934 research outputs found
Second-order matter perturbations in a LambdaCDM cosmology and non-Gaussianity
We obtain exact expressions for the effect of primordial non-Gaussianity on
the matter density perturbation up to second order in a LambdaCDM cosmology,
fully accounting for the general relativistic corrections arising on scales
comparable with the Hubble radius. We present our results both in the Poisson
gauge and in the comoving and synchronous gauge, which are relevant for
comparison to different cosmological observables.Comment: 15 pages. LaTeX file. Invited article for CQG issue on non-linear
cosmolog
Pencils and Infinite Dihedral covers of P^2
In this work we study the connection between the existence of finite dihedral
covers of the projective plane ramified along an algebraic curve C, infinite
dihedral covers, and pencils of curves containing C.Comment: 1o page
Electronic structure of crystalline binary and ternary Cd-Te-O compounds
The electronic structure of crystalline CdTe, CdO, -TeO,
CdTeO and CdTeO is studied by means of first principles
calculations. The band structure, total and partial density of states, and
charge densities are presented. For -TeO and CdTeO, Density
Functional Theory within the Local Density Approximation (LDA) correctly
describes the insulating character of these compounds. In the first four
compounds, LDA underestimates the optical bandgap by roughly 1 eV. Based on
this trend, we predict an optical bandgap of 1.7 eV for CdTeO. This
material shows an isolated conduction band with a low effective mass, thus
explaining its semiconducting character observed recently. In all these oxides,
the top valence bands are formed mainly from the O 2p electrons. On the other
hand, the binding energy of the Cd 4d band, relative to the valence band
maximum, in the ternary compounds is smaller than in CdTe and CdO.Comment: 13 pages, 15 figures, 2 tables. Accepted in Phys Rev
Nodal degenerations of plane curves and Galois covers
Globally irreducible nodes (i.e. nodes whose branches belong to the same
irreducible component) have mild effects on the most common topological
invariants of an algebraic curve. In other words, adding a globally irreducible
node (simple nodal degeneration) to a curve should not change them a lot. In
this paper we study the effect of nodal degeneration of curves on fundamental
groups and show examples where simple nodal degenerations produce
non-isomorphic fundamental groups and this can be detected in an algebraic way
by means of Galois coverings.Comment: 16 pages, 3 figure
A new approach to cosmological perturbations in f(R) models
We propose an analytic procedure that allows to determine quantitatively the
deviation in the behavior of cosmological perturbations between a given f(R)
modified gravity model and a LCDM reference model. Our method allows to study
structure formation in these models from the largest scales, of the order of
the Hubble horizon, down to scales deeply inside the Hubble radius, without
employing the so-called "quasi-static" approximation. Although we restrict our
analysis here to linear perturbations, our technique is completely general and
can be extended to any perturbative order.Comment: 21 pages, 2 figures; Revised version according to reviewer's
suggestions; Typos corrected; Added Reference
Rotational dynamics of a soft filament: wrapping transition and propulsive forces
We analyze experimentally the shape of a long elastic filament rotating in a
viscous liquid. We identify a continuous but sharp transition from a straight
to an helical shape, resulting from the competition between viscous stresses
and elastic forces. This induced helicity generates a propulsive force along
the axis of rotation. In addition, we show that the shape transition is
associated with an unstable branch in the force-torque relation. A linearized
model of the fluid-structure interaction is proposed to account for all the
features of the non-linear filament dynamics
Proximal changes in signal transduction that modify CD8+ T cell responsiveness in vivo
The antigen dose conditions the functional properties of CD8+ T cells generated after priming.
At relatively low antigen doses, efficient memory T cells may be generated, while high
antigen doses lead to tolerance. To determine the mechanisms leading to such different
functional outcomes, we compared the proximal TCR signal transduction of naive cells, to
that of memory or high-dose tolerant cells generated in vivo. In vivo activation led to the constitutive
phosphorylation of CD3 4 , recruiting Zap70, in both memory and tolerant cells. In tolerant
cells, these phenomena were much more marked, the CD3 4 and ´ chains no longer
associated, and the Src kinases p56Lck and p59Fyn were inactive. Therefore, when the antigen
load overcomes the capacities of immune control, a new mechanism intervenes to block
signal transduction: the recruitment of Zap70 to CD3 4 becomes excessive, leading to TCR
complex destabilization, Src kinase dysfunction, and signal arrest
Mutation of tyrosine 492/493 in the kinase domain of ZAP-70 affects multiple T-cell receptor signaling pathways.
The protein-tyrosine kinase ZAP-70 is implicated, together with the Src kinase p56lck, in controlling the early steps of the T-cell antigen receptor (TCR) signaling cascade. To help elucidate further the mechanism by which ZAP-70 regulates these initial events, we used a dominant-negative mutant approach. We overexpressed in the Jurkat T-cell line ZAP-70 mutated on Tyr-492 and Tyr-493 in the putative regulatory loop of its kinase domain. This mutant inhibited TCR-induced activation of nuclear factor of activated T cells by interfering with both intracellular calcium increase and Ras-regulated activation of extracellular signal-regulated kinases. Moreover, TCR-induced phosphorylation of pp36-38, thought to play a role upstream of these pathways, was found to be reduced. In contrast, overexpression of wild-type ZAP-70 induced constitutive activation of nuclear factor of activated T cells. The ZAP-70 mutant studied here could be phosphorylated on tyrosine when associated to the TCR ζ chain and was able to bind p56lck. This result demonstrates that Tyr-492 and Tyr-493 are not responsible for the Src homology domain 2-mediated association of p56lck with ZAP-70. Our data are most consistent with a model in which recruitment to the TCR allows ZAP-70 autophosphorylation and binding to p56lck, which in turn phosphorylates Tyr-492 and/or Tyr-493 with consequent up-regulation of the ZAP-70 kinase activity. ZAP-70 will then be able to effectively control phosphorylation of its substrates and lead to gene activation
Coherent States for Canonical Quantum General Relativity and the Infinite Tensor Product Extension
We summarize a recently proposed concrete programme for investigating the
(semi)classical limit of canonical, Lorentzian, continuum quantum general
relativity in four spacetime dimensions. The analysis is based on a novel set
of coherent states labelled by graphs. These fit neatly together with an
Infinite Tensor Product (ITP) extension of the currently used Hilbert space.
The ITP construction enables us to give rigorous meaning to the infinite volume
(thermodynamic) limit of the theory which has been out of reach so far.Comment: 37 p., latex2e, no figure
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