21,412 research outputs found
Minimal mechanisms for vegetation patterns in semiarid regions
The minimal ecological requirements for formation of regular vegetation
patterns in semiarid systems have been recently questioned. Against the general
belief that a combination of facilitative and competitive interactions is
necessary, recent theoretical studies suggest that, under broad conditions,
nonlocal competition among plants alone may induce patterns. In this paper, we
review results along this line, presenting a series of models that yield
spatial patterns when finite-range competition is the only driving force. A
preliminary derivation of this type of model from a more detailed one that
considers water-biomass dynamics is also presented. Keywords: Vegetation
patterns, nonlocal interactionsComment: 8 pages, 4 figure
Heart Rate Extraction from Novel Neck Photoplethysmography Signals.
This paper demonstrates for the first time how heart rate (HR) can be extracted from novel neck photoplethysmography (PPG). A novel algorithm is presented, which when tested in neck PPG signals recorded from 9 subjects at different respiratory rates, obtained good precision with respect to gold standard ECG signals. Mean absolute error (MAE), standard deviation error (SDAE) and root-mean-square error (RMSE) resulted in 1.22, 1.54 and 1.98 beats per minute (BPM), respectively. HRneck estimation showed strong correlation (R=0.94) with reference HRECG. Good agreement between both techniques was also demonstrated by Bland-Altman analysis. The bias between mean HR paired differences was -0.16 BPM and 95% limits of agreement (LoA) were (-4.7, 4.4). Comparatively, for widely used finger PPG, errors were slightly smaller (MAE=0.38 BPM, SDAE=0.48 BPM, RMSE=0.62BPM) and the correlation with reference ECG was also very close to 1 (R=0.99). Bias of -0.04 BPM and 95% LoA (-1.5, 1.4), also showed high degree of agreement. However, these findings show the potential the neck could have as an alternative body location for wearable monitors, aiming to reduce the number of sensing sites whilst still providing access to a wide variety of physiological parameters
Preface "Nonlinear processes in oceanic and atmospheric flows"
Nonlinear phenomena are essential ingredients in many oceanic and atmospheric
processes, and successful understanding of them benefits from multidisciplinary
collaboration between oceanographers, meteorologists, physicists and
mathematicians. The present Special Issue on ``Nonlinear Processes in Oceanic
and Atmospheric Flows'' contains selected contributions from attendants to the
workshop which, in the above spirit, was held in Castro Urdiales, Spain, in
July 2008. Here we summarize the Special Issue contributions, which include
papers on the characterization of ocean transport in the Lagrangian and in the
Eulerian frameworks, generation and variability of jets and waves, interactions
of fluid flow with plankton dynamics or heavy drops, scaling in meteorological
fields, and statistical properties of El Ni\~no Southern Oscillation.Comment: This is the introductory article to a Special Issue on "Nonlinear
Processes in Oceanic and Atmospheric Flows'', published in the journal
Nonlinear Processes in Geophysics, where the different contributions are
summarized. The Special Issue itself is freely available from
http://www.nonlin-processes-geophys.net/special_issue103.htm
Plankton blooms in vortices: The role of biological and hydrodynamic time scales
We study the interplay of hydrodynamic mesoscale structures and the growth of
plankton in the wake of an island, and its interaction with a coastal
upwelling. Our focus is on a mechanism for the emergence of localized plankton
blooms in vortices. Using a coupled system of a kinematic flow mimicking the
mesoscale structures behind the island and a simple three component model for
the marine ecosystem, we show that the long residence times of nutrients and
plankton in the vicinity of the island and the confinement of plankton within
vortices are key factors for the appearance of localized plankton bloomsComment: 29 pages, 9 figure
Biological activity in the wake of an island close to a coastal upwelling
Hydrodynamic forcing plays an important role in shaping the dynamics of
marine organisms, in particular of plankton. In this work we study the
planktonic biological activity in the wake of an island which is close to an
upwelling region. Our research is based on numerical analysis of a kinematic
flow mimicking the hydrodynamics in the wake, coupled to a three-component
plankton model. Depending on model parameters different phenomena are
described: a) The lack of transport of nutrients and plankton across the wake,
so that the influence of upwelling on primary production on the other side of
the wake is blocked. b) For sufficiently high vorticity, the role of the wake
in facilitating this transport and leading to an enhancement of primary
production. Finally c) we show that under certain conditions the interplay
between wake structures and biological growth leads to plankton blooms inside
mesoscale hydrodynamic vortices that act as incubators of primary production.Comment: 42 pages, 9 figure
From car to bike. Marketing and dialogue as a driver of change
The Paris Climate Agreement has sent a key message to the international community regarding the need to increase efforts to move towards a low-carbon economy and help slow climate change, while underpinning global long-term economic growth and sustainable development. COP 21 recognizes the social, economic and environmental value of voluntary mitigation actions and their co-benefits for adaptation, health and sustainable development. In this framework, the PTP Cycle project, running from 2013 to 2016 and funded by the European Commission through the Intelligent Energy Europe program, introduces a non-market approach through voluntary participation in the adoption of sustainable transport modes such as cycling, based on marketing to potential customers through Personalized Travel Plans. The medium-sized city of Burgos (Spain) and the cities of Ljubljana, Riga, Antwerp and London
