4,335 research outputs found
Regularization of odd-dimensional AdS gravity: Kounterterms
As an alternative to the Dirichlet counterterms prescription, I introduce the
concept of Kounterterms as the boundary terms with explicit dependence on the
extrinsic curvature K_{ij} that regularize the AdS gravity action. Instead of a
Dirichlet boundary condition on the metric, a suitable choice of the boundary
conditions --compatible with any asymptotically AdS (AAdS) spacetime-- ensures
a finite action principle for all odd dimensions. Background-independent
conserved quantities are obtained as Noether charges associated to asymptotic
symmetries and their general expression appears naturally split in two parts.
The first one gives the correct mass and angular momentum for AAdS black
holes and vanishes identically for globally AdS spacetimes. Thus, the second
part is a covariant formula for the vacuum energy in AAdS spacetimes and
reproduces the results obtained by the Dirichlet counterterms method in a
number of cases. It is also shown that this Kounterterms series regularizes the
Euclidean action and recovers the correct black hole thermodynamics in odd
dimensions.Comment: 35+6 pages, 8 references and an appendix added, improved discussion
on boundary conditions and geometrical origin of Kounterterms. Version
accepted in JHE
Transgression forms and extensions of Chern-Simons gauge theories
A gauge invariant action principle, based on the idea of transgression forms,
is proposed. The action extends the Chern-Simons form by the addition of a
boundary term that makes the action gauge invariant (and not just
quasi-invariant). Interpreting the spacetime manifold as cobordant to another
one, the duplication of gauge fields in spacetime is avoided. The advantages of
this approach are particularly noticeable for the gravitation theory described
by a Chern-Simons lagrangian for the AdS group, in which case the action is
regularized and finite for black hole geometries in diverse situations. Black
hole thermodynamics is correctly reproduced using either a background field
approach or a background-independent setting, even in cases with asymptotically
nontrivial topologies. It is shown that the energy found from the thermodynamic
analysis agrees with the surface integral obtained by direct application of
Noether's theorem.Comment: 28 pages, no figures. Minor changes in the introduction, final
comments and reference
A fluorescence-activatable reporter of flavivirus NS2B–NS3 protease activity enables live imaging of infection in single cells and viral plaques
The genus Flavivirus in the family Flaviviridae comprises
many medically important viruses, such as dengue virus (DENV),
Zika virus (ZIKV), and yellow fever virus. The quest for thera-
peutic targets to combat flavivirus infections requires a better
understanding of the kinetics of virus–host interactions during
infections with native viral strains. However, this is precluded by
limitations of current cell-based systems for monitoring flavivi-
rus infection in living cells. In the present study, we report the
construction of fluorescence-activatable sensors to detect the
activities of flavivirus NS2B–NS3 serine proteases in living cells.
The system consists of GFP-based reporters that become fluo-
rescent upon cleavage by recombinant DENV-2/ZIKV proteases
in vitro. A version of this sensor containing the flavivirus inter-
nal NS3 cleavage site linker reported the highest fluorescence
activation in stably transduced mammalian cells upon DENV-2/
ZIKV infection. Moreover, the onset of fluorescence correlated
with viral protease activity. A far-red version of this flavivirus
sensor had the best signal-to-noise ratio in a fluorescent Dulbec-
co’s plaque assay, leading to the construction of a multireporter
platform combining the flavivirus sensor with reporter dyes for
detection of chromatin condensation and cell death, enabling
studies of viral plaque formation with single-cell resolution.
Finally, the application of this platform enabled the study of
cell-population kinetics of infection and cell death by DENV-2,
ZIKV, and yellow fever virus. We anticipate that future studies
of viral infection kinetics with this reporter system will enable
basic investigations of virus–host interactions and facilitate
future applications in antiviral drug research to manage flavivi-
rus infections.International Centre for Genetic Engineering and Biotechnology Grant CRP/CRI18-02.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Centro de Investigación en Enfermedades Tropicales (CIET)UCR::Vicerrectoría de Docencia::Salud::Facultad de Microbiologí
Reciprocal and dynamic control of CD8 T cell homing by dendritic cells from skin- and gut-associated lymphoid tissues
T cell activation by intestinal dendritic cells (DC) induces gut-tropism. We show that, reciprocally, DC from peripheral lymph nodes (PLN-DC) induce homing receptors promoting CD8 T cell accumulation in inflamed skin, particularly ligands for P- and E-selectin. Differential imprinting of tissue-tropism was independent of Th1/Th2 cytokines and not restricted to particular DC subsets. Fixed PLN-DC retained the capacity to induce selectin ligands on T cells, which was suppressed by addition of live intestinal DC. By contrast, fixed intestinal DC failed to promote gut-tropism and instead induced skin-homing receptors. Moreover, the induction of selectin ligands driven by antigen-pulsed PLN-DC could be suppressed “in trans” by adding live intestinal DC, but PLN-DC did not suppress gut-homing receptors induced by intestinal DC. Reactivation of tissue-committed memory cells modified their tissue-tropism according to the last activating DC's origin. Thus, CD8 T cells activated by DC acquire selectin ligands by default unless they encounter fixation-sensitive signal(s) for gut-tropism from intestinal DC. Memory T cells remain responsive to these signals, allowing for dynamic migratory reprogramming by skin- and gut-associated DC
Caracterización de la cobertura arbórea en una pastura del trópico seco en Tolima, Colombia.
