Determination of total, organic solvent extractable, volatile and tetraalkyllead in fish, vegetation, sediment and water samples

Procedures for the determination of total, hexane extractable, volatile and tetraalkyllead in fish, vegetation, sediment and water samples are given. Detection limits, better than those obtainable by any other published methods, are in the range of 10–50 ppb-total Pb, 2-ppb-hexane extractable Pb, 0.5–1.5 ppb-volatile Pb and 0.5 ppb-tetraalkyllead. Standard reference samples from National Bureau of Standards were used as controls where applicable and satisfactory agreement was obtained between accepted values and values obtained by the proposed procedure.     

Investigation of Pretreated Silicon Wafers for CVD Growth of Diamond Film

Difference between lattice constants of silicon (Si) and diamond is approximately 52%. Therefore Si_1—xC_x which has a lattice constant between two materials should be formed on Si substrate to be diamond nucleation sites and reduce the stress between the diamond film and Si substrate. Si wafers with carbonization and dc-biasing pretreatment were prepared in a microwave plasma chemical vapor deposition (CVD) system, then they were investigated by Raman spectroscopy, Photoluminescence (PL), chemical etching and scanning electron microscope (SEM) to study the pretreatment effect. This was achieved by studying a series of samples pretreated by carbonization and dc-biasing.     

Die quantitative Bestimmung von Quecksilber in organischen Verbindungen

Ohne Zusammenfassung     

Observation of dynamical instability for a Bose-Einstein condensate in a moving 1D optical lattice

We have experimentally studied the unstable dynamics of a harmonically trapped Bose-Einstein condensate loaded into a 1D moving optical lattice. The lifetime of the condensate in such a potential exhibits a dramatic dependence on the quasimomentum state. This is unambiguously attributed to the onset of dynamical instability, after a comparison with the predictions of the Gross-Pitaevskii theory. Deeply in the unstable region we observe the rapid appearance of complex structures in the atomic density profile, as a consequence of the condensate phase uniformity breakdown.     

Electrochemical capacitive properties of CNT fibers spun from vertically aligned CNT arrays

Due to their lightweight, large surface area; excellent electrical conductivity; and mechanical strength, carbon nanotube (CNT) fibers show great potentials in serving as both electrode materials and current collectors in supercapacitors. In this paper, the capacitive properties of both as-spun CNT fibers and electrochemically activated CNT fibers have been investigated using cyclic voltammetry and electrochemical impedance spectroscopy. It is found that the as-spun CNT fibers exhibit a very low specific capacitance of 2.6 F g⁻¹, but electrochemically activated CNT fibers show considerably improved specific capacitance. The electrochemical activation has been realized by cyclic scanning in a wide potential window. Different electrolytes have also been examined to validate the applicability of our carbon materials and the activation mechanism. It is believed that such an activation process can significantly improve the surface wetting of the CNT fibers by electrolyte (aqueous Na₂SO₄ solution). The cycling stability and rate-dependence of the capacitance have been studied, and the results suggest practical applications of CNT fibers in electrochemical supercapacitors.     

Ultrasound enhanced growth and cholesterol removal of Lactobacillus fermentum FTDC 1311 in the parent cells but not the subsequent passages

The aim of this study was to evaluate the effect of ultrasound on the intestinal adherence ability, cell growth, and cholesterol removal ability of parent cells and subsequent passages of Lactobacillus fermentum FTDC 1311. Ultrasound significantly decreased the intestinal adherence ability of treated parent cells compared to that of the control by 11.32% (P < 0.05), which may be due to the protein denaturation upon local heating. Growth of treated parent cells also decreased by 4.45% (P < 0.05) immediately upon ultrasound (0-4 h) and showed an increase (P < 0.05) in the viability by 2.18-2.34% during the later stage of fermentation (12-20 h) compared to that of the control. In addition, an increase (P < 0.05) in assimilation of cholesterol (>9.74%) was also observed for treated parent cells compared to that of the control, accompanied by increased (P < 0.05) incorporation of cholesterol into the cellular membrane. This was supported by the increased ratio of membrane cholesterol:phospholipids (C:P), saturation of cholesterol in the apolar regions, upper phospholipids regions, and polar regions of membrane phospholipids of parent cells compared to that of the control (P < 0.05). However, such traits were not inherited by the subsequent passages of treated cells (first, second, and third passages). Our data suggested that ultrasound treatment could be used to improve cholesterol removal ability of parent cells without inducing permanent damage/defects on treated cells of subsequent passages.     

