• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.1
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• pp.9-17
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• 2017

Characteristics of aerodynamic damping ratios of a helical $180^{\circ}$ model which shows better aerodynamic behavior in both along-wind and across-wind responses on a super tall building was investigated by an aeroelastic model test. The aerodynamic damping ratio was evaluated from the wind-induced responses of the model by using Random Decrement (RD) technique. Further, various triggering levels in evaluation of aerodynamic damping ratios using RD technique were also examined. As a result, it was found that when at least 2000 segments were used for evaluating aerodynamic damping ratio for ensemble averaging, the aerodynamic damping ratio can be obtained more consistently with lower irregular fluctuations. This is good agreement with those of previous studies. Another notable observation was that for square and helical $180^{\circ}$ models, the aerodynamic damping ratios in along-wind direction showed similar linear trends with reduced wind speeds regarding of building shapes. On the other hand, for the helical $180^{\circ}$ model, the aerodynamic damping ratio in across-wind direction showed quite different trends with those of the square model. In addition, the aerodynamic damping ratios of the helical $180^{\circ}$ model showed very similar trends with respect to the change of wind direction, and showed gradually increasing trends having small fluctuations with reduced wind speeds. Another observation was that in definition of triggering levels in RD technique on aerodynamic damping ratios, it may be possible to adopt the triggering levels of "standard deviation" or "${\sqrt{2}}$ times of the standard deviation" of the response time history if RD functions have a large number of triggering points. Further, these triggering levels may result in similar values and distributions with reduced wind speeds and either may be acceptable.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.40-48
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• 2016

To observe the rail-slab interaction in continuous welded railway(CWR) bridge when earthquake occurs, additional axial rail stresses and relative longitudinal displacements between rail and bridge deck were calculated with input of various load combinations and 3 different types of seismic loads to an analytical model. As results of analysis, it can be found that standard response spectrum proposed by Korea Rail(KR) network authority for earthquake design showed less additional axial rail stresses than allowable levels, but greater relative longitudinal displacement between rail and bridge deck, which means that adjustment of relative longitudinal displacement within a standard level is much more difficult than axial train stress. Additionally, if a large-scaled earthquake as occurred at Kobe, Japan comes up, then both of additional axial rail stress and relative displacement in rail-bridge deck may exceed allowable levels, which indicates to make proper design guides against sudden earthquake occurrence.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.171-178
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• 2008

The object of this study is to propose a rate of vibration increase in the analysis of temporary rail non-fixed in the vertical direction and characterize the nonlinear dynamic behavior of temporary rail while considering longitudinal and latitudinal load, vibration and lifting. The rate of vibration increase is proposed through measurement of an actual structure that is largely affected by loading and vibration of the superstructure. Dynamic behavior was additionally characterized by the dynamic response resulting from nonlinear dynamic finite element analysis with vehicle loading, including the rate of vibration increase. As a result, the rate of vibration increase by the vibration of an Auto Bar Machine is determined as 7% and the maximum stress in the analysis of the nonlinear rail is increased 14.5% over that of linear rail, and temporary rail is shown to be very sensitive to the velocity of the superstructure.

• Korean Journal of Optics and Photonics
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• v.14 no.5
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• pp.545-554
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• 2003

Design of the optical modulator composed of a three-waveguide coupler and CPW traveling-wave electrodes was carried out. Switching phenomena of three-waveguide couplers were analyzed by using the coupled mode theory, and the coupling-lengths of the devices were calculated by means of the FDM. CPW traveling-wave electrodes were analysed by the CMM and SOR simulation technique in order to find the conditions of phase-velocity and impedance matching. Traveling-wave modulators were fabricated on z-cut LiNbO$_3$ substrate. Ti was in-diffused in LiNbO$_3$ to make waveguides and Au electrodes were built on the waveguides by the electrolyte technique. The fabricated modulator chip was end-polished, pig-tailed and packaged in a brass mount with K-connector. The insertion loss and the switching voltage of the optical modulator were about 4㏈ and 19V, respectively. Network analyzer was used to obtain the S parameter and the corresponding RF response. From the measurement, parameters of the traveling-wave electrodes were extracted to be Z$_{c}$= 45 Ω, N$_{eff}$=2.20, and $\alpha$$_{0}$=0.055/cm√GHZ. The measured optical response R($\omega$) was compared with the theoretically estimated one, showing both responses agree well. The measurement results revealed that 3㏈ bandwidth turned out to be about 13 GHz.

• Journal of the Korean Chemical Society
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• v.51 no.5
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• pp.447-458
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• 2007

The purpose of this study was to explore high school teacher's and students' perceptions of learning difficulties of the ‘chemical bond' unit of the Chemistry II in the 7th national curriculum. The participants in this study were consisted of a teacher and his students(85) from the Chemistry II classrooms: they all answered to the questionnaire, and then some students and the teacher were interviewed individually. The results showed that there were big differences between the teacher's and his students' perceptions of 1) the most difficult unit for understanding; 2) concepts they learned; and 3) the most difficult concept for understanding in the classroom. Students thought that electro-negativity unit was the most difficult to understand while teacher thought molecular structure unit was the hardest unit to teach. And teacher taught all 32 subjects of chemical bond unit to students, but some students could not remember they learned all of them. Most difficult parts for students to understand were ‘Coulomb force' and ‘dipole moment', while the most difficult part for the teacher to teach was ‘the conceptual difference between atomic bond and intermolecular force'. The reasons caused the students' learning difficulties were analyzed and discussed based on the interview data, and then further study was presented.

