Microscopic Theory of Organic Superconductors

A microscopic theory of organic superconductors based on the concept of partial electron dielectrization is developed from first principles. Self-consistent equations for the superconducting order parameter () and insulating order parameter (D) are derived using a Green's function technique and equation of motion method. The theory is applied to explain the experimental results in the two-dimensional organic superconductor k-(BEDT-TTF)₂ Cu(NCS)₂. The present model explains coexistence of spin density wave (SDW) state and superconductivity state in the system. The behavior of superconducting order parameter (), insulating order parameter (D), specific heat, density of state, free energy, and critical field is also studied for the system k-(BEDT-TTF)₂ Cu(NCS)₂.     

On the impact of TiN film thickness variations on the effective work function of poly-Si/TiN/SiO/sub 2/ and poly-Si/TiN/HfSiON gate stacks

The impact of TiN film thickness variations on the effective work function (WF) of poly-Si/TiN/SiO/sub 2/ and poly-Si/TiN/HfSiON interfaces has been investigated. The electrical signatures of these gate stacks indicate that the concentration of Hf-Ti and Ti-Si bonds at the (poly-Si/TiN)/HfSiON and (poly-Si/TiN)/SiO/sub 2/ interface plays a significant role on the control of the gate stacks' WF. The density of these interfacial bonds and the related work function changes are correlated to the degree of nucleation of the TiN film on the dielectric.     

Uphill permeation model of gold(III) and its separation from base metals using thiourea derivatives as ionophores across a liquid membrane

This work deals with carrier-facilitated membrane transport of Au(III) from chloride media across a polymer-immobilised liquid membrane (PILM) using as organic reagents N-(thiocarbamoyl)benzamide derivatives and N-benzoylthiourea derivatives, denoted as 2a–c and 3a–f, respectively. Both the composition of the organic membrane solvent and the type of carrier have a marked effect on gold permeation. Recovery and permeability of gold using 2a–c and 3a–f across a PILM proceed in the following order: 3e≈3d≈3c?3f>3b≈3a≈2a≈2b≈2c. In view of the performance of these carriers, 3c was selected as a metal receptor for detailed studies of Au(III) in permeation. A model is presented for the permeation of Au(III) (61 μM) in 0.5 M Cl⁻ at pH 2.5 using 3c as a membrane carrier. The mathematical equations describing the rate of permeation are derived to correlate the membrane permeability coefficient with diffusional and equilibrium parameters. The mass transfer coefficient was calculated from the described model as 1.1×10⁻⁵ m s⁻¹, and the thickness of the aqueous boundary was later calculated to be 65 μm. Several polymeric supports were tested for impregnation of the organic extractant, and Durapore (Millipore) afforded the maximum flux for Au(III), yielding a value of 1.1×10⁻¹⁴ mol m⁻² s. The relationship between flux and support characteristics is derived and a mathematical equation is presented. Of the several diluents used, cumene had the most satisfactory performance in terms of PILM stability and metal transport. Of the different reagents used, 0.5 M sodium thiocyanate in 0.5 M NaCl at pH 2.5 served most efficiently as the stripping agent. More than 80% of the Au(III) could be readily separated using 3c in the presence of various metals such as Cu(II), Fe(III) and Zn(II).     

Fabrication and characterization of SiC-AIN alloys

SiC-AIN alloys were prepared by the carbothermal reduction of silica and alumina, derived from an intimate mixture of silica, aluminium chloride and starch. The resulting single-phase SiC-AIN powder was hot-pressed without additives to a high density. The dense bodies had a fine-grained uniform microstructure. The Young's elastic modulus, microhardness, fracture toughness, thermal expansion and thermal conductivity were measured as functions of composition. The creep behaviour of the SiC-AIN alloy was compared with that of silicon carbide.     

Scanning electron microscopy studies of abraded rubber surfaces

The surfaces of polybutadiene rubber (BR) and styrene-butadiene rubber (SBR) subjected to different degrees of abrasion have been studied by scanning electron microscopy (SEM). In the case of SBR it has been shown that abrasion begins with marks in the direction of rotation which are followed by fine ribbing and then by the formation of coarse, angular and prominent ridges. Prolonged abrasion produces folding and cavities on the surface. This change in abrasion mechanism has been explained as a result of heat build-up and high crack growth rate in SBR which occur beyond a certain stage. These help in softening the matrix and removing the surface. On the other hand, fractured surfaces of BR show that ridges begin to form at about 250 revolutions and there is no characteristic difference between the abraded surfaces at lower or higher degrees of abrasion.     

Loading time history for tornado-generated missiles

Nuclear power plant structures in the USA are designed for impact by tornado-generated missiles. The design load for flexure and shear can be obtained from the deceleration of the missile on impact. The paper gives a simple method to determine the deceleration of the most critical pipe missile. Results, obtained by the simple method, are compared with full-scale test results. The comparisons between the predicted and actual deceleration time histories show excellent correlation.     

