4,263 research outputs found
Effect of the spin-orbit interaction on the thermodynamic properties of crystals: The specific heat of bismuth
In recent years, there has been increasing interest in the specific heat
of insulators and semiconductors because of the availability of samples with
different isotopic masses and the possibility of performing \textit{ab initio}
calculations of its temperature dependence using as a starting point the
electronic band structure. Most of the crystals investigated are elemental
(e.g., germanium) or binary (e.g., gallium nitride) semiconductors. The initial
electronic calculations were performed in the local density approximation and
did not include spin-orbit interaction. Agreement between experimental and
calculated results was usually found to be good, except for crystals containing
heavy atoms (e.g., PbS) for which discrepancies of the order of 20% existed at
the low temperature maximum found for . It has been conjectured that
this discrepancies result from the neglect of spin-orbit interaction which is
large for heavy atoms (1.3eV for the valence electrons of
atomic lead). Here we discuss measurements and \textit{ab initio} calculations
of for crystalline bismuth (1.7 eV), strictly speaking a
semimetal but in the temperature region accessible to us ( 2K) acting as a
semiconductor. We extend experimental data available in the literature and
notice that the \textit{ab initio} calculations without spin-orbit interaction
exhibit a maximum at 8K, about 20% lower than the measured one. Inclusion
of spin-orbit interaction decreases the discrepancy markedly: The maximum of
is now only 7% larger than the measured one. Exact agreement is obtained
if the spin-orbit hamiltonian is reduced by a factor of 0.8.Comment: 4 pages, 3 figure
Cosmological Bianchi Class A models in S\'aez-Ballester theory
We use the S\'aez-Ballester (SB) theory on anisotropic Bianchi Class A
cosmological model, with barotropic fluid and cosmological constant, using the
Hamilton or Hamilton-Jacobi approach. Contrary to claims in the specialized
literature, it is shown that the S\'aez-Ballester theory cannot provide a
realistic solution to the dark matter problem of Cosmology for the dust epoch,
without a fine tunning because the contribution of the scalar field in this
theory is equivalent to a stiff fluid (as can be seen from the energy--momentum
tensor for the scalar field), that evolves in a different way as the dust
component. To have similar contributions of the scalar component and the dust
component implies that their past values were fine tunned. So, we
reinterpreting this null result as an indication that dark matter plays a
central role in the formation of structures and galaxy evolution, having
measureable effects in the cosmic microwave bound radiation, and than this
formalism yield to this epoch as primigenius results. We do the mention that
this formalism was used recently in the so called K-essence theory applied to
dark energy problem, in place to the dark matter problem. Also, we include a
quantization procedure of the theory which can be simplified by reinterpreting
the theory in the Einstein frame, where the scalar field can be interpreted as
part of the matter content of the theory, and exact solutions to the
Wheeler-DeWitt equation are found, employing the Bianchi Class A cosmological
models.Comment: 24 pages; ISBN: 978-953-307-626-3, InTec
Gamma Ray Bursts with peculiar temporal asymmetry
Based on the study of temporal asymmetry of 631 gamma ray bursts from the
BATSE 3B catalog by Link and Epstein [Ap J 466, 764 (1996)], we identify the
population of bursts whose rising times are longer than their decays, thus
showing atypical profiles. We analyse their sky distribution, morphology,
time-space clustering and other average properties and compare them with those
associated with the bulk of the bursts. We show how most of the peculiar bursts
analysed are consistent with recent fireball models, but a fraction of bursts
(% of the total sample) appear to be inconsistent.Comment: mn style (included in the submission), 4 figures that must be printed
separately. Submitted to Monthly Notices of RA
¿Qué hacer con los pobres? Elites y sectores populares en Santiago de Chile 1840-1895
Study on the phenomenon of the poor and poverty in Santiago city in the 19th century, and the reaction of the political and economic elit
Could an endoneurial endothelial crosstalk between Wnt/β-catenin and Sonic Hedgehog pathways underlie the early disruption of the infra-orbital blood-nerve barrier following chronic constriction injury?
