Showing papers by "Karlsruhe Institute of Technology published in 1982"

The chemical potential of radiation

Abstract: In a thermodynamic treatment electromagnetic radiation of any kind is described. The difference between thermal and non-thermal radiation is accounted for by introducing the chemical potential of photons. Instead of an effective temperature all kinds of radiation have the real temperature of the emitting material. As a result Planck's law for thermal radiation is extended to radiation of any kind. The concept of the chemical potential of radiation is discussed in detail in conjunction with light-emitting diodes, two-level systems, and lasers. It allows the calculation of absorption coefficients, of emission spectra of luminescent materials, and of radiative recombination lifetimes of electrons and holes in semiconductors. Theoretical emission spectra are compared with experimental data on GaAs light-emitting diodes and excellent agreement is obtained.

Calculation of Secondary Currents in Channel Flow

Abstract: A model is presented for calculating the flow in channels with turbulence-driven secondary motion, with an emphasis on open channel flow. Algebraic expressions are derived for the Reynolds stresses in the momentum equations for the secondary motion by simplifying modelled Reynolds stress equations. A simple eddy viscosity model is used for the shear stresses in the logitudinal momentum equation. The kinetic energy k, and the dissipation rate ϵ of the turbulent motion appearing in the algebraic and eddy viscosity expressions are determined from transport equations for these quantities. The restricting influence of a free surface on the length scale of turbulence is accounted for by a special free surface boundary condition for ϵ. The resulting set of equations is solved with a marching forward numerical procedure for three-dimensional boundary layers. The model is tested by application to developed two-dimensional closed and open channel flow, closed square duct flow, and flow in open channels of various width-to-depth-ratios. Most features of these flows are simulated well by the model, including the reduction of the eddy viscosity near the free surface and the depression of the velocity maximum below the surface.

Quantum Dynamics of Tunneling between Superconductors

Abstract: A functional integral formulation is used to treat the quantum dynamics of a microscopic model of a Josephson junction, including the dissipative effects of quasiparticle tunneling. The calculation is carried to a point where it makes contact with, and therefore substantiates, recent work by Caldeira and Leggett in which the system is treated by analogy with the quantum Brownian motion of a massive particle coupled to a phenomenological heat bath.

On a quasiclassical Langevin equation

Abstract: It is shown that the motion of a quantum mechanical particle coupled to a dissipative environment can be described by a Langevin equation where the stochastic force is generalized such that its power spectrum is in accordance with the fluctuation-dissipation theorem. This generalized Langevin equation has an interesting range of applicability. It includes the quasiclassical regime provided that the damping, that is, the coupling of the particle to its environment, is sufficiently strong.

Generalized Polynomial Remainder Sequences

Abstract: Given two polynomials over an integral domain, the problem is to compute their polynomial remainder sequence (p.r.s.) over the same domain. Following Habicht, we show how certain powers of leading coefficients enter systematically all following remainders. The key tool is the subresultant chain of two polynomials. We study the primitive, the reduced and the improved subresultant p.r.s. algorithm of Brown and Collins as basis for Computing polynomial greatest common divisors, resultants or Sturm sequences. Habicht’s subresultant theorem allows new and simple proofs of many results and algorithms found in different ways in Computer algebra.

The energy levels of muonic atoms

Abstract: The theory of muonic atoms is a complex and highly developed combination of nuclear physics, atomic physics, and quantum electrodynamics. Perhaps nowhere else in microscopic physics are such diverse branches so intimately intertwined and yet readily available for precise experimental verification or rejection. In the present review we summarize and discuss all of the most important components of muonic atom theory, and show in selected cases how this theory meets experimental measurements.

