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Displaying Results 301 - 325 of 338 on page 13 of 14
Marked
Mark
On Pade Approximations and the Preservation of Quadratic Stability for Switched Linear Systems
(2010)
Shorten, R.; Corless, M.; Sajja, S.; Solmaz, S.
On Pade Approximations and the Preservation of Quadratic Stability for Switched Linear Systems
(2010)
Shorten, R.; Corless, M.; Sajja, S.; Solmaz, S.
Abstract:
In this note we consider the stability preserving properties of diagonal Pad´e approximations to the matrix exponential. We show that while diagonal Pad´e approximations preserve quadratic stability when going from continuous-time to discrete-time, the converse is not true. We discuss the implications of this result for discretising switched linear systems. We also show that for continuous-time switched systems which are exponentially stable, but not quadratically stable, a Pad´e approximation may not preserve stability.
http://eprints.nuim.ie/2248/
Marked
Mark
Strict Positive Realness of Descriptor Systems in State Space
(2010)
Zeheb, Ezra; Shorten, Robert; Sajja, S. Shravan K.
Strict Positive Realness of Descriptor Systems in State Space
(2010)
Zeheb, Ezra; Shorten, Robert; Sajja, S. Shravan K.
Abstract:
In this paper we give necessary and sufficient spectral conditions for various notions of strict positive realness for single input single output Descriptor Systems. These conditions only require calculation of eigenvalues of a single matrix. A new characterization of the KYP lemma for descriptor systems is also derived, and its implications for the absolute stability are briefly discussed.
http://eprints.nuim.ie/2247/
Marked
Mark
Input Disturbance Rejection in Channel Signal-to-Noise Ratio Constrained Feedback Control
(2008)
Rojas, A.J.; Middleton, R.H.; Freudenberg, J.S.; Braslavsky, J.H.
Input Disturbance Rejection in Channel Signal-to-Noise Ratio Constrained Feedback Control
(2008)
Rojas, A.J.; Middleton, R.H.; Freudenberg, J.S.; Braslavsky, J.H.
Abstract:
Communication channels impose a number of obstacles to feedback control. One recent line of work considers the problem of feedback stabilisation subject to a constraint on the channel signal-to-noise ratio (SNR). It has been shown for continuous-time systems that the optimal control problem of achieving the infimal SNR can be formulated as a linear quadratic Gaussian (LQG) control problem with weights chosen as in the loop transfer recovery (LTR) technique. The present paper extends this formulation to: discretetime systems; communications over channels with memory; and input disturbance rejection. By using this formulation, we derive exact expressions for the linear time invariant (LTI) controller that achieves the infimal SNR under the effect of time-delay and additive coloured noise. We then quantify the infimal SNR required for both stabilisation and input disturbance rejection for a relative degree one, minimum phase plant and a memoryless Gaussian channel.
http://eprints.nuim.ie/2245/
Marked
Mark
Integrating Cell-level Kinetic Modeling into the Optimization of Cancer Therapeutics
(2009)
Krippendorff, Ben-Fillippo
Integrating Cell-level Kinetic Modeling into the Optimization of Cancer Therapeutics
(2009)
Krippendorff, Ben-Fillippo
Abstract:
Cancer therapy benefits today from the availability of new promising classes of drugs such as therapeutic proteins. Due to their ability to specifically bind targets in the body they allow to modulate specific chemical reactions and ultimately to modify the functional response of the cell, such as cell growth or cell division. Targeting receptor systems by competitive inhibition is the objective of various protein drugs in development and on the market. Many targeted receptor systems also constitute a degradation mechanism for the drug via endocytosis and a thorough understanding of the complex interplay between the drug's pharmacokinetics and its effect, is largely missing. For complex diseases such as cancer, systems biology models of therapeutically relevant cellular processes have proven valuable for identifying potent drug targets. So far, such information about the dynamics of the targeted system is neglected in later stages of the drug development process when pharmacoki...
http://eprints.nuim.ie/2252/
Marked
Mark
State Reconstruction in Spatially Distributed BioProcess Systems using Reduced Order Models: Application to the Gluconic Acid Production.
