Continuous variable teleportation as a quantum channel

A quantum channel consisting of continuous variable quantum teleportation based on the standard protocol is investigated. It is shown that a quantum channel for continuous variable teleportation by an aribitrary entangled state is equivalent to a generalized thermalizing channel. We also study the transmission of nonclassical states by a teleportation channel with a two-mode squeezed-vacuum state in a noisy environment. The transmisson performance is evaluated by using the Glauber-Sudarshan P function and the nonclassical depth. Finally, we compare the results obtained to those of a noisy direct transmission channel. It is shown that the teleportation channel performs better than the direct transmission channel in a certain region.     

水在不均匀纳米通道内自扩散性质的分子动力学研究

本文用分子动力学(MD)方法模拟了受限水在不均匀润湿性微通道中的自扩散性质.通过考察不均匀润湿通道内水的自扩散行为,发现在微通道中水的扩散性质表现出明显的尺度效应,随着通道高度的增加水的扩散增强.更重要的是,由于通道高度的不同,通道内的不均匀润湿段对水的扩散与均匀通道相比有不同的影响.当通道高度为0.8 nm时,不均匀润湿通道内水的扩散增强;当通道高度为1.0 nm时,不均匀润湿通道内水的扩散减弱;而当通道高度达到1.2 nm时,不均匀润湿通道内水的扩散基本相同.     

空气中单个激光等离子体通道的形成条件

利用皮秒和飞秒激光研究了激光在空气中聚焦产生单个等离子体通道的条件.研究发现，能量为8—12mJ皮秒激光被焦距为15cm的透镜聚焦后，可以产生较为稳定的单个通道.通过横向纵向阴影成像分析发现，通道的管壁对聚焦产生的自发光具有箍缩作用，而通道内部却有利于光的传输.同时还发现，当采用短焦距透镜时，能量低于10mJ的飞秒激光在空气中较易形成单个等离子通道. 关键词： 等离子体通道 皮秒激光 飞秒激光 阴影成像     

通道靶对超强激光加速质子束的聚焦效应

发散角过大是制约超强激光与固体靶相互作用加速产生高能质子束应用的一个重大物理难题.本文提出了一种结构化的通道靶型,与超强激光相互作用可提高质子束的发散特性,通道壁上产生的横向电荷分离静电场可对质子有效聚焦.采用二维particle-in-cell粒子模拟程序对激光通道靶相互作用过程进行了研究,分析了加速质子束的性能特点.模拟结果表明,与传统平面靶相比,通道靶可以在不过多损失能量的情况下产生具有更好准直性的质子束,尤其当通道靶的直径与激光焦斑尺寸和质子源尺寸相当时,横向静电场能够有效聚焦质子束,并且可保证相对较高的激光能量利用率.     

基于基追踪去噪的水声正交频分复用稀疏信道估计

针对传统的l₂-范数信道估计精度低的问题, 提出了一种基于基追踪去噪(BPDN)的水声正交频分复用稀疏信道估计方法, 该方法针对水声信道的稀疏特性, 利用少量的观测值即可以很高的精度估计出信道冲激响应. 与贪婪追踪类算法相比, 基于BPDN算法的稀疏信号估计具有全局最优解, 采用l₂-l₁范数准则估计信号, 同时考虑了观测值含噪情况, 通过调整正则化参数控制估计信号稀疏度和残余误差之间的平衡. 仿真分析了导频分布、正则化参数等对BPDN 算法的影响以及BPDN算法与最小平方(LS)、正交匹配追踪(OMP)信道估计算法的性能. 湖试结果表明, 在稀疏信道下, 基于BPDN的信道估计方法明显优于LS和OMP信道估计方法.     

