97 research outputs found
Ab-Initio Calculation of the Metal-Insulator Transition in Lithium rings
We study how the Mott metal-insulator transition (MIT) is affected when we
have to deal with electrons with different angular momentum quantum numbers.
For that purpose we apply ab-initio quantum-chemical methods to lithium rings
in order to investigate the analogue of a MIT. By changing the interatomic
distance we analyse the character of the many-body wavefunction and discuss the
importance of the orbital quasi-degeneracy within the metallic regime.
The charge gap (ionization potential minus electron affinity) shows a minimum
and the static electric dipole polarizability has a pronounced maximum at a
lattice constant where the character of the wavefunction changes from
significant to essentially -type. In addition, we examine rings with
bond alternation in order to answer the question under which conditions a
Peierls distortion occurs.Comment: 9 pages, 11 figure
Metallic bonding due to correlations: A quantum chemical ab-initio calculation of the cohesive energy of mercury
Solid mercury in the rhombohedral structure is unbound within the
self-consistent field (Hartree-Fock) approximation. The metallic binding is
entirely due to electronic correlations. We determine the cohesive energy of
solid mercury within an ab-initio many-body expansion for the correlation part.
Electronic correlations in the shell contribute about half to the cohesive
energy. Relativistic effects are found to be very important. Very good
agreement with the experimental value is obtained.Comment: 4 pages, 1 figur
The convergence of the ab-initio many-body expansion for the cohesive energy of solid mercury
A many-body expansion for mercury clusters of the form E = \sum_{i<j}\Delta
\epsilon_{ij} + \sum_{i<j<k}\Delta \epsilon_{ijk} + ... \quad, does not
converge smoothly with increasing cluster size towards the solid state. Even
for smaller cluster sizes (up to n=6), where van der Waals forces still
dominate, one observes bad convergence behaviour. For solid mercury the
convergence of the many-body expansion can dramatically be improved by an
incremental procedure within an embedded cluster approach. Here one adds the
coupled cluster many-body electron correlation contributions of the embedded
cluster to the bulk HF energy. In this way we obtain a cohesive energy (not
corrected for zero-point vibration) of 0.79 eV in perfect agreement with the
experimental value.Comment: 10 pages, 3 figures, accepted PR
Isolation and Characterization of Ischemia-Derived Astrocytes (IDAs) with Ability to Transactivate Quiescent Astrocytes
Reactive gliosis involving activation and proliferation of astrocytes and microglia, is a widespread but largely complex and graded glial response to brain injury. Astroglial population has a previously underestimated high heterogeneity with cells differing in their morphology, gene expression profile, and response to injury. Here, we identified a subset of reactive astrocytes isolated from brain focal ischemic lesions that show several atypical characteristics. Ischemia-derived astrocytes (IDAs) were isolated from early ischemic penumbra and core. IDA did not originate from myeloid precursors, butrather from pre-existing local progenitors. Isolated IDA markedly differ from primary astrocytes, as they proliferate in vitro with high cell division rate, show increased migratory ability, have reduced replicative senescence and grow in the presence of macrophages within the limits imposed by the glial scar. Remarkably, IDA produce a conditioned medium that strongly induced activation on quiescent primary astrocytes and potentiated the neuronal death triggered by oxygen-glucose deprivation. When re-implanted into normal rat brains, eGFP-IDA migrated around the injection site and induced focal reactive gliosis. Inhibition of gamma secretases or culture on quiescent primary astrocytes monolayers facilitated IDA differentiation to astrocytes. We propose that IDA represent an undifferentiated, pro-inflammatory, highly replicative and migratory astroglial subtype emerging from the ischemic microenvironment that may contribute to the expansion of reactive gliosis.Fil: Villarreal, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Rosciszewski, Gerardo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Murta, Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Cadena, María Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Usach, Vanina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; ArgentinaFil: Dodes Traian, Martín Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; ArgentinaFil: Setton, Clara Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; ArgentinaFil: Barbeito, Osvaldo Luis. Instituto Pasteur de Montevideo; UruguayFil: Ramos, Alberto Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; Argentin
Do We Know Our Brain? A Challenge of Senses
One of the most important challenges of the current scientists is to bring their knowledge, methods, procedures, and results to the society. Education is a main resource that students have to shape their future. So, it is fundamental to create bridges between science and education, through new forms of science divulgation. The objective of this BAW project was to improve students? knowledge about the brain functioning, brain protection, and also how tobecome neuroscientist in Argentina. For that purpose, during Brain Awareness Week (BAW) in March 2018, we visited three secondary schools located in Misiones province: Instituto Roque Gonza´lez (Posadas), Instituto Madre de laMisericordia (Posadas), and Escuela Provincial de Educacion Técnica (E.P.E.T.) N° 50 (Leandro N. Alem). We developed the project through guide questions, group games, sense tests, and a final talk with a total of more than 200 students.We focused on the participation of the students: They were able to experience themselves and many questions arose during the talks, which were very dynamic and varied among the different schools. Children, together with the professors and school directors, enjoyed and took advantage of the opportunity of having neuroscientists in the schools. Teachers repeatedly thanked us for bringing our research and knowledge to very distant provinces like Misiones.This work was supported by grants of SAN (BAW); Transportes Rio Uruguay; E.P.E.T. N° 50 and G. Rosciszewski family.Fil: Rosciszewski, Gerardo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Murta, Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Cadena, María Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Cieri, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Ramos, Alberto Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaXXXIII Reunión Anual de la Sociedad Argentina de Investigación en NeurocienciasCórdobaArgentinaSociedad Argentina de Investigación en Neurociencia
A simple environment-dependent overlap potential and Cauchy violation in solid argon
We develop an analytic and environment-dependent interatomic potential for
the overlap repulsion in solid argon, based on an approximate treatment of the
non-orthogonal Tight-Binding theory for the closed-shell systems. The present
model can well reproduce the observed elastic properties of solid argon
including Cauchy violation at high pressures, yet very simple. A useful and
novel analysis is given to show how the elastic properties are related to the
environment-dependence incorporated into a generic pairwise potential. The
present study has a close link to the broad field of computational materials
science, in which the inclusion of environment dependence in short-ranged
repulsive part of a potential model is sometimes crucial in predicting the
elastic properties correctly.Comment: 10 pages, 3 figure
First Principles Calculation of Elastic Properties of Solid Argon at High Pressures
The density and the elastic stiffness coefficients of fcc solid argon at high
pressures from 1 GPa up to 80 GPa are computed by first-principles
pseudopotential method with plane-wave basis set and the generalized gradient
approximation (GGA). The result is in good agreement with the experimental
result recently obtained with the Brillouin spectroscopy by Shimizu et al.
