• Journal of the Korean Geographical Society
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• v.38 no.4
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• pp.610-629
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• 2003

Ecotourism has been considered as sustainable tourism since it has been believed to preserve the environment of a tourist destination as well as to satisfy the various needs of tourists. However, most of destinations recently developed for ecotourism have confronted environmental degradation. Therefore, it is necessary to challenge and reestablish the concept of ecotourism. This study seeks to provide new perspectives on the concept of ecotourism by estimating the sustainability of three ecotourism destinations in Jeju Island. The Yae-Rae Dong Ecotourism Village shows a high level of sustainability, while the Ah-Bu Oh-rum at Song-Dang Ri and the Experience Beach at Jong-Dal Ri shows a low level of sustainability. In result, the ecotourism in itself is not sustainable tourism, and further this study suggests that appropriate planning, development, and management of a destination are important factors to decide the success of sustainable tourism.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.6
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• pp.801-806
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• 2004

The pilot study was conducted to (i) investigate the ability of various membrane integrity monitoring methods to detect changes in membrane integrity during operation, and (ii) determine the impact of membrane damage on microbial removal by microfiltration. Two variations of air pressure hold tests were investigated for direct integrity monitoring: pressure decay (PD) and diffusive air flow (DAF) tests which are most commonly used integrity tests for microfiltration (MF) membranes. Both PD and DAF tests were sensitive enough to detect one damaged fiber out of 66,000 under field operaing conditions. Indirect integrity monitoring such as turbidity and particle counting, however, responded poorly to defects in membrane systems. Microbial challenge study was performed using both new and deliberately damaged membranes, as well as varying the state of fouling of the membrane. This study demonstrated that MF membrane with nominal pore size $0.2{\mu}m$ was capable of removing various pathogens including coliform, spore, and cryptosporidium, at the level required by drinking water regulations, even when high operating pressures were applied. A sharp decrease in average log reduction value (LRV) was observed when one fiber was damaged, emphasizing the importance of membrane integrity in control of microbial contamination.

• Journal of Korean Society on Water Environment
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• v.22 no.1
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• pp.97-103
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• 2006

Excess sludge treatment and disposal currently represent a rising challenge for domestic or wastewater treatment plants due to economic, environmental and regulation factors. Conventional gravity sedimentation process has been widely used in sludge thickening. The operation method of the process is very simple, but the process requires long detention time for sludge thickening, uses polymers, and shows low sludge thickening efficiency. To solve the problems, we studied on DAF (Dissolved Air Flotation) system. We use bulking sludge of a paper manufacturing plant. The effects of parameters such as SVI (Sludge Volume Index), storage time, initial concentration and wet density of excess sludge were examined. The results showed that the more SVI was low, the more sludge was thickened. As storage time goes by, SVI was increased and thickening performance was deteriorated. In order to improve flotation performance at high concentration, high recycling ratio and pressure did not increase the concentration due to thickening limitation. The addition of 0.8 g/L of loess was increased flotation efficiency of 1.41 times.

• Atmosphere
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• v.16 no.2
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• pp.159-168
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• 2006

Journal of the Korean Meteorological Society (JKMS) is confronted by a huge challenge. Following the long-term plan of the Korean Meteorological Society (KMS), the JKMS has entered a new era in 2006 in the sense that the all papers are published in English. Tremendous efforts are needed to accomplish the original goal of JKMS becoming an internationally recognized journal. A forum was held in this connection with the subject of the vitalization of the JKMS at the Spring Meeting of the Korean Meteorological Society held at Gwangju, 2006. A number of special topics were presented at the forum and active and vigorous discussions followed. Professor Dong-Kyou Lee presented strategies to increase the number of submission to the JKMS. Professor Seon Ki Park gave a presentation on how JKMS can grow into the SCI journal. The Editor-in-Chief of JKMS, professor H. Joe Kwon introduced the on-line review system of JKMS which had launched in 2006. This manuscript is presented on the basis of the presentations and the discussions at the forum for the purpose of finding the way in aiming the direction of the long-term goal of the KMS.

• Environmental Analysis Health and Toxicology
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• v.21 no.4 s.55
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• pp.349-355
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• 2006

Dextromethorphan hydrobromide (DXM) has been widely used as a nonopioid antitussive drug with low toxicity and low potential for drug dependency. DXM is a psychotropic drug since 2003 in our country. This study was performed to investigate the immunotoxicity induced by abuse of DXM. Mice were orally exposed to DXM dissolved in saline as concentration of 30, 60, and 120 mg/kg b.w. before (day-2) or after (day+2) immunization (OVA-antigen, day 0). Thereafter, we measured the increased rate of body weight, relative weight of organ (thymus, spleen, liver, kidney) and OVA-specific IgM level in sera. In addition, mouse splenocytes were exposed to various concentration of DXM $(0.001{\sim}100{\mu}M)$ and cultured with B cell mitogen (LPS) and splenocytes proliferations (SP) were measured by MTT-assay. Thymus-weight were slightly changed on day 9 after administration of DXM, but body-, spleen-, liver-, and kidney-weight were not different between control group and DXM-treated group. SP to LPS were significantly decreased at high concentration $(100{\mu}M)$ when compared with controls. When DXM was administered before or after immunization with OVA-antigen, OVA-specific IgM levels were significantly lowered in a dose-dependent manner. These results indicate that DXM nay depress the primary humoral immune response to the initial antigenic challenge.

