Long time-base observations of surf noise

A year of surf noise observations in the very near shore region of La Jolla Shores beach are presented. Ambient sound levels and surface wave height were recorded for 9 min every hour from July 1997 through June 1998 at a monitoring station located 360 m seaward of the beach in 8-m deep water. Sound segments that were dominated by the noise from breaking surf formed the basis of a correlation analysis between surf noise level and wave height, wave period, wind speed, and mean water depth. The analysis shows that surf noise is primarily determined by wave height, and scales approximately with the wave height squared. The surface wave energy flux onto the beach also scales with wave height squared, leading to the conclusion that the conversion of the mechanical energy of the surface wave field into noise energy is approximately constant. In fact, the ratio of noise energy to surface wave energy flux varies by up to a factor of 3 over the range of energy fluxes considered (100-3000 W per m).     

利用海浪噪声自相关实现散射体无源探测

提出了一种利用海浪噪声自相关实现散射体无源探测的新方法.将各接收器记录噪声信号的自相关减去所有接收器记录噪声信号自相关的平均值,得到散射信号的到达结构,然后结合基尔霍夫移位算法实现对散射体的探测.与利用背景噪声互相关提取格林函数从而实现散射体探测的方法不同,自相关无需考虑各个接收器之间的大量数据传输及时间同步问题,这为相距较远的多接收器和移动平台目标探测提供了极大的方便.将所提出的方法应用于实验数据中,最终探测结果与实际测量结果相比差别不大,验证了方法的有效性.     

不同叶轮形式下离心泵噪声特性对比研究

针对具有无短叶片和有短叶片两种叶轮形式的离心泵,对设计状态下离心泵内部流场进行了全三维、非定常数值模拟,对比分析了其非定常流场特性和噪声辐射特性。流场分析表明:叶轮叶片和蜗舌的相互作用造成了叶片表面强烈的压力脉动,对长短叶片的叶轮形式,在局部增加长叶片表面压力脉动的同时,短叶片表面的压力脉动保持较低水平;同时能够有效降低泵体进口压力脉动,但出口压力脉动有所增强。以叶轮叶片表面作为声源辐射面,对比分析了两种叶轮的偶极子噪声辐射特性,结果表明:长短叶片结构通过改变声能在频域上的分布,从而能有效降低总声压级。     

Ambient noise near the sea-route

Ambient noise data measured in an experiment conducted in shallow water near a sea-route were analyzed. It was observed that, at low frequency, the horizontal correlation has an obvious difference from that predicted by the classical ambient noise model. The theoretical analyses show that this phenomenon is caused by wind noise together with the discrete shipping noise nearby. An ambient noise model was proposed to include the effects caused by both the noise sources. Data measured at different times verify that the proposed model can be used to forecast the ambient noise field in shallow water near the sea-route. Supported by the National Natural Science Foundation of China (Grant No. 10734100), the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX1-YW-12-2), the National Basic Research Program of China (Grant No. 2007CB209603), and the Open Foundation of China National Petroleum Corporation Key Laboratory (Grant No. GPKL0804)     

Underwater radiated noise from modern commercial ships

Underwater radiated noise measurements for seven types of modern commercial ships during normal operating conditions are presented. Calibrated acoustic data (<1000 Hz) from an autonomous seafloor-mounted acoustic recorder were combined with ship passage information from the Automatic Identification System. This approach allowed for detailed measurements (i.e., source level, sound exposure level, and transmission range) on ships of opportunity. A key result was different acoustic levels and spectral shapes observed from different ship-types. A 54 kGT container ship had the highest broadband source level at 188 dB re 1 μPa@1m; a 26 kGT chemical tanker had the lowest at 177 dB re 1 μPa@1m. Bulk carriers had higher source levels near 100 Hz, while container ship and tanker noise was predominantly below 40 Hz. Simple models to predict source levels of modern merchant ships as a group from particular ship characteristics (e.g., length, gross tonnage, and speed) were not possible given individual ship-type differences. Furthermore, ship noise was observed to radiate asymmetrically. Stern aspect noise levels are 5 to 10 dB higher than bow aspect noise levels. Collectively, these results emphasize the importance of including modern ship-types in quantifying shipping noise for predictive models of global, regional, and local marine environments.     

