding explanation for why perovskite materials make such good solar cells has been cast into doubt thanks to new measurements. Previously, physicists ascribed the favorable optoelectronic properties of lead halide perovskites to the behavior of quasiparticles called polarons within the material’s crystal lattice. Now, however, detailed experiments at Germany’s BESSY II synchrotron revealed that no large polarons are present. The work sheds fresh light on how perovskites can be optimized for real-world applications, including light-emitting diodes, semiconductor lasers, and radiation detectors as well as solar cells.

Lead halide perovskites belong to a family of crystalline materials with an ABX₃ structure, where A is cesium, methylammonium (MA), or formamidinium (FA); B is lead or tin; and X is chlorine, bromine, or iodine. They are promising candidates for thin-film solar cells and other optoelectronic devices because their tuneable bandgaps enable them to absorb light over a broad range of wavelengths in the solar spectrum. Charge carriers (electrons and holes) also diffuse through them over long distances. These excellent properties give perovskite solar cells a power conversion efficiency of more than 18%, placing them on a par with established solar-cell materials such as silicon, gallium arsenide, and cadmium telluride.

Researchers are still unsure, however, exactly why charge carriers travel so well in perovskites, especially since perovskites contain far more defects than established solar-cell materials. One hypothesis is that polarons – composite particles made up of an electron surrounded by a cloud of ionic phonons, or lattice vibrations – act as screens, preventing charge carriers from interacting with the defects.

Charge-transport mystery deepens in promising solar-cell materials, Isabelle Dumé, Physics World

Artist's representation of the circular phonons. (Courtesy: Nadja Haji and Peter Baum, University Konstanz)

Topics: Applied Physics, Lasers, Magnetism, Materials Science, Phonons

When a magnetic material is bombarded with short pulses of laser light, it loses its magnetism within femtoseconds (10^–15 seconds). The spin, or angular momentum, of the electrons in the material, thus disappears almost instantly. Yet all that angular momentum cannot simply be lost. It must be conserved – somewhere.

Thanks to new ultrafast electron diffraction experiments, researchers at the University of Konstanz in Germany have now found that this “lost” angular momentum is in fact transferred from the electrons to vibrations of the material’s crystal lattice within a few hundred femtoseconds. The finding could have important implications for magnetic data storage and for developments in spintronics, a technology that exploits electron spins to process information without using much power.

In a ferromagnetic material, magnetism occurs because the magnetic moments of the material’s constituent atoms align parallel to each other. The atoms and their electrons then act as elementary electromagnets, and the magnetic fields are produced mainly by the spin of the electrons.

Because an ultrashort laser pulse can rapidly destroy this alignment, some scientists have proposed using such pulses as an off switch for magnetization, thereby enabling ultra-rapid data processing at frequencies approaching those of light. Understanding this ultrafast demagnetization process is thus crucial for developing such applications as well as for better understanding the foundations of magnetism.

Researchers find ‘lost’ angular momentum, Isabelle Dumé, Physics World

Topography of the two-dimensional crystal on top of the microscopically small wire indicated by dashed lines. Excitons freely move along the wire-induced dent, but cannot escape it in the perpendicular direction. (Courtesy: Florian Dirnberger)

Topics: Applied Physics, Condensed Matter Physics, Electrical Engineering

Using a technique known as strain engineering, researchers in the US and Germany have constructed an “excitonic wire” – a one-dimensional channel through which electron-hole pairs (excitons) can flow in a two-dimensional semiconductor like water through a pipe. The work could aid the development of a new generation of transistor-like devices.

In the study, a team led by Vinod Menon at the City College of New York (CCNY) Center for Discovery and Innovation and Alexey Chernikov at the Dresden University of Technology and the University of Regensburg in Germany deposited atomically thin 2D crystals of tungsten diselenide (fully encapsulated in another 2D material, hexagonal boride nitride) atop a 100 nm-thin nanowire. The presence of the nanowire created a small, elongated dent in the tungsten diselenide by slightly pulling apart the atoms in the 2D material and so inducing strain in it. According to the study’s lead authors, Florian Dimberger and Jonas Ziegler, this dent behaves for excitons much like a pipe does for water. Once trapped inside, they explain, the excitons are bound to move along the pipe.

Strain guides the flow of excitons in 2D materials, Isabelle Dumé, Physics World

Artist's rendition of a future colony on Mars., e71lena via Shutterstock

Topics: Applied Physics, Energy, Mars, Space Exploration

(Inside Science) -- Mars is known for its dust storms, which can cause problems for lander equipment and block out the sun that fuels solar panels. These punishing storms, which can last for weeks, have already caused damage to equipment and even killed NASA’s Opportunity rover. But they could also be dangerous to astronauts on the ground, who would rely on solar power for oxygen, heat, and water cleansing during future missions.

