Waves & Packets
May. 18, 2013

70's era 'Hofstadter's Butterfly' finally confirmed
The City College of New York
A team of physicists has definitively proven the existence of an effect known as Hofstadter’s Butterfly. The concept goes back to 1976 when Douglas Hofstadter calculated the energy levels of electrons exposed to a magnetic field in a 2D lattice. When plotted, the electronic energy spectrum takes on a complex pattern that resembles a butterfly due to the behavior of electrons under the influence of external magnetic and periodic electric fields. Moreover, the plot is a fractal, indeed one of the first quantum fractals discovered in physics.

The butterfly plot results when parametrically speaking the lattice constant and the magnetic length are commensurate. This parameter space has been hard to reach experimentally, however; and although the butterfly pattern has appeared in physics textbooks as a theoretical concept of quantum mechanics for nearly 40 years, this is the first experimental observation of it. Graphene layers on boron-nitride substrates allow for 2-D crystal structures where the magnetic fields required to observe the butterfly spectrum are more accessible.

The light and dark sections of the pattern, respectively, correspond to light “gaps” in energy level that electrons cannot cross and dark areas where they can move freely. What this means in terms of electrical conductivity and applications remains to be seen. This work is published in Nature. Other groups working on the problem have published their results in Nature and Science.More

First research results with MeerKAT prototype, KAT-7, reveals strong flares in Circinus X-1
Science 2.0
As part of the development of MeerKAT, a scientific test array of 7 dishes, KAT-7, has been constructed and commissioned in South Africa’s Karoo desert. The KAT-7 was originally conceived to be a test platform, but it has performed so well that it is being used to produce new scientific results. A team of South African astronomers have reported new results on Circinus X-1, a bright and highly variable X-ray binary. Circinus X-1 has a ~17 day periodicity in its x-ray brightness with intermittent radio flares. But it also has a longer-term envelope of brightness spanning at least 3 orders of magnitude over a period of ~35-40 years. The causes of these variable x-ray and radio emissions, and the role of the jet accompanying them, are open questions. One suggestion is that there is an ultrarelativistic jet from the core of the object, which would indicate that a black hole is not required in order to produce a highly relativistic jet.

As reported in a paper to appear in the Monthly Notices of the Royal Astronomical Society, the new observations reveal two strong synchrotron-flaring radio sources of Circinus X-1, stronger than those observed earlier this decade and in the last. They are in fact comparable to those observed in the 1970s. The authors suggest that change in the accretion rate is responsible for long-term radio brightness variation and recent dramatic brightening of Circinus X-1.More

Optical flashes could signal birth of black holes
Physics World
The death of a massive star can give rise to the formation of a massive black hole with a telltale gamma-ray burst. But some dying stars are thought to produce a black hole without any kind of flash — seemingly disappearing from the visible sky in an event known as an "unnova". So it has been unclear what a stellar death and black hole birth really looks like. When a star collapses the event leads to an outflow of neutrinos and a reduction of mass. This reduction of mass leads to a strong outward flow of surrounding gas, now suddenly subject to a reduced gravitational force from the star. This strong outflow results in heating, which can be detected, albeit with difficulty, as a characteristic glow. In an analysis published in Astrophysical Journal Letters, a researcher at Caltech is proposing a new observable of unnovas, i.e., an initial flash generated by the shockwave as it hits the outer layers of a red supergiant that would be 10–100 times brighter than the gaseous glow. Such a flash would be more frequent than gamma-ray bursts; would be isotropic instead of beamed; and have peak wavelengths in the ultraviolet and visible spectrum; may have application in a wider diversity of explosive events. This theory is presumably testable through wide-field transient surveys such as those available through Pan-STARRS. MoreMore

New X-ray method peers in to early cell differentiation
Alpha Galileo Foundation
An international team of scientists using a new x-ray method recorded the internal structure and cell movement inside a living frog embryo in greater detail than ever before. Previous methods required a contrast agent and large X-ray dose that can harm living organisms. But the new method, described in Nature, is non-destructive. With this method the researchers were able to watch joint and individual cell movements during the period when embryo cells are becoming differentiated and the organism starts to take form. One manifestation of cellular differentiation is change in the refractive index. As x-rays pass through different types of tissues at variable speeds, diffraction occurs. In turn, this generates a characteristic intensity distribution at a certain distance behind the embryo. Rotating the embryo in a coherent bundle of X-rays produces a microtomographic image.More

