基于周期反转模式的表面暗电流抑制

为了抑制电子倍增CCD的表面暗电流,运用Shockley-Read-Hall理论解释了表面暗电流的产生过程,通过曲线拟合建立了表面暗电流的理论模型,定量分析了电子倍增CCD从反转模式切换到非反转模式后表面暗电流的恢复特征时间.根据这一时间特性提出了周期反转模式的概念,在信号积分期里对成像区时钟进行调制,加入周期反转脉冲,使器件以小于表面暗电流恢复特征时间的周期在反转与非反转模式之间切换.仿真结果表明,随着周期反转频率的提高.表面暗电流明显减小.当时钟周期为0.2 ms时,平均表面暗电流降低到0.051 nA/cm2,接近反转模式的水平,与理论分析完全一致,验证了周期反转模式的可行性.     

Enhanced responsivity of non-steady-state photoinduced electromotive force sensors using asymmetric interdigitated contacts

The responsivity at a constant detection area of non-steady-state photoinduced electromotive force (photo-emf) detectors is improved by a factor equal to the number of contact pairs contained in asymmetric interdigitated surface contacts. The polar nature of photo-emf current generation requires contact asymmetry in which one increases the total signal by blocking the illumination between alternate contact pairs, in distinct contrast to the behavior of conventional interdigitated contacts fabricated upon isotropic photoconductors.     

Spatially Periodic System with Infinite Globally Coupled Oscillators Driven by Temporal-Spatial Noise

In this paper, we study spatially periodic system with infinite globally coupled oscillators driven by temporal-spatial noise and subject to a constant force. The results show that the system exhibits the phenomena of the non-equilibrium phase transition, transport of particles, and the anomalous hysteresis cycle for the mean field and the probability current.     

Feedback control of two-headed Brownian motors in flashing ratchet potential

We presented a detailed investigation on the movement of two-headed Brownian motors in an asymmetric potential under a feedback control.By numerical simulations the direct current is obtained.The current is periodic in the initial length of spring.There is an optimal value of the spring constant.And the dependence of the current on the opposing force is reversed.Then we found that when the change of the temperature and the opposing force have optimal values,the Brownian motors can also obtain the optimal efficiency.     

High-efficiency deterministic Josephson vortex ratchet

We investigate experimentally a Josephson vortex ratchet--a fluxon in an asymmetric periodic potential driven by a deterministic force with zero time average. The highly asymmetric periodic potential is created in an underdamped annular long Josephson junction by means of a current injector providing an efficiency of the device up to 91%. We measured the ratchet effect for driving forces with different spectral content. For monochromatic high-frequency drive the rectified voltage becomes quantized. At high driving frequencies we also observe chaos, subharmonic dynamics, and voltage reversal due to the inertial mass of a fluxon.     

Net Voltage and Phenomenon of Resonance Induced by Chaotic Signal for a Superconducting Junctions Device

The effects of a quenched chaotic signal on the over-damped motion of the electron pairs of a superconducting junctions device are studied. It is shown that the chaotic signal can induce the net voltage and the phenomenon of resonance.     

Net Voltage and Phenomenon of Resonance Induced by Chaotic Signal for a Superconducting Junctions Device

The effects of a quenched chaotic signal on the over-damped motion of the electron pairs of a superconducting junctions device are studied. It is shown that the chaotic signal can induce the net voltage and the phenomenon of resonance.     

0.14 THz双环超材料慢波结构表面波振荡器数值研究

本文研究了一种太赫兹波段双环超材料慢波结构, 并具有同轴引出结构的相对论过模表面波振荡器. 设计了超材料同轴过模慢波结构; 通过色散特性, 进行了模式选择和过模结构电子束电参数和几何参数的设计; 根据超材料同轴慢波结构的特点, 设计了具有同轴引出结构的末端同轴输出段. 粒子模拟结果表明, 在电子束电压为600 kV和电流为1.0 kA, 引导磁场为2.0 T 时, 同轴超材料慢波结构过模表面波振荡器输出稳定单频的0.141 THz电磁波, 峰值功率为316.8 MW.     

