FMRI data are acquired as complex-valued spatiotemporal images. Despite the fact that several stu... more FMRI data are acquired as complex-valued spatiotemporal images. Despite the fact that several studies have identified the presence of novel information in the phase images, they are usually discarded due to their noisy nature. Several approaches have been devised to incorporate magnitude and phase data, but none of them has performed between-group inference or classification. Multiple kernel learning (MKL) is a powerful field of machine learning that finds an automatic combination of kernel functions that can be applied to multiple data sources. By analyzing this combination of kernels, the most informative data sources can be found, hence providing a better understanding of the analyzed learning task. This paper presents a methodology based on a new MKL algorithm (ν-MKL) capable of achieving a tunable sparse selection of features' sets (brain regions' patterns) that improves the classification accuracy rate of healthy controls and schizophrenia patients by 5% when phase data is included. In addition, the proposed method achieves accuracy rates that are equivalent to those obtained by the state of the art lp-norm MKL algorithm on the schizophrenia dataset and we argue that it better identifies the brain regions that show discriminative activation between groups. This claim is supported by the more accurate detection achieved by ν-MKL of the degree of information present on regions of spatial maps extracted from a simulated fMRI dataset. In summary, we present an MKL-based methodology that improves schizophrenia characterization by using both magnitude and phase fMRI data and is also capable of detecting the brain regions that convey most of the discriminative information between patients and controls.
Eduardo viveiros de castro & Carlos fausto, La Puissance et l'acte : la parenté dans les... more Eduardo viveiros de castro & Carlos fausto, La Puissance et l'acte : la parenté dans les basses terres d'Amérique du Sud. Les systèmes de parenté dans les basses terres d'Amérique du Sud s'ordonnent sur un continuum entre deux pôles : l'échange restreint amazonien, ...
El ser humano se ve a sí mismo como tal. La Luna, la serpiente, el jaguar y la madre de la viruel... more El ser humano se ve a sí mismo como tal. La Luna, la serpiente, el jaguar y la madre de la viruela lo ven, sin embargo, como un tapir o un pecarí, que ellos matan (Baer 1994:224).
... À parte isso, elas podem ter todas as histórias que se queira, mas essa não é a questão. Deve... more ... À parte isso, elas podem ter todas as histórias que se queira, mas essa não é a questão. Devem-nos elas o que são, ou não? ... Os conteúdos, isso continua a ser história, a experiência dos homens no curso do tempo. ...
Les contributions reunies dans Les Complexites de l'alliance doivent leur origineau semi... more Les contributions reunies dans Les Complexites de l'alliance doivent leur origineau seminaire de recherche sur les strategies de Palliance matrimo niale que Francoise Heritier-Auge a dirige au College de France de 1983 a 1986. Elles sont consacrees a Pexamen des structures ...
... Page 3. Eduardo Viveiros de Castro From the Enemy's Point of View Humanity and Divin... more ... Page 3. Eduardo Viveiros de Castro From the Enemy's Point of View Humanity and Divinity in an Amazonian Society Translated by Catherine V. Howard The University of Chicago Press Chicago et> London Page 4. Eduardo ...
We compute the phase diagram of a biased graphene bilayer. The existence of a ferromagnetic phase... more We compute the phase diagram of a biased graphene bilayer. The existence of a ferromagnetic phase is discussed with respect both to carrier density and temperature. We find that the ferromagnetic transition is first order, lowering the value of U relatively to the usual Stoner criterion. We show that in the ferromagnetic phase the two planes have unequal magnetization and that the electronic density is hole like in one plane and electron like in the other.
The gap in bilayer graphene (BLG) can directly be controlled by a perpendicular electric field. B... more The gap in bilayer graphene (BLG) can directly be controlled by a perpendicular electric field. By tuning the field through zero at a finite rate in neutral BLG, excited states are produced. Due to screening, the resulting dynamics is determined by coupled non-linear Landau-Zener models. The generated defect density agrees with Kibble-Zurek theory in the presence of subleading logarithmic corrections. After the quench, population inversion occurs for wavevectors close to the Dirac point. This could, at least in principle provide a coherent source of infra-red radiation with tunable spectral properties (frequency and broadening). Cold atoms with quadratic band crossing exhibit the same dynamics.
