4,404 research outputs found
Cosmological scaling solutions of minimally coupled scalar fields in three dimensions
We examine Friedmann-Robertson-Walker models in three spacetime dimensions.
The matter content of the models is composed of a perfect fluid, with a
-law equation of state, and a homogeneous scalar field minimally
coupled to gravity with a self-interacting potential whose energy density
red-shifts as , where a denotes the scale factor. Cosmological
solutions are presented for different range of values of and .
The potential required to agree with the above red-shift for the scalar field
energy density is also calculated.Comment: LaTeX2e, 11 pages, 4 figures. To be published in Classical and
Quantum Gravit
Structure and genetic diversity in wild and cultivated populations of Zapote mamey (Pouteria sapota, Sapotaceae) from southeastern Mexico: its putative domestication center
Tropical fruit trees are an important component of the human diet; however, little is known about their genetic diversity levels. Zapote mamey (Pouteria sapota) is a tree native to southeastern Mexico and Central America, and Mexico is the leading producer in the world. Studies of the genetic diversity of Zapote mamey have been based on cultivated materials using morphological and biochemical characterization or dominant molecular markers. To gain a deeper understanding about the conservation status of Zapote mamey in its center of origin and domestication, we collected 188 individuals from eight wild and five cultivated populations in southeastern Mexico and characterized them using eight microsatellite loci. STRUCTURE, 3D-PCoA, and neighbor-joining analyses showed three groups in the wild gene pool and one group in the cultivated gene pool. FST values were significant between wild and cultivated gene pools, among the four groups observed and among the 13 populations collected (0.13, 0.25, and 0.36, respectively). Overall, we found low levels of genetic diversity (A = 2.77, HO = 0.29, HE = 0.39), permutation tests did not show significant differences between wild and cultivated gene pools. The Garza–Williamson index showed low values in both gene pools (wild = 0.16, cultivated = 0.11) and the Bottleneck program indicated a decrease in genetic diversity in both gene pools (wild, P = 0.027; cultivated, P = 0.054); both analyses suggest a potential genetic bottleneck within this species. This study can help to generate adequate sampling techniques and to develop effective management strategies for Zapote mamey of southeastern Mexico
Ischemic Stroke and Epilepsy in a Patient with Tourette´s Syndrome: Association with the Antiphospholipid Syndrome and Good Response to Levetiracetam
The role played by different humoral factors, including antiphospholipid antibodies, in the pathogenesis of Tourette syndrome (TS) is still presently unclear. We present a patient with chronic and severe TS who, at the age of 16 years, presented an ischemic stroke in the left posterior cerebral artery and/or postero-inferior temporal branch of the left medial cerebral artery. A complete study was negative with the exception of a positive lupus anticoagulant. The stroke was related with the primary antiphospholipid syndrome (APS). The stroke manifested visual abnormalities and thereafter by secondary generalized complex partial seizures. The epileptic syndrome was initially difficult to control but responded dramatically to levetiracetam. With this therapy, the manifestations of TS, especially the tics, improved. We conclude that some TS cases may present APS. In addition, levetiracetam may be useful in the management of TS. Further investigations should pursue both these facts
Gestión Comunitaria de Recursos Naturales y de Empresas en Santa Catarina Ixtepeji y Villa Hidalgo Yalalag de la Sierra Norte de Oaxaca
La investigación busca promover las iniciativas locales y las capacidades de las comunidades indÃgenas para el manejo sustentable de los recursos naturales y el desarrollo de las empresas; de forma general, se busca identificar y fortalecer los elementos de la lógica social y productiva de las comunidades que respondan en términos de empleo y de reducción de la pobreza, a los retos que presentan los cambios globales y las restricciones económicas del paÃs; y se busca abordar en lo particular, la problemática relacionada al mantenimiento y ampliación de las herramientas estratégicas que favorecen la gestión empresarial comunitaria.
