Showing papers by "Karlsruhe Institute of Technology published in 1978"

Asymmetric flows and instabilities in symmetric ducts with sudden expansions

Abstract: Flow visualization and laser-Doppler anemometry have been used to provide a detailed description of the velocity characteristics of the asymmetric flows which form in symmetric, two-dimensional, plane, sudden-expansion geometries. The flow and geometry boundary conditions which give rise to asymmetric flow are indicated, and the reason for the phenomenon is shown to lie in disturbances generated at the edge of the expansion and amplified in the shear layers. The spectral distributions of the fluctuations in velocity are quantitatively related to the dimensions of the two unequal regions of flow recirculation. It is also shown that the intensity of fluctuating energy in these low Reynolds number flows can be larger than that in corresponding turbulent flows.

Predictions of Heat and Mass Transfer in Open Channels

Abstract: The paper describes a three-dimensional model for calculating the distribution of velocity, temperature, and pollutant concentration in open channel flows, and a depth-averaged two-dimensional version for situations with insignificant stratification and secondary currents. Both models are restricted to parabolic flows where influences cannot be transmitted upstream. The turbulent stresses and heat/concentration fluxes appearing in these equations are determined from the so-called k-ϵ turbulence model that solves differential transport equations for the turbulence kinetic energy k and the rate of its dissipation ϵ. In the depth-averaged model, the bottom shear stress, surface heat flux and turbulence production due to bottom shear are accounted for by source/sink terms in the relevant equations. The 3D calculations compare favorably with available measurements. The 2D and 3D predictions agree well for high Froude numbers; for a Froude number of 5 they agree only for the rough bed, while for the smooth bed they start to deviate significantly at a Froude number of 10.

Raman scattering, superconductivity, and phonon density of states of stoichiometric and nonstoichiometric TiN

Abstract: Raman scattering and superconductivity of titanium nitride with various N deficiencies have been investigated. While in stoichiometric superconducting TiN second-order Raman scattering is predominant, first-order Raman scattering increases with increasing N deficiency. The first-order Raman spectrum which agrees well with the phonon density of states shifts to higher frequencies when the N deficiency grows. This frequency shift is particularly strong at small N deficiencies (\ensuremath{\sim}5%) and is coupled with a drastic drop of ${T}_{c}$. The shift of the phonon density of states indicates phonon anomalies in stoichiometric TiN at 200 ${\mathrm{cm}}^{\ensuremath{-}1}$ in close agreement with just performed neutron studies. In almost stoichiometric TiN the mean-square frequencies $〈{\ensuremath{\omega}}^{2}〉$ from the Raman spectra are in good agreement with corresponding specific-heat data. The similarities between the nonstoichiometric Ti${\mathrm{N}}_{0.55}$ and TiC are discussed.

Formation of shear bands in sand bodies as a bifurcation problem

Abstract: The paper reports on the results of theoretical and experimental investigations on the spontaneous formation of shear bands in sand bodies. The phenomenon is considered as a bifurcation problem. Consequently, material response and configuration-dependent loading determine the bifurcation mode. Both Coulomb's and Roscoe's solutions of inclination of the shear band can be correct theoretically and experimentally. The first one holds for non-rotating stress axes, the second one for co-rotating stress and strain increment axes during failure. Values in between can occur if the rotation of principal stress axes is not equal to one of these limits. If Coulomb's inclination of shear band occurs, there is a thin deforming material layer separating rigid bodies. Inside the shear band non-coaxiality of strain increment and stress holds from the beginning. If Roscoe's inclination of shear band occurs, it is separating two deforming bodies. Inside the shear band strain increment and stress are coaxial at peak.

LISPB — IV. Crustal structure of Northern Britain

Abstract: Summary. This paper presents those results from the 1974 Lithospheric Seismic Profile in Britain (LISPB) which relate to the compressional velocity structure of the crust and uppermost mantle beneath Northern Britain. A combination of interpretation techniques suitable for modelling laterally inhomogeneous media, including two-dimensional ray-tracing and time-term analysis, has resulted in a detailed seismic cross-section across the Caledonian orogenic belt. The main features of this section are a possible horizontal discontinuity in the Pre-Caledonian’basement, a change in the relationship between the lower crust and the uppermost mantle from north to south and a considerable thickening of the crust beneath the Caledonian fold belt. These results place considerable constraints upon tectonic models for the evolution of the Caledonides in particular in their implication of differing crustal structures north and south of the Southern Uplands and their indication of the primary significance of the Southern Uplands Fault.

