672 research outputs found
Mixed-symmetry fields in de Sitter space: a group theoretical glance
We derive the characters of all unitary irreducible representations of the (d+1)-dimensional de Sitter spacetime isometry algebra so(1,d+1), and propose a dictionary between those representations and massive or (partially) massless fields on de Sitter spacetime. We propose a way of taking the flat limit of representations in (anti-) de Sitter spaces in terms of these characters, and conjecture the spectrum resulting from taking the flat limit of mixed-symmetry fields in de Sitter spacetime. We identify the equivalent of the scalar singleton for the de Sitter (dS) spacetime. © 2017, The Author(s)4511Nsciescopu
Elastomer Characterization Method for Trapped Rubber Processing
The increasing high-volume demand for polymer matrix composites (PMCs) brings into focus the need for autoclave alternative processing. Trapped rubber processing (TRP) of PMCs is a method capable of achieving high pressures during polymer matrix composite processing by utilizing thermally induced volume change of a nearly incompressible material inside a closed cavity mold. Recent advances in rubber materials and computational technology have made this processing technique more attractive. Elastomers can be doped with nanoparticles to increase thermal conductivity and this can be further tailored for local variations in thermal conductivity for TRP. In addition, recent advances in computer processing allow for simulation of coupled thermomechanical processes for full part modeling. This study presents a method of experimentally characterizing prospective rubber materials. The experiments are designed to characterize the dynamic in situ change in temperature, the dynamic change in volume, and the resulting real-time change in surface pressure. The material characterization is specifically designed to minimize the number and difficulty of experimental tests while fully capturing the rubber behavior for the TRP scenario. The experimental characterization was developed to provide the necessary data for accurate thermomechanical material models of nearly incompressible elastomeric polymers for use in TRP virtual design and optimization
Flato-Fronsdal theorem for higher-order singletons
We prove a generalised Flato-Fronsdal theorem for higher-order, scalar and
spinor, singletons. In the resulting infinite tower of bulk higher-spin fields,
we point out the occurrence of partially-massless fields of all depths. This
leads us to conjecture a holographic duality between a higher-spin gravity
theory around with the aforementioned spectrum of fields, and a
free of fundamental (higher-order) scalar and spinor singletons. As a
first check of this conjecture, we find that the total Casimir energy vanishes
at one loop.Comment: 19 pages, no figure
General solutions of the Wess-Zumino consistency condition for the Weyl anomalies
The general solutions of the Wess-Zumino consistency condition for the
conformal (or Weyl, or trace) anomalies are derived. The solutions are
obtained, in arbitrary dimensions, by explicitly computing the cohomology of
the corresponding Becchi-Rouet-Stora-Tyutin differential in the space of
integrated local functions at ghost number unity. This provides a purely
algebraic, regularization-independent classification of the Weyl anomalies in
arbitrary dimensions. The so-called type-A anomaly is shown to satisfy a
non-trivial descent of equations, similarly to the non-Abelian chiral anomaly
in Yang-Mills theory.Comment: 9 pages. RevTeX fil
Millimeter dust continuum emission unveiling the true mass of giant molecular clouds in the Small Magellanic Cloud
CO observations have been so far the best way to trace molecular gas in
external galaxies, but at low metallicity the gas mass deduced could be largely
underestimated. At present, the kinematic information of CO data cubes are used
to estimate virial masses and trace the total mass of the molecular clouds.
Millimeter dust emission can also be used as a dense gas tracer and could
unveil H2 envelopes lacking CO. These different tracers must be compared in
different environments. This study compares virial masses to masses deduced
from millimeter emission, in two GMC samples: the local molecular clouds in our
Galaxy and their equivalents in the Small Magellanic Cloud (SMC), one of the
nearest low metallicity dwarf galaxy. In our Galaxy, mass estimates deduced
from millimeter emission are consistent with masses deduced from gamma ray
analysis and trace the total mass of the clouds. Virial masses are
systematically larger (twice on average) than mass estimates from millimeter
dust emission. This difference decreases toward high masses and has already
been reported in previous studies. In the SMC however, molecular cloud masses
deduced from SIMBA millimeter observations are systematically higher (twice on
average for conservative values of the dust to gas ratio and dust emissivity)
than the virial masses from SEST CO observations. The observed excess can not
be accounted for by any plausible change of dust properties. Taking a general
form for the virial theorem, we show that a magnetic field strength of ~15
micro Gauss in SMC clouds could provide additional support to the clouds and
explain the difference observed. Masses of SMC molecular clouds have therefore
been underestimated so far. Magnetic pressure may contribute significantly to
their support.Comment: 10 pages, 2 figures, Astronomy & Astrophysics accepte
The Exploitation of Toxic Fish from the Terminal Pleistocene in Maritime Southeast Asia: A Case Study from the Mindoro Archaeological Sites, Philippines
Representatives of the Diodontidae family (porcupinefish) are known to have been fished by prehistoric Indo-Pacific populations; however, the antiquity of the use of this family is thus far unknown. We report here on the presence of Diodontidae in the archaeological sites of Bubog I, II, and Bilat in Mindoro, Philippines, dating back to c. 13,000 BP (Before Present). This evidence demonstrates the early exploitation by islanders of poisonous fish. Every part of porcupinefish can be toxic, but the toxicity is mostly concentrated in some organs, while other parts are edible. The continuous presence of Diodontidae remains throughout the stratigraphic record of these Philippines shell middens suggests that porcupinefish were prepared by human inhabitants of the sites to render them safe for consumption, indicating an advanced cultural knowledge of the preparation needed to separate the toxic principle from the edible parts. This constitutes one of the rare examples of poison processing by humans, aside from the contentious wooden stick poison applicator from Border Cave (South Africa)
Examination of the atmospheric conditions associated with high and low summer ozone levels in the lower troposphere over the Eastern Mediterranean
Deep Self-Taught Learning for Handwritten Character Recognition
Recent theoretical and empirical work in statistical machine learning has
demonstrated the importance of learning algorithms for deep architectures,
i.e., function classes obtained by composing multiple non-linear
transformations. Self-taught learning (exploiting unlabeled examples or
examples from other distributions) has already been applied to deep learners,
but mostly to show the advantage of unlabeled examples. Here we explore the
advantage brought by {\em out-of-distribution examples}. For this purpose we
developed a powerful generator of stochastic variations and noise processes for
character images, including not only affine transformations but also slant,
local elastic deformations, changes in thickness, background images, grey level
changes, contrast, occlusion, and various types of noise. The
out-of-distribution examples are obtained from these highly distorted images or
by including examples of object classes different from those in the target test
set. We show that {\em deep learners benefit more from out-of-distribution
examples than a corresponding shallow learner}, at least in the area of
handwritten character recognition. In fact, we show that they beat previously
published results and reach human-level performance on both handwritten digit
classification and 62-class handwritten character recognition
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