Observation of controlled,electrochemically induced friction force modulations in the nano-Newton range

The local chemical properties of the contacting asperities in a real tribosystem are of crucial importance for the resulting macroscopic tribo-behavior. Thus, the lateral forces acting on the tip of a standalone scanning force and friction microscope have been investigated as a function of controlled surface chemistry, realized by potentiostatic control of the sample. The results obtained show a clear dependence of nanoscale friction behavior upon changes in the electrochemical state of the system.     

Structure and importance of logspace-MOD class

We refine the techniques of Beigelet al. [4] who investigated polynomial-time counting classes, in order to make them applicable to the case of logarithmic space. We define the complexity classes and demonstrate their significance by proving that all standard problems of linear algebra over the finite ringsZ/kZ are complete for these classes. We then define new complexity classes LogFew and LogFew and identify them as adequate logspace versions of Few and Few. We show that LogFew is contained in and that LogFew is contained in for allk. Also an upper bound for in terms of computation of integer determinants is given from which we conclude that all logspace counting classes are contained in.     

Non-numerical modeling techniques in structural optimization

Structural optimization encompasses much more than just solving numerical optimization problems. As computer capabilities increase, the entire process of modeling structural optimization problems must be considered. In particular, the creation, transformation and evaluation of the underlying concepts, rather than just brute numerical power, are becoming a more and more dominant factor in finding safe-guarded solutions. In this paper a layer-based model of the total structural optimization process is presented. Each layer contains individual components, a major number of which are of non-numerical nature.Computerization of the non-numerical components requires new programming paradigms. The selection of an appropriate optimization method, to be discussed as a typical non-numerical problem, is difficult because a wide variety of distinct methods exist. Therefore, automated assistance based upon experience and knowledge gained through current research is of prime interest.     

Bounds on the sizes of irredundant test sets and sequences for combinational logic networks

We present a method of determining lower and upper bounds on the number of tests required to detect all detectable faults in combinational logic networks. The networks are composed of AND, OR, NAND, NOR, and XOR gates. The fault model assumes that single stuck-at-zero faults occur on the lines of the networks, with the additional requirement that XOR gates be tested with all possible input combinations. The goal is to provide a simple and efficient implementation that processes the fanout-free subnetworks separately, and then combines the results without the need to consider the effects of reconvergent fanout. We introduce the concepts of irredundant test sets, where no test can be deleted regardless of the order of test application, and irredundant test sequences, where every test detects at least one additional fault when tests are applied in order. Identifying and differentiating between these types of collections of tests allows us to understand more precisely the mechanisms and expected performance of test generation and test compaction methods. We apply our test counting technique and two other published procedures to a set of benchmark circuits. Our bounds are shown to compare favorably to the results obtained by the other published approaches. We obtain minimal and maximal test sets and test sequences using a greedy optimization technique. Our bounds are shown to produce tight bounds for the smaller circuits; they grow more conservative as the size of the circuits increase.     

Morphological stability and crystal structure of CVD-grown zinc selenide

The evolution of micromorphologies has been studied for polycrystalline ZnSe layers grown by low pressure CVD processes in the systems: Zn-Se-H₂-Ar (Se method) and Zn-H₂Se-Ar (H₂Se method). We have found differences in morphological features, apparently due to specific growth and nucleation mechanisms. In technological applications coarse or fine grained materials with homogeneous grain size distribution are often advantageous. Such materials have been successfully prepared under kinetically controlled growth conditions with continuous nucleation, i.e. in contrast to the H₂Se method with deposition temperatures up to 800 °C by the Se method only at T 600 °C and higher supersaturations. In the system Zn-Se-H₂-Ar the reaction rate constant is comparatively higher, and therefore the layer growth at higher temperatures is mainly diffusion-limited with boundary layer resistance. Correspondingly there is a tendency to morphological instabilities with normal grain growth and texture formation. Abnormal or secondary grain growth occurs as a result of recrystallisation during long-time CVD processes. Results of X-ray texture measurements are analysed in relation to different growth morphologies.     

Integrating forward-chaining rules with operations and permanent knowledge bases

Traditionally, rule-based forward-chaining systems are considered to be standalone, working on a volatile memory. This paper focuses on the integration of forward-chaining rules with command-driven programming paradigms in the context of permanent, integrated knowledge bases. A system architecture is proposed that integrates the data management functions of large computerized knowledge bases into a module called a knowledge base management system (KBMS). Experiences we had in integrating rules with operations into a prototype KBMS called DALI are surveyed. For this integration, a new form of production rule, called the activation pattern controlled rule, is introduced, which augments traditional forward-chaining rules by a second, additional left-hand side, which allows making rules sensitive to calls of particular operations. Activation pattern controlled rules play an important role in DALI's system architecture, because they facilitate the storage of knowledge that has been specified relying on mixed programming, a combination of data-driven, command-driven, and preventive programming. The general problems of implementing permanent knowledge bases that contain rules and operations are discussed, and an algorithm for implementating activation pattern controlled rules, called IPTREAT, a generalization of the TREAT algorithm, is provided. Furthermore, the paper intends to clarify the differences between traditional, volatile rule-based systems and rule-based systems that are geared toward knowledge integration by supporting a permanent knowledge base.This paper is an extended and significantly revised version of a paper entitled Integrating Rules into a Knowledge Base Management System, which was presented at the First International Conference on Systems Integration, April 1990 [1].     

