Thermal Expansion of Compounds of Zircon Structure

The thermal expansion behavior of 13 members of ABO₄ compounds of the zircon family is examined in terms of crystal chemical (size, charge, and mass of cations) and crystallographic ( a and c ) parameters. The systematic trend in the thermal expansion coefficients, α_a and α_c, with the ionic radii, r _A and r _B, can be explained in terms of the unique arrangement of M-O polyhedra along a and c directions of this lattice. In the zircon structure, edge-sharing ZrO₈ dodecahedra form a chain along the a direction while the chain along the c direction consists of alternate edgesharing SiO₄ tetrahedra and ZrO₈ triangular dodecahedra. Substitution in the A sites affects a and α_a more than c and α_c and the reverse is true for replacements in the B sites. Unequal valencies on the A and B sites affect thermal expansion coefficients, particularly α_c.     

Preparation and characterisation of silver particulate films on softened polystyrene substrates

The preparation of silver particulate films on softened polystyrene (PS) substrates and their characterisation using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and optical absorption spectroscopy is reported in this paper. Silver films of 150 nm thickness were vacuum deposited onto PS coated glass substrates held at temperatures in the range 415–475 K at different deposition rates of 4 to 12 Å/s. SEM studies indicate that films deposited at 415 K are close to a semicontinuous structure and the structure is discontinuous at higher temperatures. The film morphology is strongly dependent on the deposition rate at any given substrate temperature. The film agglomeration increases with increasing rate of deposition. In the XPS studies, considerable attenuation of the signal corresponding to silver is observed at lower electron take of angles (ETOAs). This indicates that Ag is formed beneath the PS surface. Optical absorption studies showed an interesting red shift of the plasmon resonance wavelength for lower deposition rates again indicating that a sub-surface particulate structure is formed at lower deposition rates. These results are consistent with reported observations.     

Electrical properties of vacuum annealed CdS films

Cadmium sulphide (CdS) films were evaporated in vacuum on glass substrates maintained at room temperature. These films were later annealed in vacuum at temperatures in the range 30 to 300° C. The variation of d.c. electrical conductivity was studied in the temperature range 100 to 300 K. While the conductivity data in the range 100 to 150 K were observed to follow Mott's variable range hopping process, the conductivity in the high-temperature region (150 to 300 K) could be explained by Seto's model.     

Data Cube: A Relational Aggregation Operator Generalizing Group-By, Cross-Tab, and Sub-Totals

Data analysis applications typically aggregate data across manydimensions looking for anomalies or unusual patterns. The SQL aggregatefunctions and the GROUP BY operator produce zero-dimensional orone-dimensional aggregates. Applications need the N-dimensionalgeneralization of these operators. This paper defines that operator, calledthe data cube or simply cube. The cube operator generalizes the histogram,cross-tabulation, roll-up,drill-down, and sub-total constructs found in most report writers.The novelty is that cubes are relations. Consequently, the cubeoperator can be imbedded in more complex non-procedural dataanalysis programs. The cube operator treats each of the Naggregation attributes as a dimension of N-space. The aggregate ofa particular set of attribute values is a point in this space. Theset of points forms an N-dimensional cube. Super-aggregates arecomputed by aggregating the N-cube to lower dimensional spaces.This paper (1) explains the cube and roll-up operators, (2) showshow they fit in SQL, (3) explains how users can define new aggregatefunctions for cubes, and (4) discusses efficient techniques tocompute the cube. Many of these features are being added to the SQLStandard.     

Properties of brush plated CdS films

Cadmium sulphide (CdS) thin films were deposited for the first time using the brush plating technique from the precursors on titanium and conducting glass substrates. The films were polycrystalline possessing single-phase hexagonal structure. Surface morphological studies indicated increase of grain size with increase of post deposition temperature. Optical band gap of 2.39 eV was obtained. XPS studies indicated the formation of CdS. Photo electrochemical cell studies indicated higher current and voltages compared to earlier reports on thin film electrodes. Mott–Schottky studies exhibited n-type behaviour with a carrier density of 10¹⁸ cm⁻³. Spectral response measurements indicated a quantum efficiency of 0.35.     

Effect of Iron Impurity and a Cd Trace Addition on the Delayed Ageing of Al-7Si-0.3 Mg Casting Alloy

Abstract

Iron in aluminium alloys is considered to be an impurity. It forms intermetallic compounds with Al and elements Si and Mg; these coarse intermetallic compounds impair the mechanical properties. An increase in hardness and decrease in UTS, YS, and ductility was observed with an increase in Fe content in the range 0.2 to 0.8% in an Al-7Si-0.3Mg Alloy. Further analysis showed higher hardening rate of the alloy at 0.8% Fe compared to 0.2% Fe with the tensile flow curves. Studies were carried out on the effect of chemical composition (Mg, Fe), solidification rate, heat treatment (delayed ageing with Cd trace addition) on microstructure and mechanical properties of the alloy. Chill castings were found to possess higher mechanical properties than sand castings.     

Characteristics of brush plated copper indium telluride films

Copper indium telluride (CIT) films were deposited for the first time by the brush plating technique at different substrate temperatures in the range of 30–80 °C and at a constant deposition current density of 1 mA cm^?2.The Films exhibited single phase CIT. The grain size increased with increase of substrate temperature. Optical band gap of the films varied in the range of 0.98–1.00 eV. Atomic force microscopy studies indicated that the grain size and surface roughness vary from 20 to 50 nm and 1.0 to 1.5 nm, respectively with increase of substrate temperature. The films exhibited photoconductivity.     

Bacterial enzyme mediated biosynthesis of gold nanoparticles

Development of synthesis methods for anisotropic metal nanoparticles is of considerable interest due to their remarkable optoelectronic properties. Various shapes ranging from rods to cubes to tetrapods and prisms may be obtained by chemical methods. Here we show that anisotropic gold nanoparticles can be synthesized biologically by the bacterium Actinobacter spp. when challenged with gold chloride in the presence of Bovine serum albumin (BSA). We also observed that synthesis of gold nanoparticles occur with simultaneous induction of the protease enzyme secreted by the bacterium in the presence of BSA. The presence of BSA helps to enhance the rate of gold nanoparticles biosynthesis and may also impart some shape control. Controlling simple experimental conditions like incubation temperature and presence or absence of oxygen have drastic effect on the reaction rate and the morphology of the particles. Various assay experiments show that the presence of enzyme protease can act as a reducing as well as shape directing agent.