激光脉冲放大器增益通量耦合系统解

研究了一个激光脉冲放大器增益通量系统解的问题.首先讨论了较一般的系统, 然后引入一个同伦映射.再利用映射的性质, 引进一个人工参数, 将求解非线性问题转化为求解一系列线性问题.再逐次地求出对应的线性问题的解, 最后得到了原模型解的近似展开式.可以看出, 同伦映射方法是一个解析的方法.它是通过函数的解析运算并用初等函数来表达近似解,其不同于用离散数值运算的数值计算方法.因此通过同伦映射解, 还可以对它继续进行解析运算, 从而可以进行微分和积分等运算来得到与激光脉冲放大器增益通量相关的其他物理量的性态.     

980nm泵浦掺铒光纤放大器增益特性的理论研究

从均匀加宽三能级结构的速率方程组和光传输方程出发 ,在引入光场与掺杂分布的重叠因子后 ,忽略放大自发辐射 (ASE)时 ,得到了 980nm波段泵浦的掺铒光纤放大器 (EDFA)速率方程组在稳态情况下的解析解 ,并利用数值模拟结果对放大器的增益、泵浦阈值、最佳光纤长度进行了分析和讨论.     

基于可分离组合式信号的Hammerstein输出误差滑动平均系统辨识研究

考虑实际生产过程中的不可测噪声,提出一种基于可分离组合式信号的Hammerstein输出误差滑动平均系统辨识方法.通过可分离组合式信号源实现了Hammerstein输出误差滑动平均系统中静态非线性环节和动态线性环节的分离,解决了中间不可测变量的估计问题.基于辅助模型辨识思想和相关分析法估计Hammerstein输出误差滑动平均系统中静态非线性和动态线性环节的参数,避免了采用迭代法辨识Hammerstein模型时存在模型参数初始化和收敛性难以证明的问题,并有效补偿噪声信号的干扰.仿真结果验证了上述方法的有效性.     

考虑微观结构噪声与跳跃影响的波动建模

现有的金融高频数据研究,并未充分考虑微观结构噪声对波动建模和预测的影响.以非参数化方法为理论框架,基于高频数据,采用适当方法分离出波动中的微观结构噪声成份,构建了新的跳跃方差和连续样本路径方差,将已实现波动分解为连续样本路径方差、跳跃方差和微观结构噪声方差.同时考虑微观结构噪声和跳跃对波动的影响,对HAR-RV-CJ模型进行改进,提出了HAR-RV-N-CJ模型和LHAR-RV-N-CJ模型.通过上证综指高频数据进行实证,结果表明新模型在模型拟合和预测方面均优于HAR-RV-CJ模型.     

基于白噪声的网络传染病模型动力学分析北大核心CSCD

该文基于确定性网络传染病模型,建立了白噪声影响下的随机网络传染病模型,证明了模型全局解的存在唯一性,利用随机微分方程理论得到了传染病随机灭绝和随机持久的充分条件.结果表明,白噪声对网络传染病传播动力学有很大的影响,白噪声能有效抑制传染病的传播,大的白噪声甚至能让原本持久的传染病变得灭绝.最后,通过数值模拟验证了理论结果.     

内外噪声扰动下放牧生态系统的稳态转换现象

生态系统的稳态转换可能会造成生态环境的退化和巨大的经济损失,研究稳态转换如何受随机因素影响非常必要.文章研究放牧模型在高斯噪声和Lévy噪声共同作用下的稳态转变现象.首先介绍了放牧模型的确定性方程,然后利用Janicki-Weron算法产生Lévy噪声,并通过四阶Runge-Kutta算法对放牧系统进行数值模拟,最后基于稳态概率密度分别分析了内噪声和外噪声对系统稳态转换行为的影响.研究发现两种噪声均可诱导系统产生稳态转换现象,但作用相反;高斯噪声强度的增大可以诱导放牧系统从高植被态向荒漠态转换,而Lévy噪声的强度、稳定性指标和偏斜参数的增大均可促进放牧系统从荒漠态向高植被态的恢复.     

噪声抑制Cohen-Grossberg神经网络模型的指数增长（英文）

本文研究了噪声对Cohen-Grossberg神经网络模型的影响,当Cohen-Grossberg神经网络模型的解为指数增长时,若加入适当的噪声可以使得相对应的随机Cohen-Grossberg神经网络模型的解为多项式增长,即噪声可以抑制Cohen-Grossberg神经网络模型的指数增长.     

