3,474 research outputs found
Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields
The behavior of the nonlinear susceptibility and its relation to the
spin-glass transition temperature , in the presence of random fields, are
investigated. To accomplish this task, the Sherrington-Kirkpatrick model is
studied through the replica formalism, within a one-step
replica-symmetry-breaking procedure. In addition, the dependence of the
Almeida-Thouless eigenvalue (replicon) on the random fields
is analyzed. Particularly, in absence of random fields, the temperature
can be traced by a divergence in the spin-glass susceptibility ,
which presents a term inversely proportional to the replicon . As a result of a relation between and , the
latter also presents a divergence at , which comes as a direct consequence
of at . However, our results show that, in the
presence of random fields, presents a rounded maximum at a temperature
, which does not coincide with the spin-glass transition temperature
(i.e., for a given applied random field). Thus, the maximum
value of at reflects the effects of the random fields in the
paramagnetic phase, instead of the non-trivial ergodicity breaking associated
with the spin-glass phase transition. It is also shown that still
maintains a dependence on the replicon , although in a more
complicated way, as compared with the case without random fields. These results
are discussed in view of recent observations in the LiHoYF
compound.Comment: accepted for publication in PR
Magnetic susceptibility anisotropies in a two-dimensional quantum Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions
The magnetic and thermodynamic properties of the two-dimensional quantum
Heisenberg antiferromagnet that incorporates both a Dzyaloshinskii-Moriya and
pseudo-dipolar interactions are studied within the framework of a generalized
nonlinear sigma model (NLSM). We calculate the static uniform susceptibility
and sublattice magnetization as a function of temperature and we show that: i)
the magnetic-response is anisotropic and differs qualitatively from the
expected behavior of a conventional easy-axis QHAF; ii) the Neel second-order
phase transition becomes a crossover, for a magnetic field B perpendicular to
the CuO(2) layers. We provide a simple and clear explanation for all the
recently reported unusual magnetic anisotropies in the low-field susceptibility
of La(2)CuO(4), L. N. Lavrov et al., Phys. Rev. Lett. 87, 017007 (2001), and we
demonstrate explicitly why La(2)CuO(4) can not be classified as an ordinary
easy-axis antiferromagnet.Comment: 6 pages, 3 figures, Revtex4, accepted for publication in Phys. Rev.
Dynamics of topological defects in a spiral: a scenario for the spin-glass phase of cuprates
We propose that the dissipative dynamics of topological defects in a spiral
state is responsible for the transport properties in the spin-glass phase of
cuprates. Using the collective-coordinate method, we show that topological
defects are coupled to a bath of magnetic excitations. By integrating out the
bath degrees of freedom, we find that the dynamical properties of the
topological defects are dissipative. The calculated damping matrix is related
to the in-plane resistivity, which exhibits an anisotropy and linear
temperature dependence in agreement with experimental data.Comment: 4 pages, as publishe
Edible coatings with polysaccharides and bioactive compounds from exhausted olive oil pomace to extend the shelf life of strawberry
Introduction: Exhausted or delipidified olive oil pomace (EOP) is a by-product generated from the olive pomace after air drying and hexane extraction of residual oil [1]. This by-product is rich in phenolic compounds, such as hydroxytyrosol, tyrosol and catechol, with associated properties: antioxidant, antimicrobial, anti- inflammatory, anti-diabetic, anti-carcinogenic and anti-HIV [1, 2]. Coatings and films are materials used for example to increase the shelf life of perishable fruits and vegetables. They can be made of polysaccharides, lipids and proteins from natural sources. It is essential to include bioactive compounds in the formulation to achieve bioactive properties, such as antimicrobial and antioxidant activities [3]. In this work a coating was performed using alginate and an extract rich in phenolics from EOP to increase the shelf life of strawberry (Fragaria ananassa). Objectives: To develop an edible coating using alginate and an extract rich in phenolics from EOP. To apply the coating to a perishable fruit, such as strawberry. To determine the moisture loss of the coated strawberry. To observe the natural decay of strawberry. To determine the growing curves of mesophilic aerobic bacteria, psychrophilic bacteria, Enterobacteriaceae, yeasts and molds in the coated strawberry. Conclusions: The formulation 2 % alginate + 5 % EOP extract can be successfully used as an edible coating. The application of the coating on strawberry are effective to prevent moisture loss, maintaining the quality of the fruits. It prevents the proliferation of several bacteria, such as psychrophilic bacteria, mesophilic aerobic bacteria, yeasts and molds.info:eu-repo/semantics/publishedVersio
Derivation of the generalized Non Linear Sigma Model in the presence of the Dzyaloshinskii-Moriya interaction
We derive the long-wavelength non-linear sigma model for a two-dimensional
Heisenberg system in the presence of the Dzyaloshinskii-Moriya and
pseudodipolar interactions. We show that the system is a non-conventional
easy-axis antiferromagnet, displaying an anomalous coupling between the
magnetic field and the staggered order parameter. Our results are in good
agreement with recent experimental data for undoped La2CuO4 compounds.Comment: Proceedings of SCES05, to appear on Physica
Finite-momentum Bose-Einstein condensates in shaken 2D square optical lattices
We consider ultracold bosons in a 2D square optical lattice described by the
Bose-Hubbard model. In addition, an external time-dependent sinusoidal force is
applied to the system, which shakes the lattice along one of the diagonals. The
effect of the shaking is to renormalize the nearest-neighbor hopping
coefficients, which can be arbitrarily reduced, can vanish, or can even change
sign, depending on the shaking parameter. It is therefore necessary to account
for higher-order hopping terms, which are renormalized differently by the
shaking, and introduce anisotropy into the problem. We show that the
competition between these different hopping terms leads to finite-momentum
condensates, with a momentum that may be tuned via the strength of the shaking.
