Showing papers by "Technische Universität Darmstadt published in 1987"

Architecture and implementation of the Darmstadt database kernel system

Abstract: The multi-layered architecture of the DArmStadt Data Base System (DASDBS) for advanced applications is introduced DASDBS is conceived as a family of application-specific database systems on top of a common database kernel system. The main design problem considered here is, What features are common enough to be integrated into the kernel and what features are rather application-specific? Kernel features must be simple enough to be efficiently implemented and to serve a broad class of clients, yet powerful enough to form a convenient basis for application-oriented layers. Our kernel provides mechanisms to efficiently store hierarchically structured complex objects, and offers operations which are set-oriented and can be processed in a single scan through the objects. To achieve high concurrency in a layered system, a multi-level transaction methodology is applied. First experiences with our current implementation and some lessons we have learned from it are reported.

Electrets: Dielectrics with Quasi-Permanent Charge or Polarization

Abstract: The present review of very recent electret work starts with a history-oriented introduction which refers to important early studies of charge storage in insulators; a number of relevant surveys are listed for further information on previous electret research. This paper concentrates on work published during the last few years and especially on papers not covered in earlier reviews. New electret materials and novel experimental techniques are briefly discussed; here, inorganic substances and methods for the nondestructive determination of charge or polarization profiles are given special consideration. Recent developments on the subject of charge storage and transport, and of radiation effects in electrets, are reported. A major topic is the ongoing investigation of piezo-, pyro-, and ferroelectricity in polymer electrets where many new results were obtained during the last few years, The paper concludes with a discussion of a small number of interesting electret applications which may serve as examples for the large amount of device applications suggested in the literature.

Surface Chargine of Dielectrics by Secondary Emission and the Determination of Emission Yield

Abstract: A new method for the determination of the secondary emission yield of dielectrics is discussed. Results are given for Teflon® , Aclar, Kapton® , and Mylar® . Surfaces of dielectrics irradiated with electrons of energies above 2 keV become negatively charged. For lower energies the number of backscattered primaries plus backward emitted secondaries eventually exceeds that of the incoming primaries. Then the surface can be positively charged. It was recognized that this effect might lead to a simple method for the determination of the total backscatter plus secondary emission yield. This effect is used to determine the total emission yield curve in one run with a single beam energy.

Towards a Basic Relational NF2 Algebra Processor

Abstract: Relations with relation-valued attributes (NF2 relations) are proposed to serve as a model for internal data structures of a data base system. A related NF2 relational algebra is described and a suitable subset of it is selected to define the interface of a basic NF2 algebra processor. It will be shown that specific projection-selection-join-sequences expressed in 1NF relations at the conceptual level are mapped to nested projection-selection sequences of the internal of NF2 relations. Costly joins therefore can be eliminated and substituted by equivalent cheaper linear queries. The selection of the subset of NF2 algebra operations is motivated by this join elimination and by the restriction to single-scan operations.

LIPP investigation of piezoelectricity distributions in PVDF poled with various methods

Abstract: Laser-induced pressure pulses (LIPP's) were used to investigate the distribution of polarization and piezoelectric e-constant in the thickness direction of 22 μm thick films of polyvinylidenefluoride (PVDF) with a resolution of 1 to 2 μm. The samples were poled with four different methods, namely a newly developed electron beam technique and the older field, thermal, and corona methods. Results obtained on such samples indicate the existence of different distributions of the piezoelectricity or polarization, ranging from highly uniform profiles for the field-poled samples to step-shaped (monomorph-type) or bidrectional (bimorph-type) distributions for the electron-beam poled samples. The results demonstrate the influence of the fields set up by space charge on the poling process.

Experiences with Process Fault Detection Methods via Parameter Estimation

Abstract: Fault detection and fault diagnosis of technical processes become more important in the course of progressive automation. Computer based fault supervision methods are developed which allow the early detection and localization of process faults during normal operation. The use of process models enables to estimate process state variables and parameters which are influenced by faults. The contribution concentrates on fault diagnosis based on process parameters. The general procedure is outlined, comprising parameter estimation, feature extraction, fault decision and classification. Experimental results are given for the detection of several faults in an electrical drive/centrifugal pump set and an steam heated heat exchanger.

