307 research outputs found
Feature-based interference from unattended visual field during attentional tracking in younger and older adults
The ability to attend to multiple objects that move in the visual field is
important for many aspects of daily functioning. The attentional capacity for
such dynamic tracking, however, is highly limited and undergoes age-related
decline. Several aspects of the tracking process can influence performance.
Here, we investigated effects of feature-based interference from distractor
objects that appear in unattended regions of the visual field with a
hemifield-tracking task. Younger and older participants performed an
attentional tracking task in one hemifield while distractor objects were
concurrently presented in the unattended hemifield. Feature similarity between
objects in the attended and unattended hemifields as well as motion speed and
the number of to-be-tracked objects were parametrically manipulated. The
results show that increasing feature overlap leads to greater interference
from the unattended visual field. This effect of feature-based interference
was only present in the slow speed condition, indicating that the interference
is mainly modulated by perceptual demands. High-performing older adults showed
a similar interference effect as younger adults, whereas low-performing adults
showed poor tracking performance overall
The semi-presidential system of Cape Verde: the relationship between the executive and the legislative powers = O sistema semi-presidencialista caboverdiano: a relação entre os poderes executivo e legislativo
e article analyses the relationship established between the executive
and legislative powers in the Cape Verdean government system
where researchers seek to understand it, taking into account their theoretical
and constitutional setting practice. It should be noted the prominence
of the debate and studies undertaken to understand how the scienti c
academy seeks to eradicate this problem. Two issues are relevant in this
debate: the rst reporting to the theoretical and constitutional con guration
of Cape Verdean government system and the other to its policy and
legislative practice.
Keywords: Cape Verde. Semi-presidential System. Systems of Government.
Legislative and Executive Powers.O artigo procura analisar a relação que se estabelece entre o poder
executivo e legislativo no sistema de governo cabo-verdiano, onde Investigadores
buscam compreendê-lo, tendo em conta a sua con guração
prática, teórica e constitucional. Há que realçar a proeminência do debate
e dos estudos realizados no sentido de compreender como é que a academia
cientí ca procura debelar esta problemática. Duas questões são
pertinentes neste debate: a primeira refere-se à con guração teórico-constitucional
do sistema de governo cabo-verdiano e a outra à prática política
e legislativa.
Palavras-chave: Cabo Verde. Sistema Semi-presidencialista. Sistemas de Governo.
Poder legislativo e Poder Executivo
Flux of Atmospheric Neutrinos
Atmospheric neutrinos produced by cosmic-ray interactions in the atmosphere
are of interest for several reasons. As a beam for studies of neutrino
oscillations they cover a range of parameter space hitherto unexplored by
accelerator neutrino beams. The atmospheric neutrinos also constitute an
important background and calibration beam for neutrino astronomy and for the
search for proton decay and other rare processes. Here we review the literature
on calculations of atmospheric neutrinos over the full range of energy, but
with particular attention to the aspects important for neutrino oscillations.
Our goal is to assess how well the properties of atmospheric neutrinos are
known at present.Comment: 68 pages, 26 figures. With permission from the Annual Review of
Nuclear & Particle Science. Final version of this material is scheduled to
appear in the Annual Review of Nuclear & Particle Science Vol. 52, to be
published in December 2002 by Annual Reviews (http://annualreviews.org
Anomalous magneto-oscillations in two-dimensional systems
The frequencies of Shubnikov-de Haas oscillations have long been used to
measure the unequal population of spin-split two-dimensional subbands in
inversion asymmetric systems. We report self-consistent numerical calculations
and experimental results which indicate that these oscillations are not simply
related to the zero-magnetic-field spin-subband densities.Comment: 4 pages, 3 figures; changed content (clarifications
Theory of Incompressible States in a Narrow Channel
We report on the properties of a system of interacting electrons in a narrow
channel in the quantum Hall effect regime. It is shown that an increase in the
strength of the Coulomb interaction causes abrupt changes in the width of the
charge-density profile of translationally invariant states. We derive a phase
diagram which includes many of the stable odd-denominator states as well as a
novel fractional quantum Hall state at lowest half-filled Landau level. The
collective mode evaluated at the half-filled case is strikingly similar to that
for an odd-denominator fractional quantum Hall state.Comment: 4 pages, REVTEX, and 4 .ps file
A Fermi Fluid Description of the Half-Filled Landau Level
We present a many-body approach to calculate the ground state properties of a
system of electrons in a half-filled Landau level. Our starting point is a
simplified version of the recently proposed trial wave function where one
includes the antisymmetrization operator to the bosonic Laughlin state. Using
the classical plasma analogy, we calculate the pair-correlation function, the
static structure function and the ground state energy in the thermodynamic
limit. These results are in good agreement with the expected behavior at
.Comment: 4 pages, REVTEX, and 4 .ps file
Spectral Properties of Three Dimensional Layered Quantum Hall Systems
We investigate the spectral statistics of a network model for a three
dimensional layered quantum Hall system numerically. The scaling of the
quantity is used to determine the critical exponent for
several interlayer coupling strengths. Furthermore, we determine the level
spacing distribution as well as the spectral compressibility at
criticality. We show that the tail of decays as with
and also numerically verify the equation
, where is the correlation dimension and the
spatial dimension.Comment: 4 pages, 5 figures submitted to J. Phys. Soc. Jp
Stationary Metrics and Optical Zermelo-Randers-Finsler Geometry
We consider a triality between the Zermelo navigation problem, the geodesic
flow on a Finslerian geometry of Randers type, and spacetimes in one dimension
higher admitting a timelike conformal Killing vector field. From the latter
viewpoint, the data of the Zermelo problem are encoded in a (conformally)
Painleve-Gullstrand form of the spacetime metric, whereas the data of the
Randers problem are encoded in a stationary generalisation of the usual optical
metric. We discuss how the spacetime viewpoint gives a simple and physical
perspective on various issues, including how Finsler geometries with constant
flag curvature always map to conformally flat spacetimes and that the Finsler
condition maps to either a causality condition or it breaks down at an
ergo-surface in the spacetime picture. The gauge equivalence in this network of
relations is considered as well as the connection to analogue models and the
viewpoint of magnetic flows. We provide a variety of examples.Comment: 37 pages, 6 figure
Electron Correlations in Partially Filled Lowest and Excited Landau Levels
The electron correlations near the half-filling of the lowest and excited
Landau levels (LL's) are studied using numerical diagonalization. It is shown
that in the low lying states electrons avoid pair states with relative angular
momenta corresponding to positive anharmonicity of the interaction
pseudopotential . In the lowest LL, the super-harmonic behavior of
causes Laughlin correlations (avoiding pairs with )
and the Laughlin-Jain series of incompressible ground states. In the first
excited LL, is harmonic at short range and a different series of
incompressible states results. Similar correlations occur in the paired
Moore-Read state and in the and
states, all having small total parentage from and 3 and large
parentage from . The and states are
different from Laughlin and states and, in finite
systems, occur at a different LL degeneracy (flux). The series of Laughlin
correlated states of electron pairs at ,
, , and is proposed, although only in the
state pairing has been confirmed numerically. In the second
excited LL, is sub-harmonic at short range and (near the
half-filling) the electrons group into spatially separated larger
droplets to minimize the number of strongly repulsive pair states at and 5.Comment: 10 pages, 8 figures, submitted to PR
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