口琴簧片振动频率的理论与实验研究

口琴是常见的乐器之一。通过推导了口琴簧片振动频率的计算公式,进而揭示了簧片几何尺寸对振动频率的影响,并对录制好的口琴音频文件进行快速傅里叶变换（FFT）,从而推断口琴簧片振动的频率。     

具有直线结构的三原子分子振动模型

给出了直线结构的三原子分子振动的一个模型,该模型通过角簧实现弯曲振动模式.建立了该模型的振动微分方程组.求解方程组得到了3个本征振动频率和对应的振动模式.就二氧化碳、羰基硫和氰化氢3个三原子分子,使用文献数据验证了所给出的模型.结果表明按该模型的3个振动频率与文献结果吻合良好.     

巴西果效应分离过程的计算颗粒力学模拟研究

采用离散单元模型对巴西果问题进行了模拟研究,采用本数学模型可以准确地预测出垂直机械振动导致的不同大小颗粒的分离现象.分析了影响振动床内颗粒分层的因素,讨论了振动频率、振动幅度等参数对分层的影响,发现振动频率和振动幅度会对分离效果造成较大的影响.当振动频率或振动幅度较小时,颗粒整体分离效果都较差,但分离的稳定性较好,当振动频率或振动幅度较大时,整体分离效果仍然较差,同时分离的稳定性也较差,振动分离过程中存在一个频率和振幅适中的最优操作点. 关键词： 分层 振动 模式形成 离散单元方法     

温度对抛物量子点中强耦合磁极化子性质的影响

采用线性组合算符法和LLP变换法,研究了温度对抛物量子点中强耦合磁极化子性质的影响.首次得到了抛物量子点中强耦合磁极化子的基态能量和振动频率随温度的变化规律.结果表明,量子点中强耦合磁极化子的振动频率随温度的升高而减小,随量子点的受限强度、回旋频率和耦合强度的增加而增大.而基态能量随回旋频率、耦合强度和温度变化的规律与磁极化子的状态性质密切相关.磁极化子基态能量和振动频率随量子点的受限强度、回旋频率和耦舍强度的变化情况受温度的显著影响,不过,温度对磁极化子基态能量和振动频率的影响只有在较高温度(O<γ<0.5)时才显现.     

振动频率对抛物量子阱中极化子性质的影响

采用改进的线性组合算符和幺正变换相结合的方法研究振动频率对抛物量子阱中极化子性质的影响,理论推导得到极化子有效质量和相互作用能的表达式,结果显示极化子的有效质量和相互作用能都是振动频率的函数.当耦合强度取不同值时,分别讨论了有效质量比和相互作用能随着振动频率的变化关系;以及当振动频率取定值时,相互作用能和有效质量比与电...     

关于乐器的声谱

有些普通物理学课本和现行高中物理学课本在声学部分都谈到乐器的声谱,但沒有作进一步的说明。例如,福里斯、季莫列娃合著的“普通物理学”,对弦的振动谱和乐器的声谱同时作了介绍,对二者的区别和联系,并未作交代。这样,有些同志便将弦的振动谱和乐器的声谱当成一回事;又认为弦振动的泛音振幅一定随频率的增大而减小,高阶泛音的振幅一定     

抛物量子点中弱耦合束缚极化子的相互作用能

研究了抛物量子点中弱耦合束缚极化子的性质,采用改进的线性组合算符和幺正变换方法导出了束缚极化子的振动频率、有效质量和相互作用能。讨论了量子点的有效受限长度、电子LO声子耦合强度和库仑场对抛物量子点中弱耦合极化子的振动频率、有效质量和相互作用能的影响。数值计算结果表明:弱耦合束缚极化子的振动频率和相互作用能随有效受限长度的减少而急剧增大,振动频率随库仑势以及电子LO声子耦合强度的增加而增加,而相互作用能随库仑势以及电子LO声子耦合强度的增加而减小。有效质量仅与电子LO声子耦合强度有关。     