(2005)
Garcıa, Mıriam; Vilas, Carlos; Banga, Julio R.; Lyubenova, Velislava N.; Ignatova, Maya...
State Reconstruction in Spatially Distributed BioProcess Systems using Reduced Order Models: Application to the Gluconic Acid Production.
(2005)
Garcıa, Mıriam; Vilas, Carlos; Banga, Julio R.; Lyubenova, Velislava N.; Ignatova, Maya N.; Alonso, Antonio A.
Abstract:
In this work, the dissipative nature of spatially distributed bioprocess systems is exploited to develop efficient state observers based on a low dimensional dynamic representation of the original set of partial differential equations. The approach we suggest combines standard observer design techniques for bioreactors with efficient model reduction methodologies based on projection of the original concentration fields on low dimensional subspaces capturing the slow dynamics of the process. Aspects related with the location of sensors and their influence on the ability to reconstruct concentration fields will also be considered. Finally, the different aspects of the methodology, as well as the efficiency of the resulting observers will be illustrated on a case study of industrial interest, namely a tubular bioreactor producing gluconic acid by Aspergillus Niger.
http://eprints.nuim.ie/1908/
Marked
Mark
Design and Analysis of a General Recurrent Neural Network Model for Time-Varying Matrix Inversion
(2005)
Zhang, Yunong; Ge, Shuzhi Sam
Design and Analysis of a General Recurrent Neural Network Model for Time-Varying Matrix Inversion
(2005)
Zhang, Yunong; Ge, Shuzhi Sam
Abstract:
Following the idea of using first-order time derivatives, this paper presents a general recurrent neural network (RNN) model for online inversion of time-varying matrices. Different kinds of activation functions are investigated to guarantee the global exponential convergence of the neural model to the exact inverse of a given time-varying matrix. The robustness of the proposed neural model is also studied with respect to different activation functions and various implementation errors. Simulation results, including the application to kinematic control of redundant manipulators, substantiate the theoretical analysis and demonstrate the efficacy of the neural model on time-varying matrix inversion, especially when using a power-sigmoid activation function.
http://eprints.nuim.ie/2278/
Marked
Mark
Ligand accumulation counteracts therapeutic inhibition of receptor systems
(2009)
Krippendorff, Ben-Fillippo; Oyarzun, Diego; Huisinga, Wilhelm
Ligand accumulation counteracts therapeutic inhibition of receptor systems
(2009)
Krippendorff, Ben-Fillippo; Oyarzun, Diego; Huisinga, Wilhelm
Abstract:
Targeting receptor systems by competitive inhibition is the objective of various protein drugs in development and on the market. A variety of receptor systems also constitute a degradation mechanism for ligand and drug via endocytosis and therefore influence the microenvironment of the cell. A thorough understanding of the complex interplay between ligand kinetics, drug pharmacokinetics, and the drug effect arising from the inhibition of the receptor by competing with the natural ligand is largely missing. Based on a mathematical model of the drug-ligand-receptor dynamics we show that receptor inhibition may lead to accumulation of the natural ligand in the microenvironment of the cell, with counteracting impact on the inhibitory effect of the drug. In the absence of receptor-independent ligand degradation, we prove analytically that this counteracting effect cannot be eliminated by changing the structural properties of the drug, like the affinity, nor by changing drug dosage. It is...
http://eprints.nuim.ie/2401/
Marked
Mark
An Analytic Characterization of a Stabilizing Feedback for LTI Plants
(2009)
Peters, Andrés A.; Oyarzún, Diego A.; Silva, Eduardo I.; Salgado, Mario E.
An Analytic Characterization of a Stabilizing Feedback for LTI Plants
(2009)
Peters, Andrés A.; Oyarzún, Diego A.; Silva, Eduardo I.; Salgado, Mario E.
Abstract:
The characterization of all stabilizing controllers via the Youla Parameterization requires prior knowledge of one stabilizing feedback. This task is trivial in the case of stable plants. In the unstable case, one needs to use a suitable design technique to obtain such a stabilizing controller. The resulting controller is usually not an explicit function of plant dynamical features. In this paper, we propose a stabilizing controller design such that the sensitivity function can be expressed as an explicit function of the non-minimum phase zeros, time delays, and unstable poles of the plant (and their directions in the multiple-input multiple-output case). These dynamical features are known to impose fundamental limitations on control performance. The results in this paper highlight their relevance since they are shown to be the minimum information required to build a stabilizing controller.
http://eprints.nuim.ie/2509/
Marked
Mark
Multiple Model Kalman Filters: A Localization Technique for RoboCup Soccer
(2010)
Quinlan, Michael J.; Middleton, Richard H.
