Design, fabrication, testing and packaging of a silicon micromachined radio frequency microelectromechanical series (RF MEMS) switch

RF characterization and packaging of a single pole single throw (SPST) direct contact microelectromechanical (MEMS) series radio frequency (RF) switch is reported. Precise thickness of the silicon MEMS structure is achieved using a specially developed silicon Deep Reactive Ion Etching (DRIE) thinning process. A stress free release process is employed which ensures a high yield of released microstructures. The design of the device is based on stiffness equations derived from first principles. Displacement of the actuator under applied field is measured to confirm electrostatic pull in, which occurs in the 30–50 V range. The variation of contact resistance with time has been measured and is found to have a power law decay, in agreement with theoretical models. At the bare die level the insertion loss, return loss and the isolation of the switch were measured to be ?0.43 dB, ?25 dB and ?21 dB, respectively at 10 GHz. The devices were packaged in commercially available RF packages and mounted in alumina boards for post package characterization. Due to the presence of bond wires in the signal path of the packaged devices, the RF performance was found to degrade at high frequencies. However, losses were measured to be at acceptable levels up to 2 GHz. Factors contributing to insertion loss at the die and package device levels are discussed in detail with possible solutions.     

AN INTEGRATED PROCESS FOR THE RECOVERY OF TUNGSTEN AND TIN FROM A COMBINED WOLFRAMITE–SCHEELITE–CASSITERITE CONCENTRATE

This article presents results of the studies on development of viable process route for quantitative recovery of tungsten and tin values occurring together in the form of a multimineral concentrate of wolframite, scheelite, and cassiterite. The investigations were carried out using a tin–tungsten multimineral ore from Kyrgyzstan (Central Asia). Tungsten minerals in this ore occur both as distinct liberated mineral phases and as composites, viz. ultrafine dissemination of wolframite in scheelite and vice versa. Cassiterite also has similar characteristics, albeit to a lesser extent, with few grains containing ex-solution intergrowth of columbite/tantalite and very fine dissemination of tungsten minerals in its lattice. The complex nature of occurrence of both tungsten and tin minerals necessitated an integrated process comprising physical beneficiation and chemical extraction. The process route that was developed gave a tungsten and tin recovery of about 80 and 90%, respectively, on treating a primary gravity preconcentrate analyzing 16.5% WO₃ and 25.7% Sn.     

Identification of β-SiC surrounded by relatable surrounding diamond medium using weak Raman surface phonons

It is difficult to detect β-SiC using micro-Raman scattering, if it is surrounded by carbon medium. Here, β-SiC is identified in the presence of a relatable surrounding diamond medium using subtle, but discernible Raman surface phonons. In this study, diamond/β-SiC nanocomposite thin film system is considered in which nanosized β-SiC crystallites are surrounded by a relatable nanodiamond medium that leads to the appearance of a weak Raman surface phonon band at about 855 cm^???1. Change in the nature of the surrounding material structure and its volume content when relatable, will affect the resultant Raman response of β-SiC phase as seen in the present case of diamond/β-SiC nanocomposite thin films.     

Investigation of metallurgical and mechanical properties of 21st century nickel-based superalloy 686 by electron beam welding technique

Electron Beam Welding (EBW) was performed on the highly corrosion resistance superalloy 686. The present research work investigates the metallurgical and mechanical properties of the weld joint fabricated by Electron Beam Welding technique, and the results are compared with the base metal. Optical and Scanning Electron Microscope (SEM) analysis were carried out to study the structural properties of the weld joint. The fine equiaxed dendritic structure was revealed in the Center Fusion Zone (CFZ). The columnar dendrite was noticed in the Transition Fusion Zone (TFZ). Energy-dispersive X-ray spectroscopy (EDS) analysis results show that segregation of Mo and W were noticed in the sub-grain boundary. X-ray diffraction analysis (XRD) confirmed the presence of Mo and W rich phases in the weldment. Tensile testing was carried out to evaluate the strength and ductility of the weld joint. The result revealed that the weld strength was equal to the base metal strength. The presence of Mo and W-rich intermetallic phase reduced the ductility and toughness of the weld joint compared to base metal. Bend test confirmed the defect-free weld joint that was achieved in the Electron Beam Welding technique. The corrosion rate of base metal and EBW weldment are calculated in the synthetic seawater environment with the help of Potentiodynamic polarization experiment, and corrosion rate is measured with Tafel’s interpolation technique. The corrosion test result shows that the resistance of EBW weldment is lesser than base metal corrosion resistance because of the microsegregation of alloying elements in the interdendritic region.     

