8,284 research outputs found
Improved multimedia server I/O subsystems
This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.---- Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.The main function of a continuous media server is to concurrently stream data from storage to multiple clients over a network. The resulting streams will congest the host CPU bus, reducing access to the system's main memory, which degrades CPU performance. The purpose of this paper is to investigate ways of improving I/O subsystems of continuous media sewers. Several improved I/O subsystem architectures are presented and their performances evaluated. The proposed architectures use an existing device, namely the Intel i960RP processor. The objective of using an I/O processor is to move the stream and its control from the host processor and the main memory. The ultimate aim is to identify the requirements for an integrated I/O subsystem for a high performance scalable media-on-demand server
Fractionalization in a square-lattice model with time-reversal symmetry
We propose a two-dimensional time-reversal invariant system of essentially
non-interacting electrons on a square lattice that exhibits configurations with
fractional charges e/2. These are vortex-like topological defects in the
dimerization order parameter describing spatial modulation in the electron
hopping amplitudes. Charge fractionalization is established by a simple
counting argument, analytical calculation within the effective low-energy
theory, and by an exact numerical diagonalization of the lattice Hamiltonian.
We comment on the exchange statistics of fractional charges and possible
realizations of the system.Comment: 4 pages, 3 figures, RevTex 4. (v2) improved discussion of lattice
effects and confinement; clearer figure
Arc/gas electrode
A gas/arc electrode is disclosed for use under vacuum conditions where a first housing encloses a second housing, with an end of the second housing extending through an opening in the first housing and having an outlet orifice. Provisions are made for circulating a coolant through the first housing to surround and cool the second housing. An electrical current and a gas, such as argon, as passed through the second housing, with the current flowing through a narrow stream of the ionized gas flowing through the outlet orifice to a workpiece to be treated. The second housing forms a chamber which has a cross sectional area, in a plane perpendicular to the direction of gas flow, of at least ten times the cross sectional area of the outlet orifice such that a gas pressure can be maintained in the chamber to reduce erosion of the chamber walls
Local molecular field theory for the treatment of electrostatics
We examine in detail the theoretical underpinnings of previous successful
applications of local molecular field (LMF) theory to charged systems. LMF
theory generally accounts for the averaged effects of long-ranged components of
the intermolecular interactions by using an effective or restructured external
field. The derivation starts from the exact Yvon-Born-Green hierarchy and shows
that the approximation can be very accurate when the interactions averaged over
are slowly varying at characteristic nearest-neighbor distances. Application of
LMF theory to Coulomb interactions alone allows for great simplifications of
the governing equations. LMF theory then reduces to a single equation for a
restructured electrostatic potential that satisfies Poisson's equation defined
with a smoothed charge density. Because of this charge smoothing by a Gaussian
of width sigma, this equation may be solved more simply than the detailed
simulation geometry might suggest. Proper choice of the smoothing length sigma
plays a major role in ensuring the accuracy of this approximation. We examine
the results of a basic confinement of water between corrugated wall and justify
the simple LMF equation used in a previous publication. We further generalize
these results to confinements that include fixed charges in order to
demonstrate the broader impact of charge smoothing by sigma. The slowly-varying
part of the restructured electrostatic potential will be more symmetric than
the local details of confinements.Comment: To be published in J Phys-Cond Matt; small misprint corrected in Eq.
(12) in V
Interplay of local hydrogen-bonding and long-ranged dipolar forces in simulations of confined water
Spherical truncations of Coulomb interactions in standard models for water
permit efficient molecular simulations and can give remarkably accurate results
for the structure of the uniform liquid. However truncations are known to
produce significant errors in nonuniform systems, particularly for
electrostatic properties. Local molecular field (LMF) theory corrects such
truncations by use of an effective or restructured electrostatic potential that
accounts for effects of the remaining long-ranged interactions through a
density-weighted mean field average and satisfies a modified Poisson's equation
defined with a Gaussian-smoothed charge density. We apply LMF theory to three
simple molecular systems that exhibit different aspects of the failure of a
naive application of spherical truncations -- water confined between
hydrophobic walls, water confined between atomically-corrugated hydrophilic
walls, and water confined between hydrophobic walls with an applied electric
field. Spherical truncations of 1/r fail spectacularly for the final system in
particular, and LMF theory corrects the failings for all three. Further, LMF
theory provides a more intuitive way to understand the balance between local
hydrogen bonding and longer-ranged electrostatics in molecular simulations
involving water.Comment: Submitted to PNA
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