Showing papers by "Leibniz University of Hanover published in 1991"

Solitary excitations in one-dimensional magnets

Abstract: The present status of theoretical and experimental investigations of solitary excitations in one-dimensional magnetic systems is reviewed. A survey of exact solutions to the nonlinear equations of motion for pertinent classical chain systems (sine-Gordon chain and ferromagnetic Heisenberg chains with various anisotropies) is given. Particular emphasis is devoted to the role of solitons in the thermodynamics of such systems. Models corresponding to real quasi-one-dimensional magnets are broadly discussed to demonstrate the properties of their solitary excitations. The experimental significance of such nonlinear excitations in the static and dynamic quantities of such systems is discussed in detail. The models and model substances are the easy-plane ferromagnet (model substances CsNiF3 and (C6H11NH3)CuBr3), the easy-plane antiferromagnet (CH3)4NMnCl3) and the S = ½ Ising chain with transverse interactions (CsCoCl3). The quantum aspects of solitary excitations are treated in some theoretical detail....

α‐Methylidene‐ and α‐Alkylidene‐β‐lactams from Nonproteinogenic Amino Acids

Abstract: Treatment of methyl 2-(1-hydroxyalkyl)prop-2-enoates 1 with conc. HBr solution afforded methyl (Z)-2-(bromomethyl)alk-2-enoates 2, which were transformed regioselectively into N-substituted methyl (E)-2- (aminomethyl)alk-2-enoates 3 (SN2 reaction) and into N-substituted methyl 2-(1-aminoalkyl)prop-2-enoates 4(SN2′ reaction). Regiocontrol of nucleophilic attack by amine was accomplished simply by choice of solvent, the SN2 reaction occurring in MeCN and the SN2′ reaction in petroleum ether. Hydrolysis and lactamization afforded β-lactams 7 and 8, containing an exocyciic alkylidene and methylidene group at C(3), respectively.

On the development of creativity in children

Abstract: There seems to be a quantitative increase in creativity scores through the years of childhood and adolescence, with some strong declines at certain developmental stations. However, earlier studies give no information about qualitative changes in creativity development. Traditional divergent thinking tests, for example, give more or less pure quantitative information about cognitive skills. The present investigation examined age trends using the recently developed Test zum schopferischen Denken—Zeichnerisch, or in English, Test for Creative Thinking‐Drawing Production (TCT‐DP). The TCT‐DP recognizes qualitative response categories. In the present investigation, the TCT‐DP was administered to children between four and eight years of age (N = 272) from kindergarten and the first two school grades. In addition to a quantitative analysis, a special qualitative analysis of the drawings shows how and in which way different subcomponents of creativity develop. Six developmental stages of creativity, clo...

Terminology in semiconductor electrochemistry and photoelectrochemical energy conversion (Recommendations 1991)

Abstract: In this document recommendations for the usage of symbols and terminology in semiconductor electrochemistry are given. Energy levls in the bulk of the solid and the electrolyte including their interface are introduced and kinetic parameters defined. In addition a terminology on photoelectrochemical cells is recommended. In the latter case, it is distinguished between two modes of operation in these cells, i.e. photovoltaic cells in which radiant energy is converted into electrical energy and photoelectrolysis cells in which radiant chemistry causes a net chemical conversion

Fusarium oxysporum: status in bioethanol production.

Abstract: Fermentation of lignocellulosic materials to ethanol and other solvents provides an alternative way of treating wastes and producing chemical feedstocks and fuel additives. Considerable efforts have been made in past 10 years to improve the process based on lignocellulosic biomass and hydrolysate that contains a complex mixture of sugars, decomposition products of sugars, and sometimes the inhibitory levels of soluble lignin. Despite the relative abundance of D-xylose in crop and forest residues it has not been found efficiently fermentable by most of the microorganisms. Recent research has revealed that D-xylose may be fermented to ethanol and organic acids. Recently, several strains of Fusarium oxysporum have been found to have potential for converting not only D-xylose, but also cellulose to ethanol in a one-step process. Distinguishing features of F. oxysporum for ethanol production in comparison to other organisms are identified. These include the advantage of in situ cellulase production and cellulose fermentation, pentose fermentation, and the tolerance of sugars and ethanol. The main disadvantage is the slow conversion rate when compared with yeast.

Reliability of Risk Management: Market Insurance, Self-Insurance and Self-Protection Reconsidered

Abstract: This paper examines the three main tools of risk management in a setting where reliability cannot be guaranteed. Thus, for example, insurers might be insolvent, sprinkler systems might be inoperative and alarm systems might be faulty. These types of nonreliability are shown to have significant consequences for risk management. In particular, the relationships between increased risk aversion and the use of the various risk management tools do not carry over from models with full reliability. Moreover, the well-known result of Ehrlich and Becker, that market insurance and self-insurance are substitutes, is shown to fail in the presence of nonreliability risk.

β-NMR studies of spin-lattice relaxation in glassy and layer-crystalline compounds

Abstract: The method of beta-radiation detected NMR (β-NMR), complementing and extending the potential of conventional NMR, and its experimental realization by the new β-NMR spectrometer at the research reactor of KFA Julich are described with respect to spin-lattice relaxation (SLR) studies. Recent applications to oxide and electrolyte glasses and a crystalline layered compound are reviewed. It is shown that a deviation from single-exponential SLR is a signature of local disorder in the vicinity of the β-NMR probes. The temperature and, especially, the magnetic field (or frequency) dependence of the SLR rate allow one to trace various dynamic processes, such as thermally activated excitations of disorder modes, anomalous ionic diffusion, molecular motions below and above the glass transition, and low-dimensional diffusion.

Wave-Induced Pore Pressure in Rubble Mound Breakwaters

Abstract: Experimental results from large scale tests are presented for the distribution of wave-induced pore pressure within rubble mound breakwaters, for the reflection coefficients and the damping of wave motion through the armour and under-layer. The results are then discussed with respect to application and further research.

The significance of root development of spinach and kohlrabi for N fertilization

Abstract: N fertilizer recommendatons are based on the Nmin content in the useable soil layer. However, for spinach, information from the literature differs for both depth of useable soil layer and N fertilizer recommendations. The objectives of these experiments were to study the importance of different soil zones for N supply to spinach and to kohlrabi, and to examine the relationship between N supply in the useable soil layer and yield of spinach.

Single-shot autocorrelator for KrF subpicosecond pulses based on two-photon fluorescence of cadmium vapor at X = 508 nm

Abstract: By excitation of cadmium vapor with a high-peak-power KrF excimer laser pulse, fluorescence of an atomic transition at λ = 508 nm is induced by a two-photon ionization process followed by fast recombination The nonlinear response of the medium is used to develop a simple single-shot autocorrelator for subpicosecond KrF excimer laser pulses operating down to intensities of less than 109W/cm2 We have measured 360-fs (FWHM) pulses at λ = 248 nm with a time resolution of 15 fs

A parameterization for modelling the meteorological effects of tall forests — A case study of a large clearing

Abstract: A parameterization scheme has been developed to describe the effects of a tall forest on the mean structure of the atmospheric boundary layer (ABL). The main advantage of the scheme is that dynamical and thermodynamical effects of a forest surface can be simulated satisfactorily using only a coarse-grid resolution within numerical models. Thereby, the canopy layer is parameterized as a quasi-subgrid phenomenon. This makes it possible to study meteorological phenomena within the ABL in a very economical way (with respect to computational time) whereby, nevertheless, more detailed information concerning the forest surface is taken into account than could be done using the same grid resolution and quite simple assumptions describing the canopy, e.g., the effective roughness. The applicability in numerical models is shown by using a slightly modified two-dimensional version of the mesoscale model FITNAH. For comparison, simulations with a high numerical grid resolution within the canopy have been carried out. Model results reproduce the known meteorological phenomena in forested areas, e.g., a stable thermal stratification near the surface during the day, and at night, a neutral — or slightly unstable condition — and, in general, reduced windspeed within the canopy layer. Diurnal variations and spatial distributions of temperature and humidity are found to be similar for both cases. Also, a thermally-induced local circulation system in the vicinity of a large clearing has been simulated satisfactorily. A comparison of the calculated results verifies that the parameterization scheme is quite suitable for simulating the effects of plant canopies on the distributions of meteorological variables in the ABL.

Preparation and Selected Reactions of t‐Butyl 2‐Methylene‐3‐oxoalkanoates

Abstract: The title class of 1,1-diactivated ethylenes has been prepared in two steps from aldehydes and t-butyl acrylate by (i) DABCO-catalyzed coupling to give t-butyl 2-(hydroxyalkyl)-2-propenoates 11 and (ii) low-temperature Jones oxidation, followed by swift work up at low temperature. The resulting t-butyl 2-methylene-3-oxoalkanoates 12 are stabilized by sterically demanding and also by aromatic groups R. For primary unhindered alkyl groups, stability is low. The compounds enter into Michael reactions, hetero Diels-Alder additions with enol ethers, and self-dimerization.

Inhibition of adenylate-cyclase-coupled G protein complex by ototoxic diuretics and cis-platinum in the inner ear of the guinea pig.

Abstract: The enzyme adenylate cyclase produces the second messenger cAMP and is located in the mammalian inner ear, predominantly in the stria vascularis and to a lesser extent in the organ of Corti. It is coupled to hormone receptors and regulating G proteins in the outer cell membrane. By means of immunofluorescence in cryostat sections of the guinea pig cochlea, we could demonstrate the G proteins GS and Gi, which belong to the adenylate cyclase complex. These proteins had their highest density in the stria vascularis. In membrane preparations of this tissue, the adenylate cyclase complex was inhibited by ototoxic drugs (furosemide, ethacrynic acid and cis-platinum). Stimulation at different sites of the enzyme system showed that the target of these drugs was probably the regulating G protein complex and not the enzyme molecule itself. Inhibition depended on the concentration of the drug and the incubation time.

Population dynamics of biofilm development during start-up of a butyrate-degrading fluidized-bed reactor

Abstract: Population dynamics during start-up of a fluidized-bed reactor with butyrate or butyrate plus acetate as sole substrates as well as biofilm development on the sand substratum were studied microbiologically, immunologically and by scanning electron microscopy. An adapted syntrophic consortium consisting of Syntrophospora sp., Methanothrix soehngenii, Methanosarcina mazei and Methanobrevibacter arboriphilus or Methanogenium sp. achieved high-rate butyrate degradation to methane and carbon dioxide. Desulfovibrio sp., Methanocorpusculum sp., and Methanobacterium sp. were also present in lower numbers. Immunological analysis demonstrated methanogens antigenically related to Methanobrevibacter ruminantium M1, Methanosarcina mazei S6, M. thermophila TM1, Methanobrevibacter arboriphilus AZ and Methanothrix soehngenii Opfikon in the biofilm. Immunological analysis also showed that the organisms isolated from the butyrate-degrading culture used as a source of inoculum were related to M. soehngenii Opfikon, Methanobacterium formicicum MF and Methanospirillum hungatei JF1.

Does orthotopic liver transplantation heal Wilson's disease? Clinical follow-up of two liver-transplanted patients.

Abstract: Two patients with Wilson's disease (WD) underwent orthotopic liver transplantation, one for subacute liver failure and the other for severe oesophageal haemorrhage. After transplantation both patients fully recovered within five months, and copper metabolism returned to normal. Follow-up examinations were continued for 4 and 6 years. Clinical as well as electrophysiological testing in these two patients yielded better results than in most of 12 WD-patients being conventionally treated for a similar period or even longer.