Waves & Packets
Jan. 26, 2013

Physicists confirm surprisingly small proton radius
The Paul Scherrer Institute
The initial results puzzled the world three years ago: the charge radius of the proton measured in exotic hydrogen, in which the electron orbiting the nucleus is replaced by a negatively charged muon, yielded a value significantly smaller than the one from previous investigations of regular hydrogen or electron-proton-scattering. Protons, which contain of 3 quarks held together by gluons, actually have internal geometric, electronic and magnetic structures. Those structures can presumably be changed under the influence of a muon, which is more massive than an electron, but is carries the same charge as an electron.

A new measurement by the same team, reported in Science, confirms the value of the proton’s electric charge radius, and for the first time determined the magnetic radius of the proton via laser spectroscopy of muonic hydrogen.

Physicists around the world have been actively seeking a solution to the proton size puzzle. Previous measurements in regular hydrogen and by electron-proton-scattering are being reanalyzed and even repeated. Theorists of various disciplines suggested ways to explain the discrepancy. Very interesting proposals explain the discrepancies by physics beyond the standard model. Other explanations suggest a proton structure of higher complexity than assumed today that only reveals itself under the influence of the heavy muon.More

Just how does graphene convert light into electricity?
Nanotech Web
Graphene is very good at absorbing light over a very wide range of wavelengths, ranging from the visible to the infrared. III-V semiconductors do not work over such a wide range. Researchers are unsure as to the exact mechanisms behind graphene's unusual photo-response, believing that any combination of five different mechanisms — photovoltaic, thermoelectric, bolometric, photo-desorption of oxygen, or phototransistor amplification — may be at play. Recent photoconductivity experiments on graphene transistors, reported in Nature Photonics, have now revealed that photovoltaic and a photo-induced bolometric effect dominate the photo-response due to hot photo-carrier generation and subsequent lattice heating through electron-phonon cooling channels. These hot carriers produce photovoltaic current, but lattice heating produces a bolometric current in the opposite direction. Balances between the two mechanisms can be manipulated by doping and back gate voltages. More

Laser doppler cooling proposal may aid spectroscopy on anti-hydrogen
Physics World
In paper appearing in the Journal of Physics B, a team of physicists is proposing a method to Doppler-cool magnetically trapped anti-hydrogen atoms. Physicists working on CERN's ALPHA experiment have been steadily capturing and storing significant amounts of anti-hydrogen since 2010. In 2011 they were able to stably trap anti-hydrogen atoms for 1,000 seconds. With that long lifetime, in 2012 they were able to make measurements of resonant quantum transitions. (The atomic spectra of anti-hydrogen compared to that of hydrogen may help explain why there is more matter than anti-matter in the universe.) This proposed method of laser cooling would reduce the energy of the anti-atoms from 500 millikelvin to 20 millikelvin, thus reducing the line-broadening effects during spectroscopy. This proposal overcomes challenges left in previous proposals by reducing the number of lasers needed to achieve the objective, and also reducing the pulse times.More

Physicists debut new compact source for neutrons
American Physical Society
Physics working in Germany and the Los Alamos National Lab have recorded the first radiograph with a laser-neutron source. Intense neutron sources are generally either nuclear reactor based like ILL, or accelerator based like SNS. In the current work, reported in Physical Review Letters, the team used the TRIDENT laser at LANL to generate neutrons in a two-step process. Short laser pulses strike a thin, deuterium-rich plastic target, accelerating electrons to high enough speeds to knock out a stream of deuterons. The deuterons travel five millimeters to a stout beryllium rod, where they undergo nuclear reactions that produce neutrons. The source itself is small enough to pack into a suitcase, while sufficiently powerful lasers could easily fit on a lab bench. More

Increase your options for graduate or REU program admissions
The NSBP GradApps and REUApps services are open to all students and allows them to upload all the elements of an admissions application, including academic and work history, transcripts, letters of recommendation and a personal statement. Graduate and REU programs can subscribe to these databases to increase the programs' applicant pool, while at the same time allowing students can put their credentials in front of more programs than to which they would otherwise apply. More

