Nonlinear electrophoresis of dielectric particles in Newtonian fluids

In classical electrokinetics, the electrophoretic velocity of a dielectric particle is a linear function of the applied electric field. Theoretical studies have predicted the onset of nonlinear electrophoresis at high electric fields because of the nonuniform surface conduction over the curved particle. However, experimental studies have been left behind and are insufficient for a fundamental understanding of the parametric effects on nonlinear electrophoresis. We present in this work a systematic experimental study of the effects of buffer concentration, particle size, and particle zeta potential on the electrophoretic velocity of polystyrene particles in a straight rectangular microchannel for electric fields of up to 3 kV/cm. The measured nonlinear electrophoretic particle velocity is found to exhibit a 2(±0.5)-order dependence on the applied electric field, which appears to be within the theoretically predicted 3- and 3/2-order dependences for low and high electric fields, respectively. Moreover, the obtained nonlinear electrophoretic particle mobility increases with decreasing buffer concentration (for the same particle) and particle size (for particles with similar zeta potentials) or increasing particle zeta potential (for particles with similar sizes). These observations are all consistent with the theoretical predictions for high electric fields.     

Sol–gel polycondensation of tetraethoxysilane in ethanol in presence of vinyl modified guar gum: synthesis of novel nanocompositional adsorbent materials

Novel nanocomposite adsorbent materials were synthesized by condensation polymerization of TEOS in the presence of saponified guar-graft-poly(acrylonitrile) (SG) as template. The effect of changing the molecular size of SG on the final properties of the composite materials was investigated in this paper. The composites were thermally treated at temperatures ranging from 80 to 1100 °C, to obtain materials of different performance. The chemical, structural and textural characteristics of the composites were determined by FTIR, XRD, TGA-DSC and SEM studies. Their adsorption properties were monitored in terms of Zn (II) binding capacity which could be tailored by changing the template size and sintering temperature. The adsorption capacity of the composite at room temperature was enhanced five times when thermally treated at 900 °C with a maximum adsorption of 3.58 meq/g of the zinc (II). The adsorption could be further optimized to higher values and the materials could be successfully recycled for three consecutive cycles without any significant loss in the adsorption capacity.     

Enhanced Production of High-Quality Biomass, δ-Aminolevulinic Acid,Bilipigments, and Antioxidant Capacity of a Food Alga <Emphasis Type="Italic">Nostochopsis lobatus</Emphasis>

The growing interest in natural food has raised the global demand for nutraceuticals. We studied enhanced production of biomass, delta-aminolevulinic acid (delta-ALA), bili pigments and antioxidant capacity of a food alga Nostochopsis lobatus in a full-factorial (three level) design with supplemental Zn, glutamine, and Zn + glutamine in batch culture. Production of biomass, pigments, and antioxidant capacity all were higher under immobilized cell cultures in comparison to free cell cultures. Maximum biomass (2,390 mg dry wt l(-1)), delta-ALA (2.715 microg mg(-1) dry wt h(-1)), phycocyanin (98.50 mg g(-1) dry wt), phycoerythrin (158.0 mg g(-1) dry wt), and antioxidant capacity (140.50 mumoles ascorbic acid equivalent capacity g(-1) fresh wt) were recorded when Zn and glutamine were supplemented together in the growth medium at pH 7.8. These effects were found to be significantly related to the activities of glutamine synthetase (GS(max): 490.2 nmoles mg protein(-1) min(-1)), glutamate synthase (GOGAT(max): 27.0 nmoles mg protein(-1) min(-1)), and glutamate dehydrogenase (GDH(max): 159.9 nmoles mg protein(-1) min(-1)). This study shows that N. lobatus could be a promising bioresource for the production of nutritionally rich biomass, delta-ALA, bili pigments, and antioxidants. Use of immobilized cells in batch culture supplemented with Zn and glutamine could be an effective approach for scaling up production for commercial use.     

