Licenciado en Filosofía y una Licenciatura en educación, mención Lengua y Literatura. Docente e investigador sobre el ser humano y el recorrido que hacemos para conquistar la felicidad.
A manera de introducción La lectura en torno a la figura del hecho de un Jesús histórico siempre ... more A manera de introducción La lectura en torno a la figura del hecho de un Jesús histórico siempre genera interrogante, a veces, o por lo menos así lo siente mi persona, da miedo, siempre nos quedamos en el plano de saber que Jesús es el hijo de Dios y ya. No nos gusta ahondar porque creemos que ofendemos a Dios. ¡Nada más ingenuo! Deseo que al leer las líneas de estas reflexiones te unas a este sentir de mirar a Jesús sumergido en la historia de su tiempo, pero también a la historia de nuestros tiempos, y de manera especial, a la historia de nuestra propia existencia. La Galilea en la historia y Jesús en su historia Nadie puede negar la existencia de Galilea, como afirma Aguirre (2002): "En tiempo de Jesús, Galilea era un reino vasallo de Roma bajo la dinastía herodiana, mientras que Judea estaba bajo el control directo de Roma, que tenía allí un prefecto que dependía del legado de Siria". (p.3) Al googlear podemos llegar a encontrar la región de Galilea y con quien limita y toda su tradición en la actualidad. Por tanto, los caminos y senderos que nos narran los evangelios hacen ver que su contexto narrativo tiene una razón de ser. Ahora bien, el pueblo llamado Nazaret, también puede ser encontrado en la biblioteca de Alejandría del siglo XXI: Google. ¿Qué busco con esto? Que los relatos bíblicos narran la historia de un hombre que recorrió las calles y las aldeas de regiones que son constatables bien sea si nos dirigimos hacia allá como destinos turísticos o con ganas de conocer, o sencillamente con el hecho de estar en casa y acceder desde el flameante internet.
We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell ... more We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell of conducting fluid to investigate the relationship between the Earth's toroidal magnetic field and the time-dependent anomalous rotation of the solid inner core. We compute the induced toroidal magnetic field and inner core rotation maintained by the interaction of time-independent, axisymmetric outer core fluid flow with models of the poloidal magnetic field. Three possible models of the azimuthal flow in the outer core are investigated: two thermal wind flows inside the tangent cylinder (predicted by some numerical models of the geodynamo) and a columnar flow outside the inner core tangent cylinder inferred from the geomagnetic westward drift. Results indicate that electromagnetic torques tightly couple the inner core rotation to the fluid motion. Electromagnetic spin-up of the inner core occurs through damped torsional oscillations with periodicity near 4 years depending on the strength of the poloidal magnetic field. In steady state the thermal winds inside the tangent cylinder generate a peak toroidal field of 25 mT accompanying a prograde inner core rotation rate of lø/yr. In contrast, the columnar westward drift model generates toroidal field with peak intensity near 4 mT and a small, retrograde anomalous inner core rotation of-0.013ø/yr. The weak retrograde motion of the inner core produced by electromagnetic coupling to the westward drift cannot explain the seismically inferred prograde anomalous rotation.
Physics of The Earth and Planetary Interiors, 1999
An analytical model is developed for the electromagnetic torques exerted on the mantle by the pol... more An analytical model is developed for the electromagnetic torques exerted on the mantle by the poloidal magnetic field of the core interacting with a laterally heterogeneous conducting layer at the base of the mantle. Torques due to changes in both orientation and intensity of a dipolar poloidal field are included. Contrary to earlier suggestions, our calculations predict that the trajectory of the magnetic pole during a polarity reversal is not strongly affected by heterogeneity in mantle electrical conductivity. q 0031-9201r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
Geodynamic models of heat transport and the thermal evolution of Earth's interior require knowled... more Geodynamic models of heat transport and the thermal evolution of Earth's interior require knowledge of thermal conductivity for high-pressure phases at relevant temperatures and pressures. Here we present new data on radiative and lattice heat transfer in mantle materials determined from optical spectroscopy and time-resolved optical radiometry. The pressure dependence of optical absorption in ferropericlase (Mg,Fe)O, and silicate perovskite (Mg,Fe)SiO 3 , has been determined in the IR through UV regions up to 133 GPa. Whereas (Mg,Fe)O exhibits a strong pressure dependence of absorption and spectral changes associated with the high-spin (HS) to low-spin (LS) transition of Fe 2+ [Goncharov, A.F., Struzhkin, V.V., Jacobsen, S.D. 2006. Reduced radiative conductivity of low-spin (Mg,Fe)O in the lower mantle. Science 312, 1205-1208], the pressure dependence of optical absorption in (Mg,Fe)SiO 3 is relatively weak. We observe a moderate increase in absorption with pressure for (Mg,Fe)SiO 3 in the visible and infrared spectral range due to a red-shift of absorption in ultraviolet, however the crystal-field transitions of Fe 2+ become weaker with pressure and disappear above 50 GPa as a result of the HS-LS transition in (Mg,Fe)SiO 3 . Intervalence charge-transfer transitions in silicate perovskite shift to higher energies with pressure. The temperature dependence of the optical absorption of (Mg,Fe)O measured up to 65 GPa and 800 K is moderate below 30 GPa and weak above 30 GPa. Thus, the temperature correction of the radiative conductivity is insignificant. The estimated total pressure-dependent radiative conductivity (in approximation of a large grain size) is lower than expected from the pressure extrapolation of the ambient and low-pressure data . Mantle values of thermal conductivity and the geotherm from phonon lifetimes. Science 283, 1699Science 283, -1706. Dependence of diffusive radiative transfer on grain-size, temperature, and Fe-content: implications for mantle processes. J. Geodyn. 40, 51-72]. A new method has been developed to measure thermal diffusivity of mantle materials at high P-T using time-resolved radiometry combined with a pulsed-IR source. Here, the technique is tested on MgO to 32 GPa and used to obtain a functional pressure dependence of thermal diffusivity and calculated thermal conductivity of the lower mantle.