Vera Schorbach, a professor of wind energy at the Hamburg University of Applied Sciences in Germany, was curious to see whether wind turbines could harness the power of these storms, filling in for solar panels on the Red Planet during times of need.

"I asked myself, 'Why don't they have a wind turbine if they have dust storms,'" said Schorbach, the lead author of a study about the potential for wind power on Mars published recently in the journal Acta Astronautica.

Could martian dust storms help astronauts keep the lights on? Joshua Rapp Leam, Astronomy/Inside Science

GIF source: article link below

Topics: Applied Physics, Education, Research, Thermodynamics

Also note the Hyper Physics link on the Second Law of Thermodynamics, particularly "Time's Arrow."

"The two most powerful warriors are patience and time," Leo Tolstoy, War, and Peace

The short answer

We can measure time intervals — the duration between two events — most accurately with atomic clocks. These clocks produce electromagnetic radiation, such as microwaves, with a precise frequency that causes atoms in the clock to jump from one energy level to another. Cesium atoms make such quantum jumps by absorbing microwaves with a frequency of 9,192,631,770 cycles per second, which then defines the international scientific unit for time, the second.

The answer to how we measure time may seem obvious. We do so with clocks. However, when we say we’re measuring time, we are speaking loosely. Time has no physical properties to measure. What we are really measuring is time intervals, the duration separating two events.

Throughout history, people have recorded the passage of time in many ways, such as using sunrise and sunset and the phases of the moon. Clocks evolved from sundials and water wheels to more accurate pendulums and quartz crystals. Nowadays when we need to know the current time, we look at our wristwatch or the digital clock on our computer or phone. 

The digital clocks on our computers and phones get their time from atomic clocks, including the ones developed and operated by the National Institute of Standards and Technology (NIST).

How Do We Measure Time? NIST

FIG. 1. Temporal evolution of chamber pressure assuming nominal operation for 30 s followed by a 40 s interval with flow rate reduced 100×. The colors correspond to 1 kW, 10 kW, 100 kW, and 1 MW power levels. The process is then repeated.

Topics: Applied Physics, Computer Modeling, NASA, Space Exploration, Spaceflight

Abstract

Hall effect thrusters operating at power levels in excess of several hundreds of kilowatts have been identified as enabling technologies for applications such as lunar tugs, large satellite orbital transfer vehicles, and solar system exploration. These large thrusters introduce significant testing challenges due to the propellant flow rate exceeding the pumping speed available in most laboratories. Even with proposed upgrades in mind, the likelihood that multiple vacuum facilities will exist in the near future to allow long-duration testing of high-power Hall thrusters operating at power levels in excess of 100 kW remains extremely low. In this article, we numerically explore the feasibility of testing Hall thrusters in a quasi-steady mode defined by pulsing the mass flow rate between a nominal and a low value. Our simulations indicate that sub-second durations available before the chamber reaches critical pressure are sufficiently long to achieve the steady-state current and flow field distributions, allowing us to characterize thruster performance and the near plume region.

I. INTRODUCTION

Hall effect thrusters (HETs) are spacecraft electric propulsion (EP) devices routinely used for orbit raising, repositioning, and solar system exploration applications. To date, the highest power Hall thruster flown is the 4.5 kW BPT-4000 launched in 2010 aboard the Advanced EHF satellite¹ (which the HET helped to deliver to the correct orbit after a failure of the primary chemical booster), although a 13 kW system is being readied for near-term flight operation as part of the Lunar Gateway,² and thrusters at 50^3,4–100 kW^s power levels have been demonstrated in the laboratory. Solar cell advancements and a renewed interest in nuclear power have led the aerospace community to consider the use of Hall thrusters operating at even higher power levels. Multi-hundred kW EP systems would offer an economical solution for LEO to GEO orbit raising or for the deployment of an Earth-to-Moon delivery tug, and power levels in excess of 600 kW could be utilized for crewed transport to Mars.^5–9 While such power levels could be delivered using existing devices, a single large thruster requires less system mass and has a reduced footprint than a cluster of smaller devices.¹⁰

Quasi-steady testing approach for high‐power Hall thrusters, Lubos Brieda, Yevgeny Raitses, Edgar Choueiri, Roger Myers, Michael Keidar, Journal of Applied Physics

Hybrid device: A diagram of the layers in the new soft pressure sensor. (Courtesy: the University of Texas at Austin)

Topics: Applied Physics, Biotechnology, Nanotechnology

Wearable pressure sensors are commonly used in medicine to track vital signs, and in robotics to help mechanical fingers handle delicate objects. Conventional soft capacitive pressure sensors only work at pressures below 3 kPa, however, meaning that something as simple as tight-fitting clothing can hinder their performance. A team of researchers at the University of Texas has now made a hybrid sensor that remains highly sensitive over a much wider range of pressures. The new device could find use in robotics and biomedicine.

