Adaptive Approach (adaptive + approach)

Distribution by Scientific Domains

Selected Abstracts

Adaptive approach for nonlinear sensitivity analysis of reaction kinetics

Illia Horenko
Abstract We present a unified approach for linear and nonlinear sensitivity analysis for models of reaction kinetics that are stated in terms of systems of ordinary differential equations (ODEs). The approach is based on the reformulation of the ODE problem as a density transport problem described by a Fokker,Planck equation. The resulting multidimensional partial differential equation is herein solved by extending the TRAIL algorithm originally introduced by Horenko and Weiser in the context of molecular dynamics (J. Comp. Chem. 2003, 24, 1921) and discussed it in comparison with Monte Carlo techniques. The extended TRAIL approach is fully adaptive and easily allows to study the influence of nonlinear dynamical effects. We illustrate the scheme in application to an enzyme-substrate model problem for sensitivity analysis w.r.t. to initial concentrations and parameter values. 2005 Wiley Periodicals, Inc. J Comput Chem 26: 941,948, 2005 [source]

A performance-oriented adaptive scheduler for dependent tasks on grids,

Luiz F. Bittencourt
Abstract A scheduler must consider the heterogeneity and communication delays when scheduling dependent tasks on a grid. The task-scheduling problem is NP-Complete in general, which led us to the development of a heuristic for the associated optimization problem. In this work we present a dynamic adaptive approach to schedule dependent tasks onto a grid based on the Xavantes grid middleware. The developed dynamic approach is applied to the Path Clustering Heuristic, and introduces the concept of rounds, which take turns sending tasks to execution and evaluating the performance of the resources. The adaptive extension changes the size of rounds during the process execution, taking task attributes and resources performance as parameters, and it can be adopted in other task schedulers. The experiments show that the dynamic round-based and adaptive schedule can minimize the effects of performance losses while executing processes on the grid. Copyright 2007 John Wiley & Sons, Ltd. [source]

A conceptual selenium management model

Peter M Chapman
Abstract We describe herein a conceptual selenium (Se) management model, directed toward coal mining in western Canada, but which can be applied to other coal mines and, with appropriate modification, to other industrial sources of Se to aquatic and terrestrial environments. This conceptual model provides a transparent means to integrate and synthesize existing information that can be used to provide an adaptive approach for managing ecological exposures and associated risk. It is particularly useful for visualizing and subsequently developing management interventions for Se control and risk reduction. The model provides a structured process by which critical information needs can be identified and addressed. It effectively provides the foundation for making management decisions related to Se discharges to aquatic and terrestrial environments by showing interrelationships of the various media and receptors as well as primary sources, release mechanisms, secondary sources, and exposure pathways. [source]

Robust adaptive remeshing strategy for large deformation, transient impact simulations

Tobias Erhart
Abstract In this paper, an adaptive approach, with remeshing as essential ingredient, towards robust and efficient simulation techniques for fast transient, highly non-linear processes including contact is discussed. The necessity for remeshing stems from two sources: the capability to deal with large deformations that might even require topological changes of the mesh and the desire for an error driven distribution of computational resources. The overall computational approach is sketched, the adaptive remeshing strategy is presented and the crucial aspect, the choice of suitable error indicator(s), is discussed in more detail. Several numerical examples demonstrate the performance of the approach. Copyright 2005 John Wiley & Sons, Ltd. [source]

A combined rh -adaptive scheme based on domain subdivision.

Formulation, linear examples
Abstract An adaptive scheme is proposed in which the domain is split into two subdomains. One subdomain consists of regions where the discretization is refined with an h -adaptive approach, whereas in the other subdomain node relocation or r -adaptivity is used. Through this subdivision the advantageous properties of both remeshing strategies (accuracy and low computer costs, respectively) can be exploited in greater depth. The subdivision of the domain is based on the formulation of a desired element size, which renders the approach suitable for coupling with various error assessment tools. Two-dimensional linear examples where the analytical solution is known illustrate the approach. It is shown that the combined rh -adaptive approach is superior to its components r - and h -adaptivity, in that higher accuracies can be obtained compared to a purely r -adaptive approach, while the computational costs are lower than that of a purely h -adaptive approach. As such, a more flexible formulation of adaptive strategies is given, in which the relative importance of attaining a pre-set accuracy and speeding-up the computational process can be set by the user. Copyright 2001 John Wiley & Sons, Ltd. [source]

