Tuning of crystal phase structure in hydrated WO3 nanoparticles under wet chemical conditions and studies on their photochromic properties

Hydrated tungsten oxide nanoparticles have been synthesized using a simple wet chemical method while varying the concentration of HCl. XRD studies show that the variation in HCl concentration from 1 M to 6 M in the reaction results into gradual change in crystal structure of hydrated WO₃ from hexagonal (WO₃·0.33H₂O) to pure orthorhombic (WO₃·H₂O), through a series of samples with mixed phase of the two indifferent ratios. The similar variations in the degree of hydration and phase variations have also been observed from Raman, FTIR and TGA studies. The average crystallite size of the hydrated WO₃ particles was estimated to be ～26 nm from XRD line broadening and AFM studies showed the formation of spherical shaped particles for all the samples. The photochromic studies were carried out on the composite films of these materials in the polymeric matrix of polyvinyl alcohol (PVA) while exposing to UV light. The composite films show interesting variations in the photochromic behavior depending on the crystal structure of hydrated WO₃ filler. The photochromic behavior has been explained on the basis of EPR spectra of hydrated WO₃.     

The dynamics of copolymers in homopolymer matrices

The ability of a polymer chain to relax when it is deformed, and the ease to which this relaxation occurs, dramatically influences the macroscopic properties of the polymeric material. However, the local segmental relaxation processes in multi-component polymer systems are not well understood. The impact of the dynamics of one component on the dynamics of the other is not simply proportional to the relative amounts of each component, as one might expect. This paper discusses recent results using neutron techniques and Monte Carlo simulation that monitor the dynamic properties of a copolymer in a homopolymer matrix. In particular, the results indicate that altering either copolymer sequence distribution or copolymer composition will dramatically impact the dynamics of the copolymer that is surrounded by homopolymers. These results provide important fundamental information on the coupling of the dynamics of two components in a multi-component polymer system. This data also offer insight into the local segmental relaxation processes in multi-component polymer systems, which are not well understood and yet influence the ultimate properties of these mixtures     

Very Strong Inhibition of Glucosidases by C(2)‐Substituted Tetrahydroimidazopyridines

The C(2)‐substituted imidazoles 11 , 15 – 17 , 19 , 21 , 23 / 24 , 28 – 31 , 37 , and 38 have been prepared from the known 2,3‐unsubstituted imidazole 7 via the iodoimidazole 10 , and tested as inhibitors of β‐ and α‐glucosidases. Introduction of hydrophobic and flexible substituents, such as in 28 and 29 , led to a very strong inhibition of β‐glucosidases, with K_i values for 29 of 1.2 and 0.11 nM against β‐glucosidases from almonds and Caldocellum saccharolyticum, respectively. A slow onset of the inhibition was observed for the strongly inhibiting 16 , 28 – 31 , 37 , and 38 . While the introduction of a hydroxymethyl or a phenethyl substituent as in 17 and 30 led to stronger inhibition, the 1′‐hydroxyphenethyl derivatives 37 and 38 were weaker inhibitors than 16 and 29 . This result is interpreted in the light of a conformational change of the substrate on the way to the transition state. The substituent at C(2) has only a moderate influence on the selectivity of the inhibition of two β‐ and one α‐glucosidases, increasing it by a maximal factor of ca. 10 ( 16 ), or decreasing it by a maximal factor of ca. 15 ( 37 ).     

Integral transforms for shock-shock interaction — Three dimensional planar wings

Résumé Si une onde de choc de force arbitraire rencontre une aile pointue aplatie qui se déplace à une vitesse supersonique, une région de perturbations est générée. Une expression analytique explicite en termes de perturbations de pression est trouvée par l'application de transformations d'intégrales au problème des conditions initiales-limites. La théorie est appliquée au problème de l'interaction d'une onde de choc plane et d'une aile delta plane (avec des bords d'attaque définiment supersoniques) en petite incidence. Les résultats numériques pour la répartition des pressions sont présentés.     

Computational experience with an interior point algorithm on the satisfiability problem

We apply the zero-one integer programming algorithm described in Karmarkar [12] and Karmarkar, Resende and Ramakrishnan [13] to solve randomly generated instances of the satisfiability problem (SAT). The interior point algorithm is briefly reviewed and shown to be easily adapted to solve large instances of SAT. Hundreds of instances of SAT (having from 100 to 1000 variables and 100 to 32,000 clauses) are randomly generated and solved. For comparison, we attempt to solve the problems via linear programming relaxation with MINOS.     

Coherent-light-shadow spot of a crack under mode I loading: Theory and experiment

The coherent-light-shadow field formed by crack-tip deformation under Mode 1 loading is studied theoretically and experimentally. First-order approximation of geometrical optics and higher order expansions are examined in the theoretical development. The wave-optical analysis shows that the interference fringe spacing around the caustic is approximately proportional toKsu−2/15 for the near-tip singular field, and, that the peak amplitude of the light-intensity distribution around the caustic is proportional toK ^4/15. The effects of diffraction on the measurement of the caustic diameter are examinediin detail. The analysis and accompanying experiments show that the diffraction effect alone could lead toK estimation errors of ±20 percent or more, if the edge of the shadow spot or it the peak-intensity point is used to determine the caustic diameter. An alternate measure of caustic diameter is therefore suggested for practical use. Effects of the size of the nominal initial curve and crack-tip bluntness onK measurements are included. Finally, possible applications of the coherent-light-shadow spot in fracture mechanics are outlined.     

An interior point algorithm to solve computationally difficult set covering problems

We present an interior point approach to the zero–one integer programming feasibility problem based on the minimization of a nonconvex potential function. Given a polytope defined by a set of linear inequalities, this procedure generates a sequence of strict interior points of this polytope, such that each consecutive point reduces the value of the potential function. An integer solution (not necessarily feasible) is generated at each iteration by a rounding scheme. The direction used to determine the new iterate is computed by solving a nonconvex quadratic program on an ellipsoid. We illustrate the approach by considering a class of difficult set covering problems that arise from computing the 1-width of the incidence matrix of Steiner triple systems.     

CURE CHARACTERISTICS OF HYDROXYL TERMINATED POLYBUTADIENE PREPOLYMER WITH BLOCKED TOLUENE DIISOCYANATE-Ⅰ

Controlled release of TDI and hence the cure characteristics of several blocked TDI with HTPB are reported. The reactions were followed through viscosity measurements as a function of time and temperature under the catalytic influence of triethylamine. The effect of nature of substituents present on the end capping substrate, temperature, solvent, basicity of catalyst and kinetics thereon have been studied.