6,854 research outputs found
Stabilization of acoustic modes using Helmholtz and Quarter-Wave resonators tuned at exceptional points
Acoustic dampers are efficient and cost-effective means for suppressing
thermoacoustic instabilities in combustion chambers. However, their design and
the choice of their purging air mass flow is a challenging task, when one aims
at ensuring thermoacoustic stability after their implementation. In the present
experimental and theoretical study, Helmholtz (HH) and Quarter-Wave (QW)
dampers are considered. A model for their acoustic impedance is derived and
experimentally validated. In a second part, a thermoacoustic instability is
mimicked by an electro-acoustic feedback loop in a rectangular cavity, to which
the dampers are added. The length of the dampers can be adjusted, so that the
system can be studied for tuned and detuned conditions. The stability of the
coupled system is investigated experimentally and then analytically, which
shows that for tuned dampers, the best stabilization is achieved at the
exceptional point. The stabilization capabilities of HH and QW dampers are
compared for given damper volume and purge mass flow.Comment: 34 pages, 19 figures, acepted in the Journal of Sound and Vibratio
Polynomial-Time Approximation Scheme for Data Broadcast
The data broadcast problem is to find a schedule for broadcasting a given set
of messages over multiple channels. The goal is to minimize the cost of the
broadcast plus the expected response time to clients who periodically and
probabilistically tune in to wait for particular messages.
The problem models disseminating data to clients in asymmetric communication
environments, where there is a much larger capacity from the information source
to the clients than in the reverse direction. Examples include satellites,
cable TV, internet broadcast, and mobile phones. Such environments favor the
``push-based'' model where the server broadcasts (pushes) its information on
the communication medium and multiple clients simultaneously retrieve the
specific information of individual interest.
This paper presents the first polynomial-time approximation scheme (PTAS) for
data broadcast with O(1) channels and when each message has arbitrary
probability, unit length and bounded cost. The best previous polynomial-time
approximation algorithm for this case has a performance ratio of 9/8
Fabricating management practices : "Responsible Care" and Corporate Social Responsibility.
Purpose this study focuses on the policy of Corporate Social Responsibility (CSR) launched in the chemical industry in the 1980s and known as “Responsible Care”. The debate surrounding this issue prompts us to question the ever-changing nature of this policy and the way to measure the performance achieved. Methodology Our findings are drawn from analysis of a double set of data including a longitudinal survey and a current case study. Blending these two data sets allows a better understanding of the ongoing building process of “Responsible Care” and, more broadly, of corporate social responsibility. Findings this paper asserts that, contrary to the common wisdom developed in research, companies do not simply react to stakeholder pressure. Companies autonomously develop ways to protect their environment and so contribute to changing Society's expectations. Thus, performance cannot be read without a dynamic perspective in mind. Research limitations/implications Our findings lead us to reconsider the assessment of companies' sustainable performances by taking into account the fabricating process of sustainable activities. The main limitation of this research stems from the single unit of analysis considered. Broader studies will be necessary to enrich our understanding of corporate policies. Originality/value of the paper Our paper stands apart from the traditional view of organizations as cynical actors and attempts to provide a more complex picture of the behaviours observed.Performance management; Performance measurement; “Responsible Care”; Corporate Social Responsibility;
Experimental validation and physical modelling of vocal folds pathologies
Voiced sounds involve self-sustained vocal folds oscillations due to the
interaction between the airflow and the vocal folds. Common vocal folds
pathologies like polyps and anatomical asymmetry degrade the mechanical vocal
fold properties and consequently disturb the normal oscillation pattern
resulting in an abnormal sound production. Treatment of voice abnormalities
would benefit from an improved understanding between the pathology and the
resulting oscillation pattern which motivates physical vocal folds modelling.
The current study applies a theoretical vocal folds model to vocal folds
pathologies. The theoretical vocal folds model is validated using an
experimental set-up simulating the human phonatory apparatus. It consists in a
pressure reservoir, a self-oscillating latex replica of the vocal folds and an
acoustical resonator. The effects of pathologies are simulated by modifying the
replica's geometry, elasticity, and homogeneity under controlled experimental
conditions. In general, we observed a close match between measurements and
theoretical predictions, which is all the more surprising considering the
crudeness of the theoretical mode
Differentially Private Empirical Risk Minimization
Privacy-preserving machine learning algorithms are crucial for the
increasingly common setting in which personal data, such as medical or
financial records, are analyzed. We provide general techniques to produce
privacy-preserving approximations of classifiers learned via (regularized)
empirical risk minimization (ERM). These algorithms are private under the
-differential privacy definition due to Dwork et al. (2006). First we
apply the output perturbation ideas of Dwork et al. (2006), to ERM
classification. Then we propose a new method, objective perturbation, for
privacy-preserving machine learning algorithm design. This method entails
perturbing the objective function before optimizing over classifiers. If the
loss and regularizer satisfy certain convexity and differentiability criteria,
we prove theoretical results showing that our algorithms preserve privacy, and
provide generalization bounds for linear and nonlinear kernels. We further
present a privacy-preserving technique for tuning the parameters in general
machine learning algorithms, thereby providing end-to-end privacy guarantees
for the training process. We apply these results to produce privacy-preserving
analogues of regularized logistic regression and support vector machines. We
obtain encouraging results from evaluating their performance on real
demographic and benchmark data sets. Our results show that both theoretically
and empirically, objective perturbation is superior to the previous
state-of-the-art, output perturbation, in managing the inherent tradeoff
between privacy and learning performance.Comment: 40 pages, 7 figures, accepted to the Journal of Machine Learning
Researc
cK¢ Modèle de connaissances pour le calcul de situations didactiques
International audienceCours à l'école d'été de didactique des mathématiques, 2003, présentant le modèle cK¢ et le cadre théorique dans lequel il a été construit, ainsi que divers exemples
cK¢ Modèle de connaissances pour le calcul de situations didactiques
International audienceCours à l'école d'été de didactique des mathématiques, 2003, présentant le modèle cK¢ et le cadre théorique dans lequel il a été construit, ainsi que divers exemples
Interest of 50% nitrous oxide and oxygen premix sedation in gerodontology
Elderly patients presenting cardiovascular, respiratory, or neurological disorders require a specific dental care approach, especially patients presenting Alzheimer’s disease. Sedative procedures can prevent dental care-induced stress, even when there is effective pain control, but they have to be adapted to accommodate age-induced physiological modifications, age-related pathologies, and the concomitant treatments. In many situations, routine sedative prescriptions for dental care, such as benzodiazepine or antihistaminics, are not recommended for these patients. Nitrous oxide inhalation together with a specific behavioral threshold is currently the only sedative procedure adapted to cognitively-impaired elderly patients. Nitrous oxide is able to curb stress and its cardiovascular consequences, improve oxygenation, and optimize cooperation during dental care, making not only rehabilitation treatments but also routine dental care a viable option
Cheminements autour de l'identité urbaine
Cet article propose une analyse synthétique autour de la question des identités urbaines, entendues à la fois comme le reflet des pratiques et perceptions individuelles dans la ville, et comme le résultat d'expressions collectives qui traduisent le jeu identitaire auquel se prêtent les individus et les groupes. La production de l'identité urbaine est aussi analysée à partir de la notion de ressources, et au travers des "représentations objectales" qui cristallisent des significations sans cesse négociées et renouvelées, et qui sont souvent soumises aux conflits
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