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ABSTRACT: Abstract
Background
Progressive remodelling of the left ventricle (LV) following myocardial infarction (MI) is an outcome of spatial-temporal cellular interactions among different cell types that leads to heart failure for a significant number of patients. Cellular populations demonstrate temporal profiles of flux post-MI. However, little is known about the relationship between cell populations and the interaction strength among cells post-MI. The objective of this study was to establish a conceptual cellular interaction model based on a recently established graph network to describe the interaction between two types of cells.
Results
We performed stability analysis to investigate the effects of the interaction strengths, the initial status, and the number of links between cells on the cellular population in the dynamic network. Our analysis generated a set of conditions on interaction strength, structure of the network, and initial status of the network to predict the evolutionary profiles of the network. Computer simulations of our conceptual model verified our analysis.
Conclusions
Our study introduces a dynamic network to model cellular interactions between two different cell types which can be used to model the cellular population changes post-MI. The results on stability analysis can be used as a tool to predict the responses of particular cell populations.
BMC Systems Biology. 01/2010;
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ABSTRACT: Progressive remodelling of the left ventricle (LV) following myocardial infarction (MI) is an outcome of spatial-temporal cellular interactions among different cell types that leads to heart failure for a significant number of patients. Cellular populations demonstrate temporal profiles of flux post-MI. However, little is known about the relationship between cell populations and the interaction strength among cells post-MI. The objective of this study was to establish a conceptual cellular interaction model based on a recently established graph network to describe the interaction between two types of cells.
We performed stability analysis to investigate the effects of the interaction strengths, the initial status, and the number of links between cells on the cellular population in the dynamic network. Our analysis generated a set of conditions on interaction strength, structure of the network, and initial status of the network to predict the evolutionary profiles of the network. Computer simulations of our conceptual model verified our analysis.
Our study introduces a dynamic network to model cellular interactions between two different cell types which can be used to model the cellular population changes post-MI. The results on stability analysis can be used as a tool to predict the responses of particular cell populations.
BMC Systems Biology 01/2010; 4 Suppl 1:S5. · 3.15 Impact Factor
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ABSTRACT: Optimal path planning is a key problem for the control of autonomous unmanned ground vehicles. Particle swarm optimization has been used to solve the optimal problem in the static environment; however, optimal path planning for UGV groups in a dynamical environment has not been fully discussed. Accordingly, a dynamic obstacle-avoidance path planning for an unmanned ground vehicle group was considered as optimal problem for shortest path with formation constraints. The problem was formulated in Cartesian space with detectable velocity of both the vehicles and obstacles. The fitness function was defined by minimizing the trajectory of the group while keeping the V-shape formation of the group. Stable region of the parameters are determined by analyzing the convergence of the PSO algorithm. The simulation results demonstrated that the augmented particle swarm optimization could get the shortest path while keeping the V-formation and converged very fast.
Systems, Man and Cybernetics, 2009. SMC 2009. IEEE International Conference on; 11/2009
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ABSTRACT: Bioinformatics and systems biology are two booming research areas studying live organisms. Though having different focuses, bioinformatics and systems biology often share same or similar engineering and computer science methods to elucidate the mechanisms of multi-level biological systems. Regulatory mechanisms underlying biological processes involve interactions at cellular, sub-cellular, genomic and genetic levels. Accordingly, we need to bridge the gaps of biomedical researches at different levels of studies and foster the interdisciplinary and multidisciplinary research between both bioinformatics and systems biology domains. The synergic research on integrating bioinformatics and systems biology facilitates the advances in biology and medicine.
International Journal of Computational Biology and Drug Design 01/2009; 2(3):207-20.
