Santiago de Querétaro, Mexico
Santiago de Querétaro, Mexico

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Fernandez I.,Complutense University of Madrid | Frenking G.,University of Marburg | Merino G.,Research Center Estudios Avanzados
Chemical Society Reviews | Year: 2015

The concept of aromaticity was initially introduced in chemistry to account for the stability, reactivity, molecular structures, and other properties of many unsaturated organic compounds. Despite that, it has been extended to other species with mobile electrons including saturated systems, transition structures, and even inorganic molecules. In this review, we focus on the aromaticity of a particular family of organometallic compounds known as metallabenzenes, which are characterized by the formal replacement of a CH group in benzene by an isolobal transition metal fragment. In addition, aromaticity of related compounds such as heterometallabenzenes is considered as well. To this end, we shall describe herein the insight gained by the available experimental data as well as by the application of the state-of-the-art computational methods developed as descriptors for aromaticity together with a critical evaluation of their performance to quantitatively estimate the strength of aromaticity of these systems. © 2015 The Royal Society of Chemistry.


Roig P.,Research Center Estudios Avanzados
Nuclear and Particle Physics Proceedings | Year: 2015

Exclusive semi-leptonic decays of the tau lepton offer a clean probe to study the hadronization of QCD currents in its non-perturbative regime and learn about resonance dynamics, which drives strong interactions in these processes. In this theory outlook, I will use the simplest non-trivial di-pion tau decays to illustrate briefly recent theoretical progress on these analyses and their comparison to data. © 2015 Elsevier B.V.


Guzman P.,Research Center Estudios Avanzados
Plant Science | Year: 2014

Major components of the ubiquitin proteasome system are the enzymes that operate on the transfer of ubiquitin to selected target substrate, known as ubiquitin ligases. The RING finger is a domain that is present in key classes of ubiquitin ligases. This domain coordinates the interaction with a suitable E2 conjugase and the transfer of ubiquitin from the E2 to protein targets. Additional domains coupled to the same polypeptide are important for modulating the function of these ubiquitin ligases. Plants contain several types of E3 ubiquitin ligases that in many cases have expanded as multigene families. Some families are specific to the plant lineage, whereas others may have a common ancestor among plants and other eukaryotic lineages. Arabidopsis Tóxicos en Levadura (ATLs) and BCA2 zinc finger ATLs (BTLs) are two families of ubiquitin ligases that share some common structural features. These are intronless genes that encode a highly related RING finger domain, and yet during evolutionary history, their mode of gene expansion and function is rather different. In each of these two families, the co-occurrence of transmembrane helices or C2/C2 (BZF finger) domains with a selected variation on the RING finger has been subjected to strong selection pressure in order to preserve their unique domain architectures during evolution. © 2013 Elsevier Ireland Ltd.


Lopez Castro G.,Research Center Estudios Avanzados | Quintero N.,Research Center Estudios Avanzados
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Searches of lepton-number violation in different processes are very useful to constrain the parameter space of Majorana neutrinos. Here we use available upper bounds on the branching fractions of B -→D0π+μ-μ- and D0→(π-π-/K-π-) μ-μ- decays to derive constraints on the mass and mixings of Majorana neutrinos by assuming they are produced resonantly in these four-body decays. While the excluded region obtained from B- decays are competitive with existing limits from three-body D- and B - decays, it is shown that experimental improvements on D0 decays offer a good potential to provide similar results. © 2013 American Physical Society.


Quintero N.,Research Center Estudios Avanzados
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We study lepton-number-violating (LNV) decays of heavy flavors (τ lepton and top quark) induced by a doubly-charged Higgs boson in the Higgs triplet model. It is found that the branching fractions of LNV τ-→ℓ+M1-M2- decays are highly suppressed compared with the current experimental limits. On the other hand, for LNV top-quark decays, the most optimistic branching ratios for t→bℓ +ℓ+W- turn out to be at the level of ∼10-7-10-8. The observation of these rare top-quark decays would be a clear signal of LNV processes, and their nonobservation would allow us to constrain the parameters of the Higgs triplet model. © 2013 American Physical Society.