BackgroundBlood–nerve barrier disruption is pivotal in the development of neuroinflammation, peripheral sensitization, and neuropathic pain after peripheral nerve injury. Activation of toll-like receptor 4 and inactivation of Sonic Hedgehog signaling pathways within the endoneurial endothelial cells are key events, resulting in the infiltration of harmful molecules and immunocytes within the nerve parenchyma. However, we showed in a previous study that preemptive inactivation of toll-like receptor 4 signaling or sustained activation of Sonic Hedgehog signaling did not prevent the local alterations observed following peripheral nerve injury, suggesting the implication of another signaling pathway.MethodsUsing a classical neuropathic pain model, the infraorbital nerve chronic constriction injury (IoN-CCI), we investigated the role of the Wnt/β-catenin pathway in chronic constriction injury-mediated blood–nerve barrier disruption and in its interactions with the toll-like receptor 4 and Sonic Hedgehog pathways. In the IoN-CCI model versus control, mRNA expression levels and/or immunochemical detection of major Wnt/Sonic Hedgehog pathway (Frizzled-7, vascular endothelial-cadherin, Patched-1 and Gli-1) and/or tight junction proteins (Claudin-1, Claudin-5, and Occludin) readouts were assessed. Vascular permeability was assessed by sodium fluorescein extravasation.ResultsIoN-CCI induced early alterations in the vascular endothelial-cadherin/β-catenin/Frizzled-7 complex, shown to participate in local blood–nerve barrier disruption via a β-catenin-dependent tight junction protein downregulation. Wnt pathway also mediated a crosstalk between toll-like receptor 4 and Sonic Hedgehog signaling within endoneurial endothelial cells. Nevertheless, preemptive inhibition of Wnt/β-catenin signaling before IoN-CCI could not prevent the downregulation of key Sonic Hedgehog pathway readouts or the disruption of the infraorbital blood–nerve barrier, suggesting that Sonic Hedgehog pathway inhibition observed following IoN-CCI is an independent event responsible for blood–nerve barrier disruption.ConclusionA crosstalk between Wnt/β-catenin- and Sonic Hedgehog-mediated signaling pathways within endoneurial endothelial cells could mediate the chronic disruption of the blood–nerve barrier following IoN-CCI, resulting in increased irreversible endoneurial vascular permeability and neuropathic pain development
In search for natural wormholes
We have investigated 631 time profiles of gamma ray bursts from the BATSE
database searching for observable signatures produced by microlensing events
related to natural wormholes. The results of this first search of topologically
nontrivial objects in the Universe can be used to constrain their number and
mass.Comment: Mod. Phys. Lett. A. (in press) Latex (revtex style) with no figure
Neutrinos from Accreting Neutron Stars
The magnetospheres of accreting neutron stars develop electrostatic gaps with
huge potential drops. Protons and ions, accelerated in these gaps along the
dipolar magnetic field lines to energies greater than 100 TeV, can impact onto
a surrounding accretion disc. A proton-induced cascade so develops, and
-emission is produced from charged pion decays. Using GEANT4, a computer
code that tracks particles produced in high energy collisions, we have
calculated the resulting -spectrum with extensive disc shower simulations.
We show that the -spectrum produced out of the proton beam is a power law.
We use this result to propose accretion-powered X-ray binaries (with highly
magnetized neutron stars) as a new population of point-like -sources for
km-scale detectors, such as ICECUBE. As a particular example we discuss the
case of A0535+26. We show that ICECUBE should find A0535+26 to be a periodic
-source: one for which the formation and loss of its accretion disc can be
fully detected. Finally, we briefly comment on the possibility that smaller
telescopes, like AMANDA, could also detect A0535+26 by folding observations
with the orbital period.Comment: 7 pages, 5 figures. Updates to match accepted version in Astrophys.
Bay leaves extracts as active additive for food protective coatings
Ethanolic extracts of bay leaves were obtained using the Soxhlet method (extraction yield of 22.3 ± 1.2%) and further analyzed through different methods, thus determining the chemical composition with gas chromatography, phenolic content with the Folin–Ciocalteu technique (11.8 ± 0.4% wt.) and antioxidant power with the radical 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) method (75.06%). Furthermore, its effect on the growth of two bacteria, Escherichia coli and Bacillus cereus, and on two yeasts, Candida glabrata and Saccharomyces cerevisiae, was determined, showing a minimum inhibitory concentration of 0.65 mg/mL on the growth of B. cereus. Finally, edible films were prepared using different polymers (carboxymethyl cellulose, gum Arabic, polyvinyl pyrrolidone, and polyvinyl alcohol) containing 0, 5, 10, or 15% wt. of bay leaf extract as troubleshooting for perishable fruits, specifically for cultivated strawberry. The prepared composites presented reduced water vapor permeabilities (up to 4.3 × 10−7 g·Pa−1·m−1·h−1), high specific transparencies (≈30%/mm), as well as the effective blocking of ultraviolet radiation (>99.9%). In vivo tests showed that the most suitable treatment for strawberry protection was the impregnation with a composite comprising polyvinyl alcohol and a 15% wt. bay leaf extract, resulting in a noteworthy reduction in mass loss (22% after 6 days). It can be asserted that food packaging with the designed composites would be an effective alternative for the reduction in postharvest losses
Inequality and Spatial Convergence in the Mexico City Metropolitan Area, 1989-2010
The analysis of inequality and polarization patterns between by regions of a national economy is central to ascertain their possibilities of future economic development. In this work we study such patterns in municipalities and boroughs of Mexico City Metropolitan Area (Zona Metropolitana de la Ciudad de Mexico, ZMCM). The evolution of inequality and polarization in this important area of Mexico is studied with new proposals of measurement using spatially conditioned indexes and through a dynamic transition analysis. The results confirm that the territorial inequality has grown among the municipalities and boroughs that integrate the ZMCM. Moreover, this phenomenon coincides with an increase of the polarization characterized by the formation of four subgroups or convergence clubs
- …