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ABSTRACT: Biological complexity and limited quantitative measurements impose major challenges to standard engineering methodologies for modeling of biological pathways. A new approach is presented to describe the dynamics of the left ventricle (LV) remodeling process post myocardial infarction (MI) in terms of the experimental measurements. MI is a leading cause of congestive heart failure, and currently there is a lack of biomarkers to predict how the left ventricle (LV) will respond to injury. The objective of this study is to measure extracellular matrix (ECM) gene levels in the LV post-MI to identify candidate factors that are predictive of remodeling post MI. Left ventricle from unoperated control mice (n=6) and the remote and infarct regions from 7 day post-MI mice (n=7) were studied. Of the 84 genes evaluated, 51 were differentially expressed in the post-MI LV. Significantly up regulated genes included α1 collagen I and Spp1 (osteopontin; all p≪0.05). In the plasma, matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1, and Spp1 (osteopontin) levels increased post-MI (all p≪0.05). Data analysis illustrated those changes in expression of matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1), osteopontin (Spp1), and collagen correlated with each other. Mathematical simulation further illustrated the interaction among these factors and transforming growth factor β (TGF-β). In conclusion, the 5 proteins identified may be useful macrophage-dependent biomarkers for predicting changes in LV remodeling post-MI. The novelty of this study lies in the combination of experimental results with mathematical model.
Machine Learning and Cybernetics, 2008 International Conference on; 08/2008
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ABSTRACT: Age-related skeletal muscle sarcopenia has been extensively studied and smooth muscle sarcopenia has been recently described, but age-related cardiac sarcopenia has not been previously examined. Therefore, we evaluated adult (7.5+/-0.5 months; n = 27) and senescent (31.8+/-0.4 months; n = 26) C57BL/6J mice for cardiac sarcopenia using physiological, histological, and biochemical assessments. Mice do not develop hypertension, even into senescence, which allowed us to decouple vascular effects and monitor cardiac-dependent variables. We then developed a mathematical model to describe the relationship between age-related changes in cardiac muscle structure and function. Our results showed that, compared to adult mice, senescent mice demonstrated increased left ventricular (LV) end diastolic dimension, decreased wall thickness, and decreased ejection fraction, indicating dilation and reduced contractile performance. Myocyte numbers decreased, and interstitial fibrosis was punctated but doubled in the senescent mice, indicating reparative fibrosis. Electrocardiogram analysis showed that PR interval and QRS interval increased and R amplitude decreased in the senescent mice, indicating prolonged conduction times consistent with increased fibrosis. Intracellular lipid accumulation was accompanied by a decrease in glycogen stores in the senescent mice. Mathematical simulation indicated that changes in LV dimension, collagen deposition, wall stress, and wall stiffness precede LV dysfunction. We conclude that age-related cardiac sarcopenia occurs in mice and that LV remodeling due to increased end diastolic pressure could be an underlying mechanism for age-related LV dysfunction.
Experimental Gerontology 05/2008; 43(4):296-306. · 3.74 Impact Factor
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ABSTRACT: Genetic regulatory networks (GRN) can be described by differential equations with SUM logic which has been found in many natural systems. Identification of the network components and transcriptional rates are critical to the output behavior of the system. Though transcriptional rates cannot be measured in vivo, biologists have shown that they are alterable through artificial factors in vitro.
This study presents the theoretical research work on a novel nonlinear control and stability analysis of genetic regulatory networks. The proposed control scheme can drive the genetic regulatory network to desired levels by adjusting transcriptional rates. Asymptotic stability proof is conducted with Lyapunov argument for both noise-free and additive noises cases. Computer simulation results show the effectiveness of the control design and robustness of the regulation scheme with additive noises.
With the knowledge of interaction between transcriptional factors and gene products, the research results can be applied in the design of model-based experiments to regulate gene expression profiles.
