• Journal of Periodontal and Implant Science
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• 제47권2호
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• pp.106-115
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• 2017

Purpose: The possibility of immediate or early loading has become popular in implant dentistry. A prerequisite for the immediate or early loading of an implant prosthesis is the achievement of initial stability in the implant. Moreover, in response to clinicians' interest in verifying clinical stability to determine the optimal time point for functional loading, a non-invasive method to assess implant stability has been developed on the basis of resonance frequency analysis (RFA). The primary objective of this study was to monitor the stability of sandblasted, large-grit, and acid-etched (SLA) implants with different diameters during the early phases of healing by RFA. The secondary objective was to evaluate how the initial stability of implants varied depending on different surface modifications and other contributing factors. Methods: Thirty-five implants (25 SLA implants and 10 resorbable blasting media [RBM] implants) placed in 20 subjects were included. To measure implant stability, RFA was performed at baseline and at 1, 2, 3, 4, 6, and 10 weeks after surgery. Results: The longitudinal changes in the implant stability quotient (ISQ) values were similar for the SLA implants with different diameters and for the RBM implants. During the initial healing period, the ISQ decreased after installation and reached its lowest values at 1 week and 2 weeks, respectively. The mean ISQ values in the SLA implants were significantly higher in ${\varnothing}5.0mm$ implants than in ${\varnothing}4.0mm$ implants. Men showed a higher ISQ than women. Mandibular sites showed a higher ISQ than maxillary sites. Conclusions: All implants used in this study are suitable for immediate or early loading under appropriate indications. A wider diameter and SLA surface treatment of implants could improve the stability, if the implant is fixed with at least 30 Ncm of insertion torque.

• Smart Structures and Systems
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• 제25권6호
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• pp.719-732
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• 2020

Real-time hybrid simulation (RTHS) which combines physical experiment with numerical simulation is an advanced method to investigate dynamic responses of structures subjected to earthquake excitation. The desired displacement computed from the numerical substructure is applied to the experimental substructure by a servo-hydraulic actuator in real time. However, the magnitude decay and phase delay resulted from the dynamics of the servo-hydraulic system affect the accuracy and stability of a RTHS. In this study, a robust stability analysis procedure for a general single-degree-of-freedom structure is proposed which considers the uncertainty of servo-hydraulic system dynamics. For discussion purposes, the experimental substructure is a portion of the entire structure in terms of a ratio of stiffness, mass, and damping, respectively. The dynamics of the servo-hydraulic system is represented by a multiplicative uncertainty model which is based on a nominal system and a weight function. The nominal system can be obtained by conducting system identification prior to the RTHS. A first-order weight function formulation is proposed which needs to cover the worst possible uncertainty envelope over the frequency range of interest. Then, the Nyquist plot of the perturbed system is adopted to determine the robust stability margin of the RTHS. In addition, three common delay compensation methods are applied to the RTHS loop to investigate the effect of delay compensation on the robust stability. Numerical simulation and experimental validation results indicate that the proposed procedure is able to obtain a robust stability margin in terms of mass, damping, and stiffness ratio which provides a simple and conservative approach to assess the stability of a RTHS before it is conducted.

• 서비스연구
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• 제6권2호
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• pp.99-116
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• 2016

