驻波热声发动机振荡频率转换特性

为了研究驻波热声发动机的起振特性和频率转换特性,理解频率模态转换发生的条件,根据热声网络理论,对不同充气压力下驻波热声发动机的基频和二阶频率下的阈值温度进行预测.计算在不同充气压力和加热温度下驻波热声发动机的品质因子,分析在不同条件下的起振状态和频率转换特性,并在自行设计的驻波热声发动机实验台上测量起振温度和频率转换条件,将测量结果与计算结果进行对比验证.计算的起振频率和频率转换特性随充气压力的变化趋势与实验结果符合较好.     

有界双层结构SH导波频散特性分析

为了检测附着防腐层层状结构中是否存在剥离、孔洞等缺陷,利用超声SH导波研究层状结构频散特性的影响因素,基于弹性及粘弹性波动理论并依据Navier运动位移方程推导了附着防腐层双层结构的频散方程,并分析了防腐层剥离缺陷状态对频散特性的影响.结果表明:通过研究SH导波频散特性的变化可反映附着防腐层的双层结构是否存在剥离缺陷;防腐层产生剥离缺陷时,导波SH_0模态发生频散且向防腐层横波速度渐近.防腐层剥离缺陷尺寸增大,回波信号幅值增加,截点振动速度变慢,导波能量衰减减小.     

一种新的宽频带信号频率欠采样估计方法

提出了一种新的基于欠采样技术的宽频带信号频率估计方法．利用两个独立欠采样通道得到的有模糊的信号频率信息，结合一定的解模糊和配对方法得到无模糊的信号频率估计．该方法不受两个欠采样通道间不一致性的影响，且两通道的采样数据可并行处理，增强了算法的实用性．     

Coupling of Pi2 wave energy in the inner magnetosphere as inferred from low-latitude ground observations

Taking advantage of high time-resolution (1 s) geomagnetic field measurements obtained at low-latitude stations, we investigated frequency differences of Pi2 pulsations between the dayside and the nightside. Firstly, we examined two Pi2 cases globally observed by multiple ground stations and found that the dominant frequency peaks at the dayside showed latitudinal dependence, i.e., the higher (lower) frequency peak was predominant at lower (higher) latitude. We also noticed that the dominant Pi2 frequency on the nightside was apparently higher than that on the dayside. We argue that the multiple frequency peaks observed on the ground are harmonics of a plasmaspheric cavity resonance mode (CRM) and that the latitudinal dependence of the dominant frequency peaks may result from the energy coupling between the CRM and field line resonance (FLR) occurred in the near Earth space. We also argue that the frequency difference between the dayside and the nightside could be caused by the reason that a higher harmonic was observed in the nightside plasmasphere but was not effectively observed in the dayside. In addition, we statistically examined 829 Pi2 events that were simultaneously recorded at Kakioka (KAK, Maglat=27.2°) and Jicamarca (JIC, Maglat=0.0°), the two stations separated by ～10 h in local time (LT) and one of them (JIC) is located at the dip equator. We found that the Pi2 frequency observed at KAK on the nightside was higher than that observed at JIC on the dayside on average. After investigating the occurrence histogram of the frequency difference (Δf=f _JIC?f _KAK) for the events simultaneously observed at KAK and JIC, we found that close to half of the events had the identical frequency (|Δf|<1.0 mHz). The statistical results are consistent with the facts reflected by case studies.     

一种改进的正弦波频率谱估计方法

当OVSS谱估计方法中构造的奇异矩阵的行数大于信号频率个数加1时，会产生虚假的正弦信号，在实际应用时容易造成误判．本文通过修正OVSS谱估计式的分母，由原来单一的正交乘积，变为多个正交乘积的加权求和得到了一种改进算法．改进算法能彻底消除伪峰，且性能稳定，分辨率高．仿真结果表明改进算法整体上优于OVSS方法．     

基于频域分析的脉搏波信号研究

在人体血液循环系统中,推动血液流动的能源来自心脏的搏动。采用现代测试技术理论,从能量传递的角度,对系统的激励和响应特性进行了理论分析。指出在动脉管壁上测得的压力波信号,作为血液循环系统对心脏搏动激励的响应,含有反映人体健康状况的信息,并进行了实验研究。     

高频地波雷达短波电台干扰频谱特性研究

短波电台干扰是高频地波雷达的主要干扰源,通过建立了各种短波电台干扰的理论模型,系统分析了干扰信号的频谱特性,并进行了实际雷达干扰信号的频谱分析研究,得出了干扰信号的典型频谱特征,实验和仿真结果证明了理论的正确性,从而为高频地波雷达的干扰抑制、目标检测和海态特征的研究提供了理论和试验依据.     

