Time-varying non linear modeling of electrodynamic loudspeakers

This paper deals with the time-varying nonlinear analytical modeling of the electrodynamic loudspeaker. We propose a model which takes into account the variations of Small signal parameters. The six Small signal parameters (R_e, L_e, Bl, R_ms, M_ms, C_ms) depend on both time and input current. The electrodynamic loudspeaker is characterized by the electrical impedance which, precisely measured, allows us to construct polynomial functions for each Small signal parameter. By using this analytical model, we propose to compare two identical electrodynamic loudspeakers. One of them is supposed to be run in and the other one is not. The experimental methodology is based on a precise measurement. In all the paper, the time scale is assumed to be much longer than one period of the harmonic excitation.     

高灵敏度表面光学非线性测量法

提出了一种测量非透明材料表面光学非线性的新方法：挡板反射4F测量法。该方法在反射4F相位相干成像系统的基础上,在4F系统的像平面放置一个与系统入射面光阑相匹配的不透明挡板,通过测量不同情况下的反射率,实现对材料光学非线性的测量。详细介绍了该方法的基本原理,并通过数值模拟计算了入射角对测量灵敏度的影响。该方法具有单脉冲测量,可同时得到材料的非线性吸收与折射系数等特点。结果表明,在相同条件下挡板反射4F测量法的灵敏度比反射Z扫描方法高2个数量级。     

高灵敏度表面光学非线性测量法

提出了一种测量非透明材料表面光学非线性的新方法:挡板反射4F测量法。该方法在反射4F相位相干成像系统的基础上,在4F系统的像平面放置一个与系统入射面光阑相匹配的不透明挡板,通过测量不同情况下的反射率,实现对材料光学非线性的测量。详细介绍了该方法的基本原理,并通过数值模拟计算了入射角对测量灵敏度的影响。该方法具有单脉冲测量,可同时得到材料的非线性吸收与折射系数等特点。结果表明,在相同条件下挡板反射4F测量法的灵敏度比反射Z扫描方法高2个数量级。     

On the origin of irreversibility in classical electrodynamic measurement processes

We present a new formalism for the microscopic classical electrodynamics of point charges in which the dynamic absence of self-interactions is enforced by the action principle, without eliminating the field degrees of freedom. In this context, free local radiation fields are dynamically prohibited. Instead radiation is carried by charge-field functionals of the current which have a negative parity under mathematical time reversal. This leads to the dynamic requirement of a physical time arrow in the equations of motion in order to preserve the overall mathphysical time-reversal symmetry of the formalism. Since this physical time arrow emerges electrodynamically without the need of external thermodynamic or cosmological criteria, it offers a dynamical explanation for the origin of irreversibility in classical electrodynamic measurement processes.

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材料吸声系数双传声器测量的参数识别方法

本文提出了在普通房间中利用双传声器对多孔性和纤维性吸声材料吸声系数测量时的参数识别方法。利用Delany&Bazley经验模型对测量数据进行了参数识别,建立了材料的阻抗模型,并计算出材料全频带的吸声系数。与驻波管方法得到的吸声系数相比,在0～3000Hz范围内,二者都能较好地吻合。通过在不同的环境中进行对比测试,说明该方法具有较好的重复性和准确性。     

The measurement of the free field impulse response of microphones in a laboratory environment

A method is presented of measuring the free field frequency and impulse response of microphones by using a pulse technique in an ordinary laboratory environment. The pressure transient generated by exciting a loudspeaker with a narrow pulse is detected at some point in the loudspeaker's far field by a “reference” microphone whose response is assumed flat over the frequency range of interest. The microphone to be tested is then substituted in exactly the same position and its response to the transient measured. The outputs of the two microphones are accurately sampled and deconvolved by using a discrete Fourier transform technique to give the magnitude and phase parts of the “test” microphone's frequency response, and hence, via the discrete Fourier transform, its response to a delta function of pressure propagating in the free field. The computed impulse responses are presented and the accuracy of the method discussed.To illustrate the use of the method, the free field frequency response and free field correction curves of a one inch instrumentation microphone are measured. The method is then used to measure the pressure which occurs at the centre of the flat end-face of a long a cylinder when excited by an impulse of acoustic pressure propagating in the free field from various angles of incidence.     

