预倾镜相位共轭系统在强激光对运动目标跟瞄中的应用

由于受到各种大气湍流、热晕等因素的影响．强激光在大气传输中会产生波前畸变，利用光学相位共轭技术可以补偿激光大气传输造成的波前畸变．提出了利用预倾镜方法实现对运动目标跟踪瞄准同时补偿波前畸变．对此项技术进行了室内模拟实验。实验结果表明采用预倾镜方法的有效性。     

利用相位共轭镜补偿由强散射象差介质引起的畸变的能力

本文对在象差介质同时具有非均匀吸收和相位畸变并且相位共轭镜的有效区域有限的条件下利用光学相位共轭对波面和图象的补偿结果作了分析,指出利用聚光系统可以改善对强散射介质引起的波象差的补偿效果,并采用透镜作为聚光系统,用在四波混频条件下的光折变晶体Ce:SBN作为相位共轭镜对经过玻璃的粗磨毛面后的波面和图象进行了恢复实验,并获得了满意的结果。文中还对利用光折变相位共轭镜的反射率与入射光强有关的特点来补偿象差介质的非均匀吸收的可能性,以及非线性吸收对补偿效果的影响作了讨论。     

动态热晕畸变相位共轭补偿

本文报导了电场作用下的C(60)甲苯溶液的非稳运动自泵浦相位共轭补偿实验研究，描述了不同程度波前畸变的位相补偿能力。实验结果表明，由于介质的非稳运动引起相位共轭光束具有较大的振幅起伏，其时间特性依赖于电场强度。     

受激布里渊散射波前畸变校正仿真实验

采用受激布里渊散射（SBS）现象的自泵浦相位共轭镜（PCM）特性在改善激光相位分布进而提高光斑能量集中度方面具有重大应用价值。基于后向SBS散射光的相位共轭特性,数值模拟了不同畸变程度和不同取样孔径对SBS-PCM校正效果的影响,并搭建SBS-PCM波前畸变补偿实验系统,对不同影响因素的补偿效果进行验证。仿真及实验研究结果表明:在弱畸变情况下光斑经系统补偿后相对强畸变情况分布更均匀规整,光斑能量集中度更高;在强畸变情况下大取样孔径显示出优势,校正效果更佳。仿真和实验结果均表明,SBS-PCM有较强波前畸变校正能力。     

利用相位共轭实现单根光纤直接传输图象

利用相位共轭介质——光折变晶体掺铁铌酸锂(Fe:LiNbO_3)产生的简并四波混频的波前反转性质,补偿了多模光纤由于模色散引起传输图象的畸变,实现单根多模光纤直接传输图象;研究了相位共轭对传输图象光场偏振态的影响。     

用相位共轭技术实现区域目标的激光传输畸变补偿

相位共轭技术通过“时间反演”过程进行激光传输畸变补偿，具有快响应、高灵敏度、高稳定性，以及结构简单、价格低廉等优点。但通常主动信标光，采用相位共轭方法难以实现区域目标的大气传输畸变补偿。本文介绍我们首次提出了解决方案－成象减裁加阈值共轭镜，并用ＢａＴｉＯ３自泵浦相位共轭镜对静太和模拟湍流畸变进行了原理性实验。     

利用四波混频消除图像畸变的局限性

一、引言 在大多数理论研究中,人们仅在平面泵浦和探测波的条件下研究四波混频产生位相共扼波的机理、手段。然而在实际应用简并四波混频共轭波补偿大气干扰时,入射到位相共轭镜上的探测波不可能是理想平面波。但是在大多用相位共轭消畸变的方案中都忽略了畸变探测波在简并四波混频中产生什么样的“共轭波”这个问题。本文将讨论利用简并四波混频消除通过湍流大气传输图像的畸变问题。     

SBS激光器实验研究

YAG棒激光器的热效应可引起波前畸变，利用受激布里渊散射(SBS)相位共轭镜(PCM)能补偿这些畸变。实验研究SBS对激光棒热效应的影响。通过SBS振荡腔的新颖设计，在抽运能量为17J，重复频率为5Hz时，得到稳定输出的能量为19mJ、脉宽为10．7ns的高质量激光脉冲。     

相位共轭技术在补偿高功率激光器动态波前像差中的应用

对于高功率激光器光束畸变的实际问题,目前提出的有些方法只能对像差进行有效的补偿,却不能补偿自相位调制所引起的畸变.针对激光谐振腔的失调问题进行简单理论分析及编写数值程序进行计算,提出相位共轭法能够对上述两种畸变进行有效的补偿,进一步针对实际采用相位共轭补偿技术的高功率Nd:YAG MOPA激光器的典型实验来进行分析,采用波前像差的PV值和RMS值的结果作为系统分析参数,得出相位共轭技术能有效地改善高功率激光器光束输出质量.     

光学相位共轭若干基本问题的讨论

光学相位共轭是一类重要的非线性光学效应。具有补偿波前畸变等特点,而在自适应光学、空间信息处理等方面显示出应用前景。本文使用矩阵光学方法,对光学相位共轭、准相位共轭中的一些基本问题提出讨论。例如:     

Statistical service assurances for traffic scheduling algorithms

Network services for the most demanding advanced networked applications which require absolute, per-flow service assurances can be deterministic or statistical. By exploiting the statistical properties of traffic, statistical assurances can extract more capacity from a network than deterministic assurances. We consider statistical service assurances for traffic scheduling algorithms. We present functions, so-called effective envelopes, which are, with high certainty, upper bounds of multiplexed traffic. Effective envelopes can be used to obtain bounds on the amount of traffic on a link that can be provisioned with statistical service assurances. We show that our bounds can be applied to a variety of traffic scheduling algorithms. In fact, one can reuse existing admission control functions for scheduling algorithms with deterministic assurances. We present numerical examples which compare the number of flows with statistical assurances that can be admitted with our effective envelope approach to those achieved with existing methods     

Approximation of finite-energy random processes by continuous processes (Corresp.)

