Showing papers by "Technical University of Dortmund published in 1988"

The hierarchical basis multigrid method

Abstract: We derive and analyze the hierarchical basis-multigrid method for solving discretizations of self-adjoint, elliptic boundary value problems using piecewise linear triangular finite elements. The method is analyzed as a block symmetric Gauβ-Seidel iteration with inner iterations, but it is strongly related to 2-level methods, to the standard multigridV-cycle, and to earlier Jacobi-like hierarchical basis methods. The method is very robust, and has a nearly optimal convergence rate and work estimate. It is especially well suited to difficult problems with rough solutions, discretized using highly nonuniform, adaptively refined meshes.

Geo-Relational Algebra: A Model and Query Language for Geometric Database Systems

Abstract: The user's conceptual model of a database system for geometric data should be simple and precise: easy to learn and understand, with clearly defined semantics, expressive: allow to express with ease all desired query and data manipulation tasks, efficiently implementable.

Physical training intervention in female shift workers: I. The effects of intervention on fitness, fatigue, sleep, and psychosomatic symptoms.

Abstract: A physical training intervention was carried out on 75 nurses and nursing aides working irregular shifts to determine the effects of such an intervention on health, sleep-wakefulness and adaptation to shiftwork. The study design and changes in physical fitness, fatigue, sleep and psychosomatic symptoms are examined. Training (T) and control (C) groups were built randomly from matched sets of subjects. Questionnaire, laboratory and field studies were done before and after a controlled physical training programme lasting four months. Maximal oxygen consumption and muscle strength increased and heart rates at rest and at work decreased significantly in the T but not in the C group. General fatique during the shift cycle, and fatigue during the night shifts were reduced, whereas fatigue during the evening shifts increased owing to the intervention. Sleep length increased slightly and musculoskeletal symptoms were reduced. The results suggest that moderate physical training increases the physical fitness of fe...

The behaviour of drag-reducing cationic surfactant solutions

Abstract: The behaviour of two types of drag reducing surfactant solutions was studied in turbulent flows in pipes of different diameters. Our surfactant systems contained rod-like micelles; they consisted of equimolar mixtures ofn-tetradecyltrimethylammonium bromide,n-hexadecyltrimethylammonium bromide, and sodium salicylate. The structure of the turbulence was studied using a laser-Doppler anemometer in a 50 mm pipe. In the turbulent flow regime both surfactant solutions exhibited characteristic flow regimes. These flow regimes can be influenced by changing the amount of excess salt, the surfactant concentration, or the temperature. Shear viscosity measurements in laminar pipe and Couette flows show the occurrence of the so-called shear-induced state, where the viscosity increases and the surfactant solution becomes viscoelastic. The shape of the turbulent velocity profile depends on the flow regime. In the turbulent flow regime at low Reynolds numbers, velocity profiles similar to those observed for dilute polymer solutions are found, whereas at maximum drag reduction conditions more “S-shaped” profiles that show deviations from a logarithmic profile occur. An attempt is made to explain the drag reduction by rod-like micelles by combining the results of the rheological and the turbulence structure measurements.

Crack‐Resistance Curves of Surface Cracks in Alumina

Abstract: The resistance of coarse-grained alumina to stable crack growth, initiated from “naturally’occurring surface flaws, was studied in strength tests with a bend-bar technique. The surface cracks experienced R-curve behavior over the first few hundred micrometers; i.e., the applied crack driving force had to be increased with crack extension. Compared to R curves generated from long cracks in standard single-edge-notched-bend specimens, the surface-crack curves have lower initial values. The possible influence of localized residual stresses, counteracting the applied crack driving force, is discussed.