BMC Genomics 02/2008; 9 Suppl 1:S21. · 4.07 Impact Factor
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Journal of Molecular and Cellular Cardiology 01/2008; 43(6):664-6. · 5.17 Impact Factor
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ABSTRACT: We evaluate the performance of the MODerate Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF)/Albedo algorithm using observations from MODIS instruments aboard NASA's Terra (EOS AM-1) and Aqua (EOS PM-1) platforms. This "combined" albedo product is evaluated against continuous field measurements from SURFace RADiation Budget Network (SURFRAD) and Atmospheric Radiation Measurement Southern Great Plains (ARM/SGP) stations, and through an internal analysis of the product's quality assurance (QA) fields. The combined product is compared to the initial MODIS albedo product, which used observations from the Terra satellite only. During the spring and summer months, the combined product showed a slight improvement over the original Terra-only albedo product, with a root mean square error (RMSE) of 0.0130 and a bias of about -0.02. As with the Terra-only product, accuracy drops during the fall and winter months at some sites. Jin et al. found that increased heterogeneity of validation sites during the fall and winter months is partially responsible for this drop in accuracy. The additional data provided by the Aqua platform changes high-quality albedo estimations only slightly, which underscores the stability of the MODIS algorithm. The most significant benefit of the combined product is a near 50% decrease in lower quality backup algorithm retrievals for the entire globe. A decrease in backup algorithm retrievals improves the overall accuracy of the MODIS albedo product, as it reduces algorithm reliance upon an a priori determination of the underlying surface anisotropy that is not entirely data derived.
IEEE Transactions on Geoscience and Remote Sensing 07/2006; · 2.89 Impact Factor
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ABSTRACT: This paper presents the research work on a permanent magnet brushless DC motor and its adaptive controller design on a high speed, high performance application. The motor is prototyped, assembled and tested. Torque-speed curve measured from dynamometer tests is used to verify the results. A newly developed nonlinear adaptive controller is designed with real time estimation of uncertainties, such as load torque and viscous friction, while driving the motor follow a known speed profile. Virtual control is identified and asymptotic stability proof is conducted with Lyapunov argument. Simulation and test results show the effectiveness of such design.
Applied Power Electronics Conference and Exposition, 2006. APEC '06. Twenty-First Annual IEEE; 04/2006
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ABSTRACT: Asymmetrical half-bridge dc-dc converter has favorable features, which allow the converter to operate at higher frequencies with higher power density. However, asymmetrical half bridge dc-dc converter displays nonlinear dc gain variation with input voltage and duty cycle. The conventional compensator design is based on a small-signal transfer function of power stage and worst case has to be considered in the closed-loop design. With the variation of input line, the system loop gain deviates from the nominal designed trajectory, and correspondingly, the system bandwidth, phase margin and gain margin are going to vary with input voltage line. As a result, the system steady-state and dynamic performance are affected as well. This paper proposes an adaptive nonlinear compensation approach to adjust the system loop gain dynamically and thus achieve unified system loop gain, bandwidth and performance. The adaptive digital compensation algorithm is simulated and verified based on PSIM simulation software
Applied Power Electronics Conference and Exposition, 2006. APEC '06. Twenty-First Annual IEEE; 04/2006
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IEEE T. Geoscience and Remote Sensing. 01/2006; 44:1555-1565.
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ABSTRACT: This paper presents the research work on a permanent magnet brushless DC motor and its adaptive controller design on a high speed, high performance application. FEA has been used for the motor design and optimization. The motor is prototyped, assembled and tested. Torque-speed curve measured from dynamometer tests is used to verify the FE results. A newly developed nonlinear adaptive controller is designed with real time estimation of uncertainties, such as load torque and viscous friction, while driving the motor to a known speed profile. Virtual control is identified and asymptotic stability proof is conducted with Lyapunov argument.
Electrical Machines and Systems, 2005. ICEMS 2005. Proceedings of the Eighth International Conference on; 10/2005
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ABSTRACT: In this paper, synchronization of a Lorenz-system transmitter is studied under the assumption that one of the three state variables is not transmitted and that transmitter parameters are not known a priori. An adaptive algorithm is proposed to estimate both the state and system parameters. It is shown by Lyapunov arguments and persistent excitation analysis that asymptotic stability of state and parameter estimation is guaranteed. Simulation results are included to demonstrate properties of the algorithm.
American Control Conference, 2003. Proceedings of the 2003; 07/2003
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ABSTRACT: A robust control is designed for a class of uncertain systems, the proposed control is distinct and novel in that it does not require any information of a bounding function on nonlinear uncertainties in the system. Instead, the uncertainties to be compensated for are generated by an exogenous system whose dynamics are either completely unknown or partially unknown. The only requirements on the exogenous system are that its unknown dynamics are bounded by a known function and that its output is bounded. The proposed robust control is based on a nonlinear observer that estimates the uncertainties. It is shown that, under different sets of conditions, local, semiglobal, or global stability of uniform ultimate boundedness or asymptotic stability can be achieved.
