Showing papers by "Leibniz University of Hanover published in 1980"

The Influence of the Blading Surface Roughness on the Aerodynamic Behavior and Characteristic of an Axial Compressor

Abstract: The conversion of energy in an axial compressor is influenced in great measure by the surface quality of the blading. To achieve low flow losses, the roughness values of the blade surface must be below certain limits. However, the blade surface, which is hydraulically smooth on commissioning of the machine, is in many cases attacked by dirt, corrosion and erosion during operation. For investigation of the influence of the surface quality on the efficiency, flow rate, pressure ratio, and the shifting of the characteristic curves, systematic measurements were taken on a three-stage axial compressor with smooth and uniformly rough blading. The roughness was produced by applying loose emery grain of different grades.

ESR Studies on the Reduction Process of Silver Zeolites

Abstract: It is shown by in situ ESR studies that H2 reduction of dehydrated AgA- and AgX-zeolites proceeds via intermediate formation of Agn+6 (n 200°C) crystal growth leads to larger crystallites (10–50 nm) as indicated by x-ray line broadening.

Cycloadditions of Allyl Cations, 21. Synthesis and 1H NMR Spectra of Bicyclo[3.2.1]octa‐2,6‐Dienes and 3‐Methylenebicyclo[3.2.1]oct‐6‐enes from Bicyclo[3.2.1]oct‐6‐en‐3‐ones Methylated at C‐2 and C‐4

Abstract: Bicyclo[3.2.1]oct-6-en-3-ones 5–8, methylated at C-2 and C-4, have been transformed into methylated bicyclo[3.2.1]octa-2,6-dienes 19–24 and 3-methylenebicyclo[3.2.1]oct-6-enes 16–18 by three routes: 1) Conversion into tertiary alcohols 9–11 with methylmagnesium halide and dehydration. 2) Reduction to epimeric secondary alcohols 12–15 with LiAlH4 and also i-Bu2AlH, followed by dehydration. 3) Methylenation with CH2Br2, Zn/TiCl4 in THF/CH2Cl2. — The reduction of 2,4-methylated bicyclo[3.2.1]oct-6-en-3-ones 5–8 with LiAlH4 and i-Bu2AlH gives axial and equatorial alcohols; the sterically more demanding i-Bu2AlH attacks preferentially from the exo side, yielding predominantly axial alcohols. Physical, spectroscopic, and chemical properties of the resulting bicyclo[3.2.1]oct-6-en-3-ols 12–15 have been correlated by conformational analysis. Axial alcohols form hydrogen bonds intramolecularly, giving inter al. lower melting points and shorter retention times than equatorial alcohols, a sharp OH band in the IR, and a downfield 1H NMR shift of the signals of the olefinic protons 6-H, 7-H (in CCl4 solvent). They also show marked coupling (3J = 10–12 Hz) of the OH proton in solvent CCl4. Exceptions to these trends are ascribed to flattening of the six-membered ring. The dehydration of the sterically hindered tertiary 3-methylbicyclo[3.2.1]oct-6-en-3-ols 9–11 with phosphoryl chloride in pyridine produces bicyclo[3.2.1]octa-2,6-dienes 19–21 in high yields, but requires forcing conditions (≈100°C) compared to secondary alcohols (0–25°C). Bicyclo[3.2.1]octa-2,6-dienes, unlike the isomeric 3-methylenebicyclo[3.2.1]oct-6-enes, form crystalline AgNO3 complexes. 2,3,4,4-Tetramethylbicyclo[3.2.1]octa-2,6-diene (21) reacts with atmospheric oxygen at ambient temperature and −20°C to give 2,4,5,5-tetramethyl-3-oxatricyclo[4.2.1.02,4]non-7-ene (26). Cycloadditionen von Allyl-Kationen, 21. Synthese und 1H-NMR-Spektren von Bicyclo[3.2.1]octa-2,6-dienen und 3-Methylenbicyclo[3.2.1]oct-6-enen aus 2,4-methylierten Bicyclo[3.2.1]oct-6-en-3-onen 2,4-Methylierte Bicyclo[3.2.1]oct-6-en-3-one 5–8 wurden auf drei Wegen in methylierte Bicyclo[3.2.1]octa-2,6-diene 19–24 und 3-Methylenbicyclo[3.2.1]oct-6-ene 16–18 umgewandelt: 1) Reaktion mit Methylmagnesiumhalogenid zum tertiaren Alkohol 9–11 und Dehydratation. 2) Reduktion zu den entsprechenden epimeren sekundaren Alkoholen 12–15 mit LiAlH4 und i-Bu2AlH und anschliesende Dehydratation. 3) Direkte Methylenierung mit CH2Br2, Zn/TiCl4 in THF/CH2Cl2. — Die Reduktion der 2,4-methylierten Bicyclo[3.2.1]oct-6-en-3-one 5–8 mit LiAlH4, und i-Bu2ALH liefert axiale und aquatoriale Alkohole; das sterisch anspruchsvollere i-Bu2AlH greift vorzugsweise von der exo-Seite an unter Bildung axialer Alkohole. Physikalische, spektroskopische und chemische Eigenschaften der resultierenden Bicyclo[3.2.l]oct-6-en-3-ole 12–15 werden uber die Konformationsanalyse korreliert. Axiale Alkohole gehen intramolekulare Wasserstoffbrucken ein und haben niedrigere Schmelzpunkte und kurzere Retentionszeiten als aquatoriale Alkohole, eine scharfe OH-Bande im IR und eine Tieffeldverschiebung der olefinischen Protonen 6-H, 7-H im 1H-NMR-Spektrum. Sie zeigen auserdem eine ausgepragte Kopplung (3J = 10–12 Hz) des OH-Protons im Losungsmittel CCl4. Ausnahmen gegenuber diesen Trends werden einer Abflachung des sechsgliedrigen Rings zugeschrieben. Die Dehydratation der sterisch gehinderten tertiaren 3-Methylbicyclo[3.2.l]oct-6-en-3-ole 9–11 mit Phosphoroxychlorid in Pyridin liefert Bicyclo[3.2.l]octa-2,6-diene 19–21 in hoher Ausbeute, aber benotigt forcierende Bedingungen (≈100°C) im Vergleich zu den sekundaren Alkoholen (0–25°C). Anders als 3-Methylenbicyclo[3.2.l]oct-6-ene bilden die gespannten isomeren Bicyclo[3.2.l]octa-2,6-diene kristalline AgNO3-Komplexe. 2,3,4,4-Tetramethylbicyclo[3.2.l]octa-2,6-dien (21) reagiert bei Raumtemperatur und −20°C mit atmospharischem Sauerstoff unter Bildung von 2,4,5,5-Tetramethyl-3-oxatricyclo[4.2.1.02,4]non-7-en (26).

