The Experts below are selected from a list of 8592 Experts worldwide ranked by ideXlab platform

Alex Alvarado - One of the best experts on this subject based on the ideXlab platform.

  • discrete time accuracy analysis of the time domain Regular Perturbation model for unamplified links
    arXiv: Signal Processing, 2021
    Co-Authors: Astrid Barreiro, Gabriele Liga, Tobias Fehenberger, Alex Alvarado
    Abstract:

    The accuracy of a discrete-time channel model based on Regular Perturbation is numerically studied for unamplified links. We analyse the distance between discrete nonlinear interference points and show that such distance can be used to estimate the effective channel memory.

  • Regular Perturbation on the group velocity dispersion parameter for nonlinear fibre optical communications
    Nature Communications, 2020
    Co-Authors: Vinicius Oliari, Erik Agrell, Alex Alvarado
    Abstract:

    Communication using the optical fibre channel can be challenging due to nonlinear effects that arise in the optical propagation. These effects represent physical processes that originate from light propagation in optical fibres. To obtain fundamental understandings of these processes, mathematical models are typically used. These models are based on approximations of the nonlinear Schrodinger equation, the differential equation that governs the propagation in an optical fibre. All available models in the literature are restricted to certain regimes of operation. Here, we present an approximate model for the nonlinear optical fibre channel in the weak-dispersion regime, in a noiseless scenario. The approximation is obtained by applying Regular Perturbation theory on the group-velocity dispersion parameter of the nonlinear Schrodinger equation. The proposed model is compared with three other models using the normalized square deviation metric and shown to be significantly more accurate for links with high nonlinearities and weak dispersion.

  • Regular Perturbation on the group velocity dispersion parameter for nonlinear fibre optical communications
    Nature Communications, 2020
    Co-Authors: Vinicius Oliari, Erik Agrell, Alex Alvarado
    Abstract:

    Communication using the optical fibre channel can be challenging due to nonlinear effects that arise in the optical propagation. These effects represent physical processes that originate from light propagation in optical fibres. To obtain fundamental understandings of these processes, mathematical models are typically used. These models are based on approximations of the nonlinear Schrodinger equation, the differential equation that governs the propagation in an optical fibre. All available models in the literature are restricted to certain regimes of operation. Here, we present an approximate model for the nonlinear optical fibre channel in the weak-dispersion regime, in a noiseless scenario. The approximation is obtained by applying Regular Perturbation theory on the group-velocity dispersion parameter of the nonlinear Schrodinger equation. The proposed model is compared with three other models using the normalized square deviation metric and shown to be significantly more accurate for links with high nonlinearities and weak dispersion. Nonlinear effects have been studied in optical fiber communications channels under various specified parameter regimes. Here, the authors develop an approximate model via Perturbation that is more accurate for the highly nonlinear regime.

  • Regular Perturbation for the weak dispersion regime
    International Conference on Transparent Optical Networks, 2019
    Co-Authors: Vinicius Oliari, Erik Agrell, Alex Alvarado
    Abstract:

    We present a novel analytical model for the lossless fiber in the weak-dispersion regime. The model is compared to three other models via simulations using the split-step Fourier method. These simulations explore the validity of the models with respect to parameters that affect the signal after the fiber propagation. In one of the systems under consideration, the proposed model is accurate until 8.7 dBm while the others are accurate only until 2.4 dBm. The impact of the modulation format is analyzed for three of the models. Our results show differences up to 1.82 dB in the maximum power in which the proposed model remains accurate when changing from quadrature phase shifting keying to 8-ary quadrature amplitude modulation.

Claudio E Merelli - One of the best experts on this subject based on the ideXlab platform.

  • dynamic coefficients of finite length journal bearing evaluation using a Regular Perturbation method
    International Journal of Mechanical Sciences, 2019
    Co-Authors: Claudio E Merelli, Daniel O Barila, Gustavo Gabriel Vignolo, Lidia M Quinzani
    Abstract:

    ABSTRACT A set of simple expressions is deduced for static and dynamic parameters associated to hydrodynamic journal bearings (JB). The behavior of this system is governed by two dimensionless numbers, the aspect ratio, L/D, and the eccentricity ratio, η. In a previous work, we presented a Regular Perturbation method that extended the Ocvirk solution and successfully described isothermal JBs up to L/D and η of ∼1/2. Presently, we extend that methodology, modified using a smaller Perturbation parameter, to obtain analytical expressions of the dynamic coefficients, as well as static variables like friction factor, load carrying capacity, lubricant flow rate and phase angle. The deduced expressions successfully describe the static and dynamic behavior of JBs up to L/D and η of ∼3/4.

