Thermische Nachbehandlung der laserstrahlgeschweißten Al‐Legierungen AlSi1MgMn und AlCu4Mg1

Post heat treatment of the laser beam welded aluminium alloys AlSi1MgMn and AlCu4Mg1 Laser beam welded age hardenable aluminium alloys often exhibit a loss in strength in the fusion and the heat affected zones, compared to the uninfluenced base material. A material‐compatible combination among a base material, a welding filler material, as well as welding parameters and a suitable post heat treatment of the welded joint allows to improve the weld seam properties. The base material AlSi1MgMn (6082) was welded in the aging condition T4 using AlSi12 and AlSi7Mg ‐ filler materials and the welded joint was completely aged at different temperatures and times, in order to adjust an almost constant hardness profile over the base material, heat affected zone and fusion zone. The base material AlCu4Mg1 (2024) was welded in the aging condition T351 using a AlCu6Mn ‐ filler material and the welded joint was naturally aged. The aging behaviour, the residual stress, the static and dynamic properties of welded joints were examined. The properties can be clearly improved by the post heat treatment.     

Unusual dysprosium ceramic nano-fiber growth in a supercritical aqueous solution

The formation of nano-size ceramic fibers having diameters as small as 20 nm is described. This material was obtained by a simple precipitation reaction from a supercritical aqueous dysprosium bromide solution at high temperatures (450°C). The nano-structures have unusually high structural stability for extended time periods in this extreme solvent environment. The experimental procedures are described and analysis of the materials by scanning and transition electron microscopy, and x-ray diffraction is presented. The new materials may have useful applications as high-strength, corrosion resistant materials or as stable catalyst supports for extreme conditions.     

Numerische Lösung von Anfangswertaufgaben gewöhnlicher Differentialgleichungen n-ter Ordnung

In the present paper a new method is given for the numerical treatment of the initial problemsy ⁽ⁿ⁾=f(x,y,y′, ...,y ^(n?1),y ⁽ⁱ⁾ (x _o )=y _o ⁽ⁱ⁾ , i=0, 1, ...,n?1. This method is an one-step process of order four. For a class of linear differential equations the exact solution is obtained. Moreover some numerical results are presented.     

Fluid-structure interaction: A general method used in the ceasemt computer programs

This paper presents a general method to calculate the dynamic behaviour of coupled fluid-structure systems. It is shown how this method can be easily implemented in finite element computer codes. Some applications in the case of axisymetric and three dimensional structures are compared either with analytical or with experimental results. A reference is given for fluid-structure interaction in piping systems.     

Parallel efficiency of domain decomposition methods

Data communication among processors is a key problem to increase performance of parallel algorithms for multiprocessors. In this paper, we investigate different types of domain decomposition methods on the distributed memory multiprocessor and give the estimates of their speedup and efficiency based on the computational complexity and the communication overheads.     

Nanoparticles and polarons: active centers in thin film sensor devices

The spectroscopic characterization of localized charges in thin film devices is addressed. We demonstrate their existence and show their particular contribution to the operation of sensor devices. Examples in oxidic and polymeric thin films systems are given in which the localized states dominate the electronic properties.     

Covering with Ellipses

We address the problem of how to cover a set of required points by a small number of axis-parallel ellipses that avoid a second set of forbidden points. We study geometric properties of such covers and present an efficient randomized approximation algorithm for the cover construction. This question is motivated by a special pattern recognition task where one has to identify ellipse-shaped protein spots in two-dimensional electrophoresis images.     

Ethics committees: time to experiment with standards

Ethics committees now exist in most hospitals. Their recent establishment in many institutions was a response to a 1991 mandate by the Joint Commission on Accreditation of Healthcare Organizations (JCAHO). Proposed or new legislation in a few states is elevating the status of these committees, either requiring their use in certain cases, allowing them to substitute for judicial review, or granting immunity to those who follow their advice. Despite these recent JCAHO and legislative developments, it is widely recognized that there is a significant lack of data on the effectiveness of these committees and that committee members often lack the requisite education and skills for effective participation in case consultation. We argue that before granting ethics committees additional authority, there is a need for more research on their performance and a period of experimentation with quality standards governing their membership and operations.