The problem of coherent reflecton of an acoustic plane wave from a random seabed consisting of a randomly inhomogeneous sediment layer overlying a uniform elastic sea floor is considered in this analysis. The random perturbation in the sediment layer is attributable to the sound-speed variations, resulting in volume scattering due to medium inhomogenieties. An approach based upon perturbation theory, combining with a derived Green's function for a slab bounded above and below respectively by a fluid and an elastic half space ,is employed to obtain an analytic solution for the coherent field in the sediment layer. A linear system is then constructed to facilitate the analysis of the coherent reflection field. The results of the coherent reflection coefficient for various sediment randomness, frequency , sediment thickness, and sea floor elasticity have been numerically generated and analyzed. It was found that the higher/larger size of randomness , frequency, thickness, and shear-wave speed, the lower the coherent reflection. Physical interpretation for the characteristics of various results were provided.

Push-pull charge-transfer organic molecules exhibit large second-order nonlinear optical nonlinearity , and have been used to manufacture efficient photonic devices .We study a series of CT molecules by using the two-photon scattering method with a tunable femto-second pulsed-laser to obtain the value of the molecular first hyperpolarizability (£]) .We discuss the relationship between the£]value and chemical structure , and compare the£]values with the two-level model prediction for several incident laser excitation wavelength.

A Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) was used to measure size distributions, hygroscopicity, and volatility during the May 2003 Aerosol Intensive Operational Period at the Central Facility of the Atmospheric Radiation Measurement Southern Great Plains site. Hygroscopic growth factor distributions for particles at eight dry diameters ranging from 0.012 µm to 0.600 µm were measured. These measurements, along with backtrajectory clustering, were used to infer aerosol composition and evolution. The hygroscopic growth of the smallest and largest particles analyzed was typically less than that of particles with dry diameters of about 0.100 µm. Condensation of secondary organic aerosol on nucleation mode particles may be responsible for the minimal growth observed at the smallest sizes. Growth factor distributions of the largest particles typically contained a non-hygroscopic mode believed to be composed of dust. A model was developed to characterize the hygroscopic properties of particles within a size distribution mode through analysis of the fixed-size hygroscopic growth measurements. This model was used to examine three cases in which the sampled aerosol evolved over a period of hours or days. Additionally, size and hygroscopicity information were combined to model the aerosol as a population of multi-component particles. With this model, the aerosol hygroscopic growth factor f(RH), relating the submicron scattering at high RH to that at low RH, is predicted. The f(RH) values predicted when the hygroscopic fraction of the aerosol is assumed to be metastable agree better with measurements than do those predicted under the assumption of crystalline aerosol. Agreement decreases at RH greater than 65%. This multi-component aerosol model is used to derive cloud condensation nuclei (CCN) spectra for comparison with spectra measured directly with two Desert Research Institute (DRI) CCN spectrometers. Among the 1490 pairs of DMA/TDMA-predicted and DRI-measured CCN concentrations at various critical supersaturations from 0.02-1.05%, the sample number-weighted mean R2 value is 0.74. CCN concentrations are slightly overpredicted at both the lowest (0.02-0.04%) and highest (0.80-1.05%) supersaturations measured. Overall, this multi-component aerosol model based on size distributions and size-resolved hygroscopicity yields reasonable predictions of the humidity-dependent optical properties and CCN spectra of the aerosol.

This thesis intends to design a set of acoustics measurement system, it can measure the rough surface to have the scattering influence regarding the sound wave. And this set of acoustics measurement system will be able to provide the rough surface establishment function, acoustics measurement precise pinpointing for position and rough surface accurate shape data. Establishing the main environment take the Institute of Undersea Technology large experiment water tank as the system. The experiment water tank sets up XYZ table which can control the three translation directions migration. Because this experiment needs five degrees-of-freedom except for three translation directions migration and also has two axes rotary motion. In order to measure scattering field so we need to design the rotary mechanism for two axes that enables the microphone to achieve themovements in five degrees-of-freedom. In this experiment has to conformity themeasurement of laser system¡¦s rough surface position, the position of microphone shooting and receiving point, and establishes scraper position which rough surface used. In order to compare the scattering state of the shape of rough surface and the soundwave beats the rough surface after we integrate all the information, we can realize where directional sound wave beats and what¡¦s the shape of this rough surface. Except for conformity position, this equipment¡¦s localization is all by the programcontrolmotor. It can save time in adjusting position for experimenter in an effective way and itmay abridge the experiment time effectively.

