Waves & Packets
Apr. 28, 2012

Sun's twin discovered — The perfect SETI target?
Discovery News
Astronomers have identified a clone to our sun lying only 200 light-years away, a yellow dwarf that is exactly the same mass, temperature and chemical composition as our nearest star. In a recent paper reporting on observations of the star — called HP 56948 — astronomer Jorge Melendez of the University of San Paulo, Brazil, calls it "the best solar twin known to date." the chemical composition of HP 56548 has unusual amounts of aluminum, calcium, magnesium, and silicon -- by the same ratio as our sun has. This means terrestrial planets could exist around HP 56548. Simply put, the nearby presence of a twin star potentially offers a fascinating experiment in parallel evolution. More

Germany sends optical-clock signal over nearly 1000 km
Physics World
As reported in Science, physicists in Germany have sent a burst of light over a distance of 920 km down an optical fiber – with its frequency remaining stable to the 19th decimal place. As well as supporting the development of highly accurate "optical clocks", the breakthrough could also be used in a range of commercial and scientific applications including precision spectroscopy, geodesy and very-long-baseline astronomy. In addition to spectroscopy and metrology, such optical networks could be used in fundamental physics. The rate at which an optical clock beats is determined by the value of the fine structure. Comparing optical clocks in different locations could reveal variations in this constant, which could point to new physics. Optical clocks are also governed by Einstein's theory of relativity and, for example, tick at slightly different rates when at different altitudes. Comparing clocks could reveal deviations from what is predicted by theory, and also lead to new physics.More

Scientists discover bilayer structure in efficient solar material
Brookhaven National Lab
High resolution x-ray scattering studies of one of the best-performing organic photovoltaic materials reveal an unusual bilayer lamellar structure. The bilayer may help explain the material's superior performance at converting sunlight to electricity, and guide the synthesis of new materials with even better properties. The material is a polycarbazole conjugated polymer with a chainlike carbon backbone with alkyl side chains. In a conjugated polymer, the backbone provides the path for electrical conductivity and the alkyl side chains, similar to simple oils, provide the solubility required for processing. In the material used in this study, which is reported in Nature Communications, the polymer's conjugated backbone pairs "phase separate" from their alkyl side chains and this gives rise to the bilayer structure, and that gives the material the ability to move electrons around — both "donating" and "accepting" them. The current material is able to convert sunlight to electricity with efficiency as high as 7.2 percent in organic solar cells. But new syntheses guided by this structure-function result will inevitably lead to more efficient materials.More

How to walk with a cup of coffee
American Physical Society
Each morning, on their way to the scientific frontier, physicists try to solve a frustratingly complex mechanical problem: how to walk with a full cup of coffee, without letting it slosh over the sides. In Physical Review E, two physicists report their study of the biomechanics of walking with coffee and the factors that lead to spills. In a complex interplay between the geometry and motion of a cup via the biomechanics of walking, and the fluid properties of the coffee, it turns out that noise — potentially caused by uneven steps or small jerks of the cup — plays an important role in amplifying the natural oscillations of coffee into a full-blown spill. Staying focused on the coffee may provide feedback damping, averting reaching the critical amplitude that leads to the coffee spilling over. There are many places where this research could go. One obvious place is to use tea instead of coffee, or study the effect of adding lemon, cream, or both.More

Pentawatt laser could produce dense electron-positron plasma and intense gamma rays
American Physical Society
The next generation of ultrahigh-power lasers, reaching the range of 10 petawatts, will enable new light-matter interactions, according to simulations published in Physical Review Letters. A team of physicists from England, France and Germany have shown via computer simulations that 10 petawatt pulses hitting an aluminum foil could produce an electron-positron plasma 10 million times denser than any previous experiment, as well as a record-breaking intensity of gamma rays. The team had to account for nonlinear quantum electrodynamic (QED) processes such as synchrotron production of gamma rays by electrons accelerated in the strong laser field. Also there is the electron-positron pair production from gamma rays. These two effects, made important by the strong laser field, lead to a new plasma regime called a "plasma." Producing a QED plasma would not only would allow studies of conditions similar to those in plasmas produced by black holes and pulsars, but could improve cancer treatment as part of new ion acceleration systems, and they could provide attosecond pulses for metrology with unprecedented precision.More

