Diffusion in a crowded environment

We analyze a pair of diffusion equations which are derived in the infinite system--size limit from a microscopic, individual--based, stochastic model. Deviations from the conventional Fickian picture are found which ultimately relate to the depletion of resources on which the particles rely. The macroscopic equations are studied both analytically and numerically, and are shown to yield anomalous diffusion which does not follow a power law with time, as is frequently assumed when fitting data for such phenomena. These anomalies are here understood within a consistent dynamical picture which applies to a wide range of physical and biological systems, underlining the need for clearly defined mechanisms which are systematically analyzed to give definite predictions.Comment: 4 pages, 3 figures, minor change

Low work function of the (1000) Ca2N surface

Polymer diodes require cathodes that do not corrode the polymer but do have low work function to minimize the electron injection barrier. First-principles calculations demonstrate that the work function of the (1000) surface of the compound Ca2N is half an eV lower than that of the elemental metal Ca (2.35 vs. 2.87 eV). Moreover its reactivity is expected to be smaller. This makes Ca2N an interesting candidate to replace calcium as cathode material for polymer light emitting diode devices.Comment: 3 pages, 4 figures, accepted by J. Appl. Phy

Relativistic Nucleus-Nucleus Collisions: Zone of Reactions and Space-Time Structure of a Fireball

A zone of reactions is determined and then exploited as a tool in studying the space-time structure of an interacting system formed in a collision of relativistic nuclei. The time dependence of the reaction rates integrated over spatial coordinates is also considered. Evaluations are made with the help of the microscopic transport model UrQMD. The relation of the boundaries of different zones of reactions and the hypersurfaces of sharp chemical and kinetic freeze-outs is discussed.Comment: 6 pages, 5 figure

On the origin dependence of multipole moments in electromagnetism

The standard description of material media in electromagnetism is based on multipoles. It is well known that these moments depend on the point of reference chosen, except for the lowest order. It is shown that this "origin dependence" is not unphysical as has been claimed in the literature but forms only part of the effect of moving the point of reference. When also the complementary part is taken into account then different points of reference lead to different but equivalent descriptions of the same physical reality. This is shown at the microscopic as well as at the macroscopic level. A similar interpretation is valid regarding the "origin dependence" of the reflection coefficients for reflection on a semi infinite medium. We show that the "transformation theory" which has been proposed to remedy this situation (and which is thus not needed) is unphysical since the transformation considered does not leave the boundary conditions invariant.Comment: 14 pages, 0 figure

Shear flow, viscous heating, and entropy balance from dynamical systems

A consistent description of a shear flow, the accompanied viscous heating, and the associated entropy balance is given in the framework of a deterministic dynamical system, where a multibaker dynamics drives two fields: the velocity and the temperature distributions. In an appropriate macroscopic limit their transport equations go over into the Navier-Stokes and the heat conduction equation of viscous flows. The inclusion of an artificial heat sink can stabilize steady states with constant temperatures. It mimics a thermostating algorithm used in non-equilibrium molecular-dynamics simulations.Comment: LaTeX 2e (epl.cls + sty-files for Europhys Lett included); 7 pages + 1 eps-figur

Kinetic cross coupling between non-conserved and conserved fields in phase field models

We present a phase field model for isothermal transformations of two component alloys that includes Onsager kinetic cross coupling between the non-conserved phase field and the conserved concentration field. We also provide the reduction of the phase field model to the corresponding macroscopic description of the free boundary problem. The reduction is given in a general form. Additionally we use an explicit example of a phase field model and check that the reduced macroscopic description, in the range of its applicability, is in excellent agreement with direct phase field simulations. The relevance of the newly introduced terms to solute trapping is also discussed

Artikel 17 van de Preparatenrichtlijn 1999/45/EG is verschillend geimplementeerd in EU lidstaten. Een onderzoek naar hoe Vergiftigingen Informatie Centra worden geinformeerd over gevaarlijke preparaten.

