[Show abstract][Hide abstract] ABSTRACT: The calcium signaling plays a vital role in flow-dependent vascular endothelial cell (VEC) physiology. Variations in fluid shear stress and ATP concentration in blood vessels can activate dynamic responses of cytosolic-free [Formula: see text] through various calcium channels on the plasma membrane. In this paper, a novel dynamic model has been proposed for transient receptor potential vanilloid 4 [Formula: see text]-mediated intracellular calcium dynamics in VECs induced by fluid shear stress and ATP. Our model includes [Formula: see text] signaling pathways through P2Y receptors and [Formula: see text] channels (indirect mechanism) and captures the roles of the [Formula: see text] compound channels in VEC [Formula: see text] signaling in response to fluid shear stress (direct mechanism). In particular, it takes into account that the [Formula: see text] compound channels are regulated by intracellular [Formula: see text] and [Formula: see text] concentrations. The simulation studies have demonstrated that the dynamic responses of calcium concentration produced by the proposed model correlate well with the existing experimental observations. We also conclude from the simulation studies that endogenously released ATP may play an insignificant role in the process of intracellular [Formula: see text] response to shear stress.
Biomechanics and Modeling in Mechanobiology 01/2015; 14(5). DOI:10.1007/s10237-015-0647-3 · 3.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we describe a classification framework for binary shapes that have scale, rotation and strong viewpoint variations. To this end, we develop several novel techniques. First, we employ the spectral magnitude of log-polar transform as a local feature in the bag-of-words model. Second, we incorporate contextual information in the bag-of-words model using a novel method to extract bi-grams from the spatial co-occurrence matrix. Third, a novel metric termed ‘weighted gain ratio’ is proposed to select a suitable codebook size in the bag-of-words model. The proposed metric is generic, and hence it can be used for any clustering quality evaluation task. Fourth, a joint learning framework is proposed to learn features in a data-driven manner, and thus avoid manual fine-tuning of the model parameters. We test our shape classification system on the animal shapes dataset and significantly outperform state-of-the-art methods in the literature.
[Show abstract][Hide abstract] ABSTRACT: In this paper, a multiple generalized NARMA-L2 model is proposed for the identification and control of discrete nonlinear systems. It provides a global input-output representation for nonlinear systems by making use of the good local approximation property of NARMA-L2 model without encountering the curse of dimensionality problem. With the identified model, the control problem is then transformed into a constrained optimization problem based on the weighted one-step-ahead predictive control law. Simulation studies demonstrate the effectiveness of the proposed model structure.
2014 11th IEEE International Conference on Control & Automation (ICCA); 06/2014
[Show abstract][Hide abstract] ABSTRACT: We consider the L2-stability analysis of single-input–single-output SISO systems with periodic and nonperiodic switching gains and described by integral equations that can be specialised to the form of standard differential equations. For the latter, stability literature is mostly based on the application of quadratic forms as Lyapunov-function candidates which lead, in general, to conservative results. Exceptions are some recent results, especially for second-order linear differential equations, obtained by trajectory control or optimisation to arrive at the worst-case switching sequence of the gain. In contrast, we employ a non-Lyapunov framework to derive L2-stability conditions for a class of linear and nonlinear SISO systems in integral form, with monotone, odd-monotone and relaxed monotone nonlinearities, and, in each case, with periodic or nonperiodic switching gains. The derived frequency-domain results are reminiscent of i the Nyquist criterion for linear time-invariant feedback systems and ii the Popov-criterion for time-invariant nonlinear feedback systems with the Lur'e-type nonlinearity. Although overlapping with some recent results of the literature for periodic gains, they have been derived independently in essentially the Popov framework, are different for certain classes of nonlinearities and address some of the questions left open, with respect to, for instance, the synthesis of the multipliers and numerical interpretation of the results. Apart from the novelty of the results as applied to the dwell-time problem, they reveal an interesting phenomenon of the switched systems: fast switching can lead to stability, thereby providing an alternative framework for vibrational stability analysis.
