• Earthquakes and Structures
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• v.17 no.2
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• pp.233-244
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• 2019

In this work, we have studied the effects of different soil thicknesses, haunch heights, reinforcement forms and construction technologies on the seismic performance of a composite precast fabricated utility tunnel by pseudo-static tests. Five concrete specimens were designed and fabricated for low-cycle reciprocating load tests. The hysteretic behavior of composite precast fabricated utility tunnel under simulated seismic waves and the strain law of steel bars were analyzed. Test results showed that composite precast fabricated utility tunnel met the requirements of current codes and had good anti-seismic performance. The use of a closed integral arrangement of steel bars inside utility tunnel structure as well as diagonal reinforcement bars at its haunches improved the integrity of the whole structure and increased the bearing capacity of the structure by about 1.5%. Increasing the thickness of covering soil within a certain range was beneficial to the earthquake resistance of the structure, and the energy consumption was increased by 10%. Increasing haunch height within a certain range increased the bearing capacity of the structure by up to about 19% and energy consumption by up to 30%. The specimen with the lowest haunch height showed strong structural deformation with ductility coefficient of 4.93. It was found that the interfaces of haunches, post-casting self-compacting concrete, and prefabricated parts were the weak points of utility tunnel structures. Combining the failure phenomena of test structures with their related codes, we proposed improvement measures for construction technology, which could provide a reference for the construction and design of practical projects.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.2
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• pp.131-136
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• 1985

The calculation of the resulting fluid motion is an important problem of ship hydrodynamics. For a partially immersed body the condition of constant pressure at the free surface can be linearized. The resulting linear boundary-value problem for the velocity potential is the Neumann-Kelvin problem. The two-dimensional Neumann-Kelvin problem is studied for the half-immersed circular cylinder by Ursell. Maruo introduced a slender body approach to simplify the Neumann-Kelvin problem in such a way that the integral equation which determines the singularity distribution over the hull surface can be solved by a marching procedure of step by step integration starting at bow. In the present pater for the two-dimensional Neumann-Kelvin problem, it has been suggested that any solution of the problem must have singularities in the corners between the body surface and free surface. There can be infinitely many solutions depending on the singularities in the coroners.

• Journal of the Mineralogical Society of Korea
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• v.27 no.3
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• pp.159-168
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• 2014

Holocene plaeoenvironmental changes were interpreted by grain size and mineral analyses of a piston core (HB 13-2), obtained along the western slope of the Hupo Basin, Korea. The core sediments are characterized by two discrete, sedimentary facies: upper unit (0-0.4 mbsf) dominated by bioturbation structures with weak lamination, and lower unit (0.4-3.3 mbsf) characterized by intensified bioturbation toward bottom. Analysis of sensitive grain size and sortable silt demonstrated that the inflow of the Tsushima Warm Current (TWC) into the Hupo Basin strengthen from the period of sediment deposition over 0.82 mbsf. The minerals of the core sediments are composed mainly of quartz, microcline, orthoclase, albite and clay minerals including chlorite, kaolinite and illite. No noticeable changes of the mineral percentage was observed according to the grain size and depth of the samples. The integral breadth (${\Delta}^{\circ}2{\theta}$) of clay minerals from 1.4 mbsf to top layer shows an increasing trend, which clearly means climate warming from the period of sediment deposition above 1.4 mbsf. This interval correlates with the Holocene climate optimum at Mid Holocene.

• The Korean Journal of Ecology
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• v.24 no.3
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• pp.191-202
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• 2001

Human being has extensively invaded, occupied, and used the natural environment as a consequence of the advance of civilization. Mankind has increasingly modified the environment for his own benefit. Such modification has not only caused the extinction of many other species but also, caused human being himself to confront to serious environmental problems. The recognition of this fact by human is expressed in the establishment and development of restoration ecology. This new study fold is, in fact, an "Eco-technology" directed towards healing of damages to the environment. The goal is to reestablish processes and functions in a damaged site, imitating the way of healing works that an integral natural system carries out. Ecological restoration uses different treatments and approaches according to extents of the existing damage and to the specific goal to be achieved. An ecological diagnosis is, therefore, required prior to restoration practice. The cost and efforts to achieve a proposed goal can be significantly reduced when a restoration plan is formulated upon the results of well-conducted ecological diagnosis. Under such perspectives, restoration ecology is a practical science, which aims to solve the problems of the real world based on the existing ecological principle. Furthermore, restoration ecology offers opportunities to test the ecological concepts and theories obtained by means of the former ecological studies. Human being exploited natural environment excessively for his comfort on one hand but damaged it inevitably on the other hand. Such intensive resource utilization and continuous environmental damaging will extend into the future and ultimately jeopardize the survival of humankind if no prompt action is taken. In the present situation, we must not continue such lives without any preparation. We have to cope with the environmental crises approaching near us by pursuing the ecological restoration that reduce the unnecessary use, recruit the deficient part, and strengthen the weak portion in our environment. Restoration ecology could be recognized as the ecology for the future in such viewpoints.