본 연구의 목적은 금리추세가 국내생명보험회사들의 자산운용 실태에 미치는 영향을 분석하여 문제점을 도출하고, 자산운용전략에 대한 방향성을 제시하고자 하였다. 연구방법은 2000년~2014년 동안에 국내 생명보험회사들의 자산현황 및 운용자산 내역, 자산배분실태, 유가증권 내역을 시계열 분석하였고, 총자산 및 자산별 수익률을 분석하였으며, 금리 주가와 운용수익률 간의 상관관계와 회귀분석을 실시하였다. 분석결과는 안전자산인 국공채의 비중은 증가한 반면에 위험자산인 주식의 비중은 감소하여 수익성 보다 안정성 위주로 자산운용을 하고 있었다. 금리와 총자산수익률, 운용자산수익률, 유가증권수익률 간에 높은 양(+)의 상관계수가 산출되었으며, 금리와의 상관관계에서 총자산수익률 보다는 운용자산수익률의 상관관계가 높았고, 운용자산수익률 보다는 유가증권수익률의 상관관계가 더 높았다. KOSPI 주가지수와 운용수익률 간에는 상관계수가 음(-)으로 나타났다. 시사점은 안정성 위주의 자산운용으로 금리하락이 역마진 리스크를 높이고 있어서 자산운용의 변화가 필요하다는 것이다.

• 조명전기설비학회논문지
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• 제26권9호
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• pp.64-72
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• 2012

The interest in wind power generation area such as developing and operating wind-diesel pilot complex in remote and island regions that have difficulty in having power plant and connecting to power system is growing rapidly in the world. We have installed and researched the hybrid system in Sekgok Pilot Complex to meet the new generation system. From the monitored data of the system, the performance of each diesel power plant is outstanding. However, step out problem was detected with respect to load sharing and synchronization with decentralized power supply. An advanced controller design having better response time and stability is needed to solve such problem. In this paper, we proposed the algorithm, through digital controller of Governor, which is applied to hybrid system. As a result, we obtained the stable frequency value in variable loading conditions. Also, we proved the advanced response time and stability through the simulation and experiment by applying additional current signal to the control algorithm.

• IEIE Transactions on Smart Processing and Computing
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• 제2권3호
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• pp.148-159
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• 2013

An analysis of the throughput and stability region of random access systems is currently of interest in research and industry. This study evaluated the performance of a multiuser random access channel with a retransmission gain. The channel was composed of a media access control (MAC) determined by the transmission probabilities and a multiuser communication channel characterized by the packet reception probabilities as functions of the number of packet transmissions and the collision status. The analysis began with an illustrative two-user channel, and was extended to a general multiuser channel. For the two-user channel, a sufficient condition was derived, under which the maximum throughput was achieved with a control-free MAC. For the channel with retransmission gain, the maximum steady throughput was obtained in a closed form. The condition under which the random access channel can acquire retransmission gain was also obtained. The stability region of the general random access channel was derived. These results include those of the well-known orthogonal channel, collision channel and slotted Aloha channel with packet reception as a special instance. The analytical and numerical results showed that exploiting the retransmission gain can increase the throughput significantly and expand the stability region of the random access channel. The analytical results predicted the performance in the simulations quite well.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1244-1250
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• 2008

The site of interest is a residence redevelopment area which has excavation construction with cut-off walls. The site is located over Dong-Mang-Bong tunnel and Seoul No. 6 subway tunnel. This study analyzed numerically the influence of vibrations from No. 6 subway tunnel to the basement of the redeveloped apartment away from the distance about 11m. Kyoung-bu highspeed railway's time history model with linearly reduced maximum acceleration is applied to take into the subway maximum speed of 75km/h. The maximum velocity of vibration for the cross section of the interest was estimated as 0.28cm/sec which satisfied the allowable standard of 0.5cm/sec for apartment and residence of Seoul.

• 항공우주시스템공학회지
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• 제15권6호
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• pp.33-41
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• 2021

As interest in drones controlled by remote technology rapidly increases worldwide, drones are used in many fields such as military, rescue, and transportation as future innovations in many countries. In particular, as the drone has been spotlighted as a new future strategic industry, it is also used for public purposes such as disaster relief and crime investigation. However, security concerns such as the penetration of major national facilities, collisions with aircraft, and the possibility of privacy infringement due to aerial photography are also being raised. Unlike the increased interest in drones, there have been few studies on drone use, drone safety, and public attitudes toward drone use. This paper analyzed the perceptions of drone attitudes, drone stability and policy support for drones for Korean and United Kingdom.

