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951.
Oscillating nature of current pulses under d.c. excitation in subnormal region with longitudinal magnetic field at pressure
range 0.20 torr to 0.85 torr have been studied. The frequency, bandwidth, peak-peak voltage, cut-off current and rise time
of the current pulses have been observed with pressure, average tube current and magnetic field. A study of these oscillograms
in magnetic field, average tube current and pressure are presented. The probable mechanism for the generation of oscillation
based on space-charge field modification with magnetic field is discussed 相似文献
952.
S. Longo G. Comunale C. Gorse M. Capitelli 《Plasma Chemistry and Plasma Processing》1993,13(4):685-700
Two simple kinetic models of a Ne-buffered XeCl laser discharge are presented based on different simplifications of the chemical kinetics of a complex model that recently appeared in the literature. When applied to the study of a small-volume XeCl laser, the results of both simple and complex models are in satisfactory agreement with the experiments. Shifting to a larger-volume laser, both models show problems due to loss of stability of the discharge. A one-dimensional modelling is performed, and it is found that different assumptions on the kinetics of the NeXe+ ion in the discharge lead to completely different results as regards the effect of a preionization-triggered instability. 相似文献
953.
Pascal triangles are formulated for computing the coefficients of the B-spline series representation of the compactly supported
spline-wavelets with minimum support and their derivatives. It is shown that with the alternating signs removed, all these
sequences are totally positive. On the other hand, truncations of the reciprocal Euler-Frobenius polynomials lead to finite
sequences for orthogonal wavelet decompositions. For this purpose, sharp estimates are given in terms of the exact reconstruction
of these approximate decomposed components.
Research supported by NSF Grant DMS 89-0-01345 and ARO Contract No. DAAL 03-90-G-0091. 相似文献
954.
We discuss possible experiments which can exploit recently-developed techniques to accumulate, store, and manipulate low-energy positrons to measure the parameters associated with positron annihilation radiation from media of astrophysical interest. Media discussed include collections of dust grains, partially ionized gases, He, H2, and other molecular gases and gas mixtures, including polycyclic aromatic hydrocarbon (PAH) molecules relevant to the interstellar medium. 相似文献
955.
C. Cooper 《Random Structures and Algorithms》1993,4(4):469-472
Let D 2(n) be the probability space of 2-regular digraphs on n vertices with the uniform measure. As n tends to infinity, the probability that the digraphs are 2-connected tends to 1. © 1993 John Wiley & Sons, Inc. 相似文献
956.
Summary A new gas chromatographic method using an automatic purge-and-trap system coupled to a GC with mass selective detection to analyze styrene at the parts-per-trillions (ng kg–1) level is described. The method shows a good sensitivity and the detection limit is 10 ng kg–1 with a relative standard deviation (RSD) of 4.7% for 164 ng kg–1 styrene in olive oil. This analytical method has been successfully applied to the analysis of styrene in extra-virgin olive oil from the European market. 相似文献
957.
Earth-orbiting spacecraft often contain solar arrays or antennas supported by a preloaded mast. Due to weight and cost considerations, the supporting structures of the spacecraft appendages are made extremely light and flexible. Therefore, it is essential to investigate the influence of all physical and structural parameters on the dynamic behavior of the overall structure. The governing equation of motion and its general solution for the preloaded mast are developed. Furthermore, the mass moment of inertia of the mast subjected to bending vibrations is included in the governing equation of motion to investigate its influence on determining the circular frequencies. To verify the developed formulations, a finite element technique was implemented. The accuracy and limitation of the technique on calculating the circular frequencies are discussed. Although the study described in this paper primarily focuses on the mast for the space station solar arrays, the developed formulations and techniques can be applied to any large and flexible beam in zero gravity. 相似文献
958.
Necessary conditions for energy-minimizing deformations are derived for a theory of sheets in which the strain energy function depends on the second derivatives of the deformation as well as its first derivatives. All of these conditions are extensions of well-known necessary conditions in classical calculus of variations. The interpretation of some of these conditions as material stability conditions is explained. 相似文献
959.
Diana C. Skigin Miriam L. Gigli Marina E. Inchaussandague Néstor E. Bonomo Claudio I. Valencia 《International Journal of Infrared and Millimeter Waves》1993,14(6):1323-1339
Theoriginal and theenhanced Maxwell-Garnett estimates for the permittivity of a particulate medium are applied to the reflection of light by a composite dielectric slab. The reflection coefficients for incident s and p polarizations are calculated and some curves are plotted and discussed. 相似文献
960.
The behavior of zirconium atoms at the W(100) surface associated with oxygen adsorption at different sample temperatures has been studied by Auger electron spectroscopy (AES), ion scattering spectroscopy (ISS), and the relative change of the work function (Δф) measured by the onset of the secondary electron energy distribution. The results have revealed: (i) adsorption of zirconium onto the W(100) surface followed by the elevation of the sample temperature up to 1710 K in an oxygen partial pressure of 2.7 × 10−4 induces complete diffusion of zirconium atoms into the W(100) substrate; (ii) further exposure of oxygen induces co-existence of oxygen and tungsten on the surface at 1710 K, resulting in a work function of 4.37 eV; (iii) keeping the sample temperature at 1710 K, simple evacuation of the system has resulted in surface segregation of zirconium atoms to the surface to form a zirconium atomic layer on the top-most surface, reducing the work function to 2.7 eV. The results have revealed that this specific behavior of zirconium atoms at high temperature assures, with very good reproducibility, the highly stable performance and long service life of Zr---O/W(100)-emitters in practical use, even in a low vacuum of 10−6 Pa. 相似文献