Showing papers by "Karlsruhe Institute of Technology published in 1981"

Photosynthetic activity, chloroplast ultrastructure, and leaf characteristics of high-light and low-light plants and of sun and shade leaves.

Abstract: The photosynthetic CO2-fixation rates, chlorophyll content, chloroplast ultrastructure and other leaf characteristics (e.g. variable fluorescence, stomata density, soluble carbohydrate content) were studied in a comparative way in sun and shade leaves of beech (Fagus sylvatica) and in high-light and low-light seedlings. 1. Sun leaves of the beech possess a smaller leaf area, higher dry weight, lower water content, higher stomata density, higher chlorophyll a/b ratios and are thicker than the shade leaves. Sun leaves on the average contain more chlorophyll in a leaf area unit; the shade leaf exhibits more chlorophyll on a dry weight basis. Sun leaves show higher rates for dark respiration and a higher light saturation of photosynthetic CO2-fixation. Above 2000 lux they are more efficient in photosynthetic quantum conversion than the shade leaves. 2. The development of HL-radish plants proceeds much faster than that of LL-plants. The cotyledons of HL-plants show a higher dry weight, lower water content, a higher ratio of chlorophyll a/b and a higher gross photosynthesis rate than the cotyledons of the LL-plants, which possess a higher chlorophyll content per dry weight basis. The large area of the HL-cotyledon on the one hand, as well as the higher stomata density and the higher respiration rate in the LL-cotyledon on the other hand, are not in agreement with the characteristics of sun and shade leaves respectively. 3. The development, growth and wilting of wheat leaves and the appearance of the following leaves (leaf succession) is much faster at high quanta fluence rates than in weak light. The chlorophyll content is higher in the HL-leaf per unit leaf area and in the LL-leaf per g dry weight. There are no differences in the stomata density and leaf area between the HL- and LL-leaf. There are fewer differences between HL- and LL-leaves than in beech or radish leaves. 4. The chloroplast ultrastructure of shade-type chloroplasts (shade leaves, LL-leaves) is not only characterized by a much higher number of thylakoids per granum and a higher stacking degree of thylakoids, but also by broader grana than in sun-type chloroplasts (sun leaves, HL-leaves). The chloroplasts of sun leaves and of HL-leaves exhibit large starch grains. 5. Shade leaves and LL-leaves exhibit a higher maximum chlorophyll fluorescence and it takes more time for the fluorescence to decline to the steady state than in sun and HL-leaves. The variable fluorescence VF (ratio of fluorescence decrease to steady state fluorescence) is always higher in the sun and HL-leaf of the same physiological stage (maximum chlorophyll content of the leaf) than in the shade and LL-leaf. The fluorescence emission spectra of sun and HL-leaves show a higher proportion of chlorophyli fluorescence in the second emission maximum F2 than shade and LL-leaves. 6. The level of soluble carbohydrates (reducing sugars) is significantly higher in sun and HL-leaves than in shade and LL-leaves and even reflects changes in the amounts of the daily incident light. 7. Some but not all characteristics of mature sun and shade leaves are found in HL- and LL-leaves of seedlings. Leaf thickness, dry weight, chlorophyll content, soluble carbohydrate level, photosynthetic CO2-fixation, height and width of grana stacks and starch content, are good parameters to describe the differences between LL- and HL-leaves; with some reservations concerning age and physiological stage of leaf, a/b ratios, chlorophyll content per leaf area unit and the variable fluorescence are also suitable.

Theory of the bulk photovoltaic effect in pure crystals

Abstract: A theory is presented for the intrinisic anomalous bulk photovoltaic effect observed in noncentrosymmetric crystals, e.g., BaTi${\mathrm{O}}_{3}$. An exact formula is derived for the calculation of the short-circuit photovoltaic current in a pure crystal in terms of its Bloch states and energy bands. Unlike a conventional field or diffusion current, the photovoltaic current is essentially determined by the change of wave functions upon photoexcitation of an electron from the valence to the conduction band. Our theory also reveals that the bulk photovoltaic effect can occur even in pure nonpyroelectric piezoelectric crystals, e.g., Te and GaP, which have no polar axis and therefore no a priori direction for the photovoltaic current.

