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Papers by Daniel Martínez

Research paper thumbnail of Decaying, two-dimensional, Navier-Stokes turbulence at very long times

Physica D-nonlinear Phenomena, 1991

Two-dimensional Navier-Stokes turbulent decay has been followed numerically for very long times. ... more Two-dimensional Navier-Stokes turbulent decay has been followed numerically for very long times. The code is spectral, satisfies periodic boundary conditions, and does not make use of hyperviscosity or any'small-scale smoothing. The resolution is (512) 2 , the initial Reynolds number based on the box dimension is about 14000, and the run continues for over 290 initial eddy turnover times. Isolated vortices form, and the turbulence has become highly intermittent in the manner seen by McWilliams and Brachet et al., for times greater than about 30. However, it is not the case that merger of like-signed vortices stops; it only slows down. By t = 210, the final merger is complete, and the vorticity distribution is dominated by one large vortex of either sign. The negative (positive) vortices each occupy about two percent of the box area, and together account for over 98 percent of the total enstrophy. Their alignment suggests the formation of an Ewald lattice with a basic cell containing two point vortices. The ratio of enstrophy to energy continues to decrease monotonically, and the picture is consistent with a "selective decay" process, as described some time ago. A not-entirely-understood phenomenon is the concentration of the vorticity into two cores, suggestive of a negative-temperature state of the discrete line vortex model.

Research paper thumbnail of Selective decay and coherent vortices in two-dimensional incompressible turbulence

Physical Review Letters, 1991

Research paper thumbnail of Lattice Boltzmann Magnetohydrodynamics

Lattice gas and lattice Boltzmann methods are recently developed numerical schemes for simulating... more Lattice gas and lattice Boltzmann methods are recently developed numerical schemes for simulating a variety of physical systems. In this paper a new lattice Boltzmann model for modeling two-dimensional incompressible magnetohydrodynamics (MHD) is presented. The current model fully utilizes the flexibility of the lattice Boltzmann method in comparison with previous lattice gas and lattice Boltzmann MHD models, reducing the number of moving directions from 36 in other models to 12 only. To increase computational efficiency, a simple single time relaxation rule is used for collisions, which directly controls the transport coefficients. The bidirectional streaming process of the particle distribution function in this paper is similar to the original model [ H. Chen and W. H. Matthaeus, Phys. Rev. Lett., 58, 1845(1987), S.Chen, H.Chen, D.Martínez and W.H.Matthaeus, Phys. Rev. Lett. 67,3776 (1991)], but has been greatly simplified, affording simpler implementation of boundary conditions and increasing the feasibility of extension into a workable three-dimensional model. Analytical expressions for the transport coefficients are presented. Also, as example cases, numerical calculation for the Hartmann flow is 1 performed, showing a good agreement between the theoretical prediction and numerical simulation, and a sheet-pinch simulation is performed and compared with the results obtained with a spectral method. PACS numbers: 52.30.-q, 52.65.+z

Research paper thumbnail of Lattice Boltzmann model for simulation of magnetohydrodynamics

Physical Review Letters, 1991

Research paper thumbnail of Physical symmetry and lattice symmetry in the lattice Boltzmann method

Physical Review E, 1997

The lattice Boltzmann method (LBM) is regarded as a specific finite difference discretization for... more The lattice Boltzmann method (LBM) is regarded as a specific finite difference discretization for the kinetic equation of the discrete velocity distribution function. We argue that for finite sets of discrete velocity models, such as LBM, the physical symmetry is necessary for obtaining ...

Research paper thumbnail of On boundary conditions in lattice Boltzmann methods

Physics of Fluids, 1996

A lattice Boltzmann boundary condition for simulation of fluid flow using simple extrapolation is... more A lattice Boltzmann boundary condition for simulation of fluid flow using simple extrapolation is proposed. Numerical simulations, including two-dimensional Poiseuille flow, unsteady Couette flow, lid-driven square cavity flow, and flow over a column of cylinders for a range of ...