Results of finite-amplitude convection experiments in a rotating spherical shell are presented. W... more Results of finite-amplitude convection experiments in a rotating spherical shell are presented. Water (Prandtl number P = 7) and liquid gallium (P = 0.027) have been used as working fluids. In both liquids, convective velocities could be measured in the equatorial plane using an ultrasonic Doppler velocimetry technique. The parameter space has been systematically explored, for values of the Ekman and Rayleigh numbers E > 7 10 −7 and Ra < 5 10 9 . Both measured convective velocity and zonal circulation are much higher in liquid gallium than in water. A scaling analysis is formulated, which shows that higher convective velocities are an effect of the low Prandtl number in liquid gallium, and that higher zonal flows can be explained through a Reynolds stress mechanism. The Reynolds numbers in gallium (Re = 250 − 2000) are higher indeed than in water (Re = 25 − 250). An inertial regime sets up at high Re, in which kinetic energy does not dissipate at the scale of convective eddies and is transferred up to the scale of the container, where it is dissipated through Ekman friction of zonal flow. This upwards energy transfer can be seen as an effect of quasigeostrophic turbulence. Applying the scaling relations to an hypothetic non-magnetic flow in the Earth's core yields Reynolds numbers of the order of 10 8 , in fair agreement with values required for dynamo action, convective velocities of order 10 −3 m/s, zonal flow of similar amplitude, and eddy scales as low as 10 km.
We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell ... more We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell of conducting fluid to investigate the relationship between the Earth's toroidal magnetic field and the time-dependent anomalous rotation of the solid inner core. We compute the induced toroidal magnetic field and inner core rotation maintained by the interaction of time-independent, axisymmetric outer core fluid flow with models of the poloidal magnetic field. Three possible models of the azimuthal flow in the outer core are investigated: two thermal wind flows inside the tangent cylinder (predicted by some numerical models of the geodynamo) and a columnar flow outside the inner core tangent cylinder inferred from the geomagnetic westward drift. Results indicate that electromagnetic torques tightly couple the inner core rotation to the fluid motion. Electromagnetic spin-up of the inner core occurs through damped torsional oscillations with periodicity near 4 years depending on the strength of the poloidal magnetic field. In steady state the thermal winds inside the tangent cylinder generate a peak toroidal field of 25 mT accompanying a prograde inner core rotation rate of lø/yr. In contrast, the columnar westward drift model generates toroidal field with peak intensity near 4 mT and a small, retrograde anomalous inner core rotation of-0.013ø/yr. The weak retrograde motion of the inner core produced by electromagnetic coupling to the westward drift cannot explain the seismically inferred prograde anomalous rotation.
The main characteristics of the Earth's dynamo are reviewed. The combined actions of Coriolis and... more The main characteristics of the Earth's dynamo are reviewed. The combined actions of Coriolis and Lorentz forces lead to the so-called "magnetostrophic" regime. We derive an estimate of the power needed to sustain the magnetic field in this regime. We show that an experiment with liquid sodium can be designed to operate in the magnetostrophic regime. Such an experiment would bring most valuable informations on the mechanisms of planetary dynamos. In order to prepare this large-scale experiment and explore the magnetostrophic balance, a smaller scale liquid sodium set-up has been designed and is being built. It consists of a rapidly rotating spherical shell filled with liquid sodium, in which motions are set by spinning at a different rotation rate an inner core permeated by a strong magnetic field. We discuss the processes that can be explored with this new device.
Physics of The Earth and Planetary Interiors, 2008
In order to explore the magnetostrophic regime expected for planetary cores, in which the Lorentz... more In order to explore the magnetostrophic regime expected for planetary cores, in which the Lorentz forces balance the Coriolis forces, experiments have been conducted in a rotating sphere filled with liquid sodium, with an imposed dipolar magnetic field (the DTS setup). The field is produced by a permanent magnet enclosed in an inner sphere, which can rotate at a separate rate, producing a spherical Couette flow. The flow properties are investigated by measuring electric potentials on the outer sphere, the induced magnetic field in the laboratory frame just above the rotating outer sphere, and velocity profiles inside the liquid sodium using ultrasonic Doppler velocimetry. This article focuses on the time-averaged axisymmetric part of the flow. The electric potential differences measured at several latitudes can be linked to azimuthal velocities, and are indeed found to be proportional to the azimuthal velocities measured by Doppler velocimetry. The Doppler profiles show that the angular velocity of the fluid is relatively uniform in most of the fluid shell, but rises near the inner sphere, revealing the presence of a “magnetic wind”, and gently drops towards the outer sphere. The transition from a magnetostrophic flow near the inner sphere to a geostrophic flow near the outer sphere is controlled by the local Elsasser number. For Rossby numbers up to order 1, the observed velocity profiles all show a similar shape. Numerical simulations in the linear regime are computed, and synthetic velocity profiles are compared with the measured ones. A good agreement is found for the angular velocity profiles. In the geostrophic region, a torque-balance model provides very good predictions. Radial velocities change sign with the Rossby number, as expected for an Ekman-pumping dominated flow. For a given Rossby number the amplitude of the measured angular velocity is found to vary by as much as a factor of 3. Comparison with numerical simulations suggests that this is due to variations in the electric coupling between liquid sodium and the inner copper sphere, implying an effect equivalent to a reduction of the inner sphere electric conductivity by as much as a factor 100. We show that the measured electric potential difference can be used as a proxy of the actual fluid velocity. Using this proxy in place of the imposed differential velocity, we find that the induced magnetic field varies in a consistent fashion, and displays a peculiar peak in the counter-rotating regime. This happens when the fluid rotation rate is almost equal and opposite to the outer sphere rotation rate. The fluid is then almost at rest in the laboratory frame, and the Proudman–Taylor constraint vanishes, enabling a strong meridional flow. We suggest that dynamo action might be favored in such a situation.
