The Experts below are selected from a list of 46635 Experts worldwide ranked by ideXlab platform
Flavio Frohlich - One of the best experts on this subject based on the ideXlab platform.
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network targeted multi site direct cortical stimulation enhances working memory by modulating Phase Lag of low frequency oscillations
Cell Reports, 2019Co-Authors: Sankaraleengam Alagapan, Justin Riddle, Wei Angel Huang, Eldad Hadar, Hae Won Shin, Flavio FrohlichAbstract:Summary Working memory is mediated by the coordinated activation of frontal and parietal cortices occurring in the theta and alpha frequency ranges. Here, we test whether electrically stimulating frontal and parietal regions at the frequency of interaction is effective in modulating working memory. We identify working memory nodes that are functionally connected in theta and alpha frequency bands and intracranially stimulate both nodes simultaneously in participants performing working memory tasks. We find that in-Phase stimulation results in improvements in performance compared to sham stimulation. In addition, in-Phase stimulation results in decreased Phase Lag between regions within working memory network, while anti-Phase stimulation results in increased Phase Lag, suggesting that shorter Phase Lag in oscillatory connectivity may lead to better performance. The results support the idea that Phase Lag may play a key role in information transmission across brain regions. Thus, brain stimulation strategies to improve cognition may require targeting multiple nodes of brain networks.
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network targeted multi site direct cortical stimulation enhances working memory by modulating Phase Lag of low frequency oscillations
bioRxiv, 2019Co-Authors: Sankaraleengam Alagapan, Justin Riddle, Wei Angel Huang, Eldad Hadar, Hae Won Shin, Flavio FrohlichAbstract:Working memory, an important component of cognitive control, is supported by the coordinated activation of a network of cortical regions in the frontal and parietal cortices. Oscillations in theta and alpha frequency bands are thought to coordinate these network interactions. Thus, targeting multiple nodes of the network with brain stimulation at the frequency of interaction may be an effective means of modulating working memory. We tested this hypothesis by identifying regions that are functionally connected in theta and alpha frequency bands and intracranially stimulating both regions simultaneously in participants undergoing invasive monitoring. We found that in-Phase stimulation resulted in improvement in performance compared to sham stimulation. In contrast, anti-Phase stimulation did not affect performance. In-Phase stimulation resulted in decreased Phase Lag between regions within working memory network while anti-Phase stimulation resulted in increased Phase Lag suggesting that shorter Phase Lag in oscillatory connectivity may lead to better performance. The results support the idea that Phase Lag may play a key role in information transmission across brain regions. More broadly, brain stimulation strategies that aim to improve cognition may be better served targeting multiple nodes of brain networks.
Ramon Quintanilla - One of the best experts on this subject based on the ideXlab platform.
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on the Phase Lag heat equation with spatial dependent Lags
Journal of Mathematical Analysis and Applications, 2017Co-Authors: Zhuangyi Liu, Ramon Quintanilla, Yang WangAbstract:Abstract In this paper we investigate several qualitative properties of the solutions of the dual-Phase-Lag heat equation and the three-Phase-Lag heat equation. In the first case we assume that the parameter τ T depends on the spatial position. We prove that when 2 τ T − τ q is strictly positive the solutions are exponentially stable. When this property is satisfied in a proper sub-domain, but 2 τ T − τ q ≥ 0 for all the points in the case of the one-dimensional problem we also prove the exponential stability of solutions. A critical case corresponds to the situation when 2 τ T − τ q = 0 in the whole domain. It is known that the solutions are not exponentially stable. We here obtain the polynomial stability for this case. Last section of the paper is devoted to the three-Phase-Lag case when τ T and τ ν ⁎ depend on the spatial variable. We here consider the case when τ ν ⁎ ≥ κ ⁎ τ q and τ T is a positive constant, and obtain the analyticity of the semigroup of solutions. Exponential stability and impossibility of localization are consequences of the analyticity of the semigroup.
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On the existence and uniqueness in Phase-Lag thermoelasticity
Meccanica, 2017Co-Authors: Antonio Magaña, Ramon QuintanillaAbstract:This paper is devoted to analyze the Phase-Lag thermoelasticity problem. We study two different cases and we prove, for each one of them, that the solutions of the problem are determined by a quasi-contractive semigroup. As a consequence, existence, uniqueness and continuous dependence of the solutions are obtained.
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Spatial behavior in Phase-Lag heat conduction
Differential and Integral Equations, 2015Co-Authors: Ramon Quintanilla, Reinhard RackeAbstract:In this paper, we study the spatial behavior of solutions to the equations obtained by taking formal Taylor approximations to the heat conduction dual-Phase-Lag and three-Phase-Lag theories, reflecting Saint-Venant's principle. Depending on the relative order of derivation, with respect to the time, we propose different arguments. One is inspired by the arguments for parabolic problems and the other is inspired by the arguments for hyperbolic problems. In the first case, we obtain a Phragmen-Lindelof alternative for the solutions. In the second case, we obtain an estimate for the decay as well as a domain of influence result. The main tool to manage these problems is the use of an exponentially weighted Poincare inequality.
