2,024 research outputs found
Two-component Bose gases with one-body and two-body couplings
We study the competition between one-body and two-body couplings in
weakly-interacting two-component Bose gases, in particular as regards field
correlations. We derive the meanfield theory for both ground state and
low-energy pair excitations in the general case where both one-body and
two-body couplings are position-dependent and the fluid is subjected to a
state-dependent trapping potential. General formulas for phase and density
correlations are also derived. Focusing on the case of homogeneous systems, we
discuss the pair-excitation spectrum and the corresponding excitation modes,
and use them to calculate correlation functions, including both quantum and
thermal fluctuation terms. We show that the relative phase of the two
components is imposed by that of the one-body coupling, while its fluctuations
are determined by the modulus of the one-body coupling and by the two-body
coupling. One-body coupling and repulsive two-body coupling cooperate to
suppress relative-phase fluctuations, while attractive two-body coupling tends
to enhance them. Further applications of the formalism presented here and
extensions of our work are also discussed.Comment: published versio
Information Extraction from Documents: Question Answering vs Token Classification in real-world setups
Research in Document Intelligence and especially in Document Key Information
Extraction (DocKIE) has been mainly solved as Token Classification problem.
Recent breakthroughs in both natural language processing (NLP) and computer
vision helped building document-focused pre-training methods, leveraging a
multimodal understanding of the document text, layout and image modalities.
However, these breakthroughs also led to the emergence of a new DocKIE subtask
of extractive document Question Answering (DocQA), as part of the Machine
Reading Comprehension (MRC) research field. In this work, we compare the
Question Answering approach with the classical token classification approach
for document key information extraction. We designed experiments to benchmark
five different experimental setups : raw performances, robustness to noisy
environment, capacity to extract long entities, fine-tuning speed on Few-Shot
Learning and finally Zero-Shot Learning. Our research showed that when dealing
with clean and relatively short entities, it is still best to use token
classification-based approach, while the QA approach could be a good
alternative for noisy environment or long entities use-cases
Uncertainty Quantification for Eigenvalue-Realization-Algorithm, A Class of Subspace System Identification
In Operational Modal Analysis, the modal parameters (natural frequencies, damping ratios and mode shapes), obtained from Stochastic System Identication of structures, are subject to statistical uncertainty from ambient vibration measurements. It is hence necessary to evaluate the condence intervals of these obtained results. This paper will propose an algorithm that can eciently estimate the uncertainty on modal parameters obtained from the Eigensystem-Realization-Algorithm (ERA).En Analyse modale, les paramètres modaux (fréquences, amortissements et déformées), obtenus à partir des methodes stochastiques sont sujet à des erreurs d'incertitude. Il est nécessaire d'évaluer les intervalles de conance correspondants. Ce calcul est fait pour une classe d'algorithmes sous espaces appelés ERA (Eigensystem-Realization-Algorithm)
Multi-order covariance computation for estimates in stochastic subspace identification using QR decompositions
International audienceFor applications as Operational Modal Analysis (OMA) of vibrating structures, an output-only LTI system with state and measurement noise can be identified using subspace methods. While these identification techniques have been very suitable for the identification of such mechanical, aeronautical or civil structures, covariance expressions of the estimates of the system matrices are difficult to obtain and theoretical results from literature are hard to implement for output-only systems with unknown noise properties in practice. Moreover, the model order of the underlying system is generally unknown and due to noise and model errors, usual statistical criteria cannot be used. Instead, the system is estimated at multiple model orders and some GUI driven stabilization diagram containing the resulting modal parameters is used by the structural engineer. Then, the covariance of the estimates at these different model orders is an important information for the engineer, which, however, would be computationally expensive to obtain with the existing tools. Recently a fast multi-order version of the stochastic subspace identification approach has been proposed, which is based on the use of the QR decomposition of the observability matrix at the largest model order. In this paper, the corresponding covariance expressions for the system matrix estimates at multiple model orders are derived and successfully applied on real vibration data
Uncertainty Quantification for Modal Parameters from Stochastic Subspace Identification on Multi-Setup Measurements
International audienceIn operational modal analysis, the modal parameters (natural frequencies, damping ratios and mode shapes), obtained with stochastic subspace identification from ambient vibration measurements of structures, are subject to statistical uncertainty. It is hence necessary to evaluate the uncertainty bounds of the obtained results, which can be done by a first-order perturbation analysis. To obtain vibration measurements at many coordinates of a structure with only a few sensors, it is common practice to use multiple sensor setups for the measurements. Recently, a multi-setup subspace identification algorithm has been proposed that merges the data from different setups prior to the identification step to obtain one set of global modal parameters, taking the possibly different ambient excitation characteristics between the measurements into account. In this paper, an algorithm is proposed that efficiently estimates the covari-ances on modal parameters obtained from this multi-setup subspace identification. The new algorithm is validated on multi-setup ambient vibration data of the Z24 Bridge, benchmark of the COST F3 European network
The smallest macroscale tensile test - a model to describe constrained flow at the microscale
This work addresses the strain response and plastic flow behavior of grain boundary or interface containing materials during small scale mechanical testing. We introduce a set of geometric criteria allowing us to constrain a sample to obtain macroscopic-like flow behavior on a microscale test, as shown in Figure 1. Furthermore, the featured parameter, the blocked volume ratio, provided a new description of plasticity of microscale tensile samples in a constrained volume due to external interfaces such as coating and grain boundaries. The proposed description was experimentally validated with different Ni-based materials and different constraints (grain boundary and coating interfaces). The developed theory would open new research avenues in establishing the connection between microscale response to bulk properties as follows:
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Life history linked to immune investment in developing amphibians
The broad diversity of amphibian developmental strategies has been shaped, in part, by pathogen pressure, yet trade-offs between the rate of larval development and immune investment remain poorly understood. The expression of antimicrobial peptides (AMPs) in skin secretions is a crucial defense against emerging amphibian pathogens and can also indirectly affect host defense by influencing the composition of skin microbiota. We examined the constitutive or induced expression of AMPs in 17 species at multiple life-history stages. We found that AMP defenses in tadpoles of species with short larval periods (fast pace of life) were reduced in comparison with species that overwinter as tadpoles and grow to a large size. A complete set of defensive peptides emerged soon after metamorphosis. These findings support the hypothesis that species with a slow pace of life invest energy in AMP production to resist potential pathogens encountered during the long larval period, whereas species with a fast pace of life trade this investment in defense for more rapid growth and development
Amenability of groups and -sets
This text surveys classical and recent results in the field of amenability of
groups, from a combinatorial standpoint. It has served as the support of
courses at the University of G\"ottingen and the \'Ecole Normale Sup\'erieure.
The goals of the text are (1) to be as self-contained as possible, so as to
serve as a good introduction for newcomers to the field; (2) to stress the use
of combinatorial tools, in collaboration with functional analysis, probability
etc., with discrete groups in focus; (3) to consider from the beginning the
more general notion of amenable actions; (4) to describe recent classes of
examples, and in particular groups acting on Cantor sets and topological full
groups
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