• 대한수학회보
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• 제47권4호
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• pp.743-750
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• 2010

For several Banach spaces X and Y and operator ideal $\cal{U}$, if $\cal{U}$(X, Y) denotes the component of operator ideal $\cal{U}$; according to Freedman's definitions, it is shown that a necessary and sufficient condition for a closed subspace $\cal{M}$ of $\cal{U}$(X, Y) to have the alternative Dunford-Pettis property is that all evaluation operators $\phi_x\;:\;\cal{M}\;{\rightarrow}\;Y$ and $\psi_{y^*}\;:\;\cal{M}\;{\rightarrow}\;X^*$ are DP1 operators, where $\phi_x(T)\;=\;Tx$ and $\psi_{y^*}(T)\;=\;T^*y^*$ for $x\;{\in}\;X$, $y^*\;{\in}\;Y^*$ and $T\;{\in}\;\cal{M}$.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.269-273
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• 2000

This paper describes Active Noise Control (ANC) using Discrete Wavelet Transform (DWT) Domain Least Mean Square (LMS) Method. DWT-LMS is one of the transform domain input decorrelation LMS and improves the convergence speed of adaptive filter especially when the input signal is highly correlated. Conventional transform domain LMS's use Discrete Cosine Transform (DCT) because it offers linear band signal decomposition and fast transform algorithm. Wavelet transform can project the input signal into the several octave band subspace and offers more efficient sliding fast transform algorithm. In this paper, we propose Wavelet transform domain LMS algorithm and shows its performance is similar to DCT LMS in some cases using ANC simulation.

• 한국통신학회논문지
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• 제33권4C호
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• pp.336-341
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• 2008

본 논문에서는 신호의 반 파장 간격으로 안테나 소자를 배치한 빔형성 시스템에서 다이버시티 이득을 얻을 수 있는 빔형성 알고리즘을 제안한다. 제안된 알고리즘은 수신 신호 공간을 스팬(span)하는 고유 벡터들을 이용하여 빔형성 한다. 본 논문에서는 채널 추정을 위한 최적의 고유 공간 차수를 정하기 위한 기준도 제안한다. 제안된 알고리즘을 적용한 빔형성 시스템은 기존의 빔형성 시스템과는 달리 각 퍼짐이 증가함에 따라 다이버시티 이득을 얻어 그 성능이 개선된다. 본 논문은 제안된 알고리즘의 설명과 함께 다양한 컴퓨터 시뮬레이션을 통한 제안 알고리즘의 성능 분석을 제공한다.

• ETRI Journal
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• 제40권6호
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• pp.714-725
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• 2018

Destination-assisted jamming (DAJ) is usually used to protect confidential information against untrusted relays and eavesdroppers in wireless networks. In this paper, a DAJ-based untrusted relay network with multiple antennas installed is presented. To increase the secrecy, a joint optimization of beamforming and power allocation at the source and destination is studied. A matched-filter precoder is introduced to maximize the cooperative jamming signal by directing cooperative jamming signals toward untrusted relays. Then, based on generalized singular-value decomposition (GSVD), a novel transmitted precoder for confidential signals is devised to align the signal into the subspace corresponding to the confidential transmission channel. To decouple the precoder design and optimal power allocation, an iterative algorithm is proposed to jointly optimize the above parameters. Numerical results validate the effectiveness of the proposed scheme. Compared with other schemes, the proposed scheme shows significant improvement in terms of security performance.

• Journal of applied mathematics & informatics
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• 제39권3_4호
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• pp.487-496
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• 2021

In this paper we show that if A ∈ L(X) and B ∈ L(Y), X and Y complex Banach spaces, then A ⊕ B ∈ L(X ⊕ Y) is subscalar if and only if both A and B are subscalar. We also prove that if A, Q ∈ L(X) satisfies AQ = QA and Q^p = 0 for some nonnegative integer p, then A has property (C) (resp. property (𝛽)) if and only if so does A + Q (resp. property (𝛽)). Finally, we show that A ∈ L(X, Y) and B, C ∈ L(Y, X) satisfying operator equation ABA = ACA and BA ∈ L(X) is subscalar with property (𝛿) then both Lat(BA) and Lat(AC) are non-trivial.

• 대한전자공학회논문지SD
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• 제38권12호
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• pp.56-65
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• 2001

본 논문은 이상적인 균일한 무손실 유전체를 갖는 일반적인 3차원 연결선 구조에서의 커패시턴스 추출 시, 널리 사용되는 일차 대조법(First-order collocation) 외에 고차 구적법을 결합하여 사용함으로써 정확성을 제고하고, 반복적 행렬-벡터의 곱을 효율적으로 수행하기 위한 알고리즘을 제안한다. 제안된 기법은 연결선에서 전기적 성질이 집중되어 있는 코너나 비아를 포함한 경우에 일차 대조법 대신에 구적법을 이용하여 고차로 근사함으로써 정확성을 보장한다. 또한, 이 기법은 경계 요소 기법에서 행렬의 대부분이 수치적으로 저차 계수(low rank)를 이룬다는 회로상의 전자기적 성질을 이용하여 모형차수를 축소함으로써 효율성을 증진한다. 이 기법은 SVD(Singular Value Decomposition)에 기반한 저차 계수 행렬 축소 기법과 신속한 행렬의 곱셈 연산을 위한 Krylov-subspace 차수 축소 기법인 Gram-Schmidt 알고리즘을 도입함으로써 효율적인 연산을 수행할 수 있다. 제안된 방법은 허용 오차 범위 내에서 효율적으로 행렬-벡터의 곱셈을 수행하며, 이를 기존의 연구에서 제시된 기법과의 성능 평가를 통하여 보인다.

