Claudia Timofte | University of Bucharest (original) (raw)
Papers by Claudia Timofte
On the Asymptotic Behavior of a Reaction-diffusion System in a Porous Medium
Nucleation and Atmospheric Aerosols, 2011
The aim of this paper is to analyze the convection and diffusion of a solute in a porous medium, ... more The aim of this paper is to analyze the convection and diffusion of a solute in a porous medium, under the influence of non‐smooth chemical reactions taking place on the pore surfaces. Our model consists of a system of two coupled convection‐diffusion equations, one in the fluid part and another one on the boundaries of the grains of the porous medium. The coupling is made through a nonlinear reaction term, modeling the mass exchange between the bulk and, respectively, the surface concentration.
Journal of Theoretical and Applied Mechanics, 2003
Using the generalized method of moments and a central limit theorem, we shall describe a large cl... more Using the generalized method of moments and a central limit theorem, we shall describe a large class of thermal dispersion phenomena occurring in some macrohomogeneous systems. We shall be interested in computing the macroscale coefficients in terms of the microscale coefficients and the system geometry. Also, the functional dependence of the effective coefficients on the velocity and the spatial scale parameters is analyzed.
CCDC 724175: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Mathematical Modelling and Analysis, Dec 31, 2003
![Research paper thumbnail of (<i>S</i>)-[2-(1-Aminoethyl)phenyl]chloro(3-chloropyridine)palladium(II) acetone 0.25-solvate](https://attachments.academia-assets.com/113959524/thumbnails/1.jpg)
](Acta Crystallographica Section E-structure Reports Online, Oct 4, 2006
metal-organic papers m2792 Calmuschi-Cula et al. [Pd(C 8 H 10 N)Cl(C 5 H 4 ClN)]Á0.25C 3 H 6 O
arXiv (Cornell University), Feb 12, 2020
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two mode... more We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation.
HAL (Le Centre pour la Communication Scientifique Directe), 2023
We study the homogenization of a scalar problem posed in a composite medium made up of two materi... more We study the homogenization of a scalar problem posed in a composite medium made up of two materials, a positive and a negative one. An important feature is the presence of a flux jump across their oscillating interface. The main difficulties of this study are due to the sign-changing coefficients and to the appearance of an unsigned surface integral term in the variational formulation. A proof by contradiction (nonstandard in this context) and T−coercivity technics are used in order to cope with these difficulties.
HAL (Le Centre pour la Communication Scientifique Directe), 2021
We study the homogenization of a diffusion-type problem, for sign-changing conductivities with ex... more We study the homogenization of a diffusion-type problem, for sign-changing conductivities with extreme contrasts. The weak limit, which is proved to be the same as in the elliptic case of positive conductivities, has an explicit dependence on the conductivities.
Zeitschrift für angewandte Mathematik und Physik
The model analyzed in this paper has its origins in the description of composites made by a hosti... more The model analyzed in this paper has its origins in the description of composites made by a hosting medium containing a periodic array of inclusions coated by a thin layer consisting of sublayers of two different materials. This two-phase coating material is such that the external part has a low diffusivity in the orthogonal direction, while the internal one has high diffusivity along the tangential direction. In a previous paper (Amar in IFB 21:41–59, 2019), by means of a concentration procedure, the internal layer was replaced by an imperfect interface. The present paper is concerned with the concentration of the external coating layer and the homogenization, via the periodic unfolding method, of the resulting model, which is far from being a standard one. Despite the fact that the limit problem looks like a classical Dirichlet problem for an elliptic equation, in the construction of the homogenized matrix and of the source term, a very delicate analysis is required.
Asymptotic analysis for non-local problems in composites with different imperfect contact conditions
Applicable Analysis
ABSTRACT. This paper deals with the homogenization of a nonlinear problem mod-elllng chemica! rea... more ABSTRACT. This paper deals with the homogenization of a nonlinear problem mod-elllng chemica! reactive flows through periodically perforated domains. The chemical reactions take place on the walls of the porous médium. The effective behavior of these reactive flows is described by a new elliptic boundary-value problem contalning an extra zero-order term which captures the effect of the chemical reactions. 1.
Proceedings of XXIV AIMETA Conference 2019, 2020
We study the overall thermal conductivity of a composite material obtained by inserting in a host... more We study the overall thermal conductivity of a composite material obtained by inserting in a hosting medium an array of finely mixed inclusions made of perfect heat conductors. The physical properties of this material are useful in applications and are obtained using the periodic unfolding method. The peculiarity of this problem calls for a suitable choice of test functions in the unfolding procedure, which leads to a non-standard variational two-scale problem, that cannot be written in a strong form, as usual.
