Showing papers by "Karlsruhe Institute of Technology published in 1983"

Experimental and Theoretical Investigation of Backward-Facing Step Flow

Abstract: Laser-Doppler measurements of velocity distribution and reattachment length are reported downstream of a single backward-facing step mounted in a two-dimensional channel. Results are presented for laminar, transitional and turbulent flow of air in a Reynolds-number range of 70 < Re < 8000. The experimental results show that the various flow regimes are characterized by typical variations of the separation length with Reynolds number. The reported laser-Doppler measurements do not only yield the expected primary zone of recirculating flow attached to the backward-facing step but also show additional regions of flow separation downstream of the step and on both sides of the channel test section. These additional separation regions have not been previously reported in the literature.Although the high aspect ratio of the test section (1:36) ensured that the oncoming flow was fully developed and two-dimensional, the experiments showed that the flow downstream of the step only remained two-dimensional at low and high Reynolds numbers.The present study also included numerical predictions of backward-facing step flow. The two-dimensional steady differential equations for conservation of mass and momentum were solved. Results are reported and are compared with experiments for those Reynolds numbers for which the flow maintained its two-dimensionality in the experiments. Under these circumstances, good agreement between experimental and numerical results is obtained.

Constraints for the estimation of displacement vector fields from image sequences

Abstract: Smoothness constraints have been used to facilitate the estimation of displacement vector fields. Differing from HORN and SCHUNCK 81 who employ a general smoothness requirement, this contribution reports an analysis of an "oriented smoothness" requirement: a change in the displacement vector field is only constrained in the direction perpendicular to the characteristic gray value variation based on which the displacement vector is estimated. An iterative solution for the resulting system of nonlinear partial differential equations is developed. It is shown how this system of equations relates to the one derived by HORN and SCHUNCK 81.

Diffusion and Localization in a Dissipative Quantum System

Abstract: The motion of a quantum mechanical particle is studied in the presence of a periodic potential and frictional forces. Depending on the parameters, the behavior changes from diffusion to localization.

New Naturally Occurring Amino Acids

Abstract: The majority of the 500 or so naturally occurring amino acids known today were discovered during the last 30 years, for example during the search for new antibiotics in the culture media of microorganisms, or as components of the antibiotics in fungi, seeds, in numerous plants and fruits, and in the body fluids of animals. Some 240 of these amino acids occur free in nature, some only as intermediates in metabolism. This article provides an overview of the developments that have taken place in this area since 1956 when the last review appeared. Summary accounts are presented, dealing with new unsaturated amino acids, cyclopropane- and cyclobutane-amino acids, heterocyclic amino acids, halogen-containing amino acids sulfur-, selenium- and phosphorus-containing amino acids as well as aliphatic amino acids. In a few cases, e. g. betalamic acid and muscaflavin, the biosynthesis is described in detail.

Solving algebraic problems with high accuracy

Abstract: Publisher Summary This chapter presents the new methods of solving algebraic problems with high accuracy. Examples of such problems are the solving of linear systems, eigenvalue/eigenvector determination, computing zeros of polynomials, sparse matrix problems, computation of the value of an arbitrary arithmetic expression, in particular, the value of a polynomial at a point, nonlinear systems, linear, quadratic, and convex programming over the field of real or complex numbers as well as over the corresponding interval spaces. All the algorithms based on new methods have some key properties in common: (1) every result is automatically verified to be correct by the algorithm; (2) the results are of high accuracy, that is, the error of every component of the result is of the magnitude of the relative rounding error unit; (3) the solution of the given problem is automatically shown to exist and to be unique within the given error bounds; and (4) the computing time is of the same order as comparable floating-point algorithm. The key property of the algorithms is that error control is performed automatically by the computer without any requirement on the part of the user, such as estimating spectral radii. The error bounds for all components of the inverse of the Hilbert 15 × 15 matrix are as small as possible, that is, left and right bounds differ only by one in the 12 place of the mantissa of each component. It is called least significant bit accuracy.

Zonoids and Related Topics

Abstract: A zonoid is a convex body in euclidean space which can be approximated, in sense of the Hausdorff metric, by finite vector sums of line segments Several equivalent definitions are known, and zonoids appear in some surprisingly different contexts The purpose of the present survey article is twofold After giving some basic definitions and properties of zonotopes and zonoids, we describe the various ways in which zonoids enter the discussion of a number of seemingly unrelated topics The stress is here on interrelations between the geometry of convex bodies and other fields The second part treats those results and problems concerning zonoids and their generalizations which are of interest within the theory of convex bodies

An effective pair potential for liquid acetonitrile

Abstract: A six site potential model has been developed for liquid acetonitrile, based on atomic interaction parameters taken from studies of other liquids and partial charges derived by ab initio calculations. When used in molecular dynamics simulations, the model yields results in good agreement with experimental data on the thermodynamics, structure, self diffusion coefficients and reorientational correlation times of the liquid.

Real Zeros of Polynomials

Abstract: Let A be a polynomial over Z, Q or Q(α) where α is a real algebraic number. The problem is to compute a sequence of disjoint intervals with rational endpoints, each containing exactly one real zero of A and together containing all real zeros of A. We describe an algorithm due to Kronecker based on the minimum root Separation, Sturm’s algorithm, an algorithm based on Rolle’s theorem due to Collins and Loos and the modified Uspensky algorithm due to Collins and Aritas. For the last algorithm a recursive version with correctness proof is given which appears in print for the first time.

Computing in Algebraic Extensions

Abstract: The aim of this chapter is an introduction to elementary algorithms in algebraic extensions, mainly over Q and, to some extent, over GF(p). We will talk about arithmetic in Q(α) and GF(p n ) in Section 1 and some polynomial algorithms with coefficients from these domains in Section 2. Then, we will consider the field K of all algebraic numbers over Q and show constructively that K indeed is a field, that multiple extensions can be replaced by single ones and that K is algebraically closed, i.e. that zeros of algebraic number polynomials will be elements of K (Section 4 — 6). For this purpose we develop a simple resultant calculus which reduces all Operations on algebraic numbers to polynomial arithmetic on long integers together with some auxiliary arithmetic on rational intervals (Section 3). Finally, we present some auxiliary algebraic number algorithms used in other chapters of this volume (Section 7). This chapter does not include any special algorithms of algebraic number theory. For an introduction and survey with an extensive bibliography the reader is referred to Zimmer [15].

Inhibition by mevinolin of plant growth, sterol formation and pigment accumulation

Abstract: To obtain information on the importance of a functional mevalonate synthesis for plant growth and development, we investigated the effect of mevinolin, a highly specific inhibitor of 3-hydroxy-3-methylglutaryl (HMG) coenzyme A reductase (the mevalonate-producing enzyme) on growth, sterol accumulation and pigment formation of radish seedlings (Raphanus sativus L. cv. Saxa Treib) and in part also wheat seedlings (Triticum aestivum L. cv. Kolibri). Mevinolin applied during germination inhibits root elongation and development of lateral roots in etiolated and light-grown radish seedlings. This effect cannot be overcome by exogenous GA3, but by addition of mevalonic acid, the product of the internally inhibited reaction. This emphazises the specifity of the mevinolin effect and indicates that the biosynthesis of mevalonic acid is a mandatory requirement for root growth. In light-grown radish seedlings mevinolin also affects hypocotyl length-growth and inhibits sterol accumulation, but has little effect on the chlorophyll and carotenoid accumulation in the chloroplasts of the cotyledons. This indicates the possible presence of an independent mevalonate synthesizing pathway within the plastids and suggests a low transport rate of mevinolin from the radish roots to the cotyledons. When mevinolin is directly applied to the leaves at higher concentrations, it also reduces the light-induced chlorophyll and carotenoid accumulation as has been shown with etiolated primary leaves of wheat. This inhibition is age-dependent and proceeds to a higher extent in older than in younger etiolated leaf tissue. From our results we conclude that plastids possess an independent HMG-CoA reductase. In the cotyledons of radish, mevinolin seems to induce a senescence retardation and sun-type growth response, as has been evaluated by measuring the fast and slow chlorophyll fluorescence induction kinetics (Kautsky effect). These responses may be due to inhibitor-induced changes in the intracellular phytohormone balance.

Stress intensity factor at the surface and at the deepest point of a semi-elliptical surface crack in plates under stress gradients

Abstract: The weight function method is used to calculate stress intensity factors for a semi-elliptical surface crack in a plate exposed to stress gradients.

The analysis ofk-step iterative methods for linear systems from summability theory

Abstract: Using the theory of Euler methods from summability theory, we investigate general iterative methods for solving linear systems of equations. In particular, for a given Euler method, a regionS of the complex plane is determined such that ak-step iterative method converges if the eigenvalues of an iteration operatorT are contained inS. For a givenS, optimal methods are described, and upper and lower bounds are derived for the associated asymptotic rate of convergence. Special attention is given to two-step methods with complex parameters.

Heat transfer in nucleate boiling of mixtures

Abstract: An equation for predicting heat transfer coefficients for nucleate boiling of mixtures is derived. This expression contains only one adjustable parameter and the liquid-phase mass transfer coefficient. If the adjustable parameter is put equal to unity, comparison with the most recent data for the SF/sub 6/-CF/sub 2/-Cl/sub 2/ system gives a mass transfer coefficient of 2 X 10/sup -4/ m/s, which is of the same order of magnitude as the value obtained in physical and chemical absorption and in fallingfilm vaporization. The new equation corresponds particularly well with the experimental observation that the heat transfer coefficient is less dependent on the heat flux density and the pressure for nucleate boiling of mixtures than in the case of the pure components.

The Long-Range Seismic Refraction Experiment in the Rhenish Massif

Abstract: The long-range seismic refraction experiment to investigate the crust and uppermost mantle structure beneath the Rhenish Massif was completed during 1978 and 1979. It included a 600-km-long main profile extending from the Paris Basin in the southwest, across the Massif itself, to the Hessian Depression in the northeast, and three cross-profiles, up to 170 km long, almost wholly located in the Massif itself. Interpretation of the data, including ray-tracing through laterally inhomogeneous media and calculation of synthetic seismograms, has yielded the following velocity-depth information.

Experimental Evidence for a Structure-Induced Minimum of the Density of States at the Fermi Energy in Amorphous Alloys

Abstract: Photoemission spectra are reported for the valence band of quench-condensed Au x Sn 100−x (0⩽x⩽100) films in the amorphous state. It is found that the valence-band spectra for the 20⩽x⩽80 region, measured just after condensation exhibit a decrease in intensity towards the Fermi energy E F which can be understood in terms of a minimum in the density of states near E F . The minimum seems to be induced by a maximum in the structure factor and is correlated with the stability of the amorphous state.

The Biexciton Levels and Nonlinear Optical Transitions in ZnO

Abstract: The controversy about the level scheme of the biexcitons in ZnO is solved by two-photon reabsorption spectroscopy. Three levels are detected, corresponding to the possible combinations of A and B valence band holes. The diamagnetic shift of these states is below 2 × 10−6 eV T−2 in agreement with the small exciton and biexciton radii. In forward two-photon Raman scattering, two excitation induced renormalizations of the polariton dispersion are observed, partly involving transitions to the biexciton level. The M-band luminescence and the resonance structure observed in backward two-photon Raman scattering are reconsidered in terms of the new level scheme. Das Problem des Termschemas der Biexzitonen in ZnO wird durch Zweiphotonen-Reabsorptionsspektroskopie gelost. Drei Biexzitonenniveaus werden beobachtet entsprechend den moglichen Kombinationen von Lochern aus den A- und B-Valenzbandern. Die diamagnetische Verschiebung dieser Zustande liegt unter 2 × 10−6 eV T−2 in Ubereinstimmung mit den kleinen Exzitonen- und Biexzitonenradien. Die Zweiphotonen-Ramanstreuung in Vorwartsrichtung zeigt zwei anregungsinduzierte Renormierungen der Polaritonendispersion, die sich teilweise auf Ubergange zum Biexziton zuruckfuhren lassen. Die Lumineszenz der M-Bande und die Resonanz in der Zweiphotonen-Ramanstreuung in Ruckwartsrichtung werden im Rahmen des neuen Biexzitonen-Termschemas diskutiert.