A laser pistonphone based on self-mixing interferometry for the absolute calibration of measurement microphones

A laser pistonphone for the absolute calibration of microphones at low frequencies has been developed at UME. The motion of an electro-dynamically driven piston in a small close cavity produces a sound pressure. Accurate measurement of the piston displacement, by self-mixing interferometry, enables this sound pressure to be calculated, and consequently the pressure sensitivity of a microphone, exposed to this sound pressure, to be determined. Absolute calibrations of type LS1P and WS1P microphones have been carried out with an uncertainty of less than 0.15 dB. The performance of the laser pistonphone has been validated by comparing the measured microphone sensitivities with those obtained by the closed coupler reciprocity method.     

Single-beam Z-scan measurement of the third-order optical nonlinearities of triarylmethane dyes

Solid-state dye-doped polymers are an attractive alternative to the conventional liquid-dye solutions. The search for new materials which have potential application in optoelectronic devices has lead us to probe the organic dyes. The solid state being a better medium when compared to a liquid medium has lead to the incorporation of dyes in the polymer matrix. The study of nonlinear characteristics of dyes in polymeric media is essential for developing such potential application devices. In this paper, the third-order nonlinear optical properties of three dyes from the Triarylmethane family were measured in 1-Butanol and in dye-doped polymer films by the Z-scan technique using a cw diode-pumped Nd:YAG laser at 532 nm. The Z-scan technique has also been used to present the observation of a nonlinear refractive index resulting from the photochromism of one of the dyes. These materials exhibit a large negative optical nonlinearity resulting due to the thermal effect. The relative contributions from the nonlinear absorption (NLA) and nonlinear refraction (NLR) are dependent on the chemical structure and linear absorption of the dyes. The dyes exhibited a nonlinear refractive coefficient n ₂, a nonlinear absorption coefficient β, and susceptibility x⁽³⁾ on the order of 10^?8 cm²/W, 10^?4 cm/W, and 10^?6 esu, respectively, in both liquid and solid media. The results show that these dyes have potential applications in nonlinear optics.     

Quantum non-demolition measurement of photon number using weak nonlinearities

We propose an alternative method for the quantum non-demolition measurement of photon numbers wherein weak cross-Kerr nonlinearities are to be used. The usual approach to quantum non-demolition measurements of quantum number involves encoding the photon number, through a cross-Kerr interaction, into a phase shift of a probe coherent state which is then detected through balanced homodyning. Weak nonlinearities produce small phase shifts which are difficult to detect and distinguish. In the method we propose, unbalanced homodyning acts as a displacement operator on the probe beam coherent state such that the cross-Kerr interaction encodes the photon number into the amplitude of a new coherent state. The value of the photon number can be determined by inefficient photon counting on the new coherent state. Our proposed method requires fewer resources than does the usual approach.     

Experimental evaluation of nonlinearities of small-sized insertable gradient coils

A phase imaging technique is proposed to map out and quantify gradient nonlinearities of small-sized insertable gradient coils, assuming the whole-body system gradients are highly linear in the domain of interest. The theory is developed and simple equations are derived to allow quantification. It is applied to a 4-loop 18-cm diameter cylindrical gradient coil of optimal design. Experimental gradient nonlinearity maps are obtained for different fields of view. Gradient non-linearities are quantified locally and in regions of interest, showing close agreement with model data.     

Single beam Z-scan measurement of the third order optical nonlinearities of styryl7 dye

The optical nonlinearity of styryl7 dye in ethanol solution at different concentrations has been studied using pulsed Nd:YAG laser at 532 nm as the source of excitation. The optical responses were characterized by measuring the intensity dependent refractive index (n₂) of the medium using the Z-scan technique. The open aperture Z-scan trace of the dye in solution displayed saturable absorption. The closed aperture Z-scan trace of the dye exhibited a negative nonlinearity. The styryl7 dye at 1 mM concentration exhibited nonlinear refractive co-efficient n₂ = −1.24 × 10⁻⁸ cm²/W, nonlinear absorption coefficient β = − 3.9 × 10⁻⁴ cm/W and real and imaginary parts of third-order nonlinear optical susceptibility χ³ = 3.26 × 10⁻⁶ esu in ethanol. These results showed that the dye has potential application in nonlinear optics.     

