A two-unit priority standby system subject to random shocks and Releigh failure-time distribution

This paper deals with the cost-benifit analysis of a two-unit priority standby system subject to random shocks. The priority unit gets preference both for repair and operation over the ordinary unit and has three modes- Normal, Quasi-normal and Total-failure. The ordinary unit has only two-modes- Normal and Total-failure. The distributions of shock-time, repair-time of the ordinary unit and failure time of the priority unit are negative exponential. The distribution of the repair-time of the priority unit is taken to be general while the time to failure of ordinary unit follows Releigh distribution. Various characteristics related to system effectiveness have been obtained by using the regenerative point technique.     

Synthesis and antitumor activity of 1-β-D-arabinofuranosylcytosine conjugates of optical isomers of ether and thioether lipids

Four 1-β-D-arabinofuranosylcytosine conjugates (ara-C) (1a, b and 2a, b) ofsn−1 andsn−3 isomers of 1-O-octadecyl-2-O-palmitoylglycerol and its 1-S-alkyl analogue have been synthesized, and their antitumor activity against L1210 lymphoid leukemia in mice were compared with those of the previous conjugates (3a, b) of racemates in order to determine the significance of chirality of the glycerol moieties for activity. Administration (i.p.) of a single dose (300 mg/kg) of conjugates ofsn−1 (1a),sn−3 (2a) andrac (3a) isomers of the ether lipid increased lifespan of i.p. implanted L1210 lymphoid leukemic DBA/2J mice by 169, 175 and 236%, respectively. Thesn−1 (1b),sn−3 (2b), andrac (3b) isomers of the thioether lipid with a single dose of 300 mg/kg produced an increase in lifespan values of 238, 263 and 250%, respectively. The results indicate that chirality of the glycerol moieties appears not to be critical for the activity, and racemates 3a and 3b are promising prodrugs of ara-C for further clinical investigations. This material was presented in part at the 81 st Annual Meeting of the American Association for Cancer Research in Washington, D.C., May, 1990 (Abstract No. 2493).     

DC built-in self-test for linear analog circuits

DC testing of analog circuits is cheaper than AC testing and covers many fault classes, including some that AC tests cannot detect. This efficient, low-cost, built-in self-test (BIST) methodology uses the checksum encodings of matrix representations to uncover faults that affect a circuit's DC transfer function     

Multi-standby system with repair and replacement policy

This paper investigates the mathematical model of a system composed of (m + 1) non-identical units—one functioning and m standbys. Each unit of the system has four possible states—normal, partial failure, total failure and repair facility—the last one meaning that the totally failed unit is being attended to at the repair facility where it might be either repaired or eventually rejected and replaced. The normal and partial failure states are up states while the other two are down states. The system breaks down when the (m + 1)th unit after total failure is finally rejected and no standby remains to replace it. Several reliability characteristics of interest to system designers as well as operations managers have been computed. Results obtained earlier are verified as particular cases.     

A two (multicomponent) unit parallel system with standby and common cause failure

This paper investigates the mathematical model of a system composed of two non-identical active parallel units and one cold standby. A unit has N components, each having a constant failure and repair rate. These vary from component to component. Several reliability characteristics of interest to system designers as well as operations managers have been computed. Results obtained earlier are verified as particular cases.     

Studies on β-alkoxypropionitriles as solvents for extractive distillation

Five solvents of the β-alkoxypropionitrile series have been studied by gas-chromatographyin order to examine their potential usefulness as solvents for extractive distillation. Four isomers of C₄-olefin and a diene were used as solutes for the determination of activity coefficients at infinite dilution at 30°C. Relative volatilities were calculated for these solvents and compared with those for other commercial solvents used currently. Relative volatilities of seven C₄-hydrocarbons in two solvents were also studied and compared with the existing literature data for β-methoxypropionitrile containing 5% antisolvent. The present g.c. studies show that besides the well-studied β-methoxypropionitrile, the second member of the series, β-ethoxypropionitrile, also has the potential for use as a selective solvent.     

Fabrication and testing of Al–SiCp composite poppet valve guides

Composite materials are replacing the materials used in various fields and are the candidate materials for future growth. Metal matrix composites are the class of composite materials finding vast applications in automotive, aircraft, defense, sports, and appliance industries. In the present work, Al–SiC_p composites with 5–30 wt.% of SiC particulates were fabricated using powder metallurgy as well as casting processes. Mechanical alloying of aluminum and SiC particles was done prior to compaction so as to enhance the properties of the fabricated powder metal components. A custom built sliding valve guide wear test rig was fabricated to simulate the valve stem/guide wear under cold start condition of an engine by reciprocation of a valve stem under different imposed loads, against a stationary poppet valve guide. The hardness and radial crushing load was measured for the Al–SiC_p composite poppet valve guides and were found better than the cast iron poppet valve guides presently used in engines. The wear test of the poppet valve guides was done using valve guide wear test rig, which revealed that the Al-20 wt.% SiC_p and Al-30 wt.% SiC_p composite poppet valve guides have higher wear resistance than the cast iron poppet valve guides. The hardness, radial crushing load, and wear resistance of Al–SiC_p composite poppet valve guides were found to increase with increase in weight percent of SiC_p. The microstructural analysis of the cast and PM Al–SiC_p composites was also done using scanning electron microscope. Finite element analysis of the Al–SiC_p composite poppet valve guide was also done using Ansys software, which supports the successful implementation of the Al–SiC_p composite poppet valve guides for automobiles.     

Preparation of Polystyrene/Clay Nanocomposites by Free‐Radical Polymerization in Dispersion

Fully exfoliated PS/clay nanocomposites were prepared via FRP in dispersion. Na‐MMT clay was pre‐modified using MPTMS before being used in a dispersion polymerization process. The objective of this study was to determine the impact of the clay concentrations on the monomer conversion, the polymer molecular weight, and the morphology and thermal stability of the nanocomposites prepared via dispersion polymerization. DLS and SEM revealed that the particle size decreased and became more uniformly distributed with increasing clay loading. XRD and TEM revealed that nanocomposites at low clay loading yielded exfoliated structures, while intercalated structures were obtained at higher clay loading.

     

Preparation,structural and thermo-mechanical properties of lithium aluminum silicate glass–ceramics

Lithium aluminum silicate glasses of composition (wt%) 12.6Li₂O–71.7SiO₂–5.1Al₂O₃–4.9K₂O–3.2B₂O₃–2.5P₂O₅ were prepared by the melt quench technique. These glasses were converted to glass–ceramics based on DTA data. X-ray diffraction (XRD) and Fourier transform infra-red spectroscopy (FTIR) were used to discern the phases evolved in the glass–ceramics. Phase morphology was studied using scanning electron microscopy (SEM). Thermal expansion coefficient (TEC) and glass transition temperature (T_g) of all samples were measured using thermo-mechanical analyzer (TMA). It was found that 3 h dwell time at crystallization temperature yielded samples with good crystallinity with a TEC of 9.461 × 10⁻⁶ °C⁻¹. Glass–ceramic-to-metal compressive seal with SS-304 was fabricated using LAS glass–ceramic. The presence of metal housing and compressive stresses at the glass–ceramic-to-metal interface reduced average grain size and changed the overall microstructure.