Fabrication of oligo‐glycerol based hydrolase responsive amphiphilic nanocarriers

Herein, we report on the synthesis of a new class of novel non‐ionic amphiphiles using triglycerol as a core, which is further functionalized with hydrophilic units poly(ethylene glycol) monomethyl ether (M_n: 350 and 550) and a pair of hydrophobic alkyl chains (C₁₈ or C₁₅) via chemo‐enzymatic approach. Fluorescence measurements and dynamic light scattering studies showed that all of the synthesized amphiphilic systems spontaneously self‐ assemble in aqueous solution, which is further confirmed by the transmission electron microscopy. Encapsulation of hydrophobic moieties like Nile red and nimodipine was studied using ultraviolet‐visible (UV‐vis) and fluorescence spectrometer techniques. A cytotoxicity study of the amphiphiles using A549, HeLa, and MCF7 cell, which showed that all of the synthesized nanocarriers are well tolerated at the concentrations studied. The release profile of encapsulated Nile red in synthesized amphiphilic system was studied in the presence of the immobilized enzyme (Novozym 435).     

Instability of the separated shear layer in flow past a cylinder: Forced excitation

The receptivity of the separated shear layer for Re = 300 flow past a cylinder is investigated by forced excitation via an unsteady inflow. In order to isolate the shear layer instability, a numerical experiment is set up that suppresses the primary wake instability. Computations are carried out for one half of the cylinder, in two dimensions. The flow past half a cylinder with steady inflow is found to be stable for Re = 300. However, an inlet flow with pulsatile perturbations, of amplitude 1% of the mean, results in the excitation of the shear layer mode. The frequency of the perturbation of the inlet flow determines the frequency associated with the shear layer vortices. For a certain range of forced frequencies the recirculation region undergoes a low‐frequency longitudinal contraction and expansion. An attempt is made to relate this instability to a global mode of the wake determined from a linear stability analysis. Interestingly, this phenomenon disappears when the outflow boundary of the computational domain is shifted sufficiently downstream. This study demonstrates the need of carefully investigating the effect of the location of outflow boundaries if the computational results indicate the presence of low‐frequency fluctuations. The effect of Re and amplitude of unsteadiness at the inlet are also presented. All computations have been carried out using a stabilized finite element formulation of the incompressible flow equations. Copyright © 2007 John Wiley & Sons, Ltd.     

TEA CO2 laser-induced photodissociation of UF6 via interspecies V-V energy transfer from multiple photon excited halomethanes

The dissociation of UF₆ sensitized by multiple photon excitation of a series of halomethanes: CF₄, CF₃Cl, and CF₂Cl₂ has been investigated. The roles of various experimental parameters like exciting frequency, fluence and pressures of sensitizer/UF₆ on the dissociation yield were studied to examine (1) the characteristics of the sensitizer/UF₆ system and (2) the coupling of vibrational energy between two molecular systems. The efficiency of the energy transfer process was estimated on the basis of long range dipole-dipole interaction to gain an understanding of the dissociation process.     

Separation of tritium from deuterium by pulsed NH3 laser-selective multiple photon dissociation of CTCl3

The multiple photon dissociation of ppm level CTCl₃ in CDCl₃ and the selectivity of T/D separation were investigated using a pulsed ammonia laser. The effect of laser frequency, fluence and buffer gas pressure on the dissociation rate and isotopic selectivity were studied. The depletion of CDCl₃ was not observed within experimental errors. A lower limit of single step selectivity factor was found to be >5000 at 133 Pa substrate pressure.     

Fast finite difference solution for steady-state Navier-Stokes equations using the BID method

A first biharmonic boundary value problem is obtained by combining the coupled steady-state Navier-Stokes equations in their stream-function-vorticity formulation. This biharmonic boundary value problem is solved by a fast biharmonic solver developed by the authors wherein the idea of preconditioned conjugate gradient method is used. The biharmonic driver (BID) method using this solver has been found fast converging, and produces accurate results up to moderately large Reynolds numbers. Also, the mesh size does not affect the convergence rate.     

An extension of the edge covering problem

In this paper we define a weightedr-covering problem, and show that there exists an optimum solution of ther-covering problem which can be decomposed into the sum of a rounded down solution of its linear relaxation and an optimal solution of a weighted edge covering problem on a reduced graph. Vertexr-packing problem can also be reduced to ther-covering problem.     

Polarization and interactions of colloidal particles in ac electric fields

Micrometer-sized polystyrene particles form two-dimensional crystals in alternating current (ac) electric fields. The induced dipole-dipole interaction is the dominant force that drives this assembly. We report measurements of forces between colloidal particles in ac electric fields using optical tweezers and find good agreement with the point dipole model. The magnitude of the pair interaction forces depends strongly on the bulk solution conductivity and decreases as the ionic strength increases. The forces also decrease with increasing field frequency. The salt and frequency dependences are consistent with double layer polarization with a characteristic relaxation frequency omega(CD) approximately a(2)/D, where a is the particle radius and D is the ion diffusivity. This enables us to reinterpret the order-disorder transition reported for micrometer-sized polystyrene particles [Lumsdon et al., Langmuir 20, 2108 (2004)], including the dependence on particle size, frequency, and ionic strength. These results provide a rational framework for identifying assembly conditions of colloidal particles in ac fields over a wide range of parameters.