Por lo tanto, es importante analizar las interrelaciones socio-económicas que existen entre las dimensiones; social comunitaria y de las empresas comunitarias. La permanencia de estas empresas ha sido una de las expresiones de la virtud de esta relación. La disyuntiva que se presenta actualmente es acerca de la evolución de esta relación, y como se conjugan las dimensiones económicas, socio-técnicas, administrativas y ambientales, considerando a la estructura polÃtico cultural especÃfica de estas comunidades. Es por esto que, la investigación requerirá de la actualización del conocimiento de la temática, ya que las modificaciones de la economÃa mundial, la constancia y magnitud de los cambios tecnológicos, los cambios estructurales de las economÃas e instituciones nacionales, están permeando a las regiones y localidades. Y de emplear métodos y conceptos para conocer, detectar, identificar, analizar esos cambios como tareas necesarias para generar aportaciones al diseño de polÃticas y estrategias de instituciones y empresas que contemplen en sus objetivos la salvaguarda del empleo, la reducción de la pobreza y la mejora de la calidad de vida de la comunidad, desde la perspectiva del desarrollo local que se enfoca al manejo de los recursos locales.
AsÃ, se tiene como objetivo general: analizar desde un enfoque multidisciplinario, la gestión de los recursos naturales y de las empresas, en las comunidades indÃgenas de Santa Catarina Ixtepeji y Villa Hidalgo Yalalag en la Sierra Norte de Oaxaca, desde la perspectiva del Desarrollo Local, que privilegie el empleo y el ingreso, la sustentabilidad de los recursos naturales y donde la participación constituya un elemento esencial en los cambios requeridos para salvaguardar lo común.
En esta presentación se exponen fundamentalmente los elementos para el diseño de una investigación con las caracterÃsticas que aquà se describen. Se pretende que a partir del debate se pueda incorporar nuevos elementos en el proyecto, y sobretodo definir con precisión el enfoque conceptual y metodológico de un fenómeno que por su complejidad requiere de una convocatoria a diferentes aportaciones. La investigación está proyectada a realizarse durante un año a partir de septiembre próximo
Preparation of nanostructured nickel aluminate spinel powder from spent NiO/Al2O3 catalyst by mechano-chemical synthesis
In this paper, the possibility of mechano-chemical synthesis, as a single step process for preparation of nanostructured nickel aluminate spinel powder from NiO/Al2O3 spent catalyst was investigated. Powder samples were characterized in terms of composition, morphology, structure, particle size and surface area using complementary techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA) and volumetric adsorption of nitrogen. It was found that formation of spinel was possible after 60 h of milling with no heat treatment. Additionally, influence of mechanical activation on the heat treatment temperature was discussed. It was observed that heat treatment of 15 h milled sample at 1100 °C is enough to produce nickel aluminate spinel. A product of direct mechanical milling showed higher value of surface area (42.3 m2/g) and smaller crystallite size (12 nm) as compared to the heat treated product.Gobierno de España ENE 2007-67926-C02-0
Integrable models and degenerate horizons in two-dimensional gravity
We analyse an integrable model of two-dimensional gravity which can be
reduced to a pair of Liouville fields in conformal gauge. Its general solution
represents a pair of ``mirror'' black holes with the same temperature. The
ground state is a degenerate constant dilaton configuration similar to the
Nariai solution of the Schwarzschild-de Sitter case. The existence of
solutions and their relation with the solution given by the 2D
Birkhoff's theorem is then investigated in a more general context. We also
point out some interesting features of the semiclassical theory of our model
and the similarity with the behaviour of AdS black holes.Comment: Latex, 16 pages, 1 figur
Estimating the longitudinal magnetic field in the chromosphere of quiet-Sun magnetic concentrations
Details of the magnetic field in the quiet Sun chromosphere are key to our
understanding of essential aspects of the solar atmosphere. We aim to determine
the longitudinal magnetic field component (B_lon) of quiet Sun regions
depending on their size. We estimated B_lon by applying the weak-field
approximation (WFA) to high-spatial-resolution Ca II 854.2 nm data taken with
the Swedish 1m Solar Telescope. Specifically, we analyzed the estimates
inferred for different spectral ranges using the data at the original cadence
and temporally integrated signals. The longitudinal magnetic field in each
considered plasma structure correlates with its size. Using a spectral range
restricted to the line core leads to chromospheric longitudinal fields varying
from 50 G at the edges to 150-500 G at the center of the structure. These
values increase as the spectral range widens due to the photospheric
contribution. However, the difference between this contribution and the
chromospheric one is not uniform for all structures. Small and medium-sized
concentrations show a steeper height gradient in B_lon compared to their
chromospheric values, so estimates for wider ranges are less trustworthy.
