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971.
B.S. Kang S. Kim F. Ren K. Ip Y.W. Heo B.P. Gila C.R. Abernathy D.P. Norton S.J. Pearton 《Applied Physics A: Materials Science & Processing》2005,80(2):259-261
Bulk Pt/ZnO Schottky rectifiers show gas sensitivities for CO of 4% and 8%, respectively, at 150 °C for 1 and 10% CO in N2. The current or voltage changes are time dependent, with an activation energy of 40.7 kJmol-1. Over a limited range of partial pressures of CO (PCO) in the ambient gas, the on-state resistance R of the sensor at fixed bias voltage decreased according to R=(RO+A(PCO)0.5)-1, where A is a constant and RO is the resistance in N2. Since these devices are also sensitive to H2 and C2H4, the ZnO rectifiers appear promising for a range of gas-sensing applications. PACS 81.05.Dz; 73.61.Ga; 72.80.Ey 相似文献
972.
Lores M Llompart M Sanchez-Prado L Garcia-Jares C Cela R 《Analytical and bioanalytical chemistry》2005,381(6):1294-1298
Photodegradation is a possible way to eliminate organic pollutants from the environment but, at the same time, can be a source of toxic byproducts. The photochemical conversion of triclosan, a common pollutant in continental waters, into dichlorodibenzo-p-dioxin (DCDD) has been confirmed in our preliminary experiments employing photo-SPME (photo-solid-phase microextraction) using 18-W UV irradiation at 254-nm wavelength. Under these conditions, triclosan is rapidly photodegraded (70% of triclosan was degraded in 2 min); the most important novel aspect of this work is the conversion of triclosan to DCDD directly on the polydimethylsiloxane coating of the SPME fiber. Moreover, this conversion is also confirmed in non-buffered aqueous photodegradation experiments using SPME as the extraction technique. In all the experiments of this study, analysis was carried out by gas chromatography–electronic impact mass spectrometry (GC–EI/MS). 相似文献
973.
Structural mobility is useful for the estimation of structural power flows in coupled systems. Although the methods of measuring structural mobilities are easily found for one-dimensional beam structures, few are available for cylindrical shells. In this paper, a new method is proposed for the measurement of the structural mobilities of a circular cylindrical shell. A point force excitation is used instead of circumferential modal forces which are difficult to implement in practice. This method utilizes the least squares technique to obtain the transfer function components of different circumferential modes from the measured data. Experiments were carried out on a circular cylindrical shell with different end conditions excited by a point force to verify the feasibility of this proposed method. 相似文献
974.
Blowing of silica microforms on silicon carbide 总被引:1,自引:0,他引:1
Silicon carbide ceramics have great potential for use in harsh environment applications, however many technical challenges still need to be addressed, including high temperature stability. The oxidation of SiC in air up to temperatures of 2053 K was conducted and resulted in the formation of a thermally grown silica scale that does not prove to be protective for very high temperature applications because of its rapid degradation. Examination of the oxide scale using scanning electron microscopy revealed the presence of striking features formed in a manner analogous to conventional glass blowing techniques. These features occurred for oxidation temperatures of at least 1773 K. The interfacial reaction between SiC and the oxide scale is responsible for the production of gases that must somehow escape. If the viscosity of the silica scale is low enough then it can be deformed freely by this pressure buildup. 相似文献
975.
César Ricardo Teixeira Tarley Eduardo da Costa Figueiredo Geraldo Domingues Matos 《Analytical sciences》2005,21(11):1337-1342
The present paper describes the on-line coupling of a flow-injection system to a new technique, thermospray flame furnace-AAS (TS-FF-AAS), for the preconcentration and determination of copper in water samples. Copper was preconcentrated onto polyurethane foam (PUF) complexed with ammonium O,O-diethyldithiophosphate (DDTP), while elution was performed using 80% (v/v) ethanol. An experimental design for optimizing the copper preconcentration system was established using a full factorial (2(4)) design without replicates for screening and a Doehlert design for optimization, studying four variables: sample pH, ammonium O,O-diethyldithiophosphate (DDTP) concentration, presence of a coil and the sampling flow rate. The results obtained from the full factorial and based on a Pareto chart indicate that only the pH and the DDTP concentration, as well as their interaction, exert influence on the system within a 95% confidence level. The proposed method provided a preconcentration factor of 65 fold, thus notably improving the detectability of TS-FF-AAS. The detection limit was 0.22 microg/dm3 and the precision, expressed as the relative standard deviation (RSD) for eight independent determinations, was 2.7 and 1.1 for copper solutions containing 5 and 30 microg/dm3, respectively. The procedure was successfully applied for copper determination in water samples. 相似文献
976.
Robson Matos Mohamed F. Meidine John F. Nixon Bernadette F. Trigo Passos Edgar Niecke Detlef Barion 《Journal of organometallic chemistry》1990,390(3)
Different types of ligating behaviour of the R
R′ ring system are reported; the sp2 hybridised phosphorus is the donor atom in Pt(0), W(0) and Rh(I) complexes, whereas ligation of the sp3 hybridised phosphorus atom is preferred by Pd(II), and both phosphorus atoms are ligated in dinuclear Pt(II) systems. 相似文献
977.
Crystallographic data for the oxoapatites of general formula Ca8
Ln
2(PO4)6O2 withLn=La, Pr-Ho) have been obtained from X-ray powder data. The vibrational spectra, which are also discussed, allow to make a proposal about the location of the lanthanide cations present in these lattices. 相似文献
978.
979.
980.
A. Del Guerra A. Giazotto M.A. Giorgi A. Stefanini D.R. Botterill H.E. Montgomery P.R. Norton G. Matone 《Nuclear Physics B》1976,107(1):65-81
Threshold π+ electroproduction has been measured at momentum transfers 6k26 of 0.45, 0.58 and 0.88 (GeV/c)2, extending the range of earlier measurements. Using PCAC and current algebra-based models we have deduced the axial vector form factor of the nucleon GA(k2), and find that the dipole parametrisation is favoured over the monopole. The value of MA in the dipole parametrisation is, in a weak PCAC model, 0.96 ± 0.03 GeV, in excellent agreement with neutrino measurements. The threshold cross section is also in excellent agreement with the predictions of a fixed-t dispersion relation model. 相似文献