Modeling mode arrivals in the 1995 SWARM experiment acoustic transmissions

As part of the Shallow Water Acoustics in a Random Medium (SWARM) experiment, a 16 element WHOI vertical line array (WVLA) was moored in 70 m of water off the New Jersey coast. A 400-Hz acoustic tomography source was moored some 32-km shoreward of this array, such that an acoustic path was created that was anti-parallel to the primary propagation direction for shelf-generated internal wave solitons. The presence of these soliton internal waves in the acoustic waveguide causes significant coupling of energy between propagating acoustic modes, creating fluctuations in modal intensities and modal peak arrival times, as well as time spreading of the pulses. Two methods by which acoustic propagation and scattering in soliton-filled waveguides can be modeled are presented here in order to understand and explain the scattering observed in the SWARM field data. The first method utilizes the Preisig and Duda [IEEE J. Ocean. Eng. 22, 256-269 (1997)] Sudden Interface Approximation (SIA) to represent the solitons. The second method, which is computationally slower, uses a finely meshed, "propagated" thermistor record to simulate the solitons in the SWARM experiment waveguide. Both numerical methods are found to generate scattering characteristics that are similar to the SWARM field data.     

浅海中沉积层参数对多途到达时差反演声速剖面的影响

本文以简正波模型和声线模型为基础，通过计算机仿真，研究了浅海多途到达时延差结构与沉积层密度、声速、传播损失系数等参数的关系，针对100m左右浅海和600-1300Hz的信号频率，对两种模型仿真结果进行了比较，结果表明，声线模型仿真得到的多途到达时延差结构与简正波模型仿真的结果基本一致，沉积层参数失配对基于声线模型的多途到达时差反演SSP的影响为：反演声速剖面的均方根误差的变化小于1.45m/s，平均误差的变化小于2.60m/s，在所使用的频段内，浅海沉积层参数对多途到达时差反演浅海声速剖面的影响不大，工程应用中可以忽略不计。     

Confined quantum time of arrivals

We show that formulating the quantum time of arrival problem in a segment of the real line suggests rephrasing the quantum time of arrival problem to finding states that evolve to unitarily collapse at a given point at a definite time. For the spatially confined particle, we show that the problem admits a solution in the form of an eigenvalue problem of a compact and self-adjoint time of arrival operator derived by a quantization of the classical time of arrival, which is canonically conjugate with the Hamiltonian in a closed subspace of the Hilbert space.     

Difference approach to the analysis of resistivity recovery data for irradiated short-range ordered alloys

Electrical resistivity recovery (RR) data for irradiated concentrated alloys typically consist of two inseparable parts, one resulting from defect annihilation and the other from short-range order (SRO) effects. These parts exhibit different behaviour and often follow opposite trends. Therefore, in this case, analysis of RR data within the conventional method is too complicated. A new approach to data analysis of such a two-component RR is proposed. The approach involves a new quantity, the difference RR (DRR), which is composed of RR dependences of two similar samples irradiated to different defect concentrations. It is shown that the SRO formation proper and the stages corresponding to the onset of long-range migration of Frenkel pair defects, formed in each part of RR, can be clearly related to certain features of the DRR plots. This interrelationship allows detecting and identifying these stages in each part of RR separately. The validity of the approach is illustrated by analysis of the available pairwise RR data for Fe–16Cr–20Ni and Fe–4Cr alloys. It makes it possible to detect the small contribution from the SRO formation to RR in Fe–4Cr, which we failed to observe previously. It is shown that stage III of Fe–4Cr, which has a negligible contribution to the part of RR induced by defect annihilation, is clearly observed in the part induced by SRO formation.     

Identification of fish vocalizations from ocean acoustic data

A new method for identification of fish vocalizations based on auditory analysis and support vector machine (SVM) classification is presented. In this method, high resolution features have been extracted from fish vocalization data using the amplitude modulation spectrogram (AMS) of the input signals to facilitate the identification of grunts and growls made by a highly vocal wild fish, Porichthys notatus. The comparison results made from ocean audio recordings verify the effectiveness of the proposed method in identifying various types of fish vocalizations. The relationships between signal-to-noise ratio (SNR) and ocean temperature with the accuracy of the proposed method have also been quantified. Moreover, a context-aware prediction algorithm is introduced for estimating the continuous data.     