Split agent-based routing in interconnected networks

Constandinos X. Mavromoustakis
Abstract Adaptive behaviour of swarm-based agents (BT Technol. J. 1994; 12:104,113; AAMAS Conference '02, Melbourne, Australia, Month 1,2, 2002; Softcomput. J. 2001; 5(4):313,317.) is being studied in this paper with respect to network throughput for a certain amount of data traffic. Algorithmically complex problems like routing data packets in a network need to be faced with a dynamically adaptive approach such as agent-based scheme. Particularly in interconnected networks where multiple networks are participating in order to figure a large-scale network with different QoS levels and heterogeneity in the service of delay sensitive packets, routing algorithm must adopt in frequent network changes to anticipate such situations. Split agent-based routing technique (SART) is a variant of swarm-based routing (Adapt. Behav. 1997; 5:169,207; Proceedings of 2003 International Symposium on Performance Evaluation of Computer and Telecommunication Systems,SPECTS, Montreal, Canada, July 20,24, 2003; 240,247.) where agents are split after their departure to the next node on a hop-by-hop basis. Packets that are delay sensitive are marked as prioritized which agents recognize-as being a part of a packet- and try to influence the two-way routing tables. Thorough examination is made, for the performance of the proposed algorithm in the network and the QoS offered, taking into account a number of metrics. It is shown that the split agent routing scheme applied to interconnected networks offers a decentralized control in the network and an efficient way to increase overall performance and packet control reducing at the same time the packet loss concept. Copyright 2004 John Wiley & Sons, Ltd. [source]

The role of research for integrated management of invasive species, invaded landscapes and communities

Yvonne M. Buckley
Summary 1Invaded landscapes and ecosystems are composed of multiple interacting networks and feed-back loops, sometimes leading to unexpected effects of management actions. In order to plan management for invaded systems we need to explicitly consider management goals before putting actions in place. Actions taken must be justified in terms of their amelioration of impacts of invaders, contribution to the management goals and the costs incurred. 2This Special Profile brings together papers on the management of invasive plants, transgenes, animals and diseases, leading to conclusions with clear policy and management relevance and contributing to some of the hottest current topics in invasion ecology: unexpected impacts of invaders, restoration of invasion resistance, distribution mapping, spatial epidemiology, escape of transgenes, community interactions and complex effects of management. 3As papers in this Special Profile demonstrate, management for amelioration of the impacts of invasive species will include a wide range of manipulations, not just of the invader itself but of both abiotic and biotic components of the system. In fact, several papers in this Special Profile show that indirect management of the community may be more effective than removal of the invader alone. 4As little information is generally available at the beginning of a management programme, an adaptive approach should be taken and the management objectives/goals revised throughout the management process. New methods are emerging for adaptive management; an example is presented in this Special Profile where a Bayesian model used for assessing eradication goals can be updated throughout the management process leading to refinement of management. 5Synthesis and applications. Applied research should be directed at providing decision support for managers throughout the management process and can be used to provide predictive tools for risk assessment of new invaders. The science of invasion ecology has much to contribute to the new challenge of natural or enhanced movement of organisms in relation to climate change. Methods and information from invasion ecology can be used to assess management goals, management actions and the risks of potential translocations before they are put in place. [source]

Speed control of differentially driven wheeled mobile robots,model-based adaptive approach

L. Huang
In this paper, the issue concerning model-based adaptive control for a differentially driven wheeled mobile robot is addressed. By choosing state variables directly related to its speeds (linear and angular), the robot's dynamic model becomes simple with good properties. The controller takes account of the robot dynamics and the coupling between the motions of two wheels, and thus achieves better speed tracking than commonly used model-free PID controller does. The effectiveness of the model free controllers (mostly PID) in some situations is also discussed. Simulation studies are done to verify the effectiveness of the proposed approaches. 2005 Wiley Periodicals, Inc. [source]

A novel adaptive bilateral control scheme using similar closed-loop dynamic characteristics of master/slave manipulators

Jee-Hwan Ryu
This article presents a novel adaptive bilateral control scheme for obtaining ideal responses for teleoperation systems with uncertainties. A condition that is equivalent to getting an ideal response in teleoperation has been found to be making the closed-loop dynamics of master and slave manipulators a similar form. An adaptive approach is applied to achieve similarity for the uncertain master and slave manipulators. Using the similar closed-loop dynamic characteristics of master/slave teleoperation systems, excellent position and force tracking performance has been obtained without estimating the impedance of human and environment. The validity of the theoretical results is verified by experiments. 2001 John Wiley & Sons, Inc. [source]

Vegetation restoration of secondary bare saline-alkali patches in the Songnen plain, China

