Comment on "Phase-shifting shearing interferometer"

The role of the liquid-crystal layer in the phase-shifting shearing interferometer that was proposed by Griffin [Opt. Lett. 26, 140 (2001)] is analyzed. An extra voltage-dependent phase difference is produced when the phase retarder is oriented at an angle from the optical axis of the laser beam such that the interferogram will not repeat itself after a 2pi phase change of the liquid-crystal retarder in either the common Mach-Zehnder interferometer or the phase-shifting shearing interferometer.     

A hybrid coupling interface method for elliptic complex interface problems

We propose a coupling interface method (CIM) under Cartesian grid for solving elliptic complex interface problems in arbitrary d dimensions, where the coefficients, the source terms, and the solutions may be discontinuous or singular across the interfaces. It consists of a first-order version (CIM1) and a second-order version (CIM2). In one dimension, this finite difference method at a grid point adjacent to the interface is derived based on piecewise linear (CIM1) or quadratic (CIM2) approximation of the solution and two jump conditions. The method is extended to high dimensions through a dimensionby-dimension approach. To connect information from each dimension, a coupled equation for the principal derivatives is derived through the jump conditions in each coordinate direction. For CIM2, one-side interpolation for cross derivatives is need. This coupling approach reduces number of grid point in the finite difference stencil. The hybrid method uses CIM1 or CIM2 adaptly for complex interface. Numerical tests demonstrate that CIM1 and CIM2 are respectively first order and second order in the maximal norm with less error as compared with other methods. In addition, the hybrid CIM can solve complex interface problems in two and three dimensions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Structure Analysis of the Repair of Iron Centers Protein YtfE and Its Interaction with NO

Molecular mechanisms underlying the repair of nitrosylated [Fe–S] clusters by the microbial protein YtfE remain poorly understood. The X‐ray crystal structure of YtfE, in combination with EPR, magnetic circular dichroism (MCD), UV, and ¹⁷O‐labeling electron spin echo envelope modulation measurements, show that each iron of the oxo‐bridged Fe^II–Fe^III diiron core is coordinatively unsaturated with each iron bound to two bridging carboxylates and two terminal histidines in addition to an oxo‐bridge. Structural analysis reveals that there are two solvent‐accessible tunnels, both of which converge to the diiron center and are critical for capturing substrates. The reactivity of the reduced‐form Fe^II–Fe^II YtfE toward nitric oxide demonstrates that the prerequisite for N₂O production requires the two iron sites to be nitrosylated simultaneously. Specifically, the nitrosylation of the two iron sites prior to their reductive coupling to produce N₂O is cooperative. This result suggests that, in addition to any repair of iron centers (RIC) activity, YtfE acts as an NO‐trapping scavenger to promote the NO to N₂O transformation under low NO flux, which precedes nitrosative stress.     

Sensitivity Enhancement of Polyorganophosphazenes to Radiation with 2,2,4,4,6,6-Hexakis(2-Hydroxyethyl Methacrylate)Cyclotriphosphazene Monomer and its Application for Negative Resists

Abstract

This work focuses on the application of a multifunctional phosphazene monomer, 2,2,4,4,6,6-hexakis(2-hydroxyethyl methacrylate)-cyclotriphosphazene (6-Hema) for enhancement of the sensitivity of polyphosphazenes to both ⁶⁰Co and E-beam radiation. Specifically, elastomeric and glassy phosphazene polymer films treated with 6-Hema were irradiated under vacuum, and the gel content was determined. The Charlesby-Pinner approach was used to compare the radiation sensitivities of these films. This served as the basis for eventually preparing SiO₂ wafers with thin films of the glassy polyphosphazenes mixed with or overcoated by the 6-Hema monomer. The SiO₂ wafers prepared with the most sensitive polymer/monomer system were patterned with an ERC electron beam accelerator/scanning electron microscope computer-driven instrument. It was determined that these negative resist films were 1-2 orders of magnitude more sensitive to radiation than the polymers without the monomer.     