晶格热振动对准二维强耦合极化子有效质量的影响

采用Tokuda改变的线性组合算符法和改进的LLP变分法，研究了晶格热振动对无限势垒量子阱中电子与界面光学声子强耦合、与体纵光学声子弱耦合系统的影响，推导出作为阱宽和温度函数的极化子有效质量的表达式. 尤其得到了量子阱中极化子的振动频率及其随阱宽和温度变化的规律. 对KI/AgCl/KI量子阱进行了数值计算，结果表明，极化子的振动频率和有效质量随阱宽的增加而减小、随温度的升高而减小，但不同支声子与电子相互作用对极化子的振动频率和有效质量的贡献以及它们随阱宽和温度的变化情况大不相同. 关键词： 量子阱 强耦合极化子 振动频率 有效质量 温度依赖性     

Rashba效应对量子线中束缚磁极化子性质的影响

采用改进的线性组合算符和幺正变换相结合的方法研究了Rashba效应对抛物量子线中强耦合束缚磁极化子性质的影响.计算了抛物量子线中强耦合束缚磁极化子的有效质量和振动频率,对Rb Cl材料的数值计算结果表明:量子线中强耦合束缚磁极化子的振动频率随受限强度和回旋频率的增加而增大;有效质量与磁极化子的受限强度、回旋频率和电子面密度有关,在Rashba效应影响下有效质量随上述各量的变化曲线都发生了分裂.     

一种提高时间平均数字全息测振条纹模式对比度的方法

针对基于时间平均数字全息法的微振动原位检测,提出了一种有效提高振动条纹模式对比度的方法,进而可准确获得待测面振幅分布.首先针对实际振动过程中物体存在纵向微位移而引起的相位误差进行校正;然后去除记录过程中物光场散斑引起的相位噪音,有效提高了被第一类零阶贝塞尔函数调制的条纹对比度;最后利用第一类零阶贝塞尔函数的变化规律和条纹级数,定量估计全场的振幅分布.搭建了以声波作为激励源的时间平均全息测振实验系统,采用频率分别为0、1 100、2 000和9 000 Hz的正弦声波激励簧片进行实验验证.结果表明,以振动频率2 000Hz为例,本方法能够有效提高振动调制条纹质量,并计算得到三级零点处的振幅值分别为109.4nm、244.2nm、356.4nm,与理论值相比较,误差分别为6.31%、3.34%和3.78%,在允许范围之内,证明了该方法的有效性.     

Measurement of the flow and its vibration in Japanese traditional bamboo flute using the dynamic PIV

All wind instruments produce sound due to the vibration of air inside of the instrument. In the case of a trumpet or a clarinet, the mouth or a reed helps to generate variable tones. In the case of a flute, there is no mechanical vibration. Additional detail about the flow and the sound vibration inside and outside of the flute are investigated in order to understand the mechanism of the wind instrument and to aid in the manufacture of quality instruments. In this report, a traditional Japanese bamboo flute was investigated experimentally. The dynamic PIV technique was applied to measure the vibration. Two kinds of experiments were performed. Argon-gas flow containing an oil mist as tracer particles both inside and outside the bamboo flute was measured using a high frequency pulse laser. The periodical flow near a hole of the bamboo flute was successfully measured. The flow was found to go into and out from the flute and the balance of a mass flow rate and the averaged velocity were almost zero at the hole. Then, the flow in the bamboo flute was visualized when a human played the instrument, using a CW-laser and water-mist as the tracer. It was discovered that the two instructors had unique methods for playing the flue instrument.     

Oscillation threshold of a clarinet model: a numerical continuation approach

This paper focuses on the oscillation threshold of single reed instruments. Several characteristics such as blowing pressure at threshold, regime selection, and playing frequency are known to change radically when taking into account the reed dynamics and the flow induced by the reed motion. Previous works have shown interesting tendencies, using analytical expressions with simplified models. In the present study, a more elaborated physical model is considered. The influence of several parameters, depending on the reed properties, the design of the instrument or the control operated by the player, are studied. Previous results on the influence of the reed resonance frequency are confirmed. New results concerning the simultaneous influence of two model parameters on oscillation threshold, regime selection and playing frequency are presented and discussed. The authors use a numerical continuation approach. Numerical continuation consists in following a given solution of a set of equations when a parameter varies. Considering the instrument as a dynamical system, the oscillation threshold problem is formulated as a path following of Hopf bifurcations, generalizing the usual approach of the characteristic equation, as used in previous works. The proposed numerical approach proves to be useful for the study of musical instruments. It is complementary to analytical analysis and direct time-domain or frequency-domain simulations since it allows to derive information that is hardly reachable through simulation, without the approximations needed for analytical approach.     

