Shear-induced configurations of confined colloidal suspensions

We show that geometric confinement dramatically affects the shear-induced configurations of dense monodisperse colloidal suspensions; a new structure emerges, where layers of particles buckle to stack in a more efficient packing. The volume fraction in the shear zone is controlled by a balance between the viscous stresses and the osmotic pressure of a contacting reservoir of unsheared particles. We present a model that accounts for our observations and helps elucidate the complex interplay between particle packing and shear stress for confined suspensions.     

Potential for the use of ultrasound in the extraction of antioxidants from Rosmarinus officinalis for the food and pharmaceutical industry

Ultrasound was used to increase the extraction efficiency of carnosic acid from the herb Rosmarinus officinalis using butanone, ethyl acetate and ethanol as solvents. Both dried and fresh leaves of the herb were extracted and, when performed at the same temperature, sonication improved the yields of carnosic acid for all three solvents and shortened the extraction times. Sonication also reduced the solvent effect so that ethanol, which is a poor solvent under conventional conditions, reached a similar level of extraction efficiency to the other two when sonicated. The extraction of dried herb with ethanol proved to be more efficient than that of fresh material, probably due to the water present in the latter.     

Binding constant determination of drugs toward subdomain IIIA of human serum albumin by near-infrared dye-displacement capillary electrophoresis

Drug binding to serum albumin influences several important pharmacological properties such as toxicity, solubility, activity, distribution, and excretion. It is therefore of interest to have methodologies that allow for the determination of drug-albumin affinity constants while simultaneously providing information on the location of the drug binding site. In the present work we describe a method for the determination of binding constants of drugs known to bind to subdomain IIIA of serum albumin. Drugs used in the study were ketoprofen, ibuprofen, quinidine, naproxen, imipramine, and clofibrate. Binding constants of the drugs were determined by near-infrared dye-displacement capillary electrophoresis. The dye-displacement technique uses a competitive-type interaction between the drug of interest and a dye probe to arrive at a binding constant. A heptamethine cyanine dye was used as a probe for drug binding at subdomain IIIA of serum albumin. The utility of the dye as a noncovalent label for serum albumin was investigated. Additionally, the ability of the method to illustrate enantioselective binding is shown. The dye displacement technique has advantages over current electrophoresis-based techniques in that it is faster and uses less reagent.     

Hindered axial-equatorial carbonyl exchange in an Fe(CO)(4)(PR(3)) complex of a rigid bicyclic phosphine

Variable-temperature (13)C NMR spectra for a series of Fe(CO)(4)(PR(3)) complexes ligated by phosphatri(3-methylindolyl)methane (1), phosphatri(pyrrolyl)methane (2), P(N-3-methylindolyl)(3) (3), and P(N-pyrrolyl)(3) (4) are reported. Ligand 2 was prepared by reaction of tri(pyrrolyl)methane with PCl(3) in THF and Et(3)N. Compound 2 is stable to methanolysis, hydrolysis, and aerial oxidation at room temperature. Reactions of 2 with selenium powder and Rh(acac)(CO)(2) yield phosphatri(pyrrolyl)methane selenide (5) and Rh(acac)(CO)(2) (6), respectively. The carbonyl stretching frequency in the IR spectrum of 6 and the magnitude of (1)J(Se)(-)(P) in the (31)P NMR spectrum of 5 indicate that 2 is a strong pi-acid and a weak sigma-base, commensurate with its lack of reactivity with CH(3)I. The trend in the decreasing basicity of 2 and related phosphines and phosphites was determined to be P(NMe(2))(3) > 3 > 4 > 1 > P(OPh)(3) > 2. IR data for a series of Rh(acac)(CO)(PR(3)) complexes indicate the trend in decreasing pi-acceptor ability to be 2 approximately 1 > 4 > P(OPh)(3) > 3 > PPh(3). Phosphines 1-4 were reacted with Fe(2)(CO)(9) to yield Fe(CO)(4)(1) (7), Fe(CO)(4)(2) (8), Fe(CO)(4)(3) (9), and Fe(CO)(4)(4) (10), respectively. IR data for 7-10 support the trend in pi-acidity listed above. Variable-temperature (13)C NMR spectra for compounds 8-10 show a single doublet resonance for the carbonyls in the temperature range from -80 to 20 degrees C indicative of rapid intramolecular rearrangement of carbonyls between axial and equatorial sites. However, the (13)C NMR spectrum for 7 shows slowed axial-equatorial carbonyl exchange at 20 degrees C. The limiting slow-exchange spectrum is observed at -20 degrees C. Hindered carbonyl exchange in 7 is attributed to the rigid 3-fold symmetry and steric bulk of 1. In addition to characterization of the new compounds by NMR ((1)H, (13)C, and (31)P) spectroscopy, IR spectroscopy, mass spectrometry, and elemental analysis, compounds 2, 7, 9, and 10 were further characterized by X-ray crystallography.     

