The multifrequency Siberian Radioheliograph

The 10-antenna prototype of the multifrequency Siberian radioheliograph is described. The prototype consists of four parts: antennas with broadband front-ends, analog back-ends, digital receivers and a correlator. The prototype antennas are mounted on the outermost stations of the Siberian Solar Radio Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom by an analog fiber optical link, laid in an underground tunnel. After mixing, all signals are digitized and processed by digital receivers before the data are transmitted to the correlator. The digital receivers and the correlator are accessible by the LAN. The frequency range of the prototype is from 4 to 8 GHz. Currently the frequency switching observing mode is used. The prototype data include both circular polarizations at a number of frequencies given by a list. This prototype is the first stage of the multifrequency Siberian radioheliograph development. It is assumed that the radioheliograph will consist of 96 antennas and will occupy stations of the West-East-South subarray of the SSRT. The radioheliograph will be fully constructed in autumn of 2012. We plan to reach the brightness temperature sensitivity about 100 K for the snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and polarization measurement accuracy about a few percent. First results with the 10-antenna prototype are presented of observations of solar microwave bursts. The prototype abilities to estimate source size and locations at different frequencies are discussed

Metal-insulator transition in disordered 2DEG including temperature effects

We calculate self-consistently the mutual dependence of electron correlations and electron-defect scattering for a two dimensional electron gas at finite temperature. We employ an STLS approach to calculate the electron correlations while the electron scattering rate off Coulombic impurities and surface roughness is calculated using self-consistent current-relaxation theory. The methods are combined and self-consistently solved. We discuss a metal-insulator transition for a range of disorder levels and electron densities. Our results are in good agreement with recent experimental observations.Comment: 4 pages, RevTeX + epsf, 5 figure

About the relation between the quasiparticle Green's function in cuprates obtained from ARPES data and the magnetic susceptibility

Angle resolved photoemission spectroscopy (ARPES) provides a detailed view of the renormalized band structure in cuprates and, consequently, is a key to the self-energy and the quasiparticle Green's function. Such information gives a clue to the comparison of ARPES with scanning tunneling microscopy, inelastic neutron scattering (INS), and Raman scattering data. Here we touch on a potential possibility of such a comparison with the dynamical magnetic susceptibility measured in INS experiments. Calculations based on the experimentally measured quasiparticle self-energies in cuprates lead to the estimated magnetic susceptibility response with many-body effects taken into account.Comment: Will be presented at the M2S-HTSC-VIII conference in Dresde

Synthesis and characterization of Nb2O5@C core-shell nanorods and Nb2O5nanorods by reacting Nb(OEt)5via RAPET (reaction under autogenic pressure at elevated temperatures) technique

The reaction of pentaethoxy niobate, Nb(OEt)5, at elevated temperature (800 °C) under autogenic pressure provides a chemical route to niobium oxide nanorods coated with amorphous carbon. This synthetic approach yielded nanocrystalline particles of Nb2O5@C. As prepared Nb2O5@C core-shell nanorods is annealed under air at 500 °C for 3 h (removing the carbon coating) results in neat Nb2O5nanorods. According to the TEM measurements, the Nb2O5crystals exhibit particle sizes between 25 nm and 100 nm, and the Nb2O5crystals display rod-like shapes without any indication of an amorphous character. The optical band gap of the Nb2O5nanorods was determined by diffuse reflectance spectroscopy (DRS) and was found to be 3.8 eV

Short- and long-term associations between widowhood and mortality in the United States: longitudinal analyses

Background Past research shows that spousal death results in elevated mortality risk for the surviving spouse. However, most prior studies have inadequately controlled for socioeconomic status (SES), and it is unclear whether this ‘widowhood effect’ persists over time. Methods Health and Retirement Study participants aged 50+ years and married in 1998 (n = 12 316) were followed through 2008 for widowhood status and mortality (2912 deaths). Discrete-time survival analysis was used to compare mortality for the widowed versus the married. Results Odds of mortality during the first 3 months post-widowhood were significantly higher than in the continuously married (odds ratio (OR) for men = 1.87, 95% CI: 1.27, 2.75; OR for women = 1.47, 95% CI: 0.96, 2.24) in models adjusted for age, gender, race and baseline SES (education, household wealth and household income), behavioral risk factors and co-morbidities. Twelve months following bereavement, men experienced borderline elevated mortality (OR = 1.16, 95% CI: 1.00, 1.35), whereas women did not (OR = 1.07, 95% CI: 0.90, 1.28), though the gender difference was non-significant. Conclusion The ‘widowhood effect’ was not fully explained by adjusting for pre-widowhood SES and particularly elevated within the first few months after widowhood. These associations did not differ by sex

Electromigration of Single-Layer Clusters

Single-layer atom or vacancy clusters in the presence of electromigration are studied theoretically assuming an isotropic medium. A variety of distinctive behaviors distinguish the response in the three standard limiting cases of periphery diffusion (PD), terrace diffusion (TD), and evaporation-condensation (EC). A general model provides power laws describing the size dependence of the drift velocity in these limits, consistent with established results in the case of PD. The validity of the widely used quasistatic limit is calculated. Atom and vacancy clusters drift in opposite directions in the PD limit but in the same direction otherwise. In absence of PD, linear stability analysis reveals a new type of morphological instability, not leading to island break-down. For strong electromigration, Monte Carlo simulations show that clusters then destabilize into slits, in contrast to splitting in the PD limit. Electromigration affects the diffusion coefficient of the cluster and morphological fluctuations, the latter diverging at the instability threshold. An instrinsic attachment-detachment bias displays the same scaling signature as PD in the drift velocity.Comment: 11 pages, 4 figure

Symmetry in the insulator - quantum Hall - insulator transitions observed in a Ge/SiGe quantum well

We examine the magnetic field driven insulator-quantum Hall-insulator transitions of the two dimensional hole gas in a Ge/SiGe quantum well. We observe direct transitions between low and high magnetic field insulators and the $\nu=1$ quantum Hall state. With increasing magnetic field, the transitions from insulating to quantum Hall and quantum Hall to insulating are very similar with respect to their transport properties. We address the temperature dependence around the transitions and show that the characteristic energy scale for the high field transition is larger.Comment: 4 page

Effects of misalignments in the optical vortex transformation performed by holograms with embedded phase singularity

Spatial characteristics of diffracted beams produced by a "fork" hologram from an incident circular Laguerre-Gaussian beam whose axis differ from the hologram optical axis are studied theoretically. General analytical representations for the complex amplitude distribution of a diffracted beam are derived in terms of superposition of Kummer beams or hypergeometric-Gaussian beams. The diffracted beam structure is determined by combination of the "proper" topological charge m of the incident vortex beam and the topological charge l of the singularity "imparted" by the hologram. Evolution of the diffracted beam structure is studied in detail for several combinations of m and l and for various incident beam displacements with respect to the optical axis of the hologram. Variations of the intensity and phase distribution due to the incident beam misalignment are investigated and possible applications for the purposeful optical-vortex beam generation and optical measurements are discussed.Comment: 23 pages, 8 figure

Macroscopic anisotropy in superconductors with anisotropic gaps

It is shown within the weak-coupling model that the macroscopic superconducting anisotropy for materials with the gap varying on the Fermi surface cannot be characterized by a single number, unlike the case of clean materials with isotropic gaps. For clean uniaxial materials, the anisotropy parameter $\gamma (T)$ defined as the ratio of London penetration depths, $\lambda_c/\lambda_{ab}$, is evaluated for all $T$'s. Within the two-gap model of MgB$_2$, $\gamma (T)$ is an increasing function of $T$.Comment: 4 pages, 2 figure