Examinando por Materia "Laplace transform"
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Ítem Laguerre-gauss filters in reverse time migration image reconstruction(Sociedade Brasileira de Geofisica, 2017-01-01) Castrillón, J.G.P.; Montoya, O.L.Q.; Sierra-Sosa, D.; Universidad EAFIT. Escuela de Ciencias; Modelado MatemáticoReverse time migration (RTM) solves the acoustic or elastic wave equation by means of the extrapolation from source and receiver wavefield in time. A migrated image is obtained by applying a criteria known as imaging condition. The cross-correlation between source and receiver wavefields is the commonly used imaging condition. However, this imaging condition produces spatial low-frequency noise, called artifacts, due to the unwanted correlation of the diving, head and backscattered waves. Several techniques have been proposed to reduce the artifacts occurrence. Derivative operators as Laplacian are the most frequently used. In this work, we propose a technique based on a spiral phase filter ranging from 0 to 2p, and a toroidal amplitude bandpass filter, known as Laguerre-Gauss transform. Through numerical experiments we present the application of this particular filter on three synthetic data sets. In addition, we present a comparative spectral study of images obtained by the zero-lag cross-correlation imaging condition, the Laplacian filtering and the Laguerre-Gauss filtering, showing their frequency features. We also present evidences not only with simulated noisy velocity fields but also by comparison with the model velocity field gradients that this method improves the RTM images by reducing the artifacts and notably enhance the reflective events. © 2017 Sociedade Brasileira de Geofísica.Ítem On the effusion time of drugs from the open pore of a spherical vesicle(ELSEVIER SCIENCE BV, 2016-06-01) Simon, L.; Ospina, J.; Simon, L.; Ospina, J.; Universidad EAFIT. Departamento de Ciencias; Lógica y ComputaciónSolute permeation through a spherical liposomal vesicle was analyzed using Fick's second law and a mixed Neumann-Dirichlet boundary condition. The first-principles approach was necessary to help calculate the effusion time of a medication through a pore located on the surface of the device. An infinite series of Bessel functions represented the concentration in the Laplace domain. This method yielded closed-form expressions for the characteristic time and the Laplace-transformed fraction of drug released, which was approximated by the first term of the series. The time constant was inversely proportional to the diffusion coefficient in the system and decreased as the pore size increased. It took 4 times the effusion time to unload nearly ninety-eight percent of the pharmaceutical ingredient. (C) 2016 Elsevier B.V. All rights reserved.Ítem Prediction of in-vivo iontophoretic drug release data from in-vitro experiments-insights from modeling(ELSEVIER SCIENCE INC, 2015-12-01) Simon, L.; Ospina, J.; Ita, K.; Simon, L.; Ospina, J.; Ita, K.; Universidad EAFIT. Departamento de Ciencias; Lógica y ComputaciónA strategy was developed to predict in-vivo plasma drug levels from data collected during in-vitro transdermal iontophoretic delivery experiments. The method used the principle of mass conservation and the Nernst-Planck flux equation to describe molecular transport across the skin. Distribution and elimination of the drug in the body followed a one- or two-compartment open model. Analytical expressions for the relaxation constant and plasma drug concentration were developed using Laplace transforms. The steady-state dermal flux was appropriate for predicting drug absorption under in-vivo conditions only when the time constant in the skin was far greater than its value in the blood compartment. A simulation study was conducted to fully assess the performance of estimations based on the equilibrium flux approximation. The findings showed that the normalized integral of squared error decreased exponentially as the ratio of the two time constants (blood/skin) increased. In the case of a single compartment, the error was reduced from 0.15 to 0.016 when the ratio increased from 10 to 100. The methodology was tested using plasma concentrations of a growth-hormone releasing factor in guinea pigs and naloxone in rats. © 2015 Elsevier Inc. All rights reserved.Ítem A three-dimensional semi-analytical solution for predicting drug release through the orifice of a spherical device(ELSEVIER SCIENCE BV, 2016-07-25) Simon, L.; Ospina, J.; Simon, L.; Ospina, J.; Universidad EAFIT. Departamento de Ciencias; Lógica y ComputaciónThree-dimensional solute transport was investigated for a spherical device with a release hole. The governing equation was derived using the Fick's second law. A mixed Neumann-Dirichlet condition was imposed at the boundary to represent diffusion through a small region on the surface of the device. The cumulative percentage of drug released was calculated in the Laplace domain and represented by the first term of an infinite series of Legendre and modified Bessel functions of the first kind. Application of the Zakian algorithm yielded the time-domain closed-form expression. The first-order solution closely matched a numerical solution generated by Mathematica (R). The proposed method allowed computation of the characteristic time. A larger surface pore resulted in a smaller effective time constant. The agreement between the numerical solution and the semi-analytical method improved noticeably as the size of the orifice increased. It took four time constants for the device to release approximately ninety-eight of its drug content. © 2016 Elsevier B.V. All rights reserved.Ítem Two-dimensional transport analysis of transdermal drug absorption with a non-perfect sink boundary condition at the skin-capillary interface(ELSEVIER SCIENCE INC, 2013-07-01) Simon, Laurent; Ospina, Juan; Simon, Laurent; Ospina, Juan; Universidad EAFIT. Departamento de Ciencias; Lógica y ComputaciónA transient percutaneous drug absorption model was solved in two dimensions. Clearance of the topically-applied pharmaceutical occured at the skin-capillary boundary. Timolol penetration profiles in the dermal tissue were produced revealing concentration gradients in the directions normal and parallel to the skin surface. Ninety-eight percent of the steady-state flux was reached after 85. h or four time constants. The analytical solution procedure agreed with published results. As the clearance rate increased relative to diffusion, the delivery rate and amount of drug absorbed into the bloodstream increased while the time to reach the equilibrium flux decreased. Researchers can apply the closed-form expressions to simulate the process, estimate key parameters and design devices that meet specific performance requirements. © 2013 Elsevier Inc.