Cosmological implications of different baryon acoustic oscillation data

In this work, we explore the cosmological implications of different baryon acoustic oscillation(BAO) data, including the BAO data extracted by using the spherically averaged one-dimensional galaxy clustering(GC) statistics(hereafter BAO1) and the BAO data obtained by using the anisotropic two-dimensional GC statistics(hereafter BAO2). To make a comparison, we also take into account the case without BAO data(hereafter NO BAO). Firstly, making use of these BAO data, as well as the SNLS3 type Ia supernovae sample and the Planck distance priors data, we give the cosmological constraints of the ΛCDM, the w CDM, and the Chevallier-Polarski-Linder(CPL) model. Then, we discuss the impacts of different BAO data on cosmological consquences, including its effects on parameter space, equation of state(Eo S), figure of merit(Fo M), deceleration-acceleration transition redshift,Hubble parameter H(z), deceleration parameter q(z), statefinder hierarchy S_3(1)(z), S_4(1)(z) and cosmic age t(z). We find that:(1)NO BAO data always give a smallest fractional matter density ?_(m0), a largest fractional curvature density ?k0and a largest Hubble constant h; in contrast, BAO1 data always give a largest ?_(m0), a smallest ?_(k0) and a smallest h.(2) For the w CDM and the CPL model, NO BAO data always give a largest Eo S w; in contrast, BAO2 data always give a smallest w.(3) Compared with the case of BAO1, BAO2 data always give a slightly larger Fo M, and thus can give a cosmological constraint with a slightly better accuracy.(4) The impacts of different BAO data on the cosmic evolution and the comic age are very small, and cannot be distinguished by using various dark energy diagnoses and the cosmic age data.     

Overtone singing: Productive mechanisms and acoustic data

Overtone singing is where one person sings in two voices, the first voice represented by the fundamental and the second by an enhanced harmonic. Overtone singing is performed in chest register. Tuning of the first or second formant and a reduction of the formant bandwidth down to 20 Hz make harmonics prominent. Narrowing the pharynx, velar constriction, variation of the small mouth opening, and a tension of the walls of the mouth cavity are used. Changing prominent harmonics has the effect of creating an overtone melody with sustained tones, tone steps, and trillos.     

Vibration and acoustic data for a punch press

Mode shape, radiation ratio and damping data obtained from pure tone vibration shaker tests on a 170 kN mechanical C frame punch press are presented in this paper. The experimental results show the value of the radiation ratio to be very dependent upon the structure for frequencies below 1 kHz. Above this frequency the assumption of unity for the radiation ratio can be made. Values of the damping ratio are of the order of 0·01 for the modes which have been defined; however, data from blanking operations show that this value can increase by a factor of two to three.     

Some experimental data for the design of acoustic arrays

The frequency spectra of resonant vibration of a PZT4 piezoelectric plate was observed, for width-to-thickness ratios ranging from 0·3 to 4·0. The results give useful information for the design of line arrays applicable, for example, to medical diagnostic sonars. The effect of backing and impedance matching on PZT4 ceramic slabs was also studied experimentally.     

Fluctuating magnetic fields

Some problems pertaining to the behaviour of a classical spin under the influence of a random Gaussian magnetic field are discussed. It is shown that, in agreement with simple expectations, the magnetic moment is effectively decreased to lowest order. Various physical applications and connections with group theory are pointed out.     

The short-range nucleon-nucleon repulsion

The short-range repulsion (0.2–0.4 fm) between nucleons is investigated. The opposing effects of ω-meson exchange and ε-meson (J^p = 0⁺) exchange are investigated, and the relation to Regge behaviour is demonstrated using fixed-s dispersion relations. The energy dependence of the short-range interaction is emphasized, and experimental data on polarization in elastic NN scattering at high energy are used to give the necessary coupling constant.     