We introduce two dimensional fermionic band models with two orbitals per lattice site, or one spi... more We introduce two dimensional fermionic band models with two orbitals per lattice site, or one spinful orbital, and which have a non-zero topological Chern number that can be changed by varying the ratio of hopping parameters. A topologically non-trivial insulator is then realized if there is one fermion per site. When interactions in the framework of the Hubbard model are introduced, the effective hopping parameters are renormalized and the system's topological number can change at a certain interaction strength, U =Ū , smaller than that for the Mott transition. Two different situations may then occur: either the anomalous Hall conductivity σxy changes abruptly atŪ , as the system undergoes a transition from one topologically non-trivial insulator to another, or the transition is through an anomalous Hall metal, and σxy changes smoothly between two different quantized values as U grows. Restoring time-reversal symmetry by adding spin to spinless models, the half-filled system becomes a Z2 topological insulator. The topological number ν then changes at a critical couplingŪ and the quantized spin Hall response changes abruptly. PACS numbers: 71.10Fd, 71.27.+a, 73.43.-f
Bilayer graphene -two coupled single graphene layers stacked as in graphiteprovides the only know... more Bilayer graphene -two coupled single graphene layers stacked as in graphiteprovides the only known semiconductor with a gap that can be tuned externally through electric field effect. Here we use a tight binding approach to study how the gap changes with the applied electric field. Within a parallel plate capacitor model and taking into account screening of the external field, we describe real back gated and/or chemically doped bilayer devices. We show that a gap between zero and midinfrared energies can be induced and externally tuned in these devices, making bilayer graphene very appealing from the point of view of applications. However, applications to nanotechnology require careful treatment of the effect of sample boundaries. This being particularly true in graphene, where the presence of edge states at zero energy -the Fermi level of the undoped system -has been extensively reported. Here we show that also bilayer graphene supports surface states localized at zigzag edges. The presence of two layers, however, allows for a new type of edge state which shows an enhanced penetration into the bulk and gives rise to band crossing phenomenon inside the gap of the biased bilayer system.
Summation of strongly divergent perturbation series. [Journal of Mathematical Physics 25, 3492 (1... more Summation of strongly divergent perturbation series. [Journal of Mathematical Physics 25, 3492 (1984)]. Gustavo A. Arteca, Francisco M. Fernández, Eduardo A. Castro. Abstract. A new method for summing strongly divergent perturbation series is presented. ...
Elaborating the discrete hydrocarbon molecule bicyclo[2.2.2]-2,5,7-octatriene in three-dimensions... more Elaborating the discrete hydrocarbon molecule bicyclo[2.2.2]-2,5,7-octatriene in three-dimensions, a unique, hypothetical allotrope of carbon is produced. Such a structure possesses a principal 6-fold axis; along this axis are hexagonal, organic tunnels with about a 5.70 Å outside tunnel diameter across opposite vertices, and an actual, inside diameter of 4.16 Å when taking into account the covalent radius of tetrahedral carbon. Across opposite edges, the outside hexagonal tunnel diameter is 4.94 Å, and the inside tunnel diameter is 3.61 Å. These tunnels are lined alternately with hexagonally disposed ethane-like functions and hexagonally disposed ethene-like functions that stack along the tunnel axis. The lattice lies in space group P6/mmm, and it has the Schläfli symbol given by (6, 3 2/5 ), it is therefore topologically related to the graphitediamond hybrids. Because of the hexagonal symmetry of the unit cell, and also due to the fact that its polygonality is six, the structure has been given the name hexagonite. There are 10 carbon atoms in the unit of pattern, and the density is 2.50 g/cm 3 ; bordered by the densities of graphite at 2.27 g/cm 3 and diamond at 3.56 g/cm 3 . Its large organic channels, lined with π organic functions, may make it particularly useful as an organic zeolite material, or alternatively as a host lattice for ionic conduction. The electronic band structure of the empty, hexagonal host lattice is described.
