182 research outputs found
Macroscopic urban dynamics: Analytical and numerical comparisons of existing models
In this paper we compare a single reservoir model and a trip-based model under piecewise linear MFD and a piecewise constant demand. These assumptions allow to establish the exact solution of the accumulation-based model, and continuous approximations of the trip-based model at any order using Taylor series
Backward-wave regime and negative refraction in chiral composites
Possibilities to realize a negative refraction in chiral composites in in
dual-phase mixtures of chiral and dipole particles is studied. It is shown that
because of strong resonant interaction between chiral particles (helixes) and
dipoles, there is a stop band in the frequency area where the backward-wave
regime is expected. The negative refraction can occur near the resonant
frequency of chiral particles. Resonant chiral composites may offer a root to
realization of negative-refraction effect and superlenses in the optical
region
Symmetry and reciprocity constraints on diffraction by gratings of quasi-planar particles
Symmetry and reciprocity constraints on polarization state of the field
diffracted by gratings of quasi-planar particles are considered. It is shown
that the optical activity effects observed recently in arrays of quasi-planar
plasmonic particles on a dielectric substrate are due to the reflection of the
field at the air-dielectric slab interface and are proportional to this
reflection coefficient.Comment: 11 pages, 3 figures, 12 references; minor corrections for better
appearanc
Determination of Effective Permittivity and Permeability of Metamaterials from Reflection and Transmission Coefficients
We analyze the reflection and transmission coefficients calculated from
transfer matrix simulations on finite lenghts of electromagnetic metamaterials,
to determine the effective permittivity and permeability. We perform this
analysis on structures composed of periodic arrangements of wires, split ring
resonators (SRRs) and both wires and SRRs. We find the recovered
frequency-dependent permittivity and permeability are entirely consistent with
analytic expressions predicted by effective medium arguments. Of particular
relevance are that a wire medium exhibits a frequency region in which the real
part of permittivity is negative, and SRRs produce a frequency region in which
the real part of permeability is negative. In the combination structure, at
frequencies where both the recovered real part of permittivity and permeability
are simultaneously negative, the real part of the index-of-refraction is found
also to be unambigously negative.Comment: *.pdf file, 5 figure
Blending of nanoscale and microscale in uniform large-area sculptured thin-film architectures
The combination of large thickness ( m), large--area uniformity (75
mm diameter), high growth rate (up to 0.4 m/min) in assemblies of
complex--shaped nanowires on lithographically defined patterns has been
achieved for the first time. The nanoscale and the microscale have thus been
blended together in sculptured thin films with transverse architectures.
SiO () nanowires were grown by electron--beam evaporation onto
silicon substrates both with and without photoresist lines (1--D arrays) and
checkerboard (2--D arrays) patterns. Atomic self--shadowing due to
oblique--angle deposition enables the nanowires to grow continuously, to change
direction abruptly, and to maintain constant cross--sectional diameter. The
selective growth of nanowire assemblies on the top surfaces of both 1--D and
2--D arrays can be understood and predicted using simple geometrical shadowing
equations.Comment: 17 pages, 9 figure
Optomagnetic composite medium with conducting nanoelements
A new type of metal-dielectric composites has been proposed that is
characterised by a resonance-like behaviour of the effective permeability in
the infrared and visible spectral ranges. This material can be referred to as
optomagnetic medium. The analytical formalism developed is based on solving the
scattering problem for considered inclusions with impedance boundary condition,
which yields the current and charge distributions within the inclusions. The
presence of the effective magnetic permeability and its resonant properties
lead to novel optical effects and open new possible applications.Comment: 48 pages, 13 figures. accepted to Phys. Rev. B; to appear vol. 66,
200
Experimental warming interacts with soil moisture to discriminate plant responses in an ombrotrophic peatland
International audienceQuestionA better understanding of the response of Sphagnum mosses and associated vascular plants to climate warming is relevant for predicting the carbon balance of peatlands in a warmer world. Open-top chambers (OTCs) have been used to investigate the effect on soil biogeochemical processes in peatlands, but little information is available on the effects of OTCs on microclimate conditions and the associated response of the plant community. We aimed to understand how simulated warming and differences in soil moisture affect plant species cover.LocationA Sphagnum-dominated peatlands in French Jura.MethodsWe used OTCs to measure the effect of a near-ground temperature increase (+1.5 °C on average) on vegetation dynamics over five growing seasons (2008–2012) in a Sphagnum-dominated peatland, in two adjacent microhabitats with different hydrological conditions – wet and dry. Microclimatic conditions and plant species abundance were monitored at peak biomass in years 1, 2, 3 and 5 and monthly during the plant growing season in year 5.ResultsThe response to warming differed between vascular plants and bryophytes, as well as among species within these groups, and also varied in relation to soil moisture. Andromeda polifolia abundance responded positively to warming, while Vaccinium oxycoccus responded negatively, and Eriophorum vaginatum showed a high resistance.ConclusionDepth of rooting of vascular plants appeared to control the response in plant abundance, while moss abundance depended on various other interacting factors, such as shading by the vascular plant community, precipitation and soil moisture
