Monte Carlo and molecular dynamics simulation of argon clusters andn-alkanes in the confined regions of zeolites

Geometry and energy of argon clusters confined in zeolite NaCaA are compared with those of free clusters. Results indicate the possible existence of magic numbers among the confined clusters. Spectra obtained from instantaneous normal mode analysis of free and confined clusters give a larger percentage of imaginary frequencies for the latter indicating that the confined cluster atoms populate the saddle points of the potential energy surface significantly. The variation of the percentage of imaginary frequencies with temperature during melting is akin to the variation of other properties. It is shown that confined clusters might exhibit inverse surface melting, unlike medium-to-large-sized free clusters that exhibit surface melting. Configurational-bias Monte Carlo (CBMC) simulations ofn-alkanes in zeolites Y and A are reported. CBMC method gives reliable estimates of the properties relating to the conformation of molecules. Changes in the conformational properties ofn-butane and other longern-alkanes such asn-hexane andn-heptane when they are confined in different zeolites are presented. The changes in the conformational properties ofn-butane andn-hexane with temperature and concentration is discussed. In general, in zeolite Y as well as A, there is significant enhancement of thegauche population as compared to the pure unconfined fluid. Contribution No. 1260 from the Solid State and Structural Chemistry Unit     

Joining of Carbon-Carbon Composites by Graphite Formation

Joining of carbon-carbon (C-C) composites by graphite formation, using manganese, magnesium, and aluminum interlayers, has been investigated. The process involved the formation of a metal carbide by chemical reaction between the metal interlayer and the composite, followed by the decomposition of the carbide and evaporation of the metal at elevated temperatures. The maximum bonding temperature in these experiments was 2200°C. Bonding of composite specimens occurred when manganese or a powder mixture of aluminum and graphite was used as interlayers. Attempts to join C-C pieces using a magnesium interlayer were unsuccessful. The double notch shear strengths of the joints produced using Mn interlayers were very low and ranged from 0.15 to 1.61 MPa at test temperatures of 1200° and 1400°C. The interlayer, after completion of the joining operation, consisted, in most cases, only of graphite. The joints produced with aluminum plus graphite interlayers were even weaker, with strength values of 0.11 MPa or less. The presence of aluminum could be detected in some of these joints, suggesting incomplete dissociation of Al₄C₃ at the maximum bonding temperature of 2150°C.     

Studies on thermal stability and behaviour of polyacetal and thermoplastic polyurethane elastomer blends

The influence of thermoplastic polyurethane (TPU) elastomer on the rigidity of polyacetal (polyoxymethylene, POM) was studied by determining heat deflection temperature (HDT). The higher the content of TPU in the POM/TPU blend, the lower the HDT of the blend, as would be expected. A comparative study of the recycle capability of POM and the blends was carried out by measuring melt flow index (MFI) on each successive extrusion. Stress-strain behaviour of the virgin material and that obtained after fourth-time extrusion was analysed for POM and the blends. The effect of γ-radiation on the mechanical behaviour of the blends was investigated. The kinetics of thermal degradation of POM, TPU and their blends was studied. The kinetic parameters, viz. activation energy and the order of reaction, were established. The values of the activation energy of the blends were found to be higher than those of the POM and TPU, indicating improved stability of the resultant blends.     

Chemomechanical transduction in the actomyosin molecular motor by 2',3'-dideoxydidehydro-ATP and characterization of its interaction with myosin subfragment 1 in the presence and absence of actin

The effect of torsional freedom about the N-glycoside bond of ATP in the ability of the nucleoside triphosphate to support chemomechanical transduction (Takenaka et al., 1978) has been investigated by examining the ability of the nucleotide analogue 2',3'-dideoxy-2',3'-didehydro-ATP (1b, enf-ATP) to act as a substrate for myosin subfragment 1 in the presence and absence of actin and to support actin sliding in the standard in vitro motility assay. By converting the ribosyl ring of the natural substrate to the rigid and almost planar enofuranosyl ring, effects on torsional freedom about the N-glycoside bond due to changes in ribosyl ring pucker and/or by steric interferences of the protons attached to the 2' and 3' carbons are eliminated allowing for increased torsional freedom about the N-glycoside bond. The data indicate that this enofuranosyl analogue is an excellent substrate for subfragment 1 and actosubfragment 1 and produces actin sliding velocities which are twice as fast as those observed with ATP in the standard in vitro motility assay. The analogue diphosphate is trapped in S1 by the common P(i) analogues, but the rate of formation of the ternary complex formed with Vi is very slow compared to that observed with MgADP. Similar conformations of S1 are formed with Mg.enf-ATP and MgATP under steady-state conditions, but S1 with bound Mg.enf-ADP differs significantly from that observed with MgADP.     

