微波场作用下的溶质扩散通量

微波场协同溶质扩散机理是强化传质研究的苇要内容,由于微波热效应的干扰,微波场协同极性分子扩散的实验研究尚未取得大的进展.基于液体扩散机制,利用微波场对偶极分子的作用以及分子间相互作用能的影响,建立了微波场协同溶质分子扩散的关系式,得出了微波协同极性分子扩散是通过改变分子间的相互作用能来增强溶质分子扩散的结论.微波场的协同作用依赖分子的电偶极矩,温度较高时,电偶极矩越人强化效果越明显.微波场还可以通过削弱分子问动态氢键来增大扩散通量.该结论可为微波强化传质的理论和实验研究提供参考.     

Resonant microwave conductivity response to ac current in La0.7Pb0.3MnO3 crystals

An experimental study of the effect of low-frequency transport current on the microwave conductivity of single-crystal La_0.7Pb_0.3MnO₃ is reported. In the absence of an external magnetic field, the microwave conductivity response to a current follows a relaxation behavior. In a nonzero external magnetic field, the response spectrum exhibits a peak of resonant amplitude enhancement. The resonant response has a nonlinear nature. The temperature and field dependences of the main parameters of the microwave response correlate directly with the behavior of the magnetoresistance. The results obtained are analyzed within the oscillator approximation. Electronic phase separation is proposed as a possible mechanism for the current action. Fiz. Tverd. Tela (St. Petersburg) 41, 2187–2192 (December 1999)     

Weak disorder strongly improves the selective enhancement of diffusion in a tilted periodic potential

The diffusion of an overdamped Brownian particle in a tilted periodic potential is known to exhibit a pronounced enhancement over the free thermal diffusion within a small interval of tilt values. Here we show that weak disorder in the form of small, time-independent deviations from a strictly spatially periodic potential may further boost this diffusion peak by orders of magnitude. Our general theoretical predictions are in excellent agreement with experimental observations.     

径向渡越时间振荡器的初步实验研究

 对径向渡越时间振荡器进行了实验研究，在非最优化条件下得到了辐射功率大于30MW、主频为3.66GHz的微波，同时研究了微波功率随电压、电流的变化，所得结果和规律与理论分析和数值模拟基本相符。     

径向渡越时间振荡器的初步实验研究

对径向渡越时间振荡器进行了实验研究,在非最优化条件下得到了辐射功率大于30MW、主频为3.66GHz的微波,同时研究了微波功率随电压、电流的变化,所得结果和规律与理论分析和数值模拟基本相符。     

Rotational Diffusion in Prolate Symmetric top Molecules

A comparative analysis of theoretical and experimental rotational diffusion constants was performed for a series of liquid phase prolate symmetric top molecules. It was observed that the tumbling diffusion constants, D⊥, predicted by the extended Hynes-Kapral Weinberg (HKW) model were invariably in closer agreement with experiment than were values determined by the Hu-Zwanzig (HZ) slip model of molecular reorientation. The HKW theory also yielded superior estimates of D‖ for two -CCI³ rotors. However, the experimental spinning diffusion coefficients for methyl (-CD³) rotors were much closer to the slip (Free Rotor) limit.     

Characteristics of Germanium n+/p junctions formed by phosphorus diffusion from on indium-gallium-phosphide layer

Although numerous studies have been previously reported for the formation of Ge p–n junctions, there is still a lack of research on Ge junctions formed by solid-phase diffusion doping, which typically uses the diffusion phenomenon of phosphorus (P) atoms from InGaP for the fabrication of a Ge n⁺/p subcell in a III–V multi-junction cell. Here, we investigate the characteristics of Ge n⁺/p junctions achieved by the InGaP-based diffusion technique at 450–650 °C with SIMS, ECV, and J–V analyses. In addition, through a multiple error function fitting method, diffusivity, peak position, and activation energy values are accurately estimated from raw In/Ga/P/Ge SIMS profiles. The extracted activation energy values for In/Ga/P atoms are much lower than previously reported, indicating that a faster diffusion phenomenon occurs during the simultaneous diffusion of In/Ga/P into Ge. A non-annealed InGaP-deposited junction shows Ohmic behavior with a high current density because of leakage currents by many interfacial point defects. After a 550 °C anneal, the current density is reduced by 3–4 orders of magnitude and a small on/off-current ratio is obtained. Compared to this 550 °C annealed junction, a current density increases ∼10 times in the 650 °C sample due to an increased n-type carrier concentration.     

