Twin roller quenching technique and preparation of glasses of high melting ionic solids

A rapid quenching technique with a quenching rate of roughly 106°C/sec has been developed to prepare glassy samples of ABO3 type materials. Glasses of potassium lithium niobate have been prepared by this technique. These glasses have been characterized by x-ray diffraction, electron diffraction and differential scanning calorimetry techniques to assess the quality of the obtained glasses.

Regression Rate Studies in Hypergolic System

Regression ra tes of a hypergolic combination of fuel and oxidiser have been experimentally measured as a function of chamber pressure, mass flux and the percentage component of the hypergolic compound in natural rubber. The hypergolic compound used is difurfurylidene cyclohexanone (DFCH) which is hypergolic with the oxidiser red fuming nitric acid (RFNA) with ignition dela y of 60-70 ms. The data of weight loss versus time is obtained for burn times varying between 5 and 20 seconds. Two methods of correlating the data using mass flux of oxidiser and the total flux of hot gases have shown that index n of the regression law r=aGoxn or r=aGnxn-1 (x the axial distance) is about 0.5 or a little lower and not 0.8 even though the flow through the port is turbulent. It is argued that the reduction of index n is due to heterogeneous reaction between the liquid oxidiser and the hypergolic fuel component on the surface.

Crystallography of solid-liquid interface and evolution of texture during directional solidification of Tb0.3Dy0.7Fe1.95 alloy

The effect of growth texture on the magnetostriction of ternary Tb0.3Dy0.7Fe1.95 was studied by conducting unidirectional solidification experiments using a zoning set-up. Detailed texture evolutions were studied using X-ray diffraction on samples obtained by varying growth rates from 18 to 72 cm/h, under a temperature gradient of 100 degrees C/cm. The estimated texture co-efficient and pole figures of the samples indicate that during the onset of the solidification, < 110 > and < 331 >/'rotated < 110 >' texture components nucleate and grow in all the samples. However, as the solidification progresses, < 112 > texture component becomes dominant at higher growth rate. This results in an improvement of magnetostriction from 1000 to 1300 microstrains for samples grown at growth rates of 18 and 72 cm/h respectively. The transition of preferred growth direction occurs through intermediate orientations < 123 >. An attempt has been made in this paper to explain the occurrence of different growth texture by considering the stability of growing interface, its planar packing fraction and atomic stacking sequence of several low index planes. (C) 2010 Elsevier Ltd. All rights reserved.

Simulation of Influence of Bilayer Melting on Dynamics and Thermodynamics of Interfacial Water

We investigate the effect of bilayer melting transition on thermodynamics and dynamics of interfacial water using molecular dynamics simulation with the two-phase thermodynamic model. We show that the diffusivity of interface water depicts a dynamic crossover at the chain melting transition following an Arrhenius behavior until the transition temperature. The corresponding change in the diffusion coefficient from the bulk to the interface water is comparable with experimental observations found recently for water near 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles Phys. Chem. Chem. Phys. 13, 7732 (2011)]. The entropy and potential energy of interfacial water show distinct changes at the bilayer melting transition, indicating a strong correlation in the thermodynamic state of water and the accompanying first-order phase transition of the bilayer membrane. DOI: 10.1103/PhysRevLett.110.018303

Influence of clofibrate administration on the rate of synthesis of macromolecules in regenerating rat liver

Administration of the antihypercholesterolaemic drug clofibrate stimulates the rates of synthesis of nucleic acids and proteins in rat liver. The biosynthesis of mitochondrial proteins also is enhanced by the drug. In drug-fed animals, the rates of incorporation in vivo of radioactive precursors into DNA, RNA and proteins are stimulated even when the liver undergoes regeneration following partial hepatectomy. The rate of synthesis of mitochondrial proteins in the regenerative phase is higher in clofibrate-fed animals. These effects are consistent with the hepatomegalic and mitochondria-proliferating property of the drug.

Structural effects of a dimer interface mutation on catalytic activity of triosephosphate isomerase.The role of conserved residues and complementary mutations

The active site of triosephosphate isomerase (TIM, EC: 5.3.1.1), a dimeric enzyme, lies very close to the subunit interface. Attempts to engineer monomeric enzymes have yielded well-folded proteins with dramatically reduced activity. The role of dimer interface residues in the stability and activity of the Plasmodium falciparum enzyme, PfTIM, has been probed by analysis of mutational effects at residue 74. The PfTIM triple mutant W11F/W168F/Y74W (Y74W*) has been shown to dissociate at low protein concentrations, and exhibits considerably reduced stability in the presence of denaturants, urea and guanidinium chloride. The Y74W* mutant exhibits concentration-dependent activity, with an approximately 22-fold enhancement of kcat over a concentration range of 2.5–40 μm, suggesting that dimerization is obligatory for enzyme activity. The Y74W* mutant shows an approximately 20-fold reduction in activity compared to the control enzyme (PfTIM WT*, W11F/W168F). Careful inspection of the available crystal structures of the enzyme, together with 412 unique protein sequences, revealed the importance of conserved residues in the vicinity of the active site that serve to position the functional K12 residue. The network of key interactions spans the interacting subunits. The Y74W* mutation can perturb orientations of the active site residues, due to steric clashes with proximal aromatic residues in PfTIM. The available crystal structures of the enzyme from Giardia lamblia, which contains a Trp residue at the structurally equivalent position, establishes the need for complementary mutations and maintenance of weak interactions in order to accommodate the bulky side chain and preserve active site integrity.

