663 research outputs found
Phase-diagram of two-color lattice QCD in the chiral limit
We study thermodynamics of strongly coupled lattice QCD with two colors of
massless staggered fermions as a function of the baryon chemical potential
in 3+1 dimensions using a new cluster algorithm. We find evidence that
the model undergoes a weak first order phase transition at which
becomes second order at a finite . Symmetry considerations suggest that
the universality class of these phase transitions should be governed by an
field theory with collinear order, with N=3 at and
N=2 at . The universality class of the second order phase
transition at appears to be governed by the decoupled XY fixed
point present in the field theory. Finally we show that the
quantum (T=0) phase transition as a function of is a second order mean
field transition.Comment: 31 pages, 12 figure
Recommended from our members
Apnea, bradycardia and desaturation spells in premature infants: impact of a protocol for the duration of 'spell-free' observation on interprovider variability and readmission rates.
ObjectiveTo study the impact of implementing a protocol to standardize the duration of observation in preterm infants with apnea/bradycardia/desaturation spells before hospital discharge on length of stay (LOS) and readmission rates.Study designA protocol to standardize the duration of in-hospital observation for preterm infants with apnea, bradycardia and desaturation spells who were otherwise ready for discharge was implemented in December 2013. We evaluated the impact of this protocol on the LOS and readmission rates of very low birth weight infants (VLBW). Data on readmission for apnea and an apparent life-threatening event (ALTE) within 30 days of discharge were collected. The pre-implementation epoch (2011 to 2013) was compared to the post-implementation period (2014 to 2016).ResultsThere were 426 and 368 VLBW discharges before and after initiation of the protocol during 2011 to 2013 and 2014 to 2016, respectively. The LOS did not change with protocol implementation (66±42 vs 64±42 days before and after implementation of the protocol, respectively). Interprovider variability on the duration of observation for apneic spells (F-8.8, P=0.04) and bradycardia spells (F-17.4, P<0.001) decreased after implementation of the protocol. The readmission rate for apnea/ALTE after the protocol decreased from 12.1 to 3.4% (P=0.01).ConclusionImplementing an institutional protocol for VLBW infants to determine the duration of apnea/bradycardia/ desaturation spell-free observation period as recommended by the American Academy of Pediatrics clinical report did not prolong the LOS but effectively reduced interprovider variability and readmission rates
Gauge and matter fields as surfaces and loops - an exploratory lattice study of the Z(3) Gauge-Higgs model
We discuss a representation of the Z(3) Gauge-Higgs lattice field theory at
finite density in terms of dual variables, i.e., loops of flux and surfaces. In
the dual representation the complex action problem of the conventional
formulation is resolved and Monte Carlo simulations at arbitrary chemical
potential become possible. A suitable algorithm based on plaquette occupation
numbers and link-fluxes is introduced and we analyze the model at zero
temperature and finite density both in the weak and strong coupling phases. We
show that at zero temperature the model has different first order phase
transitions as a function of the chemical potential both for the weak and
strong coupling phases. The exploratory study demonstrates that alternative
degrees of freedom may successfully be used for Monte Carlo simulations in
several systems with gauge and matter fields.Comment: Typos corrected and some statements refined. Final version to appear
in Phys. Rev.
Studies on lipolytic bacteria in stored fish Etroplus suratensis (Bloch)
The distribution of total hectrotrophic bacteria (THB) and lipolytic bacteria in various regions (body surface, gill, intestine and flesh) of fish Etroplus suratensis (Bloch) during storage at 28 ± 2°C and 4°C was studied. Pseudomonas dominated at reduced temperature whereas at 28 ± 2°C and in fresh condition Vibrio, Aeromonas, and Acinetobacter dominated. Lipolytic activity was elaborated by the members of various genera and their activity varied in different lipid compounds (tributyrin, tween 80, tween 60, tween 40 and tween 20). Tributyrin was utilized by majority of the isolates. All the selected isolates preferred a temperature of 35°C and pH 6.0 for their maximum growth. Aeromonas and Vibrio showed maximum growth at 0.5% NaCl concentration while 3% NaCl was found to be optimum for Pseudomonas
Kosterlitz-Thouless Universality in a Fermionic System
A new extension of the attractive Hubbard model is constructed to study the
critical behavior near a finite temperature superconducting phase transition in
two dimensions using the recently developed meron-cluster algorithm. Unlike
previous calculations in the attractive Hubbard model which were limited to
small lattices, the new algorithm is used to study the critical behavior on
lattices as large as . These precise results for the first time
show that a fermionic system can undergo a finite temperature phase transition
whose critical behavior is well described by the predictions of Kosterlitz and
Thouless almost three decades ago. In particular it is confirmed that the
spatial winding number susceptibility obeys the well known predictions of
finite size scaling for and up to logarithmic corrections the pair
susceptibility scales as at large volumes with for .Comment: Revtex format; 4 pages, 2 figure
A Multi-level Algorithm for Quantum-impurity Models
A continuous-time path integral Quantum Monte Carlo method using the
directed-loop algorithm is developed to simulate the Anderson single-impurity
model in the occupation number basis. Although the method suffers from a sign
problem at low temperatures, the new algorithm has many advantages over
conventional algorithms. For example, the model can be easily simulated in the
Kondo limit without time discretization errors. Further, many observables
including the impurity susceptibility and a variety of fermionic observables
can be calculated efficiently. Finally the new approach allows us to explore a
general technique, called the multi-level algorithm, to solve the sign problem.