Magnetostatic field noise near metallic surfaces

We develop an effective low-frequency theory of the electromagnetic field in equilibrium with thermal objects. The aim is to compute thermal magnetic noise spectra close to metallic microstructures. We focus on the limit where the material response is characterised by the electric conductivity. At the boundary between empty space and metallic microstructures, a large jump occurs in the dielectric function which leads to a partial screening of low-frequency magnetic fields generated by thermal current fluctuations. We resolve a discrepancy between two approaches used in the past to compute magnetic field noise spectra close to microstructured materials.     

Predictions of noise disturbance near large airports

This report examines the relationship between public annoyance with aircraft noise, objective measures of the noise itself, and mediating social or psychological conditions which affect the noise-annoyance relationship.     

A model for the horizontal directionality of breaking wave noise in the surf zone

A model is presented for the horizontal directionality of the noise generated by individual breaking waves in the surf zone. The model is based on the interaction between sound radiated by ringing bubbles created in a breaking wave crest and the population of acoustically quiescent bubbles left on the seaward side of the wave in the shallow water waveguide. The effect of the quiescent bubbles is to absorb sound from all but the very ends of the breaking crest, resulting in the formation of "acoustic hot-spots." The model calculations are in good agreement with observations of the horizontal directionality of noise from individual breaking waves in the surf zone.     

Traffic noise annoyance near light controlled intersections

Four hundred noise samples were taken at varying distances from three light-controlled intersections, from which the increments in percentile level above those predicted for the equivalent free flow case were derived. No factors other than those included in the prediction method could be discerned, and linear regression of the whole sample was used to establish the relationship between the increment, $\text{ΔL}{}_{\mathrm{<mtext>n</mtext>}}$, and distance, $\text{x}\text{(m)}$, from the intersection, e.g. $\text{ΔL}{}_{10}\text{= 3·21 ? 0·01}\text{x}$. A postal social survey with 12 environmental questions was sent to 30 subjects at each of six free and six interrupted flow sites, where 18-h noise measurements were made. A 69 per cent response was obtained. The slope of the regression line between question scores and $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$ was found to differ between free and interrupted flow, but those against $\text{L}{}_{\mathrm{<mtext>50</mtext>}}$ were similar. The ‘dissatisfaction’ score and a composite ’annoyance’ score correlated well, 0·76, but ‘dissatisfaction’ gave a slightly higher score for free flow than interrupted, and ‘annoyance’ the reverse. This suggests that $\text{L}{}_{\mathrm{<mtext>50</mtext>}}$ is a useful indicator of subjective response if both free and interrupted flows are involved. However the data also supports the use of the logarithm of percentage of heavy vehicles as an indicator of dissatisfaction in the interrupted flow case.     

Effects of non-Gaussian noise near supercritical Hopf bifurcation

We have studied the effects of non-Gaussian colored noise in a chemical oscillation system, the well-known Brusselator model, in the parameter region close to the supercritical Hopf bifurcation. With the variation of the parameter q, which quantifies the deviation from Gaussian character, the signal-to-noise ratio of noise induced oscillation exhibits a bell-shaped change, indicating the presence of resonant activity. The cooperative effects of q and the correlation time τ on the performance of noise induced oscillation are also investigated. Interestingly, resonance-like behavior can be induced by either q or τ when the other parameter is properly fixed. Stochastic normal form theory is used to analyze these nontrivial effects and the simulation results are well reproduced. This work provides us comprehensive understanding of how non-Gaussian noise influences the dynamics in chemical oscillation systems.     

