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Interconnected System (interconnected + system)

Distribution by Scientific Domains
Engineering66%

Selected Abstracts

Climate change, genotypic diversity and gene flow in reef-building corals

ECOLOGY LETTERS, Issue 4 2004
David J. Ayre
Abstract In the ocean, large-scale dispersal and replenishment by larvae is a key process underlying biological changes associated with global warming. On tropical reefs, coral bleaching, degradation of habitat and declining adult stocks are also likely to change contemporary patterns of dispersal and gene flow and may lead to range contractions or expansions. On the Great Barrier Reef, where adjacent reefs form a highly interconnected system, we use allozyme surveys of c. 3000 coral colonies to show that populations are genetically diverse, and rates of gene flow for a suite of five species range from modest to high among reefs up to 1200 km apart. In contrast, 700 km further south on Lord Howe Island, genetic diversity is markedly lower and populations are genetically isolated. The virtual absence of long-distance dispersal of corals to geographically isolated, oceanic reefs renders them extremely vulnerable to global warming, even where local threats are minimal. [source]

Near-lithostatic pore pressure at seismogenic depths: a thermoporoelastic model

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006
Francesca Zencher
SUMMARY A model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure. This configuration is thought to be pertinent to the South Iceland seismic zone (SISZ) and to other tectonically active regions of recent volcanism, where volatiles are continuously released by ascending magma below the brittle,ductile transition. Poroelastic parameters are computed for basaltic rock. The model is 1-D, the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium. Environment conditions are considered, pertinent to basalt saturated with water at shallow depth (case I) and at mid-crustal depth (case II). If the intrinsic permeability of the rock is high, no significant effects are observed in the pressure field but advective heat transfer shifts the brittle,ductile transition to shallower depths. If the intrinsic permeability is low, the pressure-dependent permeability can propagate near-lithostatic pore pressures throughout most of the transition layer, while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition. Geometrical parameters characterizing the fracture distribution are important in determining the effective permeability: in particular, if an interconnected system of fractures develops within the transition layer, the effective permeability may increase by several orders of magnitude and near-lithostatic pore pressure propagates upwards. These modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the SISZ, in connection with the two 2000 June M= 6.5 earthquakes, including: (i) fluid pressure pulses in deep wells, (ii) low resistivity at the base of the seismogenic layer, (iii) low VP/VS ratio and time-dependent seismic tomography, (iv) heterogeneity of focal mechanisms, (v) shear wave splitting, (vi) high b -value of deep foreshocks, (vii) triggered seismicity and (viii) Radon anomalies. [source]

Model reduction of interconnected linear systems

OPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 3 2009
H. Sandberg
Abstract The problem of model reduction of linear systems with certain interconnection structure is considered in this paper. To preserve the interconnection structure between subsystems in the reduction, special care needs to be taken. This problem is important and timely because of the recent focus on complex networked systems in control engineering. Two different model reduction methods are introduced and compared in this paper. Both methods are extensions to the well-known balanced truncation method. Compared with earlier work in the area these methods use a more general linear fractional transformation framework, and utilize linear matrix inequalities. Furthermore, new approximation error bounds that reduce to classical bounds in special cases are derived. The so-called structured Hankel singular values are used in the methods, and indicate how important states in the subsystems are with respect to a chosen input,output map for the entire interconnected system. It is shown how these structured Hankel singular values can be used to select an approximation order. Finally, the two methods are applied to a model of a mechanical device. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Unit commitment at frequency security condition

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2001
X. Lei
In island grids and weakly interconnected power systems, the loss of a large proportion of generation will cause the system frequency to fall dramatically. In order to ensure a stable operation with the lowest impact to the system, the disturbed power balance must be equalized within a short specified time by activating the second-reserve of on-line units or by load shedding or both. Unit commitment procedures shall consider these factors to ensure a reliable power supply while minimizing the fuel costs. This paper presents a unit commitment procedure taking the frequency security condition of systems into account. The procedure commits and optimizes units, calculates necessary second-reserve capability, and allocates them among the available on-line units. Parallel to the minimization of daily fuel costs, a specified frequency minimum following the loss of generation is employed as a criterion for maintaining system security. A case study on typical island systems with a large number of different units is demonstrated using the proposed procedure. Results from the study validated robust performance of the proposed procedure that minimizes fuel costs while maintaining frequency security condition. This paper considers only the frequency security condition to be handled. However, it can also be extended with other criteria such transmission capability during transient conditions of interconnected systems. [source]

Dissipativity and stability of interconnections

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 5-6 2007
Jan C. Willems
Abstract A new definition of dissipativity is proposed. It is purely in terms of the rate of supply that goes in and out of a dynamical system. It is proven that dissipativity is equivalent to the existence of a non-negative storage. Several results regarding the dissipativity of systems defined by quadratic differential forms are given, and some open questions are mentioned. These ideas are applied to the question of stability of interconnected systems. Copyright © 2006 John Wiley & Sons, Ltd. [source]

CONTROL OF INTERCONNECTED JUMPING SYSTEMS: AN H, APPROACH

ASIAN JOURNAL OF CONTROL, Issue 1 2004
Magdi S. Mahmoud
ABSTRACT This paper investigates, by using an approach, the problems of stochastic stability and control for a class of interconnected systems with Markovian jumping parameters. Both cases of finite- and infinite-horizon are studied. It is shown that the problems under consideration can be solved if a set of coupled differential or algebraic Riccati equations are solvable. [source]