7,645 research outputs found
Online Estimation of Battery Lifetime for Wireless Sensors Network
Battery is a major hardware component of wireless sensor networks. Most of
them have no power supply and are generally deployed for a long time.
Researches have been done on battery physical model and their adaptation for
sensors. We present an implementation on a real sensor operating system and how
architectural constraints have been assumed. Experiments have been made in
order to test the impact of some parameter, as the application throughput, on
the battery lifetime
Edge flutter of long beams under follower loads
The linear instability of a beam tensioned by its own weight is considered.
It is shown that for long beams, in the sense of an adequate dimensionless
parameter, the characteristics of the instability caused by a follower force do
not depend on the length. The asymptotic regime significantly differs from that
of short beams: flutter prevails for all types of follower loads, and flutter
is localized at the edge of the beam. An approximate solution using matched
assymptotic expansion is proposed for the case of a semi-infinite beam. Using a
local criterion based on the stability of waves, the characteristics of this
regime as well as its range of application can be well predicted. These results
are finally discussed in relation with cases of flow-induced instabilities of
slender structures.Comment: to appear in Journal of Mechanics of Materials and Structure
Logical and Algebraic Characterizations of Rational Transductions
Rational word languages can be defined by several equivalent means: finite
state automata, rational expressions, finite congruences, or monadic
second-order (MSO) logic. The robust subclass of aperiodic languages is defined
by: counter-free automata, star-free expressions, aperiodic (finite)
congruences, or first-order (FO) logic. In particular, their algebraic
characterization by aperiodic congruences allows to decide whether a regular
language is aperiodic.
We lift this decidability result to rational transductions, i.e.,
word-to-word functions defined by finite state transducers. In this context,
logical and algebraic characterizations have also been proposed. Our main
result is that one can decide if a rational transduction (given as a
transducer) is in a given decidable congruence class. We also establish a
transfer result from logic-algebra equivalences over languages to equivalences
over transductions. As a consequence, it is decidable if a rational
transduction is first-order definable, and we show that this problem is
PSPACE-complete
Trace element geochemistry of ordinary chondrite chondrules: the type I/type II chondrule dichotomy
We report trace element concentrations of silicate phases in chondrules from
LL3 ordinary chondrites Bishunpur and Semarkona. Results are similar to
previously reported data for carbonaceous chondrites, with rare earth element
(REE) concentrations increasing in the sequence olivine < pyroxene <
mesostasis, and heavy REE (HREE) being enriched by 1-2 orders of magnitude
(CI-normalized) relative to light REE (LREE) in ferromagnesian silicates,
although no single olivine with very large LREE/HREE fractionation has been
found. On average, olivine in type II chondrules is poorer in refractory
lithophile incompatible elements (such as REE) than its type I counterpart by a
factor of ~2. This suggests that olivine in type I and II chondrules formed by
batch and fractional crystallization, respectively, implying that type II
chondrules formed under faster cooling rates (> ~ 10 K/h) than type I
chondrules. Appreciable Na concentrations (3-221 ppm) are measured in olivine
from both chondrule types; type II chondrules seem to have behaved as closed
systems, which may require chondrule formation in the vicinity of protoplanets
or planetesimals. At any rate, higher solid concentrations in type II chondrule
forming regions may explain the higher oxygen fugacities they record compared
to type I chondrules. Type I and type II chondrules formed in different
environments and the correlation between high solid concentrations and/or
oxygen fugacities with rapid cooling rates is a key constraint that chondrule
formation models must account for.Comment: 46 pages, 7 figure
ESTIMATION OF INCOME DISTRIBUTION AND DETECTION OF SUBPOPULATIONS: AN EXPLANATORY MODEL
Inequality and polarization analyses are complementary but conceptually different. They are usually implemented independently in practic e, with different a priori assumptions and different tools. In this paper, we develop a unique method to study simultaneously these different and complementary concerns. Based on mixture models, the method we develop includes at the same time : an estimation of income distribution with no a priori assumptions - a decomposition in several homogeneous subpopulations - an explanatory model to study the structure of the income distribution.
Geometrical Folding Transitions of the Triangular Lattice in the Face-Centred Cubic Lattice
We study the folding of the regular two-dimensional triangular lattice
embedded in the regular three-dimensional Face-Centred Cubic lattice, a
discrete model for the crumpling of membranes. Possible folds are complete
planar folds, folds with the angle of a regular tetrahedron (71 degrees) or
with that of a regular octahedron (109 degrees). We study this model in the
presence of a negative bending rigidity K, which favours the folding process.
We use both a cluster variation method (CVM) approximation and a transfer
matrix approach. The system is shown to undergo two separate geometrical
transitions with increasing |K|: a first discontinuous transition separates a
phase where the triangular lattice is preferentially wrapped around octahedra
from a phase where it is preferentially wrapped around tetrahedra. A second
continuous transition separates this latter phase from a phase of complete
folding of the lattice on top of a single triangle.Comment: 25 pages, uses harvmac(b) and epsf, 14+1 figures include
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