• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.693-702
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• 2001

One of the major characteristics of C language is that it allows us to use pointer type variables to access any area of virtual address space. So, we can read/write/execute from/to virtual memory area not controlled delicately by operating system. We can access such memory area by using format string and it can be a vulnerability of C language from the point of secure programming. In this paper, we analyze in detail the process of security attack based on format string and then exploit a new virus style attack which is stepwise and durable with some actual scenarios to warn the severity of it, and grope for some preliminary responding actions.

• The Korean Journal of Applied Statistics
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• v.20 no.3
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• pp.605-618
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• 2007

Adaptive sampling design is the selection procedure which depends on observed values of the variable of interest. It is the method which could be applied to the rare and unapproachable population. Adaptive cluster sampling strategies are more efficient than simple random sampling on equivalent sample size. Adaptive sampling with new estimators through the Rao-blackwell method have lower variance than Horvitz-Thompson (HT) and Hansen-Hurwitz (HH). Also, to determine suitable sample size, it was used expected sample and the method finding appropriate sample size by changing initial sample size were studied.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.185-185
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• 2011

기존 장대레일 궤도의 안정성 평가는 궤도 매개변수에 대하여 고정된 안전측의 값을 사용하는 결정론적인 해석에 의존해서 평가되어져 왔다. 그러나 실제현장의 궤도조건은 많은 영향인자들에 의해 그 특성이 불확실하게 변하고 있다. 따라서 온도하중에 의한 궤도 좌굴에 영향을 미치는 궤도 구성인자들의 불확실성 및 임의성을 보다 합리적으로 고려하기 위해서 확률론적 기법을 적용하는 것이 필수적이다. 본 연구에서는 기존 본 연구진에 의해 개발된 장대레일 궤도의 좌굴확률 평가시스템을 이용하여 좌굴 취약도 곡선을 나타내었으며, 궤도 좌굴에 영향을 미치는 주요변수 중 하나인 도상횡저항력에 대한 영향을 분석하였다. 좌굴확률 평가시스템에서는 장대레일 궤도의 좌굴확률을 산정하기 위하여 구조물의 안정과 파괴를 판단할 수 있는 기준을 한계상태방정식으로 표현하고, 이 한계상태방정식으로부터 확률론적 기법 중 하나인 AFOSM(Advanced First Order Second Moment) 방법을 이용하여 파괴확률의 간접적인 지표인 신뢰도지수(${\beta}$)를 통해 좌굴확률을 계산한다. 한계상태방정식에서 구조물의 강도(보유성능)에 해당하는 부분은 궤도의 허용좌굴온도이고, 하중(요구성능)에 해당하는 부분은 레일온도하중으로써 현재 레일온도와 중립온도의 차로 반영된다. 허용좌굴온도 산정에 고려되는 주요변수는 곡선반경(Radius), 도상횡저항력(Lateral Ballast Resista nce), 연직도상강성(Vertical Ballast Stiffness), 궤도 틀림량(Misalignment), 틀림길이(Half Wave Length), 열차운행속도(Velocity)이다. 각 확률변수들이 갖는 확률분포는 모두 정규분포로 가정하였다. 궤도의 기하학적 특성은 곡선반경 5,000m에 대해 고려하였으며, 열차는 KTX의 제원을 사용하여 정지된 상태에서 고려하였다. 틀림량과 틀림길이는 이에 대한 통계적 특성자료가 부족하여 확률변수로 고려하지 않고 결정론적 값으로 취급하였다. 레일온도의 통계적 특성치는 본 연구진에 의해 구축된 기후요소 및 레일온도 DB를 근거로 결정하였으며, 중립온도는 선로관리지침에 따라 $25{\pm}3^{\circ}C$를 기준으로 결정하였다. 또한 도상횡저항력은 실측 데이터를 참고로 하여 평균값에서 10%의 변동량을 갖는 것으로 보고 통계적 특성치를 결정하였다. 도상횡저항력이 좌굴확률에 미치는 영향을 매우 큰 것을 알 수 있었으며, 레일온도 $60^{\circ}C$일 때 도상횡저항력이 증가하면서 감소되는 좌굴확률이 도상저항력이 커질수록 그 감소량이 작아지는 것을 알 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5C
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• pp.486-492
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• 2003