Rhinegraben and the Alpine system

Abstract: The regional stress field in and around the Rhinegraben rift system and in the adjacent parts of the Alps has been investigated by a series of “doorstopper” in situ stress determinations. This is a stress-relief method that measures rock strain by destressing the rock with an overcoring operation. The maximum component of horizontal compression was found to trend approximately northwest to north-northwest. The excess horizontal stress culminates in the central Alps, decreases abruptly at the northern margin of this mountain range, and has relatively low values in the foreland area of the Rhinegraben. Alpine folding and thrusting ceased in Pliocene time, but strong epeirogenic uplift continues today. While plate-tectonics compression relaxed, stresses caused by topographic effects and unloading increased within the rising mountain body. The directions of maximum horizontal compression are about normally oriented to the isobases of Holocene uplift. The measured excess stresses obviously are not sufficient for thrust progression, since the Alps are considerably consolidated. The Rhinegraben was formed as an extensional rift valley in mid-Eocene to early Miocene time. The remaining zone of weakness trends about parallel to the sinistral shear of the active regional stress field. Because of this, the rift belt has been remodeled into a shear zone; its slip rates are related to the lateral extension of the Alpine mountain body farther south. Deflected by two changes in the graben's axial trend, the neotectonic deformations of the individual graben segments demonstrate a varying interaction of shear with compression in one case or shear with extension in the others. Where active shearing ceases at the northern end of the graben, the shift of the South German block is transmitted directly to the northward adjacent Rhenish massif. This massif reacts by secondary movements along pre-existing discontinuities, by horizontal flexuring, and by seismic activity. Farther north, in the Lower Rhine embayment, the Holocene peri-Alpine stress regime causes extensional rifting and subsidence. Tectonic effects to be ascribed to the Holocene regional stress pattern may be recognized back to mid-Pliocene time. Before that, in early Pliocene to mid-Miocene time, tectonic deformations were controlled by different stress regimes. Plate-tectonics processes in the rigid sphere were complemented by plastic mass compensations within the asthenosphere. Mantle rise was an additional factor controlling the Tertiary process of extensional rifting.

Molybdenum disilicide as a component of modern high-temperature composites

Abstract: A review is presented of the progress in research on, and the development and applications of molybdenum disilicide, MoSi/sub 2/. The review covers silicide coatings on metals, the powder metallurgy of molybdenum disilicide, its use as a heating element in laboratory and industry, and includes also recent studies on wire-reinforced composites and on the use of this intermetallic compound as a protective coating on tantalum and niobium alloys.

A depth-averaged mathematical model for the near field of side discharges into open-channel flow

Abstract: A two-dimensional mathematical model is described for the calculation of the depth-averaged velocity and temperature or concentration distribution in open-channel flows, an essential feature of the model being its ability to handle recirculation zones. The model employs the depth-averaged continuity, momentum and temperature/concentration equations, which are solved by an efficient finite-difference procedure. The ‘rigid lid’ approximation is used to treat the free surface. The turbulent stresses and heat or concentration fluxes are determined from a depth-averaged version of the so-called k, e turbulence model which characterizes the local state of turbulence by the turbulence kinetic energy k and the rate of its dissipation e. Differential transport equations are solved for k and e to determine these two quantities. The bottom shear stress and turbulence production are accounted for by source/sink terms in the relevant equations. The model is applied to the problem of a side discharge into open-channel flow, where a recirculation zone develops downstream of the discharge. Predicted size of the recirculation zone, jet trajectories, dilution, and isotherms are compared with experiments for a wide range of discharge to channel velocity ratios; the agreement is generally good. An assessment of the numerical accuracy shows that the predictions are not influenced significantly by numerical diffusion.

Transverse bed slopes in curved alluvial streams

Abstract: Forty-nine experiments were conducted in three different constant radius, erodible bed, curved flumes using two different sediments to investigate the relationship between channel geometry, flow and sediment properties, and bed topography An analytical model based on moment equilibrium of the flow and force equilibrium of the bed particles is used to develop an equation for the mean radial bed slope in terms of the friction factor, flow depth and velocity, channel radius, and particle densimetric Froude number The relation is found to be in good agreement with reported experimental data and with bed topography measured by Hooke in a sinuous channel

Heat generation at the tip of a moving crack

Abstract: The high energy concentration at the tip of a moving crack causes irreversible deformations and produces heat as a consequence. The resulting temperatures were calculated by consideration of the crack tip as a moving heat-source of rectangular shape. In brittle materials with very small plastic zones and high crack velocities, these temperatures are predicted to be higher than 1000 K. For the experimental verification of these calculations, a very sensitive radiation thermometer was developed. It registers the intensity of the radiation at four wavelengths. By comparison of these intensities with that of black body radiation, the temperature was determined as 3200 K for glass and 4700 K for quartz.

Real-time green's functions in many body problems

Abstract: It is shown that the superoperators acting on the Liouville space of a system of fermions (bosons) with a given number of degrees of freedom form an algebra which corresponds to that of a system of “superfermions” (“superbosons”) with a doubled number of degrees of freedom. Discussed are different reformulations of quantum statistical mechanics in terms of the superparticles and their relationship to the time-path technique and to thermo field dynamics. The classical analogue of the superoperator formulation is shown to coincide with the Martin Siggia Rose formalism.