Nonlinear Differential Equations and Applications NoDEA, 2019
We study the thermal properties of a composite material in which a periodic array of finely mixed... more We study the thermal properties of a composite material in which a periodic array of finely mixed perfect thermal conductors is inserted. The suitable model describing the behaviour of such physical materials leads to the so-called equivalued surface boundary value problem. To analyze the overall conductivity of the composite medium (when the size of the inclusions tends to zero), we make use of the homogenization theory, employing the unfolding technique. The peculiarity of the problem under investigation asks for a particular care in developing the unfolding procedure, giving rise to a non-standard two-scale problem.
Heat Transfer Problems
Homogenization results for dynamical
T-coercivity for the asymptotic analysis of scalar problems with sign-changing coefficients in thin periodic domains
Electronic Journal of Differential Equations, Jun 26, 2021
The asymptotic behavior of the solution of a class of elliptic problems modeling diffusion in som... more The asymptotic behavior of the solution of a class of elliptic problems modeling diffusion in some periodic perforated media is analyzed. We consider, at the microscale, an elliptic equation with various nonlinear conditions prescribed on the boundary of the perforations and we prove that the effective behavior of the solution of such a problem is governed by another elliptic equation, which, depending on the type of the conditions imposed on the surface of the cavities, can contain extra zeroorder terms.
This paper deals with the homogenization of a nonlinear model for heat conduction through the ext... more This paper deals with the homogenization of a nonlinear model for heat conduction through the exterior of a domain containing periodically distributed conductive grains. We assume that on the walls of the grains we have climatizators governing the heat flux through the boundary. The effective behavior of this nonlinear flow is described by a new elliptic boundary-value problem containing an extra zero-order term which captures the effect of the boundary climatization.
Upscaling of reaction-diffusion problems in composites with imperfect interfaces
Biomath Communications Supplement, 2018
The homogenization of some reaction-diffusion problems in a highly heterogeneous composite medium... more The homogenization of some reaction-diffusion problems in a highly heterogeneous composite medium formed by two connected constituents separated by an imperfect interface is analyzed. The main feature of our setting is represented by the fact that, across this imperfect interface, both the solution and its flux are assumed to exhibit jumps. Several models arise at the limit. In particular, a modified bidomain model is obtained and compared to some existing models in the literature (see [1]-[4]). Our results can serve as a tool for biochemists interested in studying the complex mechanisms involved in the calcium dynamics in living cells.
Journal of Mathematical Analysis and Applications, 2021
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two mode... more We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation.
On the Asymptotic Behavior of a Reaction-diffusion System in a Porous Medium
Nucleation and Atmospheric Aerosols, 2011
The aim of this paper is to analyze the convection and diffusion of a solute in a porous medium, ... more The aim of this paper is to analyze the convection and diffusion of a solute in a porous medium, under the influence of non‐smooth chemical reactions taking place on the pore surfaces. Our model consists of a system of two coupled convection‐diffusion equations, one in the fluid part and another one on the boundaries of the grains of the porous medium. The coupling is made through a nonlinear reaction term, modeling the mass exchange between the bulk and, respectively, the surface concentration.
Journal of Theoretical and Applied Mechanics, 2003
Using the generalized method of moments and a central limit theorem, we shall describe a large cl... more Using the generalized method of moments and a central limit theorem, we shall describe a large class of thermal dispersion phenomena occurring in some macrohomogeneous systems. We shall be interested in computing the macroscale coefficients in terms of the microscale coefficients and the system geometry. Also, the functional dependence of the effective coefficients on the velocity and the spatial scale parameters is analyzed.
CCDC 724175: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Mathematical Modelling and Analysis, Dec 31, 2003
Acta Crystallographica Section E-structure Reports Online, Oct 4, 2006
metal-organic papers m2792 Calmuschi-Cula et al. [Pd(C 8 H 10 N)Cl(C 5 H 4 ClN)]Á0.25C 3 H 6 O
arXiv (Cornell University), Feb 12, 2020
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two mode... more We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation.
HAL (Le Centre pour la Communication Scientifique Directe), 2023
We study the homogenization of a scalar problem posed in a composite medium made up of two materi... more We study the homogenization of a scalar problem posed in a composite medium made up of two materials, a positive and a negative one. An important feature is the presence of a flux jump across their oscillating interface. The main difficulties of this study are due to the sign-changing coefficients and to the appearance of an unsigned surface integral term in the variational formulation. A proof by contradiction (nonstandard in this context) and T−coercivity technics are used in order to cope with these difficulties.