Network Competition and Industry Structure

The prevailing trend in the US telecommunications industry istoward industry convergence and market competition. This paperexamines possible scenarios for developments in the telecommunicationsmarket as a result of further industry convergence and changesin the political and regulatory environments toward competition.It studies the cost structures of the industry under a hierarchicallayered network architecture framework and addresses some potentialeconomic problems. Vertical and horizontal integration may bea natural outgrowth of competition in the converging industries.The paper concludes with a call for clearer economic analysisof future market structure on behalf of public policy makers,particularly with regard to quantification of underlying changesin consumers‘ purchasing behavior and providers’cost structure.     

Modeling Flow in Cylindrical Extruder Dies

Volumetric flowrate was studied in the die of a single screw extruder. Variables included the ratio of die length to die diameter, barrel to die diameter, barrel and die temperature, screw speed and product moisture. Die conductance was determined graphically and analytically. Results indicated that for a constant pressure drop across the die, increasing temperature, die diameter or moisture increased flowrate. Dimensional analysis was used to study the effect of each parameter on the flow through the extruder die. An expression for temperature rise due to viscous dissipation for isothermal flow in the die was developed and nomographs are presented.     

On the simulation of continuous non-linear filters A comparative study of second- and third-order approximations

Among several second-order approximations to the filter of a non-linear system, it is found that the extended Kalman filter is generally the most versatile. The second-order likelihood filter, also known ns the Detchmendy—Sridhar filter is inferior to the ahove and at the same time involves more computation. In the special ease when analytical expressions For the gaussian expectation integrals of the non-linearities can be found, the extended Kalman filter can be further improved by using stochastic linear approximations as suggested by Sunahara. The third-order likelihood filter derived in this paper is more accurate than the above, but calls for considerable storage space and computing time.     

Composition of Undigested Peptide Fragments from Gluten with Regard to Bioavailability of Essential Amino Acids

Our purpose was to isolate and characterize the high molecular weight peptides resulting from the in vitro digestion of wheat gluten in a system simulating actual in vivo conditions, and to determine to what extent essential amino acids were included in these peptides. Large peptides were separated from the smaller products by CuSephadex G-25, TLE and TLC, treated with dansyl chloride for end group determination, and redansylated to identify the remaining amino acids. Fifteen peptides, hexapeptides or larger, were isolated and were found to contain about 16.1% of the threonine, 15.2% of the methionine and 12.3% of the lysine originally present in wheat gluten.     

Strategies for targeting marker bacterial oxygenases involved in transformation of hydrocarbons in contaminated soil

A variety of activities leads to release of petroleum products in soil. In this study, DNA extracted from oil and grease contaminated soil by a simple technique was used as a template for Polymerase Chain Reaction based assays. Target gene sequences of certain key bacterial oxygenases involved in transformation of aromatic hydrocarbons viz. naphthalene dioxygenase, catechol 2,3‐dioxygenase, cytochrome P‐450cam monooxygenase as well as eubacterial 16S rRNA gene, were evaluated for determining the presence of microbial genotypes in soil. It was concluded that duplex, nested and multiplex PCR assay strategies in combination with residue analysis can play a crucial role in the selection of treatment processes as well as monitoring the efficacy of bioremedial technique.     

Uniaxial Extensional Viscosity During Extrusion Cooking from Entrance Pressure Drop Method

Uniaxial extensional viscosity of corn meal at moisture contents of 30 and 35% (dry weight basis) and temerature of 160 and 180°C was estimated from entrance pressure'drop measurements during extrusion cooking. The value of the shear component of the entrance pressure drop was an order of magnitude below that of the extensional component. Food doughs exhibited shear thinning and extension thinning behavior during processing conditions used. Increasing moisture and temperature decreased extensional viscosity at higher extension rates. The Trouton ratio ranged from 25 to 50 and was affected by product moisture content, barrel temperature, and deformation rate.