Crystal structure, incommensurate magnetic order and ferroelectricity in mn1−x_{1-x}cux_{x}wo4{_4} (x=0-0.19)

We have carried out a systematic study on the effect of Cu doping on nuclear, magnetic, and dielectric properties in Mn$_{1-x}$Cu$_{x}$WO$_4$ for ${0}\leq{x}\leq{0.19}$ by a synergic use of different techniques, viz, heat capacity, magnetization, dielectric, and neutron powder diffraction measurements. Via heat capacity and magnetization measurements we show that with increasing Cu concentration magnetic frustration decreases, which leads to the stabilization of commensurate magnetic ordering. This was further verified by temperature-dependent unit cell volume changes derived from neutron diffraction measurements which was modeled by the Gr\"{u}neisen approximation. Dielectric measurements show a low temperature phase transition below about 9-10 K. Further more, magnetic refinements reveal no changes below this transition indicating a possible spin-flop transition which is unique to the Cu doped system. From these combined studies we have constructed a magnetoelectric phase diagram of this compound.Comment: 9 pages, 9 figures, accepted for publication in PR

Charmless B→PV,VVB \to PV, VV decays and new physics effects in the mSUGRA model

By employing the QCD factorization approach, we calculate the new physics contributions to the branching radios of the two-body charmless $B \to PV$ and $B \to VV$ decays in the framework of the minimal supergravity (mSUGRA) model. we choose three typical sets of the mSUGRA input parameters in which the Wilson coefficient $C_{7\gamma}(m_b)$ can be either SM-like (the case A and C) or has a flipped-sign (the case B). We found numerically that (a) the SUSY contributions are always very small for both case A and C; (b) for those tree-dominated decays, the SUSY contributions in case B are also very small; (c) for those QCD penguin-dominated decay modes, the SUSY contributions in case B can be significant, and can provide an enhancement about $30$ to the branching ratios of $B \to K^*(\pi,\phi,\rho)$ and $K \phi$ decays, but a reduction about $30$ to $B\to K(\rho, \omega)$ decays; and (d) the large SUSY contributions in the case B may be masked by the large theoretical errors dominated by the uncertainty from our ignorance of calculating the annihilation contributions in the QCD factorization approach.Comment: 34 pages, 8 PS figures, this is the correct version

Driving light pulses with light in two-level media

A two-level medium, described by the Maxwell-Bloch (MB) system, is engraved by establishing a standing cavity wave with a linearly polarized electromagnetic field that drives the medium on both ends. A light pulse, polarized along the other direction, then scatters the medium and couples to the cavity standing wave by means of the population inversion density variations. We demonstrate that control of the applied amplitudes of the grating field allows to stop the light pulse and to make it move backward (eventually to drive it freely). A simplified limit model of the MB system with variable boundary driving is obtained as a discrete nonlinear Schroedinger equation with tunable external potential. It reproduces qualitatively the dynamics of the driven light pulse

Rotating system for four-dimensional transverse rms-emittance measurements

Knowledge of the transverse four-dimensional beam rms-parameters is essential for applications that involve lattice elements that couple the two transverse degrees of freedom (planes). Of special interest is the removal of inter-plane correlations to reduce the projected emittances. A dedicated ROtating System for Emittance measurements (ROSE) has been proposed, developed, and successfully commissioned to fully determine the four-dimensional beam matrix. This device has been used at the High Charge injector (HLI) at GSI using a beam line which is composed of a skew quadrupole triplet, a normal quadrupole doublet, and ROSE. Mathematical algorithms, measurements, and results for ion beams of 83Kr13+ at 1.4 MeV/u are reported in this paper.Comment: 11 pages, 10 figure

Complex macrocycle exploration: parallel, heuristic, and constraint-based conformer generation using ForceGen.

