B cell activation and affinity discrimination by receptor segregation?

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Liquid crystal films on curved surfaces: An entropic sampling study

The confining effect of a spherical substrate inducing anchoring (normal to the surface) of rod-like liquid crystal molecules contained in a thin film spread over it has been investigated with regard to possible changes in the nature of the isotropic-to-nematic phase transition as the sample is cooled. The focus of these Monte Carlo simulations is to study the competing effects of the homeotropic anchoring due to the surface inducing orientational ordering in the radial direction and the inherent uniaxial order promoted by the intermolecular interactions. By adopting entropic sampling procedure, we could investigate this transition with a high temperature precision, and we studied the effect of the surface anchoring strength on the phase diagram for a specifically chosen geometry. We find that there is a threshold anchoring strength of the surface below which uniaxial nematic phase results, and above which the isotropic fluid cools to a radially ordered nematic phase, besides of course expected changes in the phase transition temperature with the anchoring strength. In the vicinity of the threshold anchoring strength we observe a bistable region between these two structures, clearly brought out by the characteristics of the corresponding microstates constituting the entropic ensemble.Comment: 14 pages, 5 figure

Liquid crystal director fluctuations and surface anchoring by molecular simulation

We propose a simple and reliable method to measure the liquid crystal surface anchoring strength by molecular simulation. The method is based on the measurement of the long-range fluctuation modes of the director in confined geometry. As an example, molecular simulations of a liquid crystal in slab geometry between parallel walls with homeotropic anchoring have been carried out using the Monte Carlo technique. By studying different slab thicknesses, we are able to calculate separately the position of the elastic boundary condition, and the extrapolation length

Front-end electronics for drift tubes in a high-rate environment

A front-end electronics readout for drift tubes in a high-rate environment is presented. This system allows us to encode several pieces of information (leading edge time, trailing edge time, signal charge and piled-up hits from multiple tracks) into a single readout channel that is presented to the TDC. The advantage of active baseline restoration compared to bipolar signal shaping is discussed

Rate effects in high-resolution drift chambers

The impact of high counting rates on the spatial resolution of cylindrical drift tubes is investigated in detail and the results are compared with simulations. Electronics effects and space-charge effects are quantitatively analysed. A spatial resolution of $\sigma < 80\,\mu\mathrm{m}$ can be achieved even at rates as high as 1500\,Hz/cm wire length (300\,kHz per wire)

Resolution limits of drift tubes

Measurements of the drift-tube response to charged particle tracks are compared with a complete simulation. The measured resolution of typically 80\,$\mu$m agrees well with the simulation and allows the individual factors limiting the resolution such as diffusion, charge deposit fluctuations, gas gain fluctuations and signal processing to be studied. The results with respect to the dependence of the drift chamber resolution on gas gain, gas pressure and electronics parameters are reported

Dependence of Drift Tube Performance on the Anode Wire Diameter

Cylindrical pressurized drift tubes with different anode wire diameters wereoperated in a 170~GeV muon test beam. The dependences of spatialresolution, efficiency and streamer probability on the anode wirediameter were measured. The resolution measurements are compared with a simulation

Bestimmung der Haftfestigkeit von aufgedampften, metallischen Dickschichten auf Polymersubstrat

Inaktivkomponenten in der Batterieherstellung, wie z. B. Stromsammler, Separator oder die Kontaktierungstaps rücken zunehmend in den Fokus der Forschung. Der Wechsel zu leichteren und günstigeren Materialien ist Gegenstand aktueller Forschungsarbeiten. In diesem Zusammenhang wird auch das Potential von Verbundstromkollektoren näher betrachtet. Dabei handelt es sich um Polymerfolien, die beidseitig mit 0,5 µm bis 1,5 µm dicken Aluminium- oder Kupferschichten metallisiert sind. Als Verbundmaterial müssen dabei im Vergleich zu konventionellen, metallischen Stromkollektoren zusätzliche Materialeigenschaften betrachtet werden. Dazu gehört vor allem die Haftfestigkeit der metallischen Beschichtungen auf den Folien. Es muss ausgeschlossen werden, dass durch wechselnde mechanische Beanspruchungen oder chemische Wechselwirkungen (z.B. mit dem Elektrolyten) in der Li-Ionen-Batteriezelle Delaminationen auftreten und sich die Metallisierung ablöst. Dazu ist eine quantitative Methode zur Bestimmung der Haftfestigkeit notwendig. Nur so kann eine Korrelation zwischen der Haftfestigkeit und dem Verhalten in der Zelle hergestellt werden. Bisherige Versuchsmethoden decken den Anwendungsfall von beidseitig metallisierten Polymersubstraten als Stromkollektorfolie jedoch nicht ab. Aus diesem Grund werden in dieser Studie Prüfverfahren zur Bestimmung der Haftfestigkeit, die bereits in Normen spezifiziert werden, zur Bewertung der Haftfestigkeiten der Verbundfolien adaptiert und bewertet. Die betrachteten Verfahren umfassen Schälversuche, Stirnabzugs- und Zugschertests, welche hinsichtlich ihrer Eignung zur Beurteilung der Haftfestigkeit von Verbundstromkollektoren evaluiert werden. Dabei werden Verbundfolien mit unterschiedlicher Schicht- sowie Substratdicke und variierendem Beschichtungsmaterial berücksichtigt, sodass die Sensitivität der Verfahren zur Bestimmung der Haftfestigkeit aufgelöst und darauf aufbauend deren Eignung zur Charakterisierung der Verbundfolien bewertet werden kann

Topological Defects in Nematic Droplets of Hard Spherocylinders

Using computer simulations we investigate the microscopic structure of the singular director field within a nematic droplet. As a theoretical model for nematic liquid crystals we take hard spherocylinders. To induce an overall topological charge, the particles are either confined to a two-dimensional circular cavity with homeotropic boundary or to the surface of a three-dimensional sphere. Both systems exhibit half-integer topological point defects. The isotropic defect core has a radius of the order of one particle length and is surrounded by free-standing density oscillations. The effective interaction between two defects is investigated. All results should be experimentally observable in thin sheets of colloidal liquid crystals.Comment: 13 pages, 16 figures, Phys. Rev.