299 research outputs found
FEATURE-BASED GEOMETRIC MODELLING AND ANALYSIS OF MULTIBODY MECHANICAL SYSTEM BEHAVIOUR
The aim of this paper is to present a modelling system and an application to analyse
the mechanical behaviour of a gear-box. Designing a new type of gear-box, there is a
real need for the concurrent engineering activities of the designers of geometric modelling,
mesh generation and mechanical analysis. In this system own developed contact types of
finite elements (FEM) have been used.
The new system contains some programs of the earlier system ASSYM (CASM
Lab.) for modelling the casing as the superstructure of a gear-box and its bearings as
FEM contact-macroelements. In the proposed system the designers can use the modeller
CAEDS (IBM Corp.) for feature-based geometric modelling and for generating the global
mesh model of casing, the FEM analysis processor Mac/NASTRAN (MacNeal-Schwendler
Corp.) and the new version of the N_SIM program (CASM Lab.) for modelling the pairs
of gears and the bearings, furthermore the New Grid (N.G.) preprocessor (CASM Lab.).
The N.G. can introduce the local mesh models of macroelements to the global mesh of
gear-box casing
Study of a high spatial resolution 10B-based thermal neutron detector for application in neutron reflectometry: the Multi-Blade prototype
Although for large area detectors it is crucial to find an alternative to
detect thermal neutrons because of the 3He shortage, this is not the case for
small area detectors. Neutron scattering science is still growing its
instruments' power and the neutron flux a detector must tolerate is increasing.
For small area detectors the main effort is to expand the detectors'
performances. At Institut Laue-Langevin (ILL) we developed the Multi-Blade
detector which wants to increase the spatial resolution of 3He-based detectors
for high flux applications. We developed a high spatial resolution prototype
suitable for neutron reflectometry instruments. It exploits solid 10B-films
employed in a proportional gas chamber. Two prototypes have been constructed at
ILL and the results obtained on our monochromatic test beam line are presented
here
Characterizing the morphology of the debris disk around the low-mass star GSC 07396-00759
Context. Debris disks have commonly been studied around intermediate-mass
stars. Their intense radiation fields are believed to efficiently remove the
small dust grains that are constantly replenished by collisions. For lower-mass
stars, in particular M-stars, the dust removal mechanism needs to be further
investigated given the much weaker radiation field produced by these objects.
Aims. We present new polarimetric observations of the nearly edge-on disk
around the pre-main sequence M-type star GSC 07396-00759, taken with VLT/SPHERE
IRDIS, with the aim to better understand the morphology of the disk, its dust
properties, and the star-disk interaction via the stellar mass-loss rate.
Methods. We model our observations to characterize the location and properties
of the dust grains using the Henyey-Greenstein approximation of the polarized
phase function and evaluate the strength of the stellar winds. Results. We find
that the observations are best described by an extended and highly inclined
disk (i\approx 84.3\,^{\circ}\pm0.3) with a dust distribution centered at a
radius au. The polarized phase function is best
reproduced by an anisotropic scattering factor and small
micron-sized dust grains with sizes m. We furthermore
discuss some of the caveats of the approach and a degeneracy between the grain
size and the porosity. Conclusions. Even though the radius of the disk may be
over-estimated, our results suggest that using a given scattering theory might
not be sufficient to fully explain key aspects such as the shape of the phase
function, or the dust grain size. With the caveats in mind, we find that the
average mass-loss rate of GSC 07396-00759 can be up to 500 times stronger than
that of the Sun, supporting the idea that stellar winds from low-mass stars can
evacuate small dust grains from the disk
SPHERE: the exoplanet imager for the Very Large Telescope
Observations of circumstellar environments to look for the direct signal of
exoplanets and the scattered light from disks has significant instrumental
implications. In the past 15 years, major developments in adaptive optics,
coronagraphy, optical manufacturing, wavefront sensing and data processing,
together with a consistent global system analysis have enabled a new generation
of high-contrast imagers and spectrographs on large ground-based telescopes
with much better performance. One of the most productive is the
Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE)
designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE
includes an extreme adaptive optics system, a highly stable common path
