Reaction dynamics study of O- + C2H2 with crossed beams and density-functional theory calculations

The reactions between O(-) and C(2)H(2) have been studied using the crossed-beam technique and density-functional theory (DFT) calculations in the collision energy range from 0.35 to 1.5 eV (34-145 kJmol). Both proton transfer and C-O bond formation are observed. The proton transfer channel forming C(2)H(-) is the dominant pathway. The center-of-mass flux distributions of the C(2)H(-) product ions are highly asymmetric, with maxima close to the velocity and direction of the precursor acetylene beam, characteristic of direct reactions. The reaction quantitatively transforms the entire reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the proton is transferred in a configuration in which both the breaking and the forming bonds are extended. The C-O bond formation channel producing HC(2)O(-) displays a distinctive kinematic picture in which the product distribution switches from predominantly forward scattering with a weak backward peak to sideways scattering as the collision energy increases. At low collision energies, the reaction occurs through an intermediate that lives a significant fraction of a rotational period. The asymmetry in the distribution leads to a lifetime estimate of 600 fs, in reasonable agreement with DFT calculations showing that hydrogen-atom migration is rate limiting. At higher collision energies, the sideways-scattered products arise from repulsive energy release from a bent transition state.     

Spectrophotometric determination of p.p.b. levels of long-chain amines in waters and raffinates

An analytical procedure is described for the determination of p.p.b. levels of long-chain amines in river and sea water and uranium processing raffinates. The method involves extraction of the amine as an ion-association complex with chromate from sulphuric acid media into chloroform. The extracted chromium(VI) is then determined spectrophotometrically with diphenylcarbazide. With a 100-ml sample, the limit of detection for Alamine 336 (a commercial tertiary amine mixture) is 15 p.p.b.     

Quantum state-resolved study of the four-atom reaction OH- (X1sigma+) + D2 (X1sigma(g)+, v = 0) --> HOD (X1A', v') + D- (1S)

The D+ transfer reaction between OH- (X1sigma+) and D2 was studied with crossed molecular beam experiments and quantum chemical calculations at collision energies of 89 and 68 kJ/mol. The D- product ions were observed and measured for the first time in the crossed beam experiments. The center-of-mass (c.m.) flux distributions of the D- product ions exhibit significant asymmetry, and their maxima are close to the velocity and direction of the precursor D2 beam. The data are consistent with a direct mechanism that occurs on a time scale significantly less than a rotational period of the transient complex formed by approaching reactants. The D+ transfer results primarily in the excitation of the H-O-D bending vibrational mode of the molecular product. The experimental observation is in agreement with theoretical results showing that, during the D+ transfer, the H-O-D bond angle changes significantly.     

Dynamic nuclear polarization at 9T using a novel 250GHz gyrotron microwave source

In this communication, we report enhancements of nuclear spin polarization by dynamic nuclear polarization (DNP) in static and spinning solids at a magnetic field strength of 9T (250 GHz for g=2 electrons, 380 MHz for 1H). In these experiments, 1H enhancements of up to 170+/-50 have been observed in 1-13C-glycine dispersed in a 60:40 glycerol/water matrix at temperatures of 20K; in addition, we have observed significant enhancements in 15N spectra of unoriented pf1-bacteriophage. Finally, enhancements of approximately 17 have been obtained in two-dimensional 13C-13C chemical shift correlation spectra of the amino acid U-13C, 15N-proline during magic angle spinning (MAS), demonstrating the stability of the DNP experiment for sustained acquisition and for quantitative experiments incorporating dipolar recoupling. In all cases, we have exploited the thermal mixing DNP mechanism with the nitroxide radical 4-amino-TEMPO as the paramagnetic dopant. These are the highest frequency DNP experiments performed to date and indicate that significant signal enhancements can be realized using the thermal mixing mechanism even at elevated magnetic fields. In large measure, this is due to the high microwave power output of the 250 GHz gyrotron oscillator used in these experiments.     