This paper begins with a review of the Euler relation for the polyhedra and presents the correspo... more This paper begins with a review of the Euler relation for the polyhedra and presents the corresponding Schläfli relation in n, the polygonality, and p, the connectivity of the polyhedra. The use of ordered pairs as given by (n, p), the Schläfli symbols, to organize the mapping of the polyhedra and its extension into the two-dimensional (2D) and three-dimensional (3D) networks is described. The topological form index, represented by l, is introduced and is defined as the ratio of the polygonality, n, to the connectivity, p, in a structure, it is given by l = n/p. Next a discussion is given of establishing a conventional metric of length in order to compare topological properties of the polyhedra and networks in 2D and 3D. A fundamental structural metric is assumed for the polyhedra. The metric for the polyhedra is, in turn, used to establish a metric for tilings in the Euclidean plane. The metrics for the polyhedra and 2D plane are used to establish a metric for networks in 3D. Once the metrics have been established, a conjecture is introduced, based upon the metrics assumed, that the area of the elementary polygonal circuit in the polyhedra and 2D and 3D networks is proportional to a function of the topological form index, l, for these structures. Data of the form indexes and the corresponding elementary polygonal circuit areas, for a selection of polyhedra and 2D and 3D networks is tabulated, and the results of a least squares regression analysis of the data plotted in a Cartesian space are reported. From the regression analysis it is seen that a quadratic in l, the form index, successfully correlates with the corresponding elementary polygonal circuit area data of the polyhedra and 2D and 3D networks. A brief discussion of the evident rigorousness of the Schläfli indexes (n, p) over all the polyhedra and 2D and 3D networks, based upon the correlation of the topological form index with elementary polygonal circuit area in these structures, and the suggestion that an Euler-Schläfli relation for the 2D and 3D networks, is possible, in terms of the Schläfli indexes, concludes the paper.
A correct relationship between orbital SCF energies and total SCF energy for atoms and positive a... more A correct relationship between orbital SCF energies and total SCF energy for atoms and positive atomic ions is deduced. We report the results of the application of such relationship for the various isoelectronic series presented by Rao and Sen [J. Chem. Phys. 70, 586 (1979)]. Different calculations are compared and the goodness of each method is comparatively discussed.
Comment on the off‐diagonal HellmannFeynman formula. [The Journal of Chemical Physics 73, 4711 (... more Comment on the off‐diagonal HellmannFeynman formula. [The Journal of Chemical Physics 73, 4711 (1980)]. Eduardo A. Castro, Francisco M. Fernández. Abstract. A new sufficient condition is given for variational wave functions ...
FMRI data are acquired as complex-valued spatiotemporal images. Despite the fact that several stu... more FMRI data are acquired as complex-valued spatiotemporal images. Despite the fact that several studies have identified the presence of novel information in the phase images, they are usually discarded due to their noisy nature. Several approaches have been devised to incorporate magnitude and phase data, but none of them has performed between-group inference or classification. Multiple kernel learning (MKL) is a powerful field of machine learning that finds an automatic combination of kernel functions that can be applied to multiple data sources. By analyzing this combination of kernels, the most informative data sources can be found, hence providing a better understanding of the analyzed learning task. This paper presents a methodology based on a new MKL algorithm (ν-MKL) capable of achieving a tunable sparse selection of features' sets (brain regions' patterns) that improves the classification accuracy rate of healthy controls and schizophrenia patients by 5% when phase data is included. In addition, the proposed method achieves accuracy rates that are equivalent to those obtained by the state of the art lp-norm MKL algorithm on the schizophrenia dataset and we argue that it better identifies the brain regions that show discriminative activation between groups. This claim is supported by the more accurate detection achieved by ν-MKL of the degree of information present on regions of spatial maps extracted from a simulated fMRI dataset. In summary, we present an MKL-based methodology that improves schizophrenia characterization by using both magnitude and phase fMRI data and is also capable of detecting the brain regions that convey most of the discriminative information between patients and controls.
Eduardo viveiros de castro & Carlos fausto, La Puissance et l'acte : la parenté dans les... more Eduardo viveiros de castro & Carlos fausto, La Puissance et l'acte : la parenté dans les basses terres d'Amérique du Sud. Les systèmes de parenté dans les basses terres d'Amérique du Sud s'ordonnent sur un continuum entre deux pôles : l'échange restreint amazonien, ...
El ser humano se ve a sí mismo como tal. La Luna, la serpiente, el jaguar y la madre de la viruel... more El ser humano se ve a sí mismo como tal. La Luna, la serpiente, el jaguar y la madre de la viruela lo ven, sin embargo, como un tapir o un pecarí, que ellos matan (Baer 1994:224).
