Some sulfides of gold and silver: Composition,mineral mineral assemblage,and conditions of formation

Characteristic mineral assemblage and special features of the composition of Au and Ag sulfides of gold-silver deposits have been established. The forms of the occurrence of Au and Ag in the minerals of the early and last stages have been analyzed. The conditions for the formation of uytenbogaardtite and petrovskaite in supergene and low-temperature hydrothermal processes have been considered. A thermodynamic model explaining their genesis in the oxidation zones is presented.     

Ceramic Composites Fabricated by Selective Laser Sintering

Selective laser sintering (SLS) uses a computer controlled laser beam to create objects directly from the CAD data without part-specific tooling. In this paper, the effect of material and processing parameters on the microstructure and mechanical properties of an alumina/aluminum phosphate composite fabricated by SLS is described. The precursor material is a blend of alumina and ammonium phosphate powder. This paper deals primarily with the effect of alumina particle size and material composition on the strength of the composite. A constitutive equation is also proposed to relate the mechanical properties of the composite to its microstructural characteristics.     

Optoelectronic charge coupled device (OECCD) using InP MIScapacitor array

An optoelectronic charge coupled device (OECCD) which is directly compatible with an incident optical signal is proposed. The nonlinear partial differential equation consisting of optical generation and recombination is solved in one dimension using the Crank-Nicolson finite-difference scheme. The charge transfer inefficiency is the main parameter considered for the calculation     

Robot manipulator kinematic compensation using a generalized jacobian formulation

The kinematic error compensation of robot manipulators is at present being attempted by improving the precision of the nominal robot kinematic parameters. This paper addresses the problem of kinematic compensation using a new mathematical joint model proposed to account for shortcomings in existing methods. The corrected manipulator transformation is formulated in terms of “generalized Jacobians”: relating differential errors at the joints to the differential change in the manipulator transformation. The details of application are discussed for a particular industrial manipulator.     

Growth,characterization and electrical anisotropy in GaTe—a natural semiconducting superlattice

GaTe is a III–VI semiconductor which has layered structure with large anisotropy in electrical properties. Growth of single crystals by the Bridgman technique permitted the measurement of thermoelectric power in orthogonal directions from which the anisotropy of hole effective masses were determined for the first time. From resistivity and Hall effect measurements the carrier activation energies and scattering mechanisms between 10–300°K were found. Study of the temperature dependence of conductivity revealed a variety of conduction mechanisms including weak localization below 20°K, hopping conduction between 20–50 K and band conduction in and across the layer planes atT>70 K. Weak localization was confirmed through observation of negative magnetoresistance. TheI–V characteristics showed quantized behaviour due to tunneling across potential barriers, which may be due to stacking faults between layer planes as observed by TEM studies.     

Exciton energies of wurtzite CdS nanoparticles

We have determined exciton energies for wurtzite CdS nanoparticles, both theoretically and experimentally. The empirical pseudopotential method has been used to calculate the bulk band structure. The discretization of reciprocal space was considered to get the energy gap and the corresponding exciton energy as a function of the nanoparticles size. The CdS nanoparticles were prepared by colloidal methods and the exciton energies were determined from optical absorption measurements. A good agreement between the calculated and the experimental exciton energies is obtained when an average over the experimental size distribution of the nanoparticles is included in the calculation.     

A lower carbon footprint process for production of metals from their oxide sources

This paper will describe the solid oxide membrane (SOM) process as it applies to the energy-efficient and environmentally sound production of magnesium from magnesium oxide. Also, it will describe the challenges encountered while using this process for the production of transition metals like titanium from its higher oxides. Finally, a novel magnesiothermic SOM process will be proposed that can enable production of transition metals from its higher oxides.