International Journal of Systems Science 03/2014; 45(3):682-701. DOI:10.1080/00207721.2012.724199 · 2.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, the switching stabilisation problem of second-order switched linear systems is studied. By extending the best case switching signal (BCSS) criteria for second-order switched linear systems with two subsystems to the general case with any finite number of subsystems, necessary and sufficient conditions for regional stabilisability of second-order switched linear systems with any finite number of subsystems are proposed in this paper. The main idea of this paper is to divide all the subsystems in a region into two groups based on their trajectory directions in that region. By comparing pairwise, the most “stable” subsystem for each group in a region can be determined and the BCSS analysis among all the subsystems in that region is reduced to the BCSS analysis between the two most “stable” subsystems in that region.
[Show abstract][Hide abstract] ABSTRACT: Calcium ion is a secondary messenger of mammalian spermatozoa. The dynamic change of its concentration plays a vital role in the process of sperm motility, capacitation, acrosome and fertilization. Progesterone released by the cumulus cells, as a potent stimulator of fertilization, can activate the calcium channels on the plasma membrane, which in turn triggers the dynamic change of intracellular calcium concentration. In this paper, a mathematical model of calcium dynamic response in mammalian spermatozoa induced by progesterone is proposed and numerical simulation of the dynamic model is conducted. The results show that the dynamic response of calcium concentration predicted by the model is in accordance with experimental evidence. The proposed dynamic model can be used to explain the phenomena observed in the experiments and predict new phenomena to be revealed by experimental investigations, which will provide the basis to quantitatively investigate the fluid mechanics and biochemistry for the sperm motility induced by progesterone.
[Show abstract][Hide abstract] ABSTRACT: The paper deals with the L
2-stability analysis of multi-input-multi-output (MIMO) systems, governed by integral equations, with a matrix of periodic/aperiodic time-varying gains and a vector of monotone, non-monotone and quasi-monotone nonlinearities. For nonlinear MIMO systems that are described by differential equations, most of the literature on stability is based on an application of quadratic forms as Lyapunov-function candidates. In contrast, a non-Lyapunov framework is employed here to derive new and more general L
2-stability conditions in the frequency domain. These conditions have the following features: i) They are expressed in terms of the positive definiteness of the real part of matrices involving the transfer function of the linear time-invariant block and a matrix multiplier function that incorporates the minimax properties of the time-varying linear/nonlinear block. ii) For certain cases of the periodic time-varying gain, they contain, depending on the multiplier function chosen, no restrictions on the normalized rate of variation of the time-varying gain, but, for other periodic/aperiodic time-varying gains, they do. Overall, even when specialized to periodic-coefficient linear and nonlinear MIMO systems, the stability conditions are distinct from and less restrictive than recent results in the literature. No comparable results exist in the literature for aperiodic time-varying gains. Furthermore, some new stability results concerning the dwell-time problem and time-varying gain switching in linear and nonlinear MIMO systems with periodic/aperiodic matrix gains are also presented. Examples are given to illustrate a few of the stability theorems.
[Show abstract][Hide abstract] ABSTRACT: Regulation of intracellular calcium ion concentration ([Ca(2+)]in) in fibroblasts induced by exogenous electrical stimulation could be applied to control gene expressions selectively which in turn modulate the function of the fibroblasts. Regarding the mechanism for electric-field-induced Ca(2+) influx via voltage-gated Ca(2+) channels and/or stretch-activated cation channels in the fibroblasts, a dynamic mathematical model is proposed to quantify the [Ca(2+)]in dynamics in response to direct current or alternating current electric fields. Simulation results demonstrate that the changes in [Ca(2+)]in predicted by our dynamic model are consistent with the experimental data in the literature. The proposed dynamic model could provide not only more insights into the electric-field-induced intracellular Ca(2+) response but also a quantitative way to regulate the [Ca(2+)]in dynamics by controlling the external electrical stimulation.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we focus on the identification of discrete-time piecewise affine (PWA) systems from noisy data. This problem consists of the estimation of both the local affine subsystems and the partition of the regression space. A two-stage robust identification approach is proposed to estimate the local affine subsystems in the presence of noise. This approach includes an optimization-based initial estimation process and a least-squares-based refinement procedure. In addition, to estimate the partition of the regression space for continuous dynamic PWA systems, an intersection approach is proposed as an alternative to the widely used pattern recognition approaches. Simulation studies demonstrate the effectiveness of the two-stage identification approach and the intersection approach in noisy case.