IEEE Transactions on Automatic Control 03/2003; · 2.11 Impact Factor
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Neural Processing Letters. 01/2003; 18:81-95.
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ABSTRACT: We explore a synergistic approach to use the complementary angular samplings from the Multi-angle Imaging SpectroRadiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) to improve MODIS surface bidirectional reflectance distribution function (BRDF) and albedo retrieval. Preliminary case studies show that MODIS and MISR surface bidirectional reflectance factors (BRFs) are generally comparable in the green, red, and near infrared. An information index is introduced to characterize the information content of directional samplings, and it is found that MISR angular observations can bring additional information to the MODIS retrieval, especially when the MISR observations are close to the principal plane. We use the BRDF parameters derived from the MISR surface BRFs as a priori information and derive a posteriori estimates of surface BRDF parameters with the MODIS observations. Results show that adding MISR angular samplings can reduce the relative BRF prediction error by up to 10% in the red and green, compared to the retrievals from MODIS-only observations which are close to the cross-principal plane.
IEEE Transactions on Geoscience and Remote Sensing 08/2002; · 2.89 Impact Factor
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C. Schaaf,
A. Strahler,
Feng Gao,
W. Lucht, Yufang Jin,
Xiaowen Li,
Xiaoyang Zhang,
E. Tsvetsinskaya,
J.-P. Muller,
P. Lewis,
M. Barnsley,
G. Roberts,
C. Doll,
Shunlin Liang,
D. Roy,
J. Privette
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ABSTRACT: Annual sequences of the first reprocessed albedo, bidirectional reflectance distribution function (BRDF), and nadir BRDF-adjusted surface reflectance (NBAR) products are being evaluated. BRDF model parameters (or weights) are used to compute black sky albedo at local solar noon and white sky albedo and to compute surface reflectance at a common nadir geometry. In addition to these standard resolution albedo, BRDF, and NBAR products, which are provided in the integerized sinusoidal grid projection, the BRDF parameters, black sky albedos (at local solar noon), and white sky albedos are now also being operationally produced in a global geographic projection known as the Climate Modeling Grid (CMG). These are currently available at a 0.25 degree spatial resolution, although there is community interest in a 0.05 degree resolution. In addition to the operational CMGs, coarser 0.5 degree and 1 degree resolution versions of the reprocessed albedo data have also been produced for the ISLSCP-II initiative. The global distribution of these albedos (as they vary throughout the year) are presented, as well as discussions of the most recent evaluations of the quality of the standard products.
Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International; 07/2002
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ABSTRACT: The normalized difference vegetation index (NDVI) has been widely applied in optical remote sensing. However, it has been demonstrated that NDVI is still partially affected by atmospheric path scattering and bidirectional (illumination and viewing geometry) effects. In this paper we present the benefit of using a bidirectional NDVI, and we discuss the problems in using the maximum NDVI composite method. Based on the assumption that a clear day has a larger NDVI value and a cloudy day has a smaller NDVI value (smaller reflectance in the near-infrared band and larger reflectance in red band due to atmospheric path scattering), the ratio of squared observed NDVI values and calculated NDVI values is used as a weight in our inversion method. The calculated NDVI values are derived from previously inverted bidirectional reflectance distribution functions (BRDFs). The inversion process will loop until all weights converge. Our research on the early Terra/MODIS data using a semiempirical kernel-driven BRDF model (the RossThick-LiTransit model) shows that this new method can improve inversion results whenever some cloudy pixels are not filtered out. As cloud detection and subpixel cloudiness are always a problem, this technique should still be very useful in improving the quality of BRDF inversion.
IEEE Transactions on Geoscience and Remote Sensing 07/2002; · 2.89 Impact Factor
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Control and Automation, 2002. ICCA. Final Program and Book of Abstracts. The 2002 International Conference on; 02/2002