We find that the multi-level algorithm is able to generate an exponentially
large number of configurations with an effort that grows as a polynomial in
inverse temperature such that configurations with a positive sign dominate over
those with negative signs. Our algorithm can be easily generalized to other
multi-impurity problems.Comment: 9 pages, 8 figure
Mortality of olive ridley turtles during nesting season along Chennai coast
Sporadic nesting activities of olive ridley turtle
(Lepidochelys olivacea) are often reported along the
Chennai coast in northern Tamil Nadu. These turtles
approach the beaches for nesting in the Tamil month
of Panguni and have thus derived the local name
“Panguni aamai”. As in every year, with the onset of
annual nesting season in early 2017, mortality of
turtles along the Chennai coast was recorded. From
02.01.2017 to 07.01.2017, a total of seven adult turtle
carcasses were observed in 20km stretch of beach
between Marina beach and Kanathur Reddykuppam
Two-Hole Bound States from a Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet
Identifying the correct low-energy effective theory for magnons and holes in
an antiferromagnet has remained an open problem for a long time. In analogy to
the effective theory for pions and nucleons in QCD, based on a symmetry
analysis of Hubbard and t-J-type models, we construct a systematic low-energy
effective field theory for magnons and holes located inside pockets centered at
lattice momenta (\pm pi/2a,\pm pi/2a). The effective theory is based on a
nonlinear realization of the spontaneously broken spin symmetry and makes
model-independent universal predictions for the entire class of lightly doped
antiferromagnetic precursors of high-temperature superconductors. The
predictions of the effective theory are exact, order by order in a systematic
low-energy expansion. We derive the one-magnon exchange potentials between two
holes in an otherwise undoped system. Remarkably, in some cases the
corresponding two-hole Schr\"odinger equations can even be solved analytically.
The resulting bound states have d-wave characteristics. The ground state wave
function of two holes residing in different hole pockets has a d_{x^2-y^2}-like
symmetry, while for two holes in the same pocket the symmetry resembles d_{xy}.Comment: 35 pages, 11 figure
Non-perturbative Quantum Dynamics of the Order Parameter in the Pairing Model
We consider quantum dynamics of the order parameter in the discrete pairing
model (Richardson model) in thermodynamic equilibrium. The integrable
Richardson Hamiltonian is represented as a direct sum of Hamiltonians acting in
different Hilbert spaces of single-particle and paired/empty states. This
allows us to factorize the full thermodynamic partition function into a
combination of simple terms associated with real spins on singly-occupied
states and the partition function of the quantum XY-model for Anderson
pseudospins associated with the paired/empty states. Using coherent-state
path-integral, we calculate the effects of superconducting phase fluctuations
exactly. The contribution of superconducting amplitude fluctuations to the
partition function in the broken-symmetry phase is shown to follow from the
Bogoliubov-de Gennes equations in imaginary time. These equations in turn allow
several interesting mappings, e.g., they are shown to be in a one-to-one
correspondence with the one-dimensional Schr\"odinger equation in
supersymmetric Quantum Mechanics. However, the most practically useful approach
to calculate functional determinants is found to be via an analytical
continuation of the quantum order parameter to real time, \Delta(\tau -> it),
such that the problem maps onto that of a driven two-level system. The
contribution of a particular dynamic order parameter to the partition function
is shown to correspond to the sum of the Berry phase and dynamic phase
accumulated by the pseudospin. We also examine a family of exact solutions for
two-level-system dynamics on a class of elliptic functions and suggest a
compact expression to estimate the functional determinants on such
trajectories. The possibility of having quantum soliton solutions co-existing
with classical BCS mean-field is discussed.Comment: 34 pages (v2: Typos corrected, references added
Kosterlitz Thouless Universality in Dimer Models
Using the monomer-dimer representation of strongly coupled U(N) lattice gauge
theories with staggered fermions, we study finite temperature chiral phase
transitions in (2+1) dimensions. A new cluster algorithm allows us to compute
monomer-monomer and dimer-dimer correlations at zero monomer density (chiral
limit) accurately on large lattices. This makes it possible to show
convincingly, for the first time, that these models undergo a finite
temperature phase transition which belongs to the Kosterlitz-Thouless
universality class. We find that this universality class is unaffected even in
the large N limit. This shows that the mean field analysis often used in this
limit breaks down in the critical region.Comment: 4 pages, 4 figure
- …