S.-C. Jiang
Abstract Questions: What factors limit vegetation restoration of secondary bare saline-alkaline patches (BSAP) in the Songnen grassland of northeast China? Is there any adaptive approach to promote revegetation in the shortest time possible and at a low cost? Location: Northeast China. Methods: Considering the climate, soil saline-alkalization and available seed sources, a new approach was adopted to restore vegetation in BSAP, which were formed by the degradation of typical Leymus chinensis grasslands owing to long-term overgrazing. The experimental treatments included no treatment (CK), fencing (F), fencing+inserting cornstalks (FS), fencing+inserting cornstalks+sowing L. chinensis (FSL) and fencing+inserting cornstalks+sowing Puccinellia chinampoensis (FSP). The assumptions behind inserting cornstalks were not only that they would create safe sites for initial revegetation but also that they would enhance seed input by trapping and containing the seeds from seed movement on the BSAP surface. Results: Seed bank shortage was an important factor limiting initial revegetation in BSAP; seed movement on the BSAP surface could provide the necessary seed source if it were contained by effective measures. Vegetation at the sites FS, FSL and FSP was restored well in terms of the above-ground biomass and coverage. Inserted cornstalks acted as safe sites that enhanced the plant survival rate in BSAP; they also enhanced the ability to contain seed movement, thus providing a seed source for initial revegetation. Along with initial revegetation, tussocks around cornstalks can provide better safe sites, which in turn can accelerate subsequent vegetation restoration in BSAP. Conclusions: The approach entails the strategic use of diverse seed sources and the construction of safe sites with agricultural byproducts (cornstalks); therefore, it is a low-cost method and can be used on a widespread scale. The results provide vigorous support in favor of vegetation restoration in BSAP and severely degraded grasslands in the region. In practice, this approach can be used in degraded ecosystems with compacted soil surfaces (including arid and salt-affected soils) to promote revegetation in various regions. [source]

Strategies of family farms to strengthen their resilience

Ika Darnhofer
Abstract Resilience thinking offers a framework to emphasize dynamics and interdependencies across time, space and domains. It is based on understanding social,ecological systems as complex, and future developments as unpredictable, thus emphasizing adaptive approaches to management. In this paper the four clusters of factors that have been identified as building resilience in large-scale social,ecological systems are applied at the farm level. Suggestions on how these factors could be operationalized at the farm level are derived from workshops held with family farmers in Austria. The results show that farmers understand change as unpredictable and unfolding, have a number of strategies to ensure the flexibility and adaptability of their farm and build extensive networks to diversify information and income sources. However, these strategies, while ensuring adaptability and transformability, compete for scarce resources. The farmers thus face trade-offs between strategies that ensure the adaptive capacity of their farm over the long term and those ensuring profitability over the short term. Copyright 2010 John Wiley & Sons, Ltd and ERP Environment. [source]

Management of diabetes using adaptive control

Roman Hovorka
Abstract The review focuses on adaptive systems for insulin treatment in type 1 diabetes. The review consists of two parts. First, adaptive approaches are described, which exploit infrequent glucose measurements (four to seven measurements per day). Second, adaptive approaches are described, which exploit frequent or continuous glucose measurements (every hour or more often). Each part is further divided into two subparts separating off-line and on-line adaptive techniques. The latter represents treatment strategies, which rely on continuous re-assessment of the glucoregulatory system. The former refers to treatment strategies, which are fixed for a day or longer and are revisited from time to time. It is concluded that the role of adaptive approaches will increase as new continuous glucose-sensing monitors reach the market. Copyright 2004 John Wiley & Sons, Ltd. [source]

Dealing with uncertainty: adaptive approaches to sustainable river management

M.J. CLARKArticle first published online: 5 AUG 200
Abstract 1.Sustainable river management is the proclaimed aim of many agencies and institutions, but it remains challenging to bring this worthy ideal from the level of political rhetoric to that of practical river management. 2.Amongst the many drivers that already pressure the river manager, from internal institutional goals, through political aspirations to systemic change within the biophysical process system, one common element emerges, that of prevailing uncertainty. 3.Once it has been accepted that conventional science and engineering approaches to uncertainty (risk) minimization may be sub-optimal in a truly holistic (biophysical, socio-economic, political) system, the challenge emerges of developing a more appropriate framework without destroying over-burdened managers and management systems in the process. 4.It is argued that the necessary components are often already in place or under consideration. A linked model is proposed comprising practical measures of sustainability, robust approaches to uncertainty (if necessary, involving attitude change), responsive (adaptive) management frameworks, and an important underpinning of fuzzy decision support. Copyright 2002 John Wiley & Sons, Ltd. [source]