Temperature fields in a liquid due to the thermocapillary motion of bubbles and drops

 Experiments were performed on the motion of isolated air bubbles and drops of Fluorinert FC-75 moving in a Dow-Corning silicone oil under the action of an applied temperature gradient in a reduced gravity environment aboard the Space Shuttle in orbit. The disturbance of the imposed temperature field due to the motion of the objects was studied optically using a shearing interferometer with a Wollaston prism and the results of a typical bubble run were compared with theoretical predictions. Also, the liquid velocity field surrounding the bubbles and drops has been qualitatively investigated in a few runs by the observation of tracer particles dispersed in the continuous phase fluid. The measurement techniques are described, and the results for the temperature and flow fields are presented and discussed. Received: 27 June 2000/Accepted: 17 November 2000     

Effect of viscosity on ultrasound wave reflection from a solid/liquid interface

A study of the simulated reflection of a wideband ultrasound shear wave from the solid/viscous fluid interface is presented. Various parameters affecting reflection factors including the material properties of the solid, fluid properties like density and viscosity, and the operating frequency are discussed. Simulated ultrasonic response waveforms are compared with the experimentally obtained data for NIST traceable calibration standards of viscosity. A good agreement was observed between the simulated and experimental waveforms at various viscosities and for different solid substrates.     

On identical nature of the superconductivity mechanisms in 30 K and 90 K superconductors

A systematic study of Zn substitution in both lanthanum and yttrium-based oxide superconductors withT _cof 30 K and 90 K has been carried out simultaneously under identical conditions. Contrary to the general belief, the results indicate that the mechanism responsible for superconductivity in 30 K compounds is unlikely to be radically different from that of the 90 K compounds.     

Singularities in Gaussian random fields

This paper studies a class of Gaussian random fields defined on lattices that arise in pattern analysis. Phase transitions are shown to exist at a critical temperature for these Gaussian random fields. These are established by showing discontinuous behavior for certain field random variables as the lattice size increases to infinity. The discontinuities in the statistical behavior of these random variables occur because the growth rates of the eigenvalues of the inverse of the variance-covariance matrix at the critical temperature are different from the growth rates at noncritical temperatures. It is also shown that the limiting specific heat has a phase transition with a power law behavior. The critical temperature occurs at the end point of the available values of temperature. Thus, although the critical behavior is not extreme, caution should be exercised when using such models near critical temperatures.Research supported by AFOSR Grant No. 91-0048 and by USARO Grant No. DAAL03-90-G-0103.     

A Facile Route to Some Useful Homochiral Alkyl Imidazolidin-2-one-4(S)-carboxylates

A general, high yielding route to optically pure alkyl 1 N-alkyl and 1 N-acyl substituted imidazolidin-2-one-4(S)-carboxylates, with diverse potential uses in asymmetric synthesis, is reported.     

Facile synthesis of N-aryl pyrroles via Cu(II)-mediated cross coupling of electron deficient pyrroles and arylboronic acids

N-Arylation of electron-deficient pyrroles has been achieved by cross-coupling with arylboronic acids at room temperature in the presence of stoichiometric amounts of copper(II) acetate. The generality of this reaction has been established with variously substituted pyrroles as well as boronic acids. A key intermediate in the synthesis of a matrix metalloprotease inhibitor has been achieved using this methodology.     

An efficient and chemoselective Cbz-protection of amines using silica-sulfuric acid at room temperature

A simple, facile, and chemoselective N-benzyloxycarbonylation of amines using silica-sulfuric acid that proceeds under solvent-free conditions at room temperature has been achieved. These reactions are applicable to a wide variety of primary (aliphatic and cyclic) secondary amines, amino alcohols, and heterocyclic amines.     

Selective lateral metalation and electrophilic quenching of c-4 functionalized isoxazoles. IX. Direct formation of the C-N bond utilizing an electrophilic nitrogen source

C-5 Lithio-alkylisoxazoles were quenched with dialkyl azodicarboxylates to form the C-5 alkylhydrazine derivatives in synthetically useful yields.     

On solving large instances of the capacitated facility location problem

We present two sets of results pertaining to the solution of capacitated facility location problems that are large, especially with regard to the number of customers. One set of results relates to customer aggregation, while another set of results concerns the judicious selection of variable-upper-bounding (VUB) constraints to include in the initial integer-programming formulation.