We calculate the boundaries between the Mott-insulator and the different
superfluid phases, and present the time-of-flight images expected to be
observed experimentally. Our results open up new possibilities for the
realization of bosonic analogs of the FFLO phase describing inhomogeneous
superconductivity.Comment: 7 pages, 7 figure
Role of the transverse field in inverse freezing in the fermionic Ising spin-glass model
We investigate the inverse freezing in the fermionic Ising spin-glass (FISG)
model in a transverse field . The grand canonical potential is
calculated in the static approximation, replica symmetry and one-step replica
symmetry breaking Parisi scheme. It is argued that the average occupation per
site is strongly affected by . As consequence, the boundary phase
is modified and, therefore, the reentrance associated with the inverse freezing
is modified too.Comment: 6 pages, 3 figures, accepted for publication in PR
Specific heat and non-linear susceptibility in spin glasses with random fields
We study magnetic properties of spin glass SG systems under a random field
(RF), beased on the suggestion that RFs can be induced by a weak transverse
field in the compound LiHoYF. We consider a cluster spin model
that allows long-range disordered interactions among clusters and short-range
interactions inside the clusters, besides a local RF for each spin following a
Gaussian distribution with standard deviation . We adopt the one-step
replica symmetry breaking (RSB) approach to get an exactly solvable
single-cluster problem. We discuss the behavior of order parameters, specific
heat , nonlinear susceptibility and phase diagrams for
different disorder configurations. In the absence of RF, the exhibits
a divergence at , while the shows a broad maximum at a temperature
around 30 above , as expected for conventional SG systems.
The presence of RF changes this scenario. The still shows the maximum
at that is weakly dependent on . However, the is
displaced to lower temperatures, enhancing considerable the ration
. Furthermore, the divergence in is replaced by a rounded
maximum at a temperature , which becomes increasingly higher than
as enhances. As a consequence, the paramagnetic phase is unfolded in
three regions: (i) a conventional paramagnetism (; (ii) a region with
formation of short-range order with frozen spins (); (iii) a
region with slow growth of free-energy barriers slowing down the spin dynamics
before the SG transition () suggesting an intermediate Griffiths
phase before the SG state. Our results reproduce qualitatively some findings of
LiHoYF as the rounded maximum of behavior triggered by
RF.Comment: 9 pages, 6 figure
Synthesis of a Plant-based Dust Suppressant and Testing on Coal from Moatize, Mozambique
The dust suppressant was synthesized using Pinus elliottii resin as raw material for the new plant-based formulation. The dust suppressant formulation was prepared by solubilizing rosin in a ternary solution containing calcium chloride, ultrapure water, and ethanol in a molar ratio of 1:2:8. After centrifugation the supernatant was collected, 20 mL of 2 % γ-polyglutamic acid dissolved in an aqueous ethanol solution was added, and the mixture was stirred for 2 hours. The dust suppressant formulation included Pinus extract and γ-PGA acid, resulting in a plant-based dust suppressant. The performance of the new formulation in reducing PM10 was significantly superior (82.7 %) to that of water. This suppressant is suitable for spraying onto coal ore piles and hopper cars carrying coal ore. The wettability of the product was analyzed by the Walker test, which confirmed its adhesiveness to coal dust.
This work is licensed under a Creative Commons Attribution 4.0 International License
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