106 research outputs found
The influence of methodological procedures on hydrological classification performance
ABSTRACT: Hydrological classification has emerged as a suitable procedure to disentangle the inherent hydrological complexity of river networks. This practice has contributed to determining key biophysical relations in fluvial ecosystems and the effects of flow modification. Thus, a plethora of classification approaches, which agreed in general concepts and methods but differed largely in specific procedures, have emerged in the last decades. However, few studies have compared the implication of applying contrasting approaches and specifications over the same hydrological data. In this work, using cluster analysis and modelling approaches, we classify the entire river network covering the northern third of the Iberian Peninsula. Specifically, we developed classifications of increasing level of detail, ranging from 2 to 20 class levels, either based on raw and normalized daily flow series and using two contrasting approaches to determine class membership: classify-then-predict (ClasF) and predict-thenclassify (PredF). Classifications were compared in terms of
their statistical strength, the hydrological interpretation, the ability to reduce the bias associated with underrepresented parts of the hydrological space and their spatial correspondnece. The results highlighted that both the data processing and the classification strategy largely influenced the classification outcomes and properties, although differences among procedures were not always statistically significant. The normalization of flow data removed the influence of flow magnitude and generated more complex classifications in which a wider range of hydrologic characteristics were considered. The application of the PredF strategy produced, in most of the cases, classifications with higher discrimination ability and presented greater ability to deal with the presence of distinctive gauges in the data set than using the ClasF strategy.This study was partly funded by the Spanish
Ministry of Economy and Competitiveness as part of the project
MARCE (Ref: CTM-2009-07447; http://marce.ihcantabria.es/) and
the Ministry of Agriculture, Food and Environment as part of the
project RECORAM (ref: 132/2010). José Barquín is supported
by a Ramon y Cajal grant (ref: RYC-2011-08313) of the Ministry
of Economy and Competitiveness
Modelling the impact of climate and land use changes on forest bird species for adaptive management of the Northern Sierra Madre Natural Park (Philippines)
Conservation Biology - ol
Field of inserted charges during Scanning Electron Microscopy of non-conducting samples
Three different approaches to calculating the electric potential in an inhomogeneous dielectric next to vacuum due to a charge distribution built up by the electron beam are investigated. An analytical solution for the electric potential cannot be found by means of the image charge method or Fourier analysis, both of which do work for a homogenous dielectric with a planar interface to vacuum. A Born approximation gives a good approach to the real electric potential in a homogenous dielectric up to a relative dielectric constant of 5. With this knowledge the electric potential of an inhomogenous dielectric is calculated. Also the electric field is calculated by means of a particle-mesh method. Some inhomogeneous dielectric configurations are calculated and their bound charges are studied. Such a method can yield accurate calculations of the electric potential and can give quantitative insight in the charging process. A capacitor model is described to estimate the potential due to the charge build up. It describes the potential build up in the first microseconds of the charging. Thereafter, it seems that more processes have to be taken into account to describe the potential well. This potential can further be used in a macroscopic approach to the collective motion of the electrons described by the Boltzmann transport equations or a derived density model, which can be a feasible alternative approximation to the more commonly used Monte-Carlo simulation of individual trajectories
Josephson supercurrent through a topological insulator surface state
Topological insulators are characterized by an insulating bulk with a finite
band gap and conducting edge or surface states, where charge carriers are
protected against backscattering. These states give rise to the quantum spin
Hall effect without an external magnetic field, where electrons with opposite
spins have opposite momentum at a given edge. The surface energy spectrum of a
threedimensional topological insulator is made up by an odd number of Dirac
cones with the spin locked to the momentum. The long-sought yet elusive
Majorana fermion is predicted to arise from a combination of a superconductor
and a topological insulator. An essential step in the hunt for this emergent
particle is the unequivocal observation of supercurrent in a topological phase.
Here, we present the first measurement of a Josephson supercurrent through a
topological insulator. Direct evidence for Josephson supercurrents in
superconductor (Nb) - topological insulator (Bi2Te3) - superconductor e-beam
fabricated junctions is provided by the observation of clear Shapiro steps
under microwave irradiation, and a Fraunhofer-type dependence of the critical
current on magnetic field. The dependence of the critical current on
temperature and length shows that the junctions are in the ballistic limit.
Shubnikov-de Haas oscillations in magnetic fields up to 30 T reveal a
topologically non-trivial two-dimensional surface state. We argue that the
ballistic Josephson current is hosted by this surface state despite the fact
that the normal state transport is dominated by diffusive bulk conductivity.
The lateral Nb-Bi2Te3-Nb junctions hence provide prospects for the realization
of devices supporting Majorana fermions
Early detection of left ventricular diastolic dysfunction using conventional and speckle tracking echocardiography in a large animal model of metabolic dysfunction
Left ventricular (LV) diastolic dysfunction is one of the important
mechanisms responsible for symptoms in patients with heart failure. The
aim of the current study was to identify parameters that may be used to
detect early signs of LV diastolic dysfunction in diabetic pigs on a
high fat diet, using conventional and speckle tracking echocardiography.
