Neutron Powder Diffraction Study in La<Subscript>0.85</Subscript>Ag<Subscript>0.15</Subscript>MnO<Subscript>3</Subscript>

La_0.85Ag_0.15MnO₃, the colossal magnetoresistance compound was prepared and the neutron powder diffraction patterns at different temperatures down to 19 K were recorded to study their crystal structure and magnetic properties. These patterns were analyzed by the Rietveld refinement technique and are found to be free from any impurity phase. The compound is found to crystallize in a mixture of R[`3]cRoverline{3}c and Pnma space group and the phase fraction is found to vary with temperature. A cross-over from R[`3]cRoverline{3}c dominated high temperature phase to Pnma dominated low temperature phase at around 130 K was observed. At low temperatures, especially below 285 K, the diffraction patterns could be refined by including the magnetic reflections corresponding to ferromagnetic structure. The refined magnetic moment of Mn ions is found to be along b axis of the unit cell with a maximum moment of 3.74 μ_B at 19 K and this value is comparable to the saturation magnetization observed at 20 K from magnetization measurement.     

Performance of a two channel suspended flat plate solar air heater

In the present communication, an analytical model to study the performance of a two channel suspended flat plate air heater is presented. The effect of different parameters, e.g. spacing between the plates, plate length, same and different flow rates of air in the two channels of the air heater, on the air temperature has been studied. A comparison of single channel and two channel air heaters has also been made. Numerical calculations have been made for a typical cold day in Delhi, viz. Jan. 26, 1980.     

Low-temperature ultrasonic dyeing of silk

Silk was dyed with cationic, acid and metal-complex dyes at low temperatures in the presence of ultrasonic energy for relatively short durations. The results in terms of dye uptake were compared with those obtained by conventional processes run at higher temperatures and for longer dyeing times. It was found that the ultrasonic energy helps in obtaining good fast dyeings, simultaneously conserving energy and reducing the time required for the dyeing process. In some cases the dye uptake was even higher than that obtained by the conventional dyeing procedures.     

In situ generated diphenylsiloxane‐polyimide adduct‐based nanocomposites

Arylsiloxane was incorporated into polyimide (PI) via electronic interaction with polyamic acid (PAA)/PI, and a wide spectrum of properties were evaluated for different compositions. The samples prepared with relatively low concentrations (0.0001–0.1%) of oligomers showed unusual synergism, which is attributed to the generation of nanostructures dispersed in the continuous PI matrix. The incorporation of siloxane with bulky phenyl groups contributed to enhanced thermal stability as determined by thermogravimetric analysis. Water uptake and methanol absorption by these composites were evaluated and correlated with the underlying micro‐ and nanostructures. Fourier Transform Infrared (FTIR) spectroscopy was used to elucidate the probable reaction mechanism (including in situ polymerization of arylsilanol), and to study the synthetic aspects associated with the molecular composites and nanocomposites formation. POLYM. ENG. SCI., 45:142–152, 2005. © 2004 Society of Plastics Engineers     

Mechanism and specificity of immunoprotection induced by mycobacterial proteins against experimental tuberculosis in mice

Mechanism of immunoprotection and specificity of two highly immunoprotective mycobacterial proteins, viz. 71 and 30 kDa were investigated. The adoptive transfer studies indicated that immunoprotection was mainly mediated by cooperative effect of CD4+ and CD8+ (66.7-73.3% on the basis of percent survival) which was further enhanced marginally by supplementation of B cells, natural killer cells, dendritic cells, macrophages and other immune cells. The specificity studies indicated that both the proteins did not cross react with the unrelated intracellular pathogens i.e. Aspergillus fumigatus, Salmonella typhi and Leishmania donovani as seen by T cell proliferation assay. The protection imparted by these mycobacterial proteins was also specific as the 71 and 30 kDa primed mice did not exhibit any cross protection against sublethal challenge of S typhi. The results indicate 71 and 30 kDa mycobacterial proteins to contain T cell specific epitopes responsible for specific immunoprotection, thus indicating their potential role as antituberculous vaccine candidates.     