Effect of candicidin on cholesterol and bile acid metabolism in the rat

Sterol metabolism studies were carried out in rats maintained on a diet containing a polyene antibiotic, candicidin, (30 mg/kg/day) for 2-1/2 months. Compared to the controls, the candicidintreated animals had a smaller food intake and weight gain during this period. There was no difference between the 2 groups in serum cholesterol levels, biliary cholesterol or bile acid concentrations. However, in the experimental group, liver cholesterol content decreased by 27% and hepatic HMG-CoA reductase increased by 36%. Candicidin administration produced an 84% increase in neutral sterol output without change in bile acid output. Cholesterol absorption was reduced 80% by candicidin feeding. The weight of ventral prostate was reduced 33% by candicidin administration. Prostatic HMG-CoA reductase levels were 3 times higher than those of the liver, but enzyme activity was unchanged by candicidin treatment.     

Microtubule sensors and sensor array based on polyaniline synthesized in the presence of poly(styrene sulfonate)

Microtubule sensors for glucose, urea, and triglyceride were fabricated based on poly(styrene sulfonate)-polyaniline (PSS-PANI) composites synthesized within the pores of track-etched polycarbonate membranes. The synthesis of a sufficiently thick and conducting PSS-PANI film at pH 5 provided the advantage of immobilizing enzymes during polymerization. This resulted in the improvement of sensor response for urea and triglyceride by a factor of approximately 10(2) with a significant increase in the linear region of response compared to polyaniline-based sensors, where the enzymes were immobilized by physical adsorption after the polymerization. The sensors based on urea and triglyceride were found to have a higher linear range of response, better sensitivity, improved multiple use capability, and faster response time compared to the potentiometric and amperometric sensors based on polyaniline. A microtubule sensor array for glucose, urea, and triglyceride based on PSS-PANI was fabricated by immobilization of three different sets of enzymes on three closely spaced devices and its response was found to be free from cross-interference when a sample containing a mixture of the above analytes was analyzed in a single measurement.     

Modeling multiaxial impact behavior of a glassy polymer

In many applications of polymers, impact performance is a primary concern. Impact tests experimentally performed on molding prototypes yield useful data for a particular structural and impact loading case. But, it is generally not practical in terms of time and cost to experimentally characterize the effects of a wide range of design variables. A successful numerical model for impact deformation and failure of polymers can provide convenient and useful guidelines on product design and therefore decrease the disadvantages that arise from purely experimental trial and error. Since the specimen geometry and loading mode for multiaxial impact test provides a close correlation with practical impact conditions and can conveniently provide experimental data, the first step of validating a numerical model is to simulate this type of test. In this paper, we create a finite element analysis model using ABAQUS/Explicit to simulate the deformation and failure of a glassy ABS (acrylonitrile-butadiene-styrene) polymer in the standard ASTM D3763 multiaxial impact test. Since polymers often exhibit different behavior in uniaxial tensile and compression tests, the uniaxial compression or tensile tests are generally not representative of the three-dimensional deformation behavior under impact loading. A hydrostatic pressure effect (controlled by the parameter γ) is used to generalize a previously developed constitutive model ("DSGZ" model) so that it can describe the entire range of deformation behavior of polymers under any monotonic loading modes. The generalized DSGZ model and a failure criterion are incorporated in the FEA model as a user material subroutine. The phenomenon of thermomechanical coupling during plastic deformation is considered in the analysis. Impact load vs. displacement and impact energy vs. displacement curves from FEA simulation are compared with experimental data. The results show good agreement. Finally, equivalent stress, strain, strain rate and temperature distributions in the polymer disk are presented. Electronic Publication     

Managing Role-Based Access Control Policies for Grid Databases in OGSA-DAI Using CAS

In this paper, we present a role-based access control method for accessing databases through the Open Grid Services Architecture – Data Access and Integration (OGSA-DAI) framework. OGSA-DAI is an efficient Grid-enabled middleware implementation of interfaces and services to access and control data sources and sinks. However, in OGSA-DAI, access control causes substantial administration overhead for resource providers in virtual organizations (VOs) because each of them has to manage a role-map file containing authorization information for individual Grid users. To solve this problem, we used the Community Authorization Service (CAS) provided by the Globus Toolkit to support the role-based access control (RBAC) within OGSA-DAI. CAS uses the Security Assertion Markup Language (SAML). Our method shows that CAS can support a wide range of security policies using role-privileges, role hierarchies, and constraints. The resource providers need to maintain only the mapping information from VO roles to local database roles and the local policies in the role-map files, so that the number of entries in the role-map file is reduced dramatically. Also, unnecessary authentication, mapping and connections can be avoided by denying invalid requests at the VO level. Thus, our access control method provides increased manageability for a large number of users and reduces day-to-day administration tasks of the resource providers, while they maintain the ultimate authority over their resources. Performance analysis shows that our method adds very little overhead to the existing security infrastructure of OGSA-DAI.