Domain-wall profile in the presence of anisotropic exchange interactions: Effective on-site anisotropy

Starting from a D-dimensional XXZ ferromagnetic Heisenberg model in an hypercubic lattice, it is demonstrated that the anisotropy in the exchange coupling constant leads to a D-dependent effective on-site anisotropy interaction often ignored for D>1. As a result the effective width of the wall depends on the dimensionality of the system. It is shown that the effective one-dimensional Hamiltonian is not the one-dimensional XXZ version as assumed in previous theoretical work. We derive a new expression for the wall profile that generalizes the standard Landau-Lifshitz form. Our results are found to be in very good agreement with earlier numerical work using the Monte Carlo method. Preceding theories concerning the domain wall contribution to magnetoresistance have considered the role of D only through the modification of the density of states in the electronic band structure. This Brief Report reveals that the wall profile itself contains an additional D dependence for the case of anisotropic exchange interactions.Comment: 4 pages; new title and abstract; 1 figure comparing our results with earlier numerical work; a more general model containing the usual on-site anisotropy; new remarks and references on the following two topics: (a) experimental evidence for the existence of spin exchange anisotropy, and (b) preceding theories concerning the domain wall contribution to magnetoresistance; to appear in Phys. Rev.

Relevance of cell subcompartmentalization techniques to predict adverse effects of metals in bivalves and fish

Subcellular fractionation is an interesting technique to study metal cell compartmentalization and helps on evaluating the impact of a contaminant in an organism. It provides a better understanding about the fate and behaviour of metals within cell compartments, being then able to identify if metals experience a detoxification process or, on the contrary, they are trophically available. Having this information about metals and metalloids is crucial in the context of risk assessment, as it provides valuable information about their behaviour throughout the food chain at different trophic levels. Coastal and marine environments are often affected by dangerous spillages. Pollutants tend to accumulate in water, soils and sediments, where they can become readily available to species, such as bivalves and fish. These species are often used as bioindicators as they can provide information about the trophic transfer and/or the accumulation and of different pollutants. After a bibliographic search, the protocols used to study the subcellular fractionation on bivalves and fish exposed to metals have been highlighted. This literature mini review focuses on the different protocols used for studying this issue and the improvements that subcellular fractionation has brought to the topic. Nonetheless, future research needs and perspectives are pointed out as they can improve the robustness of using such techniques for risk assessment

Analysis for water conflict transformation

This article proposes and fleshes out an analytical method designed to support efforts to transform inequitable and unsustainable transboundary water arrangements. Such ‘transformative analysis’ leverages socio-ecological thinking to critically evaluate the processes that have established and maintain an arrangement, including hydro-diplomacy itself. Transformative analysis facilitates the interpretation of strategies to deflect transformation, identification of destructive forms of cooperation, and strategic classification of opportunities for transformation. The assertions are premised on an understanding of the particularities of water conflict, and followed by a discussion of ways researchers may overcome the challenges inherent in the method