Absolute negative mobility induced by thermal equilibrium fluctuations

A novel transport phenomenon is identified that is induced by inertial Brownian particles which move in simple one-dimensional, symmetric periodic potentials under the influence of both a time periodic and a constant, biasing driving force. Within tailored parameter regimes, thermal equilibrium fluctuations induce the phenomenon of absolute negative mobility (ANM), which means that the particle noisily moves backwards against a small constant bias. When no thermal fluctuations act, the transport vanishes identically in these tailored regimes. ANM can also occur in the absence of fluctuations on grounds which are rooted solely in the complex, inertial deterministic dynamics. The experimental verification of this new transport scheme is elucidated for the archetype symmetric physical system: a convenient setup consisting of a resistively and capacitively shunted Josephson junction device.     

Transport Characteristics of Mesoscopic Radio-Frequency Single Electron Transistor

The transport property of a quantum dot under the influence of external time-dependent field is investigated. The mesoscopic device is modelled as semiconductor quantum dot coupled weakly to superconducting leads via asymmetric double tunnel barriers of different heights. An expression for the current is deduced by using the Landauer-Buttiker formula, taking into consideration of both the Coulomb blockade effect and the magnetic field. It is found that the periodic oscillation of the current with the magnetic field is controlled by the ratio of the frequency of the applied ac-field to the electron cyclotron frequency. Our results show that the present device operates as a radio-frequency single electron transistor.     

Nonlinear response of Josephson fluxonic diode to radiation based on geometry and incident radiation point

The stimulated generation of vortex and antivortex pairs in reverse-biased Josephson fluxonic diode is used for detecting induced current signal. Radiation signal can either be coupled directly to the junction by modulating the bias current or be added to the control current that is responsible for the reversing magnetic field inside the Josephson fluxonic diode. Sensitivity to signals is a function of geometry and device dimensions, bias, and control quiescent points. Numerical simulations have been performed for both bias and control current to obtain the most appropriate configurations and quiescent points for detection.     

Current to frequency conversion in a Josephson circuit

The voltage oscillations which occur in an ideally current-biased Josephson junction were proposed to make a current standard for metrology. We demonstrate similar oscillations in a more complex Josephson circuit derived from the Cooper pair box: the quantronium. When a constant current I is injected in the gate capacitor of this device, oscillations develop at the frequency f(B)=I/2e, with e the electron charge. We detect these oscillations through the sidebands induced at multiples of f(B) in the spectrum of a microwave signal reflected on the circuit, up to currents I exceeding 100 pA. We discuss the potential interest of this current-to-frequency conversion experiment for metrology.     

Three-Pulse ELDOR Theory Revisited

The current theory of three-pulse electron double resonance (PELDOR) has been generalized to the case, when paramagnetic particles (spin labels) in pairs or groups have the electron paramagnetic resonance (EPR) spectra, which overlap essentially or coincide. The PELDOR signal modulation induced by the dipole–dipole interaction between paramagnetic spin ½ particles in pairs embedded in disordered systems has been analyzed comprehensively. It has been shown that the PELDOR signal contains additional terms in contrast to the situation considered in the current theory, when the EPR spectra of the spin labels in the pairs do not overlap. In disordered systems, the pairs of spin labels have the characteristic dipolar interaction frequency. According to the current theory for pairs of spin labels, the PELDOR signal reveals the modulation with this characteristic frequency. The additional terms, which are obtained in this work, do not change the modulation frequency of the PELDOR signal for pairs of spin labels. However, these additional terms should be taken into account when analyzing the amplitude of the PELDOR signal and the amplitude of the modulation of the PELDOR signal. The consistent approach to treating the PELDOR data for the groups containing three or more spin labels has been outlined on the basis of the results for pairs of spin labels. It has been also analyzed how the spin flips and molecular motion or molecular isomerization can affect the manifestation of the interaction between the spin labels in PELDOR experiments. PELDOR experiments for the stable biradicals (biradicals I containing 1-oxyl-2,2,5,5-tetramethylpyrroline-3-yl spin labels and biradicals II containing 3-imidazoline spin labels) have been performed. The results have been interpreted within the theory developed in this work.     

