Waves & Packets
Apr. 20, 2013

The interesting life of a water molecule caged in a buckyball
American Physical Society
Fullerenes, a carbon allotrope related to graphene and the subject of the 1996 Nobel Prize in Chemistry, are large molecular cages built entirely of carbon atoms. Two years ago organic chemists were able to open a buckyball, insert a water molecule, and then close it back with the water encapsulated therein. Computer simulations of such a water-containing buckball has shown that it responds in a surprising way to an electric field, allowing the whole structure to be driven in either direction through a carbon nanotube. Apparently the buckyball biases the orientation of the water’s permanent dipole moment, and energy needed to bring that about eventually results in linear motion. Surprisingly however, when the electric field reaches a certain critical value, the water molecule flips orientation, owing perhaps to an induced polarity due to the water-fullerene interaction. This research is published in Physical Review Letters.More

Dark lightning sheds light on gamma-ray mystery
Physics World
Scientists at the Florida Institute of Technology say they have found a dramatic new relativistic feedback discharge mechanism that could explain how thunderstorms can produce flashes of gamma radiation. Called "dark lightning", the effect is silent, invisible to the eye and a potential threat to airplane passengers – at least according to the researchers' models. This is because such lightning has the potential to produce intense terrestrial gamma-ray flashes and could deliver a radiation dose equal to a full-body X-ray-tomography scan to nearby air travelers. TGFs are extremely bright pulses of gamma rays emanating from the Earth's atmosphere. They last just a few tenths of a millisecond but are capable of temporarily blinding satellite-based instruments located hundreds of kilometers away. The findings are reported in the Journal of Geophysical Research — Space Physics. More

Why condensed matter physicists should pay attention to atomic physics
American Physical Society
VideoBriefAt the APS March meeting in Baltimore, William Phillips of the Joint Quantum Institute described the many ways that trapped atoms are being used to understand the physics of solidsMore

Scientists make spreadable transistor films
Cornell University
Scientists at the Cornell High Energy Synchrotron Source, Stanford University, and King Abdullah University of Science and Technology have developed a novel process of spreading extremely thin organic transistors, and used synchrotron X-rays to watch how the films crystallize. In work described in Physica Status Solidi Rapid Research Letters, the coating procedure, called solution shearing, is like the buttering of a slice of toast. The “butter” was a solution of a semiconducting molecule called TIPS pentacene. The “toast” was a silicon wafer kept at a specific temperature, and the “knife” was a highly polished edge of a second silicon wafer. The drying dynamics were captured using a high speed x-ray camera. High-speed solution shearing, in which a drop of dissolved material is spread by a coating knife onto the substrate, has emerged as a versatile, yet simple coating technique to prepare high-mobility organic thin film transistors, and is a simple lab-based prototype for large-area slot-die coating. More

Photometric variability discovered in warm, strongly magnetic white dwarf raises new questions
White dwarfs, the final stage of stellar evolution for the vast majority of stars, exhibit a menagerie of spectral characteristics. Types of white dwarfs are classified by their spectral characteristics, with type “DQV” having carbon lines and variable luminosity. One cause of variability in stellar luminosity is boiling at the surface, which causes waves in the stellar core. These waves cause changes in in the star’s shape that are a function of the star’s interior structure. Asteroseismology is a commonly used tool to investigate the interior structure and composition of stars by studying the variability in their luminosity. A team of astronomers have reported variability and spectral data on a new DQV white dwarf in the Sloan Digital Sky Survey, SDSS J1036+6522.

The data, to be reported in the Astrophysical Journal, raise confounding questions about this particular star and the cause of the variability. This DQV white dwarf is significantly cooler than any of the other known DQVs. Cool DQVs are not known to pulsate. The variability is sinusoidal with no higher harmonics, and SDSS J1036+6522 has a significant magnetic field (identified by Zeeman effects in the spectra). Magnetic fields have been suggested to cause nonlinear variability observed in many DQVs. These questions may be resolved through reanalysis of prior data, and/or the development of new theories and hypotheses. More

Researchers make movie of metal complex neighbors jointly moving electrons
Forschungsverbund Berlin e.V.
Applying pulse-probe X-ray methods, researchers at the Max-Born-Institute and the Ecole Polytechnique Federale de Lausanne have observed an extremely fast, electron transfer induced collective motions in ~100 molecular ions in a crystal of transition metal complexes. Such complexes are attractive as primary light absorbers in molecular solar cells and other devices of molecular optoelectronics. Reported in the Journal of Chemical Physics, the time-dependent electron density maps made from X-ray snapshots taken with 100 fs long hard x-ray flashes show that electrons move from the metal atoms (Fe in this case) to its organic ligands (3 bipyridines). Counterions also moved to the bypyridine ligands. Though only one complex in the crystal was directly excited, the X-ray movie shows the many-body character of charge transfer, i.e., a delocalization of the changes in electron density over approximately 30 complexes around the directly excited one. While cooperative effects in other transition-metal complexes have been attributed to entropic origins, to internal pressure, elastic interactions or to strong intermolecular interaction, these new observations of electronic polarons underline the important role played by weakly shielded, long-range Coulombic forces.More

Kepler sees five-planet system with most Earth-like exoplanet yet
University of Washington
Astronomers using NASA’s Kepler space telescope have discovered a 5-planet system that, as reported in Science, contains two exoplanets that may be the best candidates to harbor human life. The new system, Kepler-62, is just one of a backlog of many systems in the Kepler mission data.