• Smart Structures and Systems
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• 제10권2호
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• pp.131-154
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• 2012

In this paper, it is aimed to determine the seismic behaviour of highway bridges by nondestructive testing using ambient vibration measurements. Eynel Highway Bridge which has arch type structural system with a total length of 216 m and located in the Ayvaclk county of Samsun, Turkey is selected as an application. The bridge connects the villages which are separated with Suat U$\breve{g}$urlu Dam Lake. A three dimensional finite element model is first established for a highway bridge using project drawings and an analytical modal analysis is then performed to generate natural frequencies and mode shapes in the three orthogonal directions. The ambient vibration measurements are carried out on the bridge deck under natural excitation such as traffic, human walking and wind loads using Operational Modal Analysis. Sensitive seismic accelerometers are used to collect signals obtained from the experimental tests. To obtain experimental dynamic characteristics, two output-only system identification techniques are employed namely, Enhanced Frequency Domain Decomposition technique in the frequency domain and Stochastic Subspace Identification technique in time domain. Analytical and experimental dynamic characteristic are compared with each other and finite element model of the bridge is updated by changing of boundary conditions to reduce the differences between the results. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of highway bridges. After finite element model updating, maximum differences between the natural frequencies are reduced averagely from 23% to 3%. The updated finite element model reflects the dynamic characteristics of the bridge better, and it can be used to predict the dynamic response under complex external forces. It is also helpful for further damage identification and health condition monitoring. Analytical model of the bridge before and after model updating is analyzed using 1992 Erzincan earthquake record to determine the seismic behaviour. It can be seen from the analysis results that displacements increase by the height of bridge columns and along to middle point of the deck and main arches. Bending moments have an increasing trend along to first and last 50 m and have a decreasing trend long to the middle of the main arches.

• Smart Structures and Systems
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• 제11권5호
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• pp.533-553
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• 2013

In this paper, system identification of a cable-stayed bridge in Korea, the Hwamyung Bridge, is performed using vibration responses measured by a wireless sensor system. First, an acceleration based-wireless sensor system is employed for the structural health monitoring of the bridge, and wireless sensor nodes are deployed on a deck, a pylon and several selected cables. Second, modal parameters of the bridge are obtained both from measured vibration responses and finite element (FE) analysis. Frequency domain decomposition and stochastic subspace identification methods are used to obtain the modal parameters from the measured vibration responses. The FE model of the bridge is established using commercial FE software package. Third, structural properties of the bridge are updated using a modal sensitivity-based method. The updating work improves the accuracy of the FE model so that structural behaviors of the bridge can be represented better using the updated FE model. Finally, cable forces of the selected cables are also identified and compared with both design and lift-off test values.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2009년도 정기 학술대회
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• pp.421-424
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• 2009

사장교 케이블의 감쇠비를 추정하기 위하여 실교량 계측을 수행하였다. 사장교 케이블은 감쇠비가 낮고, 고유 진동수가 케이블의 길이에 따라 넓은 범위에 걸쳐 분포하므로, 바람이나 지점 가진에 의하여 과도한 진동이 발생될 수 있다. 케이블 진동 현상의 원인과 발생되고 진행되는 구조는 다양하나, 진동 현상의 가장 중요한 요소는 감쇠비이며, 케이블 진동의 과도한 진동을 감소시키기 위하여, 케이블의 감쇠비를 증가시키는 방법이 널리 사용되고 있다. 사장교 케이블의 다양한 진동 현상에 대한 발생 여부를 판단하고, 케이블 댐퍼와 같은 여러 제진 대책을 설계하고, 설치된 케이블 제진 대책의 성능을 검증하기 위해서는, 케이블의 감쇠비를 추정하는 것이 매우 중요하다. 일반적으로 사용되어져 온 케이블의 감쇠비 추정 방법은 정해진 모드로 자유 진동을 발생시킨 후, 진폭의 감소 추세로부터 Logarithmic Decrement를 계산하여 감쇠비를 구하는 방법이다. 그러나 수백m에 이르는 긴 케이블에서 정해진 모드의 자유 진동을 발생시키는 것은 쉽지 않다. 최근에는 상시 진동으로부터 감쇠비를 추정하는 여러 기법들이 개발되어져 왔으며, Frequency Domain Decomposition Method나 Stochastic Subspace Identification Method 등이 많이 사용되고 있다. 이 논문에서는, 상시진동 기반의 기법들을 사용하여, 사장교 케이블의 감쇠비를 추정하였으며, 추정된 감쇠비의 신뢰도를 높이기 위해, 측정시간을 늘리고, 가진 풍하중의 영향을 반영하여 보정하였다. 또한 추정된 감쇠비를 Buffeting 진동과 와류 진동과 같이 진동 현상과 진폭별로 분석하였다.

• Smart Structures and Systems
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• 제10권4_5호
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• pp.353-373
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• 2012

The instrumented Canton Tower is a 610 m high-rise structure, which has been considered as a benchmark problem for structural health monitoring (SHM) research. In this paper, an improved automatic modal identification method is presented based on a natural excitation technique in conjunction with the eigensystem realization algorithm (NExT/ERA). In the proposed modal identification method, damping ratio, consistent mode indicator from observability matrices (CMI_O) and modal amplitude coherence (MAC) are used as criteria to distinguish the physically true modes from spurious modes. Enhanced frequency domain decomposition (EFDD), the data-driven stochastic subspace identification method (SSI-DATA) and the proposed method are respectively applied to extract the modal parameters of the Canton Tower under different environmental conditions. Results of modal parameter identification based on output-only measurements are presented and discussed. User-selected parameters used in those methods are suggested and discussed. Furthermore, the effect of environmental conditions on the dynamic characteristics of Canton tower is investigated.