Adaptation of Chloroplast-Ultrastructure and of Chlorophyll- Protein Levels to High-Light and Low-Light Growth Conditions

Abstract: Adaptation In saturating light radish seedlings grown in high-light growth conditions (90 W · m⁻²) possess a much higher photosynthetic capacity on a chlorophyll and leaf area basis than the low-light grown plants (10 W · m⁻²). The higher CO₂-fixation rate of HL-plants is due to the presence of HL-chloroplasts which possess a different ultrastructure and also different levels of the individual chlorophyll-carotenoid-proteins than the LL-chloroplasts of LL-seedlings. 1. Ultrastructure: The high-light adapted chloroplasts are characterized by fewer photo­ synthetic membranes per chloroplast section, by low grana stacks (only few thylakoids per granum), a lower stacking degree of thylakoids, a higher proportion of non-appressed membranes (stroma thylakoids + end grana membranes) and a high starch content. The LL-chloroplasts possess no starch, their grana stacks are higher (up to 17 thylakoids per granum) and also significantly broader than that of HL-chloroplasts. 2. Chlorophyll-proteins: The photosynthetic apparatus of HL-chloroplasts contains a larger proportion of chlorophyll a-proteins of photosystem I (CPIa + CPI) and of photosystem II (CPa, the presumable reaction center of PS II) than the LL-chloroplasts which possess a higher proportion of light-harvesting chlorophyll a/b-proteins (LHCP₁, LHCP₂, LHCP₃, LHCPy). The higher levels of LHCPs in LL-plants are associated with a higher ground fluorescence fo and maximum fluorescence fp of the in vivo chlorophyll. 3. Chlorophyll and carotenoid ratios: The chloroplasts of HL-plants possess a higher proportion of chlorophyll a and β-carotene (higher values for the ratios chlorophyll a /b and lower values for a/c and x/c) which reflect the increased level of the chlorophyll a/β-carotene-proteins CPIa, CPI and CPa. The higher level of light-harvesting chlorophyll a/b-xanthophyll-proteins (LHCPs) in LL-plants is also indicated by an increased content of xanthophylls and chlorophyll b as seen from lower a/b and higher x/c and a/c ratios. 4. The results indicate that plants possess the capacity for an ontogenetic adaptation of their photosynthetic apparatus to the incident light intensity. The HL-chloroplasts of HL-plants which contain less antenna chlorophyll, are adapted for a more efficient photosynthetic quantum conversion at light saturation than the LL-chloroplasts with high grana stacks. The correlation between higher levels of light-harvesting chlorophyll a/b-proteins (LHCPs) and a higher stacking degree of thylakoids, and the involvement of LHCPs in stacking is discussed.

Examples of Turbulence Models for Incompressible Flows

Abstract: The paper describes some currently available models for calculating turbulent stresses and heat or mass fluxes in incompressible flow which are more generally applicable than the Prandtl mixing-length hypothesis. These include models employing transport equations for the intensity and the length scale of the turbulent motion, notably the k-t model, as well as second-order closure schemes based on transport equations for the turbulent stresses and heat or mass fluxes themselves. The individual models are introduced briefly, their merits and demerits are discussed, and typical examples of calculations relevant to aerospace problems are presented.

A new determination of the π N sigma term using hyperbolic dispersion relations in the (ν 2 ,t) plane

Abstract: Dispersion relations in the (ν2,t) plane along hyperbolas are used in order to extrapolate the invariant isospin-even πN amplitude D+(ν2,t) to the Cheng-Dashen point, ν=0, t=2μ. The fluctuation of the results obtained with different hyperbolas gives a realistic estimate of the errors, except for errors of the partial wave solution and of the ππ $$ - N\bar N$$ amplitudes assumed at t < 4μ2 —If our ππ $$ - N\bar N$$ partial waves are used, which are based on the ππs-wave scattering length a 0 0 =0.28 μ-1, the result for the sigma term is 64±8 MeV, in agreement with earlier determinations.—The discrepancy with the theoretical prediction σπN≈ 30 MeV is smaller by only 8 MeV, if our $$ - N\bar N$$ amplitudes are modified in such a way that the threshold behaviour of the ππs-wave agrees with Weinberg's prediction a 0 0 =0.16 μ-1. Further progress depends on new accurate experimental π±p scattering data in the Coulomb interference region at low energies.

A Turbulence Model for Buoyant Flows and Its Application to Vertical Buoyant Jets

Abstract: Publisher Summary Many flows in engineering practice and in the environment are influenced by buoyancy forces arising from density differences or are caused by such forces, like in the case of free-convection flows. Waste fluid discharged into the environment has a density different from the latter, which leads to a buoyancy-induced rise or fall of the discharged fluid. The rise is limited by the presence of a stable stratification in the environment, like inversion layers in the atmosphere or thermoclines in the upper part of oceans, and such stable stratifications have a strong damping effect on the turbulence and inhibit the mixing and the spreading of pollutants; on the other hand, turbulent mixing and pollutant spreading are enhanced under unstably stratified conditions. Density currents driven by some existing density difference might occur in the atmosphere and in oceans and other large water bodies, and free convection flows arise from the presence of heat sources such as heated surfaces or fires and occur frequently in rooms as well as in the atmosphere.

