The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform

Vincent H Poor - One of the best experts on this subject based on the ideXlab platform.

  • risk aware day ahead scheduling and real time dispatch for electric vehicle charging
    IEEE Transactions on Smart Grid, 2014
    Co-Authors: Lei Yang, Junshan Zhang, Vincent H Poor
    Abstract:

    This paper studies risk-aware day-ahead scheduling and real-time dispatch for electric vehicle (EV) charging, aiming to jointly optimize the EV charging cost and the risk of the Load Mismatch between the forecast and the actual EV Loads, due to the random driving activities of EVs. It turns out that the consideration of the Load Mismatch risk in the objective function significantly complicates the risk-aware day-ahead scheduling problem (indeed it involves nonconvex optimization). A key step taken here is to utilize a hidden convexity structure to recast this problem as a two-stage stochastic linear program, and then solve it by using the L-shaped method. Since the computational complexity grows exponentially in the number of EVs, an estimation algorithm is developed based on importance sampling to mitigate the computational complexity. Further, a distributed risk-aware real-time dispatch algorithm is developed, in which the aggregator needs to compute only the shadow prices for each EV to optimize its own charging strategy in a distributed manner. It is shown, based on real data, that the proposed risk-aware day-ahead scheduling algorithm using importance sampling can significantly reduce the overall charging cost with a small number of samples.

Mark Potse - One of the best experts on this subject based on the ideXlab platform.

  • st segment elevation by current to Load Mismatch an experimental and computational study
    Heart Rhythm, 2011
    Co-Authors: Mark G Hoogendijk, Mark Potse, Alain Vinet, Jacques M T De Bakker, Ruben Coronel
    Abstract:

    Background Recently, we demonstrated that ajmaline caused ST segment elevation in the heart of an SCN5A mutation carrier by excitation failure in structurally discontinuous myocardium. In patients with Brugada syndrome, ST segment elevation is modulated by cardiac sodium ( I Na ), transient outward ( I to ), and L-type calcium currents ( I CaL ). Objective To establish experimentally whether excitation failure by current-to-Load Mismatch causes ST segment elevation and is modulated by I to and I CaL . Methods In porcine epicardial shavings, isthmuses of 0.9, 1.1, or 1.3 mm in width were created parallel to the fiber orientation. Local activation was recorded electrically or optically (di-4-ANEPPS) simultaneously with a pseudo-electrocardiogram (ECG) before and after ajmaline application. Intra- and extracellular potentials and ECGs were simulated in a computer model of the heart and thorax before and after introduction of right ventricular structural discontinuities and during varying levels of I Na , I to , and I CaL . Results In epicardial shavings, conduction blocked after ajmaline in a frequency-dependent manner in all preparations with isthmuses ≤1.1 mm width. Total conduction block occurred in three of four preparations with isthmuses of 0.9 mm versus one of seven with isthmuses ≥1.1 mm ( P I Na , I to , and I CaL . Reduction of I to and increase of I CaL resulted in a higher excitatory current, overcame subepicardial excitation failure, and reduced the ST segment elevation. Conclusions Excitation failure by current-to-Load Mismatch causes ST segment elevation and, like ST segment elevation in Brugada patients, is modulated by I to and I CaL .

  • mechanism of right precordial st segment elevation in structural heart disease excitation failure by current to Load Mismatch
    Heart Rhythm, 2010
    Co-Authors: Mark G Hoogendijk, Mark Potse, Andre C Linnenbank, Arie O Verkerk, Hester Den M Ruijter, Shirley C M Van Amersfoorth, Eva C Klaver, Leander Beekman, Connie R Bezzina, Pieter G Postema
    Abstract:

