Gas-Liquid Chromatography and Mass Spectrometry in Methylation Analysis of Polysaccharides

New methylation procedures and the combined application of gas-liquid chromatography and mass spectrometry for the qualitative and quantitative analysis of mixtures of methylated sugars permit methylation analysis of polysaccharides to be performed more accurately, faster, and with less material than previously.     

Differential scanning calorimetry of chlorinated polyethylenes

The heats of fusion of low-density polyethylene and chlorinated polyethylenes of varying chlorine content have been investigated by differential scanning colorimetry (DSC). Linear correlations are found between the chlorine content and the apparent heat of fusion, crystallinity, and the maximum specific heat measured in the temperature range 90–120°C. The effect of heat treatment on crystallinity is shown to be strongly dependent on the chlorine content of the polymers.     

Protein Microarrays on Carboxymethylated Dextran Hydrogels: Immobilization, Characterization and Application

Tetraoctadecylammonium bromide (TOAB, (CH₃(CH₂)₁₇)₄N⁺Br^–) has been used to print temporary hydrophobic barriers on carboxymethylated dextran (CMD) hydrogels to create a generic platform for protein microarray applications. The primary reason for printing temporary hydrophobic barriers is to prevent cross-contamination and overflow during microdrop dispensing. Equally important is to eliminate the risk for non-specific binding to the barriers during analyte exposure. This has been accomplished by introducing a regeneration step that removes the barriers after ligand immobilization. The overall fabrication process was characterized by microscopic wetting, atomic force microscopy, imaging ellipsometry, fluorescence microscopy, surface plasmon microscopy and biospecific interaction analysis. A series of model proteins including transferrin, Protein A, anti-myoglobin and bovine serum albumin was spotted into the TOAB-defined areas under different experimental conditions, e.g. at increased humidity and reduced substrate temperature or with glycerol as an additive in the protein solution. Much emphasis was devoted to studies aiming at exploring the homogeneity and activity of the immobilized proteins. The printed barriers were removed after protein immobilization using tert-n-butyl alcohol (TBA). TBA was found to be a very efficient agent as compared to previously used salt regeneration solutions, and the regeneration time could be reduced from 30 to 10 minutes. Finally, the potential of using the well established CMD hydrogel chemistry as a platform for protein microarrays was exploited using surface plasmon microscopy.     

Quantum Integrable and Nonintegrable Nonlinear Schrödinger Models for Realizable Bose–Einstein Condensation in d+1 Dimensions (d = 1, 2, 3)

We evaluate finite-temperature equilibrium correlators for thermal time ordered Bose fields to good approximations by new methods of functional integration in d=1,2,3 dimensions and with the trap potentials V(r)0. As in the translationally invariant cases, asymptotic behaviors fall as to longer-range condensate values for and only for d=3 in agreement with experimental observations; but there are generally significant corrections also depending on due to the presence of the traps. For d=1, we regain the exact translationally invariant results as the trap frequencies 0. In analyzing the attractive cases, we investigate the time-dependent c-number Gross–Pitaevskii (GP) equation with the trap potential for a generalized nonlinearity –2c||²ⁿ and c<0. For n=1, the stationary form of the GP equation appears in the steepest-descent approximation of the functional integrals. We show that collapse in the sense of Zakharov can occur for c=0 and nd2 and a functional E _NLS[]0 even when V(r)0. The singularities typically arise as -functions centered on the trap origin r=0.     

The composition and optical absorption coefficient of atmospheric particulate matter

The optical absorption spectra of atmospheric dust as determined by transmission and diffuse reflectance spectroscopic methods is discussed in the 0.4 to 40 um wavelength range. Quantitative measurements are presented which show the imaginary refractive index to be about 0.007i, with little wavelength dependence, in the 0.4 to 1.3 μm spectral interval. The absorption coefficients of individual materials found in atmospheric dust are also given. This work suggests that atmospheric dust may be composed mainly of weakly absorbing particles contaminated with small amounts of very strongly absorbing materials such as free carbon. The implications of this are discussed from the point of view of laser beam attenuation and lidar return signals. Mie theory computations for ruby lidar wavelengths are shown which suggest that for some models of atmospheric dust, the concept of an average imaginary refractive index may be misleading. Thus, it may be necessary to consider the individual complex refractive indices and size distributions of more than one constituent material present in the dust. This implies that anthropogenic contributions to the atmospheric aerosol, such as free carbon and other strong absorbers, may be of greater optical significance than their relative concentrations might indicate.     

Quantum-dot quantum-interference infrared design proposal photodetector: and modeling of performance characteristics

A novel design of an IR photodetector operating at wavelengths around 10 microm is presented. It is based on a three-level quantum coherence effect in semiconductor quantum dots as measured in balanced-homodyne detection in a Mach-Zehnder interferometer. The advantage of this design is the combination of room-temperature operation and fast response time, whereas the major drawback is the high noise-equivalent power.     

Separation of oligonucleotides in N-methyl-formamide-based polymer matrices by capillary electrophoresis

N-Methylformamide (NMF)-based matrices for capillary electrophoretic separation of nucleic acids have been developed. The use of an organic solvent as liquid base for the separation matrices allowed a hydrophobic polymer, C16-derivatized 2-hydroxyethyl cellulose (HEC), to be employed as structural element in the sieving medium. With a matrix consisting of 5% w/v of this polymer dissolved in NMF containing 50 mM ammonium acetate, p(dA)12-18 and p(dA)40-60 oligonucleotides were baseline separated. The addition of ammonium acetate to the buffer and separation matrix resulted in enhanced separation efficiency. Furthermore, it was possible to tailor the sieving performance of the separation medium by the use of a binary mixture of C16-derivatized HEC and PVP. Differences in sieving behavior of the various matrices evaluated are discussed.     

Assessing the contribution of natural sources to the global mercury cycle: The importance of intercomparing dynamic flux measurements

In order to constrain the contribution of natural sources of mercury to the global atmospheric cycle we need to: 1. assess the methods used to measure mercury flux, 2. characterize those factors most important in controlling emissions, 3. develop a database of emissions from representative locations, and 4. develop a means of scaling up measured emissions to estimate fluxes on a regional basis. This paper describes how an international multi-collaborator project, the Nevada SToRMS Project, held September 1997 in Reno, Nevada, USA, contributed to our ability to constrain natural source mercury emissions. This study entailed a field intercomparison of those methods typically applied to measure mercury flux from substrate combined with evening workshops and roundtable discussions. The project was unique in that it focused on assessing our ability to measure the flux of an environmental contaminant. This is more difficult than measurement of the concentration of a contaminant because of the number and nature of the variables which influence the field flux measurements, including experimental design, spatial heterogeneity, and temporally changing environmental conditions. As a result of the Nevada SToRMS Project, rapid and significant advances in our understanding of how to constrain emission fluxes from large areas of mercury enrichment were realized. Because this intercomparison was a multi-investigator project, the results and implications of the project have been broadly circulated. The sincere scientific collaboration that evolved amongst those working on the study has led to significant advancements in our understanding of the fate and transport of mercury in the environment. Received: 1 July 1999 / Revised: 14 September 1999 / Accepted: 18 September 1999