Multiple Model Kalman Filters: A Localization Technique for RoboCup Soccer
(2010)
Quinlan, Michael J.; Middleton, Richard H.
Abstract:
In the Standard Platform League (SPL) there are substantial sensor limitations due to the rapid motion of the camera, the limited field of view of the camera, and the limited number of unique landmarks. These limitations place high demands on the performance and robustness of localization algorithms. Most of the localization algorithms implemented in RoboCup fall broadly into the class of particle based filters or Kalman type filters including Extended and Unscented variants. Particle Filters are explicitly multi-modal and therefore deal readily with ambiguous sensor data. In this paper, we discuss multiple-model Kalman filters that also are explicitly multi-modal. Motivated by the RoboCup SPL, we show how they can be used despite the highly multi-modal nature of sensed data and give a brief comparison with a particle filter based approach to localization.
http://eprints.nuim.ie/2510/
Marked
Mark
Filtered Gaussian Processes for Learning with Large Data-Sets
(2005)
Shi, Jian Qing; Murray-Smith, Roderick; Titterington, D. Mike; Pearlmutter, Barak A.
Filtered Gaussian Processes for Learning with Large Data-Sets
(2005)
Shi, Jian Qing; Murray-Smith, Roderick; Titterington, D. Mike; Pearlmutter, Barak A.
Abstract:
Kernel-based non-parametric models have been applied widely over recent years. However, the associated computational complexity imposes limitations on the applicability of those methods to problems with large data-sets. In this paper we develop a filtering approach based on a Gaussian process regression model. The idea is to generate a smalldimensional set of filtered data that keeps a high proportion of the information contained in the original large data-set. Model learning and prediction are based on the filtered data, thereby decreasing the computational burden dramatically.
http://eprints.nuim.ie/2511/
Marked
Mark
On Wireless Local Area Networks
(2010)
Huang, Kaidi
On Wireless Local Area Networks
(2010)
Huang, Kaidi
Abstract:
Wireless Local Area Networks (WLANs) have been widely developed during this decade, due to their mobility and exibility. During this period, IEEE 802.11 has become the dominant WLAN protocol. This thesis reports on research into WLANs, especially IEEE 802.11 networks. Since IEEE 802.11 denes rules at the MAC and Physical (PHY) layers, which are introduced in Chapter 1, the rst part (Chapters 2, 3 and 4) of this thesis deals with analytical models for the Distributed Coordination Function (DCF) of the IEEE 802.11 MAC, while the second part (Chapters 5 and 6) focuses on the transmission rates provided by the IEEE 802.11 PHY layer. Analytical models are widely adopted in research into WLANs, especially IEEE 802.11 networks. Despite dierences in details of published analytical models, most of them share common hypotheses. To ensure condence in the predictions made by the analytical models that are based on these common hypotheses, Chapter 2 identies these common hypotheses, and investi...
http://eprints.nuim.ie/2576/
Marked
Mark
On the large deviations of a class of modulated additive processes
(2011)
Duffy, Ken; Macci, Claudio; Torrisi, Giovanni Luca
On the large deviations of a class of modulated additive processes
(2011)
Duffy, Ken; Macci, Claudio; Torrisi, Giovanni Luca
Abstract:
We prove that the large deviation principle holds for a class of processes inspired by semi-Markov additive processes. For the processes we consider, the sojourn times in the phase process need not be independent and identically distributed. Moreover the state selection process need not be independent of the sojourn times. We assume that the phase process takes values in a finite set and that the order in which elements in the set, called states, are visited is selected stochastically. The sojourn times determine how long the phase process spends in a state once it has been selected. The main tool is a representation formula for the sample paths of the empirical laws of the phase process. Then, based on assumed joint large deviation behavior of the state selection and sojourn processes, we prove that the empirical laws of the phase process satisfy a sample path large deviation principle. From this large deviation principle, the large deviations behavior of a class of modulated addit...
http://eprints.nuim.ie/2637/
Marked
Mark
Mathematical modelling of autophagy pathway.
