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1.
It is demonstrated that the radiation of red sprites and blue jets formed in the upper atmosphere is due to the superluminescence of highly excited atomic oxygen induced by an acoustic wave. The field observations of the effect of acoustic waves on the atmosphere are presented. The responses that represent high-frequency electromagnetic and optical pulses are obtained. The laboratory experimental study of the gas discharge is performed to simulate the processes in the upper atmosphere. 相似文献
2.
利用瑞利散射法可以对团簇的尺寸以及团簇形成的演变过程进行研究, 这种方法非常简单易行且对团簇是非破坏性的. 通过对纯氙气以及氢氙混合气体形成的团簇的瑞利散射进行测量, 研究并分析了瑞利散射强度随时间、初始背压 以及气体混合比例的变化, 由此估算了在不同情况下形成团簇的平均尺寸. 通过获得的氢氙混合气体瑞利散射强度与背压的关系I=(1.5 ×10-5)P6.47, 发现了混合气体中氢气对氙团簇形成的促进作用, 并从热力学和分子间作用力的角度进行了理论分析, 得到了氢氙混合气体不易于液化这一新现象, 为实现高背压下更大尺寸团簇的产生提供了可能. 所获得的结果为今后基于氙团簇的X射线产生实验, 以及基于氘氙混合气体的中子产生实验研究提供了良好的实验依据. 相似文献
3.
L. P. Babich E. N. Donskoy I. M. Kutsyk 《Journal of Experimental and Theoretical Physics》2008,107(1):49-60
Monte Carlo simulations of transport of the bremsstrahlung produced by relativistic runaway electron avalanches are performed for altitudes up to the orbit altitudes where terrestrial gamma-ray flashes (TGFs) have been detected aboard satellites. The photon flux per runaway electron and angular distribution of photons on a hemisphere of radius similar to that of the satellite orbits are calculated as functions of the source altitude z. The calculations yield general results, which are recommended for use in TGF data analysis. The altitude z and polar angle are determined for which the calculated bremsstrahlung spectra and mean photon energies agree with TGF measurements. The correlation of TGFs with variations of the vertical dipole moment of a thundercloud is analyzed. We show that, in agreement with observations, the detected TGFs can be produced in the fields of thunderclouds with charges much smaller than 100 C and that TGFs are not necessarily correlated with the occurrence of blue jets and red sprites. 相似文献
4.
Jobin K. Antony Nilesh J. Vasa S.R. Chakravarthy R. Sarathi 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(17-18):2509-2516
Nano-aluminum particles are produced by a wire explosion process in different inert gas ambience. It is observed that generated particles have different sizes and it follows log–normal probability distribution. The particle size produced by the wire explosion process varies depending on the thermal conductivity of the medium and the operating pressure of the gas. To understand the mechanism of nano-particle formation, the optical-emission spectroscopic technique is used for measuring characteristics of plasma generated during the wire explosion process. Strong emission lines were observed from the species formed during the wire explosion process. Plasma temperatures are estimated based on local thermal equilibrium principle and using Al emission lines. Plasma temperature of more than 8000 K is observed in an Ar ambient. The optical emission study clearly indicates that the intensity of plasma increases with an increase in the ambient pressure. Further, it is observed that an increase in the pressure of the gas, the plasma temperature also increases. The study shows that the plasma temperature in the He gas is lesser than in the Ar gas. The plasma temperature due to the discharge plays a significant role on nano-particle formation. In addition, it is observed that irrespective of polarity, emission characteristics are almost the same. 相似文献
5.
The flow of various liquids and gases over single-walled carbon nanotube bundles induces an electrical signal (voltage/current)
in the sample along the direction of the flow. The electrical response generated by the flow of liquids is found to be logarithmic
in the flow speed over a wide range. In contrast, voltage generated by the flow of gas is quadratically dependent on the gas
flow velocity. It was found that the underlying physics for the generation of electrical signals by liquids and gases are
different. For the liquid, the Coulombic interaction between the ions in the liquid and the charge carriers in the nanotube
plays a key role while electrical signal generation due to gas flow is due to an interplay of Bernoulli’s principle and Seebeck
effect. Unlike the liquid case which is specific to the nanotubes, the gas flow effect can be seen for a variety of solids
ranging from single and multi-walled carbon nanotubes, graphite and doped semiconductors. 相似文献
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7.