    Background The Brugada sign has been associated with mutations in SCN5A and with right ventricular structural abnormalities. Their role in the Brugada sign and the associated ventricular arrhythmias is unknown. Objective The purpose of this study was to delineate the role of structural abnormalities and sodium channel dysfunction in the Brugada sign. Methods Activation and repolarization characteristics of the explanted heart of a patient with a loss-of-function mutation in SCN5A (G752R) and dilated cardiomyopathy were determined after induction of right-sided ST-segment elevation by ajmaline. In addition, right ventricular structural discontinuities and sodium channel dysfunction were simulated in a computer model encompassing the heart and thorax. Results In the explanted heart, disappearance of local activation in unipolar electrograms at the basal right ventricular epicardium was followed by monophasic ST-segment elevation. The local origin of this phenomenon was confirmed by coaxial electrograms. Neither early repolarization nor late activation correlated with ST-segment elevation. At sites of local ST-segment elevation, the subepicardium was interspersed with adipose tissue and contained more fibrous tissue than either the left ventricle or control hearts. In computer simulations entailing right ventricular structural discontinuities, reduction of sodium channel conductance or size of the gaps between introduced barriers resulted in subepicardial excitation failure or delayed activation by current-to-Load Mismatch and in the Brugada sign on the ECG. Conclusion Right ventricular excitation failure and activation delay by current-to-Load Mismatch in the subepicardium can cause the Brugada sign. Therefore, current-to-Load Mismatch may underlie the ventricular arrhythmias in patients with the Brugada sign.

Craig S Henriquez - One of the best experts on this subject based on the ideXlab platform.

  • Microscopic variations in interstitial and intracellular structure modulate the distribution of conduction delays and block in cardiac tissue with source-Load Mismatch.
    Europace : European pacing arrhythmias and cardiac electrophysiology : journal of the working groups on cardiac pacing arrhythmias and cardiac cellula, 2020
    Co-Authors: Marjorie Letitia Hubbard, Craig S Henriquez
    Abstract:

    Reentrant activity in the heart is often correlated with heterogeneity in both the intracellular structure and the interstitial structure surrounding cells; however, the combined effect of cardiac microstructure and interstitial resistivity in regions of source-Load Mismatch is largely unknown. The aim of this study was to investigate how microstructural variations in cell arrangement and increased interstitial resistivity influence the spatial distribution of conduction delays and block in poorly coupled regions of tissue. Two-dimensional 0.6 cm × 0.6 cm computer models with idealized and realistic cellular structure were used to represent a monolayer of ventricular myocytes. Gap junction connections were distributed around the periphery of each cell at 10 μm intervals. Regions of source-Load Mismatch were added to the models by increasing the gap junction and interstitial resistivity in one-half of the tissue. Heterogeneity in cell shape and cell arrangement along the boundary between well-coupled and poorly coupled tissue increased variability in longitudinal conduction delays to as much as 10 ms before the onset of conduction block, resulting in wavefront breakthroughs with pronounced curvature at distinct points along the boundary. Increasing the effective interstitial resistivity reduced source-Load Mismatch at the transition boundary, which caused a decrease in longitudinal conduction delay and an increase in the number of wavefront breakthroughs. Microstructural variations in cardiac tissue facilitate the formation of isolated sites of wavefront breakthrough that may enable abnormal electrical activity in small regions of diseased tissue to develop into more widespread reentrant activity.

  • a microstructural model of reentry arising from focal breakthrough at sites of source Load Mismatch in a central region of slow conduction
    American Journal of Physiology-heart and Circulatory Physiology, 2014
    Co-Authors: Marjorie Letitia Hubbard, Craig S Henriquez
    Abstract:

    Regions of cardiac tissue that have a combination of focal activity and poor, heterogeneous gap junction coupling are often considered to be arrhythmogenic; however, the relationship between the properties of the cardiac microstructure and patterns of abnormal propagation is not well understood. The objective of this study was to investigate the effect of microstructure on the initiation of reentry from focal stimulation inside a poorly coupled region embedded in more well-coupled tissue. Two-dimensional discrete computer models of ventricular monolayers (1 × 1 cm) were randomly generated to represent heterogeneity in the cardiac microstructure. A small, central poorly coupled patch (0.40 × 0.40 cm) was introduced to represent the site of focal activity. Simulated unipolar electrogram recordings were computed at various points in the tissue. As the gap conductance of the patch decreased, conduction slowed and became increasingly complex, marked by fractionated electrograms with reduced amplitude. Near the limit of conduction block, isolated breakthrough sites occurred at single cells along the patch boundary and were marked by long cell-to-cell delays and negative deflections on electrogram recordings. The strongest determinant of the site of wavefront breakthrough was the connectivity of the brick wall architecture, which enabled current flow through small regions of overlapping cells to drive propagation into the well-coupled zone. In conclusion, breakthroughs at the size scale of a single cell can occur at the boundary of source-Load Mismatch allowing focal activations from slow conducting regions to produce reentry. These breakthrough regions, identifiable by distinct asymmetric, reduced amplitude electrograms, are sensitive to tissue architecture and may be targets for ablation.

