• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1089-1098
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• 1992

This paper concerns a discrete time control of noncolocated flexible mechanical systems by using time delay relation. A stability criterion of closed-loop system is derived in discrete time domain and a graphic method is developed for designing controllers. Based on this method, a derivative controller is designed for a simply supported uniform beam in the cases of colocation without time delay and of noncolocation with time delay. Some simulation results show the effectiveness of the suggested control.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.13-13
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• 2000

This paper considers delay-dependent guaranteed cost control for uncertain time-delay systems with norm-bounded parametric uncertainties. A new delay-dependent condition for the existence of the guaranteed cost control law is presented in terms of linear matrix inequalities (LMI). An algorithm involving convex optimization is proposed to design a controller which guarantees the suboptimal minimum of the guaranteed cost of the closed-loop system for all admissible uncertainties.

• KIEE International Transaction on Systems and Control
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• v.2D no.2
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• pp.92-96
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• 2002

This paper is concerned with properties of a Lyapunov functional of state delay systems. It is shown that if a state delay system has a pure imaginary pole for some state delay, then no Lyapunov functional satisfying a Lyapunov condition exists periodically with respect to change of the state delay. This periodic property is unique in state delay systems and has been well known in the frequency domain stability conditions. However, in the time domain stability conditions using a Lyapunov functional, the periodic property is not known explicitly.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.336-341
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• 2004

In this paper, a hybrid stabilization approach involving both passivity observer/passivity controller and wave variables is addressed to stabilize a teleoperation system with fixed time delay. To guarantee the stability of master or slave side, passivity observer/passivity controller are applied. But, passivity observer/passivity controller cannot deal with communication delay, and thus even small communication delay cause the system to be unstable. To cope with this problem, wave variables are additionally employed to have robustness to fixed communication delays. To show the validity of our proposed approach, several computer simulation results are illustrated.

• Kyungpook Mathematical Journal
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• v.47 no.3
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• pp.425-438
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• 2007

In this paper, we establish some new oscillation criteria for a second-order delay dynamic equation $$u^{{\Delta}{\Delta}}(t)+p(t)u(\tau(t))=0$$ on a time scale $\mathbb{T}$. The results can be applied on differential equations when $\mathbb{T}=\mathbb{R}$, delay difference equations when $\mathbb{T}=\mathbb{N}$ and for delay $q$-difference equations when $\mathbb{T}=q^{\mathbb{N}}$ for q > 1.

• KIEE International Transaction on Systems and Control
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• v.12D no.1
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• pp.39-42
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• 2002

This paper focuses on the asymptotic stability of a class of neutral linear systems with mixed time-varying delay arguments. Using the Lyapunov method, a delay-dependent stability criterion to guarantee the asymptotic stability for the systems is derived in terms of linear matrix inequalities (LMIs). The LMIs can be easily solved by various convex optimization algorithms. Two numerical examples are given to illustrate the proposed methods.

• International Journal of Aeronautical and Space Sciences
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• v.5 no.1
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• pp.94-100
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• 2004

Ionospheric time delay is the biggest error source for single-frequency DGPSapplications, including time transfer and Wide Area Differential GPS (WADGPS).Currently, there are many attempts to develop real-time ionospheric time delayestimation techniques to reduce positioning error due to the ionospheric time delay.Klobuchar model is now widely used for ionosphehc time delay calculation forsingle-frequency users. It uses flat surface at night time and cosine surface atdaytime[1], However, the model was developed for worldwide ionosphere fit, it isnot adequate for local area single-frequency users who want to estimateionospheric time delay accurate1y[2]. Therefore, 3-D ionosphere model usingtomographic estimation has been developed. 3-D tomographic inversion modelshows better accuracy compared with prior a1gorithms[3]. But that existing 3-Dmodel still has problem that it requires many coefficients and measurements forgood accuracy. So, that algorithm has Umitation with many coefficients incontinuous estimation at the small region which is obliged to have fewermeasurements.In this paper, we developed an modified 3-D ionosphehc time delay modelusing tomography, which requires only fewer coefficients. Because the combinationsof our base coefficients correspond to the full coefficients of the existing model, ourmodel has equivalent accuracy to the existing. We confirmed our algorithm bysimulations. The results proved that our modified algohthm can perform continuousestimation with fewer coefficients.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.7
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• pp.299-303
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• 2005

This paper proposes an analytic method can estimate delay time considering crosstalk noise at an arbitrary node of RC-class interconnects under saturated ramp input using a simple closed-form expression. In the case of single interconnects, algebraic expression presented in existent research can estimate delay time under ramp input using delay time under step input, and we applied it to estimate delay time considering crosstalk noise. As the result, we can provide a intuitive analysis about signal integrity of circuits that include crosstalk noise reducing computational complexity significantly.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.7-17
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• 2006

In this paper, we proposed an optical true time-delay (TTD) for planar phased array antennas (PAAs), which is composed of a wavelength-dependent optical true time delay (WDOTTD) followed by a wavelength-independent optical true time delay (WIOTTD). The WDOTTD is a fiber Bragg gratings (FBGs) Prism and the WDOTTD is a fiber delay-lines matrix of which each component consists of a certain length of fiber connected to cross-ports of a 2${\times}$2 MEMS switch. A 10-GHz 2-bit${\times}$4-bit two-dimensional optical TTD has been fabricated by cascading a WDOTTD with a maximum time delay of 810 ps to a WIOTTD of $\pm$50 ps. Time delay and insertion loss for each radiation angle have been measured. Time delay error for the WIOTTD has been measured to be less than $\pm$1 ps. We have also designed a two-dimensional 10-GHz PAA composed of 8${\times}$8 microstrip patch antenna elements driven by the proposed TTD. The radiation patterns of this PAA have been obtained by simulation and analyzed.

• Health Policy and Management
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• v.13 no.4
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• pp.115-130
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• 2003

Reperfusion delay in patients with acute myocardial infarction leads to increased morbidity and mortality. We sought to measure the rates of reperfusion delay and to identify factors associated with reperfusion delay after arrival to hospitals. We included 360 patients who had acute myocardial infarction with ST-elevation or left bundle branch block on electrocardiogram and received reperfusion therapy from the three participating academic medical centers from 1997 to 2000. Through retrospective chart review, we collected data about time to reperfusion therapy, patient and hospital factors potentially associated with reperfusion delay. Factors independently associated with reperfusion delay were determined by logistic regression analysis. Median door­to­needle time was 60.0 minutes, and median door­to­balloon time was 102.5 minutes. According to recommendation of the American College of Cardiology/American Heart Association Guidelines, 226 out of 264(85.6％) of thrombolytic patients and 43 out of 96(44.8％) percutaneous transluminal coronary angioplasty(PTCA) patients experienced reperfusion delay. The significant factors associated with delay were type of reperfusion therapy, patient factors including hypertension and delayed symptom onset to presentation(>4 hours), and hospital factors including nocturnal presentation(6pm∼8am), weekend, and an individual hospital. A significant proportion of patients experienced reperfusion delay. The identified predictors of reperfusion delay may help design a hospital system to reduce the delay in reperfusion therapy