New observation of stellar explosion could be sign of dual-core star
Ars Technica
Binary stars have attract each other gravitationally. At some point they could get so close to each other that they share a common envelope but still having separated cores, a so-called common envelop event. But heretofore there has not been any direct evidence of such events. In Science a team of astronomers are suggesting that some intermediate luminosity red transients may indeed be examples of such stellar events, a conclusion they reached by modeling of recombination of electrons and ions in the plasma when the stars' envelopes merge. The researchers compared their model both to V838 Monocerotis and V1309 Scorpii, two separate events long believed to be binary star mergers. Their predictions matched both the luminosity and duration of the events, lending strong support to the idea that these were caused by common envelope events. More

Novel cells of indium phosphide nanowires produce impressive photovoltaic efficiency
Nature News
A research team in Sweden has fabricated cells of nanowire antennae that can turn nearly 14 percent of the incoming light into electricity. Though flat conventional InP solar cell devices have shown upwards of 22 percent efficiency, those systems had much more material space density. As reported in Science, the new devices were fabricated by depositing gold flecks on a semiconductor substrate and then using vapor solid growth to make filaments that are roughly 1.5 micrometers tall and 180 nanometers wide. In this configuration plasmon resonances tend to increase photo-adsorption efficiency. The wires act as antennae and thus it is believed that more photons can actually be absorbed with less photo-collecting material. Tuning the wire heights and diameters may lead to cells optimized for absorption of specific wavelengths. Then a multi-junction photocell can collect a broader spectrum of solar radiation. More

On the hot, irradiated center of our galaxy
At the center of our galaxy there are dense clouds of molecular gases, copious stars forming and dying, and of course a central supermassive black hole. The combined effects of the various gravitational forces and radiation emissions from stellar activity stretch and contract the cloud shapes, subsequentially heating them. In fact clouds near the galaxy center can be as much 200K, or 20 times hotter than clouds that are closer to Earth. A team of astronomers have used the Atacama Pathfinder telescope to take rotational spectra of formaldehyde in gas clouds in the central 100 parsecs of the galaxy, which can be mapped to their temperatures. Spectra from 22 different positions indicate gas temperatures from 50 K to over 100 K, with a typical temperature of 85 K. There are reasons to exclude the possibilities that UV or x-ray radiation could be heating the gas. However, cosmic rays and mechanical heating due to turbulence remain viable causes. More refined studies that resolve the dynamic and ionization structures of the clouds will reveal which is the more dominant cause. This work is published in Astronomy & Astrophysics. More

Physicists achieve breakthrough in single-photon detector
Karlsruhe Institute of Technology
Ultrafast, efficient, and reliable single-photon detectors are among the most sought-after components in photonics and quantum communication, which have not yet reached maturity for practical applications. But an international team of physicists has achieved a decisive breakthrough by integrating single-photon detectors with nanophotonic chips. Described in Nature Communications, the detector combines near-unity detection efficiency with high timing resolution and has a very low error rate. The detector consists of superconducting niobium nitride nanowires fabricated directly on top of a nanophotonic waveguide, which is fabricated directly on a chip. When a photon is absorbed, the nanowire’s superconductivity is lost, which is detected as an electric signal. The probability of detection increases with increasing waveguide length. The device has only been tested using telecommunications wavelengths (~1550 nm), but the architecture can be used for visible wavelengths, making it an important tool for astronomy, biophysics, and single-molecule spectroscopy. More

