一种高精度的电力系统谐波分析方法

针对电力系统谐波的危害和谐波治理的需要,提出了一种高精度的电力系统谐波分析算法,利用该算法可快速获得电力系统基波及各次谐波的高精度幅值和相位.提出并证明了该算法的收敛性定理,给出了利用该算法进行谐波分析的仿真实例.仿真结果表明,提出的谐波测量方法与其他方法相比具有更高的计算精度高和更快的计算速度,因而在电力系统谐波测量中有较大的应用价值.     

电力系统谐波分析的一种快速神经网络算法

提出了一种基于最小二乘递推法(RLS)的正交基神经网络算法来分析电力系统谐波参数.该方法根据谐波分析的特点,采用RLS训练神经网络权值,有效地避免了梯度下降法存在局部极小的问题,并且对降低噪声影响有显著作用.电力系统谐波分析的仿真结果表明,该算法经过一次神经网络训练即可获得各次谐波高精度的幅值和相位.     

Attosecond synchronization of high-harmonic soft x-rays

Subfemtosecond light pulses can be obtained by superposing several high harmonics of an intense laser pulse. Provided that the harmonics are emitted simultaneously, increasing their number should result in shorter pulses. However, we found that the high harmonics were not synchronized on an attosecond time scale, thus setting a lower limit to the achievable x-ray pulse duration. We showed that the synchronization could be improved considerably by controlling the underlying ultrafast electron dynamics, to provide pulses of 130 attoseconds in duration. We discuss the possibility of achieving even shorter pulses, which would allow us to track fast electron processes in matter.     

Mode locking of electron spin coherences in singly charged quantum dots

The fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum information processing. We show here that dephasing can be overcome by using a periodic train of light pulses to synchronize the phases of the precessing spins, and we demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. This mode locking leads to constructive interference of contributions to Faraday rotation and presents potential applications based on robust quantum coherence within an ensemble of dots.     

植物生理学教学改革的探讨

从教学理念、教学内容及教学形式3方面,探讨如何在植物生理教学中培养学生的综合能力,提高学生创新能力,为培养高素质的创新人才做出贡献。     

基于LabVIEW的农网谐波监测平台设计与开发

针对农村电网谐波源的复杂特性,设计了基于LabVIEW技术的、开放式的农网谐波监测平台,该平台既可以通过高速数据采集卡获取实际电网或标准谐波源中的谐波信号,也可以加载基于LabView或Matlab仿真生成的任意组合的虚拟谐波信号。集成了FFT等多种信号处理方法,用于谐波信号的检测与分析。仿真算例表明,运用基于汉宁窗的FFT方法检测农网常见谐波,可以获得较理想的结果。     

Bats use echo harmonic structure to distinguish their targets from background clutter

When echolocating big brown bats fly in complex surroundings, echoes arriving from irrelevant objects (clutter) located to the sides of their sonar beam can mask perception of relevant objects located to the front (targets), causing "blind spots." Because the second harmonic is beamed more weakly to the sides than the first harmonic, these clutter echoes have a weaker second harmonic. In psychophysical experiments, we found that electronically misaligning first and second harmonics in echoes (to mimic the misalignment of corresponding neural responses to harmonics in clutter echoes) disrupts the bat's echo-delay perception but also prevents clutter masking. Electronically offsetting harmonics to realign their neural responses restores delay perception but also clutter interference. Thus, bats exploit harmonics to distinguish clutter echoes from target echoes, sacrificing delay acuity to suppress masking.     

计及转子阻尼效应的定子谐波漏抗

给出考虑转子谐波对定子谐波的阻尼作用时,鼠笼式异步电动机定子绕组谐波漏抗的计算方法.这一方法在参数计算准确度方面优于传统方法;同时对变极调速异步电动机,当其定子磁势谐波含量比正规绕组较大时,其电磁计算尤为重要。     

多功能平衡变压器谐波滤波模型及参数计算

提出了较为完善的多功能平衡牵引变压器谐波滤波模型,采用数学Ｍａｔｈｃａｄ ７．０对模型进行了求解和计算,研究了参数变化对原方高次谐波电流大小的影响,为参数的合理选取提供了理论依据。     

Genetic meaning of zooecial chamber shapes in fossil bryozoans: fourier analysis

Fourier harmonic amplitudes quantitatively characterize chamber shapes of fossil tubular bryozoans. The odd-numbered harmonics, particularly the seventh, carry evolutionary information. The phenotypically plastic second and sixth harmonics measure zooecial orientation and packing, respectively. As a measure of crowding, the sixth harmonic reflects mechanistic growth response to paleoenvironmental conditions.     

