16,979 research outputs found
Effective potential for composite operators and for an auxiliary scalar field in a Nambu-Jona-Lasinio model
We derive the effective potentials for composite operators in a
Nambu-Jona-Lasinio (NJL) model at zero and finite temperature and show that in
each case they are equivalent to the corresponding effective potentials based
on an auxiliary scalar field. The both effective potentials could lead to the
same possible spontaneous breaking and restoration of symmetries including
chiral symmetry if the momentum cutoff in the loop integrals is large enough,
and can be transformed to each other when the Schwinger-Dyson (SD) equation of
the dynamical fermion mass from the fermion-antifermion vacuum (or thermal)
condensates is used. The results also generally indicate that two effective
potentials with the same single order parameter but rather different
mathematical expressions can still be considered physically equivalent if the
SD equation corresponding to the extreme value conditions of the two potentials
have the same form.Comment: 7 pages, no figur
Lookahead Strategies for Sequential Monte Carlo
Based on the principles of importance sampling and resampling, sequential
Monte Carlo (SMC) encompasses a large set of powerful techniques dealing with
complex stochastic dynamic systems. Many of these systems possess strong
memory, with which future information can help sharpen the inference about the
current state. By providing theoretical justification of several existing
algorithms and introducing several new ones, we study systematically how to
construct efficient SMC algorithms to take advantage of the "future"
information without creating a substantially high computational burden. The
main idea is to allow for lookahead in the Monte Carlo process so that future
information can be utilized in weighting and generating Monte Carlo samples, or
resampling from samples of the current state.Comment: Published in at http://dx.doi.org/10.1214/12-STS401 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
An in-host model of HIV incorporating latent infection and viral mutation
We construct a seven-component model of the in-host dynamics of the Human
Immunodeficiency Virus Type-1 (i.e, HIV) that accounts for latent infection and
the propensity of viral mutation. A dynamical analysis is conducted and a
theorem is presented which characterizes the long time behavior of the model.
Finally, we study the effects of an antiretroviral drug and treatment
implications.Comment: 10 pages, 7 figures, Proceedings of AIMS Conference on Differential
Equations and Dynamical Systems (2015
Critical Behavior in the Rotating D-branes
The low energy excitation of the rotating D3-branes is thermodynamically
stable up to a critical angular momentum density. This indicates that there is
a corresponding phase transition of the =4 large super Yang-Mills
theory at finite temperature. On the side of supergravity, we investigate the
phase transition in the grand canonical ensemble and canonical ensemble. Some
critical exponents of thermodynamic quantities are calculated. They obey the
static scaling laws. Using the scaling laws related to the correlation length,
we get the critical exponents of the correlation function of gauge field. The
thermodynamic stability of low energy excitations of the rotating M5-branes and
rotating M2-branes is also studied and similar critical behavior is observed.
We find that the critical point is shifted in the different ensembles and there
is no critical point in the canonical ensemble for the rotating M2-branes. We
also discuss the Hawking-Page transition for these rotating branes. In the
grand canonical ensemble, the Hawking-Page transition does not occur. In the
canonical ensemble, however, the Hawking-Page transition may appear for the
rotating D3- and M5-branes, but not for the rotating M2-branes.Comment: Revtex, 17 pages, minor changes, the discussion on the Hawking-Page
transition and references adde
Cluster dynamical mean field theory of quantum phases on a honeycomb lattice
We have studied the ground state of the half-filled Hubbard model on a
honeycomb lattice by performing the cluster dynamical mean field theory
calculations with exact diagonalization on the cluster-impurity solver. Through
using elaborate numerical analytic continuation, we identify the existence of a
`spin liquid' from the on-site interaction U=0 to (between and
) with a smooth crossover correspondingly from the charge fluctuation
dominating phase into the charge correlation dominating phase. The
semi-metallic state exits only at U=0. We further find that the magnetic phase
transition at from the `spin liquid' to the N\'{e}el antiferromagnetic
Mott insulating phase is a first-order quantum phase transition. We also show
that the charge fluctuation plays a substantial role on keeping the `spin
liquid' phase against the emergence of a magnetic order.Comment: 5 pages and 8 figure
Magnetic Bose glass phases of coupled antiferromagnetic dimers with site dilution
We numerically investigate the phase diagram of two-dimensional site-diluted
coupled dimer systems in an external magnetic field. We show that this phase
diagram is characterized by the presence of an extended Bose glass, not
accessible to mean-field approximation, and stemming from the localization of
two distinct species of bosonic quasiparticles appearing in the ground state.
