Design and analysis of a state observer for the temperature front of a retification column

In order to achieve optimal energy-saving, load-dependent operation of rectification columns, development and implementation of model-based control concepts are necessary. This paper reports on the design and step-by-step testing of a state observer for the estimation of two state variables which cannot be measured directly, namely the vapour rate and the location of mass transfer zone (temperature front) in the stripping section of a production column. The procedure is described, and the relevant simulation and operation results are presented and discussed. Initial experience, gained when the concept was put into practical operation, is reported.     

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Who invented ray tracing?

We provide some remarks on the very early developments of the visualization techniques conducted during the European Renaissance. It is shown that the basic principle of ray tracing was already presented by Albrecht Dürer (1471–1528) in 1525. This article is intended to be of common interest; it is not a scientific report.     

Working with ARMs: Complexity Results on Atomic Representations of Herbrand Models

An atomic representation of a Herbrand model (ARM) is a finite set of (not necessarily ground) atoms over a given Herbrand universe. Each ARM represents a possibly infinite Herbrand interpretation. This concept has emerged independently in different branches of computer science as a natural and useful generalization of the concept of finite Herbrand interpretation. It was shown that several recursively decidable problems on finite Herbrand models (or interpretations) remain decidable on ARMs.The following problems are essential when working with ARMs: Deciding the equivalence of two ARMs, deciding subsumption between ARMs, and evaluating clauses over ARMs. These problems were shown to be decidable, but their computational complexity has remained obscure so far. The previously published decision algorithms require exponential space. In this paper, we prove that all mentioned problems are coNP-complete.     

A 64 kbit/s Videophone codec with forward analysis and control

A new combination of coding methods for a 64 kbit/s transmission system for typical videophone situations is investigated. The codec structure is based on a standard hybrid discrete cosine transform (DCT) codec with temporal prediction. The picture is divided blockwise into changed and unchanged areas. One motion vector with subpel accuracy is computed and transmitted for each block of the changed area. For the forward analysis, the prediction error is calculated in the whole picture. Only the blocks with the highest prediction errors are updated by a DCT with a perception adaptive quantization. The number of DCT update blocks depends on the remaining bits after the transmission of the overhead information. The codec is controlled by a forward analysis of the prediction error and is not based on a buffer control. The spatial resolution of the source signal is reduced in two steps to prevent a codec overload caused by too much activity between two frames.     

Werkstoffprüfung von Hochleistungskeramik mit Zugproben

Mechanical testing of high-performance ceramics with tensile specimens Mechanical properties of engineering ceramics are often measured in bending. The principal limitations of these tests are discussed for linear-elastic and plastic material behaviour. From this the requirement of tensile tests is derived. For room temperature fatigue tests an optimized concept of gripping round specimens is presented. High temperature tests are performed with flat specimens allowing static and quasistatic experiments with continuous strain measurement up to ca. 1400 °C. For sintered silicon nitride tensile creep curves are reported and compared with results from bending tests.