Theoretical total ionization cross-sections of CH x,CF x,SiH x,SiF x ( ) and CCl 4 targets by electron impact

Total ionization cross-sections of electron impact are calculated for the molecular targets CH_x, CF_x, SiH_x, SiF_x (x = 1-4) and CCl₄ at incident energies 20-3 000 eV. The calculation is based on Complex Scattering Potential approach, as developed by us recently. This leads to total inelastic cross-sections, from which the total ionization cross-sections are extracted by reasonable physical arguments. Extensive comparisons are made here with the previous theoretical and experimental data. The present results are satisfactory except for the CF_x and SiF_x (x = 1-3) radicals, for which the experimental data are lower than most of the theories by more than 50%. Received 23 May 2002 / Received in final form 24 October 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: knjoshipura@yahoo.com     

Serre's generalization of Nagao's theorem: An elementary approach

Let be a smooth projective curve over a field . For each closed point of let be the coordinate ring of the affine curve obtained by removing from . Serre has proved that is isomorphic to the fundamental group, , of a graph of groups , where is a tree with at most one non-terminal vertex. Moreover the subgroups of attached to the terminal vertices of are in one-one correspondence with the elements of , the ideal class group of . This extends an earlier result of Nagao for the simplest case .

Serre's proof is based on applying the theory of groups acting on trees to the quotient graph , where is the associated Bruhat-Tits building. To determine he makes extensive use of the theory of vector bundles (of rank 2) over . In this paper we determine using a more elementary approach which involves substantially less algebraic geometry.

The subgroups attached to the edges of are determined (in part) by a set of positive integers , say. In this paper we prove that is bounded, even when Cl is infinite. This leads, for example, to new free product decomposition results for certain principal congruence subgroups of , involving unipotent and elementary matrices.

     

Measurement of the resonant d(mu)t molecular formation rate in solid HD

Measurements of muon-catalyzed dt fusion ( d(mu)t-->4He + n + mu(-)) in solid HD have been performed. The theory describing the energy dependent resonant molecular formation rate for the reaction (mu)t + HD-->[(d(mu)t)pee](*) is compared to experimental results in a pure solid HD target. Constraints on the rates are inferred through the use of a Monte Carlo model developed specifically for the experiment. From the time-of-flight analysis of fusion events in 16 and 37 microg x cm(-2) targets, an average formation rate consistent with 0.897+/-(0.046)(stat)+/-(0.166)(syst) times the theoretical prediction was obtained.     

Spin waves and electronic interactions in La2CuO4

The magnetic excitations of the square-lattice spin-1/2 antiferromagnet and high- T(c) parent compound La2CuO4 are determined using high-resolution inelastic neutron scattering. Sharp spin waves with absolute intensities in agreement with theory including quantum corrections are found throughout the Brillouin zone. The observed dispersion relation shows evidence for substantial interactions beyond the nearest-neighbor Heisenberg term which can be understood in terms of a cyclic or ring exchange due to the strong hybridization path around the Cu4O4 square plaquettes.     

Measurements of F2 and xF(nu)(3) - xF(nu;)(3) from CCFR nu(mu)-Fe and nu;(mu)-Fe Data in a Physics Model-Independent Way

We report on the extraction of the structure functions F2 and DeltaxF(3) = xF(nu)(3)-xF(nu;)(3) from CCFR nu(mu)-Fe and nu;(mu)-Fe differential cross sections. The extraction is performed in a physics model-independent (PMI) way. This first measurement of DeltaxF(3), which is useful in testing models of heavy charm production, is higher than current theoretical predictions. The ratio of the F2 (PMI) values measured in nu(mu) and mu scattering is in agreement (within 5%) with the predictions of next-to-leading-order parton distribution functions using massive charm production schemes, thus resolving the long-standing discrepancy between the two sets of data.