On the one hand, non-magnetic impurities doped into the dimer-singlet phase of
a weakly coupled dimer system are known to free up local magnetic moments. The
deviations of these local moments from full polarization along the field can be
mapped onto a gas of bosonic quasiparticles, which undergo condensation in zero
and very weak magnetic fields, corresponding to transverse long-range
antiferromagnetic order. An increasing magnetic field lowers the density of
such quasiparticles to a critical value at which a quantum phase transition
occurs, corresponding to the quasiparticle localization on clusters of local
magnets (dimers, trimers, etc.) and to the onset of a Bose glass. Strong
finite-size quantum fluctuations hinder further depletion of quasiparticles
from such clusters, and thus lead to the appearance of pseudo-plateaus in the
magnetization curve of the system. On the other hand, site dilution hinders the
field-induced Bose-Einstein condensation of triplet quasiparticles on the
intact dimers, and it introduces instead a Bose glass of triplets. A thorough
numerical investigation of the phase diagram for a planar system of coupled
dimers shows that the two above-mentioned Bose glass phases are continuously
connected, and they overlap in a finite region of parameter space, thus
featuring a two-species Bose glass. The quantum phase transition from Bose
glass to magnetic order in two dimensions is marked by novel universal
exponents.Comment: 15 pages, 16 figure
Thermoelectric Properties of Silicon Carbide Nanowires with Nitrogen Dopants and Vacancies
The thermoelectric properties of cubic zincblend silicon carbide nanowires
(SiCNWs) with nitrogen impurities and vacancies along [111] direction are
theoretically studied by means of atomistic simulations. It is found that the
thermoelectric figure of merit ZT of SiCNWs can be significantly enhanced by
doping N impurities together with making Si vacancies. Aiming at obtaining a
large ZT, we study possible energetically stable configurations, and disclose
that, when N dopants locate at the center, a small number of Si vacancies at
corners are most favored for n-type nanowires, while a large number of Si
vacancies spreading into the flat edge sites are most favored for p-type
nanowires. For the SiCNW with a diameter of 1.1 nm and a length of 4.6 nm, the
ZT value for the n-type is shown capable of reaching 1.78 at 900K. The
conditions to get higher ZT values for longer SiCNWs are also addressed.Comment: 9 pages, 10 figure
A planning study for palliative spine treatment using StatRT and megavoltage CT simulation.
Megavoltage CT (MVCT) simulation on the TomoTherapy Hi·Art system is an alternative to conventional CT for treatment planning in the presence of severe metal artifact. StatRT is a new feature that was implemented on the TomoTherapy operator station for performing online MVCT scanning, treatment planning and treatment delivery in one session. The clinical feasibility of using the StatRT technique and MVCT simulation to palliative treatment for a patient with substantial spinal metallic hardware is described. A patient with metastatic non-small-cell lung cancer involving the thoracic spine underwent conventional kilovoltage CT simulation. The metal artifact due to stainless steel spine-stabilizing rods was too severe for treatment planning, despite attempts to correct using density override. The patient was then re-scanned using MVCT on a tomotherapy unit. Plans were generated using both StatRT and conventional tomotherapy planning (Tomo plan) with different settings for comparison. StatRT planning ran a total of five iterations in a short planning window (10-15 min). Two Tomo plans were generated using: (1) five iterations in the "full scatter" mode, and (2) 300 iterations in the "beamlet" mode. It was noted that the DVH of the StatRT plan was almost identical to the Tomo plan optimized by the "full scatter" mode and the same number of iterations. Dose distribution analysis reveals that these three planning methods yielded comparable doses to heart, lungs and targets. This work also demonstrated that undermodulation can result in a high degree of thread effects. The overall time for the treatment process (including 7 minutes for simulation, 15 minutes for contouring, 10 minutes for planning and 5 minutes for delivery) decreases from hours to around 40 minutes using the StatRT procedure. StatRT is a feasible treatment-planning tool for physicians to scan, contour and treat patients within one hour. This can be particularly beneficial in urgent palliative treatments
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