Zur Rolle und Verantwortung von Ärzten und Forschern in systemmedizinischen Kontexten: Ergebnisse einer qualitativen Interviewstudie

Background

Systems medicine is characterized by the integration of large amounts of data from manifold data sources and links approaches of systems biology and medical science with informatics and predictive methods of mathematical modeling. This results in a close cooperation of physicians and scientists. Therefore, the expertise of researchers becomes increasingly important regarding the processing and interpretation of patient data. This raises questions of how cooperation between the different actors is managed and to what extent and how the roles and ascribed responsibilities of physicians and scientists change in the context of systems medicine.

Methods

To answer these questions, we conducted a qualitative interview study with physicians and researchers from different fields of systems medicine in order to reconstruct their experiences and perceptions.

Results and conclusions

Based on the empirical analysis two conceptions of systems medicine can be identified. The first conception is characterized by a clear division of competences and tasks between physicians and researchers: researchers serve as service providers, physicians as translational, interdisciplinary trained experts. In the second conception, the division of competences and tasks between physicians and researchers can no longer strictly be drawn: professionals act as a multidisciplinary team, implying close mutual cooperation. Both conceptions indicate (potential) role conflicts of physicians and researchers particularly resulting from the discrepancy between medical and science ethos as well as their specific norms of conduct and objectives. As a consequence, from a normative perspective, it should be clarified which responsibilities legitimately can be attributed to physicians and researchers working in systems medicine. In this regard, it seems to be appropriate to differentiate between more patient-orientated contexts of medical care and fields of basic research.

     

High‐temperature oxidation and compressive strength of Cr2AlC MAX phase foams with controlled porosity

Cr₂AlC foams have been processed for the first time containing low (35 vol%), intermediate (53 vol%), and high (75 vol%) content of porosity and three ranges of pore size, 90‐180 μm, 180‐250 μm, and 250‐400 μm. Sacrificial template technique was used as the processing method, utilizing NH₄HCO₃ as a temporary pore former. Cr₂AlC foams exhibited negligible oxidation up to 800°C and excellent response up to 1300°C due to the in‐situ formation of an outer thin continuous protective layer of α‐Al₂O₃. The in‐situ α‐Al₂O₃ protective layer covered seamlessly all the external surface of the pores, even when they present sharp angles and tight corners, reducing significantly the further oxidation of the foams. The compressive strength of the foams was 73 and 13 MPa for 53 vol% and 75 vol% porosity, respectively, which increased up to 128 and 24 MPa after their oxidation at 1200°C for 1 hour. The increase in the compressive strength after the oxidation was caused by the switch from inter‐ to transgranular fracture mode. According to the excellent high‐temperature response, heat exchangers and catalyst supports are the potential application of these foams.     

Thermal Shock Resistance of Ladle Castables

High purity alumina-spinel( A-MA) and alumina-magnesia( A-M) castables are widely used in steel ladles due to their resistance against slag penetration and corrosion. With a calcium magnesium aluminate bond( CMA) excellent slag penetration resistance can be achieved which results in high wear resistance due to reduced structural spalling. This paper investigates the impact of matrix compositions and CMA-binder content of A-MA and A-M castables on thermal shock resistance( TSR). Standardized thermal shock tests have been applied with sample quenching from 950 ℃ down to room temperature. Results show that all castables are significantly damaged after 5 cycles despite their differences in microstructure. However,the mix with 12%CMA gave TSR that is at similar good level as the reference mix with 6% CAC( 70% alumina cement). While a similar strength level was achieved before and after the thermal cycling,the formulation with 12% CMA contains 0. 6% less total Ca O. The A-MA castables perform better on average than the A-M mixes with this test method. Within the group of A-M castables the mix with 18% CMA and 0. 5% SiO_2 gave superior TSR,similar good as castables of the A-MA group. The introduction of CMA in an A-M castable allows reduction of free Mg O and SiO_2-addition. The reduction of SiO_2 has been found beneficial for the TSR. This was also found during a thermal cycling trial at high temperature between 1 100 and 1 500 ℃. Here the A-M mix with18% CMA and 0. 5% SiO_2 performed better than the SiO_2-free A-MA castable.     

NUMERICAL SIMULATION OF ALLOY SOLIDIFICATION BY A TWO－PHASE MODEL

本文介绍了合金凝固传输过程中的二相流数学模型．该模型描述了固－液界面的传输现象和液相对流对宏观偏析的影响，并考虑了生核过程，热和溶质的过冷效应，及固相颗粒的宏观运动，从而把宏观传输过程和微观结构结合起来．采用该模型，对Ａｌ－４％Ｃｕ等轴晶合金的凝固进行了完整的数值模拟．