Waves & Packets
Mar. 30, 2013

ATRAP reports precise measurements of antiproton magnetic moment and proton spin flip
CERN Press Office
The Antihydrogen TRAP experiment at CERN's Antiproton Decelerator has reported via Physical Review Letters a new measurement of the antiproton magnetic moment made with an unprecedented uncertainty of 4.4 parts per million. This result is 680 times more precise than previous measurements, and matches the data on the proton itself. The accepted value of the proton's magnetic moment is 2.792847356(23). The value for the antiproton determined in this work is −2.792845(12), revealing an equal magnitude and opposite sign as the proton value within experimental uncertainty. The ATRAP team is also reporting a new method for measuring single proton spin flips, which is applicable to antiprotons as well. This new method may make it possible to determine the proton and antiproton magnetic moments with even more precision, perhaps by a factor of 104. Writing in Physics Viewpoint Hudson and Saltzberg describe the significance of this result as "…extending CPT’s shatterproof standing for the time being." Charge-parity-time symmetry is a tenet of the standard model, and violations of the CPT theorem would absolutely alter our understanding of the universe. The CPT theorem is safe for now, but there is a day of reckoning coming as the fundamental reason for the imbalance of matter and antimatter in the universe has yet to be discovered.More

Search for dark matter annihilations in the Sun turn up no muon neutrinos
American Physical Society
One of the most promising and experimentally accessible candidates for dark matter are so-called Weakly Interacting Massive Particles (WIMPs). WIMPs may become gravitationally bound in the Sun where their subsequent decays can be detected as flux of high energy muon neutrinos with a neutrino telescope such as IceCube. In 2009 the IceCube Collaboration reported limits on muon flux from WIMP annihilations from the Sun based on three months of data collection. In a new Physical Review Letters paper IceCube is reporting a comprehensive search for muon neutrinos over a 12 month period with a more advance detector geometry. The collaboration reports no muon neutrinos above background. But they have achieved new limits that strongly constrain dark matter models. More

Are magnetic monopoles in polar volcanic rocks?
American Physical Society
Dirac first proposed the existence of magnetic monopoles in 1931. If they exist, monopoles would have been created as the early universe cooled, and some of them would have subsequently stuck to atomic nuclei with magnetic moments. Magnetic monopoles trapped in the Earth's core would be transported via geophysical fluid dynamics through the mantle and back up to the surface. In this model researchers estimate that monopoles are about six times more plentiful in old rocks at high-latitudes than in the planet as a whole. As reported in Physical Review Letters, passing rock samples through a DC-SQUID magnetometer has set a limit that no more than about one monopole exists per ten kilograms of rock, essentially no monopoles were found. (A lingering current in the coil would be indicative of a monopole.) Over the years researchers have also looked for monopoles in meteorites and the Moon all to no avail. But another approach to find monopoles is through proton collisions, efforts that CMS, ATLAS and MoEDAL are pursuing at CERN.More

Ultrathin 'metascreen' forms latest invisibility cloak
Physics World
The first "mantle" invisibility cloak — in which a very thin "metascreen" cancels light scattering off an object, making it invisible — has been built by a team of researchers in the US and reported in the New Journal of Physics. The cloak is just microns thick and can hide 3-D objects from microwaves in their natural environment, in all directions and from all of the observers' positions. The team claims that its device should be easier to produce than cloaks that depend on the anisotropic bulk permittivity and permeability of the cloaking material. The mantle cloak instead depends upon on an extremely thin "metascreen" that, when struck by incident electromagnetic radiation, produces an electromagnetic field in antiphase to the radiation scattered from the incident object, so making the object invisible. That is, the phase difference between the scattered fields from the cloak and the object being cloaked interfere and cancel each other out. The cloak showed optimal functionality when the microwaves were at a frequency of 3.6 GHz and over a moderately broad bandwidth. The researchers are now hoping to extend the cloak to try to find one that works at visible frequencies, and they also want to look at applications of the technology. More