Pulsar that alternates between x-ray and radio emissions puzzles astronomers
University of Manchester
A pulsar that is able, without warning, to dramatically switch from predominantly emitting x-ray pulses to emitting a highly-organized pattern of radio pulses has astronomers stumped. Observations reported in Science show that the emission type flips on a roughly half-hour timescale. Astronomers have known for some time that some radio-emitting pulsars suddenly and unpredictably change the pattern and intensity of their radio pulses. It is also known that a handful of radio pulsars can also be detected at x-ray frequencies. However, the x-ray signal is so weak that nothing is known of its variability. Combining observations of pulsar PSR B0943+10 from the XMM-Newton, LOFAR and GMRT telescopes, a large team of astronomers observed that the two types of emissions changed simultaneously, and that when one was weak the other was bright. Surprisingly there seems to be a locked intensity relationship in that when the brightness of the radio emission halved, the x-ray emission brightened by a factor of two. The researchers were also able to determine that the weak x-ray emissions have pulse-like character. The mechanisms of these phenomena, be it the equation of state of the star's interior or its mechanical rotation, are totally open questions. More

Physics solves mystery of 380-year-old Rembrandt
Brookhaven National Lab
Old Man in Military Costume was painted by Rembrandt in the years 1630-31. Long ago art denizens as well as materials scientists spotted another portrait lurking beneath the painting, but it was only faintly distinguishable using available methods. The painting has been previously investigated with infrared, neutron and conventional X-ray methods — without a satisfactory result. Researchers at BNL and DESY have developed macro X-ray fluorescence analysis (MA-XRF), a relatively new method to examine a painting that has two layers like the Rembrandt. The method allows scientists to determine the chemical composition of the surface and the layers below. By scanning the whole painting with an X-ray beam, it is possible to see the layer beneath a repainted picture in a way that is non-destructive. So far they have only tested the method on a mock-up sample of the painting provided by the Getty Museum in Los Angeles. Comparison of tests on the mock paint done at DESY, NSLS and using a portably x-ray source show that MA-XRF can yield results that heretofore have not been obtainable. This work is reported in the Journal of Analytical Atomic Spectrometry. More

National Society of Black Physicists jobs board postings
Caribbean Science Foundation - Student Program for Innovation in Science and Engineering
Carl Albert Rouse Research Fellowship for Undergraduates
Victor M. Blanco Research Fellowship for Undergraduates
LIGO Summer Undergraduate Research Fellowship (SURF)
Vacuum Equipment Group Leader
Visiting Assistant Professor of Physics
WIPAC Director
Tenure-Track Faculty Position in Experimental Plasma Physics
Undergraduate Research Assistantship
NanoJapan: International Research Experience for Undergraduates
Research Experiences for Undergraduates: Materials Physics at the University of Florida
Astronomy/Astrophysics Grad Student Summer Researcher at National Solar Observatory in India
Summer Research Student
NASA Postdoctoral Fellowships
Faculty Position in Astrophysical Dynamics
REU summer program on complex materials
Assistant Professor of Physics-Tenure Track Bates College
REU Student
National Radio Astronomy Observatory Research Experience for Undergraduates More

Latest research from Journal of Physics D: Applied Physics
IOP Publishing
Hydrogenation enabled scrolling of graphene

ESR and TSL study of hole capture in PbWO 4  : Mo,La and PbWO 4  : Mo,Y scintillator crystals

High quality of IWO films prepared at room temperature by reactive plasma deposition for photovoltaic devices

Atmospheric pressure plasma jet annealed ZnO films for MgZnO/ZnO heterojunctions

Ferromagnetism at room temperature of c - and m -plane GaN : Gd films grown on different substrates by reactive molecular beam epitaxy


Latest research from Physical Review Letters — Editor's Suggestions
American Physical Society
Pseudospin-Resolved Transport Spectroscopy of the Kondo Effect in a Double Quantum Dot

Quantum Heating of a Nonlinear Resonator Probed by a Superconducting Qubit

Pinning of Fermionic Occupation Numbers

Effects of Particle Shape on Growth Dynamics at Edges of Evaporating Drops of Colloidal Suspensions

Self-Assembled Nanowires with Giant Rashba Split Bands