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91.
92.
93.
94.
Let M be an irreducible projective variety, over an algebraically closed field k of characteristic zero, equipped with an action of a connected algebraic group S over k. Let E
G
be a principal G-bundle over M equipped with a lift of the action of S on M, where G is a connected reductive linear algebraic group. Assume that E
G
admits a reduction of structure group to a maximal torus TG. We give a necessary and sufficient condition for the existence of a T-reduction of E
G
which is left invariant by the action of S on E
G
. 相似文献
95.
P. Paasche C. Angelescu S. Ananthamurthy D. Biswas T. Valenzuela G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(2):183-188
We have measured the storage instabilities of electrons in a Penning trap at low magnetic fields. These measurements are carried
out as a function of the trapping voltage, for different magnetic fields. It is seen that these instabilities occur at the
same positions when the trapping voltage is expressed as a percentage of the maximum voltage, given by the stability limit.
The characteristic frequencies at which these instabilities occur, obey a relation that is given by n
zω
z + n
+ω
+ + n
-ω
- = 0, where ω
z, ω
+ and ω
- are the axial, perturbed cyclotron and the magnetron frequencies of the trapped electrons respectively, and the n's are integers. The reason for these instabilities are attributed to higher order static perturbations in the trapping potential.
Received 5 August 2002 / Received in final form 14 October 2002 Published online 17 December 2002
RID="a"
ID="a"Present address: Dept. of Physics, Rampurhat College, Rampurhat, Birbhum, West Bengal, India.
RID="b"
ID="b"e-mail: werth@mail.uni-mainz.de 相似文献
96.
Let X be a Riemann surface equipped with a projective structure. Let
be a square-root of the holomorphic cotangent bundle K
X
. Consider the symplectic form on the complement of the zero section of
obtained by pulling back the symplectic form on K
X
using the map 2. We show that this symplectic form admits a natural quantization. This quantization also gives a quantization of the complement of the zero section in K
X
equipped with the natural symplectic form. 相似文献
97.
Anjan Biswas Swapan Konar Essaid Zerrad 《International Journal of Theoretical Physics》2007,46(1):157-169
The intra-channel collision of optical solitons, with dual-power law nonlinearity, is studied in this paper by the aid of
quasi-particle theory. The perturbation terms that are considered in this paper are the nonlinear gain and saturable amplifiers
along with filters. The suppression of soliton-soliton interaction, in presence of these perturbation terms, is acheived.
The numerical simulations support the quasi-particle theory.
OCIS codes: 060.2310; 060.4510; 060.5530; 190.3270; 190.4370. 相似文献
98.
Mrinmay Pal Somnath Bandyopadhyay Palas Biswas Rimlee Debroy M. C. Paul Ranjan Sen Kamal Dasgupta S. K. Bhadra 《Optical and Quantum Electronics》2007,39(14):1231-1243
In this paper, gain flatness is studied for simultaneous 16-ITU-T channel amplifications at C-band (1,532–1,558 nm) in a single
stage EDFA for WDM application at different average inversion levels. The inversion levels are varied due to the change of
the input signal levels from the targeted operating point and also for dropping few numbers of channels. Specially designed
gain flattening filter (GFF) is used in order to get the flat gain with gain variation ±0.5 dB for −20 dBm/ch input signal
power (total input signal power is −8.0 dBm) at a fixed average inversion level which is maintained by proper selection of
optimum fibre length and pump power. A specific loss spectrum of GFF is obtained by writing a chirped fibre Bragg grating
of length 20 mm. Gain variations are studied by changing the total input signal levels from −8.0 dBm to −20.0 dBm and maintained
within 20.0 ± 0.5 dB by using automatic gain control (AGC) circuit. About 15 out of 16 channels are dropped and observed ±
0.5 dB gain-variation which is an important parameter in optical network system. 相似文献
99.
The mechanical design of the target module of an accelerator driven subcritical nuclear reactor system (ADSS) calls for an
analysis of the related thermal-hydraulic issues because of large amount of heat deposition in the spallation region during
the course of nuclear interactions with the molten lead bismuth eutectic (LBE) target. The LBE also should carry the entire
heat generated as a consequence of the spallation reaction. The problem of heat removal by the LBE is a challenging thermal-hydraulic
issue. For this, one has to examine the flows of low Prandtl number fluids (LBE) in a complex ADSS geometry. In this study,
the equations governing the laminar flow and thermal energy are solved numerically using the streamline upwind Petrov-Galerkin
(SUPG) finite element (FE) method. The target systems with a straight and a nozzle guide have been considered. The principal
purpose of the analysis is to trace the flow and temperature distribution and thereby to check the suitability of the flow
guide in avoiding the recirculation or stagnation zones in the flow space that may lead to hot spots.
相似文献
100.
W.Y. Zhang C.H. Chiu L.C. Zhang K. Biswas H. Ehrenberg W.C. Chang J. Eckert 《Journal of magnetism and magnetic materials》2007
The effect of refractory element addition on phase transformation, crystallization behavior and magnetic properties of Pr8.5Fe81.5B10 (addition-free) and Pr8.5Fe81.5M2B10 (M=V, Cr, Nb, Zr, Ti) ribbons has been investigated. The annealed addition-free ribbon as well as the samples with V or Cr additions are mainly composed of the metastable Pr2Fe23B3 phase, whereas annealed ribbons with Nb, Zr or Ti additions primarily consist of Pr2Fe14B and a minor amount of Fe3B/boride. The complete suppression of the metastable Pr2Fe23B3 phase due to Nb, Zr or Ti additions leads to a significant enhancement of the magnetic properties. For example, the remanence, the coercivity and the energy product are remarkably increased from 2.5 kG, 0.4 kOe and 0.2 MG Oe for the addition-free material to 9.2 kG, 4.7 kOe and 7.6 MG Oe for the specimens with Nb addition. The successful elimination of the metastable Pr2Fe23B3 phase is believed to profit from two factors: (a) Nb, Zr or Ti atoms substitute the Pr site, comparatively increase the Pr content, and thus inhibit the nucleation of Pr-lean Pr2Fe23B3 phases, and (b) the formation of Nb, Zr, or Ti borides consumes some part of B, which hinders the generation of the B-rich Pr2Fe23B3 phase. 相似文献