Monte Carlo study of the growth of L12L1_2 ordered domains in fcc A3BA_3B binary alloys

A Monte Carlo study of the late time growth of $L1_2$ ordered domains on a fcc $A_3B$ binary alloy is presented. The energy of the alloy has been modeled by a nearest neighbor interaction Ising hamiltonian. The system exhibits a fourfold degenerated ground-state and two kinds of interfaces separating ordered domains: flat and curved antiphase boundaries. Two different dynamics are used in the simulations: the standard atom-atom exchange mechanism and the more realistic vacancy-atom exchange mechanism. The results obtained by both methods are compared. In particular we study the time evolution of the excess energy, the structure factor and the mean distance between walls. In the case of atom-atom exchange mechanism anisotropic growth has been found: two characteristic lengths are needed in order to describe the evolution. Contrarily, with the vacancy-atom exchange mechanism scaling with a single length holds. Results are contrasted with existing experiments in $Cu_3Au$ and theories for anisotropic growth

Thermodynamics of Ferrotoroidic Materials: Toroidocaloric Effect

The three primary ferroics, namely ferromagnets, ferroelectrics and ferroelastics exhibit corresponding large (or even giant) magnetocaloric,electrocaloric and elastocaloric effects when a phase transition is induced by the application of an appropriate external field. Recently the suite of primary ferroics has been extended to include ferrotoroidic materials in which there is an ordering of toroidic moments in the form of magnetic vortex-like structures, examples being LiCo(PO_4)_3 and Ba_2CoGe_2O_7. In the present work we formulate the thermodynamics of ferrotoroidic materials. Within a Landau free energy framework we calculate the toroidocaloric effect by quantifying isothermal entropy change (or adiabatic temperature change) in the presence of an applied toroidic field when usual magnetization and polarization may also be present simultaneously. We also obtain a nonlinear Clausius-Clapeyron relation for phase coexistence.Comment: 10 pages, 5 Figure

Modulated phases in multi-stage structural transformations

For multistage displacive structural transitions we present a general framework that accounts for various intermediate modulated phases, elastic constant, phonon, and related thermodynamic anomalies. Based on the presence or absence of modulated phases we classify these transformations in four categories and apply this approach to four different representative materials Ni-Mn-Ga (or \ensuremath{\alpha}\ensuremath{-}\mathrm{U}), NiTi(Fe), Ni-Al, and Cu-Zn-Al. We suggest that the anomalous increase in elastic constants and phonon frequency observed when approaching the martensitic transition from above is a signature of the commensurate modulated phase

Thermodynamics of multicaloric effects in multiferroic materials; application to metamagnetic shape memory alloys and ferrotoroidics

We develop a general thermodynamic framework to investigate multicaloric effects in multiferroic materials. This is applied to the study of both magnetostructural and magnetoelectric multiferroics. Landau models with appropriate interplay between the corresponding ferroic properties (order parameters) are proposed for metamagnetic shapememory and ferrotoroidic materials, which, respectively, belong to the two classes of multiferroics. For each ferroic property, caloric effects are quantified by the isothermal entropy change induced by the application of the corresponding thermodynamically conjugated field. The multicaloric effect is obtained as a function of the two relevant applied fields in each class of multiferroics. It is further shown that multicaloric effects comprise the corresponding contributions from caloric effects associated with each ferroic property and the crosscontribution arising from the interplay between these ferroic properties. This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials

A novel double-layer mucoadhesive Tablet containing probiotic strain for vaginal administration: Design, development and technological evaluation