• Structural Engineering and Mechanics
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• v.52 no.3
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• pp.573-593
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• 2014

Pounding between adjacent buildings is a significant challenge in metropolitan areas because buildings of different heights collide during earthquake excitations due to varying dynamic properties and narrow separation gaps. The seismic responses of adjacent buildings of varying height, coupled through soil subjected to earthquake-induced pounding, are evaluated in this paper. The lumped mass model is used to simulate the buildings and soil, while the linear visco-elastic contact force model is used to simulate pounding forces. The results indicate while the taller building is almost unaffected when the shorter building is very short, it suffers more from pounding with increasing height of the shorter building. The shorter building suffers more from the pounding with decreasing height and when its height differs substantially from that of the taller building. The minimum required separation gap to prevent pounding is increased with increasing height of the shorter building until the buildings become almost in-phase. Considering the soil effect; pounding forces are reduced, displacements and story shears are increased after pounding, and also, minimum separation gap required to prevent pounding is increased.

• Geomechanics and Engineering
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• v.9 no.6
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• pp.793-813
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• 2015

Characterization of discontinuous media is an endeavor that poses great challenge to engineers in practice. Since the inherent defects in cracked domains can substantially influence material resistance and govern its behavior, a lot of work is dedicated to efficiently model such effects. In order to overcome difficulties of material instability problems, one needs to comprehensively represent the geometry of cracks along with their impact on the mechanical properties of the intact material. In the present study, stress-strain results from laboratory experiments on Inada granite was used to derive crack tensor as a tool for the evaluation of fractured domain stability. It was found that the formulations proposed earlier could satisfactorily be employed to attain crack tensor via the invariants of which judgment on cracks population and induced anisotropy is possible. The earlier criteria based on crack tensor analyses were reviewed and compared to the results of the current study. It is concluded that the geometrical parameters calculated using mechanical properties could confidently be used to judge the anisotropy as well as strength of the cracked domain.

• Structural Engineering and Mechanics
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• v.76 no.6
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• pp.675-685
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• 2020

As the classical response surface method (RSM), the polynomial RSM is so easy-to-apply that it is widely used in reliability analysis. However, the trade-off of accuracy and efficiency is still a challenge and the "curse of dimension" usually confines RSM to low dimension systems. In this paper, based on the univariate decomposition, the polynomial RSM is executed in a new mode, called as DPRSM. The general form of DPRSM is given and its implementation is designed referring to the classical RSM firstly. Then, in order to balance the accuracy and efficiency of DPRSM, its adaptive order revision around the most probable point (MPP) is proposed by introducing the univariate polynomial order analysis, noted as RDPRSM, which can analyze the exact nonlinearity of the limit state surface in the region around MPP. For testing the proposed techniques, several numerical examples are studied in detail, and the results indicate that DPRSM with low order can obtain similar results to the classical RSM, DPRSM with high order can obtain more precision with a large efficiency loss; RDPRSM can perform a good balance between accuracy and efficiency and preserve the good robustness property meanwhile, especially for those problems with high nonlinearity and complex problems; the proposed methods can also give a good performance in the high-dimensional cases.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.314-324
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• 2020

Due to the nonlinearity and environmental uncertainties, the design of the ship's steering controller is a long-term challenge. The purpose of this study is to design an intelligent autopilot based on Extended Kalman Filter (EKF) trained Radial Basis Function Neural Network (RBFNN) control algorithm. The newly developed free running model scaled surface vessel was employed to execute the motion control experiments. After describing the design of the EKF trained RBFNN autopilot, the performances of the proposed control system were investigated by conducting experiments using the physical model on lake and simulations using the corresponding mathematical model. The results demonstrate that the developed control system is feasible to be used for the ship's motion control in the presences of environmental disturbances. Moreover, in comparison with the Back-Propagation (BP) neural networks and Proportional-Derivative (PD) based control methods, the EKF RBFNN based control method shows better performance regarding course keeping and trajectory tracking.

• The Journal of Asian Finance, Economics and Business
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• v.10 no.2
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• pp.281-300
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• 2023

Recently, the call for better accountability and social responsibility from corporations has been regularly voiced, both in the academic literature and in public discussions. This poses a challenge to the existing literature in understanding consumption behaviors to direct them toward sustainable development. This study investigates the purchase intention of Gen Z consumers in Vietnam with green packaging products. Data were collected from 914 respondents by online questionnaire and then analyzed using OLS. The results suggest the significant influence of customers' income and packaging in driving customers' intention to use environmentally-friendly products. Specifically, consumers in a higher income class participate more actively in green purchases. However, problems associated with inadequate packaging are also illustrated, resulting in the poor perception of green messages and poor practice of ecological actions. Besides, subjective norms and green trust are found to be adversely related to green consumer intention. In addition, gender disparity in green behavior is reported, where female consumers show a higher tendency to ecological consumption than their male counterparts. Other demographic factors are also included in the model as control variables, which are age, education, price, environmental literacy, environmental concern, and psychological awareness, but they do not have a significant impact on green purchase intention.