Physics of The Earth and Planetary Interiors, 2007
It has been suggested about 20 years ago that the liquid close to the inner core boundary (ICB) i... more It has been suggested about 20 years ago that the liquid close to the inner core boundary (ICB) is supercooled and that a sizable mushy layer has developed during the growth of the inner core. The morphological instability of the liquid-solid interface which usually results in the formation of a mushy zone has been intensively studied in metallurgy, but the freezing of the inner core occurs in very unusual conditions: the growth rate is very small, and the pressure gradient has a key role, the newly formed solid being hotter than the adjacent liquid.
Physics of The Earth and Planetary Interiors, 2001
Results of finite-amplitude convection experiments in a rotating spherical shell are presented. W... more Results of finite-amplitude convection experiments in a rotating spherical shell are presented. Water (Prandtl number P=7) and liquid gallium (P=0.027) have been used as working fluids. In both liquids, convective velocities could be measured in the equatorial plane using an ultrasonic Doppler velocimetry technique. The parameter space has been systematically explored, for values of the Ekman and Rayleigh numbers E>7×10−7 and Ra<5×109. Both measured convective velocity and zonal circulation are much higher in liquid gallium than in water. A scaling analysis is formulated, which shows that higher convective velocities are an effect of the low Prandtl number in liquid gallium, and that higher zonal flows can be explained through a Reynolds stress mechanism. The Reynolds numbers in gallium (Re=250–2000) are higher indeed than in water (Re=25–250). An inertial regime sets up at high Re, in which kinetic energy does not dissipate at the scale of convective eddies and is transferred up to the scale of the container, where it is dissipated through Ekman friction of zonal flow. This upwards energy transfer can be seen as an effect of quasigeostrophic (QG) turbulence. Applying the scaling relations to an hypothetic non-magnetic flow in the Earth’s core yields Reynolds numbers of the order of 108, in fair agreement with values required for dynamo action, convective velocities of order 10−3 m/s, zonal flow of similar amplitude, and eddy scales as low as 10 km.
Physics of the Earth and Planetary Interiors, 1995
We have built an experimental set-up to study the interaction between one single vertical vortex ... more We have built an experimental set-up to study the interaction between one single vertical vortex of liquid gallium, generated by a disk, and a transverse magnetic field. Magnetic Reynolds number of 0.1 has been reached. This experiment has been conducted on a rotating table. Therefore the dominant forces are Coriolis and Lorentz forces, as in the Earth's core. We measured pressure profiles at the top of the vortex, differences in electrical potentials between some points in the vortex, and the magnetic field induced by the flow. To understand the velocity flow of the vortex, we introduced a simple two-dimensional model which predicts well these three types of measurements. The Elsasser number (ratio of Lorentz to Coriolis forces) is the critical parameter for the dynamical aspect of the vortex. Under the influence of the magnetic field, the vortex is slowed down but remains two-dimensional or geostrophic, up to Elsasser number 0.2. On the other hand, the size of the vortex increases with the strength of the magnetic field. The induced magnetic field forms a horizontal dipole perpendicular to the imposed field, and has a significant vertical component associated with the geometry of electrical currents and insulating boundaries, and not with the helicity.
Physics of the Earth and Planetary Interiors, 1999
An analytical model is developed for the electromagnetic torques exerted on the mantle by the pol... more An analytical model is developed for the electromagnetic torques exerted on the mantle by the poloidal magnetic field of the core interacting with a laterally heterogeneous conducting layer at the base of the mantle. Torques due to changes in both orientation and intensity of a dipolar poloidal field are included. Contrary to earlier suggestions, our calculations predict that the trajectory of the magnetic pole during a polarity reversal is not strongly affected by heterogeneity in mantle electrical conductivity. q 0031-9201r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell ... more We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell of conducting fluid to investigate the relationship between the Earth's toroidal magnetic field and the time-dependent anomalous rotation of the solid inner core. We compute the induced toroidal magnetic field and inner core rotation maintained by the interaction of time-independent, axisymmetric outer core fluid flow with models of the poloidal magnetic field. Three possible models of the azimuthal flow in the outer core are investigated: two thermal wind flows inside the tangent cylinder (predicted by some numerical models of the geodynamo) and a columnar flow outside the inner core tangent cylinder inferred from the geomagnetic westward drift. Results indicate that electromagnetic torques tightly couple the inner core rotation to the fluid motion. Electromagnetic spin-up of the inner core occurs through damped torsional oscillations with periodicity near 4 years depending on the strength of the poloidal magnetic field. In steady state the thermal winds inside the tangent cylinder generate a peak toroidal field of 25 mT accompanying a prograde inner core rotation rate of lø/yr. In contrast, the columnar westward drift model generates toroidal field with peak intensity near 4 mT and a small, retrograde anomalous inner core rotation of-0.013ø/yr. The weak retrograde motion of the inner core produced by electromagnetic coupling to the westward drift cannot explain the seismically inferred prograde anomalous rotation.