Emulsion Polymerization of Acrylic Monomers Stabilized by Poly(Ethylene Oxide)

Abstract

The stability of acrylic latices stabilized by poly(ethylene oxide) (PEO) is governed by the bridging flocculation process during polymerization. The final latex particle size increases with increasing concentration of initiator, PEO, or NaCl. The total scrap formed during the reaction increases rapidly with increasing NaCl concentration due to the ionic strength effect. It is shown that the final latex particle size decreases rapidly with an increase in the agitation speed. The amount of total scrap formed during polymerization is generally greater at a higher agitation speed. These results suggest that the fraction of the particle surface covered by PEO and the ratio of the thickness of the PEO adsorption layer to that of the electric double layer of the latex particles should play an important role in determining the final latex particle size and colloidal stability.     

Semibatch Emulsion Polymerization of Butyl Acrylate: Effect of Functional Monomers

Abstract

The concentration of sodium lauryl sulfate (SLS) in the initial reactor charge is the most important parameter in determining the latex particle size during semibatch emulsion polymerization of butyl acrylate in the presence of acrylic acid (AA), methacrylic acid, or hydroxyethyl methacrylate. The final latex particle size decreases with increasing concentration of SLS, NP-40, or functional monomer. The carboxylic monomer AA is the most efficient functional monomer to nucleate and then stabilize the latex particles. The plot of log N _f vs log SLS shows a slope of 0.4–0.8, which is more consistent with Feeney's analysis based on the coagulative nucleation mechanism. Experimental data also show that the particle size first decreases to a minimum and then increases with an increase in the concentration of the neutralizing agent NaHCO₃. The optimal concentration NaHCO₃ for achieving the smallest latex particle size occurs at a point close to 0.15–0.29%. Experimental data of the particle size distribution and molecular weight distribution show that the aqueous phase reaction can play a very important role during the particle nucleation period.     

Exploring ground states and excited states of spin-1 Bose–Einstein condensates by continuation methods

A pseudo-arclength continuation method (PACM) is employed to compute the ground state and excited state solutions of spin-1 Bose–Einstein condensates (BEC). The BEC is governed by the time-independent coupled Gross–Pitaevskii equations (GPE) under the conservations of the mass and magnetization. The coupling constants that characterize the spin-independent and spin-exchange interactions are chosen as the continuation parameters. The continuation curve starts from a ground state or an excited state with very small coupling parameters. The proposed numerical schemes allow us to investigate the effect of the coupling constants and study the bifurcation diagrams of the time-independent coupled GPE. Numerical results on the wave functions and their corresponding energies of spin-1 BEC with repulsive/attractive and ferromagnetic/antiferromagnetic interactions are presented. Furthermore, we reveal that the component separation and population transfer between the different hyperfine states can only occur in excited states due to the spin-exchange interactions.     

A novel derivatization approach for simultaneous determination of glyoxal, methylglyoxal, and 3-deoxyglucosone in plasma by gas chromatography-mass spectrometry

A two-step derivatization approach has been developed to enable the simultaneous analysis of glyoxal, methylglyoxal, and 3-deoxyglucosone by the most efficient and widely applied GC-MS methodology. These three analytes are reactive carbonyl compounds associated with the formation of advanced glycation and lipoxidation end products, a process thought to contribute to uremic toxicity and referred to as "carbonyl stress". Effective analysis of these compounds would facilitate understanding these compounds' role in diabetes-related complications. Plasma samples were deproteinized by acetonitrile, followed by a two-step derivatization approach. Pooled plasma samples from healthy individuals were used as the "blank" for preparing calibration standards. The concentrations of the analytes in the "blank" were first determined by standard addition method. Calibration parameters were accordingly established and used to analyze these compounds in plasma samples collected from healthy individuals and diabetic patients. Analytical findings are comparable with those reported in the literature. Quantitation data can be further improved by making available and using isotopically labeled analogs of these analytes as the internal standards.