5,527 research outputs found
High-resolution radio imaging of two luminous quasars beyond redshift 4.5
Context. Radio-loud active galactic nuclei in the early Universe are rare.
The quasars J0906+6930 at redshift z=5.47 and J2102+6015 at z=4.57 stand out
from the known sample with their compact emission on milliarcsecond (mas)
angular scale with high (0.1-Jy level) flux densities measured at GHz radio
frequencies. This makes them ideal targets for very long baseline
interferometry (VLBI) observations. Aims. By means of VLBI imaging we can
reveal the inner radio structure of quasars and model their brightness
distribution to better understand the geometry of the jet and the physics of
the sources. Methods. We present sensitive high-resolution VLBI images of
J0906+6930 and J2102+6015 at two observing frequencies, 2.3 and 8.6 GHz. The
data were taken in an astrometric observing programme involving a global
five-element radio telescope array. We combined the data from five different
epochs from 2017 February to August. Results. For one of the highest redshift
blazars known, J0906+6930, we present the first-ever VLBI image obtained at a
frequency below 8 GHz. Based on our images at 2.3 and 8.6 GHz, we confirm that
this source has a sharply bent helical inner jet structure within ~3 mas from
the core. The quasar J2102+6015 shows an elongated radio structure in the
east-west direction within the innermost ~2 mas that can be described with a
symmetric three-component brightness distribution model at 8.6 GHz. Because of
their non-pointlike mas-scale structure, these sources are not ideal as
astrometric reference objects. Our results demonstrate that VLBI observing
programmes conducted primarily with astrometric or geodetic goals can be
utilized for astrophysical purposes as well.Comment: 8 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
Classical Tensors and Quantum Entanglement II: Mixed States
Invariant operator-valued tensor fields on Lie groups are considered. These
define classical tensor fields on Lie groups by evaluating them on a quantum
state. This particular construction, applied on the local unitary group
U(n)xU(n), may establish a method for the identification of entanglement
monotone candidates by deriving invariant functions from tensors being by
construction invariant under local unitary transformations. In particular, for
n=2, we recover the purity and a concurrence related function (Wootters 1998)
as a sum of inner products of symmetric and anti-symmetric parts of the
considered tensor fields. Moreover, we identify a distinguished entanglement
monotone candidate by using a non-linear realization of the Lie algebra of
SU(2)xSU(2). The functional dependence between the latter quantity and the
concurrence is illustrated for a subclass of mixed states parametrized by two
variables.Comment: 23 pages, 4 figure
A Note on Normal Forms of Quantum States and Separability
We study the normal form of multipartite density matrices. It is shown that
the correlation matrix (CM) separability criterion can be improved from the
normal form we obtained under filtering transformations. Based on CM criterion
the entanglement witness is further constructed in terms of local orthogonal
observables for both bipartite and multipartite systems.Comment: 8 page
Avaliação das alterações na cobertura vegetal de área no Estado do Mato Grosso do Sul entre 1990 e 2010 por meio de imagens Landsat TM.
Imagens Landsat/TM dos anos de 1990 e 2010 de área no Estado de Mato Grosso do Sul foram transformadas em imagens de reflectância e classificadas quanto à presença, ao porte e à densidade de cobertura vegetal do solo, com base nos valores calculados de NDVI e de reflectância na banda do infravermelho próximo (ρivp). Pela fusão digital das imagens classificadas de ambos os anos foi possível tipificar e quantificar as alterações ocorridas no período. Áreas da classe delimitada pelos valores de NDVI entre 0,55 e 0,75, associadas em sua maioria às pastagens, cobriam 60,2% da área de estudo em 1990 e 64,0% em 2010. As áreas da classe associada à vegetação densa com grande presença de espécies arbóreas (cerrado e matas de galeria) foram reduzidas de 31,1% para 24,5% no mesmo período, redução provocada, sobretudo, pelo aumento das áreas com pastagens. As lavouras com vegetação herbácea verde cobrindo completamente o solo na data de aquisição das imagens e algumas áreas de silvicultura foram associadas a valores de NDVI acima de 0,75 e ρivp ≥ 0,40 e totalizaram áreas equivalentes a 4,3% da área de estudo em 1990 e 2,2 % em 2010. As áreas com vegetação esparsa ou ausente compreendiam menos de 10% da área de estudo em ambos os anos, e normalmente estavam associadas a pastagens com sinais de degradação, locais destinados a lavouras, solo exposto, feições urbanas e corpos d?água
Cortes compensados para la deformación principal alpina en el borde sur oriental del Sistema Central español (Zona de Tamajón, Guadalajara)
Las estructuras alpinas principales del borde sur oriental del Sistema Central Español (zona de Tamajón) resultan ser dos cabalgamientos de dirección N70oE, con dirección de transporte hacia el SE, con retrocabalgamientos y fallas de transferencia asociadas. La dirección de transporte de
los cabalgamientos es coherente con la dirección de acortamiento horizontal de la "etapa Guadarrama" (N1500E), a la cual están asociados genéticamente. El efecto de los cabalgamientos en la cobertera mesozoica es el desarrollo de diferentes tipos de pliegues asimétricos. El acortamiento, deducido de la restauración de cortes geológicos, es de 17-19
Double collinear splitting amplitudes at next-to-leading order
We compute the next-to-leading order (NLO) QCD corrections to the 1 -> 2 splitting amplitudes in different dimensional regularization (DREG) schemes. Besides recovering previously known results, we explore new DREG schemes and analyze their consistency by comparing the divergent structure with the expected behavior predicted by Catani's formula. Through the introduction of scalar-gluons, we show the relation among splittings matrices computed using different schemes. Also, we extended this analysis to cover the double collinear limit of scattering amplitudes in the context of QCD+QED
Further results on entanglement detection and quantification from the correlation matrix criterion
The correlation matrix (CM) criterion is a recently derived powerful
sufficient condition for the presence of entanglement in bipartite quantum
states of arbitrary dimensions. It has been shown that it can be stronger than
the positive partial transpose (PPT) criterion, as well as the computable cross
norm or realignment (CCNR) criterion in different situations. However, it
remained as an open question whether there existed sets of states for which the
CM criterion could be stronger than both criteria simultaneously. Here, we give
an affirmative answer to this question by providing examples of entangled
states that scape detection by both the PPT and CCNR criteria whose
entanglement is revealed by the CM condition. We also show that the CM can be
used to measure the entanglement of pure states and obtain lower bounds for the
entanglement measure known as tangle for general (mixed) states.Comment: 13 pages, no figures; added references, minor changes; section 4.3
added, to appear in J. Phys.
Classical Tensors and Quantum Entanglement I: Pure States
The geometrical description of a Hilbert space asociated with a quantum
system considers a Hermitian tensor to describe the scalar inner product of
vectors which are now described by vector fields. The real part of this tensor
represents a flat Riemannian metric tensor while the imaginary part represents
a symplectic two-form. The immersion of classical manifolds in the complex
projective space associated with the Hilbert space allows to pull-back tensor
fields related to previous ones, via the immersion map. This makes available,
on these selected manifolds of states, methods of usual Riemannian and
symplectic geometry. Here we consider these pulled-back tensor fields when the
immersed submanifold contains separable states or entangled states. Geometrical
tensors are shown to encode some properties of these states. These results are
not unrelated with criteria already available in the literature. We explicitly
deal with some of these relations.Comment: 16 pages, 1 figure, to appear in Int. J. Geom. Meth. Mod. Phy
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