Molecular pair-correlation function of liquid acetonitrile from X-ray and neutron-diffraction studies

Abstract: X-ray-diffraction studies on liquid acetonitrile at 20°C were carried out at a wavelength of 0·7 A. The data were corrected for polarization, absorption, Compton scattering and multiple scattering. The coherent distinct differential cross section was separated into intramolecular and intermolecular contributions. Whereas from the intramolecular coherent cross section the structure of the molecule in the liquid was determined, the intermolecular coherent cross section, together with intermolecular contributions from neutron-scattering data on CD3C14N and CD3C15N, was employed to determine three expansion coefficients of the molecular pair-correlation function.

Regulation of chloroplast development by red and blue light

Abstract: There are specific differences between red and blue light greening of etiolated seedlings of Hordevm vulgare L. Blue light results in a different prenyl lipid composition of chloroplast as compared to red light of equal quanta density. This is documented by a much higher prenylquinone content, higher chlorophyll a/b ratios, and lower values for the ratio xanthophylls to carotenes (x/c). The photosynthetic activity of “blue light” chloroplasts (Hill reaction) is higher than that of “red light” chloroplasts. These differences in prenylquinone composition and Hill-activity are associated with a different ultrastructure of chloroplasts. “Red light” chloroplasts exhibit a much higher grana content than “blue light” chloroplasts. The difference in thylakoid composition, photosynthetic activity and chloroplast structure found between blue and red light greening are similar to those found between sun and shade leaves and those between plants grown under high and low light intensities.

Stimulated Intrinsic Recombination Processes in II–VI Compounds†

Abstract: The intrinsic recombination processes are investigated in highly excited II–VI compound semiconductors which involve the following scattering processes: the exciton-exciton scattering (P2 line), the exciton-electron or -hole scattering, and the sattering of an exciton by emission of a longitudinal optical phonon. From the stationary rate equations the laser threshold and the maxima of the spontaneous and stimulated emission for the various processes are determined. Experimental investigations of these emission processes are carried out for CdS platelets, ZnO and ZnTe crystals. Good agreement between experimental results and theoretical predictions for the temperature dependences of the laser thresholds, and of the emission maxima is obtained. In stark angeregten II–VI-Halbleitern werden die intrinsischen Rekombinationsprozesse untersucht, denen folgende Streuprozesse zu Grunde liegen: die Exziton-Exziton-Streuung (P2-Linie), die Exziton-Elektron oder -Loch-Streuung und die Streuung eines Exzitions unter Emission eines longitudinalen optischen Phonons. Aus den stationaren Bilanzgleichungen werden die Laserschwelle und die Maxima der spontanen und stimulierten Emission der verschiedenen Prozesse bestimmt. Experimentelle Untersuchungen dieser Emissionsprozesse an CdS-Plattchen, ZnO- und ZnTe-Kristallen werden durchgefuhrt. Gute Ubereinstimmung zwischen Experiment und Theorie wird fur die Temperaturabhangigkeiten der Laserschwellen und der Emissionsmaxima erhalten.

Measurable selection theorems for optimization problems

Abstract: In this paper we attempt a unification of several selection theorems in the literature by introducing the notion of a selection class and give sufficient conditions for the existence of measurable e-maximizers. Various special cases are discussed. Finally, as an application of the selection theorem of Kuratowski and Ryll-Nardzewski [12] a Baire classification of e-maximizers is determined.

The Adrenal Cortex of Amphibia

Abstract: Publisher Summary This chapter discusses the structure of the adrenal islets and functions of adrenocortical secretions. Amphibian adrenocortical tissue secretes steroid hormones of the accepted vertebrate type, the major ones being corticosterone and aldosterone. Anatomically, it differs from the gland in Amniota in that it lies ventrally on the kidney and intermingles with the renal tubules and interstitium. The adrenocortical homologue comprises discrete or scattered tissues set about the ventral surface of the functional opisthonephros kidney. Bilateral branches of the dorsal aorta supply both the gland and the kidneys. The blood exits through venules into renal veins to enter the posterior vena cava. Venous blood from the renal portal vein enters numerous small vessels to reach the outer edges of the kidneys and is also carried to the vena cava by the renal veins. The inter-renal islets are on the ventro-median surface of each kidney in the anuran type and are set principally in the midline between the two kidneys in the urodelan type. With the low power light microscope, adrenal islet cells are seen to contain fat, which gives a characteristic appearance. In general, the adrenal islets of Anura are arranged to form more or less compact strands. In the Urodela, the islets are mostly cast into patches seen along the midline where the two halves of the kidney meet.