  • microscopic variations in interstitial and intracellular structure modulate the distribution of conduction delays and block in cardiac tissue with source Load Mismatch
    Europace, 2012
    Co-Authors: Marjorie Letitia Hubbard, Craig S Henriquez
    Abstract:

    Aims Reentrant activity in the heart is often correlated with heterogeneity in both the intracellular structure and the interstitial structure surrounding cells; however, the combined effect of cardiac microstructure and interstitial resistivity in regions of source–Load Mismatch is largely unknown. The aim of this study was to investigate how microstructural variations in cell arrangement and increased interstitial resistivity influence the spatial distribution of conduction delays and block in poorly coupled regions of tissue. Methods and results Two-dimensional 0.6 cm × 0.6 cm computer models with idealized and realistic cellular structure were used to represent a monolayer of ventricular myocytes. Gap junction connections were distributed around the periphery of each cell at 10 μm intervals. Regions of source–Load Mismatch were added to the models by increasing the gap junction and interstitial resistivity in one-half of the tissue. Heterogeneity in cell shape and cell arrangement along the boundary between well-coupled and poorly coupled tissue increased variability in longitudinal conduction delays to as much as 10 ms before the onset of conduction block, resulting in wavefront breakthroughs with pronounced curvature at distinct points along the boundary. Increasing the effective interstitial resistivity reduced source–Load Mismatch at the transition boundary, which caused a decrease in longitudinal conduction delay and an increase in the number of wavefront breakthroughs. Conclusion Microstructural variations in cardiac tissue facilitate the formation of isolated sites of wavefront breakthrough that may enable abnormal electrical activity in small regions of diseased tissue to develop into more widespread reentrant activity.

Mark G Hoogendijk - One of the best experts on this subject based on the ideXlab platform.

  • st segment elevation by current to Load Mismatch an experimental and computational study
    Heart Rhythm, 2011
    Co-Authors: Mark G Hoogendijk, Mark Potse, Alain Vinet, Jacques M T De Bakker, Ruben Coronel
    Abstract:

    Background Recently, we demonstrated that ajmaline caused ST segment elevation in the heart of an SCN5A mutation carrier by excitation failure in structurally discontinuous myocardium. In patients with Brugada syndrome, ST segment elevation is modulated by cardiac sodium ( I Na ), transient outward ( I to ), and L-type calcium currents ( I CaL ). Objective To establish experimentally whether excitation failure by current-to-Load Mismatch causes ST segment elevation and is modulated by I to and I CaL . Methods In porcine epicardial shavings, isthmuses of 0.9, 1.1, or 1.3 mm in width were created parallel to the fiber orientation. Local activation was recorded electrically or optically (di-4-ANEPPS) simultaneously with a pseudo-electrocardiogram (ECG) before and after ajmaline application. Intra- and extracellular potentials and ECGs were simulated in a computer model of the heart and thorax before and after introduction of right ventricular structural discontinuities and during varying levels of I Na , I to , and I CaL . Results In epicardial shavings, conduction blocked after ajmaline in a frequency-dependent manner in all preparations with isthmuses ≤1.1 mm width. Total conduction block occurred in three of four preparations with isthmuses of 0.9 mm versus one of seven with isthmuses ≥1.1 mm ( P I Na , I to , and I CaL . Reduction of I to and increase of I CaL resulted in a higher excitatory current, overcame subepicardial excitation failure, and reduced the ST segment elevation. Conclusions Excitation failure by current-to-Load Mismatch causes ST segment elevation and, like ST segment elevation in Brugada patients, is modulated by I to and I CaL .