The vigilance threshold of conventional fuzzy ART algorithm decide whether to permit the mismatch between any input pattern and stored pattern. If the vigilance threshold was large, despite of little difference among input and stored patterns, the input pattern may be classified to new category. On the other hand, if the vigilance threshold was small, the similarity between two patterns may be accepted in spite of lots of difference and the input pattern are classified to category of the stored pattern. Therefore, the vigilance threshold for the image recognition must be experientially set for the good result. Moreover, it may occur in the fuzzy ART algorithm that the information of stored patterns is lost in the weight-adjusting process and the rate of pattern recognition is dropped. In this paper, I proposed the enhanced fuzzy ART algorithm that supports the dynamical setting of the vigilance threshold using the generalized intersection operator of fuzzy logic and the weight value being adaptively set in proportional to the current weight change and the previous weight by reflecting the frequency of the selection of winner node. For the performance evaluation of the proposed method, we applied to the recognition of container identifiers from shipping container images. The experiment showed that the proposed method produced fewer clusters than conventional ART2 and fuzzy ART algorithm. and had tile higher recognition rate.

• Journal of the Korean Data and Information Science Society
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• v.28 no.5
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• pp.1055-1067
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• 2017

Most previous works to study for the depression of the disabilities in Korea have analyzed the repeated measured data of each individual under the mutually independent assumption. In this study, Korea Welfare Panel data of the disabilities surveyed additionally every three years are analyzed to detect the significant exploratory variables by the linear mixed models. A suitable correlation matrix is considered for the dependency of repeated measurement of each individual. The random effect to reflect the characteristics of the individuals as well as the fixed effect is included in the fitted linear mixed model. By the residual plot of the fixed effect model, the problem that the averages of residuals of each individual do not seem to be around zero is described. Further, the residual plot and the Q-Q plot coming from the selected final model are shown that the problem is modified well.

• Journal of Advanced Navigation Technology
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• v.20 no.3
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• pp.252-257
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• 2016

In this paper a novel access scheme for uplink multiuser transmission based on IEEE 802.11ax random access in in-aircraft wireless sensor networks is proposed. The proposed scheme provides an efficient access control mechanism with three divisions of OFDMA backoff counter (OBO): access, deferring, dropping, which controls the number of potential uplink transmission stations. The proposed scheme can be used efficiently in in-aircraft wireless sensor network where a large number of sensors need to be supported. By using the proposed scheme, since in-aircraft sensors attempt channel access using the proposed differentiated OBO parameters, the number of stations exceeds the access capacity can be efficiently controlled. This paper also provides the mathematical analysis of the proposed scheme, regarding the optimal parameters. According to the performance analysis, the proposed scheme is able to efficiently control the access behavior of wireless sensors in the network.

• Journal of Navigation and Port Research
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• v.45 no.6
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• pp.284-297
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• 2021

A simple kinematic model for the prediction of ship manoeuvres based on trial data is proposed in this study. The model consists of first order differential equations in surge, sway, and yaw directions which simulate the time series of each velocity component. Actually instead of sea trial data, dynamic model simulations are conducted with randomly varied control inputs such as propeller revolution rates and rudder angles. Based on learning of control inputs and velocity outputs of dynamic model simulations in sufficient time, kinematic model coefficients are optimized so that the kinematic model can be approximately reproduce the velocity outputs of dynamic model simulations with arbitrary control inputs. The resultant kinematic model is verified with new dynamic simulation sets.

