Waves & Packets
Jun. 1, 2013

Redefining the ampere with the help of graphene
Physics World
Researchers in the United Kingdom have created the world's first single-electron graphene pump. The device could be used to redefine the standard unit of current, the ampere, in terms of the electron charge — a fundamental constant of nature. Currently the ampere is defined as the current through two parallel conductors one meter apart that results in a certain force between the two conductors. Making such macroscopic measurements is error prone and depends on the kilogram, which itself is subject to "unsettled" standard. Precision metrologists would like a standard that depends upon transport measurements of a single electron. As described in Nature Nanotechnology the device takes advantage of the low-dimensionality of graphene and the ability to control electron mobility in the material on a per electron basis. Besides closing the so-called quantum metrology triangle, which can lead to determining just how constant Planck's constant really is, the device could represent a significant advance in quantum information processing.More

Astronomers using Chandra, XMM-Newton, Swift and RXTE find hidden exotic neutron stars
Chanda X-ray Observatory
When a massive star runs out of fuel its core collapses to form either a black hole or a neutron star. The gravitational energy released in this process blows the outer layers away in a supernova explosion and leaves the neutron star behind. Most neutron stars are spinning rapidly — a few times a second — but a small fraction have a relatively low spin rate of once every few seconds, while generating occasional large blasts of X-rays. Because the only plausible source for the energy emitted in these outbursts is the magnetic energy stored in the star, these objects are called "magnetars."

In a 3 year observation campaign with 4 different telescopes, astronomers observed magnetar SGR 0418, revealing properties that does not fit with that pattern of similar magnetars. SGR 0418 has a relatively weak surface magnetic field, but it has periodic outbursts of strong fields. This suggests that the magnetic energy is in the star's interior. The crust is weak and periodically cracks releasing the magnetic outburst. If this model is correct then other quiet neutron stars can 'wake up' with a magnetic outburst perhaps once per year. Another model leads to the possibility that a significant fraction of gamma-ray bursts might be caused by the formation of magnetars rather than black holes, and that the contribution of magnetar births to gravitational wave signals would be larger than previously thought. These new results on SGR 0418 are published in the Astrophysical Journal.More

Towards an African telescope network
South Africa.info
South African scientists are working on a project to expand radio astronomy in Africa by recycling disused telecommunications dishes, rendered obsolete by the arrival of fiber optic telecommunications cables, that are spread out over a number of African countries in order to create an African network of radio telescopes. The African VLBI Network project, which is being driven by SKA South Africa and the Hartebeesthoek Radio Astronomy Observatory (HartRAO) near Johannesburg, aims both to fill a major gap in the global VLBI network and, by boosting engineering and science skills development across the continent, to pave the way for the arrival of the SKA. There are at least 26 satellite dishes, possibly more, spread out over Africa that could become a part of the new VLBI network. The engineering processes have already begun on converting a 32-meter satellite communications antenna at Kuntunse in Ghana that was previously owned by Vodaphone Ghana. Conceivably the idea can be extended by transplanting dishes from the US and Europe to Africa, or by buying new ones, or by converting dishes in Asia, the Caribbean, Central and South America. In any case the African VLBI Network will advance global VLBI science by closing the coverage gaps in the existing global array. More

Physicists make new experimental verification of complementarity
Researchers in Australia have demonstrated that, contrary to what the Heisenberg uncertainty relation may suggest, particle properties such as position and momentum can be measured simultaneously with high precision. The Heisenberg Uncertainty Principle suggests that any device used to make simultaneous measurement of complementary variables, i.e., those represented by non-commuting self-adjoint operators, will give inherently imprecise estimates. In 1935 Einstein, Podolsky and Rosen challenged this principle with the famous EPR paradox by considering systems that are quantum mechanically entangled. Subsequently more general articulations of complementarity relations have been expressed over the years. The new result, reported in Physical Review Letters, experimentally verifies universally valid complementarity relations. And by using polarization properties of photons rather than position and momentum, the results show that Einstein, Podolsky and Rosen were correct. More