Biochemical and structural characterization of residue 96 mutants of Plasmodium falciparum triosephosphate isomerase: active-site loop conformation, hydration and identification of a dimer-interface ligand-binding site

Plasmodium falciparum TIM (PfTIM) is unique in possessing a Phe residue at position 96 in place of the conserved Ser that is found in TIMs from the majority of other organisms. In order to probe the role of residue 96, three PfTIM mutants, F96S, F96H and F96W, have been biochemically and structurally characterized. The three mutants exhibited reduced catalytic efficiency and a decrease in substrate-binding affinity, with the most pronounced effects being observed for F96S and F96H. The k(cat) values and K-m values are (2.54 +/- 0.19) x 10(5) min(-1) and 0.39 +/- 0.049 mM, respectively, for the wild type; (3.72 +/- 0.28) x 10(3) min(-1) and 2.18 +/- 0.028 mM, respectively, for the F96S mutant;(1.11 +/- 0.03) x 10(4) min(-1) and 2.62 +/- 0.042 mM, respectively, for the F96H mutant; and (1.48 +/- 0.05) x 10(5) min(-1) and 1.20 +/- 0.056 mM, respectively, for the F96W mutant. Unliganded and 3-phosphoglycerate (3PG) complexed structures are reported for the wild-type enzyme and the mutants. The ligand binds to the active sites of the wild-type enzyme (wtPfTIM) and the F96W mutant, with a loop-open state in the former and both open and closed states in the latter. In contrast, no density for the ligand could be detected at the active sites of the F96S and F96H mutants under identical conditions. The decrease in ligand affinity could be a consequence of differences in the water network connecting residue 96 to Ser73 in the vicinity of the active site. Soaking of crystals of wtPfTIM and the F96S and F96H mutants resulted in the binding of 3PG at a dimer-interface site. In addition, loop closure at the liganded active site was observed for wtPfTIM. The dimer-interface site in PfTIM shows strong electrostatic anchoring of the phosphate group involving the Arg98 and Lys112 residues of PfTIM.

Influence of Lithium Fluoride on the Burning Rate of AP-Polyester Propellant

THE addition of catalysts normally serves the purpose of imparting a desired burning rate change in a composite propellant. These may either retard or enhance the burning rate. Some often quoted catalysts are oxides, chromites and chromates of metals. A lot of work has been done on rinding the effect of the addition of some of these catalysts on the burning rate; however, none seems to have appeared on the influence of lithium fluoride (LiF). Only qualitative reduction in the burning rate of composite propellants with the addition of LiF was reported by Williams et al.1 Dickinson and Jackson2 reported a slight decrease in the specific impulse of composite propellant with the addition of LiF; however, they made no mention of the effect of its addition on the burning rate. We have studied the effect of the addition of varying amounts of LiF on the burning rate of Ammonium Perchlorate (AP)-Polyester propellant.

Rate of ribonucleic acid chain growth in Mycobacterium tuberculosis H37Rv.

Two methods were employed to measure the rate of ribonucleic acid (RNA) chain growth in vivo in Mycobacterium tuberculosis H37Rv cultures growing in Sauton medium at 37 degrees C, with a generation time of 10 h. In the first, the bacteria were allowed to assimilate [3H]uracil or [3H]guanine into their RNA for short time periods. The RNA was then extracted and hydrolyzed with alkali, and the radioactivity in the resulting nucleotides and nucleosides was measured. The data obtained by this method allowed the calculation of the individual nucleotide step times during the growth of RNA chains, from which the average rate of RNA chain elongation was estimated to be about 4 nucleotides per s. The second method employed the antibiotic rifampin, which specifically inhibits the initiation of RNA synthesis without interfering with the elongation and completion of nascent RNA chains. Usint this method, the transcription time of the 16S, 23S, and 5S ribosomal RNA genes was estimated to be 7.6 min, which corresponds to a ribosomal RNA chain growth rate of 10 nucleotides per s.

The effect of lecithin on the burning rate of AP-Al---polyester propellant

Abstract is not available.

In situ cryocrystallization of low melting chloro and bromo substituted anilines

In situ cryocrystallographic Studies of chloro and bromo substituted anilines have been performed to evaluate the role of halogen...halogen interactions and the subsequent formation of supramolecular assemblies in the solid state. Ortho Cl/Br substituted anilines are isostructural and belong to the trigonal P3(1) space group. Halogen...halogen intermolecular contacts along with stronger N-H center dot center dot center dot N hydrogen bonds generate helical motifs along the crystallographic c-axis. (C) 2009 Elsevier B.V. All rights reserved.