Enhancing Concurrency in Layered Systems

Abstract: To enhance concurrency in a layered system architecture, a multi-level transaction approach is proposed. Low-level operations issued by some higher level action are treated as a layer-specific subtransaction. Thus, according to the rule of level-by-level serializability, semantic knowledge about application-specific actions can be utilized, and still single high-level actions may be interleaved on a deeper layer. In the case of a nested two-phase locking protocol this means that low-level locks are released prematurely and only semantic locks are held until the end of an application transaction. Due to this characteristic of subtransactions, transaction aborts have to be performed by compensating low-level changes through inverse high-level operations rather than backing them out on the page level. Besides developing implementation guidelines for a multi-level concurrency control protocol, various mechanisms to cope with hot spots are discussed within the presented framework.

An intercomparison of LaCoste and Romberg Model-D gravimeters: results of the International D-meter Campaign 1983

Abstract: Summary. The LaCoste and Romberg Model-D gravimeter has found many applications in studies of geophysical processes around the world. To assist in evaluating the results of these studies the performance of 13 Model-D gravimeters from seven countries was determined during a two-week observing campaign in 1983 on calibration ranges in the Federal Republic of Germany. Independent analyses of the data were carried out by the Institute of Physical Geodesy (IPG), Federal Republic of Germany, the Earth Physics Branch (EPB), Canada, and the International Latitude Observatory of Mizusawa (LOM), Japan. All instruments were found to have significant non-linear calibration functions (1 0-60 pGal corrections) and periodic error terms (2-7 pGal amplitudes). Calibration functions for most gravimeters were expressible in terms of third-order polynomials but a few instruments exhibited shorter wavelength structure. The calibration results appear to be similar to those obtained by the manufacturer's laboratory method, Cloudcroft Junior. Redundant observations taken at different reset-screw positions were used to estimate the uncertainties of the calibration functions. It is shown that the accuracy of a D-meter can be expressed in terms of the repeatability of readings and the uncertainty of its calibration function. For the average D-meter the present calibration error exceeds that associated with repeatability when gravity differences are greater than about 26 mGal. Although variations in precision and residual drift of the D-meters could not be clearly linked to environmental factors, the best results were obtained by D21 which was distinguished from the other gravimeters by having an extra thermostatized enclosure. Instruments transported in the manufacturer's cases without a special suspension system tended to give inferior precision. It

The influence of water and of alkali promotor on the carbon number distribution of Fischer-Tropsch products formed over iron catalysts

Abstract: The carbon number distribution of Fischer-Tropsch products formed over an alkalized precipitated iron catalyst has been studied as a function of the water vapor pressure of the synthesis gas. The carbon number distribution of formed hydrocarbons is characterized by a bimodal Schulz-Flory distribution of growth probabilities P1 ≈ 0.6 and P2 ≈ 0.87 attributed to unpromoted and promoted (alkalized) sites on the catalyst surface. Promoted sites are more stable with respect to oxidation (deactivation) by water than unpromoted sites. The growth probability of unpromoted sites decreases with increasing ratio P/P — Studies using Mossbauer spectroscopy have shown that iron foils treated with water containing some K2CO3 yield smaller fractions of iron oxides at the surface than those treated with pure water. Also studies on reduced precipitated iron catalysts using SIMS have shown that alkaline treatment reduces the oxidation of iron by water. These results are interpreted in terms of electronic effects.

The ALGIC Silicon Compiler System: Implementation, Design Experience and Results

Abstract: In this paper we present the ALGIC silicon compiler system. Starting from a structural and functional description of digital VLSI circuits, the system generates automatically the corresponding layout in a full custom design style. Main components of the ALGIC system are a system monitor module, a parameterisable macrocell generator, an appropriate floorplanner with 100% routing solution including planar VDD/GND trees and a block-oriented timing verifier. One essential feature of the system is the high degree of integration between all program modules using the concept of abstract data types. The flexibility and performance of the whole system is demonstrated by real design examples in the field of DSP applications.