Control and Automation (ICCA), 2013 10th IEEE International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: The acute effects of leg anaerobic exercises on the stiffness and local hemodynamics in human common carotid artery are investigated in this paper. The results show that leg anaerobic exercises increase the arterial stiffness and significantly modulate local hemodynamic parameters in the common carotid artery including systolic blood pressure, mean blood pressure, pulse blood pressure, maximum shear stress, minimum shear stress and oscillatory shear index. Linear correlation analysis shows that systolic blood pressure, mean blood pressure, pulse blood pressure, minimum shear stress and oscillatory shear index might be the key hemodynamic factors in exercise-induced increase in arterial stiffness. The results are helpful for understanding the mechanism underlying the control of arterial function via exercise-induced hemodynamic modulation.
Control and Automation (ICCA), 2013 10th IEEE International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Many practical systems can be modelled as switched systems, whose stability problem is challenging even for linear subsystems. In this article, the stability problem of second-order switched linear systems with a finite number of subsystems under arbitrary switching is investigated. Sufficient and necessary stability conditions are derived based on the worst-case analysis approach in polar coordinates. The key idea of this article is to partition the whole state space into several regions and reduce the stability analysis of all the subsystems to analysing one or two worst subsystems in each region. This article is an extension of the work for stability analysis of second-order switched linear systems with two subsystems under arbitrary switching.
International Journal of Control 12/2012; 85(12):1-19. DOI:10.1080/00207179.2012.713987 · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hysteresis, observed in many gene regulatory networks, has a pivotal impact on biological systems, which enhances the robustness of cell functions. In this paper, a general model is proposed to describe the hysteretic gene regulatory network by combining the hysteresis component and the transient dynamics. The Bouc-Wen hysteresis model is modified to describe the hysteresis component in the mammalian gene regulatory networks. Rigorous mathematical analysis on the dynamical properties of the model is presented to ensure the bounded-input-bounded-output (BIBO) stability and demonstrates that the original Bouc-Wen model can only generate a clockwise hysteresis loop while the modified model can describe both clockwise and counter clockwise hysteresis loops. Simulation studies have shown that the hysteresis loops from our model are consistent with the experimental observations in three mammalian gene regulatory networks and two E.coli gene regulatory networks, which demonstrate the ability and accuracy of the mathematical model to emulate natural gene expression behavior with hysteresis. A comparison study has also been conducted to show that this model fits the experiment data significantly better than previous ones in the literature. The successful modeling of the hysteresis in all the five hysteretic gene regulatory networks suggests that the new model has the potential to be a unified framework for modeling hysteresis in gene regulatory networks and provide better understanding of the general mechanism that drives the hysteretic function.
[Show abstract][Hide abstract] ABSTRACT: Primarily motivated by some characteristics of the human visual cortex (HVC), we propose a new facial expression recognition scheme, involving a statistical synthesis of hierarchical classifiers. In this scheme, the input images of the database are first subjected to local, multi-scale Gabor-filter operations, and then the resulting Gabor decompositions are encoded using radial grids, imitating the topographical map-structure of the HVC. The codes are fed to local classifiers to produce global features, representing facial expressions. Experimental results show that such a hybrid combination of the HVC structure with a hierarchical classifier significantly improves expression recognition accuracy when applied to wide-ranging databases in comparison with the results in the literature. Furthermore, the proposed system is not only robust to corrupted data and missing information, but can also be generalized to cross-database expression recognition.
[Show abstract][Hide abstract] ABSTRACT: The piecewise affine (PWA) model represents an attractive model structure for approximating nonlinear systems. In this paper, a procedure for obtaining the PWA autoregressive exogenous (ARX) (autoregressive systems with exogenous inputs) models of nonlinear systems is proposed. Two key parameters defining a PWARX model, namely, the parameters of locally affine subsystems and the partition of the regressor space, are estimated, the former through a least-squares-based identification method using multiple models, and the latter using standard procedures such as neural network classifier or support vector machine classifier. Having obtained the PWARX model of the nonlinear system, a controller is then derived to control the system for reference tracking. Both simulation and experimental studies show that the proposed algorithm can indeed provide accurate PWA approximation of nonlinear systems, and the designed controller provides good tracking performance.
