1,532 research outputs found
Nonsingular electrovacuum solutions with dynamically generated cosmological constant
We consider static spherically symmetric configurations in a Palatini
extension of General Relativity including and Ricci-squared terms, which
is known to replace the central singularity by a wormhole in the electrovacuum
case. We modify the matter sector of the theory by adding to the usual Maxwell
term a nonlinear electromagnetic extension which is known to implement a
confinement mechanism in flat space. One feature of the resulting theory is
that the non-linear electric field leads to a dynamically generated
cosmological constant. We show that with this matter source the solutions of
the model are asymptotically de Sitter and possess a wormhole topology. We
discuss in some detail the conditions that guarantee the absence of
singularities and of traversable wormholes.Comment: 7 double-column pages; v2: several changes in abstract and
introductio
A correspondence between modified gravity and General Relativity with scalar fields
We describe a novel procedure to map the field equations of nonlinear
Ricci-based metric-affine theories of gravity, coupled to scalar matter
described by a given Lagrangian, into the field equations of General Relativity
coupled to a different scalar field Lagrangian. Our analysis considers examples
with a single and real scalar fields, described either by canonical
Lagrangians or by generalized functions of the kinetic and potential terms. In
particular, we consider several explicit examples involving theories and
the Eddington-inspired Born-Infeld gravity model, coupled to different scalar
field Lagrangians. We show how the nonlinearities of the gravitational sector
of these theories can be traded to nonlinearities in the matter fields, and how
the procedure allows to find new solutions on both sides of the correspondence.
The potential of this procedure for applications of scalar field models in
astrophysical and cosmological scenarios is highlighted.Comment: 14 pages; v2: section IIID extended, some minor corrections,
references update
Mapping nonlinear gravity into General Relativity with nonlinear electrodynamics
We show that families of nonlinear gravity theories formulated in a
metric-affine approach and coupled to a nonlinear theory of electrodynamics can
be mapped into General Relativity (GR) coupled to another nonlinear theory of
electrodynamics. This allows to generate solutions of the former from those of
the latter using purely algebraic transformations. This correspondence is
explicitly illustrated with the Eddington-inspired Born-Infeld theory of
gravity, for which we consider a family of nonlinear electrodynamics and show
that, under the map, preserve their algebraic structure. For the particular
case of Maxwell electrodynamics coupled to Born-Infeld gravity we find, via
this correspondence, a Born-Infeld-type nonlinear electrodynamics on the GR
side. Solving the spherically symmetric electrovacuum case for the latter, we
show how the map provides directly the right solutions for the former. This
procedure opens a new door to explore astrophysical and cosmological scenarios
in nonlinear gravity theories by exploiting the full power of the analytical
and numerical methods developed within the framework of GR.Comment: 11 pages. v2: next discussions inserted, refs added; matches the
version accepted for publication in EPJ
The Deubiquitinating Enzyme USP48 Interacts with the Retinal Degeneration-Associated Proteins UNC119a and ARL3
Proteins related to the ubiquitin-proteasome system play an important role during the differentiation and ciliogenesis of photoreceptor cells. Mutations in several genes involved in ubiquitination and proteostasis have been identified as causative of inherited retinal dystrophies (IRDs) and ciliopathies. USP48 is a deubiquitinating enzyme whose role in the retina is still unexplored although previous studies indicate its relevance for neurosensory organs. In this work, we describe that a pool of endogenous USP48 localises to the basal body in retinal cells and provide data that supports the function of USP48 in the photoreceptor cilium. We also demonstrate that USP48 interacts with the IRD-associated proteins ARL3 and UNC119a, and stabilise their protein levels using different mechanisms. Our results suggest that USP48 may act in the regulation/stabilisation of key ciliary proteins for photoreceptor function, in the modulation of intracellular protein transport, and in ciliary trafficking to the photoreceptor outer segment
Nonsingular electrovacuum solutions with dynamically generated constant
Abstract We consider static spherically symmetric configurations in a Palatini extension of General Relativity including R 2 and Ricci-squared terms, which is known to replace the central singularity by a wormhole in the electrovacuum case. We modify the matter sector of the theory by adding to the usual Maxwell term a nonlinear electromagnetic extension which is known to implement a confinement mechanism in flat space. One feature of the resulting theory is that the non-linear electric field leads to a dynamically generated cosmological constant. We show that with this matter source the solutions of the model are asymptotically de Sitter and possess a wormhole topology. We discuss in some detail the conditions that guarantee the absence of singularities and of traversable wormholes