Diffusion and Ion Mixing in Amorphous Alloys

Abstract: Tracer impurity diffusion and ion beam mixing in amorphous (a-)Ni/sub 50/Zr/sub 50/ were measured. A correlation between the metallic radius of an impurity and its tracer diffusivity was observed; it is similar to that found in crystalline ..cap alpha..-Zr and ..cap alpha..-Ti. In addition, the temperature dependence of diffusion in a-NiZr exhibits Arrhenius behavior. Ion beam mixing of different impurities in a-NiZr correlates with tracer diffusivity at both high and low temperatures. At higher temperatures radiation enhanced diffusion (RED) was observed. The activation enthalpy of the RED diffusion coefficient is 0.3 eV/atom.

Electric Strength of Small Insulating Distances

Abstract: The capabilities of modern materials and new technologies allow significant size reductions to be achieved particularly in the field of low-voltage equipment. The limits encountered are often due not so much to technical or physical factors, but to widely varying safety requirements determined in many cases by earlier technological capabilities and the limits and specifications based thereon. This paper reports further results obtained from an extensive research project. Exposure of a large number of test specimens to various environmental conditions has proved conclusively that spacings on the surfaces of insulating materials are affected only if contamination is significant. Under heavy contamination these so-called creepage distances form tracks leading sooner or later to failure. Comparatively clean creepage distances however are not affected by tracking and should therefore only be dimensioned on the basis of their short-term electric strength. The results of this extensive series of tests are a statistically verified basis for the dimensioning of rather clean, small creepage distances (>10 mm). They can be incorporated directly into the relevant standards. Other results from the research project will be reported on conclusion of current investigations. However, it is expected that this work will not be completed before 1988.

Collectivity in composite fragment emission from relativistic heavy ion collisions

Abstract: Composite fragments of 2 < Z < 10 have been measured in the Plastic Ball Spectrometer in 200 MeV/nucleon Au + Au and Au + Fe collisions. Strong azimuthal alignment of the fragments reveal the collective behaviour of the reaction.

Contribution on the Specification of an Aging Test for the Insulation of Enclosed, Air-Insulated Switchgear

Abstract: Because of high humidity and condensation, layers of moisture are formed on the surface of insulating materials in indoor switchgear installations which, as a result of contamination, are conductive electrolytic boundary layers. When this happens, electrochemical interactions can produce aging of the insulating material surfaces that may even lead to failure of the insulation. Basic investigations were carried out on a rod-shaped model insulator with simul taneous subjection to an electric field, moisture, and polution. Electrical, chemical, and optical diagnostic methods make it possible to determine aging related surface changes. Based on these results and taking into account the results of work done by the International Working Group IEC-SC17/WGIO "Aging Tests", proposals are discussed for an aging test for enclosed indoor switchgear. In particular, procedures are discussed for simulating the aging phenomena with time compression. The suitability or nonsuitability of individual parameters are discussed.

Time-And Space-Dependent Radiation-Induced Conductivity in Polymer Films: the "TRAPEZOID" Model

Abstract: In a number of polymer electrets, radiation-induced conductivity (RIC) and its time and space dependence were investigated. Electron-transmission experiments yielded the initial deposition profiles; measurements of the rear-electrode voltages during irradiation with a monoenergetic electron beam permitted determination of the time and the dose-rate dependence of the RIC. From these data, the space-charge and field profiles, and their temporal variations, were calculated on the basis of a newly developed "trapezoid" model for the spatial profile of the RIC.

Pion and photon bremsstrahlung in a heavy ion reaction model with friction

Abstract: Based on a classical dynamical model of nuclear motion with a velocity dependent friction force we calculate pionic and electromagnetic bremsstrahlung emitted in heavy ion collisions with bombarding energies between 20 and 84 MeV/n. For arbitrary projectile-target combinations and with a fixed value of the only parameter of the model, the friction coefficientκ, our calculations reproduce the observed beam energy and target mass dependence for pions. The gamma yields, calculated with the same value ofκ, reproduce the measured dependence of the cross-section on energy and target mass, but underestimate the published data by a factor two. This is a good agreement in view of the discrepancies between different experimental groups.

