• Title/Summary/Keyword: Range dependent environment

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Detection Range of Passive Sonar System in Range-Dependent Ocean Environment (거리의존 해양환경에서 수동소나체계의 표적탐지거리예측)

  • Kim, Tae-Hak;Kim, Jea-Soo
    • The Journal of the Acoustical Society of Korea
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    • v.16 no.4
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    • pp.29-34
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    • 1997
  • The prediction of detection range of a passive sonar system is essential to estimate the performance and to optimize the operation of a developed sonar system. In this paper, a model for the prediction of detection range in a range-dependent ocean environment based on the sonar equation is developed and tested. The prediction model calculates the transmission loss using PE propagation model, signal excess, and the detection probability at each target depth and range. The detection probability is integrated to give the estimated detection range. In order to validate the developed model, two cases are considered. One is the case when target depth is known. The other is the case when the target depth is unknown. The computational results agree well with the previously published results for the range-independent environment. Also,the developed model is applied to the range-dependent ocean environment where the warm eddy exists. The computational results are shown and discussed. The developed model can be used to find the optimal frequency of detection, as well as the optimal search depth for the given range-dependent ocean environment.

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Underwater Sound Propagation in a range-dependent Shallow water environment (비균질한 천해에서의 수중음파 전파)

  • Na, Jeong-Yeol
    • The Journal of the Acoustical Society of Korea
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    • v.6 no.4
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    • pp.64-73
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    • 1987
  • Low frequency sound propagation in a range-dependent shallow water environment of the Korea Strait has been studied by using the adiabatic coupled mode, ADIAB. The range-dependent environment is unique in terms of horizontal variations of sound velocity profiles, sediment thickness and attenuation coefficients and water depths. For shallow source and receiver depths, the most important mechanism involved in the propagation loss is the depth changing character of mode functions that strongly depends on the local sound velocity profile. Application of the adiabatic coupled mode theory to shallow water environment is reasonable when higher modes are attenuated due to bottom interaction effects. Underwater sound propagation in a range-dependent shallow-water environment.

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Modeling of ambient noise in ocean environment using coupled mode (연성모드법을 이용한 해양 배경소음 모델링)

  • Park, Jungyong;Kwon, Hyuckjong
    • The Journal of the Acoustical Society of Korea
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    • v.41 no.4
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    • pp.397-409
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    • 2022
  • A model is developed for the calculation of sea surface generated ambient noise in the range dependent ocean environment. The sources are located in the horizontal plane all around and their depths are at the near-surface. The receiver array is located in the range dependent ocean waveguide. One-way coupled mode method is used to model the acoustic propagation between the sources and receiver in the range dependent waveguide, and the cross spectral density matrix of noise is derived. In simulation, noise intensity, beamforming result and coherence function are calculated from the cross spectral density matrix. These results are compared with those in the range independent environment. The modeling result shows the effect of the vertical directionality and asymmetry characteristics of the horizontal plane.

Optimal Search Depth for the Sonar Systems in a Range-Dependent Ocean Environment (거리종속 환경에서 소나의 최적운용수심에 대한 연구)

  • Lee, Jae-Hoon;Kim, Jea-Soo;Yoo, Jin-Soo;Byun, Yang-Hun;Cho, Jung-Hong
    • The Journal of the Acoustical Society of Korea
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    • v.27 no.1
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    • pp.47-56
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    • 2008
  • In the detection of an underwater target, there exists an optimal search depth for the sonar systems, at which the Probability of Detection is maximized. The optimal search depth is dependent on the depths of the target and sonar, the sound speed profile, and the bathymetry. In this paper, we address this question in range-dependent environments, particularly for the bathymetry with slope and with warm eddy. For range-dependent bathymetry, the typical sound profile in the East Sea of Korea was used. The detection range was greater when the sonar was located in deep water than in shallow water. As for the case of eddy, mesoscale warm eddy was used, and the detection range was greater when looking out of the warm eddy than when looking into the eddy.

Location-Based Services for Dynamic Range Queries

  • Park Kwangjin;Song Moonbae;Hwang Chong-Sun
    • Journal of Communications and Networks
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    • v.7 no.4
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    • pp.478-488
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    • 2005
  • To conserve the usage of energy, indexing techniques have been developed in a wireless mobile environment. However, the use of interleaved index segments in a broadcast cycle increases the average access latency for the clients. In this paper, we present the broadcast-based location dependent data delivery scheme (BBS) for dynamic range queries. In the BBS, broadcasted data objects are sorted sequentially based on their locations, and the server broadcasts the location dependent data along with an index segment. Then, we present a data prefetching and caching scheme, designed to reduce the query response time. The performance of this scheme is investigated in relation to various environmental variables, such as the distributions of the data objects, the average speed of the clients, and the size of the service area.

