Mobility of Bloch Walls via the Collective Coordinate Method

We have studied the problem of the dissipative motion of Bloch walls considering a totally anisotropic one dimensional spin chain in the presence of a magnetic field. Using the so-called "collective coordinate method" we construct an effective Hamiltonian for the Bloch wall coupled to the magnetic excitations of the system. It allows us to analyze the Brownian motion of the wall in terms of the reflection coefficient of the effective potential felt by the excitations due to the existence of the wall. We find that for finite values of the external field the wall mobility is also finite. The spectrum of the potential at large fields is investigated and the dependence of the damping constant on temperature is evaluated. As a result we find the temperature and magnetic field dependence of the wall mobility.Comment: 20 pages, 5 figure

Propuesta metodológica para la integración en SIG de métodos de participación social para la planificación y gestión de sistemas de dunas litorales. El ejemplo del parque natural de Corralejo (Fuerteventura, Islas Canarias)

El propósito de esta comunicación es presentar una propuesta metodológica para el uso de los SIG como herramienta para la integración de la percepción social en la planificación y gestión de los sistemas de dunas costeras en las Islas Canarias. Este ejercicio de aplicación inicial se ha desarrollado en el Parque Natural de Corralejo (Fuerteventura).The purpose of this communication is to present a methodological proposal for the use of GIS as tool for the integration of methods of social perception in planning and management of coastal dune systems in the Canary Islands. This exercise of initial application has been developed in Corralejo Natural Park (Fuerteventura)

Bricolage as Survival, Growth and Transformation:the Role of Patchworking in the Social Agency of Migrant Entrepreneurs

This article examines the patch-working strategies of migrant entrepreneurs as a form of social agency. ‘Patch-working’ – the reliance on supplementary forms of income to support business activity – is often seen as a means of cushioning the financial vulnerability of small firms. However, the mechanisms and forms that patch-working takes tend to be overlooked. Evidence from 42 West Midlands’ firms shows that, despite the highly constrained operating environment, the exercise of social agency can help to cushion against disadvantage and to rework their current conditions through patch-working. This allows for business growth, and even transformational growth in some cases, rather than sheer survival. Even so, our findings show that the agency of migrant entrepreneurs brings about only minor improvements in revenue and is certainly not capable of fundamentally changing either the nature of the sector or the structure of the labour market in which they are embedded

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.

ADC Quantization Requirements

In this document, we analyze the impact of the quantization at the input of the demultiplexer. The required number of bits of the Analog-to-Digital-Converter (ADC) is obtained, along with the corresponding quantization losses.Preprin