线性变压器源驱动相对论速调管放大器的初步实验

利用新研制的紧凑型线性变压器驱动源（LTD）脉冲功率源二极管产生的电子束源,开展了S波段长脉冲相对论速调管放大器（RKA）的初步实验研究。采用无箔空心阴极和0.9 T恒流源引导磁场从LTD二极管引出了电压600 kV、束流6 kA、脉宽150 ns的环形电子束,该电子束经过1个同轴输入腔和2个同轴调制腔的调制后,产生了幅度5 kA、脉宽110 ns的基波调制束流,采用该调制束流驱动同轴微波提取腔,辐射输出了峰值功率820 MW/110 ns的辐射微波,效率28％,增益36 dB。同时,开展了重复脉冲RKA和相位特性的实验研究,重复频率10 Hz运行时,辐射微波达到800 MW/100 ns,相位抖动小于 20°。     

Observation of steps in the microwave impedance of superconducting microbridges

Steps similar to those seen in the d.c. I—V characteristics have been noted in the onset of the microwave frequency current-driven superconducting-to-normal transition of tin and lead microbridges. These steps are well described by the theory of Skocpol, Beasley, and Tinkham, and are apparently caused by the generation of localized phase slip sites in the microbridges. The observed microwave dissipation and critical current hysteresis result from the diffusion of quasiparticles generated in the phase slip process. Heating effects were not found to limit the observation of these steps.     

线性变压器源驱动相对论速调管放大器的初步实验

 利用新研制的紧凑型线性变压器驱动源（LTD）脉冲功率源二极管产生的电子束源,开展了S波段长脉冲相对论速调管放大器（RKA）的初步实验研究。采用无箔空心阴极和0.9 T恒流源引导磁场从LTD二极管引出了电压600 kV、束流6 kA、脉宽150 ns的环形电子束,该电子束经过1个同轴输入腔和2个同轴调制腔的调制后,产生了幅度5 kA、脉宽110 ns的基波调制束流,采用该调制束流驱动同轴微波提取腔,辐射输出了峰值功率820 MW/110 ns的辐射微波,效率28％,增益36 dB。同时,开展了重复脉冲RKA和相位特性的实验研究,重复频率10 Hz运行时,辐射微波达到800 MW/100 ns,相位抖动小于 20°。     

Nonlinear microwave response of YBCO single crystal in constant magnetic field

The generation of a microwave second harmonic by a YBCO single crystal in a dc magnetic field was studied. We found that the signal existed only when there was a direct screening current. As a result, the pinning current as a function of magnetic field can be derived directly from the second harmonic intensity versus the magnetic field. The experimental data were interpreted in terms of a generalized model of the critical state taking into account diffusion of vortices and the absence of a barrier stopping vortices from leaving the sample. We have shown that, in a decreasing dc magnetic field, the current density is considerably lower than both the critical and screening current densities in an increasing dc field. Our experiments indicate that vortices are not the sources of radiation at the double frequency. A relation between the mechanism of harmonic generation in the Meissner phase and modulation of the order parameter by the microwave magnetic field (Ginzburg-Landau nonlinearity) is discussed. It is remarkable that, by measuring the second harmonic intensity in the Meissner state versus temperature, one can obtain the magnetic field penetration depth as a function of temperature with fairly good accuracy. Zh. éksp. Teor. Fiz. 115, 2242–2253 (June 1999)     

外部光注入混沌激光器产生超宽带微波信号的研究

利用外部光注入混沌激光器产生了完全符合美国联邦通信委员会关于室内无线通信频谱限定的超宽带(UWB)微波信号.基于外部光注入光反馈半导体激光器的速率方程组,理论研究了外部及内部参量对半导体激光器输出混沌UWB脉冲信号的影响.研究表明,UWB信号的-10 dB带宽随着光注入强度、注入失谐量以及线宽增强因子的增大而增大,随着激光器偏置电流的增大而减小.同时,UWB信号的中心频率在5–8 GHz范围内变化.在实验中,通过设定其他参量和调节光注入强度,得到中心频率及带宽可调谐的混沌UWB微波信号,传输速率达到500 Mbit/s.实验结果与理论分析相符合. 关键词： 半导体激光器 混沌激光 光生微波技术 超宽带信号     

A study of density in electron-cyclotron-resonance plasma

A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data     

Optical phase modulators using deformable waveguides actuated by micro-electro-mechanical systems

An optical phase modulator is presented by using micro-electro-mechanical systems to actuate deformable silicon waveguides. Via mechanically stretching the waveguide length, the optical path is extended, resulting in a phase shift. The experimental results show that a phase shift of near 0.4π is achieved at 200 V for both TE- and TM-polarized waves by cascading six phase modulation units, agreeing well with the theoretical prediction. The power consumption is estimated to be smaller than 0.2 mW at 200 V, mainly resulting from the leakage current.     