Preservation of information at the core of black holes
American Physical Society
General relativity predicts that all information about the quantum states of matter is lost at the singularity at the cores of black holes. But one of the basic tenets of quantum mechanics is that information is preserved, thus there is apparently a fundamental incompatibility between general relativity and quantum mechanics, i.e., in quantum gravity, that needs to be resolved. In a new paper published in Physical Review Letters, two physicists show that the quantization in spherically symmetric black holes is indeed possible within the framework loop quantum gravity. Their analysis follows from the supposition that the core of the black hole is a highly curved space-time rather than a singularity. While the resulting quantum space-times resolve the singularity present in the classical theory, further research will be needed to establish whether these results solve the information loss paradox and if the approach may be generalized to other classes of black holes. More

Autonomous spacecraft navigation with pulsars
MIT Technology Review
Navigation of space vehicles gets more and more uncertain the further the vehicles get from Earth. But researchers at the Max Planck Institute for Radio Astronomy in Germany have worked out the practical details for an autonomous spacecraft navigation system using pulsars signals. Pulsars regularly emit radiation in the radio, x-ray and sometimes even gamma regions of the EM spectrum. If a space vehicle could measure the arrival time of pulses from at least three different pulsars and comparing this with their predicted arrival time, it would be possible to work out its position in three-dimensional space. The key is to find a radiation detector that gives good performance at a low weight. It turns out that with today’s technology a suitable radio wave detector would have considerable size and weight. But x-ray detectors offer considerable reductions in both size and weight. In a paper posted on arXiv the researchers describe the basic principles of spacecraft navigation using pulsars and report on the current development status of this novel technology. More

Artificial magnetic monopoles discovered
University of Cologne
A team of researchers in Germany have managed to create artificial magnetic monopoles by merging skyrmions, a topological excitation where a large number of spins organize in compact vortex structures. These magnetic vortices are found in a wide range of chiral magnets, and they influence the movements of the electrons in exactly the same manner as magnetic fields. Prior results showed how to make the skymions visible. These new observations of artificial magnetic monopoles, reported in Science, resulted from asking what happens when the skyrmion lattice is destroyed. When that is done the magnetic vortices coalesce, and when they do the resulting magnetic structures have similar characteristics to the magnetic monopole postulated by Paul Dirac in 1931. It remains to be seen if these magnetic monopoles in materials can really be related to subatomic monopoles, but control of skyrmion phases could likely have applications in spintronic devices. More

Near-IR tool may enable brain mapping
Optics and Photonics News
Physicists at the University of Texas — Arlington have developed a two-photon optogenetic tool that could help map out neurons and track their interactions in different areas of the brain. In previous work, the researchers used a tiny near-infrared tool to stimulate a light-sensitive protein in living cells and neurons of the brain. In their new work, reported in Optics Letters, they introduced the gene for a protein that is responsive to light into an ex vivo sample of excitable tissue cells. They then used a fiber-optic NIR beam of light to precisely excite a neuronal circuit in the tissue. They could then observe responses in the excited area and other parts of the neural circuit. This could be a very useful tool in the brain mapping initiative underway in the US, Europe and China, as well as in large number of photonic diagnostic tests.More

Photoionization microscopy directly maps out hydrogen wave function
American Physical Society
A multi-national team of physicists have directly imaged the nodal structure of a hydrogen atom's wave function in a static dc field. As reported in Physical Review Letters, the researchers exposed a beam of hydrogen atoms to a transverse laser field that excited the electrons to 2s and 2p orbitals. The presence of the dc field places the Rydberg electron above the classical ionization threshold but below the field-free ionization energy. The electron cannot exit against the dc field, but it is a free particle in many other directions. Projections of different electron trajectories combine to make interference patterns, and the researchers utilized an electrostatic lens to magnify the outgoing electron wave without disrupting its quantum coherence. The measured interference pattern matches the nodal features of the hydrogen wave function, which can be calculated analytically. The demonstration establishes the microscopy technique as a quantum probe and provides a benchmark for more complex systems. Having made this demonstration for Stark states, the team plans to do so for Zeeman states next. More

