具有频率噪声的单模激光线性模型随机共振

将频率有涨落的周期信号输入单模激光增益模型,计算出输出光强的相关函数及功率谱,对信噪比随噪声强度和系统参数的变化进行了研究. 结果表明:信噪比随频率噪声强度的变化、抽运噪声强度的变化、量子噪声强度的变化均出现随机共振;信噪比随增益系数和损失系数的变化也出现随机共振. 关键词： 频率噪声 功率谱 随机共振     

周期性边界条件下多孔介质方腔内自然对流换热数值研究

对充满多孔介质的倾斜方腔,在其上下壁面绝热、右侧壁面维持恒温To及左侧壁面温度基于To随时间按正弦规律变化的情况下,采用Brinkman扩展达西模型和SIMPLER算法对方腔内的自然对流与换热进行了非稳态数值模拟,方腔倾角α的范围为0°～90°,Pr数为1,Ra数为106.计算研究不同的振荡频率和方腔倾角对方腔内对流换热的影响.数值模拟结果表明:振荡频率f为60π,方腔倾角为43°时,方腔内的换热最强.     

顺式羰基铑碘络合物催化甲醇制乙酸反应的动力学研究

本文运用密度泛函理论DFT-B3LYP方法,对铑、碘元素采用相对论校正赝势基组SDD,对C、O、H采用6-311+G(2d,p)基组,计算研究了顺式羰基铑碘络合物催化甲醇羰基化制乙酸反应的微观机理,优化了各反应物、中间体和过渡态的构型特征,用频率分析方法和内禀反应坐标方法对过渡态进行了验证,运用Kozuch撰写的能量跨度模型获得循环反应的动力学信息,确定了决定循环反应速率的决速过渡态和决速中间体,并利用转化频率评估了催化性能与温度的变化关系.     

超声波流速测量的多普勒频移提取方法研究

为了提高超声波多普勒法测量复杂流体流量的精度,针对流体的超声回波频率的复杂性,本文研究多普勒流速测量中的频偏提取方法。以傅里叶分析为理论基础,设计了硬件电路并获得代表回波平均频率的信号,然后以该信号作为输入,以数字鉴频法获得回波多普勒频移。基于该方法设计了一种超声多普勒流量测量系统,实验结果显示:油水混合流体流量的测量误差在3%以内,从而证实了此频偏提取方法的有效性。     

金溶胶中邻羟基苯甲酸吸附行为的密度泛函理论与实验研究

研究了邻羟基苯甲酸(OHBA)的常规拉曼散射(NRS)光谱以及其吸附在Au纳米颗粒上的表面增强拉曼散射(SERS)光谱。以氯金酸为原料,柠檬酸三钠为还原剂,用化学还原法制备了球形的金纳米粒子溶胶,采用激光显微拉曼光谱仪(激发波长为785 nm),测定OHBA分子的NRS光谱及其吸附在Au纳米颗粒上的SERS光谱。同时,应用密度泛函理论(DFT),在B3LYP/6-31+G**(C,H,O)/LANL2DZ(Au)水平上,对OHBA分子进行了结构优化,在此基础上计算了OHBA分子的NRS光谱以及其吸附在Au纳米颗粒上两种不同吸附构型下的SERS光谱,并和实验值进行比较。结果表明,OHBA分子通过羧基吸附构型的计算值比通过羟基吸附构型的计算值与实验值符合的更好。最后,利用GaussView可视化软件对其振动模式进行了全面归属。通过对邻羟基苯甲酸分子拉曼谱峰的详细指认能够得出：Au溶胶中的邻羟基苯甲酸分子,是通过羧基倾斜地吸附在Au纳米颗粒表面的。可视化软件直观形象地展示出了该分子的结构特征和分子基团振动情况,对其振动峰位的归属提供了重要依据。本文工作对推进邻羟基苯甲酸在生物医药等领域进一步的应用具有重要作用。     

无人值守变电站电力设备音频监测及故障诊断系统

针对智能变电站的无人值守需求及现有故障诊断系统的不足,提出一种电力设备音频监测及故障诊断系统。根据变电站电力设备音频信号信噪比较低的特点,采用具有强鲁棒性的梅尔频率倒谱系数作为判断音频信号异常的特征参数,在此基础上根据音频特征构成多样本观测序列,并采用隐马尔科夫模型进行故障诊断,通过对比对数似然估计概率的输出值确定故障类型。该方法具有实时性较强的优势,也避免了现有故障诊断方法要求较大样本容量的缺陷。实验结果表明,该故障诊断系统具有较高的识别率和鲁棒性。     

多速率STFT超宽带信号瞬时频率估计研究

提出多速率短时傅里叶变换(Multi Rate Short Time Fourier Transform,MR-STFT)瞬时频率估计算法,提高了超宽带信号瞬时频率估计精度。该方法将多速率信号处理算法与短时傅里叶变换(STFT)技术相结合,兼顾采样频率和被测频率,将宽频范围进行分段采样,对分段处理结果进行拟合,构成多速率STFT算法,实现超宽带信号瞬时频率的高精度测量。论文通过对仿真信号和实测信号进行处理,研究了方法的可行性和频率估计精度,结果表明MR-STFT算法较大提高了超宽带信号瞬时频率估计精度,尤其对低信噪比的超宽带信号效果显著。     

Strengthened Hyper-Raman Lines with the Coherent Superposition State

High-order harmonic generations from a one-dimensional Coulomb potential atom are calculated with the initial state prepared as a coherent superposition between its ground and first excited states. When the energy difference of the two states is small, we can choose proper laser pulse such that the first excited state can be excited only to other bound states instead of being ionized. We show that only the hyper-Raman lines are observable instead of the harmonics. The energy difference of the ground and the first excited state can be deduced from the highest peak of the hyper-Raman lines. We further show that the similar results can be obtained by using a combination of two laser pulses with different frequencies interacting with the atom initially at the ground state.     

Evaluation of Optical Properties of Self-Frequency-Doubling Crystal Yb：GdYAl3（BO3）4 for Laser Applications

Yb：GdYAl3 （B03）4 （Yb：GdYAB） is investigated as a new laser crystal for potential applications in self-frequency doubling. The emission and absorption properties of Yb：GdYAB crystal are studied, and the emission decay times of the upper laser level are measured. The emission cross sections are evaluated using the absorption cross section and principle of reciprocity. The other laser performance parameters, such as the minimum inversion fraction βmin, pump saturation intensity Isat and minimum pump intensity 1rain, are also calculated. The results are discussed in the framework of requirements for an effective diode-pumped Yb^3＋ laser system. Yb：GdYAB is expected to exhibit the most useful laser properties and to be superior to Yb：YAB crystal that has been excellent self-frequency-doubling crystal at present in many key spectroscopic parameter values.     

Orthogonally Linearly Polarized Dual Frequency Nd：YAG Lasers with Tunable Frequency Difference and Its Application in Precision Angle Measurement

The orthogonally linearly polarized dual frequency Nd： YA G lasers with two quarter wave plates in laser resonator are proposed. The intra-cavity variable birefringence, which is caused by relative rotation of these two wave plates in laser inner cavity, results in the frequency difference of the dual frequency laser also changeable. The theory model based on the Jones matrix is presented, as well as experimental results. The potential application of this phenomenon in precision roll-angle measurement is also discussed.