LaB6场发射尖锥的场发射特性研究

报道了六硼化镧（LaB6）场发射尖锥的场发射性能。采用电化学腐蚀方法制作了LaB6场发射尖锥，并在10-2～10-7 Pa 的宽真空度范围内对单尖LaB6场发射二极管的发射特性进行了测试。发现残余气体电离产生的离子轰击对LaB6场发射阴极尖锥表面起到了离子清洗作用，使LaB6场发射尖锥在低真空工作后发射电流大幅度提高。离子轰击是一种适用于LaB6场发射阴极的激活处理方法。     

Improving Key Rate of Optical Fiber Quantum Key Distribution System Based on Channel Tomography

We investigate the key rate of polarization-coded optical fiber-based quantum key distribution system (QKD) with BB84 protocol by channel tomography. The quantum bit error rate (QBER) of the QKD system under depolarizing channel is obtained by analyzing output density operators, transmission rate of channel, transmission rate of the receiver and dark count of single photon detector. According to the estimated QBER an LDPC chosen adaptively is applied to information reconciliation and the practical final key rate is discussed. Analysis results show that compared with cascade scheme and no channel knowledge the key rate can be improved by the proposed reconciliation scheme with channel tomography.     

Mutual Information of Pauli Channels with Correlated Noise

A general formula for the mutual information of the Paufi channels with memory modelled by correlated noise is derived. It is shown that the mutual information depends on the channel shrinking factor, the input state parameter and the channel memory coefficient. The analyses based on the general formula reveal that the entanglement is always a useful resource to enhance the mutual information of some Pauli channels, such as the bit flip channel and the bit-phase flip channel. Our analyses also show that the entanglement is not advantageous to the reliable transmission of classical information for some Pauli channels at any time, such as the phase flip channel and the phase damping channel.     

微针肋槽道内去离子水换热特性

设计了槽肋比为1:2和2:1的矩形大长宽比微针肋散热器,并实验研究了去离子水在其内的流动换热性能。结果表明:当进口温度为40 ℃、微针肋槽道在雷诺数小于650、最高壁面温度低于77 ℃时,单位面积散热量可达21.32 W/cm2。当雷诺数一定时,同一个槽道壁面温度沿着流动方向不断增加、同一个位置壁面温度随着加热功率的增加而增大,局部努谢尔数沿着流动方向先减小后逐渐增加并趋于定值。当针肋流动换热长度较长时,其入口效应可以忽略,槽道平均努谢尔数随着雷诺数的增大而增大,与加热功率无关;为了更好地表达微针肋槽道内的换热特性,考虑了槽肋比、流动雷诺数等影响,拟合了去离子水在微针肋槽道内的对流换热关系式。     

浅水时变多途信道特性分析与模型实验研究

时变多途水声信道是影响水声通信性能的一个重要因素,深入了解水声信道挣性并对水声信道进行建模具有重要的研究意义。本文在分析传统时变信道模型基础上,从时域角度出发,提出采用AR(ρ)模型对已有的浅水时变多途信道模型中的小尺度衰落分量进行修正。然后基于莲花湖实测信道数据,分析了时变信道各个路径的幅度、时延、时间相干系数、系统传递函数等特性,并对修正模型进行了验证正。从仿真结果来看,修正模型与试验结果拟合的很好。本文从多个方面对水声信道特性进行了分析,有助于对水声信道的深入了解,同时为水声通信系统性能评估提供了一种仿真信道模型。     