XPS studies of the thermal behaviour of passivated Zircaloy‐4 surfaces

Abstract: The composition and the chemical states of components of Zircaloy-4 (zirconium alloy) surfaces were studied in the temperature range between room temperature and 500°C. Each sample was kept at constant temperature (25, 100, 200, 300, 400, 500°C) for up to 16 hours. The changes of composition and chemical states of the Zircaloy-4 surface during heating were monitored by x-ray photoelectron spectroscopy (XPS). Originally, the components form well-defined layers elucidated by angle-resolved x-ray photoelectron spectroscopy (ARXPS). In contrast to depth profiling using ion sputtering, ARXPS is non-destrutive. However, it is applicable for layers of up to a few nanometres thickness only. The experiments showed a decomposition of the ZrO2 coverage above 200°C accompanied by oxygen diffusion into the bulk. These processes lead to the reduction of ZrO2 to metallic zirconium on the surface at 300°C and higher temperatures. The oxygen diffusion into the bulk was indicated by AES depth profiles. The layered structure observed up to a heating temperature of 200°C could not be seen at higher temperatures. After Zr metal appears at the surface during the heating process, a reaction with the adsorbed hydrocarbons takes place, leading to the formation of zirconium carbide. Though the depth resolution of an AES depth profile does not permit identification of layers with thicknesses in the nanometre region, the temperature-dependent behaviour of oxyen is reflected by its AES profiles, showing features in accordance with the results from ARXPS, especially with respect to the fact that well-defined layers vanish above 200°C.

Physical training intervention in female shift workers: II. The effects of intervention on the circadian rhythms of alertness, short-term memory, and body temperature

Abstract: The effects of a physical training intervention on the circadian rhythms of alertness, short-term memory performance (SAM-test) and oral temperature (t 0) were studied in 75 nurses and nursing aides working irregular shifts in a hospital. Measurements were made every two hours during the days of one morning and two night shifts. In the training group (T), fatigue decreased significantly during the night but not during the day compared to the control group (C). No significant changes were found in the circadian rhythms of the SAM-test and t 0 between the groups, but inside the T group, performance in the SAM-test improved significantly during the day and night shifts, and the mesor and amplitude of t 0 decreased during the day of a morning shift. The results suggest that physical training can induce changes in the circadian rhythms of shift workers which may be interpreted as an adaptation to shift work.

Determination of Crack‐Bridging Forces in Alumina

Abstract: In alumina, R-curve behavior is frequently attributed to “wake” effects which partially shield the crack tip from the applied stress. A novel method is introduced to prove the existence of crack-bridging wake effects and to examine their influence on toughness. Short double-cantilever-beam (DCB) specimens were modified to contain a machined notch at the back face of the specimen. As the growing crack enters this rear notch, the load-bearing capacity of the specimen, and thus the effectiveness of the wake to withstand fracture, is determined. This paper describes the use of such a specimen to evaluate the magnitude of the bridging stresses developed and the contribution of the wake to toughness in polycrystalline alumina.

Rheological and drag reduction characteristics of xanthan gum solutions

Abstract: The rheological and turbulent drag reducing characteristics of commercial and purified xanthan gum solutions of concentrations 50–500 ppm have been studied with and without addition of 100 ppm NaCl. The purification by soxlet extraction of xanthan gum using 95% ethanol is effective in removing low-molecular-weight impurities from xanthan. The increased content of higher molecular-weight xanthan in purified xanthan is evident from rheological and drag reduction behavior. The addition of 100 ppm salt to dilute solutions introduces semi-flexibility in xanthan gum solution without occurrence of self-association. The change in molecular behavior in the presence of salt is evident from rheological normal-stress and turbulent drag reduction behaviors.

The Beam and Detector for a High Precision Measurement of {CP} Violation in Neutral Kaon Decays

Abstract: The K0 beam and detector used for a high-precision measurement of the CP-violation parameter ϵ′ at the CERN Super Proton Synchrotron (SPS) are described. The beam provides KL and KS alternately through a common decay region. The detection of the decays is based on wire chambers and calorimeters without employing a magnet. The trigger and readout system achieve a high selectively for the suppressed, CP-violating, two-pion decays of the KL by incorporation of hard-wired processors. The readout is based on Fastbus for maximum data rates.

