25,677 research outputs found

    V-V Bond-Length Fluctuations in Vox

    Full text link
    We report a significantly stronger suppression of the phonon contribution to the thermal conductivity in VOx than can be accounted for by disorder of the 16 % atomic vacancies present in VO. Since the transition from localized to itinerant electronic behavior is first-order and has been shown to be characterized by bond-length fluctuations in several transition-metal oxides with the perovskite structure, we propose that cooperative V-V bond-length fluctuations play a role in VO similar to the M-O bond-length fluctuations in the perovskites. This model is able to account for the strong suppression of the thermal conductivity, the existence of a pseudogap confirmed by thermoelectric power, an anomalously large Debye-Waller factor, the temperature dependence of the magnetic susceptibility, and the inability to order atomic vacancies in VO.Comment: 5 pages, 5 figure

    A Super-Integrable Discretization of the Calogero Model

    Full text link
    A time-discretization that preserves the super-integrability of the Calogero model is obtained by application of the integrable time-discretization of the harmonic oscillator to the projection method for the Calogero model with continuous time. In particular, the difference equations of motion, which provide an explicit scheme for time-integration, are explicitly presented for the two-body case. Numerical results exhibit that the scheme conserves all the(=3)(=3) conserved quantities of the (two-body) Calogero model with a precision of the machine epsilon times the number of iterations.Comment: 22 pages, 5 figures. Added references. Corrected typo

    Ferromagnetic features on zero-bias conductance peaks in ferromagnet/insulator/superconductor junction

    Full text link
    We present a formula for tunneling conductance in ballistic ferromagnet/ferromagnetic insulator/superconductor junctions where the superconducting state has opposite spin pairing symmetry. The formula can involve correctly a ferromagnetism has been induced by effective mass difference between up- and down-spin electrons. Then, this effective mass mismatch ferromagnet and standard Stoner ferromagnet have been employed in this paper. As an application of the formulation, we have studied the tunneling effect for junctions including spin-triplet p-wave superconductor. The conductace spectra show a clear difference between two ferromagnets depending upon the way of normalization of the conductance. Especially, a essential difference is seen in zero-bias conductance peaks reflecting characteristics of each ferromagnets. From obtained results, it will be suggested that the measurements of the tunneling conductance in the junction provide us a useful information about the mechanism of itinerant ferromagnetism in metal.Comment: 8 pages, 8 figures, references added to the first versio

    New results on catalyzed BBN with a long-lived negatively-charged massive particle

    Full text link
    It has been proposed that the apparent discrepancies between the inferred primordial abundances of 6Li and 7Li and the predictions of big bang nucleosynthesis (BBN) can be resolved by the existence of a negatively-charged massive unstable supersymmetric particle (X-) during the BBN epoch. Here, we present new BBN calculations with an X- particle utilizing an improved nuclear reaction network including captures of nuclei by the particle, nuclear reactions and beta-decays of normal nuclei and nuclei bound to the X- particles (X-nuclei), and new reaction rates derived from recent rigorous quantum many-body dynamical calculations. We find that this is still a viable model to explain the observed 6Li and 7Li abundances. However, contrary to previous results, neutral X-nuclei cannot significantly affect the BBN light-element abundances. We also show that with the new rates the production of heavier nuclei is suppressed and there is no signature on abundances of nuclei heavier than Be in the X--particle catalyzed BBN model as has been previously proposed. We also consider the version of this model whereby the X- particle decays into the present cold dark matter. We analyze the this paradigm in light of the recent constraints on the dark-matter mass deduced from the possible detected events in the CDMS-II experiment. We conclude that based upon the inferred range for the dark-matter mass, only X- decay via the weak interaction can achieve the desired 7Li destruction while also reproducing the observed 6Li abundance.Comment: 6 pages, 2 figure

    Relativistic r-modes in Slowly Rotating Neutron Stars: Numerical Analysis in the Cowling Approximation

    Get PDF
    We investigate the properties of relativistic rr-modes of slowly rotating neutron stars by using a relativistic version of the Cowling approximation. In our formalism, we take into account the influence of the Coriolis like force on the stellar oscillations, but ignore the effects of the centrifugal like force. For three neutron star models, we calculated the fundamental rr-modes with l=m=2l'=m=2 and 3. We found that the oscillation frequency σˉ\bar\sigma of the fundamental rr-mode is in a good approximation given by σˉκ0Ω\bar\sigma\approx \kappa_0 \Omega, where σˉ\bar\sigma is defined in the corotating frame at the spatial infinity, and Ω\Omega is the angular frequency of rotation of the star. The proportional coefficient κ0\kappa_0 is only weakly dependent on Ω\Omega, but it strongly depends on the relativistic parameter GM/c2RGM/c^2R, where MM and RR are the mass and the radius of the star. All the fundamental rr-modes with l=ml'=m computed in this study are discrete modes with distinct regular eigenfunctions, and they all fall in the continuous part of the frequency spectrum associated with Kojima's equation (Kojima 1998). These relativistic rr-modes are obtained by including the effects of rotation higher than the first order of Ω\Omega so that the buoyant force plays a role, the situation of which is quite similar to that for the Newtonian rr-modes.Comment: 22 pages, 8 figures, accepted for publication in Ap

    Protocol-based verification of message-passing parallel programs

    Get PDF
    © 2015 ACM.We present ParTypes, a type-based methodology for the verification of Message Passing Interface (MPI) programs written in the C programming language. The aim is to statically verify programs against protocol specifications, enforcing properties such as fidelity and absence of deadlocks. We develop a protocol language based on a dependent type system for message-passing parallel programs, which includes various communication operators, such as point-to-point messages, broadcast, reduce, array scatter and gather. For the verification of a program against a given protocol, the protocol is first translated into a representation read by VCC, a software verifier for C. We successfully verified several MPI programs in a running time that is independent of the number of processes or other input parameters. This contrasts with alternative techniques, notably model checking and runtime verification, that suffer from the state-explosion problem or that otherwise depend on parameters to the program itself. We experimentally evaluated our approach against state-of-the-art tools for MPI to conclude that our approach offers a scalable solution

    Lifetimes of ultralong-range strontium Rydberg molecules in a dense BEC

    Get PDF
    The lifetimes and decay channels of ultralong-range Rydberg molecules created in a dense BEC are examined by monitoring the time evolution of the Rydberg population using field ionization. Studies of molecules with values of principal quantum number, nn, in the range n=49n=49 to n=72n=72 that contain tens to hundreds of ground state atoms within the Rydberg electron orbit show that their presence leads to marked changes in the field ionization characteristics. The Rydberg molecules have lifetimes of 15μ\sim1-5\,\mus, their destruction being attributed to two main processes: formation of Sr2+^+_2 ions through associative ionization, and dissociation induced through LL-changing collisions. The observed loss rates are consistent with a reaction model that emphasizes the interaction between the Rydberg core ion and its nearest neighbor ground-state atom. The measured lifetimes place strict limits on the time scales over which studies involving Rydberg species in cold, dense atomic gases can be undertaken and limit the coherence times for such measurements.Comment: 9 pages, 8 figure
    corecore