interface, several types of coronagraphs and three science instruments. Two of
them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager
and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared
(NIR) range in a single observation for efficient young planet search. The
third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to
look for the reflected light of exoplanets and the light scattered by debris
disks. This suite of three science instruments enables to study circumstellar
environments at unprecedented angular resolution both in the visible and the
near-infrared. In this work, we present the complete instrument and its on-sky
performance after 4 years of operations at the VLT.Comment: Final version accepted for publication in A&
Strong, Ultra-narrow Peaks of Longitudinal and Hall Resistances in the Regime of Breakdown of the Quantum Hall Effect
With unusually slow and high-resolution sweeps of magnetic field, strong,
ultra-narrow (width down to ) resistance peaks are observed in
the regime of breakdown of the quantum Hall effect. The peaks are dependent on
the directions and even the history of magnetic field sweeps, indicating the
involvement of a very slow physical process. Such a process and the sharp peaks
are, however, not predicted by existing theories. We also find a clear
connection between the resistance peaks and nuclear spin polarization.Comment: 5 pages with 3 figures. To appear in PR
Calculating functional diversity metrics using neighborâjoining trees
The study of functional diversity (FD) provides ways to understand phenomena as complex as community assembly or the dynamics of biodiversity change under multiple pressures. Different frameworks are used to quantify FD, either based on dissimilarity matrices (e.g. Rao entropy, functional dendrograms) or multidimensional spaces (e.g. convex hulls, kernel-density hypervolumes), each with their own strengths and limits. Frameworks based on dissimilarity matrices either do not enable the measurement of all components of FD (i.e. richness, divergence, and regularity), or result in the distortion of the functional space. Frameworks based on multidimensional spaces do not allow for comparisons with phylogenetic diversity (PD) measures and can be sensitive to outliers.
We propose the use of neighbor-joining trees (NJ) to represent and quantify FD in a way that combines the strengths of current frameworks without many of their weaknesses. Importantly, our approach is uniquely suited for studies that compare FD with PD, as both share the use of trees (NJ or others) and the same mathematical principles.
We test the ability of this novel framework to represent the initial functional distances between species with minimal functional space distortion and sensitivity to outliers. The results using NJ are compared with conventional functional dendrograms, convex hulls, and kernel-density hypervolumes using both simulated and empirical datasets.
Using NJ, we demonstrate that it is possible to combine much of the flexibility provided by multidimensional spaces with the simplicity of tree-based representations. Moreover, the method is directly comparable with taxonomic diversity (TD) and PD measures, and enables quantification of the richness, divergence and regularity of the functional space
New records and detailed distribution and abundance of selected arthropod species collected between 1999 and 2011 in Azorean native forests
[Background] In this contribution we present detailed distribution and abundance data for arthropod species identified during the BALA Âż Biodiversity of Arthropods from the Laurisilva of the Azores (1999-2004) and BALA2 projects (2010-2011) from 18 native forest fragments in seven of the nine Azorean islands (all excluding Graciosa and Corvo islands, which have no native forest left).[New information] Of the total 286 species identified, 81% were captured between 1999 and 2000, a period during which only 39% of all the samples were collected. On average, arthropod richness for each island increased by 10% during the time frame of these projects. The classes Arachnida, Chilopoda and Diplopoda represent the most remarkable cases of new island records, with more than 30% of the records being novelties. This study stresses the need to expand the approaches applied in these projects to other habitats in the Azores, and more importantly to other less surveyed taxonomic groups (e.g. Diptera and Hymenoptera). These steps are fundamental for getting a more accurate assessment of biodiversity in the archipelago.AMCS was supported by a Marie Curie Intra-European Fellowship (IEF 331623 âCOMMSTRUCTâ) and by a Juan de la Cierva Fellowship (IJCI-2014-19502) funded by the Spanish âMinisterio de EconomĂa y Competitividadâ.Peer Reviewe
- âŠ