87,880 research outputs found
A New Method of Calculating the Spin-Wave Velocity of Spin-1/2 Antiferromagnets With Symmetry in a Monte Carlo Simulation
Motivated by the so-called cubical regime in magnon chiral perturbation
theory, we propose a new method to calculate the low-energy constant, namely
the spin-wave velocity of spin-1/2 antiferromagnets with symmetry in
a Monte Carlo simulation. Specifically we suggest that can be determined by
when the squares of the spatial and temporal winding numbers are
tuned to be the same in the Monte Carlo calculations. Here and are
the inverse temperature and the box size used in the simulations when this
condition is met. We verify the validity of this idea by simulating the quantum
spin-1/2 XY model. The obtained by using the squares of winding numbers is
given by which is consistent with the known values of in
the literature. Unlike other conventional approaches, our new idea provides a
direct method to measure . Further, by simultaneously fitting our Monte
Carlo data of susceptibilities and spin susceptibilities to
their theoretical predictions from magnon chiral perturbation theory, we find
is given by which agrees with the one we obtain by the
new method of using the squares of winding numbers. The low-energy constants
magnetization density and spin stiffenss of quantum spin-1/2
XY model are determined as well and are given by
and , respectively. Thanks to the prediction power of
magnon chiral perturbation theory which puts a very restricted constraint among
the low-energy constants for the model considered here, the accuracy of we present in this study is much precise than previous Monte Carlo result.Comment: 5 pages, 7 figure
Mapping cyberspace: visualising, analysing and exploring virtual worlds
In the past years, with the development of computer networks such as the Internet
and world wide web (WWW), cyberspace has been increasingly studied by
researchers in various disciplines such as computer sciences, sociology, geography,
and cartography as well. Cyberspace is mainly rooted in two computer technologies:
network and virtual reality. Cybermaps, as special maps for cyberspace, have been
used as a tool for understanding various aspects of cyberspace. As recognised,
cyberspace as a virtual space can be distinguished from the earth we live on in many
ways. Because of these distinctions, mapping it implies a big challenge for
cartographers with their long tradition of mapping things in clear ways. This paper,
by comparing it to traditional maps, addresses various cybermap issues such as
visualising, analysing and exploring cyberspace from different aspects
Acceleration computing process in wavelength scanning interferometry
The optical interferometry has been widely explored for surface measurement due to the advantages of non-contact and high accuracy interrogation. Eventually, some interferometers are used to measure both rough and smooth surfaces such as white light interferometry and wavelength scanning interferometry (WSI). The WSI can be used to measure large discontinuous surface profiles without the phase ambiguity problems. However, the WSI usually needs to capture hundreds of interferograms at different wavelength in order to evaluate the surface finish for a sample. The evaluating process for this large amount of data needs long processing time if CPUs traditional programming is used. This paper presents a parallel programming model to achieve the data parallelism for accelerating the computing analysis of the captured data. This parallel programming is based on CUDATM C program structure that developed by NVIDIA. Additionally, this paper explains the mathematical algorithm that has been used for evaluating the surface profiles. The computing time and accuracy obtained from CUDA program, using GeForce GTX 280 graphics processing unit (GPU), were compared to those obtained from sequential execution Matlab program, using Intel® Core™2 Duo CPU. The results of measuring a step height sample shows that the parallel programming capability of the GPU can highly accelerate the floating point calculation throughput compared to multicore CPU
Very High Precision Determination of Low-Energy Parameters: The 2-d Heisenberg Quantum Antiferromagnet as a Test Case
The 2-d spin 1/2 Heisenberg antiferromagnet with exchange coupling is
investigated on a periodic square lattice of spacing at very small
temperatures using the loop-cluster algorithm. Monte Carlo data for the
staggered and uniform susceptibilities are compared with analytic results
obtained in the systematic low-energy effective field theory for the staggered
magnetization order parameter. The low-energy parameters of the effective
theory, i.e.\ the staggered magnetization density , the spin stiffness , and the spin wave
velocity are determined with very high precision. Our study
may serve as a test case for the comparison of lattice QCD Monte Carlo data
with analytic predictions of the chiral effective theory for pions and
nucleons, which is vital for the quantitative understanding of the strong
interaction at low energies.Comment: 5 pages, 4 figures, 1 tabl
Investigation of a universal behavior between N\'eel temperature and staggered magnetization density for a three-dimensional quantum antiferromagnet
We simulate the three-dimensional quantum Heisenberg model with a spatially
anisotropic ladder pattern using the first principles Monte Carlo method. Our
motivation is to investigate quantitatively the newly established universal
relation near the quantum critical
point (QCP) associated with dimerization. Here , , and are
the N\'eel temperature, the spinwave velocity, and the staggered magnetization
density, respectively. For all the physical quantities considered here, such as
and , our Monte Carlo results agree nicely with the
corresponding results determined by the series expansion method. In addition,
we find it is likely that the effect of a logarithmic correction, which should
be present in (3+1)-dimensions, to the relation
near the investigated QCP only sets in significantly in the region
with strong spatial anisotropy.Comment: 5 pages, 7 figures, 2 table
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