Non-Gaussianity dynamics of two-mode squeezed number states subject to different types of noise based on cumulant theory

We provide a measure to characterize the non-Gaussianity of phase-space function of bosonic quantum states based on the cumulant theory. We study the non-Gaussianity dynamics of two-mode squeezed number states by analyzing the phase-averaged kurtosis for two different models of decoherence: amplitude damping model and phase damping model.For the amplitude damping model, the non-Gaussianity is very fragile and completely vanishes at a finite time. For the phase damping model, such states exhibit rich non-Gaussian characters. In particular, we obtain a transition time that such states can transform from sub-Gaussianity into super-Gaussianity during the evolution. Finally, we compare our measure with the existing measures of non-Gaussianity under the independent dephasing environment.     

Skyrmions of different types

We suggest two models of skyrmions. In one of them the vector mesonsZ ⁰ andW ^± may stabilize the skyrmion formed by Higgs bosons. In another the skyrmion is composed of three preons via the interaction with the Higgs bosons.     

用声场空间变换识别水下噪声源

本文提出利用声场空间变换技术进行噪声源的分离与识别。     

Shot noise measurements in a wide-channel transistor near pinch-off

We study a shot noise of a wide channel gated high-frequency transistor at a temperature of 4.2 K near pinch-off. In this regime, a transition from the metallic to the insulating state is expected to occur, accompanied by the increase in the partition noise. The dependence of the noise spectral density on current is found to be slightly nonlinear. At low currents, the differential Fano factor is enhanced compared to the universal value 1/3 for metallic diffusive conductors. We explain this result by the effect of thermal fluctuations in a nonlinear regime near pinch-off, without calling for the enhanced partition noise.     

Underwater moving noise source identification based on hybrid near-field acoustical holography

Near-field acoustical holography (NAH) is a powerful tool for identifying noise sources and visualizing acoustic field. By recording the acoustic pressures in the near-field, the acoustic quantities in the whole 3-D field can be reconstructed and predicted. However, the current theory of NAH is not applicable to tracking large scale moving noise sources. Therefore, the hybrid near-field acoustical holography is developed for reconstructing acoustic radiation, which is derived from statistically optimized ne...     

Sound scattering by bubble clouds near the sea surface

The classical exact formulation required to evaluate the form function (or the scattering cross-section, SCS) of a single, ideal, air bubble in a boundless liquid is briefly recalled. It is then immediately generalized to the case of a round cloud of many possibly interacting such bubbles of known volume concentration, contained within the same boundless medium. This is further generalized to the case when the bubble cloud is near a free surface. The presence of the nearby pressure release surface, assumed flat, substantially alters the cloud's scattering cross-section relative to its value in the absence of boundaries. We then use an earlier technique of ours [i.e., see I.E.E.E. J. Ocean. Eng. 20, 285-293 (1995)] based on the method of images that uses the addition theorem for the spherical wave functions, to relate all the scattered sound fields to a common origin and thus obtain the (modified) SCS of the cloud now near the boundary. This formulation accounts for all orders of multiple scattering and yields an infinite set of coupled algebraic equations for the coupling coefficients. This set is then solved for the coupling coefficients in terms of infinite sums of products of pairs of Wigner 3-j symbols, which are then used to construct and evaluate the form function. We display numerical results in four cases that correspond to geographical sites in which the bubble concentrations within the cloud have been measured along a couple of oblique upward directions, or have been assumed to have increasing (and in a few instances, purposely unrealistically high) values. In all cases considered here the bubble clouds are only a few meters beneath the sea surface and consist of ideal bubbles. The results are also compared to those found in the absence of a boundary in all the cases considered.     

Vector-scalar noise fields formed by an excited sea surface

Vector-scalar noise fields in a waveguide were studied using computer simulation. A stochastic model of dynamic acoustic noise was used in the calculations. Noise field parameters on a single vector-scalar module and spatial correlation functions on vector-scalar arrays in a homogeneous waveguide were analyzed. Calculations were performed for vertically and horizontally located arrays. It was shown that the vector-scalar noise field characteristics depend on the bottom parameters and the state of the ocean surface due to the wind force. The calculation results can be used to predict the characteristics of detection and direction finding of signal sources for vector-scalar arrays working in a waveguide against the background of sea noise.