Structure and Photodissociation Spectra of Mixed Ethene-Acetone Clusters

Infrared photodissociation spectra of the mixed complexes C2H4-CH3COCH3 and C2H4-(CH3COCH3)2 have been observed after size selecting them by scattering from a helium beam combined with mass spectrometric detection. The excitation of the v7-out of plane symmetric wagging mode of ethene near its gas phase frequency at 949.3 cm-1 with a cw-CO2 laser leads to a characteristic depletion of the cluster beam. The dissociation spectrum of the 1:1 complex can be explained by two peaks at 950.8 and 961.6 cm-1. Calculations of minimum energy configurations and band shifts based on an empirical site-site potential show that these frequencies can be attributed to the absorption of two different isomers. They correspond to the two different binding patterns of the H atoms of ethene to the O atom of acetone and those of acetone to the C-C group of ethene, respectively. For the 1:2 complex, a large peak at 958.5 cm-1 and a smaller onearound 940.5 cm-1 are found which can be explained in a similar manner by several isomers found in the structure calculations

A descriptive analysis of relations between parents' self-reported smoking behavior and infants' daily exposure to environmental tobacco smoke

<p>Abstract</p> <p>Background</p> <p>The aims of the present study were to examine relations between parents' self-reported smoking behavior and infants' daily exposure to environmental tobacco smoke, as assessed by urinary cotinine-to-creatinine ratio (CCR), and to describe the CCR over seven days among infants at home.</p> <p>Methods</p> <p>A convenience sample of 27 households was drawn. Each household had to have at least one daily tobacco smoker and one child up to three years of age. Over a seven-day period, urine samples were obtained from the child daily. To examine relations between parents' self-reported smoking and infants' daily CCR, generalized estimating equation (GEE) analysis was used.</p> <p>Results</p> <p>The data revealed that infants from households with indoor smoking had higher CCRs than infants in households with outdoor smoking. CCRs were higher in girls than in boys. Older infants had lower CCRs than younger infants. Smoking outside the home versus inside the home, infant's gender, and infants' age accounted for 68% of the variance in CCR in a GEE data analysis model. No increase or decrease of CCR over time was found.</p> <p>Conclusion</p> <p>The findings suggest that parents' self-reported smoking indoors at home versus outdoors is predictive of CCR among infants three and younger. Higher CCR concentrations in girls' urine need further examination. Furthermore, significant fluctuations in daily CCR were not apparent in infants over a seven-day time period.</p

Herstellung von dünnen Elektrolytschichten mittels Laserablation und Kathodenzerstäubung für Hochtemperatur-Brenn

Solid oxide fuel cells (SOFCs) are presently operated at temperatures between 800 and 1000°C. Lowering the operation temperature to 600°C at unchanged power density would increase the durability of the fuel cell stack. Alternative electrolyte materials with a higher electric conductivity and thinner electrolyte films show a possibility to reach this objective. Within this work preferable 1-2 µm thin yttrium oxide stabilised zirconia oxide (YSZ) electrolyte films are deposited using two well known physical vapour deposition (PVD) processes, the pulsed laser deposition (PLD) process and the sputtering process. Alternatively lanthanum gallate films of the system La1-xSrxGa1-yMgyO3-1/2(x+y) (LSGM) are deposited using the PLD process. The films are analysed with regard to the crystal phases, element distribution, crystal growth, morphology and gas tightness. Electrochemical analyses give information about the power density of the fuel cells. A reduction of the YSZ electrolyte film thickness of 7-8 µm to 1.5-2 µm causes an increase of the leakage rate of 1-2 magnitudes. Layer growth models in the literature confirm the morphology of the electrolyte coatings. The typical columnar crystallite structure of PVD films is induced at high process gas pressures. Whereas small pressures promote the growth of dense coatings. By increasing the process gas pressure the transfer of the disordered cubical into the cubical YSZ structure is verified. Partial reduction of the nickel oxide (NiO) grains of the substrate at the film to substrate interface can be proved at little oxygen supply and temperatures > 400°C. The oxygen bound to the NiO diffuse across the YSZ matrix of the substrate into the growing film. Small process gas pressures induce a crystal structure orthogonal to the (100) crystal layer. The concentration ratio of the elements Zr and Y confirm the formation of 8 mol% Y2O3 stabilised ZrO2. No influences of the film thickness on the electric power density of the fuel cells are measured. Amorph deposited LSGM films crystallise after heat treatment in air. At 1200°C only the LSGM phase is formed. Treated films at this temperature are electrochemical characterised afterwards. Ni diffusion from the anode substrate into the electrolyte (12 at%) and further into the cathode (22 at%) cause an electronic short-circuit of the fuel cell after a few minutes. Therefore no current voltage curves are recorded. LSGM is not suitable as an electrolyte material in direct contact with Ni/YSZ anode cermets for solid oxide fuel cell applications

Pulsed laser deposition of yttria-stabilized zirconia for solid oxide fuel cell applications

Yttria stabilized zirconia (YSZ) films were grown by pulsed laser deposition (PLD) from a 8YSZ target using a KrF excimer laser source (248 nm). The films have been deposited under oxygen atmospheres on porous NiO/YSZ substrates heated from room temperature to 600 degreesC. YSZ films were obtained in the range of 1-2 mum thickness. The films have been investigated with respect to surface morphology, microstructure and film-substrate interface interaction. The film morphology varied from columnar to an irregular crystalline structure depending on the oxygen pressure and the substrate temperature, In all cases the films consisted of YSZ with the cubic fluorite structure. The formation of oxide layers under low oxygen pressures on the NiO/YSZ substrates is due to a film-substrate redox interaction. The NiO grains close to the coating interface are partially reduced and serve as an oxygen source for the oxidation of the film. The measured He leakaae rates to analyze the gas tightness of the YSZ films have so far shown no improvements as compared with uncoated substrates. (C) 2002 Elsevier Science B.V. All rights reserved