Formation of NiZr2 Binary Metallic Glass： Experimental and Molecular Dynamics Analyses

The local atomic structure of an amorphous NiZr2 alloy is identified by using x-ray diffraction, transmission electron microscopy, and differential scanning calorimeter. Based on the experimental results, molecular dynamics simulation is performed to investigate the glass formation of liquid NiZr2 alloy. Some relevant features of the pair correlation functions are in good agreement with those obtained by experiment. The pair analysis parameters are calculated, suggesting that there exist icosahedral ordering, four-fold symmetrical bipyramid and triangular- faced polyhedral units in the amorphous NiZr2 structure. The result is beneficial to open avenues toward the understanding of fundamental theoretical problems of glass formation of simple binary alloys.     

Depth dependence of the anomalous thermal behavior of Cu(110)

We report the results of a mirror electron microscope low energy electron diffraction (MEM-LEED) study of anomalous thermal behavior caused by enhanced thermal vibrational motion on a clean Cu(110) surface. The enhanced vibrational amplitudes cause diffracted intensities to deviate from simple Debye-Waller behavior. These deviations become apparent between 550 K and 600 K; i.e. at about 0.45 of the bulk melting temperature. Because of the finite penetration of low energy electrons, LEED intensities contain information about both surface and subsurface order. Our LEED results are analyzed to extract this information using a kinematical model in which the electron attenuation and the depth and temperature dependent vibrational amplitudes are parametrized. For a large range of model parameters, we conclude that by 850 K large anharmonic vibrations are present in several layers and at least two subsurface layers may have melted.     

Growth exponent in the Domany-Kinzel cellular automaton

Dynamic heterogeneities, i.e. the presence of molecules with different mobilities, have been established as one of the key features of the physics of supercooled liquids. Here we study in detail how the mobility of an individual molecule fluctuates with time. Our analysis is based on a time series of molecular dynamics simulations for a low molecular weight glass-former, propylene carbonate. We find that the variation of mobility with time of initially slow molecules significantly differs from that of initially fast molecules. We explicitly show the relation to the rate memory parameter which recently has been introduced to quantify the mobility fluctuations as observed via multidimensional NMR experiments. In this way qualitative agreement between simulation and experiment can be established although the time scales of simulation and NMR experiment differ by many orders of magnitude. Received 10 April 2000 and Received in final form 21 September 2000     

Experimental study of the origin of the second-order nonlinearities induced in thermally poled fused silica

Second-harmonic generation (SHG) experiments at the surfaces and in the volumes of thermally poled commercial fused-silica samples have been performed. The experimental results show, for the first time to our knowledge and in agreement with our model, that second-order nonlinearity is induced on both cathodic and anodic interfaces. No contribution from the bulk of the sample could be detected. Moreover, our data also reveal that reorientable moieties are at the origin of the induced nonlinearity. The second-order susceptibility, evaluated by a surface SHG experiment, is chi((2))(333)~1 pm/V . The estimated susceptibility associated with the dc Kerr effect is negligible.     

基于弱非线性实现非破坏性测量两光子Bell态及三光子Greenberger-Horne-Zeilinger态

基于弱非线性及线性光学元件提出非破坏性测量两光子Bell态及三光子 Greenberger-Horne-Zeilinger (GHZ)态方案. 方案中, 首先应用光束分束器及交叉克尔非线性介质对两光子Bell态进行对称性分析, 进而结合控制非门提出三光子分析方案实现对八个三光子GHZ态完全且非破坏性区分. 关键词： Bell态测量 Greenberger-Horne-Zeilinger态测量 弱非线性 量子非破坏性测量     

Experimental verification of focus tailoring using circularly polarized vortex beams with annular pupil mask

The focusing properties of circularly polarized vortex beam are experimentally verified by examining two-photon fluorescent emission patterns inside an fluorescent microsphere. Very good agreements between the experimental and theoretical results have been obtained. Annular pupil masks are used to tailor the profile at the focus. When an circularly polarized beam with the appropriate handedness is used in combination with an annular pupil aperture, a strong longitudinal component is observed, which results in a raised center and a smaller focal spot. This interesting focusing property can be utilized in applications that require a distinct longitudinal component.