• Journal of Environmental Impact Assessment
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• v.23 no.5
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• pp.364-378
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• 2014

Ecological Footprint (EF) in Korea has increased steeply over the past 50 years and, thus, the overshoot. It has been known that the main causes of the overshoot are population growth and the increase of the consumption intensity per person. In this study, the EF trend in Korea is analyzed for the past 50 years and it is found the major cause of the rapid increase of EF in Korea is the increase of the consumption intensity per person. Among the sectors of the consumption, Carbon Footprint (CF) from the energy consumption and Grazing Land Footprint and Fishing Grounds Footprint from the protein consumption are the major players for the increase. It is also found that if current trend of the EF per person would be maintained until 2060, EF in Korea would be expected to increase also continuously, despite of the decrease of the population from 2031. Therefore, the direction of the environmental management should be considered for inducing the change of the individual consumption patterns and the behavioral changes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.1
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• pp.43-55
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• 1997

Existing theories and experimental results on mud bed consolidation, fluidization and erosion are briefly reviewed. The importance of the history of bed shear strength profile which experiences periodic and random consolidation and fluidization is qualitatively discussed by reanalyzing a field data set in Youngkwang area of Korea. According to the results of existing laboratory experiments and the reanalyzing, the numerical modelling of mud or pollutant transport without considering consolidation and fluidization may cause the time lag between the hydrodynamic forcing and the increment of sediment and bed-originated pollutant concentrations in water column. The time lag can derive serious error in the transport direction, consequently in the budget of a heavy-concentrated bottom-originated substance, especially in macrotidal environments with relatively high wave energy.

• Korean Journal of Agricultural and Forest Meteorology
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• v.17 no.3
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• pp.236-247
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• 2015

Domestic agricultural and forest management suffers disturbances arising from rapid economic, social and environmental changes including climate change. Sustainable management has emerged as a key to overcoming these challenges. From the domestic and international viewpoint, we have identified mainly three (i.e. indicator, accounting, and ecological) approaches to sustainable management of agricultural and forest ecosystems. Compared to persistent investment in indicator and accounting approaches, we find the paucity of the domestic efforts in ecological approach. The latter approach can be facilitated based on the long-term meteorological and flux data including the ecosystem-level energy, matter and information flows, which have been monitored and managed by Korea Meteorological Administration, Rural Development Administration and Korea Forest Service. In order to keep up with vigorous international efforts toward sustainable ecosystem management, more interdisciplinary, multidisciplinary and transdisciplinary collaborations among diverse domestic sectors and institutes are essential.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.4
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• pp.520-528
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• 2015

The piezoelectric-hydraulic actuator is a hybrid device that consists of a hydraulic pump driven by a piezo-stack coupled to a conventional hydraulic cylinder. The actuator is of compact size, but can produce a moderate energy output. Such hybrid actuators are currently being researched and developed in many industrialized countries due to the requirement for high performance and compact flight systems. In a previous study, we designed and manufactured a unidirectional hybrid actuator. However, the blocking force was not as high as expected. Therefore, in this study, we redesigned the pump chamber and hydraulic cylinder and also improved the system by removing the air bubbles. Two different types of piezo-stacks were used. In order to achieve bidirectional capabilities in the actuator, commercial solenoid valves were used to control the direction of the output cylinder. Experimental testing of the actuator in unidirectional and bidirectional modes was performed to examine performance issues related to driving frequency, bias pressure, reed valve thickness, etc. The results showed that the maximum blocking force was measured as 970.2N when the frequency was 185Hz.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.13 no.2
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• pp.124-137
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• 2010

This study was started with the objective of restoring abandoned embanked farms, which are recently increasing, to mud flat by putting in least amount of energy in the aspect of environmental restoration. For the direction and establishment of the proposal for the restoration of mud flat using embanked farms, a case of Maipo Wetland in Hongkong was analyzed, and a proposal was prepared considering the condition of mud flat in Gochang. The restoration of mud flat in Gochang is intended to create various wetland ecological spaces as well as to provide opportunities for experience, education, recreation, and tourism. Effort was made to development an environment closest to the local ecological environment considering the shape and topographical condition of existing abandoned farms. For construction of the habitat, a target species was chosen and the plan for selection, planting, and management of species of trees suitable for the target species was established. In addition, the water level will be controlled by water gates to conform to the resting, spawning, breeding, and migration period considering the behavioral pattern of waders, the target species. The research on the restoration of mud flat in Korea is in incipient stage and this study provided an opportunity to review the possibility of restoration of abandoned embanked farms to mud flat. For the success of mud flat restoration from a long-term perspective, development of acclimating design infrastructure, technology improvement for mud flat restoration, and basis of partnership for the maintenance should be prepared in a systematical way.

