Physica C-superconductivity and Its Applications, 2007
We show that the main features of the cuprates superconductors phase diagram can be derived consi... more We show that the main features of the cuprates superconductors phase diagram can be derived considering the disorder as a key property of these materials. Our basic point is that the high pseudogap line is an onset of phase separation which generates compounds made up of regions with distinct doping levels. Calculations with the Bogoliubov-deGennes approach yield good agreement with the measured values of T∗ and Tc.
The Cahn-Hilliard equation is related with a number of interesting physical phenomena like the sp... more The Cahn-Hilliard equation is related with a number of interesting physical phenomena like the spinodal decomposition, phase separation and phase ordering dynamics. On the other hand this equation is very stiff an the difficulty to solve it numerically increases with the dimensionality and therefore, there are several published numerical studies in one dimension (1D), dealing with different approaches, and much fewer in two dimensions (2D). In three dimensions (3D) there are very few publications, usually concentrate in some specific result without the details of the used numerical scheme. We present here a stable and fast conservative finite difference scheme to solve the Cahn-Hilliard with two improvements: a splitting potential into a implicit and explicit in time part and a the use of free boundary conditions. We show that gradient stability is achieved in one, two and three dimensions with large time marching steps than normal methods.
Physica C-superconductivity and Its Applications, 2007
The dual nature of the electronic structure of stripes in La2−xSrxCuO4 was characterized by many ... more The dual nature of the electronic structure of stripes in La2−xSrxCuO4 was characterized by many experiments. We present here an attempt to characterize this dual behavior based on the Cahn-Hilliard theory of a phase separation transition which is assumed to occur at the high pseudogap temperature. The resulting inhomogeneous low doping system is formed of hole-rich (metallic like) regions embedded in a hole-poor (insulator like). This inhomogeneous configuration is analyzed by a new method within the Bogoliubov-deGennes superconducting theory. This approach describes well the electronic nodal-antinodal dichotomy and parts of the phase diagram.
We report the development of an SPMD parallel application which computes the macroscopic thermal ... more We report the development of an SPMD parallel application which computes the macroscopic thermal dispersion in porous media. The performance of SPMD programs is strongly affected by dynamic load imbalancing factors. The use of a suitable load balancing algorithm is essential for overcoming the effects of these imbalancing factors. We developed nine versions of the SPMD application, each one adopting
We show that the main features of the cuprates superconductors phase diagram can be derived consi... more We show that the main features of the cuprates superconductors phase diagram can be derived considering the disorder as a key property of these materials. Our basic point is that the high pseudogap line is an onset of phase separation which generates compounds made up of regions with distinct doping levels. We calculate how this continuous temperature dependent phase separation process occurs in high critical temperature superconductors (HTSC) using the Cahn-Hilliard approach, originally applied to study alloys. Since the level of phase separation varies for different cuprates, it is possible that different systems with average doping level pm exhibit different degrees of charge and spin segregation. Calculations on inhomogeneous charge distributions in form of stripes in finite clusters performed by the Bogoliubov-deGennes superconducting approach yield good agreement to the pseudogap temperature T*(pm), the onset of local pairing amplitudes with phase locked and concomitantly, how they develop at low temperatures into the superconducting phase at Tc(pm) by percolation.
A general expression is found for the magnetic field generated by a long rectilinear current plac... more A general expression is found for the magnetic field generated by a long rectilinear current placed in a static background gravitational field. Then it is applied to the case of uniform, Schwarzschild, general Reissner-Nordstrom and ``charge-equal-to-mass'' Reissner-Nordstrom background metrics. All the calculations are very simple and can easily be done in the classroom.
Physica A-statistical Mechanics and Its Applications, 2005
The Cahn-Hilliard equation is related with a number of interesting physical phenomena like the sp... more The Cahn-Hilliard equation is related with a number of interesting physical phenomena like the spinodal decomposition, phase separation and phase ordering dynamics. On the other hand this equation is very stiff an the difficulty to solve it numerically increases with the dimensionality and therefore, there are several published numerical studies in one dimension (1D), dealing with different approaches, and much fewer in two dimensions (2D). In three dimensions (3D) there are very few publications, usually concentrate in some specific result without the details of the used numerical scheme. We present here a stable and fast conservative finite difference scheme to solve the Cahn-Hilliard with two improvements: a splitting potential into a implicit and explicit in time part and a the use of free boundary conditions. We show that gradient stability is achieved in one, two and three dimensions with large time marching steps than normal methods.
We show that the main features of the cuprates superconductors phase diagram can be derived consi... more We show that the main features of the cuprates superconductors phase diagram can be derived considering the disorder as a key property of these materials. Our basic point is that the high pseudogap line is an onset of phase separation which generates compounds made up of regions with distinct doping levels. We calculate how this continuous temperature dependent phase separation process occurs in high critical temperature superconductors (HTSC) using the Cahn-Hilliard approach, originally applied to study alloys. Since the level of phase separation varies for different cuprates, it is possible that different systems with average doping level pm exhibit different degrees of charge and spin segregation. Calculations on inhomogeneous charge distributions in form of stripes in finite clusters performed by the Bogoliubov-deGennes superconducting approach yield good agreement to the pseudogap temperature T*(pm), the onset of local pairing amplitudes with phase locked and concomitantly, how they develop at low temperatures into the superconducting phase at Tc(pm) by percolation.