Reserve constrained multi-area economic dispatch employing differential evolution with time-varying mutation

For a power pool that involves several generation areas interconnected by tie-lines, the objective of economic dispatch (ED) is to determine the most economical generation dispatch strategy that could supply the area load demands without violating the tie-line capacity constraints. The objective of multi-area economic dispatch (MAED) is to determine the generation levels and the interchange power between areas which would minimize total fuel cost while satisfying power balance constraint, upper/lower generation limits, ramp rate limits, transmission constraints and other practical constraints. In reserve constrained MAED (RCMAED) problem inter-area reserve sharing can help in reducing the operational cost while ensuring that spinning reserve requirements in each area are satisfied. The tie-line limits too play a pivotal role in optimizing the cost of operation. The cost curves of modern generating units are discontinuous and non-convex which necessitates the use of powerful heuristic search based methods that are capable of locating global solutions effectively, with ease. This paper explores and compares the performance of various differential evolution (DE) strategies enhanced with time-varying mutation to solve the reserve constrained MAED (RCMAED) problem.The performance is tested on (i) two-area, four generating unit system, (ii) four area, 16-unit system and (iii) two-area, 40-unit system. The results are found to be superior compared to some recently published results.     

Rheological properties of black gram (Phaseolus mungo) batter: characterisation of flour from native and modified rice and their effect on batter viscosity

Rheological properties of black gram batter as a function of soaking time, and effect of flour from native and thermally modified rice on black gram batter have been studied. Greater increase in hydration capacity of black gram dhal was observed during 5–15 min of soaking, a gradual increase up to 90 min and a marginal increase beyond this period. Apparent viscosity of batter showed 100% increase up to 90 min and less than 20% increase beyond 120 min, and shear‐thinning nature of batter indicated that they were pseudo‐plastic in nature. Yield stress and consistency index showed greater changes after 90 min, while flow behaviour index did not show significant change beyond 90 min of soaking. Compared with the addition of native rice flour, incorporation of flaked rice flour and expanded rice flour into black gram batter significantly increased the cold paste viscosity of the batter, probably because of their greater water‐holding capacity, compared with that from native rice. Differences in physicochemical characteristics and pasting behaviour of these flour slurries, as studied by Rapid Visco Analyser, corroborated these results by the typical profile of pregelatinised products for flaked rice and expanded rice in comparison to native rice.     

Preparation,characterization and thermolysis of nitrate and perchlorate salts of 2,4,6-trimethylaniline

Nitrate and perchlorate salts of 2,4,6-trimethylaniline have been prepared and characterized by X-ray crystallography and gravimetric analyses. Their thermal decomposition has been studied by TG, TG–DSC and ignition/explosion delays. It has been observed that proton transfer from substituted anilinium ion to nitrate and perchlorate ion regenerate amine, HNO₃ and HClO₄ in condensed phase at higher temperature, where oxidation–reduction between amine and acids leads to ignition and explosion. The kinetics of thermal decomposition was evaluated by applying model fitting as well as isoconversional methods. The values of calculated activation energy of nitrate and perchlorate salts are 77.9 and 118.2 kJ mol^?1 respectively. The possible pathways of thermolysis of these salts have also been proposed.     

Influence of cure via network structure on mechanical properties of a free-radical polymerizing thermoset

An improved understanding has been achieved regarding the relationships among cure chemistry, network structure, and final physical properties of vinyl ester (VE) resins, a thermoset polymer often used as the matrix of fiber reinforced polymers. Mechanical properties of the polymer are found to depend on both cure schedule and cure formulation. The possibilities of phase separation and micro-gel formation being the cause for these differences in mechanical properties are examined. The VE/styrene (S) system does not phase separate under the conditions studied. Though bulk properties of the resin are unaffected by the details of the cure, the microscopic morphology, in particular the type of cross-link formed (intermolecular bond or intramolecular bond), is sensitive to both cure temperature and initiation mechanism as determined by cure formulation. An analysis of cure kinetics shows that both temperature and initiation mechanism affect the apparent ‘reaction order’ of the VE/S system as determined by the autocatalytic equation. This apparent reaction order is interpreted as being an indication of the degree of heterogeneity in the resin. By controlling cure temperature and cure formulation, it is possible to minimize the apparent reaction order and thereby optimize physical properties. Finally, a theory is adapted from other non-network polymer systems to qualitatively describe how cure temperature and initiation mechanism may alter the heterogeneity in network structure via micro-gel formation and how these changes in structure affect changes in the mechanical properties.     

Performance of suspended flat plate air heater

In this communication, a heat transfer model to predict the transient behaviour of a suspended flat plate solar collector with constant flow of fluid (air) above the absorber has been presented. A reflecting sheet with an air gap between the absorber plate and bottom insulation to reduce heat loss has been used. The effect, on performance of the air heater, of the parameters viz, spacing between cover and plate, heat capacity of air and absorber plate, flow rate of fluid and collector length have been studied. The effect of changing the averaging inlet temperature with varying collector length has also been studied.