Ein neuer Weg zur quantitativen Erfassung der Vorgänge beim kontrollierten Walzen

Qualitative Ableitung der Größe ?addierte Endverformung“ und ihre quantitative Beschreibung über temperaturabhängige Additionskoeffizienten. Vorausberechnung von Streckgrenze und Festigkeit aus dem Stichplan. Berechnung eines Übergangspunktes der Kristallinität und hieraus Konstruktion der Kerbschlagzähigkeitskurve.     

Time-dependent behavior of fine-grained model material in resonant column experiments

Cyclic shear experiments with saturated and dry fine-grained corundum powder, i.e. -Al₂O₃ particles, have been conducted in a resonant column device. After an increase of total pressure the shear stiffness showed a slight decrease and a subsequent increase with time. The equivalent viscous damping ratio followed an opposite trend. The increase of shear stiffness with time did not stop after the end of primary consolidation, which cannot be explained with the slight reduction of void ratio during secondary consolidation. Stiffening of grain contacts through different dissolution-precipitation mechanisms and creep at particle contacts can explain the increase of shear stiffness with time, which has also been observed in natural soils by other researchers. Smaller rates of stiffness increase of dry samples support the idea of dissolution-precipitation mechanisms in the pore water. Higher rates for samples with smaller particles show an effect of surface-to-volume ratio.The study described in this paper was sponsored by the German Research Council (DFG), Research Group FOR 371-2. The support is gratefully appreciated.We would like to thank Professor Gudehus for many interesting discussions and valuable advice.We thank the Institute of Mechanical Process Engineering and Mechanics and the Laboratory for Electron Microscopy, University of Karlsruhe, for providing the electron micrographs and the Institute for Ceramics in Mechanical Engineering for the grain size distribution.     

F. L. Bauer 80

Zusammenfassend lässt sich de lege lata jedenfalls festhalten, dass Softwareagenten mangels Rechtspersönlichkeit und Geschäftsfähigkeit keine eigenen Willenserklärungen abgeben und damit nicht nach Stellvertretungsrecht behandelt werden können. Prof. Dr. Peter Sester, s. S. 311     

Effect of pH,co-monomer content,and surfactant structure on the swelling behavior of microgel-azobenzene-containing surfactant complex

The contraction/swelling transition of anionic PNIPAM-co-AAA particles can be manipulated by light using interactions with cationic azobenzene-containing surfactant. In this study the influence of pH-buffers and their concentrations, the charge density (AAA content) in microgel particles as well as the spacer length of the surfactant on the complex formation between the microgel and surfactant is investigated. It is shown that the presence of pH buffer can lead to complete blocking of the interactions in such complexes and the resulting microgel contraction/swelling response. There is a clear competition between the buffer ions and the surfactant molecules interacting with microgel particles. When working in pure water solutions with fixed concentration (charge density) of microgel, the contraction/swelling of the particles is controlled only by relative concentration (charge ratio) of the surfactant and AAA groups of the microgel. Furthermore, the particle contraction is more efficient for shorter spacer length of the surfactant. The onset point of the contraction process is not affected by the surfactant hydrophobicity. This work provides new insight into the interaction between microgel particles and photo-sensitive surfactants, which offers high potential in new sensor systems.     

Electronically controllable microvalves based on smart hydrogels: magnitudes and potential applications

Electronically controllable microvalves based on temperature sensitive hydrogels as actuators are described. A thermal-electronic interface was used for electronic control of the liquid flow. The hydrogel actuators were directly placed in a flow channel. They used the process medium as the swelling agent. Because of the direct placement into the channel the elastic properties of the hydrogel actuator were utilized to improve the pressure insensitivity, to achieve high particle tolerance and to avoid a leakage flow. The microvalves show an extremely simple structure. They can be fabricated using conventional micro technology within a few technical steps. The microvalves can also be miniaturized to a currently unrivalled extent of about 4 /spl mu/m/spl times/4 /spl mu/m/spl times/1/spl mu/m. Valves for "laboratory on chip" applications can already be obtained. The switching times of the electronically controllable microvalves based on hydrogels are 0.3 s to 10 s.     

Robust Positively Invariant Cylinders in Constrained Variable Structure Control

This paper proposes the use of cylinders as primary invariant sets to be used in certain state-constrained control designs. Following the idea originally introduced by O'Dell, the primary invariant set is intersected with the state constraints to yield sets which retain the invariance under some conditions. Although several results presented here apply to fairly general nonlinear systems and primary invariant sets of any shape, the focus is on constrained sliding-mode control (SMC) using infinite cylinders as the primary invariant set. Their use is motivated by a coordinate transformation where the sliding motion is decoupled from the overall convergence to the origin. Robust positive invariance conditions are given for cylinders having convex and compact cross sections. For the case of cylinders with ellipsoidal cross sections, the invariance condition is given in the form of a linear matrix inequality. Further, a decision procedure to qualify each state constraint is given as a tool for the selection of the switching gain. A numerical example for a third-order plant illustrates the method.     

F. L. Bauer 80

Zusammenfassend lässt sich de lege lata jedenfalls festhalten, dass Softwareagenten mangels Rechtspersönlichkeit und Geschäftsfähigkeit keine eigenen Willenserklärungen abgeben und damit nicht nach Stellvertretungsrecht behandelt werden können. Prof. Dr. Peter Sester, s. S. 311