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We study repertoire selection in a network of natural antibodies that is maintained by stimulatory idiotypic interactions. The natural antibody repertoire develops in an environment of self epitopes to which the self-reactive B cell clones are completely tolerant. For the modeling formalism, we extend the shape space framework so that each antibody is represented by several randomly chosen shapes. B cell clones are generated stochastically and are removed whenever their density falls below an extinction threshold. The idiotypic interactions are governed by a log bell-shaped interaction function. The natural antibody repertoire in the model is formed by percolation: the network is autonomously activated following a point stimulation. Our main conclusion is that the natural antibody repertoire organizes itself in such a way that most sel...
In deze scriptie wordt verslag gedaan van een onderzoek naar de presentatie van primaire links (met name) op de homepages van vier gemeentelijke websites: Utrecht, Haarlem, Amersfoort en Leeuwarden. In dat onderzoek staat de vraag centraal: welke presentatie van primaire links in de navigatiebalk (wel of geen afrolmenu, wel of geen ‘mouse rollover effect’) en welk aantal ervan helpt de bezoeker het meest efficiënt en effectief op weg naar de door hem/haar gezochte informatie of dienst, en hoe tevreden zijn ze daar uiteindelijk over.
We present the first calculations, by computer simulation, of the Frank elastic constants of a liquid crystal composed of freely rotating and translating molecules. Extensive calculations are performed for hard prolate ellipsoids at a single density, and for hard spherocylinders at three densities. For ellipsoids, the resulting Frank constants are of the same order of magnitude as those found experimentally, and in the expected ratios. For spherocylinders, elastic constants increase rapidly with density. Existing density functional theories are only moderately successful in predicting elastic constants. Includes an erratum, published in vol. 42; 6; 1990 -p. 3641
Since the work of Onsager, systems of hard spherocylinders have played a special role as the theoretician’s “ideal” nematic liquid crystals. It is, however, well-known that the Onsager theory is only a good description for extremely nonspherical particles. A quantitative measure for the range of validity of this theory is obtained from direct numerical calculation of the third through fifth virial coefficients of hard spherocylinders with length-to-width ratios, LID, between 1 and lo6. The phase diagram of spherocylinders with “realistic” LID ratios can only be obtained by computer simulation. We report molecular dynamics and Monte Carlo simulations for spherocylinders with LID = 5. These calculations suggest that the oldest model for a hard-core nematic may, in fact, have a smectic liquid-crygalline phase as well. Includes an erratum...
In order to get dipole-moment derivatives, ∂ú/∂Sj that are free from rotational contributions, we used Crawford's method applied to a new type of reference molecule. The agreement with earlier calculated rotational correction terms is good, the applicability of the new reference molecule is wider. The rotational contributions to the ∂ú/∂Sj-quantities are presented for a number of C2v- and C3v-type molecules.
A longitudinal study of bone changes in the mandible was conducted. Duplicate radiographs were taken at 3-month intevals with the use of a positioning instrument, which included an aluminum calibrating wedge. The in-duplicate values obtained over the investigation period made it possible to assess the precision of the method and to analyze effects that take place with time. Significant bone changes were observed in seven volunteers between various observation periods at intervals of 6 and 9 months.
In het onderwijs wordt veel gesproken over het aanleren van vaardigheden. Wat zijn vaardigheden? Welke zijn van toepassing op het onderwijs? In de praktijk blijkt dat bepaalde vaardigheden van leerlingen niet altijd gestructureerd worden aangeleerd en getraind. Hoofdvraag: Hoe wordt het aanleren van vaardigheden op school toegepast in de praktijk? Subvragen: 1. Wat zijn vaardigheden. 2. Hoe weet een school of docent aan welke vaardigheden aandacht moet worden besteed en dit wordt vertaald naar een school- of lesprogramma. 3. Is er met betrekking tot de dagelijkse lespraktijk sprake van overlap of ontbreken van het aanleren van vaardigheden? De beantwoording van deze vragen vindt plaats in twee hoofdstukken. Ten eerste wordt aan de hand van literatuur en internetbronnen een inleiding op hoofdlijnen gegeven over vaardigheden (hoofdst...
The Stratego language for program transformation is based on a strategy-controlled application of basic rewrite rules. These rewrite rules have only local knowledge of the input term they are rewriting. Information gained elsewhere in the transformation of the input tree is unknown. Getting this context information available elsewhere in the transformation will make the rewrite system more specific for its current input, hence more powerful. Dynamic rules are rewrite rules that can be generated at runtime. They may contain specific information aimed at the current input that has just become known. In Stratego 0.10 the dynamic rule system has been completely revised and now offers rule (re-/un-)defining, scoping, refined scoping by scope-labeling, forking followed by intersection or union in controlflow situations, and rule set extendi...
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