Rotational motion in liquid water is anisotropic: a nuclear magnetic resonance and molecular dynamics simulation study

Experimental NMR measurements of the deuterium and (17)O T(1) relaxation times in deuterium-enriched liquid water have been performed from 275 to 350 K. These relaxation times can yield rotational correlation times of appropriate molecule-fixed unit vectors if the quadrupole coupling constants and asymmetry parameters are known. We determine the latter from ab initio studies of water clusters and experimental chemical shift measurements. We find that the rotational correlation time for the OD bond vector in D(2)(16)O varies from 5.8 ps at 275 K to 0.86 ps at 350 K, and that the rotational correlation time for the out-of-plane vector of dilute D(2)(17)O in D(2)(16)O varies from 4.4 ps at 275 K to 0.64 ps at 350 K. These results indicate that the rotational motion of water is anisotropic. Molecular dynamics simulations of liquid water are in good agreement with these experiments at the higher temperatures, but the simulation results are considerably faster than experiment at the lower temperatures.     

Chemical aerosol detection and identification using Raman scattering

Early warning of the presence of chemical agent aerosols is an important component in the defense against such agents. A Raman spectrometer has been constructed for the purpose of detecting and identifying chemical aerosols. We report the detection and identification of a low‐concentration chemical aerosol in atmospheric air using 532‐nm continuous wave laser Raman scattering. We have demonstrated the Raman scattering detection and identification of an aerosol of isovanillin of mass concentration of 1.8 ng/cm³ with a signal‐to‐noise ratio of about 19 in 30 s for the 1116‐cm⁻¹ mode with a Raman cross section of 3.3 × 10⁻²⁸ cm² using 8‐W double‐pass laser power. Copyright © 2014 John Wiley & Sons, Ltd.     

On damage diagnosis for a wind turbine blade using pattern recognition

With the increased interest in implementation of wind turbine power plants in remote areas, structural health monitoring (SHM) will be one of the key cards in the efficient establishment of wind turbines in the energy arena. Detection of blade damage at an early stage is a critical problem, as blade failure can lead to a catastrophic outcome for the entire wind turbine system. Experimental measurements from vibration analysis were extracted from a 9 m CX-100 blade by researchers at Los Alamos National Laboratory (LANL) throughout a full-scale fatigue test conducted at the National Renewable Energy Laboratory (NREL) and National Wind Technology Center (NWTC). The blade was harmonically excited at its first natural frequency using a Universal Resonant EXcitation (UREX) system. In the current study, machine learning algorithms based on Artificial Neural Networks (ANNs), including an Auto-Associative Neural Network (AANN) based on a standard ANN form and a novel approach to auto-association with Radial Basis Functions (RBFs) networks are used, which are optimised for fast and efficient runs. This paper introduces such pattern recognition methods into the wind energy field and attempts to address the effectiveness of such methods by combining vibration response data with novelty detection techniques.     

Coherent anti-Stokes Raman scattering and normal anti-Stokes Raman scattering due to LO phonons in GaP using cw diode lasers

Coherent anti-Stokes Raman scattering (CARS) and normal anti-Stokes Raman scattering (NARS) have been measured in (001) GaP at room temperature due to the 403 cm⁻¹ LO phonons using a continuous wave (CW) 785.0 nm fixed-wavelength pump laser and a CW Stokes laser tunable in the 800-830 nm wavelength range. CARS measurements are normally made using pulsed lasers. The use of CW diode lasers allows a more accurate comparison between the measured and calculated values of the CARS signal. The pump and Stokes laser beams were linearly polarized perpendicular to each other, same as the pump and normal Stokes/anti-Stokes scattered light for the GaP sample used in this work. The pump and Stokes laser powers incident upon the GaP sample, located in the focal plane of a 20 mm effective focal length lens, were <20 and 50 mW, respectively. The diameter of the laser beams in the focal plane of the focusing lens was determined to 40±5 μm. The pump and Stokes laser beam intensities incident upon the 0.3 mm thick GaP sample were <2 and 5 kW cm², respectively. The powers of the CARS and NARS signals were measured using a Raman spectrometer. The signal output of the Raman spectrometer was calibrated using the pump laser and several neutral density filters. The Raman linewidth (full-width at half-maximum) of the LO phonons was determined to be 0.95±0.05 cm⁻¹, using the variation of the CARS signal with the wavelength of the Stokes laser. The measured powers of the CARS and NARS signals are about a factor of 5 and 1.5, respectively, smaller than those calculated from the corresponding theoretical expressions.