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Phase-Lag heat conduction : decay rates for limit problems and well-posedness
Journal of Evolution Equations, 2014Co-Authors: Karin Borgmeyer, Ramon Quintanilla, Reinhard RackeAbstract:In two recent papers, the authors have studied conditions on the relaxation parameters in order to guarantee the stability or instability of solutions for the Taylor approximations to dual-Phase-Lag and three-Phase-Lag heat conduction equations. However, for several limit cases relating to the parameters, the kind of stability was unclear. Here, we analyze these limit cases and clarify whether we can expect exponential or slow decay for the solutions. Moreover, rather general well-posedness results for three-Phase-Lag models are presented. Finally, the exponential stability expected by spectral analysis is rigorously proved exemplarily.
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qualitative aspects in dual Phase Lag heat conduction
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2007Co-Authors: Ramon Quintanilla, Reinhard RackeAbstract:We investigate the equation of the dual-Phase-Lag heat conduction proposed by Tzou. To describe this equation, we use the Phase Lag of the heat flux and the Phase Lag of the gradient of the temperature. We analyse the basic properties of the solutions of this problem. First, we prove that when both parameters are positive, the problem is well posed and the spatial decay of solutions is controlled by an exponential of the distance. When the Phase Lag of the gradient of the temperature is bigger than the Phase Lag of the heat flux, the problem is exponentially stable (which is a natural property to expect for a heat equation) and the spatial behaviour is controlled by an exponential of the square of the distance. Also, a uniqueness result for unbounded solutions is proved in this case.
Magdy A. Ezzat - One of the best experts on this subject based on the ideXlab platform.
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On the Phase- Lag Green–Naghdi thermoelasticity theories
Applied Mathematical Modelling, 2016Co-Authors: Ahmed S. El-karamany, Magdy A. EzzatAbstract:Abstract In this work, we proposed three models of generalized thermoelasticity: a single –Phase - Lag Green–Naghdi theory of type III, a dual-Phase–Lag Green–Naghdi theory of type II and of type III. The solid is assumed to be linear anisotropic inhomogeneous. A unified heat conduction law and heat transport equation are given, which consolidate the three theories and also the Lord–Shulman theory and the Green–Naghdi theory of type II. Dissipative inequality is derived, constitutive equations and thermodynamic restrictions are given. The speed of thermal wave propagation is given, for each of the three theories in case of isotropic solid. A uniqueness theorem is proved for the considered theories. Variational characterization of solution is established. An application is given for isotropic thermoelastic solid and the results are presented graphically.
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On the dual-Phase-Lag thermoelasticity theory
Meccanica, 2013Co-Authors: Ahmed S. El-karamany, Magdy A. EzzatAbstract:The uniqueness and reciprocal theorems are proved without the use of Laplace Transforms for the Dual-Phase-Lag thermoelasticity theory. Variational principle is established for a linear anisotropic and inhomogeneous thermoelastic solid. The dissipative inequality is used to obtain a continuous dependence result for isotropic solid.
Th. Monovasilis - One of the best experts on this subject based on the ideXlab platform.
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Symplectic partitioned Runge–Kutta methods with the Phase-Lag property
Applied Mathematics and Computation, 2012Co-Authors: Th. MonovasilisAbstract:Abstract In this work specially tuned symplectic partitioned Runge–Kutta (SPRK) methods with minimum Phase-Lag and Phase fitted have been considered. The general framework for constructing SPRK methods with minimum Phase-Lag is given.
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Symplectic Partitioned Runge–Kutta methods with minimal Phase-Lag
Computer Physics Communications, 2010Co-Authors: Th. Monovasilis, Z. Kalogiratou, T. E. SimosAbstract:Abstract Symplectic Partitioned Runge–Kutta (SPRK) methods with minimal Phase-Lag are derived. Specifically two new symplectic methods are constructed of second and third order with fifth Phase-Lag order. The methods are tested on the numerical integration of Hamiltonian problems and the Schrodinger equation.
T. E. Simos - One of the best experts on this subject based on the ideXlab platform.
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A New Modified RKN Method by Using the Phase‐Lag Properties
2011Co-Authors: D. F. Papadopoulos, T. E. SimosAbstract:In this paper a new modified RKN method developed, based on combination of the nullification of Phase‐Lag and amplification factor with the nullification of their integrals.
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Symplectic Partitioned Runge–Kutta methods with minimal Phase-Lag
Computer Physics Communications, 2010Co-Authors: Th. Monovasilis, Z. Kalogiratou, T. E. SimosAbstract:Abstract Symplectic Partitioned Runge–Kutta (SPRK) methods with minimal Phase-Lag are derived. Specifically two new symplectic methods are constructed of second and third order with fifth Phase-Lag order. The methods are tested on the numerical integration of Hamiltonian problems and the Schrodinger equation.
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Symmetric Eighth Algebraic Order Methods with Minimal Phase-Lag for the Numerical Solution of the Schrödinger Equation
Journal of Mathematical Chemistry, 2002Co-Authors: T. E. Simos, Jesus Vigo-aguiarAbstract:In this paper some new eighth algebraic order symmetric eight-step methods are introduced. For these methods a direct formula for the computation of the Phase-Lag is given. Based on this formula, the calculation of free parameters is done in order the Phase-Lag to be minimal. The new methods have better stability properties than the classical one. Numerical illustrations on the radial Schrödinger equation indicate that the new method is more efficient than older ones.
