Waves & Packets
Jun. 30, 2012

X-ray pulses lead to better models of matter under extreme conditions
Stanford National Accelerator Laboratory
When an X-ray laser pulse hits a sample, the photons quickly strip away electrons from the innermost shells of the sample's atoms. In a process known as Auger decay, other electrons quickly fall in to fill the holes, only to be hit by subsequent photons and ejected in turn. Eventually the sample absorbs so much energy that it turns into a hot plasma and flies apart. In order to identify the kinetics and mechanism of the exact process it is necessary to collect information on the sample before the damage from the X-rays sets in, a technique known as "diffract before destroy." In work reported in Physical Review Letters a team at SLAC found that in a nanocluster of argon the Auger decay process was delayed, i.e., it took just a little longer than predicted for outer electrons to fall in and fill holes in atoms' inner shells. During the brief time the holes remained open, the atom was essentially "transparent" to further damage from the laser beam, because it had no electrons in position to be stripped away. This fundamental work can have wide implications ranging from plasma physics to matter in extreme conditions such as in astrophysical settings. More

New method allows direct measurement of orbit, mass and atmospheric properties of exoplanets
European Southern Observatory
For the first time a clever new technique has allowed astronomers to study a nontransiting exoplanet in detail. The exoplanet, Tau Boötis b, does not pass between Earth and its parent star meaning that astronomers cannot use the "transit method" where they would look for small dips in the star's light-curve that occur when a planet crosses between it and the observing instrument, and where scientists can sometimes can do spectroscopy. Instead the team used a new method and ESO's Very Large Telescope to directly catch the faint glow from Tau Boötis b, teasing out the weak signal of the planet from the much stronger one from the parent star. This method uses the velocity of the planet in orbit around its parent star to distinguish its radiation from that of the star and also from features coming from the Earth's atmosphere. Amongst their determinations, reported in Nature, are the mass of the planet, its orbital tilt angle, its atmospheric composition and temperature, which surprisingly gets cooler with increasing height above the planet's surface. This particular result is the exact opposite as found for other hot Jupiter exoplanets. More

Astronomers pinpoint elusive galaxy after a decadelong hunt
Max Plank Institute of Astronomy
An international team of astronomers has managed for the first time to determine the distance of the galaxy HDF850.1, well known among astronomers as being one of the most productive star-forming galaxies in the observable universe. While the galaxy is invisible to optical telescopes like Hubble, it is by far the brightest source of submillimeter emission in the Hubble Deep Field, indicating that prodigious star formation is happening in the galaxy. Recent upgrades to the IRAM interferometer in the French Alps, which acts like a gigantic millimeter telescope, allowed the team to collect the spectral lines from HD850.1 that are necessary for an accurate distance measurement. The distance from Earth turns out to be 12.5 billion light-years. And knowing the distance, the researchers were also able to put the galaxy into context. HDF850.1 turns out to be part of a group of around a dozen protogalaxies that formed within the first billion years of cosmic history — only one of two such primordial clusters known to date. This work is reported in Nature. More

SETI on the SKA: Can the Square Kilometer Array be used to hunt for extraterrestrial signals?
Astrobiology Magazine
The science goals of the Square Kilometer Array are primarily for seeking neutral hydrogen in the early universe, for examining emission from pulsars and black holes and exploring cosmic magnetism. But the interim director of the SKA telescope says that the search for extraterrestrial intelligence, SETI, is on the list of SKA science cases and he expects to receive competitive proposals for SETI projects. SETI searches have rarely been attempted on very long baselines, the first was reported only earlier this year. The very long baselines available in SKA would eliminate terrestrial radio interference problems that plague SETI and any other short-baseline observations. Moreover, the SKA will reportedly be sensitive enough to detect airport radar at 50 to 60 light years away. Though there are many variables about any possible extraterrestrial life that could make an SKA based ET search futile.More

Physicists watch individual viruses infecting individual bacteria
California Institute of Technology
Using single-molecule fluorescence, a team of biophysicists at Caltech have been able, for the first time, to watch viruses infecting individual bacteria by transferring their DNA, and to measure the rate at which that transfer occurs. Shedding light on the early stages of infection by this type of virus, the scientists have determined that it is the cells targeted for infection, rather than the amount of genetic material within the viruses themselves, that dictate how quickly the bacteriophage's DNA is transferred. This study also sheds light on the problem of polymer translocation more generally. The work is reported in Current Biology. More

Stretching graphene makes quantum dots
Physics World
Physicists at the National Institute of Standards and Technology have modified the electrical properties of graphene simply by stretching the material. The team created a system where graphene membranes were stretched over a patterned insulating substrate which was itself over a conducting plate. They were able to stretch the graphene by applying a voltage to the plate below and an AFM tip above. The counteracting forces introduced strain in the graphene, and the researchers observed that when they pulled the graphene membrane into the tentlike shape, the region at the apex acted just like a quantum dot. They were also able to determine that the electron trajectories in the stretched graphene were more like circles instead of the usual straight lines, and in that regard it was as if the sample had been exposed to a magnetic field. The research is reported in Science. More

X-ray vision exposes aerosol structures
Stanford National Accelerator Laboratory
Researchers at SLAC have captured the most detailed images to date of airborne soot particles, a key contributor to global warming and a health hazard. The images reveal the particles' surprisingly complex nanostructures and could ultimately aid the understanding of atmospheric processes important to climate change, as well as the design of cleaner combustion sources, from car engines to power plants. In this particular study, published in Nature, the researchers found that soot particles are like magnetized snowflakes, no two are alike and they have an array of fractal dimensions. This work also pioneers an important new method for studying soot and similar particles that are difficult to image while airborne, and tend to clump together and lose their shape when placed on a surface for examination under a microscope.More