  • dynamic coefficients of finite length journal bearing evaluation using a Regular Perturbation method
    International Journal of Mechanical Sciences, 2019
    Co-Authors: Claudio E Merelli, Daniel O Barila, Gustavo Gabriel Vignolo, Lidia M Quinzani
    Abstract:

    Fil: Merelli, Claudio Ernesto. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Planta Piloto de Ingenieria Quimica. Universidad Nacional del Sur. Planta Piloto de Ingenieria Quimica; Argentina. Universidad Nacional del Sur. Departamento de Ingenieria Quimica; Argentina

Noreen Sher Akbar - One of the best experts on this subject based on the ideXlab platform.

  • mhd eyring prandtl fluid flow with convective boundary conditions in small intestines
    International Journal of Biomathematics, 2013
    Co-Authors: Noreen Sher Akbar
    Abstract:

    In this paper, we have discussed the food movement in stomach with thermal boundary conditions. Eyring–Prandtl fluid model is considered. Formulation of the considered phenomena have been developed for both fixed and moving frame of references. Regular Perturbation is used to find the solution of stream function, temperature profile and pressure gradient. Analysis has been carried out for velocity, "stream function, temperature, pressure gradient and heat transfer". Appearance of pressure gradient is quite complicated so to get the expression for pressure rise we have used numerical integration. It is perceived that the velocity close to the channel walls is not same in outlook of the Eyring–Prandtl fluid parameter taken as β and Hartman number M. The velocity decreases by increasing β and M.

  • peristaltic flow of a tangent hyperbolic fluid in an inclined asymmetric channel with slip and heat transfer
    Progress in Computational Fluid Dynamics, 2012
    Co-Authors: Noreen Sher Akbar, S. Nadeem, Tasawar Hayat, S Obaidat
    Abstract:

    The peristaltic flow of a magnetohydrodynamic (MHD) Tangent hyperbolic fluid in an inclined asymmetric channel is investigated. The governing equations for the proposed fluid model are derived in Cartesian coordinates system. Simultaneous effects of slip and heat transfer have been taken into account for the present analysis. Regular Perturbation method is utilised to get the solutions for stream function, temperature, pressure gradient and heat transfer coefficients. The present solutions are compared with the existing work and comparison is shown through table. The presented graphical results analyse the variations of embedded parameters into the flow system.

  • effects of temperature dependent viscosity on peristaltic flow of a jeffrey six constant fluid in a non uniform vertical tube
    Communications in Nonlinear Science and Numerical Simulation, 2010
    Co-Authors: S. Nadeem, Noreen Sher Akbar
    Abstract:

    Abstract This paper deals with the influence of heat transfer and temperature dependent viscosity on peristaltic flow of a Jeffrey-six constant fluid. The two-dimensional equations of Jeffrey-six constant fluid are simplified by making the assumptions of long wave length and low Reynolds number. The arising equations are solved for temperature, velocity profile and axial pressure gradient using Regular Perturbation method and homotopy analysis method. The integration appeared in the pressure rise is treated numerically to find the solution. The expressions for pressure rise, temperature, pressure gradient and stream functions are sketched for various embedded parameters and interpreted. The graphical results are also presented for five different wave shapes.

  • effects of induced magnetic field on peristaltic flow of johnson segalman fluid in a vertical symmetric channel
    Applied Mathematics and Mechanics-english Edition, 2010
    Co-Authors: S. Nadeem, Noreen Sher Akbar
    Abstract:

    In this paper, the influence of heat transfer and induced magnetic field on peristaltic flow of a Johnson-Segalman fluid is studied. The purpose of the present investigation is to study the effects of induced magnetic field on the peristaltic flow of non-Newtonian fluid. The two-dimensional equations of a Johnson-Segalman fluid are simplified by assuming a long wavelength and a low Reynolds number. The obtained equations are solved for the stream function, magnetic force function, and axial pressure gradient by using a Regular Perturbation method. The expressions for the pressure rise, temperature, induced magnetic field, pressure gradient, and stream function are sketched and interpreted for various embedded parameters.

  • influence of heat transfer on a peristaltic flow of johnson segalman fluid in a non uniform tube
    International Communications in Heat and Mass Transfer, 2009
    Co-Authors: S. Nadeem, Noreen Sher Akbar
    Abstract:

    The present investigation deals with the peristaltic motion of an incompressible non-Newtonian fluid in a non-uniform tube for long wavelength. The mechanical properties of the material are represented by the constitutive equation for a Johnson Segalman fluid. The resulting problem for velocity field and temperature profile is solved using (i) Regular Perturbation method (ii) Homotopy analysis method. The influence of various emerging parameters on the flow is shown through graphs and discussed.

James Ledoux - One of the best experts on this subject based on the ideXlab platform.

  • Regular Perturbation of v geometrically ergodic markov chains
    Journal of Applied Probability, 2013
    Co-Authors: Déborah Ferré, Loïc Hervé, James Ledoux
    Abstract:

    In this paper, new conditions for the stability of V-geometrically ergodic Markov chains are introduced. The results are based on an extension of the standard Perturbation theory formulated by Keller and Liverani. The continuity and higher Regularity properties are investigated. As an illustration, an asymptotic expansion of the invariant probability measure for an autoregressive model with independent and identically distributed noises (with a nonstandard probability density function) is obtained.