(2010)
Zebrowska, Magdalena
Mathematical modelling of autophagy pathway.
(2010)
Zebrowska, Magdalena
Abstract:
A system modelling autophagy is a new area of research. Current understanding of each step in this biochemical pathway is limited. The study of this mechanism is interesting in several aspects: autophagy plays an important role in physiological cellular processes, is a survival mechanism under external stress and is also connected with cancer and neurodegenerative diseases [Cuervo, 2004; Kondo et al., 2005; Levine, 2007; Pan et al., 2008]. Autophagy is the pathway for degradation of redundant or faulty cell components. This important mechanism occurs in all eukaryotic cells as a part of cell’s everyday activities and plays an important role in cell growth and development (cellular differentiation, immunity, cellular homeostasis). This work proposes a simple mathematical model of autophagy pathway as a system with feedback, which controls the level of the total amino acid pool. Feedback comes from the amino acids which a...
http://eprints.nuim.ie/2653/
Marked
Mark
Piecewise smooth systems and monotonicity.
(2011)
O'Donoghue, Yoann
Piecewise smooth systems and monotonicity.
(2011)
O'Donoghue, Yoann
Abstract:
In this thesis we study piecewise smooth and switched positive systems and investigate the monotonicity properties of such systems. We describe many examples of such systems, particulary drawing from the mathematical biology literature, in order to motivate the work in later chapters. We describe the mathematical theory behind our work in Chapters 3 and 4. In particular we review the theory of LTI systems, positive LTI systems and monotone systems, indicating how monotonicity can be used to determine the asymptotic behaviour of positive LTI systems. We also discuss issues which arise in the study of piecewise smooth and switched linear systems and review solution concepts for such systems. In Chapter 5, we extend the Kamke conditions for smooth monotonic systems to piecewise smooth systems, and in certain cases show that they are equivalent to the monotonicity of the system.
http://eprints.nuim.ie/2660/
Marked
Mark
Providing fairness and maximising throughput in 802.11 wireless mesh network.
(2010)
Cao, Qizhi,
Providing fairness and maximising throughput in 802.11 wireless mesh network.
(2010)
Cao, Qizhi,
Abstract:
The thesis addresses two questions: how to provide fairness in 802.11 wireless mesh networks and how to maximize the overall throughput in an distributed way. Fairness and efficiency are two fundamental issues in wireless networks, which are widely researched in both wired and wireless networks. We consider 802.11 wireless networks due to their ubiquity and practical importance. The likely trend of the wireless networks is toward the use of multi-hop wireless networks (so-called mesh networks), which provide the potential of serving the users in larger converage with higher throughput. However, achieving fairness and efficiency remain bottleneck issues in the rollout of production-quickly mesh networks.
http://eprints.nuim.ie/2661/
Marked
Mark
Power evaluation and performance enhancement of CSMA/CA based WLANs.
(2010)
Fang, Minyu
Power evaluation and performance enhancement of CSMA/CA based WLANs.
(2010)
Fang, Minyu
Abstract:
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) based Wireless Local Area Networks (WLANs) are becoming pervasive. As the most commonly employed standard in WLANs, IEEE 802.11 not only gives rise to health and safety concern from the general public, but also has the potential for enhanced performance. Our contributions in this thesis are twofold: (1) We extend a recently introduced model of transmitted power in WLANs to cover unsaturated conditions when stations do not always have packets to send. we implement an experimental verification of the original analytic model and the extended one. We confirm the estimated maximum power is substantially lower than the International Commission on Non-Ionizing Radiation Protection (ICNIRP) limit; (2) We propose two decentralized Multiple Access Control (MAC) schemes that converge to collision-free schedules almost surely and therefore improve throughput performance. In adopting decentralized learning techniques, the convergen...
http://eprints.nuim.ie/2666/
Marked
Mark
Computational Physiology
(2006)
Huisinga, Wilhelm
Computational Physiology
(2006)
Huisinga, Wilhelm
Abstract:
The junior research group (JRG) is active in the field of mathematical modelling and numerical analysis of multiscale problems for stochastic and deterministic systems, with a strong focus on applications to life sciences. The current projects are on conformation dynamics, hybrid modelling and pharmacokinetics.
http://eprints.nuim.ie/2686/
Marked
Mark
Ambient Radiofrequency Power: the Impact of the Number of Devices in a Wi-Fi Network
(2009)
Malone, David; Malone, Lesley A.
