19,183 research outputs found
Kinks and waterfalls as signatures of competing order in angle-resolved photoemission spectra of La_{2-x}Sr_xCuO_4
We show that the so-called kinks and waterfalls observed in angle-resolved
photoemission spectra of La2-xSrxCuO4, a prototypical high-Tc superconducting
cuprate, result from the coupling of quasiparticles with two distinct nearly
critical collective modes with finite characteristic wave vectors, typical of
charge and spin fluctuations near a stripe instability. Both phonon-like charge
and spin collective modes are needed to account for the kinked quasiparticle
dispersions. This clarifies the long-standing question whether kinks are due to
phonons or spin waves and the nature of the bosonic mediators of the
electron-electron effective interaction in La2-xSrxCuO4.Comment: 5 pages, 4 figure
New Damped Lyα Metallicities from Echellette Spectrograph and Imager Spectroscopy of Five Palomar Sky Survey Quasars
This paper presents chemical abundance measurements for 12 new z > 3 damped Lyα systems discovered toward five quasars from the Palomar Sky Survey. We determine H I column densities from profile fits to the observed damped Lyα profiles and measure ionic column densities and limits for all observed metal line transitions. This data set, acquired with the Echellette Spectrograph and Imager on the Keck II telescope, adds to the rapidly growing database of damped Lyα abundances. It will impact studies of chemical evolution in the early universe and help identify candidates for detailed follow-up observations with echelle spectrographs. We report the discovery of the first quasar sight line with four cosmologically distinct damped Lyα systems
New Damped Lya Metallicities from ESI Spectroscopy of Five Palomar Sky Survey Quasars
This paper presents chemical abundance measurements for 12 new z>3 damped Lya
systems discovered toward five quasars from the Palomar Sky Survey. We
determine HI column densities from profile fits to the observed damped Lya
profiles and measure ionic column densities and limits for all observed
metal-line transitions. This dataset, acquired with the Echellette Spectrograph
and Imager on the KeckII telescope, adds to the rapidly growing database of
damped Lya abundances. It will impact studies of chemical evolution in the
early universe and help identify candidates for detailed follow-up observations
with echelle spectrographs. We report the discovery of the first quasar
sightline with four cosmologically distinct damped Lya systems.Comment: 14 pages, 20 figures. Accepted to ApJS, May 9, 200
Fermion localization on branes with generalized dynamics
In this letter we consider a specific model of braneworld with nonstandard
dynamics diffused in the literature, specifically we focus our attention on the
matter energy density, the energy of system, the Ricci scalar and the thin
brane limit. As the model is classically stable and capable of localize
gravity, as a natural extension we address the issue of fermion localization of
fermions on a thick brane constructed out from one scalar field with
nonstandard kinetic terms coupled with gravity. The contribution of the
nonstandard kinetic terms in the problem of fermion localization is analyzed.
It is found that the simplest Yukawa coupling support
the localization of fermions on the thick brane. It is shown that the zero mode
for left-handed can be localized on the thick brane depending on the values for
the coupling constant .Comment: 6 pages, 3 figure
Nonholonomic Ricci Flows: II. Evolution Equations and Dynamics
This is the second paper in a series of works devoted to nonholonomic Ricci
flows. By imposing non-integrable (nonholonomic) constraints on the Ricci flows
of Riemannian metrics we can model mutual transforms of generalized
Finsler-Lagrange and Riemann geometries. We verify some assertions made in the
first partner paper and develop a formal scheme in which the geometric
constructions with Ricci flow evolution are elaborated for canonical nonlinear
and linear connection structures. This scheme is applied to a study of
Hamilton's Ricci flows on nonholonomic manifolds and related Einstein spaces
and Ricci solitons. The nonholonomic evolution equations are derived from
Perelman's functionals which are redefined in such a form that can be adapted
to the nonlinear connection structure. Next, the statistical analogy for
nonholonomic Ricci flows is formulated and the corresponding thermodynamical
expressions are found for compact configurations. Finally, we analyze two
physical applications: the nonholonomic Ricci flows associated to evolution
models for solitonic pp-wave solutions of Einstein equations, and compute the
Perelman's entropy for regular Lagrange and analogous gravitational systems.Comment: v2 41 pages, latex2e, 11pt, the variant accepted by J. Math. Phys.
with former section 2 eliminated, a new section 5 with applications in
gravity and geometric mechanics, and modified introduction, conclusion and
new reference
Superconductivity, Josephson coupling and order parameter symmetry in striped cuprates
We consider a renormalization group study of the problem of coupled stripes
of holes in cuprates. We use a model of a mesh of horizontal and vertical
stripes and study the problemof superconductivity via the Josephson coupling.
