Analysis of grain boundary movement analogous to dislocation movement – both with a matrix having precipitates

In the present investigation it has been shown exemplarily for an austenite microstructure containing carbonitrides that the specific restraining force of a grain boundary due to the distribution of precipitates can be described by a modified Orowan's law, so that the grain boundary movement is considered to be analogous to the dislocation movement. This is achieved by using a modified restraining force F_r (corresponding to the cubic geometry of the particles), a detailed thermodynamic analysis of the precipitates (in this case, carbonitrides) and selected relation for the interparticle spacing L_a. The specific restraining force and the interparticle spacing depend on temperature within the austenite range. Each temperature is attached to a couple (F_r/L_a). The plot F_r against shows straight lines for each steel and from their average slope, a shear module G' of grain boundaries, which is about 64300 N·cm^?2, is obtained. Hence, it is possible to describe the specific restraining force of a grain boundary with the help of Orowan's law or as it is conventionally done by using Zener's modell. At a critical temperature T*, which is different for each steel, the specific restraining force is equal to the driving force of the grain boundary. The corresponding values of L_a are also different for each steel and the steel which is the most resistant to grain coarsening is allowed to have the greatest value of L_a which still retains the capacity of impeding grain coarsening.     

Trends beim Einsatz von Realzeitrechnern für Forschung und Entwicklung in der Technischen Chemie

Trends in the use of real-time computers for research and development in industrial chemistry. Computers are integral parts of the complex equipment of chemical production plants. They are tools for computer aided process control. In production plants as well as in research and development laboratories, dedicated computer systems are used more and more. E. g., nearly all measuring devices will be controlled by their own microprocessors in the near future. In chemical engineering, however, the most significant developments are taking place in the software domain. The main trend in applications-software developments is the enhanced importance of the support of the plant operators by means of improved user interfaces. Within the research and development field, the software must be more flexibly adaptable to changes in the process equipment and due to changing control algorithms than in production plants. Moreover, efforts are being made to improve control by exploiting as much as possible a priori knowledge on the system in question. A current development in this direction, which will become stronger with time, is known under the heading ?expert systems”?, in which heuristic know-how of operators is made available and usable in process computers to improve control.     

Tailoring of Surfaces with Ultrathin Layers for Controlled Binding of Biopolymers and Adhesion and Guidance of Cells

Various strategies are described for the bio-functionalization of solid substrates by design of interfacial architectures. The first approach is based on the self-assembly process of long-chain thiol molecules from solution to a (noble) metal surface. If some of these building blocks carry a binding site (ligand) for proteins (receptors, antibodies, etc.) the metal surface can be tailored for maximum specific binding while simultaneously minimizing nonspecific adsorption. The second concept is based on polymers that are covalently attached to (oxide) surfaces. The preparation of these (end-) grafted functional polymers involves either the binding of preformed macromolecules to corresponding sites at the surface of the support or the recently introduced “grafting-from” method, by which an initiator molecule is first covalently bound to the surface and then activated — either by heat or light — in the presence of suitable monomer units such that a polymer chain grows from the solid/solution interface. Finally, the functionalization of patterned surfaces by peptide chains that mimic the binding domains of cell adhesion proteins is summarized. It is demonstrated that not only the selective adhesion of neuronal cells can then be controlled, but also their development with the outgrowth of dendrites and axons.     

Toward a secure Kerberos key exchange with smart cards

Public key Kerberos (PKINIT) is a standard authentication and key establishment protocol. Unfortunately, it suffers from a security flaw when combined with smart cards. In particular, temporary access to a user’s card enables an adversary to impersonate that user for an indefinite period of time, even after the adversary’s access to the card is revoked. In this paper, we extend Shoup’s key exchange security model to the smart card setting and examine PKINIT in this model. Using this formalization, we show that PKINIT is indeed flawed, propose a fix, and provide a proof that this fix leads to a secure protocol.     

Automatisches Sicherheitstesten

Moderne Testgeneratoren finden Schwachstellen in Eingabeschnittstellen von Programmen, indem sie in Sekunden tausende Eingaben zufällig erzeugen. Die Werkzeuge lassen sich leicht von jedermann einsetzen–zum Angriff oder zur Verteidigung.     

Facets of the Fully Mixed Nash Equilibrium Conjecture

In this work, we continue the study of the many facets of the Fully Mixed Nash Equilibrium Conjecture, henceforth abbreviated as the FMNE\mathsf{FMNE} Conjecture, in selfish routing for the special case of n identical users over two (identical) parallel links. We introduce a new measure of Social Cost, defined as the expectation of the square of the maximum congestion on a link; we call it Quadratic Maximum Social Cost. A Nash equilibrium is a stable state where no user can improve her (expected) latency by switching her mixed strategy; a worst-case Nash equilibrium is one that maximizes Quadratic Maximum Social Cost. In the fully mixed Nash equilibrium, all mixed strategies achieve full support.     

Tracking control for boundary controlled parabolic PDEs with varying parameters: Combining backstepping and differential flatness

The combination of backstepping-based state-feedback control and flatness-based trajectory planning and feedforward control is considered for the design of an exponentially stabilizing tracking controller for a linear diffusion-convection-reaction system with spatially and temporally varying parameters and nonlinear boundary input. For this, in a first step the backstepping transformation is utilized to determine a state-feedback controller, which transforms the original distributed-parameter system into an appropriately chosen exponentially stable distributed-parameter target system of a significantly simpler structure. In a second step, the flatness property of the target system is exploited in order to determine the feedforward controller, which allows us to realize the tracking of suitably prescribed trajectories for the system output. This results in a systematic procedure for the design of an exponentially stabilizing tracking controller for the considered general linear diffusion-convection-reaction system with varying parameters, whose applicability and tracking performance is evaluated in simulation studies.