Absence of phase transitions in Holstein systems.

Abstract: We consider a model of a particle, which is positioned at fixed discrete-lattice sites and interacts with the phonons of the lattice, described by a generalized Holstein Hamiltonian. As physically interesting situations, the molecular polaron, the Frenkel-exciton\char21{}phonon system in molecular aggregates, and the small polaron in a crystal are included. We prove that, for optical-phonon dispersions, there is no abrupt (nonanalytical) phase transition of the ground state as the phonon coupling increases. This result holds for both finite-N-site models and infinite-site models. For nonzero temperature, the free energy is smooth for arbitrary phonon dispersions. Furthermore, we show that the ground-state wave function of a small polaron is delocalized for any coupling strength. As a consequence, the self-trapping transition is a smooth crossover which is not accompanied by a localization transition or a nonanalytical change of the ground state.

Ternary pnictides MNi2−xPn2 (M ≡ Sr and rare earth metals, Pn ≡ Sb, Bi) with defect CaBe2Ge2 and defect ThCr2Si2 structures

Abstract: The compounds MNi 2− x Sb 2 (M ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) and MNi 2− x Bi 2 (M ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy) crystallize with a defect CaBe 2 Ge 2 structure, which was refined from single-crystal X-ray data for LaNi 1.51 Sb 2 ( R = 0.014 for 17 variable parameters and 328 structure factors). SrNi 2− x Sb 2 and EuNi 2− x Sb 2 have a defect ThCr 2 Si 2 structure, which was refined for EuNi 1.53 Sb 2 to a residual of R = 0.030 (10 variables, 189 structure factors). The compounds have relatively large homogeneity ranges with differences in the cell volumes of up to 3%. The temperature dependence of the electrical conductivity of LaNi 2− x Sb 2 indicates metallic behaviour. Some results of phase equilibria studies of the corresponding ternary systems are reported. The defect formation for nickel sites is qualitatively rationalized from bonding considerations.

Spin Dependent Parton Distributions in Polarized Deep Inelastic Lepton Nucleon Scattering

Abstract: We analyze the recently measured first moment Г p (Q 2) of the structure functiong 1 (x,Q 2) obtained in deep inelastic scattering of polarized electrons from polarized protons. It is shown that the recent experimental result Г p (〈Q 2〉≃10 GeV2)≃ 0.113 implies a polarized strange quark sea whose total polarization Δs(μ2)≃−0.22 is comparable to Δμ(μ2)≃0.74 and Δd(μ2)≃−0.50 already at a typically hadronic scale μ=0(1 GeV). Most remarkably, the total polarization due to quark distributions Δμ(μ2)+Δd(μ2)+Δs(μ2) practically vanishes which implies that the spin of the proton is carried by the gluons, ΔG(μ2), and/or the angular momentum of the partons. This surprising conjecture can be experimentally tested with heavy quark production in longitudinally polarized lepton-nucleon scattering. In particular the (real) photon-gluon fusion process γg→Q $$\bar Q$$ provides a rather unique measure of ΔG(x,Q 2).

Geo-Relational Algebra: A Model and Query Language for Geometric Database Systems

Abstract: The user's conceptual model of a database system for geometric data should be simple and precise: easy to learn and understand, with clearly defined semantics, expressive: allow to express with ease all desired query and data manipulation task, efficiently implementable.