Simulation of nitrogen mineralization and transport in loess-parabrown earths: plot experiments

Abstract: In order to simulate the Nmin distributions in field plot experiments, a first order kinetic model for mineralization is combined with a transport model described earlier in this journal. Comparison of simulated and experimental figures shows satisfying agreement. The main advantages of these models are: i. only few and easy to measure input data are required and ii. both model equations, for mineralization and transport of Nmin, are simple to solve rendering short computing times even using a microcomputer.

Generalized mean squared error comparisons of biased regression estimators

Abstract: Gunst and Mason (1976) compare several regression estimators with respect to the generalized mean squared error criterion. The purpose of this paper is to extend their results to homogeneous linear estimators. Specific consideration is dedicated to the iteration estimator which is a new biased alternative to least squares.

Long-term experience with the use of synthetic filter fabrics in coastal engineering

Abstract: Various types of synthetic filter fabrics are available for geotechnical applications. Especially in the field of coastal engineering a lot of experiences are generally known. Unfortunately technical recommendations and testing regulations for specific implimentations of geotextiles are not generally available and some actual examples of damage of coastal structures urgently require investigations on long-term resistance. A research program oriented towards the development of guidelines for testing geotextiles, the development of filtration rules and the clarification of long-term resistance of fabrics was carried out. This paper deals with testing procedures associatied with the estimation of the opening size and the permeability to water of fabrics. Results of investigations on long-term resistance are described and filtration rules for selecting a fabric according to the special requirements of the application are given.

The Behavior of a Closed-Cycle Gas Turbine with Time Dependent Operating Conditions

Abstract: The closed-cycle gas turbine can be applied in thermal power stations using fossil, nuclear or solar energy. Here the behavior of the closed-cycle gas turbine plant under time dependent operating conditions is particularly important. A theoretical model was developed which unlike previously applied methods also considers the transient processes in the heat exchanging units, the heat transfer between the working medium and the internally insulated hot-gas pipes, and the condition of the blading. For examination of the model, measurements were taken on a closed-cycle air turbine. The results of the calculation made for comparison with the test results show the reliability of the calculation model. There is conformity of the measured speeds of the turbo group and of the pressures, temperatures and mass flows of the cycle with the theoretical values until a new steady-state condition is reached.

Laser coagulation in the upper GI tract: a preliminary light and scanning electron microscopic study.

Abstract: Experimentally intact as well as artificially damaged mucosa of porcine stomach was endoscopically coagulated with Nd:YAG laser beams. Energy, intensity pattern, and time of application of the irradiation was varied and supracellular changes of the coagulated mucosa were subsequently investigated with the scanning electron microscope. The mucosa, damaged by laser beams, showed three typical zones: 1. a superficial, central carbonisation zone protected with a thin layer of coagulated mucus; 2. an elevated hyperemic ring with complete loss of superficial epithelium, but intact basement membrane and a blood clotting of the mucosal capillaries; 3. normal mucosa. After coagulating artificially induced bleeding of the mucosa the irradiated centre showed a deep depression with a carbonized surface. Two weeks later regeneration had occurred and there was complete reepithelialisation of the mucosa to about two-thirds of normal thickness.

