共查询到20条相似文献,搜索用时 15 毫秒
1.
Kroesen G.M.W. Schram D.C. Timmermans C.J. de Haas J.C.M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(6):985-991
The energy balance for electrons and heavy particles constituting a plasma in partial local thermodynamic equilibrium is derived. The formulation of the energy balance used allows for evaluation of the source terms without knowledge of the particle and radiation transport situation, since most of the contributions that arise from that situation (diffusion, local capture of radiation, etc.) are taken into account in the nonequilibrium term. The small correction for the contribution of the loss of excited states, which is slightly overestimated in this approach, can usually be neglected. The overpopulation factor, which can often be evaluated from measurements of the pressure, electron density, and temperature, becomes one of the most important plasma parameters; in the energy balance it accounts for most of the phenomena which may be difficult to evaluate otherwise. As an illustration, some rate coefficients are given for an argon plasma, and the evolution of the several terms of the electron energy equation in a flowing cascaded arc is discussed 相似文献
2.
Koyama K. Nakayama Y. Ohi T. Horinouchi K. Sasao H. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1997,25(4):598-602
The density distribution and the velocity of copper neutral atoms emitted from a single cathode spot in 40 A vacuum arc were measured by the two-dimensional (2-D) laser-induced fluorescence method. The density was calibrated from the two-dimensional fluorescence image observed by a CCD camera. The gap space was almost filled with the copper atoms, and the density reached 5×1019/m3. We varied the wavelength of the laser light and measured the velocity of the copper atoms emitted from the cathode spot using the effect of Doppler shift. The velocity of the copper atoms was about 10 km/s 相似文献
3.
Lins G. Paulus I. Pohl F. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1989,17(5):676-678
Dielectric recovery data were obtained for vacuum arcs between chromium copper butt contacts 30 mm in diameter and 2 mm apart. The 50-Hz arc current was forced to zero at its maximum of 200 A in about 1 μs. Following current zero, high-voltage pulses of a sufficient amplitude to always cause breakdown were applied to the gap. Gap recovery is characterized by the measured breakdown voltage as a function of time. Dielectric strength of the gap rises sharply within the first few microseconds after current zero, reaching its final value in about 10 μs. Neutral copper concentration in the center of the gap was measured by laser-induced fluorescence under conditions very similar to those of the recovery measurements. In contrast to the fast gap recovery, the copper vapor concentration does not change substantially during the first 100 μs from its value of 1.4×1018 m -3 near current zero. It is concluded that the neutral copper vapor concentration does not play a decisive role in gap recovery under these experimental conditions. This is corroborated by the fact that the mean free path for electron-impact ionization of copper atoms exceeds the gap length by four orders of magnitude 相似文献
4.
The conformai Killing equations in resolved form and their first and second integrability conditions are obtained in the compact spin coefficient formalism for arbitrary spacetimes. To facilitate calculations an operatorL is introduced which agrees with the Lie derivative only when operating on quantities with GHP weights (0,0). The resulting equations are used to find the conditions for the existence of a two dimensional non-Abelian group of homothetic motions in a twisting typeN vacuum spacetime. The equivalence of two such sets of metrics is established, metrics that were recently the subject of independent investigations by Herlt on the one hand and by Ludwig and Yu on the other. 相似文献
5.
We formulate local thermodynamical stability conditions for states of quantum lattice systems, and show that these conditions are implied by, and in the case of translationally invariant states equivalent to, those of Kubo-Martin-Schwinger (KMS). 相似文献
6.
Martial Mazars 《Molecular physics》2013,111(13-14):1909-1925
Yukawa potentials are often used as effective potentials for systems such as colloids, plasmas, etc. When the Debye screening length is large, the Yukawa potential tends to the non-screened Coulomb potential; in this small screening limit, or Coulomb limit, the potential is long-ranged. As is well known in computer simulation, a simple truncation of the long-ranged potential and the minimum image convention are insufficient to obtain accurate numerical data on systems. The Ewald method for bulk systems, i.e. with periodic boundary conditions in all three directions of space, has already been derived for the Yukawa potential [Molec. Phys. 88, 1357 (1996); J. Chem. Phys. 113, 10459 (2000)], but for systems with partial periodic boundary conditions, the Ewald sums have only recently been obtained [J. Chem. Phys. 126, 056101 (2007)]. In this paper, we provide a closed derivation of the Ewald sums for Yukawa potentials in systems with periodic boundary conditions in only two directions and for any value of the Debye length. Special attention is paid to the Coulomb limit and its relation to the electroneutrality of systems. 相似文献
7.
Martial Mazars 《Molecular physics》2013,111(13-14):1927-1936
Yukawa potentials may be long-ranged when the Debye screening length is large. In computer simulations, such long-ranged potentials have to be taken into account with convenient algorithms to avoid systematic bias in the sampling of the phase space. Recently, we provided Ewald sums for quasi-two-dimensional systems with Yukawa interaction potentials [J. Chem. Phys. 126, 056101 (2007); Molec. Phys. paper I of this series]. Sometimes, Lekner sums are used as an alternative to Ewald sums for Coulomb systems. In the present work, we derive the Lekner sums for quasi-two-dimensional systems with Yukawa interaction potentials and we give numerical tests for practical implementations. The main result of this paper is to emphasize that Lekner sums cannot be considered as an alternative to Ewald sums for Yukawa potentials. As a conclusion to this work: Lekner sums should not be used for quasi-two-dimensional systems with Yukawa interaction potentials. 相似文献
8.
Geoffrey L. Sewell 《Communications in Mathematical Physics》1977,55(1):53-61
We prove that local thermodynamical stability (LTS), as defined in [1], implies the KMS conditions in quantum lattice systems, without any assumption of translational invariance. This result, together with those of [1], establishes the equivalence between the LTS and the KMS conditions for such systems. 相似文献
9.