二值形态运算的感知器模型及其应用

给出了二值形态运算模型与感知器模型之间的关系.以此为基础对传统的二值数学形态学基本运算进行了推广,建立了基于感知器的形态运算模型.新的模型为传统的二值形态运算赋予了可调节机制.计算机模拟实验表明该方法较传统的二值形态运算有效.     

基于极端积算子的LL型模糊数的最小一乘回归

针对模糊输入和模糊输出数据系统中的回归分析问题,考虑到系统中依赖关系不确定性特点以及模型稳健性和求解准确性等需求,建立一个模糊最小一乘优化模型。首先利用能诱导出LL型模糊数乘法保形运算的唯一T-模,即极端积算子,结合扩张原理,给出LL型模糊数间加法和乘法的运算规则。其次,基于LL型模糊数间的完备距离,得到模糊线性回归模型的参数估计,由此给出考虑清晰参数或清晰输入的两个简约模型及相应参数估计。通过计算Kim & Bishu测度、贴近测度和输出展形差异测度,比较与其他7种回归方法的优劣,并由模型的敏感性分析,充分说明本文算法的有效性和稳健性。     

一类具有饱和发生率的确定和随机SIRS模型的稳定性

考虑了一类具有饱和发生率的确定和随机SIRS模型,计算出基本再生数,得到随机模型正解的全局存在性及唯一性,在一定的噪声扰动条件下,应用微分算子和伊藤公式证明了无病平衡点的p-阶指数稳定,同时,讨论了随机模型的解围绕确定性模型平衡点的渐近行为,最后分析了噪声干扰对随机模型稳定性的影响.     

功率放大器失真问题研究及预失真建模

电子器件中的功率放大器常常伴随着非线性失真效应.为解决此类非线性失真问题,通过研究无记忆和有记忆功放的失真特性,运用最小二乘法来构建多种形式的特性拟合函数,在选择了效果较好的特性拟合函数基础上,根据实际约束条件进行预失真模型的建立,使失真处理后的输出信号趋于线性,最后从信号的功率谱密度的角度出发检验预失真模型的补偿效果,证明模型具有较好的可行性和准确性.     

功率放大器非线性特性及预失真建模

信号的功率放大器是电子通信系统的关键器件之一,功放的输出信号相对于输入信号可能产生非线性变形,这将带来无益的干扰信号,研究其机理并采取措施改善,具有重要意义.通过利用无记忆非线性功放和记忆非线性功放的实测数据用数学方法对其分别进行建模,而后使用前置预失真器的方法改善功放的非线性特性,并对其中预失真器的建模做了研究,采用间接学习型结构构建预失真器模型.仿真结果显示功放非线性模型结合预失真器模型能够很好地逼近实际情况,并且能很好地抑制带外频谱扩展.     

功率放大器非线性特性及预失真建模研究

针对无记忆功率放大器的非线性特性及预失真建模的问题,首先建立了多项式模型、极坐标Saleh模型和基于正交三角函数的模型并利用MATLAB对其进行了求解,然后给出了无记忆多项式预失真处理器特性函数表达式及最小二乘解.针对记忆功率放大器的非线性特性及预失真建模的问题,首先建立了记忆多项式模型并对其进行了求解,然后建立了相应的有记忆多项式预失真模型并利用最小二乘法进行了求解,并提出了联合功率放大器特性和输入信号幅值范围的有记忆功放自适应预失真模型.最后求出所给输入信号、输出信号以及加入预失真后线性系统的输出信号的功率谱密度,并计算和比较了信道的带外失真参数ACPR;结果显示,加入预失真后大大提升了系统的性能,线性特性明显加强.     

运用多目标规划优化功放的预失真模型

预失真技术是克服功率放大器非线性失真的一种非常有效的方法.许多研究者从数学建模的思想角度出发,建立了关于功放与预失真的各类级数模型,以实现线性增益输出.但是在应用通信系统中,这些模型不能有效地动态实现功放效率尽可能高的要求.在和记忆多项式模型的基础上,创新地运用多目标规划的方法优化功放的预失真模型.在满足一定的线性化输出的同时,尽可能地得到更高的功放效率,而且能同时计算出增益系数与模型参数.对于数据量为1000的无记忆功放得到增益倍数为1.82649,预失真模型的NMSE值为-41.5633.数据量为73920的有记忆功放得到增益倍数为9.5969,预失真模型的NMSE值为-24.3682.     

Comparison of a Momentum Device with a Turbulent Reattachment Device

The jet profile of a momentum amplifier is used to find the optimum distance between receiver and outlet nozzle, as well as the most favorable receiver width. The receivers are designed for digital operation, so that good discrimination is assured. With the help of the output characteristic and of the control line resistance, the response time can be calculated. With equal discrimination, without considering response time, the boundary layer amplifier allows essentially higher amplification.     

