某乘用车加速工况车内轰鸣声诊断分析及控制方法

该文针对某乘用车加速工况出现的轰鸣声进行诊断分析与控制。首先通过主观评价确定问题工况,通过实车测试发现2400 r/min左右车内存在明显轰鸣声。利用阶次分析、模态分析及错频验证可知,发动机激励经悬置传递副车架,引起副车架的共振,进而传递到车内引起轰鸣声。最后通过传递分析及柔性连接点导纳法,优化副车架橡胶衬套结构。结果表明,优化后在2400 r/min声压总级与2阶声压差值为7.5 dB(A);声压总级较原状态降低2 d B(A),2阶噪声降低7.8 d B(A),声压总级和2阶噪声声压差值增大,轰鸣声明显减小,主观评价可接受。     

速调管离子噪声特性的模拟分析

 离子噪声已成为影响现代微波管性能的一个重要因素，采用一维混合模型研究了速调管的离子噪声，用自编的1维粒子模拟程序对速调管的离子噪声特性进行了分析。采用小信号近似，从理论上推导出了速调管离子噪声与相位畸变关系的表达式，表明微波管相位噪声直接来源于管内离子量的变化。模拟了有离子噪声时速调管的相位特性，对模拟过程做了离子诊断并与实验结果进行比较，证明了模拟过程的正确性。探讨了电子束电流、电压以及聚焦磁场对离子噪声的影响规律，束电流与束电压改变后，离子噪声的周期与大小相应改变，增大束电流，离子噪声幅度会下降，并趋于稳定，而在束电流不变的情况下，离子噪声存在一个最小值。束电流与束电压确定，存在最佳的磁场使离子噪声幅度最小。     

平交路口交通噪声的测量分析与模型计算结果

本文给出了对有交通控制信号的十字型平交路口,交通噪声(以下简称路口噪声)的测量及统计分析结果。指出用统计声级L_50和L_90来衡量时,路口噪声比所谓自由车流噪声要高出3—7dB(A);而用L_10和等效声级L_eq的衡量时,两者几乎没有区别,虽然两者给人的感觉有所不同。通过与点声源路口噪声模型的计算结果对比,得出路口噪声统计声级L_50增高是因为两条道路相交,横路上车辆的运动噪声对总噪声能量的贡献。文中还讨论了路口噪声的统计分布和瞬时噪声级与交通控制信号之间的关系等问题。     

平方泵噪声驱动的单模激光立方模型及光强定态概率分布

合理地引入了平方泵噪声到单模激光的立方模型中. 得到封闭的光强朗之万方程. 基于作者早期关于非线性外噪声的近似福克-普朗克方程(AFPE)的工作，得到了光强概率分布的AFPE，求出了该AFPE的归一化定态概率分布的精确解析表达式，并根据表达式对泵噪声实部和虚部之间的关联系数λ的对称性，得出了若干关于系统定态统计性质的普遍结论. 关键词： 平方泵噪声 单模激光的立方模型 光强定态概率分布 统计性质重复出现     

部分车辆成组的多车道混合车流噪声的计算机模拟

本文给出一种一次性综合模拟多车道多车种随机车流噪声的计算机模拟的简化方法，详细推导了用于预报部分车辆成组行驶的随机车流噪声的数学模型（M_2模型）的车头时距分布函数、概率密度函数和平均时距表达式及相应的随机数变换式。文中还给出了计算机程序框图，并将M_2模型模拟结果与据车头时距为负指数分布的M_1模型的模拟结果作了比较。计算机程序是根据我国交通噪声测量统计方法编制的，只要在程序中输入车流量、车流成份，测点离各车道及等效车道的距离诸参量，计算机便能自动输出L_10、L_50、L_eq等声级值，预报值与实测值良好一致。     