• The Korean Journal of Food And Nutrition
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• v.20 no.1
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• pp.96-101
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• 2007

Thoughts on beef consumption and Korean beef were surveyed through questionnaire, with 150 housewives living in Seoul and its metropolitan area as subjects. The reasons for buying Korean beef were revealed as taste/quality(56.5%) and sanitation/safety(27.8%). The places of purchase were meat shops(42.3%), department stores, discount stores or super stores(28.1%), and agricultural cooperative stores or livestock cooperative stores(19.9%). The average purchase amount of Korean beef was 0.84 kg and the price was 22 USD(20,944 Won; 1 USD = 950 Won), and 61.7% of consumers thought the price of Korean beef was expensive. The major reason for buying imported beef was indicated as low price(78.0%) and the purchase locations were discount stores, department stores(39.4%) and meat shops (31.1%). When the subjects were surveyed on brands of Korean beef 73.3% had heard of branded beef but only 48% had purchased it. The reasons for buying branded beef were revealed as taste(40.0%) and sanitation(25.2%). When subjects were asked to compare branded beef with general Korean beef, 51.1% gave an answer of 'Very good/Good' for taste and quality, 'Similar' was 22.4% and 'No difference' was 29.9%, suggesting that the trust for branded beef was not strong yet. The important factors for buying branded beef were indicated as quality/taste(54.9%) and sanitation/safety(38.9%) and subjects were willing to pay up to 18.0% more for branded beef compared to the price of general Korean beef.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.3
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• pp.60-66
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• 2012

This paper aims to constitute a feedback vibration control system using wireless sensor networks and experiment it on a model structure to verify its effectiveness. For the purpose, we set up a feedback vibration control system composed of a wireless input/output(I/O) sensor node based on bluetooth, a home-made shear type MR damper, a shaker which generates a constant size of sine wave, and a simple beam model structure. The vibration control experiment was performed by shaking the 1/4 point of beam with a shaker. At the moment of shaking, we controled the vibration with MR damper which was placed vertically on the center of beam. Simultaneously, by acquiring acceleration response at the 2/4 point of beam, we evaluated the effectiveness of control capability. The control command was set to send a voltage signal to MR damper when the acceleration response, acquired from the wireless I/O sensor node placed at the center of beam, was more than a certain amount. Although the realtime feedback vibration control system constituted in this paper is effective only within a limited command system, it has been proven that the system was able to effectively decrease the vibration of structure by generating a control command aimed for realtime purpose. The system also showed a possibility to be used as a structural response control system adapting a variety of semi-active control algorithm.

• Korean Journal of Culture and Social Issue
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• v.24 no.4
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• pp.563-592
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• 2018

In this research, it was examined whether the importance of value of self(i.e., self-referenced values) and the perceived importance of values of average Koreans(i.e., culture-referenced values) differ according to social class. In Study 1, differences in the importance of self-referenced values according to the social class of 1,140 adults aged over 19 years old were examined using Korean data from the World Values Survey. Findings showed that higher social class was associated with higher levels of Hedonism (which belongs to the individualistic value domain) and Benevolence, and lower levels of Tradition (which belongs to the collectivistic value domain) and Universalism. In Study 2, culture-referent questionnaires were added to examine the differences in self-referenced values and culture-referenced values according to social class. Findings showed that higher social class was associated with greater importance attached to individualistic value domain (namely, Power and Achievement), and as a result of Study 1, less importance attached to Benevolence towards the self. On the contrary, for culture-referent ratings, higher social class was associated with lower perceptions of the importance of individualistic value domain (namely, Self-direction and Hedonism) and greater importance attached to Tradition (which belongs to the collectivistic value domain) for average Koreans. These results suggest that the importance of self-referenced values and culture-referenced values differ by social class. The need for social class research taking into account culture and the importance of the culture-referent ratings is highlighted. Future directions for research are discussed.

• Journal of Hospice and Palliative Care
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• v.7 no.1
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• pp.17-28
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• 2004

Purpose: Even though there have been various efforts for the dying with dignity of terminal patients, no researches focused on the public attitudes. Methods: In February 2004, we sampled 1,055 persons over 20 years of age from the sixteen cities and local districts of Korea through the quota sampling method according to their gender, age, and location. We conducted a telephone survey with a structured questionnaire on the attitudes toward dying with dignity and hospice palliative care. Results: The most important conditions for the dying with dignity on the patients' views were 'removing burdens for other people' (27.8%). Over the half of the samples chose their home as a preference for place of death (54.8%). 82.3% of the respondents agreed to the idea of withdrawing the medically futile life-sustaining treatment. Fifty seven percents of the answered public said that they intended to use the hospice service in case of terminal illness. Eighty percents thought that health care insurance should cover hospice service, and 80.9% gave positive response to the necessity of advance directives. Respondents emphasized 'the financial support for the terminal patients' (29.8%), 'covering hospice service with health insurance' (16.5%), and 'the education and public relation for settlement of desirable dying culture and hospice service' (15.9%) as the roles and responsibilities of the government for the dying with dignity. Conclusion: This study shows that there is a possibility of significant consensus on hospice and palliative care system for the dying with dignity of patients and reduction of the suffering for their families among the general public.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.2
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• pp.10-18
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• 2001

The very large floating structure which can be used for as airport may be as large as several kilometer long and wide. The first order wave forces as well as wave drift forces are very important forces on such a very large floating structures. In the present study, the time simulation of motion responses for dolphin-moored VLFS in waves is presented. The hydrodynamic coefficients and wave forces involved in the equations are obtained from a three-dimensional panel method in the frequency domain. The horizontal drift forces and mooring forces for dolphin systems are taken into account. As for numerical example, time domain analyses are carried out for a VLFS(Phase I) in irregular wave condition.