  • Regular Perturbation of V -geometrically ergodic Markov chains
    Journal of Applied Probability, 2013
    Co-Authors: Déborah Ferré, Loïc Hervé, James Ledoux
    Abstract:

    In this paper, new conditions for the stability of V-geometrically ergodic Markov chains are introduced. The results are based on an extension of the standard Perturbation theory formulated by Keller and Liverani. The continuity and higher Regularity properties are investigated. As an illustration, an asymptotic expansion of the invariant probability measure for an autoregressive model with i.i.d. noises (with a non-standard probability density function) is obtained.

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

  • effects of partial slip on the peristaltic transport of a hyperbolic tangent fluid model in an asymmetric channel
    Computational Mathematics and Mathematical Physics, 2015
    Co-Authors: Safia Akram, S. Nadeem
    Abstract:

    In the present analysis, we have modeled the governing equations of two dimensional hyperbolic tangent fluid model under the assumptions of long wavelength and low Reynolds number. The flow is investigated in a wave frame of reference moving with the velocity of the wave. The governing equations of hyperbolic tangent fluid have been solved using Regular Perturbation method. The expression for pressure rise has been calculated using numerical integrations. The behavior of different physical parameters have been discussed graphically.

  • peristaltic flow of a tangent hyperbolic fluid in an inclined asymmetric channel with slip and heat transfer
    Progress in Computational Fluid Dynamics, 2012
    Co-Authors: Noreen Sher Akbar, S. Nadeem, Tasawar Hayat, S Obaidat
    Abstract:

    The peristaltic flow of a magnetohydrodynamic (MHD) Tangent hyperbolic fluid in an inclined asymmetric channel is investigated. The governing equations for the proposed fluid model are derived in Cartesian coordinates system. Simultaneous effects of slip and heat transfer have been taken into account for the present analysis. Regular Perturbation method is utilised to get the solutions for stream function, temperature, pressure gradient and heat transfer coefficients. The present solutions are compared with the existing work and comparison is shown through table. The presented graphical results analyse the variations of embedded parameters into the flow system.

  • effects of temperature dependent viscosity on peristaltic flow of a jeffrey six constant fluid in a non uniform vertical tube
    Communications in Nonlinear Science and Numerical Simulation, 2010
    Co-Authors: S. Nadeem, Noreen Sher Akbar
    Abstract:

    Abstract This paper deals with the influence of heat transfer and temperature dependent viscosity on peristaltic flow of a Jeffrey-six constant fluid. The two-dimensional equations of Jeffrey-six constant fluid are simplified by making the assumptions of long wave length and low Reynolds number. The arising equations are solved for temperature, velocity profile and axial pressure gradient using Regular Perturbation method and homotopy analysis method. The integration appeared in the pressure rise is treated numerically to find the solution. The expressions for pressure rise, temperature, pressure gradient and stream functions are sketched for various embedded parameters and interpreted. The graphical results are also presented for five different wave shapes.

  • effects of induced magnetic field on peristaltic flow of johnson segalman fluid in a vertical symmetric channel
    Applied Mathematics and Mechanics-english Edition, 2010
    Co-Authors: S. Nadeem, Noreen Sher Akbar
    Abstract:

    In this paper, the influence of heat transfer and induced magnetic field on peristaltic flow of a Johnson-Segalman fluid is studied. The purpose of the present investigation is to study the effects of induced magnetic field on the peristaltic flow of non-Newtonian fluid. The two-dimensional equations of a Johnson-Segalman fluid are simplified by assuming a long wavelength and a low Reynolds number. The obtained equations are solved for the stream function, magnetic force function, and axial pressure gradient by using a Regular Perturbation method. The expressions for the pressure rise, temperature, induced magnetic field, pressure gradient, and stream function are sketched and interpreted for various embedded parameters.

  • peristaltic flow of a williamson fluid in an asymmetric channel
    Communications in Nonlinear Science and Numerical Simulation, 2010
    Co-Authors: S. Nadeem, Safia Akram
    Abstract:

    Abstract In this work, we have presented a peristaltic flow of a Williamson model in an asymmetric channel. The governing equations of Williamson model in two dimensional peristaltic flow phenomena are constructed under long wave length and low Reynolds number approximations. A Regular Perturbation expansion method is used to obtain the analytical solution of the non-linear problem. The expressions for stream function, pressure gradient and pressure rise have been computed. The pertinent features of various physical parameters have been discussed graphically. It is observed that, (the non-dimensional Williamson parameter) for large We , the curves of the pressure rise are not linear but for very small We it behave like a Newtonian fluid.