在空气与氩气组成的混合气体的介质阻挡放电实验中,采用发射光谱法,首次研究了放电气隙分别为:1, 4和2 mm三层放电气隙中的放电丝的光谱特性。这与以往的单层放电气隙或者是双层放电气隙中的放电丝在光谱特性方面有很大的不同。实验通过采集氮分子第二正带系(C3Πu→B3Πg)谱线,计算出不同放电气隙中的放电丝的分子振动温度。利用氮分子离子391.4 nm谱线强度与氮分子394.1 nm谱线的强度之比得到不同放电气隙中放电丝的电子平均能量。增加氩气在混合气体中的比例,得到分子振动温度及电子平均能量随着氩气含量增加的变化趋势。实验结果表明:在同一氩气含量下,分子振动温度从小到大的顺序为:2 mm放电气隙,1 mm放电气隙,4 mm放电气隙。电子平均能量从小到大的顺序为:4 mm放电气隙,2 mm放电气隙,1 mm放电气隙。三层放电气隙中放电丝的分子振动温度及电子平均能量均随着氩气含量的增加而减小。 相似文献
8.
V. I. Yusupov A. N. Konovalov V. A. Ul’yanov V. N. Bagratashvili 《Acoustical Physics》2016,62(5):537-544
We investigate the specific features of acoustic signals generated in water under the action of cw laser radiation with a power of 3 W at wavelengths of 0.97, 1.56, and 1.9 μm, emerging from an optical fiber. It is established that when a fiber tip without an absorbing coating is used, quasi-periodic pulse signals are generated according to the thermocavitation mechanism due to the formation and collapse of vapor–gas bubbles of millimeter size. In this case, the maximum energy of a broadband (up to 10 MHz) acoustic signal generated only at wavelengths of 1.56 and 1.9 μm is concentrated in the range of 4–20 kHz. It is shown that when there is no absorbing coating, an increase in the laser-radiation absorption coefficient in water leads to an increase in the frequency of generated acoustic pulses, while the maximum pressure amplitudes in them remain virtually constant. If there is an absorbing coating on the laser-fiber tip, a large number of small vapor–gas bubbles are generated at all laser-radiation wavelengths used. This leads to the appearance of a continuous amplitude-modulated acoustic signal, whose main energy is concentrated in the range of 8–15 kHz. It is shown that in this case, increasing the absorption coefficient of laser radiation in water leads to an increase in the power of an acoustic emission signal. The results can be used to explain the high therapeutic efficiency of moderate-power laser-fiber apparatus. 相似文献
9.
E. Kh. Baksht I. D. Kostyrya M. I. Lomaev D. V. Rybka V. F. Tarasenko 《Physics of Wave Phenomena》2008,16(3):199-206
The results of experimental study on generation of ultrashort avalanche electron beams (UAEB) in gas-filled diodes are considered.
The spatial distribution of the flux of runaway electrons and X-rays generated in the gas diode fed by nanosecond high-voltage
pulses was studied. It was shown that the UAEB in the gas-filled diode (at an air pressure of 1 atm) with sharply nonuniform
electric field is generated from the interelectrode region into a solid angle exceeding 2π sr. Narrowing of the cathode-anode
gap results in a decrease in the current amplitude of the beam generated to side walls of the gas diode and an increase in
the beam current pulse duration in both axial and radial directions. Current pulses of the beam initiated from the side surface
of the tubular cathode were detected. 相似文献
10.
We investigate how the intensity and duration of an attosecond pulse generated from high-order harmonic generation are affected by the pressure and thickness of the gas jet by taking into account the macroscopic propagation of both fundamental and harmonic fields. Our simulations show that, limited by the propagation effects, especially the absorption of harmonics, the intensity of an attosecond pulse cannot be improved by just independently increasing the gas pressure or the medium length. On the other hand, due to good phase-matching conditions, the duration of a generated attosecond pulse can be improved by changing the gas pressure. 相似文献
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12.
The neutrino luminosity of a stellar medium because of plasmon decay to a neutrino pair via nonstandard tensor interaction in a degenerate electron gas subjected to the effect of a magnetic field such strong that the electrons of the gas are in the lowest Landau level is calculated. Relative limits on nonstandard coupling constants are obtained from a comparison of the results of this calculation with the neutrino luminosity generated in the respective standard process proceeding under the same conditions. 相似文献
13.