NIST mini-sensor measures magnetic activity in human brain
NIST Tech Beat
Scientists at the National Institute of Science and Technology in the U.S. and Physikalisch-Technische Bundesanstalt in Germany have used a sensor to measure alpha waves in the brain associated with a person opening and closing their eyes as well as signals resulting from stimulation of the hand. The measurements were verified by comparing them with signals recorded by a superconducting quantum interference device. The current results, which are published in Biomedical Optics Express, indicate the NIST mini-sensor may be useful in magnetoencephalography, a noninvasive procedure that measures the magnetic fields produced by electrical activity in the brain. The technique also has some cross-over to fusion reactor research. The mini-sensor consists of a container of about 100 billion rubidium atoms in a gas, a low-power infrared laser and fiber optics for detecting the light signals that register magnetic field strength. The rubidium atoms absorb more light as the magnetic field increases.More

NASA's WISE catches aging star erupting with dust
Images from NASA's Wide-field Infrared Survey Explorer (WISE) reveal an old star in the throes of a fiery outburst, spraying the cosmos with dust. The aging star, catalogued as WISE J180956.27-330500.2, is in the "red giant" phase of its life where it expands and eventually makes dust that becomes the seed material for new solar systems. Our own sun will expand into a red giant in about 5 billion years. Results indicate the star recently exploded with copious amounts of fresh dust, equivalent in mass to our planet Earth. The star is heating the dust and causing it to glow with infrared light. These latest findings offer a rare, real-time look at the process by which stars like our sun seed the universe with building blocks for other stars, planets and even life.More

Experimental realization of delayed-choice entanglement swapping
Motivated by the question of which kind of physical interactions and processes are needed for the production of quantum entanglement, the radical idea of delayed-choice entanglement swapping has been suggested. According to this idea entanglement can be "produced a posteriori, after the entangled particles have been measured and may no longer even exist." The successful experimental verification of delayed-choice entanglement swapping was achieved by using four photons. Specifically, two sets of entangled photons were generated. A party named Victor received one photon from each set. Then, the party Alice received one of the two remaining photons, and the party Bob received the remaining photon. Now, Victor has two measurement options. If he considers the entangled state for his two photons, then the photon pair of Bob and Alice becomes entangled. If he selects a separable state for his pair of photons, the same state occurs in the photon pair of Bob and Alice. This effectively projects the two already registered photons (by Bob and Alice) onto one of two mutually exclusive quantum states in which the photons are either entangled (quantum correlations) or separable (classical correlations). This can also be viewed as "quantum steering into the past." This result is reported in Nature Physics.More

X-rays create a window on glass formation
European Synchrotron Radiation Source
Glass is made by heating mixtures of quartz sand (silica, SiO2) with sodium and calcium carbonates (Na2CO3, CaCO3) to 1500°C and kept at this temperature for many days. An individual grain of silica normally melts at very high temperatures (1700°C). Adding carbonates triggers chemical reactions that lower this temperature. However, the interplay between the geometry of the grains and the rate of chemical reactions during the early stages of the melting which starts already well below 1000°C, have remained a mystery to date. To probe these chemical reactions scientists used X-ray microtomography at the European Synchrotron Radiation Facility (ESRF) to get real time changes in shape and positions of all grains in a given volume. The sequences of microtomography images confirmed the importance of good contact between grains of different substances, as it is these contacts which determine whether or not the mixture turns into liquid glass. By merging hundreds of X-ray tomography images, the scientists produced a video sequence visualizing how different grains in the mixture move and fuse, one after the other, into molten glass as the temperature rose from 750°C to 930°C. The report is published in the Journal of the American Ceramic Society. More

CMS experiment observes new Xi_b beauty particle
The CMS experiment has submitted a paper for publication describing the first observation of a new, excited beauty baryon known as the Ξ*b0, with a statistical significance of more than 5 standard deviations (5σ) above the expected background. The mass is measured to be 5945.0 ± 2.8 MeV. The observation was made in a data sample of proton — proton collisions delivered in 2011 by CERN's Large Hadron Collider (LHC) operating at a center-of-mass energy of 7 TeV. The well-established quark model predicts the existence of so-called Ξb baryons containing one beauty (b) quark, one strange (s) quark, and either an up (u) quark, which results in a neutral Ξb0 baryon, or a down (d) quark, which results in a charged Ξb-baryon. These may exist with various values of the quantum numbers for angular momentum (J) and parity (P). The ground-state, lowest-mass Ξb baryons — both charged and neutral — have been previously observed.More

