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101.
This work deals with the Paschen law in electrical breakdown of gases at pd values around the Paschen minimum. From the Townsend model, it is possible to deduce theoretical forms of the coefficients in Paschen's law, of which our calculated values are in the range of the tabulated values from the literature. These formulae show that the breakdown voltage must be influenced by the inter‐electrode distance, while the product pd remains a key parameter. This is confirmed by the Paschen curves measured in an argon discharge for inter‐electrode distances varying from 2 to 9 cm (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
102.
Katarzyna Raulin Odile Cristini-Robbe Patrice Baldeck Olivier Stéphan Christophe Kinowski Sylvia Turrell Bruno Capoen Mohamed Bouazaoui 《Journal of nanoparticle research》2010,12(4):1459-1467
A novel method for direct laser writing of two-dimensional cadmium sulfide (CdS) semiconductor nanoparticle microstructures
is reported. A two photon or a higher-order multiphoton absorption process, originating from femtosecond laser pulses, was
used to decompose CdS precursors dispersed in a zirconia thin film previously dip-coated on a glass substrate. The kinetics
of nanoparticle formation as a function of laser power were monitored in situ by photoluminescence spectroscopy. Raman spectroscopy
was also performed to characterize the structural changes of the zirconia matrix under irradiation and to verify the formation
of CdS nanoparticles. Results show that CdS nanoparticles were formed by two-photon absorption (TPA) with or without the help
of an additional carbazole photoinitiator. 相似文献
103.
Isotopic ratio measurement of methane in ambient air using mid-infrared cavity leak-out spectroscopy 总被引:1,自引:0,他引:1
H. Dahnke D. Kleine W. Urban P. Hering M. Mürtz 《Applied physics. B, Lasers and optics》2001,72(1):121-125
We report on infrared laser spectroscopic measurements of the isotopic composition of methane (12CH4, 13CH4) in natural air samples with a cavity ring-down technique. A CO overtone sideband laser is utilized to excite a high-finesse
cavity which provides an effective optical absorption path length of 3.6 km. We achieved a detection limit of 105 ppt methane
in ambient air using an integration time of 20 s. This corresponds to a minimum detectable absorption of 1.9×10-9 /cm. Rapid determination of the 13C/12Cisotopic ratio of methane in ambient air without sample preconcentration or gas processing is realized. The present system
requires only few minutes for an isotopic ratio measurement with a precision of 11%o .
Received: 14 July 2000 / Revised version: 25 October 2000 / Published online: 6 December 2000 相似文献
104.
Abstract Numerous studies have demonstrated the importance to include pressure as a kinetic parameter in the elucidation of inorganic reaction mechanisms. These studies have specially led to a better understanding and a systematic classification of solvent exchange and ligand substitution reactions of octahedral complexes of transition metal elements. The mechanistic picture for substution reactions on square planar complexes is well established and involves a concurrent bimolecular attack by solvent and the nucleophile on the substrate with a considerable discrimination among different entering groups. The search for factor promoting the conversion of the normal associative mode of activation into a dissociative process has then attracted much attention. Two attempts to induce dissociation, as studied by high-pressure NMR, are presented: one is to prevent the formation by means of sterically hindered ligands, the other one is to promote bond weakening at the leaving group. 相似文献
105.
P. C. Urban 《Journal of Dispersion Science and Technology》2013,34(2-3):233-254
Conductometric coap titration and Maron's3 method of plotting polymer concentration vs. soap concentration is used to determine the molecular adsorption area (MAA) of potassium oleate in a number of polymer and copolymer latex systems. It is demonstrated that the MAA of potassium oleate increases in the series polystyrene→ polybutadiene→polystyrene-coacrylonitrile as well as in a series of polystyrene-coacrylonitrile systems with increasing acrylonitrile content in the polymer composition It is further demonstrated that the MAA increases with temperature at rates dependent on the chemical nature of the polymer systems. The composition induced increases in the MAA correlate as well with the polar nature of the polymer and are attributed to decreasing solubility of the lyophilic segment of the emulsifier chain in the polymer. Temperature induced MAA increases are attributed to Increasing mobility of the hydrophylic emulsifier segment in the aqueous phase. 相似文献
106.
An experiment is discussed in which CO can be excited up to energies of several electronvolts by the absorption of infrared radiation from a relatively low-power CO laser. Furthermore, experimental results are examined through kinetic modelling. In the experiment, the beam of an intracavity-chopped CO laser operating on all lines at 500 mW and containing a few milliwatts of the fundamental ν= 1→0 band component, is focused into an absorption cell containing a mixture of CO and Ar. The absorption of this infrared radiation is monitored by the optoacoustic effect. A second CO laser operating cw and capable of providing 8 W on all lines but not lasing on the ν= 1→0 band component, is then focused into the same volume in the absorption cell. With both lasers simultaneously focused into the absorption cell, strong fluorescence from the irradiated region is detected by a photomultiplier tube. Modulation of the signal intensity with time is observed, and indicates chemical destruction of the CO in the cell. An analysis and kinetic modelling calculation of this experiment shows that it is possible to excite CO up to high vibrational quantum numbers (ν40) at gas temperatures up to 800 K. by means of CO laser irradiation at the fundamental ν= 1→0 band component. One source responsible for the fluorescence signal observed in the experiment is identified as the 4th positive A 1Π→X 1Σ+ spontaneous emission. Although the present kinetic model does not incorporate the chemical processes that may lead to the production of additional fluorescing species such as C2, good agreement is obtained with the observed fluorescence signal characteristics. 相似文献
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