Geophysical and Astrophysical Fluid Dynamics, 2005
We report measurements of electric potentials at the surface of a spherical container of liquid s... more We report measurements of electric potentials at the surface of a spherical container of liquid sodium in which a magnetized inner core is differentially rotating. The azimuthal angular velocities inferred from these potentials reveal a strong super-rotation of the liquid sodium in the equatorial region, for small differential rotation. Super-rotation was observed in numerical simulations by Dormy et al. (Dormy, E., Cardin, P. and Jault, D., MHD flow in a slightly differentially rotating spherical shell, with conducting inner core, in a dipolar magnetic field, Earth Planet. Sci. Lett., 1998, 160, 15--30). We find that the latitudinal variation of the electric potentials in our experiments differs markedly from the predictions of a similar numerical model, suggesting that some of the assumptions used in the model – steadiness, equatorial symmetry, and linear treatment for the evolution of both the magnetic and velocity fields – are violated in the experiments. In addition, radial velocity measurements, using ultrasonic Doppler velocimetry, provide evidence of oscillatory motion near the outer sphere at low latitude: it is viewed as the signature of an instability of the super-rotating region.
For the ®rst time,¯ow velocity is measured in a vortex of liquid gallium, using the pulsed Dopple... more For the ®rst time,¯ow velocity is measured in a vortex of liquid gallium, using the pulsed Doppler shift ultrasonic method. At the top of a copper cylinder ®lled with liquid gallium, we spin a disk and create a turbulent vortex with a dominant nearly axisymmetric velocity ®eld with little variation in the axial direction. The velocity pro®les are shown to be well resolved and in quantitative agreement with earlier observations. Reliable velocity measurements in liquid gallium could be obtained only after serious problems due to the formation of oxides were solved. This work opens the way to performing accurate velocity measurements in other liquid metals; preliminary results for liquid sodium are shown.
Aim To investigate global patterns of phylogenetic beta diversity (phylobetadiversity, PBD) compo... more Aim To investigate global patterns of phylogenetic beta diversity (phylobetadiversity, PBD) components in bats (Chiroptera), testing whether the strong dispersal barriers among realms led to lineage differentiation between them and whether the flight capability of the study group created distance-decay patterns in PBD, with lower turnover rates between the closest biogeographical regions.
For more than four decades the International Union for the Conservation of Nature (IUCN) has been... more For more than four decades the International Union for the Conservation of Nature (IUCN) has been assessing the global threat status for species and publishing the results in the periodically updated IUCN Red List of threatened species. Additionally, numerous countries have published national lists of threatened species, often based on IUCN criteria and guidelines for application of IUCN Red List criteria at regional levels. To assess how similar, or how different, national red lists are from the global red list, we compared threatened species lists of four countries (Brazil, Colombia, China, and the Philippines) with the 2008 IUCN Red List. We found notable differences falling into three categories: (1) a number of species (an average of 20% of the species pool considered in each of the four countries) have been listed nationally as threatened, but have yet to be globally assessed by IUCN, (2) some species (14% average) are considered globally threatened by IUCN, but are not listed nationally, and (3) a handful of species (2% average) are not considered threatened by IUCN, but are nationally threatened. However, for most species, the threat assessments concur. In other words, most species are either considered threatened both nationally and globally, or else not considered globally threatened and not listed nationally. Such possible comparison between national red lists and IUCN's Red List is a high priority both for IUCN and for national red listing agencies.
Knowledge of biodiversity is woefully inadequate. Only a fraction of the planet's species has bee... more Knowledge of biodiversity is woefully inadequate. Only a fraction of the planet's species has been described by science (the "Linnean shortfall"). Even for described species, scientists often have only fragmentary information about their distributions (the "Wallacean" shortfall). These shortfalls in biodiversity knowledge place serious limitations on the ability to conserve biodiversity in the face of the ongoing extinction crisis. Here, I test the hypothesis that data deficiency may be used to guide surveys and inventories to regions that would increase the probability of discovering new species. I compiled global distribution maps for all Data Deficient amphibian species (species described up to 2004) and constructed a Data Deficiency (DD) surface (the DD surface was based on distribution information obtained from the IUCN Red List). Then, I compared the type-locality sites of new amphibian species descriptions (species described between 2005 and 2009) with the DD surface in order to check if new species discoveries were significantly more abundant within the DD surface or not. Even though the amphibian DD species surface covers only 8% of Earth's land area, 79% of the amphibian species discovered between 2005 and 2009 were within the DD surface. The results suggest that directing surveys towards areas of known data deficiency will likely result in the discovery of species new to science, helping to address the Linnean shortfall. Incorporating DD information from the IUCN Red List may provide an efficient methodology for strategically targeting surveys and inventories, maximizing the chances of obtaining high conservation benefits from them, and helping minimize the costs associated with such endeavours.