Ambient Radiofrequency Power: the Impact of the Number of Devices in a Wi-Fi Network
(2009)
Malone, David; Malone, Lesley A.
Abstract:
This paper considers how the total radiofrequency power varies as the number of devices in a Wi-Fi network increases. Under the assumption that all devices in the network always have data to transmit, we show that work from network engineering can be adapted to calculate the total transmitted power, accounting for the possibility of multiple devices transmitting at the same time. The paper focuses on total transmitted power as it gives an upper bound on exposure and makes the impact of multiple devices clear. The results show that the number of devices does have a significant impact on the radiated power. For example, one station transmitting small packets in unicast mode gives about half the nominal power value, to reach nominal value around 25 devices are required, and 150% of the nominal value is achieved around 350 devices. We see that 802.11's transmission protocol is usually effective in limiting the power even in very large 802.11 networks.
http://eprints.nuim.ie/2643/
Marked
Mark
A control theoretic approach to mitigate viral escape in HIV
(2011)
Hernandez Vargas, Esteban Abelardo
A control theoretic approach to mitigate viral escape in HIV
(2011)
Hernandez Vargas, Esteban Abelardo
Abstract:
A very important scientific advance was the identification of HIV as a causative agent for AIDS. HIV infection typically involves three main stages: a primary acute infection, a long asymptomatic period and a final increase in viral load with a simultaneous collapse in healthy CD4+T cell count during which AIDS appears. Motivated by the worldwide impact of HIV infection on health and the difficulties to test in vivo or in vitro the different hypothesis which help us to understand the infection, we study the problem from a control theoretic perspective. We present a deterministic ordinary differential equation model that is able to represent the three main stages in HIV infection. The mechanism behind this model suggests that macrophages could be long-term latent reservoirs for HIV and may be important in the progression to AIDS. To avoid or slow this progression to AIDS, antiretroviral drugs were introduce in the late eighties. However, these drugs are not always successful causing ...
http://eprints.nuim.ie/2774/
Marked
Mark
Topics in Cooperative Control
(2011)
Knorn, Florian
Topics in Cooperative Control
(2011)
Knorn, Florian
Abstract:
The main themes of this thesis are networked dynamic systems and related cooperative control problems. We shall contribute a number of technical results to the stability theory of switched positive systems, and present a new cooperative control paradigm that leads to several cooperative control schemes which allow multi-agent systems to achieve a common goal while, at the same time, satisfying certain local constraints. In this context, we also discuss a number of practical applications for our results. On a very abstract level, we first investigate the stability of an unforced dynamic system or network that switches between different configurations. Next, a control input is included to regulate the aggregate behaviour of the network. Lastly, looking at a particular instance of this problem setting, an estimation component is added to the mix. To be more specific, we first derive a number of necessary and sufficient, easily verifiable conditions for the existence of common co-positi...
http://eprints.nuim.ie/2776/
Marked
Mark
Bearing-based selection in mobile spatial interaction
(2009)
Strachan, Steven; Murray-Smith, Roderick
Bearing-based selection in mobile spatial interaction
(2009)
Strachan, Steven; Murray-Smith, Roderick
Abstract:
We introduce a mobile spatial interactive application that uses a combination of a GPS, inertial sensing, gestural interaction, probabilistic models and Monte Carlo sampling, with vibration and audio feedback. This system allows the probing or querying of targets in a local area, based on a model of the local environment and specific context variables of interest, to enable a rich, embodied and location–aware spatial interaction. An experiment was conducted to investigate how spatial target selection at different distances, target separations and target widths is affected by a system with added ‘typical’ noise characteristics. Results showed that the successful selection of targets in the virtual environment is maximised with a combination of high angular separation and angular width.