The most common types of pressure sensors rely on piezoresistive, piezoelectric, capacitive, and/or optical mechanisms to operate. When such devices are compressed, their electrical resistance, voltage, capacitance, or light transmittance (respectively) changes in a well-characterized way that can be translated into a pressure reading.

The high sensitivity and long-term stability of capacitive pressure sensors make them one of the most popular types, and they are often incorporated into soft, flexible sensors that can be wrapped around curved surfaces. Such sensors are popular in fields such as prosthetics, robotics, and biometrics, where they are used to calibrate the strength of a robot’s grip, monitor pulse rates, and blood pressure, and measure footstep pressure. However, these different applications involve a relatively wide range of pressures: below 1 kPa for robotic electronic skin (e-skin) and pulse monitoring; between 1 and 10 kPa for manipulating objects; and more than 10 kPa for blood pressure and footstep pressure.

Wearable pressure sensors extend their range, Isabelle Dumé, Physics World

Image source: link below

Topics: Applied Physics, Einstein, General Relativity, Special Relativity

According to Einstein’s theory of special relativity, first published in 1905, light can be converted into matter when two light particles collide with intense force. But, try as they might, scientists have never been able to do this. No one could create the conditions needed to transform light into matter — until now.

Physicists claim to have generated matter from pure light for the first time — a spectacular display of Einstein’s most famous equation.

This is a significant breakthrough, overcoming a theoretical barrier that seemed impossible only a few decades ago.

What does E=mc² mean? The world’s most famous equation is both straightforward and beyond comprehension at the same time: “Energy equals mass times the speed of light squared.” 

At its most fundamental level, it means energy and mass are various forms of the same thing. Energy may transform into mass and vice versa under the right circumstances. 

However, imagine a light beam transforming into, say, a paper clip, and it seems like pure magic. That’s where the “speed of light squared” factors in. It determines how much energy a paper clip or any piece of matter contains. The speed of light is the factor needed to make mass and energy equal. If every atom in a paper clip could be converted to pure energy, it would generate 18 kilotons of TNT. That’s around the size of the Hiroshima bomb from 1945. 

(Still can’t picture it? Me neither.) 

You can go the other way, too: if you crash two highly energized light particles, or photons, into each other, then you can create energy and mass. It sounds simple enough, but no one has been able to make it happen.

Since they couldn’t accelerate light particles, the team opted for ions and used the Relativistic Heavy Ion Collider (RHIC) to accelerate them at extreme speeds. In two accelerator rings at RHIC, the accelerated gold ions to 99.995% of the speed of light. With 79 protons, a gold ion has a strong positive charge. When a charged heavy ion is accelerated to incredible speeds, a strong magnetic field swirls around it. 

That magnetic field produces “virtual photons.” So, in a roundabout way, they accelerated light particles by piggybacking them on an ion.

When the team sped the ions in the accelerator rings with significant energy, the ions nearly collided, allowing the photon clouds surrounding them to interact and form an electron-positron pair — essentially, matter. They published their work in the journal Physical Review Letters.

Scientists observed what Einstein predicted a century ago, Teresa Carey, Free Think

Surfing excitons: Cambridge’s Alexander Sneyd with the transient-absorption microscopy set-up. (Courtesy: Alexander Sneyd)

Topics: Alternate Energy, Applied Physics, Materials Science, Nanotechnology, Solar Power

Organic solar cells (OSCs) are fascinating devices where layers of organic molecules or polymers carry out light absorption and subsequent transport of energy – the tasks that make a solar cell work. Until now, the efficiency of OSCs has been thought to be constrained by the speed at which energy carriers called excitons to move between localized sites in the organic material layer of the device. Now, an international team of scientists led by Akshay Rao at the UK’s University of Cambridge has shown that this is not the case. What is more, they have discovered a new quantum mechanical transport mechanism called transient delocalization, which allows OSCs to reach much higher efficiencies.

When light is absorbed by a solar cell, it creates electron-hole pairs called excitons and the motion of these excitons plays a crucial role in the operation of the device. An example of an organic material layer where light absorption and transport of excitons takes place is in a film of well-ordered poly(3-hexylthiophene) nanofibers. To study exciton transport, the team shone laser pulses at such a nanofiber film and observed its response.

