338 research outputs found
Typification of names in genus Hieracium based on original herbarium material of Alexis Jordan and Alexandre Boreau
181 names of Hieracium species going back to original herbarium material of Alexis Jordan or Alexandre Boreau are lectotypified, 27 are neotypified. The study is based on herbarium specimens of the Université Catholique de Lyon (LY) and Ville d’Angers (ANG), Martrin-Donos’s herbarium at the Institut Botanique de Montpellier (MPUTarn) and Arvet-Touvet’s herbarium at the Musée d’Histoire Naturelle de Grenoble (GRM-AT). The type specimens are illustrated by photographs of the entire herbarium sheets with some detail views of flower heads and leaves. Usual nomenclatural synonyms are given for each taxon
Investigation of four-year chemical composition and organic aerosol sources of submicron particles at the ATOLL site in northern France
This study presents the first long-term online measurements of submicron (PM1) particles at the ATOLL (ATmospheric Observations in liLLe) platform, in northern France. The ongoing measurements using an Aerosol Chemical Speciation Monitor (ACSM) started at the end of 2016 and the analysis presented here spans through December 2020. At this site, the mean PM1 concentration is 10.6 μg m-3, dominated by organic aerosols (OA, 42.3%) and followed by nitrate (28.9%), ammonium (12.3%), sulfate (8.6%), and black carbon (BC, 8.0%). Large seasonal variations of PM1 concentrations are observed, with high concentrations during cold seasons, associated with pollution episodes (e.g. over 100 μg m-3 in January 2017). To study OA origins over this multiannual dataset we performed source apportionment analysis using rolling positive matrix factorization (PMF), yielding two primary OA factors, a traffic-related hydrocarbon-like OA (HOA) and biomass-burning OA (BBOA), and two oxygenated OA (OOA) factors. HOA showed a homogeneous contribution to OA throughout the seasons (11.8%), while BBOA varied from 8.1% (summer) to 18.5% (winter), the latter associated with residential wood combustion. The OOA factors were distinguished between their less and more oxidized fractions (LO-OOA and MO-OOA, on average contributing 32% and 42%, respectively). During winter, LO-OOA is identified as aged biomass burning, so at least half of OA is associated with wood combustion during this season. Furthermore, ammonium nitrate is also a predominant aerosol component during cold-weather pollution episodes - associated with fertilizer usage and traffic emissions. This study provides a comprehensive analysis of submicron aerosol sources at the recently established ATOLL site in northern France from multiannual observations, depicting a complex interaction between anthropogenic and natural sources, leading to different mechanisms of air quality degradation in the region across different seasons
Geodesic and Path Motion in the Nonsymmetric Gravitational Theory
We study the problem of test-particle motion in the Nonsymmetric
Gravitational Theory (NGT) assuming the four-velocity of the particle is
parallel-transported along the trajectory. The predicted motion is studied on a
static, spherically symmetric background field, with particular attention paid
to radial and circular motions. Interestingly, it is found that the proper time
taken to travel between any two non-zero radial positions is finite. It is also
found that circular orbits can be supported at lower radii than in General
Relativity for certain forms of motion.
We present three interactions which could be used as alternate methods for
coupling a test-particle to the antisymmetric components of the NGT field. One
of these takes the form of a Yukawa force in the weak-field limit of a static,
spherically symmetric field, which could lead to interesting phenomenology.Comment: 17 pages, REVTeX 3.0 with amssymb.st
Born-Infeld Theory and Stringy Causality
Fluctuations around a non-trivial solution of Born-Infeld theory have a
limiting speed given not by the Einstein metric but the Boillat metric. The
Boillat metric is S-duality invariant and conformal to the open string metric.
It also governs the propagation of scalars and spinors in Born-Infeld theory.
We discuss the potential clash between causality determined by the closed
string and open string light cones and find that the latter never lie outside
the former. Both cones touch along the principal null directions of the
background Born-Infeld field. We consider black hole solutions in situations in
which the distinction between bulk and brane is not sharp such as space filling
branes and find that the location of the event horizon and the thermodynamic
properties do not depend on whether one uses the closed or open string metric.
Analogous statements hold in the more general context of non-linear
electrodynamics or effective quantum-corrected metrics. We show how Born-Infeld
action to second order might be obtained from higher-curvature gravity in
Kaluza-Klein theory. Finally we point out some intriguing analogies with
Einstein-Schr\"odinger theory.Comment: 31 pages, 4 figures, LaTex; Some comments and references adde
Grain Boundaries in Graphene on SiC(000) Substrate
Grain boundaries in epitaxial graphene on the SiC(000) substrate are
studied using scanning tunneling microscopy and spectroscopy. All investigated
small-angle grain boundaries show pronounced out-of-plane buckling induced by
the strain fields of constituent dislocations. The ensemble of observations
allows to determine the critical misorientation angle of buckling transition
. Periodic structures are found among the flat
large-angle grain boundaries. In particular, the observed highly ordered grain boundary is assigned to the previously
proposed lowest formation energy structural motif composed of a continuous
chain of edge-sharing alternating pentagons and heptagons. This periodic grain
boundary defect is predicted to exhibit strong valley filtering of charge
carriers thus promising the practical realization of all-electric valleytronic
devices
Atomic Configuration of Nitrogen Doped Single-Walled Carbon Nanotubes
Having access to the chemical environment at the atomic level of a dopant in
a nanostructure is crucial for the understanding of its properties. We have
performed atomically-resolved electron energy-loss spectroscopy to detect
individual nitrogen dopants in single-walled carbon nanotubes and compared with
first principles calculations. We demonstrate that nitrogen doping occurs as
single atoms in different bonding configurations: graphitic-like and
pyrrolic-like substitutional nitrogen neighbouring local lattice distortion
such as Stone-Thrower-Wales defects. The stability under the electron beam of
these nanotubes has been studied in two extreme cases of nitrogen incorporation
content and configuration. These findings provide key information for the
applications of these nanostructures.Comment: 25 pages, 13 figure
High-resolution record of the Northern Hemisphere climate extending into the last interglacial period
Correlation between the neonatal EEG and the neurological examination in the first year of life in infants with bacterial meningitis
CO2 dynamics and related air-ice-sea gas transfer in spring pack and land fast sea ice
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