• 한국환경과학회지
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• 제30권9호
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• pp.741-752
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• 2021

Gardens are known to provide relaxation, including psychological stability and mental rest. Recently, social interest in gardens has been growing in various ways, including the increase of groups sensitive to environmental pollution and a rising interest in the overall management of natural resources. In reality, however, the owners of housing gardens lack fundamental knowledge for creating and maintaining the gardens, directly and indirectly. This limitation presents a number of problems and challenges. Therefore, this study conducted an analysis of various aspects relating to the creation and maintenance of housing gardens, reflecting the sense of ownership. The study aimed to examine the current status, and based on this, it was intended to present improvement measures for practical and efficient creation of housing gardens and their maintenance in the future.

• Asia Marketing Journal
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• 제12권3호
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• pp.43-62
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• 2010

은행서비스에서 고객지향성의 중요성이 더욱 커지고 있다. 조직의 고객지향적 문화와 전략이 급증함에도 불구하고, 국내 마케팅 문헌에서 고객지향성과 그에 따른 성과를 분석한 논문이 제한적이었다. 특히, 최근의 기준금리 상승에 따른 고객들의 금리민감도가 더욱 커질 수 있는 상황에서, 본 연구의 목표는 기업의 마케팅 노력인 고객지향성의 효과를 측정한다. 먼저 고객지향성과 금리민감도, 고객지향성과 고객애호도, 그리고 금리민감도와 고객애호도의 관계를 고찰한다. 또한 예금이자율과 대출이자율의 조절효과를 통해 고개지향성-금리민감도, 고객지향성-고객애호도의 관계에 어떠한 영향을 미치는가를 조사한다. 본 연구의 모형을 테스트하기 위하여, 국내 은행을 이용하는 304명의 고객을 이용하였다. 연구 결과 고객지향성과 고객애호도의 관계는 유의하게 평가된 반면, 고객지향성-금리민감도, 금리민감도와 고객애호도의 관계는 유의하지 않게 나타났다. 고객지향성이 높이 평가되어도 금리변동에 따른 경쟁상품간의 금리비교에 의해 고객의 금리민감도는 고객지향성의 효과가 상쇄되는 결과를 발생시키고, 금리민감도는 고객애호도에 유의한 영향을 미치지 않는다. 무엇보다도, 예금이자율과 대출이자율에 따른 조절효과가 완전히 상반되는 결과를 가져온 것이 흥미롭다. 예금이자율의 경우, 고객지향성-금리민감도, 고객지향성-고객애호도에 영향을 주지 않았으나, 대출이자율은 두 관계에 유의한 조절효과를 나타내었다. 본 연구의 결과는 아직 위의 관계에 대한 조명이 미숙한 상태에서, 향후 은행들이 어떻게 전략을 구축하여야 하는가에 대한 방향을 제공하였다는 점에서 그 연구의 공헌과 의의를 찾을 수 있다.

• 터널과지하공간
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• 제3권1호
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• pp.96-107
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• 1993

This paper deals with the analysis of rock slope stability using the distinct element method. This method consists in analysis of the interaction of discrete block assemblage delimited by elementary joints, which permits to consider the heterogeneous, anisotropic and discontinuous features of the rock mass. In particular, we were able to show that this method, and especially the BRIG3D software, is an outstanding tool which gives informations of greatest interest in order to analyze the toppling mechanisms. We have confirmed the fundamental role of the rock mass structure with different simulations. In the case of toppling phenomena, the essential parameter is the dip of major discontinuities. It has an influence on the intensity and volume of deformations. The anisotropic and heterogeneous features of the rock mass play also an important role. It is proved by insertion of thick rock bars in the structure or varying rock block sizes in the mass. These models modified considerably the stress distribution and the deformation distribution. Finally, we have analyzed the influence of mechanical parameters such as friction angle and tangential stiffness.