天然纤维素太赫兹和红外光谱分析研究

为研究太赫兹波技术在植物中纤维素检测的应用前景。选取玉米、麦壳、芦苇进行太赫兹时域光谱检测,并与纤维素粉作为参考样品进行比较,分析结果表明上述三种植物样品和参考样品在1.75,1.62,1.1和0.7 THz等频率处均有明显特征吸收峰。比较几种样品的吸收强度情况,纤维素粉在1.62 THz处吸收最强,采用化学分析方法检测玉米、麦壳以及芦苇中纤维素含量,并与太赫兹波检测比较,发现在该频率处植物中纤维素含量越高,则其在太赫兹波中的吸收峰也越高,说明植物纤维素能在该频率段内发生晶格振动,使其官能团出现变形、弯曲或伸缩等变化。利用密度泛函理论对纤维素进行量子化学计算,也获得纤维素在0.7,1.1和1.75 THz处特征吸收峰,表明了太赫兹时域光谱能用于植物纤维素检测。最后,用红外光谱技术对玉米和纤维素粉进行检测,探讨纤维素分子微结构的扭转及振动模式,并把它们的特征吸收谱与量子化学计算进行比较,实验结果和理论计算基本一致。这为植物纤维素的检测判断提供了一种新方法。     

Vibration characteristics of pipe organ reed tongues and the effect of the shallot, resonator, and reed curvature

Pipe organ reed pipes sound when a fixed-free curved brass reed mounted on a shallot connected to a resonator is forced to vibrate by an impressed static air pressure. Five sets of experiments were performed in order to investigate the influence of the most important parameters which could affect the tone of a reed pipe. First, the phase difference between the pressure variation in the shallot and the boot, and its relationship to the motion of the reed tongue were analyzed to compare their phases and their spectra. Next, the frequency dependence of the reed on three basic parameters (reed thickness, its vibrating length, and the imposed static air pressure) was investigated in an attempt to determine an empirical equation for the frequency. For each trial, two of the variables were kept constant while the third was altered in order to construct an equation giving frequency as a function of the three variables. Third, experiments were conducted using three different types of shallots: the American (or English) style, the French style, and the German style. The results show that for each shallot, the frequency increases linearly with thickness and linearly with air pressure (over the normal operating range of the reed). For each of the shallots, frequency varies inversely with length when the other variables are held constant. The effect on the reed spectrum of using the three different types of shallot was also investigated, as was the effect of reducing the interior volume of each type. Progressively filling the shallot interior generally decreases the frequency of the vibrating reed. The effect of the resonators on frequency and spectrum was studied because the resonator is an integral part of the resulting tone; virtually every reed stop has some type of resonator. The resonator tends to raise the Q of the impedance peaks and reduce the fundamental frequency. Finally, the influence of the type and degree of curvature on reed vibration was briefly examined; increasing the reed curvature tends to decrease the vibration frequency and increase the sound intensity by creating a richer spectrum.     

Theoretical design and experimental verification of a tunable floating vibration isolation system

A fluid-type floating vibration isolation system was developed based on anti-resonance mechanism. The mathematical model was derived for theoretical analysis. The system enables completely isolate vibration at any specific frequency, when the frequency of anti-resonance of the floating vibration isolation system is adjusted to the vibration frequency by tuning the added mass of flowing fluid. Since the approach only alters the inertial force of added mass rather than changing the entire system stiffness, the robustness of the system’s static stability remains during a tuning process, and the system can perform vibration isolation superbly at very low frequencies. A prototype of fluid-type floating vibration isolation system was designed, built and tested to validate the mathematical model. The experimental results illustrated a good agreement with the theoretical analysis.     