Exciton wave functions were thought to be localized due to strong couplings with lattice vibrations (phonons) and electron-hole interactions. This means the excitons would move slowly from one localized site to the next. However, the team observed that the excitons were diffusing at speeds 1000 times greater than what had been shown for similar samples in previous research. These speeds correspond to a ground-breaking diffusion length of about 300 nm for such crystalline films. This means energy can be transported much faster and more efficiently than previously thought.

Exciton ‘surfing’ could boost the efficiency of organic solar cells, Rikke Plougmann, Physics World

FIG. 1. Schematic of the motivation and the method for this paper.

Topics: Applied Physics, Chemistry, Physics, Plasma, Research

ABSTRACT

Cold atmospheric plasmas have great application potential due to their production of diverse types of reactive species, so understanding the production mechanism and then improving the production efficiency of the key reactive species are very important. However, plasma chemistry typically comprises a complex network of chemical species and reactions, which greatly hinders the identification of the main production/reduction reactions of the reactive species. Previous studies have identified the main reactions of some plasmas via human experience, but since plasma chemistry is sensitive to discharge conditions, which are much different for different plasmas, widespread application of the experience-dependent method is difficult. In this paper, a method based on graph theory, namely, vital nodes identification, is used for the simplification of plasma chemistry in two ways: (1) holistically identifying the main reactions for all the key reactive species and (2) extracting the main reactions relevant to one key reactive species of interest. This simplification is applied to He + air plasma as a representative, chemically complex plasma, which contains 59 species and 866 chemical reactions, as reported previously. Simplified global models are then developed with the key reactive species and main reactions, and the simulation results are compared with those of the full global model, in which all species and reactions are incorporated. It was found that this simplification reduces the number of reactions by a factor of 8–20 while providing simulation results of the simplified global models, i.e., densities of the key reactive species, which are within a factor of two of the full global model. This finding suggests that the vital nodes identification method can capture the main chemical profile from a chemically complex plasma while greatly reducing the computational load for simulation.

Simplification of plasma chemistry by means of vital nodes identification

Bowen Sun, Dingxin Liu, Yifan Liu, Santu Luo, Mingyan Zhang, Jishen Zhang, Aijun Yang, Xiaohua Wang, and Mingzhe Rong, Journal of Applied Physics

Figure 1. The size contrast between conventional accelerator facilities and chip-based accelerators is dramatic. (a) The Next Linear Collider Test Accelerator facility at SLAC was used for early laser-acceleration experiments in 2012–15. (Image courtesy of the Archives and History Office/SLAC National Accelerator Laboratory.) (b) The first dielectric laser accelerator chips demonstrated at SLAC were made of fused silica and were each the size of a grain of rice. (Image courtesy of Christopher Smith/SLAC National Accelerator Laboratory.)

Topics: Applied Physics, Modern Physics, Particle Physics

Physics Today 74, 8, 42 (2021); https://doi.org/10.1063/PT.3.4815

Particle accelerators are among the most important scientific tools of the modern age. Major accelerator facilities, such as the 27-km-circumference Large Hadron Collider in Switzerland, where the Higgs boson was recently discovered, allow scientists to uncover fundamental properties of matter and energy. But the particle energies needed to explore new regimes of physics have increased to the TeV scale and beyond, and accelerator facilities based on conventional technologies are becoming prohibitively large and costly. Even lower-energy, smaller-scale accelerators used in medicine and industry are often cumbersome devices; they can weigh several tons and cost millions of dollars.

Efforts are consequently underway to develop more compact, less expensive accelerator technologies. One approach, a dielectric laser accelerator (DLA), uses an ultrafast IR laser to deliver energy to electrons inside a microchip-scale device. Efficient, ultrafast solid-state lasers and semiconductor fabrication methods developed over the past two decades have enabled a new breed of photonic devices that can sustain accelerating fields one to two orders of magnitude larger than conventional microwave-cavity accelerators.

The approach has the potential to dramatically shrink particle accelerators, thereby enabling ultrafast tabletop electron diffraction and microscopy experiments and tunable x-ray sources. An international effort is now underway to develop a laser-driven accelerator integrated on a silicon photonics platform: an “accelerator on a chip.”

