Analyse der potentiellen Explosionswirkung von kurzzeitig in die Atmosphäre freigesetzten Brenngasmengen. Teil 2: Überprüfung der Modellgesetze anhand der Analyse von Schadensfällen

Analysis of the potential explosive effect of amounts of cßmbustible gases released into the atmosphere . Part 2: Testing of models on the basis of cases of damage. A theoretical model set up to estimate the strength of undampened atmospheric gas cloud explosions occurring after bursting of vessels has been secured by thorough analysis of constructional damage caused by three explosions involving vessel contents of up to 30 tonnes of hydrocarbons. The maximum peak pressure of the pressure wave at the edge of the cloud was found to be ca. 0.3 bar. Diagrams are presented which facilitate estimation of peak pressure and time of action of the deflagration pressure wave as function of the distance and the mass of gas released.     

Butadiene rubbers: topological constraints and microscopic deformation by mechanical and small angle neutron scattering investigation

Summary Results of stress-strain measurements are reported for butadiene rubbers of varying crosslink density. The fluctuation of the effective tube diameter of the polymer networks was investigated under uniaxial elongation by mechanical measurements as well as by small angle neutron scattering (SANS) which probe the local orientation on a segmental scale. The effect of topological constraints on the microscopic deformation of the butadiene network chains is well described within a tube approach. For the first time, experiments at large deformations and for polydisperse sample are presented. Excellent agreement between the statistical mechanical model and the experimental results is obtained. Received: 20 November 2001 /Revised version: 5 March 2002/ Accepted: 5 March 2002     

Harvesting latent and usage-based metadata in a course management system to enrich the underlying educational digital library

In this case study, we demonstrate how in an integrated digital library and course management system, metadata can be generated using a bootstrapping mechanism. The integration encompasses sequencing of content by teachers and deployment of content to learners. We show that taxonomy term assignments and a recommender system can be based almost solely on usage data (especially correlations on what teachers have put in the same course or assignment). In particular, we show that with minimal human intervention, taxonomy terms, quality measures, and an association ruleset can be established for a large pool of fine-granular educational assets.     

Mitteilungen/announcements

A series of telechelic additives with molecular weights of 500–1500 for polyolefins was prepared by reaction of telechelic polyolefins with amino-, carboxy-and aldehyde end groups were obtained by hydrogenation of the corresponding telechelic polybutadienes which were prepared by radical polymerization of butadiene with appropriate functional initiators as well as by anionic polymerization of butadiene and termination with carbon dioxide, ethylene oxide and chloroacetaldehyde dimethyl acetal. Oligomeric polyolefins with stabilizer end groups attached by non-hydrolyzable C C-bonds were obtained by end-capping of living polybutadiene with appropriate functional additive components and subsequent hydrogenation. Preliminary tests of some of the telechelic additives demonstrated excellent compatibility with polypropylene and efficiencies similar to low-molecular standard additives.     

Development of histamine-immunoreactivity in the Central nervous system of the two locust species Schistocerca gregaria and Locusta migratoria

Locusts are attractive model preparations for cellular investigations of neurodevelopment. In this study, we investigate the immunocytochemical localization of histamine in the developing ventral nerve cord of two locust species, Schistocerca gregaria and Locusta migratoria. Histamine is the fast neurotransmitter of photoreceptor neurons in the compound eye of insects, but it is also synthesized in interneurons of the central nervous system. In the locust ventral nerve cord, the pattern of histamine-immunoreactive neurons follows a relatively simple bauplan. The histaminergic system comprises a set of single, ascending projection neurons that are segmentally arranged in almost every neuromere. The neurons send out their axons anteriorly, forming branches and varicosities throughout the adjacent ganglia. In the suboesophageal ganglion, the cell bodies lie in a posteriolateral position. The prothoracic ganglion lacks histaminergic neurons. In the posterior ganglia of the ventral nerve cord, the somata of the histaminergic neurons are ventromedially positioned. Histamine-immunoreactivity starts around 50% of embryonic development in interneurons of the brain. Subsequently, the neurons of the more posterior ganglia of the ventral nerve cord become immunoreactive. From 60% embryonic development, the pattern of soma staining in the nerve cord appears mature. Around 65% of embryonic development, the photoreceptor cells show histamine-immunoreactivity. The histaminergic innervation of the neuropile develops from the central branches toward the periphery of the ganglia and is completed right before hatching.     

Methods for Optical Shape Measurement and their Measurement Uncertainty

There is a wide spectrum of optical 3-D sensors based on only a few basic principles. We calculate the measurement uncertainty for several “paradigm” methods, by means of the Cramér-Rao lower bound. It turns out that when all other sources of noise are neglected, the shot noise becomes the ultimate limit of the measurement uncertainty and the measurement uncertainty can be traced back to a Heisenberg uncertainty product. Consequently, making one of the factors uncertain, the other factor will become more precise. The different methods vary only by the way how this “uncertainty” is generated.