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991.
A transient suppression method for piezoelectric ceramic transducer is presented. By adding some special pedestal pulses to the original transmitted signal, the transient effects in the output of the transducer can be just precisely transmission by use of a narrowband transducer. canceled, thereby achieving the broadband The experimental results show that the transient responses of the sinusoid pulses and coded signals are suppressed successfully and the acoustic waveforms radiated into the surrounding water are improved significantly. 相似文献
992.
Accelerated Multi-Level Atoms in an Electromagnetic Vacuum and Fulling--Davies--Unruh Effect 下载免费PDF全文
We consider, from the point of view of a coaccelerated frame, a uniformly accelerated multi-level atom in interaction with vacuum quantum electromagnetic fields in the multi-polar coupling scheme, and calculate the rate of change of the atom's energy assuming a thermal bath at a finite temperature T in the Rindler wedge. Comparison with the spontaneous excitation rate of the atom calculated in the instantaneous inertial frame of the atom shows that both the inertial and coaccelerated observer would agree with each other only when the temperature of the thermal bath equals the FDU value TFDU = α/2π. 相似文献
993.
We study some properties of the simplest neutron stars (NSs) in the Glendenning Moszkowski (GM) model, the hybrid derivative coupling (HD) model and the Zimanyi Moszkowski (ZM) model in the framework of relativistic mean field (RMF) theory with and without the interaction by exchanging the ~-meson. We show that the maximal mass of the NSs becomes smaller, but the redshift becomes larger from the GM model to the HD model, then to the ZM model. The interaction with the 6-meson exchange enlarges the maximal mass of neutron stars, increases the relative population of charged particles (proton, electron and muon) and descends the relative population of neutron. 相似文献
994.
We construct a two-layer feedback neural network by a Monte Carlo based algorithm to store memories as fixed-point attractors or as limit-cycle attractors. Special attention is focused on comparing the dynamics of the network with limit-cycle attractors and with fixed-point attractors. It is found that the former has better retrieval property than the latter. Particularly, spurious memories may be suppressed completely when the memories are stored as a long-limit cycle. Potential application of limit-cycle-attractor networks is discussed briefly. 相似文献
995.
Effect of Elongation on Critical Gradient for Toroidal Electron Temperature Gradient Modes 下载免费PDF全文
The electron temperature gradient mode is investigated in elongated toroidal plasmas with a gyrokinetic integral eigenmode equation code. Dependence of the critical electron temperature gradient on the elongation is calculated. It is found that when the elongation increases, the growth rate spectrum is greatly shifted towards shorter poloidal wavelength, and then the poloidal wavenumber at which the mode is destabilizing critically in elongated plasmas will be larger than that in circular plasmas. 相似文献
996.
Hatim Mohamed El-Khair Dirar 《中国物理快报》2008,25(12):4480-4481
ZnS quantum dots (QDs), prepared by soft-condensation, exhibit robust structure of a quantum size equal 3.13 nm mediated two-dimensional gum Arabic surfactant as characterized by scan tunnelling microscope (STM). Strong blue-shifted absorption and emission bands are depicted by optical characterization even for the sample stored under ambient condition for two weeks. These enhancements can be attributed to the completely passivated surface trap states by Gum Arabic. 相似文献
997.
Arbab I. Arbab 《中国物理快报》2008,25(12):4497-4500
We investigate a cosmological model of a phantom energy with a variable cosmological constant (∧) depending on the energy density (ρ) as ∧∝ρ^α,α=const and a variable gravitational constant G. The model requires α 〈 0 and a negative gravitational constant. The cosmological constant evolves with time as ∧ ∝ t^-2. For ω 〉 - 1 and α 〈 -1 the cosmological constant ∧ 〈 0, G 〉 0 and ρ decrease with cosmic expansion. For ordinary energy (or dark energy), i.e.ω 〉 -1, we have -1 〈 α〈 0 and β 〉 0 so that G〉0 increases with time and p decreases with time. Cosmic acceleration with dust particles is granted, provided -2/3 〈α〈 0 and ∧〉0. 相似文献
998.
We study the non-thermal photon emission from shell-type supernova remnants (SNRs) in the frame of a two-zone model. In this model, the sites of acceleration, escape and subsequent radiation of particles (both electron and proton) are divided into acceleration and escape zones, respectively. The particle distributions consist of two components, one is produced inside the acceleration zone, the other in the escape zone. We apply this model to two young and one old shell-type SNRs and show that the observed multi-waveband photon spectra for the three SNRs can be explained well in this model and high-energy γ-rays from these SNRs may have hadronic origins. 相似文献
999.
1000.
边界元法循环平稳近场声全息理论研究 总被引:2,自引:0,他引:2
循环平稳声场是工程中经常遇到的一种特殊非平稳声场,声压信号受到调制作用,导致频谱出现边带现象,经典的近场声全息技术重建得到的声场无法反映声场的调制特性.在平面循环平稳近场声全息基础上,提出一种边界元法的循环平稳近场声全息技术,用二阶循环统计量理论代替传统的傅里叶分析,并以声压的循环谱密度取代其频谱及功率谱密度作为重建量,可用于循环平稳声场中具有复杂表面声源的辐射声场.由于循环谱密度对循环平稳信号具有解调功能,用该方法重建得到的循环谱密度能有效地反映调制和载波信号的信息.仿真分析与实验表明了本理论的有效性和精度能满足工程要求. 相似文献