Photo induced collisions with laser cooled He* atoms

This paper presents an experimental investigation of cold collisions between metastable helium atoms in an optical trap at 1 mK. Penning (PI) and associative (AI) ionization reactions are distinguished using a mass spectrometer and studied under influence of near resonant laser light. Dramatic enhancement, by more than a factor 15, of the ion rate is observed when the laser is tuned close to resonance. Experimental findings are well-described, on an absolute scale, by model predictions. Received: 9 February 1998 / Revised: 4 May 1998 / Accepted: 14 May 1998     

Surface Aggregation of Candida albicans on Glass in the Absence and Presence of Adhering Streptococcus gordonii in a Parallel-Plate Flow Chamber: A Surface Thermodynamical Analysis Based on Acid-Base Interactions

Adhesive interactions between yeasts and bacteria are important in the maintenance of infectious mixed biofilms on natural and biomaterial surfaces in the human body. In this study, the extended DLVO (Derjaguin-Landau-Verwey-Overbeek) approach has been applied to explain adhesive interactions between C. albicans ATCC 10261 and S. gordonii NCTC 7869 adhering on glass. Contact angles with different liquids and the zeta potentials of both the yeasts and bacteria were determined and their adhesive interactions were measured in a parallel-plate flow chamber.Streptococci were first allowed to adhere to the bottom glass plate of the flow chamber to different seeding densities, and subsequently deposition of yeasts was monitored with an image analysis system, yielding the degree of initial surface aggregation of the adhering yeasts and their spatial arrangement in a stationary end point. Irrespective of growth temperature, the yeast cells appeared uncharged in TNMC buffer, but yeasts grown at 37 degrees C were intrinsically more hydrophilic and had an increased electron-donating character than cells grown at 30 degrees C. All yeasts showed surface aggregation due to attractive Lifshitz-van der Waals forces. In addition, acid-base interactions between yeasts, yeasts and the glass substratum, and yeasts and the streptococci were attractive for yeasts grown at 30 degrees C, but yeasts grown at 37 degrees C only had favorable acid-base interactions with the bacteria, explaining the positive relationship between the surface coverage of the glass by streptococci and the surface aggregation of the yeasts. Copyright 1999 Academic Press.     

High-spin structure of yrast-band in 78Kr

Lifetime of levels up to 22⁺, have been measured in ⁷⁸Kr and an oblate shape is assigned to the ground state using the CSM and the configuration dependent shell correction calculations. Calculations further show that ⁷⁸Kr is highly γ-soft nucleus. The experimental Q _t values coupled with theoretical calculations indicate an oblate shape for ⁷⁸Kr at low spins and triaxial shape at higher spins     

Structure of 72,74Se at high spin

Lifetimes of high spin states up to { }=22⁺ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in ^{72, 74}Se. The Q _t values derived from these measurements indicate that prolate shape stabilizes for ⁷²Se, while a triaxial shape develops for ⁷⁴Se at higher spins. Comparison of the observed trend in Q _t with spin for ^{72, 74}Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.     

Studies on the valence electronic structure of Fe and Ni in Fe x Ni1−x alloys

K _β-to-K _α X-ray intensity ratios of Fe and Ni in pure metals and in Fe _x Ni_1−x alloys (x=0.20, 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV γ-rays from a ²⁴¹Am point source, to understand as to why the properties of permalloy Fe_0.2Ni_0.8 is distinct from other alloy compositions. It is observed that the valence electronic structure of Fe_0.2Ni_0.8 alloy is totally different from other alloys which may be attributed to its special magnetic properties.     

IMPROVEMENT OF FLUIDIZABILITY OF FINE POWDERS ——A COMPUTER STUDY

Simulations of the gas fluidization of a cohesive powder were performed using the Stokesian Dynamics method and an agglomeration-deagglomeration model to investigate methods of improving the fluidizability of fine powders. Three techniques (a) high gas velocity (b) vibration-assisted fluidization and (c) tapered fluidizer were used in the simulations which provided detailed information on the bed microscopy such as the motion of 1 O0 particles in a fluidizing vessel along with the formation and destruction of cohesive bonds dudng collisions. While all three techniques were found to effectively improve the fluidizability of a strongly cohesive powder, we suggest a combination of high velocity fluidization assisted by extemal vibration of the fluidized bed to minimize entrainment of particles.     

Iterative methods for stabilized discrete convection-diffusion problems

In this paper we study the computational cost of solving theconvection-diffusion equation using various discretization strategiesand iteration solution algorithms. The choice of discretizationinfluences the properties of the discrete solution and alsothe choice of solution algorithm. The discretizations consideredhere are stabilized low-order finite element schemes using streamlinediffusion, crosswind diffusion and shock-capturing. The latter,shock-capturing discretizations lead to nonlinear algebraicsystems and require nonlinear algorithms. We compare variouspreconditioned Krylov subspace methods including Newton-Krylovmethods for nonlinear problems, as well as several preconditionersbased on relaxation and incomplete factorization. We find thatalthough enhanced stabilization based on shock-capturing requiresfewer degrees of freedom than linear stabilizations to achievecomparable accuracy, the nonlinear algebraic systems are morecostly to solve than those derived from a judicious combinationof streamline diffusion and crosswind diffusion. Solution algorithmsbased on GMRES with incomplete block-matrix factorization preconditioningare robust and efficient.     

Fabrication of polystyrene hollow microspheres as laser fusion targets by optimized density-matched emulsion technique and characterization

Inertial confinement fusion, frequently referred to as ICF, inertial fusion, or laser fusion, is a means of producing energy by imploding small hollow microspheres containing thermonuclear fusion fuel. Polymer microspheres, which are used as fuel containers, can be produced by solution-based micro-encapsulation technique better known as density-matched emulsion technique. The specifications of these microspheres are very rigorous, and various aspects of the emulsion hydrodynamics associated with their production are important in controlling the final product. This paper describes about the optimization of various parameters associated with density-matched emulsion method in order to improve the surface smoothness, wall thickness uniformity and sphericity of hollow polymer microspheres. These polymer microshells have been successfully fabricated in our lab, with 3–30 μm wall thickness and 50–1600 μm diameters. The sphericity and wall thickness uniformity are better than 99%. Elimination of vacuoles and high yield rate has been achieved by adopting the step-wise heating of W₁/O/W₂ emulsion for solvent removal.