Showing papers by "Leibniz University of Hanover published in 1982"

A method for determining concentration profiles at the soil-root interface by thin slicing rhizospheric soil

Abstract: A method is described for the determination of concentration gradients in the vicinity of plant roots. Plants are grown in small containers in which the roots are separated from the soil by a screen of nylon cloth. Root hairs but not roots penetrate the screen into the soil. In order to investigate the rhizospheric soil, the soil is frozen by liquid nitrogen and sliced into layers about 0.06 mm thick by means of a refrigerated microtome.

Defects and Cation Diffusion in Magnetite (IV): Nonstoichiometry and Point Defect Structure of Magnetite (Fe3-δO4)

Abstract: Nonstoichiometry and point defect structure of magnetite have been studied experimentally by thermogravimetry covering the stability range of magnetite between 900 and 1400 °C. A cation deficit is observed at high and a cation excess at low oxygen activities corresponding to cation vacancies and iron interstitials as the predominant point defects, respectively. An overexponential temperature dependence occurs for the defect concentrations in stoichiometric magnetite.

Oxygen mass transfer into aerated CMC solutions in a bubble column.

Abstract: Differing findings on the volumetric mass transfer coefficients k(L)a in CMC solutions in bubble column bioreactors have been reported in the literature. Therefore, oxygen mass transfer was studied again in CMC solutions in a 14-cm-i.d. x 270-cm-height bubble column using different spargers. The k(L)a values were determined along with the dispersion coefficients by fitting the prediction of the axial dispersed plug model with the experimental oxygen concentration profiles in the liquid phase. Surprisingly, the obtained liquid phase dispersion coefficients for CMC solution are higher than one would expect from correlations. The k(L)a data depend largely on the flow regime. In general, they are lower than those reported in the literature. The data for developing slug and established slug flow are dependent on the gas velocity and the effective viscosity of the solution and can br correlated by a simple correlation. This correlation describes k(L)a values measured on fermentation broth of Penicillium chrysogenum with striking agreement.

Experimental study of partial liver resection with a combined CO2 and Nd:YAG laser

Abstract: The use of the CO2 laser in liver surgery is mainly limited by the lack of coagulation of the larger vessels. In an experimental study, partial liver resections were performed on pigs with a Nd:YAG as well as with a combined CO2 and Nd: YAG laser. The best cutting efficiency was obtained with the CO2 laser. On the other hand, the Nd:YAG laser and the combined laser sources showed excellent hemostasis at the cutting edge corresponding with a width of necrosis at about 5 mm in histomorphometric examination and zones with histologically different characteristics. Rebleedings from the resection lines were avoided in all cases using the combined CO2 and Nd:YAG laser.

The formation of the Schottky barrier at the V/Si interface

Abstract: Synchrotron radiation photoemission measurements have been used to study the behavior of the Schottky barrier height φ bn and electronic structure of the V/Si interface for both cleaved Si(111)- (2X1) and sputter-cleaned Si(111)—(7 X 7) surfaces. Although the Schottky barrier height φ bn of the clean surface is influenced by surface reconstruction (and by steps), the barrier becomes pinned at low (~ 2 A) V coverage at a position essentially independent of the initial clean surface structure. Formation of the bulk V metal band structure is not complete until ∼ 30–40 A V coverage, indicating coverage-dependent structural effects in the growth of the metal film. These effects also seem to produce secondary influences on φ bn ,which are manifested as a gradual increase of φ bn ,with higher coverage or mild (~200°C) annealing. However, upon higher temperature annealing (>350°C) the trend reverses, with φ bn decreasing to a value (∼0.64 eV) characteristic of the bulk VSi2contact which is formed at 500–550 °C; this change in the behavior of φ bn is directly correlated with the onset of atomic mixing across the interface.

