Critical Lines and Massive Phases in Quantum Spin Ladders with Dimerization

We determine the existence of critical lines in dimerized quantum spin ladders in their phase diagram of coupling constants using the finite-size DMRG algorithm. We consider both staggered and columnar dimerization patterns, and antiferromagnetic and ferromagnetic inter-leg couplings. The existence of critical phases depends on the precise combination of these patterns. The nature of the massive phases separating the critical lines are characterized with generalized string order parameters that determine their valence bond solid (VBS) content.Comment: 9 pages 10 figure

Enhanced Inflation in the Dirac-Born-Infeld framework

We consider the Einstein equations within the DBI scenario for a spatially flat Friedmann-Robertson-Walker (FRW) spacetime without a cosmological constant. We derive the inflationary scenario by applying the symmetry transformations which preserve the form of the Friedmann and conservation equations. These form invariance transformations generate a symmetry group parametrized by the Lorentz factor \ga. We explicitly obtain an inflationary scenario by the cooperative effect of adding energy density into the Friedmann equation. For the case of a constant Lorentz factor, and under the slow roll assumption, we find the transformation rules for the scalar and tensor power spectra of perturbations as well as their ratio under the action of the form invariance symmetry group. Within this case and due to its relevance for the inflationary paradigm, we find the general solution of the dynamical equations for a DBI field driven by an exponential potential and show a broad set of inflationary solutions. The general solution can be split into three subsets and all these behave asymptotically as a power law solution at early and at late times.Comment: 9 pages, revtex 4.

A novel familial mutation in the PCSK1 gene that alters the oxyanion hole residue of proprotein convertase 1/3 and impairs its enzymatic activity.

Four siblings presented with congenital diarrhea and various endocrinopathies. Exome sequencing and homozygosity mapping identified five regions, comprising 337 protein-coding genes that were shared by three affected siblings. Exome sequencing identified a novel homozygous N309K mutation in the proprotein convertase subtilisin/kexin type 1 (PCSK1) gene, encoding the neuroendocrine convertase 1 precursor (PC1/3) which was recently reported as a cause of Congenital Diarrhea Disorder (CDD). The PCSK1 mutation affected the oxyanion hole transition state-stabilizing amino acid within the active site, which is critical for appropriate proprotein maturation and enzyme activity. Unexpectedly, the N309K mutant protein exhibited normal, though slowed, prodomain removal and was secreted from both HEK293 and Neuro2A cells. However, the secreted enzyme showed no catalytic activity, and was not processed into the 66 kDa form. We conclude that the N309K enzyme is able to cleave its own propeptide but is catalytically inert against in trans substrates, and that this variant accounts for the enteric and systemic endocrinopathies seen in this large consanguineous kindred

Monopoles, noncommutative gauge theories in the BPS limit and some simple gauge groups

For three conspicuous gauge groups, namely, SU(2), SU(3) and SO(5), and at first order in the noncommutative parameter matrix h\theta^{\mu\nu}, we construct smooth monopole --and, some two-monopole-- fields that solve the noncommutative Yang-Mills-Higgs equations in the BPS limit and that are formal power series in h\theta^{\mu\nu}. We show that there exist noncommutative BPS (multi-)monopole field configurations that are formal power series in h\theta^{\mu\nu} if, and only if, two a priori free parameters of the Seiberg-Witten map take very specific values. These parameters, that are not associated to field redefinitions nor to gauge transformations, have thus values that give rise to sharp physical effects.Comment: 30 pages, no figure

Brown Dwarfs in the Pleiades Cluster Confirmed by the Lithium Test

We present 10 m Keck spectra of the two Pleiades brown dwarfs Teide 1 and Calar 3 showing a clear detection of the 670.8 nm Li resonance line. In Teide 1, we have also obtained evidence for the presence of the subordinate line at 812.6 nm. A high Li abundance (log N(Li) >= 2.5), consistent with little if any depletion, is inferred from the observed lines. Since Pleiades brown dwarfs are unable to burn Li the significant preservation of this fragile element confirms the substellar nature of our two objects. Regardless of their age, their low luminosities and Li content place Teide 1 and Calar 3 comfortably in the genuine brown dwarf realm. Given the probable age of the Pleiades cluster, their masses are estimated at 55 +- 15 Jupiter masses.Comment: 14 pages gzipped and uuencoded. Figures are included. Also available at http://www.iac.es/. Accepted for publication in ApJ Letter

