Structure and properties of silver-doped calcium phosphate nanopowders

Stable and antimicrobial silver-doped calcium phosphate nanopowders were synthesized using sol–gel route by setting the atomic ratio of Ag/(Ag+Ca) at 3% and (Ca+ Ag)/P at 1.67. Prior to synthesis of nanopowders, influence of time of hydrolyzation on pH and density of precursors were comprehensively studied. Hydrolyzation time was found to have profound influence on pH of constituent precursors. Sufficient hydrolysis resulted in early maturation of sol. Scanning electron microscopy (SEM) showed the heterogeneous and agglomerated state of particles with average size of 3.9± 1.9 μm. Energy dispersive X-ray spectroscopy (EDX) presented uniform distribution of O, Ag, Ca and P elements in nanopowder. Fourier transform infrared spectroscopy (FTIR) confirmed the formation of apatitic structure, whereas X-ray diffraction (XRD) revealed the multiphase constitution of nanopowders primarily composed of β-TCP, Ag and other hybrid phases. Crystallite size and lattice parameters of β-TCP and Ag phases were increased with the rise in calcination temperature. Thermogravimetric analysis (TGA) showed three regions of weight change and indicated the high thermal stability of nanopowders. Disk diffusion method was used to test the antimicrobial resistance of nanopowders against Escherichia coli and Staphylococcus aureus bacterial strains. All nanopowders exhibited antimicrobial resistance against both E. coli and S. aureus bacteria.     

Thermal Expansion of CeO2, Ho2O3, and Lu2O3 from 100° to 300°K by an X-Ray Method

Thermal expansion of CeO₂, Ho₂O₈, and Lu₂O₃ was determined from 100° to 300°K by a back-reflection X-ray technique. The variation of thermal expansion with temperature is the same as that of specific heat for CeO₂ and Ho₂O₃; these oxides obey the Grueneisen model of thermal expansion in the temperature range studied.     

Semantical considerations on intention dynamics for BDI agents

The BDI paradigm is a powerful means for constructing intelligent agents in terms of their beliefs, desires, and intentions. For this paradigm to bear its full potential, it must incorporate considerations from rationality. This paper develops a set of postulates for intelligent agents who deliberate about their intentions and actions. However, even simple postulates can lead to paradoxical results when formalized naively. We propose an approach based on temporal possibility and action that avoids those problems. This approach incorporates a formal model based on branching time in which a probabilistic analysis of choice can be captured. In this manner, the intuitions of the BDI paradigm can be reconciled with those of rational agency.     

Effective elastic constant theory of transverse wave interaction in a piezoelectric semiconductor

Small-signal low-frequency current gains of the npn and pnp transistor sections of high and low power thyristors were measured by a three-terminal technique. From their dependence upon current and temperature it was found that the saturation current dependence of the isolated centre junction primarily determines temperature stability. Current gain measured at a series of temperatures, and plotted para-metrically with anode current, qualitatively correctly predicts the temperature dependence of the two-terminal latching currents. Gold-doping predictably leads to a low current gain for the pnp section.     

KINETIC ANALYSIS OF COMPLEX REACTION SYSTEMS-METHANOL CONVERSION TO LOW MOLECULAR WEIGHT OLEFINS

An analysis of the selectivity data when converting methanol to low molecular weight hydrocarbons suggests that methane, propylene and propane are formed by the primary reaction of methanol decomposition, Ethane, carbon monoxide and dimethyl ether are formed by primary reactions and participate in secondary reactions. Carbon dioxide and ethylene are produced by secondary reactions.     

Characteristics of electrochemically deposited Nickel-cobalt-tungsten alloy semiconductor diodes

Ternary Ni-Co-W alloy semiconductor diodes were fabricated by the method of electrodeposition and their properties were studied. Determination of barrier height of ternary alloy semiconductor diode from T-V and C-V measurements showed that it was alloy composition dependent and lay between alloy component semiconductor barrier height values.     

On the evaluation of transition matrices in finite fields

A technique for evaluating the transition matrix A^k of a linear sequential machine has been given by Seherba and Roesser by transforming matrix A into a matrix A_R in the real field, finding the powers A_R ^k of.A_R In in the real field and then transforming A_R ^k back to finite field. A technique for the same problem is suggested by carrying out all the computations in the finite field only, thus avoiding the cumbersomeness of the earlier technique.     

Sliding mode of control of flexible spacecraft under disturbance torque

A control system design is presented for large angle rotational manoeuvres of a spacecraft-beam-tip body (an antenna or a reflector) configuration. Although this approach is applicable to three-axis manoeuvres, for simplicity only single-axis control is treated here. It is assumed that an unknown but bounded disturbance torque acts on the spacecraft. A sliding mode attitude control law is derived for slewing of the space vehicle. This slewing control law requires only the attitude error and its derivative for feedback. It does not need any information on the elastic motion of the system. For the damping of the elastic motion, a stabilizer is seperately designed based on the asymptotically decoupled system describing the elastic deflections in two orthogonal planes. Simulation results are presented to show that precise large rotational manoeuvres can be performed using an attitude controller and elastic mode stabilizer in spite of the uncertainty in the system.     

Design of piston bowl geometry for better combustion in direct-injection compression ignition engine

The current computational fluid dynamics (CFD) study presents the effect of piston bowl geometry on the performance and emissions of a direct-injection diesel engine. Different piston bowl profiles, namely, hemispherical combustion chamber (HCC), shallow depth combustion chamber (SCC) and toroidal combustion chamber (TCC), have been created with a baseline compression ratio of 17.5. CONVERGE^TM CFD code coupled with the SAGE combustion model was used for numerical analysis. It is observed that the TCC piston bowl geometry renders better air–fuel mixture inside the cylinder, which leads to a homogeneous charge. Further, numerical experiments are carried out to analyze suitable TCC piston bowl geometry by varying the depth of the bowl. Out of all the cases, the case with 1.26 mm decrease in depth of bowl from the baseline (TCC) design gives better emissions and performance characteristics.