Surface plasmon in 2D Anderson insulator with interactions

We study the effect of interactions on the zero-temperature a.c. conductivity of 2D Anderson insulator at low frequencies. We show that the enhancement of the real part of conductivity due to the Coulomb correlations in the occupation numbers of localized states results in the change of the sign of imaginary part within a certain frequency range. As a result, the propagation of a surface plasmon in a localized system becomes possible. We analize the dispersion law of the plasmon for the two cases: unscreened Coulomb interactions and the interactions screened by a gate electrode spaced by some distance from the electron plane.Comment: latex 22 pages + 2 uuencoded figure

From Anderson to anomalous localization in cold atomic gases with effective spin-orbit coupling

We study the dynamics of a one-dimensional spin-orbit coupled Schrodinger particle with two internal components moving in a random potential. We show that this model can be implemented by the interaction of cold atoms with external lasers and additional Zeeman and Stark shifts. By direct numerical simulations a crossover from an exponential Anderson-type localization to an anomalous power-law behavior of the intensity correlation is found when the spin-orbit coupling becomes large. The power-law behavior is connected to a Dyson singularity in the density of states emerging at zero energy when the system approaches the quasi-relativistic limit of the random mass Dirac model. We discuss conditions under which the crossover is observable in an experiment with ultracold atoms and construct explicitly the zero-energy state, thus proving its existence under proper conditions.Comment: 4 pages and 4 figure

Influence of parallel magnetic fields on a single-layer two-dimensional electron system with a hopping mechanism of conductivity

Large positive (P) magnetoresistance (MR) has been observed in parallel magnetic fields in a single 2D layer in a delta-doped GaAs/AlGaAs heterostructure with a variable-range-hopping (VRH) mechanism of conductivity. Effect of large PMR is accompanied in strong magnetic fields by a substantial change in the character of the temperature dependence of the conductivity. This implies that spins play an important role in 2D VRH conductivity because the processes of orbital origin are not relevant to the observed effect. A possible explanation involves hopping via double occupied states in the upper Hubbard band, where the intra-state correlation of spins is important.Comment: 10 pages, 4 jpeg figure

Electron beam induced radio emission from ultracool dwarfs

We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters and different magnetic field strengths for a relatively small region and short time-scale in an attempt to interpret the recent discovered intense radio emission from ultracool dwarfs. We find that a large amount of electromagnetic field energy can be effectively released from the beam-driven ECM, which rapidly heats the surrounding plasma. A rapidly developed high-energy tail of electrons in velocity space (resulting from the heating process of the ECM) may produce the radio continuum depending on the initial strength of the external magnetic field and the electron beam current. Both significant linear polarization and circular polarization of electromagnetic waves can be obtained from the simulations. The spectral energy distributions of the simulated radio waves show that harmonics may appear from 10 to 70$\nu_{\rm pe}$ ($\nu_{\rm pe}$ is the electron plasma frequency) in the non-relativistic case and from 10 to 600$\nu_{\rm pe}$ in the relativistic case, which makes it difficult to find the fundamental cyclotron frequency in the observed radio frequencies. A wide frequency band should therefore be covered by future radio observations.Comment: 10 pages, 19 figures, accepted for publication in the Astrophysical Journa

Dynamics of a quantum particle in low-dimensional disordered systems with extended states

We investigate the dynamics of a quantum particle in disordered tight-binding models in one and two dimensions which are exceptions to the common wisdom on Anderson localization, in the sense that the localization length diverges at some special energies. We provide a consistent picture for two well-known one-dimensional examples: the chain with off-diagonal disorder and the random-dimer model. In both cases the quantum motion exhibits a peculiar kind of anomalous diffusion which can be referred to as bi-fractality. The disorder-averaged density profile of the particle becomes critical in the long-time regime. The $q$-th moment of the position of the particle diverges with time whenever $q$ exceeds some $q_0$. We obtain $q_0=2$ for off-diagonal disorder on the chain (and conjecturally on two-dimensional bipartite lattices as well). For the random-dimer model, our result $q_0=1/2$ corroborates known rigorous results.Comment: 20 pages, 12 figures, 1 table. Note added on the recent work by Lepri et a

