5,453 research outputs found
On a novel approach for optimizing composite materials panel using surrogate models
This paper describes an optimization procedure to design thermoplastic composite panels under axial compressive load conditions. Minimum weight is the goal. The panel design is subject to buckling constraints. The presence of the bending-twisting coupling and of particular boundary conditions does not allow an analytical solution for the critical buckling load. Surrogate models are used to approximate the buckling response of the plate in a fast and reliable way. Therefore, two surrogate models are compared to study their effectiveness in composite optimization. The first one is a linear approximation based on the buckling constitutive equation. The second consists in the application of the Kriging surrogate. Constraints given from practical blending rules are also introduced in the optimization. Discrete values of ply thicknesses is a requirement. An ad-hoc discrete optimization strategy is developed, which enables to handle discrete variables
VLA observations of candidate high-mass protostellar objects at 7 mm
We present radio continuum observations at 7 mm made using the Very Large
Array towards three massive star forming regions thought to be in very early
stages of evolution selected from the sample of Sridharan et al. (2002).
Emission was detected towards all three sources (IRAS 18470-0044, IRAS
19217+1651 and IRAS 23151+5912). We find that in all cases the 7 mm emission
corresponds to thermal emission from ionized gas. The regions of ionized gas
associated with IRAS 19217+1651 and IRAS 23151+5912 are hypercompact with
diameters of 0.009 and 0.0006 pc, and emission measures of 7.0 x 10^8 and 2.3 x
10^9 pc cm^(-6), respectively.Comment: 17 pages, 5 figures, accepted by The Astronomical Journa
Subcycle squeezing of light from a time flow perspective
Light as a carrier of information and energy plays a fundamental role in both
general relativity and quantum physics, linking these areas that are still not
fully compliant with each other. Its quantum nature and spatio-temporal
structure are exploited in many intriguing applications ranging from novel
spectroscopy methods of complex many-body phenomena to quantum information
processing and subwavelength lithography. Recent access to subcycle quantum
features of electromagnetic radiation promises a new class of time-dependent
quantum states of light. Paralleled with the developments in attosecond
science, these advances motivate an urgent need for a theoretical framework
that treats arbitrary wave packets of quantum light intrinsically in the time
domain. Here, we formulate a consistent time domain theory of the generation
and sampling of few-cycle and subcycle pulsed squeezed states, allowing for a
relativistic interpretation in terms of induced changes in the local flow of
time. Our theory enables the use of such states as a resource for novel
ultrafast applications in quantum optics and quantum information.Comment: 24 pages, 7 figures (including supplementary information
Weak localization and spin splitting in inversion layers on p-type InAs
We report on the magnetoconductivity of quasi two-dimensional electron
systems in inversion layers on p-type InAs single crystals. In low magnetic
fields pronounced features of weak localization and antilocalization are
observed. They are almost perfectly described by the theory of Iordanskii,
Lyanda-Geller and Pikus. This allows us to determine the spin splitting and the
Rashba parameter of the ground electric subband as a function of the electron
density.Comment: Accepted for publication in Phys. Rev. B, 4 page
Terugkeer naar de veertigurige werkweek
Nederlandse werknemers werken relatief weinig. Verschillen
tussen OESO-landen in aantal gewerkte uren per werkende
kunnen slechts deels worden verklaard door verschillen
in arbeidsmarktinstituties. Sociale normen omtrent de
gebruikelijke
werktijd lijken veel belangrijker
Excursion Sets and Non-Gaussian Void Statistics
Primordial non-Gaussianity (NG) affects the large scale structure (LSS) of
the universe by leaving an imprint on the distribution of matter at late times.
Much attention has been focused on using the distribution of collapsed objects
(i.e. dark matter halos and the galaxies and galaxy clusters that reside in
them) to probe primordial NG. An equally interesting and complementary probe
however is the abundance of extended underdense regions or voids in the LSS.
The calculation of the abundance of voids using the excursion set formalism in
the presence of primordial NG is subject to the same technical issues as the
one for halos, which were discussed e.g. in arXiv:1005.1203. However, unlike
the excursion set problem for halos which involved random walks in the presence
of one barrier , the void excursion set problem involves two barriers
and . This leads to a new complication introduced by what
is called the "void-in-cloud" effect discussed in the literature, which is
unique to the case of voids. We explore a path integral approach which allows
us to carefully account for all these issues, leading to a rigorous derivation
of the effects of primordial NG on void abundances. The void-in-cloud issue in
particular makes the calculation conceptually rather different from the one for
halos. However, we show that its final effect can be described by a simple yet
accurate approximation. Our final void abundance function is valid on larger
scales than the expressions of other authors, while being broadly in agreement
with those expressions on smaller scales.Comment: 28 pages (18+appendices), 7 figures; v2 -- minor changes in sec 3.2,
version published in PR
The Low End of the Initial Mass Function in Young LMC Clusters: I. The Case of R136
We report the result of a study in which we have used very deep broadband V
and I WFPC2 images of the R136 cluster in the Large Magellanic Cloud from the
HST archive, to sample the luminosity function below the detection limit of 2.8
Mo previously reached. In these new deeper images, we detect stars down to a
limiting magnitude of m_F555W = 24.7 (~ 1 magnitude deeper than previous
works), and identify a population of red stars evenly distributed in the
surrounding of the R136 cluster. A comparison of our color-magnitude diagram
with recentely computed evolutionary tracks indicates that these red objects
are pre-main sequence stars in the mass range 0.6 - 3 Mo. We construct the
initial mass function (IMF) in the 1.35 - 6.5 Mo range and find that, after
correcting for incompleteness, the IMF shows a definite flattening below ~ 2
Mo. We discuss the implications of this result for the R136 cluster and for our
understanding of starburst galaxies formation and evolution in general.Comment: 29 pages, 6 tables, 11 figures included + 3 external files, accepted
for publication by Ap.
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