Patch relative importance to metapopulation viability: the neotropical marsupial Micoureus demera... more Patch relative importance to metapopulation viability: the neotropical marsupial Micoureus demerarae as a case study Animal Conservation (2002) 5, 45-51 Abstract As metapopulation dynamics is thought to play an important role in the conservation of mammals, mainly owing to the fragmentation process, a Population Viability Analysis (PVA) was used to evaluate the role and importance of individual patches to the metapopulation persistence of the long-furred wooly mouse opossum, Micoureus demerarae, a neotropical arboreal marsupial. The metapopulation under study comprises eight small Atlantic Forest patches at Poço das Antas Biological Reserve, southeastern Brazil. The analysis indicates that the local populations may be divided into three groups:
A manera de introducción La lectura en torno a la figura del hecho de un Jesús histórico siempre ... more A manera de introducción La lectura en torno a la figura del hecho de un Jesús histórico siempre genera interrogante, a veces, o por lo menos así lo siente mi persona, da miedo, siempre nos quedamos en el plano de saber que Jesús es el hijo de Dios y ya. No nos gusta ahondar porque creemos que ofendemos a Dios. ¡Nada más ingenuo! Deseo que al leer las líneas de estas reflexiones te unas a este sentir de mirar a Jesús sumergido en la historia de su tiempo, pero también a la historia de nuestros tiempos, y de manera especial, a la historia de nuestra propia existencia. La Galilea en la historia y Jesús en su historia Nadie puede negar la existencia de Galilea, como afirma Aguirre (2002): "En tiempo de Jesús, Galilea era un reino vasallo de Roma bajo la dinastía herodiana, mientras que Judea estaba bajo el control directo de Roma, que tenía allí un prefecto que dependía del legado de Siria". (p.3) Al googlear podemos llegar a encontrar la región de Galilea y con quien limita y toda su tradición en la actualidad. Por tanto, los caminos y senderos que nos narran los evangelios hacen ver que su contexto narrativo tiene una razón de ser. Ahora bien, el pueblo llamado Nazaret, también puede ser encontrado en la biblioteca de Alejandría del siglo XXI: Google. ¿Qué busco con esto? Que los relatos bíblicos narran la historia de un hombre que recorrió las calles y las aldeas de regiones que son constatables bien sea si nos dirigimos hacia allá como destinos turísticos o con ganas de conocer, o sencillamente con el hecho de estar en casa y acceder desde el flameante internet.
We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell ... more We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell of conducting fluid to investigate the relationship between the Earth's toroidal magnetic field and the time-dependent anomalous rotation of the solid inner core. We compute the induced toroidal magnetic field and inner core rotation maintained by the interaction of time-independent, axisymmetric outer core fluid flow with models of the poloidal magnetic field. Three possible models of the azimuthal flow in the outer core are investigated: two thermal wind flows inside the tangent cylinder (predicted by some numerical models of the geodynamo) and a columnar flow outside the inner core tangent cylinder inferred from the geomagnetic westward drift. Results indicate that electromagnetic torques tightly couple the inner core rotation to the fluid motion. Electromagnetic spin-up of the inner core occurs through damped torsional oscillations with periodicity near 4 years depending on the strength of the poloidal magnetic field. In steady state the thermal winds inside the tangent cylinder generate a peak toroidal field of 25 mT accompanying a prograde inner core rotation rate of lø/yr. In contrast, the columnar westward drift model generates toroidal field with peak intensity near 4 mT and a small, retrograde anomalous inner core rotation of-0.013ø/yr. The weak retrograde motion of the inner core produced by electromagnetic coupling to the westward drift cannot explain the seismically inferred prograde anomalous rotation.
Physics of The Earth and Planetary Interiors, 1999
An analytical model is developed for the electromagnetic torques exerted on the mantle by the pol... more An analytical model is developed for the electromagnetic torques exerted on the mantle by the poloidal magnetic field of the core interacting with a laterally heterogeneous conducting layer at the base of the mantle. Torques due to changes in both orientation and intensity of a dipolar poloidal field are included. Contrary to earlier suggestions, our calculations predict that the trajectory of the magnetic pole during a polarity reversal is not strongly affected by heterogeneity in mantle electrical conductivity. q 0031-9201r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
Geodynamic models of heat transport and the thermal evolution of Earth's interior require knowled... more Geodynamic models of heat transport and the thermal evolution of Earth's interior require knowledge of thermal conductivity for high-pressure phases at relevant temperatures and pressures. Here we present new data on radiative and lattice heat transfer in mantle materials determined from optical spectroscopy and time-resolved optical radiometry. The pressure dependence of optical absorption in ferropericlase (Mg,Fe)O, and silicate perovskite (Mg,Fe)SiO 3 , has been determined in the IR through UV regions up to 133 GPa. Whereas (Mg,Fe)O exhibits a strong pressure dependence of absorption and spectral changes associated with the high-spin (HS) to low-spin (LS) transition of Fe 2+ [Goncharov, A.F., Struzhkin, V.V., Jacobsen, S.D. 2006. Reduced radiative conductivity of low-spin (Mg,Fe)O in the lower mantle. Science 312, 1205-1208], the pressure dependence of optical absorption in (Mg,Fe)SiO 3 is relatively weak. We observe a moderate increase in absorption with pressure for (Mg,Fe)SiO 3 in the visible and infrared spectral range due to a red-shift of absorption in ultraviolet, however the crystal-field transitions of Fe 2+ become weaker with pressure and disappear above 50 GPa as a result of the HS-LS transition in (Mg,Fe)SiO 3 . Intervalence charge-transfer transitions in silicate perovskite shift to higher energies with pressure. The temperature dependence of the optical absorption of (Mg,Fe)O measured up to 65 GPa and 800 K is moderate below 30 GPa and weak above 30 GPa. Thus, the temperature correction of the radiative conductivity is insignificant. The estimated total pressure-dependent radiative conductivity (in approximation of a large grain size) is lower than expected from the pressure extrapolation of the ambient and low-pressure data . Mantle values of thermal conductivity and the geotherm from phonon lifetimes. Science 283, 1699Science 283, -1706. Dependence of diffusive radiative transfer on grain-size, temperature, and Fe-content: implications for mantle processes. J. Geodyn. 40, 51-72]. A new method has been developed to measure thermal diffusivity of mantle materials at high P-T using time-resolved radiometry combined with a pulsed-IR source. Here, the technique is tested on MgO to 32 GPa and used to obtain a functional pressure dependence of thermal diffusivity and calculated thermal conductivity of the lower mantle.