Point Defects in Oxide Solid Solutions (IV). Correlated Diffusion of Cations and Vacancies in (Co, Mg)O-Mixed Crystals

Abstract: Magnesium tracer diffusion coefficients have been determined experimentally for the oxide solid solution (CoxMg1 - x)1 - δO as a function of temperature and composition x 2612Mg was used as the stable tracer isotope and analysed by mass spectrometry Combination of these data with previously obtained data on Co-tracer diffusion allowed to explain quantitatively the pronounced correlation effects during cation diffusion and to calculate the individual jump frequencies of the cations Finally, chemical diffusion coefficients of the vacancies are derived and compared with data from relaxation experiments

A New Method for Detection and Location of Distributed Partial Discharges (Cable Faults) in High Voltage Cables Under External Interference

Abstract: Todays partial discharge (PD) detection and location methods in high voltage cables are limited by the influence of external interferences as well as by the type and properties of the cable and by the nature of PD impulses. The problems of the existing methods could be overcome by the development of a new electronic PD detection and location method of high sensitivity and accuracy. It allows the recording and evaluation of partial discharges in HV cables even under the influence of external interference. The accuracy of location is 99.8% yielding a sensitivity down to 1 pC.

Synthesis of α,β-Unsaturated and Other Reactive Acyl Cyanides

Abstract: Synthesen von α,β-ungesattigten und anderen reaktiven Acylcyaniden Reaktive aliphatische Acylcyanide (1–10, siehe Tab. 1) werden aus Acylchloriden, Natriumiodid und Kupfer(I)-cyanid unter verschiedenen Bedingungen dargestellt. Die Reaktion verlauft uber die Acyliodide.

An Experimental Investigation of Rotating Stall Flow in a Centrifugal Compressor

Abstract: The flow through a centrifugal compressor impeller and a vaneless diffuser was investigated using unsteady pressure transducers and stationary probes when the compressor operated in the rotating stall region of the compressor map. The inlet velocity profile of the impeller was measured with traversing probes and was found to be significantly different from the profiles measured in an unthrottled condition. A zone of reverse flow was detected close to the suction duct wall as well as a strong swirl induced by the impeller. Circumferentially and meridionally spaced transducers made it possible to determine the stall frequency and the number of stall cells. The amplitude of the flow distortion as a function of meridional position was calculated from meridionally spaced transducers.Copyright © 1982 by ASME

Formation and rate of formation of ventifacts in Victoria land, Antarctica

Abstract: Land surfaces in southern Victoria Land, Antarctica, totally devoid of vegetation, are actively sculptured by winds that often reach velocities of more than 100 km/h. Deflation and abrasion are thus key factors in the process of slope formation. Water erosion, active only during the short summer period, is limited to a few localities. Experiments in a wind tunnel proved that ventifacts in the Dry Valleys can be formed within a few decades or, at most, a few centuries. Yearly abrasion rates average a few millimeters. Considerable variability is caused by the different exposures of the ventifacts within the microrelief and by varying rock resistance. The importance of ice crystals (snow) as an abrasive agent should not be overestimated. (The translation is by William Ban of the University of Saskatchewan, Saskatoon.)

Wave run-up at sea dikes under oblique wave approach

Abstract: Besides wave impact forces, erosion of the inner side of a sea dike is a serious cause of destruction. Therefore, wave run-up and overtopping effects have to be considered with respect to the safety of a dike. Strong relations were found between both these influences (TAUTENHAIN et.al., 1980, 1981, 1982), based on experiments in a wave flume and using an energy conservation concept. However, under natural conditions, an oblique wave approach has to be considered. This paper deals with the influence of wave direction on wave runup on a smooth dike slope in order to provide a basis for calculating the overtopping rates for both regular and irregular waves.

Notes on, and a Check-List of Acridoidea (Saltatoria) Collected in Somalia (East Africa)

Abstract: SUMMARYCollections from Somalia (East Africa) of 44 species of Acridoidea (Saltatoria) partly from coastal dunes (Mogadishu-Gesira) and partly from riverbanks and plantations (Afgoi-Balad) are annotated. Thirteen species were found on coastal dunes only, 19 species in plantations only. Comments on some material from British Museum have been included. Nineteen species are first records from Somalia, including Odontomelus somalicus n. sp. Johnsen, Acrotylus somaliensis n. sp. Schmidt and Heteracris rantae africanus n. ssp. Schmidt. A check-list of the Acridoidea of Somalia (= former French, British and Italian Somaliland) is given and a zoogeographical grouping of the species is proposed. From the area 92 genera with a total of 189 species are known of which 43 seem to be endemic.

