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A new type of planar fuel cell based on printed circuit board (PCB) technology has been developed. This planar design consists of an open cathode side which allows a completely passive, self-breathing operation of the fuel cell. P...
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A new type of planar fuel cell based on printed circuit board (PCB) technology has been developed. This planar design consists of an open cathode side which allows a completely passive, self-breathing operation of the fuel cell. Power densities of 100 mW/cm~2 at 500 mV with hydrogen were achieved. Long-term operation for more than 1500 h has been demonstrated. The operation behavior of planar hydrogen in free-breathing PEMFC concerning stability, water management and temperature distribution are examined. The effects of diffusion layer thickness and cathode opening ratios on the performance of this fuel cell type were characterized. Moreover, the amount of water removed from the anode and the temperature distribution of the cathode side were determined.
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Recently, the claim was made that cracks in silicate glasses propagate by the nucleation, growth, and coalescence of cavities at crack tips, which is the same way as in metals but at a much smaller scale. This hypothesis for crack...
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Recently, the claim was made that cracks in silicate glasses propagate by the nucleation, growth, and coalescence of cavities at crack tips, which is the same way as in metals but at a much smaller scale. This hypothesis for crack growth is based in part on the measurement of surface displacements near the tip of an emerging crack, which is the point at which a crack front intersects the side surface of the specimen. Surface displacements measured by atomic force microscopy were less than theoretically predicted. The difference between the theoretical and experimental displacements was attributed to a plastic zone surrounding the tip of the moving crack. In this paper, we show that the theoretical analysis used earlier was based on an incorrect assumption about the functional dependence of the displacement with distance from the crack tip. We use a full three-dimensional finite element analysis combined with an asymptotic solution of the crack geometry to obtain a solution to the surface displacement problem. We show that the calculated displacements are fully consistent with those experimentally measured by using an atomic force microscope. No divergence from elastic behavior is observed. Our results support the view that crack propagation in glass is entirely brittle. No evidence for plasticity at the crack tips is obtained.
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A constant temperature hot-wire anemometer enabling automatic rapid scanning of the wire overheat was built to perform free stream disturbance measurement sin the shock wind tunnel of the Institute for Aerodynamics and Gasdynamics...
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A constant temperature hot-wire anemometer enabling automatic rapid scanning of the wire overheat was built to perform free stream disturbance measurement sin the shock wind tunnel of the Institute for Aerodynamics and Gasdynamics at Stuttgart University. It is shown that such a system brings real advantages in terms of testing time.
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We compared the properties of ZnO thin-film transistors in the inverted coplanar geometry on thermally grown silicon oxide gate dielectric to devices on silicon nitride, grown by plasma-enhanced chemical vapor deposition at 150℃ ...
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We compared the properties of ZnO thin-film transistors in the inverted coplanar geometry on thermally grown silicon oxide gate dielectric to devices on silicon nitride, grown by plasma-enhanced chemical vapor deposition at 150℃ or magnetron sputtering at room temperature. The ZnO semiconductor was sputtered without substrate heating at oxygen partial pressures in the range of 10~(-5)-10~(-4) Torr. At the lowest oxygen partial pressture, transistor characteristics were similar for all dielectrics. The field-effect mobility approached ～5 cm~2/V s and devices generally operated in depletion mode. With increasing oxygen partial pressure, the mobility decreased by 1000×on SiO_2,whereas the decrease on silicon nitride was considerably smaller. On SiO_2 the threshold voltage was＞30 V but＜5 V on silicon nitride. Devices on SiO_2 operated in enhancement mode, whereas they operated in depletion mode on PECVD silicon nitride. Photoluminescence of ZnO revealed that deep-level emission depended on the specific dielectric on which ZnO was grown. Green emission for ZnO on chemically vapor-deposited silicon nitride was consistent with the presence of oxygen vacancies in ZnO. Yellow emission for ZnO on silicon oxide was associated with electron acceptor defects, such as oxygen adsorbed in grain boundaries or interstitially in ZnO. We concluded that differences in transistor properties were attributable to modification of ZnO defect chemistry, mediated by growth on a specific dielectric.