Results of finite-amplitude convection experiments in a rotating spherical shell are presented. W... more Results of finite-amplitude convection experiments in a rotating spherical shell are presented. Water (Prandtl number P = 7) and liquid gallium (P = 0.027) have been used as working fluids. In both liquids, convective velocities could be measured in the equatorial plane using an ultrasonic Doppler velocimetry technique. The parameter space has been systematically explored, for values of the Ekman and Rayleigh numbers E > 7 10 −7 and Ra < 5 10 9 . Both measured convective velocity and zonal circulation are much higher in liquid gallium than in water. A scaling analysis is formulated, which shows that higher convective velocities are an effect of the low Prandtl number in liquid gallium, and that higher zonal flows can be explained through a Reynolds stress mechanism. The Reynolds numbers in gallium (Re = 250 − 2000) are higher indeed than in water (Re = 25 − 250). An inertial regime sets up at high Re, in which kinetic energy does not dissipate at the scale of convective eddies and is transferred up to the scale of the container, where it is dissipated through Ekman friction of zonal flow. This upwards energy transfer can be seen as an effect of quasigeostrophic turbulence. Applying the scaling relations to an hypothetic non-magnetic flow in the Earth's core yields Reynolds numbers of the order of 10 8 , in fair agreement with values required for dynamo action, convective velocities of order 10 −3 m/s, zonal flow of similar amplitude, and eddy scales as low as 10 km.
We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell ... more We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell of conducting fluid to investigate the relationship between the Earth's toroidal magnetic field and the time-dependent anomalous rotation of the solid inner core. We compute the induced toroidal magnetic field and inner core rotation maintained by the interaction of time-independent, axisymmetric outer core fluid flow with models of the poloidal magnetic field. Three possible models of the azimuthal flow in the outer core are investigated: two thermal wind flows inside the tangent cylinder (predicted by some numerical models of the geodynamo) and a columnar flow outside the inner core tangent cylinder inferred from the geomagnetic westward drift. Results indicate that electromagnetic torques tightly couple the inner core rotation to the fluid motion. Electromagnetic spin-up of the inner core occurs through damped torsional oscillations with periodicity near 4 years depending on the strength of the poloidal magnetic field. In steady state the thermal winds inside the tangent cylinder generate a peak toroidal field of 25 mT accompanying a prograde inner core rotation rate of lø/yr. In contrast, the columnar westward drift model generates toroidal field with peak intensity near 4 mT and a small, retrograde anomalous inner core rotation of-0.013ø/yr. The weak retrograde motion of the inner core produced by electromagnetic coupling to the westward drift cannot explain the seismically inferred prograde anomalous rotation.
The main characteristics of the Earth's dynamo are reviewed. The combined actions of Coriolis and... more The main characteristics of the Earth's dynamo are reviewed. The combined actions of Coriolis and Lorentz forces lead to the so-called "magnetostrophic" regime. We derive an estimate of the power needed to sustain the magnetic field in this regime. We show that an experiment with liquid sodium can be designed to operate in the magnetostrophic regime. Such an experiment would bring most valuable informations on the mechanisms of planetary dynamos. In order to prepare this large-scale experiment and explore the magnetostrophic balance, a smaller scale liquid sodium set-up has been designed and is being built. It consists of a rapidly rotating spherical shell filled with liquid sodium, in which motions are set by spinning at a different rotation rate an inner core permeated by a strong magnetic field. We discuss the processes that can be explored with this new device.
Physics of The Earth and Planetary Interiors, 2008
In order to explore the magnetostrophic regime expected for planetary cores, in which the Lorentz... more In order to explore the magnetostrophic regime expected for planetary cores, in which the Lorentz forces balance the Coriolis forces, experiments have been conducted in a rotating sphere filled with liquid sodium, with an imposed dipolar magnetic field (the DTS setup). The field is produced by a permanent magnet enclosed in an inner sphere, which can rotate at a separate rate, producing a spherical Couette flow. The flow properties are investigated by measuring electric potentials on the outer sphere, the induced magnetic field in the laboratory frame just above the rotating outer sphere, and velocity profiles inside the liquid sodium using ultrasonic Doppler velocimetry. This article focuses on the time-averaged axisymmetric part of the flow. The electric potential differences measured at several latitudes can be linked to azimuthal velocities, and are indeed found to be proportional to the azimuthal velocities measured by Doppler velocimetry. The Doppler profiles show that the angular velocity of the fluid is relatively uniform in most of the fluid shell, but rises near the inner sphere, revealing the presence of a “magnetic wind”, and gently drops towards the outer sphere. The transition from a magnetostrophic flow near the inner sphere to a geostrophic flow near the outer sphere is controlled by the local Elsasser number. For Rossby numbers up to order 1, the observed velocity profiles all show a similar shape. Numerical simulations in the linear regime are computed, and synthetic velocity profiles are compared with the measured ones. A good agreement is found for the angular velocity profiles. In the geostrophic region, a torque-balance model provides very good predictions. Radial velocities change sign with the Rossby number, as expected for an Ekman-pumping dominated flow. For a given Rossby number the amplitude of the measured angular velocity is found to vary by as much as a factor of 3. Comparison with numerical simulations suggests that this is due to variations in the electric coupling between liquid sodium and the inner copper sphere, implying an effect equivalent to a reduction of the inner sphere electric conductivity by as much as a factor 100. We show that the measured electric potential difference can be used as a proxy of the actual fluid velocity. Using this proxy in place of the imposed differential velocity, we find that the induced magnetic field varies in a consistent fashion, and displays a peculiar peak in the counter-rotating regime. This happens when the fluid rotation rate is almost equal and opposite to the outer sphere rotation rate. The fluid is then almost at rest in the laboratory frame, and the Proudman–Taylor constraint vanishes, enabling a strong meridional flow. We suggest that dynamo action might be favored in such a situation.
