Chaotic RF pulses generated by a periodically driven oscillator

The effect of a periodic drive signal on a chaotic rf oscillator is considered. The possibility to obtain chaotic pulse trains (rf pulses) of a preset duration is experimentally demonstrated.     

Stochastic resonance in a bistable system driven by a chaotic signal

The behavior of a bistable oscillator under the action of a chaotic signal from a Rössler oscillator with a spiral attractor is considered. The influence of the width of the main spectral line of the chaotic drive signal on the signal to noise ratio at the response system’s output has been studied.     

Gas-discharge gap passage by injected high-energy electrons driven by a high-voltage pulse

The motion of high-energy electrons in a gas-discharge gap filled by nitrogen at atmospheric pressure has been simulated. Electrons were driven by a subnanosecond high-voltage pulse with an amplitude of 150 kV. It is established that the injected electrons can reach the anode only for a very high initial energy, which cannot be provided by means of explosive emission. Therefore, under usual experimental conditions, electron emission from the cathode cannot account for the main fraction of electrons generated in a gas-filled diode at atmospheric pressure.     

Stable supercontinuum pulse generated by modulation instability in a dispersion-managed fiber

We study on non-linear localized waves on continuous wave background in a dispersion and non-linearity management fibre. We find a stable supercontinuum pulse can be generated from a small modulation on continuous wave in a proper management way, for which the pulse spectrum width and its growth rate can be controlled well by the management parameters. Additionally, we demonstrate a Kuznetsov–Ma breather like non-linear localized wave can exist in a periodic dispersion management fibre, and its spectrum evolution is distinctive from the Kuznetsov–Ma breather’s.     

行波热声发动机驱动的脉管制冷机研究

通过改变热声发动机谐振直路长度,研究系统在不同工作频率下的性能.研究发现,在一定条件下降低频率可以显著改善脉管制冷机的性能.在工作压力为2.7 MPa,加热功率为2 350W,工作频率为45 Hz时,双向进气型单级脉管制冷机获得了80.9 K的最低制冷温度,这是目前用热声制冷方法获得的最低制冷温度.     

Estimation of photon dose generated by a short pulse high power laser

The authors obtain a new equation to estimate the forward component of a photon dose generated through the interaction between a target and a short pulse high power laser. As the equation is quite simple, it is useful for calculating the photon dose. The equation shows that the photon dose is proportional to the electron temperature in the range>3 MeV and proportional to the square of the electron temperature in the range<3 MeV. The dose estimated with this method is roughly consistent with the result of Monte Carlo simulation. With some assumptions and corrections, it can reproduce experimental results obtained and the dose result calculated at other laboratories.     

线性压缩机驱动的80K单级脉管制冷机设计与实验研究

结合美国标准与技术研究院(NIST)的回热器计算软件REGEN3.2,成功设计了1台单级斯特林型脉管制冷机.采用惯性管调相,在2.5MPa充气压力和60Hz频率下,获得无负荷制冷温度59K.在压缩机输入电功率为250W时,80K获得了3.8W的制冷量,与设计计算结果吻合得较好.     

高速列车交会压力波特性分析

因动车组在高速交会时产生的瞬变交会压力波对车体侧壁变形、列车运行噪声及运行安全性都有不可忽视的影响,该文利用高速列车的实际测试数据,从3方面对高速列车在明线交汇和隧道交汇情况下的压力波进行深入分析:交会压力波的时-频特性,主要参数值及其与车速的关系,交会压力波对车体侧壁振动的激励作用。特别对压力波所产生的冲击响应谱进行深入分析,得到不同阻尼比下的频率响应。该文分析结果为进一步研究瞬变交会压力波对车体侧壁变形的影响、对列车运行噪声的贡献等提供新的参考依据。     

Properties of GaAs films deposited by pulse periodic technique

GaAs is a III-V compound possessing high mobility and a direct band gap of 1.43 eV , making it a very suitable candidate for photovoltaic applications. Thin GaAs films were prepared at room temperature by plating an aqueous solution containing GaCl₃ and As₂O₃ at a pH of 2. The current density was kept as 50 mA cm⁻² and the duty cycle was varied in the range 10–50%. The films were deposited on titanium and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. The surface roughness of the films varied from 3 nm to 6 nm as the duty cycle increased. Raman spectra indicated both the LO and TO phonons for the films deposited at duty cycles above 25%. Photoelectrochemical studies indicated that the current and voltage output are higher than earlier reports on thin film electrodes.     

Dispersion of Cherenkov radio pulse generated by a cascade shower on the Moon surface

Phenomena accompanying the propagation of a short bipolar radio pulse with duration of ～1 ns through the Earth’s ionosphere are considered. Such pulses can be generated by a cascade shower caused by an ultrahigh-speed cosmic particle on the Moon’s surface. It is shown that the width of the radio pulse increases by almost two orders of magnitude as a result of dispersion. A method is proposed for retaining the real sensitivity of a detector. The possibility of using dispersion for separating informative signals from local interferences is considered. The power of a cosmic-particle-induced radio signal is compared to the power of cosmic radio-frequency interferences.     