El objetivo de este estudio fue caracterizar la vegetación leñosa perenne de un potrero arbolado del Magdalena Tolimense en Colombia. El inventario forestal se realizó mediante el establecimiento de parcelas temporales de muestreo. La estimación del porcentaje de oclusión de la copa de los árboles se obtuvo mediante fotografías digitales al cenit y su análisis en el software libre Gap Light Analyzer. La radicación fotosintéticamente activa (RAFA) transmitida por la copa se midió con un ceptómetro Accupar LP-80. Se encontraron 21 especies leñosas perennes en un área de muestreo de 54 ha. Con menor porcentaje de oclusión fueron: Pseudosamanea guachapele (64%) y Prosopis juliflora (63%), lo que sugiere incluirlas en diseños de sistemas silvopastoriles; algunas especies poseen potencial maderable como ingreso adicional al ganadero. Se encontró una importante diversidad de especies leñosas para ser introducidas en pasturas, sin perjudicar la producción de materia seca comestible para el ganado
Mass, Angular Momentum and Thermodynamics in Four-Dimensional Kerr-AdS Black Holes
In this paper, the connection between the Lorentz-covariant counterterms that
regularize the four-dimensional AdS gravity action and topological invariants
is explored. It is shown that demanding the spacetime to have a negative
constant curvature in the asymptotic region permits the explicit construction
of such series of boundary terms. The orthonormal frame is adapted to
appropriately describe the boundary geometry and, as a result, the boundary
term can be expressed as a functional of the boundary metric, extrinsic
curvature and intrinsic curvature. This choice also allows to write down the
background-independent Noether charges associated to asymptotic symmetries in
standard tensorial formalism. The absence of the Gibbons-Hawking term is a
consequence of an action principle based on a boundary condition different than
Dirichlet on the metric. This argument makes plausible the idea of regarding
this approach as an alternative regularization scheme for AdS gravity in all
even dimensions, different than the standard counterterms prescription. As an
illustration of the finiteness of the charges and the Euclidean action in this
framework, the conserved quantities and black hole entropy for four-dimensional
Kerr-AdS are computed.Comment: 15 pages,no figures,few references added,JHEP forma
Small intestine lamina propria dendritic cells promote de novo generation of Foxp3 T reg cells via retinoic acid
To maintain immune homeostasis, the intestinal immune system has evolved redundant regulatory strategies. In this regard, the gut is home to a large number of regulatory T (T reg) cells, including the Foxp3+ T reg cell. Therefore, we hypothesized that the gut environment preferentially supports extrathymic T reg cell development. We show that peripheral conversion of CD4+ T cells to T reg cells occurs primarily in gut-associated lymphoid tissue (GALT) after oral exposure to antigen and in a lymphopenic environment. Dendritic cells (DCs) purified from the lamina propria (Lp; LpDCs) of the small intestine were found to promote a high level of T reg cell conversion relative to lymphoid organ–derived DCs. This enhanced conversion by LpDCs was dependent on TGF-β and retinoic acid (RA), which is a vitamin A metabolite highly expressed in GALT. Together, these data demonstrate that the intestinal immune system has evolved a self-contained strategy to promote T reg cell neoconversion
T cell mediated cerebral hemorrhages and microhemorrhages during passive Aβ immunization in APPPS1 transgenic mice
<p>Abstract</p> <p>Background</p> <p>Immunization against amyloid-β (Aβ), the peptide that accumulates in the form of senile plaques and in the cerebrovasculature in Alzheimer's disease (AD), causes a dramatic immune response that prevents plaque formation and clears accumulated Aβ in transgenic mice. In a clinical trial of Aβ immunization, some patients developed meningoencephalitis and hemorrhages. Neuropathological investigations of patients who died after the trial showed clearance of amyloid pathology, but also a powerful immune response involving activated T cells probably underlying the negative effects of the immunization.</p> <p>Results</p> <p>To define the impact of T cells on this inflammatory response we used passive immunization and adoptive transfer to separate the effect of IgG and T cell mediated effects on microhemorrhage in APPPS1 transgenic mice. Neither anti Aβ IgG nor adoptively transferred T cells, alone, led to increased cerebrovascular damage. However, the combination of adoptively transferred T cells and passive immunization led to massive cerebrovascular bleeding that ranged from multiple microhemorrhages in the parenchyma to large hematomas.</p> <p>Conclusions</p> <p>Our results indicate that vaccination can lead to Aβ and T cell induced cerebral micro-hemorrhages and acute hematomas, which are greatly exacerbated by T cell mediated activity.</p
Counterterms and dual holographic anomalies in CS gravity
The holographic Weyl anomaly associated to Chern-Simons gravity in 2n+1
dimensions is proportional to the Euler term in 2n dimensions, with no
contributions from the Weyl tensor. We compute the holographic energy-momentum
tensor associated to Chern-Simons gravity directly from the action, in an
arbitrary odd-dimensional spacetime. We show, in particular, that the
counterterms rendering the action finite contain only terms of the Lovelock
type.Comment: 10 pages, no figure
Robust and accurate modeling approaches for migraine Per-Patient prediction from ambulatory data
Migraine is one of the most wide-spread neurological disorders, and its medical treatment represents a high percentage of the costs of health systems. In some patients, characteristic symptoms that precede the headache appear. However, they are nonspecific, and their prediction horizon is unknown and pretty variable; hence, these symptoms are almost useless for prediction, and they are not useful to advance the intake of drugs to be effective and neutralize the pain. To solve this problem, this paper sets up a realistic monitoring scenario where hemodynamic variables from real patients are monitored in ambulatory conditions with a wireless body sensor network (WBSN). The acquired data are used to evaluate the predictive capabilities and robustness against noise and failures in sensors of several modeling approaches. The obtained results encourage the development of per-patient models based on state-space models (N4SID) that are capable of providing average forecast windows of 47 min and a low rate of false positives
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