Sociolinguistics and the Politics of Helping: Language Use in the Political Mobilization of Low-Income Groups

Abstract: Intelligible communication between different groups and classes in a society is a precondition for the existence of a 'public' in the classical, political sense of that term. The importance of such communication for a democratic policy was highlighted in the sixties when both reformers and revolutionaries generally failed in their efforts to educate or politicize tow-income groups. In this essay we discuss sociolinguistic theories as they bear on this question. First, we critically assess theories that bring the methods of linguistics to micro-sociological studies of speech behaviour Then we relate this work to the rich ethnographic literature on low-income culture, placing this amalgam of linguistics and ethnography in a larger political economic context We conclude by suggesting some moral and political implications of such a project.

Design and Investigations of a Three Dimensionally Twisted Diffuser for Centrifugal Compressors

Abstract: For a 90-deg centrifugal compressor impeller with an extremely distorted exit flow distribution a vaned diffuser has been designed. The maximum flow angle difference across the diffuser width at the entrance is 29 deg. In order to match the vane inlet angle to this flow angle distribution the diffuser vanes are three dimensionally twisted. The map of the compressor with the twisted diffuser is compared with those using a commonly designed cambered vane diffuser and a straight channel diffuser. On the basis of detailed flow field measurements directly before and behind the diffuser and of the static pressure distribution along the diffuser, the performance of the twisted diffuser is discussed.Copyright © 1982 by ASME

New Dihydropyrans: Lewis Acid Catalyzed Cycloadditions of α,β‐Unsaturated Acyl Cyanides to Simple Unactivated Olefins and Dienes. Practical Route to Derivatives of Rose Oxide

Abstract: The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1819. DOI:10.1002/anie.198218190

Investigations on orbital velocities and pressures in irregular waves

Abstract: This paper deals with the results of hydraulic model investigations of orbital velocities and pressures in irregular waves. Different simulation methods in the time and frequency domain were checked or developed, and the theoretical results compared with measurements. Using simulation methods based on linear wave theory, results with good correlation are obtained, at locations near the water surface, however, a tendency towards over- or underestimation exists.

Disc-electrophoretic pattern of proteins during the postembryonic development of Formica polyctena (Foerster) (Ins. Hym. Form.) after treatment with sodium dodecylsulfate

Abstract: 1. 1. During larval and pupal development of Formica polyctena the protein patterns were studied by sodium dodecylsulfate-containing polyacrylamid slab gel electrophoresis. 2. 2. Before electrophoresis was carried out the proteins were fractionated into water soluble, urea soluble and SDS soluble fractions. 3. 3. About 60 protein bands could be separated electrophoretically. The molecular weights for these bands were determined. 4. 4. Some of the proteins separated could be demonstrated only in the larvae, others only in the pupae, but the basic pattern remained very constant. 5. 5. Two-dimensional electrophoresis demonstrated that haemolymph proteins are complex compounds which split into definite lower molecular polypeptides after treatment with SDS.

Rainfall fluctuations and sunspot variability

Abstract: Mean monthly values of sunspot relative numbers and 290 precipitation records are investigated and compared by means of power-spectrum, numerical band-pass filter and cross-spectrum analysis. Spectral-analysis of variance and numerical bandpass filtering indicate significant cyclical variance components in the time scale of solar activity at some stations. Cross-spectral computations show however, that these series are uncorrelated with sunspots when viewed in a wide geographically distribution.

A new approach to dehydrocamphenilone and camphenilone

Abstract: Eine neue Darstellung von Dehydrocamphenilon und Camphenilon Benzilsaureumlagerung von Dehydrocarbocamphenilon (4) ergibt die α-Hydroxysaure 5, welche mit Bleitetraacetat oxidativ zu Dehydrocamphenilon (2) decarboxyliert wird. Die gleiche Reaktionsfolge fuhrt von Carbocamphenilon (9) zu Camphenilon (3).