打击乐器和膜、棒、板的振动--物理与音乐专题之四

藉助捶打、敲击、抓奏、刮奏、摇奏、弹拨等方法几乎可以使任何刚性物体发声．打击乐器就是利用这种方式发出乐音的乐器．它们大致可以分为两类：一类是有调打击乐器如木琴、钟琴、钢板琴、定音鼓和中国编钟等，此类乐器有音阶的变化，可以独立表演乐曲；另一类是无调打击乐器，如各种鼓、     

关于弦振动实验中的驻波解

利用波的合成所形成的驻波现象来检测波的参量:波速、波长和频率并进而研究一些物理现象,在大学物理实验中是有启发和实际意义的。本刊曾先后刊载了黄涛和郝乃澜的两篇文章,对弦振动实验中的有关问题进行了探讨。但不得不指出的是郝文在定解问题的处理、推导和得出结论时,     

XY2型分子伸缩振动与弯曲振动耦合研究

本文研究一种推广的局域模模型，我们用局域坐标描述非线性ＸＹ２分子的伸缩振动，用简正坐标描述弯曲振动；对用曲线内坐标写出的势能函数和Ｇ矩阵元进行Ｔａｙｌｏｒ展开，保留了弯曲振动与伸缩振动耦合的交叉项，获得各阶哈密顿量，略去了五次以上的高阶项；用它对实验数据进行非线性最小二乘法的拟合，得出各个势能参数值，并用它们计算了Ｈ２Ｏ分子的振动光谱，计算结果与实验数据符合得较好。     

低温制冷机微振动输出的测量和控制方法

低温制冷机微振动输出是在设计和实际使用过程中的重要指标。为了准确测量出低温制冷机自身微振动输出,提出了采用弹簧和细线的悬置方式测量微振动输出的方法,消除了因为支撑和装夹等因素的影响,并对2.8W/80K斯特林制冷机压缩机和膨胀机各方向的振动输出进行测试,分析了振动输出产生的原因和控制方法,对于整机优化设计与性能改进具有指导意义。     

用打点计时器作弦振动实验

在传统的普物实验教材中,常用电动音叉与一端固定的弦来作“弦的振动实验”,如图1所示。实验时常用方法是固定弦长L,改变张力T,或改变张力T的同时调节弦长L,使弦上产生基频或某次谐频共振。由于张力T改变时,弦线的线密度将随之改变,这会给实验带来误差。另外,实验中策动源频率不可改变,使实验的“自由度”受到一定限制。用音频振荡器(可用音讯——1甲型)的功率输出去驱动打点计时器(可用中学物理实验用的)作弦的振动实验可以固定弦长和张力,而改变策动源的频率(频率的大小可以由刻度盘读出,也可以用频率计测出)。     

一种测量功率超声振动系统振速比的简单方法

本文提出了一种测量功率超声振动系统中振动速度比的简单方法。与传统的测量方法相比,本方法将力学量转变为电学量的测量,将绝对测量变成了相对测量,降低了对实验设备的要求,有利于提高测试精度。     

弦线与音叉垂直情况下弦振动的研究

如图1所示，当音叉的位置由图la变为图fo时，则弦线驻波的波腹数减少为原来（偶数）的一半，此现象有的称为二分频现象．对此现象现已有文章‘’‘通过建立物理模型解数理方程的方法得出某些具体结果，但在教学中更希望能从基本物理规律出发对此现象做出解释．本文就此试研究如下．一、基本分析由振动和波动理论可知，要使图1装置形成稳定的驻波须有两个条件，一为弦线长度为半波长的整数倍，一为音叉给予弦线一合拍作用力对弦线总是做正功．设弦线上激发某一频率的驻波，若无能量损耗，则不需外力作用，弦线的运动状态就会一直维持下去．此…     

不同水质的拉曼光谱研究

测量了不同浓度杂质水的拉曼光谱的,并与蒸馏水的拉曼光谱线进行比较和分析.结果表明,水中所含杂质的浓度越高其对应拉曼谱线弯曲振动的强度就越大,弯曲振动与伸缩振动的强度比也越大,而且拉曼光谱线峰下的面积也随着杂质浓度的增大而增加.     

耦合型高频光纤振动传感器实验研究

提出了一种耦合型高频光纤振动传感器,并设计了相应的解调电路和信号处理系统.对高频振动信号的响应波形和频率进行了测量,研究了光纤传感器对不同的振动强度和不同方向的振动信号的响应,分析了不同结构和不同材质的传输介质对光纤传感器测量结果的影响.实验证明所设计的耦合型高频光纤振动传感器截止频率达到8 kHz,振幅测量灵敏度为325 mV/mm,频率和幅值响应误差小于1%.     

音叉振动的研究

一、问题的提出众所周知,在耳朵近旁将一只振动着的音叉绕其对称轴旋转一周,听到的音响增强和减弱各四次.实验表明,音响出现极大的四个方向在图1所示的±x和±y方向,图中虚线表示的四个方向音响则出现极小.实验还表明,音响出现增强减弱的次数和方向与音叉的频率无关.     

A study on the best irradiation dose of X-ray for Hep-2 cells by Fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR) was employed to study the human epidermis larynx carcinoma cell lines (Hep-2) which were irradiated by different doses of X-ray.The results show that (1) the irradiation of X-ray damages the structure of the CH3 groups of the thymine in DNA,which restrains the reproduction of Hep-2 cells effectively,(2) the 8 Gy dose of X-ray irradiation changes the framework and the relative contents of some proteins,lipids and the nucleic acid molecules intercellular in the greatest degree,and (3) the 8 Gy dose of X-ray irradiation is the best irradiation dose for lowering the degree of the cancerization of Hep-2 cells according to the criteria for the degree of the cancerization reported recently.Meanwhile,the apoptosis of these cells were detected by using flow cytometry (FCM) primarily.It shows that the apoptotic ratio of the Hep-2 cells depends on the irradiation dose to some extent,but is not linearly.And the apoptotic ratio of the 12 Gy dose group is the maximum (20.36%),but the apoptotic ratios of the 2 to 8 Gy dose groups change little.     