The acoustic wave propagation in a rotating ideal gas with density stratification due to the rotation is considered. To describe the waves propagating normally to the rotation axis, an equation for a scalar quantity that is a function of density is proposed. The frequency dependences of the phase and group velocities of an acoustic-gyroscopic wave are presented. It is shown that the stratification of gas leads to an exponential amplitude decay for an acoustic wave generated near the rotation axis and has no effect on the inertial-gyroscopic wave. 相似文献
14.
通过数值模拟三维传播方程研究了双色场产生高次谐波过程中宏观效应的影响,重点分析了阿秒脉冲的时域形状.在6 fs/800 nm和21.3 fs/400 nm组成的双色场中,通过调节双色场间的相对延时,双色场各焦点相对于气体盒子入口的间距和双色场束腰半径和气体压强等参数,可以在平台区得到超宽带连续谱.对该连续谱中420—540 eV的谐波直接进行滤波后可以得到时间同步性很好的单个阿秒脉冲.这种性质对实验上通过双色场方案产生超短的阿秒脉冲非常有利.
关键词:
传播效应
阿秒脉冲
时间同步性 相似文献
15.
Technical Physics - Parameters of a beam of runaway electrons and X-ray radiation generated in a gas diode at different atmospheric pressures are studied. It is shown that the maximum beam currents... 相似文献
16.
S. Bollanti T. Letardi C.E. Zheng 《Applied Physics A: Materials Science & Processing》2000,71(3):255-260
Some closed expressions for the flight ranges of the spherical particle ejected from a laser-produced plasma target in buffer
gas are given as a function of its initial velocity, diameter, and some parameters of the properties for gas and particle
material. It is shown that when estimating the ranges of the particulates generated from the laser target, the decline of
viscosity with the decrease of the gas pressure has to be considered.
Received: 3 March 2000 / Accepted: 28 March 2000 / Published online: 5 July 2000 相似文献
17.
M. Amielh Y. Jiang U. Kristiansen P.-O. Mattei D. Mazzoni 《Journal of Turbulence》2013,14(10):650-676
Our study is focused on a phenomenon often encountered in flow carrying pipes, since flow instabilities caused by geometric features may generate acoustic signals and, thereafter, interact with these signals in such a way that powerful pure tones are produced. A modern example is found in the so-called ‘singing risers’, or the gas pipes connecting gas production platforms to the transport network. But the flow generated resonance in a fully corrugated circular pipe may be silenced by the addition of relatively low frequency flow oscillations induced by an acoustic generator. Experiments reported here, aimed at investigating in more detail the coupling between the flow in the pipe, the acoustically generated flow oscillations and the emitted resulting noise, are performed in a specifically designed facility. A rectangular transparent channel using glass walls enables us to use optical techniques to describe in detail the flow field in the corrugation vicinity, in addition to more standard hot-wire anemometry and acoustic pressure measurements with microphones, with and without the acoustically generated low-frequency oscillations. 相似文献
18.
Calculations of the time form and amplitude of the acoustic signal generated in an absorbing gas that fills the cuvette of an opticoacoustical receiver in the case of a nonlinear nonsteady interaction with a single laser pulse are performed. Expressions relating the parameters of the acoustic signal with the characteristics of the laser pulse are derived, and an expression is proposed for the parameter characterizing the nonlinearity of the absorption of the given gas. 相似文献
19.
We predict that the flow of unpolarized current in electron-doped GaAs and InP at room temperature is unstable at high electric fields to the dynamic formation of spin-polarized current pulses. Spin-polarized current is spontaneously generated because the conductivity of a spin-polarized electron gas differs from that of an unpolarized electron gas, even in the absence of spin-orbit interaction. Magnetic fields are not required for the generation of these spin-polarized current pulses, although they can help align the polarization of sequential pulses along the same axis. 相似文献
20.
强激光脉冲在水中的自聚焦传输、成丝、击穿及击穿后产生的声波,近年来成为强激光脉冲传输应用研究领域的一个热点。强激光脉冲电离产生的空泡在溃灭过程中,对周围水体产生压缩,从而在水下产生声波。在现有理论基础上,考虑空泡含气量、水的粘滞系数和水的表面张力系数对空泡运动及其产生声波的影响。给出双空泡运动方程,分析空泡间距对空泡溃灭和其产生声压关系。根据实际情况,计算不同温度情况下单空泡和双空泡运动过程及其产生的声压,并进行相互比较。计算结果表明: 水温越高,空泡运动时达到的最小半径越小,空泡振荡周期和溃灭时间延长,产生声压越高。随双空泡间距减小,空泡溃灭时达到的最小半径线性减小,而其产生的最大声压则单调增大。 相似文献