Magnetic field dependence of the maximum Josephson current in a double-barrier junction

The influence of a constant magnetic field on the maximum Josephson current of a double-barrier junction is studied. Owing to the peculiarity of the current–phase relation of this composite device, the resulting Fraunhofer-like pattern shows an overall enhancement of the maximum Josephson current with respect to the usual single-junction curves for very small difference in the coupling energies of the two pairs of adjacent layers in the system.     

W波段交错双栅返波振荡器高频系统

将矩形交错双栅结构作为慢波电路并提出与之配套的过渡结构和输出耦合器,设计了利用带状电子注工作在W波段的返波振荡器。提出的过渡结构和耦合器解决了该类直波导型器件的信号传输衰减大、反射强等难题。相对于传统圆形电子注器件,该器件得到了较大的功率提升。利用三维粒子模拟计算的方法,在电流12 mA时通过调节工作电压,在92~98 GHz频带内得到了数W的稳定平均功率输出,信号中心频率非常接近设计频率,且单色性好,谐波分量小。     

利用Duffing系统周期跳跃的弱超声导波识别

在超声导波检测中,由小缺陷产生的弱回波信号有可能淹没在噪声信号中从而造成漏检风险,通过分析Duffing系统随策动力幅值变化的分岔特性,获得了系统发生周期跳跃的临界状态,将与策动力同频率的弱回波信号作为干扰项叠加到Duffing系统临界状态中,相当于改变了策动力的幅值,从而引起临界状态的周期跳跃,依据系统的周期跳跃实现...     

太赫兹波段Smith-Purcell辐射的介质加载光栅高频特性

提出了一种用于Smith-Purcell效应器件的介质加载光栅慢波结构,通过研究该结构的注-波互作用过程,推导出带电子注的色散方程,并数值求解出波的线性增长率.利用色散方程,结合电磁场传播的边界条件,推导出Smith-Purcell效应振荡器工作所需的起振电流.详细研究了高频结构长度、电子注主要参数和介质相对介电常数对起振电流的影响,并与普通金属光栅结构进行了比较.结果表明:保持其他参数不变时,高频结构长度越短,起振电流越大;保持高频结构参数不变时,起振电流随电子注厚度和注-栅距离的增大而增大,随电子注电压的增大而减小;与金属光栅相比,介质的引入提高了注-波互作用的增长率,有效减小了振荡器的起振电流.理论计算结果与软件CHIPIC的模拟结果比较符合.     

Effect of genome sequence on the force-induced unzipping of a DNA molecule

We considered a dsDNA polymer in which distribution of bases are random at the base pair level but ordered at a length of 18 base pairs and calculated its force elongation behaviour in the constant extension ensemble. The unzipping force F(y) vs. extension y is found to have a series of maxima and minima. By changing base pairs at selected places in the molecule we calculated the change in F(y) curve and found that the change in the value of force is of the order of few pN and the range of the effect depending on the temperature, can spread over several base pairs. We have also discussed briefly how to calculate in the constant force ensemble a pause or a jump in the extension-time curve from the knowledge of F(y).     

Monte Carlo method for the Schrödinger equation with an asymmetric periodic potential

A new numerical method is proposed for solving the Cauchy problem for the Schrödinger equation with an asymmetric periodic potential superimposed by a constant electric field. The solution to the Cauchy problem is used to determine the electron’s mean momentum as a function of time, initial conditions, and the applied field. Given an initial state, the mean momentum characterizes the mean current and the conductivity of an asymmetric periodic structure known as the ratchet potential.     

A new design of pulsed laser diode driver system for multistate quantum key distribution

In this paper, we describe a new design of laser diode driver system based on MOSFET current mirror and digital signal controller (DSC). The system is designed to emit stream pairs of photons from three semiconductor laser diodes. The DSC is able to switch between the three laser diodes at constant rate. The duty cycle is maintained at 1% in order to reduce its thermal effect and thus prolong the laser diodes’ life cycles. The MOSFET current mirror circuits are capable of delivering constant modulation current with peak current up to 58 mA to each laser diode. This laser driver system will allow the generating biphotons automatically with qubit rate around 8-13% for μ less than or equal to 1, thus making it practical for six-states quantum key distribution implementation.