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241.
A method for suppressing self-modulation in backward-wave tubes is proposed. Additional delay is introduced into the feedback
circuit, owing to which the output signal amplitude affects the electron beam current that enters into the interaction space.
Numerical simulations demonstrate that the operating current in the single-frequency oscillation mode may be increased roughly
twofold. 相似文献
242.
Yu. V. Sanochkin 《Technical Physics》2003,48(5):546-551
It is shown that, along with gravity waves, surface and internal waves caused by van der Waals forces may exist in a liquid
with a horizontal free surface. A dispersion relation is found by using the stepwise approximation for the coefficients of
a wave equation derived for these waves. The surface waves are similar to surface gravity waves in dispersion and amplitude
distribution but differ in frequency by several orders of magnitude. Another sequence of roots in the spectrum corresponds
to internal van der Waals waves that have an upper frequency bound and the dispersion law typical of a multimode waveguide. 相似文献
243.
K. Zhang 《Calculus of Variations and Partial Differential Equations》2003,17(1):85-103
Let be a linear subspace of real matrices without rank-one matrices and let be a finite set. Suppose is a bounded arcwise connected Lipschitz domain and is a sequence of bounded vector-valued mappings in such that in as , where is the closed -neighbourhood and the distance function to . We give estimates for such that up to a subsequence, in for some fixed . In other words, we give estimates on such that separates gradient Young measure. The two point set with is a special case of such sets up to a translation.
Received: 20 July 2001 / Accepted: 23 January 2002 / Published online: 5 September 2002 相似文献
244.
This article provides a status report on discrete mathematics in America's schools, including an overview of publications
and programs that have had major impact. It discusses why discrete mathematics should be introduced in the schools and the
authors' efforts to advocate, facilitate, and support the adoption of discrete mathematics topics in the schools. Their perspective
is that discrete mathematics should be viewed not only as a collection of new and interesting mathematical topics, but, more
importantly, as a vehicle for providing teachers with a new way to think about traditional mathematical topics and new strategies
for engaging their students in the study of mathematics. 相似文献
245.
The construction of non-Abelian affine Toda models is discussed in terms of its underlying Lie algebraic structure. It is shown that a subclass of such non-conformal two-dimensional integrable models naturally leads to the construction of a pair of actions, which share the same spectra and are related by canonical transformations. 相似文献
246.
247.
248.
The paper concerns several diagnostic techniques, which have been used in pulsed-power plasma experiments, i.e. Plasma-Focus and Z-Pinch devices, and which can be adapted to studies of Magnetic Confinement Fusion (MCF) facilities, e.g. Stellarators and Tokamaks. The application of Nuclear Track Detectors (NTDs) for time-integrated ion measurements in MCF experiments is described and the use of such detectors for time-resolved ion measurements is discussed. The application of special ?erenkov-type detectors for time resolved measurements of fast runaway electrons is considered. Also discussed is the use of selected nuclear reactions for measurements of fusion products, e.g. fast neutrons. 相似文献
249.
Quantum operations with a charge solid-state qubit whose logical states are formed by two spatially separated localized states of an electron in the double-dot structure are studied theoretically. We show that it is possible to perform various one-qubit rotations making use of the microwave pulses tuned to the resonances between the localized states and the excited state delocalized over the nanostructure. An explicit analytic expression for the time-dependent electron state vector is derived, and the appropriate pulse parameters are determined. 相似文献
250.
S. N. Artemenko 《JETP Letters》2004,79(6):277-281
It is shown theoretically that the Luttinger liquid can exist in quasi-one-dimensional conductors in the presence of impurities in a form of a collection of bounded Luttinger liquids. The conclusion is based on the observation by Kane and Fisher that a local impurity potential in Luttinger liquid acts, at low energies, as an infinite barrier. This leads to a discrete spectrum of collective charge and spin density fluctuations, so that interchain hopping can be considered as a small parameter at temperatures below the minimum excitation energy of the collective modes. The results are compared with recent experimental observation of a Luttinger-liquid-like behavior in thin NbSe3 and TaS3 wires. 相似文献