Physics of The Earth and Planetary Interiors, 2007
It has been suggested about 20 years ago that the liquid close to the inner core boundary (ICB) i... more It has been suggested about 20 years ago that the liquid close to the inner core boundary (ICB) is supercooled and that a sizable mushy layer has developed during the growth of the inner core. The morphological instability of the liquid-solid interface which usually results in the formation of a mushy zone has been intensively studied in metallurgy, but the freezing of the inner core occurs in very unusual conditions: the growth rate is very small, and the pressure gradient has a key role, the newly formed solid being hotter than the adjacent liquid.
Physics of The Earth and Planetary Interiors, 2001
Results of finite-amplitude convection experiments in a rotating spherical shell are presented. W... more Results of finite-amplitude convection experiments in a rotating spherical shell are presented. Water (Prandtl number P=7) and liquid gallium (P=0.027) have been used as working fluids. In both liquids, convective velocities could be measured in the equatorial plane using an ultrasonic Doppler velocimetry technique. The parameter space has been systematically explored, for values of the Ekman and Rayleigh numbers E>7×10−7 and Ra<5×109. Both measured convective velocity and zonal circulation are much higher in liquid gallium than in water. A scaling analysis is formulated, which shows that higher convective velocities are an effect of the low Prandtl number in liquid gallium, and that higher zonal flows can be explained through a Reynolds stress mechanism. The Reynolds numbers in gallium (Re=250–2000) are higher indeed than in water (Re=25–250). An inertial regime sets up at high Re, in which kinetic energy does not dissipate at the scale of convective eddies and is transferred up to the scale of the container, where it is dissipated through Ekman friction of zonal flow. This upwards energy transfer can be seen as an effect of quasigeostrophic (QG) turbulence. Applying the scaling relations to an hypothetic non-magnetic flow in the Earth’s core yields Reynolds numbers of the order of 108, in fair agreement with values required for dynamo action, convective velocities of order 10−3 m/s, zonal flow of similar amplitude, and eddy scales as low as 10 km.
Physics of the Earth and Planetary Interiors, 1995
We have built an experimental set-up to study the interaction between one single vertical vortex ... more We have built an experimental set-up to study the interaction between one single vertical vortex of liquid gallium, generated by a disk, and a transverse magnetic field. Magnetic Reynolds number of 0.1 has been reached. This experiment has been conducted on a rotating table. Therefore the dominant forces are Coriolis and Lorentz forces, as in the Earth's core. We measured pressure profiles at the top of the vortex, differences in electrical potentials between some points in the vortex, and the magnetic field induced by the flow. To understand the velocity flow of the vortex, we introduced a simple two-dimensional model which predicts well these three types of measurements. The Elsasser number (ratio of Lorentz to Coriolis forces) is the critical parameter for the dynamical aspect of the vortex. Under the influence of the magnetic field, the vortex is slowed down but remains two-dimensional or geostrophic, up to Elsasser number 0.2. On the other hand, the size of the vortex increases with the strength of the magnetic field. The induced magnetic field forms a horizontal dipole perpendicular to the imposed field, and has a significant vertical component associated with the geometry of electrical currents and insulating boundaries, and not with the helicity.
Physics of the Earth and Planetary Interiors, 1999
An analytical model is developed for the electromagnetic torques exerted on the mantle by the pol... more An analytical model is developed for the electromagnetic torques exerted on the mantle by the poloidal magnetic field of the core interacting with a laterally heterogeneous conducting layer at the base of the mantle. Torques due to changes in both orientation and intensity of a dipolar poloidal field are included. Contrary to earlier suggestions, our calculations predict that the trajectory of the magnetic pole during a polarity reversal is not strongly affected by heterogeneity in mantle electrical conductivity. q 0031-9201r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell ... more We use numerical calculations of magnetic induction by axisymmetric motions in a spherical shell of conducting fluid to investigate the relationship between the Earth's toroidal magnetic field and the time-dependent anomalous rotation of the solid inner core. We compute the induced toroidal magnetic field and inner core rotation maintained by the interaction of time-independent, axisymmetric outer core fluid flow with models of the poloidal magnetic field. Three possible models of the azimuthal flow in the outer core are investigated: two thermal wind flows inside the tangent cylinder (predicted by some numerical models of the geodynamo) and a columnar flow outside the inner core tangent cylinder inferred from the geomagnetic westward drift. Results indicate that electromagnetic torques tightly couple the inner core rotation to the fluid motion. Electromagnetic spin-up of the inner core occurs through damped torsional oscillations with periodicity near 4 years depending on the strength of the poloidal magnetic field. In steady state the thermal winds inside the tangent cylinder generate a peak toroidal field of 25 mT accompanying a prograde inner core rotation rate of lø/yr. In contrast, the columnar westward drift model generates toroidal field with peak intensity near 4 mT and a small, retrograde anomalous inner core rotation of-0.013ø/yr. The weak retrograde motion of the inner core produced by electromagnetic coupling to the westward drift cannot explain the seismically inferred prograde anomalous rotation.