Acoustic methods have long been used to rapidly and synoptically survey marine organisms of ecological and economic importance. Direct sampling furnishes biological data such as abundance, biomass, direct measurements of organism size and species identification, but encounters problems such as net avoidance, small sampling volumes, and catch destruction of delicate specimens. Understanding the scattering mechanisms of fish is challenge due to the fact that fish anatomy is complex and the acoustic scattering characteristics are correspondingly complex. For example, (Nash,1987) qualitatively illustrated the influence of the various anatomical components of fish on scattering by performing length-wise acoustic scans of whole fish, dissected swimbladders. The swimbladder is the main control factor of fish¡¦s floating and diving. This research will carry on the measure the target with acoustic characteristic of imitative air swimbladder of Tsuchida Seisakusho. We use the imitative air swimbladder and collocate the Reversed Engineering to measure the Backscattering intensity of the swimbldder which is different medium. We set up experiment in an acoustic water tank of dimension (4mo3.5mo2m) located in National Sun Yat-sen University. The projector and receiver both are transducer of fish finder with directivity and frequency response at 200k Hz. The signal receptor used Data Acquisition System of NI 6129 with sample rate at 800kHz. The target set up of this research is referring to (Timothy K. Stanton,2004), and we use servo motor to control the incidence angle of the target. Preliminary research is pointed out, the target strength will change by the incidence geometry of the target, and the target diameter is the factor of the target strength.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes bibliographical references and vita.

Thesis (Ph.D.)--York University, 2007. Graduate Programme in Physics and Astronomy. / Typescript. Includes bibliographical references (leaves 224-234). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR39044

Thesis (Ph. D.)--Lehigh University, 2001. / Includes vita. Includes bibliographical references (leaves 103-108).

Thesis (Ph. D.)--University of Hong Kong, 1988.

In this thesis, a detailed description of acoustic cloaking is put forth using a coating consisting of discrete layers, enabling the cancellation of the scattered field around the object. This particular approach has previously only been applied to electromagnetic waves, for which it was observed that cloaking could be achieved using isotropic materials over a finite bandwidth. The analysis begins with a presentation of the theoretical formulation, which is developed using classical scattering theory for the scattered acoustic field of an isotropic sphere coated with multiple layers. Unlike previous works on acoustic scattering from spherical bodies, the criteria for acoustic cloaking is that the scattered field in the surrounding medium be equal to zero, and seeking a solution for the layer properties which achieve this condition. To effectively investigate this situation, approximate solutions are obtained by assuming either quasi-static limits or thin shells, which provide valuable insight into the fundamental nature of the scattering cancellation. In addition, using these approximate solutions as a guide, exact numerical solutions can be obtained, enabling the full dynamics of the parameter space to be evaluated. Based on this analysis, two distinct types of acoustic cloaking were found: a plasmonic cloak and an anti-resonance cloak. The plasmonic cloak is a non-resonant type of cloak, named plasmonic because of its analogous behavior to the non-resonant cloak observed in electromagnetic waves which utilizes plasmonic materials to achieve the necessary properties. Due to the non-resonant behavior, this type of cloak offers the possibility of a much broader range of cloaking. To expand this design beyond wavelengths on the order of the uncloaked scatterer, multilayered cloak designs are investigated. The anti-resonance cloak, as the name suggests, uses the anti-resonances of the modes within the cloaking layer to supplement the non-resonant plasmonic cloaking of the scattered field. Although somewhat more limited in bandwidth due to the presence of anti-resonances (and the accompanying resonances), this type of cloak enables a larger reduction in the scattering strength, compared with using a single elastic layer utilizing only non-resonant cloaking. A thorough investigation of the design space for a single isotropic elastic cloaking layer is performed, and the necessary elastic properties are discussed. The work in this thesis describes the investigation of the theoretical formulation for acoustic cloaking, expanding upon the use of scattering cancellation previously developed for the cloaking of electromagnetic waves. This work includes a detailed look at the different physical phenomena, including both resonant and non-resonant mechanisms, that can be used to achieve the necessary scattering cancellation and which can be applied to a wide range of scattering configurations for which cloaking would be desirable. In addition to laying out a broad theoretical foundation, the use of limiting cases and practical examples demonstrates the effectiveness and feasibility of such an approach to the acoustic cloaking of a spherical object. / text