2,851 research outputs found
Physical Simulation of Inarticulate Robots
In this note we study the structure and the behavior of inarticulate robots.
We introduce a robot that moves by successive revolvings. The robot's structure
is analyzed, simulated and discussed in detail
Robust classification via MOM minimization
We present an extension of Vapnik's classical empirical risk minimizer (ERM)
where the empirical risk is replaced by a median-of-means (MOM) estimator, the
new estimators are called MOM minimizers. While ERM is sensitive to corruption
of the dataset for many classical loss functions used in classification, we
show that MOM minimizers behave well in theory, in the sense that it achieves
Vapnik's (slow) rates of convergence under weak assumptions: data are only
required to have a finite second moment and some outliers may also have
corrupted the dataset.
We propose an algorithm inspired by MOM minimizers. These algorithms can be
analyzed using arguments quite similar to those used for Stochastic Block
Gradient descent. As a proof of concept, we show how to modify a proof of
consistency for a descent algorithm to prove consistency of its MOM version. As
MOM algorithms perform a smart subsampling, our procedure can also help to
reduce substantially time computations and memory ressources when applied to
non linear algorithms.
These empirical performances are illustrated on both simulated and real
datasets
Directional Dynamics along Arbitrary Curves in Cellular Automata
This paper studies directional dynamics in cellular automata, a formalism
previously introduced by the third author. The central idea is to study the
dynamical behaviour of a cellular automaton through the conjoint action of its
global rule (temporal action) and the shift map (spacial action): qualitative
behaviours inherited from topological dynamics (equicontinuity, sensitivity,
expansivity) are thus considered along arbitrary curves in space-time. The main
contributions of the paper concern equicontinuous dynamics which can be
connected to the notion of consequences of a word. We show that there is a
cellular automaton with an equicontinuous dynamics along a parabola, but which
is sensitive along any linear direction. We also show that real numbers that
occur as the slope of a limit linear direction with equicontinuous dynamics in
some cellular automaton are exactly the computably enumerable numbers
Constraining short-range spin-dependent forces with polarized He
We have searched for a short-range spin-dependent interaction using the spin
relaxation of hyperpolarized He. Such a new interaction would be mediated
by a hypothetical light scalar boson with \CP-violating couplings to the
neutron. The walls of the He cell would generate a pseudomagnetic field and
induce an extra depolarization channel. We did not see any anomalous spin
relaxation and we report the limit for interaction ranges between
and : , where () are the (pseudo)scalar coupling
constant, improving the previous best limit by 1 order of magnitude
Search for a new short-range spin-dependent force with polarized Helium 3
Measuring the depolarization rate of a He hyperpolarized gas is a
sensitive method to probe hypothetical short-range spin-dependent forces. A
dedicated experiment is being set up at the Institute Laue Langevin in Grenoble
to improve the sensitivity. We presented the status of the experiment at the
10th PATRAS Workshop on Axions, WIMPs and WISPs.Comment: Presented at the 10th PATRAS Workshop on Axions, WIMPs and WISP
Évaluation de la croissance et de l'activité antagoniste de pseudozyma SPP. en conditions in situ
Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2008-2009Dans cette étude, nous avons comparé le potentiel de lutte biologique et le développement de quatre espèces du genre Pseudozyma {P. antárctica, P. flocculosa, P. fusiformata et P. rugulosa), reconnues pour leur production de glycolipides aux propriétés antifongiques in vitro. Pour ce faire, nous avons d'abord généré des transformants GFP et conçu des amorces spécifiques pour chacune des espèces testées. Par la suite, nous avons pu observer ces espèces en conditions naturelles et quantifier leurs populations en temps réel, sur des feuilles saines et infectées par le blanc. Bien que Pseudozyma spp. présentent plusieurs caractéristiques similaires, seulement P. flocculosa a été en mesure de contrôler efficacement le blanc et de croître en sa présence, comme en témoigne l'augmentation constante de sa population, tel qu'observée en qRT-PCR. De tels résultats suggèrent ainsi que la production de glycolipides n'est pas le seul facteur définissant l'activité antagoniste de Pseudozyma spp. en conditions naturelles. De plus, ces résultats soulignent également la nécessité d'avoir recours à des tests in situ pour une juste évaluation du potentiel de lutte biologique d'un champignon ainsi qu'une compréhension exhaustive de son écologie, et ce toujours dans le but d'optimiser l'efficacité d'un agent de lutte biologique potentie
When dunes move together, structure of deserts emerges
Crescent shaped barchan dunes are highly mobile dunes that are usually
presented as a prototypical model of sand dunes. Although they have been
theoretically shown to be unstable when considered separately, it is well known
that they form large assemblies in desert. Collisions of dunes have been
proposed as a mechanism to redistribute sand between dunes and prevent the
formation of heavily large dunes, resulting in a stabilizing effect in the
context of a dense barchan field. Yet, no models are able to explain the
spatial structures of dunes observed in deserts. Here, we use an agent-based
model with elementary rules of sand redistribution during collisions to access
the full dynamics of very large barchan dune fields. Consequently, stationnary,
out of equilibrium states emerge. Trigging the dune field density by a sand
load/lost ratio, we show that large dune fields exhibit two assymtotic regimes:
a dilute regime, where sand dune nucleation is needed to maintain a dune field,
and a dense regime, where dune collisions allow to stabilize the whole dune
field. In this dense regime, spatial structures form: the dune field is
structured in narrow corridors of dunes extending in the wind direction, as
observed in dense barchan deserts
Description of the unsteady flow pattern from peak efficiency to near surge in subsonic centrifugal compressor stage
This paper aims to describe the flow structure modifications when the operating point moves from peak efficiency to near stall condition in a moderate pressure ratio centrifugal compressor stage consisted of a splittered unshrouded impeller and a vaned diffuser. The investigations are based on three-dimensional U-RANS simulation results. The flow is described in the impeller and in the vaned diffuser through time-averaged flow quantities and unsteady fluctuations. Results show that at low mass flow rate, the effects of secondary flow in the impeller are more pronounced, inducing both, high time-averaged values and temporal fluctuations of the flow angle near the shroud at the diffuser inlet, leading to vane suction side boundary layer separation. Pressure waves due to impeller diffuser interaction spread through the vaned diffuser generating unsteadiness which intensifies at near surge condition
-Limit Sets of Cellular Automata from a Computational Complexity Perspective
This paper concerns -limit sets of cellular automata: sets of
configurations made of words whose probability to appear does not vanish with
time, starting from an initial -random configuration. More precisely, we
investigate the computational complexity of these sets and of related decision
problems. Main results: first, -limit sets can have a -hard
language, second, they can contain only -complex configurations, third,
any non-trivial property concerning them is at least -hard. We prove
complexity upper bounds, study restrictions of these questions to particular
classes of CA, and different types of (non-)convergence of the measure of a
word during the evolution.Comment: 41 page
- …