Microchip accelerators, Joel England, Peter Hommelhoff, Robert L. Byer, Physics Today

A team of researchers created a new method to capture ultrafast atomic motions inside the tiny switches that control the flow of current in electronic circuits. Pictured here are Aditya Sood (left) and Aaron Lindenberg (right). Courtesy: Greg Stewart/SLAC National Accelerator Laboratory

Topics: Applied Physics, Electrical Engineering, Nanotechnology, Semiconductor Technology

A new ultrafast imaging technique that captures the motion of atoms in nanoscale electronic devices has revealed the existence of a short-lived electronic state that could make it possible to develop faster and more energy-efficient computers. The imaging technique, which involves switching the devices on and off while taking snapshots of them with an electron diffraction camera, could also help researchers probe the limits of electronic switching.

“In general, we know very little about the intermediate phases materials pass through during electronic switching operations,” explains Aditya Sood, a postdoctoral researcher at the US Department of Energy’s SLAC National Accelerator Laboratory and lead author of a paper in Science about the new method. “Our technique allows for a new way to visualize this process and therefore address what is arguably one of the most important questions at the heart of computing – that is, what are the fundamental limits of electronic switches in terms of speed and energy consumption?”

Ultrafast electron diffraction camera

Sood and colleagues at SLAC, Stanford University, Hewlett Packard Labs, Pennsylvania State University, and Purdue University chose to study devices made from vanadium dioxide (VO₂) because the material is known to transition between insulating and electrically conducting states near room temperature. It thus shows promise as a switch, but the exact pathway underlying electric field-induced switching in VO₂ has long been a mystery, Sood tells Physics World.

To take snapshots of VO₂’s atomic structure, the team used periodic voltage pulses to switch an electronic device made from the material on and off. The researchers synchronized the timing of these voltage pulses with the high-energy electron pulses produced by SLAC’s ultrafast electron diffraction (UED) camera. “Each time a voltage pulse excited the sample, it was followed by an electron pulse with a delay that we could tune,” Sood explains. “By repeating this process many times and changing the delay each time, we created a stop-motion movie of the atoms moving in response to the voltage pulse.”

This is the first time that anyone has used UED, which detects tiny atomic movements in a material by scattering a high-energy beam of electrons off a sample, to observe an electronic device during operation. “We started thinking about this subject three years ago and soon realized that existing techniques were simply not fast enough,” says Aaron Lindenberg, a professor of materials science and engineering at Stanford and the study’s senior author. “So we decided to construct our own.”

‘Stop-motion movie of atoms’ reveals short-lived state in nanoscale switch, Isabelle Dumé, Physics World

FIG. 1. Schematics of pulse sequences for spin-locking measurement with (a) two π/2 pulses and (b) two composite pulses. (c) Schematics of a SCROFULOUS composite pulse composed of three pulses. (d) Evolution of the spin state in the Bloch sphere. The spin state is initialized to the |0⟩ state by the first laser pulse. (e) The first π/2 pulse rotates the spin by 90∘ to the (−y)-direction. A y-driving microwave field is applied parallel to the spin in the rotation frame. (f) The second π/2 pulse rotates the spin by 90∘ to the (−z)-direction in the pulse sequence pattern A, or (g) the second −π/2 pulse rotates the spin by −90∘ to the z-direction in the pulse sequence pattern B. Finally, the spin state is read out from the PL by applying the second laser pulse. (h) Schematics of the experimental setup.

Topics: Applied Physics, Electrical Engineering, Materials Science, Optics

ABSTRACT

We present results of near-field radio-frequency (RF) imaging at micrometer resolution using an ensemble of nitrogen-vacancy (NV) centers in diamond. The spatial resolution of RF imaging is set by the resolution of an optical microscope, which is markedly higher than the existing RF imaging methods. High sensitivity RF field detection is demonstrated through spin locking. SCROFULOUS composite pulse sequence is used for manipulation of the spins in the NV centers for reduced sensitivity to possible microwave pulse amplitude error in the field of view. We present procedures for acquiring an RF field image under spatially inhomogeneous microwave field distribution and demonstrate a near-field RF imaging of an RF field emitted from a photolithographically defined metal wire. The obtained RF field image indicates that the RF field intensity has maxima in the vicinity of the edges of the wire, in accord with a calculated result by a finite-difference time-domain method. Our method is expected to be applied in a broad variety of application areas, such as material characterizations, characterization of RF devices, and medical fields.</em>

Near-field radio-frequency imaging by spin-locking with a nitrogen-vacancy spin sensor, Shintaro Nomura^1,a), Koki Kaida¹, Hideyuki Watanabe², and Satoshi Kashiwaya³, Journal of Applied Physics

In their experiments, the researchers used ultrathin crystals consisting of a single layer of atoms. These sheets were sandwiched between two layers of mirror-like materials. The whole structure acts as a cage for light and is called a microcavity.