Interpretation of multi-frequency acoustic data: effects of fish orientation

One goal of fisheries acoustics is to develop objective classification or identification methods to automate allocation of acoustic backscatter to species. Classification schemes rely on consistent relationships for successful apportionment of acoustic backscatter to species. A method is developed that compares frequency-dependent volume backscatter from an acoustical survey of Atlantic herring (Clupea harengus) to investigate the potential for classifying herring. Predicted backscattering patterns by a Kirchhoff-ray approximation are used to explain the observed relationships and evaluate the potential for classification of multi-frequency data. Combining predicted backscatter with observations of the frequency-dependent volume backscatter gave approximately 40% classification success, which is not sufficient for survey purposes. However, this method highlighted potential consequences that fish orientation may have on classification schemes and density and abundance estimates. This method of comparing multi-frequency volume backscatter appears to be beneficial for detecting behavioral changes by groups of fish, which may be used to select target strength values for density or abundance estimates. Utilizing predicted target strengths from numerical or analytical solutions or approximations, appropriate target strengths could be selected and would provide more accurate estimates of fish density and abundance.     

Emission of underwater acoustic orbital angular momentum and data transmission

Emission of underwater acoustic orbital angular momentum(OAM) is studied as well as underwater acoustic communications with OAM multiplexing. Theoretical acoustic properties for circular phased array are analyzed based on point source theory. We optimize and design an array prototype based on cymbal transducer. The diameter of array prototype is 180 mm, the number of array elements is 10, and the working frequency is 25 k Hz. It emits acoustic OAM with topological charges-3 to 3. The favorable results provide the theoretical basis for emitting acoustic OAM with different topological charges. We encode on-off states of acoustic OAM with different topological charges according to ASCII code to realize underwater acoustic communications. The transmission results suggest that acoustic OAM with various topological charges have intrinsically orthogonal properties. This research will offer potential applications in underwater acoustic communications.     

声轨道角动量水下发射与数据传输实验

研究了声轨道角动量水下发射技术与多路复用的水下数据传输,基于点源理论推导了相控圆周阵列发射声轨道角动量的基本原理,分析了干扰项的阶数成分及干扰项对主项的影响,优化设计了基于Cymbal换能器的阵列样机,阵列样机直径为Φ180 mm,阵元数为10元,工作频率为25 kHz,通过对阵列阵元的相位调控实现了-3至3六阶声轨道角动量的发射,验证了基于相控原理实现不同拓扑荷数声轨道角动量发射的理论。通过利用各阶声轨道角动量的开关状态进行数据编码,进行了基于声轨道角动量多路复用的水下数据传输实验,实验结果表明,不同拓扑荷数的声轨道角动量具有良好的正交性质,可以利用基于声轨道角动量的多路复用技术实现水下数据传输功能。     

Fluctuating forces in plasmadynamics

Using the concept of the Vlasov-Landau-Langevin equation we discuss the structure of fluctuating forces á la Landau and Lifshitz in plasmadynamical equations for weakly coupled one component plasma. Explicit expressions for stress tensor and heat current vector components correlation functions are derived displaying non-markovian behaviour.     

Fluctuating field near spinodal

Phase ordering kinetics with a non-conserved scalar order parameter is studied near a lability boundary of a first-order phase transition. A large-scale structure of this field is found to appear. Under some conditions it is analogous to a fractal structure in the critical region of a second-order transition. The chains and localized groups of new phase nuclei are generated by the maxima of the order parameter density. The results are compared with fluctuation inducing of continuous phase transitions predicted in the framework of the renormalization group (RG) approach.     

Characterization of a cylindrical rod by inversion of acoustic scattering data

In this paper, a new approach is proposed for nondestructive characterization of immersed and embedded isotropic rod-shaped samples by inversion of acoustic scattering data. The normal mode expansion technique is used for modelling the scattered field and the compression incident and compression scattered waves are considered. Genetic algorithm is the inversion technique used for estimating the elastic wave velocities and density of the rods from their measured backscattered pressure spectrum. The inversion technique is capable of computing the parameter values that best fit a particular set of data. A perturbation study is conducted on the sensitivity of the resonance frequencies to changes in elastic properties and density of the rods. The numerical results indicate that proper selection of resonance frequencies leads to accurate measurement of elastic constants and density. The proposed approach showed very good convergence and the results obtained were found to agree very well with available data.