Some effects of enhanced UV-B irradiation on the growth and composition of plants.

Abstract: Barley (Hordeum vulgare), corn (Zea mays), bean (Phaseolus vulgaris), and radish (Raphanus sativus) seedlings were continuously irradiated under a lighting device for 5–10 d at an increased ultraviolet (UV)-B fluence rate. In their growth parameters, composition, and leaf surface, these four species responded differently to the increased UV-B exposure. Bean seedlings suffered the most serious effects, radish and barley less, and corn was hardly influenced at all. In all plant species, the fresh weight, the leaf area, the amounts of chlorophylls, carotenoids and the galactolipids of the chloroplasts were reduced. The lipid content of the corn and bean seedlings also diminished. But all the irradiated plants showed a rise in their protein content compared to the control plants. The content of flavonoids increased in barley and radish seedlings by about 50%. The effects on growth parameters and composition were more extensive with increasing UV-B fluence rates, at least as shown in the case of barley seedlings. The fresh weights fell proportionally with the chlorophylls and carotenoids. In contrast, the flavonoid content of barley leaves rose parallel to the increasing UV-B fluence rates and reached 180% of the value in the control plants with the highest UV-B fluence rate. Scorching appeared regularly in the form of bronze leaf discoloration at the highest UV-B fluence rates. Scanning electron micrographs of the leaf surface of UV-B irradiated plants showed deformed epidermal structures.

Trap‐door problem with dry sand: A statical approach based upon model test kinematics

Abstract: The trap-door problem with dry sand is treated in a statical analysis based upon model test kinematics. Integration of the equilibrium conditions along horizontal slices and introducing the mean value for the vertical stresses yields a differential equation for the trap-door force. Concerning the constitutive response of sand a statical model of a moving shear band is proposed as an internal boundary. Solutions for the trap-door force for the active and passive modes and for the ultimate and residual states are discussed.

The choice of Gaussian basis sets for molecular electronic structure calculations

Abstract: The choice of Gaussian type basis sets for electronic structure calculations of molecules is discussed in detail for treatments on the SCF and Cl level. This article is organized in the following sections : I. Introduction, II. Mathematical foundation of the LCAO-MO method, III. Basis sets of first and second row atoms in SCF calculations, IV. Transition metals, V. Beyond-Hartree-Fock calculations, VI. Summary.Detailed proposals are made for the choice of basis sets at various levels of computational expense.

Group properties of utt=[F(u)ux]x

Abstract: The group properties and the associated Lie algebra are developed for the subject quasilinear wave equation, for arbitrary f[fϵC2(R), f > 0, f ≠ 0]. From the resulting information sets of explicit invariant solutions are constructed for wave propagation in gases and for the transonic equation.

The system hydrogen - water up to 440°C and 2500 bar pressure

Abstract: The system H2 — H2O has been studied isochorically from 0.5 to 90 mol-% H2 and up to 440°C and 2500 bar pressure using an autoclave containing two sapphire windows through which phase transitions could be observed at elevated temperatures and pressures. — The system was found to exhibit so-called “gas-gas” immiscibility with a critical curve proceeding to higher temperatures and pressures from the critical point of pure water. Within the range of these experiments, the critical temperature of H2—H2O mixtures does not change greatly from that of pure water (e.g. Tc = 381.3°C at pc = 2520 bar for 38 mol-% H2). pVT measurements have been made in the homogeneous region and excess volumes have been calculated at 400°C and at different pressures. At 300 bar, the excess volumes are relatively large and positive (e.g. VE = 58.0 cm3 mol−1 at 40 mol-% H2) whereas at 2500 bar, excess volumes of H2—H2O mixtures indicate only small positive or negative departures from ideality.

Flows of dilute hydrolyzed polyacrylamide solutions in porous media under various solvent conditions

Abstract: Experimental results on pressure losses of flows of dilute polymer solutions through porous media are summarized. The polymer products employed in this study consisted of partially hydrolyzed polyacrylamides (HPAM) with different degrees of hydrolysis. The effect of the hydrolysis on the pressure drop is investigated in a porous media test section designed to minimize polymer degradation. The investigations were carried out for various solvent conditions, and it is shown that the maximum increase in pressure drop is mainly dependent on the molecular weight of the polymers. The onset of the polymer action is measured for various fluid and solvent properties. Particular attention is given to measurements near θ-conditions. The results stress the importance of the solvent properties on the actions of the polymers and on the resultant pressure drop for porous media flows. The addition of salt ions to solutions of partially hydrolyzed polyacrylamides yields onset behavior previously observed for nonionic polymers. The differences measured between various solvent properties can be explained by the actual hydrodynamic molecule dimensions for a given molecular weight and polymer concentration. To quantify the influences of the solvent properties on the polymers, measurements were carried out in aqueous solutions for various pH values and therefore at various degrees of dissociation. The importance of separating polymer effects caused by their linear dimension in the solution from those that are introduced by and increase in solvent viscosity is shown. Measurements were performed to quantify the effects of solvent viscosity on the polymer action and to separate these effects from those due to changes in molecule dimensions. The implications of the present results are stressed in connection with applications of polymer solutions in tertiary oil recovery, and the positive features of the molecule actions on flow in such applications are described.

Interpretation of the unusual behavior of H2O and D2O at low temperature: Are concepts of percolation relevant to the “puzzle of liquid water”?

Abstract: This talk will summarize the present status of an ongoing research program designed to answer the question posed in the title. Since a snapshot of liquid water with a subpicosecond shutter speed reveals that this system (a hydrogen-bonded liquid) is above its percolation threshold, it is tempting to imagine that connectivity concepts of the sort encompassed in percolation theory may prove useful. We find that the traditional approach of random-bond percolation theory-developed to describe the onset of gelation - is not sufficient, since water is well above its gelation threshold. Hence we develop a new correlated-site percolation model, whose predictions are found to be in quantitative agreement with molecular dynamics calculations and in qualitative agreement with a wide range of experimental data on low-temperature water. The picture that emerges is that of an “infinite” hydrogen-bonded network subject to continuous restructuring. At any instant of time, there are many strained and broken bonds. Tiny patches of this network have a local density and local entropy lower than the global density and global entropy of the network. These patches — described by correlated-site percolation theory — are all possible sizes and are characterized by highly ramified (“tree-like”) shapes, just as in random-site percolation. In particular, this model explains the paradoxical facts that at sufficiently low temperature, the isothermal compressibility KT ∝ <(δV)2TPN and the constant-pressure specific heat CP ∝ <(δS)2TPN increase as T decreases, while the thermal expansivity αP ∝ <δVδSTPN is negative. Finally, we discuss some ongoing calculations and experiments designed to provide additional tests of the overall picture.

Cello-A New Detector at PETRA

Abstract: A description of the design characteristics of CELLO, a large 4Π magnetic detector at PETRA, is given and first results of beam operation are presented.

A Reynolds-stress closure model of turbulence applied to the calculation of a highly curved mixing layer

Abstract: The measurements in a highly curved mixing layer reported by Castro & Bradshaw (1976) are used to evaluate the performance of a calculation method based on the solution of modelled transport equations for the Reynolds stresses and the dissipation rate of turbulent energy. The model reproduces the suppression of turbulence by stabilizing curvature and, downstream of the curved region, where the flow returns asymptotically to being a plane mixing layer, calculated values of turbulent intensity and shear stress overshoot the plane-layer values in accordance with the experimental observations. The results are compared with those obtained by Townsend (1980) from a rapid-distortion model which correctly predicts the streamwise variation of the shear stress to intensity ratio. By contrast, calculations based on a conventional two-equation eddy-viscosity model fail badly to account for curvature effects on this flow.

Ionic Currents as Control Mechanism in Cytomorphogenesis

Abstract: As plant cells develop into multicellular organisms, three-dimensional patterns are formed without the cells possessing genetically laid down plans for these patterns. Therefore, a cell needs additional information for its proper spatial development to indicate, for instance, in which direction it should grow or in which plane it should divide. This information generally comes from external physical factors such as light, gravity, or pressure or from chemical factors such as ion or hormone gradients. Some examples of the effects of such factors on the morphogenesis of plant cells are illustrated in Figs. 1 and 2. When, for instance, zygotes of the brown algae Fucus and Pelvetia, which are practically nonpolar cells, are exposed to light from one side or only partly illuminated or exposed to a K+ gradientthey grow on the side turned away from the light or at the shaded side or on the side with the higher K+ concentration, respectively (Bentrup 1971, Bentrup et al. 1967, Jaffe 1968). When the tip-growing tubes of the yellow-green alga Vaucheria are locally irradiated with blue light, an additional growth zone is formed on this spot, which leads to branching within a few hours (Kicherer and Weisenseel, unpublished).