Physicists propose a solution to a critical barrier to producing fusion
Princeton Plasma Physics Laboratory
In hot plasma experiments, tiny, bubble-like islands collect impurities from the container walls and cool the plasma. Two physicists have linked these islands of impurities to the so-called "density limit," which prevents fusion reactors from operating at maximum efficiency. Reporting in Physical Review Letters, the PPPL physicists pieced together several decades of observations from different specialties of physics: radiation physics, plasma energy transport theory, and magnetohydrodynmics. In an interview with Waves and Packets, Luis Delgado-Aparicio explained that their work looks just at the point in time at the threshold of where the impurity islands just start to form. This would be before the Modified Rutherford Equation applies, which describes the growth of the impurity islands; and after the so-called Greenwald limit is reached, which follows from a power balance just as the islands are about to grow. The model that Delgado-Aparicio and PPPL's David Gates developed includes more of the detailed local physics in the plasma, including the temperature, spatial location and main composition of the impurities. The plan now is to test this new theory with experiments on a tokamak called Alcator C-Mod at MIT, and on the DIII-D tokamak at General Atomics in San Diego. Among other things, they intend to see if injecting power directly into the islands will lead to higher density. If so, that could help future tokamaks reach the extreme density and 100-million-degree temperatures that fusion requires.More

2-D Ising model produces quantum computer
National Institute of Science and Technology
An international team including participants from Australia, South Africa, and the United States has constructed a tiny crystal that acts like a quantum computer so powerful it would take a computer the size of the known universe to match it. This work, published in Nature, picks up on a prediction by Feynman that a quantum simulator—a special-purpose "analogue" processor built using quantum bits (qubits)—would be inherently suited to solving large many-body and correlated problems. The heart of the simulator is a rotating two-dimensional crystal of beryllium ions confined in a Penning trap. Each atom becomes a tiny quantum magnet, and the discreet quantum magnetic states can be exploited as qubits by carefully timed microwave and laser pulses. Previous results have involved just a few tens of qubits, but this new result has raised that by an order of magnitude.More

Proliferation risks of magnetic fusion energy: clandestine production, covert production and breakout
Institute of Physics
In an article recently published in Nuclear Fusion, researchers from Princeton University have shown that prospective magnetic fusion power systems would pose a much lower risk of being used for the production of weapon-usable materials than nuclear fission reactors and their associated fuel cycle.More

Mega-impacts of asteroids with Earth occurred more frequently than previously thought
Giant asteroids, similar or larger than the one believed to have killed the dinosaurs, hit Earth billions of years ago with more frequency than previously thought. By studying ancient rocks in Australia and using computer models, researchers estimate that approximately 70 asteroids the same size or larger impacted Earth 1.8 to 3.8 billion years ago. During the same period, approximately four similarly-sized objects hit the moon. The team's findings, reported in Nature, support the theory Jupiter, Saturn, Uranus and Neptune formed in different orbits nearly 4.5 billion years ago, migrating to their current orbits about 4 billion years ago. This event triggered a solar system-wide bombardment of comets and asteroids called the "Late Heavy Bombardment." The team created a model of the ancient main asteroid belt and tracked what would have happened when the orbits of the giant planets changed. They discovered the innermost portion of the belt became destabilized and could have delivered numerous big impacts to Earth and the moon over long time periods. There were at least 12 mega-impacts during the so-called Archean period 2.5 to 3.7 billion years ago, a formative time for life on Earth. This finding supports the hypothesis for many giant asteroid impacts during Earth's early history.More

National Society of Black Physicists jobs board postings
Kenyon College One-year Visiting Assistant Professor of Physics
Faculty Positions in Science, Technology, and Innovation
NASA Postdoctoral Fellowships
High School Instructor of Physics
Entrepreneurship for Scientists and Engineers in East Africa
Director, South African Astronomical Observatory
Tenure Track (Open Rank) Faculty Position — Stony Brook Center for Science and Mathematics Education
National Astrophysics and Space Science Program
Postdoctoral Research Associate PositionsMore

Latest research from Physica B: Condensed Matter
IOP Journal
Bose–Einstein condensation of a relativistic Bose gas in a harmonic potential

Smearing induced dynamical stability of NbN and MoN in rocksalt structure

Electronic structural properties and formation energy of Sn1−xPbxO2 solid solutions electrode

A comparative study of electronic structure and magnetic properties of SrCrO3 and SrMoO3

Band structures of two dimensional solid/air hierarchical phononic crystalsMore

Latest research from Journal of Physics Education
IOP Journal
Rolling friction on a wheeled laboratory cart

Return trajectory of the SpaceShipTwo spacecraft—numerical solution

The ATLAS detector on a smartphone

An inexpensive digital infrared camera

Making a fish tank cloud chamberMore