The two possibly habitable planets in this system, dubbed Kepler-62e and Kepler-62f, are 1.61 and 1.4 times Earth’s size, respectively. Kepler-62e orbits the star in 122.4 (Earth) days, Kepler-62f in 267.3 days. Kepler-62e gets about 20 percent more solar flux than Earth does. Kepler-62f receives about half as much. Kepler-62 is a K-type star somewhat colder and smaller than our Sun, and is only 1,200 light-years from Earth. In a separate paper, submitted to Astrophysical Journal Letters, researchers show that these planets are the first viable candidates for habitable zone water planets.

In an interview with Waves and Packets, Professor Abel Mendez of the University of Puerto Rico’s Planet Habitability Laboratory said that the habitable zone is the region around a star where an Earth-like planet could support surface liquid water. “We only consider main sequence MKGF stars. Bigger stars are prone to damaging UV,” says Mendez.

UV radiation can dissociate water vapor and make H2 gas. A sequence of events could then evolve where the planetary atmosphere is drawn into the host star. However, Mendez points out that M-stars emit many flares that seem tolerable by planets. More

2 X-ray studies show the importance of particle and void sizes
In two separate studies on two very different materials, scientists have shown the importance of void spaces in the function of materials. In the first study, scientists in Canada looked at air bubbles in gluten-free bread dough using high-resolution X-ray computed tomography. Air bubbles in bread dough are important determinants of the texture of the final product. During the dough mixing process air bubbles get smaller and smaller. Gluten and salt tend to support gas retention, removing either reduces the gas holding properties of the dough. The hope is that this research will help scientists and bakers understand how to make better gluten-free products. Read More

Using a similar technique, researchers at ETH-Zurich used the TOMCAT beamline at Swiss Light Source at the Paul Scherrer Institute to look at the microstructure of battery graphite electrodes. The size, distribution, and configuration of the atoms in the electrode have a major influence on a battery’s discharging and charging speed. Lithium ions that move through the electrode travel a tortuous path. The more tortuous the path, the longer it takes charge and discharge the battery. As reported in Advanced Energy Materials, these researchers found that round to potato-shaped particles mostly have a positive influence on ion flow. Plate-like ones such as those in the anode, provide unfavorable conditions for rapid charge transport. Graphite electrodes also exhibit direction-dependent differences in path length of over 300 percent with a porosity of forty percent. Read MoreMore

National Society of Black Physicists jobs board postings
NASA Postdoctoral Fellowships
Assistant Editor, Physical Review D
Summer Internship
MIT Physics Lecturer/Sr. Lecturer
Martin and Michele Cohen Dean of Science
Visiting Assistant Professor
Wiess Instructorship in Physics and Astronomy
Upper School Physics Teacher
Summer Intern
Postdoctoral Fellowship - Stanford Molecular Imaging Scholars Program
Postdoctoral Fellowship - Stanford Molecular Imaging Scholars Program

Dark lightning sheds light on gamma-ray mystery
Physics World
Scientists at the Florida Institute of Technology say they have found a dramatic new relativistic feedback discharge mechanism that could explain how thunderstorms can produce flashes of gamma radiation. Called "dark lightning", the effect is silent, invisible to the eye and a potential threat to airplane passengers – at least according to the researchers' models.More

Do elliptical galaxies have dark matter halos?
Kepler's laws tell us that stars further from the center of their galaxies should have lower rotational velocities. But rotation curves (plots of velocity vs. distance) of stars in spiral galaxies show that the rotational velocities remain constant as distance from the center increases.More

Are there signs of SUSY in Planck data?
Physics World
Evidence of supersymmetry could be lurking in the cosmic microwave background, according to a UK-based physicist who has calculated how the theory could affect fluctuations in the CMB.More

Latest research from Journal of Physics: Condensed Matter
IOP Publishing
Local electromagnetic properties of magnetic pnictides: a comparative study probed by NMR measurements

Optical second-harmonic generation from two-dimensional hexagonal crystals with broken space inversion symmetry

Neutron diffraction study of the non-Fermi liquid compound CeNiGa 2 : magnetic behaviour as a function of pressure and temperature

Mössbauer spectroscopy of europium-doped fluorochlorozirconate glasses and glass ceramics: optimization of storage phosphors in computed radiography

Surface nanobubbles and micropancakesMore

Latest research from Journal of Chemical Physics
American Institute of Physics
Direct simulation of proton-coupled electron transfer across multiple regimes

Hydrodynamically enforced entropic Brownian pump

Solvation structures of protons and hydroxide ions in water

Electropumping of water with rotating electric fields

Inducement by directional fields of rotational and translational phase ordering in polymer liquid-crystals