[Show abstract][Hide abstract] ABSTRACT: Switched systems (such as those suitably representing next-generation communication networks, advanced embedded systems, chemical process control systems, networked power systems, teams of autonomous agents, etc.) are usually represented in state space form, as state space models give a more complete description of the system dynamics. In practice, however, we often make use of input-output models for identification and control purposes. Vast literature acknowledges that if we have one input-output model corresponding to each subsystem of the switched system, then at the switching instants, none of these input-output models can properly describe the system behaviour. Although the above problem is known to exist, there are very few effective and readily usable results (to our best knowledge) that exists in the open literature on the explicit form of the input-output models at the switching instants. In this paper, we rigorously develop a rather simple, yet effective, procedure to derive the input-output models from switching state space models. We call the additional input-output models during switching as the "transition models." We further rigorously prove that the models are invariant to coordinate transformations of the states. The advantage of our approach is its relative simplicity (and thus an easily adoptable methodology), and its ready applicability for the typically more difficult classes of switched nonlinear systems and MIMO systems. Simulations show that utilizing these transition models improves the performance of the controllers and identification of switched systems significantly.
Control and Intelligent Systems 01/2011; 39(1). DOI:10.2316/Journal.201.2011.1.201-2223
[Show abstract][Hide abstract] ABSTRACT: In this paper, the feedback stabilization problem of planar switched linear systems with two subsystems under arbitrary switching is investigated. An easily checkable sufficient and necessary condition for quadratic stabilization is derived using the geometric approach. For systems which cannot be quadratically stabilized, a sufficient condition for asymptotical stabilization is also given.
9th IEEE International Conference on Control and Automation, ICCA 2011, Santiago, Chile, December 19-21, 2011; 01/2011
[Show abstract][Hide abstract] ABSTRACT: A hysteresis model is proposed to describe calcium-mediated Ciliary beat frequency (CBF) in airway epithelial cells. In this dynamic model, the kinetics of coupling between calcium and CBF is posited as a two-step configuration. First, Ca²+ directly binds to or indirectly acts on the axonemal proteins to modulate the activity of axonemal proteins. This step can be modeled by a Hill function in biochemistry. In the second step, the activity of axonemal proteins interacts with the sliding velocity of axonemal microtubules, the equivalent to regulating the CBF. The well-known Bouc-Wen model for hysteresis in mechanical engineering, which can only generate the stable clockwise hysteresis loops, is modified to describe the counter clockwise hysteresis loops commonly observed in the biological experiments. Based upon this new hysteresis model, the dynamic behavior of calcium-regulated CBF in epithelial airway cells is investigated through simulation studies. The numerical results demonstrate that the CBF dynamics in airway epithelial cells predicted by the hysteresis model is more consistent with the experimental observations than that predicted by previous static model in the literature.
[Show abstract][Hide abstract] ABSTRACT: In this paper, a dynamic model is proposed to quantify the relationship between fluid flow and Cl(-)-selective membrane current in vascular endothelial cells (VECs). It is assumed that the external shear stress would first induce channel deformation in VECs. This deformation could activate the Cl(-) channels on the membrane, thus allowing Cl(-) transport across the membrane. A modified Hodgkin-Huxley model is embedded into our dynamic system to describe the electrophysiological properties of the membrane, such as the Cl(-)-selective membrane current (I), voltage (V) and conductance. Three flow patterns, i. e., steady flow, oscillatory flow, and pulsatile flow, are applied in our simulation studies. When the extracellular Cl(-) concentration is constant, the I-V characteristics predicted by our dynamic model shows strong consistency with the experimental observations. It is also interesting to note that the Cl(-) currents under different flow patterns show some differences, indicating that VECs distinguish among and respond differently to different types of flows. When the extracellular Cl(-) concentration keeps constant or varies slowly with time (i.e. oscillates at 0.02 Hz), the convection and diffusion of Cl(-) in extracellular space can be ignored and the Cl(-) current is well captured by the modified Hodgkin-Huxley model alone. However, when the extracellular Cl(-) varies fast (i.e., oscillates at 0.2 Hz), the convection and diffusion effect should be considered because the Cl(-) current dynamics is different from the case where the convection-diffusion effect is simply ignored. The proposed dynamic model along with the simulation results could not only provide more insights into the flow-regulated electrophysiological behavior of the cell membrane but also help to reveal new findings in the electrophysiological experimental investigations of VECs in response to dynamic flow and biochemical stimuli.
Biomechanics and Modeling in Mechanobiology 11/2010; 10(5):743-54. DOI:10.1007/s10237-010-0270-2 · 3.15 Impact Factor