New method of finding planets scores its first discovery
Harvard-Smithsonian Center for Astrophysics
The two most prolific techniques for finding exoplanets are radial velocity (looking for wobbling stars) and transits (looking for dimming stars). A team of astronomers has developed a new method that relies on Einstein's special theory of relativity. The new method looks for three small effects that occur simultaneously as a planet orbits the star. Einstein's "beaming" effect causes the star to brighten as it moves toward us, tugged by the planet, and dim as it moves away. The brightening results from photons "piling up" in energy, as well as light getting focused in the direction of the star's motion due to relativistic effects. The team also looked for signs that the star was stretched into a football shape by gravitational tides from the orbiting planet. The third small effect was due to starlight reflected by the planet itself. Altogether, these three effects lead to the BEER algorithm, relativistic BEaming, Ellipsoidal, and Reflection/emission modulations. The team used the BEER algorithm to discover Kepler-76b, now dubbed the "Einstein's planet." It is located about 2,000 light-years from Earth. It is tidally locked to its star, which it orbits every 1.5 days. Its diameter is about 25 percent larger than Jupiter and it is twice as massive. The method and finding are discussed in a paper accepted by the Astrophysical Journal.More

Why does nature form exoplanets so easily?
Thanks to the Kepler Space Telescope, COROT, and ground-based observatories, the number of exoplanets that have been found is large (over 3,000 candidates and 114 confirmed) and growing. There seems to be planets everywhere, and some at least have in the past harbored life-forms that we would recognize. And a few could even harbor human-like creatures today. A recent paper published in American Scientists asks the seemingly simple question, "Why does nature form exoplanets so easily?" This is a basic question that often occupies the minds of "creationists" who claim that scientists do not know how the planets formed. In fact we have two good models of planet formation; the "bottom-up" approach also known as "core accretion", in which small objects combine to form larger objects, and the "top-down" approach also known "gravitational Instability", which involves a large cloud of gas and dust that fragment into smaller chunks. Both models have their challenges, but most of planets detected so far are thought to have been formed by the core-accretion process. More observations and finer classification schemes will certainly reveal more knowledge, but we may be facing a future without Kepler.More

Physicists discover a new kind of friction
Technische Universität München
A team of physicists in Germany has discovered a previously unknown type of friction that they call "desorption stick." In AFM studies of pulling a polymer stand over various test surfaces, they found the two expected friction mechanisms, sliding and sticking. But they also found a very low internal friction within the polymer coil that depended neither on the speed of movement nor on the support surface or adhesive strength of the polymer. The chemical nature of the surface, the solvent and their interaction with the polymer is the determinate factor in internal friction. The details of the study are published in Angewandte Chemie.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. Several former NSF officials have written to Congressman Smith, saying that it is generally impossible to predict which areas of research will eventually be viewed as groundbreaking, and the proposed legislation would require the NSF Director to accurately predict the future. The motivation for the legislation seems to be the feeling that NSF sometimes awards "questionable" grants, i.e., the old "Golden Fleece" characterization of science. Where before only grants in social sciences, biology and environmental science were usually targeted in this way, this new legislation would apply to all of science, engineering, education and human resource development. Though by itself the proposal may have little chance of becoming law, if it is attached to a bill required to be passed in a pinch, like in the case of the amendment that was passed in March and is now affecting political science research, this could be a new requirement for researchers to articulate in their NSF grant applications.More

National Society of Black Physicists jobs board postings
Laboratory Manager I (Instructional Laboratory Manager)
Deputy Division Director, Division of Physics (PHY)
NASA Postdoctoral Fellowships

70's era 'Hofstadter's Butterfly' finally confirmed
The City College of New York
A team of physicists has definitively proven the existence of an effect known as Hofstadter’s Butterfly. The concept goes back to 1976 when Douglas Hofstadter calculated the energy levels of electrons exposed to a magnetic field in a 2D lattice.More

NASA's Fermi, Swift see 'shockingly bright' gamma ray burst
A burst of gamma rays from a dying star has been observed by the Fermi and Swift gamma-ray space telescopes. Gamma-ray bursts are the universe's most luminous explosions.More

Reflection from electron mirror confirms Einstein's thought experiment
Max-Planck-Institut für Quantenoptik
A team of physicists has managed to carry out Einstein’s 1905 Gedankenexperiment where he suggested that reflection from a mirror moving close to the speed of light could in principle result in bright light pulses of short wavelengths.More

Latest research from Europhysics Letters
IOP Publishing
Interaction of atomic quantum gases with a single carbon nanotube<

Geometric signature of complex synchronisation scenarios

Electron pockets and pseudogap asymmetry observed in the thermopower of underdoped cuprates

Symmetry-protected topological phases of alkaline-earth cold fermionic atoms in one dimension

The new phase of HgF2 at high pressure


Latest research from Physical Review Letters
American Physical Society
Midfield Wireless Powering of Subwavelength Autonomous Devices

Generating Far-Field Orbital Angular Momenta from Near-Field Optical Chirality

Bose-Einstein Condensation of Atoms in a Uniform Potential

Surface Plasmon Lasing Observed in Metal Hole Arrays

Observing Rydberg Atoms to Survive Intense Laser Fields

Fundamental Vibration of Molecular Hydrogen