Topics: Applied Physics, Bose-Einstein Condensate, Lasers, Nanotechnology, Optics

Physicists have taken a step towards realizing the smallest-ever solid-state laser by generating an exotic quantum state known as a Bose-Einstein condensate (BEC) in quasiparticles consisting of both matter and light. Although the effect has so far only been observed at ultracold temperatures in atomically thin crystals of molybdenum diselenide (MoSe₂), it might also be produced at room temperature in other materials.

When particles are cooled down to temperatures just above absolute zero, they form a BEC – a state of matter in which all the particles occupy the same quantum state and act in unison, like a superfluid. A BEC made up of tens of thousands of particles behaves as if it were just one giant quantum particle.

An international team of researchers led by Carlos Anton-Solanas and Christian Schneider from the University of Oldenburg, Germany; Sven Höfling of the University of Würzburg, Germany; Sefaattin Tongay at Arizona State University, US; and Alexey Kavokin of Westlake University in China, has now generated a BEC from quasiparticles known as exciton-polaritons in atomically thin crystals. These quasiparticles form when excited electrons in solids couple strongly with photons.

“Devices that can control these novel light-matter states hold the promise of a technological leap in comparison with current electronic circuits,” explains Anton-Solanas, who is in the quantum materials group at Oldenburg’s Institute of Physics. “Such optoelectronic circuits, which operate using light instead of electric current, could be better and faster at processing information than today’s processors.”

Anton-Solanas, Schneider, and colleagues studied crystals of MoSe₂ that were just a single atomic layer thick. MoSe₂belongs to a family of materials known as transition-metal dichalcogenides (TMDCs). In their bulk form, these materials act as indirect band-gap semiconductors. Still, when scaled down to a monolayer thickness, they behave as direct band-gap semiconductors, capable of efficiently absorbing and emitting light.

In their experiments, the researchers assembled sheets of MoSe₂ less than a nanometer thick and sandwiched them between alternating layers of silicon dioxide and titanium dioxide (SiO₂/TiO₂), which reflect light like a mirror. The resulting structure is known as a microcavity and acts as a cage for light. “It’s like trapping the light-emitting material in a room filled with mirrors and mirrors only,” Tongay tells Physics World. “The light gets reflected these mirrors and is absorbed by the material back and forth.”

Exotic quantum state could make smallest-ever laser, Isabelle Dumé, Physics World

Liquidated3672 (2021), Theodore Lee Jones, CallMeTed.com.

Topics: Applied Physics, Biology, Microscopy, Molecules

A major challenge in cell biology remains to unravel is how cells control their biochemical reaction cycles. For instance, how do they regulate gene expression in response to stress? How does their metabolism change when resources are scarce? Control theory has proven useful in understanding how networks of chemical reactions can robustly tackle those and other tasks.¹ The essential ingredients in such approaches are chemical feedback loops that create control mechanisms similar to the circuits that regulate, for example, the temperature of a heating system, the humidity of an archive, or the pH of a fermentation tank.

Theories for the control of biochemical reactions have largely focused on homogeneous, well-stirred environments. However, macromolecules inside cells are often highly organized in space by specialized subunits called organelles. Some organelles, such as the cell nucleus, are bound by a membrane. By contrast, another class of organelles—biomolecular condensates—show the hallmark physical properties of liquid-like droplets, and they provide chemically distinct environments for biochemical reactions.^2–4

Such droplets can act as microreactors for biochemical reactions in a living cell (see figure 1). Their liquid nature sustains the fast diffusion of reactants while their specific composition gives rise to the partitioning of reactants in or out of the droplets. In general, the concentrations of reactants inside condensates differ from the concentrations outside. Those differences modify reaction fluxes, which, in turn, can dramatically affect reaction yield and other properties of chemical reactions. Just how such modified fluxes govern the biochemistry inside cells remains poorly understood.

Drops in Cells, Christoph Weber, Christoph Zechner, Physics Today

An unidentified flying object as seen in a declassified Department of Defense video, DoD

Topics: Aerodynamics, Applied Physics, Biology, Exoplanets, General Relativity, SETI

May 17, 2019- No, little green men aren't likely after the conquest of humanity. Boyd's piece for Phys.org highlights the reason why the Pentagon wants to identify UFOs: they're unidentified. If a warfighter on the ground or in the sky can't ID an object, that creates an issue since they don't know if it's friendly, adversarial, or neutral.

U.S. Navy pilots and sailors won't be considered crazy for reporting unidentified flying objects, under new rules meant to encourage them to keep track of what they see writes Iain Boyd for Phys.org.