Investigation of the low temperature behaviour of the Anderson lattice

Abstract: A recently developed new perturbational approach to the nonlocal correlations in the Anderson lattice model is used to study low temperature properties. These include the one particle excitation spectra and possible instabilities towards magnetic or superconducting states. The method rests upon a systematic and in principle exact incorporation of the large interaction energy, the Coulomb repulsionU between local electrons on the same lattice site, into the low energy dynamics of quasiparticles and phonons. The resulting dressing of quasiparticles and their resulting effective interactions are treated in the frame of established approximations: The former in NCA, self-consistently adapted to the lattice (LNCA), and the interacting low energy problem with help of ladder summations for the two-particle scattering. Numerical results for the one particle properties are presented, which show an interesting collective effect in the formation of a Kondo lattice state. Stoner-like expressions for various susceptibilitites are derived. Criteria for the occurrence of magnetic and different superconducting phases are given which clearly exhibit the role of quasiparticle band structure, electron-electron interaction and electronphonon interaction.

Observation of B0 − B0 mixing

Abstract: B0 − B0 mixing has been observed for the first time2. Using the ARGUS detector at the DORIS II storage ring we have studied the decay of the ϒ(4S) meson into a pair of B mesons. We found one explicitly mixed event, a decay ϒ(4S) → B0B0, which has been completely reconstructed. Furthermore, we observe a 4 standard deviation signal of 24.8 events with like-sign lepton pairs and a 3 standard deviation signal of 4.1 events containing one reconstructed B0(B0) and an additional fast l±. This shows that B0 − B0 oscillations are substantial with a mixing parameter r of r = 0.21 ± 0.08.

Amalgamation of Regular Incidence-Polytopes

Abstract: We discuss the following problem from the theory of regular incidence-polytopes. Given two regular d-incidence-polytopes 9X and !?2 such that the facets of 0>2 °d the vertex-figures of 0\\ are isomorphic to some regular (d l)-incidence-polytope 3C, is there a regular (d +1)incidence-polytope X with facets of type ^ and vertex-figures of type &•?. Such amalgamations X of 0\\ and 0*2 along 3iT exist (and then in fact very small ones) at least under the assumption that 0>, and 9*2 have the so-called degenerate amalgamation property with respect to 3if. We prove some results on preassigning the (d l)-dimensional medial section-complex 3if for self-dual (d + l)-dimensional regular incidence-polytopes X.

Theory of the Optical Stark Effect in Semiconductors

Abstract: The light-induced changes of the properties of a semiconductor caused by an ultra-short strong laser pulse with a central frequency well below the fundamental absorption edge are investigated. Renormalization and time evolution of one- and two-particle properties are discussed using a nonequilibrium Green's function formalism. Numerical results for the absorption spectra are presented. Es werden die lichtinduzierten Anderungen der Eigenschaften eines Halbleiters untersucht, die durch einen starken ultrakurzen Laserimpuls mit einer Mittenfrequenz unterhalb der Grundgitter-absorptionskante verursacht werden. Mit einem Nichtgleichgewichts-Greenfunktionen-Formalismus werden Renormierung und Zeitentwicklung von Ein- und Zweiteilcheneigenschaften diskutiert. Numerische Ergebnisse fur die Absorptionsspektren werden angegeben.

Code Selection Techniques: Pattern Matching, Tree Parsing, and Inversion of Derivors

Abstract: Significant progress in the area of formal tools to support the construction of code generators in recent years has come along with a severe terminological confusion. Closely related techniques appear in different styles, further obscured by ad-hoc extensions. We try to alleviate this situation by suggesting that the code selection task should be understood as the problem of inversion of a hierarchic derivor. This understanding leads to several interesting generalizations. More expressive formalisms heterogeneous tree languages, regular tree languages, derivor images can be used to define the code selectors input language. In all cases, we retain the ability to decide the completeness of the code selector specification as a side-effect of code selector generation. The extension to nonlinear matching, in combination with matching relative to a subsignature M with a nonmvial equational theory, allows to express the non-syntactic conditions formerly associated with a production in a Graham-GlanviUe style code generator description. Due to space restrictions, such extensions can only be sketched here, while the emphasis of this paper lies on motivating and demonstrating our reformulation of the classical pattern matching approach to code generation.