A practical prediction method for the stochastic insulation effect of a sound barrier with arbitrary random noise excitation

A sound barrier is often used as a typical noise control device to modify sound propagation characteristics. Also, statistical parameters such as the median value of sound level, $\text{L}{}_{\mathrm{x}}$, as well as the lower order statistical values of sound energy or level, are important for noise evaluation and regulation problems. In this paper, a new trial of statistical prediction for the stochastic insulation effect of a sound barrier is proposed in a special case where the insulation system parameters have to be improved, especially from a methodological viewpoint. Moreover, the improved probability density function (pdf) of output response corresponding to the above parameter change is expressed in the general form of a statistical series expansion taking the original pdf before the system improvement as the first expansion term. The experimental results of applying it in trial to the actual noise data are in good agreement with theory.     

水下隔声结构设计及评价方法

为使用混响法快捷地测量水下结构物的辐射噪声,需基于港口或海岸建造海上混响水池。针对内外都是水情况下的海上混响水池壁面隔声问题,设计了一种带梁空气夹层板水下隔声结构,通过仿真比较了不同参数的空气夹层板的隔声性能。为评价声波无规入射情况下水下大尺寸隔声结构隔声性能,提出了一种混响评价方法,通过隔声实验比较了混响法与脉冲法的不同。结果表明：带梁空气夹层板的水下隔声性能优异,声波无规入射情况下,面板厚度0.015 m、空气层厚度0.020 m的带梁空气夹层板在2～10 kHz频段插入损失大于20 dB;混响法可以有效评价大尺寸水下隔声结构的平均隔声性能,其反映的声波无规入射的平均隔声性能更接近于实际应用情况。     

一种时间序列的弱非线性检验方法

时间序列的非线性是判定该时间序列具有混沌特性的必要条件.提出一种基于线性和非线性AR模型归一化多步预测误差比值的非线性检验量δ_NAR,采用替代数据法来检测时间序列中的弱非线性.以Lorenz时间序列为例,分析了估计非线性检验量δ_NAR时各相关参数对弱非线性检测性能的影响.通过混沌时间序列非线性检测试验,对4种混沌时间序列中的3种,非线性检验量δ_NAR都表现出比基于AIC模型选择准则的非线性检验量相似文献   

Determination of uncertainty in environmental noise measurements by bootstrap method

An effective method for real-time evaluation of confidence intervals associated to quantile (L_q) and equivalent (L_eq) levels in environmental noise measurements is presented. The non-parametric surrogate data (or bootstrap) method, is described here in its basic form, valid for independent and identically distributed data, but is readily extendible to the treatment of dependent data. Application to actual measurements are shown which illustrate the practical effectiveness of real-time error evaluation during environmental monitoring.     

Adaptive nonlinear neuro-controller with an integrated evaluation algorithm for nonlinear active noise systems

An adaptive nonlinear neuro-controller with an integrated evaluation algorithm for nonlinear active noise control systems is proposed to attenuate the nonlinear and non-Gaussian noises. Inspired by the structure of the Hammerstein or Wiener model, the proposed controller is realized by the static nonlinear memory function mapping on the basis of a single neuron. A generalized filtered-X gradient descent algorithm based on an integrated evaluation criterion is developed to adaptively adjust the weights of the controller, where the weighted sum of Renyi's quadratic error entropy and the mean square error is applied as the integrated performance index, which improves the performance of the adaptive algorithm by introducing the information entropy. In addition, the convergence of the proposed approach is analyzed, and the computational complexity among different methods is investigated. The proposed scheme can effectively attenuate the nonlinear and non-Gaussian noises and has a relative simple structure and less learning parameters. The simulation results demonstrate the validity of the proposed method for attenuating the nonlinear and non-Gaussian noises.     