Ballistic nanofriction

Sliding parts in nanosystems such as Nano ElectroMechanical Systems (NEMS) and nanomotors, increasingly involve large speeds, and rotations as well as translations of the moving surfaces; yet, the physics of high speed nanoscale friction is so far unexplored. Here, by simulating the motion of drifting and of kicked Au clusters on graphite - a workhorse system of experimental relevance -- we demonstrate and characterize a novel "ballistic" friction regime at high speed, separate from drift at low speed. The temperature dependence of the cluster slip distance and time, measuring friction, is opposite in these two regimes, consistent with theory. Crucial to both regimes is the interplay of rotations and translations, shown to be correlated in slow drift but anticorrelated in fast sliding. Despite these differences, we find the velocity dependence of ballistic friction to be, like drift, viscous

Implementation of an innovative, integrated electronic medical record (EMR) and public health information exchange for HIV/AIDS

Louisiana is severely affected by HIV/AIDS, ranking fifth in AIDS rates in the USA. The Louisiana Public Health Information Exchange (LaPHIE) is a novel, secure bi-directional public health information exchange, linking statewide public health surveillance data with electronic medical record data. LaPHIE alerts medical providers when individuals with HIV/AIDS who have not received HIV care for >12 months are seen at any ambulatory or inpatient facility in an integrated delivery network. Between 2/1/2009 and 1/31/2011, 488 alerts identified 345 HIV positive patients. Of those identified, 82% had at least one CD4 or HIV viral load test over the study follow-up period. LaPHIE is an innovative use of health information exchange based on surveillance data and real time clinical messaging, facilitating rapid provider notification of those in need of treatment. LaPHIE successfully reduces critical missed opportunities to intervene with individuals not in care, leveraging information historically collected solely for public health purposes, not health care delivery, to improve public health

A Sino-German 6 cm polarization survey of the Galactic plane II. The region from 129 degree to 230 degree longitude

Linearly polarized Galactic synchrotron emission provides valuable information about the properties of the Galactic magnetic field and the interstellar magneto-ionic medium, when Faraday rotation along the line of sight is properly taken into account. We aim to survey the Galactic plane at 6 cm including linear polarization. At such a short wavelength Faraday rotation effects are in general small and the Galactic magnetic field properties can be probed to larger distances than at long wavelengths. The Urumqi 25-m telescope is used for a sensitive 6 cm survey in total and polarized intensities. WMAP K-band (22.8 GHz) polarization data are used to restore the absolute zero-level of the Urumqi U and Q maps by extrapolation. Total intensity and polarization maps are presented for a Galactic plane region of 129 degree < l < 230 degree and |b| < 5 degree in the anti-centre with an angular resolution of 9'5 and an average sensitivity of 0.6 mK and 0.4 mK Tb in total and polarized intensity, respectively. We briefly discuss the properties of some extended Faraday Screens detected in the 6 cm polarization maps. The Sino-German 6 cm polarization survey provides new information about the properties of the magnetic ISM. The survey also adds valuable information for discrete Galactic objects and is in particular suited to detect extended Faraday Screens with large rotation measures hosting strong regular magnetic fields.Comment: 17 pages, 20 figures, accepted by A&amp;A. Resolutions of the figures have been significantly reduced. For version with full resolution, see http://159.226.88.6/zmtt/6cm/papers/gao.paper2.pd

Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun

The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere - a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases.Comment: 73 pages, 21 figures ; Space Science Reviews (accepted December 10th, 2015); accepted versio

A burst with double radio spectrum observed up to 212 GHz

We study a solar flare that occurred on September 10, 2002, in active region NOAA 10105 starting around 14:52 UT and lasting approximately 5 minutes in the radio range. The event was classified as M2.9 in X-rays and 1N in H\alpha. Solar Submillimeter Telescope observations, in addition to microwave data give us a good spectral coverage between 1.415 and 212 GHz. We combine these data with ultraviolet images, hard and soft X-rays observations and full-disk magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic Imaging data are used to identify the locations of X-ray sources at different energies and to determine the X-ray spectrum, while ultra violet images allow us to characterize the coronal flaring region. The magnetic field evolution of the active region is analyzed using Michelson Doppler Imager magnetograms. The burst is detected at all available radio-frequencies. X-ray images (between 12 keV and 300 keV) reveal two compact sources and 212 GHz data, used to estimate the radio source position, show a single compact source displaced by 25" from one of the hard X-ray footpoints. We model the radio spectra using two homogeneous sources, and combine this analysis with that of hard X-rays to understand the dynamics of the particles. Relativistic particles, observed at radio wavelengths above 50 GHz, have an electron index evolving with the typical soft-hard-soft behaviour.Comment: Submitted to Solar Physics, 20 pages, 8 fugure