We discuss the evolution of the Fermi surface with doping and temperature, the
existence of Luttinger and/or Fermi liquid behavior, the presence of pre-formed
Cooper pairs and the symmetry and magnitude of the superconducting order
parameter.Comment: final version published on Phys.Rev.Lett. 80, 4040 (1998
Robust nonparametric detection of objects in noisy images
We propose a novel statistical hypothesis testing method for detection of
objects in noisy images. The method uses results from percolation theory and
random graph theory. We present an algorithm that allows to detect objects of
unknown shapes in the presence of nonparametric noise of unknown level and of
unknown distribution. No boundary shape constraints are imposed on the object,
only a weak bulk condition for the object's interior is required. The algorithm
has linear complexity and exponential accuracy and is appropriate for real-time
systems. In this paper, we develop further the mathematical formalism of our
method and explore important connections to the mathematical theory of
percolation and statistical physics. We prove results on consistency and
algorithmic complexity of our testing procedure. In addition, we address not
only an asymptotic behavior of the method, but also a finite sample performance
of our test.Comment: This paper initially appeared in 2010 as EURANDOM Report 2010-049.
Link to the abstract at EURANDOM repository:
http://www.eurandom.tue.nl/reports/2010/049-abstract.pdf Link to the paper at
EURANDOM repository: http://www.eurandom.tue.nl/reports/2010/049-report.pd
Applications of quantum integrable systems
We present two applications of quantum integrable systems. First, we predict
that it is possible to generate high harmonics from solid state devices by
demostrating that the emission spectrum for a minimally coupled laser field of
frequency to an impurity system of a quantum wire, contains multiples
of the incoming frequency. Second, evaluating expressions for the conductance
in the high temperature regime we show that the caracteristic filling fractions
of the Jain sequence, which occur in the fractional quantum Hall effect, can be
obtained from quantum wires which are described by minimal affine Toda field
theories.Comment: 25 pages of LaTex, 4 figures, based on talk at the 6-th international
workshop on conformal field theories and integrable models, (Chernogolovka,
September 2002
Avaliação da fertilidade a campo de sêmen bubalino congelado com antioxidantes: resultados preliminares para inseminação artificial em tempo fixo.
A avaliação da fertilidade a campo de sêmen congelado com antioxidantes foi realizada através do uso da IATF. Foram utilizadas 23 fêmeas cÃclicas das raças Murrah e Mediterrâneo, com idade e peso médio de (4,87 ± 2,60 anos e 528,5 ± 113,4 kg), divididas em dois grupos (CONT, n=13 e VIT/PENTOX, n=10), sincronizadas com protocolo Ovsynch e inseminadas seguindo o mesmo procedimento de descongelação seminal para ambos os grupos. O Grupo CONT foi inseminado com sêmen congelado à base de diluidor TES-TRIS e para o Grupo VIT/PENTOX foi utilizado sêmen criopreservado com diluidor TES-TRIS associado aos antioxidantes (vitamina C: 2,5 mM; pentoxifilina: 3,5 mM). O diagnóstico de gestação foi realizado por ultrassonografia, 56 dias após a IATF. Para a comparação das taxas de concepção foi utilizado o teste binomial (P<0,05). Não houve diferença significativa na taxa de concepção (38,5% e 30,0%) entre os Grupos CONT e VIT/PENTOX, respectivamente. O uso de antioxidante no sêmen congelado não foi suficiente para elevar as taxas reprodutivas, visto que as taxas de concepção entre os grupos não diferiram.PIBIC-2011
Age-Metallicity Relation of the Universe in Neutral Gas: The First 100 Damped Lyα Systems
We discuss accurate metallicity measurements for 125 damped Lyα (DLA) systems at 0.5 < z < 5, including ≈50 new measurements from our recently published Echellette Spectrograph and Imager surveys. This data set is analyzed to determine the age-metallicity relation of neutral gas in the universe. Contrary to previous analyses, this sample shows statistically significant evolution in the cosmic mean metallicity. The best linear fit for metallicity evolution is -0.26 ± 0.07 dex per unit redshift. The DLA systems continue to maintain a floor in metallicity of ≈1/700 solar, independent of observational effects. This metallicity threshold limits the prevalence of primordial gas in high-redshift galaxies and stresses the correspondence between damped systems and star formation. Finally, we comment on an apparent "missing metals problem:" the mean metallicity of the damped systems is ≈10 times lower than the value expected from their inferred star formation history. This problem is evident in current theoretical treatments of galaxy formation and may indicate a serious flaw in our understanding of the interplay between star formation and metal enrichment
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