Synthesis of a new chiral bis-arsine ligand based on natural carbohydrates

Transition-metal-catalyzed asymmetric allylic substitutions have become one of the most powerful tools for asymmetric C−C bond formation.1 Chiral diphosphine ligands have been some of the largest classes of ligands used in asymmetric substitutions. Trost developed the chiral ligand, which played a crucial role in the improvement of Pdcatalyzed asymmetric substitutions.2 Based on the Trost modular ligand (TML) system 3 a family of ligands has been prepared. We recently reported the synthesis and application of the novel chiral bis-arsine ligand 2 derived from TML.http://blucherproceedings.com.br/articles/details/2323Fil: Parajón Puenzoa, Sol C. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Orgánica; Argentina.Fil: Parajón Puenzoa, Sol C. Universidad Nacional de Córdoba. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina.Fil: Parajón Puenzoa, Sol C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil: Parajón Puenzoa, Sol C. Universidad de Buenos Aires. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Hidratos de Carbonos; Argentina.Fil: Arata Badano, Joaquín. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Orgánica; Argentina.Fil: Arata Badano, Joaquín. Universidad Nacional de Córdoba. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina.Fil: Lopez Vidal, Martin G. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Orgánica; Argentina.Fil: Lopez Vidal, Martin G. Universidad Nacional de Córdoba. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina.Fil: Varela, Oscar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil: Varela, Oscar. Universidad de Buenos Aires. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Hidratos de Carbonos; Argentina.Fil: Martín, Sandra E. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Orgánica; Argentina.Fil: Martín, Sandra E. Universidad Nacional de Córdoba. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina.Química Orgánic

An L-type substellar object in Orion: reaching the mass boundary between brown dwarfs and giant planets

We present J-band photometry and low-resolution optical spectroscopy (600-1000 nm) for one of the faintest substellar member candidates in the young sigma Ori cluster, SOri 47 (I=20.53, Bejar et al. 1999). Its very red (I-J)=3.3+/-0.1 color and its optical spectrum allow us to classify SOri 47 as an L1.5-type object which fits the low-luminosity end of the cluster photometric and spectroscopic sequences. It also displays atmospheric features indicative of low gravity such as weak alkaline lines and hydride and oxide bands, consistent with the expectation for a very young object still undergoing gravitational collapse. Our data lead us to conclude that SOri 47 is a true substellar member of the sigma Ori cluster. Additionally, we present the detection of LiI in its atmosphere which provides an independent confirmation of youth and substellarity. Using current theoretical evolutionary tracks and adopting an age interval of 1-5 Myr for the sigma Ori cluster, we estimate the mass of SOri 47 at 0.015+/-0.005 Msun, i.e. at the minimum mass for deuterium burning, which has been proposed as a definition for the boundary between brown dwarfs and giant planets. SOri 47 could well be the result of a natural extension of the process of cloud fragmentation down to the deuterium burning mass limit; a less likely alternative is that it has originated from a protoplanetary disc around a more massive cluster member and later ejected from its orbit due to interacting effects within this rather sparse (~12 objects/pc^3) young cluster.Comment: 9 pages, 3 figures, accepted for publication in ApJ Letter

Flux flow resistivity and vortex viscosity of high-Tc films

The flux flow regime of high-T$_{\rm c}$ samples of different normal state resistivities is studied in the temperature range where the sign of the Hall effect is reversed. The scaling of the vortex viscosity with normal state resistivity is consistent with the Bardeen-Stephen theory. Estimates of the influence of possible mechanisms suggested for the sign reversal of the Hall effect are also given.Comment: 3 pages. 4 figures upon reques

Uniformly Accelerated Mirrors. Part 2: Quantum Correlations

We study the correlations between the particles emitted by a moving mirror. To this end, we first analyze $$, the two-point function of the stress tensor of the radiation field. In this we generalize the work undertaken by Carlitz and Willey. To further analyze how the vacuum correlations on $I^-$ are scattered by the mirror and redistributed among the produced pairs of particles, we use a more powerful approach based on the value of $T_{\mu\nu}$ which is conditional to the detection of a given particle on $I^+$. We apply both methods to the fluxes emitted by a uniformly accelerated mirror. This case is particularly interesting because of its strong interferences which lead to a vanishing flux, and because of its divergences which are due to the infinite blue shift effects associated with the horizons. Using the conditional value of $T_{\mu\nu}$, we reveal the existence of correlations between created particles and their partners in a domain where the mean fluxes and the two-point function vanish. This demonstrates that the scattering by an accelerated mirror leads to a steady conversion of vacuum fluctuations into pairs of quanta. Finally, we study the scattering by two uniformly accelerated mirrors which follow symmetrical trajectories (i.e. which possess the same horizons). When using the Davies-Fulling model, the Bogoliubov coefficients encoding pair creation vanish because of perfectly destructive interferences. When using regularized amplitudes, these interferences are inevitably lost thereby giving rise to pair creation.Comment: 30 pages, 9 postscript figure

A test of the biogenicity criteria established for microfossils and stromatolites on quaternary tufa and speleothem materials formed in the “Twilight zone” at Caerwys, UK

© 2015, Mary Ann Liebert, Inc. The ability to distinguish the features of a chemical sedimentary rock that can only be attributed to biology is a challenge relevant to both geobiology and astrobiology. This study aimed to test criteria for recognizing petrographically the biogenicity of microbially influenced fabrics and fossil microbes in complex Quaternary stalactitic carbonate rocks from Caerwys, UK. We found that the presence of carbonaceous microfossils, fabrics produced by the calcification of microbial filaments, and the asymmetrical development of tufa fabrics due to the more rapid growth of microbially influenced laminations could be recognized as biogenic features. Petrographic evidence also indicates that the development of "speleothem-like" laminae was related to episodes of growth interrupted by intervals of nondeposition and erosion. The lack of any biogenic characteristics in these laminae is consistent with their development as a result of variation in the physicochemical parameters that drive calcite precipitation from meteoric waters in such environmental settings