Finite element modeling of electromagnetic fields and waves using NASTRAN

The various formulations of Maxwell's equations are reviewed with emphasis on those formulations which most readily form analogies with Navier's equations. Analogies involving scalar and vector potentials and electric and magnetic field components are presented. Formulations allowing for media with dielectric and conducting properties are emphasized. It is demonstrated that many problems in electromagnetism can be solved using the NASTRAN finite element code. Several fundamental problems involving time harmonic solutions of Maxwell's equations with known analytic solutions are solved using NASTRAN to demonstrate convergence and mesh requirements. Mesh requirements are studied as a function of frequency, conductivity, and dielectric properties. Applications in both low frequency and high frequency are highlighted. The low frequency problems demonstrate the ability to solve problems involving media inhomogeneity and unbounded domains. The high frequency applications demonstrate the ability to handle problems with large boundary to wavelength ratios

Integrated land use modelling of agri-environmental measures to maintain biodiversity at landscape level

Integrated land use models (ILM) are increasingly applied tools for the joint assessment of complex economic-environmental farming system interactions. We present an ILM that consists of the crop rotation model CropRota, the bio-physical process model EPIC, and the farm optimization model FAMOS[space]. The ILM is applied to analyze agri-environmental measures to maintain biodiversity in an Austrian landscape. We jointly consider the biodiversity effects of land use intensity (i.e. nitrogen application rates and mowing frequencies) and landscape development (e.g. provision of landscape elements) using a rich indicator set and region specific species-area relationships. The cost-effectiveness of agri-environmental measures in attaining alternative biodiversity targets is assessed by scenario analysis. The model results show the negative relationships between biodiversity maintenance and gross margins per ha. The absence of agri-environmental measures likely leads to a loss of semi-natural landscape elements such as orchard meadows and hedges as well as to farmland intensifications. The results are also relevant for external cost estimates. However, further methodologies need to be developed that can jointly and endogenously consider the complexities of the socio-economic land use system at farm and regional levels as well as the surrounding natural processes at sufficient detail for biodiversity assessments.Integrated farm land use modeling, biodiversity indicators, agri-environmental policy, landscape elements, Agricultural and Food Policy, Crop Production/Industries, Environmental Economics and Policy, Farm Management, Food Security and Poverty, Land Economics/Use, Production Economics,

Effective Perrin theory for the anisotropic diffusion of a strongly hindered rod

Slender rods in concentrated suspensions constitute strongly interacting systems with rich dynamics: transport slows down drastically and the anisotropy of the motion becomes arbitrarily large. We develop a mesoscopic description of the dynamics down to the length scale of the interparticle distance. Our theory is based on the exact solution of the Smoluchowski-Perrin equation; it is in quantitative agreement with extensive Brownian dynamics simulations in the dense regime. In particular, we show that the tube confinement is characterised by a power law decay of the intermediate scattering function with exponent 1/2.Comment: to appear in EP

Exclusion Processes with Internal States

We introduce driven exclusion processes with internal states that serve as generic transport models in various contexts, ranging from molecular or vehicular traffic on parallel lanes to spintronics. The ensuing non-equilibrium steady states are controllable by boundary as well as bulk rates. A striking polarization phenomenon accompanied by domain wall motion and delocalization is discovered within a mesoscopic scaling. We quantify this observation within an analytic description providing exact phase diagrams. Our results are confirmed by stochastic simulations.Comment: 4 pages, 3 figures. Version as published in Phys. Rev. Let

Enhanced Diffusion of a Needle in a Planar Course of Point Obstacles

The transport of an infinitely thin, hard rod in a random, dense array of point obstacles is investigated by molecular dynamics simulations. Our model mimics the sterically hindered dynamics in dense needle liquids. The center-of-mass diffusion exhibits a minimum, and transport becomes increasingly fast at higher densities. The diffusion coefficient diverges according to a power law in the density with an approximate exponent of 0.8. This observation is connected with a new divergent time scale, reflected in a zig-zag motion of the needle, a two-step decay of the velocity-autocorrelation function, and a negative plateau in the non-Gaussian parameter.Comment: accepted for publication in Phys. Rev. Let

Online service delivery models : an international comparison in the public sector

Governments around the world are facing the challenge of responding to increased expectations by their customers with regard to public service delivery. Citizens, for example, expect governments to provide better and more efficient electronic services on the Web in an integrated way. Online portals have become the approach of choice in online service delivery to meet these requirements and become more customer-focussed. This study describes and analyses existing variants of online service delivery models based upon an empirical study and provides valuable insights for researchers and practitioners in government. For this study, we have conducted interviews with senior management representatives from five international governments. Based on our findings, we distinguish three different classes of service delivery models. We describe and characterise each of these models in detail and provide an in-depth discussion of the strengths and weaknesses of these approaches

