2,967 research outputs found
Coarse-grained loop algorithms for Monte Carlo simulation of quantum spin systems
Recently, Syljuasen and Sandvik proposed a new framework for constructing
algorithms of quantum Monte Carlo simulation. While it includes new classes of
powerful algorithms, it is not straightforward to find an efficient algorithm
for a given model. Based on their framework, we propose an algorithm that is a
natural extension of the conventional loop algorithm with the split-spin
representation. A complete table of the vertex density and the worm-scattering
probability is presented for the general XXZ model of an arbitrary S with a
uniform magnetic field.Comment: 12 pages, 7 figures, insert a word "squared" in the first line of the
caption of Fig.7 and correct the label of vertical axis of Fig.
A Reversibility Parameter for a Markovian Stepper
Recent experimental studies on the stepwize motion of biological molecular
motors have revealed that the ``characteristic distance'' of a step is usually
less than the actual step size. This observation implies that the
detailed-balance condition for kinetic rates of steps is violated in these
motors. In this letter, in order to clarify the significance of the
characteristic distance, we study a Langevin model of a molecular motor with a
hidden degree of freedom. We find that the ratio of the characteristic distance
to the step size is equal to unity if the dominant paths in the state space are
one dimensional, while it deviates from unity if the dominant paths are
branched. Therefore, this parameter can be utilized to determine the
reversibility of a motor even under a restricted observation.Comment: 6 pages, 2 figures - minor revision
Two-dimensional super Yang-Mills theory investigated with improved resolution
In earlier work, N=(1,1) super Yang--Mills theory in two dimensions was found
to have several interesting properties, though these properties could not be
investigated in any detail. In this paper we analyze two of these properties.
First, we investigate the spectrum of the theory. We calculate the masses of
the low-lying states using the supersymmetric discrete light-cone (SDLCQ)
approximation and obtain their continuum values. The spectrum exhibits an
interesting distribution of masses, which we discuss along with a toy model for
this pattern. We also discuss how the average number of partons grows in the
bound states. Second, we determine the number of fermions and bosons in the
N=(1,1) and N=(2,2) theories in each symmetry sector as a function of the
resolution. Our finding that the numbers of fermions and bosons in each sector
are the same is part of the answer to the question of why the SDLCQ
approximation exactly preserves supersymmetry.Comment: 20 pages, 10 figures, LaTe
Vector-axialvector mixing from a chiral effective field theory at finite temperature
We study the vector-axialvector mixing in a hot medium and its evolution
toward the chiral phase transition using different symmetry restoration
scenarios based on the generalized hidden local symmetry framework. We show
that the presence of the meson reduces the vector spectral function
around meson mass and enhances it around meson mass. The coupling
strength of to and vanishes at the critical temperature due
to the degenerate - masses. This feature holds rigorously in the
chiral limit and still stays intact to good approximation for the physical pion
mass.Comment: v2:11 pages, 6 figures, reorganized and expanded the text, new plots
and references added, main result and conclusions unchange
Fate of Vector Dominance in the Effective Field Theory
We reveal the full phase structure of the effective field theory for QCD,
based on the hidden local symmetry (HLS) through the one-loop renormalization
group equation including quadratic divergences. We then show that vector
dominance (VD) is not a sacred discipline of the effective field theory but
rather an accidental phenomenon peculiar to three-flavored QCD. In particular,
the chiral symmetry restoration in HLS model takes place in a wide phase
boundary surface, on which the VD is realized nowhere. This suggests that VD
may not be valid for chiral symmetry restoration in hot and/or dense QCD.Comment: 4 pages, 3 figures. One reference added. Minor modification to
shorten the manuscript. This is the version to appear in Physical Review
Letter
Collapse Dynamics of a Star of Dark Matter and Dark Energy
In this work, we study the collapse dynamics of an inhomogeneous spherically
symmetric star made of dark matter (DM) and dark energy (DE). The dark matter
is taken in the form of a dust cloud while anisotropic fluid is chosen as the
candidate for dark energy. It is investigated how dark energy modifies the
collapsing process and is examined whether dark energy has any effect on the
Cosmic Censorship Conjecture. The collapsing star is assumed to be of finite
radius and the space time is divided into three distinct regions and
, where represents the boundary of the star and
denotes the interior (exterior) of the star. The junction
conditions for matching over are specified. Role of Dark
energy in the formation of apparent horizon is studied and central singularity
is analyzed.Comment: 13 page
Finite-size Scaling of Correlation Ratio and Generalized Scheme for the Probability-Changing Cluster Algorithm
We study the finite-size scaling (FSS) property of the correlation ratio, the
ratio of the correlation functions with different distances. It is shown that
the correlation ratio is a good estimator to determine the critical point of
the second-order transition using the FSS analysis. The correlation ratio is
especially useful for the analysis of the Kosterlitz-Thouless (KT) transition.
