2,361 research outputs found
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 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 are scattered by the mirror and redistributed
among the produced pairs of particles, we use a more powerful approach based on
the value of which is conditional to the detection of a given
particle on . 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 , 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
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