A study of the prostate, androgens and sexual activity of male rats
BACKGROUND: The prostate is a sexual gland that produces important substances for the potency of sperm to fertilize eggs within the female reproductive tract, and is under complex endocrine control. Taking advantage of the peculiar behavioral pattern of copulating male rats, we developed experimental paradigms to determine the influence of sexual behavior on the level of serum testosterone, prostate androgen receptors, and mRNA for androgen receptors in male rats displaying up to four consecutive ejaculations. METHODS: The effect of four consecutive ejaculations was investigated by determining levels of (i) testosterone in serum by solid phase RIA, (ii) androgen receptors at the ventral prostate with Western Blots, and (iii) androgen receptors-mRNA with RT-PCR. Data were analyzed with a one-way ANOVA followed by a post hoc application of Dunnett's test if required. RESULTS: The constant execution of sexual behavior did not produce any change in the weight of the ventral prostate. Serum testosterone increased after the second ejaculation, and remained elevated even after four ejaculations. The androgen receptor at the ventral prostate was higher after the first to third ejaculations, but returned suddenly to baseline levels after the fourth ejaculation. The level of mRNA increased after the first ejaculation, continued to increase after the second, and reached the highest peak after the third ejaculation; however, it returned suddenly to baseline levels after the fourth ejaculation. CONCLUSION: Four consecutive ejaculations by sexually experienced male rats had important effects on the physiological responses of the ventral prostate. Fast responses were induced as a result of sexual behavior that involved an increase and decrease in androgen receptors after one and four ejaculations, respectively. However, a progressive response was observed in the elevation of mRNA for androgen receptors, which also showed a fast decrease after four ejaculations. All of these changes with the prostate gland occurred in the presence of a sustained elevation of testosterone in the serum that started after two ejaculations. A consideration of these fast-induced changes suggests that the nerve supply plays a key role in prostate physiology during the sexual behavior of male rats
LiNi0.5Mn1.5O4 Thin Films Grown by Magnetron Sputtering under Inert Gas Flow Mixtures as High-Voltage Cathode Materials for Lithium-Ion Batteries
Delivering a commercial high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) cathode electrode for Li-ion batteries would result in a significant step forward in terms of energy density. However, the structural ordering of the spinel and particle size have considerable effects on the cathode material's cyclability and rate capability, which are crucial challenges to address. Here, a novel mid-frequency alternating current dual magnetron sputtering method was presented, using different Ar-N-2 gas mixtures ratios for the process gas to prepare various LNMO thin films with highly controlled morphology and particle size; as determined from X-ray diffraction, Raman spectroscopy and electron microscopy. It resulted in enhanced cycling and rate performance. This processing method delivered N-containing LNMO thin film electrodes with up to 15 % increased discharge capacity at 1 C (120 mAh g(-1)) with respect to standard LNMO (grown under only Ar gas flow) thin film electrodes, along with outstanding rate performance up to 10 C (99 mAh g(-1)) in the operating voltage window 3.5-4.85 V vs. Li+/Li. Besides, electrochemical impedance spectroscopy results showed that the intricate phase transitions present in standard LNMO electrodes were almost suppressed in N-containing LNMO thin films grown under different Ar-N-2 gas flow mixtures
La mala educación : narrativas del Banco Mundial desde un enfoque léxico-relacional
A través de diferentes marcos estratégicos, el Banco Mundial ha generado un grupo de recomendaciones sobre polÃticas educativas que, analizados por medio de técnicas cualitativas, resultan de sesgo neoliberal y constantes a lo largo del tiempo. A partir de la incorporación de técnicas computacionales es posible analizar grandes volúmenes de datos no estructurados con técnicas estadÃsticas. Utilizando el blog de la institución se registran cambios en el léxico utilizado en la construcción de narrativas para el perÃodo 2010-2020, llegando a la conclusión de que los términos asociados a palabras clave siguen asociadas a palabras utilizadas por la ideologÃa neoliberal.A través de diferents marcs estratègics, el Banc Mundial ha generat un conjunt de recomanacions sobre polÃtiques educatives que, analitzades per mitjà de tècniques qualitatives, resulten ser de biaix neoliberal i constants al llarg del temps. A partir de la incorporació de tècniques computacionals és possible analitzar grans volums de dades no estructurades amb tècniques estadÃstiques. Utilitzant el blog de la institució es registren canvis en el lèxic utilitzat en la construcció de narratives pel perÃode 2010-2020, arribant a la conclusió que els termes associats a paraules clau segueixen associats a paraules utilitzades per la ideologia neoliberal
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