Atmospheric turbulence in phase-referenced and wide-field interferometric images: Application to the SKA

Phase referencing is a standard calibration procedure in radio interferometry. It allows to detect weak sources by using quasi-simultaneous observations of closeby sources acting as calibrators. Therefore, it is assumed that, for each antenna, the optical paths of the signals from both sources are similar. However, atmospheric turbulence may introduce strong differences in the optical paths of the signals and affect, or even waste, phase referencing for cases of relatively large calibrator-to-target separations and/or bad weather. The situation is similar in wide-field observations, since the random deformations of the images, mostly caused by atmospheric turbulence, have essentially the same origin as the random astrometric variations of phase-referenced sources with respect to the phase center of their calibrators. In this paper, we present the results of a Monte Carlo study of the astrometric precision and sensitivity of an interferometric array (a realization of the Square Kilometre Array, SKA) in phase-referenced and wide-field observations. These simulations can be extrapolated to other arrays by applying the corresponding corrections. We consider several effects from the turbulent atmosphere (i.e., ionosphere and wet component of the troposphere) and also from the antenna receivers. We study the changes in dynamic range and astrometric precision as a function of observing frequency, source separation, and strength of the turbulence. We find that, for frequencies between 1 and 10 GHz, it is possible to obtain images with high fidelity, although the atmosphere strongly limits the sensitivity of the instrument compared to the case with no atmosphere. Outside this frequency window, the dynamic range of the images and the accuracy of the source positions decrease. [...] (Incomplete abstract. Please read manuscript.)Comment: 9 pages, 11 figures. Accepted for publication in A&A

Comparação entre protocolos para extração de DNA total de Ricinus communis L.

bitstream/CNPA/19674/1/COMTEC252.pd

Pairing of Cooper Pairs in a Fully Frustrated Josephson Junction Chain

We study a one-dimensional Josephson junction chain embedded in a magnetic field. We show that when the magnetic flux per elementary loop equals half the superconducting flux quantum $\phi_0=h/2e$, a local \nbZ_2 symmetry arises. This symmetry is responsible for a nematic Luttinger liquid state associated to bound states of Cooper pairs. We analyze the phase diagram and we discuss some experimental possibilities to observe this exotic phase.Comment: 4 pages, 4 EPS figure

Uso de extratos de plantas aromáticas no desenvolvimento de plântulas de hortaliças.

O objetivo deste trabalho foi verificar se existe efeito positivo ou negativo de extratos aquosos de plantas aromáricas no desenvolvimento inicial de plantulas de rucula, tomate, pimenta e alface em condições de laboratório.ref. 14036. Edição dos Resumos do VIII Congresso Brasileiro de Agroecologia, Porto Alegre, nov. 2013

Optimal simulation of two-qubit Hamiltonians using general local operations

We consider the simulation of the dynamics of one nonlocal Hamiltonian by another, allowing arbitrary local resources but no entanglement nor classical communication. We characterize notions of simulation, and proceed to focus on deterministic simulation involving one copy of the system. More specifically, two otherwise isolated systems $A$ and $B$ interact by a nonlocal Hamiltonian $H \neq H_A+H_B$. We consider the achievable space of Hamiltonians $H'$ such that the evolution $e^{-iH't}$ can be simulated by the interaction $H$ interspersed with local operations. For any dimensions of $A$ and $B$, and any nonlocal Hamiltonians $H$ and $H'$, there exists a scale factor $s$ such that for all times $t$ the evolution $e^{-iH'st}$ can be simulated by $H$ acting for time $t$ interspersed with local operations. For 2-qubit Hamiltonians $H$ and $H'$, we calculate the optimal $s$ and give protocols achieving it. The optimal protocols do not require local ancillas, and can be understood geometrically in terms of a polyhedron defined by a partial order on the set of 2-qubit Hamiltonians.Comment: (1) References to related work, (2) protocol to simulate one two-qudit Hamiltonian with another, and (3) other related results added. Some proofs are simplifie

Transmission through quantum networks

We propose a simple formalism to calculate the conductance of any quantum network made of one-dimensional quantum wires. We apply this method to analyze, for two periodic systems, the modulation of this conductance with respect to the magnetic field. We also study the influence of an elastic disorder on the periodicity of the AB oscillations and we show that a recently proposed localization mechanism induced by the magnetic field resists to such a perturbation. Finally, we discuss the relevance of this approach for the understanding of a recent experiment on GaAs/GaAlAs networks.Comment: 4 pages, 5 EPS figure

Optimal estimation of two-qubit pure-state entanglement

We present optimal measuring strategies for the estimation of the entanglement of unknown two-qubit pure states and of the degree of mixing of unknown single-qubit mixed states, of which N identical copies are available. The most general measuring strategies are considered in both situations, to conclude in the first case that a local, although collective, measurement suffices to estimate entanglement, a non-local property, optimally.Comment: REVTEX, 9 pages, 1 figur

Calculation of reduced density matrices from correlation functions

It is shown that for solvable fermionic and bosonic lattice systems, the reduced density matrices can be determined from the properties of the correlation functions. This provides the simplest way to these quantities which are used in the density-matrix renormalization group method.Comment: 4 page

Probing the jet base of the blazar PKS1830-211 from the chromatic variability of its lensed images. Serendipitous ALMA observations of a strong gamma-ray flare

The launching mechanism of the jets of active galactic nuclei is observationally poorly constrained, due to the large distances to these objects and the very small scales (sub-parsec) involved. In order to better constrain theoretical models, it is especially important to get information from the region close to the physical base of the jet, where the plasma acceleration takes place. In this paper, we report multi-epoch and multi-frequency continuum observations of the z=2.5 blazar PKS1830-211 with ALMA, serendipitously coincident with a strong $\gamma$-ray flare reported by Fermi-LAT. The blazar is lensed by a foreground z=0.89 galaxy, with two bright images of the compact core separated by 1". Our ALMA observations individually resolve these two images (although not any of their substructures), and we study the change of their relative flux ratio with time (four epochs spread over nearly three times the time delay between the two lensed images) and frequency (between 350 and 1050 GHz, rest-frame of the blazar), during the $\gamma$-ray flare. In particular, we detect a remarkable frequency-dependent behaviour of the flux ratio, which implies the presence of a chromatic structure in the blazar (i.e., a core-shift effect). We rule out the possiblity of micro- and milli-lensing effects and propose instead a simple model of plasmon ejection in the blazar's jet to explain the time and frequency variability of the flux ratio. We suggest that PKS1830-211 is likely one of the best sources to probe the activity at the base of a blazar's jet at submillimeter wavelengths, thanks to the peculiar geometry of the system. The implications of the core-shift in absorption studies of the foreground z=0.89 galaxy (e.g., constraints on the cosmological variations of fundamental constants) are discussed.Comment: Accepted for publication in A&