Multiobjective analog/RF circuit sizing using an improved brain storm optimization algorithm

This paper presents a multiobjective analog/RF circuit sizing tool using an improved brain storm optimization (IMBSO) algorithm with the purpose of analyzing the tradeoffs between competing performance specifications of analog/RF circuit block. A number of improvements are incorporated into IMBSO algorithm at different steps. At first, the clustering step of IMBSO algorithm is augmented with k-means\(++\) seeding technique to select the initial cluster centroids while clustering using k-means clustering technique. As a second improvement, the proposed IMBSO algorithm makes use of random probabilistic decision-making of river formation dynamics scheme to select optimal cluster centroids during population generation step. As a third improvement, an adaptive mutation operator is incorporated inside the IMBSO algorithm to generate new population. Finally, two separate constraint handling techniques are employed to handle both boundary and functional constraints during analog/RF circuit optimization. The performance of the proposed IMBSO algorithm is demonstrated in finding optimal Pareto fronts among different performance specifications of a two-stage operational amplifier circuit, a folded cascode amplifier circuit and a low noise amplifier circuit.     

Voltage amplification transfer function analysis of the operational amplifier in the negative capacitance circuits for vibration control with piezoceramics

Piezo elements due to their ability of converting mechanical energy into electrical energy and vice versa can be found in numerous mechanical vibration damping and absorbing applications. A desired effect may be customized by an external impedance shunt branch connected to the plates of the piezo element. The negative capacitance connected in serial with the passive shunt significantly improves the damping and absorbing performance of such systems. Negative capacitance circuit is built of an impedance converter realized by the operational amplifier. Since the amplifiers are not the ideal elements, the performance of the proposed systems is limited. This is due to the maximum voltages and currents that the operational amplifiers are able to generate. This effect causes instabilities and limits the operational area of the impedance converter. In the paper, the amplification transfer function of the non-ideal operational amplifier in the negative impedance converter is studied, and the necessary modification with the additional passive elements is proposed. The influence of the certain imperfections in the design, and its improvements are shown on the system consisting of the 1DOF mechanical oscillator, and a shunted piezo element. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impedance Losses in Negative Capacitance Circuits for Semi-Passive Vibration Control with Piezo-Ceramics

Damping or absorbing effect in vibration control applications with piezo elements may be customized by an external impedance shunt branch connected to the plates of the piezo element. The negative capacitance present in the shunt significantly improves the damping and absorbing performance of such systems. The circuit is built up of an electronic gyrator realized by the operational amplifier, which is in reality not the ideal element. Therefore the performance of the proposed systems is limited, concerning the maximum voltages and currents at which the operational amplifiers can operate. In the paper, the finite gain of the operational amplifier, together with the loss impedances and the feedback gain factor is studied. The influence of the certain imperfections in the design of the electronic gyrator is based on 1DOF mechanical oscillator, with a piezo stack. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new probabilistic fuzzy model: Fuzzification–Maximization (FM) approach

Over the past few decades, fuzzy logic systems have been used for nonlinear modeling and approximation in many fields ranging from engineering to science. In this paper, a new fuzzy model is developed from the probabilistic and statistical point of view. The proposed model decomposes the input–output characteristics into noise-free part and probabilistic noise part and identifies them simultaneously. The noise-free model recovers the nominal input–output characteristics of the target system and the noise model gives approximation to the probabilistic nature of the added noise. To identify the two submodels simultaneously, we propose the Fuzzification–Maximization (FM). Finally, some simulations are conducted and the effectiveness of the proposed method is demonstrated through the comparison with the previous methods.     

The effect of actuator parameters on the critical flow velocity of a fluidic amplifier

The effect of actuator parameters on the critical flow velocity of the fluidic amplifier in liquid-jet hammers has been investigated numerically and experimentally. The flow in the fluidic amplifier and actuators coupled with the rigid body movement of the impacting body has been simulated using a commercial CFD software package, Fluent. The flow is modeled by the RNG-based κ–ε turbulence model and the incompressible Navier–Stokes equations. Dynamic layering method and a user-defined function written in C programming language are used to update the mesh in the simulations. The results show that, increasing the piston diameter decreases rapidly the critical flow velocity as the piston diameter is less than a certain value. The critical flow velocity increases sharply as the piston rod diameter is greater than a certain value, and increases nearly linearly with mass of the impacting body, and is independent on stroke length of the impacting body. The findings of the numerical investigations agree well with corresponding experimental results.