• Korean Journal of Construction Engineering and Management
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• v.6 no.4 s.26
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• pp.80-90
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• 2005

Activity durations retain probabilistic and stochastic natures due to diverse factors causing the delay or acceleration of activity completion. These natures make the final project duration to be a random variable. These factors are the major source of financial risk. Extending the Stochastic Project Scheduling Simulation system (SPSS) developed in previous research; this research presents a method to estimate how the final project duration behaves when activity durations change randomly. The final project cost is estimated by considering the fluctuation of indirect cost, which occurs due to the delay or acceleration of activity completion, along with direct cost assigned to an activity. The final project cost is estimated by considering how indirect cost behaves when activity duration change. The method quantifies the amount of contingency to cover the expected delay of project delivery. It is based on the quantitative analysis to obtain the descriptive statistics from the simulation outputs (final project durations). Existing deterministic scheduling method apply an arbitrary figures to the amount of delay contingency with uncertainty. However, the stochastic method developed in this research allows computing the amount of delay contingency with certainty and certain degree of confidence. An example project is used to illustrate the quantitative analysis method using simulation. When the statistical location and shape of probability distribution functions defining activity durations change, how the final project duration and cost behave are ascertained using automated sensitivity analysis method

• Journal of Periodontal and Implant Science
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• v.35 no.3
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• pp.537-548
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• 2005

1. 목적 이 연구의 목적은 기존의 평가기준에 따라 관찰자에 의해 주관적으로 판단된 치은형과 실제 치은두께와의 상관관계를 규명하고 임상검사 시에 측정할 수 있는 변수들과 치은두께의 연관성을 평가하는 것이다. 2 방법 211명의 치과대학생(22-43세, 평균 24.7세)을 연구대상으로 하여 상악중절치부위에서 국소마취하에 근관 치료용 파일을 치은에 삽입하여 두께를 측정하고 임상검사를 통해 치주낭깊이, 치태지수, 치은지수, 치은퇴축, 체형 및 비만도, 피부형, 치경부의 형태, 관측자가 임의로 판단한 치은형을 기록하였다. 임상사진으로 치관의 폭경과 길이의 비율, 치은외형의 만곡정도를 조사하고 평행촬영법을 이용한 방사선사진으로 치아의 장평비율 및 치아의 치관 폭경과 치경부 폭경의 비율을 조사하였다. 전체 대상을 치은의 두께를 기준으로 평균두께보다 얇은 군과 두꺼운 군의 두 개의 군으로 분류하여 임상검사 사에 측정한 변수들이 각 군 간에 유의할 만한 차이를 보이는지와 임의로 판단한 치은형이 실제 치은두께와 연관이 있는지를 알아보았다. 통계처리는 Student t-test를 이용하였다. 3. 결과 치주낭 깊이, 치은지수, 체형 및 비만도, 피부형, 치아의 형태, 치경부의 형태, 치아의 장평비율의 경우 실제 측정하여 얻은 치은의 두께와의 상관관계는 통계적으로 유의성이 없었다. 치은의 형태는 치은의 두께와 상관성은 보이고 있으나 통계적으로 유의하지 않았다. 관측자가 임의로 평가한 치은형과 실제 측정치도 유의할만한 일치를 보이지 않고 있다. 4. 결론 치은의 형태는 치은의 두께를 예상하는데 약간의 도움이 될 수 있으나 실제 치은의 두께는 임상적으로 간단히 측정할 수 있는 겸사지수들과 직접적인 상관관계를 보이지 않았다. 따라서 치료결과의 예측에 있어서 치은형을 분류하여 예상하는 것은 큰 도움이 되지 않는다고 할 수 있다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1A
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• pp.39-48
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• 2012

This study deals with numerical determination of stress intensity factors of adhesively patch-repaired plates with cracks at V-shaped or semicircular notches. The p-convergent anisoparametric model are considered and then three-dimensional virtual crack closure technique is presented using formulations of anisoparametric elements. In assumed displacement fields of an element, strain-displacement relations and three-dimensional constitutive equations are derived with three-dimensional hierarchical shape functions expanded from one-dimensional Lobatto functions. Transfinite mapping technique is used to represent a circular boundary. The present model provides accuracy and simplicity in terms of stress concentration factor, stress distribution, the number of degrees of freedom, and non-dimensional stress intensity factor as compared with previous works in literatures. Stress intensity factors obtained by the three-dimensional virtual crack closure technique are estimated with respect to the variation of width of finite plate, radius of notch root, angular inclination of V-shaped notch, and crack length.