Showing papers by "Technical University of Dortmund published in 1982"

A simple constitutive equation for polymer fluids based on the concept of deformation-dependent tensorial mobility

Abstract: Some time ago a theory of elastic fluids such as concentrated polymer solutions and melts was presented based on the concept of a multitude of penetrating statistical continua. The configurations of these depend on the deformation history, and their relative motion is determined by the coordinated part-stress in connection with a tensorial mobility which is a function of all configuration tensors. The simples special case of thise theory is given by a model with only one configuration tensor which both the stress and mobility tensors depend on. In this paper a further specialization is introduced by assuming a linear dependency of stress as well as of mobility tensors on the configuration tensor. Some relationship to a modified retation model, recently presented by Curtiss and Bird, is hereby established. This model which is of the rate-type and is non-linear in the configuration and stress tensors, respectively, nevertheless permits analytic solutions of some of the most important types of flow. These are explicitly given for both steady and transient extensional and shear flows. Besides shear thinning and non-vanishing first and second normal-stress differences, an extensional viscosity with finite asymptotic values as well as non-exponential stress relaxation and start-up curves are predicted, with stress-overshoot at least in the case of shear flow.

Scaling Violations and the Gluon Distribution of the Nucleon

Abstract: Using recent data on deep inelastic lepton-nucleon scattering an attempt is made to extract the gluon distributionG(x, Q 2=4 GeV2) from the observed scaling violations of structure functions. The accuracy of the data allows only for a rough determination of the gluon distribution. In particular it is found that a hard gluon distributionis consistent with present measurements. Implications of the hard gluon distribution for charm production in the gluon fusion model and for the perturbative contributions to σ L /σ T are further discussed. Finally, analytic parametrizations of the QCDx- andQ 2-dependence of quark and gluon distributions are presented facilitating further possible applications.

Experimental-study of opposite-sign dimuons produced in neutrino and antineutrino interactions

Abstract: A large sample of opposite-sign dimuons, produced by the interaction of neutrinos and antineutrinos in iron, is analysed. The data agree very well with the hypothesis that the extra muon is the product of charm decay. They yield information on the strength and space-time structure of the charmproducing weak current. The strange-sea structure functionxs(x) is determined. The difference between neutrino and antineutrino dimuon production is analysed to provide a value of the Kobayashi-Maskawa weak mixing angleθ2.

On the Theory of Specification, Implementation, and Parametrization of Abstract Data Types

Abstract: In the framework of a category spec of equational speoficatlons of abstract data types, tmplementations are defined to be certain pairs of morphlsms with a common target Th~s concept covers, among others, arbitrary recurslon schemes for defining the derived operations It is shown that for given single steps of a multilevel tmplementatlon, there is always a multtlevel tmplementatlon composed of these steps, but there ts no effective construction of th~s overall implementauon Some suggestions are gtven for practtcal composition of tmplementat~ons Utdlzmg pushouts Parametric specifications and parameter assignments are defined to be spectal morphlsms in spec, and parameter substitution ~s made precise by means of pushouts Since actual parameters can agam be parametrtc, parameter subsututton can be tterated. Thts tterauon ts shown to be assoctatwe Whtle the subject is being treated on a syntactical level in terms of speclfieauons, the imtlal algebra approach ts adopted as providing an appropriate semantics for spec~ficauons, and the effects of the present concepts and results on the initial algebras are studied

Angle-resolved photoemission from polar and nonpolar zinc oxide surfaces

Abstract: We report the first angle-resolved photoemission spectra (ARPES) of polar and nonpolar surfaces of an ionic wurtzite-type compound semiconductor. We present experimental results obtained at photon energies between 20 and 80 eV on the polar zinc and oxygen and the nonpolar ($10\overline{1}0$) surfaces of ZnO and identify surface-induced features by comparison with recent theoretical calculations. Comparison between ARPES experiments and theory confirms the determination of the surface-atom geometry at $\mathrm{ZnO}(10\overline{1}0)$ by low-energy electron diffraction studies.

Transient Optical Spectra of a Dense Exciton Gas in a Direct-Gap Semiconductor

Abstract: The observation is reported of a remarkable persistence of the $1s$ exciton resonance in transient picosecond absorption spectra of GaAs under conditions of resonant optical excitation up to pair densities two orders of magnitude above the Mott density. The stability (excess linewidth 0.8 meV at $n=6\ifmmode\times\else\texttimes\fi{}{10}^{16}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) of this dense exciton gas against decay into the energetically more favorable continuum of electron-hole pairs is due to the relatively weak self-screening of discrete excitons.

A unified approach to a variety of constitutive models for polymer fluids based on the concept of configuration-dependent molecular mobility *)

Abstract: The concept of a configuration-dependent tensorial drag (or mobility) coefficient developed some sixteen years ago is presented in a more generalized manner. In particular, the special case of a one-mode model is discussed. This is shown to be equivalent to the one-mode Leonov model as well as to a recently published model of Dashner and VanArsdale.