两路输入前置光放大星间微波光子链路优化

考虑到星间微波光子链路传输损耗大且多路微波信号之间交调干扰严重,利用前置光放大来提高链路的信号噪声失真比RSNDR。建立了两路输入前置光放大星间微波光子链路模型,推导出了RSNDR的解析表达式。通过优化马赫-曾德尔调制器的直流偏置相移,使得在给定输入射频信号功率条件下RSNDR最大,并进一步分析了前置光放大器参数对最优直流偏置相移和RSNDR的影响。仿真结果表明,前置光放大改变了影响RSNDR的主要因素,使信号放大的倍数大于噪声和三阶交调(IM3)放大的倍数,从而提高了链路的RSNDR。当前置光放大器增益为20dB、噪声系数为3dB时,最优的RSNDR比不加前置光放大器时提高24dB。前置光放大器增益和噪声系数对最优的RSNDR影响很大,而对最优的直流偏置相移几乎无影响。     

双模环型激光增益噪声模型的非线性效应

讨论了一个双模环型激光增益噪声模型，其中考虑了完全饱和效应且乘法噪声由增益系数涨落引起。在共振及两模具有相同泵参数时，获得了光强联合定态分布的精确解析表达式。通过与现有的双模激光摸型（其中乘法噪声由损失系数涨落引起）的比较，发现乘法噪声系数的非线性效应减弱了乘法噪声给激光光强统计性质带来的反常特性，并且这种减弱随着乘法噪声增强或损失系数减小而愈加明显。     

微弱信号源的和波束定向方法与分裂波束定向方法的性能比较

本文讨论水下辐射噪声源的精确定向问题，给出被动声纳和波束定向与分裂波束定向方法的性能比较。指出在一定信噪比下，分裂波束精确测向技术比和波束定向技术具有较高的定向精度。但是，随着信噪比的下降，两者趋于一致。推导了估计定向精度的分析表达式，给出在直线阵和圆弧阵情况下，延时估计和声源入射角偏差之间的换算公式和数值模拟结果。同时给出数字式声纳用以计算入射信号左波束和右波束数据的互谱来实现分裂波束定向的方法。     

晶粒间界相及结构缺陷对HDDR 粘结磁体矫顽力的影响

本文根据氢化／歧化／脱氢／重组（HDDR）Nd-Fe-B 磁粉晶粒边界微结构的特点,建立了缺陷区内的磁晶各向异性常数K1´及交换积分常数A1´的双变量连续变化模型,研究了晶粒间界相厚度d及晶粒表面结构缺陷厚度r0对磁体矫顽力的影响。结果表明：晶粒表面各向异性常数K1(0)、交换积分常数A1(0)及r0取不同值时,磁体的矫顽力Hc均随d增加而增大。K1(0)和A1(0)取确定值时,相同的d值对应的Hc随r0的增大而上升。r0和d取确定值时,Hc随K1(0)或A1(0)的减小而增大。当d 为1nm,r0 在 (2~5) nm范围内,A1(0)和K1(0)的值分别在A1和K1值的(0.6~0.7)范围内变动时,计算的矫顽力与实验值符合得很好。     

室内可见光无载波幅度相位调制系统性能分析

针对室内可见光通信调制技术问题,提出翻转光无载波幅度相位调制和单极性光无载波幅度相位调制两种功率有效的调制方案,二者分别采用"正、负模块极性分组"以及"零值位置极性编码"方法实现信号单极性处理,以满足可见光通信"强度调制/直接检测"的要求.基于朗伯辐射模型,考虑到高斯背景光噪声的可见光直射传输信道,推导了包括直流偏置光无载波幅度相位调制在内的三种调制方案的误比特率闭式表达式,仿真验证了其准确性.在此基础上,分析比较了三者频带利用率,讨论了信道参量对光无载波幅度相位调制系统误码性能的影响,结果表明,在5m×5m×3m的室内场景下,与发射机辐射角为30°和45°相比,0°时的系统误码性能分别优于6.9dB和29.9dB;收发机距离为1m时,误码性能比2m时改善近12dB.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.