The Effect of Temperature Gradient and Primary Arm Tip Velocity on Secondary Dendrite Arm Spacing at Steady-state Conditions Solidification

A numerical procedure is presented by which the coarsening of secondary dendrite arms, during steady state solidification can be simulated. The numerical results are compared with experimental data obtained for binary Al-Cu alloys. Very good agreement of the measurements with the theoretical predictions is obtained for the spacing of secondary dendrite arms during solidification. Based on these results, a generally applicable function could be established for finally secondary dendrite arm spacing as a function of alloy composition, temperature gradient and primary arm tip velocity.     

Gestufte Kontrolle bei Videoüberwachungsanlagen

Moderne Videoüberwachungssysteme k?nnen über die übertragung und Aufnahme von Videobildern hinaus diese auch auswerten. Sie k?nnen dadurch zum einen die Gefahrenabwehr verbessern, sie greifen dadurch zum anderen aber auch tiefer in die Grundrechte der Betroffenen ein. Um hier zu einem neuen, angemessenen Ausgleich zwischen Sicherheit und Freiheit zu gelangen, wird für Gestaltung und Einsatz der modernen Videoüberwachungssysteme (1.) ein Drei-Stufen-Modell vorgestellt (2.). Dieses wird sodann verfassungs- und datenschutzrechtlich hergeleitet (3.) und in seiner Ausgestaltung rechtlich begründet (4.). Schlie?lich wird er?rtert, wie das Drei-Stufen-Modell im Rahmen von Erlaubnistatbest?nden zur Anwendung gebracht werden kann (5.).     

High pressure and high temperature annealing on nitrogen aggregation in lab-grown diamonds

Diamond single crystals were grown by a high-pressure high-temperature gradient method using a molten Fe–Ni catalyst in a split-sphere apparatus at a pressure of 5.5 GPa and a temperature of 1473–1873 K. The as-grown crystals, ranging in size from 0.2 to 0.6 g, were generally deep yellow in color because of intake of nitrogen impurity during the process. Two different annealing methods were used to change their color to light and vivid yellow. One method involved annealing at 5.5 GPa and 2193–2473 K within the split-sphere apparatus. The other involved annealing of E-beam irradiated crystals at 1773 K in a high-vacuum furnace at 10⁻⁶ Torr. Distribution of C-center nitrogen, single substitutional nitrogen, and A-center nitrogen defects, a pair of nearest-neighbor nitrogen, were thoroughly studied by FT–IR spectroscopy. Upon annealing, C-center nitrogen defects decreased by 10–60%, while A-center nitrogen defects increased by 5–70%. It was confirmed that the irradiation process and intake of nickel impurity enhanced the nitrogen aggregation rate, which followed the second order kinetics. Measured activation energies were in the range of 2.88–3.01 eV, which were not strongly affected by the irradiation process. The results indicate that the nitrogen aggregation rate was enhanced by vacancies and interstitials introduced by E-beam irradiation.     

Feasibility of contact and noncontact material handling using traveling waves and transition characteristics

The feasibility of using traveling waves as a mechanism for industrial material handling is examined. A prototype was constructed to experimentally investigate the feasibility of the proposed method. Two kinds of transport methods are investigated: frictional drive and acoustic levitation. Experimental transport speed characteristics are presented. The transition characteristics from acoustic levitation to frictional drive are also experimentally examined.     

In situ hydrogen plasma treatment for improved transport of (4 0 0) oriented polycrystalline silicon films

Polycrystalline silicon (poly-Si) films were deposited on glass by very high-frequency (100 MHz) plasma enhanced chemical vapor deposition from a gaseous mixture of SiF₄ and H₂ with small amounts of SiH₄. (2 2 0) oriented films prepared at small SiF₄/H₂ ratios (<30/40 sccm) showed intrinsic transport properties of poly-Si. However, the room temperature dark conductivity (σ_d) of the (4 0 0) oriented film was very high for intrinsic poly-Si, 7.2×10⁻⁴S/cm. This conductivity exhibited a T^−1/4 behavior, suggesting a high defect density at the grain boundaries. It was found that in situ hydrogen plasma treatment successfully produced (4 0 0) oriented poly-Si with a reasonably low σ_d of 4.5×10⁻⁷S/cm and a good photoconductivity of 1.3×10⁻⁴S/cm.     

Users’ willingness to pay for web identity management systems

Electronic services such as virtual communities or electronic commerce demand user authentication. Several more or less successful federated identity management systems have emerged to support authentication across diverse service domains in recent years. In this paper, we explore the determinants for success and failure of such systems with a focus on Germany representing one of the largest markets in Europe. To achieve this goal, we analyze the preferences and willingness to pay of prospective users by conducting a choice-based conjoint analysis. Our results indicate that users prefer simple systems where an intermediary takes care of their data. An additional market analyses confirms these findings and contradicts the assumptions of many researchers, especially in the fields of engineering and computer science, supporting systems with higher and higher levels of privacy and security.     

Musculoskeletal, visual and psychosocial stress in VDU operators before and after multidisciplinary ergonomic interventions. A 6 years prospective study—Part II

A prospective epidemiological field study covering a 2 years period has earlier been published (Appl. Ergon. (1998) 29(5) 335). The study has a parallel group design with two intervention groups (T and S) and one control group (C) of Visual Display Unit (VDU) operators. The present paper covers the period from 2 to 6 years of the study. After 3.5 years, the C group got the same intervention in terms of new lighting system, new workplaces and at last an optometric examination and corrections if needed. The C group reported a significant reduction in visual discomfort after interventions while the two groups (T and S) continued to report significant reduction of visual discomfort after 6 years. By supporting the forearm on the table top, the C group reported significant reduction of shoulder and neck pain while the T group reported significant reduction in shoulder and back pain after 6 years. Organizational and psychosocial factors at work and outside work did not show any significant changes during the study period.     

A suggested effective method for unidirectional solidification under rotating magnetic field in the space experiments

In order to save costs and time during the unidirectional solidification experiments, it is necessary to obtain more and more information by solidifying one sample in a rotating magnetic field (RMF) to be performed on the space station. The macro- and microstructure developing during solidification is significantly influenced by the intensity and frequency of magnetic field, the solid/liquid interface velocity as well as the temperature gradient. A method by which one of the aforementioned four parameters can repeatedly be changed during the solidification is described. By this method, the transient phenomena occurring during parameters modification can also be observed. The results of earth experiments carried out by this method with Al7Si1Fe alloy are presented.