10,208 research outputs found
Auxetic two-dimensional lattice with Poisson's Ratio arbitrarily close to -1
In this paper we propose a new lattice structure having macroscopic Poisson's
ratio arbitrarily close to the stability limit -1. We tested experimentally the
effective Poisson's ratio of the micro-structured medium; the uniaxial test has
been performed on a thermoplastic lattice produced with a 3d printing
technology. A theoretical analysis of the effective properties has been
performed and the expression of the macroscopic constitutive properties is
given in full analytical form as a function of the constitutive properties of
the elements of the lattice and on the geometry of the microstructure. The
analysis has been performed on three micro-geometry leading to an isotropic
behaviour for the cases of three-fold and six-fold symmetry and to a cubic
behaviour for the case of four-fold symmetry.Comment: 26 pages, 12 figures (26 subfigures
Polar cap magnetic field reversals during solar grand minima: could pores play a role?
We study the magnetic flux carried by pores located outside active regions
with sunspots and investigate their possible contribution to the reversal of
the global magnetic field of the Sun. We find that they contain a total flux of
comparable amplitude to the total magnetic flux contained in polar caps. The
pores located at distances of 40--100~Mm from the closest active region have
systematically the correct sign to contribute to the polar cap reversal. These
pores can predominantly be found in bipolar magnetic regions. We propose that
during grand minima of solar activity, such a systematic polarity trend, akin
to a weak magnetic (Babcock-Leighton-like) source term could still be operating
but was missed by the contemporary observers due to the limited resolving power
of their telescopes.Comment: 11 pages, 9 figures, accepted for publication in
Astronomy&Astrophysic
Effective properties of a new auxetic triangular lattice: an analytical approach
In this article we propose a new auxetic periodic lattice with negative Poisson's ratio which tends to the limit ?=-1 under particular conditions. We have studied its generation and kinematic, and we give a full description of the mechanical properties of this innovative model. Calibrating the geometrical configuration of the lattice and the mechanical properties of the constituent material we are able to have a Poisson's ratio which is arbitrarily close to -1
Different methods of evaluation of Monilinia laxa on apricot flowers and branches
- Organic apricot production is currently not profitable.
- The main obstacle to sustainable profitability is brown rot caused by the fungus Monilinia laxa (Aderh. & Ruhl).
- In the current apricot germplasm no source of total resistance has been shown, but some varieties are expressing interesting levels of tolerance.
- A good evaluation of the M. laxa symptoms is essential for a precise diagnosis of the infection and to appreciate differences between tolerant and susceptible varieties and genotypes
Mg II Absorption Systems in SDSS QSO Spectra
We present the results of a MgII absorption-line survey using QSO spectra
from the SDSS EDR. Over 1,300 doublets with rest equivalent widths greater than
0.3\AA and redshifts were identified and measured. We
find that the rest equivalent width ()
distribution is described very well by an exponential function , with
and \AA. Previously reported power law
fits drastically over-predict the number of strong lines. Extrapolating our
exponential fit under-predicts the number of \AA systems,
indicating a transition in near \AA. A combination of
two exponentials reproduces the observed distribution well, suggesting that
MgII absorbers are the superposition of at least two physically distinct
populations of absorbing clouds. We also derive a new redshift parameterization
for the number density of \AA lines:
and \AA. We find that the distribution steepens with decreasing redshift,
with decreasing from \AA at to \AA at
. The incidence of moderately strong MgII lines does not
show evidence for evolution with redshift. However, lines stronger than
\AA show a decrease relative to the no-evolution prediction with
decreasing redshift for . The evolution is stronger for
increasingly stronger lines. Since in saturated absorption lines is an
indicator of the velocity spread of the absorbing clouds, we interpret this as
an evolution in the kinematic properties of galaxies from moderate to low z.Comment: 50 pages, 26 figures, accepted for publication in Ap
DIPSI: a Monte Carlo generator for elastic vector meson production in charged lepton-proton scattering
We present a Monte Carlo generator for exclusive vector meson production in
charged lepton-proton interactions, l+p --> l+p+V, based on a QCD leading
logarithm model calculation according to which the cross section for this
process is proportional to the square of the gluon momentum density in the
proton. The generator can be used for both fixed target and collider
kinematics. Each event is assigned a weight equal to its cross section, so that
the independent variables can be generated according to convenient
distributions, not necessarily identical to the physics ones.Comment: 24 pages, 7 figures, Latex, to be published in Computer Physics
Communication
Preparation of pure and mixed polarization qubits and the direct measurement of figures of merit
Non-classical joint measurements can hugely improve the efficiency with which
certain figures of merit of quantum systems are measured. We use such a
measurement to determine a particular figure of merit, the purity, for a
polarization qubit. In the process we highlight some of subtleties involved in
common methods for generating decoherence in quantum optics.Comment: 5 pages, 3 figures, 1 tabl
Characterization of Trypanosoma brucei isolated from lymph nodes of rats
Forms of Trypanosoma brucei isolated from lymph nodes of cyclically or intravenously infected rats, at different stages of infection, were morphologically compared with the corresponding bloodstream forms. Unlike the pleomorphic bloodstream trypanosome population, the lymph node trypanosome population was essentially monomorphic and resembled the slender forms of the bloodstream. Values for the morphometric parameters indicated a position between the slender and the stumpy forms. The number of trypanosomes/ml of blood showed the well-known periodic fluctuations while the number of trypanosomes/g of lymph node remained fairly constant. Serology revealed that lymph node trypanosome populations differed antigenically from the trypanosome populations isolated simultaneously from the bloodstrea
Simulations of turbulent convection in rotating young solar-like stars: Differential rotation and meridional circulation
We present the results of three-dimensional simulations of the deep
convective envelope of a young (10 Myr) one-solar-mass star, obtained with the
Anelastic Spherical Harmonic code. Since young stars are known to be faster
rotators than their main sequence counterparts, we have systematically studied
the impact of the stellar rotation speed, by considering stars spinning up to
five times as fast as the Sun. The aim of these nonlinear models is to
understand the complex interactions between convection and rotation. We discuss
the influence of the turbulence level and of the rotation rate on the intensity
and the topology of the mean flows. For all of the computed models, we find a
solar-type superficial differential rotation, with an equatorial acceleration,
and meridional circulation that exhibits a multicellular structure. Even if the
differential rotation contrast decreases only marginally for high rotation
rates, the meridional circulation intensity clearly weakens according to our
simulations. We have also shown that, for Taylor numbers above a certain
threshold (Ta>10^9), the convection can develop a vacillating behavior. Since
simulations with high turbulence levels and rotation rates exhibit strongly
cylindrical internal rotation profiles, we have considered the influence of
baroclinic effects at the base of the convective envelope of these young Suns,
to see whether such effect can modify the otherwise near cylindrical profiles
to produce more conical, solar-like profiles.Comment: 32 pages, 18 figures, 2 tables, to appear in Ap
Les PME-ETI cotées en bourse : la crise accentue les disparités et souligne les différences de réactivité.
Les PME-ETI cotées en bourse sont plus hétérogÚnes que leurs homologues non cotées en termes de dynamisme et de performance. En 2009, les plus rentables montrent une capacité de rebond supérieure.PME, ETI, bourse, taux de marge, endettement, fonds propres.
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