1,949 research outputs found
Bifurcation-based parameter tuning in a model of the GnRH pulse and surge generator
We investigate a model of the GnRH pulse and surge generator, with the
definite aim of constraining the model GnRH output with respect to a
physiologically relevant list of specifications. The alternating pulse and
surge pattern of secretion results from the interaction between a GnRH
secreting system and a regulating system exhibiting fast-slow dynamics. The
mechanisms underlying the behavior of the model are reminded from the study of
the Boundary-Layer System according to the "dissection method" principle. Using
singular perturbation theory, we describe the sequence of bifurcations
undergone by the regulating (FitzHugh-Nagumo) system, encompassing the rarely
investigated case of homoclinic connexion. Basing on pure dynamical
considerations, we restrict the space of parameter search for the regulating
system and describe a foliation of this restricted space, whose leaves define
constant duration ratios between the surge and the pulsatility phase in the
whole system. We propose an algorithm to fix the parameter values to also meet
the other prescribed ratios dealing with amplitude and frequency features of
the secretion signal. We finally apply these results to illustrate the dynamics
of GnRH secretion in the ovine species and the rhesus monkey
Frequency stability of a wavelength meter and applications to laser frequency stabilization
Interferometric wavelength meters have attained frequency resolutions down to
the MHz range. In particular, Fizeau interferometers, which have no moving
parts, are becoming a popular tool for laser characterization and
stabilization. In this article, we characterize such a wavelength meter using
an ultra-stable laser in terms of relative frequency instability
and demonstrate that it can achieve a short-term instability
and a frequency drift of order
MHz/day. We use this apparatus to demonstrate frequency control of a
near-infrared laser, where a frequency instability below
from 1 s to 2000 s is achieved. Such performance is for example adequate for
ions trapping and atoms cooling experiments.Comment: 5 pages, 4 figure
PBS-Calculus: A Graphical Language for Coherent Control of Quantum Computations
We introduce the PBS-calculus to represent and reason on quantum computations
involving coherent control of quantum operations. Coherent control, and in
particular indefinite causal order, is known to enable multiple computational
and communication advantages over classically ordered models like quantum
circuits. The PBS-calculus is inspired by quantum optics, in particular the
polarising beam splitter (PBS for short). We formalise the syntax and the
semantics of the PBS-diagrams, and we equip the language with an equational
theory, which is proved to be sound and complete: two diagrams are representing
the same quantum evolution if and only if one can be transformed into the other
using the rules of the PBS-calculus. Moreover, we show that the equational
theory is minimal. Finally, we consider applications like the implementation of
controlled permutations and the unrolling of loops.Comment: 55 pages. This is the full version of a paper published at MFCS'2
An anticipative kinematic limitation avoidance algorithm for collaborative robots : two-dimensional case
This paper presents an anticipative robot kinematic limitation avoidance algorithm for collaborative robots. The main objective is to improve the performance and the intuitivity of physical human-robot interaction. Currently, in such interactions, the human user must focus on the task as well as on the robot configuration. Indeed, the user must pay a close attention to the robot in order to avoid limitations such as joint position limitations, singularities and collisions with the environment. The proposed anticipative algorithm aims at relieving the human user from having to deal with such limitations by automatically avoiding them while considering the user's intentions. The framework developed to manage several limitations occurring simultaneously in three-dimensional space is first presented. The algorithm is then presented and detailed for each individual limitation of a spatial RRR serial robot. Finally, experiments are performed in order to assess the performance of the algorithm
New concepts of inertial measurements with multi-species atom interferometry
In the field of cold atom inertial sensors, we present and analyze innovative
configurations for improving their measurement range and sensitivity,
especially attracting for onboard applications. These configurations rely on
multi-species atom interferometry, involving the simultaneous manipulation of
different atomic species in a unique instrument to deduce inertial
measurements. Using a dual-species atom accelerometer manipulating
simultaneously both isotopes of rubidium, we report a preliminary experimental
realization of original concepts involving the implementation of two atom
interferometers first with different interrogation times and secondly in phase
quadrature. These results open the door to a new generation of atomic sensors
relying on high performance multi-species atom interferometric measurements
