Analysis of an improved width-flow concept for the production of ribbed strips by cold rolling

In today's increasingly competitive business environment, companies must look for innovative solutions to survive the competition. In the metal forming industry the engineers are turning to new technologies in order to achieve the goals. One new innovative process is the macroscopic structuration of strips by cold rolling for use in light-weight constructions. Components with a macro-structured surface demonstrate - on the condition of equal weight - a higher area moment of inertia and consequently a higher stiffness than non-structured workpieces. The subjects presented in this paper refer to ribbed sheets produced in a cold-rolling process. Particularly the material flow into the rib pocket is studied in a simplified model as a function of different set-up parameters like tool geometry, deformation, and friction. The theoretical investigations are carried out by the upper-bound theory. The results are compared with an FEM-analysis.     

Symmetric Non-rigid Registration: A Geometric Theory and Some Numerical Techniques

This paper proposes ℒ₂- and information-theory-based (IT) non-rigid registration algorithms that are exactly symmetric. Such algorithms pair the same points of two images after the images are swapped. Many commonly-used ℒ₂ and IT non-rigid registration algorithms are only approximately symmetric. The asymmetry is due to the objective function as well as due to the numerical techniques used in discretizing and minimizing the objective function. This paper analyzes and provides techniques to eliminate both sources of asymmetry. This paper has five parts. The first part shows that objective function asymmetry is due to the use of standard differential volume forms on the domain of the images. The second part proposes alternate volume forms that completely eliminate objective function asymmetry. These forms, called graph-based volume forms, are naturally defined on the graph of the registration diffeomorphism f, rather than on the domain of f. When pulled back to the domain of f they involve the Jacobian J _f and therefore appear “non-standard”. In the third part of the paper, graph-based volume forms are analyzed in terms of four key objective-function properties: symmetry, positive-definiteness, invariance, and lack of bias. Graph-based volume forms whose associated ℒ₂ objective functions have the first three properties are completely classified. There is an infinite-dimensional space of such graph-based forms. But within this space, up to scalar multiple, there is a unique volume form whose associated ℒ₂ objective function is unbiased. This volume form, which when pulled back to the domain of f is (1+det(J _f )) times the standard volume form on Euclidean space, is exactly the differential-geometrically natural volume form on the graph of f. The fourth part of the paper shows how the same volume form also makes the IT objective functions symmetric, positive semi-definite, invariant, and unbiased. The fifth part of the paper introduces a method for removing asymmetry in numerical computations and presents results of numerical experiments. The new objective functions and numerical method are tested on a coronal slice of a 3-D MRI brain image. Numerical experiments show that, even in the presence of noise, the new volume form and numerical techniques reduces asymmetry practically down to machine precision without compromising registration accuracy.

MEDICAL FOUNDATIONS OF AN EXPERT SYSTEM FOR CHRONIC OBSTRUCTIVE LUNG DISEASE

Physicians have already expressed widespread interest in using expert systems. Numerous medical expert systems have appeared, but only a few of them have proven successful. In this article, several criteria that are crucial to the success of an expert system in clinical practice are indicated. The medical foundations of an expert system now being developed according to these criteria are given. The intended purpose of this expert system is to be an effective instrument for the physician in performing the challenging task of caring for patients suffering from chronic obstructive lung disease or high-risk persons. Our aim is to create a system for everyday use that will have several features not provided by the contemporary expert systems in the field of pulmonary diseases. The technical concept of this expert system and especially the pivotal points of its implementation are described in a companion article (Quatember, 1990).     

Hot‐Rolling Experiments on Deformation Behaviour of Oxide Scale

A new test technique developed by the authors allows to investigate the brittle‐ductile behaviour of oxide scale during the hot‐rolling process. Sandwich specimens were pre‐oxidised and then welded so as to be gas‐tight. A micro‐alloyed deep‐drawing quality steel (interstitial free steel) and a fine‐grained low‐pearlite structural steel served as test material. The experiments were performed at temperatures up to 1050 °C. Optical metallography was used to describe the changes of the scale layers. The method is quite good to describe the results qualitatively whereas it is rather difficult to derive quantitative results.     

A regularised estimator for long-range dependent processes

There is significant interest in long-range dependent processes since they occur in a wide range of phenomena across different areas of study. Based on the available models capable of describing long-range dependence, various parameter estimation methods have been developed. In this paper we revisit the maximum likelihood estimator and its computationally efficient approximations: Whittle’s Estimator and the Circulant Embedding Estimator. In particular, this paper proves the asymptotic properties of the Circulant Embedding estimator and establishes the asymptotic equivalence between the three estimators. Furthermore, it is shown that the three methods are ill-conditioned and thus highly sensitive to the presence of measurement errors. Finally, we introduce a regularisation method that improves the performance of the maximum likelihood methods when the datasets have been largely contaminated with errors.     

A new approach for kinetic modeling and optimization of rubber molding

Although extensive research has been carried out on the understanding of the complex vulcanization process, the influence of reversion through exposure time and temperature on the vulcanization degree remains unclear. Therefore, the main aim of this study was a novel optimization approach that can help the industrial practitioners to select the optimal operating parameters, exposure time, and molding temperature, to achieve desired vulcanization degree of selected product. Spheres of four different diameters (2.5, 5, 10, and 20 cm) were selected as test geometry for simulation and optimization of rubber molding. Obtained vulcanization rheometer data for commercially available rubber blend (NR/SBR) were fitted by a new modeling approach, dividing vulcanization curve into two fitting sets: curing and reversion. The heat transfer equations for chosen geometry were coupled with proposed kinetic model. A new temperature-dependent kinetic parameter x, as the maximal reversion degree, was introduced, enabling determination of the lowest operating molding temperature (T_min = 132.36 °C), preventing high reversion and overheating of the rubber product. The final optimization goal was assessment of the optimal temperature and vulcanization time dependence on the rubber products dimensions. Proposed models have precise prediction with R² values greater than 0.8328 and MAPE less than 2.3099%.     

Synthesis and characterization of photopolymers with azo units. Interfacial polyaddition,photolysis, photodegradation

The synthesis of an aryl alkyl azo diisocyanate and a model azo urea is described. From the azo diisocyanate new azo polyureas were created by interfacial polyaddition. Molecular weights M_n in the range of 6000 to 9000 were determined by gel permeation chromatography (GPC). Photolysis and thermolysis of both, model compounds and polymers, were studied by UV-spectroscopy and differential scanning calorimetry (DSC), respectively, and the results were compared with those of similar azo amides. Photochemical polymer degradation was followed by GPC.