Positron trapping at quantum-dot-like particles on metal surfaces

Measurements of the positron annihilation-induced Auger electron (PAES) spectra from the Fe-Cu alloy surfaces with quantum-dot-like Cu nanoparticles embedded in Fe reveal a decrease of the Fe M_2,3VV positron annihilation-induced Auger signal intensity and an enhancement of the Cu one for surfaces created by enriching the Cu content of the Fe-Cu alloy. These experimental results are analyzed by performing calculations of positron surface states and annihilation characteristics at the Fe(1 0 0) surface with quantum-dot-like Cu nanoparticles embedded in the top atomic layers of the host substrate. Estimates of the positron binding energy and annihilation characteristics reveal their strong sensitivity to the nanoparticle coverage. Theoretical core annihilation probabilities are compared with experimental ones estimated from the measured Auger peak intensities. The observed behavior of the Fe and Cu PAES signal intensities is explained by theoretical calculations as being due to trapping of positrons in the regions of Cu nanoparticles embedded in the top atomic layers of Fe.     

Ultra-Broad-Band LiNbO3 Electro-Optic Modulators with Novel Complex Electrode

The characteristics of Z- cut LiNbO3 optical modulators with novel complex electrode are discussed by using the finite element method (FEM) and studied experimentally in this paper. The travelling wave electrode consists of upper and lower parts. It can easily realize phase velocity matching between microwave and optical wave and drastically reduce microwave electrode loss. An electrooptic modulator with larger than 100 GHz bandwidth and half wave voltage 6 V is designed, fabricated and measured. Vπ is 5.1 V and the attenuation coefficient a0 is 0.3 dB/(cm· GHz1/2 ). The experimental results show that the modulator has great potentiality for expanding bandwidth.     

Ultra-Broad-Band LiNbO_3 Electro-Optic Modulators with Novel Complex Electrode

1 IntroductionFOr LiNbO3 modulators, the bandwidth is mainly restricted by the microwaveattenuation of the travelling--wave electrode and the phase velocity ndsmatch betWeenmicrowave and optical wave in the devices. When the phase velocity matching issatisfied it is very i~rtant to decrease the microwave attenuation for expandingbandwidth. The thecrowave propagating lOSS is the main source Of the microwaveattenuation in the interactive region. The larger the cross-sectional area or the lOn…     

铁电阴极相对论行波管初步研究

研究了铁电材料的电子发射特性,根据实验和数值模拟结果给出了铁电发射特性的定性解释,并指出目前的几种铁电发射理论都不足以完备地解释各种实验现象。设计了Pierce型铁电阴极电子枪,实现了束流的二级压缩,其总束流大于100 A。在此基础上,分析和设计了具有盘荷波导慢波结构的相对论行波管,得到了带宽500 MHz,增益约25 dB的X波段行波放大输出。     

波导内场增强法测量微波气体击穿

提出并研究了波导内场增强法测量微波气体击穿的实验方案,在密闭波导内加金属针实现电场增强,通过调节微波源辐射功率及两针距离,使微波传输达到气体击穿的条件。介绍了实验原理及诊断方法,进行了频率2.86 GHz、脉宽180 ns的微波在0.1 MPa空气中的击穿实验,分析了实验中得到的典型波形。结果表明实验现象与设计吻合,验证了该方案研究微波气体击穿的可行性。     

Photon-assisted Shot noise of the double quantum dot interferometer in weak Kondo regime

The shot noise of a parallel double quantum dot (DQD) system under the perturbation of microwave fields is investigated in the weak Kondo regime. Peak-valley structures exhibit in the differential conductance and shot noise, and side resonant peaks emerge around the Kondo peak due to the absorption and emission of photons. The shot noise is sensitively dependent on the adjusting approach through changing the gate voltages. Large resonant Fano factor accompanying photon-induced side peaks appear by simultaneously varying the two gate voltages. The photon suppression and enhancement of shot noise have been evaluated corresponding to the coherent and incoherent current correlation. The destructive interference causes the suppression of shot noise by changing the Aharonov–Bohm phase.