We also present a generalized scheme of the probability-changing cluster
algorithm, which has been recently developed by the present authors, based on
the FSS property of the correlation ratio. We investigate the two-dimensional
quantum XY model of spin 1/2 with this generalized scheme, obtaining the
precise estimate of the KT transition temperature with less numerical effort.Comment: 4 pages, RevTeX4, to appear in Phys. Rev. B, Rapid Communication
Recent Developments of World-Line Monte Carlo Methods
World-line quantum Monte Carlo methods are reviewed with an emphasis on
breakthroughs made in recent years. In particular, three algorithms -- the loop
algorithm, the worm algorithm, and the directed-loop algorithm -- for updating
world-line configurations are presented in a unified perspective. Detailed
descriptions of the algorithms in specific cases are also given.Comment: To appear in Journal of Physical Society of Japa
Implementation of a novel PCR based method for detecting malaria parasites from naturally infected mosquitoes in Papua New Guinea
<p>Abstract</p> <p>Background</p> <p>Detection of <it>Plasmodium species </it>in mosquitoes is important for designing vector control studies. However, most of the PCR-based detection methods show some potential limitations. The objective of this study was to introduce an effective PCR-based method for detecting <it>Plasmodium vivax </it>and <it>Plasmodium falciparum </it>from the field-caught mosquitoes of Papua New Guinea.</p> <p>Methods</p> <p>A method has been developed to concurrently detect mitochondrial cytochrome b (<it>Cyt b</it>) of four human <it>Plasmodium </it>species using PCR (<it>Cytb</it>-PCR). To particularly discriminate <it>P. falciparum </it>from <it>P. vivax</it>, <it>Plasmodium ovale </it>and <it>Plasmodium malariae</it>, a polymerase chain reaction-repeated fragment length polymorphism (PCR-RFLP) has further been developed to use with this method. However, due to limited samples number of <it>P. ovale </it>and <it>P. malariae</it>; this study was mainly confined to <it>P. vivax </it>and <it>P. falciparum</it>. The efficiency of <it>Cytb</it>-PCR was evaluated by comparing it with two 'gold standards' enzyme linked immunosorbent assay specific for circumsporozoite protein (CS-ELISA) using artificially infected mosquitoes; and nested PCR specific for small subunit ribosomal RNA (<it>SSUrRNA</it>) using field caught mosquitoes collected from three areas (Kaboibus, Wingei, and Jawia) of the East Sepic Province of Papua New Guinea.</p> <p>Results</p> <p>A total of 90 mosquitoes were artificially infected with three strains of <it>Plasmodium</it>: <it>P. vivax-</it>210 (<it>n </it>= 30), <it>P. vivax</it>-247 (<it>n </it>= 30) and <it>P. falciparum </it>(<it>n </it>= 30). These infected mosquitoes along with another 32 unfed mosquitoes were first checked for the presence of <it>Plasmodium </it>infection by CS-ELISA, and later the same samples were compared with the <it>Cytb</it>-PCR. CS-ELISA for <it>P. vivax</it>-210, <it>P. vivax</it>-247 and <it>P. falciparum </it>detected positive infection in 30, 19 and 18 mosquitoes respectively; whereas <it>Cytb</it>-PCR detected 27, 16 and 16 infections, respectively. The comparison revealed a close agreement between the two assays (κ = 0.862, 0.842 and 0.894, respectively for Pv-210, Pv-247 and <it>P. falciparum </it>groups). It was found that the eight CS-ELISA-positive mosquitoes detected negative by <it>Cytb</it>-PCR were false-positive results. The lowest detection limit of this <it>Cytb</it>-PCR was 10 sporozoites. A highly concordance result was also found between nested PCR and <it>Cytb</it>-PCR using 107 field caught mosquitoes, and both tests concordantly detected <it>P. falciparum </it>in an <it>Anopheles punctulatus </it>mosquito collected from Kaboibus. Both tests thus suggested an overall sporozoite rate of 0.9% (1/107) in the study areas. Subsequently, PCR-RFLP efficiently discriminated <it>P. falciparum </it>from <it>P. vivax </it>for all of the <it>Cytb</it>-PCR positive samples.</p> <p>Conclusion</p> <p>A single step PCR based method has been introduced here that is highly sensitive, efficient and reliable for identifying <it>P. vivax </it>and <it>P. falciparum </it>from mosquitoes. The reliability of the technique was confirmed by its ability to detect <it>Plasmodium </it>as efficiently as those of CS-ELISA and nested PCR. Application of the assay offers the opportunity to detect vector species of Papua New Guinea and may contribute for designing further vector control programmes.</p
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