The Influence on the Meridional Impeller Shape on the Energy-Transfer in Centrifugal Compressors

Abstract: Three radial flow impellers were tested having an elliptic blade shape and identical blade geometry at inlet and exit but different shapes of the meridional contours. The compressor maps with pressure ratios up to 2.9:1 are compared using time-dependent measurements of the static pressure at the shroud and of the flow angles closely downstream of the impeller. From these measurements, the influence of impeller shap on the jet-and-wake flow is discussed. It is shown that with increasing impeller length, the wake zone at the suction side of the blades can be only partially influenced and friction losses become dominant with respect to compressor performance. A smooth curvature of the meridional cross section of the impeller channel leads to a better jet-wake ratio at impeller exit. Accordingly, the performance characteristic shows higher values especially when the mass flow is increased.Copyright © 1980 by ASME

Safe Yield in a Coastal Ground‐Water Regime

Abstract: The limiting factors for the, safe yield in the investigated coastal area were sea water along the coastline and saline water at about 250 m below sea level. Both types of salt water will intrude into existing wells, when the potential heads are changed sufficiently by increasing pumping. Besides this, the recharge rate due to precipitation affects the potential head. In a hilly central part of the region, water infiltrates into the ground, and seeps to the saturated zone where it flows some kilometers to flat marshy regions near the coast and estuaries. There it comes up to drainage systems near the land surface (long cycle). In the marshy region the infiltrated water exfiltrates into drains and ditches after a short passage of some meters in the upper zone of the aquifer (short cycle). The calibration of a digital ground-water model gave the existing ground-water budget. The prognostication of the safe yield was based on these results. The most interesting problem of model calculations was to take into consideration the dependence of the recharge rate on the depth of the ground-water table below the land surface. If the ground-water level is lowered by pumping below the drainage system, the short cycle will be interrupted. The downward seeping water flows within a saturated zone to the wells and affects the potential head. The greater the drawdown, the greater is the recharge rate. The depression of the water table by pumping is compensated up to a certain degree.

Calculation of Four-Quadrant Characteristics of Turbines

Abstract: For handling of extreme operation conditions of turbines or in cases of disturbance or breakdown of turbine plants, it is important to have knowledge about the characteristics far away from the design point. This paper explains the attempt of a calculation method for computing the complete four-quadrant characteristics of a turbine on the basis of the mean section cascade characteristics of the blading. The cascade characteristics for normal and backward flow are pointed out and with these are calculated the stage characteristic lines for perfect gas. The turbine characteristics are computed by superimposition of the stage characteristics and compared to measuring results.Copyright © 1980 by ASME

State-estimation in a pursuit-evasion-game with incomplete information-exchange

Abstract: Treated is a class of pursuit-evasion-games with incomplete information-exchange. After describing the game optimal strategies for several information-patterns are given based on a geometrical approach. Then attention is focussed on a game in which some of the opponent's statevariables and his strategy are unknown. The player-system is approximated by another system to which observer-theory can be applied. Observability is discussed and several conditions for complete observability of the approximated system are given.

Experimental evaluation of heat exchange between water surface and atmosphere

Abstract: The heat balance of a water body mainly depends upon the heat exchange processes at the water surface. An experimental method has been developed for determining the heat exchange, the exchange coefficient and the equilibrium temperature. The measuring equipment consists of two similar, well insulated pools which are exposed to the meteorological conditions of the Lower Weser River, Germany. The water temperature of the first pool (Ti) is artificially adjusted to the actual river temperature either by cooling or heating. The temperature of the second pool (T2) is held constant above the temperature T-| . The difference in power inputs required W2 - W-j is equivalent to the net rate of heat exchange due to the increase of temperature to AT above the river temperature.

European integration as a financial adjustment problem

Abstract: The European summit in Dublin has shown that any further European integration will be determined in great measure by agreement on the financing of future Community budgets and by the EC’s expenditure policy. This article shows how the political controversy about the Community’s budget expenditure and receipts can be raised to a more rational level by the adoption of an economic approach.

Changes in the pattern of fatty acids of the lipids extracted from Formica polyctena Foerster during the cocoon period (Ins. Hym. Form.).

Abstract: 1. 1. The fatty acids present in the lipids extracted by diethylether from six developmental stages of the cocoon period of females (queens), workers and males of Formica polyctena Foerster were investigated by use of gas-liquid chromatography. 2. 2. In all three forms the presence of even-numbered both saturated and unsaturated, and odd-numbered acids of chain lengths between C 7 and C 20 was found. 3. 3. The proportion of short-chained fatty acids present in the fatty acid fraction was significantly higher in the white pupae during organogenesis. 4. 4. The main fatty acids found were 18:1, 16:0, 18:0, 18:2, and 16:1 (in decreasing order when expressed as per cent of the total fatty acids). In male pharate adults there was a very high amount of 17:0 acid. 5. 5. The results obtained were discussed in relation to the different development processes, the low oxygen consumption during the pupal period and the different objectives of the two adult female castes.