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71.
A. A. Zakharenko 《Pramana》2007,69(4):617-629
In this work, the experimental results of the creation of the second non-dispersive Zakharenko wave (C
ph = C
g ≠ 0) in the negative roton branch (the so-called second sound) of the bulk elementary excitations (BEEs) energy spectra are
introduced. Several BEE signals detected by a bolometer situated in the isotopically pure liquid helium-II at low temperatures
∼100 mK are shown, which give evidence of negative roton creation in the liquid by helium atomic beams striking the liquid
surface. The negative roton signals were clearly distinguished by the following ways: the negative roton signal created by
helium atomic beams appeared earlier than the positive roton signal created by the beams, and presence of both positive and
negative roton signals together. It is natural that the negative roton creation by the beams requires the 4He-atom energies ∼12 K, while the positive roton creation by the atomic beams requires energies ∼35 K. Therefore, successive
increase in the heater power resulting in an increase in the 4He-atom energies gives solid evidence that the negative rotons are first created in the liquid by the helium atomic beams.
相似文献
72.
在时间分辨的模式下, 实验研究了天鹅绒阴极产生的双脉冲相对论强流电子束的束心运动、束包络和束的发射度. 在实验中, 电子束流强度和电子束心运动用电阻环进行测试, 而电子束和石英玻璃的相互作用产生的契仑科夫辐射用来给出电子束包络和发射度信息. 电子束和石英玻璃作用产生的契仑科夫辐射用1台8幅分幅相机记录. 实验结果表明, 天鹅绒阴极产生的相对论强流双脉冲电子束在束流大小、束心运动轨迹、束包络及束发射度等方面具有较好的一致性. 相似文献
73.
A. Chafiq 《Optics Communications》2007,278(1):142-146
In order to avoid the severe axial intensity oscillations which appear when an ideal Mathieu beam is truncated, we propose to modulate it by a flattened multi-Gaussian envelope. The obtained beam, which is referred as flattened Mathieu-Gauss (FTMG) beam, can be expanded into a finite series of Mathieu-Gauss beams with various waists. The propagation study of this beam reveals that the axial intensity is unchanged within a certain propagation distance as for super-Gaussian-Bessel beams or Gori’s flattened Bessel beams. By using Collins formula, we derive closed-form expressions of FTMG beam propagating through a paraxial axisymmetric ABCD optical system. Some numerical calculations and discussions are also given. 相似文献
74.
An approximate analytical propagation formula of the elliptical Gaussian beams through a paraxial ABCD optical system with a circular aperture is obtained on the basis of the expansion of a hard-edged aperture into a finite sum of complex Gaussian functions. And the parameter characteristics of the truncated beams including the beam propagation factor and the kurtosis parameter are also studied in detail by using the second-order-moments method. 相似文献
75.
Based on the extended Huygens-Fresnel integral formula, analytical formulae for the elements of cross-spectral density matrix of partially polarized electromagnetic twist anisotropic Gaussian Schell-model (TAGSM) beam propagating in turbulent atmosphere can been derived by a tensor method. Our main attention was focus on the effect of the atmospheric turbulence, twist parameters and partial coherence on the spectral degree of polarization, the spectral degree of coherence and the spectral density. Numerical calculation results and analysis are given. 相似文献
76.
Melanie Schnell Dr. Gerard Meijer Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(33):6010-6031
Research with cold molecules has developed rapidly in recent years. There is now a variety of established methods for cooling molecules into the millikelvin range. Nevertheless, a focal point of current research is directed toward finding new ways to bring the temperature of molecules even closer to absolute zero. Samples of cold molecules offer not only important applications for high‐resolution spectroscopy, which benefit from the increased interaction time of slow molecules with electromagnetic radiation; they also promise access to an exotic regime of chemical reactivity, in which phenomena such as quantum tunneling and quantum resonances predominate. This review begins with an introduction to the methods by which cold molecules can be prepared, with special emphasis on Stark deceleration and traps. In addition to applications of cold molecules that have already been partially achieved, an important focus of the review concentrates on possible future applications, and both aspects are illustrated with selected examples. 相似文献
77.
78.
Using the Riesz basis approach, we study a sandwich beam that is composed of an outer stiff layer and a compliant middle layer.
The dynamic behavior and analyticity of the system are obtained based on a detailed spectral analysis and Riesz basis generation.
As a consequence, the analyticity of the solution and the exponential stability of the system are concluded.
This work was supported by the National Natural Science Foundation of China, Program for New Century Excellent Talents in
the Universities of China and by the National Research Foundation of South Africa. 相似文献
79.
V. N. Il'in 《Journal of Applied Spectroscopy》1999,66(6):971-975
An interference method for controlling the refractive index of liquids pumped through a capillary is considered. The liquid
is sounded by two systems of interference bands, the period of which differs by an insignificant value prescribed by the condition
of nonius coincidence. An analytical expression is obtained to calculate the refractive index of the liquid controlled in
automatic reading of the interference patterns.
Institute of Electronics, National Academy of Sciences of Belarus, 22 Logoiskii Trakt, Minsk, 220841, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 832–835, November–December, 1999. 相似文献