Dithiomethylether as a ligand in the hydrogenase h-cluster

An X-ray crystallographic refinement of the H-cluster of [FeFe]-hydrogenase from Clostridium pasteurianum has been carried out to close-to atomic resolution and is the highest resolution [FeFe]-hydrogenase presented to date. The 1.39 A, anisotropically refined [FeFe]-hydrogenase structure provides a basis for examining the outstanding issue of the composition of the unique nonprotein dithiolate ligand of the H-cluster. In addition to influencing the electronic structure of the H-cluster, the composition of the ligand has mechanistic implications due to the potential of the bridge-head gamma-group participating in proton transfer during catalysis. In this work, sequential density functional theory optimizations of the dithiolate ligand embedded in a 3.5-3.9 A protein environment provide an unbiased approach to examining the most likely composition of the ligand. Structural, conformational, and energetic considerations indicate a preference for dithiomethylether as an H-cluster ligand and strongly disfavor the dithiomethylammonium as a catalytic base for hydrogen production.     

The fundamental properties of the direct injection method in the analysis of gaseous reduced sulfur by gas chromatography with a pulsed flame photometric detector

In this study, the fundamental aspects of gas chromatography with a pulsed flame photometric detector were investigated through the calibration of gaseous reduced sulfur compounds based on the direct injection method. Gaseous standards of five reduced sulfur compounds (hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide) were calibrated as a function of injection volume and concentration level. The results were evaluated by means of two contrasting calibration approaches: fixed standard concentration method (variable volumetric injection of standard gases prepared at a given concentration) and fixed standard volume method (injection of multiple standards with varying concentrations at a given volume). The optimum detection limit values of reduced sulfur compounds, when estimated at 100 μL of injection volume, ranged from 2.37 pg (carbon disulfide) to 4.89 pg (dimethyl sulfide). Although these detection limit values improved gradually with decreasing injection volume, the minimum detectable concentration (e.g., in nmol mol⁻¹ scale) remained constant due to a balance by the sample volume reduction. The linearity property of pulsed flame photometric detector also appeared to vary dynamically with changes in its sensitivity. According to this study, the performance of pulsed flame photometric detector, when tested by direct injection method, is highly reliable to precisely describe the behavior of reduced sulfur compounds above ∼20 nmol mol⁻¹.     

The <Emphasis Type="BoldItalic">K</Emphasis>-Connection Location Problem in a Plane

This paper determines the optimal location of K connections in the plane, where a connection links pairs of existing facilities. Both uncapacitated and capacitated versions of the problem are considered. Discretization results for general polyhedral gauges and other properties are established. Two heuristic algorithms are developed for each case using the concept of a shortest path flow set coupled with a sequential location and allocation approach. Computational results show that the algorithms are efficient and accurate.     

Model-oriented ocean tomography using higher frequency, bottom-mounted hydrophones

A tomographic scheme is presented that ingests ocean acoustic measurements into an ocean model using data from bottom-mounted hydrophones. The short distances between source-receiver pairs (1-10 km) means arrival times at frequencies of 8-11 kHz are readily detectable and often distinguishable. The influence of ocean surface motion causes considerable variability in acoustic travel times. Techniques are presented for measuring travel times and removing the variability due to surface waves. An assimilation technique is investigated that uses differences in measured and modeled acoustic travel times to impose corrections on the oceanographic model. Equations relating travel time differences to oceanographic variables are derived, and techniques are presented for estimating the acoustic and ocean model error covariance matrices. One test case using a single source-receiver pair shows that the tomographic information can have an impact on constraining the solution of the ocean circulation model but can also introduce biases in the predictions. A second test case utilizes knowledge of a bias in a model-predicted variable to limit grid cells that are impacted by the tomographic data. In this case, using the tomographic data results in significant improvements in the model predictions without introducing any biases.     

Stereoselective syntheses of (+)-α- and (−)-β-conhydrine from L-aspartic acid

An efficient synthesis of (+)-α-conhydrine 1 and (−)-β-conhydrine 2 has been achieved by diastereoselective alkylation of an amino aldehyde derivative 7 with ethylmagnesium bromide or diethylzinc.     

Improved Monte Carlo renormalization group method

An extensive program to analyze critical systems using an improved Monte Carlo renormalization group method (IMCRG),⁽¹⁾ being undertaken at LANL and Cornell, is described. Here we first briefly rview the method and then list some of the topics being investigated.     

Bile pigment studies-VII New syntheses of biliverdin-IXα dimethyl ester and two related mono-vinyl-mono-ethyl isomers

Using the recently developed route through di-t-butyl b-bilene-1,19-dicarboxylates, new syntheses of biliverdin-IXα dimethyl ester (1) and two related mono-vinyl-mono-ethyl isomers (2) and (3), are described. The two dihydro-derivatives of (1) are important in connection with biosynthetic studies of the origin of algal biliproteins.