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Transient Period (transient + period)
Selected AbstractsWhen has estimation reached a steady state?INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 1 2005The Bayesian sequential test Abstract This paper is concerned with distributions of time series, which (i) are influenced by initial conditions (ii) are stimulated by an exogenous signal or (iii) are obtained by recursive estimation of underlying parameters and thus undergo a transient period. In computer intensive applications, it is desirable to stop the processing when the transient period is practically over. This aspect is addressed here from a Bayesian perspective. Under an often met assumption that the model of a system's time series is recursively estimated anyway, the computational overhead of the constructed stopping rule is negligible. Algorithmic details are presented for important normal ARX models (auto-regression with exogenous variable) and models of discrete-valued, independent, identically distributed data. The latter case provides non-parametric Bayesian estimation of credibility interval with sequential stopping. Copyright © 2004 John Wiley & Sons, Ltd. [source] An enhanced explicit rate algorithm for ABR traffic control in ATM networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2001Y. H. Long Abstract A high performance, low computational complexity rate-based flow control algorithm which can avoid congestion and achieve fairness is important to ATM available bit rate service. The explicit rate allocation algorithm proposed by Kalampoukas et al. is designed to achieve max,min fairness in ATM networks. It has several attractive features, such as a fixed computational complexity of O(1) and the guaranteed convergence to max,min fairness. In this paper, certain drawbacks of the algorithm, such as the severe overload of an outgoing link during transient period and the non-conforming use of the current cell rate field in a resource management cell, have been identified and analysed; a new algorithm which overcomes these drawbacks is proposed. The proposed algorithm simplifies the rate computation as well. Compared with Kalampoukas's algorithm, it has better performance in terms of congestion avoidance and smoothness of rate allocation. Copyright © 2001 John Wiley & Sons, Ltd. [source] The theory of currents through small bridge moleculesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2007B. L. Burrows Abstract A model to treat the theory of currents through small bridge molecules connected to leads is constructed using the time-dependent Schrödinger equation and the wide-band approximation to treat the leads. It is shown that the behaviour of the current through the bridge may be summarized by considering three time periods: a transient period, a quasi-steady -state period and a decaying period. The results obtained are compared with previous work and in particular it is shown that, under reasonable assumptions, they are in accord with the more conventional time-independent scattering theory approaches in the steady-state period. Illustrative calculations are presented for both chain and ring bridge molecules. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Correcting the short-term effect of food deprivation in a damselfly: mechanisms and costsJOURNAL OF ANIMAL ECOLOGY, Issue 1 2008Melina Campero Summary 1Mass at emergence is a life-history trait strongly linked to adult fitness. Therefore, when faced with transient food shortage in the larval stage, mass-correcting mechanisms are common. 2These correcting mechanisms may carry costs with them. On one hand, these costs may be overestimated because they can be confounded with the direct effects of the transient food shortage itself. On the other hand, costs may be underestimated by ignoring physiological costs. Another largely neglected topic is that correcting mechanisms and costs may critically depend upon other stressors that often co-occur. 3Here, we identify the mass-correcting mechanisms and their associated costs at emergence in the damselfly Coenagrion puella, after being stressed by a transient period of starvation and a subsequent exposure to pesticide stress during the larval stage. We introduce path analysis to disentangle direct costs of starvation and the mass-correcting mechanisms in terms of immune response. 4As predicted, we found no differences in mass at emergence. Starvation directly resulted in a costly delayed emergence and a decreased immune response at emergence. Mass-correcting mechanisms included a prolonged post-starvation period, reduced mass loss at emergence and compensatory growth, although the latter only in females under pesticide stress. 5The mass-correcting mechanisms were associated with beneficial effects on investment in immune response, but only in the absence of pesticide stress. Under pesticide stress, these beneficial effects were mostly undone or overruled, resulting in negative effects of the mass-correcting mechanisms in terms of immune response. 