改进BP神经网络在水轮机特性数据处理中的应用

针对原有的水轮机特性数据处理方法的不足,提出了一种改进的BP算法对水轮机特性数据进行处理.采用改进BP神经网络算法进行数据处理时,不需要依赖于具体的函数关系表达式,即可对已知离散数据进行拟合,并将提出的改进BP算法与元胞自动机理论所建立模型的计算结果进行了分析比较.计算结果表明:改进的BP神经网络算法不仅能够有效处理水轮机特性数据,而且具有很高的计算精度,可应用于水轮机的控制和优化运行当中,为进一步研究水轮机的运行性能奠定了理论基础.     

宽带太赫兹波光束轮廓和频率分布特性(英文)

利用刀口法在透射式太赫兹时域光谱系统中对脉冲太赫兹波的光束轮廓和能量的轴向分布进行测量.通过快速傅里叶变换,可以获得太赫兹脉冲的频率分布.实验结果显示,脉冲太赫兹光斑的能量符合高斯分布.实验测量到的太赫兹光斑大小与理论基本吻合,证明刀口法可用于宽带激光光束测量.该结果为太赫兹成像以及太赫兹技术在其他领域的应用奠定了基础.     

鲍鱼性腺多糖的体内抗氧化活性

采用酶水解结合乙醇醇沉的方法从皱纹盘鲍性腺中提取多糖(CAGP),并研究其体内抗氧化活性.研究发现,对于正常小鼠,200 mg/kg的CAGP可有效提高其肝组织中CAT活力及T-AOC能力(P<0.01),降低血液与肝脏MDA浓度(P<0.01);CAGP还可显著降低脑组织MAO活力(P<0.01).对于四氧嘧啶致氧化...     

阵列频率特性改进研究

传统的均匀线阵(ULA)和均匀圆阵(UCA)的实时性、宽频带特性以及旁瓣级等难以满足系统需求,通过对传统的ULA和UCA的频率特性与其阵形的关系进行了分析,提出了采用有向阵元改进UCA的综合性能。利用半圆阵的阵形结构提高了采用有向阵元的UCA的综合性能。仿真分析表明,该结构获得了更好的宽频带特性,并在具备实时性的同时有较佳的综合性能,满足了快速宽带波束形成系统的需求。     

Structure characteristics and adhesive property of humic substances extracted with different methods

The structure characteristics and adhesive property of humic substance(HS) extracted with different methods were mainly studied by terms of elementary analysis,visible spectrum,FT-IR spectroscopy,viscosity,adsorption and pelletizing experiments.The results show that HSs extracted with new method(HS-a) own higher degree of aromatization and polymerization,larger relative molecular mass and more polar functional groups than HS extracted with usual method(HS-b).The viscosity of HS-b is about 30-40 mPa·s lower ...     

波浪数据采集系统的改进与应用

通过在某电厂吸水室水位波动测试中,对现有仪器创新并取得满意的测试结果,重点阐述了试验室设备建设中,对典型仪器钽丝浪高仪的改进及与计算机系统配合的思路和方法,从而为高校试验设备的改造和更新换代提出切实可行的途径     

Electron microscopy observations of surface morphologies and particle arrangement behaviors of magnetic fluids

Magnetic fluids consisting of magnetic nanoparticles, stabilizers, and carrier liquids have attracted great attention of scientists and engineers due to their special properties, which are dependent on their special compositions and structures[1—5]. The combination of fluidity with superparamagnetic property exhibited by magnetic fluids enables us to control the flows and physical properties of such systems by magnetic fields. Up to now, many kinds of magnetic fluids and corresponding applica…     