Opportunistic spectrum access for TDMA-based cognitive radio networks

In this paper, opportunistic spectrum access is proposed for TDMA-based cognitive radio networks. In TDMA-based networks, the time is divided into slots with fixed length one by one. If a primary user (PU) needs to transmit data, one or several slots will be used. Otherwise, the slots are idle and can be utilized by secondary users (SUs). When SUs want to use the licensed channel, they should sense the channel at the beginning period of each slot. Then SUs exchange their sensing results and make the same decision about the channel state (idle or used by PUs), which could reduce the probability of false sensing. The aforementioned duration is called spectrum sensing phase. When SUs decide there is an idle channel, they contend to use the channel at the rest time of the slot. The duration is called access phase. In this period, SUs contend the channel with backoff counters. When the remaining time is less than one data transmission duration, SUs cannot transmit data packets. Therefore, the remaining time is wasted. To solve this problem, SUs transmit control packets with small length in the remaining time instead. The SU who exchange control packets successfully reserves the channel and sends a data packet prior to other SUs in access phase of the next idle slot. Obviously, this reserved transmission is without collision. The independent spectrum sensing, channel state decision and control packets reservation influence the performance of SUs. The proposed scheme is formulated with all above factors. Simulations which consist with the numerical results show the proposed access scheme achieve higher throughput than the existed scheme without channel reservation.     

光谱法研究闪电通道的导电特性

依据无狭缝光栅摄谱仪在青海获得的云对地闪电回击光谱信息,结合空气等离子体传输理论,用四种不同方法计算了同一闪电放电通道的电导率。结果表明：各种方法所得闪电核心通道的电导率数量级均为104 S·m-1;且同一通道内的电导率随通道高度的增加有减小的趋势;通道内电子与一次、二次电离离子的碰撞以及它们各自的碰撞对通道电导率的贡献不可忽略;用碰撞积分的方法计算闪电核心通道的电导率结果更为合理。在通道电导率的基础上估算了回击通道的放电电流,与辐射峰值电场实验资料所得的相应峰值电流相比,其结果在合理的范围内, 并进一步探讨了温度与电流放电特性的相关性, 为研究闪电放电电流提供了一条可行的途径。     

闪电首次回击过程中通道温度与电导率的演化特征

利用以高速摄像机为记录系统组装的无狭缝摄谱仪,在青海地区获得了多次云对地闪电首次回击过程400-900 nm波长范围的时间分辨光谱,分别计算了闪电电流核心通道和外围发光通道的温度;结合空气等离子体的传输理论,获得了闪电通道的电导率,探讨了回击过程中通道温度及电导率的演化特征.结果表明,闪电电流核心通道的温度比外围通道高约5000-7000 K,并且,与以往关于通道峰值温度持续时间的观点不同,回击过程中,通道保持高温的时间远远大于峰值放电电流存在的时间,在回击电流缓慢减小的数百微秒内,核心电流通道维持20000 K以上高温,这一特性是热效应导致雷电灾害的主要根源.     

Novel carbon nanotube field effect transistor with graded double halo channel

A novel carbon nanotube field effect transistor with symmetric graded double halo channel (GDH–CNTFET) is presented for suppressing band to band tunneling and improving the device performance. GDH structure includes two symmetric graded haloes which are broadened throughout the channel. The doping concentration of GDH channel is at maximum level at drain/source side and is reduced gradually toward zero at the middle of channel. The doping distribution at source side of channel reduces the drain induced barrier lowering (DIBL) and the drain side suppresses the band to band tunneling effect. In addition, broadening the doping throughout the channel increases the recombination of electrons and holes and acts as an additional factor for improving the band to band tunneling. Simulation results show that applying this structure on CNTFET enhances the device performance. In comparison with double halo structure with equal saturation current, the proposed GDH structure shows better characteristics and short channel parameters. Furthermore, the delay and power delay product (PDP) analysis versus on/off current ratio shows the efficiency of the proposed GDH structure.     

利用目标信道特性约束的信道匹配检测算法

浅海有源声呐的探测性能主要受到多途扩展以及混响干扰的影响.为了提高声呐系统的检测性能,根据双扩展信道匹配原理,结合混响信道与声呐目标信道特点,提出了一种基于回波特性约束的信道匹配检测算法.该算法通过最小二乘匹配追踪算法估计信道稀疏响应,并根据混响和目标信道的扩展差异,通过约束目标信道扩展对稀疏信道响应去冗余,得到更精确...     

