4,552 publications from this institution
This work describes a study of quantitative structural activity relationships (QSAR) of bis-tetraazamacrocyclic compounds. These compounds represent a novel class of very potent and selective anti-HIV inhibitors, with a new mode of action. The QSAR study correlates structural features of the compounds with anti-HIV activity, resulting in a model which has a high predictive capacity (predictive r2 = 0.79). This predictive model will be of major importance for the design of new anti-HIV inhibitors of this class. Use is made of partial least-squares (PLS) analysis, with the novelty being that structural features derived by inclusion of all sterically allowed conformations for each molecule are included in the analysis. PLS analysis was made of descriptors, including structural parameters, macrocyclic ring size, metal chelating ability, etc., and those features necessary for the observed antiviral activities of these compounds were deduced from the models. Since all sterically allowed conformations are included in the analysis, the flexibility of the molecules is also taken into account. In addition, a correlation is found (indicated by a predictive r2 value of 0.61) between inhibition of HIV-1 (HIV-2) and syncytium formation inhibition in the presence of bis-cyclam analogues, leading to the suggestion of a common target, namely, gp120, being involved in both inhibition of virus replication and syncytium formation.
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In the frame of an ESA contract aiming at the feasibility study of a compact, very stable, optically pumped cesium beam clock for Galileo, we have completed our previous analysis of the frequency stability of such a frequency reference. This analysis concerns the single optical frequency configuration. All possible noise sources are considered. Optimum operating conditions providing the best frequency stability are defined and presented It is shown, and justified by simple arguments, that a resonator using a microwave cavity with a phase difference phi = pi between the two oscillatory fields may either provide a better frequency stability than a cavity of the same length but with phi= 0, or provide a given frequency stability with a cesium consumption significantly lower than in the phi=0 configuration. The analysis is applied to the OSCAR resonator conceived and operated at Observatoire de Neuchatel, with two different operating conditions that provide very high performances: the theoretical and experimental results are in excellent agreement. It is concluded that the presented analysis can be safely used to design very high performance, compact, optically pumped cesium beam clocks.
Innovative powder preparation and post-processing techniques can be employed to obtain high density ceramic parts by means of indirect selective laser sintering. Thermally induced phase separation (TIPS) was used to produce polymer and polymer–ceramic composite particles. The effect of polymer concentration, cooling rate, stirring and alumina particles on polymer and polymer–ceramic composite particles was investigated. Homogeneous spherical alumina–polypropylene (PP) composite powder was synthesized by TIPS for selective laser sintering (SLS). Green Al2O3–PP component parts with a density of 34% could be produced by conventional SLS of the polymer under optimized laser power, scan speed, scan spacing and powder preheating temperature. Various post-processing techniques like pressure infiltration (PI), warm isostatic pressing (WIPing) or a combination of both were applied to increase the green density of the Al2O3–PP SLM parts. Infiltrating the open porosity green SLS parts with a 30vol% alumina-powder based ethanol suspension allowed to increase the sintered density, i.e. after polymer debinding and pressureless sintering in air at 1600°C, from 38 to 64% of the theoretical density (TD). WIPing of the SLS and SLS/infiltrated green parts at 135°C and 64MPa allowed raising the green density up to 93 and 83% TD and a sintered density up to 89 and 88% TD, respectively.
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Abstract In product design, a CAD model often needs to be constructed from a physical part. This process is called reverse engineering and is performed through dimensional digitising and CAD modelling. The dimensional digitising results in a cloud of points, which are input for the CAD modelling of surfaces corresponding to the object's features. Consistent with these features, some of the modelled surfaces need to join with positional, tangential or curvature continuity. This paper reports on the incorporation of these geometric boundary conditions in the CAD modelling of free-form surfaces from a cloud of points with non-uniform rational B-splines (NURBS). The described methods are illustrated with some practical, industrial examples and some alternative solutions are briefly described.
Abrasive waterjet cutting is a manufacturing process that allows cutting a wide range of materials which are often difficult to process by means of conventional cutting methods. Similar to other beam type cutting processes, the waterjet is traditionally applied in a direction perpendicular to the surface to be cut. For cutting contours in pre-formed parts, 5- or 6-axis control is required to orient the waterjet beam perpendicular to the part surface along the cutting profile. In this paper, the results of experiments, performed to test the applicability of 3-axis nozzle control for cutting 3D profile parts, are presented. In these experiments, water pressure, feed rate, stand-off distance and inclination angle were varied as the most crucial process parameters. A case study of 3D cutting demonstrates that, with 3-axis control, tolerances of the order of magnitude of the positioning accuracy of the test set-up can be obtained.
