881 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
The role of KRT5+ progenitors in chronic otitis media
Background: Chronic inflammation of the middle ear, known as chronic otitis media, is a debilitating condition of unknown aetiology that causes hearing loss in children and adults. Recent work suggests the epithelial lining of the middle ear cavity may play a role in the disease process. The hypothesis is that abnormal proliferation and differentiation of keratin-5(KRT5)-positive progenitor cells results in a maladaptive epithelial remodelling. The work here characterises KRT5+ progenitor cells and explores their contribution to middle ear epithelial homeostasis in health and chronic otitis media with effusion (COME). Methods: Murine middle ear epithelial cells from the Fbxo11Jf/+ model of COME and healthy controls were isolated by enzymatic dissociation and used for colony forming assays, immunocytochemistry and flow cytometry. Cells were grown at air-liquid interface to analyse differentiation potential and a 3Dspheroid assay was used to analyse single cell differentiation. KRT5-Cre- ERT2;R26R-Confetti multicolour reporter mice were generated to perform lineage tracing to visualise middle ear epithelial homeostasis in vivo. Results: Middle ear epithelium has cells with progenitor cell capacity that are KRT5+. These make up approximately 7% of the epithelial compartment and may have a dorso-ventral asymmetry of distribution that reverses in Fbxo11Jf/+ mice. Differentiation assays show middle ear progenitors from Fbxo11Jf/+ mice have aberrant differentiation potential with reduced bipotent differentiation ability. 3D whole-mount visualisation of the middle ear from multicolour reporter mice shows the presence of distinct KRT5+ progenitor derived clones in multiple regions of the middle ear. Conclusion: This work provides further support that KRT5+ cells are progenitor cells of the middle ear epithelium with bipotent differentiation capacity and thus may maintain the epithelium in health. These progenitor characteristics seem to be perturbed in the Fbxo11Jf/+ mouse model of COME. Understanding the mechanism underlying these changes offers the potential to identify new therapeutic targets
Simulating lattice gauge theories on a quantum computer
We examine the problem of simulating lattice gauge theories on a universal
quantum computer. The basic strategy of our approach is to transcribe lattice
gauge theories in the Hamiltonian formulation into a Hamiltonian involving only
Pauli spin operators such that the simulation can be performed on a quantum
computer using only one and two qubit manipulations. We examine three models,
the U(1), SU(2), and SU(3) lattice gauge theories which are transcribed into a
spin Hamiltonian up to a cutoff in the Hilbert space of the gauge fields on the
lattice. The number of qubits required for storing a particular state is found
to have a linear dependence with the total number of lattice sites. The number
of qubit operations required for performing the time evolution corresponding to
the Hamiltonian is found to be between a linear to quadratic function of the
number of lattice sites, depending on the arrangement of qubits in the quantum
computer. We remark that our results may also be easily generalized to higher
SU(N) gauge theories.Comment: 15 pages, 4 figures, 3 table
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.
Solutions to sign problems in lattice Yukawa models
We prove that sign problems in the traditional approach to some lattice
Yukawa models can be completely solved when the fermions are formulated using
fermion bags and the bosons are formulated in the worldline representation. We
prove this within the context of two examples of three dimensional models,
symmetric under transformations,
one involving staggered fermions and the other involving Wilson fermions. We
argue that these models have interesting quantum phase transitions that can now
be studied using Monte Carlo methods.Comment: 5 pages, 1 figure (Fixed minor typographical errors, expanded the
discussion to include solution to the sign problem with the conventional
bosonic action and added a reference.
Quantum Monte Carlo Study of Disordered Fermions
We study a strongly correlated fermionic model with attractive interactions
in the presence of disorder in two spatial dimensions. Our model has been
designed so that it can be solved using the recently discovered meron-cluster
approach. Although the model is unconventional it has the same symmetries of
the Hubbard model. Since the naive algorithm is inefficient, we develop a new
algorithm by combining the meron-cluster technique with the directed-loop
update. This combination allows us to compute the pair susceptibility and the
winding number susceptibility accurately. We find that the s-wave
superconductivity, present in the clean model, does not disappear until the
disorder reaches a temperature dependent critical strength. The critical
behavior as a function of disorder close to the phase transition belongs to the
Berezinsky-Kosterlitz-Thouless universality class as expected. The fermionic
degrees of freedom, although present, do not appear to play an important role
near the phase transition.Comment: published version, more data added to Fig 5 and clarifications in
text, 8 page
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
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
Role of the -resonance in determining the convergence of chiral perturbation theory
The dimensionless parameter , where
is the pion decay constant and is the pion mass, is expected to control
the convergence of chiral perturbation theory applicable to QCD. Here we
demonstrate that a strongly coupled lattice gauge theory model with the same
symmetries as two-flavor QCD but with a much lighter -resonance is
different. Our model allows us to study efficiently the convergence of chiral
perturbation theory as a function of . We first confirm that the leading
low energy constants appearing in the chiral Lagrangian are the same when
calculated from the -regime and the -regime as expected. However,
is necessary before 1-loop chiral perturbation theory
predicts the data within 1%. For the data begin to deviate
dramatically from 1-loop chiral perturbation theory predictions. We argue that
this qualitative change is due to the presence of a light -resonance in
our model. Our findings may be useful for lattice QCD studies.Comment: 5 pages, 6 figures, revtex forma
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
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