3,004 research outputs found

    Adjusted ADM systems and their expected stability properties: constraint propagation analysis in Schwarzschild spacetime

    Get PDF
    In order to find a way to have a better formulation for numerical evolution of the Einstein equations, we study the propagation equations of the constraints based on the Arnowitt-Deser-Misner formulation. By adjusting constraint terms in the evolution equations, we try to construct an "asymptotically constrained system" which is expected to be robust against violation of the constraints, and to enable a long-term stable and accurate numerical simulation. We first provide useful expressions for analyzing constraint propagation in a general spacetime, then apply it to Schwarzschild spacetime. We search when and where the negative real or non-zero imaginary eigenvalues of the homogenized constraint propagation matrix appear, and how they depend on the choice of coordinate system and adjustments. Our analysis includes the proposal of Detweiler (1987), which is still the best one according to our conjecture but has a growing mode of error near the horizon. Some examples are snapshots of a maximally sliced Schwarzschild black hole. The predictions here may help the community to make further improvements.Comment: 23 pages, RevTeX4, many figures. Revised version. Added subtitle, reduced figures, rephrased introduction, and a native checked. :-

    Symmetric hyperbolic system in the Ashtekar formulation

    Full text link
    We present a first-order symmetric hyperbolic system in the Ashtekar formulation of general relativity for vacuum spacetime. We add terms from constraint equations to the evolution equations with appropriate combinations, which is the same technique used by Iriondo, Leguizam\'on and Reula [Phys. Rev. Lett. 79, 4732 (1997)]. However our system is different from theirs in the points that we primarily use Hermiticity of a characteristic matrix of the system to characterize our system "symmetric", discuss the consistency of this system with reality condition, and show the characteristic speeds of the system.Comment: 4 pages, RevTeX, to appear in Phys. Rev. Lett., Comments added, refs update

    Neutron wave packet tomography

    Full text link
    A tomographic technique is introduced in order to determine the quantum state of the center of mass motion of neutrons. An experiment is proposed and numerically analyzed.Comment: 4 pages, 3 figure

    Efficient Set Sharing Using ZBDDs

    Get PDF
    Set sharing is an abstract domain in which each concrete object is represented by the set of local variables from which it might be reachable. It is a useful abstraction to detect parallelism opportunities, since it contains definite information about which variables do not share in memory, i.e., about when the memory regions reachable from those variables are disjoint. Set sharing is a more precise alternative to pair sharing, in which each domain element is a set of all pairs of local variables from which a common object may be reachable. However, the exponential complexity of some set sharing operations has limited its wider application. This work introduces an efficient implementation of the set sharing domain using Zero-suppressed Binary Decision Diagrams (ZBDDs). Because ZBDDs were designed to represent sets of combinations (i.e., sets of sets), they naturally represent elements of the set sharing domain. We show how to synthesize the operations needed in the set sharing transfer functions from basic ZBDD operations. For some of the operations, we devise custom ZBDD algorithms that perform better in practice. We also compare our implementation of the abstract domain with an efficient, compact, bit set-based alternative, and show that the ZBDD version scales better in terms of both memory usage and running time

    Microbial-induced carbonate precipitation applicability with the methane hydrate-bearing layer microbe

    Get PDF
    Production of methane gas from the methane-hydrate-bearing layer below the deep-ocean floor is expected to be crucial in the future of energy resources worldwide. During the methane gas-production phase from the methane hydrate with the depressurisation method, the depressurising zone around the production well will lose strength, causing a potential geohazard. In this study, a bio-mediated treatment to reinforce the methane hydrate layers is proposed. A urease-producing bacterium, Sporosarcina newyorkensis, was isolated for the first time from a pressure core sampled from the Nankai Trough seabed methane-hydrate-bearing layer in Japan. This newly isolated species can survive deep-seabed environments and also enhance the population under nutrient-rich conditions. In addition, it is uniquely characterised with higher urease activities under low-temperature conditions in comparison to the well-known bacterium S. pasteurii. The results of triaxial tests suggest that this bacterium can catalyse the precipitation of calcium carbonate through urea hydrolysis, which enhances the soil strength below of the ocean floor and hence reinforces the production well. This will not only make methane gas extraction safer but may also reduce sand production in the well, making extraction operations more efficient and cost effective.Japan Society for the Promotion of Science Japan Oil, Gas and Metals National Corporatio
    • 

    corecore