8,151 research outputs found
El concepto de diversidad vegetal desde la etnia mapuche a la enseñanza formal en Chile
El estudio de la terminología botánica en la lengua mapuche revela la gran importancia que la diversidad vegetal ha tenido para sus tradiciones y usos. Un colectivo de estudiantes de enseñanza media de origen mapuche conserva entre sus conocimientos de biología vegetal un rico aporte de esta información etnobotánica; sin embargo estudiantes que inician estudios universitarios de ingeniería forestal y agronomía muestran un nivel de conocimiento muy inferior. La enseñanza formal chilena puede aprovechar este potencial cultural para incorporarlo en una educación científica intercultural que favorezca la protección y respeto de los ecosistemas del Chile Central gravemente amenazados por los intereses de las grandes multinacionales que explotan sus recursos naturales
The central parsecs of M87: jet emission and an elusive accretion disc
We present the first simultaneous spectral energy distribution (SED) of M87
core at a scale of 0.4 arcsec () across the electromagnetic
spectrum. Two separate, quiescent, and active states are sampled that are
characterized by a similar featureless SED of power-law form, and that are thus
remarkably different from that of a canonical active galactic nuclei (AGN) or a
radiatively inefficient accretion source. We show that the emission from a jet
gives an excellent representation of the core of M87 core covering ten orders
of magnitude in frequency for both the active and the quiescent phases. The
inferred total jet power is, however, one to two orders of magnitude lower than
the jet mechanical power reported in the literature. The maximum luminosity of
a thin accretion disc allowed by the data yields an accretion rate of , assuming 10% efficiency. This power
suffices to explain M87 radiative luminosity at the jet-frame, it is however
two to three order of magnitude below that required to account for the jet's
kinetic power. The simplest explanation is variability, which requires the core
power of M87 to have been two to three orders of magnitude higher in the last
200 yr. Alternatively, an extra source of power may derive from black hole
spin. Based on the strict upper limit on the accretion rate, such spin power
extraction requires an efficiency an order of magnitude higher than predicted
from magnetohydrodynamic simulations, currently in the few hundred per cent
range.Comment: 18 pages, 6 figures. Accepted for publication in MNRA
Searching for a dipole modulation in the large-scale structure of the Universe
Several statistical anomalies in the CMB temperature anisotropies seem to
defy the assumption of a homogeneous and isotropic universe. In particular, a
dipole modulation has been detected both in WMAP and Planck data. We adapt the
methodology proposed by Eriksen et al. (2007) on CMB data to galaxy surveys,
tracing the large-scale structure. We analyse the NRAO VLA Sky Survey (NVSS)
data at a resolution of ~2 degrees for three different flux thresholds: 2.5,
5.0 and 10.0 mJy respectively. No evidence of a dipole modulation is found.
This result suggests that the origin of the dipole asymmetry found in the CMB
cannot be assigned to secondary anisotropies produced at redshifts around z =
1. However, it could still have been generated at redshifts higher or lower,
such as the integrated Sachs-Wolfe effect produced by the local structures.
Other all-sky surveys, like the infrared WISE catalogue, could help to explore
with a high sensitivity a redshift interval closer than the one probed with
NVSS.Comment: 6 pages, 2 figures. Some minor changes have been done from the
original manuscript. This paper is accepted by MNRA
Gapless Hamiltonians for the toric code using the PEPS formalism
We study Hamiltonians which have Kitaev's toric code as a ground state, and
show how to construct a Hamiltonian which shares the ground space of the toric
code, but which has gapless excitations with a continuous spectrum in the
thermodynamic limit. Our construction is based on the framework of Projected
Entangled Pair States (PEPS), and can be applied to a large class of
two-dimensional systems to obtain gapless "uncle Hamiltonians".Comment: 8 pages, 2 figure
Charge control in laterally coupled double quantum dots
We investigate the electronic and optical properties of InAs double quantum
dots grown on GaAs (001) and laterally aligned along the [110] crystal
direction. The emission spectrum has been investigated as a function of a
lateral electric field applied along the quantum dot pair mutual axis. The
number of confined electrons can be controlled with the external bias leading
to sharp energy shifts which we use to identify the emission from neutral and
charged exciton complexes. Quantum tunnelling of these electrons is proposed to
explain the reversed ordering of the trion emission lines as compared to that
of excitons in our system.Comment: 4 pages, 4 figures submitted to PRB Rapid Com
Estimation of the reference points for the different OMs in the Cod 3M MSE
This paper presents different methods to estimate the reference points (Blim, Bmsy and Fmsy) to be used in
the 3M NAFO cod MSE. Reference points should be specific for each of the possible realities, what defines the
different possible realities are the different OMs and, within each OM, the different iterations. The methods
presented here try to estimate the reference points by iteration for the different OMs since it is assuming that
the reference points will be interpreted as a characteristic of the “real” population. The results of some of the
methods proposed to estimate the management reference points (limit and target) seem to be not consistent
between them. The results show that in this case the proxy used as Fmsy (F30%SpR) seems quite reasonable
Standardized CPUE Indices for Greenland Halibut in NAFO Regulatory Area of Divisions 3LMNO Based on Spanish Commercial Catch Rates
A standardized CPUE series using a log-linear model for Greenland halibut in NAFO Regulatory Area of
Divisions 3LMNO, based on catch and effort data from the Spanish trawl fleet since 1992 is presented. Fixed factors
considered in the model were year, month, division, depth stratum and vessel and the interactions included were
division*month and division*depth stratum. All of these factors and interactions are statistically significant. The
total proportion of variance explained by this model is 46%. The results indicate substantial variability of CPUE
over time, with several short periods of increasing and decreasing CPUE. After having reached the lowest value of
the series in 2004, standardized CPUE has increased very substantially, reaching a value in 2006 very near the
maximum of the entire series
Assessment of the Cod Stock in NAFO Division 3M
An assessment of the cod stock in NAFO Division 3M was conducted using a Bayesian SCAA (statistical catch-at-age) model. The STACFIS catch estimates and the Flemish Cap survey indices were used to fit the model. Blim, defined as the SSB of 2007, was estimated at 15 408 t (median). Results indicate a general increase in SSB since 2005 to the highest value in 2017, decreasing sharply since then. SSB has been above Blim since 2008. Between 2013 and 2018 recruitment was at very low levels; the 2016 and 2018 values were among the lowest of the series; as a consequence, 3-year projections indicate that total biomass will decrease during the projected years, while the SSB could increase under some scenarios in the final projected year. Depending on the projected scenario, probability of SSB being below Blim in 2023 and 2024 is high (≥12%) or very low (≤5%). An increase in recruitment occurred in 2019 and 2020, reaching the 2008 level.Versión del editor
- …