A Simple and Accurate Riemann Solver for Isothermal MHD

A new approximate Riemann solver for the equations of magnetohydrodynamics (MHD) with an isothermal equation of state is presented. The proposed method of solution draws on the recent work of Miyoshi and Kusano, in the context of adiabatic MHD, where an approximate solution to the Riemann problem is sought in terms of an average constant velocity and total pressure across the Riemann fan. This allows the formation of four intermediate states enclosed by two outermost fast discontinuities and separated by two rotational waves and an entropy mode. In the present work, a corresponding derivation for the isothermal MHD equations is presented. It is found that the absence of the entropy mode leads to a different formulation which is based on a three-state representation rather than four. Numerical tests in one and two dimensions demonstrates that the new solver is robust and comparable in accuracy to the more expensive linearized solver of Roe, although considerably faster.Comment: 19 pages, 9 figure

Origins of Common Neural Inputs to Different Compartments of the Extensor Digitorum Communis Muscle

The extensor digitorum communis (EDC) is a multi-compartment muscle that allows dexterous extension of the four digits. However, the level of common input shared across different compartments of this muscle is not well understood. We seek to systematically characterize the common and independent neural input, originated from different levels of the central nervous system, to the different compartments. A motor unit (MU) coherence analysis was used to capture the different sources of common and independent input, by quantifying the coherence of MU discharge between different compartments. The MU activities were obtained from decomposition of surface electromyogram recordings. Our results showed that the MU coherence across different muscle compartments accounted for only a small proportion (60%) in the delta (1-4 Hz) band. Additionally, cross-compartment coherence between the middle and ring-little fingers tended to be higher as compared with other finger combinations. Overall, the common input shared across different fingers are found to be at low to moderate levels, in comparison with the total input, which allows dexterous control of individual digits with some degree of coordinated control of multiple digits

Nonstructural Protein-2 and the Replication of Canine Parvovirus

AbstractThe nonstructural protein-2 (NS2) of canine parvovirus (CPV) is produced from the left-hand open reading frame of the viral genome and contains 87 amino-terminal amino acids in common with nonstructural protein 1 (NS1) joined to 78 amino acids from an alternative open reading frame. In the minute virus of mice parvovirus NS2 plays a role in controlling capsid protein assembly and translation in a host-specific manner. The predicted NS2 of CPV is divergent from the proteins of the rodent parvoviruses, and the protein and its functions have not been described. We characterized the large and the small splices of CPV using reverse transcriptase–PCR. NS2 was identified using anti-peptide antibodies against the predicted C-terminal sequence and also by expressing the protein from a plasmid vector. The protein could be detected at low levels in the nucleus and the cytoplasm of a proportion of CPV-infected cells, as well as in cells transfected with the expression plasmid. Virus genomes were prepared with mutations in the splice donor or acceptor sites of the NS2-specific intron or with three different termination codons in the NS2-unique exon. Both splice donor and acceptor mutations resulted in the use of previously cryptic splice sites, and the virus containing the splice donor mutation replicated inefficiently. However, the other four mutant viruses were all viable and replicated efficiently in cat and dog cells, and two mutant viruses that were tested appeared to assemble their capsids in the same manner as did the wildtype. After inoculation of dogs an NS2 mutant virus with a termination codon in the NS2-unique exon replicated to titers similar to those seen for wildtype CPV in several tissues examined

NLSEmagic: Nonlinear Schr\"odinger Equation Multidimensional Matlab-based GPU-accelerated Integrators using Compact High-order Schemes

We present a simple to use, yet powerful code package called NLSEmagic to numerically integrate the nonlinear Schr\"odinger equation in one, two, and three dimensions. NLSEmagic is a high-order finite-difference code package which utilizes graphic processing unit (GPU) parallel architectures. The codes running on the GPU are many times faster than their serial counterparts, and are much cheaper to run than on standard parallel clusters. The codes are developed with usability and portability in mind, and therefore are written to interface with MATLAB utilizing custom GPU-enabled C codes with the MEX-compiler interface. The packages are freely distributed, including user manuals and set-up files.Comment: 37 pages, 13 figure

Fractal Generalized Zone Plates

The construction of fractal generalized zone plates (FraGZPs) from a set of periodic diffractive optical elements with circular symmetry is proposed. This allows us to increase the number of foci of a conventional fractal zone plate (FraZP), keeping the self-similarity property within the axial irradiance. The focusing properties of these fractal diffractive optical elements for points not only along but also in the close vicinity of the optical axis are investigated. In both cases analytical expressions for the irradiance are derived. Numerical simulations of the energetic efficiency of FraGZPs under plane wave illumination are carried out. In addition, some effects on the axial irradiance caused by the variation in area of their transparent rings are shown.Comment: Submitted to Optics Express, 200

Upper limit on the transition temperature for non-ideal Bose gases

In this paper we show that for a non-ideal Bose gas there exists an upper limit on the transition temperature above which Bose-Einstein condensation cannot occur regardless of the pressure applied. Such upper limits for some realistic Bose gases are estimated. This result implies that there may also exist an upper limit on the transition temperature of superconductors.Comment: 7 pages, 1 figur

Inhomogeneous accretion discs and the soft states of black hole X-ray binaries

Observations of black hole binaries (BHBs) have established a rich phenomenology of X-ray states. The soft states range from the low variability, accretion disc dominated thermal state (TD) to the higher variability, non-thermal steep power law state (SPL). The disc component in all states is typically modeled with standard thin disc accretion theory. However, this theory is inconsistent with optical/UV spectral, variability, and gravitational microlensing observations of active galactic nuclei (AGNs), the supermassive analogs of BHBs. An inhomogeneous disc (ID) model with large (~0.4 dex) temperature fluctuations in each radial annulus can qualitatively explain all of these AGN observations. The inhomogeneity may be a consequence of instabilities in radiation dominated discs, and therefore may be present in BHBs as well. We show that ID models can explain many features of the TD and SPL states of BHBs. The observed relationships between spectral hardness, disc fraction, and rms variability amplitude in BHBs are reproduced with temperature fluctuations similar to those inferred in AGNs, suggesting a unified picture of luminous accretion discs across orders of magnitude in black hole mass. This picture can be tested with spectral fitting of ID models, X-ray polarization observations, and radiation MHD simulations. If BHB accretion discs are indeed inhomogeneous, only the most disc dominated states (disc fraction > 0.95) can be used to robustly infer black hole spin using current continuum fitting methods.Comment: 5 pages, 3 figures, submitted to MNRAS Letter