• Title, Summary, Keyword: time scale

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Two-time Scale Controller Design for Vibration Reduction of High Speed Cartesian Manipulator (고속 직교 머니풀레이터의 진동 감소를 위한 Two-time scale 제어기 설계)

  • 강봉수
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.7
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    • pp.107-114
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    • 2004
  • This paper presents a two-time scale approach for vibration reduction of a high speed Cartesian manipulator. High speed manipulators would be subject to mechanical vibration due to high inertia forces acting on linkages. To achieve high throughput capability, such motion induced vibration would have to be damped quickly, to reduce settling time of the manipulator end-effector. This paper develops a two-time scale model fer a structurally-flexible Cartesian manipulator. Based on the two-time scale model, a composite controller consisting of a computed torque method for the slow time-scale rigid body subsystem, and a linear quadratic state-feedback regulator for the fast time-scale flexible subsystem, is designed. Simulation results show that the proposed two time-scale controller yields good performance in attenuating structural vibration arising due to excitation from inertial forces.

Particle-size-dependent aging time scale of atmospheric black carbon (입자 크기의 함수로 나타낸 대기 중 블랙카본의 변성시간척도)

  • Park, Sung Hoon
    • Particle and aerosol research
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    • v.5 no.2
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    • pp.45-52
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    • 2009
  • Black carbon, which is a by-product of combustion of fossil fuel and biomass burning, is the component that imposes the largest uncertainty on quantifying aerosol climate effect. The direct, indirect and semi-direct climate effects of black carbon depend on its state of the mixing with other water-soluble aerosol components. The process that transforms hydrophobic externally mixed black carbon particles into hygroscopic internally mixed ones is called "aging". In most climate models, simple parameterizations for the aging time scale are used instead of solving detailed dynamics equations on the aging process due to the computation cost. In this study, a new parameterization for the black carbon aging time scale due to condensation and coagulation is presented as a function of the concentration of hygroscopic atmospheric components and the black carbon particle size. It is shown that the black carbon aging time scale due to condensation of sulfuric acid vapors varies to a large extent depending on the sulfuric acid concentration and the black carbon particle size. This result indicates that the constant aging time scale values suggested in the literature cannot be directly applied to a global scale modeling. The aging time scale due to coagulation with internally mixed aerosol particles shows an even stronger dependency on particle size, which implies that the use of a particle-size-independent aging time scale may lead to a large error when the aging is dominated by coagulation.

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Time-varying physical parameter identification of shear type structures based on discrete wavelet transform

  • Wang, Chao;Ren, Wei-Xin;Wang, Zuo-Cai;Zhu, Hong-Ping
    • Smart Structures and Systems
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    • v.14 no.5
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    • pp.831-845
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    • 2014
  • This paper proposed a discrete wavelet transform based method for time-varying physical parameter identification of shear type structures. The time-varying physical parameters are dispersed and expanded at multi-scale as profile and detail signal using discrete wavelet basis. To reduce the number of unknown quantity, the wavelet coefficients that reflect the detail signal are ignored by setting as zero value. Consequently, the time-varying parameter can be approximately estimated only using the scale coefficients that reflect the profile signal, and the identification task is transformed to an equivalent time-invariant scale coefficient estimation. The time-invariant scale coefficients can be simply estimated using regular least-squares methods, and then the original time-varying physical parameters can be reconstructed by using the identified time-invariant scale coefficients. To reduce the influence of the ill-posed problem of equation resolving caused by noise, the Tikhonov regularization method instead of regular least-squares method is used in the paper to estimate the scale coefficients. A two-story shear type frame structure with time-varying stiffness and damping are simulated to validate the effectiveness and accuracy of the proposed method. It is demonstrated that the identified time-varying stiffness is with a good accuracy, while the identified damping is sensitive to noise.

The Congestion Control using Selective Slope Control under Multiple Time Scale of TCP (TCP의 다중 시간 간격에서 선택적 기울기 제어를 이용한 혼잡 제어)

  • Kim, Gwang-Jun;Kang, Ki-Woong;Lim, Se-Jung
    • The Journal of the Korea institute of electronic communication sciences
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    • v.2 no.1
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    • pp.10-18
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    • 2007
  • In this paper, we extend the multiple time scale control framework to window-based congestion control, in particular, TCP. This is performed by interfacing TCP with a large time scale control module which adjusts the aggressiveness of bandwidth consumption behavior exhibited by TCP as a function of "large time scale" network state. i.e., conformation that exceeds the horizon of the feedback loop as determined by RTT. Performance evaluation of multiple time scale TCP is facilitated by a simulation bench-mark environment which is based on physical modeling of self-similar traffic. If source traffic is not extended exceeding, when RTT is 450ms, in self similar burst environment, performance gain of TCP-SSC is up to 45% for ${\alpha}$=1.05. However, its is acquired only 20% performance gain for ${\alpha}$=1.95 relatively. Therefore we showed that by TCP-MTS at large time scale into a rate-based feedback congestion control, we are able to improve two times performance significantly.