Generic principles of active transport

Nonequilibrium collective motion is ubiquitous in nature and often results in a rich collection of intringuing phenomena, such as the formation of shocks or patterns, subdiffusive kinetics, traffic jams, and nonequilibrium phase transitions. These stochastic many-body features characterize transport processes in biology, soft condensed matter and, possibly, also in nanoscience. Inspired by these applications, a wide class of lattice-gas models has recently been considered. Building on the celebrated {\it totally asymmetric simple exclusion process} (TASEP) and a generalization accounting for the exchanges with a reservoir, we discuss the qualitative and quantitative nonequilibrium properties of these model systems. We specifically analyze the case of a dimeric lattice gas, the transport in the presence of pointwise disorder and along coupled tracks.Comment: 21 pages, 10 figures. Pedagogical paper based on a lecture delivered at the conference on "Stochastic models in biological sciences" (May 29 - June 2, 2006 in Warsaw). For the Banach Center Publication

The Dynamical Fingerprint of Core Scouring in Massive Elliptical Galaxies

The most massive elliptical galaxies have low-density centers or cores that differ dramatically from the high-density centers of less massive ellipticals and bulges of disk galaxies. These cores have been interpreted as the result of mergers of supermassive black hole binaries, which depopulate galaxy centers by gravitationally slingshotting central stars toward large radii. Such binaries naturally form in mergers of luminous galaxies. Here, we analyze the population of central stellar orbits in 11 massive elliptical galaxies that we observed with the integral field spectrograph SINFONI at the European Southern Observatory Very Large Telescope. Our dynamical analysis is orbit-based and includes the effects of a central black hole, the mass distribution of the stars, and a dark matter halo. We show that the use of integral field kinematics and the inclusion of dark matter is important to conclude upon the distribution of stellar orbits in galaxy centers. Six of our galaxies are core galaxies. In these six galaxies, but not in the galaxies without cores, we detect a coherent lack of stars on radial orbits in the core region and a uniform excess of radial orbits outside of it: when scaled by the core radius, the radial profiles of the classical anisotropy parameter beta are nearly identical in core galaxies. Moreover, they match quantitatively the predictions of black hole binary simulations, providing the first convincing dynamical evidence for core scouring in the most massive elliptical galaxies.Comment: 8 pages, 3 figures, accepted by Ap

An analytic solution to the Busemann-Petty problem on sections of convex bodies

We derive a formula connecting the derivatives of parallel section functions of an origin-symmetric star body in R^n with the Fourier transform of powers of the radial function of the body. A parallel section function (or (n-1)-dimensional X-ray) gives the ((n-1)-dimensional) volumes of all hyperplane sections of the body orthogonal to a given direction. This formula provides a new characterization of intersection bodies in R^n and leads to a unified analytic solution to the Busemann-Petty problem: Suppose that K and L are two origin-symmetric convex bodies in R^n such that the ((n-1)-dimensional) volume of each central hyperplane section of K is smaller than the volume of the corresponding section of L; is the (n-dimensional) volume of K smaller than the volume of L? In conjunction with earlier established connections between the Busemann-Petty problem, intersection bodies, and positive definite distributions, our formula shows that the answer to the problem depends on the behavior of the (n-2)-nd derivative of the parallel section functions. The affirmative answer to the Busemann-Petty problem for n\le 4 and the negative answer for n\ge 5 now follow from the fact that convexity controls the second derivatives, but does not control the derivatives of higher orders.Comment: 13 pages, published versio

Auftragsterminierung für die taktisch-operative Personaleinsatzplanung in Wirtschaftsprüfungsgesellschaften

Basierend auf den Ergebnissen einer empirischen Untersuchung wurde ein hierarchischer Ansatz zur Personaleinsatzplanung in Wirtschaftsprüfungsgesellschaften entwickelt, der die Teilprobleme der taktischen, der taktisch-operativen und der operativen Planung umfaßt. Der vorliegende Beitrag setzt sich mit der taktisch-operativen Planung auseinander. Das Problem wird zunächst als binäres Optimierungsproblem formuliert. Anschließend wird ein speziell an die Problemstruktur angepaßtes heuristisches Verfahrensschema vorgestellt, das unter Verwendung von Prioritätswerten randomisierte Auswahl- und Einplanungsentscheidungen trifft. Die Eignung des Verfahrensschemas wird in einer umfangreichen experimentellen Untersuchung nachgewiesen.Based upon an empirical survey, an hierarchical framework for audit-staff scheduling has been developed which distinguishes between a tactical, a tactical-operational and an operational level. In our paper we investigate the tactical-operational level. A binary optimization model is formulated, which adequately represents the problem. Afterwards, a randomized heuristic scheme specifically tailored to the problem structure is described which uses priority values to base randomized selection and scheduling decisions upon. Its suitability is demonstrated in an extensive computational experiment