Showing papers by "Karlsruhe Institute of Technology published in 1987"

Thermal conductivity of packed beds: A review

Abstract: The voluminous literature available on thermal conductivities of packed beds without fluid flow is reviewed. The discussion includes experimental methods as well as theoretical approaches. A classification of predictive models is attempted. One of these models is analysed in detail and recommended for practical use. The predictions of the model are compared with a large amount of experimental data. In the course of this comparison phenomena of physical interest and of technical significance are discussed. Most of the methods presented in this review retain validity for dispersed systems other than gas-filled packed beds and for properties other than the thermal conductivity.

Posttranscriptional regulation of c-fos mRNA expression

Abstract: The transient induction of c-fos mRNA and protein suggests that regulation occurs not only by transcriptional activation but also at the level of turnover of the gene product. Here we present evidence for the rapid turnover of c-fos mRNA and some of the requirements for its specific degradation. The half life of induced mature cytoplasmic c-fos mRNA is 9 min in both serum-starved and growing primary human fibroblasts and in NIH 3T3 cells. A structure present at the 3' end of the c-fos mRNA molecule is involved in its low stability since the substitution or the removal of the untranslated 3' portion prolongues the RNA life time. The rapid turnover of fos mRNA requires, in addition, continued protein synthesis. Treatment of cells with cycloheximide stabilizes c-fos mRNA. Washing out cycloheximide reestablishes the rapid turnover. Both changes occur with lag periods of less than 17 minutes.

A Many-Sorted Calculus Based on Resolution and Paramodulation

Abstract: The first-order calculus whose well formed formulas are clauses and whose sole inference rules are factorization, resolution and paramodulation is extended to a many-sorted calculus. As a basis for Automated Theorem Proving, this many-sorted calculus leads to a remarkable reduction of the search space and also to simpler proofs. The soundness and completeness of the new calculus and the Sort-Theorem, which relates the many-sorted calculus to its one-sorted counterpart, are shown. In addition results about term rewriting and unification in a many-sorted calculus are obtained. Practical examples and a proof protocol of an automated theorem prover based on the many-sorted calculus are presented.

Computation of high-frequency seismic wavefields in 3-D laterally inhomogeneous anisotropic media

Abstract: Summary. An algorithm for the computation of travel times, ray amplitudes and ray synthetic seismograms in 3-D laterally inhomogeneous media composed of isotropic and anisotropic layers is described. All 21 independent elastic parameters may vary within the anisotropic layers. Rays and travel times are evaluated by numerical solution of the ray tracing equations. Ray amplitudes are determined by evaluating reflection/ transmission coefficients and the geometrical spreading along individual rays. The geometrical spreading is computed approximately by numerical measurement of the cross-sectional area of the ray tube formed by three neighbouring rays. A similar approximate procedure is used for the determination of the coefficients of the paraxial ray approximation. The ray paraxial approximation makes computation of synthetic seismograms on the surface of the model very efficient. Examples of ray synthetic seismograms computed with a program package based on the described algorithm are presented.

Axisymmetric vortex breakdown with and without temperature effects in a container with a rotating lid

Abstract: A flow circulation in a closed circular-cylindrical container is produced by a rotating lid. After a transient phase from an initial state at rest a steady-flow situation is reached for a certain parameter range. In a subspace of this parameter range an undulating meridional flow occurs that may exhibit at the axis of rotation one or several separation bubbles which are interpreted as vortex breakdown. Numerical calculations on the basis of the Navier-Stokes equations for incompressible homogeneous and Boussinesq fluids enable the study of the influence of various flow parameters on the properties of these separation bubbles. The parameters varied are the Reynolds, Prandtl, Rayleigh, and Eckert numbers together with the ratio of height to radius of the container. The numerical results are in good agreement with experiments performed by Vogel, Ronnenberg, and Escudier. The stability of the fluid motions in these experiments with respect to non-axisymmetric disturbances strongly suggests that the corresponding axisymmetric solutions of the Navier-Stokes equations are stable configurations.

Rectilinear Shortest Paths and Minimum Spanning Trees in the Presence of Rectilinear Obstacles

Abstract: We study the rectilinear shortest paths and minimum spanning tree (MST) problems for a set of points in the plane in the presence of rectilinear obstacles. We use the track graph, a suitably defined grid-like structure, to obtain efficient solutions for both problems. The track graph consists of rectilinear tracks defined by the obstacles and the points for which shortest paths and a minimum spanning tree are sought. We use a growth process like Dijkstra's on the track graph to find shortest paths from any point in the set to all other points (the one-to-all shortest paths problem). For the one-to-all shortest paths problem for n points we derive an O(n min {log n, log e} + (e + k) log t) time algorithm, where e is the total number of edges of all obstacles, t is the number of extreme edges of all obstacles, and k is the number of intersections among obstacle tracks (all bounds are for the worst case). The MST for the points is constructed also in time O(n log n + (e + k) log t) by a hybrid method of searching for shortest paths while simultaneously constructing an MST. An interesting application of the MST algorithm is the approximation of Steiner trees in graphs.

