共查询到20条相似文献,搜索用时 15 毫秒
1.
R. J. Willis C. E. Capjack H. J. J. Seguin S. K. Nikumb 《Optics & Laser Technology》1988,20(6):301-307
Measurements of the electron density within an axial CO2 laser discharge subjected to a transverse rotating magnetic field are presented. Experiments were performed with a single Langmuir probe. Electron density is evaluated using Su and lam's thick sheath expression for a stationary plasma. Results are presented for a 2.7 kPa (20 torr) discharge with external pre-ionization and for a 0.7 kPa (5 torr) self-sustained discharge. 相似文献
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On the points of bifurcation along the sequence of rotating axisymmetric masses with magnetic fields
R K Kochhar 《Pramana》1975,5(5):294-302
It is shown that the points of bifurcation belonging to the third harmonics along the sequence of Maclaurin spheroids viewed
from an inertial frame are distinct from the corresponding points along the Maclaurin sequence considered stationary in a
rotating frame and occur at eccentricitye=0·73113 ande=0·99608; the Maclaurin spheroids having become dynamically unstable before the second point is reached. A toroidal magnetic
field leaves these points uneffected, while a general poloidal field may either raise or lower these points of bifurcation. 相似文献
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Nuclear magnetic resonance (NMR) experiments in pulsed magnetic fields up to 30.4 T focused on 1H and 93Nb nuclei are reported. Here we discuss the advantage and limitation of pulsed field NMR and why this technique is able to become a promising research tool. 相似文献
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We analyze the accretion of charged matter onto a rotating black hole immersed in an aligned dipolar magnetic field. We specialize
to motion in the equatorial plane and calculate the ‘Keplerian’ angular momentum distribution, the marginally stable and marginally
bound orbits, and the efficiency of mass-to-energy conversion as functions of the angular momentum of the black hole and of
the product of the dipole moment and the charge of the infalling matter. Although the detailed results are quite different
from those previously obtained in the case of an uniform magnetic field, the astrophysically relevant results are very similar;
when hydrodynamical accretion is considered, these effects of the magnetic field are always very small. But for test particles
the efficiency can be significantly increased for limited ranges of the parameters. 相似文献
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T. Weigand 《Fortschritte der Physik》2006,54(11):963-1077
We describe a large new class of four‐dimensional supersymmetric string vacua defined as compactifications of the E8 × E8 and the SO(32) heterotic string on smooth Calabi‐Yau threefolds with unitary gauge bundles and heterotic five‐branes. The conventional gauge symmetry breaking via Wilson lines is replaced by the embedding of non‐flat line bundles into the ten‐dimensional gauge group, thus opening up the way for phenomenologically interesting string compactifications on simply connected manifolds. After a detailed analysis of the four‐dimensional effective theory we exemplify the general framework by means of a couple of explicit examples involving the spectral cover construction of stable holomorphic bundles. As for the SO(32) heterotic string, the resulting vacua can be viewed, in the S‐dual Type I picture, as a generalisation of magnetized D9/D5‐brane models. In the case of the E8 × E8 string, we find a natural way to construct realistic MSSM‐like models, either directly or via a flipped SU(5) GUT scenario. 相似文献
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We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming. 相似文献
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Following Morris’s [5] consideration of a sourceless abelian gauge string in a Robertson-Walker universe with flat space sections
we have generalized the treatment to the case of arbitrary spatial curvature. We find that creation or destruction of the
gauge string is not possible if the spatial curvature is nonzero. 相似文献
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介绍了一种重复频率脉冲磁场作为高功率微波源的导引磁场的设计,该磁场电源具有功耗低、发热量小、结构紧凑等优点,符合高功率微波朝重复频率方向发展的需求。从产生脉冲磁场的电流表达式出发,根据涡流损耗不能太大、品质因数要高和电容储能要小的原则,给出了脉冲磁场产生系统的储能电容和充电电压的优化设计方法。最后将此方法应用于Ka波段返波振荡器导引磁场的设计,确定出产生脉冲磁场电路的电容和充电电压的值,并进行了仿真和实验研究,结果与理论要求吻合较好,在重复频率10 Hz条件下能稳定运行,验证了设计的合理性。 相似文献
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介绍了一种重复频率脉冲磁场作为高功率微波源的导引磁场的设计,该磁场电源具有功耗低、发热量小、结构紧凑等优点,符合高功率微波朝重复频率方向发展的需求。从产生脉冲磁场的电流表达式出发,根据涡流损耗不能太大、品质因数要高和电容储能要小的原则,给出了脉冲磁场产生系统的储能电容和充电电压的优化设计方法。最后将此方法应用于Ka波段返波振荡器导引磁场的设计,确定出产生脉冲磁场电路的电容和充电电压的值,并进行了仿真和实验研究,结果与理论要求吻合较好,在重复频率10 Hz条件下能稳定运行,验证了设计的合理性。 相似文献
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We obtain a one parameter class of stationary rotating string cosmological models of which the well-known Gödel universe is a particular case. By suitably choosing the free parameter function, it is always possible to satisfy the energy conditions. The rotation of the model hinges on the cosmological constant which turns out to be negative. String-dust distribution in Gödel-type universes is also briefly discussed. 相似文献
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The aim of the current work is the research of the influence of a tilted magnetic field direction on the spectrum and the energy level spacing distribution of a two-dimensional (2D) hydrogen atom and of an exciton in GaAs/Al0.33Ga0.67As quantum well. It was discovered that the quantum chaos (QC) is initiated with an increasing angle α between the magnetic field direction and the normal to the atomic plane. It is characterized by the repulsion of levels leading to the eliminating of the shell structure and by changing the spectrum statistical properties. The statement about the initiation of chaos and its dominance over regular motion with increasing angle α is confirmed by the results of our calculations of the classical dynamics presented in this paper. The evolution of the spatial distribution of the square of the absolute value of the wave function at an increasing angle α was observed. The differences of calculated dependencies of energies for various excited states on the tilt angle at a wide range of the magnetic field strength were described. 相似文献
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A. D. Abramov 《Russian Physics Journal》1971,14(1):25-28
The eddy-current loss is calculated for nonferromagnetic disks in a rotating magnetic field. The power loss is found as a function of the magnetic field intensity, the field rotation velocity, and the disk dimensions. The eddy-current loss was measured experimentally in rotating fields in copper, aluminum, and zinc disks; a good agreement was found with the calculated values.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 38–42, January, 1971. 相似文献
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The effect of toroidal field on the rotating magnetic field current drive in rotamak plasmas 下载免费PDF全文
A rotamak is one kind of compact spherically shaped magnetic-confinement device. In a rotamak the plasma current is driven by means of rotating magnetic field (RMF). The driven current can reverse the original equilibrium field and generate a field-reversed-configuration. In a conventional rotamak, a toroidal field (TF) is not necessary for the RMF to drive plasma current, but it was found that the present of an additional TF can influence the RMF current drive. In this paper the effect of TF on the RMF current drive in a rotamak are investigated in some detail. The experimental results show that addition of TF increases the RMF driven current greatly and enhances the RMF penetration dramatically. Without TF, the RMF can only penetrate into plasma in the edge region. When a TF is added, the RMF can reach almost the whole plasma region. This is an optimal strength of toroidal magnetic field for getting maximum plasma current when Bv and radio frequency generator power are fixed. Besides driving current, the RMF generates high harmonic fields in rotamak plasma. The effect of TF on the harmonic field spectra are also reported.[第一段] 相似文献