Feasibility of similarity coefficient map in improving morphological evaluation of T2* weighted MRI for renal cancer

The purpose of this paper is to investigate the feasibility of similarity coefficient map (SCM) in improving morphological evaluation of T₂^* weighted (T₂^*W) magnatic resonance imaging (MRI) for renal cancer. Simulation studies and in vivo 12-echo T₂^*W experiments for renal cancers were performed for this purpose. The results of the first simulation study suggest that SCM can reveal small structures which are hard to be distinguished from the background tissue in T₂^*W images and the corresponding T₂^* map. The capability of improving morphological evaluation is likely due to the improvement in signal to noise ratio (SNR) and carrier to noise ratio (CNR) by SCM technique. Compared with T₂^*W images, SCM can improve SNR by a factor ranging from 1.87 to 2.47. Compared with T₂^* maps, SCM can improve SNR by a factor ranging from 3.85 to 33.31. Compared with T₂^*W images, SCM can improve CNR by a factor raging from 2.09 to 2.43. Compared with T₂^* maps SCM can improve CNR by a factor raging from 1.94 to 8.14. For a given noise level, the improvements of SNR and CNR depend mainly on the original SNRs and CNRs in T₂^*W images, respectively. In vivo experiments confirmed the results of the first simulation study. The results of the second simulation study suggest that more echoes are used to generate SCM, and higher SNR and CNR can be achieved in SCM. In conclusion, SCM can provide improved morphological evaluation of T₂^*W MR images for renal cancer by unveiling fine structures which are ambiguous or invisible in the corresponding T₂^*W MR images and T₂^* maps. What is more, in practical application, for a fixed total sampling time, one should increase the number of echoes as much as possible to achieve SCMs with better SNR and CNR.     

Choosing the ranges for measuring the reflectivity of a prism coupler in the waveguide spectroscopy of thin films

A criterion for selecting the best ranges for measuring the reflectivity of a prism coupler, based on minimizing the error in reconstructing the parameters of thin films using the least-square method, is proposed. The effectiveness of the criterion is demonstrated by solving the inverse optical problem for a SiO_x film deposited on a silicon substrate as an example.     

Pitfalls in the Measurement of Metabolite Concentrations Using the One-Pulse Experiment in in Vivo NMR: Commentary on “On Neglecting Chemical Exchange Effects When Correcting in VivoP MRS Data for Partial Saturation”

In an article in a previous issue of the Journal of Magnetic Resonance, Ouwerkerk and Bottomley (J. Magn. Reson.148, pp. 425–435, 2001) show that even in the presence of chemical exchange, the dependence of saturation factors on repetition time in the one-pulse experiment is approximately monoexponential. They conclude from this fact that the effect of chemical exchange on the use of saturation factors when correcting for partial saturation is negligible. We take issue with this conclusion and demonstrate that because saturation factors in the presence of chemical exchange are strongly dependent upon all of the chemical parameters of the system, that is, upon all T₁'s and M₀'s of resonances in the exchange network and upon the reaction rates themselves, it is problematic to apply saturation factor corrections in situations in which any of these parameters may change. The error criterion we establish reflects actual errors in quantitation, rather than departures from monoexponentiality.     

A high-precision optical metrology system for determining the thickness of birefringent wave plates

This study develops a non-destructive measurement system for determining the thickness and refractive indices of birefringent optical wave plates. Compared to previous methods presented in the literature, the proposed metrology system provides the ability to measure the thickness of the birefringent optical plate in high-precision. The results show that for a commercially available birefringent optical wave plate with refractive indices of n_e=1.5518, n₀=1.5427 and a thickness of 452.1428 μm, the experimentally determined value for the error in the wave plate thickness measurement is just 0.046 μm. The measurement resolution of the proposed system exceeds that of the interferometer hardware itself. The proposed method provides a simple yet highly accurate means of measuring the principal optical parameters of birefringent glass wave plates.     

Sound velocity in La0.5Ca0.5MnO3

In this Letter the microscopic theory of the relative change in velocity of sound with temperature of La_0.5Ca_0.5MnO₃ is reported. The phonon Green function is calculated using the Green function technique of Zubarev in the limit of zero wave vector and low temperature. The lattice model electronic Hamiltonian in the presence of the phonon interaction with hybridization between the conduction electrons and the l-electrons is used. The relative change in velocity of sound at various temperatures is studied for different model parameters namely the position of the l-level, the effective phonon coupling strength and hybridization strength. The phonon anomalies observed experimentally at different temperatures are explained theoretically. An abrupt change in velocity at Neel temperature (TN) is observed clearly. It is observed that different parameters influence the velocity of sound.     