Evolution of Gaussian wave packets in capillary jets
A temporal analysis of the evolution of Gaussian wave packets in cylindrical capillary jets is
presented through both a linear two-mode formulation and a one-dimensional nonlinear numerical
scheme. These analyses are normally applicable to arbitrary initial conditions but our study focuses
on pure-impulsive ones. Linear and nonlinear findings give consistent results in the stages for which
the linear theory is valid. The inverse Fourier transforms representing the formal linear solution
for the jet shape is both numerically evaluated and approximated by closed formulas. After a
transient, these formulas predict an almost Gaussian-shape deformation with (i) a progressive drift
of the carrier wave number to that given by the maximum of the Rayleigh dispersion relation, (ii)
a progressive increase of its bell width, and (iii) a quasi-exponential growth of its amplitude. These
parameters agree with those extracted from the fittings of Gaussian wave packets to the numerical
simulations. Experimental results are also reported on near-Gaussian pulses perturbing the exit
velocity of a 2 mm diameter water jet. The possibility of controlling the breakup location along the
jet and other features, such as pinch-off simultaneity, are demonstrated
Characterizing the pathotype of neonatal meningitis causing <i>Escherichia coli</i> (NMEC)
Background
Neonatal meningitis-causing Escherichia coli (NMEC) is the predominant Gram-negative bacterial pathogen associated with meningitis in newborn infants. High levels of heterogeneity and diversity have been observed in the repertoire of virulence traits and other characteristics among strains of NMEC making it difficult to define the NMEC pathotype. The objective of the present study was to identify genotypic and phenotypic characteristics of NMEC that can be used to distinguish them from commensal E. coli.
Methods
A total of 53 isolates of NMEC obtained from neonates with meningitis and 48 isolates of fecal E. coli obtained from healthy individuals (HFEC) were comparatively evaluated using five phenotypic (serotyping, serum bactericidal assay, biofilm assay, antimicorbial susceptibility testing, and in vitro cell invasion assay) and three genotypic (phylogrouping, virulence genotyping, and pulsed-field gel electrophoresis) methods.
Results
A majority (67.92 %) of NMEC belonged to B2 phylogenetic group whereas 59 % of HFEC belonged to groups A and D. Serotyping revealed that the most common O and H types present in NMEC tested were O1 (15 %), O8 (11.3 %), O18 (13.2 %), and H7 (25.3 %). In contrast, none of the HFEC tested belonged to O1 or O18 serogroups. The most common serogroup identified in HFEC was O8 (6.25 %). The virulence genotyping reflected that more than 70 % of NMEC carried kpsII, K1, neuC, iucC, sitA, and vat genes with only less than 27 % of HFEC possessing these genes. All NMEC and 79 % of HFEC tested were able to invade human cerebral microvascular endothelial cells. No statistically significant difference was observed in the serum resistance phenotype between NMEC and HFEC. The NMEC strains demonstrated a greater ability to form biofilms in Luria Bertani broth medium than did HFEC (79.2 % vs 39.9 %).
Conclusion
The results of our study demonstrated that virulence genotyping and phylogrouping may assist in defining the potential NMEC pathotype
The GenTree Dendroecological Collection, tree-ring and wood density data from seven tree species across Europe
The dataset presented here was collected by the GenTree project (EU-Horizon 2020), which aims to improve the use of forest genetic resources across Europe by better understanding how trees adapt to their local environment. This dataset of individual tree-core characteristics including ring-width series and whole-core wood density was collected for seven ecologically and economically important European tree species: silver birch (Betula pendula), European beech (Fagus sylvatica), Norway spruce (Picea abies), European black poplar (Populus nigra), maritime pine (Pinus pinaster), Scots pine (Pinus sylvestris), and sessile oak (Quercus petraea). Tree-ring width measurements were obtained from 3600 trees in 142 populations and whole-core wood density was measured for 3098 trees in 125 populations. This dataset covers most of the geographical and climatic range occupied by the selected species. The potential use of it will be highly valuable for assessing ecological and evolutionary responses to environmental conditions as well as for model development and parameterization, to predict adaptability under climate change scenarios
- …