[Phys. Rev. Lett. 86, 4568 (2001)]. The Cauchy condition was found to be
strongly violated as in the experimental result, indicating large contribution
from non-central many-body force. The present result has made it clear that the
standard density functional method with periodic boundary conditions can be
successfully applied for calculating elastic properties of rare gas solids at
high pressures in contrast to those at low pressures where dispersion forces
are important.Comment: 4 pages, 5 figures, submitted to PR
Refraction of dispersive shock waves
We study a dispersive counterpart of the classical gas dynamics problem of
the interaction of a shock wave with a counter-propagating simple rarefaction
wave often referred to as the shock wave refraction. The refraction of a
one-dimensional dispersive shock wave (DSW) due to its head-on collision with
the centred rarefaction wave (RW) is considered in the framework of defocusing
nonlinear Schr\"odinger (NLS) equation. For the integrable cubic nonlinearity
case we present a full asymptotic description of the DSW refraction by
constructing appropriate exact solutions of the Whitham modulation equations in
Riemann invariants. For the NLS equation with saturable nonlinearity, whose
modulation system does not possess Riemann invariants, we take advantage of the
recently developed method for the DSW description in non-integrable dispersive
systems to obtain main physical parameters of the DSW refraction. The key
features of the DSW-RW interaction predicted by our modulation theory analysis
are confirmed by direct numerical solutions of the full dispersive problem.Comment: 45 pages, 23 figures, minor revisio
Detrimental Effects of HMGB-1 Require Microglial-Astroglial Interaction: Implications for the Status Epilepticus -Induced Neuroinflammation
Temporal Lobe Epilepsy (TLE) is the most common form of human epilepsy and available treatments with antiepileptic drugs are not disease-modifying therapies. The neuroinflammation, neuronal death and exacerbated plasticity that occur during the silent period, following the initial precipitating event (IPE), seem to be crucial for epileptogenesis. Damage Associated Molecular Patterns (DAMP) such as HMGB-1, are released early during this period concomitantly with a phenomenon of reactive gliosis and neurodegeneration. Here, using a combination of primary neuronal and glial cell cultures, we show that exposure to HMGB-1 induces dendrite loss and neurodegeneration in a glial-dependent manner. In glial cells, loss of function studies showed that HMGB-1 exposure induces NF-κB activation by engaging a signaling pathway that involves TLR2, TLR4, and RAGE. In the absence of glial cells, HMGB-1 failed to induce neurodegeneration of primary cultured cortical neurons. Moreover, purified astrocytes were unable to fully respond to HMGB-1 with NF-κB activation and required microglial cooperation. In agreement, in vivo HMGB-1 blockage with glycyrrhizin, immediately after pilocarpine-induced status epilepticus (SE), reduced neuronal degeneration, reactive astrogliosis and microgliosis in the long term. We conclude that microglial-astroglial cooperation is required for astrocytes to respond to HMGB-1 and to induce neurodegeneration. Disruption of this HMGB-1 mediated signaling pathway shows beneficial effects by reducing neuroinflammation and neurodegeneration after SE. Thus, early treatment strategies during the latency period aimed at blocking downstream signaling pathways activated by HMGB-1 are likely to have a significant effect in the neuroinflammation and neurodegeneration that are proposed as key factors in epileptogenesis.Fil: Rosciszewski, Gerardo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Cadena, María Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Auzmendi, Jerónimo Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Cieri, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Lukin, Jeronimo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Rossi, Alicia Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Murta, Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Villarreal, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Reines, Analia Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Gomes, Flávia C. A.. Universidade Federal do Rio de Janeiro; BrasilFil: Ramos, Alberto Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; Argentin
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