• The Journal of the Acoustical Society of Korea
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• 제27권3E호
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• pp.104-111
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• 2008

Recently, a method for robust time reversal focusing has been introduced to extend the period of stable focusing in time-dependent ocean environments [S. Kim et al., J. Acoust. Soc. Am. 114, 145-157, (2003)]. In this study, concept of focal-size broadening based on waveguide invariant theory in an ocean time reversal acoustics is described. It is achieved by imposing the multiple location constraints. The signal vector used in multiple location constraints are found from the theory on waveguide invariant for frequency band corresponding the extended focal range. The broadening of foci in an ocean waveguide can play an important role in the application of time reversal processing, particularly to the underwater acoustic communication with moving vehicles. The proposed method is demonstrated in the context of the underwater acoustic communication from the transmit/receive array (TRA) to a slowly moving vehicle.

• 아동학회지
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• 제30권6호
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• pp.309-321
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• 2009

This study examines trends of children's play in Korea, and academic, pragmatic, and policy issues related to it. For the purpose, the researchers reviewed play theories, national and international views of play specialists, and research articles on children's play in selected academic journals published in Korea for the last 30 years. Although Korea has been active academically as well as politically in recognizing the importance of children's play, children's play in Korea seems to have lost its position, the true value of it being often distorted or unidentified. Many specialists worn that the deprivation of play opportunities increasing in modern societies will result in many serious problems. Play research therefore need to strengthen its power by being more accountable and broadening its foci toward solving such predictable problems.