• The Journal of the Korea Contents Association
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• v.7 no.11
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• pp.111-119
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• 2007

Sensor networks are needed for special purposes such as collecting or transmitting information by using sensor devices, for which various routing protocols have been proposed. Among existing protocols, the modified PEGASIS routing technique is known to be effective when applied to cases with directional transmissions of data. However it does not consider recovery from errors or guaranteeing stability in data transmission, while sensor devices performing repetitive relays and controls are prone to errors. In this paper, a double relay routing protocol for Zigbee based sensor networks where data are transfered reliably with a linear direction. The proposed protocol is effective in the sense that it secures the relaible transmission of data with minimal energy consumption based on a directional data transfer. A streetlight control system has been presented as an application of the proposed protocol.

• Journal of Environmental Policy
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• v.5 no.3
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• pp.57-78
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• 2006

Now post 2012 greenhouse gas reduction commitment being discussed, studies about long-term GHG reduction scenarios toward 2050 have actively been worked separately from 5 years short-term approach. In this paper, background, temperature target, $CO_2$ concentration target, national emission target, and approach of long-term reduction scenarios toward 2050 particularly in European countries such as UK, Germany, France, Netherlands et al. are reviewed. After comparing GDP and emission indices between Developed (European) countries and Korea, some implications of long-term GHG reduction scenarios are deduced. Acting early owing to uncertainty in climate change impact and technology development rather than delaying reduction activity owing to scientific uncertainty in climate change is needed. Providing our society's vision of climate change and government's explicit direction through long-term GHG reduction target setting toward 2050 and economic units' preparing for those are needed.

• Structural Engineering and Mechanics
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• v.4 no.5
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• pp.513-527
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• 1996

In this paper, both an approximate expression and an exact expression for the contribution factor of an element to the natural frequency of the finite element discretized system of a structure in general and a membrane in particular have been derived from the energy conservation principle and the finite element formulation of structural eigenvalue problems. The approximate expression for the contribution factor of an element is used to predict and determine the elements to be removed in an iteration since it depends only on the quantities associated with the old system in the iteration. The exact expression for the contribution factor of an element makes it possible to check whether the element is correctly removed at the end of an iteration because it depends on both the old system and the new system in the iteration. Thus, the combined use of the approximate expression and the exact expression allows a considerable number of elements to be removed in a single iteration so that the efficiency of the evolutionary structural optimization method can be greatly improved for solving the natural frequency optimization problem of a structure. A square membrane with different boundary supports has been chosen to investigate the general evolutionary path for the fundamental natural frequency of the structure. The related results indicated that if the objective of a structural optimization is to raise the fundamental natural frequency of the structure to an optimal value, the general evolutionary path during its optimization is that the elements are gradually removed along the direction from the area surrounded by the contour of the highest value to that surrounded by the contour of the lowest value.

• Geophysics and Geophysical Exploration
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• v.22 no.4
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• pp.195-201
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• 2019

The logarithmic objective function used in waveform inversion minimizes the logarithmic differences between the observed and modeled data. Laplace-domain waveform inversions usually adopt the logarithmic objective function and the diagonal elements of the pseudo-Hessian for optimization. In this case, we apply the Levenberg-Marquardt algorithm to prevent the diagonal elements of the pseudo-Hessian from being zero or near-zero values. In this study, we analyzed the diagonal elements of the pseudo-Hessian of the logarithmic objective function and showed that there is no zero or near-zero value in the diagonal elements of the pseudo-Hessian for acoustic waveform inversion in the Laplace domain. Accordingly, we do not need to apply the Levenberg-Marquardt algorithm when we regularize the gradient direction using the pseudo-Hessian of the logarithmic objective function. Numerical examples using synthetic and field datasets demonstrate that we can obtain inversion results without applying the Levenberg-Marquardt method.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.3
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• pp.123-129
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• 2018

In this study, CFD is used to compare and analyze the flow characteristics using reflected pressure wave during the intersection of two trains in straight tunnel. Two tunnels of different lengths; 600 m and 3,400 m were designed and numerical analysis of the flow characteristics of two tunnels carried out by setting the crossing state of the two trains at a constant velocity of 27 m/s form the center of the tunnel. The simulation model was designed using the actual tunnel and subway dimensions The train motion was achieved by using the moving mesh method. For the numerical analysis, $k-{\omega}$ standard turbulence model and an ideal gas were used to set the flow conditions of three-dimensional, compressible and unsteady state. In the analysis results, it was observed that the inside of the long tunnel without interference of the reflected pressure wave was maintained at a pressure lower than the atmospheric pressure and that the flow direction was determined by the pressure gradient and shear flow. On the other hand, the flow velocity in the short tunnel was faster and the pressure fluctuation was noted to have increased due to the reflected pressure wave, with more vortices formed. In addition, the flow velocity was noted to have changed more irregularly.