1,159 research outputs found
Screening in two-dimensional foams
Using the Surface Evolver software, we perform numerical simulations of
point-like deformations in a two-dimensional foam. We study perturbations which
are infinitesimal or finite, isotropic or anisotropic, and we either conserve
or do not conserve the number of bubbles. We measure the displacement fields
around the perturbation. Changes in pressure decrease exponentially with the
distance to perturbation, indicating a screening over a few bubble diameters
Less is More: Exploiting the Standard Compiler Optimization Levels for Better Performance and Energy Consumption
This paper presents the interesting observation that by performing fewer of
the optimizations available in a standard compiler optimization level such as
-O2, while preserving their original ordering, significant savings can be
achieved in both execution time and energy consumption. This observation has
been validated on two embedded processors, namely the ARM Cortex-M0 and the ARM
Cortex-M3, using two different versions of the LLVM compilation framework; v3.8
and v5.0. Experimental evaluation with 71 embedded benchmarks demonstrated
performance gains for at least half of the benchmarks for both processors. An
average execution time reduction of 2.4% and 5.3% was achieved across all the
benchmarks for the Cortex-M0 and Cortex-M3 processors, respectively, with
execution time improvements ranging from 1% up to 90% over the -O2. The savings
that can be achieved are in the same range as what can be achieved by the
state-of-the-art compilation approaches that use iterative compilation or
machine learning to select flags or to determine phase orderings that result in
more efficient code. In contrast to these time consuming and expensive to apply
techniques, our approach only needs to test a limited number of optimization
configurations, less than 64, to obtain similar or even better savings.
Furthermore, our approach can support multi-criteria optimization as it targets
execution time, energy consumption and code size at the same time.Comment: 15 pages, 3 figures, 71 benchmarks used for evaluatio
Effect of the number of shells on the pressure and energy of two-dimensional free bubble clusters
We have performed Surface Evolver simulations of two-dimensional hexagonal bubble clusters consisting of a central bubble of area lambda surrounded by s shells or layers of bubbles of unit area. Clusters of up to twenty layers have been simulated, with lambda varying between 0.01 and 100. In monodisperse clusters (i.e., for lambda = 1) [M.A. Fortes, F Morgan, M. Fatima Vaz, Philos. Mag. Lett. 87 (2007) 561] both the average pressure of the entire Cluster and the pressure in the central bubble are decreasing functions of s and approach 0.9306 for very large s, which is the pressure in a bubble of an infinite monodisperse honeycomb foam. Here we address the effect of changing the central bubble area lambda. For small lambda the pressure in the central bubble and the average pressure were both found to decrease with s, as in monodisperse clusters. However, for large,, the pressure in the central bubble and the average pressure increase with s. The average pressure of large clusters was found to be independent of lambda and to approach 0.9306 asymptotically.
We have also determined the cluster surface energies given by the equation of equilibrium for the total energy in terms of the area and the pressure in each bubble. When the pressures in the bubbles are not available, an approximate equation derived by Vaz et al. [M. Fatima Vaz, M.A. Fortes, F. Graner, Philos. Mag. Lett. 82 (2002) 575] was shown to provide good estimations for the cluster energy provided the bubble area distribution is narrow. This approach does not take cluster topology into account. Using this approximate equation, we find a good correlation between Surface Evolver Simulations and the estimated Values of energies and pressures. (C) 2008 Elsevier B.V. All rights reserved
Auctioning Bulk Mobile Messages
The search for enablers of continued growth of SMS traffic, as well as
the take-off of the more diversified MMS message contents, open up for
enterprises the potential of bulk use of mobile messaging , instead of
essentially one-by-one use. In parallel, such enterprises or value
added services needing mobile messaging in bulk - for spot use or for
use over a prescribed period of time - want to minimize total
acquisition costs, from a set of technically approved providers of
messaging capacity.
This leads naturally to the evaluation of auctioning for bulk SMS or
MMS messaging capacity, with the intrinsic advantages therein such as
reduction in acquisition costs, allocation efficiency, and optimality.