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Variable Time-Scale Modification of Speech Using Transient Information based on LPC Cepstral Distance (LPC 켑스트럼 거리 기반의 천이구간 정보를 이용한 음성의 가변적인 시간축 변환)

  • Lee, Sung-Joo;Kim, Hee-Dong;Kim, Hyung-Soon
    • Speech Sciences
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    • v.3
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    • pp.167-176
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    • 1998
  • Conventional time-scale modification methods have the problem that as the modification rate gets higher the time-scale modified speech signal becomes less intelligible, because they ignore the effect of articulation rate on speech characteristics. Results of research on speech perception show that the timing information of transient portions of a speech signal plays an important role in discriminating among different speech sounds. Inspired by this fact, we propose a novel scheme for modifying the time-scale of speech. In the proposed scheme, the timing information of the transient portions of speech is preserved, while the steady portions of speech are compressed or expanded somewhat excessively for maintaining overall time-scale change. In order to identify the transient and steady portions of a speech signal, we employ a simple method using LPC cepstral distance between neighboring frames. The result of the subjective preference test indicates that the proposed method produces performance superior to that of the conventional SOLA method, especially for very fast playback case.

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The Congestion Control using Multiple Time Scale under Self-Similar Traffic of TCP (TCP의 자기 유사성 트래픽 조건하에서 다중 시간 간격을 이용한 혼잡 제어)

  • 김광준;윤찬호;김천석
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.8 no.2
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    • pp.310-323
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    • 2004
  • In this paper, we extend the multiple time scale control framework to window-based congestion control, in particular, TCP This is performed by interfacing TCP with a large tine scale control nodule which adjusts the aggressiveness of bandwidth consumption behavior exhibited by TCP as a function of "large time scale" network state. i.e., conformation that exceeds the horizon of the feedback loop as determined by RTT Our contribution is threefold. First, we define a modular extension of TCP-a function call with a simple interface-that applies to various flavors of TCP-e.g., Tahoe, Reno, Vegas and show that it significantly improves performance. Second, we show that multiple time scale TCP endows the underlying feedback control with preactivity by bridging the uncertainty gap associated with reactive controls which is exacerbated by the high delay-bandwidth product in broadband wide area networks. Third, we investigate the influence of three traffic control dimensions-tracking ability, connection duration, and fairness-on performance. Performance evaluation of multiple time scale TCP is facilitated by a simulation bench-mark environment which is based on physical modeling of self-similar traffic.

Tensorial Time Scales for Turbulent Gradient Transport of Reynolds Stresses (레이놀즈 응력의 난류구배수송을 위한 텐서시간척도)

  • Cho Choong Won;Kim Kyoungyoun;Sung Hyung Jin;Chung Myung Kyoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.6
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    • pp.687-695
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    • 2005
  • On the notion that the Reynolds stresses are transported with different time scale depending on the transport direction, the third order velocity correlations are represented by a new turbulent gradient transport model with tonsorial Lagrangian time scale. In order to verify the proposed model, DNS data are first obtained in a turbulent channel flow at Re = 180 and tonsorial Lagrangian time scales are computed. The present model predictions are compared with DNS data and those predicted by the third-order turbulent transport model of Hanjalic and Launder that uses a scalar time scale. The result demonstrates that the Reynolds stresses are indeed transported with different time scale depending on the transport direction.

EEG Signal Compression by Multi-scale Wavelets and Coherence analysis and denoising by Continuous Wavelets Transform (다중 웨이브렛을 이용한 심전도(EEG) 신호 압축 및 연속 웨이브렛 변환을 이용한 Coherence분석 및 잡음 제거)

  • 이승훈;윤동한
    • Journal of the Institute of Electronics Engineers of Korea SP
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    • v.41 no.3
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    • pp.221-229
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    • 2004
  • The Continuous Wavelets Transform project signal f(t) to "Time-scale"plan utilizing the time varied function which called "wavelets". This Transformation permit to analyze scale time dependence of signal f(t) thus the local or global scale properties can be extracted. Moreover, the signal f(t) can be reconstructed stably by utilizing the Inverse Continuous Wavelets Transform. In this paper, the EEG signal is analyzed by wavelets coherence method and the De-noising procedure is represented.

Design of sub-optimal regulators for the large-scale stochastic system with time-scale separation properties (여러 시간스케일로 분리 가능한 대규모 스토캐스틱 시스템의 준 최적 조정기의 설계)

  • 이종효;전기준
    • 제어로봇시스템학회:학술대회논문집
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    • pp.550-553
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    • 1986
  • This paper presents a procedure for the time-scale separation and a design method for the sub-optimal composite regulator and Kalman filter of the large-scale discrete stochastic system with two time-scale properties. Provided that the fast sub-system is asymptotically stable, the reduced-order regulator and Kalman filter for the slow sub-system with dominant modes is designed as a sub-optimal regulator for the system.

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ON THE MINIMAX VARIANCE ESTIMATORS OF SCALE IN TIME TO FAILURE MODELS

  • Lee, Jae-Won;Shevlyakov, Georgy-L.
    • Bulletin of the Korean Mathematical Society
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    • v.39 no.1
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    • pp.23-31
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    • 2002
  • A scale parameter is the principal parameter to be estimated, since it corresponds to one of the main reliability characteristics, namely the average time to failure. To provide robustness of scale estimators to gross errors in the data, we apply the Huber minimax approach in time to failure models of the statistical reliability theory. The minimax valiance estimator of scale is obtained in the important particular case of the exponential distribution.