Ultrastructural development of chloroplasts in radish seedlings grown at high- and low-light conditions and in the presence of the herbicide bentazon

Abstract: The ultrastructure of chloroplasts from radish seedlings (Raphanus sativus L.) grown at high (24 klux; 250 W · m−2) and at low-light quanta fluence rates (1 klux; 15W · m−2) exhibits differences in many structural parameters. 1. The low-light (shade-type) chloroplasts are characterized not only by higher grana stacks and a higher stacking degree of thylakoids, but also by broader grana than the high-light (sun-type) chloroplasts. The latter are larger (length and width), possess large starch grains and contain more and larger plastoglobuli than the shade-type chloroplasts of the low-light plants, which are lacking starch. 2. The photosynthesis herbicide bentazon (10−4M) induces a shade-type adaptation (broader and higher grana stacks, higher stacking degree) particularly at high and to some extent also at low-light quanta fluence rates. The starch content and the number of plastoglobuli in the high-light bentazon chloroplasts is reduced as compared to the high-light controls.

Cavitation Inception in Spool Valves

Abstract: Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under non-cavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to non-cavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves.

Nonequilibrium properties of electron-hole plasma in direct-gap semiconductors

Abstract: The gain spectra of the electron-hole plasma recombination in CdS are investigated as a function of the excitation conditions and of the lattice temperature. From a lineshape analysis which includes such many-body effects as collision broadening, single-particle energy renormalization and excitonic enhancement, average plasma parameters are obtained. In contrast to the predictions of quasi-equilibrium theory, one finds that the electron-hole plasma does not reach a full thermal quasi-equilibrium in direct-gap materials because of the short lifetimes of the carriers. The nonequilibrium effects are shown to lead to the formation of electron-hole plasma density fluctuations. No well-defined coexistence region exists. The experimental results in the phase transition region can consistently be explained by theoretical treatments of this nonequilibrium phase transition.

Molecular dynamics simulation study of the negative hydration effect in aqueous electrolyte solutions

Abstract: To study the structure breaking effect in aqueous electrolyte solutions (also termed negative hydration), a series of molecular dynamics simulation runs has been carried out. An originally uncharged, nonpolar spherical solute particle (“Xenon”) is charged step by step from g1 = 0.0 e to q1 = +0.67 e, + 1.0 e and q1 = +2.0 e (e is the positive elementary charge). At zero charge the occurrence of hydrophobic hydration is observed. The surroundings of the divalent cation also shows marked structuring: the normal “positive” ionic hydration. In an intermediate region of charge (at q1 = 1.0 e) negative hydration is detected, which proves to be a state of minimum order. Structural changes are discussed by using pair and three particle correlation functions. Hydration energies, binding energies and pair interaction energy distributions are determined. The microdynamics is studied by observing the reorientational motion and the self diffusion behaviour of the water molecules in different regions. A zone of increased mobility is located in the vicinity of the ion, which may include the innermost hydration shell. Additionally a system comprising a negatively hydrated anion has also been studied.

Coercive force and 90° domain wall motion in ferroelectric PLZT ceramics with square hysteresis loops

Abstract: The polarization reversal of some tetragonal-phase PLZT ceramics is studied. The results are explained in terms of 90° domain wall motions. A reported theory originally derived for rhombohedral-phase PLZT 6/65/35 ceramics is shown to be applicable to tetragonal-phase PLZT ceramics also by introducing the remanent degree of 90° domain alignment γ90. As a result, the calculation of coercive force is possible for various PLZT compositions considering the interaction of 90° domain wall motions and reacting forces established by the internal stress state of ferroelectric ceramics. The frequency dependence of coercive force and measurements of switching strain, including depolarization data obtained from either mechanically or electrically produced external forces, confirm the interpretation of predominantly occuring 90° reorientations and are consistent with the extended theory.