The paper shows, with extensive results as evidence from simulations
carried out in the Rotterdam School of Management e-Auction room, how
multi-attribute reverse auctions perform for the enterprise-buyer, as
well as for the messaging capacity-sellers. We compare 1- and 5-round
auctions, to show the learning effect and the benefits thereof to the
various parties. The sensitivity will be reported to changes in the
enterprise's and the capacity providers utilities and priorities
between message attributes (such as price, size, security, and
delivery delay). At the organizational level, the paper also considers
alternate organizational deployment schemes and properties for an
off-line or spot bulk messaging capacity market, subject to technical
and regulatory constraints
CMB Polarization can constrain cosmology better than CMB temperature
We demonstrate that for a cosmic variance limited experiment, CMB E
polarization alone places stronger constraints on cosmological parameters than
CMB temperature. For example, we show that EE can constrain parameters better
than TT by up to a factor 2.8 when a multipole range of l=30-2500 is
considered. We expose the physical effects at play behind this remarkable
result and study how it depends on the multipole range included in the
analysis. In most relevant cases, TE or EE surpass the TT based cosmological
constraints. This result is important as the small scale astrophysical
foregrounds are expected to have a much reduced impact on polarization, thus
opening the possibility of building cleaner and more stringent constraints of
the LCDM model. This is relevant specially for proposed future CMB satellite
missions, such as CORE or PRISM, that are designed to be cosmic variance
limited in polarization till very large multipoles. We perform the same
analysis for a Planck-like experiment, and conclude that even in this case TE
alone should determine the constraint on better than TT by 15%,
while determining , and with comparable accuracy.
Finally, we explore a few classical extensions of the LCDM model and show again
that CMB polarization alone provides more stringent constraints than CMB
temperature in case of a cosmic variance limited experiment.Comment: 14 pages, 16 figure
Urbanisation et transition nutritionnelle en Afrique sub-saharienne : les exemples du Congo et du Sénégal
Quantum Dash Actively Mode-locked Fabry-Perot Laser Module demonstrated as part of a Wavelength Tunable RZ Transmitter
International audienceA quantum dash Fabry-Perot actively modelocked laser module is tested as part of a 42.7 Gbit/s transmitter with more than 10 nm wavelength tunability. Its low chirp level is also assessed through chromatic dispersion tolerance measurements
One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c
The K2 mission has recently begun to discover new and diverse planetary
systems. In December 2014 Campaign 1 data from the mission was released,
providing high-precision photometry for ~22000 objects over an 80 day timespan.
We searched these data with the aim of detecting further important new objects.
Our search through two separate pipelines led to the independent discovery of
K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2
), orbiting a K dwarf extremely close to the 3:2 mean motion
resonance. The two planets each show transits, sometimes simultaneously due to
their proximity to resonance and alignment of conjunctions. We obtain further
ground based photometry of the larger planet with the NITES telescope,
demonstrating the presence of large transit timing variations (TTVs), and use
the observed TTVs to place mass constraints on the transiting objects under the
hypothesis that the objects are near but not in resonance. We then
statistically validate the planets through the \texttt{PASTIS} tool,
independently of the TTV analysis.Comment: 18 pages, 10 figures, accepted to A&A, updated to match published
versio
Uncertainty in the Representation of Orography in Weather and Climate Models and Implications for Parameterized Drag
The representation of orographic drag remains a major source of uncertainty for numerical weather prediction (NWP) and climate models. Its accuracy depends on contributions from both the model gridâscale orography (GSO) and the subgridâscale orography (SSO). Different models use different source orography datasets and different methodologies to derive these orography fields. This study presents the first comparison of orography fields across several operational global NWP models. It also investigates the sensitivity of an orographic drag parameterisation to the interâmodel spread in SSO fields and the resulting implications for representing the northern hemisphere winter circulation in a NWP model. The interâmodel spread in both the GSO and the SSO fields is found to be considerable. This is due to differences in the underlying source dataset employed and in the manner in which this dataset is processed (in particular how it is smoothed and interpolated) to generate the model fields. The sensitivity of parameterised orographic drag to the interâmodel variability in SSO fields is shown to be considerable and dominated by the influence of two SSO fields: the standard deviation and the mean gradient of the SSO. NWP model sensitivity experiments demonstrate that the interâmodel spread in these fields is of firstâorder importance to the interâmodel spread in parameterised surface stress, and to current known systematic model biases. The revealed importance of the SSO fields supports careful reconsideration of how these fields are generated, guiding future development of orographic drag parameterisations and reâevaluation of the resolved impacts of orography on the flow
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