Why is the Pentagon interested in UFOs? Intelligent Aerospace

The Pentagon refers to them as "transmedium vehicles," meaning vehicles moving through air, water, and space. Carolina Coastline breathlessly uses the term "defying the laws of physics." So I looked at what the paper might have meant. The objects apparently exceed the speed of sound without a sonic boom (signature of breaking the barrier). Even though this is reported by Popular Mechanics, they're quoting John Ratcliffe, whose name somehow sounds like a pejorative. Consider the source.

U.S. Navy F/A-18 flying faster than the speed of sound. The white cloud is formed by decreased air pressure and temperature around the tail of the aircraft.
ENSIGN JOHN GAY, U.S. NAVY

The speed of sound is 343 meters per second (761.21 miles per hour, 1,100 feet per second). Mach 1 is the speed of sound, Mach 2 is 1522.41 mph, Mach 3 is 2283.62 mph. NASA's X-43A scramjet sets the record at Mach 9.6 (7,000 mph), so, it's easy to see where Star Trek: The Next Generation got its Warp Speed analog from. The top speed of the F/A-18 is 1,190 mph. Pilots and astronauts under acceleration experience G Forces, and have suits to keep them from blacking out in a high-speed turn.

A Science Magazine article in 1967 reported the dimensions and speeds for the object were undeterminable. History.com reported an object exceeding 70 knots, or 80.5546 mph underwater (twice the speed of a nuclear submarine, so I can see the US Navy's concern). I found some of the descriptions on the site interesting:

5 UFO traits:

1. Anti-gravity lift (no visible means of propulsion), 2. Sudden and instantaneous acceleration (fast), 3. Hypersonic velocities without signatures (no sonic boom), 4. Low observability, or cloaking (not putting this on Romulans, or Klingons), 5. Trans-medium travel (air, water, space).

When I look at these factors, I don't get "little green men." First caveat: there are a lot of planets between us, and them with resources aplenty. Second caveat: any interest an alien intelligence might have in us is as caretakers of an experiment, or cattle. That's disturbing: ever see a rancher have conversations with a chicken, sow, or steer before slaughter?

My hypothesis (Occam's razor) - these are projections, but of a special kind:

For the first time, a team including scientists from the National Institute of Standards and Technology (NIST - 2016) have used neutron beams to create holograms of large solid objects, revealing details about their interiors in ways that ordinary laser light-based visual holograms cannot.

Holograms -- flat images that change depending on the viewer's perspective, giving the sense that they are three-dimensional objects -- owe their striking capability to what's called an interference pattern. All matter, such as neutrons and photons of light, has the ability to act like rippling waves with peaks and valleys. Like a water wave hitting a gap between the two rocks, a wave can split up and then re-combine to create information-rich interference patterns.

Move over, lasers: Scientists can now create holograms from neutrons, too, Science Daily

This of course doesn't explain the decades of observations, since holograms came into being in a 1948 paper by the Hungarian inventor Denis Gabor: “The purpose of this work is a new method for forming optical images in two stages. In the first stage, the object is lit using a coherent monochrome wave, and the diffraction pattern resulting from the interference of the secondary coherent wave coming from the object with the coherent background is recorded on the photographic plate. If the properly processed photographic plate is placed after its original position and only the coherent background is lit, an image of the object will appear behind it, in the original position.” Gabor won the Nobel Prize in 1971 for "his invention and development of the holographic method." Also: History of Holography

This is purely speculative. I have no intelligence other than what I've shared. It does in my mind, explain the physics-defying five traits described above. It does not explain the previous supposition of sightings since humans started recording history, or trying to hypothesize their sightings in antiquity. Solid objects flying at hypersonic speeds make sonic booms; projections - ball lightning, 3D laser, or solid neutron holograms - likely won't.

If these are projections (adversary, friendly, neutral), who is doing them, and why?

Topics: Alternate Energy, Applied Physics, Atomic-Scale Microscopy, Nanotechnology

When Ondrej Krivanek first considered building a device to boost the resolution of electron microscopes, he asked about funding from the U.S. Department of Energy. “The response was not positive,” he says, laughing. He heard through the grapevine that the administrator who held the purse strings declared that the project would be funded “over his dead body.”     

“People just felt it was too complicated, and that nobody would ever make it work,” says Krivanek. But he tried anyway.  After all, he says, “If everyone expects you to fail, you can only exceed expectations.”