Risk assessment based on performantial criterion for inspection of offshore structures in presence of large cracks
International audienceWhen performing risk analysis, it is often uneasy to find the link between limit state and consequences. This paper focuses on efficiency based limit states in case of large cracks on offshore structures. Randomness and uncertainties on loading as well as on crack measurement and detection are introduced.Les analyses de risque sont souvent dĂ©licates par manque de lien direct entre la fonction dâĂ©tat et les consĂ©quences. Cet article propose des fonctions dâĂ©tat de type performantiel (dĂ©placement) dans le cas dâapparitions de fissures traversantes dans des tubes mĂ©talliques de structures offshore. Les alĂ©as sur le chargement, la mesure de la fissure et la performance des inspections sont intĂ©grĂ©s dans lâanalyse de risque
Minimal Equational Theories for Quantum Circuits
We introduce the first minimal and complete equational theory for quantum
circuits. Hence, we show that any true equation on quantum circuits can be
derived from simple rules, all of them being standard except a novel but
intuitive one which states that a multi-control rotation is nothing but
the identity. Our work improves on the recent complete equational theories for
quantum circuits, by getting rid of several rules including a fairly
unpractical one. One of our main contributions is to prove the minimality of
the equational theory, i.e. none of the rules can be derived from the other
ones. More generally, we demonstrate that any complete equational theory on
quantum circuits (when all gates are unitary) requires rules acting on an
unbounded number of qubits. Finally, we also simplify the complete equational
theories for quantum circuits with ancillary qubits and/or qubit discarding
An anticipative kinematic limitation avoidance algorithm for collaborative robots : Three-dimensional case
This paper presents an anticipative robot kinematic limitation avoidance algorithm for collaborative robots. The main objective is to improve the performance and the intuitivity of physical human-robot interaction. Currently, in such interactions, the human user must focus on the task as well as on the robot configuration. Indeed, the user must pay a close attention to the robot in order to avoid limitations such as joint position limitations, singularities and collisions with the environment. The proposed anticipative algorithm aims at relieving the human user from having to deal with such limitations by automatically avoiding them while considering the user's intentions. The framework developed to manage several limitations occurring simultaneously in three-dimensional space is first presented. The algorithm is then presented and detailed for each individual limitation of a spatial RRR serial robot. Finally, experiments are performed in order to assess the performance of the algorithm
Nanometer-scale absolute laser ranging: exploiting a two-mode interference signal for high accuracy distance measurements
International audienceAbsolute distance measurement with accuracy below the micron scale is important in astronomical optical interferometry. We present here an absolute laser rangefinder which relies on the detection of a two mode interference signal. We exploit the specific signature of the signal to extract both the interferometric and synthetic phase measurements, leading to distance measurement with nanometric accuracy. A resolution of 100 pm has been achieved in 75 ÎŒs with a relatively simple laser source. Amplitude to phase coupling in the detection chains turns out to be the largest source of systematic errors. A specific detection scheme is implemented, using optical demodulation of the microwave optical signal, to reduce amplitude-to-phase related systematic errors to below the required level
Quantum Circuit Completeness: Extensions and Simplifications
Although quantum circuits have been ubiquitous for decades in quantum
computing, the first complete equational theory for quantum circuits has only
recently been introduced. Completeness guarantees that any true equation on
quantum circuits can be derived from the equational theory. We improve this
completeness result in two ways: (i) We simplify the equational theory by
proving that several rules can be derived from the remaining ones. In
particular, two out of the three most intricate rules are removed, the third
one being slightly simplified. (ii) The complete equational theory can be
extended to quantum circuits with ancillae or qubit discarding, to represent
respectively quantum computations using an additional workspace, and hybrid
quantum computations. We show that the remaining intricate rule can be greatly
simplified in these more expressive settings, leading to equational theories
where all equations act on a bounded number of qubits. The development of
simple and complete equational theories for expressive quantum circuit models
opens new avenues for reasoning about quantum circuits. It provides strong
formal foundations for various compiling tasks such as circuit optimisation,
hardware constraint satisfaction and verification
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