Physica C-superconductivity and Its Applications, 2007
We show that the main features of the cuprates superconductors phase diagram can be derived consi... more We show that the main features of the cuprates superconductors phase diagram can be derived considering the disorder as a key property of these materials. Our basic point is that the high pseudogap line is an onset of phase separation which generates compounds made up of regions with distinct doping levels. Calculations with the Bogoliubov-deGennes approach yield good agreement with the measured values of T∗ and Tc.
The Cahn-Hilliard equation is related with a number of interesting physical phenomena like the sp... more The Cahn-Hilliard equation is related with a number of interesting physical phenomena like the spinodal decomposition, phase separation and phase ordering dynamics. On the other hand this equation is very stiff an the difficulty to solve it numerically increases with the dimensionality and therefore, there are several published numerical studies in one dimension (1D), dealing with different approaches, and much fewer in two dimensions (2D). In three dimensions (3D) there are very few publications, usually concentrate in some specific result without the details of the used numerical scheme. We present here a stable and fast conservative finite difference scheme to solve the Cahn-Hilliard with two improvements: a splitting potential into a implicit and explicit in time part and a the use of free boundary conditions. We show that gradient stability is achieved in one, two and three dimensions with large time marching steps than normal methods.
Physica C-superconductivity and Its Applications, 2007
The dual nature of the electronic structure of stripes in La2−xSrxCuO4 was characterized by many ... more The dual nature of the electronic structure of stripes in La2−xSrxCuO4 was characterized by many experiments. We present here an attempt to characterize this dual behavior based on the Cahn-Hilliard theory of a phase separation transition which is assumed to occur at the high pseudogap temperature. The resulting inhomogeneous low doping system is formed of hole-rich (metallic like) regions embedded in a hole-poor (insulator like). This inhomogeneous configuration is analyzed by a new method within the Bogoliubov-deGennes superconducting theory. This approach describes well the electronic nodal-antinodal dichotomy and parts of the phase diagram.
We report the development of an SPMD parallel application which computes the macroscopic thermal ... more We report the development of an SPMD parallel application which computes the macroscopic thermal dispersion in porous media. The performance of SPMD programs is strongly affected by dynamic load imbalancing factors. The use of a suitable load balancing algorithm is essential for overcoming the effects of these imbalancing factors. We developed nine versions of the SPMD application, each one adopting
We show that the main features of the cuprates superconductors phase diagram can be derived consi... more We show that the main features of the cuprates superconductors phase diagram can be derived considering the disorder as a key property of these materials. Our basic point is that the high pseudogap line is an onset of phase separation which generates compounds made up of regions with distinct doping levels. We calculate how this continuous temperature dependent phase separation process occurs in high critical temperature superconductors (HTSC) using the Cahn-Hilliard approach, originally applied to study alloys. Since the level of phase separation varies for different cuprates, it is possible that different systems with average doping level pm exhibit different degrees of charge and spin segregation. Calculations on inhomogeneous charge distributions in form of stripes in finite clusters performed by the Bogoliubov-deGennes superconducting approach yield good agreement to the pseudogap temperature T*(pm), the onset of local pairing amplitudes with phase locked and concomitantly, how they develop at low temperatures into the superconducting phase at Tc(pm) by percolation.
A general expression is found for the magnetic field generated by a long rectilinear current plac... more A general expression is found for the magnetic field generated by a long rectilinear current placed in a static background gravitational field. Then it is applied to the case of uniform, Schwarzschild, general Reissner-Nordstrom and ``charge-equal-to-mass'' Reissner-Nordstrom background metrics. All the calculations are very simple and can easily be done in the classroom.
Physica A-statistical Mechanics and Its Applications, 2005
The Cahn-Hilliard equation is related with a number of interesting physical phenomena like the sp... more The Cahn-Hilliard equation is related with a number of interesting physical phenomena like the spinodal decomposition, phase separation and phase ordering dynamics. On the other hand this equation is very stiff an the difficulty to solve it numerically increases with the dimensionality and therefore, there are several published numerical studies in one dimension (1D), dealing with different approaches, and much fewer in two dimensions (2D). In three dimensions (3D) there are very few publications, usually concentrate in some specific result without the details of the used numerical scheme. We present here a stable and fast conservative finite difference scheme to solve the Cahn-Hilliard with two improvements: a splitting potential into a implicit and explicit in time part and a the use of free boundary conditions. We show that gradient stability is achieved in one, two and three dimensions with large time marching steps than normal methods.
We show that the main features of the cuprates superconductors phase diagram can be derived consi... more We show that the main features of the cuprates superconductors phase diagram can be derived considering the disorder as a key property of these materials. Our basic point is that the high pseudogap line is an onset of phase separation which generates compounds made up of regions with distinct doping levels. We calculate how this continuous temperature dependent phase separation process occurs in high critical temperature superconductors (HTSC) using the Cahn-Hilliard approach, originally applied to study alloys. Since the level of phase separation varies for different cuprates, it is possible that different systems with average doping level pm exhibit different degrees of charge and spin segregation. Calculations on inhomogeneous charge distributions in form of stripes in finite clusters performed by the Bogoliubov-deGennes superconducting approach yield good agreement to the pseudogap temperature T*(pm), the onset of local pairing amplitudes with phase locked and concomitantly, how they develop at low temperatures into the superconducting phase at Tc(pm) by percolation.
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Papers by Otton Silveira