Hernandez-Como N.,Research Center Estudios Avanzados | Morales-Acevedo A.,Research Center Estudios Avanzados
Solar Energy Materials and Solar Cells | Year: 2010

Mono- and poly-crystalline silicon solar cell modules currently represent between 80% and 90% of the PV world market. The reasons are the stability, robustness and reliability of this kind of solar cells as compared to those of emerging technologies. Then, in the mid-term, silicon solar cells will continue playing an important role for their massive terrestrial application. One important approach is the development of silicon solar cells processed at low temperatures (less than 300 °C) by depositing amorphous silicon layers with the purpose of passivating the silicon surface, and avoiding the degradation suffered by silicon when processed at temperatures above 800 °C. This kind of solar cells is known as HIT cells (hetero-junction with an intrinsic thin amorphous layer) and are already produced commercially (Sanyo Ltd.), reaching efficiencies above 20%. In this work, HIT solar cells are simulated by means of AMPS-1D, which is a program developed at Pennsylvania State University. We shall discuss the modifications required by AMPS-1D for simulating this kind of structures since this program explicitly does not take into account interfaces with high interfacial density of states as occurs at amorphous-crystalline silicon hetero-junctions. © 2009 Elsevier B.V. All rights reserved.


Guzman P.,Research Center Estudios Avanzados
Plant Signaling and Behavior | Year: 2012

An abundant class of E3 ubiquitin ligases encodes the RING-finger domain. The RING finger binds to the E2 ubiquitin-conjugating enzyme and brings together both the E2 and substrate. It is predicted that 477 RING finger E3 ligases exist in Arabidopsis thaliana. A particular family among them, named Arabidopsis Tóxicos en Levadura (ATL), consists of 91 members that contain the RING-H2 variation and a hydrophobic domain located at the N-terminal end. Transmembrane E3 ligases are important in several biological processes. For instance, some transmembrane RING finger E3 ligases are main participants in the endoplasmic reticulum-associated degradation pathway that targets misfolded proteins. Functional analysis of a number of ATLs has shown that some of them regulate distinct pathways in plants. Several ATLs have been shown to participate in defense responses, while others play a role in the regulation of the carbon/nitrogen response during post-germinative seedling growth transition, in the regulation of cell death during root development, in endosperm development, or in the transition to flowering under short day conditions. The ATL family has also been instrumental in evolution studies for showing how gene families are expanded in plant genomes. © 2012 Landes Bioscience.


Pacheco-Vazquez F.,Research Center Estudios Avanzados | Ruiz-Suarez J.C.,Research Center Estudios Avanzados
Nature Communications | Year: 2010

An object moving in a fluid experiences a drag force that depends on its velocity, shape and the properties of the medium. From this simplest case to the motion of a flock of birds or a school of fish, the drag forces and the hydrodynamic interactions determine the full dynamics of the system. Similar drag forces appear when a single projectile impacts and moves through a granular medium, and this case is well studied in the literature. On the other hand, the case in which a group of intruders impact a granular material has never been considered. Here, we study the simultaneous penetration of several intruders in a very low-density granular medium. We find that the intruders move through it in a collective way, following a cooperative dynamics, whose complexity resembles flocking phenomena in living systems or the movement of reptiles in sand, wherein changes in drag are exploited to efficiently move or propel. © 2010 Macmillan Publishers Limited. All rights reserved.


Manko V.S.,Research Center Estudios Avanzados
Progress of Theoretical Physics | Year: 2012

The physical properties of the Tomimatsu-Sato δ = 2 spacetime are analyzed, with emphasis on the issues of the negative mass distribution in this spacetime and the origin of a massless ring singularity. As a by-product of this analysis it is proved analytically that the Kerr spacetime with negative mass always has a massless naked ring singularity off the symmetry axis accompanied by a region with closed timelike curves.


Oliva-Aviles A.I.,Research Center Estudios Avanzados | Aviles F.,Research Center Cientifica Of Yucatan | Sosa V.,Research Center Estudios Avanzados
Carbon | Year: 2011

Aligned multi-walled carbon nanotube (MWCNT)/polymer composite films are prepared by solution casting in the presence of an alternating electric field. Application of 7 kV/m at a frequency of 60 Hz to the polymer composite melt induces MWCNT alignment in the direction of the applied field, which is maintained after polymer crystallization. The electrical conductivity and piezoresistive response of electric-field-aligned and randomly oriented 0.1-0.75 wt% MWCNT/polysulfone films are evaluated. Electrical conductivity is 3-5 orders of magnitude higher for composites with electric-field-aligned MWCNTs than for randomly oriented composites. MWCNT alignment inside the polymer matrix also increases the film piezoresistive sensitivity, enhancing the strain sensing capabilities of the composite film. © 2011 Elsevier Ltd. All rights reserved.

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