The Experts below are selected from a list of 50142 Experts worldwide ranked by ideXlab platform
William Moran - One of the best experts on this subject based on the ideXlab platform.
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Topological feedback entropy for nonlinear systems
2004Co-Authors: Girish N. Nair, Robin J. Evans, Iven Mareels, William MoranAbstract:It is well-known in the field of dynamical systems that entropy can be defined rigorously for completely deterministic open-loop systems. However, such definitions have found limited application in engineering, unlike Shannon's statistical entropy. In this paper, it is shown that the problem of communication-limited stabilization is related to the concept of topological entropy, introduced by Adler et al. as a measure of the information Rate of a continuous map on a compact topological space. Using similar open cover techniques, the notion of topological feedback entropy (TFE) is defined in this paper and proposed as a measure of the Inherent Rate at which a map on a noncompact topological space with inputs geneRates stability information. It is then proven that a topological dynamical plant can be stabilized into a compact set if and only if the data Rate in the feedback loop exceeds the TFE of the plant on the set. By taking appropriate limits in a metric space, the concept of local TFE (LTFE) is defined arid it is asserted that a plant is locally uniformly asymptotically stabilizable to a fixed point if and only if the data Rate exceeds the plant LTFE at the fixed point. An expression for the LTFE of continuously differentiable plants in Euclidean space is then given.
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Topological feedback entropy for nonlinear stabilization
IFAC Proceedings Volumes, 2004Co-Authors: Girish N. Nair, Robin J. Evans, Iven Mareels, William MoranAbstract:Abstract In this paper, it is shown that the problem of communication-limited stabilization is related to the concept of topological entropy, introduced by Adler et. al. as a measure of the information Rate of a continuous map on a compact topological space. Using open covers, the notion of topological feedback entropy (TFE) is defined and proposed as a measure of the Inherent Rate at which a map on a noncompact topological space with inputs geneRates stability information. It is then proven that a topological dynamical plant can be stabilized into a compact set if and only if the data Rate in the feedback loop exceeds the TFE of the plant on the set.
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Topological feedback entropy and Nonlinear stabilization
IEEE Transactions on Automatic Control, 2004Co-Authors: Girish N. Nair, Robin J. Evans, Iven Mareels, William MoranAbstract:It is well known in the field of dynamical systems that entropy can be defined rigorously for completely deterministic open-loop systems. However, such definitions have found limited application in engineering, unlike Shannon's statistical entropy. In this paper, it is shown that the problem of communication-limited stabilization is related to the concept of topological entropy, introduced by Adler et al. as a measure of the information Rate of a continuous map on a compact topological space. Using similar open cover techniques, the notion of topological feedback entropy (TFE) is defined in this paper and proposed as a measure of the Inherent Rate at which a map on a noncompact topological space with inputs geneRates stability information. It is then proven that a topological dynamical plant can be stabilized into a compact set if and only if the data Rate in the feedback loop exceeds the TFE of the plant on the set. By taking appropriate limits in a metric space, the concept of local TFE (LTFE) is defined at fixed points of the plant, and it is shown that the plant is locally uniformly asymptotically stabilizable to a fixed point if and only if the data Rate exceeds the plant LTFE at the fixed point. For continuously differentiable plants in Euclidean space, real Jordan forms and volume partitioning arguments are then used to derive an expression for LTFE in terms of the unstable eigenvalues of the fixed point Jacobian.
Sheng Yang - One of the best experts on this subject based on the ideXlab platform.