Corrections of hot-wire anemometer measurements near walls

Abstract: Applications of hot-wire anemometers to velocity rneaaurements near walls can result in erroneous velocity data owing to additional heat losses to the wall. It is difficult to account for these errors if calibration data are used that were obtained in calibration test rigs without walls. This has been recognized in many studies in which hot-wires were applied to measurements in wall boundary-layer flows and different suggestions for corrections have been given. The present paper summarizes these suggested corrections and points out existing differences. It is also shown that some hot-wire measurements have been performed without any corrections being applied and reasons for this are given. Whereas most of the existing suggestions for wall corrections of hot-wire data are based on experiments, the present approach uses results of a numerical study.Assuming the problem to be two-dimensional and that the wire can be replaced by a line source of heat, a numerical study is carried out for the temperature distribution downstream of the wire, and computations are performed for the heat loss from the wire in presence of the wall. Computations are performed for two Merent boundary conditions representing ideally conducting and non-conducting materials. These different boundary conditions yield large differences in the computed heat losses from the wire, and these explain the existing differences in the experimentally obtained corrections. The numerical study also shows that the large heat losses for conducting walls are due to the distorted temperature distribution in the temperature wake of the wire.Some of the results of the numerical studies were experimentally verified by the authors and a procedure haa been developed to correct instantaneous hot-wire readings for additional heat losses to a wall. For non-conducting walls, the heat losses are much smaller and are negligible for most practical measurements.

Double-blind study on the effect of cigarette smoking on the chromosomes of human peripheral blood lymphocytes in vivo

Abstract: A double-blind study with 170 smokers and 124 non-smokers revealed a doubling of the frequencies of exchange-type aberrations in the peripheral blood lymphocytes of smokers as compared with non-smokers. Smokers (N = 24) had 1 SCE more per metaphase than non-smokers (N = 20), an effect that is significant but low when compared with the effect on structural chromosomal aberrations. These results show that structural chromosomal aberrations are better indicators of the genetical effects of low chronic exposures to mutagens in man than SCEs. The frequencies of micronuclei in 3-day lymphocyte cultures showed no differences in smokers (N = 95) and non-smokers (N = 39). Non-smokers (N = 99) had significantly higher frequencies of 2nd metaphases in 48-h cultures in vitro than smokers (N = 141), indicating an effect of smoking on the stimulation of lymphocytes by PHA in vitro.

A Dictionary Machine (for VLSI)

Abstract: We present the design of a dictionary machine that is suitable for VLSI implementation, and we discuss how to realize this implementation efficiently. The machine supports the operations of SEARCH, INSERT, DELETE, and EXTRACTMIN on an arbitrary ordered set. Each of these operations takes time O(log n), where n is the number of entries present when the operation is performed. Moreover, arbitrary sequences of these instructions can be pipelined through the machine at a constant rate (i.e., independent of n and the capacity of the machine). The time O(log n) is an improvement over previous VLSI designs of dictionary machines which require time O(log N) per operation, where N is the maximum number of keys that can be stored.

Muonium in diamond

Abstract: Two muonium states have been found in diamond. "Normal" muonium shows an isotropic hyperfine interaction with a coupling constant $\frac{A}{h}=3711\ifmmode\pm\else\textpm\fi{}21$ MHz. "Anomalous" muonium is described by a $〈111〉$ axially symmetric spin Hamiltonian with coupling constants extrapolated to 0 K $\frac{|{A}_{\ensuremath{\parallel}}|}{h}=167.98\ifmmode\pm\else\textpm\fi{}0.06$ MHz and $\frac{|{A}_{\ensuremath{\perp}}|}{h}=392.59\ifmmode\pm\else\textpm\fi{}0.06$ MHz. ${A}_{\ensuremath{\parallel}}$ and ${A}_{\ensuremath{\perp}}$ are of opposite sign, and they exhibit a temperature dependence describable by a Debye model. The amplitudes of the three anomalous muonium hyperfine transitions is zero applied field increase with increasing temperature and show relative variations which give information about muonium formation and indicate that anomalous muonium is the most stable state for muons in diamond. These diamond results are compared with those from the isostructural materials silicon and germanium.

