1,107 research outputs found
Phase Transitions with Discrete Symmetry Breaking in Antiferromagnetic Heisenberg Models on a Triangular Lattice
We study phase transition behavior of the Heisenberg model on a distorted
triangular lattice with competing interactions. The ground-state phase diagram
indicates that underlying symmetry can be changed by tuning parameters. We
focus on two cases in which a phase transition with discrete symmetry breaking
occurs. The first is that the order parameter space is SO(3). In
this case, a first-order phase transition, with threefold symmetry breaking,
occurs. The second has the order parameter space SO(3). In this
case, a second-order phase transition occurs with twofold symmetry breaking. To
investigate finite-temperature properties of these phase transitions from a
microscopic viewpoint, we introduce a method to make the connection between
continuous frustrated spin systems and the Potts model with invisible states.Comment: 5 pages, 2 figure
Complete phase diagram of the spin-1/2 -- model (with ) on the honeycomb lattice
We use the coupled cluster method to investigate the ground-state (GS)
properties of the frustrated spin-1/2 -- model on the
honeycomb lattice, with nearest-neighbor exchange coupling plus
next-nearest-neighbor () and next-next-nearest-neighbor () exchanges
of equal strength. In particular we find a direct first-order phase transition
between the N\'eel-ordered antiferromagnetic phase and the ferromagnetic phase
at a value when , compared to the
corresponding classical value of -1. We find no evidence for any intermediate
phase. From this and our previous CCM studies of the model we present its full
zero-temperature GS phase diagram.Comment: 4 pages, 4 figure
Magnetic phase diagram of spatially anisotropic, frustrated spin-1/2 Heisenberg antiferromagnet on a stacked square lattice
Magnetic phase diagram of a spatially anisotropic, frustrated spin-1/2
Heisenberg antiferromagnet on a stacked square lattice is investigated using
second-order spin-wave expansion. The effects of interlayer coupling and the
spatial anisotropy on the magnetic ordering of two ordered ground states are
explicitly studied. It is shown that with increase in next nearest neighbor
frustration the second-order corrections play a significant role in stabilizing
the magnetization. We obtain two ordered magnetic phases (Neel and stripe)
separated by a paramagnetic disordered phase. Within second-order spin-wave
expansion we find that the width of the disordered phase diminishes with
increase in the interlayer coupling or with decrease in spatial anisotropy but
it does not disappear. Our obtained phase diagram differs significantly from
the phase diagram obtained using linear spin-wave theory.Comment: 22 pages, 6 figures, minor changes from previous versio
Zero temperature phases of the frustrated J1-J2 antiferromagnetic spin-1/2 Heisenberg model on a simple cubic lattice
At zero temperature magnetic phases of the quantum spin-1/2 Heisenberg
antiferromagnet on a simple cubic lattice with competing first and second
neighbor exchanges (J1 and J2) is investigated using the non-linear spin wave
theory. We find existence of two phases: a two sublattice Neel phase for small
J2 (AF), and a collinear antiferromagnetic phase at large J2 (CAF). We obtain
the sublattice magnetizations and ground state energies for the two phases and
find that there exists a first order phase transition from the AF-phase to the
CAF-phase at the critical transition point, pc = 0.28. Our results for the
value of pc are in excellent agreement with results from Monte-Carlo
simulations and variational spin wave theory. We also show that the quartic 1/S
corrections due spin-wave interactions enhance the sublattice magnetization in
both the phases which causes the intermediate paramagnetic phase predicted from
linear spin wave theory to disappear.Comment: 19 pages, 4 figures, Fig. 1b modified, Appendix B text modifie
Potts-Percolation-Gauss Model of a Solid
We study a statistical mechanics model of a solid. Neighboring atoms are
connected by Hookian springs. If the energy is larger than a threshold the
"spring" is more likely to fail, while if the energy is lower than the
threshold the spring is more likely to be alive. The phase diagram and
thermodynamic quantities, such as free energy, numbers of bonds and clusters,
and their fluctuations, are determined using renormalization-group and
Monte-Carlo techniques.Comment: 10 pages, 12 figure
DNA binding kinetics of two response regulators, PlnC and PlnD, from the bacteriocin regulon of Lactobacillus plantarum C11
<p>Abstract</p> <p>Background</p> <p>Bacteriocin production in the lactic acid bacterium <it>Lactobacillus plantarum </it>C11 is regulated through a quorum sensing based pathway involving two highly homologous response regulators (59% identity and 76% similarity), PlnC as a transcriptional activator and PlnD as a repressor. Previous <it>in vitro </it>studies have shown that both regulators bind, as homodimers, to the same DNA regulatory repeats to exert their regulatory functions. As the genes for these two proteins are located on the same auto-regulatory operon, hence being co-expressed upon gene activation, it is plausible that their opposite functions must somehow be differentially regulated, either in terms of timing and/or binding kinetics, so that their activities do not impair each other in an uncontrolled manner. To understand the nature behind this potential differentiation, we have studied the binding kinetics of the two regulators on five target promoters (P<sub><it>plnA</it></sub>, P<sub><it>plnM</it></sub>, P<sub><it>plnJ</it></sub>, P<sub><it>plnE </it></sub>and P<sub><it>plnG</it></sub>) from the bacteriocin regulon of <it>L. plantarum </it>C11.</p> <p>Results</p> <p>By using surface plasmon resonance spectroscopy we obtained parameters such as association rates, dissociation rates and dissociation constants, showing that the two regulators indeed differ greatly from each other in terms of cooperative binding and binding strength to the different promoters. For instance, cooperativity is very strong for PlnC binding to the promoter of the regulatory operon (P<sub><it>plnA</it></sub>), but not to the promoter of the transport operon (P<sub><it>plnG</it></sub>), while the opposite is seen for PlnD binding to these two promoters. The estimated affinity constants indicate that PlnC can bind to P<sub><it>plnA </it></sub>to activate transcription of the key regulatory operon <it>plnABCD </it>without much interference from PlnD, and that the repressive function of PlnD might act through a different mechanism than repression of the regulatory operon.</p> <p>Conclusion</p> <p>We have characterised the DNA binding kinetics of the two regulators PlnC and PlnD from the bacteriocin locus in <it>L. plantarum </it>C11. Our data show that PlnC and PlnD, despite their strong homology to each other, differ greatly from each other in terms of binding affinity and cooperativity to the different promoters of the <it>pln </it>regulon.</p
Static and dynamical quantum correlations in phases of an alternating field XY model
We investigate the static and dynamical patterns of entanglement in an
anisotropic XY model with an alternating transverse magnetic field, which is
equivalent to a two-component one-dimensional Fermi gas on a lattice, a system
realizable with current technology. Apart from the antiferromagnetic and
paramagnetic phases, the model possesses a dimer phase which is not present in
the transverse XY model. At zero temperature, we find that the first derivative
of bipartite entanglement can detect all the three phases. We analytically show
that the model has a "factorization line" on the plane of system parameters, in
which the zero temperature state is separable. Along with investigating the
effect of temperature on entanglement in a phase plane, we also report a
non-monotonic behavior of entanglement with respect to temperature in the
anti-ferromagnetic and paramagnetic phases, which is surprisingly absent in the
dimer phase. Since the time dynamics of entanglement in a realizable physical
system plays an important role in quantum information processing tasks, the
evolutions of entanglement at small as well as large time are examined.
Consideration of large time behavior of entanglement helps us to prove that in
this model, entanglement is always ergodic. We observe that other quantum
correlation measures can qualitatively show similar features in zero and finite
temperatures. However, unlike nearest-neighbor entanglement, the
nearest-neighbor information theoretic measures can be both ergodic as well as
non-ergodic, depending on the system parameters.Comment: 20 Pages, 13 Figures, 2 Tables, Published versio
Theory of Impurity Effects on the Spin Nematic State
The effect of magnetic bond disorder in otherwise antiferro nematic ordered
system is investigated. We introduced triangular-shaped ferromagnetic bond
disorder in the S=1 bilinear-biquadratic model on a triangular lattice. It is
shown that the coupling between the impurity magnetic moment and nonmagnetic
excitation in the bulk yields single-moment anisotropy and long-range
anisotropic interaction between impurity magnetic moments. This interaction can
induce unconventional spin-freezing phenomena observed in triangular magnet,
NiGa2S4.Comment: 19 pages, 14 figure
Impact of Different Layer Housing Systems on Eggshell Cuticle Quality and Salmonella Adherence in Table Eggs
The bacterial load on the eggshell surface is a key factor in predicting the bacterial penetration and contamination of the egg interior. The eggshell cuticle is the first line of defense against
vertical penetration by microbial food-borne pathogens such as Salmonella Enteritidis. Egg producers
are increasingly introducing alternative caging systems into their production chain as animal welfare
concerns become of greater relevance to today’s consumer. Stress that is introduced by hen aggression
and modified nesting behavior in furnished cages can alter the physiology of egg formation and
affect the cuticle deposition/quality. The goal of this study was to determine the impact of caging
systems (conventional, enriched, free-run, and free-range), on eggshell cuticle parameters and the
eggshell bacterial load. The cuticle plug thickness and pore length were higher in the free-range eggs
as compared to conventional eggs. The eggshells from alternative caging (enriched and free-range)
had a higher total cuticle as compared to conventional cages. A reduction in bacterial cell counts was
observed on eggshells that were obtained from free-range eggs as compared to the enriched systems.
An inverse correlation between the contact angle and Salmonella adherence was observed. These
results indicate that the housing systems of layer hens can modify the cuticle quality and thereby
impact bacterial adherence and food safety.Egg Farmers of Canada (EFC)
grant number: 551562, Livestock Research Innovation Corporation (LRIC) grant number 570593PID2020-
116660GB-I00, RNM-938 group (Junta de Andalucía)UCE PP 2016.05 (Universidad de Granada
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