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The power demand in the whole of Asia is expected to rise tremendously in the next two decades. If the Region's economic growth is to continue, the Asian Development Bank [...]

Abstract: The synthesis of titania membrane through sol-gel route involves hydrolysis of alkoxide peptization of hydrous oxide of titanium to obtain a sol, adjustment of the sol viscosity by including a binder and filtration of the viscous sol through a microporous support, gelation and sintering to desired temperature. The binder plays an important role in that it not only helps in adjustment of sol viscosity but also helps in binding the sol particle with porous support. Here a comparative study on the role of different binders, viz. polyvinyl alcohol, polyethyleneimine, polyacrylamide, effect of their viscosity and surface tension effect on the morphology of the titania membrane is presented. The results show that among the three binders studied polyvinyl alcohol gave rise to membranes of desired characteristics when the sol viscosity was 0.08 pa.s.

The Markstein number characterizes the effect that flame stretch has on the burning velocity. Different expressions for this number are deduced from integral analysis. According to a phenomenological law, the Markstein number can be separated into a part for the curvature of the flame and a part for the straining of the flow. This separation is analysed here. It appears that the Markstein number for curvature and the combined one for both curvature and strain are unique. It is, however, not possible to introduce a separate and unique Markstein number for the flow straining that can be used to describe its influence in different combustion situations. The theoretical and numerical analysis is applied to flat steady counterflow flames as well as to steady, imploding and expanding spherical flames.

We show how the modification by Henry et al. of the earlier van der Waals−Plateeuw thermodynamic model can be used to interpret data for hydrates in small pores even when there is a broad distribution of pore sizes. Pore size distribution effects explain the previously reported discrepancy between calculated and measured equilibrium pressures for nominal 7.5 nm radius pores. On the basis of the model, pore volume distributions are reconstructed for the silica gel samples in which the hydrates were formed and compared with distributions constructed from desorption isotherms. The excellent agreement between the calculations and experimental data supports the interpretation of how the pore size distribution present in the silica gel samples affects the observed equilibrium pressures.

The asymptotic structure of weakly strained moderately rich premixed methane-air flames stabilized in stagnation-point flows is analysed. In the asymptotic analysis the influence of strain on the mass flux, on the temperature and on the concentration of chemical species in the flame is treated as a perturbation from their values in the corresponding unstrained flame. Perturbation analysis is carried out to the first order. The deviation of the mass burning rate in the strained flame from the mass burning rate in the corresponding unstrained flame is obtained in terms of the Markstein number. Chemical reactions taking place in the flame are described by a reduced chemical-kinetic mechanism made up of four global steps. The analysis gives a sufficient number of equations from which the Markstein numbers can be calculated. Numerical calculations are performed using a chemical-kinetic mechanism made up of elementary reactions. Markstein numbers are obtained and they are found to agree reasonably well with those calculated using the results of an asymptotic analysis. Markstein numbers are also found to agree reasonably well with those deduced from experiments. An interesting finding of the present study is that the Markstein number for moderately rich flames depends on the Lewis number of both fuel and oxygen.

Equilibrium pressures for the dissociation of propane hydrate confined in silica gel pores of nominal radii 7.5, 5.0, 3.0, and, 2.0 nm were measured across a wide temperature range, and were higher than those for bulk propane hydrate. The upward shift from the bulk pressures, which depended on the pore size, was 200−300% for the smallest pore size. In each of the pressure−temperature profiles, the temperature at which the four phases (hydrate, ice, liquid water, and gas) apparently coexisted was identified, and this temperature was a linear function of the reciprocal pore size. The enthalpy of dissociation for the equilibrium involving hydrate, liquid water, and gas was estimated from the data. The change with pore size in this apparent enthalpy appeared to be analogous to the variation in the heat of melting of pore ice as sometimes reported.