Neutral Strange Particle Production in Proton Proton Collisions at $\sqrt{s}=63$-{GeV}

Abstract: The inclusive cross section for the production ofK 0 mesons, Λ and $$\bar \Lambda$$ particles in proton-proton interactions at $$\sqrt s = 63$$ GeV is presented. The produced particles have been detected in the full phase space. Behaviour of the longitudinal and transversal depandences of the cross sections are discussed. The total production cross sections for 0 mesons and Λ particles was determined to $$\sigma _{{\rm K}_S^0 } = (25.5 \pm 1.4)$$ mb andσ Λ =(7.8±1.2) mb respectively. A strong energy dependence of the production cross sections is observed.

Intersection properties of boxes in R d

Abstract: A family of sets is calledn-pierceable if there exists a set ofn points such that each member of the family contains at least one of the points. Helly’s theorem on intersections of convex sets concerns 1-pierceable families. Here the following Helly-type problem is investigated: Ifd andn are positive integers, what is the leasth =h(d, n) such that a family of boxes (with parallel edges) ind-space isn-pierceable if each of itsh-membered subfamilies isn-pierceable? The somewhat unexpected solution is: (i)h(d, 2) equals3d for oddd and 3d−1 for evend; (ii)h(2, 3)=16; and (iii)h(d, n) is infinite for all (d, n) withd≧2 andn≧3 except for (d, n)=(2, 3).

Determination of the gluon distribution in the nucleon from deep inelastic neutrino scattering

Abstract: The observed scaling violations of the nucleon structure functionF 2 and $$\bar q$$ have been analysed in the framework of perturbative QCD to determine the shape and magnitude of the gluon distribution. The data are in good agreement with leading order QCD, and the simultaneous use ofF 2 and $$\bar q$$ structure functions permits, for the first time, a reliable determination of the gluon structure function.

Many Endpoints and Few Interior Points of Geodesics

Abstract: in the sense of "all, except those in a set of first Baire category". The space of all convex surfaces in IR", endowed with Hausdorfl's metric, is a Baire space. We shall see how abnormal convex surfaces may be, by proving that most of them are so.

Preparation and properties of new modifications of RuP4 and OsP4 with CdP4-type structure

Abstract: Previously reported compounds, now assigned as β-RuP4 and β-OsP4, are confirmed to be thermodynamically stable at relatively high temperatures. New modifications of these compositions, assigned as α-RuP4 and α-OsP4, are formed at relatively low temperatures using tin as a flux. They crystallize with the monoclinic CdP4-type structure and have the following lattice constants: a = 4.686(2) A , b = 4.678(2) A , c = 7.102(3) A , β = 80.53(3)° and V = 153.58 A 3 for α-RuP4; a = 4.694(2) A , b = 4.683(2) A , c = 7.096(3) A , β = 80.43(3)° and V = 153.80 A 3 for α-OsP4. The crystal chemistry of compounds with composition MP4 (M ≡ metal) is discussed. As expected from their bonding characteristics, the α and β modifications of RuP4 and OsP4 are diamagnetic semiconductors.

Maximal aerobic power affected by maturation and body growth during childhood and adolescence.

Abstract: In a recent paper, Rutenfranz et al. (1981) studied the development of physical performance capacity relative to body composition during childhood and adolescence in representative samples of Norwegian and German schoolchildren. In this longitudinal investigation, the rate of growth in body size and composition relative to age was identical in the two cohorts of children and followed closely the trend that has been assessed for North-Europeans in general (Eveleth and Tanner 1976). However, compared on the basis of chronological age, the Norwegian children averaged higher in maximal aerobic power, which was observed in girls as well as in boys at all comparable ages. The purpose of this paper was to examine the maximal aerobic power and its rate of change as a function of maturation and body growth in order to test the hypothesis that the differences in maximal aerobic power between the Norwegian and German children are due to differences in growth and maturation with little additional effects of other factors.

Metacontrast U-shaped functions derive from two monotonic processes.

Abstract: Different underlying processes account for the descending and ascending portions of the metacontrast U-shaped function obtained in the flanking-masks paradigm. One or another process is dominant on each trial. Each process is monotonic with stimulus onset asynchrony in the region in which it can be measured. The two processes may be isolated by asking the subject to report on each trial not only target visibility but also whether target and mask appear simultaneous or not. Standard U-shaped functions could be obtained only as an artifact of averaging across these different types of trials.

New evidence for asymmetric dimer reconstruction on the Si(100)-(2×1) surface

Abstract: The electronic structure of the Si(100)-(2\ifmmode\times\else\texttimes\fi{}1) surface in the asymmetric dimer geometry has been studied using the tight-binding scattering theoretical method for semi-infinite crystals based on a realistic bulk Si description. Our results lend very strong further support to the asymmetric dimer model since they are in good agreement with all available photoemission [ultraviolet (UPS) and angle-resolved (ARUPS)] spectroscopy data, thus resolving outstanding discrepancies between previous theoretical results and experiment.

Influence of drag reducing additives on the structure of turbulence in a mixing layer

Abstract: The structure of a free turbulent mixing layer in Newtonian and drag reducing fluids is discussed using results from visualization and LDA-techniques. Particular emphasis is placed on results for the turbulent shear stress and the time correlation function.

Renormalization-convention independence beyond the leading order in deep-inelastic scattering

Abstract: The renormalization-convention independence of nonleading contributions is studied for the singlet sector of the deep-inelastic structure functions. The resulting correction terms are presented and shown to possess a unique and rather simple structure. Implications for the calculation of higher-order corrections are further discussed and quantitative estimates of the corrections to various moments are given.