Abstract Vulvovaginal candidosis caused by Candida spp. is the most prevalent vaginal infection in Europe and the second one in EE.UU, so it has become a major female concern. Probiotics bacteria have been proposed as an alternative treatment with the aim of avoiding the adverse effects associated with conventional therapies including antibiotics and other aggressive drugs for the vaginal mucosa and microbiota. The purpose of this work was to design and develop a novel vaginal tablet that contained Lactobacillus spp. bacteria as a treatment against vulvovaginal infections. A total of 21 two-layers vaginal tablets, which contained different polymeric ratios, were proposed. However, formulation F4 (20 mg Na-CMC; 50 mg Carbopol® 934; 20 mg chitosan) was selected as optimal according to its swelling index and dissolution/erosion capability. F4 tablets showed suitable technological properties for vaginal administration as well as mucoadhesion time (24.36 ± 0.88 h) and force (0.0941 N). Disintegration assay in simulated vaginal fluid (SVF, pH 5.5) showed that effervescent layer disappeared in 27.48 ± 0.05 s whilst matrix layer was totally gelled in 1 h. Two different release profiles were achieved; on the one hand, a promptly release due to the dissolution of both effervescent layer and matrix layer's surface (1.10 × 108 CFU/g), on the second hand, a prolonged released of the remaining bacteria until 24 h (5.48 × 107 CFU/g). For stability and storage study, it was found that bacteria viability was constant until 90 days in both ways of storage, in a desiccator and at room temperature, with a final dosage of 108 CFU/g which was considered appropriate for vaginal therapy (108–1010 CFU/g)

Vacancy-assisted domain-growth in asymmetric binary alloys: A Monte Carlo Study

A Monte Carlo simulation study of the vacancy-assisted domain growth in asymmetric binary alloys is presented. The system is modeled using a three-state ABV Hamiltonian which includes an asymmetry term. Our simulated system is a stoichiometric two-dimensional binary alloy with a single vacancy which evolves according to the vacancy-atom exchange mechanism. We obtain that, compared to the symmetric case, the ordering process slows down dramatically. Concerning the asymptotic behavior it is algebraic and characterized by the Allen-Cahn growth exponent x51/2. The late stages of the evolution are preceded by a transient regime strongly affected by both the temperature and the degree of asymmetry of the alloy. The results are discussed and compared to those obtained for the symmetric case

Responsabilidad civil profesional de un gestor por daños generados en la tramitación de una herencia

En este trabajo se estudia la Responsabilidad Civil de una gestoría por la forma negligente en que un profesional de su plantilla lleva a cabo la tramitación y gestión de una herencia, y los pasos a seguir para ejercer la acción de responsabilidad.<br /

Intermitten dynamics in externally driven ferroelastics and strain glasses

The interplay of elastic anisotropy and disorder dictates many of the properties of ferroic materials, specifically martensites. We use a phase-field model for ferroelastic athermal materials to study their response to an increasing external stress that couples to the strain order parameter. We show that these systems evolve through avalanches and study the avalanche-size distribution for ferroelastic systems (large anisotropy and/or small disorder) and for the strain glass (small anisotropy and/or large disorder) using various statistical analysis techniques, including the maximum likelihood method. The model predicts that in the former case the distribution is subcritical or power law (in agreement with experimental observations), whereas in the latter case it becomes supercritical. Our results are consistent with experiments on martensitic materials, and we predict specific avalanche behavior that can be tested and used as an alternative means to characterize strain glasses

Multiferroic and related hysteretic behavior in ferromagnetic shape memory alloys

We combine a Ginzburg–Landau model for a ferroelastic transition with the theory of micromagnetism to study the magnetostructural behavior leading to multicaloric effects in ferromagnetic shape memory alloys. We analyze the ferroelastic transition under different conditions of temperature, stress and magnetic field and establish the corresponding phase diagram. On the one hand, our results show that the proper combination of both fields may be used to reduce the transition hysteresis and thus improve the reversibility of the related elastocaloric effects, superelasticity and stress-mediated magnetocaloric effects. On the other hand, the stress-free magnetic field-driven and thermally driven magnetostructural evolution provides physical insight into the low-temperature field-induced domain reorientation, from which we derive strategies to modify the operational temperature ranges and thus the corresponding (magnetic) shape-memory effect.Peer ReviewedPostprint (published version