Evidence for two distinct populations of Type Ia Supernovae
Astrobites
Type Ia supernovae (SNe Ia) are a class of supernovae that do not originate from the collapse of a massive star. Instead, these supernovae are thought to occur from thermonuclear explosions of white dwarfs in binary systems. The white dwarf accretes mass from the binary companion until it reaches the Chandrasekhar mass limit — the maximum mass at which a degenerate white dwarf will be stable. After the mass surpasses this limit, the white dwarf explodes. Because they come from explosions of white dwarfs with the same initial mass, they have constant luminosity, and thus are extremely useful for astronomical distance measurements. Type Ia supernovae are all quite similar to each other, but are not exactly identical. In a new Science paper, a team of astronomers present evidence of two distinct populations: those with high velocity ejecta (>12,000 km/s) and those with normal velocity ejecta (<12,000 km/s). The results suggest that high-velocity SNe Ia likely originate from relatively younger and more metal-rich progenitors than normal-velocity SNe Ia, and are restricted to galaxies with substantial chemical evolution.More

Astrophysicists test cosmological defect detector
The Physics arXiv Blog
One of the current hot topics in cosmology is the possibility that the universe may be filled with topological defects left over from earlier times. The thinking is that soon after the Big Bang, the universe underwent a number of phase transitions in which the laws of physics were broken in various ways. When this happens, certain configurations of matter can end up persisting, becoming 'frozen' for the rest of eternity. These so-called topological defects take the form of monopoles, cosmic strings and domain walls. Nobody has observed these objects but their discovery would be a huge triumph for the theories that predict them. To make these detections, a team of physicists have described a plan to build the Global Network of Optical Magnetometers for Exotic physics, or GNOME, and report their construction and test of a prototype. Until now, the searches for evidence of dark mater have all looked for evidence of impacts between dark matter particles and ordinary matter particles. GNOME looks for an entirely different effect: evidence of the field in which these particles must exist manifest in slight wobbles in the atomic spins of every atom on the planet.More

Scientists propose revolutionary laser system to produce the next LHC
University of Southhampton
In a Nature Photonics paper, an international team of physicists has proposed a revolutionary laser system, inspired by the telecommunications technology, to produce the next generation of particle accelerators, such as the Large Hadron Collider. A useful laser for this purpose would have to operate with a femtosecond pulse rate and petawatt energy levels, a daunting challenge when needed together. The International Coherent Amplification Network sets out a new laser system composed of massive arrays of thousands of fiber lasers, for both fundamental research at laboratories such as CERN and more applied tasks such as proton therapy and nuclear transmutation. A typical CAN laser for high-energy physics may use thousands of fibers. It offers the advantage of relying on well tested telecommunication elements, such as fiber lasers and other components. The fiber laser offers an excellent efficiency due to laser diode pumping. It also provides a much larger surface cooling area and therefore makes possible high repetition rate operation.More

The controversy over metastable liquid phases of water
Physics World
The possibility that liquid water has two different phases dates back to 1992 when a computer simulation of water at temperatures below 198 K and at pressures of several thousand atmospheres found that metastable liquid water can spontaneously separate into two forms. The phase boundary between them ends in a critical point, where the two types of water become indistinguishable. The behavior was seen as the result of a balance between hydrogen bonds holding neighboring water molecules together, and forces that break those bonds. But a different team of researchers claim their computer simulations show only one liquid phase in the metastable region, which eventually freezes to ice. They assert that their simulations are correct because they run past the density has equilibrated (as the first simulations only did), and until the certain order parameters have equilibrated as well. In more recent work by these same researchers using several different atomistic models of water, they further assert that there is but one stable or metastable liquid phase that transitions to an ice-like crystal phase. They suggest that metastability of two distinct liquid phases is actually coarsening of the ordered ice-like phase. Others are not convinced and have found clear computational evidence of two coexisting metastable liquid phases and a stable crystal, all at the same temperature and pressure. More simulations, and importantly experimental investigations, are needed to resolve this controversy.More

Surviving your comprehensive exams
Dynamic Ecology
Quite likely the comprehensive exam (aka qualifying exam) is the most feared moment in an academic's life. This post should: a) be helpful to those who haven't, b) provide a place for survivors to share their advice in one place on the web, and c) help those of us who have students and have to help them navigate it. More

Letter to the editor
Waves and Packets

Dear editor,

The summary paragraph in last week's story about the Planck results makes the implication that emission of the CMB photons was caused by hydrogen recombination. However, the CMB photons are believed to have originated in the first few moments of the universe's existence, well prior to the era of recombination. These photons mediated nuclear reactions in the early universe and impacted the abundances of light nuclei. Hundreds of thousands of years later, first helium recombination and then hydrogen recombination subsequently led to the universe becoming transparent to photons instead of opaque. That is, photons that were previously scattered or absorbed by free protons and electrons were then decoupled from the matter and thus were able to propagate freely through space. Although there are photons that are associated exactly with helium and hydrogen recombination, those photons possess a line spectrum and have far less energy density than the primordial CMB photons that were emitted at the end of the inflationary epoch and whose energy distribution is now a Planck blackbody distribution to high precision.