A comparative study of different numerical models for predicting train noise in high-rise cities

Large-scale outdoor field measurements were carried out on a residential building to assess the noise levels caused by pass-by trains that run on a nearby viaduct. The experimental results were compared with different schemes for predicting noise from trains. The octave band sound power levels of the train passing by, which are required as input parameters for the Nordic prediction method for train noise (NMT), CSTB 92 and ISO 9613-2 provided in the Mithra software, were determined by an inversion method. The method of calculation of railway noise (CRN) from the UK gives the best agreement with the measured results. The NMT prediction scheme also provides a good prediction of the general trend of the experimental data, but it always overestimates the measured noise levels. As far as the quantitative agreement with experimental data is concerned, the CSTB 92 and ISO 9613-2 prediction schemes are comparatively less satisfactory.     

Electron-phonon coupling and longitudinal sound velocity of La0.5Ca0.5MnO3

In this paper, the microscopic theory of the relative change in velocity of sound with temperature of La_0.5Ca_0.5MnO₃ is reported. The phonon Green function is calculated using the Green function technique of Zubarev in the limit of zero wave vector and low temperature. The lattice model electronic Hamiltonian in the presence of the phonon interaction with hybridization between the conduction electrons and the l-electrons is used. The relative change in velocity of sound at various temperatures is studied for different model parameters, namely the position of the l-level, the effective phonon coupling strength and hybridization strength. The phonon anomalies observed experimentally at different temperatures are explained theoretically. An abrupt change in velocity at Neel temperature (T_N) is observed clearly. It is observed that different parameters influence the velocity of sound.     

Elastic properties of mono- and poly-crystalline PbO-type FeSe1−xTex (x = 0–1.0): A first-principles study

The structural parameters of the alloys are obtained as non-magnetic cases for which justification is provided. The elastic coefficients and various moduli of the monocrystalline FeSe_1−xTe_x system as a function of doping are predicted for the first time using density functional method. The bulk moduli, shear moduli, Young’s moduli, Poisson’s ratios, velocities of sound and Debye temperature of the corresponding poly-crystalline aggregates have been calculated and the results discussed.     

Equivalent magnetic noise in magnetoelectric Metglas/Pb(Mg1/3Nb2/3)O3‐PbTiO3 laminate composites

We have experimentally and theoretically investigated the equivalent magnetic noise in a magnetoelectric Metglas/ 0.7Pb(Mg_1/3Nb_2/3)O₃‐0.3PbTiO₃ laminate sensor unit by considering the constituent noise sources of dielectric loss (N_DE) and DC leakage resistance (N_R). In the low frequency range (f = 1 Hz), theory predicts that N_R dominates the noise charge (1.6 times larger than N_DE), with a 1 Hz noise of 9.1\;{\rm pt}/\sqrt {\rm Hz}. The experimental equivalent magnetic noise was 10.8\;{\rm pt}/\sqrt {\rm Hz}. This observed value is slightly higher than the predicted one, which might be due to an oversimplification of the theoretical model in terms of electrical charge amplifier and external vibration noise sources. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectral/hp least-squares finite element formulation for the Navier–Stokes equations

We consider the application of least-squares finite element models combined with spectral/hp methods for the numerical solution of viscous flow problems. The paper presents the formulation, validation, and application of a spectral/hp algorithm to the numerical solution of the Navier–Stokes equations governing two- and three-dimensional stationary incompressible and low-speed compressible flows. The Navier–Stokes equations are expressed as an equivalent set of first-order equations by introducing vorticity or velocity gradients as additional independent variables and the least-squares method is used to develop the finite element model. High-order element expansions are used to construct the discrete model. The discrete model thus obtained is linearized by Newton’s method, resulting in a linear system of equations with a symmetric positive definite coefficient matrix that is solved in a fully coupled manner by a preconditioned conjugate gradient method. Spectral convergence of the L₂ least-squares functional and L₂ error norms is verified using smooth solutions to the two-dimensional stationary Poisson and incompressible Navier–Stokes equations. Numerical results for flow over a backward-facing step, steady flow past a circular cylinder, three-dimensional lid-driven cavity flow, and compressible buoyant flow inside a square enclosure are presented to demonstrate the predictive capability and robustness of the proposed formulation.     

