Study of defect states in a-Se<Subscript>85</Subscript>Te<Subscript>15−<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films by space charge limited conduction mechanism

Current–Voltage (I–V) characteristics have been studied at various temperatures in vacuum evaporated thin films of a-Se₈₅Te_15−x Pb _x (x = 0, 2, 4, 6) alloys. These characteristics show that, at low electric fields, an ohmic behaviour is observed. However, at high electric fields (E ∼ 10⁴ V/cm), the current becomes superohmic. At high fields, in case of samples having 0 and 2 at% of Pb, the experimental data fits well with the theory of space charge limited conduction (SCLC) in case of uniform distribution of localized states in the mobility gap. Such type of behaviour is not observed at higher concentration of Pb in the present glassy system due to high conductivity. In these samples, joule heating due to large currents may prohibit the measurement of SCLC. Using the theory of SCLC for the uniform distribution of the traps, the density of localized defect states near Fermi level is calculated for these compositions. The results indicate that the density of defect states near Fermi level increases on addition of Pb to binary Se₈₅Te₁₅alloy. This is explained in terms of electronegativity of Pb as compared to host elements.     

Experience with Applying Formal Methods to Protocol Specification and System Architecture

In the last three years or so we at Enterprise Platforms Group at Intel Corporation have been applying formal methods to various problems that arose during the process of defining platform architectures for Intel's processor families. In this paper we give an overview of some of the problems we have worked on, the results we have obtained, and the lessons we have learned. The last topic is addressed mainly from the perspective of platform architects.     

Stability analysis of double-diffusive solar ponds with non-constant temperature and salinity gradients

In this communication, the stability of the double-diffusive solar ponds with non-uniform temperature and salinity gradients has been investigated. This is a further generalization of our approach to this problem initiated in Ref. [7]. Using a stochastic approach, the linearized system of basic equations of motion is reduced to a single integro-differential equation. For convective motion, this equation reduces to a time-independent Schrödinger equation for a particle moving in a potential field ƒ(Z) characterized by the non-uniform temperature and salinity gradients. This equation can, in general, be solved (exactly or approximately depending on the form of the gradient profile) by methods commonly used in quantum mechanics.

In the Appendix, we show that, for a quadratic gradient profile, the above equation has an analytical solution similar to that obtained by Zangrando using numerical computations.     

Conductivity study of polyethylene oxide (PEO) complexed with sodium bicarbonate

Ion conducting thin film polymer electrolytes based on polyethylene oxide (PEO) complexed with NaHCO₃ salt has been prepared using solution-cast technique. The complexation of NaHCO₃ salt with PEO is confirmed by XRD and IR studies. DC conductivity in the temperature range 303–368 K has been evaluated. The conductivity is found to increase in the PEO complex with the NaHCO₃ salt and also with an increase in temperature. Using this polymer electrolyte, an electrochemical cell with the configuration Na/(PEO + NaHCO₃)/(I₂ + C + electrolyte) has been fabricated and its discharge characteristics studied. Open Circuit Voltage (OCV) and Short Circuit Current (SCC) are found to be 2.69 V and 1.28 mA, respectively. Other parameters associated with the cell are evaluated and presented in this paper.     

On the improvement of detection characteristics of trans-stilbene crystals by improving crystal perfection

Organic molecular scintillating crystals are noted for their good timing and particle discrimination process. Trans-stilbene is one such candidate noted for its good particle detection characteristics for the past five decades. Progressive strengthening of detection characteristics of trans-stilbene has been attempted by improving crystal perfection. A series of timing resolution studies have been carried out for the Bridgman grown trans-stilbene crystals under different experimental conditions. The results were compared with the previously reported values. Pulse shape discrimination process has been carried out for ²⁴¹Am and ²⁵²Cf sources and good discrimination has been obtained for gamma-alpha and gamma-neutron sources from the grown organic phosphor crystal. Electronic Publication     

Biodegradation of gelatin–g-poly(ethyl acrylate) copolymers

Gelatin-g-poly(ethyl acrylate) copolymers were prepared in an aqueous medium, using K₂S₂O₈ initiator. The composition of the graft copolymers was dependent upon temperature and duration of the reaction. The number of grafting sites was small and molecular weight of the grafted poly(ethyl acrylate) branches was high. Three copolymer samples with grafting efficiencies of 33.3%, 61.0%, and 84.0%, were tested for their microbial susceptibility in a synthetic medium employing a mixed inoculum of Bacillus subtilis, Pseudomonas aeruginosa, and Serratia marcescens and the percent weight losses were 12%, 10.1%, and 6.0%, respectively, after 6 weeks of incubation. The extent of degradation seems to decrease with increasing grafting efficiency. There was initial rapid weight loss accompanied by the exponential increase in bacterial population and pH of the culture medium during the first week. The nitrogen analysis also showed the utilization of the polymer. A parallel set of experiments, carried out by employing the samples as the only source of both carbon and nitrogen, showed a marginal but definite increase in the utilization of the polymer.     

Informal and formal requirements specification languages: bridgingthe gap

The differences between informal and formal requirements specification languages are noted, and the issue of bridging the gap between them is discussed. Using structured analysis (SA) and the Vienna development method (VDM) as surrogates for informal and formal languages, respectively, two approaches are presented for integrating the two. The first approach uses the SA model of a system to guide the analyst's understanding of the system and the development of the VDM specifications. The second approach proposes a rule-based method for generating VDM specifications from a set of corresponding SA specifications. The two approaches are illustrated through a simplified payroll system case. The issues that emerge from the use of the two approaches are reported