Signal addition does not alleviate this situation as the height gradients in
B_lon are consistent with time. Finally, despite the amplified noise levels
that deconvolving processes may cause, data restored with the destretching
technique show similar results, though are affected by smearing. We obtained
B_lon estimates similar to those previously found, except for large
concentrations and wide spectral ranges. In addition, we report a correlation
between the height variation of B_lon compared to the chromospheric estimates
and the concentration size. This correlation affects the difference between the
photospheric and chromospheric magnetic flux values and the reliability of the
estimates for wider spectral ranges.Comment: 14 pages, 14 figures. Accepted for publication in Astronomy &
Astrophysics; abstract has been abridge
Conformally dressed black hole in 2+1 dimensions
A three dimensional black hole solution of Einstein equations with negative
cosmological constant coupled to a conformal scalar field is given. The
solution is static, circularly symmetric, asymptotically anti-de Sitter and
nonperturbative in the conformal field. The curvature tensor is singular at the
origin while the scalar field is regular everywhere. The condition that the
Euclidean geometry be regular at the horizon fixes the temperature to be
. Using the Hamiltonian formulation including
boundary terms of the Euclidean action, the entropy is found to be
of the standard value (), and in agreement with
the first law of thermodynamics.Comment: LaTeX ,RevTeX, 13pages, no figure
Fasciola hepatica induces eosinophil apoptosis in the migratory and biliary stages of infection in sheep
The aim of the present work was to evaluate the number of apoptotic eosinophils in the livers of sheep experimentally infected with Fasciola hepatica during the migratory and biliary stages of infection. Four groups (n = 5) of sheep were used; groups 1–3 were orally infected with 200 metacercariae (mc) and sacrificed at 8 and 28 days post-infection (dpi), and 17 weeks post-infection (wpi), respectively. Group 4 was used as an uninfected control. Apoptosis was detected using immunohistochemistry with a polyclonal antibody against anti-active caspase-3, and transmission electron microscopy (TEM). Eosinophils were identified using the Hansel stain in serial sections for caspase-3, and by ultrastructural features using TEM. At 8 and 28 dpi, numerous caspase-3+ eosinophils were mainly found at the periphery of acute hepatic necrotic foci. The percentage of caspase -3+ apoptotic eosinophils in the periphery of necrotic foci was high (46.1–53.9) at 8 and 28 dpi, respectively, and decreased in granulomas found at 28 dpi (6%). Transmission electron microscopy confirmed the presence of apoptotic eosinophils in hepatic lesions at 8 and 28 dpi. At 17 wpi, apoptotic eosinophils were detected in the infiltrate surrounding some enlarged bile ducts containing adult flukes. This is the first report of apoptosis induced by F. hepatica in sheep and the first study reporting apoptosis in eosinophils in hepatic inflammatory infiltrates in vivo. The high number of apoptotic eosinophils in acute necrotic tracts during the migratory and biliary stages of infection suggests that eosinophil apoptosis may play a role in F. hepatica survival during different stages of infection.This work was supported by EU grants (FPVII-265862-PARAVAC, H2020-635408-PARAGONE) and the Spanish Ministry of Science grant AGL2009-08726. TEM studies were carried out by the Central Services for Research of the University of Córdoba (SCAI)Veterinari
- …