It is shown that any random process with finite energy can be approximated arbitrarily closely by a mean-square continuous process. We obtain approximants that in addition have continuous sample paths with probability 1. By a straightforward extension of these results, the approximating process can be made to have differentiable sample paths. The approximation can be performed in real time, in the sense that the approximating process constructed can be regarded as the output of a causal linear time-invariant system whose input is the finite energy process that is to be approximated.     

利用高斯混合模型实现概率密度函数逼近

针对图像的概率分布密度函数的不确定,利用有限高斯混合模型逼近图像的概率分布密度函数。理论上证明了有限高斯混合模型可以以任意精度正逼近实数上的非负黎曼可积函数,特别可以逼近任意的概率分布密度函数。实例表明有限高斯混合模型逼近已知分布密度函数或未知分布密度函数时,具有逼近精度高等优点,为函数逼近提供了理论和技术支持。     

广义切比雪夫型LC滤波器的设计*

提出一种广义切比雪夫型LC滤波器的设计方法,带外传输零点可以是任意设定,其带外特性既可以对称,也可以不对称.采用此方法设计出的LC滤波器,其带内波动可以与最大平坦型滤波器一样很小,而矩形系数可以与椭圆函数型滤波器一样好.每一个传输零点的位置可以由一个元器件的取值大小控制.与椭圆函数型LC滤波器相比,相同数量的元器件,它可以实现更陡的截止特性.     

A formal logic of plans in temporally rich domains

This paper outlines a temporal logic extended with two modalities that can be used to support planning in temporally rich domains. In particular, the logic can represent planning environments that have assertions about future possibilities in addition to the present state, and plans that contain concurrent actions. The logic is particularly expressive in the ways that concurrent actions can interact with each other and allows situations where either one of the actions can be executed, but both cannot, as well as situations where neither action can be executed alone, but they can be done together. Two modalities are introduced and given a formal semantics: INEV expresses simple temporal possibility, and IFTRIED expresses counteffactual-like statements about actions.     

一种基于PPM的LDPC编译码方案

该文基于LDPC码和PPM调制方式构造了一种适用于UWB无线通信系统的低码率的编译码方案LDPC-PPM。本方案在保证系统性能的前提下,通过改变编码比特到调制符号的映射方式,不但避免了一般编码调制系统中译码和解调之间的迭代运算,而且可以应用快速Hadamard变换(FHT)和基于FHT的后验概率译码(APP-FHT)来进一步降低接收端的译码复杂度。可以证明,该方案等价于BPSK调制下的低码率的LDPC-Hadamard码。仿真结果表明,在信息比特长度是65536,该方案可以在-1.18dB处达到误比特率为 的性能,仅比采用BPSK调制的Turbo-Hadamard码差0.02dB。     

Depth efficient neural networks for division and related problems

An artificial neural network (ANN) is commonly modeled by a threshold circuit, a network of interconnected processing units called linear threshold gates. It is shown that ANNs can be much more powerful than traditional logic circuits, assuming that each threshold gate can be built with a cost that is comparable to that of AND/OR logic gates. In particular, the main results indicate that powering and division can be computed by polynomial-size ANNs of depth 4, and multiple product can be computed by polynomial-size ANNs of depth 5. Moreover, using the techniques developed, a previous result can be improved by showing that the sorting of n n-bit numbers can be carried out in a depth-3 polynomial-size ANN. Furthermore, it is shown that the sorting network is optimal in depth     

A note on digital filter synthesis

It is commonly assumed that digital filters with both poles and zeros in the complex z-plane can be synthesized using only recursive techniques while filters with zeros alone can be synthesized by either direct convolution or via the discrete Fourier transform (DFT). In this letter it is shown that no such restrictions hold and that both types of filters (those with zeros alone or those with both poles and zeros) can be synthesized using any of the three methods, namely, recursion, DFT, or direct convolution.     

An optically controllable negative resistance circuit constructed with optocouplers

An optocoupler with a Darlington configuration at the output side can be used as a one port active device with a current-controlled negative resistance by simply connecting the input and output sides in cascade. The author proposes an optically controllable negative-resistance circuit constructed with optocouplers. The breakover voltage and the holding current of the negative-resistance characteristics can be controlled widely with two external light inputs. Hence, the circuit may be applied to optronic functional switching operations. It is demonstrated that an optically controlled relaxation oscillator can be easily constructed using the circuit, and that applications of the relaxation oscillator to a light modulator and an optical Schmitt trigger can be realized by simple circuit configurations.     

气液两相流压差波动信号小波去噪中阈值规则的确定

利用小波分解、滤波、重构对压差波动信号进行去噪处理,消除实验中由于各种因素产生的噪声,得到了较为满意的压差波动实验数据,该方法与其他处理方法相比,得到的处理信号不失真且去噪效果明显。比较发现小波去噪的结果与阈值选取相关,通过分析确定合适的阈值选取规则,使得处理后的信号能满足以后分析的需要。研究表明选择的阈值可广泛应用于不同流型和不同取压间距的压差波动信号。