Research paper thumbnail of Vagus Nerve Prolonged Stimulation in Cats: Effects on Epileptogenesis (Amygdala Electrical Kindling): Behavioral and Electrographic Changes

Epilepsia, 1999

Summary: Purpose: To analyze the effect of prolonged (daily) electrical vagus nerve stimulation (... more Summary: Purpose: To analyze the effect of prolonged (daily) electrical vagus nerve stimulation (VNS) on daily amygdaloid kindling (AK) in freely moving cats.Methods: Fifteen adult male cats were implanted in both temporal lobe amygdalae, both lateral geniculate bodies, and prefrontal cortices. A bipolar hook (5-mm separation) stainless steel electrode also was implanted in the unsectioned left vagus nerve. AK only was performed on five of the cats as a control. The remaining 10 cats were recorded under the following experimental conditions: VNS (1.2–2.0 mA, 0.5-ms pulses, 30 Hz) for 1 min along with AK (1-s train, 1-ms pulses, 60 Hz, 300–600 μA), followed by VNS alone for 1 min, four times between 11:00 a.m. and 2 p.m. At different times, VNS was arrested, and AK was continued until stage VI kindling was reached.Results: The behavioral changes evoked by VNS were as follows: left miosis, blinking, licking, abdominal contractions, swallowing, and eventually yawning, meowing, upward gaze, and short head movements. Compulsive eating also was present with a variable latency. Outstanding polygraphic changes consisted of augmentation of eye movements and visual evoked potentials while the animal was awake and quiet, with immobility and upward gaze. An increase of the pontogeniculooccipital (PGO) wave density in rapid eye movement (REM) sleep also was noticeable. AK was completed (to stage VI) in the control animals without a vagus nerve implantation in 23.4 ± 3.7 trials. In animals with VNS, the AK was significantly delayed, remaining for a long time in the behavioral stages I-III and showing a reduction of afterdischarge duration and frequency. Stage VI was never reached despite 50 AK trials, except when the vagus nerve electrodes were accidentally broken or vagal stimulation was intentionally arrested. Under these circumstances, 24.4 ± 8.16 AK trials alone were necessary to reach stage VI of kindling.Conclusions: Our results indicate that left, electrical VNS interferes with AK epileptogenesis. This anticonvulsant effect could be related to the increase of REM sleep.

Research paper thumbnail of MORTALITY PATTERNS SUGGEST LACK OF SENESCENCE IN HYDRA

Senescence, a deteriorative process that increases the probability of death of an organism with i... more Senescence, a deteriorative process that increases the probability of death of an organism with increasing chronological age, has been found in all metazoans where careful studies have been carried out. There has been much controversy, however, about the potential immortality of hydra, a solitary freshwater member of the phylum Cnidaria, one of the earliest diverging metazoan groups. Researchers have suggested that hydra is capable of escaping aging by constantly renewing the tissues of its body. But no data have been published to support this assertion. To test for the presence or absence of aging in hydra, mortality and reproductive rates for three hydra cohorts have been analyzed for a period of four years. The results provide no evidence for aging in hydra: mortality rates have remained extremely low and there are no apparent signs of decline in reproductive rates. Hydra may have indeed escaped senescence and may be potentially immortal.

Research paper thumbnail of Microeconomía COMPORTAMIENTO, INSTITUCIONES Y EVOLUCIÓN

Prólogo: La economía y la riqueza de las naciones y de la gente PARTE I: Coordinación y conflicto... more Prólogo: La economía y la riqueza de las naciones y de la gente PARTE I: Coordinación y conflicto: Interacciones sociales genéricas CAPÍTULO UNO Interacciones sociales y diseño institucional CAPÍTULO DOS Orden espontáneo: Auto-organización de la vida económica CAPÍTULO TRES Preferencias y comportamiento CAPÍTULO CUATRO Fallas de coordinación y respuestas institucionales CAPÍTULO CINCO Dividiendo las ganancias de la cooperación: negociación y búsqueda de rentas PARTE II: Competencia y cooperación: Las instituciones del capitalismo CAPÍTULO SEIS Capitalismo utópico: coordinación descentralizada CAPÍTULO SIETE Intercambio: contratos, normas y poder CAPÍTULO OCHO Empleo, desempleo y salarios CAPÍTULO NUEVE Mercados de crédito, restricciones a la riqueza e ineficacia de la asignación CAPÍTULO DIEZ Las instituciones de una economía capitalista PARTE III: Cambio: La co-evolución de las instituciones y las preferencias CAPÍTULO ONCE Evolución institucional e individual CAPÍTULO DOCE Azar, acción colectiva e innovación institucional CAPÍTULO TRECE La coevolución de las instituciones y las preferencias PARTE IV: Conclusión CAPÍTULO CATORCE Governanza económica: mercados, estados y comunidades

