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21.
Ecker Gunter 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1974,2(3):130-146
If the current in a "vacuum arc" surpasses a certain critical value a conspicuous and destructive phenomenon occurs at the anode, the ANODE CONSTRICTION INSTABILITY or ANODE SPOT FORMATION [1 - 10]. This paper will give a quantitative analysis of this phenomenon within the limits of a model which can be characterized by lateral homogenity, collision dominance and small electrode separation. Matching the various model regions results in a differential equation for the anodic spot area which exhibits an anode constriction instability of the "explosive type". A marginal instability criterion is derived and evaluated for various materials. This yields extensive information about the dependence of the constriction instability on the parameters of the experimental set up. The findings are compared with the experimental results and show satisfactory agreement within the limitations of experiments and theory. 相似文献
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P. Fröbrich P.J. Jensen P.J. Kuntz A. Ecker 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):579-594
The field-induced reorientation of the magnetization of ferromagnetic films is treated within the framework of many-body Green's
function theory by considering all components of the magnetization. We present a new method for the calculation of expectation
values in terms of the eigenvalues and eigenvectors of the equations of motion matrix for the set of Green's functions. This
formulation allows a straightforward extension of the monolayer case to thin films with many layers and for arbitrary spin
and moreover provides a practicable procedure for numerical computation. The model Hamiltonian includes a Heisenberg term,
an external magnetic field, a second-order uniaxial single-ion anisotropy, and the magnetic dipole-dipole coupling. We utilize
the Tyablikov (RPA) decoupling for the exchange interaction terms and the Anderson-Callen decoupling for the anisotropy terms.
The dipole coupling is treated in the mean-field approximation, a procedure which we demonstrate to be a sufficiently good
approximation for realistic coupling strengths. We apply the new method to monolayers with spin and to multilayer systems with S=1. We compare some of our results to those where mean-field theory (MFT) is applied to all interactions, pointing out some
significant differences.
Received 19 June 2000 and Received in final form 2 August 2000 相似文献
26.
A Chain-like η5-Cp*Bi Compound with Bismuth elevenfold coordinated The reaction of (Cp*Al)4 with BiI3 in toluene at room temperature affords red crystals of the new compound (η5-CpAl)(η5-Cp*Bi)(μ-AlI4)(AlI4)2 · 2 C7H8. The solid state structure exhibits a chain-like arrangement of Cp*Bi units that are bridged by tetraiodoaluminate ions. These structural features are compared with some arene complexes of the heavy group 14 elements (tin, lead). 相似文献
27.
J. Glackin J. G. Ecker M. Kupferschmid 《Journal of Optimization Theory and Applications》2009,140(2):197-212
We present an algorithm for solving bilevel linear programs that uses simplex pivots on an expanded tableau. The algorithm
uses the relationship between multiple objective linear programs and bilevel linear programs along with results for minimizing
a linear objective over the efficient set for a multiple objective problem. Results in multiple objective programming needed
are presented. We report computational experience demonstrating that this approach is more effective than a standard branch-and-bound
algorithm when the number of leader variables is small. 相似文献
28.
Motivated by arguments in favour of spontaneous CP violation, we investigate the general conditions imposed by P and CP invariance on the Yukawa couplings in SU(2)L × SU(2)R × U(1) gauge theories. A complete discussion of these constraints is presented for two minimal Higgs sectors. In addition to the standard case of manifest CP invariance, we find two phenomenologically interesting models where the P and CP transformations are non-aligned in flavour and Higgs spaces. To a certain extent, P and CP invariance may be responsible for the existence of horizontal symmetries. An intimate connection between CP violation and the general flavour problem emerges. 相似文献
29.
In this paper, we develop a method for constructing minimum volume ellipsoids containing a wedge-shaped subset of a given
ellipsoid. This construction yields a class of ellipsoid algorithms for convex programming that use rank-two update formulae.
Research supported by the National Science Foundation, Grant No. MC582-01790. 相似文献
30.
R. Cramer M. Renkhoff J. Drees U. Ecker D. Jagoda K. Koseck G. -R. Pingel B. Remenschnitter A. Ritterskamp B. Boden V. Burkert G. Knop M. Leenen R. Sauerwein D. Schablitzky 《Zeitschrift fur Physik C Particles and Fields》1985,29(4):513-518
Elastic electron deuteron scattering was measured at the Bonn 2.5 GeV Electron-Synchrotron using a two spectrometer coincidence technique. Data were taken at values of the four momentum transfer squaredQ 2=0.50, 0.60, 0.78, 1.00, and 1.3 (GeV/c)2 at electron scattering angles θ e =77.5° to 139.0° in order to separate the magnetic dipole formfactorF M (Q 2) from the electric formfactorF E (Q 2). Experimental cross sections are compared to theoretical predictions and to measurements of other laboratories. The results indicate that contributions from meson exchange currents are not negligible in thisQ 2 region. 相似文献