Anomalous skin effect in cylindrical samples

A description is given of the anomalous skin effect in a cylinder placed in an a.c. magnetic field parallel to the cylinder axis. The necessary nonlocal relation between current density and electric field inside the sample is established with the aid of Boltzmann's transport equation. Results are presented in terms of the current density in the sample and its magnetic susceptibility

Ground-State Properties of Finite Antiferromagnetic Chains

Exact calculations are presented for the ground state of linear antiferromagnetic Heisenberg chains with open ends. The wave function and the energy are given for chains with N = 4, 6, and 8, and quantum number S = 1/2. It is shown that in the limit for N - ∞ the ground state is probably nondegenerate and the long-range order tends to zero. The short-range order shows a strongly oscillating character due to end effects persisting over relatively long distances. A comparison with closed rings is made and the connection with the observation of a reduction of the zero-point deviation in the neighbourhood of non-magnetic impurities in more-dimensional systems is pointed out

The response of metals in trapezoidal magnetic fields

The inductive response of metals to applied fields with trapezoidal time dependence is described for samples with cylindrical geometry and for slabs. The influence of coil effects and magnetoresistance is accounted for but mean free path and surface effects are ignored. Experimental data obtained for tin show a close agreement with the theoretical predictions

The response of type H superconductors to trapezoidal magnetic fields

The inductive response of type II superconductors to applied fields with trapezoidal time dependence is described for samples with a slab geometry. An extension of the critical state model which accounts for the observed waveform of the voltage, induced in the pick-up coil, is given. Typical experiments on Nb-slabs with weak pinning and flux flow in fields with both small and large amplitudes are reported

Scattered wave functions of dislocated lattices

Using a Wannier function approach and a transformation of the coordinate system it is shown that a method can be set up to calculate the scattered wave function of a dislocated lattice

The determination of the ground-state energy of an antiferromagnetic lattice by means of a renormalization procedure

An approximate value for the ground-state energy of an antiferromagnetic lattice of spins one-half is determined by means of a repeated renormalization procedure in which the lattice is divided into cells with an effective interaction. This effective interaction is determined on the basis of the spin-hamiltonian formalism

ICT Ação em desenvolvimento na Escola Helen Parkhurst Dalton, parte II

O trabalho apresenta a evolução do plano de ação para melhoria da utilização das TIC na escola Helen Parkhurst Dalton, no ensino secundário. No início do período de ação, em 2007, o uso de TIC na educação foi avaliado através de uma revisão realizada por um grupo de inspetores europeus. Essa avaliação serviu de base para um plano de desenvolvimento contínuo na escola, para promover e melhorar a utilização das TIC. Isso foi feito para resolver os pontos fracos observados, com medidas especiais, e continuar os planos de ação que já haviam sido postos em prática. Em vista de quatro pontos crí- ticos observados, foram tomadas as seguintes medidas: a coe- rência na utilização das TIC foi melhorada, em nível operacional, com a nomeação de coordenadores de escola; a utilização das TIC no ensino foi incentivada ao ser oferecida uma variedade de workshops dedicados à formação de professores; o acompanhamento dos níveis de desempenho dos alunos com o uso das TIC foi abordado por um estudo comparativo em colaboração com estudantes internacionais; a perspectiva de novos desenvolvimentos das TIC, no âmbito do domínio das tecnologias e da pedagogia, foi ampliada através da aquisição de novos equipamentos, como quadros brancos interativos, carrinhos para laptops e outros dispositivos digitais, além da criação de novos laboratórios de informática educacional. Um ano após o surgimento desta inspeção, novos planos surgiram, assim como a organização de um “debate cenário”, pelos líderes escolares, visando abordar o futuro próximo da escola. Nesse debate, a opinião sobre a educação foi renovada em relação aos aspectos organizacionais. Um dos resultados do debate foi a conscientização do papel crescente das TIC. Assim, planos para o futuro próximo da escola foram estabelecidos. Este documento é a segunda contribuição consecutiva, a fim de descrever uma ação baseada no desenvolvimento escolar

Principal response curves technique for the analysis of multivariate biomonitoring time series

Although chemical and biological monitoring is often used to evaluate the quality of surface waters for regulatory purposes and/or to evaluate environmental status and trends, the resulting biological and chemical data sets are large and difficult to evaluate. Multivariate techniques have long been used to analyse complex data sets. This paper discusses the methods currently in use and introduces the principal response curves method, which overcomes the problem of cluttered graphical results representation that is a great drawback of most conventional methods. To illustrate this, two example data sets are analysed using two ordination techniques, principal component analysis and principal response curves. Whereas PCA results in a difficult-to-interpret diagram, principal response curves related methods are able to show changes in community composition in a diagram that is easy to read. The principal response curves method is used to show trends over time with an internal reference (overall mean or reference year) or external reference (e.g. preferred water quality or reference site). Advantages and disadvantages of both methods are discussed and illustrate