Carotenoid Composition of Chlorophyll-Carotenoid-Proteins from Radish Chloroplasts

Abstract: The uneven distribution of carotenoids and chlorophylls between several chlorophyll- carotenoid-proteins isolated from radish chloroplasts by SDS-polyacrylamide-gel electrophoresis is described. Lutein and neoxanthin are enriched in the light-harvesting chlorophyll a/b-protein LHCP3, which exhibits low chlorophyll a/b ratios (1.1-1.3) and high values for the ratio chlorophyll a/β-carotene (a/c = 60-180). β-carotene is bound not only to the chlorophyll a-protein CPI + CPIa of photosystem I, but also to the chlorophyll a-protein CPa. Both chlorophyll a-proteins are characterized by high values for the ratio a/b and low values for the ratio a/c.

Chlorophyll‐protein levels and degree of thylakoid stacking in radish chloroplasts from high‐light, low‐light and bentazon‐treated plants

Abstract: The level of 7 chlorophyll-carotenoid-proteins was determined in chloroplasts from radish seedlings (Raphanus sativus L. var. Saxa Treib) grown in high-light (HL; 90 W m−2 and low-light (LL; 10 W m−2) growth conditions with and without application of the photosystem 2 herbicide bentazon (10−4M) and compared with the degree of thylakoid stacking. 1 The photosynthetic apparatus of HL-chloroplasts contains higher proportions of the photosystem 1 chlorophyll a-proteins CPI and CPIa than LL-chloroplasts or chloroplasts from bentazon-treated plants. 2 In LL-chloroplasts and in chloroplasts from bentazon-treated plants a higher proportion of light-harvesting chlorophyll a/b-proteins (LHCP1, LHCP2, LHCP3, LHCPy) is found. Bentazon treatment changes the proportion of LHCPs to about the same levels under both HL and LL-growth conditions. The amounts of free chlorophyll found in bentazon chloroplasts (27–29%) is higher than in the HL or LL-controls (16–18%). 3 The increase in degree of thylakoid stacking (% proportion of appressed membranes per total chloroplasts membranes) of LL-chloroplasts as compared to HL-chloroplasts of 7 to 9% (3rd to 5th day of illumination) is paralleled by a similar increase in the LHCPs of 5% and 8% (3rd and 5th day). The importance of light harvesting chlorophyll a/b-proteins as a prerequisite for thylakoid stacking is discussed.

Investigations of the Photovoltaic Tensor in Doped LiNbO3

Abstract: The photovoltaic current density in crystals without a center of symmetry depends bilinearly on the components of the light polarization vector via a third-rank tensor. For LiNbO3:Fe and LiNbO3: Cu the tensor properties are confirmed and three of the four non-vanishing components determined. The dependence on impurity concentration and on photon energy is also investigated. Die photovoltaische Stromdichte in Kristallen ohne Inversionszentrum hangt uber einen Tensor dritter Stufe bilinear von den Komponenten des Polarisationsvektors des Lichtes ab. Das Tensorverhalten fur LiNbO3: Fe und LiNbO3: Cu wird bestatigt und drei der vier nichtverschwindenden Komponenten werden bestimmt. Die Abhangigkeit von der Storstellenkonzentration und der Photonenenergie wird ebenfalls untersucht.

Counting and Reporting Intersections of d-Ranges

Abstract: We present a solution to the problem of reporting and counting all pairs of intersecting or overlapping d-ranges in a given set of n d-ranges. A d-range is a rectilinearly oriented rectangular d-dimensional box or brick. The three-dimensional case is presented in some detail and an 0(n log2 2 n + k) time and 0(n log2 2 n) space algorithm is developed for the reporting problem, where k is the number of reported intersecting pairs. This gives an 0(n log2 2 n) time and 0(n log 2 n) space algorithm for the counting problem. Apart from its usefulness wherever a "bounding boxes" technique is used, the development of the algorithm is of interest in its own right because of the data structures that are introduced and because of the technique used to reduce the time needed for preprocessing. Finally, the algorithm is generalized to give an 0(2 d−1 n log 2 d−n+ k) time and an 0(2d−1n log 2 d−n) space algorithm for the d-range intersection reporting problem for d ≥ 2, which again reduces to an 0(2d−1n log 2 d−1n) time and 0(2d−1n log 2 d−2n) space algorithm for the counting problem. Finally, we sketch how the reporting problem can be carried out with the same space requirements as the counting problem. The bounds presented are the best known to date.