闪电首次回击过程中通道温度与电导率的演化特征

利用以高速摄像机为记录系统组装的无狭缝摄谱仪,在青海地区获得了多次云对地闪电首次回击过程400-900 nm波长范围的时间分辨光谱,分别计算了闪电电流核心通道和外围发光通道的温度;结合空气等离子体的传输理论,获得了闪电通道的电导率,探讨了回击过程中通道温度及电导率的演化特征.结果表明,闪电电流核心通道的温度比外围通道高约5000-7000K,并且,与以往关于通道峰值温度持续时间的观点不同,回击过程中,通道保持高温的时间远远大于峰值放电电流存在的时间,在回击电流缓慢减小的数百微秒内,核心电流通道维持20000K以上高温,这一特性是热效应导致雷电灾害的主要根源.     

改进的时序多重稀疏贝叶斯学习冰下水声信道估计方法

针对时序多重稀疏贝叶斯学习信道估计方法计算复杂度高且在低信噪比时估计精度低的问题,本文提出了一种改进的时序多重稀疏贝叶斯学习正交频分复用冰下水声信道估计方法。首先,采用奇异值分解方法对接收导频矩阵进行去噪;随后利用去噪后的接收导频矩阵结合最小二乘信道估计方法获得时序多重稀疏贝叶斯信道估计的超参数矩阵、感知矩阵等先验知识;最后,利用冰下水声信道的稀疏特性和多途结构较为稳定的特点,采用时序多重稀疏贝叶斯信道估计对不同符号的冰下水声信道进行联合重建。仿真结果显示,在能量系数为0.03时,改进方法信道估计均方误差相比较于原始方法至少降低了约2.87×10-5,运算时间至少下降了约为90%。第11次北极科学考察冰下试验结果显示,改进方法的平均原始误码率略微低于原始方法,平均运算时间降低约75%。研究结果表明,利用冰下水声信道的特点,改进方法可以实现高精度冰下水声信道估计,并且有效降低系统计算复杂度。      

Characterization,modeling and simulation of the MIMO propagation channel

This article deals with several aspects relative to the MIMO propagation channel. Based on simulations and/or measurements, different approaches are used to model the propagation channel. These models are useful for the MIMO system design. Several studies are performed in order to realize realistic simulation of MIMO channel. Different measurement techniques are used in characterizing the propagation channel in various environments. Measurement campaigns made in different situations have been analyzed to obtain the relevant statistical parameters of the channel. Simulation of MIMO channel is then presented. Measurement and simulation results provide an evaluation of the capacity of MIMO channel. Obtained results show feasibility in the integration of MIMO techniques in practical wireless communication systems.     

Transformation of surface magnetostatic waves channeled by a step bias field

The propagation of magnetostatic waves in a waveguide ferromagnetic channel formed by exposing a ferromagnetic film to a step bias is simulated. Both weak and strong channel couplings are considered. The dispersion characteristics and the distributions of wave functions are calculated. It is shown that the amplitudes of “half-waves” fitting into the channel width alternately increase and decrease with increasing frequency and the half-waves pass into the channel with the largest bias.     

C-V法提取SiC隐埋沟道MOSFET沟道载流子浓度

本文对用C-V法提取SiC隐埋沟道MOSFET沟道载流子浓度的方法进行了理论和实验分析. pn结的存在所造成的埋沟MOS结构C-V曲线的畸变为沟道载流子浓度的提取带来一些问题. SiC/SiO₂界面上界面态的存在也会使提取出的数值与实际数值产生偏差. 本文首先从理论上分别分析了沟道深度和界面态对沟道载流子浓度提取结果的影响，然后对两种沟道深度的埋沟MOS结构C-V曲线进行了测试，提取出了沟道掺杂浓度. 在测试中，采用不同的扫描速率，分析了界面态对提取结果的影响. 理论分析结果和实验测 关键词： C-V法 SiC 隐埋沟道MOSFET 沟道载流子浓度