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confirmation and elimination of xylose metabolism bottlenecks in glucose phosphoenolpyruvate dependent phosphotransferase system deficient clostridium acetobutylicum for simultaneous utilization of glucose xylose and arabinose
Applied and Environmental Microbiology, 2011Co-Authors: Han Xiao, Yang Gu, Yuanyuan Ning, Yunliu Yang, Wilfrid J Mitchell, Weihong Jiang, Sheng YangAbstract:Efficient cofermentation of d-glucose, d-xylose, and l-arabinose, three major sugars present in lignocellulose, is a fundamental requirement for cost-effective utilization of lignocellulosic biomass. The Gram-positive anaerobic bacterium Clostridium acetobutylicum, known for its excellent capability of producing ABE (acetone, butanol, and ethanol) solvent, is limited in using lignocellulose because of inefficient pentose consumption when fermenting sugar mixtures. To overcome this substRate utilization defect, a predicted glcG gene, encoding enzyme II of the d-glucose phosphoenolpyruvate-dependent phosphotransferase system (PTS), was first disrupted in the ABE-producing model strain Clostridium acetobutylicum ATCC 824, resulting in greatly improved d-xylose and l-arabinose consumption in the presence of d-glucose. Interestingly, despite the loss of GlcG, the resulting mutant strain 824glcG fermented d-glucose as efficiently as did the parent strain. This could be attributed to residual glucose PTS activity, although an increased activity of glucose kinase suggested that non-PTS glucose uptake might also be elevated as a result of glcG disruption. Furthermore, the Inherent Rate-limiting steps of the d-xylose metabolic pathway were observed prior to the pentose phosphate pathway (PPP) in strain ATCC 824 and then overcome by co-overexpression of the d-xylose proton-symporter (cac1345), d-xylose isomerase (cac2610), and xylulokinase (cac2612). As a result, an engineered strain (824glcG-TBA), obtained by integrating glcG disruption and genetic overexpression of the xylose pathway, was able to efficiently coferment mixtures of d-glucose, d-xylose, and l-arabinose, reaching a 24% higher ABE solvent titer (16.06 g/liter) and a 5% higher yield (0.28 g/g) compared to those of the wild-type strain. This strain will be a promising platform host toward commercial exploitation of lignocellulose to produce solvents and biofuels.
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confirmation and elimination of xylose metabolism bottlenecks in glucose phosphoenolpyruvate dependent phosphotransferase system deficient clostridium acetobutylicum for simultaneous utilization of glucose xylose and arabinose
Applied and Environmental Microbiology, 2011Co-Authors: Han Xiao, Yuanyuan Ning, Yunliu Yang, Wilfrid J Mitchell, Weihong Jiang, Sheng YangAbstract:Efficient cofermentation of D-glucose, D-xylose, and L-arabinose, three major sugars present in lignocellulose, is a fundamental requirement for cost-effective utilization of lignocellulosic biomass. The Gram-positive anaerobic bacterium Clostridium acetobutylicum, known for its excellent capability of producing ABE (acetone, butanol, and ethanol) solvent, is limited in using lignocellulose because of inefficient pentose consumption when fermenting sugar mixtures. To overcome this substRate utilization defect, a predicted glcG gene, encoding enzyme II of the D-glucose phosphoenolpyruvate-dependent phosphotransferase system (PTS), was first disrupted in the ABE-producing model strain Clostridium acetobutylicum ATCC 824, resulting in greatly improved D-xylose and L-arabinose consumption in the presence of D-glucose. Interestingly, despite the loss of GlcG, the resulting mutant strain 824glcG fermented D-glucose as efficiently as did the parent strain. This could be attributed to residual glucose PTS activity, although an increased activity of glucose kinase suggested that non-PTS glucose uptake might also be elevated as a result of glcG disruption. Furthermore, the Inherent Rate-limiting steps of the D-xylose metabolic pathway were observed prior to the pentose phosphate pathway (PPP) in strain ATCC 824 and then overcome by co-overexpression of the D-xylose proton-symporter (cac1345), D-xylose isomerase (cac2610), and xylulokinase (cac2612). As a result, an engineered strain (824glcG-TBA), obtained by integrating glcG disruption and genetic overexpression of the xylose pathway, was able to efficiently coferment mixtures of D-glucose, D-xylose, and L-arabinose, reaching a 24% higher ABE solvent titer (16.06 g/liter) and a 5% higher yield (0.28 g/g) compared to those of the wild-type strain. This strain will be a promising platform host toward commercial exploitation of lignocellulose to produce solvents and biofuels.
Miko U F Kirschbaum - One of the best experts on this subject based on the ideXlab platform.