Self-assembled monolayer films of a metallotetraazaphthalocyanine were prepared using two different reaction conditions. The films were characterized by ellipsometry, AFM, electronic absorption spectroscopy, semiempirical MO calculations, core-level XPS, and projection of a calculated structure of the chromophore onto a surface to obtain its silhouette area for comparison with surface concentration from absorption spectroscopy. A denser packing of the chromophores is found in the SAM film prepared with bromonaphthalene at 250 °C as compared with the film from the more polar solvent DMF at 120 °C. Data is consistent with an almost vertical orientation of the chromophores in the former film. A different number of bonds connecting the chromophore with the coupling molecule is suggested as an explanation to differences in the absorption bands for the two films.

Using electrochemical and chemical probes, we demonstrate that thin films of crystalline polymethylene (PM), formed via solution decomposition of diazomethane on gold surfaces, exist in the form of a heterogeneous distribution with microscopically small pores at low average PM coverages. For evaporated gold substrates, as the PM loading increases above ~0.8 μg·cm^-2, a mass density equivalent to an ~7 nm thick, fully dense planar film, a transition from a micropore to a blocked electrode occurs. This microstructural picture is confirmed by the ability to backfill open areas with alkanethiolates and electropolymerized aniline. Parallel experiments on sputter-deposited gold films show that the blocking threshold occurs at much lower average PM coverages and alkanethiolate chemisorption data suggest that the open pores are approaching the sizes of individual molecules. These results can be rationalized by a more uniform nucleation of PM nanocrystals across sputter-deposited relative to evaporated surfaces. This ability to regulate the conformal deposition of an inert, low dielectric material at the nanometer scale on gold surfaces offers a new way to engineer electrodes with controlled, micropore dielectric barrier structures and “quasi-two-dimensional” nanocomposite films.

This paper describes our recent research on vapor and particle deposition rate processes in combustion systems. Inorganic compounds which deposit on heat exchanger surfaces and gas turbine blades are formed when the fuel and/or ingested air contain inorganic impurities. A quantitative understanding of the deposition rate of inorganic oxides, salts or soot can suggest efficient test/control strategies. Accordingly, we have developed optical methods for precise, real-time measurements of the growth rate of deposits under laboratory conditions. To demonstrate these techniques, and provide data for theory development, a deliberately simple chemical system and target geometry are described; viz. BCl3(g) is added to a premixed C3H8-air flat flame and the B2O3(l) deposition rate on an electrically heated Pt ribbon is measured interferometrically or ellipsometrically over a range of fuel/air ratios and seed levels. The stability of B2O3(l) at present seed levels and surface temperatures (ca. 1200–1300 K) reveals kinetic restrictions on B2O3(l) gasification reactions. Measured deposition rates agree with predictions of our multicomponent mass-transfer boundary layer (BL) theory, with a constrained equilibrium ((HBO2)3precluded) boundary condition. These encouraging results suggest a more general applicability for the optical methods and BL theory outlined herein, and demonstrate the role of heterogeneous kinetic barriers in determining dew points and deposition rates in combustion systems.

Simplified chemical-kinetic mechanisms were employed to calculate the structure of the dark zone formed over the burning surface of double base and nitramine propellants. It is believed that ignition delays in large-caliber-gun ballistie cycles are related to the chemistry taking place in the dark zone. Skeletal chemical-kinetic mechanisms comprising 22 elementary reactions among 15 species and 23 elementary reactions among 17 species were used to calculate the structure of the dark zone of double base and nitramine propellants, respectively. These skeletal chemical-kinetic mechanisms were previously extracted from a detailed chemical-kinetic mechanism incorporating 190 elementary reactions involving 41 species. Ignition-delay times are calculated using these mechanisms in homogeneous mixtures in which the initial concentrations of various reactants are similar to those found at the beginning of the dark zones of double base and nitramine propellants. These calculations were performed for various initial pressures and temperatures. The ignition-delay times calculated using the skeletal chemical-kinetic mechanisms are found to agree reasonably well with those calculated using the detailed chemical-kinetic mechanism. Reduced chemical-kinetic mechanisms were derived from the skeletal mechanisms by introducing steady-state approximations for a number of species. For double base propellants, a reduced mechanism of three global reactions is obtained. Reduced mechanisms using six and four global reactions are deduced for nitramine propellants. The ignition-delay times and structures of the dark zones calculated using the reduced three-step mechanism for double base propellants and six-step mechanism for nitramine propellants are in agreement with calculations made using the skeletal mechanisms. The ignition-delay times calculated using the four-step reduced mechanism for nitramine propellants are found to be significantly smaller than those calculated using the skeletal mechanism. The reduced chemical-kinetic mechanisms are expected to be useful in interior ballistics calculations.

Abstract: Reciprocal salt-pair system 2KC1 + MgSO4 ⇌ K2SO4 + MgCl2 has been studied at 35° C to eliminate the discrepancies reported by different workers and for correlating the experimental data with natural evaporation of brine (without NaCl) so as to recover potash salts.

A distillation fraction of a coal-derived liquid (tar) was cracked over a char−dolomite mixture, calcined dolomite, and silicon carbide in a fixed-bed reactor. The char−dolomite mixture (FWC) was produced from Pittsburgh No. 8 coal and dolomite in a Foster Wheeler carbonizer. The experiments were conducted under nitrogen and simulated coal gas (SCG), which was a mixture of CO, CO2, H2S, CH4, N2, and steam, at 1 and 17 atm. The conversion over these materials under nitrogen was much higher at 17 atm than at 1 atm. At higher pressures, tar molecules were trapped in the pores of the bed material and underwent secondary reactions, resulting in the formation of excess char. However, when nitrogen was replaced by SCG, the reactions that induce char formation were suppressed, thus increasing the yield of gaseous products. The analysis of the gaseous products and the spent bed materials for organic and inorganic carbons suggested that the product distribution can be altered by changing the carrier gas, temperature, and pressure.

Results of experimental and numerical studies of counterflow, partially premixed, flames burning methane in air are reported. Experimental data is obtained for the temperature profile, the axial velocity profile, the concentration profiles of various stable species and the critical conditions of the flame at extinction. The results are compared with numerical calculations performed at conditions identical to those used in the experiment. Experimental measurements and numerical calculations show that partial premixing of the reactant streams of a counterflow diffusion flame makes the flame less resistant to stretch. In addition, numerical calculations show that the reaction zone of a partially premixed flame exhibits a diffusion flame and a premixed flame-like structure. Both results are consistent with previous asymptotic analyses of the structure of partially premixed flames.

Molecular constraints for the localization of active site directed ligands (competitive inhibitors and substrates) in the active site of phospholipase A2 (PLA2) are characterized. Structure activity relationships with known inhibitors suggest that the head group interactions dominate the selectivity as well as a substantial part of the affinity. Theab initiofitting of the amide ligands in the active site was carried out to characterize the head group interactions. Based on a systematic coordinate space search, formamide is docked with known experimental constraints such as coordination of the carbonyl group to Ca2+and hydrogen bond between amide nitrogen and ND1 of His48. An optimal position for a bound water molecule is identified and its significance for the catalytic mechanism is postulated. Unlike the traditional “pseudo-triad” mechanism, the “Ca-coordinated-oxyanion” mechanism proposed here invokes activation of the catalytic water to form the oxyanion in the coordination sphere of calcium. As it attacks the carbonyl carbon of the ester, a near-tetrahedral intermediate is formed. As the second proton of the catalytic water is abstracted by the ester oxygen, its reorientation and simultaneous cleavage form hydrogen bond with ND1 of His48. In this mechanism of esterolysis, a catalytic role for the water co-ordinated to Ca2+is recognised.

Reciprocal salt-pair system 2KC1 + MgSO4⇌ K2SO4+ MgCl2has been studied at 35° C to eliminate the discrepancies reported by different workers and for correlating the experimental data with natural evaporation of brine (without NaCl) so as to recover potash salts.

AbstractIn the past two decades RNase A has been the focus of diverse investigations in order to understand the nature of substrate binding and to know the mechanism of enzyme action. Although this system is reasonably well characterized from the view point of some of the binding sites, the details of interactions in the second base binding (B2) site is insufficient. Further, the nature of ligand-protein interaction is elucidated generally by studies on RNase A-substrate analog complexes (mainly with the help of X-ray crystallography). Hence, the details of interactions at atomic level arising due to substrates are inferred indirectly. In the present paper, the dinucleotide substrate UpA is fitted into the active site of RNase A Several possible substrate conformations are investigated and the binding modes have been selected based on Contact Criteria. Thus identified RNase A-UpA complexes are energy minimized in coordinate space and are analysed in terms of conformations, energetics and interactions. The best possible ligand conformations for binding to RNase A are identified by experimentally known interactions and by the energetics. Upon binding of UpA to RNase A the changes associated with protein back bone, side chains in general and at the binding sites in particular are described. Further, the detailed interactions between UpA and RNase A are characterized in terms of hydrogen bonds and energetics. An extensive study has helped in interpreting the diverse results obtained from a number of experiments and also in evaluating the extent of changes the protein and the substrate undergo in order to maximize their interactions.

Abstract2′,3′-cyclic nucleotides are intermediates and substrates of Ribonuclease (RNase)-catalysed reactions. The characterization of the equilibrium conformation as well as the flexibility inherent in these molecules helps in understanding the enzymatic action of RNases. The present study explores parameters like phase angle, glycosydic torsion angle and hydrogen bond to find possible interrelationship between them through Molecular Dynamics (MD) simulations on 3′-GMP, 3′-UMP, A>p, G>p, U>p, C>p, GpA>p and UpA>p. Interesting results of the effect of cyclisation and other constraints such as hydrogen bond between certain groups on the equilibrium ribose conformation have emerged from this study.

AbstractDifferent modes of binding of pyrimidine monophosphates 2′–UMP, 3′–UMP, 2′-CMP and 3′-CMP to ribonuclease (RNase) A are studied by energy minimization in torsion angle and subsequently in Cartesian coordinate space. The results are analysed in the light of primary binding sites. The hydrogen bonding pattern brings out roles for amino acids such as Asn44 and Ser123 apart from the well known active site residues viz., His 12, Lys41, Thr45 and His1 19. Amino acid segments 43–45 and 119–121 seem to be guiding the ligand binding by forming a pocket. Many of the active site charged residues display considerable movement upon nucleotide binding.

This is a report on the use of 13C NMR spectroscopy to study the structure of polyethylenes, polyethylene-olefin copolymers, and polyethylene model systems, through the observation of chemical shifts and spin-lattice relaxation times of individual carbons. Information is obtained on the type and numbers of side chains of polyethylenes from solution spectra at higher temperatures. The level of detectability of side chains is established at 2 side chain carbons per 1000 skeletal carbons. The observed chemical shifts are accounted for well by standard additivity schemes. The low-density polyethylenes show spectra which are distinctly differentfrom high-density polyethylenes. The 13C-determined branch frequencies show the same general trend as the IR results, but it is also argued that the former are more accurate. Relaxation times of the various carbons of the model system C44paraffin vary from 2.94 s for the backbone methylenes to 8.33 s for the terminal methyls to 11.11 s for α-methyls. Indicative of the behavior of olefin/polyethylene copolymers is the finding that all carbons of the copolymer have spin-lattice relaxation times of about 1.5 s, except for branch methyls which are 6 s. A series of polyethylenes at this high temperature shows relaxation times for the backbone methylene varying from 1.4 to 1.7 s, indicating that at this temperature, branching does not substantially affect the dynamic behavior of polyethylene.

Nuclear divisions taking place in the hyphae ofPythium aphanidermatum have been described. Typical prophase type of nuclei with elongate chromatin fibres have been observed. Achromatic structures resembling spindle fibres with well defined poles during anaphase configuration have been noticed. A mild pretreatment with acenaphthene vapours proved instrumental in arresting the progress of nuclear division. Stages similar to early and late anaphase and telophase with deeply staining chromosomal masses have been observed. A high concentration of acenaphthene treatment resulted in the formation of giant nuclei.