A survey on the notification of information on dangerous preparations by companies to Poisons Information Centres shows that each EU Member State has made different arrangements. This is the result of missing guidelines in the Preparations Directive 1999/45/EC. The implementation of the 'Globally Harmonised System of classification and labelling of chemicals' (GHS) in the EU will replace the Preparations Directive. This is a good opportunity to harmonize product notification at an EU level and have it legally enforced. The notified product information is used for medical purposes, particularly to provide information on poisonings with these preparations. This report shows that in six countries the Poisons Information Centre (PIC) directly receives the information on the dangerous preparations. In most other countries, a governmental authority is appointed that makes the information available to the PICs. Between EU Member States different requirements are set concerning the notification of the composition of the product and the concentrations of the ingredients. There are also different procedures for notification and a considerable variety in used forms and/or applications for electronic notification. Harmonisation of product notification can be achieved if the receiving authorities first reach consensus on the required product information. Next, an agreement on an acceptable format for notification must be reached.Onderzoek naar de aanlevering van informatie over gevaarlijke preparaten door bedrijven aan Vergiftigingen Informatie Centra laat zien dat dit in elke EU lidstaat anders geregeld is. Dit komt doordat in de Europese Preparatenrichtlijn 1999/45/EG hierover geen duidelijke regels zijn vastgelegd. De invoering van het 'Globally Harmonised System of classification and labelling of chemicals' (GHS) in de EU gaat de Preparatenrichtlijn vervangen. Dit is een goed moment om op Europees niveau de aanlevering van productinformatie te harmoniseren en de vereisten wettelijk vast te leggen. De aangeleverde productinformatie wordt gebruikt voor medische doeleinden, met name het verstrekken van informatie in geval van vergiftigingen. Dit rapport laat zien dat in zes landen een Vergiftigingen Informatie Centrum hiervoor direct is aangewezen als ontvangende instantie. In de meeste andere landen wordt de productinformatie aan hen ter beschikking gesteld door een (ander) ontvangend overheidsorgaan. In EU lidstaten gelden verschillende vereisten voor de op te geven productsamenstelling en de concentraties van de ingredienten. Eveneens verschillen de procedures voor aanlevering en is er een aanzienlijke variatie in de gebruikte formulieren en/of applicaties voor elektronische aanlevering. Voor het bereiken van harmonisatie is het noodzakelijk dat de ontvangende instanties eerst consensus bereiken over de vereiste productinformatie. Daarna moet overeenstemming worden bereikt over een gemeenschappelijk formaat voor aanlevering

Mechanisms of kinetic trapping in self-assembly and phase transformation

In self-assembly processes, kinetic trapping effects often hinder the formation of thermodynamically stable ordered states. In a model of viral capsid assembly and in the phase transformation of a lattice gas, we show how simulations in a self-assembling steady state can be used to identify two distinct mechanisms of kinetic trapping. We argue that one of these mechanisms can be adequately captured by kinetic rate equations, while the other involves a breakdown of theories that rely on cluster size as a reaction coordinate. We discuss how these observations might be useful in designing and optimising self-assembly reactions

Momentum of an electromagnetic wave in dielectric media

Almost a hundred years ago, two different expressions were proposed for the energy--momentum tensor of an electromagnetic wave in a dielectric. Minkowski's tensor predicted an increase in the linear momentum of the wave on entering a dielectric medium, whereas Abraham's tensor predicted its decrease. Theoretical arguments were advanced in favour of both sides, and experiments proved incapable of distinguishing between the two. Yet more forms were proposed, each with their advocates who considered the form that they were proposing to be the one true tensor. This paper reviews the debate and its eventual conclusion: that no electromagnetic wave energy--momentum tensor is complete on its own. When the appropriate accompanying energy--momentum tensor for the material medium is also considered, experimental predictions of all the various proposed tensors will always be the same, and the preferred form is therefore effectively a matter of personal choice.Comment: 23 pages, 3 figures, RevTeX 4. Removed erroneous factor of mu/mu_0 from Eq.(44