• 대한의용생체공학회:의공학회지
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• 제10권1호
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• pp.33-42
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• 1989

도플러 효과는 혈관의 혈류속도를 측정하는데 이용된다. 대부분의 도플러 시스템은 측정위치에 대한 정보를 제공하는 펄스 도플러 시스템이다. 본 논문에서는 2차 샘플링 방식과 직렬 신호 처리를 이용한 새로운 2차원 펄스 도플러 시스템을 제안한다. 제안된 시스템은 직각 위상 검파 방식에서 동상과 $90^{\circ}$ 지연된 위상신호의 불평형성을 해결하고, 또한 직렬 신호 처리를 사용하므로서 2차원 도플러 시스템에서의 채널 간의 평형성 문제를 해결했다.

• 전자공학회논문지
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• 제52권3호
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• pp.162-170
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• 2015

BPS(bandpass sampling) 기술은 입력 신호보다 낮은 주파수로 표본화하는 것으로서, 표본화 처리만으로 기저 대역 신호를 얻을 수 있다. 이 덕분에 별도의 주파수 하향 변환기를 사용하지 않아도 되어, 수신기 회로 구현이 간소화 된다. 2차 BPS 방식은 표본화 장치를 2개 사용하는 것이며, 표본화로 인하여 aliasing 간섭이 발생하더라도 두 가지 BPS 신호를 결합함으로써 간섭 성분을 제거할 수 있다. 본 논문에서는 여러 개의 간섭이 한꺼번에 신호 성분에 aliasing 되는 경우에 대한 2차 BPS 시스템의 설계 문제를 다루었다. 신호 대 간섭 비를 극대화시키도록 interpolant 필터의 최적 위상값을 구하는 방법을 분석하였고, BPS 입력단의 전력밀도 스펙트럼 자료를 이용하여 준최적 위상값을 구하는 실용적인 공식을 도출하였다. 제안된 시스템에 대하여 컴퓨터 시뮬레이션을 수행하였고, 다중 aliasing을 고려함으로써 신호 대 간섭 비가 증가되는 것을 확인하였다.

• 대한수학회보
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• 제34권3호
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• pp.411-419
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• 1997

Using the theory of strongly continuous cosine families, we prove controllable of nonlinear second order control system and give an application.

• East Asian mathematical journal
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• 제34권5호
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• pp.651-660
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• 2018

This paper concerned the existence of positive solutions to the second order differential systems with strongly coupled integral boundary value conditions. By using Krasnoselskii fixed point theorem, we prove the existence of positive solutions according to the parameters under the proper nonlinear growth conditions.

• 대한수학회보
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• 제36권1호
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• pp.1-13
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• 1999

Sufficient conditions for controllability of semilinear second order Volterra integrodifferential systems in Banach spaces are established using the theory of strongly continuous cosine families. The results are obtained by using the Schauder fixed point theorem. An example is provided to illustrate the theory.

• Steel and Composite Structures
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• 제4권6호
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• pp.419-435
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• 2004

The safety level of a structural system designed per code specifications can not be inferred directly from the reliability of members due to the load redistribution and nonlinear inelastic structural behavior. Comparison of the system and member reliability, which is scarce in the literature, is likely to indicate any possible inconsistency of design codes in providing safe and economical designs. Such a comparative study is presented in this study for moment resisting two-dimensional steel frames designed per AISC LRFD Specifications. The member reliability is evaluated using the resistance of the beam-column element and the elastic load effects that indirectly accounts for the second-order effects. The system reliability analysis is evaluated based on the collapse load factor obtained from a second-order inelastic analysis. Comparison of the system and member reliability is presented for several steel frames. Results suggest that the failure probability of the system is about one order of magnitude lower than that of the most critically loaded structural member, and that the difference between the system and member reliability depends on the structural configuration, degree of redundancy, and dead to live load ratio. Results also suggest that the system reliability is less sensitive to initial imperfections of the structure than the member reliability. Therefore, the system aspect should be incorporated in future design codes in order to achieve more reliability consistent designs.

• Ocean Systems Engineering
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• 제1권4호
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• pp.263-283
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• 2011

The performance of a rig tie-down system on a TLP (Tension Leg Platform) is investigated for 10-year, 100-year, and 1000-year hurricane environments. The inertia loading on the derrick is obtained from the three-hour time histories of the platform motions and accelerations, and the dynamic wind forces as well as the time-dependent heel-induced gravitational forces are also applied. Then, the connection loads between the derrick and its substructure as well as the substructure and deck are obtained to assess the safety of the tie-down system. Both linear and nonlinear inertia loads on the derrick are included. The resultant external forces are subsequently used to calculate the loads on the tie-down clamps at every time step with the assumption of rigid derrick. The exact dynamic equations including nonlinear terms are used with all the linear and second-order wave forces considering that some dynamic contributions, such as rotational inertia, centripetal forces, and the nonlinear excitations, have not been accounted for in the conventional engineering practices. From the numerical simulations, it is seen that the contributions of the second-order sum-frequency (or springing) accelerations can be appreciable in certain hurricane conditions. Finally, the maximum reaction loads on the clamps are obtained and used to check the possibility of slip, shear, and tensile failure of the tie-down system for any given environment.

• 제어로봇시스템학회논문지
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• 제16권12호
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• pp.1189-1196
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• 2010

This paper provides an identification method for three-parameter models i.e. first order with dead time models and second order with dead time models. The proposed identification method is based on step response and can be easily implemented using digital microprocessors. The proposed method first identifies the order of the plant i.e. first order or second order from the behavior of the plant with constant input. After the order of the plant is determined, a test step input is applied to the system and the three parameters of the plant are obtained from the corresponding response of the plant. The output of the plant need not to be zero when the test signal is applied. The efficacy of proposed algorithms is verified through simulation and experiment.

• Journal of applied mathematics & informatics
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• 제8권1호
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• pp.129-136
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• 2001

We introduce and discuss a new numerical method for solving system of second order boundary value problems, where the solution is required to satisfy some extra continuity conditions on the subintervals in addition to the usual boundary conditions. We show that the present method gives approximations which are better than that produced by other collocation, finite difference and spline methods. Numerical example is presented to illustrate the applicability of the new method. AMS Mathematics Subject Classification : 65L12, 49J40.

• Journal of applied mathematics & informatics
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• 제22권1_2호
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• pp.263-271
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• 2006

In this paper, a quasilinear second-order system with periodic boundary conditions is studied. By the least action principle and classical theorems of variational calculus, existence results of periodic solutions are obtained.