... À parte isso, elas podem ter todas as histórias que se queira, mas essa não é a questão. Deve... more ... À parte isso, elas podem ter todas as histórias que se queira, mas essa não é a questão. Devem-nos elas o que são, ou não? ... Os conteúdos, isso continua a ser história, a experiência dos homens no curso do tempo. ...
Les contributions reunies dans Les Complexites de l'alliance doivent leur origineau semi... more Les contributions reunies dans Les Complexites de l'alliance doivent leur origineau seminaire de recherche sur les strategies de Palliance matrimo niale que Francoise Heritier-Auge a dirige au College de France de 1983 a 1986. Elles sont consacrees a Pexamen des structures ...
... Page 3. Eduardo Viveiros de Castro From the Enemy's Point of View Humanity and Divin... more ... Page 3. Eduardo Viveiros de Castro From the Enemy's Point of View Humanity and Divinity in an Amazonian Society Translated by Catherine V. Howard The University of Chicago Press Chicago et> London Page 4. Eduardo ...
We compute the phase diagram of a biased graphene bilayer. The existence of a ferromagnetic phase... more We compute the phase diagram of a biased graphene bilayer. The existence of a ferromagnetic phase is discussed with respect both to carrier density and temperature. We find that the ferromagnetic transition is first order, lowering the value of U relatively to the usual Stoner criterion. We show that in the ferromagnetic phase the two planes have unequal magnetization and that the electronic density is hole like in one plane and electron like in the other.
The gap in bilayer graphene (BLG) can directly be controlled by a perpendicular electric field. B... more The gap in bilayer graphene (BLG) can directly be controlled by a perpendicular electric field. By tuning the field through zero at a finite rate in neutral BLG, excited states are produced. Due to screening, the resulting dynamics is determined by coupled non-linear Landau-Zener models. The generated defect density agrees with Kibble-Zurek theory in the presence of subleading logarithmic corrections. After the quench, population inversion occurs for wavevectors close to the Dirac point. This could, at least in principle provide a coherent source of infra-red radiation with tunable spectral properties (frequency and broadening). Cold atoms with quadratic band crossing exhibit the same dynamics.
We introduce two dimensional fermionic band models with two orbitals per lattice site, or one spi... more We introduce two dimensional fermionic band models with two orbitals per lattice site, or one spinful orbital, and which have a non-zero topological Chern number that can be changed by varying the ratio of hopping parameters. A topologically non-trivial insulator is then realized if there is one fermion per site. When interactions in the framework of the Hubbard model are introduced, the effective hopping parameters are renormalized and the system's topological number can change at a certain interaction strength, U =Ū , smaller than that for the Mott transition. Two different situations may then occur: either the anomalous Hall conductivity σxy changes abruptly atŪ , as the system undergoes a transition from one topologically non-trivial insulator to another, or the transition is through an anomalous Hall metal, and σxy changes smoothly between two different quantized values as U grows. Restoring time-reversal symmetry by adding spin to spinless models, the half-filled system becomes a Z2 topological insulator. The topological number ν then changes at a critical couplingŪ and the quantized spin Hall response changes abruptly. PACS numbers: 71.10Fd, 71.27.+a, 73.43.-f
Bilayer graphene -two coupled single graphene layers stacked as in graphiteprovides the only know... more Bilayer graphene -two coupled single graphene layers stacked as in graphiteprovides the only known semiconductor with a gap that can be tuned externally through electric field effect. Here we use a tight binding approach to study how the gap changes with the applied electric field. Within a parallel plate capacitor model and taking into account screening of the external field, we describe real back gated and/or chemically doped bilayer devices. We show that a gap between zero and midinfrared energies can be induced and externally tuned in these devices, making bilayer graphene very appealing from the point of view of applications. However, applications to nanotechnology require careful treatment of the effect of sample boundaries. This being particularly true in graphene, where the presence of edge states at zero energy -the Fermi level of the undoped system -has been extensively reported. Here we show that also bilayer graphene supports surface states localized at zigzag edges. The presence of two layers, however, allows for a new type of edge state which shows an enhanced penetration into the bulk and gives rise to band crossing phenomenon inside the gap of the biased bilayer system.