Experimental study on SC RF cavities by using China large grain niobium for ILC

Large grain niobium has the potential of simplifying the production sequence and consequently reducing the cost of the superconducting RF cavities for ILC.To investigate the feasibility of fabrication and the possibility to achieve high gradient by large grain cavities,two 1.3 GHz cavities were made of China large grain niobium and a series of vertical tests were carried out following several different surfaces treatment procedures.Two cavities have both reached the high gradient of more than 43 MV/m repeatedly and the maximum accelerating field of 47.9 MV/m has been achieved by China large grain niobium.This paper introduces the features of the fabrication and surface treatments on the large grain cavities and presents the preliminary results of the research.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

A modified voice conversion algorithm using compressed sensing

A voice conversion algorithm,which makes use of the information between continuous frames of speech by compressed sensing,is proposed in this paper.According to the sparsity property of the concatenated vector of several continuous Linear Spectrum Pairs（LSP）in the discrete cosine transformation domain,this paper utilizes compressed sensing to extract the compressed vector from the concatenated LSPs and uses it as the feature vector to train the conversion function.The results of evaluations demonstrate that the performance of this approach can averagely improve 3.21%with the conventional algorithm based on weighted frequency warping when choosing the appropriate numbers of speech frame.The experimental results also illustrate that the performance of voice conversion system can be improved by taking full advantage of the inter-frame information,because those information can make the converted speech remain the more stable acoustic properties which is inherent in inter-frames.     

A subspace fitting algorithm of acoustic vector sensor array and corresponding matrix pre-filter design

In order to ease the pass-band response distortion of the matrix pre-filter,a simple approach for designing matrix spatial filter is proposed,which minimizes the sum of the k maximal distortion norm（k is the number of the constraint points）within the pass-band,while constraining the filter response within the stop-band.Considering the costly amount of calculation of the high-resolution methods,an algorithm with small amount of calculation based on matrix pre-filtering and subspace fitting using acoustic vector array（MF-VSSF）is proposed.Through joint processing of signal subspace of both pressure and particle velocity,the pre-filtering matrix and the signal subspace is decreased to M-dimensional（M is the number of array-element）,hence reduces the time-consumption of the matrix pre-filter design and DOA searching.Simulation results show that,the method offers the same performance as MUSIC with pre-filtering,but has much lesser amount of calculation.Moreover,the designed prefilter can efficiently suppress the interference in the stop-band and improve the estimation and resolution performance of successive DOA estimators.     

Study on the radiation problem caused by electron beam loss in accelerator tubes

The beam dynamic code PARMELA was used to simulate the transportation process of accelerating electrons in S-band SW linacs with different energies of 2.5, 6 and 20 MeV. The results indicated that in the ideal condition, the percentage of electron beam loss was 50% in accelerator tubes. Also we calculated the spectrum, the location and angular distribution of the lost electrons. Calculation performed by Monte Carlo code MCNP demonstrated that the radiation distribution of lost electrons was nearly uniform along the tube axis, the angular distributions of the radiation dose rates of the three tubes were similar, and the highest leaking dose was at the angle of 160° with respect to the axis. The lower the energy of the accelerator, the higher the radiation relative leakage. For the 2.5 MeV accelerator, the maximum dose rate reached 5% of the main dose and the one on the head of the electron gun was 1%, both of which did not meet the eligible protection requirement for accelerators. We adopted different shielding designs for different accelerators. The simulated result showed that the shielded radiation leaking dose rates fulfilled the requirement.     

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.     

Analysis of Laser-generated Rayleigh wave on viscoelastic materials

In order to understand the viscoelasticity of material, this research has been conducted to study the propagation characteristics of viscoelastic Rayleigh wave theoretically. A model is presented for the pulsed laser generation of ultrasound on viscoelastic medium surface. Referred to the Kelvin model, the frequency equation and the normal displacement of viscoelastic Rayleigh wave were derived, the influence of the viscoelastic modulus on dispersion and attenuation was discussed. From the theoretical calculation, it is shown that the effect of viscoelasticity on the attenuation of Rayleigh wave is more than that on its dispersion. In the case of a weak viscosity, the attenuation of viscoelastic Rayleigh wave is directly proportional to viscosity modulus; the effect of shear viscosity on the attenuation is much more than that of bulk viscosity. The transient response of viscoelastic Rayleigh wave was also simulated using Laplace and Hankel inversion transform, which are showed in good agreement with the theoretic predictions. The model provides a useful tool for the determination of viscoelastic parameters of medium.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

Influence of dielectric microcavity on the spontaneous emission rate of atom: a perspective on the closed-orbit theory of photons

The formulas of the quantum electrodynamics have been applied to calculate the spontaneous emission rate of excited atom in dielectric microcavity.The results exhibit damping oscillating Patterns which depend sensitively on the scaling parameter and geometrical structure.Compared with the case that the emitting atom is immersed in dielectric,the spontaneous emission rate is depressed obviously and the center or the mean value of the oscillations is intimately related to the real refractive index of the local position where the atom is.In order to explain this phenomenon,we utilize the closed-orbit theory to deal with the classical trajectories of the emitted photon.and extract the corresponding frequencies of the oscillations by Fourier transform.It is found that the oscillations can be represented in terms of the closed-orbits of the photon motion constrained in dielectric microcavity,thus providing another perspective on the spontaneous emission of atom sandwiched by dielectric slabs.