HAL (Le Centre pour la Communication Scientifique Directe), 2021
We study the homogenization of a diffusion-type problem, for sign-changing conductivities with ex... more We study the homogenization of a diffusion-type problem, for sign-changing conductivities with extreme contrasts. The weak limit, which is proved to be the same as in the elliptic case of positive conductivities, has an explicit dependence on the conductivities.
Zeitschrift für angewandte Mathematik und Physik
The model analyzed in this paper has its origins in the description of composites made by a hosti... more The model analyzed in this paper has its origins in the description of composites made by a hosting medium containing a periodic array of inclusions coated by a thin layer consisting of sublayers of two different materials. This two-phase coating material is such that the external part has a low diffusivity in the orthogonal direction, while the internal one has high diffusivity along the tangential direction. In a previous paper (Amar in IFB 21:41–59, 2019), by means of a concentration procedure, the internal layer was replaced by an imperfect interface. The present paper is concerned with the concentration of the external coating layer and the homogenization, via the periodic unfolding method, of the resulting model, which is far from being a standard one. Despite the fact that the limit problem looks like a classical Dirichlet problem for an elliptic equation, in the construction of the homogenized matrix and of the source term, a very delicate analysis is required.
Asymptotic analysis for non-local problems in composites with different imperfect contact conditions
Applicable Analysis
ABSTRACT. This paper deals with the homogenization of a nonlinear problem mod-elllng chemica! rea... more ABSTRACT. This paper deals with the homogenization of a nonlinear problem mod-elllng chemica! reactive flows through periodically perforated domains. The chemical reactions take place on the walls of the porous médium. The effective behavior of these reactive flows is described by a new elliptic boundary-value problem contalning an extra zero-order term which captures the effect of the chemical reactions. 1.
Proceedings of XXIV AIMETA Conference 2019, 2020
We study the overall thermal conductivity of a composite material obtained by inserting in a host... more We study the overall thermal conductivity of a composite material obtained by inserting in a hosting medium an array of finely mixed inclusions made of perfect heat conductors. The physical properties of this material are useful in applications and are obtained using the periodic unfolding method. The peculiarity of this problem calls for a suitable choice of test functions in the unfolding procedure, which leads to a non-standard variational two-scale problem, that cannot be written in a strong form, as usual.
Nonlinear Differential Equations and Applications NoDEA, 2019
We study the thermal properties of a composite material in which a periodic array of finely mixed... more We study the thermal properties of a composite material in which a periodic array of finely mixed perfect thermal conductors is inserted. The suitable model describing the behaviour of such physical materials leads to the so-called equivalued surface boundary value problem. To analyze the overall conductivity of the composite medium (when the size of the inclusions tends to zero), we make use of the homogenization theory, employing the unfolding technique. The peculiarity of the problem under investigation asks for a particular care in developing the unfolding procedure, giving rise to a non-standard two-scale problem.
Heat Transfer Problems
Homogenization results for dynamical
T-coercivity for the asymptotic analysis of scalar problems with sign-changing coefficients in thin periodic domains
Electronic Journal of Differential Equations, Jun 26, 2021
The asymptotic behavior of the solution of a class of elliptic problems modeling diffusion in som... more The asymptotic behavior of the solution of a class of elliptic problems modeling diffusion in some periodic perforated media is analyzed. We consider, at the microscale, an elliptic equation with various nonlinear conditions prescribed on the boundary of the perforations and we prove that the effective behavior of the solution of such a problem is governed by another elliptic equation, which, depending on the type of the conditions imposed on the surface of the cavities, can contain extra zeroorder terms.
This paper deals with the homogenization of a nonlinear model for heat conduction through the ext... more This paper deals with the homogenization of a nonlinear model for heat conduction through the exterior of a domain containing periodically distributed conductive grains. We assume that on the walls of the grains we have climatizators governing the heat flux through the boundary. The effective behavior of this nonlinear flow is described by a new elliptic boundary-value problem containing an extra zero-order term which captures the effect of the boundary climatization.
Upscaling of reaction-diffusion problems in composites with imperfect interfaces
Biomath Communications Supplement, 2018
The homogenization of some reaction-diffusion problems in a highly heterogeneous composite medium... more The homogenization of some reaction-diffusion problems in a highly heterogeneous composite medium formed by two connected constituents separated by an imperfect interface is analyzed. The main feature of our setting is represented by the fact that, across this imperfect interface, both the solution and its flux are assumed to exhibit jumps. Several models arise at the limit. In particular, a modified bidomain model is obtained and compared to some existing models in the literature (see [1]-[4]). Our results can serve as a tool for biochemists interested in studying the complex mechanisms involved in the calcium dynamics in living cells.
Journal of Mathematical Analysis and Applications, 2021
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two mode... more We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation.