Zur Mindestquerkraftbewehrung von Stahlbetonbalken

On minimum shear reinforcement amounts for reinforced concrete beams A ductile shear bearing behaviour of reinforced concrete beams is recently ensured by providing standardized amounts of minimum shear reinforcement in compliance with established detailing provisions. However, lower than minimum shear reinforcement amounts do not necessarily go along with a brittle mode of failure in all cases. Dependent on the individual layout and amount of stirrups, the contributions of other bearing capacities and the crack formation itself, the initial cracking force might be overtaken even along with further load gains and reasonable limited shear crack widths. Especially the latter one holds potential to rate the failure mode – brittle or ductile – on site. Experiments on lightly shear reinforced single span concrete beams are evaluated and rated with respect to minimum shear reinforcement amounts required. Thereby, special interest is set on the load‐deformation response obeying the critical shear crack and the structural design. Finally, the overall shear resistance as well as the stirrups' efficiency in the effective shear domain are analysed to derive suggestions for future practical application on‐site.     

Tungsten wire grid polarizer for applications in the DUV spectral range

In this paper, we present a broadband wire grid polarizer with a spectral working range down to a wavelength of 193 nm. Tungsten is chosen as grating material because it provides a high extinction ratio and transmission compared with other common grating materials. The fabrication of the grating with 100 nm period was accomplished using a spatial frequency doubling approach based on ultrafast electron beam lithography and a sophisticated deposition technique. At a wavelength of 193 nm, a transmission of about 44% and an extinction ratio of 20 was measured.     

Alcoholysis of waste fats with 2‐ethyl‐1‐hexanol using Candida antarctica lipase A in large‐scale tests

Commercial native lipase A from Candida antarctica was used to produce alkyl esters through the alcoholysis of (waste) fats with 2‐ethyl‐1‐hexanol. The process was carried out in batch stirred tank reactors (from 100 mL up to 3000 L). The content of alkyl esters in reaction mixtures was determined by gradient HPLC using an evaporative light scattering detector and the reaction progress was controlled by determining the ratio of the palmitic acid ester peak area to the oleic acid ester peak area in HPLC chromatograms. The results show that alcoholysis is the favoured reaction in presence of excess water and water‐insoluble alcohols in comparison with hydrolysis (fatty acid content <5%). The optimum amount of water for the alcoholysis was found to be 80–100% of the amount of fat. In the presence of low quantities of water both alcoholysis and hydrolysis are slow. Conversion rate increases with increasing temperature to 65–70 °C. Based on these results a large‐scale test to produce 3000 L of alkyl ester (to be used as lubricant coolant) was carried out. The experiments have proved that alcoholysis is completed after about 7–10 h depending on temperature.     

Micro-optical elements and their integration to glass and optoelectronic wafers

Polymer replication technique enables for low cost devices even in the case of aspheric or irregular shaped surfaces, submicron or other challenging structures. The use of UV-reaction moulding on semiconductors, glass or other inorganic substrates as the replication technique leads to a high degree of stability and allows for the simultaneous integration of optoelectronics or ion exchanged GRIN elements. Thin polymer layers on inorganic substrates show high flatness and lower wavefront deviations with respect to all-polymer elements. They show low lateral shrinkage during the UV-polymerisation, and the lateral thermal expansion is determined by the substrate. Furthermore, sensitive substrates can be used because the process does not involve high mechanical stress or elevated temperatures. Original structures for the replication masters are fabricated by different resist technologies. Subsequently, they are proportionally transferred by dry etching (RIE) into glass or silicon, or, the resist structure is transformed into a metal master by electroplating. The utilisation of UV-transparent replication tools allows for the use of opaque substrates (i.e. detectors). Locally UV-transparent replication tools enable a combination of replication and resist technology (leading to elements with new features) or can protect sensitive areas like bond pads from being coated with optical layers. The fabrication of isolated polymer elements on arbitrary substrates is an advantage of UV-reaction moulding against injection moulding or hot embossing. Received: 30 March 1999 / Accepted: 12 April 1999     

Crack initiation threshold as a parameter for characterizing fused alumina abrasive grains

The crack initiation threshold F_c, which is determined using the Vickers indentation technique, was used to estimate abrasion strengths of different fused alumina abrasive grains. Assuming Weibull distributed strength, the dependence of the crack initiation probability on the indentation load F according to F^−1/4 was verified. The crack initiation thresholds of Al₂O₃ crystals correlate with the strengths of the abrasive grains which were determined by static and dynamic methods.

The contents of chromium, iron, manganese and titanium in the alumina crystals were estimated by electron paramagnetic resonance and energy dispersive X-ray spectrometry measurements; the results indicate that the crack initiation thresholds are not essentially determined by these impurities.     

Electromagnetic coupling to and from shielded cables-optimizingfactors

Judging the shielding effectiveness of shielded cables often means in practice that only the transfer impedance is considered. The transfer impedance essentially characterizes the coupling via the magnetic field; the coupling via the electric field, the transfer admittance, is mostly neglected. This may be correct for shields with high optical coverage but for optimized single braided shields (coverage ≈0.8 . . . 0.9), the transfer admittance has to be taken into account. In practice, the cable shields are mostly grounded or open-ended at the line ends. With regard to the shield connections, the electromagnetic coupling to a cable by a plane wave and coupling from a cable are investigated. From the results, optimizing factors for the coupling parameters of shielded cables are deduced. By means of these optimizing factors the coupling to and from a cable can be minimized in certain applications