1,265 research outputs found
The role of forest genetic resources in responding to biotic and abiotic factors in the context of anthropogenic climate change
The current distribution of forest genetic resources on Earth is the result of a combination of natural processes and human actions. Over time, tree populations have become adapted to their habitats including the local ecological disturbances they face. As the planet enters a phase of human-induced climate change of unprecedented speed and magnitude, however, previously locally-adapted populations are rendered less suitable for new conditions, and ‘natural’ biotic and abiotic disturbances are taken outside their historic distribution, frequency and intensity ranges. Tree populations rely on phenotypic plasticity to survive in extant locations, on genetic adaptation to modify their local phenotypic optimum or on migration to new suitable environmental conditions. The rate of required change, however, may outpace the ability to respond, and tree species and populations may become locally extinct after specific, but as yet unknown and unquantified, tipping points are reached. Here, we review the importance of forest genetic resources as a source of evolutionary potential for adaptation to changes in climate and other ecological factors. We particularly consider climate-related responses in the context of linkages to disturbances such as pests, diseases and fire, and associated feedback loops. The importance of management strategies to conserve evolutionary potential is emphasised and recommendations for policy-makers are provided
Autonomous hybrid GPS/reactive navigation of an unmanned ground vehicle for precision viticulture-VINBOT
Yield forecasting can provide important benefits for wine industry in terms of quality and
efficiency. Vineyard yield estimation can be obtained using several methods being the most widely
used the method based on visual assessment and/or counting/weighing the yield components The
increasing importance of yield forecast has lead to automated solutions for the data acquisition and
allowed the first service robotics applications in viticulture. In this paper we aim to present the
preliminary results obtained in the European research project VinBot: “Autonomous cloudcomputing
vineyard robot to optimize yield management and wine quality”. The paper focuses in
the robot navigation. Robot navigation for agriculture has been a continuous research topic in the
last years. Even there is a wide number of RTK-DGPS and PPP based navigation solutions available
for precision farming, navigation in vineyards has some particularities and can benefit from other
navigation techniques. The high cost and in some cases other limitations as fix ratios (determined
by baseline distances to base stations), or communication limitations in the field make alternative
solutions desirable. In this paper, we present a hybrid reactive/GPS based navigation scheme tested
successfully in vineyard navigation. The proposed solution makes use of a laser range finder and
RGBD device to perform reactive row following and obstacle avoidance, while it can make use of
other reactive behaviors or GPS waypoint navigation for changing from row to row or field to field,
thus supporting different levels of automation. The paper includes also some experiences with
recently introduced new generation low-cost RTK-DGPS devices, that in the coming years will
enable the progressive introduction of viticulture robotsinfo:eu-repo/semantics/publishedVersio
Generalized Brans-Dicke theories
In Brans-Dicke theory a non-linear self interaction of a scalar field allows
a possibility of realizing the late-time cosmic acceleration, while recovering
the General Relativistic behavior at early cosmological epochs. We extend this
to more general modified gravitational theories in which a de Sitter solution
for dark energy exists without using a field potential. We derive a condition
for the stability of the de Sitter point and study the background cosmological
dynamics of such theories. We also restrict the allowed region of model
parameters from the demand for the avoidance of ghosts and instabilities. A
peculiar evolution of the field propagation speed allows us to distinguish
those theories from the LCDM model.Comment: 14 pages, 4 figures, version to appear in JCA
Tests of Modified Gravity with Dwarf Galaxies
In modified gravity theories that seek to explain cosmic acceleration, dwarf
galaxies in low density environments can be subject to enhanced forces. The
class of scalar-tensor theories, which includes f(R) gravity, predict such a
force enhancement (massive galaxies like the Milky Way can evade it through a
screening mechanism that protects the interior of the galaxy from this "fifth"
force). We study observable deviations from GR in the disks of late-type dwarf
galaxies moving under gravity. The fifth-force acts on the dark matter and HI
gas disk, but not on the stellar disk owing to the self-screening of main
sequence stars. We find four distinct observable effects in such disk galaxies:
1. A displacement of the stellar disk from the HI disk. 2. Warping of the
stellar disk along the direction of the external force. 3. Enhancement of the
rotation curve measured from the HI gas compared to that of the stellar disk.
4. Asymmetry in the rotation curve of the stellar disk. We estimate that the
spatial effects can be up to 1 kpc and the rotation velocity effects about 10
km/s in infalling dwarf galaxies. Such deviations are measurable: we expect
that with a careful analysis of a sample of nearby dwarf galaxies one can
improve astrophysical constraints on gravity theories by over three orders of
magnitude, and even solar system constraints by one order of magnitude. Thus
effective tests of gravity along the lines suggested by Hui et al (2009) and
Jain (2011) can be carried out with low-redshift galaxies, though care must be
exercised in understanding possible complications from astrophysical effects.Comment: 26 pages, 9 figure
VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic Imager
In this paper we describe in detail the implementation and main properties of
a new inversion code for the polarized radiative transfer equation (VFISV: Very
Fast inversion of the Stokes vector). VFISV will routinely analyze pipeline
data from the Helioseismic and Magnetic Imager (HMI) on-board of the Solar
Dynamics Observatory (SDO). It will provide full-disk maps (40964096
pixels) of the magnetic field vector on the Solar Photosphere every 10 minutes.
