2,005 research outputs found
Small Sample Bayesian Designs for Complex High-Dimensional Models Based on Information Gained Using Fast Approximations
We consider the problem of designing for complex high-dimensional computer models that can be evaluated at different levels of accuracy. Ordinarily, this requires performing many expensive evaluations of the most accurate version of the computer model to obtain a reasonable coverage of the design space. In some cases, it is possible to supplement the information from the accurate model evaluations with a large number of evaluations of a cheap, approximate version of the computer model to enable a more informed design choice. We describe an approach that combines the information from both the approximate model and the accurate model into a single multiscale emulator for the computer model. We then propose a design strategy for selecting a small number of expensive evaluations of the accurate computer model based on our multiscale emulator and a decomposition of the input parameter space. We illustrate our methodology with an example concerning a computer simulation of a hydrocarbon reservoir
Critical Point Field Mixing in an Asymmetric Lattice Gas Model
The field mixing that manifests broken particle-hole symmetry is studied for
a 2-D asymmetric lattice gas model having tunable field mixing properties.
Monte Carlo simulations within the grand canonical ensemble are used to obtain
the critical density distribution for different degrees of particle-hole
asymmetry. Except in the special case when this asymmetry vanishes, the density
distributions exhibit an antisymmetric correction to the limiting
scale-invariant form. The presence of this correction reflects the mixing of
the critical energy density into the ordering operator. Its functional form is
found to be in excellent agreement with that predicted by the mixed-field
finite-size-scaling theory of Bruce and Wilding. A computational procedure for
measuring the significant field mixing parameter is also described, and its
accuracy gauged by comparing the results with exact values obtained
analytically.Comment: 10 Pages, LaTeX + 8 figures available from author on request, To
appear in Z. Phys.
Impacts of Seagrass Dynamics on the Coupled LongâTerm Evolution of BarrierâMarshâBay Systems
Seagrass provides a wide range of economically and ecologically valuable ecosystem services, with shoreline erosion control often listed as a key service, but can also alter the sediment dynamics and waves within backâbarrier bays. Here we incorporate seagrass dynamics into an existing barrierâmarsh exploratory model, GEOMBEST++, to examine the coupled interactions of the backâbarrier bay with both adjacent (marsh) and nonadjacent (barrier island) subsystems. While seagrass reduces marsh edge erosion rates and increases progradation rates in many of our 288 model simulations, seagrass surprisingly increases marsh edge erosion rates when sediment export from the backâbarrier basin is negligible because the ability of seagrass to reduce the volume of marsh sediment eroded matters little for backâbarrier basins in which all sediment is conserved. Our model simulations also suggest that adding seagrass to the bay subsystem leads to increased deposition in the bay, reduced sediment available to the marsh, and enhanced marsh edge erosion until the bay reaches a new, shallower equilibrium depth. In contrast, removing seagrass liberates previously sequestered sediment that is then delivered to the marsh, leading to enhanced marsh progradation. Lastly, we find that seagrass reduces barrier island migration rates in the absence of backâbarrier marsh by filling accommodation space in the bay. These model observations suggest that seagrass meadows operate as dynamic sources and sinks of sediment that can influence the evolution of coupled marsh and barrier island landforms in unanticipated ways
Pre-Hawking Radiation from a Collapsing Shell
We investigate the effect of induced massive radiation given off during the
time of collapse of a massive spherically symmetric domain wall in the context
of the functional Schr\"odinger formalism. Here we find that the introduction
of mass suppresses the occupation number in the infrared regime of the induced
radiation during the collapse. The suppression factor is found to be given by
, which is in agreement with the expected Planckian distribution
of induced radiation. Thus a massive collapsing domain wall will radiate mostly
(if not exclusively) massless scalar fields, making it difficult for the domain
wall to shed any global quantum numbers and evaporate before the horizon is
formed.Comment: 10 pages, 3 figures. We updated the acknowledgments as well as added
a statement clarifying that we are following the methods first laid out in
Phys. Rev. D 76, 024005 (2007
Thermodynamic Comparison and the Ideal Glass Transition of A Monatomic Systems Modeled as an Antiferromagnetic Ising Model on Husimi and Cubic Recursive Lattices of the Same Coordination Number
Two kinds of recursive lattices with the same coordination number but
different unit cells (2-D square and 3-D cube) are constructed and the
antiferromagnetic Ising model is solved exactly on them to study the stable and
metastable states. The Ising model with multi-particle interactions is designed
