Nonequilibrium synthesis of NbAl3 and Nb-Al-V

NbAl₃, like many ordered intermetallic compounds, appears to have great potential for application as high-temperature structural material because of the high melting point and stability in high- temperature oxidizing environments. However, the D0₂₂ (tI8) lattice structure shows limited ductility at room temperature. Addition of group IVB, VB, and VIB elements to A1₃X (D0₂₂ type of compounds) as partial replacement of X is a method being applied by various researchers to promote ductility in these materials by activation of numerous dislocations and ordered twin- ning. In this study, V was added in different amounts to improve the ductility of NbAl₃. How- ever, this has an adverse effect on the oxidation response of the system, as is explained in Part II of this article. This article deals with the microstructure evolution, phase identification, and characterization of laser-clad (rapidly solidified) nominal NbAl₃ and also studies the effect of V additions on the final microstructure in this system. Laser cladding of nominal NbAl3 produces two metastable unreported phases [body-centered tetragonal (bct) and base-centered orthorhombic phases]. Addition of V suppresses the primary phase (NbAl₃) in the Nb-Al-V system. on leave from the Department of Metallurgy on leave from the Department of Metallurgy     

Depsides and depsidones as inhibitors of HIV-1 integrase: discovery of novel inhibitors through 3D database searching

Seventeen lichen acids comprising despides, depsidones, and their synthetic derivatives have been examined for their inhibitory activity against HIV-1 integrase, and two pharmacophores associated with inhibition of this enzyme have been identified. A search of the NCI 3D database of approximately 200,000 structures yielded some 800 compounds which contain one or the other pharmacophore. Forty-two of these compounds were assayed for HIV-1 integrase inhibition, and of these, 27 had inhibitory IC50 values of less than 100 microM; 15 were below 50 microM. Several of these compounds were also examined for their activity against HIV-2 integrase and mammalian topoisomerase I.     

Chaos game representation of proteins

The present report proposes a new method for the chaos game representation (CGR) of different families of proteins. Using concatenated amino acid sequences of proteins belonging to a particular family and a 12-sided regular polygon, each vertex of which represents a group of amino acid residues leading to conservative substitutions, the method can generate the CGR of the family and allows pictorial representation of the pattern characterizing the family. An estimation of the percentages of points plotted in different segments of the CGR (grid points) allows quantification of the nonrandomness of the CGR patterns generated. The CGRs of different protein families exhibited distinct visually identifiable patterns. This implies that different functional classes of proteins follow specific statistical biases in the distribution of different mono-, di-, tri-, or higher order peptides along their primary sequences. The potential of grid counts as the discriminative and diagnostic signature of a family of proteins is discussed.     

Synthesis of diene prostaglandins in freshwater fish

Biosynthesis of PGD₂, PGE₂ and PGF_2α in four species of freshwter fish,Tilapia mossambica, Cyprinus carpio, Heteropneustes fossilis andClarius batrichus was studied. Both arachidonic acid and PGH₂ were used as substrates. When PGH₂ replaced arachidonic acid in the enzymic reaction, there was a 3- to 4-fold increase in PGE₂ synthesis, but no such increase in the synthesis of PGF_2α and PGD₂ was observed.     

Triglyceride composition of Papaver somniferum seed oil.

Poppy seed oil (P. Somniferum) contains palmitic (12%), stearic (3%), oleic (20%) and linoleic acid (65%). Lipolysis with pancreatic lipase indicates the following glyceride composition: S₃ (tr), S₂U (5%), SU₂ (34%) and U₃ (61%) or saturated dilinolein (19%), oleo-dilinolein (25%), and trilinolein (27%).     

SPART analyzer: its application to aerodynamic size distribution measurement

The performance characteristics are described for a recently developed prototype instrument, the single particle aerodynamic relaxation time (SPART) analyzer. The analyzer can measure aerodynamic diameters of particulates in real time in the size range 0.2–10.0 μm at a maximum count rate of 200 particles per second.     

On solute dispersion from an elevated line source in an open-channel flow

The streamwise dispersion of contaminant molecules due to a turbulent shear flow over a gravel-bed surface is examined when the solute is released from an elevated line source. A finite-difference, implicit method is used to solve the unsteady turbulent convection-diffusion equation, employing a combined scheme of central and four-point upwind differences for the steady-state condition and the Alternating Direction Implicit (ADI) method for the unsteady equation. It is shown how the mixing of contaminant is effected by the mean velocity due to the `log-wake law' and the corresponding eddy-diffusivity, when the solute is released in terms of a -function. The results for the steady-state condition are compared with existing experimental data and some other numerical results. The results obtained by the present method are in much better agreement with the experimental data than those obtained by the previous solution scheme, when the `log-wake-law' and the corresponding eddy-diffusivity are used. Far from the source, the concentration increases with time (the rate of increase is rapid near the source), asymptotically approaching a steady state after a certain time; concentrations are about two thirds of those near the source. The behaviour of iso-concentration lines in the vertical plane is also studied.     

Interfacial Processes and Tribocharging: Effect of Plasma Surface Modification and Physisorption

The tribocharging characteristics of polymer powders have a significant impact on several industrial processes such as electrostatic powder coating and polymer powder processing. The nature of chemical species on the surface of powder influences the triboelectric charging characteristics. An atmospheric-pressure helium plasma was used to modify tribocharging properties of polystyrene microspheres and acrylic powders. Plasma surface modification reduced the magnitude of tribocharging for the test polymer powders. When tribocharged against stainless steel, the net charge-to-mass ratio (Q/M) for both polystyrene microspheres and acrylic powders was less than that for the control samples. Plasma surface modification also reduced the tribocharging of mannitol, a pharmaceutical powder, against stainless steel. Further, Mars simulant dust (JSC Mars 1) was used as a test sample to study the effect of carbon dioxide physisorption on tribocharging. The Q/M of the sample with physisorbed CO₂ was less than that of the control in all size ranges.