(boroughs of Haringey and Greenwich) developed a new policy instrument (Personalized Travel Plans) in order to increase bike patronage. Beyond potential savings of CO2, the results show that PTP as a form of Active Mobility Consultancy is a suitable instrument to influence modal shift to public transport, walking and cycling, and to address the challenges of climate change, while fostering sustainable transportation by changing mobility behaviour. These results, matching with the state-of-the-art of studies and pilot applications in other countries, allows deriving differentiated results for medium-size and large urban areas
Jupiter as an exoplanet: UV to NIR transmission spectrum reveals hazes, a Na layer and possibly stratospheric H2O-ice clouds
Currently, the analysis of transmission spectra is the most successful
technique to probe the chemical composition of exoplanet atmospheres. But the
accuracy of these measurements is constrained by observational limitations and
the diversity of possible atmospheric compositions. Here we show the UV-VIS-IR
transmission spectrum of Jupiter, as if it were a transiting exoplanet,
obtained by observing one of its satellites, Ganymede, while passing through
Jupiter's shadow i.e., during a solar eclipse from Ganymede. The spectrum shows
strong extinction due to the presence of clouds (aerosols) and haze in the
atmosphere, and strong absorption features from CH4. More interestingly, the
comparison with radiative transfer models reveals a spectral signature, which
we attribute here to a Jupiter stratospheric layer of crystalline H2O ice. The
atomic transitions of Na are also present. These results are relevant for the
modeling and interpretation of giant transiting exoplanets. They also open a
new technique to explore the atmospheric composition of the upper layers of
Jupiter's atmosphere.Comment: Accepted for publication in ApJ Letter
HD 85567: A Herbig B[e] star or an interacting B[e] binary
Context. HD 85567 is an enigmatic object exhibiting the B[e] phenomenon, i.e.
an infrared excess and forbidden emission lines in the optical. The object's
evolutionary status is uncertain and there are conflicting claims that it is
either a young stellar object or an evolved, interacting binary.
Aims. To elucidate the reason for the B[e] behaviour of HD 85567, we have
observed it with the VLTI and AMBER.
Methods. Our observations were conducted in the K-band with moderate spectral
resolution (R~1500, i.e. 200 km/s). The spectrum of HD 85567 exhibits Br gamma
and CO overtone bandhead emission. The interferometric data obtained consist of
spectrally dispersed visibilities, closure phases and differential phases
across these spectral features and the K-band continuum.
Results. The closure phase observations do not reveal evidence of asymmetry.
The apparent size of HD 85567 in the K-band was determined by fitting the
visibilities with a ring model. The best fitting radius, 0.8 +/- 0.3 AU, is
relatively small making HD 85567 undersized in comparison to the
size-luminosity relationship based on YSOs of low and intermediate luminosity.
This has previously been found to be the case for luminous YSOs, and it has
been proposed that this is due to the presence of an optically thick gaseous
disc. We demonstrate that the differential phase observations over the CO
bandhead emission are indeed consistent with the presence of a compact (~1 AU)
gaseous disc interior to the dust sublimation radius.
Conclusions. The observations reveal no sign of binarity. However, the data
do indicate the presence of a gaseous disc interior to the dust sublimation
radius. We conclude that the data are consistent with the hypothesis that HD
85567 is a YSO with an optically thick gaseous disc within a larger dust disc
that is being photo-evaporated from the outer edge.Comment: Accepted for publication in A &
Surface mixing and biological activity in the four Eastern Boundary Upwelling Systems
Eastern Boundary Upwelling Systems (EBUS) are characterized by a high
productivity of plankton associated with large commercial fisheries, thus
playing key biological and socio-economical roles. The aim of this work is to
make a comparative study of these four upwelling systems focussing on their
surface stirring, using the Finite Size Lyapunov Exponents (FSLEs), and their
biological activity, based on satellite data. First, the spatial distribution
of horizontal mixing is analysed from time averages and from probability
density functions of FSLEs. Then we studied the temporal variability of surface
stirring focussing on the annual and seasonal cycle. There is a global negative
correlation between surface horizontal mixing and chlorophyll standing stocks
over the four areas. To try to better understand this inverse relationship, we
consider the vertical dimension by looking at the Ekman-transport and vertical
velocities. We suggest the possibility of a changing response of the
phytoplankton to sub/mesoscale turbulence, from a negative effect in the very
productive coastal areas to a positive one in the open ocean.Comment: 12 pages. NPG Special Issue on "Nonlinear processes in oceanic and
atmospheric flows". Open Access paper, available also at the publisher site:
http://www.nonlin-processes-geophys.net/16/557/2009
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