Will a gas cloud light up black holes in our galactic center in September?
BBC News
A giant cloud of gas is headed towards the center of the Milky Way galaxy. On its path towards the galactic center, the cloud may reveal many unseen black holes as they accrete and heat the gas, emitting x-ray radiation in the process. In a paper published in Physical Review Letters, astronomers estimate that there should be should about 10 interactions with 'intermediate mass' black holes that may be detectable by x-ray space telescopes such as Chandra or NuStar, with the first encounters happening around September 2013.More

South Africa becomes a full member of the European Synchrotron Radiation Facility
Last week South Africa became the 20th country to join the ESRF. The synchrotron user community in South Africa is small but has had some spectacular successes in the last few years. In 2011, a research team from the University of Witwatersrand and Indiana University used ESRF beamlines ID17 and ID19 beamlines to study the brain cavities of 2 million year old fossils of Australopithecus sediba. That work was published in Science. Sasol, a South African chemical company, used ESRF to study one of its proprietary Fischer-Tropsch catalysts under realistic reactor conditions to better understand the chemical transformations on a micro and nano scale. And South African biophysicists have long used ESRF for structural biology work, and last year made a significant contribution to understanding a potential drug target against tuberculosis infection. South Africa is developing roadmap toward building its own third general light source, and the community is also developing complementary capabilities in neutron science at the SAFARI-1 research reactor. More

ALPHA reports first direct analysis of how antimatter is affected by gravity
Physics World
Current theoretical arguments predict that hydrogen and antihydrogen atoms have the same mass and should interact with gravity in the same way.More

Proposed bill would regulate NSF research funding
Ars Technica
US House Science Committee's chair, Lamar Smith has floated a bill that would require the head of the NSF to certify that every single grant funded was either in the national interest or groundbreaking.More

Einstein's gravity theory passes toughest test yet
National Radio Astronomy Observatory
A newly-discovered system containing a pulsar and its white-dwarf companion has put gravitational theories to the most extreme test yet. The two objects orbit each other once every two and a half hours.More

National Society of Black Physicists jobs board postings
Postdoctoral position in Astrophysics/Astroparticle Physics
Wiess Instructorship in Physics and Astronomy, Rice University
Tenure Track Position in Microsystems/Nanomaterials at the University of Wisconsin-Plattevillev
Faculty Positions in Science, Technology, and InnovationMore

Latest Research From Measurement Science and Technology
IOP Publishing
Submillimetric GPS distance measurement over short baselines: case study in inner consistency

Thin-film thickness profile measurement using a Mirau-type low-coherence interferometer

Simultaneous measurement of refractive index and thickness of transparent material by dual-beam confocal microscopy

Thickness measurement of transparent plates by wavelength stepping and a phase unwrapping algorithm

Calibration of a fluxgate magnetometer array and its application in magnetic object localization

Dynamic characterization of satellite assembly for responsive space applications

Method for acceleration measurement using a laser Doppler interferometer

Feasibility analysis of an achromatic quarter wave plate in a static polarizing wind imaging interferometer

Enhancing the signal-to-noise ratio of pressure sensitive paint data by singular value decomposition

Surface temperature measurements in a porous media burner using a new laser-induced phosphorescence intensity ratio technique More

The Latest Research From the Review of Scientific Instruments
AIP Publishing
Cryogenic cooling with cryocooler on a rotating system

Compact inline optical electron polarimeter

The role of lock-in phase setting in ac susceptibility measurement

First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE

Rapid thermal conductivity measurements for combinatorial thin films

Versatile plug flow catalytic cell for in situ transmission/fluorescence x-ray absorption fine structure measurements

Magnetic field calculation for a 10 MeV positron emission tomography cyclotron

Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses