Showing papers by "ETH Zurich published in 1980"

Elucidation of cross relaxation in liquids by two-dimensional N.M.R. spectroscopy

Abstract: Two-dimensional N.M.R. spectroscopy is applied to the elucidation of cross relaxation pathways in liquids. The theory underlying two dimensional studies of cross relaxation and of transient nuclear Overhauser effects is developed. The influence of the correlation time of the molecular random process is investigated. It is found that in the limit of short correlation times (extreme narrowing limit) weak negative cross-peaks are observed. However, for long correlation times (spin diffusion limit) strong positive cross-peaks can be obtained. The technique appears particularly promising for the study of cross relaxation in macromolecules. Examples of intra- and intermolecular cross relaxation in the extreme narrowing limit are presented.

Characterization of an acetate-decarboxylating, non-hydrogen-oxidizing methane bacterium.

Abstract: A methanogenic bacterium, commonly seen in digested sludge and referred to as the "fat rod" or Methanobacterium soehngenii, has been enriched to a monoculture and is characterized. Cells are gramnegative, non-motile and appear as straight rods with flat ends. They form filaments which can grow to great lengths. The structure of the outer cell envelop is similar to Methanospirillum hungatii. The organism grows on a mineral salt medium with acetate as the only organic component. Acetate is the energy source, and methane is formed exclusively from the methyl group. Acetate and carbon dioxide act as sole carbon source and are assimilated in a molar ratio of about 1.9:1. The reducing equivalents necessary to build biomass from these two precursors are obtained from the total oxidation of some acetate. Hydrogen is not used for methane formation and is not needed for growth. Formate is cleaved into hydrogen and carbon dioxide. Coenzyme M was found to be present at levels of 0.35 nmol per mg of dry cells and F420 amounted to 0.55 microgram per mg protein. The mean generation time was 9 days at 33 degrees C.

An Economic Premium Principle

Abstract: (a) The notion of premium calculation principle has become fairly generally accepted in the risk theory literature. For completeness we repeat its definition:A premium calculation principle is a functional assigning to a random variable X (or its distribution function Fx(x)) a real number P. In symbolsThe interpretation is rather obvious. The random variable X stands for the possible claims of a risk whereas P is the premium charged for assuming this risk.This is of course formalizing the way actuaries think about premiums. In actuarial terms, the premium is a property of the risk (and nothing else), e.g.(b) Of course, in economics premiums are not only depending on the risk but also on market conditions. Let us assume for a moment that we can describe the risk by a random variable X (as under a)), describe the market conditions by a random variable Z.Then we want to show how an economic premium principlecan be constructed. During the development of the paper we will also give a clear meaning to the random variable Z:In the market we are considering agents i = 1, 2, …, n. They constitute buyers of insurance, insurance companies, reinsurance companies.Each agent i is characterized by hisutility function ui(x) [as usual: ]initial wealth wi.In this section, the risk aspect is modelled by a finite (for simplicity) probability space with states s = 1, 2, …, S and probabilities πs of state s happening.

Investigation on rate — Determining factors in the microbial reduction of azo dyes

Abstract: Investigations on the effects of pH, temperature, type and concentration of respiration substrates and oxygen tension on the reduction rate of derivatives of 1-phenylazo-2-naphthol and of a variety of textile dyes served as a basis for establishing a bioassay for strictly reproducible measurements of the microbial reduction rate of azo dyes. Standard organism was a strain of Bacillus cereus isolated from soil. Dye reduction occurred with the standard organism and other facultatively or obligatory aerobic bacteria in exclusively anoxic conditions. In principle, first order kinetics of decolorization were found. Reduction products may however inhibit the reaction. All dyes not measurably reduced by living cells of B. cereus were decolorized by cell extracts of the same species. Dyes adsorbed by the cell walls were in most cases reduced at slow rates and did not influence the simultaneous reduction of non-adsorbable dyes in the medium. The observations confirm the hypothesis advanced by Gingell and Walker (1971) of an intracellular, non-enzymatic reduction of azo compounds by reduced flavin nucleotides. The rate of permeation of the dyes through the cell membrane is the primordial ratelimiting step in the microbial decolorization of azo dyes. Sulfonic acid substitution seems to be an effective inhibitor of permeation.

Surface effects and the formation of metal hydrides

Abstract: Hydrogen is stored atomically in metal hydrides. Dissociative chemisorption and associative desorption are therefore important steps in the hydrogen absorption and desorption processes. We summarize the theoretical and experimental knowledge of hydrogen chemisorption on clean and precovered metal surfaces and correlate it with the techniques for preparing metal hydrides. At the surface of hydride-forming intermetallics, precipitates of d metals and a metallic subsurface are produced by surface segregation and decomposition. The subsurface and the precipitates are able to dissociate H2. Our recent work on the surface analysis of LaNi5, FeTi, Mg2Ni and ErFe2 is reviewed.

The gross features of the lithosphere-asthenosphere system in Europe from seismic surface waves and body waves

Abstract: Long-period recordings of dispersive Rayleigh waves along numerous station lines, or ‘profiles’, in Europe have for the first time permitted a uniform inversion of these observations based on a new method of phase velocity regionalization. Regional dispersion relations obtained by this method have then been subjected to a complete inversion procedure commonly known as the ‘hedgehog’ method. The results are presented in a map outlining the thickness of the lower lithosphere (‘lid’) and the shear (S) velocities in both the ‘lid’ and the asthenosphere ‘channel’. A comparison of these results with the minimum compressional (P) wave velocities in the asthenosphere and their corresponding depths provides an estimate of theV p /V s ratio for the asthenosphere in the European area.

Reaction Paths on Multidimensional Energy Hypersurfaces

Abstract: Theoretical investigation of a chemical reaction requires detailed knowledge of the potential energy of the molecular system. As a first step in such a study, minimum-energy reaction paths have to be mapped on a generally multidimensional molecular potential surface. Even at this stage problems are encountered that have only recently been solved satisfactorily. The difficulties involved and various ways to handle them are discussed in connection with a two-parametric model potential. Three chemical reactions examined illustrate the usefulness of such theoretical investigations as well as their current limitations.

Controlled-release fertilizers

Abstract: A substantial improvement in fertility management can be expected from programming nutrient supply rates to fit the physiological requirements at different growth stages of plants and from simultaneously reducing nutrient losses as well as the cost bases for material, transportation, equipment and labor. Usage of controlled-release fertilizers (CRF) can potentially contribute toward reaching these goals. The currently available technology to regulate nutrient release from CRF is analysed and results are discussed. A partial synchronisation of nutrient release and physiological need of plants can be achieved through use of fertilizers with different release characteristics. Usage of CRF, especially those containing nitrogen, reduce nutrient losses because, at any one moment, only a small fraction of the total application is present in a readily leachable form. Similarly, volatilization losses of nitrogen are diminished. The improved efficiency of fertilizer use is economically beneficial, saves energy and reduces environmental pollution. However, since nutrient release from CRF continues in the absence of plants, toxic levels of salts can accumulate during a fallow period or, alternatively, leaching losses can be higher than with conventional fertilization. These problems can be important with winter fallow if temperatures are insufficiently low to inhibit the nutrient release. With currently available CRF it is possible to exceed conventional application rates several fold without a danger of salinity. Thus in addition to reduced nutrient losses economic benefits can also be expected from savings in labor, transport cost and equipment. On the negative side are the additional cost for controlling the nutrient release and often a lower nutrient content per unit weight of the CRF. At present the economic picture is not clear and careful analyses are desirable. CRF have been tested with a large number of different plants. Good crops can definitely be grown with CRF, yields are usually superior to those with single applications of conventional fertilizers and can approach those obtained with optimum liquid feed or split application programs. So far, usage has mainly been concerned with the nonagricultural field. Much interest exists in using CRF for rice or under plastic soil covers. Solutions to numerous difficult problems were attempted with CRF, such as nutrient supplies to street trees with roots growing under pavements or fertilization of bacteria decomposing oil spills on the surface of the sea.

Enormous yield of photoelectrons from small particles

Abstract: A new ac bridge technique allows detailed photoelectric studies on very small particles suspended in gases. The photoelectric yield $Y$ near threshold $\ensuremath{\Phi}$ still follows the Fowler-Nordheim law $Y=c{(h\ensuremath{ u}\ensuremath{-}\ensuremath{\Phi})}^{2}$; yet $c$ is generally much larger compared to surfaces of extended solids. For Ag particles of radius 20 \AA{} in an airlike mixture of ${\mathrm{N}}_{2}$ and ${\mathrm{O}}_{2}$, $c\ensuremath{\simeq}100{c}_{0}$, where ${c}_{0}$ applies to a macroscopic Ag surface in the same environment.

