3,477 research outputs found

    Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields

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    The behavior of the nonlinear susceptibility χ3\chi_3 and its relation to the spin-glass transition temperature TfT_f, 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 λAT\lambda_{\rm AT} (replicon) on the random fields is analyzed. Particularly, in absence of random fields, the temperature TfT_f can be traced by a divergence in the spin-glass susceptibility χSG\chi_{\rm SG}, which presents a term inversely proportional to the replicon λAT\lambda_{\rm AT}. As a result of a relation between χSG\chi_{\rm SG} and χ3\chi_3, the latter also presents a divergence at TfT_f, which comes as a direct consequence of λAT=0\lambda_{\rm AT}=0 at TfT_f. However, our results show that, in the presence of random fields, χ3\chi_3 presents a rounded maximum at a temperature TT^{*}, which does not coincide with the spin-glass transition temperature TfT_f (i.e., T>TfT^* > T_f for a given applied random field). Thus, the maximum value of χ3\chi_3 at TT^* 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 χ3\chi_3 still maintains a dependence on the replicon λAT\lambda_{\rm AT}, 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 LiHox_xY1x_{1-x}F4_4 compound.Comment: accepted for publication in PR

    Magnetic susceptibility anisotropies in a two-dimensional quantum Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions

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    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

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    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

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    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

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    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

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    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

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    We investigate the inverse freezing in the fermionic Ising spin-glass (FISG) model in a transverse field Γ\Gamma. 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 nn is strongly affected by Γ\Gamma. 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

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    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 LiHox_xY1x_{1-x}F4_4. 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 Δ\Delta. 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 CmC_{m}, nonlinear susceptibility χ3\chi_3 and phase diagrams for different disorder configurations. In the absence of RF, the χ3\chi_3 exhibits a divergence at TfT_f, while the CmC_{m} shows a broad maximum at a temperature TT^{**} around 30%\% above TfT_f, as expected for conventional SG systems. The presence of RF changes this scenario. The CmC_{m} still shows the maximum at TT^{**} that is weakly dependent on Δ\Delta. However, the TfT_f is displaced to lower temperatures, enhancing considerable the ration T/TfT^{**}/T_f. Furthermore, the divergence in χ3\chi_3 is replaced by a rounded maximum at a temperature TT^{*}, which becomes increasingly higher than TfT_f as Δ\Delta enhances. As a consequence, the paramagnetic phase is unfolded in three regions: (i) a conventional paramagnetism (T>TT>T^{**}; (ii) a region with formation of short-range order with frozen spins (T<T<TT^{*}<T<T^{**}); (iii) a region with slow growth of free-energy barriers slowing down the spin dynamics before the SG transition (Tf<T<TT_f<T<T^{*}) suggesting an intermediate Griffiths phase before the SG state. Our results reproduce qualitatively some findings of LiHox_xY1x_{1-x}F4_4 as the rounded maximum of χ3\chi_3 behavior triggered by RF.Comment: 9 pages, 6 figure

    Synthesis of a Plant-based Dust Suppressant and Testing on Coal from Moatize, Mozambique

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    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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