— Hakeem M. Oluseyi
Department of Physics & Space Sciences
Florida Institute of Technology

Editor's response: We regret the error and have fixed the text in archived story. MoreMore

Admissions criteria and diversity in graduate school
American Physical Society
There are about 180 physics programs listed in the AIP Graduate Programs book. The General GRE is required by 96 percent; a quarter of these have an explicitly stated minimum Quantitative GRE score for admission, with the median stated cut-off being 700. As educators, we naturally expect exams to be meaningful. Most people believe this is the case for the GRE exams, and may thus prefer high scores. But analysis of the data often finds no significant correlation between long-term success and GRE scores. The implications for diversity of using 700 as a minimum acceptable score are that nearly three quarters of Hispanics would be rejected, and significantly more than this for American Indians, African Americans, and Puerto Ricans; similarly, women are filtered out at a higher rate than men. Mixing cut-off scores with these racial and gender disparities sets the foundation of a glass ceiling erected by the lopsided treatment of minorities and women before they even set foot in grad school. More

Your time line for graduate school applications
NSBP
Your time line towards applying to graduate school should begin in earnest in the summer before you are to graduate (assuming you will be graduating after the spring semester and want to go to graduate school right away). In June-August start thinking about what areas of physics interests you, and where you want to be in 5-10 years. You should use your advanced coursework, electives and senior research project to further explore your interests in physics. If you start practicing now your should be able to take the General GRE early in the coming summer. The test is given year-round at computer-based test centers located around the world. The physics subject GRE is still a paper and pencil based test. It is offered in early October, mid-November, and early April. Unless you are really ahead of the game and are ready for the physics GRE next month, you need to key on the fall administrations as the scores for the April 2014 test will not be available in time for an application for the following fall's class. More

National Society of Black Physicists jobs board postings
NSBP
Instructor of Physics - North Carolina School of Science and Mathematics
Upper School Physics Teacher
Full-time Lecturer in Experimental Physics
Summer Internship
Schuler Postdoctoral Fellowship
Postdoctoral Fellowship - Stanford Molecular Imaging Scholars Program
Summer Undergraduate Researcher
POSTDOCTORAL RESEARCH ASSOCIATE POSITIONSMore

ATRAP reports precise measurements of antiproton magnetic moment and proton spin flip
CERN Press Office
The Antihydrogen TRAP experiment at CERN's Antiproton Decelerator has reported via Physical Review Letters a new measurement of the antiproton magnetic moment made with an unprecedented uncertainty of 4.4 parts per million.More

Astronomers find the youngest known protostars yet
Max Planck Institute for Astronomy
Using the Herschel Space Telescope and the submillimetre telescope APEX, a multi-national group of astronomers has discovered the youngest known protostar yet.More

1st cosmology results from Planck mission reveal fluctuations and anisotropies in CMB
European Space Agency
When the Universe first formed it evolved from a very hot, dense plasma of elementary particles; the so-called quark-gluon plasma, to a hot dense soup of interacting protons, electrons and photons at about 3000 degrees Kelvin.More

Latest research from Computational Science & Discovery
IOP Publishing
Utilization of efficient gradient and Hessian computations in the force field optimization process of molecular simulations

A new model for approximating RNA folding trajectories and population kinetics

Understanding the mechanisms of sickle cell disease by simulations with a discrete particle model

Explicit integration of extremely stiff reaction networks: partial equilibrium methods

Explicit integration of extremely stiff reaction networks: quasi-steady-state methods

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Latest research from JASA Express Letters
Acoustical Society of America
Covert underwater acoustic communication using dolphin sounds

Computationally efficient parabolic equation solutions to seismo-acoustic problems involving thin or low-shear elastic layers

Spectral probability density as a tool for ambient noise analysis

Detection of early reflections using multifractals

Information transfer in auditoria and room-acoustical quality

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