The study population consisted of 16 healthy Göttingen minipigs and 18
minipigs with experimentally induced metabolic dysfunction.
Echocardiography measurements were performed at baseline and 3-month
follow-up. The ratio of peak early (E) and late filling velocity (E/A
ratio) and the ratio of E and the velocity of the mitral annulus early
diastolic wave (E/Em ratio) did not change significantly in both groups.
Peak untwisting velocity decreased in the metabolic dysfunction group
(− 30.1 ± 18.5 vs. − 23.4 ± 15.5 °/ms) but not in controls
(− 38.1 ± 23.6 vs. − 42.2 ± 23.0 °/ms), being significantly different
between the groups at the 3-month time point (p < 0.05). In
conclusion, whereas E/A ratio and E/Em ratio did not change
significantly after 3 months of metabolic dysfunction, peak untwisting
velocity was significantly decreased. Hence, peak untwisting velocity
may serve as an important marker to detect early changes of LV diastolic
dysfunction.</p
Marine Biodiversity of Aotearoa New Zealand
The marine-biodiversity assessment of New Zealand (Aotearoa as known to Māori) is confined to the 200 nautical-mile boundary of the Exclusive Economic Zone, which, at 4.2 million km2, is one of the largest in the world. It spans 30° of latitude and includes a high diversity of seafloor relief, including a trench 10 km deep. Much of this region remains unexplored biologically, especially the 50% of the EEZ deeper than 2,000 m. Knowledge of the marine biota is based on more than 200 years of marine exploration in the region. The major oceanographic data repository is the National Institute of Water and Atmospheric Research (NIWA), which is involved in several Census of Marine Life field projects and is the location of the Southwestern Pacific Regional OBIS Node; NIWA is also data manager and custodian for fisheries research data owned by the Ministry of Fisheries. Related data sources cover alien species, environmental measures, and historical information. Museum collections in New Zealand hold more than 800,000 registered lots representing several million specimens. During the past decade, 220 taxonomic specialists (85 marine) from 18 countries have been engaged in a project to review New Zealand's entire biodiversity. The above-mentioned marine information sources, published literature, and reports were scrutinized to give the results summarized here for the first time (current to 2010), including data on endemism and invasive species. There are 17,135 living species in the EEZ. This diversity includes 4,315 known undescribed species in collections. Species diversity for the most intensively studied phylum-level taxa (Porifera, Cnidaria, Mollusca, Brachiopoda, Bryozoa, Kinorhyncha, Echinodermata, Chordata) is more or less equivalent to that in the ERMS (European Register of Marine Species) region, which is 5.5 times larger in area than the New Zealand EEZ. The implication is that, when all other New Zealand phyla are equally well studied, total marine diversity in the EEZ may be expected to equal that in the ERMS region. This equivalence invites testable hypotheses to explain it. There are 177 naturalized alien species in New Zealand coastal waters, mostly in ports and harbours. Marine-taxonomic expertise in New Zealand covers a broad number of taxa but is, proportionately, at or near its lowest level since the Second World War. Nevertheless, collections are well supported by funding and are continually added to. Threats and protection measures concerning New Zealand's marine biodiversity are commented on, along with potential and priorities for future research
Effectiveness of Biodiversity Surrogates for Conservation Planning: Different Measures of Effectiveness Generate a Kaleidoscope of Variation
Conservation planners represent many aspects of biodiversity by using surrogates with spatial distributions readily observed or quantified, but tests of their effectiveness have produced varied and conflicting results. We identified four factors likely to have a strong influence on the apparent effectiveness of surrogates: (1) the choice of surrogate; (2) differences among study regions, which might be large and unquantified (3) the test method, that is, how effectiveness is quantified, and (4) the test features that the surrogates are intended to represent. Analysis of an unusually rich dataset enabled us, for the first time, to disentangle these factors and to compare their individual and interacting influences. Using two data-rich regions, we estimated effectiveness using five alternative methods: two forms of incidental representation, two forms of species accumulation index and irreplaceability correlation, to assess the performance of ‘forest ecosystems’ and ‘environmental units’ as surrogates for six groups of threatened species—the test features—mammals, birds, reptiles, frogs, plants and all of these combined. Four methods tested the effectiveness of the surrogates by selecting areas for conservation of the surrogates then estimating how effective those areas were at representing test features. One method measured the spatial match between conservation priorities for surrogates and test features. For methods that selected conservation areas, we measured effectiveness using two analytical approaches: (1) when representation targets for the surrogates were achieved (incidental representation), or (2) progressively as areas were selected (species accumulation index). We estimated the spatial correlation of conservation priorities using an index known as summed irreplaceability. In general, the effectiveness of surrogates for our taxa (mostly threatened species) was low, although environmental units tended to be more effective than forest ecosystems. The surrogates were most effective for plants and mammals and least effective for frogs and reptiles. The five testing methods differed in their rankings of effectiveness of the two surrogates in relation to different groups of test features. There were differences between study areas in terms of the effectiveness of surrogates for different test feature groups. Overall, the effectiveness of the surrogates was sensitive to all four factors. This indicates the need for caution in generalizing surrogacy tests
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