Measurement of high momentum transfer reactions by recoil detection

Abstract: A method is described for studying reactions at medium energies by measuring the magnetic rigidity, time of flight, and energy loss of the resulting recoil products. The method works best for reactions with two-body final states where one of the outgoing particles is relatively light. A magnetic spectrometer with a special focal plane detector has been used. The detector consists of two position sensitive parallel plate avalanche counters and two proportional counters. Differential cross sections for the 12C(p, π+13C reaction at recoil angles which correspond to the pion being emitted at a backward angle in the center of mass have been measured at bombarding energies of 166 and 186 MeV. Data were also obtained for previously unobserved 12C(p, π0)13N reaction. Several advantages of the method are discussed.

Effects of Lecithin on Memory and Learning

Abstract: The effects of cholinergic agonists and antagonists on mnestic performance has been documented by a variety of experimental studies with animals and human beings. A summary on this topic was published by Drachman & Sahakian in 1979. These studies seem to substantiate the theory of a performance impairing effect of cholinergic antagonists, whereas a hypothesis of a memory supporting function of cholinergic agonists currently lacks empirical support and is based only on theoretical assumptions. Mainly for patients with presenile and senile dementia it could be demonstrated that mnestic impairment can be decreased by choline, physostigmine and lecithin (Etienne et al., 1979; Vroulis et al., 1981; Tweedy & Garcia, 1982; Wood & Allison, 1982; Johns et al., 1983 and Thal et al., 1983). On the other hand, Christie et al. (1979) report that lecithin had no effect on the memory performances of 12 patients with Morbus Alzheimer and only for a very few patients a tendency toward improved performance was observable.

Local Strain Approach in Multiaxial Fatigue - Feasibilities and Current Limitations -

Abstract: Applicability of the local strain approach for crack initiation life prediction of notched components under multiaxial service loading is investigated. The necessary tools in multiaxial fatigue - analyses of loading histories and notch stress-strain, deformation and damage theory - are described, and current limitations outlined. Feasibilities are illustrated by examples.

Nondestructive High-Resolution Measurement of Charge, Polarization and Piezoelectricity Distributions in Thin Dielectric Films

Abstract: Ultrasonic pulses, generated by thermoelastic effects and ablation in an opaque coupling layer deposited on the sample surface, are utilized to nondestructively determine charge, polarization and piezoelectricity profiles in thin dielectric films with a resolution of 1 to 2 μm The method utilizes a 70 ps laser light pulse to launch a less than 500 ps long pressure pulse in the sample Propagation of the laser-induced pressure pulse (LIPP) through the film causes electrode currents which directly yield the distributions Results for charge profiles in Teflon FEP and piezoelectricity profiles in PVDF are described The LIPP method has also been used to measure ultrasonic velocity and attenuation up to 1 GHz in various biased or surface charged polymer films

Crack Initiation Life Predictions Based on Elastic-Plastic Fracture Mechanics of Short Cracks

Abstract: The assessment of fatigue life under variable amplitude loading is always carried out by use of cumulative damage hypotheses, and here mostly Miner’s rule is applied. However, comparison of actual with predicted fatigue lives often show large variations of accuracy due to problems associated with load interaction effects [1]. The present investigation is dedicated to this problem in the field of crack initiation life.

Looking at Workstation Architectures from the Viewpoint of Interaction

Abstract: Today's design of sophisticated graphics workstations may be characterized by the terms 3D-system, user driven, object-oriented user interfaceand multiple-windows system with the challenge to create high levelinterfaces for the application programmers. All these properties requirea great amount of computing power, especially if we look at 3D-systemswith high images quality. On the other hand it is well-known that speed,which means system response time, is the most important aspect of interactive systems. More than any other attributes, speed decides whether a new system or technique is acceptable or not. "Not only did the speed make the user happier, but productivity went up." /Brad-85/This will be the first point of discussion treated in this article followed bya preview of current architectures, a short analysis of interaction, anobservation of implementation techniques and finally pointing out a newhardware approach for the implementation of very fast interactive systems.

Piezoelectricity profiles in PVDF

Abstract: Polyvinylidenefluoride (PVDF) is attracting considerable scientific and practical interest because of its electrical properties [1]: The material assumes piezoelectric and pyroelectric behavior after suitable poling. Several poling techniques have been used, including the thermal, corona, high-field, and, very recently, the electron-beam methods [1–3].