Vibration reduction of pulse tube cryocooler driven by single piston compressor

The development of pulse tube coolers has progressed significantly during the past two decades. A single piston linear compressor is used to in order to reduce the size and mass of a high frequency pulse tube cryocooler. The pulse tube achieved a no-load temperature of 61 K and a cooling power of 1 W@80 K with an operating frequency of 80 Hz and an electrical input power of 50 W. By itself, the single piston compressor generates a large vibration, so a set of leaf springs with an additional mass is used to reduce the vibration. The equation relating the mass, the elasticity coefficient of leaf spring and the working frequency is obtained through an empirical fit of the experimental data. The vibration amplitude is reduced from 55 mm/s to lower than 5 mm/s by using a proper leaf spring. This paper demonstrates that a single piston compressor with vibration reduction provides a good choice for a PTC.     

Transition to phase synchronization in a system with periodic dynamics under the action of a chaotic signal

Intermittent behavior has been studied near the boundary of phase synchronization in an autooscillatory system with periodic dynamics under the action of an external chaotic signal. It is shown that the intermittency obeys the same scenario as that observed in the case of interaction between two coupled chaotic oscillators.     

Nearly diffraction-limited signal generated by a lower beam-quality pump in an optical parametric oscillator

The beam quality of an optical parametric oscillator (OPO) within a singly resonant, confocal-positive branch unstable resonator is investigated. Resonator configurations have been found in which the beam quality of the outgoing signal exceeds the beam quality of the pump. Cavity magnification and pump-pulse duration are found to determine the signal beam quality. It is shown that signal M2 decreases with increasing pump-pulse duration for a given cavity magnification. In an experimental demonstration of a LiNbO3 OPO within an unstable resonator, pumped by a multitransversal mode beam, a signal beam with an almost-single transversal mode has been generated, whereas the multitransversal mode behavior of the pump beam is projected on the idler beam.     

三相异步电动机驱动振动系统的Sommerfeld效应分析

提供有限动力的原动机称为非理想原动机.在工程中,几乎所有提供动力的原动机均为非理想原动机.由非理想原动机带动的振动系统称为非理想振动系统.在非理想振动系统中,原动机与振动系统的运动状态是相互作用、相互影响的.Sommerfeld效应是由于非理想原动机在振动系统共振区附近无法提供足够动力而产出的一种非线性跳跃现象.该试验...     

Just-in-time manufacturing system: a periodic pull system

The just-in-time manufacturing system, as developed in the Toyota Motor Co., may be stated as producing or stocking ‘only the necessary items in necessary quantities at the necessary time’. When the just-in-time concept is applied to an industrial material management system, it is called a pull system, which means that the amount and time of material flow are determined by the rate and time of the actual stock consumption. Actually, in Toyota, this pull system is operated manually by means of a kanban, a sort of card or tag.

As an alternative to a kanban method, a periodic pull system (PPS) is developed as an operating policy of practising a Pull system. Due to the fact that, in a PPS, the manual information processing time of a kanban method is replaced with an instant on-line computerized processing, the material lead time is much shorter than that of a kanban system. This results in better system performance such as less lead time inventory and faster system response.

A PPS is formulated mathematically and a solution approach is provided for target stock levels, as well as the analysis of the fluctuations of in-process material flow, on-hand stock levels, target availability, etc.     

Transient thermal behavior of a water heater system driven by a heat pump

A dynamic model of a water heater system driven by a heat pump was designed to investigate transient thermal behavior of the system which was composed of a heat pump and a hot water circulation loop. Finite volume method was applied to describe the heat exchangers, and lumped parameter models were used to analyze the compressor and the hot water reservoir. Dynamic performances were evaluated as the hot water temperature changes for various sizes of the hot water reservoir. In order to compare the performance characteristics, time scale was normalized by the time constant determined from a quasi-steady state simulation of the system. From the simulation, the smaller size of the water reservoir was found to have larger transient performance degradation, and the larger size caused additional heat loss during the hot water storage period. Therefore, the reservoir size should be optimized in a design process to minimize both the heat loss and the performance degradation.     

On the possibility of obtaining attosecond pulse trains during second harmonic generation by high-intensity femtosecond pulses

The possibility of obtaining attosecond pulse trains during second harmonic generation by high-intensity femtosecond pulses is demonstrated by means of computer simulation. The attosecond pulses are formed at the basic frequency with a low efficiency (≤8%) of the energy conversion from first to second harmonic. The regimes of attosecond pulse generation at the double frequency are considered.     

单直线压缩机驱动双脉管冷指的实验研究

为了在不同位置获得不同的制冷性能,设计了一台线性对置压缩机驱动两台同轴型脉管冷指的实验方案并搭建了试验台.通过实验研究两台脉管制冷机耦合的制冷性能.实验结果显示:两台设计相同的脉管冷指性能不同,经过耦合后制冷性能差异更大,可同时达到1.79 W@60 K和1.384 W@60 K制冷量.