Trimethylsilylverbindungen der Vb-Elemente. VI. Synthese, Molekül- und Kristallstruktur des Tetrakis(trimethylsilyl)distibans im Vergleich mit Tetraphenyldistiban

Abstract: Das erstmals bei Spaltungsreaktionen am Tris(trimethylsilyl)stiban von Breunig und Mitarb. [9] isolierte Tetrakis(trimethylsilyl)distiban 1 ist mit hoher Ausbeute auch aus Lithium-bis(trimethylsilyl)antimonid · 2THF und 1,2-Dibromathan in n-Pentan zuganglich. Die im festen Zustand intensiv rote, in Losung oder in der Schmelze aber nur noch schwach gelbe Verbindung kristallisiert monoklin in der Raumgruppe P21/c mit a = 680,6(1); b = 1672,8(2); c = 1190,0(1) pm; β = 119,01(5)°; Z = 2 bei + 20°C. Nach den Ergebnissen einer Rontgenstrukturanalyse (R = 0,017) stehen beide Bis(trimethylsilyl)stibano-Gruppen transoid zueinander; charakteristische Bindungslangen und -winkel sind: SbSb 286,7(1); SbSi 259,4 pm; SiSbSi 94,46(3); SbSbSi 98,68(3) und 94,43(3)°. Wie im ahnlichen, kurzlich von Ashe III und Mitarb. [8] publizierten 2,2′,5,5′-Tetramethyldistibolyl wird auch diese Kristallstruktur durch eine nahezu lineare Abfolge von SbSb Hanteln charakterisiert. Der intermolekulare SbSb-Kontakt innerhalb einer solchen Kette ist mit 399 pm gegenuber der mit 440 pm angegebenen Summe der van-der-Waals Radien verkurzt und durfte elektronische Wechselwirkungen unbekannter Art ermoglichen, die fur die Farbigkeit verantwortlich sein konnten. In ubereinstimmung mit dieser Annahme wird eine analoge Kettenbildung bei dem im festen Zustand nur gelben, von Rehder und Mitarb. [44] strukturell bereits untersuchten Tetraphenyldistiban 5 nicht beobachtet. Trimethylsilyl Derivatives of Vb-Elements. VI. Synthesis, Molecular and Crystal Structure of Tetrakis(trimethylsilyl)distibine Compared with Tetraphenyldistibine Tetrakis(trimethylsilyl)distibine already isolated by Breunig et al. [9] from cleavage reactions of tris(trimethylsilyl)stibine may also be obtained in high yields from lithium bis(trimethylsilyl)antimonide · 2THF and 1,2-dibromoethane in n-pentane. This compound intensely red in the solid state, but only slightly yellow in solution or in the melt crystallizes in the monoclinic space group P21/c with a = 680.6(1); b = 1672.8(2); c = 1190.0(1) pm; β = 119.01(5)°; Z = 2 at +20°C. An X-ray structure determination (R = 0.017) shows the bis(trimethylsilyl)-stibino groups to be arranged in a transoid position. Characteristic bond lengths and angles are: SbSb 286.7(1); SbSi 259.4 pm; SiSbSi 94.46(3); SbSbSi 98.68(3) and 94.43(3)°. As in similiar 2,2′,5,5′-tetramethyldistibolyl published recently by Ashe III et al. [8] this crystal structure, too, is characterized by a nearly linear sequence of SbSb groups. Compared with the sum of van-der-Waals radii the intermolecular Sb-Sb contact in such a chain is shortened from 440 to 399 pm. This probably allows electronic interactions of unknown type responsible for the colour of the crystals. In keeping with this assumption an analogous formation of chains is not found in solid, only yellow tetraphenyldistibine 5 the structure of which has already been studied by Rehder et al. [44].