The effect of fine precipitate particles on the creep behaviour of ferritic model steels – II. Analysis of creep results

In view of efforts to develop ferritic creep resistant steels for applications above 600°C the effect of fine precipitate particles on the creep behaviour of ferritic model steels (20% Cr, up to 0.9 % Nb and 0.1 % C) was studied between 600 and 800°C as a function of stress, temperature and particle distribution. The analysis of the experimental results leads to the conclusion that the observed secondary creep rate can be described completely as dislocation creep by means of a modified power law: the temperature dependence is determined by that of the diffusion coefficient and of the shear modulus, the stress dependence is given by (σ-σ_th)³where σ = applied stress and σ_th = threshold stress, and the effect of the particles is described exclusively by the threshold stress which is of the order of the Orowan stress.     

Identification of Sex Pheromone Components of Nettle Caterpillar, Setothosea asigna

Gas chromatographic–electroantennographic detection (GC-EAD) analyses of female nettle caterpillar, Setothosea asigna, pheromone gland extracts revealed seven antennally active compounds. Based on their retention indices on three fused silica columns (DB-5, DB-23, and DB-210), these compounds were hypothesized and, through comparative GC, GC-EAD and GC-mass spectrometry with authentic standards, confirmed to be Δ10-undecenal, dodecanal, (E)-9-dodecenal (E9–12:Ald), (Z)-9-dodecenal, (E)-9-dodecen-1-ol, (E)-9,11-dodecadienal (E9,11–12:Ald), and (E)-9,11-dodecadienol. E9–12:Ald and E9,11–12:Ald were most abundant in female S. asigna pheromone extracts. In field trapping experiments in Palembang, Indonesia, synthetic E9–12: Ald and E9,11–12:Ald at a 1:1 ratio, but not singly, attracted S. asigna males. Attractiveness of these two aldehydes could not be enhanced further through the addition of their corresponding alcohols and/or other aldehydic candidate pheromone components. Use of E9–12:Ald and E9,11–12:Ald for pheromone-based monitoring of S. asigna populations will require lure formulations that minimize pheromone degradation by ultraviolet radiation and atmospheric oxidation.     

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.     

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