  • mechanism of right precordial st segment elevation in structural heart disease excitation failure by current to Load Mismatch
    Heart Rhythm, 2010
    Co-Authors: Mark G Hoogendijk, Mark Potse, Andre C Linnenbank, Arie O Verkerk, Hester Den M Ruijter, Shirley C M Van Amersfoorth, Eva C Klaver, Leander Beekman, Connie R Bezzina, Pieter G Postema
    Abstract:

    Background The Brugada sign has been associated with mutations in SCN5A and with right ventricular structural abnormalities. Their role in the Brugada sign and the associated ventricular arrhythmias is unknown. Objective The purpose of this study was to delineate the role of structural abnormalities and sodium channel dysfunction in the Brugada sign. Methods Activation and repolarization characteristics of the explanted heart of a patient with a loss-of-function mutation in SCN5A (G752R) and dilated cardiomyopathy were determined after induction of right-sided ST-segment elevation by ajmaline. In addition, right ventricular structural discontinuities and sodium channel dysfunction were simulated in a computer model encompassing the heart and thorax. Results In the explanted heart, disappearance of local activation in unipolar electrograms at the basal right ventricular epicardium was followed by monophasic ST-segment elevation. The local origin of this phenomenon was confirmed by coaxial electrograms. Neither early repolarization nor late activation correlated with ST-segment elevation. At sites of local ST-segment elevation, the subepicardium was interspersed with adipose tissue and contained more fibrous tissue than either the left ventricle or control hearts. In computer simulations entailing right ventricular structural discontinuities, reduction of sodium channel conductance or size of the gaps between introduced barriers resulted in subepicardial excitation failure or delayed activation by current-to-Load Mismatch and in the Brugada sign on the ECG. Conclusion Right ventricular excitation failure and activation delay by current-to-Load Mismatch in the subepicardium can cause the Brugada sign. Therefore, current-to-Load Mismatch may underlie the ventricular arrhythmias in patients with the Brugada sign.

Lei Yang - One of the best experts on this subject based on the ideXlab platform.

  • risk aware day ahead scheduling and real time dispatch for electric vehicle charging
    IEEE Transactions on Smart Grid, 2014
    Co-Authors: Lei Yang, Junshan Zhang, Vincent H Poor
    Abstract:

    This paper studies risk-aware day-ahead scheduling and real-time dispatch for electric vehicle (EV) charging, aiming to jointly optimize the EV charging cost and the risk of the Load Mismatch between the forecast and the actual EV Loads, due to the random driving activities of EVs. It turns out that the consideration of the Load Mismatch risk in the objective function significantly complicates the risk-aware day-ahead scheduling problem (indeed it involves nonconvex optimization). A key step taken here is to utilize a hidden convexity structure to recast this problem as a two-stage stochastic linear program, and then solve it by using the L-shaped method. Since the computational complexity grows exponentially in the number of EVs, an estimation algorithm is developed based on importance sampling to mitigate the computational complexity. Further, a distributed risk-aware real-time dispatch algorithm is developed, in which the aggregator needs to compute only the shadow prices for each EV to optimize its own charging strategy in a distributed manner. It is shown, based on real data, that the proposed risk-aware day-ahead scheduling algorithm using importance sampling can significantly reduce the overall charging cost with a small number of samples.

  • GLOBECOM - Risk-aware day-ahead scheduling and real-time dispatch for plug-in electric vehicles
    2012 IEEE Global Communications Conference (GLOBECOM), 2012
    Co-Authors: Lei Yang, Junshan Zhang, Dajun Qian
    Abstract:

    This paper studies risk-aware day-ahead scheduling and real-time dispatch for plug-in electric vehicles (EVs), aiming to jointly optimize the EV charging cost and the risk of the Load Mismatch between the forecasted and the actual EV Loads, due to the random driving activities of EVs. It turns out that the inclusion of the Load Mismatch risk in the objective function complicates the risk-aware day-ahead scheduling and indeed the optimization problem is nonconvex. A key step is to utilize the hidden convexity structure to recast it as a two-stage stochastic linear program, which can be solved by using the L-shaped method. Further, we develop a distributed risk-aware real-time dispatch algorithm, where the aggregator only needs to compute the shadow prices for each EV to optimize its own charging strategy in a distributed manner. We show, based on real data, that the proposed risk-aware day-ahead scheduling algorithm can reduce not only the overall charging cost, but also the peak demand of EV charging.