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Abstract: Flushing in electrical discharge machining is essential to obtain high quality results and a good productivity. The flushing conditions in electrical discharge drilling are unique compared to sinking and cutting operations due to high flushing pressures. High flushing pressures lead to high dielectric flow rates in the narrow gap between the tool electrode and the work piece. It was found out, that to much flushing results in negative process behaviour and reduces the drilling speed. However, based on the electrical energy supplied to the gap there is an optimal dielectric flow rate to achieve a high drilling speed. Furthermore it was found out that there is a direct link between removal mechanism and the dielectric flow rate. Multi pulse experiments were carried out to investigate the influence of flushing on drilling speed, removal mechanism and process behaviour. [Copyright &y& Elsevier]

Abstract: Electric discharge machining of ceramics becomes principally feasible if the ceramic material has a sufficiently high electric conductivity. This can be achieved by adding transition metal carbides, borides or nitrides such as titanium carbide. In case of electric discharge drilling the small electrode dimensions lead to higher current densities compared to die sinking. In order to avoid bursting of the ceramics by thermal shock machining parameters have to be well adjusted and the material should have a high thermal conductivity. A parameter study was carried out to observe the removal behavior depending on machine parameters such as discharge energy, pulse form and flushing conditions. [Copyright &y& Elsevier]

The semiconductor zinc oxide (ZnO) is a promising material for applications in optoelectronics, photochemistry and chemical sensing. Furthermore, ZnO structures can be grown with a large variety of sizes and shapes. Devices with ZnO rods or wires as their core elements can be used in solar cells, gas sensors or biosensors. In this article, an easy approach for the non-aqueous wet chemical synthesis of ZnO structures is presented that employs the solvent trioctylamine (TOA) and the surfactant hexamethylenetetramine (HMTA). Using the thermal decomposition method, rod-shaped structures were grown that are suitable for the fabrication of electrical devices. A detailed study was carried out to investigate the effects of various reaction parameters on the growth process. Both the concentration of the surfactant HMTA and the zinc precursor zincacetylacetonate (Zn(acac)) were found to show strong effects on the resulting morphology. In addition to structural characterisation using XRD, SEM and TEM, also optical properties of rod-shaped ZnO structures were measured. Rod-shaped structures were obtained for the following conditions: reaction time 4 h, reaction temperature 70 °C, 1 mmol of Zn(acac), 4 mmol of HMTA and 25 mL of the solvent TOA. Photoluminescence and photoluminescence excitation spectroscopy of samples grown under these conditions provided information on levels of defect states that could be critical for chemical sensing applications. Two narrow peaks around 254 and 264 nm were found that are well above the band gap of ZnO. [ABSTRACT FROM AUTHOR]

The article reports on the HIV epidemics in central and eastern Europe due to male-to-male sex. According to the emerging data from low-income and middle-income countries, men who have sex with men (MSM) suffer from the burden of these epidemics. Factors that lead to the transmission of HIV include drug use injections, heterosexual and male-to-male sex.