6Our results stress the importance of and introduce a statistical way of disentangling direct costs of starvation and the mass-correcting mechanisms themselves, and the importance of including physiological endpoints in this kind of studies. [source] Effects of diversity on diversity: consequences of competition and facilitationOIKOS, Issue 7 2008Mark Vellend Diversity in one group of species or genotypes is often correlated with diversity in a second group , prominent examples including native vs exotic species, and genetic diversity in a focal species vs species diversity in the rest of the community. I used simulation models to investigate the roles of competition and facilitation among species or genotypes in creating diversity,diversity relationships, with a focus on facilitation, which has received little theoretical attention. When competitive interactions dominate, increasing diversity in one group reduces diversity in the second group via filling of available niche space. Facilitation can create positive diversity,diversity relationships via a sampling effect, whereby a strong facilitator of the second group is more likely to be present as diversity increases in the first group, and also via one group acting as a source of biotic heterogeneity (i.e. diversifying selection) on the second group. However, the biotic heterogeneity effect is expected only under restricted conditions , with asymmetric facilitation, only during a transient period, or only over a small range of species diversity levels , and therefore seems unlikely to operate within trophic levels in natural communities. More generally, the simultaneous operation of competition and facilitation results in several different diversity,diversity relationships and underlying mechanisms. The results clarify the potential roles of positive and negative interactions in creating diversity,diversity relationships, and in determining the outcome of community dynamics in general. This study also highlights some important difficulties in incorporating facilitation into ecological theory for communities with many species. [source] Interactions between metabolic and reproductive functions in the resumption of postpartum fecundityAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2009Claudia Valeggia Lactation has long been recognized as a major determinant of interbirth intervals. The temporal pattern of nursing has been proposed as the mechanism behind lactational amenorrhea. We present a new model of the dynamic regulation of lactational amenorrhea that identifies maternal energy availability as the main determinant of ovarian resumption. Variation in the intensity of lactation remains a component of the model as a determinant of the absolute energetic cost of milk production. However, maternal energy supply determines net energy availability; a larger energy supply leaves a greater net energy surplus than a smaller energy supply (lactation costs being equal). We characterize the hormonal postpartum profile of 70 lactating Toba women of Argentina. We use C-peptide, which reflects maternal insulin production, as a measure of energy availability. Initially low, insulin production rises as the postpartum period progresses, reflecting the declining metabolic load of lactation. A short period of supernormal insulin production precedes menstrual resumption. The high levels of insulin may play a role in stimulating the resumption of ovarian activity, which in turn may help to resolve the transient period of insulin resistance. The dynamics of insulin sensitivity during lactation would aid in synchronizing the resumption of ovarian function with a reduction in the energy demands of milk production. This hypothesis is supported by the sustained weight gain experienced by lactating women during the months preceding the first postpartum menses. The link between fecundity and energy balance could serve as a mechanism for adjusting the duration of lactational amenorrhea to the relative metabolic load of lactation. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] N2O Decomposition over Fe-ZSM-5 Studied by Transient TechniquesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2009P. M. Prechtl Abstract N2O decomposition to gaseous N2 and O2 catalyzed by a commercial Fe-ZSM-5 has been studied by different transient techniques: (i) via the transient response methods at ambient pressure, (ii) via the temporal analysis of products (TAP) reactor under vacuum, and (iii) by temperature-programmed desorption (TPD) under vacuum. The catalyst was activated in He at 1323 K. Two main steps can be distinguished within the transient period of N2O decomposition under constant N2O feed at 603 K: the first step consists of molecular N2 formation and surface atomic oxygen (O)Fe. It follows a period of stoichiometric N2O decomposition to gaseous N2 and O2 with increasing conversion until steady state is reached. The observed rate increase is assigned to a slow accumulation on the surface of NOx,ads species formed from N2O and participating as co-catalyst in the N2O decomposition. The NOx,ads species accelerates the atomic oxygen recombination/desorption, which is the rate-determining step of N2O decomposition. The formation and accumulation of NOx,ads species during N2O interaction with the catalyst was confirmed by TAP studies. The amount of NOx,ads was found to depend on the number of N2O pulses injected into the TAP reactor. In the presence of adsorbed NOx on the catalyst surface (NOx,ads) the desorption of dioxygen is facilitated. This results in a shift of the oxygen desorption temperature from 744 K to considerably lower temperatures of 580 K in TPD experiments. Pulses of gaseous NO had a similar effect leading to the formation NOx,ads, thus facilitating the oxygen recombination/desorption. [source] | ||||||||||||||||