Maps and inverse maps in open quantum dynamics

Two kinds of maps that describe evolution of states of a subsystem coming from dynamics described by a unitary operator for a larger system, maps defined for fixed mean values and maps defined for fixed correlations, are found to be quite different for the same unitary dynamics in the same situation in the larger system. An affine form is used for both kinds of maps to find necessary and sufficient conditions for inverse maps. All the different maps with the same homogeneous part in their affine forms have inverses if and only if the homogeneous part does. Some of these maps are completely positive; others are not, but the homogeneous part is always completely positive. The conditions for an inverse are the same for maps that are not completely positive as for maps that are. For maps defined for fixed mean values, the homogeneous part depends only on the unitary operator for the dynamics of the larger system, not on any state or mean values or correlations. Necessary and sufficient conditions for an inverse are stated several different ways: in terms of the maps of matrices, basis matrices, density matrices, or mean values. The inverse maps are generally not tied to the dynamics the way the maps forward are. A trace-preserving completely positive map that is unital cannot have an inverse that is obtained from any dynamics described by any unitary operator for any states of a larger system.     

一种数字控制单相全桥逆变电路运动行为分析方法研究

考虑到数字控制单相全桥逆变电路PWM调制方法和滤波器、负载结构的多样性, 以及利用状态转移矩阵对系统运动行为分析方法的局限性. 通过解析表达状态转移矩阵中的元素, 本文提出了一种可以解析描述具有N个状态变量、一个开关周期内M次拓扑 变化的数字控制单相全桥逆变电路(简称N-M数字控制单相全桥逆变电路)系统参数 与运动行为关系的分析方法. 以3-3数字控制单相全桥电压逆变电路为例对上述分析方法进行了验证, 推导出了该三阶电路发生Hopf分岔的解析判别式、稳定范围及Hopf分岔振荡频率的解析表达式, 并通过Simulink仿真及电路实验证明了理论分析的正确性.     

太赫兹GaAs肖特基混频二极管高频特性分析

在太赫兹波段,存在几种新的高频效应会限制混频二极管的高频特性.应用热电子发射理论和隧道理论,研究了外延层肖特基二极管的高频特性,并以截止频率为品质因数对二极管进行优化设计.研究表明,当二极管工作频率大于等离子频率时,二极管相当于一个电容,失去了混频性能;提高基底掺杂浓度可以减小基底等离子共振效应;外延层等离子频率非常重要并且在研究外延层等离子共振效应时必须考虑传输时间效应;减小阳极直径、减小外延层厚度、提高外延层掺杂浓度可以提高二极管的工作频率.这对太赫兹波段室温混频器件的研制具有重要的参考价值.     

Two-scale image fusion of visible and infrared images using saliency detection

Military, navigation and concealed weapon detection need different imaging modalities such as visible and infrared to monitor a targeted scene. These modalities provide complementary information. For better situation awareness, complementary information of these images has to be integrated into a single image. Image fusion is the process of integrating complementary source information into a composite image. In this paper, we propose a new image fusion method based on saliency detection and two-scale image decomposition. This method is beneficial because the visual saliency extraction process introduced in this paper can highlight the saliency information of source images very well. A new weight map construction process based on visual saliency is proposed. This process is able to integrate the visually significant information of source images into the fused image. In contrast to most of the multi-scale image fusion techniques, proposed technique uses only two-scale image decomposition. So it is fast and efficient. Our method is tested on several image pairs and is evaluated qualitatively by visual inspection and quantitatively using objective fusion metrics. Outcomes of the proposed method are compared with the state-of-art multi-scale fusion techniques. Results reveal that the proposed method performance is comparable or superior to the existing methods.     

热声系统中回热器特征阻抗与传播常数的研究

针对本实验室一台声驱动热声系统,采用传递函数法研究声驱动系统中回热器的特征阻抗和传播常数.通过调节谐振管长度,改变回热器表面的阻抗,从理论上分析了回热器网络传输方程中的声传播常数、特征阻抗与系统网络元件中的阻抗、导纳和流的关系.并且进一步讨论有无换热器以及不同的加热功率对回热器网络参数的影响.结论有利于进一步量化回热器的网络参数.     

Neutron halos in the excited states for N=127 isotones

Properties of the ground states and the excited states of N=127 isotones are investigated by using the nonlinear relativistic mean field theory with the interactions PK1. By analyzing the rms of proton and neutron, the single particle energies of valence nucleon and the density distributions of neutron, proton and the last neutron, it can be found that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in 209Pb. It is also predicted that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in 207Hg, 208Tl, 210Bi and 211Po.     

Blood oxygenation monitoring using hyperspectral imaging after flap surgery

In this paper, we present a new method for the assessment of skin flap perfusion based on the non-invasive monitoring of skin blood oxygenation using hyperspectral imaging. This method consists of generation of oxyhemoglobin and deoxyhemoglobin maps in skin flap from hyperspectral image using an analytic model based on Beer–Lambert law. The results obtained on a fasciocutaneous sural flap have revealed that the oxyhemoglobin and deoxyhemoglobin maps facilitate the visualization of some differences between different areas of the flap, an aspect that clinical examination fails to do. In conclusion, the proposed method could provide a new option for a more accurate assessment of flap survival.     

Analysis of detection limit to time-resolved coherent anti-Stokes Raman scattering nanoscopy

In the implementation of CARS nanoscopy, signal strength decreases with focal volume size decreasing. A crucial problem that remains to be solved is whether the reduced signal generated in the suppressed focal volume can be detected. Here reported is a theoretical analysis of detection limit （DL） to time-resolved CARS （T-CARS） nanoscopy based on our proposed additional probe-beam-induced phonon depletion （APIPD） method for the low concentration samples. In order to acquire a detailed shot-noise limited signal-to-noise （SNR） and the involved parameters to evaluate DL, the T-CARS process is described with full quantum theory to estimate the extreme power density levels of the pump and Stokes beams determined by saturation behavior of coherent phonons, which are both actually on the order of ~ 109 W/cm2. When the pump and Stokes intensities reach such values and the total intensity of the excitation beams arrives at a maximum tolerable by most biological samples in a certain suppressed focal volume （40-nm suppressed focal scale in APIPD method）, the DL correspondingly varies with exposure time, for example, DL values are 103 and 102 when exposure times are 20 ms and 200 ms respectively.     

Coherent incoherent transition in the spin boson model with a super-ohmic bath

The temperature effect on tunnelling splitting in the spin--boson model with a super-ohmic bath is studied by the small polaron theory. The coherent--incoherent transition temperature is calculated and its dependence on dissipation strength and bare tunnelling splitting is analysed. In additional to the traditional transition point described in textbooks, a new kind of transition is found in the low dissipation region, showing different temperature dependence in the transition. The relation to the corresponding transition in the polaron--phonon system is also discussed.     

示波器电子运动规律与波形显示关系研究

本文详细地论述了示波管荧光屏上的显示波形与电子运动规律、波形周期与扫描电压周期间的关系,以便帮助学生理解和解决学习示波器原理过程中遇到的疑难、疑惑问题。