Coherent low-energy electron diffraction on individual nanometer sized objects

Today's structural biology techniques require averaging over millions of molecules to obtain detailed structural information. Derivation of the molecular structure from a scattering experiment with just one single 3D-molecule imposes major challenges. Coherent and damage-free radiation is needed to ensure sufficient elastic scattering events before destroying the molecule and a means to solve the phase problem is wanted. We have devised such a scheme using coherent low-energy electrons shaped into a collimated beam by an electrostatic microlens. Initial experiments using a carbon nanotube sample demonstrate the feasibility of coherent low-energy electron diffraction on an individual nanometer-sized object.     

Machining of micro-systems

An increasing trend towards miniaturization of mechanical components necessitates the further development of micro-machining techniques in order to produce components within given tolerances. For the dressing of multilayered, metallically bonded, fine-grained grinding wheels that are used for micro-grinding the technique of electro contact discharge dressing was developed. In the following, the determined interrelations between the variables dressing voltage, limitation of dressing current, infeed and feed of electrode, and the volume flow rate in conditioning as well as the quality factor in conditioning are presented and illustrated. Thanks to the development of new geometries of CVD-diamond micro-grinding-pencils, a reduction of edge disruptions as well as a reduction of tool diameters to a minimum of 250 μm for the machining of brittle materials could be achieved. For the micro-drilling of ductile materials the maximal drilling depth could be increased by means of an adjusted process control. The smallest examined drill diameter was 50 μm. The utilizability of the developed processes and tools was proven in the production of aerostatic micro-bearings in the scope of the collaborative research center (SFB) 516.     

Punching in industrial wood machining: an alternative production process to drilling

Drilling of wood is besides milling, sawing and grinding one of the most important production processes in industrial furniture manufacturing. For the body assembly and the fixing of fittings, boreholes are essential. They have immediate effect on quality and production costs. The process step drilling limits the output of stationary and throughfeed machines, because the workpieces have to be stopped to create the drillings at a relatively low feed speed. An essentially increased performance cannot be reached by the improvement of conventional drilling devices. The aim of the work presented in this paper is the development of an alternative production process in which blind holes can be punched. Thereby thin-walled, cylinder-shaped tools are pressed into different solid and derived timber workpieces by a simple translative movement. For it special experimental setups have been designed. The new production process opens possibilities for an optimization and acceleration of process cycles in industrial wood machining.     

Crosslinkable,nonlinear optical copolymers: Processing,corona poling,and second harmonic generation studies

Polymethacrylate copolymers, containing nonlinear optically active 4′-dialkylamino-4-nitroazobenzene side groups and crosslinkable 2-butenyl side groups were synthesized and characterized. Films of these copolymers can be thermally crosslinked at elevated temperatures and photochemically crosslinked by exposure with UV light. Both methods allow the control of the crosslinking density. A precrosslinking step, prior to the corona-poling step, can be applied to optimize alignment and relaxation of the chromophores. During corona-poling, the temperature dependence of the second harmonic generation (SHG) of an Nd-YAG laser (1.064 μm) was studied for films with different degrees of precrosslinking. Depending on the conditions of precrosslinking, the SHG signal intensity and the alignment stability can be maximized. © 1993 John Wiley & Sons, Inc.     

On Surface Modification of Polymeric Biomaterials

Surface modification with hydrophilic polymers has been beneficial in improving blood compatibility of biomaterials. Formation of dense and tightly-bonded surface layers may prevent plasma protein adsorption owing to steric repulsion. General conditions for formation of layers, protecting blood components from direct contacts with the surface, are discussed. It seems to be necessary to ensure a delicate balance between adsorption energy of the attached chains and their length. The crucial point is to get a high grafting density which is more influential than high chain length. Length should be calibrated to the size of protein molecules to meet both effective repulsion and high density of the protecting chains and to avoid chain displacement by plasma proteins.     

Fragen der Lärmminderung in der chemischen Industrie (Geräuschsituation innerhalb und außerhalb der Werke)

Questions of noise reduction in the chemical industry (noise levels inside and outside industrial sites) . In the chemical industry there are hardly any noise problems as far as working conditions are concerned. However, certain difficulties are to be expected in the neighbourhood of chemical plant. Open-air plants require special nosie reduction measures at many individual noise sources. Safety aspects must have priority. The increased demands necessitate inclusion of piping and equipment in acoustic planning. There should be adequate transition zones separating industrial and residential areas, but owing to lack of town planning desirable screening distances hardly exist. New plants can now be built with noise levels some 7 to 10 dB (A), in certain cases even more than 10 dB (A), lower than ten years ago.