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Can Trees Buy Time? An Assessment of the Role of Vegetation Sinks as Part of the Global Carbon Cycle
Climatic Change, 2003Co-Authors: Miko U F KirschbaumAbstract:Atmospheric CO_2 concentrations can be reduced by storing carbon in vegetation. However, this lowers the concentration gradient between the atmosphere and other potential carbon reservoirs, such as the oceans, and thereby reduces the subsequent Inherent Rate of removal of CO_2 from the atmosphere. Hence, storage of carbon in temporary reservoirs can reduce atmospheric CO_2 concentrations in the short term, but if the carbon is released again, it will increase concentrations in the long term. It must, therefore, be considered when, or, indeed whether, to store carbon in vegetation sinks.To determine an optimal stRategy, the exact nature of climate-change impacts needs to be considered first. Impacts can be mediated by: 1. the direct and instantaneous effect of CO_2 and its associated temperature; 2. the Rate of change in CO_2 and its associated temperature; 3. the cumulative effect of CO_2 and its associated temperature. Carbon stored in permanently maintained vegetation sinks can lower atmospheric CO_2 concentrations, but this can be done most effectively if sequestration occurs close to the time when atmospheric concentrations are to be lowered. Similarly, maximal Rates of change can be most effectively reduced by carbon sequestration close to the time of anticipated maximal Rates of change. For reducing impacts via cumulative forcing, however, early sink activity would be more effective than delayed activity.Temporary carbon stores would only be beneficial for climate change impacts related to the cumulative impact of CO_2, but it could even worsen impacts mediated via the instantaneous effect of temperature or those related to the Rate of change. Hence, the planting of trees is only beneficial in reducing climate-change impacts if the most serious impacts are those related to the cumulative effect of increased temperature. If other impacts are more serious, then the planting of trees would bring greater benefits if it is delayed until closer to the time when the most severe impacts are to be expected. However, if serious land degradation would result from deforestation, or from a failure to plant trees in the near future, then trees should still be planted in order to maximise the amount of carbon stored on land.
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to sink or burn a discussion of the potential contributions of forests to greenhouse gas balances through storing carbon or providing biofuels
Biomass & Bioenergy, 2003Co-Authors: Miko U F KirschbaumAbstract:Abstract Forests can affect net CO 2 emissions by increasing or decreasing the amount of stored carbon, or by supplying biofuels for power generation to substitute for fossil fuels. However, forests store the most carbon when they remain undisturbed and are allowed to grow to maturity, whereas using wood for bioenergy requires wood removal from forests, which reduces on-site carbon storage. Hence, it is difficult to manage a forest simultaneously for maximum carbon storage and supplying fuelwood. For developing optimal stRategies for the use of vegetation sinks, it is necessary to consider the feedbacks via the Inherent natural adjustments in the global carbon cycle. Increased atmospheric CO 2 currently provides a driving force for carbon uptake by natural carbon reservoirs, such as the world's oceans. When carbon is removed from the atmosphere and stored in biomass, it lowers the concentration gradient between the atmosphere and these other reservoirs. This reduces the subsequent Inherent Rate of CO 2 removal from the atmosphere. This means that transferring a quantity of CO 2 from the atmosphere to a biomass pool lowers the atmospheric concentration the most immediately after the initial removal, but subsequently, the atmospheric concentration trends back towards the values without biospheric removal. The optimal timing for the use of vegetation sinks therefore depends on a number of factors: the length of time over which forest growth can be maintained, whether biomass is used for energy generation and on the nature of the most detrimental aspects of climate-change impacts. Climate-change impacts related to the instantaneous effect of temperature are mitigated less by vegetation sinks than impacts that act via the cumulative effect of increased temperature. It also means that short-term carbon storage in temporary sinks is not generally beneficial in mitigating climate change.
Girish N. Nair - One of the best experts on this subject based on the ideXlab platform.
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Topological feedback entropy for nonlinear systems
2004Co-Authors: Girish N. Nair, Robin J. Evans, Iven Mareels, William MoranAbstract:It is well-known in the field of dynamical systems that entropy can be defined rigorously for completely deterministic open-loop systems. However, such definitions have found limited application in engineering, unlike Shannon's statistical entropy. In this paper, it is shown that the problem of communication-limited stabilization is related to the concept of topological entropy, introduced by Adler et al. as a measure of the information Rate of a continuous map on a compact topological space. Using similar open cover techniques, the notion of topological feedback entropy (TFE) is defined in this paper and proposed as a measure of the Inherent Rate at which a map on a noncompact topological space with inputs geneRates stability information. It is then proven that a topological dynamical plant can be stabilized into a compact set if and only if the data Rate in the feedback loop exceeds the TFE of the plant on the set. By taking appropriate limits in a metric space, the concept of local TFE (LTFE) is defined arid it is asserted that a plant is locally uniformly asymptotically stabilizable to a fixed point if and only if the data Rate exceeds the plant LTFE at the fixed point. An expression for the LTFE of continuously differentiable plants in Euclidean space is then given.