Pressure characteristics of a hydrocyclone for fine particle separation

Hydrocyclonesperformtheseparationfunctionbytakingadvantageofthedensitydifferenceamongdiffer entimmisciblephases.Forsolid liquidseparation,thehydrocycloneisastaticseparatorbasedoncentrifugalseparationinavortexgeneratedwithinthebody.Thefeedflow,usuallyenter…     

受油机头波作用下软管-锥套运动特性分析

为降低空中加油对接过程中头波作用对软管-锥套的扰动,提高空中加油对接成功率,对头波影响范围内软管-锥套运动特性进行了仿真与分析。首先,基于集中参数原理的多刚体动力学,建立了包含软管弹性及弯曲恢复力矩且长度可变的软管锥套组合体动力学模型。 然后,采用拟合半兰金体头波理论模型模拟符合受油机头部外形尺寸的头波流场。最后,通过综合考虑紊流、重力以及加油机尾流等因素的数值仿真,获得了头波作用下软管锥套的运动特性,就不同对接高度、飞行速度、软管材料、对接速度、对接方式和受油机头部外形等因素对头波作用下软管锥套运动特性的影响进行了分析。结果表明:受油机靠近锥套时,在头波作用下锥套会向远离受油机的方向运动,然后回摆;高对接高度、低飞行速度可降低头波的扰动,合理设置对接速度、对接方式、软管材料、截面类型与受油机头部外形也可降低头波对锥套的扰动。仿真结果充分说明通过优化加油设备及对接过程可以达到降低头波扰动的目的。     

几种提取苔藓植物总RNA方法的比较

将3种RNA提取方法加以比较,以期获得提取不同生境毛尖紫萼藓（Grimmia pilifera P．Beauv）总RNA的最适方法。经比较,改进后的SDS法更适合于毛尖紫萼藓总RNA的提取。此方法简单快捷,所得RNA完整性好,纯度高,试验稳定性好,可用于RT-PCR、基因克隆等进一步分子生物学研究。     

Detection and parameter estimation of sawtooth linear frequency modulated continuous wave signal

Aiming at application of long time accumulation for the detection and parameter estimation of linear frequency modulated continuous wave (LFMCW), a novel method based on the joint zero frequency searching method and quasi-MTD method is proposed to detect the sawtooth LFMCW (SLFMCW) signal and estimate its parameters. Firstly, detection of the SLFMCW signal and estimation of its period are realized by use of the zero frequency searching method. And then, the quasi-MTD method based on cyclocorrelation is utilized to finish the estimation of phase parameters and initial time-offset. The estimation of the period, chirp-rate, initial frequency and initial time-offset can be effectively realized by the method, which has low computational complexity and can provide good estimation performance in a low signal-to-noise ratio (SNR) owing to long time accumulation. Computer simulations verify the effectiveness of the algorithm.     

利用极化信息的高频地波雷达TBD检测算法

为解决复杂的杂波背景造成高频地波雷达目标检测上的困难,针对高频地波雷达的极化特性,提出了一种将极化信息与传统动态规划算法相结合的TBD检测新方法.该方法利用运动目标方向信息和极化信息对算法进行优化,并通过预检测减小计算量.在高斯背景和高频地波雷达实测数据中的仿真和检测结果表明,存在电离层杂波干扰时,基于极化信息的检测前跟踪新方法比传统动态规划算法性能明显提高.     

基于极低频电磁波的管道检测定位技术

针对传统有缆定位方式受电缆重量、信号损耗、管道等因素影响问题,提出一种基于极低频电磁波磁偶极子模型的管道内部检测器定位方法.根据极低频电磁波的特性以及发射线圈实质为螺线管的特点,研究了极低频电磁波发射天线（螺线管模型）磁场在介质中的分布规律,结合工程应用中的要求,建立了极低频电磁波的磁偶极子传输模型.磁偶极子理论计算结果表明,发射天线磁场空间的磁场强度幅值随位置的改变具有对称、双峰分布的规律.