Geophysical and Astrophysical Fluid Dynamics, 2005
We report measurements of electric potentials at the surface of a spherical container of liquid s... more We report measurements of electric potentials at the surface of a spherical container of liquid sodium in which a magnetized inner core is differentially rotating. The azimuthal angular velocities inferred from these potentials reveal a strong super-rotation of the liquid sodium in the equatorial region, for small differential rotation. Super-rotation was observed in numerical simulations by Dormy et al. (Dormy, E., Cardin, P. and Jault, D., MHD flow in a slightly differentially rotating spherical shell, with conducting inner core, in a dipolar magnetic field, Earth Planet. Sci. Lett., 1998, 160, 15--30). We find that the latitudinal variation of the electric potentials in our experiments differs markedly from the predictions of a similar numerical model, suggesting that some of the assumptions used in the model – steadiness, equatorial symmetry, and linear treatment for the evolution of both the magnetic and velocity fields – are violated in the experiments. In addition, radial velocity measurements, using ultrasonic Doppler velocimetry, provide evidence of oscillatory motion near the outer sphere at low latitude: it is viewed as the signature of an instability of the super-rotating region.
For the ®rst time,¯ow velocity is measured in a vortex of liquid gallium, using the pulsed Dopple... more For the ®rst time,¯ow velocity is measured in a vortex of liquid gallium, using the pulsed Doppler shift ultrasonic method. At the top of a copper cylinder ®lled with liquid gallium, we spin a disk and create a turbulent vortex with a dominant nearly axisymmetric velocity ®eld with little variation in the axial direction. The velocity pro®les are shown to be well resolved and in quantitative agreement with earlier observations. Reliable velocity measurements in liquid gallium could be obtained only after serious problems due to the formation of oxides were solved. This work opens the way to performing accurate velocity measurements in other liquid metals; preliminary results for liquid sodium are shown.
Aim To investigate global patterns of phylogenetic beta diversity (phylobetadiversity, PBD) compo... more Aim To investigate global patterns of phylogenetic beta diversity (phylobetadiversity, PBD) components in bats (Chiroptera), testing whether the strong dispersal barriers among realms led to lineage differentiation between them and whether the flight capability of the study group created distance-decay patterns in PBD, with lower turnover rates between the closest biogeographical regions.
For more than four decades the International Union for the Conservation of Nature (IUCN) has been... more For more than four decades the International Union for the Conservation of Nature (IUCN) has been assessing the global threat status for species and publishing the results in the periodically updated IUCN Red List of threatened species. Additionally, numerous countries have published national lists of threatened species, often based on IUCN criteria and guidelines for application of IUCN Red List criteria at regional levels. To assess how similar, or how different, national red lists are from the global red list, we compared threatened species lists of four countries (Brazil, Colombia, China, and the Philippines) with the 2008 IUCN Red List. We found notable differences falling into three categories: (1) a number of species (an average of 20% of the species pool considered in each of the four countries) have been listed nationally as threatened, but have yet to be globally assessed by IUCN, (2) some species (14% average) are considered globally threatened by IUCN, but are not listed nationally, and (3) a handful of species (2% average) are not considered threatened by IUCN, but are nationally threatened. However, for most species, the threat assessments concur. In other words, most species are either considered threatened both nationally and globally, or else not considered globally threatened and not listed nationally. Such possible comparison between national red lists and IUCN's Red List is a high priority both for IUCN and for national red listing agencies.
Knowledge of biodiversity is woefully inadequate. Only a fraction of the planet's species has bee... more Knowledge of biodiversity is woefully inadequate. Only a fraction of the planet's species has been described by science (the "Linnean shortfall"). Even for described species, scientists often have only fragmentary information about their distributions (the "Wallacean" shortfall). These shortfalls in biodiversity knowledge place serious limitations on the ability to conserve biodiversity in the face of the ongoing extinction crisis. Here, I test the hypothesis that data deficiency may be used to guide surveys and inventories to regions that would increase the probability of discovering new species. I compiled global distribution maps for all Data Deficient amphibian species (species described up to 2004) and constructed a Data Deficiency (DD) surface (the DD surface was based on distribution information obtained from the IUCN Red List). Then, I compared the type-locality sites of new amphibian species descriptions (species described between 2005 and 2009) with the DD surface in order to check if new species discoveries were significantly more abundant within the DD surface or not. Even though the amphibian DD species surface covers only 8% of Earth's land area, 79% of the amphibian species discovered between 2005 and 2009 were within the DD surface. The results suggest that directing surveys towards areas of known data deficiency will likely result in the discovery of species new to science, helping to address the Linnean shortfall. Incorporating DD information from the IUCN Red List may provide an efficient methodology for strategically targeting surveys and inventories, maximizing the chances of obtaining high conservation benefits from them, and helping minimize the costs associated with such endeavours.
Patch relative importance to metapopulation viability: the neotropical marsupial Micoureus demera... more Patch relative importance to metapopulation viability: the neotropical marsupial Micoureus demerarae as a case study Animal Conservation (2002) 5, 45-51 Abstract As metapopulation dynamics is thought to play an important role in the conservation of mammals, mainly owing to the fragmentation process, a Population Viability Analysis (PVA) was used to evaluate the role and importance of individual patches to the metapopulation persistence of the long-furred wooly mouse opossum, Micoureus demerarae, a neotropical arboreal marsupial. The metapopulation under study comprises eight small Atlantic Forest patches at Poço das Antas Biological Reserve, southeastern Brazil. The analysis indicates that the local populations may be divided into three groups:
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