For this reason VFISV is optimized to achieve an inversion speed that will
allow it to invert 16 million pixels every 10 minutes with a modest number
(approx. 50) of CPUs. Here we focus on describing a number of important
details, simplifications and tweaks that have allowed us to significantly speed
up the inversion process. We also give details on tests performed with data
from the spectropolarimeter on-board of the Hinode spacecraft.Comment: 23 pages, 9 figures (2 color). Submitted for publication to Solar
Physic
Do we know the mass of a black hole? Mass of some cosmological black hole models
Using a cosmological black hole model proposed recently, we have calculated
the quasi-local mass of a collapsing structure within a cosmological setting
due to different definitions put forward in the last decades to see how similar
or different they are. It has been shown that the mass within the horizon
follows the familiar Brown-York behavior. It increases, however, outside the
horizon again after a short decrease, in contrast to the Schwarzschild case.
Further away, near the void, outside the collapsed region, and where the
density reaches the background minimum, all the mass definitions roughly
coincide. They differ, however, substantially far from it. Generically, we are
faced with three different Brown-York mass maxima: near the horizon, around the
void between the overdensity region and the background, and another at
cosmological distances corresponding to the cosmological horizon. While the
latter two maxima are always present, the horizon mass maxima is absent before
the onset of the central singularity.Comment: 11 pages, 8 figures, revised version, accepted in General Relativity
and Gravitatio
Whole-system metabolism and CO<sub>2</sub> fluxes in a Mediterranean Bay dominated by seagrass beds (Palma Bay, NW Mediterranean)
The relationship between whole-system metabolism estimates based on planktonic and benthic incubations (bare sediments and seagrass, Posidonia oceanica meadows), and CO2 fluxes across the air-sea interface were examined in the Bay of Palma (Mallorca, Spain) during two cruises in March and June 2002. Moreover, planktonic and benthic incubations were performed at monthly intervals from March 2001 to October 2002 in a seagrass vegetated area of the bay. From the annual study, results showed a contrast between the planktonic compartment, which was heterotrophic during most of the year, except for occasional bloom episodes, and the benthic compartment, which was slightly autotrophic. Whereas the seagrass community was autotrophic, the excess organic carbon production therein could only balance the excess respiration of the planktonic compartment in shallow waters (<10 m) relative to the maximum depth of the bay (55 m). This generated a horizontal gradient from autotrophic or balanced communities in the shallow, seagrass-covered areas of the bay, to strongly heterotrophic communities in deeper areas, consistent with the patterns of CO2 fields and fluxes across the bay observed during the two extensive cruises in 2002. Finally, dissolved inorganic carbon and oxygen budgets provided NEP estimates in fair agreement with those derived from direct metabolic estimates based on incubated samples over the Posidonia oceanica meadow
The Distinguishability of Interacting Dark Energy from Modified Gravity
We study the observational viability of coupled quintessence models with
their expansion and growth histories matched to modified gravity cosmologies.
We find that for a Dvali-Gabadadze-Porrati model which has been fitted to
observations, the matched interacting dark energy models are observationally
disfavoured. We also study the distinguishability of interacting dark energy
models matched to scalar-tensor theory cosmologies and show that it is not
always possible to find a physical interacting dark energy model which shares
their expansion and growth histories.Comment: 8 pages, 5 figure
General Axisymmetric Solutions and Self-Tuning in 6D Chiral Gauged Supergravity
We re-examine the properties of the axially-symmetric solutions to chiral
gauged 6D supergravity, recently found in refs. hep-th/0307238 and
hep-th/0308064. Ref. hep-th/0307238 finds the most general solutions having two
singularities which are maximally-symmetric in the large 4 dimensions and which
are axially-symmetric in the internal dimensions. We show that not all of these
solutions have purely conical singularities at the brane positions, and that
not all singularities can be interpreted as being the bulk geometry sourced by
neutral 3-branes. The subset of solutions for which the metric singularities
are conical precisely agree with the solutions of ref. hep-th/0308064.
Establishing this connection between the solutions of these two references
resolves a minor conflict concerning whether or not the tensions of the
resulting branes must be negative. The tensions can be both negative and
positive depending on the choice of parameters. We discuss the physical
interpretation of the non-conical solutions, including their significance for
the proposal for using 6-dimensional self-tuning to understand the small size
of the observed vacuum energy. In passing we briefly comment on a recent paper
by Garriga and Porrati which criticizes the realization of self-tuning in 6D
supergravity.Comment: 27 pages, 1 figure; JHEP3 style; Some references added, and
discussion of tension constraints and unwarped solutions made more explici
Nanocrystalline silicon optomechanical cavities
"© 2018 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited"[EN] Silicon on insulator photonics has offered a versatile platform for the recent development of integrated optomechanical circuits. However, there are some constraints such as the high cost of the wafers and limitation to a single physical device level. In the present work we investigate nanocrystalline silicon as an alternative material for optomechanical devices. In particular we demonstrate that optomechanical crystal cavities fabricated of nanocrystalline silicon have optical and mechanical properties enabling non-linear dynamical behaviour and effects such as thermo-optic/free-carrier-dispersion self-pulsing, phonon lasing and chaos, all at low input laser power and with typical frequencies as high as 0.3 GHz. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing AgreementEuropean Commission project PHENOMEN (H2020-EU-713450), MINECO Severo Ochoa Excellence program (SEV-2013-0295), MINECO (FIS2015-70862-P, RYC-2014-15392) and CERCA Programme/Generalitat de Catalunya.Navarro-Urrios, D.; Capuj, N.; Maire, J.; Colombano, M.; Jaramillo-Fernandez, J.; Chavez-Angel, E.; Martín-Rodríguez, LL.... (2018). Nanocrystalline silicon optomechanical cavities. Optics Express. 26(8):9829-9839. https://doi.org/10.1364/OE.26.009829S98299839268Kippenberg, T. J., & Vahala, K. J. (2008). 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