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Topological feedback entropy for nonlinear stabilization
IFAC Proceedings Volumes, 2004Co-Authors: Girish N. Nair, Robin J. Evans, Iven Mareels, William MoranAbstract:Abstract In this paper, it is shown that the problem of communication-limited stabilization is related to the concept of topological entropy, introduced by Adler et. al. as a measure of the information Rate of a continuous map on a compact topological space. Using open covers, the notion of topological feedback entropy (TFE) is defined and proposed as a measure of the Inherent Rate at which a map on a noncompact topological space with inputs geneRates stability information. It is then proven that a topological dynamical plant can be stabilized into a compact set if and only if the data Rate in the feedback loop exceeds the TFE of the plant on the set.
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Topological feedback entropy and Nonlinear stabilization
IEEE Transactions on Automatic Control, 2004Co-Authors: Girish N. Nair, Robin J. Evans, Iven Mareels, William MoranAbstract:It is well known in the field of dynamical systems that entropy can be defined rigorously for completely deterministic open-loop systems. However, such definitions have found limited application in engineering, unlike Shannon's statistical entropy. In this paper, it is shown that the problem of communication-limited stabilization is related to the concept of topological entropy, introduced by Adler et al. as a measure of the information Rate of a continuous map on a compact topological space. Using similar open cover techniques, the notion of topological feedback entropy (TFE) is defined in this paper and proposed as a measure of the Inherent Rate at which a map on a noncompact topological space with inputs geneRates stability information. It is then proven that a topological dynamical plant can be stabilized into a compact set if and only if the data Rate in the feedback loop exceeds the TFE of the plant on the set. By taking appropriate limits in a metric space, the concept of local TFE (LTFE) is defined at fixed points of the plant, and it is shown that the plant is locally uniformly asymptotically stabilizable to a fixed point if and only if the data Rate exceeds the plant LTFE at the fixed point. For continuously differentiable plants in Euclidean space, real Jordan forms and volume partitioning arguments are then used to derive an expression for LTFE in terms of the unstable eigenvalues of the fixed point Jacobian.
Eric Torng - One of the best experts on this subject based on the ideXlab platform.
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MASS - Efficient Opportunistic Multicast via Tree Backbone for Wireless Mesh Networks
2011 IEEE Eighth International Conference on Mobile Ad-Hoc and Sensor Systems, 2011Co-Authors: Guokai Zeng, Pei Huang, Matt W. Mutka, Li Xiao, Eric TorngAbstract:In this paper, we propose a new opportunistic multicast protocol to improve multicast throughput in Wireless Mesh Networks (WMN). It builds upon opportunistic routing (OR) stRategies that have been designed to improve unicast throughput in wireless networks. The key concept in our multicast protocol is a tree backbone. Our tree backbone protocol represents a tradeoff between traditional structured multicast protocols where a complete multicast tree is constructed and unstructured protocols where multicast is treated as a collection of unicasts. Tree backbone selects multiple nodes as intermediate nodes. Each pair of upstream and downstream nodes may be multiple hops away, and packet delivery between them takes advantage of OR. For single-Rate WMNs, we show that constructing an efficient tree backbone that minimizes the number of transmissions is NP-hard, and we devise one effective heuristic algorithm for it. For multi-Rate WMNs, we investigate the Inherent Rate-distance tradeoff and propose a Euclidean opportunistic multicast protocol by devising a Euclidean tree backbone as well as an efficient Rate selection scheme to minimize the number of transmissions. In our simulations, our tree backbone multicast protocols outperform both the completely structured traditional multicast protocols and the completely unstructured unicast-based protocols augmented with OR in both throughput and delay.