多功能平衡牵引变压器谐波抑制效果研究

在已有的谐波理论分析及计算的基础上，针对多功能平衡牵引变压器ＳＧＰＨ－２６／２已设计出的滤波参数，在不同的运行工况下，测量了滤波器投入和不投入两种情况下，原方三相电压和电流的波形及畸变率。实验表明，投入滤波器后其波波效果十分明显。     

基于谐波分析的黄土高原小流域沟谷分布规律研究

研究黄土高原侵蚀沟分布规律对于土壤侵蚀评估和植被恢复模式设计具有重要意义。该文以 陕北黄土高原吴起县铁边城镇四面窑沟流域为研究区,使用1∶10 000数字高程模型（DEM） ,利用谐波分析和周期图分析方法,研究了黄土高原侵蚀沟的分布规律。结果表明,利用谐波分析和周期图分析均可得到侵蚀沟的分布周期。相比较而言,周期图分析可以更加直观地得到满足显著性检验的分布周期,但谐波分析还可以根据周期检验结果,得到对应的谐波模型。通过计算四面窑沟流域东面支沟沟谷分布周期,共得到23个满足检验要求的周期,在500～1 000 m之间显著周期最多,占总周期数的35%;在300～500 m显著周期数量次多,占26%。当谐波数为9和10时,周期显著性水平最高,对应的周期分别为1 017.35和915.60 m;在DEM上,每间隔105 m提取一个高程数据并进行谐波分析,最终得到由3个谐波组成的地形起伏谐波模型。      

浅谈工程制图教学中学生创造力的培养

工程制图课作为一门专业技术基础课,是培养学生空间思维能力、观察能力、形体分解能力、表达与图示图解能力、绘图能力的重要课程,在工程制图教学中学生创造力的培养是关键,只有学生在本课程学习中创造力提高了,才能在今后的工作中成为一个合格的工程技术人员,我们要努力培养学生的创造能力,开发他们的智力资源,为祖国现代化建设培养出大量具有创造能力的新世纪英才.     

从《齐民要术》等史籍看中国古代的肥料科学及其对后世农业发展的启示

贾思勰的《齐民要术》是中国6世纪的农业科学巨著,它也是中国古代肥料科学史籍记载的分界线。《齐民要术》记载了大量中国古代北方地区肥料科学知识,且其所述并非仅局限在北魏时期,也兼具了秦汉以来的北方地区肥料科学史籍资料。本文兼采《汜胜之书》《王祯农书》等史料中有关肥料的篇章,从而尽可能客观地展现中国古代肥料科学知识和应用的发展水平,以期为当前农业现代化和乡村振兴战略的贯彻实施提供有益借鉴。     

提高《兽医微生物学》实验教学质量加强学生动手能力

通过采取一系列措施,如加强硬件设施建设、制定严格的管理制度,使用具有鲜明特色的高水平教材体系以保证兽医微生物学实验课程的顺利完成。在完成实验课程的同时,注重学生动手能力培养,激发学生学习热情,并培养学生观察、分析、解决问题以及“联想”能力。对学生从严要求,培养学生树立良好的学风和科研意识。     

Synthesis and measurement of ultrafast waveforms from five discrete optical harmonics

Achieving the control of light fields in a manner similar in sophistication to the control of electromagnetic fields in the microwave and radiofrequency regimes has been a major challenge in optical physics research. We manipulated the phase and amplitude of five discrete harmonics spanning the blue to mid-infrared frequencies to produce instantaneous optical fields in the shape of square, sawtooth, and subcycle sine and cosine pulses at a repetition rate of 125 terahertz. Furthermore, we developed an all-optical shaper-assisted linear cross-correlation technique to retrieve these fields and thereby verified their shapes and confirmed the critical role of carrier-envelope phase in Fourier synthesis of optical waveforms.     

小波变换与傅里叶变换相结合的暂态谐波分析方法

结合小波变换良好的时频局部化特性和傅里叶变换良好的频域分析特性,提出小波变换与傅里叶变换相结合的暂态谐波分析方法。利用傅里叶变换和静态小波变换得到被测信号频域特性和时域特性,再结合连续小波变换得到暂态谐波的时频特性。理论分析和仿真试验结果表明,利用本方法得到的暂态谐波幅值与理论值一致。本方法能够准确分析电网中的暂态谐波,可为电力系统暂态谐波的分析和治理提供依据。     

配电网中滤波器对谐波放大的分析和抑制

在滤波过程中,滤波装置容易与配电网之间产生参数匹配,造成谐波放大,危及电网的正常运行。因此,在设计滤波方案时,应抑制谐波放大。研究了产生谐波放大的原因,建立了分析谐波放大的模型,分析了滤波支路的谐波放大特性和谐振特性,并提出了滤波装置的改进措施。同时的实际应用中可通过适当选择滤波支路中电抗器的电抗率来减小或避免产生谐波放大。在实际工程中,得到较好的应用,经实测效果较为理想。     

Interior structure of neptune: comparison with uranus

Measurements of rotation rates and gravitational harmonics of Neptune made with the Voyager 2 spacecraft allow tighter constraints on models of the planet's interior. Shock measurements of material that may match the composition of Neptune, the so-calied planetary ;;ice,' have been carried out to pressures exceeding 200 gigapascals (2 megabars). Comparison of shock data with inferred pressure-density profiles for both Uranus and Neptune shows substantial similarity through most of the mass of both planets. Analysis of the effect of Neptune's strong differential rotation on its gravitational harmonics indicates that differential rotation involves only the outermost few percent of Neptune's mass.     

北京市水产培训现状调查与研究

为摸清北京地区渔民的培训情况和培训需求,采用访谈和座谈方式,结合问卷调查进行调研,对获得的信息进行综合分析,基本摸清培训情况,提出以农民田间学校为载体大力培养新型农民,整合水产推广系统优势的人才、科研资源,不断创新培训方式,提高培训效率等工作思路。