Stereospecific Polymerization of Propylene: An Outlook 25 Years after Its Discovery

Abstract: In 1955 Natta and his co-workers from the Istituto di Chimica Industriale del Politecnico di Milano reported the properties of highly crystalline polypropylene and other poly-α-olefins[1] which posses, at least in long sections of the main chain, asymmetric carbon atoms of the same absolute configuration (isotactic poly-α-olefins). The discovery of the new crystalline polymers was judged at that time “revolutionary in its significance”[2] and heralded a new era in polymer science and technology. Indeed, crystalline polypropylene, because of its relatively high melting point and its outstanding mechanical properties, has found very extensive application in the field of plastics films and fibers.—25 years after this publication, it is worthwhile examining the further developments following this discovery which has had such a great scientific and industrial impact, and the problems which are still open concerning the structure of the catalytic centers and the mechanisms by which practically completely stereoregular polypropylenes are formed.

Myosin types in human skeletal muscle fibers.

Abstract: By combining enzyme histochemistry for fiber typing with immunohistochemistry for slow and fast myosin a correlation between fiber type and myosin type was sought in human skeletal muscle. Fiber typing was done by staining for myofibrillar ATPases after preincubation at discriminating pH values. Myosin types were discriminated using type specific anti-rabbit myosin antibodies shown to cross-react with human myosin and were visualized by a protein A-peroxidase method. Type I fibers were shown to contain slow myosin only, type IIA and IIB fibers fast myosin only, and type IIC fibers both myosins in various proportions. When muscle biopsies from well-trained athletes were investigated essentially the same staining pattern was observed. However, rarely occurring type I fibers with high glycolytic activity were detected containing additional small amounts of fast myosin and occasional type IIA fibers had small amounts of slow myosin. Based on the observation of various fiber types in which slow and fast myosin coexist we propose a dynamic continuum of fibers encompassing all fiber types.

Bacterial degradation of dichloromethane.

Abstract: Strain DM1, a facultative methylotrophic bacterium utilizing methanol, formate, mono-, di-, and trimethylamine, as well as dichloromethane as C1 substrates was isolated as an airborne contaminant. The organism is a strictly aerobic, gram-negative, oxidase-positive short rod, motile by a single lateral flagellum. Enzyme assays in crude extracts suggested that it assimilates C1 compounds by the serine/isocitrate lyase-negative pathway. Experiments with extended cultures demonstrated that dichloromethane is a growth-inhibitory substrate. The maximum specific growth rate of 0.11 h−1 was reached between 2 and 5 mM dichloromethane. The release of Cl−1 from dichloromethane paralleled growth in extended and continuous cultures. Molar growth yields on methanol and on dichloromethane were 18.6 and 15.7 g/mol, respectively. Since attempts to demonstrate dehalogenation of dichloromethane by crude extracts failed, a dehalogenation assay with resting cells was developed. Maximum dehalogenating activity of cell suspensions was at pH 9.0. The reaction was partially and reversibly inhibited by anaerobiosis. During a shift of a chemostat culture from methanol to dichloromethane as the carbon source, the dehalogenating activity of resting cells was increased at least 500-fold. Images

The influence of high pressure freezing on mammalian nerve tissue

Abstract: Vitrification of biological specimens in liquid nitrogen can be achieved under high pressure (2,100 bars). This procedure obviates the use of aldehyde fixation and cryoprotection (glycerol). The present work demonstrates its applicability to the freeze-etching of mammalian brain tissue. Freeze-fracture replicas from rat cerebellar cortex and subfornical organ prepared by this method are compared to conventionally processed material using aldehyde fixation, glycerination and freezing with Freon. The formation of large ice crystals is prevented in tissue blocks up to 0.5 mm thick; deep etching is markedly enhanced. Cytoplasmic microstructures such as mitochondrial cristae, microtubules and microfilaments, are readily observable against a finely granulated cytosol matrix. An additional advantage is the combined application with freeze-substitution.

Enderby land, Antarctica—an unusual Precambrian high‐grade metamorphic terrain

Abstract: The high‐grade metamorphic rocks of Enderby Land, which form part of the East Antarctic Precambrian Shield, have been subdivided into two major metamorphic complexes—the Archaean Napier Complex and the Proterozoic Rayner Complex. The Napier Complex consists predominantly of pyroxene‐quartz‐feldspar gneiss and garnet‐quartz‐feldspar gneiss, with subordinate mafic granulite, pyroxenite, and a variety of siliceous, aluminous, and ferruginous metasediments. The gneisses are intruded by several types of mafic dyke, including an abundant suite of dolerites, the Amundsen Dykes, and locally by granitic rocks and pegmatite. Much of the Rayner Complex probably represents re‐metamorphosed Napier Complex rocks, and mafic dykes occur only as metamorphosed relics. The Rayner Complex is correlated with the Proterozoic metamorphics of the MacRobertson Land coast and northern Prince Charles Mountains, for which Rb‐Sr dates of 800–1100 m.y. have been obtained. Temperatures of at least 950°C, at pressures of 8–10 k...

Dynamic CMOS amplifiers

Abstract: A family of dynamic CMOS amplifiers is presented and discussed. First, the concept of dynamic circuit is introduced. Then two groups of circuits with different biasing principles are shown, and experimental results are presented. The advantages of dynamic amplifiers are low power consumption, high voltage gain, large bandwidth, and low offset voltages.

New structure results for hydrides and deuterides of the hydrogen storage material Mg2Ni

Abstract: X-ray and neutron diffraction experiments performed on Mg2Ni(H,D)x (0 ⩽ x ⩽ 3.9) confirmed the existence of a structural phase transformation at about 235 °C. The high temperature phase (a = 6.49 A, space group Fm3m) has an antifluorite-type metal structure in which the deuterium atoms surround the nickel atoms octahedrally in a disordered manner (D−Ni =1.47 A, D−Mg = 2.30 A). Refined atomic parameters of Mg2Ni as well as absorption and desorption isotherms for the deutende and hydride phases are reported.

Influence of charge and discharge of electric double layer in pulse plating

Abstract: In pulse plating the useful values of the on and off times are limited by the rate of charging and discharging, respectively, of the electrical double layer at the electrode-solution interface. The charging and discharging times are calculated as a function of the relevant parameters (pulse current density, exchange current densityi0, capacitanceC of the double layer and others). Simple, approximate relationships are also presented for the case in which no experimental values fori0 andC are available. In order to quantify the damping of the Faradaic current the concept of ‘degree of flattening’ is introduced to describe the extent of the capacitive effects. The influence of a high degree of flattening on some deposit properties is illustrated by examples.

Micellar Solubilization of Biopolymers in Hydrocarbon Solvents III. Empirical Definition of an Acidity Scale in Reverse Micelles

Abstract: This paper deals with the problem of defining, and measuring, the pH inside the water pool (which we define as pHwp) of reverse micelles, i.e. micelles formed by surfactants dissolved in apolar solvents in the presence of minimal amounts of water. The conceptual and experimental difficulties are discussed, and it is argued that no absolute determination of pHwp is possible, mostly because water in the water pools of reverse micelles is a new solvent, for which no standardization of acidity is available. The problem can be approached only on the basis of an empirical acidity scale. An empirical acidity scale for water pools in reverse micelles of bis (2-ethyl-hexyl) sodium sulfosuccinate (AOT) in isooctane has been defined by measuring the 31P-chemical shifts of phosphate buffers. The chemical shifts in bulk water were compared to those found in reverse micelles under the assumption that the pK of phosphate ion is the same in the two systems. It was found that in most cases there was little difference (less than 0.4 pH units) between pHwp and the pH of the starting buffer in bulk water (which we define as pHst). However, this difference between pHwp and pHst may become much larger in certain cases. The difference (pHwp–pHst) is measured under a variety of conditions, and this permits the determination of an operational acidity in the micelle water pools as a function of the pHst with which the aqueous micelles are prepared. The significance of such data for interpreting the behaviour of enzymes confined in the micelles water pool is discussed. Based on the pHwp scale, the apparent pKa of phenol-red and 4-nitrophenol were determined in reverse micelles containing different buffers and different water content. The pKa values obtained were rather sensitive to changes of both these factors, which was taken to signify that organic dies have only a very limited applicability to measure the acidity of the water pools of reverse micelles.