We propose and experimentally realize methods for forming light beams with local spatial intensity minima of different types
(hollow light beams), based on application of specially shaped linear optics phase elements. The fields with local intensity
minima, obtained as a result of phase conversion, are comparable with respect to transverse dimensions, power, and intensity
gradient to the initial gaussian beam focused by means of a spherical lens. The optical layouts were assembled using photostable
optical elements and therefore make it possible to create high-power laser fields suitable not only for manipulation of microparticles
but also for laser machining of materials, in particular laser welding of metals. Using a phase element with planar symmetry,
we can select the optimal laser beam profile that will ensure no burning on the line of contact between the ends of the parts
to be welded for high penetration and will make it possible to achieve the maximum possible strength of the weld joint for
a specified laser radiation power. 相似文献
10.
Hans J. Mueller Kerstin Roetzler Christian Lathe 《Journal of Physics and Chemistry of Solids》2010,71(8):1108-1117
The Earth's deep interior is accessible only by indirect methods, first and foremost seismological studies. The interpretation of these seismic data and the corresponding numerical modelling require measurements of the elastic properties of representative Earth materials under experimental simulated in situ pressure-temperature conditions. Various experimental techniques for velocity measurements under crustal and mantle conditions and the results are described. 相似文献
11.
The temporal characteristics of two different narrow-band optical filters at 532 nm are reported. Both filters operate on the 4P(1/2) - 8S(1/2) atomic transition of potassium vapor, where the 4P(1/2) state is excited by a 770-nm, 10-ns laser pulse. The filters operate on the principle of circular birefringence induced by either the Faraday effect or two-photon transition, which is confirmed by experiments. The characteristic decay times of the filters are 5 and 0.015 mus, which is significant for the design of optical gating and signal processing with matched filters for ocean lidar. 相似文献
12.
The structure and defects of bismuth films prepared through vacuum thermal deposition on mica substrates under different conditions
(deposition rates, substrate temperatures, temperatures and times of annealing) have been investigated using atomic force
microscopy. The conditions are determined under which recrystallization occurs with increasing crystallite size during annealing,
which provides a decrease in the degree of imperfection of the films and an increase in the mobility of charge carriers. 相似文献
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15.
Folklore suggests that the split Lie-like operators of a complex partial differential equation are symmetries of the split
system of real partial differential equations. However, this is not the case generally. We illustrate this by using the complex
heat equation, wave equation with dissipation, the nonlinear Burgers equation and nonlinear KdV equations. We split the Lie
symmetries of a complex partial differential equation in the real domain and obtain real Lie-like operators. Further, the
complex partial differential equation is split into two coupled or uncoupled real partial differential equations which constitute
a system of two equations for two real functions of two real variables. The Lie symmetries of this system are constructed
by the classical Lie approach. We compare these Lie symmetries with the split Lie-like operators of the given complex partial
differential equation for the examples considered. We conclude that the split Lie-like operators of complex partial differential
equations are not in general symmetries of the split system of real partial differential equations. We prove a proposition
that gives the criteria when the Lie-like operators are symmetries of the split system. 相似文献
16.
Samples irradiated in an ESCA spectrometer emit and receive intense electron fluxes due to secondary emission. Charging and surface potential of non conducting sample is mainly determined by these electron fluxes. The measurement of the secondary electron emission energy distribution (SEED) allows the determination of the sample vacuum level and in particular its work function in the case of conducting samples. Criteria to check the correctness of (SEED) measurements are presented. 相似文献
17.
Synchronization in identical drive-response systems is a problem that can be cast in an observer design framework. In this paper we extend this approach by studying the analysis/design of partial synchronization by means of observer theory. In doing so, we introduce the concept of partial observer--an observer to reconstruct a part of the system state vector. It is also shown how the observability condition can be utilized to analyze the dynamics in an array of coupled identical systems. 相似文献
18.
The surface potentials of few-layer graphene (FLG) films in high vacuum and ambient conditions have been investigated by employing electrostatic force microscopy. It is found that the surface potential of FLG films in ambient air has a constant large depression compared to that measured in a high vacuum. Our experimental results indicate that the shift is most likely caused by the presence of ambient adsorbates on the outmost graphene surfaces. The surface potentials increase with the number of graphene layers and approach the bulk value for five or more graphene layers in high vacuum as well as in ambient air. Since the contribution of the surface adsorbates is a constant value, we further show that the thickness dependence of the surface potential can be sufficiently explained by the nonlinear Thomas-Fermi Theory in both conditions. 相似文献
19.
We derive N-particle Bell-type inequalities under the assumption of partial separability, i.e., that the N-particle system is composed of subsystems which may be correlated in any way (e.g., entangled) but which are uncorrelated with respect to each other. These inequalities provide, upon violation, experi-mentally accessible sufficient conditions for full N-particle entanglement, i.e., for N-particle entanglement that cannot be reduced to mixtures of states in which a smaller number of particles are entangled. The inequalities are shown to be maximally violated by the N-particle Greenberger-Horne-Zeilinger states. 相似文献
20.
G. G. Petrash 《Bulletin of the Lebedev Physics Institute》2007,34(7):208-213
The effect of the prepulse electron density and population of the lower laser (metastable) level on lasing characteristics of the pulsed copper vapor laser is considered. In the analysis of their effect, attention is paid to the need to consider the correlation of these parameters. It is emphasized that the effect of the prepulse electron density depends on the electron heating rate at the beginning of the excitation pulse. The conditions controlling the electron heating rate and methods for reducing the effect of this parameter are considered. 相似文献