Stokeslets-meshfree computations and theory for flow in a collapsible microchannel

We present both a theoretical model and Stokeslets-meshfree computations to study the induced flow motions and transport in a 2D microchannel with moving multiple prescribed dynamic collapses (contractions) along the upper wall. The channel is assumed to have a length that is much greater than its width, i.e., ${(\delta = W/L \ll1)}$ . The wall contractions are set to move with or without time (phase) lags with respect to each other. The theoretical analysis presented is based on the quasi-steady state approximations and the lubrication theory at the low Reynolds number flow regime. The meshfree numerical method is based on the method of fundamental solutions MFS, which uses a set of singularized force elements called Stokeslets to induce the flow motions. The flow field developments and structures induced by these wall contractions are given at various time snapshots during the collapsing cycle. The effect of the wall contractions amplitudes and the phase lags between individual contractions on the flow variables and on the time-averaged net flow over a complete cycle of contractions motions is studied. The present study is motivated by pumping mechanisms observed in insects, physiological systems that use multiple contractions to transport fluid, and the emerging novel microfluidic devices that mimic these systems.     

Doubling measures and quasiconformal maps

Part of the research for this paper was done while the author was visiting the Mittag-Leffler Institute. She wishes to thank the Institute for its hospitality. The author was also supported by Grant #DMS 9004251 from the U.S. National Science Foundation.     

On the chlorenium source in the asymmetric chlorolactonization reaction

N-Acylated N-chlorohydantoins are shown to be competent chlorenium sources in the (DHQD)(2)PHAL-mediated asymmetric chlorolactonization. The derivatives demonstrate the exact role of the N1 and N3 chlorine atoms in the parent dichlorohydantoins with the N1 chlorine serving as an inductive activator and the N3 chlorine being delivered to the substrate. The putative associated catalyst/chlorine source complex was experimentally demonstrated through a series of matched/mismatched experiments employing chiral N-chlorinated hydantoins.     

Synthesis,spectral characterization and antibacterial activity of O,O’-dialkyl and alkylene dithiophosphatogold (III)dichloride; crystal structure of [S2POCMe2CMe2O]AuCl2

Abstract

O, O’-Dialkyl and alkylene dithiophosphatogold (III)dichloride complexes of the type [(RO)₂PS₂]AuCl₂ and [S₂POGO]AuCl₂, where R?=?Et, nPr, iPr, iBu, Ph, cyclohexyl and cyclopentyl, where G?=?CMe₂CMe₂-, have been synthesized in 80-90% yields by reaction of the corresponding acid or sodium salts of the appropriate dithiophosphoric acids in 1:1 ratio with gold (III) chloride in dry dichloromethane at room temperature. The compounds have been characterized by elemental analyses, IR and (¹H, ^l3C, and ³¹P) NMR. The crystal structure of [S₂POCMe₂CMe₂O]AuCl₂, was determined. These new complexes have shown their growth inhibiting potential against various bacterial strains with moderate to good activity.     

Structural Report for Sc[(R,R)-norephedrine-pybox](OTf)3 Dimeric Complex

Abstract The title compound containing two metal centers each complexes to one enantiopure chiral norephedrine-derived pyridyl-(bis) oxazoline (pybox) ligand and linked by two hydroxide bridges, crystallizes to give rodlike form in the space group P2₁(# 4). Cell Parameters are a = 10.2344(18) ?, b = 13.952(3) ?, c = 23.371(4) ?, β = 94.586(4)°, V = 3326.6(10) ?³. The metal-hydroxide motif forms a square plane at the center of the structure with the scandium centers exhibiting a distorted pentagonal bipyramid coordination sphere consisting of the chelating ligand and two additional triflouromethyl sulfonyloxy species positioned anti to each other. Graphical abstract The complex contains two metal centers each complexes to one enantiopure chiral norephedrine-derived pyridyl-(bis) oxazoline (pybox) ligand and linked by two hydroxide bridges. Structural report for Sc[(R,R)-norephedrine-pybox](OTf)₃ dimeric complex Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Acrylic acid polymerization kinetics

The kinetics of the isothermal polymerization of acrylic acid were determined utilizing ¹H-NMR spectroscopy. The polymerization rate was observed to depend approximately on the $ \frac{3}{2} $ power of monomer and the $ \frac{1}{2} $ power of sodium persulfate concentration. This is consistent with a model in which the rate of initiation is itself dependent on the monomer concentration. The polymerization rate was also observed to have a strong dependence on percent neutralization, decreasing with increasing level of neutralization up to 75 to 100% neutralization, and then increasing again. The activation energy for the rate of polymerization was between 9 and 13 kcal/mol except for 100% neutralized acrylic acid, which had an activation energy of 18 kcal/mol. These data suggest that a transition in mechanism occurred at 100% neutralization. Increasing the ionic strength by the addition of sodium chloride also increased the rate. The dependence of the molecular weight on the above variables was also quantified for use in the model. It decreased with increasing conversion, decreasing ionic strength and increasing initiator. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2029–2047, 1997