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Steady-state Properties (steady-state + property)

Distribution by Scientific Domains

Engineering	40%

Selected Abstracts

Protein kinase A modulates A-type potassium currents of larval zebrafish (Danio rerio) white muscle fibres

ACTA PHYSIOLOGICA, Issue 2 2009
C. A. Coutts
Abstract Aims:, Potassium (K+) channels are involved in regulating cell excitability and action potential shape. To our knowledge, very little is known about the modulation of A-type K+ currents in skeletal muscle fibres. Therefore, we sought to determine whether K+ currents of zebrafish white skeletal muscle were modulated by protein kinase A (PKA). Methods:, Pharmacology and whole-cell patch clamp were used to examine A-type K+ currents and action potentials associated with zebrafish white skeletal muscle fibres. Results:, Activation of PKA by a combination of forskolin + 3-isobutyl-1-methylxanthine (Fsk + IBMX) decreased the peak current density by ,60% and altered the inactivation kinetics of A-type K+ currents. The specific PKA inhibitor H-89 partially blocked the Fsk + IBMX-induced reduction in peak current density, but had no effect on the change in decay kinetics. Fsk + IBMX treatment did not shift the activation curve, but it significantly reduced the slope factor of activation. Activation of PKA by Fsk + IBMX resulted in a negative shift in the V50 of inactivation. H-89 prevented all Fsk + IBMX-induced changes in the steady-state properties of K+ currents. Application of Fsk + IBMX increased action potential amplitude, but had no significant effect on action potential threshold, half width or recovery rate, when fibres were depolarized with single pulses, paired pulses or with high-frequency stimuli. Conclusion:, PKA modulates the A-type K+ current in zebrafish skeletal muscle and affects action potential properties. Our results provide new insights into the role of A-type K+ channels in muscle physiology. [source]

On the steady-state properties of actual flip angle imaging (AFI)

MAGNETIC RESONANCE IN MEDICINE, Issue 1 2009
Kay Nehrke
Abstract AFI (actual flip angle imaging) represents an interesting approach to map the B1 transmit fields by measuring the spatial variations of the effective flip angle. However, the accuracy of the technique relies on the adequate spoiling of transverse magnetization. In the present work configuration theory was employed to develop a proper RF and gradient spoiling scheme for the AFI technique, making the sequence robust against off-resonance without the need of large spoiling gradients. Furthermore, numerical simulations were performed to predict the steady-state signals and, hence, the accuracy of the AFI technique as a function of the sequence and tissue parameters. It is shown that the spoiling properties of the sequence are mainly defined by the phase shift increment , of the RF pulses and the diffusion sensitivity resulting from the unbalanced gradients of the sequence. Adequate spoiling may be achieved for a reasonable range of tissue parameters and flip angles for moderate spoiling gradients if a favorable value for , is chosen. Phantom and in vivo head imaging experiments show an excellent agreement with the theoretical predictions, indicating that the proper operating range of the approach may be reliably predicted by the theory. Magn Reson Med 61:84,92, 2009. © 2008 Wiley-Liss, Inc. [source]

INCOME DISTRIBUTION, TECHNICAL CHANGE AND THE DYNAMICS OF INTERNATIONAL ECONOMIC INTEGRATION

METROECONOMICA, Issue 1 2007
Michael A. Landesmann
ABSTRACT This paper explores the features of a dynamic multisectoral model that focuses on the relationship between income distribution, growth and international specialization. The model is explored both for the steady-state properties and the transitory dynamics of integrated economies. Income inequality affects the patterns of growth and international specialization as the model uses non-linear Engel curves and hence different income groups are characterized by different expenditure patterns. At the same time income distribution is also reflected in the relative wage rates of skilled to unskilled workers, i.e. the skill premium, and hence the wage structure affects comparative costs of industries which have different skill intensities. The model is applied to a situation that analyses qualitatively different economic development strategies of catching-up economies (a ,Latin American' scenario and a ,East Asian' scenario). [source]

A DUAL-MODE ADAPTIVE ROBUST CONTROLLER APPLIED TO THE SPEED CONTROL OF A THREE-PHASE INDUCTION MOTOR

ASIAN JOURNAL OF CONTROL, Issue 2 2005
Caio D. Cunha
ABSTRACT This work presents a Dual-Mode Adaptive Robust Controller applied to the angular shaft speed control of a three-phase induction motor. A liaison between a Model Reference Adaptive Controller (MRAC) and a Variable Structure Model Reference Adaptive Controller (VS-MRAC) through a tuning parameter is obtained using fuzzy logic. The basic idea of the Dual-Mode controller is adding both the advantages of the VS-MRAC transient behavior with the steady-state properties of the conventional MRAC. [source]

Transient behavior of time-between-failures of complex repairable systems

QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 4 2002
J. Bert Keats
Abstract It is well known for complex repairable systems (with as few as four components), regardless of the time-to-failure (TTF) distribution of each component, that the time-between-failures (TBFs) tends toward the exponential. This is a long-term or ,steady-state' property. Aware of this property, many of those modeling such systems tend to base spares provisioning, maintenance personnel availability and other decisions on an exponential TBFs distribution. Such a policy may suffer serious drawbacks. A non-homogeneous Poisson process (NHPP) accounts for these intervals for some time prior to ,steady-state'. Using computer simulation, the nature of transient TBF behavior is examined. The number of system failures until the exponential TBF assumption is valid is of particular interest. We show, using a number of system configurations and failure and repair distributions, that the transient behavior quickly drives the TBF distribution to the exponential. We feel comfortable with achieving exponential results for the TBF with 30 system failures. This number may be smaller for configurations with more components. However, at this point, we recommend 30 as the systems failure threshold for using the exponential assumption. Copyright © 2002 John Wiley & Sons, Ltd. [source]