108,658 research outputs found
Exploring the grand-canonical phase diagram of interacting bosons in optical lattices by trap squeezing
In this paper we theoretically discuss how quantum simulators based on
trapped cold bosons in optical lattices can explore the grand-canonical phase
diagram of homogeneous lattice boson models, via control of the trapping
potential independently of all other experimental parameters (trap squeezing).
Based on quantum Monte Carlo, we establish the general scaling relation linking
the global chemical potential to the Hamiltonian parameters of the Bose-Hubbard
model in a parabolic trap, describing cold bosons in optical lattices; we find
that this scaling relation is well captured by a modified Thomas-Fermi scaling
behavior - corrected for quantum fluctuations - in the case of high enough
density and/or weak enough interactions, and by a mean-field Gutzwiller Ansatz
over a much larger parameter range. The above scaling relation allows to
control experimentally the chemical potential, independently of all other
Hamiltonian parameters, via trap squeezing; given that the global chemical
potential coincides with the local chemical potential in the trap center,
measurements of the central density as a function of the chemical potential
gives access to the information on the bulk compressibility of the Bose-Hubbard
model. Supplemented with time-of-flight measurements of the coherence
properties, the measurement of compressibility enables one to discern among the
various possible phases realized by bosons in an optical lattice with or
without external (periodic or random) potentials -- e.g. superfluid, Mott
insulator, band insulator, and Bose glass. We theoretically demonstrate the
trap-squeezing investigation of the above phases in the case of bosons in a
one-dimensional optical lattice, and in a one-dimensional incommensurate
superlattice.Comment: 27 pages, 26 figures. v2: added references and further discussion of
the local-density approximation
A Design of MAC Model Based on the Separation of Duties and Data Coloring: DSDC-MAC
Among the access control methods for database security, there is Mandatory Access Control (MAC) model in which the security level is set to both the subject and the object to enhance the security control. Legacy MAC models have focused only on one thing, either confidentiality or integrity. Thus, it can cause collisions between security policies in supporting confidentiality and integrity simultaneously. In addition, they do not provide a granular security class policy of subjects and objects in terms of subjects\u27 roles or tasks. In this paper, we present the security policy of Bell_LaPadula Model (BLP) model and Biba model as one complemented policy. In addition, Duties Separation and Data Coloring (DSDC)-MAC model applying new data coloring security method is proposed to enable granular access control from the viewpoint of Segregation of Duty (SoD). The case study demonstrated that the proposed modeling work maintains the practicality through the design of Human Resources management System. The proposed model in this study is suitable for organizations like military forces or intelligence agencies where confidential information should be carefully handled. Furthermore, this model is expected to protect systems against malicious insiders and improve the confidentiality and integrity of data
QCDGPU: open-source package for Monte Carlo lattice simulations on OpenCL-compatible multi-GPU systems
The multi-GPU open-source package QCDGPU for lattice Monte Carlo simulations
of pure SU(N) gluodynamics in external magnetic field at finite temperature and
O(N) model is developed. The code is implemented in OpenCL, tested on AMD and
NVIDIA GPUs, AMD and Intel CPUs and may run on other OpenCL-compatible devices.
The package contains minimal external library dependencies and is OS
platform-independent. It is optimized for heterogeneous computing due to the
possibility of dividing the lattice into non-equivalent parts to hide the
difference in performances of the devices used. QCDGPU has client-server part
for distributed simulations. The package is designed to produce lattice gauge
configurations as well as to analyze previously generated ones. QCDGPU may be
executed in fault-tolerant mode. Monte Carlo procedure core is based on PRNGCL
library for pseudo-random numbers generation on OpenCL-compatible devices,
which contains several most popular pseudo-random number generators.Comment: Presented at the Third International Conference "High Performance
Computing" (HPC-UA 2013), Kyiv, Ukraine; 9 pages, 2 figure
JANUS: an FPGA-based System for High Performance Scientific Computing
This paper describes JANUS, a modular massively parallel and reconfigurable
FPGA-based computing system. Each JANUS module has a computational core and a
host. The computational core is a 4x4 array of FPGA-based processing elements
with nearest-neighbor data links. Processors are also directly connected to an
I/O node attached to the JANUS host, a conventional PC. JANUS is tailored for,
but not limited to, the requirements of a class of hard scientific applications
characterized by regular code structure, unconventional data manipulation
instructions and not too large data-base size. We discuss the architecture of
this configurable machine, and focus on its use on Monte Carlo simulations of
statistical mechanics. On this class of application JANUS achieves impressive
performances: in some cases one JANUS processing element outperfoms high-end
PCs by a factor ~ 1000. We also discuss the role of JANUS on other classes of
scientific applications.Comment: 11 pages, 6 figures. Improved version, largely rewritten, submitted
to Computing in Science & Engineerin
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