Noise Robust Emotion Recognition Feature : Frequency Range of Meaningful Signal (음성의 특정 주파수 범위를 이용한 잡음환경에서의 감정인식)

  • Kim Eun-Ho;Hyun Kyung-Hak;Kwak Yoon-Keun
    • Journal of the Korean Society for Precision Engineering
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    • v.23 no.5 s.182
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    • pp.68-76
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    • 2006
  • The ability to recognize human emotion is one of the hallmarks of human-robot interaction. Hence this paper describes the realization of emotion recognition. For emotion recognition from voice, we propose a new feature called frequency range of meaningful signal. With this feature, we reached average recognition rate of 76% in speaker-dependent. From the experimental results, we confirm the usefulness of the proposed feature. We also define the noise environment and conduct the noise-environment test. In contrast to other features, the proposed feature is robust in a noise-environment.

Environment-dependent Broadband Perfect Absorption of Metal-insulator-metal Metamaterial Systems

  • Feng Li;Yulong Tang;Qingsong Peng;Guosheng Hu
    • Current Optics and Photonics
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    • v.7 no.2
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    • pp.136-146
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    • 2023
  • Based on calculations using the macroscopic Maxwell's equations with mesoscopic boundary conditions, light absorption by a layered metal-insulator-metal (MIM) metamaterial system embedded in three different environments is investigated. Increasing the top metal thickness shifts the broad absorption band to lower dielectric-constant regions and longer wavelengths, for either TM or TE waves. Boosting the dielectric-layer thickness redshifts the broadband absorption to regions of larger dielectric constant. In air, for the dielectric-constant range of 0.86-3.40, the absorption of the system exceeds 98% across 680-1,033 nm. In seawater with optimized dielectric constant, ≥94% light absorption over 400-1,200 nm can be achieved; particularly in the wavelength range of 480-960 nm and dielectric-constant range of 0.82-3.50, the absorption is greater than 98%. In an environment with even higher refractive index (1.74), ≥98% light absorption over 400-1,200 nm can be achieved, giving better performance. The influence of angle of incidence on light absorption of the MIM system is also analyzed, and the angle tolerance for ≥90% broadband absorption of a TM wave is up to 40° in an environment with large refractive index. While the incident-angle dependence of the absorption of a TE wave is nearly the same for different circumstances, the situation is different for a TM wave.

Long range incoherent seafloor reverberation model based on coupled normal mode method (연성모드법 기반의 원거리 비상관 해저면 잔향음 모델)

  • Park, Jungyong;Choo, Youngmin;Lee, Keunhwa;Seong, Woojae
    • The Journal of the Acoustical Society of Korea
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    • v.35 no.4
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    • pp.243-252
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    • 2016
  • In this paper, the incoherent reverberation model based on coupled normal mode method is presented. In the range dependent environment, one way coupled normal mode method is used to calculate the pressure from a source to a scatterer patch and the pressure from a scatterer patch to a receiver. For the computational efficiency, the sound propagation from a source/receiver to the scatterer patch is assumed to occur only in the 2D plane where a source/receiver and scatterer patch are located. For the model verification, problems of the reverberation modeling workshop I and II sponsored by the US office of Naval Research are calculated and the results are compared with the incoherent reverberation model results based on the ray method.

Factors Influencing Global Expansion/Scalability of Small and Medium Enterprises: A Kenyan Case

  • Osano, Hezron Mogaka
    • World Technopolis Review
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    • v.8 no.1
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    • pp.21-42
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    • 2019
  • The purpose of this research was to investigate the factors influencing global expansion/scalability of Kenyan Small and Medium Enterprises (SMEs). Factor analysis and multiple/multivariate regression analysis to determine the functional relationship between independent variables (factors) and the dependent variable was used. The independent variables were: innovation & technology, fitness/appropriateness of management, global marketing strategy; and support environment and the dependent variable, global expansion/scalability. Data was collected from a survey of randomly selected firms of 205, drawn from a population of 440 firms from Kenya Manufacturers Directory, with 175 firms responding. The key findings from the research in relation to Kenyan SMEs were that: there is a functional relationship between global market strategy and global expansion; there is a functional relationship between innovation and technology orientation and global expansion, there is no significant functional relationship between supportive environment of firms and their global expansion; and there is no significant functional relationship between fitness/appropriateness of management and global expansion/scalability. The implications for practice is that the ranking of the factors in order of priority supports focusing concern on the orientation of business strategy toward global market strategy, market research geared at obtaining foreign market intelligence, innovation and technology, product adaptation, service orientation, collaborative ventures, and long-range vision as key factors in making Kenyan firms successful in the international market. The implication for policy and practice is that there is need for collaboration between industry and government in pursuing policies for global expansion/scalability and among SMEs and large enterprises particularly in areas of rapid technological change.

Shallow Water Low-frequency Reverberation Model (천해 저주파 잔향음 예측모델)

  • 김남수;오선택;나정열
    • The Journal of the Acoustical Society of Korea
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    • v.21 no.8
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    • pp.679-685
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    • 2002
  • Low-frequency mono-static reverberation model for shallow-water environment is presented. It is necessary to develop the transmission loss model to calculate the sub-bottom interaction because the ray-based transmission loss model is difficult to compute the pressure accurately which penetrates the bottom medium. In this paper reverberation level is calculated using the RAM (Range dependent Acoustic Model) to augment the multi-path expansion model because it does not estimate transmission loss accurately in shallow water. The signals generated by the L-HYREV and the GSM are compared with the observed signals and it is showed that the L-HYREV model provides a closer fit to the observed signals than those obtained using the GSM.