Vergleich von hydraulischen und chemischen Sedimenteigenschaften aus Spül- und Kernbohrungen im Raum Peine (Norddeutschland)

Comparison of hydraulic and chemical properties of sediments from flush- and core drillings in the area of Peine (Germany). Because of financial constraints, investigations of nitrate metabolism are often based on disturbed borehole samples. It is arguable, however, whether disturbed samples are suitable for these types of investigations. Disadvantages of disturbed samples in comparison to undisturbed core samples are well known and include possible contamination of the sample by mud additives, destruction of the sediment formation and the insecurity concerning the correct depth allocation. In this study, boreholes were drilled at three locations to a maximum depth of 50?m. The extracted samples, as intact sediment cores and drill cuttings, were studied with regard to chemical and hydraulic parameters of the aquifer sediments. The results show: 1. hydraulic parameters are not affected by clay-based mud; 2. disturbed samples contain less fine grain material relative to the core samples, and the hydraulic conductivity can only be estimated from catch samples; 3. catch samples contain fewer reducing agents (sulphides, organic carbon) than core samples in hydraulically passive zones (defined as K < 10^–6?m?·?s^–1); 4. the results of analyses of disturbed and undisturbed core samples are in good agreement for hydraulically active zones (K ≥ 10^–6?m?·?s^–1).     

Advanced research in millimeter-wave vacuum electronics

Selected basic research efforts currently sponsored by the U.S. Department of Defense (DOD) and the National Science Foundation (NSF) are reviewed. Major achievements are highlighted and remaining obstacles are discussed. Future advances are suggested. Opinions expressed are solely those of the author.     

70 Jahre Verfahrenstechnik an der TU Dresden

At the Technische Hochschule Dresden, the predecessor institution of the TU Dresden, a specialization “Engineer for Process Engineering” was established in 1953 with the filling of the specialist professorship for chemical engineering, and the present Institute for Process and Environmental Engineering was founded. Since then, the profile in education and research of the institute within the Faculty of Mechanical Science and Engineering of the Technische Universität Dresden (TUD) has been considerably extended. Based on this development, the current main research areas of the five chairs and research groups are presented.     

Measurement of useful properties of memory devices

It is customary to measure properties of a memory device in terms of a specific mode of memory operation. Estimating device properties relevant to a different operating mode is usually difficult, if not impossible. At the present time, memory configurations are growing in number and in basic function, ranging widely in size, speed, power, and read/write patterns. It is often necessary to select an available device for a new memory scheme. It is occasionally of interest to select a memory scheme to make best use of a device. A set of simply measured characteristic curves is proposed, which would make it possible to evaluate a given memory device in a large number of operating modes. The quantities involved are the flux, switched by pulses limited in time, amplitude, and number; reversible and irreversible flux switching; and dc properties. Examples of the use of the curves are given.     

Synchronous sampling theorem for nonlinear systems

It is shown that the sampled output of a nonlinear system with sampled-data input is given by the discrete equivalent of a Volterra series in which the kernels are the sampled Volterra kernels of the system. This theorem is then extended to the common case in which the sampled-data input is applied to the nonlinear system through a zero-order hold.     

Theory of non-linear transport in quantum waveguides

The equations for quantum ballistic transport in inhomogeneous quantum wire structures are transformed into a set of one-dimensional coupled mode equations where the coupling parameters are explicitly dependent on the shape parameters for the confinement potential. In the adiabatic approximation or in the extreme quantum limit the resulting motion is governed by an effective Hamiltonian which contains the influence of quasi-electric fields and quasi-momentum dependent forces which arise from the inhomogeneous shape parameter variation along the quantum waveguide. The subsequent transport may be described by a Boltzmann-like kinetic equation and hot-electron effects arising from variations in the waveguide profile are predicted. It is shown that transport through a wide region of an otherwise narrow wire leads to multiply-connected electron paths which will produce Aharonov-Bohm resonances. The analytical formalism is underpinned by a new numerical method suitable for 3-D studies based on representing the inhomogeneous waveguide by an equivalent network of one-dimensional wires.     

Dewatering of Brewery Sludge Produced from a Dedicated Aerobic Effluent Treatment Plant

This paper details the characterisation of sludge produced from a trickling filter effluent treatment plant dedicated to the treatment of brewery effluent and reports on centrifuge trials for thickening and dewatering it. Characterisation of the sludge revealed that the total solids content was low and variable, at 2 — 2.5% w/w dried solids (DS), and that the sludge exhibited very poor settling characteristics. A study of the rheological properties of the sludge indicated that at around 2.5% w/w DS the sludge could best be modelled by the Hershel-Bulkley equation. The variation in rheological properties with solids concentration was measured on samples thickened in the laboratory. Large scale dewatering of polyelectrolyte conditioned sludge was carried out using an Alfa Laval decanter centrifuge in order to obtain cake suitable for further processing or disposal. Operational and dosing conditions were varied and a cake with up to 25% w/w DS was produced using cationic polyelectrolytes Zetag-87 & CT85.     

Unusual case of tracheal agenesis

We describe the clinical presentation and pathological features of an unusual case of tracheal agenesis. The axial derivatives of the primitive foregut between the larynx and stomach were represented by a single structure featuring sequential segmentation into regions showing exclusively tracheal or esophageal differentiation in a pattern that is not easily classified by existing nosologic systems nor explained by the conventional hypothesis of dysontogenesis.