RHIC bags a Guinness World Record
Brookhaven National Lab
When the Relativistic Heavy Ion Collider collides gold ions at nearly the speed of light, the impact energy becomes so intense that the neutrons and protons inside the gold nuclei "melt," releasing fundamental quarks and gluons that then form a nearly friction-free primordial plasma that only existed in nature about a millionth of one second after the Big Bang. RHIC discovered this primordial, liquidlike quark-gluon plasma and measured its temperature at around 4 trillion degrees Celsius — that's 250,000 times hotter than the center of the sun. This is the highest temperature ever recorded, thus the recognition by Guinness. But it turns out that the LHC may well have achieved this temperature and more. The energy density at the LHC is a factor of three higher than at RHIC, which translates to a 30 percent increase in absolute temperature compared to the value achieved by RHIC. But the ALICE experiment, which also studies quark-gluon plasma, has not yet published an official temperature measurement of its quark-gluon plasma.More

Physicists expand the limits of the nuclear landscape
University of Tennessee
Using nuclear density functional theory calculations, physicists have dramatically widened the frontier of the nuclear landscape, i.e., the plot of isotopes that indicate whether they are known, observed, natural, exotic, stable or unstable. There are 288 nuclei found in nature with another 3,000 having been synthesized in the laboratory by adding protons or neutrons to stable nuclei. In the current work, which is reported in Nature, researchers have determined that there are about 7,000 possible combinations of protons and neutrons allowed in bound nuclei with up to 120 protons (a hypothetical element called "unbinilium"). With these new predictions it becomes possible to seriously think of "designer nuclei." For example, a pear-shaped radium-225, with 88 protons and 137 neutrons, will help us understand why there is more matter than antimatter in the universe; and terbium-149, with 65 protons and 84 neutrons, has shown an ability to attach to antibodies and irradiate cancer cells without affecting healthy cells. These new calculations also shed light into the beta decay processes in supernovas and neutron stars. More

National Research Council presents long-term priorities for US nuclear physics program
Science Daily
The National Research Council has released the report, "Nuclear Physics: Exploring the Heart of the Matter," which outlines what should be the priorities in the U.S. nuclear physics program. The report outlines the impressive accomplishments of the field in the last decade and recommends a long-term strategy for the future. Recommended priorities for the future include exploiting recent upgrades of nuclear physics facilities, the timely completion of the Facility for Rare Isotope Beams, the development and implementation of a targeted program of underground science, and the creation of two national competitions for graduate students and postdoctoral researchers. The report also advises the theoretical nuclear science community to develop a plan for exploiting the rapidly increasing power of modern computing, and to establish the infrastructure and collaborations now in order to take advantage of these capabilities as they become available. More

Latest edition of the 'Particle Physics Bible' now online
Lawrence Berkeley Laboratory
The International Particle Data Group and Lawrence Berkeley Laboratory have made available the 2012 Web edition of the Review of Particle Physics, which has been compiled and issued every two years since 1957. The publication is a panorama of the world of high energy and astroparticle physics, and is often referred to as "the Bible" of particle physics. It is chock full of results from experiments at the Large Hadron Collider and contains the latest data on Higgs bosons, supersymmetry, B mesons and much more. Many other areas are covered, including neutrino experiments, whose latest results tell us much about the mysterious properties of neutrino oscillation, in which the three types or "flavors" of neutrinos morph back and forth into one another. The new edition also reviews the status of cosmology research, with summaries of the latest results on the Big Bang, dark matter, dark energy and the early universe. More

Teaching general relativity to undergraduates
Physics Today
General relativity lies at the heart of a wide variety of exciting astrophysical and cosmological discoveries. The Laser Interferometer Gravitational-Wave Observatory and the Virgo interferometer are expected to see gravitational waves within a few years, which will be an important confirmation of general relativity in its own right. The global positioning system, which students regularly use, requires general relativity to ensure its meter-scale accuracy. Undergraduate students are taking notice of all of this and it is piquing their desire to know more about general relativity. Nelson Christensen and Thomas Moore explore teaching methods and available materials for successfully including general relativity in the undergraduate physics curriculum.More

National Society of Black Physicists jobs board postings
NSBP
Faculty Position in Astrophysics
Faculty Position in Biophysics
Assistant Professor of Astrophysics
Tenure-Track Faculty Position in Computational Materials Physics
Assistant Scholar/Scientist
Tenure-Track Faculty Position in Experimental Fusion Plasma Physics
Accelerator Physicist/Engineer (Research Associate)
SKA Project Scientist
3x Senior Astronomers — SKA Africa
National Astrophysics and Space Science Program
Postdoctoral Research Associate PositionsMore

Latest research from Research in Astronomy and Astrophysics
IOP Publishing
Spectroscopic study of globular clusters in the halo of M31 with the Xinglong 2.16 m telescope II: dynamics, metallicity and age

The LEGUE input catalog for dark night observing in the LAMOST pilot survey

The LEGUE disk targets for LAMOST's pilot survey

The nature of the companion of PSR J1719-1438: A white dwarf or an exotic object?

LAMOST Experiment for Galactic Understanding and Exploration — The survey's science plan More

Latest research from Physica Medica
Elsevier
The Education and training of clinical medical physicists in 25 European, 2 North American and 2 Australasian countries: Similarities and differences

Impact of miscentering on patient dose and image noise in X-ray CT imaging: Phantom and clinical studies

Validation of a Monte Carlo simulation for dose assessment in dental cone beam CT examinations

5-year experience of quality control for a 3-D LSO-based whole-body PET scanner: Results and considerations

Modelling the influence of thermal effects induced by radio frequency electric field on the dynamics of the ATPase nano-biomolecular motorsMore