Research paper thumbnail of Decaying, two-dimensional, Navier-Stokes turbulence at very long times

Physica D-nonlinear Phenomena, 1991

Two-dimensional Navier-Stokes turbulent decay has been followed numerically for very long times. ... more Two-dimensional Navier-Stokes turbulent decay has been followed numerically for very long times. The code is spectral, satisfies periodic boundary conditions, and does not make use of hyperviscosity or any'small-scale smoothing. The resolution is (512) 2 , the initial Reynolds number based on the box dimension is about 14000, and the run continues for over 290 initial eddy turnover times. Isolated vortices form, and the turbulence has become highly intermittent in the manner seen by McWilliams and Brachet et al., for times greater than about 30. However, it is not the case that merger of like-signed vortices stops; it only slows down. By t = 210, the final merger is complete, and the vorticity distribution is dominated by one large vortex of either sign. The negative (positive) vortices each occupy about two percent of the box area, and together account for over 98 percent of the total enstrophy. Their alignment suggests the formation of an Ewald lattice with a basic cell containing two point vortices. The ratio of enstrophy to energy continues to decrease monotonically, and the picture is consistent with a "selective decay" process, as described some time ago. A not-entirely-understood phenomenon is the concentration of the vorticity into two cores, suggestive of a negative-temperature state of the discrete line vortex model.

Research paper thumbnail of Selective decay and coherent vortices in two-dimensional incompressible turbulence

Physical Review Letters, 1991

Research paper thumbnail of Lattice Boltzmann Magnetohydrodynamics

Lattice gas and lattice Boltzmann methods are recently developed numerical schemes for simulating... more Lattice gas and lattice Boltzmann methods are recently developed numerical schemes for simulating a variety of physical systems. In this paper a new lattice Boltzmann model for modeling two-dimensional incompressible magnetohydrodynamics (MHD) is presented. The current model fully utilizes the flexibility of the lattice Boltzmann method in comparison with previous lattice gas and lattice Boltzmann MHD models, reducing the number of moving directions from 36 in other models to 12 only. To increase computational efficiency, a simple single time relaxation rule is used for collisions, which directly controls the transport coefficients. The bidirectional streaming process of the particle distribution function in this paper is similar to the original model [ H. Chen and W. H. Matthaeus, Phys. Rev. Lett., 58, 1845(1987), S.Chen, H.Chen, D.Martínez and W.H.Matthaeus, Phys. Rev. Lett. 67,3776 (1991)], but has been greatly simplified, affording simpler implementation of boundary conditions and increasing the feasibility of extension into a workable three-dimensional model. Analytical expressions for the transport coefficients are presented. Also, as example cases, numerical calculation for the Hartmann flow is 1 performed, showing a good agreement between the theoretical prediction and numerical simulation, and a sheet-pinch simulation is performed and compared with the results obtained with a spectral method. PACS numbers: 52.30.-q, 52.65.+z

Research paper thumbnail of Lattice Boltzmann model for simulation of magnetohydrodynamics

Physical Review Letters, 1991

Research paper thumbnail of Physical symmetry and lattice symmetry in the lattice Boltzmann method

Physical Review E, 1997

The lattice Boltzmann method (LBM) is regarded as a specific finite difference discretization for... more The lattice Boltzmann method (LBM) is regarded as a specific finite difference discretization for the kinetic equation of the discrete velocity distribution function. We argue that for finite sets of discrete velocity models, such as LBM, the physical symmetry is necessary for obtaining ...

Research paper thumbnail of On boundary conditions in lattice Boltzmann methods

Physics of Fluids, 1996

A lattice Boltzmann boundary condition for simulation of fluid flow using simple extrapolation is... more A lattice Boltzmann boundary condition for simulation of fluid flow using simple extrapolation is proposed. Numerical simulations, including two-dimensional Poiseuille flow, unsteady Couette flow, lid-driven square cavity flow, and flow over a column of cylinders for a range of ...