Stacking gravity tide observations in central Europe for the retrieval of the complex eigenfrequency of the nearly diurnal free-wobble

Abstract: Summary. We have used tidal gravity measurements from six stations in central Europe to investigate the resonance in the diurnal tidal band, caused by inertial coupling between the mantle and outer core of the Earth. By the use of stacking it was possible to determine the eigenfrequency and quality factor of this eigenmode, commonly called the ‘nearly diurnal free-wobble’. We assessed the effect of systematic errors from the ocean correction to the tidal measurements employing a Monte-Carlo method. The observed eigenfrequency is 1 + 1/(434 f 7) cycles per sidereal day, and is significantly higher than predicted by theories. The observed quality factor is (2.8 ? 0.5) x 10’.

Fast neutron irradiation of YBa2Cu3O7

Abstract: The influence of fast neutron irradiation on the superconducting transition temperature,T c , the transition width, upper critical field,B c2 , and critical current density,j c , has been investigated in YBa2Cu3O7 up to a fluence of 1019 cm−2 (E>1 MeV). TheT c degradation with fluence is slightly less than in PbMo6S8, but larger than in A 15 compounds. The irradiation induced increase of the normal state resistivity is accompanied by a remarkable decrease of both the intergrainj c and the superconducting volume fraction.

Concurrency control in database structures with relaxed balance

Abstract: We consider the separation of rebalancing from updates in several database structures, such as B-trees for external and AVL-trees for internal structures. We show how this separation can be implemented such that rebalancing is performed by local background processes. Our solution implies that even simple locking schemes (without additional links and copies of certain nodes) for concurrency control are efficient in the sense that at any time only a small constant number of nodes must be locked.

Type 1, blue copper proteins constitute a respiratory nitrite-reducing system in Pseudomonas aureofaciens.

Abstract: Pseudomonas aureofaciens truncates the respiratory reduction of nitrate (denitrification) at the level of N2O. The nitrite reductase from this organism was purified to apparent electrophoretic homogeneity and found to be a blue copper protein. The enzyme contained 2 atoms of copper/85 kDa, both detectable by electron paramagnetic resonance (EPR) spectroscopy. The protein was dimeric, with subunits of identical size (40 ± 3 kDa). Its pl was 6.05. The EPR spectrum showed an axial signal with g‖ at 2.21(8) and g‖ at 2.04(5) The magnitude of the hyperfine splitting (A‖= 6.36 mT) indicated the presence of type 1 copper only. The electronic spectrum had maxima at 280 nm, 474 nm and 595 nm (ɛ= 7.0 mM−1 cm−1), and a broad shoulder around 780 nm. A copper protein of low molecular mass (15 kDa), with properties similar to azurin, was also isolated from P. aureofaciens. The electronic spectrum of this protein showed a maximum at 624 nm in the visible range (ɛ= 2.5 mM−1 cm−1) and pronounced structures in the ultraviolet region. The EPR parameters were g‖= 2.26(6) and g‖= 2.05(6), with A‖= 5.8 mT. The reduced azurin transferred electrons efficiently to nitrite reductase; the product of nitrite reduction was nitric oxide. The specific nitrite-reducing activity with ascorbate-reduced phenazine methosulfate as electron donor was 1 μmol substrate min−1 mg protein−1. The reaction product again was nitric oxide. Nitrous oxide was the reaction product from hydroxylamine and nitrite and from dithionite-reduced methyl viologen and nitrite. No ‘oxidase’ activity could be demonstrated for the enzyme. Our data disprove the presumed exclusiveness of cytochrome cd1 as nitrite reductase within the genus Pseudomones.

Numerical stability of geometric algorithms

Abstract: This paper deals with the numerical problems involved in geometric computations. Our research wss very much motivated by a talk of A. R. Forrest at the 2nd ACM Symposium on Computational Geometry, Yorktown Heights, 1985, cf. [F]. There are only a very few papers in the open literature which adress the numerical problems in geometric computations. The textbooks mentioned above do not contain anything about the numerical problems in geometric computations. In an unpublished report [Ra] it is shown how to represent lines in the floating point system such that any two lines cannot intersect more than once. We refer to two papers which represent two extreme approaches in solving the numerical problems in geometric computations.

Effects of heavy metals on growth and ultrastructure of Chara vulgaris

Abstract: The toxicity of some heavy metals to the common macrophytic freshwater algaChara vulgaris was studied under laboratory conditions. For experiments, apical tips of algae containing two internodes were cultivated for fourteen days in the presence of various concentrations of cadmium, mercury or lead (as triethyl lead or lead nitrate). Fifty percent growth inhibition occurred with concentrations of 8.5×10−8 M (9.5 ppb) cadmium, 7.5×10−7M (150ppb) mercury, 1.6×10−6 M (330ppb) organic lead or 4× 10−5 M (8000 ppb) inorganic lead. Sublethal concentrations of these metals caused alterations in the fine structure of internodal cells which turned out to be at least partly metal-specific or in the case of lead, the effects depended on whether the lead was ionic or organically bound. Cadmium and inorganic lead induced disorders of cell wall microfibrils which resulted in local wall protuberances. Mercury affected the chloroplasts which mostly showed considerably increased grana stacks. In addition, mercury caused a dilation of the endoplasmic reticulum and of the mitochondrial tubuli. Organic lead damaged the membrane system of chloroplasts; sheet- or tubule-like thylakoids were disarranged and showed whorl-like structures. At higher concentrations of organic lead, tubular invaginations of the plasmalemma (“charasomes”) disappeared. The fine structure of nuclei was not altered by any of the metals.