Development and characterization of a titanosilicate ETS-10-coated optical fiber reactor towards the photodegradation of methylene blue

An optical fiber reactor (OFR) system containing uniformly distributed quartz fibers coated with titanosilicate ETS-10 crystals was investigated. Optimum ETS-10 film thickness (～1.5 μm) and coating length (15 cm) were determined from the light propagation analysis in a single ETS-10-coated fiber. The nearly constant value of the attenuation coefficient (α ≈ 0.10 cm^?1) for films with different thickness indicated uniform fiber surface coverage with these films. The extinction coefficient, ?, decreased from ～1.6 to ～1.0 μm^?1 with ETS-10 film thickness increasing from ～0.5 to ～1.5 μm, which suggested less contact per unit film thickness between light and ETS-10 crystals inside thicker films, likely due to their lower crystal packing density. Photodegradation of methylene blue (MB) conducted in the OFR showed higher photocatalytic activity for thicker ETS-10 films. Although higher MB photodegradation rates were obtained at higher light intensity, the apparent quantum efficiency, Φ, decreased with increasing light intensity. This is consistent with the charge separation mechanism for MB photodegradation in the UV light range investigated. All ETS-10 samples investigated showed ～4–5 times higher Φ values in the OFR than in the slurry reactor, likely due to the unique light/photocatalyst/reactant contact and high fiber packing density in the OFR.     

Migration of methyl groups between aliphatic amines in water

Glycine undergoes spontaneous decarboxylation in dilute aqueous solution at elevated temperatures to form methylamine. During that process, we noticed the appearance of dimethylamine and trimethylamine in smaller amounts that increased gradually with time. These observations suggested the existence of disproportionation reactions of methylamines in water, for which there appears to be no direct precedent in the literature. Every member of the methylamine series is found to yield other members of the methylamine series. When the total concentration of amine was held constant and the rate of reaction was examined as a function of changing pH using the amine itself as the buffer, the initial rate of appearance of the products was found to reach a maximum when the conjugate acid and the conjugate base were present at equivalent concentrations. Near this equivalence point, the rate of reaction varied with pH as expected for a second-order reaction between the protonated and the unprotonated species. Under similar conditions, methyl groups were also found to migrate between the nitrogen atoms of N,N-dimethyl-1,3-propanediamine in a first-order process. With dimethylamine as a common acceptor, trimethylsulfonium ion was found to be approximately 104-fold more reactive than the tetramethylammonium ion at ambient temperature.     

Update on design simulations for NIF ignition targets, and the rollup of all specifications into an error budget

Targets intended to produce ignition on NIF are being simulated and the simulations are used to set specifications for target fabrication and other program elements. Recent design work has focused on designs that assume only 1.0 MJ of laser energy instead of the previous 1.6 MJ. To perform with less laser energy, the hohlraum has been redesigned to be more efficient than previously, and the capsules are slightly smaller. Three hohlraum designs are being examined: gas fill, SiO₂ foam fill, and SiO₂ lined. All have a cocktail wall, and shields mounted between the capsule and the laser entrance holes. Two capsule designs are being considered. One has a graded doped Be(Cu) ablator, and the other graded doped CH(Ge). Both can perform acceptably with recently demonstrated ice layer quality, and with recently demonstrated outer surface roughness. Complete tables of specifications are being prepared for both targets, to be completed this fiscal year. All the specifications are being rolled together into an error budget indicating adequate margin for ignition with the new designs. The dominant source of error is hohlraum asymmetry at intermediate modes 4–8, indicating the importance of experimental techniques to measure and control this asymmetry.     

Charge development in the transition state for decarboxylations in water: spontaneous and acetone-catalyzed decarboxylation of aminomalonate

A covalent imminium adduct, formed by condensation of aminomalonate with acetone, undergoes decarboxylation (k = 0.03 s-1 at 25 degrees C) in water 30 000 times more rapidly than does aminomalonate in the absence of acetone. A Br?nsted plot of the observed rates of decarboxylation of these and other ionized carboxylic acids, as a function of the pKC-H values of the carbon acids generated by their decarboxylation, exhibits a betalg value of 0.7, indicating that the structures of the transition states for decarboxylation of the carboxylate forms of these acids approaches the structures of the carbanions generated by their decarboxylation. On the basis of an estimated pKC-H value for benzene in water ( approximately 43), extrapolation of that Br?nsted plot leads to the prediction that benzoate decarboxylation should proceed at detectable rates in water at temperatures below the critical point. That prediction was confirmed experimentally. Using this same relationship, and extrapolating to the observed rate constant for enzymatic decarboxylation of orotidine 5'-monophosphate, we estimate that the "effective" pKa value of the 6-CH group of uridine 5'-monophosphate, the product of decarboxylation, is 9.5 at the active site of yeast OMP decarboxylase.     

Measurement of Strain Localization Resulting from Monotonic and Cyclic Loading at 650 <Superscript>∘</Superscript>C in Nickel Base Superalloys

A methodology is presented for the use of the oxide scale that develops in polycrystalline Ni-base superalloys at service temperature, as a speckle pattern for μm-scale resolution strain measurements. Quantitative assessment of the heterogeneous strain field at the grain scale is performed by high-resolution SEM digital image correlation under monotonic and cyclic loading in polycrystalline Ni-base superalloys up to 650 ^°C. In the René 88DT superalloy, strain localization is observed near twin boundaries during low cycle fatigue (LCF) at intermediate temperatures, correlating with activation of {111} 〈110〉 and {111} 〈112〉 slip systems. A strong correlation between the microstructural configuration that promotes strain localization during monotonic loading and crack initiation at 650 ^°C in low cycle fatigue was observed.     

Surface-induced dissociation in tandem quadrupole mass spectrometers: A comparison of three designs

Three different devices that-can be used for surface-induced dissociation (SID) m tandem quadrupole instruments are compared here. The designs were compared by examining the fragmentation of several compounds including benzene, W(CO)₆, and (CH₃)₄N⁺. These studies show that SID can be readily implemented on a variety of tandem quadrupoIe instruments and that the spectra obtained with the in-line and 90° instruments are similar. Evidence is presented that confirms that high average internal energies and narrow distributions of internal energy are available by this technique. Efficiencies for fragmentation of odd-electron ions are on the order of those previously reported by others. The overall SID efficiency for even-electron ions is higher than that for odd-electron ions of similar structure.     

An optical waveguide acid vapor sensor

An optical waveguide sensor for the detection of acid vapors is described. The chemically sensitive reagent coating consists of bromothymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562 nm LED source and a phototransistor detector. Response to hydrochloric acid and hydrogen sulphide vapours is both rapid and reversible, with an estimated detection limit for hydrogen sulphide of less than 15 ppm. The sensors exhibits generalized response to protonic acid vapours, but does not produce an indicator response to carbon dioxide, even at large concentrations (1100 mg/l.) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a different approach, either using a reference sensor (Nafion/no indicator) or by monitoring sensor response at two wavelengths.     

Transmissive quasi-optical Ronchi phase grating for terahertz frequencies

A transmissive, square-wave Ronchi phase grating has been fabricated from the dielectric polytetrafluoroethylene to diffract an ~0.7 THz beam quasi-optically. When illuminated by a coherent, cw terahertz (THz) source, the spot separation of the ±1 diffractive orders and the diffraction efficiency were measured as a function of THz frequency and rotation angle. The grating performance depends sensitively on the refractive index, whose value can be measured with an accuracy limited by the fabrication precision. The use of these gratings for polarization-insensitive quasi-optical imaging and phased arrays is discussed.