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851.
852.
853.
A segmented hollow cathode has been designed, constructed and operated over a wide pressure range from 1 mbar to 200 mbar to determine optimum operating characteristics for a series of unique applications. The device is designed for use as a plasma source for molecular gas lasers operating in the UV and visible spectra. The cathode consists of 1 mm thick nickel disks and 0.1 mm tungsten foil disk segments stacked alternately, forming a cylindrical geometry on its outer surface and a near-spherical geometry inside. The tungsten foil disk inner diameters vary along the longitudinal axis of the cathode. With this special geometric arrangement one hollow cathode structure is embedded within another. The spacing between the segments (tungsten foil disks) creates one hollow cathode geometry, and the spherical geometry formed by the inner diameter of the segments is a second hollow cavity. This design permits one to operate the device at an expanded pressure range. The device's voltage and current characteristics are studied at different operating pressures and the optimum operating parameters such as pressure, voltage, current, and foil thickness are investigated. Helium, argon or a helium-argon mixture is used as the fill gas throughout the series of experiments  相似文献   
854.
855.
U.V. irradiation of MeOH and CH3CN solutions of trans-[Pd(PPr3n)2(NCS)2] causes a stepwise photochemical reaction. When the solvent is CH3CN the photoproduct can be conveniently isolated in a crystalline form. This compound has been shown, by X-ray analysis, to be a cyano bridged palladium(II) complex.  相似文献   
856.
Experimental methods for determining longitudinal crystal moduli of polymers were evaluated in light of recent proceesing methods that produced macroscopic Young's moduli which exceeded ultimate values as found by the x-ray diffraction method. The spectroscopic techniques of Raman and coherent inelastic neutron scattering yielded higher longitudinal crystal moduli than x-ray diffraction, and from calculations described herein it is concluded that these spectroscopic values are better estimates of the maximum Young's moduli in fully aligned and crystalline polymeric materials.  相似文献   
857.
We present numerical results on the flame attachment in the downstream vicinity of the co-flow injector lip that separates the reactive fluids at injection. Two stability diagrams show the domains where the flame is anchored, blown off, or extinguished, in terms of separating plate thickness and injection velocities of both fluids. Different anchoring modes—stagnation point counter-flow holding or edge flame anchorage—are described, depending particularly on the plate rim thickness. To cite this article: C. Nicoli et al., C. R. Mecanique 334 (2006).  相似文献   
858.
The redox bistelomerization of allyl acetate with telogens which exhibit α, ω-di(trichloromethyled) end groups catalyzed by copper, iron salts, or a ruthenium complex led to monoadducts and telechelic oligomers. These diacetates were quantitatively changed into diols. Such compounds have been characterized by both 1H- and 13C-NMR. A reactivity series has been determined and shows that both end groups must be activated to obtain the expected telechelic products in satisfactory yields.  相似文献   
859.
Easily accessible open chain and cyclic silyl enolethers show dienophilic reactivity in (4 + 2)-cycloaddition reactions with inverse electron demand equivalent to enol ethers. Preparative and kinetic results are reported.  相似文献   
860.
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