Laser photochromic velocimetry estimation of the vorticity and pressure field – two-dimensional flow in a curved vessel

 Laser photochromic velocimetry was successfully used to determine details of a steady two-dimensional flow field. In the plane of symmetry of a 90° curved tube at a Reynolds number of 250, the axial and radial velocity fields were measured using laser photochromic velocimetry combined with a technique involving interpolation of the photochromic data. The wall shear stress, vorticity, and pressure field were also estimated. The experimental results were compared with those from numerical simulation. The agreement was remarkably good lending validity to the interpolation method used for this flow field. Received: 29 May 1997 / Accepted: 13 November 1997     

A computational analysis of ordering in 2O.4 based on quantum mechanics and intermolecular forces

A computational analysis of ordering in p-ethoxybenzylidene-p-n-butylaniline (2O.4) has been carried out based on quantum mechanics and intermolecular forces. The evaluation of atomic charges and dipole moments at each atomic center has been carried out using the CNDO/2 method. The configuration energy has been computed using the modified Rayleigh-Schrödinger perturbation method at an interval of 1 Å in translation and 10° in rotations. The various possible geometrical arrangements of molecular pairs during the different modes of interactions have been considered, and the most favorable configuration of pairing has been obtained. A comparative picture of the molecular parameters, such as the total energy, binding energy, and total dipole moment of 2O.4 with other nematogen 4-4′-di-n-propoxy-azoxybenzene (DPAB) and 5-(trans-4-ethylcyclohexyl)-2-(4-cyanophenyl)-pyrimidine (ECCPP), has been given. The results are discussed in the light of experimental and other theoretical observations.     

Odd‐Even Effects in Homologous Series of 4‐Cyano‐4'‐Alkylbiphenyls(nCB): Role of Anisotropic Pair Potential

A quantum mechanical analysis has been carried out to determine the association energy of five homologous of 4‐Cyano‐4'‐Alkylbiphenyls series with alkyl group: propyl (3CB) ; butyl (4CB) ; pentyl (5CB) ; hexyl (6CB) ; hepty (7CB) using Rayleigh‐Schrodinger perturbation method for different nearest neighbour configurations of interacting pairs. The net atomic charges and dipoles have been computed using the CNDO/2 method. The complete association energy with all its components has been reported. An attempt has been made to explain the odd‐even effects at the molecular level on the basis of these results.     

Syntheses,characterization, and properties of multiblock copolymers consisting of polyisobutylene and poly(L‐lactide) segments

The syntheses of {‐poly(L ‐lactide) (PLLA)‐b‐polyisobutylene (PIB)‐}_n multiblock copolymers were accomplished for the first time by chain extension of PLLA‐b‐PIB‐b‐PLLA triblock copolymers. Well‐defined PLLA‐b‐PIB‐b‐PLLA triblock copolymers with predictable M_ns, low PDIs (1.10–1.18) and excellent blocking efficiencies were prepared by anionic ring‐opening polymerizations of L ‐lactide initiated with hydroxyallyl telechelic PIB (HO‐Allyl‐PIB‐Allyl‐OH) in toluene at 110 °C. The triblock copolymers were successfully chain extended with 4,4′‐methylenebis(phenylisocyanate) (MDI) to obtain the multiblock copolymers with good gravimetric yields of ～86 to 96%. The chain‐extended polymers were soluble in a range of common organic solvents. The block copolymers showed two glass transition temperatures in differential scanning calorimetric analysis for the PIB and PLLA blocks indicating microphase separation, which was supported by atomic force microscopy images. The as‐synthesized compression molded multiblock copolymers exhibited tensile strengths in the range of 8–24 MPa with elongations at break in the range of 2.5–400%. The static and dynamic mechanical properties showed a strong dependence on the relative PLLA content in the copolymer. The dynamic mechanical analysis also indicated microphase separation at higher PLLA compositions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3490–3505, 2009     

Wachspress type rational complex planar splines of degree (3,1)

We study the existence, uniqueness and approximation properties of rational complex planar spline interpolants of order (3, 1). We also find sufficient conditions for such interpolants to be quasiregular and quasiconformal. Examples are given. This work was carried out with the aid of MACSYMA, a large symbolic manipulation program developed at the MIT Laboratory for Computer Science and supported from 1975 to 1983 by the National Aeronautics and Space Administration under grant NSG 1323, by the Office of Naval Research under grant N00014-77C-0641, by the U.S. Department of Energy under grant ET-78-C-024687, and by the U.S. Air Force under grant F49620-79-C-020, and since 1982 by Symbolics, Inc. of Burlington, MA.     

Preparation and structural studies of a new series of bimetallic complexes

A new series of bimetallic Lewis acid, Cu(NCO)₂(NCS)₂Hg, and its complexes, L₂Cu(NCO)₂(NCS)₂Hg (L =thf,dmso, pyridine, nicotinamide and Ph₃P are prepared and studied by physical and spectroscopic methods.     

Role of dielectric medium on mesogenic compounds (BCHs) at phase transition temperature: A comparative computational analysis

A comparative computational analysis on two liquid crystalline disubstituted biphenylcyclohexanes (BCHs) of general formula R‐C₆H₁₀‐C₆H₄‐X with R: C₃H₇; X: H (BCH30) and R: C₅H₁₁; X: CN (BCH5CN) has been carried out on the basis of quantum mechanics and intermolecular forces. The evaluation of atomic charge and dipole moment at each atomic centre has been carried out through an all‐valence electron (CNDO/2) method. The configurational energy has been computed using the Rayleigh‐Schrodinger perturbation method. The total interaction energy values obtained were used to calculate the probability of each configuration in dielectric medium (i.e. non‐interacting and non‐mesogenic solvent, benzene) at room temperature, transition temperature and above transition temperature using the Maxwell‐Boltzmann's formula. The flexibility of various interacting configurations has been studied in terms of variation of probability due to small departures from the most probable configurations. Further, the various possible geometrical arrangements between a molecular pair during the different modes of interactions have been considered. An attempt has been made to develop a new and interesting model for mesogenic compounds in a dielectric medium. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase organization in laterally substituted dicyclohexylethane derivatives—A molecular model for smectogens

The present article deals with the configurational probabilities of smectogens 1, 2-bis (4-pentylcyclohexyl) ethan-1-ol (PCHE1) and 1, 2-bis (4-pentylcyclohexyl) ethan-1-one (PCHE2) with respect to translational and orientational motions. The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic charge and atomic dipole moment components at each atomic center. The modified Rayleigh-Schrodinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a ‘6-exp’ potential function has been assumed for short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the configurational probability at smectic B-isotropic transition temperature using the Maxwell-Boltzmann formula. Molecular arrangements inside a bulk of materials and smectic behavior of the compounds in terms of their relative order have been discussed. Further, a model has been developed at molecular level to understand the effect of translational/rotational rigidity on phase organization and relative flexibility of one configuration over the other.     

New modifications in 15 UD pelletron at nuclear science centre

The 15 UD pelletron at NSC has been operational and performed well during the last 11 years. There have been major modifications performed for upgradation of pelletron system over this period. Major upgradations which have been implemented are new resistor network system for voltage gradient, doublet to singlet unit conversion for accelerator units, turbopump based gas stripper system etc. In addition accelerator mass spectroscopy program has also been started. A new multi-cathode source, Wien filter etc. have been procured and will be added soon in the system. An overview of the most significant upgradations undertaken and other activities for the system are being reported in the present paper.