A New Forming Strategy to Realise Parts Designed for Deep‐drawing by Incremental CNC Sheet Forming

The work detailed in this paper focuses on a new forming strategy for the CNC incremental sheet forming (ISF) process that is appropriate to form steep flanges, e.g. for parts designed for deep‐drawing. When parts are designed for deep‐drawing, they usually contain steep or rectangular side walls that cannot be manufactured using the standard ISF strategies. Unlike prior approaches to obtain steep flanges through ISF, the present method achieves a rough approximation to the final part already in the preforming stage. This can be accomplished without excessive sheet thinning due to sheet bending and stretching at this stage. As a consequence, additional material can be used for the finishing stages, thus yielding a final part with largely reduced thinning. After basic studies on a simple benchmark problem, the new bending/stretching strategy is tested with an industrially applied part that is usually produced by deep‐drawing. Finally, the ISF workpiece is evaluated against the deep‐drawn component with respect to sheet thickness and geometric accuracy.     

Non-Clairvoyant Scheduling for Minimizing Mean Slowdown

We consider the problem of scheduling dynamically arriving jobs in a non-clairvoyant setting, that is, when the size of a job in remains unknown until the job finishes execution. Our focus is on minimizing the mean slowdown, where the slowdown (also known as stretch) of a job is defined as the ratio of the flow time to the size of the job. We use resource augmentation in terms of allowing a faster processor to the online algorithm to make up for its lack of knowledge of job sizes. Our main result is that the Shortest Elapsed Time First (SETF) algorithm, a close variant of which is used in the Windows NT and Unix operating system scheduling policies, is a $(1+\epsilon)$-speed, $O((1/\epsilon)^5 \log^2 B)$-competitive algorithm for minimizing mean slowdown non-clairvoyantly, when $B$ is the ratio between the largest and smallest job sizes. In a sense, this provides a theoretical justification of the effectiveness of an algorithm widely used in practice. On the other hand, we also show that any $O(1)$-speed algorithm, deterministic or randomized, is $\Omega(\min(n,\log B))$-competitive. The motivation for resource augmentation is supported by an $\Omega(\min(n,B))$ lower bound on the competitive ratio without any speedup. For the static case, i.e., when all jobs arrive at time 0, we show that SETF is $O(\log{B})$ competitive without any resource augmentation and also give a matching $\Omega(\log{B})$ lower bound on the competitiveness.     

A category of geometric spaces: Some computational aspects

A category of geometric spaces (non-commutative geometries) is presented here in an overview style with the objective to propose it as a field for interdisciplinary work in geometric reasoning and symbolic computation under the aspect of interactions of algebraic and geometric approaches. The problem of automated verification of geometric conditions is discussed. Possible directions of further work are included as a prospect.Sponsored by the Austrian Science Foundation (FWF), ESPRIT BRP 6471 MEDLAR II.Dedicated to Professor Dana Scott on the occasion of his 60th birthday     

Host-country Absorption of Technology: Evidence from Automotive Supply Networks in Eastern Europe

This paper provides an analysis of technology transfer in automotive supply networks in six EU candidate countries with important vehicle (component) industries. We survey more than 400 firms, representing roughly half of the automotive supply industry. In addition, we have in-depth information from 39 case studies. We address the generation, the origin, and the quality of technology transfer. In terms of generation, we look at the determinants of who receives technology along the value chain, and who passes it on. In terms of origin, we compare local and foreign-owned firms and those with mixed ownership. We also compare differences across the countries. In terms of quality, we discuss the change-inducing effects of technology as perceived by recipient firms. Our results confirm the salience of networks and the key role of MNCs for the generation and diffusion of technology. We also find that diffusion of technology happens within the countries so that host countries absorb more technology than is immediately apparent and commonly believed.     

Densification and Crystallization of Lead Titanate Aerogels

Crack-free monolithic lead titanate (PbTiO₃, or PT) aerogels were prepared via a sol-gel process and drying in supercritical carbon dioxide. The material was characterized by thermogravimetric analysis, dilatometry, helium pycnometry, and X-ray diffraction. Skeletal densification was the main reason for the observed shrinkage of the heat-treated porous material at temperatures <450°C. The transition (at temperatures of 500°-600°C) from an amorphous state to the crystalline (tetragonal) PT was accompanied by significant particle coarsening, as revealed by transmission electron microscopy. Nitrogen adsorption measurements confirmed that crystallization was preceded by the formation of interparticle necks.     

Preparation of monolithic crystalline lead titanate aerogels

Lead titanate gels were prepared via sol–gel synthesis and dried either in supercritical carbon dioxide or isopropanol. Both types of aerogels were characterized by means of thermal analysis and transmission electron microscopy. Helium pycnometry and nitrogen adsorption measurements were performed on samples that had been annealed at temperatures up to 600°C. Phase transformations and the crystallization of tetragonal PbTiO3 were monitored by X-ray diffraction. While aerogels supercritically dried in carbon dioxide disintegrate upon heat treatment, samples dried in isopropanol can be transformed to the crystalline state as monoliths. With an envelope density of 0.75 g cm-3 these ceramics exhibit a porosity of 90%. © 1998 Chapman & Hall