Research paper thumbnail of Vagus Nerve Prolonged Stimulation in Cats: Effects on Epileptogenesis (Amygdala Electrical Kindling): Behavioral and Electrographic Changes

Epilepsia, 1999

Summary: Purpose: To analyze the effect of prolonged (daily) electrical vagus nerve stimulation (... more Summary: Purpose: To analyze the effect of prolonged (daily) electrical vagus nerve stimulation (VNS) on daily amygdaloid kindling (AK) in freely moving cats.Methods: Fifteen adult male cats were implanted in both temporal lobe amygdalae, both lateral geniculate bodies, and prefrontal cortices. A bipolar hook (5-mm separation) stainless steel electrode also was implanted in the unsectioned left vagus nerve. AK only was performed on five of the cats as a control. The remaining 10 cats were recorded under the following experimental conditions: VNS (1.2–2.0 mA, 0.5-ms pulses, 30 Hz) for 1 min along with AK (1-s train, 1-ms pulses, 60 Hz, 300–600 μA), followed by VNS alone for 1 min, four times between 11:00 a.m. and 2 p.m. At different times, VNS was arrested, and AK was continued until stage VI kindling was reached.Results: The behavioral changes evoked by VNS were as follows: left miosis, blinking, licking, abdominal contractions, swallowing, and eventually yawning, meowing, upward gaze, and short head movements. Compulsive eating also was present with a variable latency. Outstanding polygraphic changes consisted of augmentation of eye movements and visual evoked potentials while the animal was awake and quiet, with immobility and upward gaze. An increase of the pontogeniculooccipital (PGO) wave density in rapid eye movement (REM) sleep also was noticeable. AK was completed (to stage VI) in the control animals without a vagus nerve implantation in 23.4 ± 3.7 trials. In animals with VNS, the AK was significantly delayed, remaining for a long time in the behavioral stages I-III and showing a reduction of afterdischarge duration and frequency. Stage VI was never reached despite 50 AK trials, except when the vagus nerve electrodes were accidentally broken or vagal stimulation was intentionally arrested. Under these circumstances, 24.4 ± 8.16 AK trials alone were necessary to reach stage VI of kindling.Conclusions: Our results indicate that left, electrical VNS interferes with AK epileptogenesis. This anticonvulsant effect could be related to the increase of REM sleep.

Research paper thumbnail of MORTALITY PATTERNS SUGGEST LACK OF SENESCENCE IN HYDRA

Senescence, a deteriorative process that increases the probability of death of an organism with i... more Senescence, a deteriorative process that increases the probability of death of an organism with increasing chronological age, has been found in all metazoans where careful studies have been carried out. There has been much controversy, however, about the potential immortality of hydra, a solitary freshwater member of the phylum Cnidaria, one of the earliest diverging metazoan groups. Researchers have suggested that hydra is capable of escaping aging by constantly renewing the tissues of its body. But no data have been published to support this assertion. To test for the presence or absence of aging in hydra, mortality and reproductive rates for three hydra cohorts have been analyzed for a period of four years. The results provide no evidence for aging in hydra: mortality rates have remained extremely low and there are no apparent signs of decline in reproductive rates. Hydra may have indeed escaped senescence and may be potentially immortal.

Research paper thumbnail of Microeconomía COMPORTAMIENTO, INSTITUCIONES Y EVOLUCIÓN

Prólogo: La economía y la riqueza de las naciones y de la gente PARTE I: Coordinación y conflicto... more Prólogo: La economía y la riqueza de las naciones y de la gente PARTE I: Coordinación y conflicto: Interacciones sociales genéricas CAPÍTULO UNO Interacciones sociales y diseño institucional CAPÍTULO DOS Orden espontáneo: Auto-organización de la vida económica CAPÍTULO TRES Preferencias y comportamiento CAPÍTULO CUATRO Fallas de coordinación y respuestas institucionales CAPÍTULO CINCO Dividiendo las ganancias de la cooperación: negociación y búsqueda de rentas PARTE II: Competencia y cooperación: Las instituciones del capitalismo CAPÍTULO SEIS Capitalismo utópico: coordinación descentralizada CAPÍTULO SIETE Intercambio: contratos, normas y poder CAPÍTULO OCHO Empleo, desempleo y salarios CAPÍTULO NUEVE Mercados de crédito, restricciones a la riqueza e ineficacia de la asignación CAPÍTULO DIEZ Las instituciones de una economía capitalista PARTE III: Cambio: La co-evolución de las instituciones y las preferencias CAPÍTULO ONCE Evolución institucional e individual CAPÍTULO DOCE Azar, acción colectiva e innovación institucional CAPÍTULO TRECE La coevolución de las instituciones y las preferencias PARTE IV: Conclusión CAPÍTULO CATORCE Governanza económica: mercados, estados y comunidades