Suspension Dry Spinning and Rheological Behavior of Ceramic-Powder-Loaded Polymer Solutions

Green ceramic fibers of Al₂O₃, Si₃N₄, Ce-ZrO₂, and SiC were prepared by suspension dry spinning of powderloaded polymer solutions. The fiber-forming polymer was ethyl methacrylate dissolved in methyl ethyl ketone. The experimental conditions for fiber formation were defined for the alumina system. Thread lengths measured as a function of extrusion rate showed a transition from capillary-limited fracture to continuous fibers in agreement with Ziabicki's theory of thread formation. The conditions for spinnability were correlated to rheological parameters. Spinnable Al₂O₃ dopes were elastic fluids with a high viscosity (60 Pa·s at 0.46 s⁻¹) under the conditions of this study.     

Promoting effect of CeO<Subscript>2</Subscript> on cyclohexanol conversion over CeO<Subscript>2</Subscript>-ZnO mixed oxide materials prepared by amorphous citrate process

CeO₂-ZnO materials were prepared by amorphous citrate process and characterized by TGA, XRD, UV-DRS and surface area measurements. TGA showed that the citrate precursors decompose in the range 350–550°C producing CeO₂-containing catalytic materials. XRD and DRS results indicated the formation of well-dispersed interstitialZn _xCe⁴⁺ _1−2x Ce³⁺ _2x O₂ solid solution on ZnO matrix. Addition of CeO₂ to ZnO produced high surface area mixed oxide materials in citrate method. Cyclohexanol conversion reaction was carried out on these catalytic materials to investigate the effect of rare earth oxide on the activity and selectivity. It was found that CeO₂ promotes the activity of ZnO without affecting the selectivity to cyclohexanone significantly. The factors such as reaction temperature and WHSV have turned out to be important for cyclohexanol conversion over CeO₂-containing ZnO catalyst materials.     

A selective diffraction order based lens plane grating shearing interferometer for the study of bent plates

A simple, elegant and flexible technique for the determination of partial slope, curvature and twist contours of bent plates is proposed. A single frequency cross-grating (SFCG) placed just ahead of the field lens collects the light reflected by the smooth plate model. From the resultant diffraction pattern formed at the Fourier transform (FT) plane, based on the desired contours, only a few orders are permitted selectively to pass through to the recording plane. This manner of real time in-situ filtering of the diffraction orders is new. While slope contours require double exposures, curvature and twist contours are obtained from single exposures.     

Multiple online auctions

Considers how the rapid transition of trade to the Internet raises critical questions about how well the time-honored methodologies, strategies, and processes that buyers and sellers use translate to the online world. Do Internet consumers effectively evaluate all available options? How do their decisions translate to seller profits? Determining whether consumer participation in multiple auctions yields optimal results offers one benchmark for evaluating the overall benefits of e-commerce.     

Potential probiotic lactic acid bacteria Lactobacillus rhamnosus (HN001), Lactobacillus acidophilus (HN017) and Bifidobacterium lactis (HN019) do not degrade gastric mucin in vitro

The mucus layer (mucin) coating the surface of the gastrointestinal tract (GIT) plays an important role in the mucosal barrier system. Any damage or disturbance of this mucin layer will compromise the host's mucosal defence function. In the present study, the ability of three potential probiotic lactic acid bacteria (LAB) strains (Lactobacillus rhamnosus HN001, Lactobacillus acidophilus HN017, Bifidobacterium lactis HN019) to degrade mucin in vitro was evaluated, in order to assess their potential pathogenicity and local toxicity. The LAB strains were incubated in medium containing hog gastric mucin (HGM, 0.3%) at 37 degrees C for 48 h, following which any decrease in carbohydrate and protein concentration in the ethanol-precipitated portion of the culture medium was determined, using phenol-sulphuric acid and bicinchonic acid (BCA) protein assays, respectively. The change in molecular weight of mucin glycoproteins, following incubation with the test strains, was monitored by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). In order to expose any ability of the test strains to degrade mucin visually and more directly, the test strains were also cultured on agarose containing 0.3% HGM and incubated anaerobically for 72 h at 37 degrees C. No significant change in the carbohydrate or protein concentration in mucin substrates was found following incubation with the test strains. No mucin fragments were derived from the mucin suspension incubated with test strains, and no mucinolysis zone was identified on agarose. These results demonstrate that the potential probiotic LAB strains tested here were unable to degrade gastrointestinal mucin in vitro, which suggests that these novel probiotic candidates are likely to be non-invasive and non-toxic at the mucosal interface.