A new method for deriving atomic charges and dipoles for n, -alkanes: investigation of transferability and geometry dependence

Atomic charge models are known to be unsatisfactory for representing the ab initio electrostatic potential (ESP) of n, -alkanes. A new method for deriving atomic charges and dipoles is proposed and applied to n-alkanes ranging from C₄ to C₁₀. Electrostatic parameters found by this method reproduce accurately the ab initio ESP. The issues of transferability and conformational dependence are also addressed by introducing charges and dipoles taken from a truncated distributed multipole analysis, in the same spirit as the restrained electrostatic potential method. A transferable model is proposed for larger alkanes (>C₁₀). We also estimate the error made when using a set of Boltzmann-weighted electrostatic parameters for all conformers. The reduced number of electrostatic sites considered in our model makes it suitable for computer simulation of liquid n-alkanes.     

SEA and contribution analysis for interior noise of a high speed train

This paper presents a detailed Statistical Energy Analysis (SEA) and contribution analysis of the interior noise of a high-speed train through extensive simulations and measurements. The SEA model was developed based on the actual geometrical parameters of a benchmark high-speed coach. Sound transmission loss levels of the structural components of the car body, which are required in the SEA model, were tested in a dedicated acoustic laboratory following international standard ISO 140-3:1995. Modal densities of these structural components were derived from measured frequency response functions using the modal counting method. Damping loss factors were obtained using the half-power bandwidth method and the vibration attenuation method. By considering the relationship between sound radiation and power transmission, coupling loss factors between structures and cavities were estimated. Source inputs to the SEA model were derived from field experiment data. Interior noise due to those sources was predicted using the SEA model and the prediction was generally in good agreement with measurement. Contribution analysis was then performed using this validated model through parametric study, and this analysis was further examined experimentally. In conclusion, for the coach that was investigated in this paper, the key factors for interior noise are sidewall vibration, bogie area noise, and floor sound transmission loss. Based on this and other engineering considerations, an interior noise control strategy can be defined.     

Impact of aircraft sound quality combined with the repetition of aircraft flyovers on annoyance as perceived activity disturbance in a laboratory context

This study focuses on perceived activity disturbance evaluated by participants who are subjected to the repetition noise of current aircraft and modified aircraft in regard to tonal quality. A previous study devoted to the sound quality of aircraft noise revealed that one of the most important perceptive features is the emergence of Doppler shifted tones. Six 20-min sound sequences were created combining two variables: number of aircraft (N₁ with six aircraft and N₂ with 10 aircraft plus one sequence without aircraft N₀) and tonality (sequences with current aircraft, sequences with +5 dB-amplified tonality and sequences with −5 dB-attenuated tonality). For all sequences, the equivalent sound level and the peak level of the loudest event are constant, except for the sequence without aircraft. Sixty-three subjects, attending two different sequences in one session, rated on a category scale the level of activity disturbance due to the noise environment when carrying out memory and concentration tasks. The order of presentation was controlled as an additional variable in the variance analyses. The perceived activity disturbance is significantly influenced by the equivalent sound level. The influence of the number of aircraft flyovers is statistically significant at the 5% level. High tonal components have no effect on perceived disturbance. Memory and concentration performances, measured by number of incorrect or correct answers, are influenced only by the order of presentation, revealing the importance of the learning effect. Reaction time, which is influenced by the equivalent sound level, seems better adapted for measuring the effect of noise on task achievement. These results are discussed in regard to related research.     

Acoustooptic 2×2 switch for radiation with different wavelengths as an element of a fiber-optic gyroscope

Planar acoustooptic 2×2 directional couplers that switch optical rays with different wavelengths are considered. A method for calculating the angular and frequency characteristics of such switches is developed, and the parameters of a switch based on a planar Ti-LiNbO₃ structure are calculated. Experiments employing bulk acoustooptic diffraction in TeO₂ are performed, confirming the basic theoretical assumptions. It is shown experimentally that the best conditions for switching optical rays directed into optical fibers can be provided nearly always by varying the diffraction angles and the frequencies of the sound waves. The functional possibilities of the 2×2 directional coupler investigated in a fiber-optic gyroscope are described. Zh. Tekh. Fiz. 67, 57–62 (July 1997)