Adaptation of a proton transfer reaction mass spectrometer instrument to employ NO+ as reagent ion for the detection of 1,3‐butadiene in the ambient atmosphere

A proton transfer reaction mass spectrometer (PTR‐MS) instrument was adapted to employ NO⁺ as a chemical reagent ion without any hardware changes by switching the reagent ion source gas from water vapor to dry air. Ionization of dry air within the hollow cathode ion source generates a very intense source of NO⁺ with only a minor impurity of NO. The intensities of the primary NO⁺ reagent ion and the unwanted impurity NO are controllable and dependent on the operational conditions of the hollow cathode ion source. Ion source tuning parameters are described, which maintain an intense source of NO⁺ while keeping the impurity NO signal to less than 2% of the total reagent ion intensity. This method is applied to the detection of 1,3‐butadiene. NO⁺ reacts efficiently with 1,3‐butadiene via a charge exchange reaction to produce only the molecular ion, which is detected at m/z 54. Detection sensitivities of the order of 45 pptv for a 1‐s measurement of 1,3‐butadiene are demonstrated. We present the first real‐time on‐line sub parts per billion measurement of 1,3‐butadiene in the ambient atmosphere. The only likely interference is from 1,2‐butadiene. Concurrent measurements of benzene are provided and suggest that the vehicular emissions are the predominant source of 1,3‐butadiene in a suburban Boston area monitoring location. Copyright © 2009 John Wiley & Sons, Ltd.     

Supramolecular Diblock Copolymers Featuring Well‐defined Telechelic Building Blocks

We report supramolecular AB diblock copolymers comprised of well‐defined telechelic building blocks. Helical motifs, formed via reversible addition‐fragmentation chain‐transfer (RAFT) or anionic polymerization, are assembled with coil‐forming and sheet‐featuring blocks obtained via atom‐transfer radical polymerization (ATRP) or ring‐opening metathesis polymerization (ROMP). Interpolymer hydrogen bonding or metal‐coordination achieves dynamic diblock architectures featuring hybrid topologies of coils, helices, and/or π‐stacked sheets that, on a basic level, mimic protein structural motifs in fully synthetic systems. The intrinsic properties of each block (e.g., circular dichroism and fluorescence) remain unaffected in the wake of self‐assembly. This strategy to develop complex synthetic polymer scaffolds from functional building blocks is significant in a field striving to produce architectures reminiscent of biosynthesis, yet fully synthetic in nature. This is the first plug‐and‐play approach to fabricate hybrid π‐sheet/helix, π‐sheet/coil, and helix/coil architectures via directional self‐assembly.     

Surface tension drawing of liquid from microplate capillary wells

Pressure differentials are routinely used to actuate flow in capillaries. We advance here an alternative means of flow generation that capitalizes on the extension of a liquid bridge achieved by the drawing of a rod through the action of surface tension. This meets the exigencies of creating controllable flow using simpler and more compact means. We found the ability to generate controllable flow to be strongly affected by the liquid bridge sustaining features, and that the use of rod diameters larger than the capillary was more conducive. The extensional flow resulting from the rupture of the liquid bridge was also found to have a strong circulation component which facilitated mixing. The approach here is highly amenable for use in capillary well microplates which have significant advantages over standard microplates. The features of this approach offer usage possibilities in biochemical applications in the field, such as in the leukocyte cell adhesion and hemagglutination tests of blood samples.     

Guided-mode refraction model for optical fiber sensing of surface crystal growth

An empirical "guided-mode refraction model" has been invoked to explain the optical attenuation of radiation in an exposed core optical fiber sensor subject to heterogeneous (surface) crystal growth. Based on Fresnel reflectance values at the internal fiber-crystal and crystal-solution interfaces, the model predictions agree with experimental observations of radial loss of radiation from the fiber core through the crystals as well as attenuation of guided radiation as a function of the radiation launch angle into the fiber.