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1

Ergodicity examined by the Thirumalai-Mountain metric for Taiwanese seismicity

Li H.-C., Chen C.-C.

Acta Geophysica

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2012

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Vol. 60, no. 3

769-793

EN

Ergodicity is a behavior generally limited to equilibrium states and is here defined as the equivalence of ensemble and temporal averages. In recent years, effective ergodicity is identified in simulated earthquakes generated by numerical fault models and in real seismicity of natural fault networks by using the Thirumalai-Mountain metric. Although the effective ergodicity is already reported for Taiwanese seismicity, an immediate doubt is the unrealistic gridded sizes for discretizing the seismic data. In this study, we re-examined the effective ergodicity in Taiwanese seismicity by using reasonable gridded sizes which corresponded with the location errors in the real earthquake catalogue. Initial time and magnitude cut-off were examined for the validity of ergodic behavior. We found that several subsets extracted from Taiwanese seismicity possessed effectively ergodic intervals and all terminations of these ergodic intervals temporally coincided with the occurrences of large earthquakes (ML < 6.5). We thus confirm the ergodicity in the crustal seismicity by using the Thirumalai-Mountain metric.

2

A statistical damage model with implications for precursory seismicity

Lee Y.-T., Turcotte D., Rundle J., Chen C.-C.

Acta Geophysica

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2012

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Vol. 60, no. 3

638-663

EN

Acoustic emissions prior to rupture indicate precursory damage. Laboratory studies of frictional sliding on model faults feature accelerating rates of acoustic emissions prior to rupture. Precursory seismic emissions are not generally observed prior to earthquakes. To address the problem of precursory damage, we consider failure in a fiber-bundle model. We observe a clearly defined nucleation phase followed by a catastrophic rupture. The fibers are hypothesized to represent asperities on a fault. Two limiting behaviors are the equal load sharing p = 0 (stress from a failed fiber is transferred equally to all surviving fibers) and the local load sharing p = 1 (stress from a failed fiber is transferred to adjacent fibers). We show that precursory damage in the nucleation phase is greatly reduced in the local-load sharing limit. The local transfer of stress from an asperity concentrates nucleation, restricting precursory acoustic emissions (seismic activity).

3

Tracking and disturbance rejection in a nonlinear control system with time delay

Chien T.-L., Chen C.-C., Wu C.-J., Huang Y.-C., Chen C.-Y.

Control and Cybernetics

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2007

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Vol. 36, no 1

59-74

EN

We consider the problem of designing a feedback control law in order to reject the unknown bounded disturbance and achieve tracking of reference inputs in control systems described by a class of nonlinear time-delay differential-algebraic equations. Based on the input-output feedback linearization technique and Lya-pimov method for nonlinear state feedback synthesis, a robust globally asymptotical output tracking controller design methodology for nonlinear time-delay control systems with delays on the states and the input is developed. The underlying theoretical approaches are the differential geometry approach and the composite Lyapunov approach. For the view of practical application, the proposed control methodology has been successfully applied to the famous nonlinear automobile idle-speed control system problem.

4

An application of feedback linearization to the tracking and almost disturbance decoupling control of nonlinear system with uncertainties

Chen C.-C., Huang Y.-C, Lin W.-J., Shen D.-C., Huang L.-A.

Control and Cybernetics

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2007

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Vol. 36, no 2

385-403

EN

This paper studies the tracking and almost disturbance decoupling problem of nonlinear systems with uncertainties, based on the feedback linearization approach. The main contribution of this study is to construct a controller, under appropriate conditions, such that the resulting closed-loop system is valid for any initial condition and bounded tracking signal with the following characteristics: input-to-state stability with respect to disturbance inputs and almost disturbance decoupling, i.e., the influence of disturbances on the L2 norm of the output tracking error can be arbitrarily attenuated by changing some adjustable parameters. Two examples, which cannot be solved by the first paper on the almost disturbance decoupling problem, are proposed in this paper to exploit the fact that the tracking and the almost disturbance decoupling performances are easily achieved by the proposed approach. In order to demonstrate the practical applicability, the paper has investigated the AMIRA ball and beam system.