http://eprints.nuim.ie/2818/
Marked
Mark
Reverse-Mode AD in a Functional Framework: Lambda the Ultimate Backpropagator
(2008)
Pearlmutter, Barak A.; Siskind , Jeffrey Mark
Reverse-Mode AD in a Functional Framework: Lambda the Ultimate Backpropagator
(2008)
Pearlmutter, Barak A.; Siskind , Jeffrey Mark
Abstract:
We show that reverse-mode AD (Automatic Differentiation)—a generalized gradient-calculation operator—can be incorporated as a first-class function in an augmented lambda calculus, and therefore into a functional-programming language. Closure is achieved, in that the new operator can be applied to any expression in the augmented language, yielding an expression in that language. This requires the resolution of two major technical issues: (a) how to transform nested lambda expressions, including those with free-variable references, and (b) how to support self application of the AD machinery. AD transformations preserve certain complexity properties, among them that the reverse phase of the reverse-mode AD transformation of a function have the same temporal complexity as the original untransformed function. First-class unrestricted AD operators increase the expressive power available to the numeric programmer, and may have significant practical implications for the construction of nume...
http://eprints.nuim.ie/3504/
Marked
Mark
Fundamental Limitations in Control over a Communication Channel
(2008)
Rojas, A.J.; Braslavsky, J.H.; Middleton, R.H.
Fundamental Limitations in Control over a Communication Channel
(2008)
Rojas, A.J.; Braslavsky, J.H.; Middleton, R.H.
Abstract:
Fundamental limitations in feedback control is a well established area of research. In recent years it has been extended to the study of limitations imposed by the consideration of a communication channel in the control loop. Previous results characterised these limitations in terms of a minimal data transmission rate necessary for stabilisation. In this paper a signal-to-noise ratio (SNR) approach is used to obtain a tight condition for the linear time invariant output feedback stabilisation of a continuous-time, unstable, non minimum phase (NMP) plant with time-delay over an additive Gaussian coloured noise communication channel. By working on a linear setting the infimal SNR for stabilisability is defined as the infimal achievable H2 norm between the channel noise input and the channel signal input. The result gives a guideline in estimating the severity of the fundamental SNR limitation imposed by the plant unstable poles, NMP zeros, time-delay as well as the channel NMP zeros, ...
http://eprints.nuim.ie/3522/
Marked
Mark
Distributed Probabilistic Synchronization Algorithms for Communication Networks
(2008)
Akar, Mehmet; Shorten, Robert
Distributed Probabilistic Synchronization Algorithms for Communication Networks
(2008)
Akar, Mehmet; Shorten, Robert
Abstract:
In this paper, we present a probabilistic synchronization algorithm whose convergence properties are examined using tools of rowstochastic matrices. The proposed algorithm is particularly well suited for wireless sensor network applications, where connectivity is not guaranteed at all times, and energy efficiency is an important design consideration. The tradeoff between the convergence speed and the energy use is studied.
http://eprints.nuim.ie/3601/
Marked
Mark
A Kalman-Yakubovich-Popov-type lemma for systems with certain state-dependent constraints
(2011)
King, Christopher K.; Griggs, Wynita M.; Shorten, Robert N.
A Kalman-Yakubovich-Popov-type lemma for systems with certain state-dependent constraints
(2011)
King, Christopher K.; Griggs, Wynita M.; Shorten, Robert N.
Abstract:
In this note, a result is presented that may be considered an extension of the classical Kalman-Yakubovich-Popov (KYP) lemma. Motivated by problems in the design of switched systems, we wish to infer the existence of a quadratic Lyapunov function (QLF) for a nonlinear system in the case where a matrix defining one system is a rank-1 perturbation of the other and where switching between the systems is orchestrated according to a conic partitioning of the state space IRn. We show that a necessary and sufficient condition for the existence of a QLF reduces to checking a single constraint on a sum of transfer functions irrespective of problem dimension. Furthermore, we demonstrate that our conditions reduce to the classical KYP lemma when the conic partition of the state space is IRn, with the transfer function condition reducing to the condition of Strict Positive Realness.
http://eprints.nuim.ie/3602/
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