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Biaxial tensile deformation tests were carried out on cruciform specimens using a CNC stretch-drawing facility designed and built at the Institute for Metal Forming Technology, Stuttgart University. The beginning of plastic yield ...
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Biaxial tensile deformation tests were carried out on cruciform specimens using a CNC stretch-drawing facility designed and built at the Institute for Metal Forming Technology, Stuttgart University. The beginning of plastic yield was monitored by temperature measurements according to the method of Sallat. The observed plastic anisotropy was modeled using the phenomenological yield criteria (Hill '48, Hill '90, Barlat'91 and BBC2000). In Banabic et al anisotropy is introduced by a means of a linear transformation of the Cauchy stress tensor applied to the material. Comparison with experimental data show that the BBC2000 criterion can successfully describe anisotropy of both the plastic strain ratio and yield of aluminum alloys.
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Ein Konzept zum Brandschutz enthält neben einer Baubeschreibung alle Maßnahmen zur Verwirklichung der gesetzlichen Forderungen. Fast alle Teile des Konzeptes, wie beispielsweise Rettungswege, Brandmeldetechnik, Blitz- und Überspan...
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Ein Konzept zum Brandschutz enthält neben einer Baubeschreibung alle Maßnahmen zur Verwirklichung der gesetzlichen Forderungen. Fast alle Teile des Konzeptes, wie beispielsweise Rettungswege, Brandmeldetechnik, Blitz- und Überspannungsschutz, betreffen auch das Elektrohandwerk. Der Beitrag stellt die einzelnen Bestandteile des Brandschutzkonzeptes vor.
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Umfangreiche Schutzmaßnahmen sichern Arbeitsmaterialien, Produktionsgüter oder geschäftliche Unterlagen. Einen Einblick in die „Sicherheitstechnik" gibt die hier beginnende Artikelserie. Der erste Teil stellt das Sicherheitskonz...
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Umfangreiche Schutzmaßnahmen sichern Arbeitsmaterialien, Produktionsgüter oder geschäftliche Unterlagen. Einen Einblick in die „Sicherheitstechnik" gibt die hier beginnende Artikelserie. Der erste Teil stellt das Sicherheitskonzept mit seinen Komponenten vor.
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Der ganzheitliche Schutz eines Gebäudes oder Betriebs beruht auf einem Sicherheitskonzept. Die Bestandteile wurden in der letzten Ausgabe aufgezeigt. Dieser Beitrag be-fasst sich mit der Sicherung von Grundstücksgrenzen. Zäune un...
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Der ganzheitliche Schutz eines Gebäudes oder Betriebs beruht auf einem Sicherheitskonzept. Die Bestandteile wurden in der letzten Ausgabe aufgezeigt. Dieser Beitrag be-fasst sich mit der Sicherung von Grundstücksgrenzen. Zäune und Alarmsysteme, äußere Videoüberwachung, Tore und Türen gehören dazu.
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Bei Neubauten oder Modernisierungsmaßnahmen ist ein Brandschutzkonzept zu erstellen. Dieses wird zusammen mit dem Bauantrag bei den genehmigenden Baubehörden eingereicht. Es enthält eine Baubeschreibung und alle Maßnahmen zur Verw...
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Bei Neubauten oder Modernisierungsmaßnahmen ist ein Brandschutzkonzept zu erstellen. Dieses wird zusammen mit dem Bauantrag bei den genehmigenden Baubehörden eingereicht. Es enthält eine Baubeschreibung und alle Maßnahmen zur Verwirklichung von gesetzlichen Forderungen. Fast alle Teile des Konzeptes, wie beispielsweise Rettungswege, Brandmeldetechnik, Blitz- und Überspannungsschutz, betreffen auch das Elektrohandwerk.
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