Randall-Sundrum brane cosmology: modification of late-time cosmic dynamics by exotic matter

In this paper we show, through the study of concrete examples, that, depending on the cosmic dynamics of the energy density of matter degrees of freedom living in the brane, Randall-Sundrum (RS) brane effects can be important not only at short distances (UV regime), but also at large cosmological scales (IR regime). Our first example relies on the study, by means of the dynamical systems tools, of a toy model based in a non-linear electrodynamics (NLED) Lagrangian. Then we show that other, less elaborated models, such as the inclusion of a scalar phantom field, and of a tachyon phantom field -- trapped in the brane -- produce similar results. The form of the RS correction seems to convert what would have been future attractors in general relativity into saddle points. The above "mixing of scales" effect is distinctive only of theories that modify the right-hand-side (matter part) of the Friedmann equation, so that, for instance, DGP-brane models do not show this feature.Comment: Latex, 12 pages, 9 eps figures. Title changed, discussion improved. Version that matches the one published in CQ

Fibras textiles naturales sustentables y nuevos hábitos de consumo

Durante años el estancamiento manufacturero de la industria textil, trajo repercusiones tanto económicas como tecnológicas y ambas desembocaron en un daño ecológico voraz; la falta de nuevas propuestas y la necesidad de complacer a un mercado cada vez más grande, permitió la generación de empresas altamente lucrativas. El siguiente artículo tienen como finalidad proporcionar información que puede resultar importante para el consumidor al momento de elegir una prenda de vestir, ofreciendo información sobre diferentes tipos de fibras textiles sustentables, que cada vez más diseñadores gráficos, industriales, ingenieros, diseñadores textiles y particularmente, para diseñadores de moda y marcas reconocidas en el sector de la industria del vestido y calzado emplean, ya no como valor agregado, más bien como una consideración prioritaria para contribuir a la conservación del medio ambiente. Sin duda alguna, es el diseñador quien juega un papel muy importante en el uso y aplicación de los textiles sustentables, ya que la forma en la que aplique el proceso creativo en estrategias de investigación, influirá en los hábitos del consumidor, creando conciencia del ciclo de vida de una prenda de vestir, pues la gran mayoría de dichas prendas no se re-usa ni recicla y termina generando montones de basura

Development of type II superlattice infrared detectors monolithically integrated on silicon substrates

The project’s objective is the development of an InAs/GaSb type II superlattice (T2SL) medium wavelength infrared photodiode directly grown on Si substrate for the use of an infrared single pixel photodiode. The T2SL has been selected as the replacement for the state-of-the-art CdHgTe (CMT). The use of Si substrate will help with the integration into the Si-based technology by reducing the fabrication process and costs. The T2SL is a photon detector with overlapping multiple quantum well structure and a type 2 bandgap alignment. The T2SL are fabricated using a combination of materials from the group III-V in order to achieve a well-controlled ultra-thin heterostructures using molecular beam epitaxy as a growth technique. The structure within the active region is designed to enhance the performance of the T2SL architecture by manipulating the thickness and doping of each layer. The direct growth of a T2SL structure on the Si substrate has achieved similar structural and optical properties when compared to that grown on the GaAs substrate. The Si architecture has an absorption edge of 5.365μm when measured at 70K: dark current density at -1V is 4x101A/cm2; responsivity (R) peak is 1.2A/W; quantum efficiency (QE) at -0.1V is 32.5%; and specific detectivity (D*) peak is 1x109cmHz½/W. The pπBn has best architecture over GaAs substrate due to the wide bandgap unipolar barrier. The pπBn has an absorption edge of 6.5 μm when measured at 77K: dark current density under -0.6V is 5x10-3A/cm2; R peak is 0.6A/W; QE at 0V and 3.25μm is 23%; and D* peak is 1x1011cmHz½/W. These results demonstrate that the D* of the pπBn structure is just one order of magnitude smaller than the state-of-the-art CMT detector which is 2x1012cmHz1/2W

Mechanism of Gene Silencing Suppression by the Geminivirus Protein TrAP

The hosts-virus arms race reaches the epigenetic level, where silencing of viral chromatin can serve as an innate defense mechanism to restrict invading DNA viruses. However, viruses can code for suppressor proteins to counter epigenetic silencing and escape host surveillance. Thus, the virus-encoded suppressors offer an untapped source of tools for the understanding of pathogenesis and chromatin regulation. TrAP is a transcription factor encoded by model DNA plant viruses of the family Geminiviridae, which is required for the expression of the virus late genes and for suppression of gene silencing. TrAP is known to interfere with the transcriptional gene-silencing (TGS) pathway by obstructing the methyl cycle in the cytoplasm. Nonetheless, multiple metabolic pathways other than chromatin regulation utilize the methyl donor, and TrAP mainly localizes to the nucleus; furthermore, TrAP is predicted to interact with the transcriptional machinery. Thus, we asked whether TrAP directly suppressed TGS. We first generated TrAP-stable transgenic plants, and through transcriptome and biochemical assays, we demonstrated that TrAP hampered TGS. We then identified TrAP-interacting partners using a proteomics approach, confirmed by protein interaction experiments in vivo and in vitro. To determine whether these interactions were physiologically relevant, we performed virus infection assays in various host genetic backgrounds. We demonstrated that TrAP interacts with multiple SET-domain proteins in Arabidopsis. Particularly, the H3K9me2 histone methyltransferase, Su(var)3-9 homolog 4/Kryptonite (SUVH4/KYP) is a bona fide cellular target of TrAP. TrAP expression phenocopies several TGS mutants, reduces the repressive H3K9me2 mark and CHH DNA methylation, and reactivates many endogenous KYP-repressed loci in vivo. KYP binds to the viral chromatin and controls its methylation to combat virus infection. We conclude that TrAP attenuates TGS by inhibiting KYP activity. Furthermore, we show that TrAP interacts with other proteins, such as the methyl cycle enzymes SAMe-synthetase 2 (SAM2) and the S-adenosyl homocysteine hydrolase 1 (SAHH1), the RNA processing Enhanced silencing phenotype 3 (ESP3), and the chromatin remodeler Relative of early flowering 6 (REF6). Our findings provide new insight in the host antiviral defense and virus counter- defense at an epigenetic level and provide a model system to study chromatin regulation, and virus infection

Mechanism of Gene Silencing Suppression by the Geminivirus Protein TrAP

The hosts-virus arms race reaches the epigenetic level, where silencing of viral chromatin can serve as an innate defense mechanism to restrict invading DNA viruses. However, viruses can code for suppressor proteins to counter epigenetic silencing and escape host surveillance. Thus, the virus-encoded suppressors offer an untapped source of tools for the understanding of pathogenesis and chromatin regulation. TrAP is a transcription factor encoded by model DNA plant viruses of the family Geminiviridae, which is required for the expression of the virus late genes and for suppression of gene silencing. TrAP is known to interfere with the transcriptional gene-silencing (TGS) pathway by obstructing the methyl cycle in the cytoplasm. Nonetheless, multiple metabolic pathways other than chromatin regulation utilize the methyl donor, and TrAP mainly localizes to the nucleus; furthermore, TrAP is predicted to interact with the transcriptional machinery. Thus, we asked whether TrAP directly suppressed TGS. We first generated TrAP-stable transgenic plants, and through transcriptome and biochemical assays, we demonstrated that TrAP hampered TGS. We then identified TrAP-interacting partners using a proteomics approach, confirmed by protein interaction experiments in vivo and in vitro. To determine whether these interactions were physiologically relevant, we performed virus infection assays in various host genetic backgrounds. We demonstrated that TrAP interacts with multiple SET-domain proteins in Arabidopsis. Particularly, the H3K9me2 histone methyltransferase, Su(var)3-9 homolog 4/Kryptonite (SUVH4/KYP) is a bona fide cellular target of TrAP. TrAP expression phenocopies several TGS mutants, reduces the repressive H3K9me2 mark and CHH DNA methylation, and reactivates many endogenous KYP-repressed loci in vivo. KYP binds to the viral chromatin and controls its methylation to combat virus infection. We conclude that TrAP attenuates TGS by inhibiting KYP activity. Furthermore, we show that TrAP interacts with other proteins, such as the methyl cycle enzymes SAMe-synthetase 2 (SAM2) and the S-adenosyl homocysteine hydrolase 1 (SAHH1), the RNA processing Enhanced silencing phenotype 3 (ESP3), and the chromatin remodeler Relative of early flowering 6 (REF6). Our findings provide new insight in the host antiviral defense and virus counter- defense at an epigenetic level and provide a model system to study chromatin regulation, and virus infection

Asymptotic Properties of a Supposedly Regular (Dirac-Born-Infeld) Modification of General Relativity

We apply the dynamical systems tools to study the asymptotic properties of a cosmological model based on a non-linear modification of General Relativity in which the standard Einstein-Hilbert action is replaced by one of Dirac-Born-Infeld type. It is shown that the dynamics of this model is extremely rich: there are found equilibrium points in the phase space that can be associated with matter-dominated, matter-curvature scaling, de Sitter, and even phantom-like solutions. Depending on the value of the overall parameters the dynamics in phase space can show multi-attractor structure into the future (multiple future attractors may co-exist). This is a consequence of bifurcations in control parameter space, showing strong dependence of the model's dynamical properties on the free parameters. Contrary to what is expected from non-linear modifications of general relativity of this kind, removal of the initial spacetime singularity is not a generic feature of the corresponding cosmological model. Instead, the starting point of the cosmic dynamics -- the past attractor in the phase space -- is a state of infinitely large value of the Hubble rate squared, usually associated with the big bang singularity.Comment: 12 pages, Revtex, 12 eps figures. Several new references added. Minor changes in the main text. Discussion improve