to represent a monatomic system or an alloy. Two solutions of the model exhibit
the crystallization of liquid, and the ideal glass transition of supercooled
liquid respectively. Based on the solutions, the thermodynamics on both
lattices was examined. In particular, the free energy, energy, and entropy of
the ideal glass, supercooled liquid, crystal, and liquid state of the model on
each lattice were calculated and compared with each other. Interactions between
particles farther away than the nearest neighbor distance are taken into
consideration. The two lattices show comparable properties on the transition
temperatures and the thermodynamic behaviors, which proves that both of them
are practical to describe the regular 3-D case, while the different effects of
the unit types are still obvious.Comment: 27 pages, 13 figure
Action at a distance as a full-value solution of Maxwell equations: basis and application of separated potential's method
The inadequacy of Li\'{e}nard-Wiechert potentials is demonstrated as one of
the examples related to the inconsistency of the conventional classical
electrodynamics. The insufficiency of the Faraday-Maxwell concept to describe
the whole electromagnetic phenomena and the incompleteness of a set of
solutions of Maxwell equations are discussed and mathematically proved. Reasons
of the introduction of the so-called ``electrodynamics dualism concept"
(simultaneous coexistence of instantaneous Newton long-range and
Faraday-Maxwell short-range interactions) have been displayed. It is strictly
shown that the new concept presents itself as the direct consequence of the
complete set of Maxwell equations and makes it possible to consider classical
electrodynamics as a self-consistent and complete theory, devoid of inward
contradictions. In the framework of the new approach, all main concepts of
classical electrodynamics are reconsidered. In particular, a limited class of
motion is revealed when accelerated charges do not radiate electromagnetic
field.Comment: ReVTeX file, 24pp. Small corrections which do not have influence
results of the paper. Journal reference is adde
High-Order Discontinuous Galerkin Method for Boltzmann Model Equations
High-order Runge-Kutta discontinuous Galerkin (DG) method is applied to the kinetic model equations describing rarefied gas flows. A conservative DG discretization of nonlinear collision relaxation term is formulated for Bhatnagar-Gross-Krook and ellipsoidal statistical models. The numerical solutions using RKDG method of order up to four are obtained for two flow problems: the heat transfer between parallel plates and the normal shock wave. The convergence of RKDG method is compared with the conventional secondorder finite volume method for the heat transfer problem. The normal shock wave solutions obtained using RKDG are compared with the experimental measurements of density and velocity distribution function inside the shock
EPR-Bell Nonlocality, Lorentz Invariance, and Bohmian Quantum Theory
We discuss the problem of finding a Lorentz invariant extension of Bohmian
mechanics. Due to the nonlocality of the theory there is (for systems of more
than one particle) no obvious way to achieve such an extension. We present a
model invariant under a certain limit of Lorentz transformations, a limit
retaining the characteristic feature of relativity, the non-existence of
absolute time resp. simultaneity. The analysis of this model exemplifies an
important property of any Bohmian quantum theory: the quantum equilibrium
distribution cannot simultaneously be realized in all
Lorentz frames of reference.Comment: 24 pages, LaTex, 4 figure
D0 Matrix Mechanics: New Fuzzy Solutions at Large N
We wish to consider in this report the large N limit of a particular matrix
model introduced by Myers describing D-brane physics in the presence of an RR
flux background. At finite N, fuzzy spheres appear naturally as non-trivial
solutions to this matrix model and have been extensively studied. In this
report, we wish to demonstrate several new classes of solutions which appear in
the large N limit, corresponding to the fuzzy cylinder,the fuzzy plane and a
warped fuzzy plane. The latter two solutions arise from a possible "central
extension" to our model that arises after we account for non-trivial issues
involved in the large N limit. As is the case for finite N, these new solutions
are to be interpreted as constituent D0-branes forming D2 bound states
describing new fuzzy geometries.Comment: revised version: references added, derivation of "central extensions"
improved upon. To appear in JHE
Assessing competency for concealed-weapons permits - The physician's role
Shortly after the shootings in Newtown, Connecticut, two of us received letters from our county sheriff in North Carolina asking whether one of our patients had medical or physical conditions that would preclude issuance of a permit to carry a concealed weapon. Uncomfortable with our limited knowledge about such permits and our expected role, and fearing that our participation could affect our relationships with patients, we began exploring the ethical, legal, and policy considerations regarding physician involvement in this process
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