Summation of strongly divergent perturbation series. [Journal of Mathematical Physics 25, 3492 (1... more Summation of strongly divergent perturbation series. [Journal of Mathematical Physics 25, 3492 (1984)]. Gustavo A. Arteca, Francisco M. Fernández, Eduardo A. Castro. Abstract. A new method for summing strongly divergent perturbation series is presented. ...
Elaborating the discrete hydrocarbon molecule bicyclo[2.2.2]-2,5,7-octatriene in three-dimensions... more Elaborating the discrete hydrocarbon molecule bicyclo[2.2.2]-2,5,7-octatriene in three-dimensions, a unique, hypothetical allotrope of carbon is produced. Such a structure possesses a principal 6-fold axis; along this axis are hexagonal, organic tunnels with about a 5.70 Å outside tunnel diameter across opposite vertices, and an actual, inside diameter of 4.16 Å when taking into account the covalent radius of tetrahedral carbon. Across opposite edges, the outside hexagonal tunnel diameter is 4.94 Å, and the inside tunnel diameter is 3.61 Å. These tunnels are lined alternately with hexagonally disposed ethane-like functions and hexagonally disposed ethene-like functions that stack along the tunnel axis. The lattice lies in space group P6/mmm, and it has the Schläfli symbol given by (6, 3 2/5 ), it is therefore topologically related to the graphitediamond hybrids. Because of the hexagonal symmetry of the unit cell, and also due to the fact that its polygonality is six, the structure has been given the name hexagonite. There are 10 carbon atoms in the unit of pattern, and the density is 2.50 g/cm 3 ; bordered by the densities of graphite at 2.27 g/cm 3 and diamond at 3.56 g/cm 3 . Its large organic channels, lined with π organic functions, may make it particularly useful as an organic zeolite material, or alternatively as a host lattice for ionic conduction. The electronic band structure of the empty, hexagonal host lattice is described.
This paper begins with a review of the Euler relation for the polyhedra and presents the correspo... more This paper begins with a review of the Euler relation for the polyhedra and presents the corresponding Schläfli relation in n, the polygonality, and p, the connectivity of the polyhedra. The use of ordered pairs as given by (n, p), the Schläfli symbols, to organize the mapping of the polyhedra and its extension into the two-dimensional (2D) and three-dimensional (3D) networks is described. The topological form index, represented by l, is introduced and is defined as the ratio of the polygonality, n, to the connectivity, p, in a structure, it is given by l = n/p. Next a discussion is given of establishing a conventional metric of length in order to compare topological properties of the polyhedra and networks in 2D and 3D. A fundamental structural metric is assumed for the polyhedra. The metric for the polyhedra is, in turn, used to establish a metric for tilings in the Euclidean plane. The metrics for the polyhedra and 2D plane are used to establish a metric for networks in 3D. Once the metrics have been established, a conjecture is introduced, based upon the metrics assumed, that the area of the elementary polygonal circuit in the polyhedra and 2D and 3D networks is proportional to a function of the topological form index, l, for these structures. Data of the form indexes and the corresponding elementary polygonal circuit areas, for a selection of polyhedra and 2D and 3D networks is tabulated, and the results of a least squares regression analysis of the data plotted in a Cartesian space are reported. From the regression analysis it is seen that a quadratic in l, the form index, successfully correlates with the corresponding elementary polygonal circuit area data of the polyhedra and 2D and 3D networks. A brief discussion of the evident rigorousness of the Schläfli indexes (n, p) over all the polyhedra and 2D and 3D networks, based upon the correlation of the topological form index with elementary polygonal circuit area in these structures, and the suggestion that an Euler-Schläfli relation for the 2D and 3D networks, is possible, in terms of the Schläfli indexes, concludes the paper.
A correct relationship between orbital SCF energies and total SCF energy for atoms and positive a... more A correct relationship between orbital SCF energies and total SCF energy for atoms and positive atomic ions is deduced. We report the results of the application of such relationship for the various isoelectronic series presented by Rao and Sen [J. Chem. Phys. 70, 586 (1979)]. Different calculations are compared and the goodness of each method is comparatively discussed.
Comment on the off‐diagonal HellmannFeynman formula. [The Journal of Chemical Physics 73, 4711 (... more Comment on the off‐diagonal HellmannFeynman formula. [The Journal of Chemical Physics 73, 4711 (1980)]. Eduardo A. Castro, Francisco M. Fernández. Abstract. A new sufficient condition is given for variational wave functions ...
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