ForceGen is a template-free, non-stochastic approach for 2D to 3D structure generation and conformational elaboration for small molecules, including both non-macrocycles and macrocycles. For conformational search of non-macrocycles, ForceGen is both faster and more accurate than the best of all tested methods on a very large, independently curated benchmark of 2859 PDB ligands. In this study, the primary results are on macrocycles, including results for 431 unique examples from four separate benchmarks. These include complex peptide and peptide-like cases that can form networks of internal hydrogen bonds. By making use of new physical movements ("flips" of near-linear sub-cycles and explicit formation of hydrogen bonds), ForceGen exhibited statistically significantly better performance for overall RMS deviation from experimental coordinates than all other approaches. The algorithmic approach offers natural parallelization across multiple computing-cores. On a modest multi-core workstation, for all but the most complex macrocycles, median wall-clock times were generally under a minute in fast search mode and under 2 min using thorough search. On the most complex cases (roughly cyclic decapeptides and larger) explicit exploration of likely hydrogen bonding networks yielded marked improvements, but with calculation times increasing to several minutes and in some cases to roughly an hour for fast search. In complex cases, utilization of NMR data to constrain conformational search produces accurate conformational ensembles representative of solution state macrocycle behavior. On macrocycles of typical complexity (up to 21 rotatable macrocyclic and exocyclic bonds), design-focused macrocycle optimization can be practically supported by computational chemistry at interactive time-scales, with conformational ensemble accuracy equaling what is seen with non-macrocyclic ligands. For more complex macrocycles, inclusion of sparse biophysical data is a helpful adjunct to computation

Inelastic current-voltage characteristics of atomic and molecular junctions

We report first-principles calculations of the inelastic current-voltage (I-V) characteristics of a gold point contact and a molecular junction in the nonresonant regime. Discontinuities in the I-V curves appear in correspondence to the normal modes of the structures. Due to the quasi-one-dimensional nature of these systems, specific modes with large longitudinal component dominate the inelastic I-V curves. In the case of the gold point contact, our results are in good agreement with recent experimental data. For the molecular junction, we find that the inelastic I-V curves are quite sensitive to the structure of the contact between the molecule and the electrodes thus providing a powerful tool to extract the bonding geometry in molecular wires.Comment: 4 pages, 3 figure

Optimal Diversity Combining Based on Noisy Channel Estimation

The performances of coherent diversity receivers with noisy channel estimation are examined. Fading channel gain estimates are modeled as sums of the true fading channel gain values plus independent Gaussian distributed estimation errors. The optimal diversity receiver for coherent reception with noisy channel state information and independent and identically distributed fading channels is derived. Exact expressions for the average error probability of optimal diversity MPSK with noisy channel estimation are derived for Rayleigh and Ricean fading channels; closed-form expressions are obtained for some special cases. Some interesting observations regarding practical diversity receiver design for higher-order modulation formats are drawn

Chorus acceleration of radiation belt relativistic electrons during March 2013 geomagnetic storm

Abstract The recent launching of Van Allen probes provides an unprecedent opportunity to investigate variations of the radiation belt relativistic electrons. During the 17-19 March 2013 storm, the Van Allen probes simultaneously detected strong chorus waves and substantial increases in fluxes of relativistic (2 - 4.5 MeV) electrons around L = 4.5. Chorus waves occurred within the lower band 0.1-0.5fce (theelectron equatorial gyrofrequency), with a peak spectral density ∼10-4 nT 2/Hz. Correspondingly, relativistic electron fluxes increased by a factor of 102-103 during the recovery phase compared to the main phase levels. By means of a Gaussian fit to the observed chorus spectra, the drift and bounce-averaged diffusion coefficients are calculated and then used to solve a 2-D Fokker-Planck diffusion equation. Numerical simulations demonstrate that the lower-band chorus waves indeed produce such huge enhancements in relativistic electron fluxes within 15 h, fitting well with the observation. Key Points Initial RBSP correlated data of chorus waves and relativistic electron fluxes A realistic simulation to examine effect of chorus on relativistic electron flux Chorus yields huge increases inelectron flux rapidly, consistent with data

Topological orders and Edge excitations in FQH states

Fractional quantum Hall (FQH) liquids contain extremely rich internal structures which represent a whole new kind of ordering. We discuss characterization and classification of the new orders (which is called topological orders). We also discuss the edge excitations in FQH liquids, which form the so-called chiral Luttinger liquids. The chiral Luttinger liquids at the edges also have very rich structures as a reflection of the rich topological orders in the bulk. Thus, edge excitations provide us a practical way to measure topological orders in experiments.Comment: 67 pages, plain-tex, 3 figures. The section about spin vector was rewritten to make it more readabl