The metre

A musical wind instrument transforms a constant pressure input from the player's mouth into a fluctuating pressure output in the form of a radiating sound wave. In reed woodwind and brass instruments, this transformation is achieved through a nonlinear coupling between two vibrating systems: the flow control valve formed by the mechanical reed or the lips of the player, and the air column contained by the pipe. Although the basic physics of reed wind instruments was developed by Helmholtz in the nineteenth century, the application of ideas from the modern theory of nonlinear dynamics has led to recent advances in our understanding of some musically important features of wind instrument behaviour. As a first step, the nonlinear aspects of the musical oscillator can be considered to be concentrated in the flow control valve; the air column can be treated as a linear vibrating system, with a set of natural modes of vibration corresponding to the standing waves in the pipe. Recent models based on these assumptions have had reasonable success in predicting the threshold blowing pressure and sounding frequency of a clarinet, as well as explaining at least qualitatively the way in which the timbre of the sound varies with blowing pressure. The situation is more complicated for brass instruments, in which the player's lips provide the flow valve. Experiments using artificial lips have been important in permitting systematic studies of the coupling between lips and air column; the detailed nature of this coupling is still not fully understood. In addition, the assumption of linearity in the air column vibratory system sometimes breaks down for brass instruments. Nonlinear effects in the propagation of high amplitude sound waves can lead to the development of shock waves in trumpets and trombones, with important musical consequences.     

A novel multi-cavity Helmholtz muffler

A novel multi-cavity Helmholtz muffler is proposed. The multi-cavity Helmholtz muffler is composed of steel structures and silicone membranes. With suitable construction, the Helmholtz muffler can be designed to exhibit negative mass density in low frequency, and the muffling frequency can be adjusted when we change the internal structure of the cavity,which will be very attractive for noise control. In this paper, we investigate the influence of the membranes and the cavities on noise reduction characteristics with theoretical calculations and simulations. The results show that the numbers of membranes and the volumes of the cavities can have a great effect on the position of the muffling frequency. The number of cavities can have a great effect on the width of the muffling frequency(reduce the noise by 10 dB). With different combinations of the membranes and cavities, we can get different muffling frequencies, which can meet different muffling demands in practical applications and is more flexible than the traditional Helmholtz cavity.     

Measurement of vocal-tract influence during saxophone performance

This paper presents experimental results that quantify the range of influence of vocal tract manipulations used in saxophone performance. The experiments utilized a measurement system that provides a relative comparison of the upstream windway and downstream air column impedances under normal playing conditions, allowing researchers and players to investigate the effect of vocal-tract manipulations in real time. Playing experiments explored vocal-tract influence over the full range of the saxophone, as well as when performing special effects such as pitch bending, multiphonics, and "bugling." The results show that, under certain conditions, players can create an upstream windway resonance that is strong enough to override the downstream system in controlling reed vibrations. This can occur when the downstream air column provides only weak support of a given note or effect, especially for notes with fundamental frequencies an octave below the air column cutoff frequency and higher. Vocal-tract influence is clearly demonstrated when pitch bending notes high in the traditional range of the alto saxophone and when playing in the saxophone's extended register. Subtle timbre variations via tongue position changes are possible for most notes in the saxophone's traditional range and can affect spectral content from at least 800-2000 Hz.     

Helmholtz腔与弹性振子耦合结构带隙

为提高Helmholtz型声子晶体低频隔声性能,设计了一种Helmholtz腔与弹性振子的耦合结构,通过声压场及固体振型对其带隙产生机理进行了详细分析,建立了相应的弹簧-振子系统等效模型,并采用理论计算和有限元计算两种方法研究了各结构参数对其带隙的影响情况.研究表明,该结构可等效为双自由度系统振动,在低频范围内具有两个带隙;在6 cm的尺寸下,其第一带隙下限可低至24.5 Hz,而同尺寸无弹性振子结构只能达到42.1 Hz,带隙下限降低了40%,较传统Helmholtz结构具有更为优良的低频隔声特性.另外,在框体尺寸一定的情况下,降低结构间距、增大开口空气通道长度及振子质量、增大左侧腔体体积等方式,是增大带隙宽度、提高低频隔声效果的主要手段.