Interferometric measurement of the apparent longitudinal electrostrictive effect in isotactic polypropylene

By the application of high electric fields, small dilatations are induced in samples of polypropylene. These strains are detected at double frequency using a Michelson interferometer. This corresponds to the measurement of the proportionality factor between strain and the square of the electric field strength. Experimental results and a macroscopic discussion based on thermodynamics are presented. From X-ray experiments it is concluded that the majority of the investigated polymers can be regarded as isotropic, while two polymers show a slight anisotropy. With the exception of one material, the different isotactic polypropylenes show quite similar electrostrictive behavior. The purpose of the thermodynamic considerations is to study how the viscoelastic response of polymeric materials might influence the observed values.     

An automatic nonrigid registration for stained histological sections.

Automatic computer-based analyses of histological sections which are differently stained require that they are related to each other. Most registration methods are only able to perform rigid-body motion and are sensitive to noise and artifacts. Histological images, however, are accompanied by several artifacts and different contrasts, which require a nonrigid registration. In this paper, we present a hierarchical nonrigid registration algorithm able to align images, which contain minor image artifacts. The algorithm requires no a priori knowledge of the true image. The hierarchical design of the algorithm enhances robustness and accuracy, and saves computational costs. The proposed algorithm is decomposed into a fast, coarse, rigid registration step and a slower, but finer, nonrigid step. For the coarse registration, we use image pyramids, while for the second step, we combine a point-based registration with an elastic thin-plate spline interpolation. Accuracy tests, performed for 20 histological images obtained from human arteries, have shown that the error measure is acceptable, and that the image noise does not cause a problem. The associated convergence rate of the mean pixel displacement error during the rigid and nonrigid registrations is satisfying. The algorithm can be applied to various multicontrast elastic registration problems in medical imaging and may be extended to three dimensions.     

Contractors take command: from a demand-based towards a producer oriented model in German construction

The construction process in Germany is traditionally dominated by the client and its agent - the architect. This results in severe problems for the construction companies which do not enter into the process until all the important decisions have been made. In particular, the rate of utilization of their facilities is more or less fully dependent on other actors rather than themselves. Recently, the larger construction companies with nationwide and international activities have initiated changes to take over the construction process and assume the leading position within the project coalition. This has been achieved by integrating parts of the construction project that have been under the command of other actors. At the beginning of the process, this concerns part of the work traditionally performed by the architect on behalf of the client, at the other end it concerns the function of the client itself. So it is the producer who - inside a deep crisis which affects the whole of the industry over the last few years - takes command inside the construction process. This will result in restructuring the entire industry and will cause severe problems for other actors, in particular the small and medium construction companies degraded to subcontractors only. En Allemagne, le secteur de la construction a toujours ete domine par le client et son agent, l'architecte. Cette situation est a l'origine de serieux problemes pour les entreprises de construction qui n'entrent en jeu que lorsque toutes les decisions importantes ont ete prises. En particulier, l'utilisation de leurs capacites depend pratiquement entierement d'autres acteurs plutot que d'eux-memes. Recemment, les plus grandes entreprises de construction, actives tant sur le marche national qu'a l'etranger, se sont engagees dans des processus de transformation afin de prendre le controle des activites de construction et de jouer un role pilote au sein des projets de construction. Pour cela, ils ont du integrer des elements des projets de construction qui jusqu'ici etaient sous la coupe d'autres acteurs. En aval de ce procede, il s'agit de reprendre le controle sur les travaux executes d'habitude par l'architecte pour le compte de son client; en amont, c'est la fonction du client lui-meme qui se trouve modifee. En pleine crise qui affecte l'ensemble de l'industrie depuis ces dernieres annees, c'est donc le producteur qui prend le commandement du processus de construction. L'ensemble de l'industrie va donc se trouver restructuree, ce qui ne manquera pas de soulever des problemes pour d'autres acteurs, notamment les petites et moyennes entreprises de ce secteur qui se trouvent releguees au rang de sous-traitants.     

Drop tower experiments on sticking, restructuring, and fragmentation of preplanetary dust aggregates

For the determination of the aggregation efficiency of preplanetary dust, we performed impact experiments with fractal dust aggregates in the drop tower Bremen. We found that for the lowest impact velocities, the dust aggregates, which consisted of micron-sized, monodisperse SiO₂ spheres, hit and stuck with no measurable impact restructuring. For intermediate collision velocities, compact aggregate structures formed, and at the highest impact velocities, aggregates were fragmented. Our experimental results are in quantitative agreement with a numerical dust aggregate collision model (Dominik, C., Tielens, A. G. G. M. 1997, Astrophysical Journal vol. 480, p. 647), when the latest experimental values for the rolling-friction and break-up energies are used. However, the presence of a rarefied gas flow, in which the incoming aggregates were embedded, increased the threshold velocity for sticking. Although the impinging aggregates were disintegrated at high impact velocities, the resulting fragments were dragged back to the target on which they could stick due to a then considerably lower collision velocity. This aerodynamically-supported aggregation process might be responsible for the rapid growth of preplanetary bodies in the size range from ∼0.1 m to ∼10 m. Such a rapid growth is necessary to prevent a loss of most of the solid bodies of these sizes due to gas-drag-induced fast orbital decay.     

Persönliches

Ohne Zusammenfassung     

Stand und Trends bei der Entwicklung leckfreier oszillierender Verdrängerpumpen

Leakfree oscillating positive-displacement pumps – state of the art and trends of development . Leak- and maintenance-free oscillating positive-displacement pumps are very important for avoiding pollution and improving the reliability of plants. Technical progress in the field of hydraulic diaphragm- and tube-pumps for high pressures are explained. The actual data (pressure, efficiency, temperature) and experience with different fluids are surveyed. The various hydraulic control systems, the diaphragm design, and methods for rupture-control are compared. Further development trends are explained.     

Die Wechselbeziehung von Bauteilverhalten und zeitgeraffter Wettersimulation

Time-lapse weathering of wooden building elements was carried out with the help of a double climate chamber with two sections, one with computer controlled exterior climate, the other with interior climate. This test arrangement enabled reactions of building parts most similar to reactions under natural weather conditions. As related to the building parts construction, time-lapse factors up till 10 were reached (1 year in 36 days). By computerized simulation procedures, which are applied parallel to time-lapsed weathering, building elements, just in their developing state, can be tested for their suitability under certain border conditions. For the technological transfer and for the export of prefabricated houses into regions with deviating climate conditions, the risk of damage can be minimized by this method.     

Parameter estimation and optimization techniques for discrete-time semi-Markov models of H.264/AVC video traffic

We investigate a variety of known and new approaches for the estimation of the parameters of discrete-time semi-Markovian traffic models. We focus on modeling video traffic, since the accurate representation of its long-term autocorrelation is a challenge to the parameter estimation methods. The modeling techniques are applied to sample H.264/AVC-encoded video traces. We study their ability to reflect the autocorrelation and variability of the original traffic and also the delay probabilities of a resulting SMP/GI/1 queueing system. The delay probabilities are determined both by simulation and verified analysis of the queue.