Studies of palladium electrodeposition from baths based on Pd(NH3)2X2 Part II: X=Br and X=NO2

The chemistry and electrochemistry of electroplating baths based on Pd(NH₃)₂Br₂ and Pd(NH₃)₂(NO₂)₂ has been investigated and compared with that previously reported for Pd(NH₃)₂Cl₂. It is shown that electroactive species in all the baths is Pd(NH₃) ₄ ²⁺ and, hence, the mechanisms and current efficiencies for the cathodic deposition of palladium metal are similar in all three media. On the other hand, only in bromide electrolytes is the palladium found to dissolve anodically.     

Electrocatalyst performance in industrial water electrolysers

Electrocatalyst materials used in industrial water electrolysis equipment must meet stringent requirements for long-term stability. Low electrode overvoltages must be sustained over prolonged periods of normal operation, including power interruptions. This paper presents an overview of the catalyst systems currently favoured for use in alkaline electrolyte. Performance data covering test periods exceeding 30 000 h are presented for representative commercial electrocatalysts. Results obtained in 100 000-A unipolar cells are correlated in detail with expectations based on measurements in laboratory and pilot-plant equipment.Particular attention is given to the effects of open-circuit conditions on electrode stability. An accelerated reverse-potential cycling test is described which allows identification of materials expected to withstand industrial operating conditions. It is found that the better materials which have been identified can be used with confidence, at least in electrolysers of the unipolar design in which potential variations encountered during current interruptions are modest.     

Multitemporal passive microwave mapping in MACHYDRO'90

MACHYDR0'90 was an experiment conducted in Pennsylvania in 1990 to study the synergistic use of remote sensors in multitemporal hydrologic studies. As part of this mission the pushbroom microwave radiometer was flown and used to produce brightness temperature maps. Verification studies and vegetation algorithms for mixed land cover areas are described     

A new family of yeast genes implicated in ergosterol synthesis is related to the human oxysterol binding protein

We have identified three yeast genes, KES1, HES1 and OSH1, whose products show homology to the human oxysterol binding protein (OSBP). Mutations in these genes resulted in pleiotropic sterol-related phenotypes. These include tryptophan-transport defects and nystatin resistance, shown by double and triple mutants. In addition, mutant combinations showed small but apparently cumulative reductions in membrane ergosterol levels. The three yeast genes are also functionally related as overexpression of HES1 or KES1 alleviated the tryptophan-transport defect in kes1Δ or osh1Δ mutants, respectively. Our study implicates this new yeast gene family in ergosterol synthesis and provides comparative evidence of a role for human OSBP in cholesterol synthesis.     

Analysis of tungsten and titanium migration during ESD contact burnout

A physical and chemical analysis of a machine model (MM) electrostatic discharge (ESD) failure in a silicon circuit was carried out. Focused ion beam (FIB) was used to make cross sections through the region of contact burnout. The resulting samples were analyzed using scanning electron microscopy (SEM) and two-dimensional (2-D) auger electron spectroscopic (AES) mapping. It is shown for the first time that both titanium (Ti) and tungsten (W) migrated throughout the melted silicon filament. Large pellets of the W plug were embedded in the bulk silicon but only on the cathode side of the junction. Mechanisms are discussed to explain these phenomena. These involve the melting of titanium disilicide (TiSi/sub 2/), dissolution of Ti and W in the molten silicon and the formation of W pellets through electromigration at temperatures below /spl sim/1800 K.     

Ab-initio primitive cell parameters from single convergent-beam electron diffraction patterns: a converse route to the identification of microcrystals with electrons.

A new method for the ab initio derivation of Buerger-reduced primitive cell parameters from coordinate measurements of spots on single convergent-beam electron diffraction (CBED) patterns is described, which does not involve trial-and-error. The pattern can be taken along any zone axis, and misorientations of the crystallite by as much as a few degrees are taken into account without loss of accuracy. This derivation of cell parameters by least-squares analysis of the measurements has been automated in a program called NRCBED. Present accuracy is about 1% on lengths and 2 degrees on angles, but could be significantly improved by modelling projector lens aberrations, or by using a microscope without a projector lens. With present technology, it is possible to obtain a CBED pattern and a semi-quantitative energy-dispersive X-ray (EDX) analysis simultaneously from a single microcrystal a few hundred Angstr?ms across. It becomes therefore possible to identify the material of the crystal on a single CBED pattern: a cell parameter database for known compounds is searched with the primitive cell parameters obtained in the above way, and with a mask describing the EDX results qualitatively. Feasibility is demonstrated on a crystallite of CeO2 500 Angstr?ms across. With this new approach, trial-and-error should disappear from the solution of other long-standing problems: interpretation of X-ray powder patterns for new compounds in the presence of impurity lines, or in the case of multiple phases should become straight-forward.     

Highly integrated direct conversion receiver for GSM/GPRS/EDGE with on-chip 84-dB dynamic range continuous-time /spl Sigma//spl Delta/ ADC

This paper describes a highly digitized direct conversion receiver of a single-chip quadruple-band RF transceiver that meets GSM/GPRS and EDGE requirements. The chip uses an advanced 0.25-/spl mu/m BiCMOS technology. The I and Q on-chip fifth-order single-bit continuous-time sigma-delta (/spl Sigma//spl Delta/) ADC has 84-dB dynamic range over a total bandwidth of /spl plusmn/135 kHz for an active area of 0.4 mm/sup 2/. Hence, most of the channel filtering is realized in a CMOS IC where digital processing is achieved at a lower cost. The systematic analysis of dc offset at each stage of the design enables to perform the dc offset cancellation loop in the digital domain as well. The receiver operates at 2.7 V with a current consumption of 75 mA. A first-order substrate coupling analysis enables to optimize the floor plan strategy. As a result, the receiver has an area of 1.8 mm/sup 2/.     

Dynamics of the transient buildup of emission inNd3+-doped fiber lasers

The two-stage process of the transient buildup of emission in Nd ⁴⁺-doped fiber lasers is described both experimentally and theoretically. After switching on the pump, spontaneous emission increases first until the gain becomes sufficient to compensate for the cavity losses; the laser field then develops and reaches the steady state after more or less regular oscillations. During this second stage, an almost chaotic spiking is obtained either for high pumping rates and/or at low temperatures. The whole set of these dynamical scenarios is not described under the usual assumptions of uniform cavity losses over the whole field spectrum and of pure homogeneous broadening for the transition line, but rather a modified form of the Maxwell-Bloch equations which retains some frequency dependence for the losses in the cavity and the inhomogeneous broadening as well is proposed     

A distributed approach for access and visibility task with a manikin and a robot in a virtual reality environment

This paper presents a new method, based on a multi-agent system and on a digital mock-up technology, to assess an efficient path planner for a manikin or a robot for an access and visibility task taking into account ergonomic constraints or joint and mechanical limits. In order to solve this problem, the human operator is integrated in the process optimization to contribute to a global perception of the environment. This operator cooperates, in real time, with several automatic local elementary agents. The result of this work validates solutions through the digital mock-up; it can be applied to simulate maintainability and mountability tasks.