The correctors that Krivanek, Niklas Dellby, and other colleagues subsequently designed for the scanning transmission electron microscope did exceed expectations. They focus the microscope’s electron beam, which scans back and forth across the sample like a spotlight and make it possible to distinguish individual atoms and to conduct chemical analysis within a sample. For his pioneering efforts, Krivanek shared The Kavli Prize in nanoscience with the German scientists Harald Rose, Maximilian Haider, and Knut Urban, who independently developed correctors for conventional transmission electron microscopes, in which a broad stationary beam illuminates the entire sample at once.

Electron microscopes, invented in 1931, long-promised unprecedented clarity, and in theory could resolve objects a hundredth the size of an atom. But in practice, they rarely get close because the electromagnetic lenses they use to focus electrons deflected them in ways that distorted and blurred the resulting images.

The aberration correctors designed by both Krivanek’s team and the German scientists deploy a series of electromagnetic fields, applied in multiple planes and different directions, to redirect and focus wayward electrons. “Modern correctors contain more than 100 optical elements and have software that automatically quantifies and fixes 25 different types of aberrations,” says Krivanek, who co-founded a company called Nion to develop and commercialize the technology.

That level of fine-tuning allows microscopists to fix their sights on some important pursuits, such as producing smaller and more energy-efficient computers, analyzing biological samples without incinerating them, and being able to detect hydrogen, the lightest element, and a potential clean-burning fuel.

The Vast Potential of Atomic-Scale Microscopy, Ondrej Krivanek, Scientific American

The black phosphorus composite material connected by carbon-phosphorus covalent bonds has a more stable structure and a higher lithium-ion storage capacity. Credit: DONG Yihan, SHI Qianhui, and LIANG Yan

Topics: Alternative Energy, Applied Physics, Battery, Nanotechnology, Research

A new electrode material could make it possible to construct lithium-ion batteries with a high charging rate and storage capacity. If scaled up, the anode material developed by researchers at the University of Science and Technology of China (USTC) and colleagues in the US might be used to manufacture batteries with an energy density of more than 350 watt-hours per kilogram – enough for a typical electric vehicle (EV) to travel 600 miles on a single charge.

Lithium ions are the workhorse in many common battery applications, including electric vehicles. During operation, these ions move back and forth between the anode and cathode through an electrolyte as part of the battery’s charge-discharge cycle. A battery’s performance thus depends largely on the materials used in the electrodes and electrolyte, which need to be able to store and transfer many lithium ions in a short period – all while remaining electrochemically stable – so they can be recharged hundreds of times. Maximizing the performance of all these materials at the same time is a longstanding goal of battery research, yet in practice, improvements in one usually come at the expense of the others.

“A typical trade-off lies in the storage capacity and rate capability of the electrode material,” co-team leader Hengxing Ji tells Physics World. “For example, anode materials with high lithium storage capacity, such as silicon, are usually reported as having low lithium-ion conductivity, which hinders fast battery [charging]. As a result, the increase in battery capacity usually leads to a long charging time, which represents a critical roadblock for more widespread adoption of EVs.”

Black phosphorus composite makes a better battery, Isabelle Dumé, Physics World

Gentle breeze: illustration of the B-TENG triboelectric nanogenerator, which harvests electricity that is generated by fluttering polymer strips. (Courtesy: Xin Chen/Xiaojing Mu/Ya Yang)

Topics: Applied Physics, Nanotechnology, Polymers, Research

A new low-cost nanogenerator that can efficiently harvest electrical energy from ambient wind has been created by Ya Yang at the Beijing Institute of Nanoenergy and Nanosystems of the Chinese Academy of Sciences and colleagues. The team reports that the device achieves high electrical conversion efficiencies for breezes of 4–8 m/s (14–28 km/h) and says that it could be used to generate electricity in everyday situations, where conventional wind turbines are not practical.

As the drive to develop renewable sources of energy intensifies, there is growing interest in harvesting ambient energy in everyday environments. From breezes along city streets to the airflows created as we walk, the mechanical energy contained in ambient wind is abundant. The challenge is to harvest this every in an efficient and practical way. This has proven difficult using existing technologies such as piezoelectric films, which operate at very low power outputs.

Yang’s team based their new design around two well-known phenomena in physics. The first is the Bernoulli effect, which causes the fluttering of two adjacent flags to couple. If separated by a very small gap, the flags will flutter in-phase, while at slightly larger separations, they flap out-of-phase, and symmetrically about a central plane. The second is the triboelectric effect – the familiar phenomenon behind the “static electricity” that is created when different objects are rubbed together and then separated – resulting in opposite electrical charges on the objects and a voltage between the two.

Fluttering polymer ribbons harvest electrical energy, Physics World