Interaction of a granular stream with an obstacle

We investigate numerically the interaction of a stream of granular particles with a resting obstacle in two dimensions. For the case of high stream velocity we find that the force acting on the obstacle is proportional to the square of the stream velocity, the density and the obstacle size. This behaviour is equivalent to that of non-interacting hard spheres. For low stream velocity a gap between the obstacle and the incoming stream particles appears which is filled with granular gas of high temperature and low density. As soon as the gap appears the force does not depend on the square of velocity of the stream but the dependency obeys another law.     

Texturvererbung und Transformation aus der austenitischen in die martensitische Phase bei streckbelasteten 18/8 CrNi-Rundstählen

Fasertexturen – Blechtexturen. Transformationsmechanismen fcc – hcp – bcc. Selektion der Gleit- und Scherrichtungen durch Textur und Zugspannung. Texturmessung mit Neutronenbeugung. Rekonstruktion der gemessenen bcc-Texturverteilung als Vererbung aus der fcc-Phase bei gleichzeitiger Verkippung der neugebildeten bcc-Kristallite durch weitere Verformung. Gemisch aus Nishiyama-Wasserman- und Kurdjumov-Sachs-Transformation mit jeweils zwei erlaubten Gleit- und Scherrichtungen.     

Photoinduced switching of the current through a single molecule: effects of surface plasmon excitations of the leads

The photoinduced switch of the current through a single molecule is studied theoretically by including plasmon excitations of the leads. A molecule weakly linked to two spherical nanoelectrodes is considered resulting in sequential charge transmission scheme. Taking the molecular charging energy (relative to the equilibrium lead chemical potential) to be comparable to the molecular excitation energy, an efficient current switch in a low voltage range becomes possible. A remarkable enhancement of the current is achieved due to simultaneous plasmon excitations in the electrodes. The behavior is explained by an increased molecular absorbance due to oscillator strength transfer from the electrode plasmon excitations and by a net excitation energy motion from the electrodes to the molecule.     

The mechanism of phosphorylation of natural nucleosides and anti-HIV analogues by nucleoside diphosphate kinase is independent of their sugar substituents

The reaction mechanism of the phosphoryl transfer catalyzed by dinucleoside diphosphate kinase from Dictyostelium discoideum is investigated by semiempirical AM1 molecular orbital computation of an active site model system on the basis of various X-ray crystallographic structures. The computational results suggest that the phosphoryl transfer from adenosine triphosphate to the His122 residue is accompanied by the simultaneous shift of a proton from the histidine residue to one of the oxygen atoms of the gamma phosphate group. This involves a doubly protonated His122 residue whilst this residue is neutral in its ternary complex with ADP and the transition state analogue AlF(3). The proposed mechanism is thus analogous to that of phosphoryl transfer by cyclic adenosine monophosphate dependent protein kinase and uridine/cytidine monophosphate kinase as found in our earlier work and clarifies the role of the ribose 3'-OH group. Furthermore, the energetics of phosphoryl transfer onto other nucleoside analogues such as 3'-azido-3'-deoxythymidine-diphosphate and 2',3'-dideoxy-2',3'-didehydro-thymidine-diphosphate are investigated. The calculated reaction barriers for the phosphorylation of the diphosphates by the enzyme are all within a range of 13.1 kJ mol(-1), which suggests that variations in the activation energies alone cannot account for the experimentally observed differences in enzymatic activity. Consequences for the design of new anti-HIV nucleoside analogues are discussed. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2268/2002/f360_s.pdf or from the author.     

Die Ingenieurbauwerke für die Verkehrserschließung der Neuen Landesmesse in Stuttgart

The engineering structures for the traffic development of the Neuen Landesmesse in Stuttgart, Germany. The highly visual parking garage has been accepted as a new landmark by the public and offers 4100 parking lots on 125000 m². The fundamental principle of the steel‐composite‐design consists essentially in a jointless and bearingless structure. The steel truss beams with main spans of ca. 100 m length are quasi rigid connected with the main columns and are therefore integrated in spatial main system similar to the chassis‐principle in the automotive industry. This main idea of a semi‐integral construction system has been also design decisive for the steel‐composite bridges of the new trade fair area. Repetitive design elements suggest a uniform overall impression of the traffic structures of the new trade fair area.     

Soil carbon,soil nitrate,and soil emissions of nitrous oxide during cultivation of energy crops

Carbon (C) sequestration and soil emissions of nitrous oxide (N₂O) affect the carbon dioxide (CO₂) advantage of energy crops. A long-term study has been performed to evaluate the environmental effects of energy crop cultivation on the loamy sand soil of the drier northeast region of Germany. The experimental field, established in 1994, consisted of columns (0.25 ha each) cultivated with short rotation coppice (SRC: Salix and Populus) and columns cultivated with annual crops. The columns were subdivided into four blocks, with each receiving different fertilization treatments. The soil C content was measured annually from 1994 until 1997, and then in 2006. Soil N₂O levels were measured several times per week from 1999 to 2007. Water-filled pore space (WFPS) and soil nitrate measurements have been performed weekly since 2003. Increased C stocks were found in SRC columns, and C loss was observed in blocks with annual crops. The soil from fertilized blocks had higher levels of C than the soil from non-fertilized blocks. SRC cropping systems on dry, loamy sand soils are advantageous relative to annual cropping systems because of higher C sequestration, lower fertilized-induced N₂O emissions, and reduced background N₂O emissions in these soils. SRC cropping systems on dry, loamy sand soils have a CO₂ advantage (approximately 4 Mg CO₂ ha⁻¹ year⁻¹) relative to annual cropping systems.