Regression modeling on stratified data with the lasso

We consider the estimation of regression models on strata defined using a categorical covariate, in order to identify interactions between this categorical covariate and the other predictors. A basic approach requires the choice of a reference stratum. We show that the performance of a penalized version of this approach depends on this arbitrary choice. We propose a refined approach that bypasses this arbitrary choice, at almost no additional computational cost. Regarding model selection consistency, our proposal mimics the strategy based on an optimal and covariate-specific choice for the reference stratum. Results from an empirical study confirm that our proposal generally outperforms the basic approach in the identification and description of the interactions. An illustration on gene expression data is provided.Comment: 23 pages, 5 figure

Compact and explicit physical model for lateral metal-oxide-semiconductor field-effect transistor with nanoelectromechanical system based resonant gate

We propose a simple analytical model of a metal-oxide-semiconductor field-effect transistor with a lateral resonant gate based on the coupled electromechanical equations, which are self-consistently solved in time. All charge densities according to the mechanical oscillations are evaluated. The only input parameters are the physical characteristics of the device. No extra mathematical parameters are used to fit the experimental results. Theoretical results are in good agreement with the experimental data in static and dynamic operation. Our model is comprehensive and may be suitable for any electromechanical device based on the field-effect transduction

The Politics of Derek Walcott’s Poetic Drama

This essay focuses on Derek Walcott’s The Haitian Earth, a chronicle of Haiti’s violent revolution led by Toussaint l’Ouverture, Jean-Jacques Dessalines and Henri Christophe. Far from painting a romantic idealization of those legendary heroes, Walcott gives a fairly unsavoury realistic picture of what power does to men in a postcolonial context, and of how violent models can be appropriated and made worse. The use of language, dialect, of different registers of creole and standard English plays a major role in drawing the dividing-line between morality and unethical, bestial behaviour. The essay also focus on an unpublished musical comedy, Marie Laveau, which was however staged and recorded in Trinidad, in which dialogism develops between several forms of language, including that of songs, and also between two separate worlds. In Haitian Earth, Walcott seems to have opted for a realistic pessimism, while in the musical comedy Marie Laveau, he has chosen an unrealistic, somewhat romantic faith in man’s ability to reform himself and in human redemption at large.

When Optimal Centralized Mechanism Prescribes<br />to Follow Agent's Recommendation

Working Paper du GATE 2003-05This paper investigates to which extent the optimal centralized mechanism as defined by the Revelation Principle may optimally prescribe to follow the agent's recommendation. We define two sub-cases, called delegation and authority, being parts of the consideredcentralized organization, a decision being delegated to the agent when his recommendation is followed by the principal. We assume that there are both adverse selection and moral hazard under delegation and moral hazard under authority and the agent is risk neutral but protected by limited liability on utility. We find that delegation can be efficient even if the principal'stalent is higher than the expected talent of the unknown agent.Dans quelle mesure le mécanisme centralisé optimal défini par le principe de révélation peut-il prescrire de suivre la recommandation de l'agent? Deux sous-cas, délégation et autorité, faisant partie de l'organisation centralisée optimale sont définis, une décision étant déléguée à l'agent lorsque sa recommandation est suivie par le principal. On suppose qu'il y a à la fois sélection adverse et aléa moral dans le cas de la délégation, et aléa moral dans le cas de l'autorité. L'agent est neutre vis à vis du risque et protégé par une contrainte de responsabilité limitée. On montre que la délégation peut être efficace même lorsque le talent du principal estsupérieur à l'espérance du talent de l'agent

Energy dissipation on quantum systems and 2D materials

Understanding the nanoscale energy dissipation is nowadays among few priorities particularly in solid state systems. Breakdown of topological protection, loss of quantum information and disorder-assisted hot electrons scattering in graphene are few examples, where the presence of energy dissipation has a great impact on the studied object. It is therefore critical to know, how and where the energy leaks. The aim of this project is to address this issue by using a highly sensitive pendulum geometry Atomic Force Microscope (p-AFM), oscillating like a tiny pendulum over the sample surface. The microscope is perfectly suited to measure tiny amounts of dissipation, the tip position is controlled with atomic accuracy owing to a tunnelling current and the enhanced sensitivity allows to distinguish between electronic, phononic or van der Waals type of dissipation. The measurements can be performed in a wide range of temperatures from T=5K to room temperature and in magnetic fields spanning from B=0T to B= ± 7T. The design of the sample holder allows to perform dissipation measurements while passing electric current in the plane as well as to apply in-plane voltage to the the sample surface as well as adding two contact wires. The experiments showed that the mechanical oscillations of the cantilever and the sample surface can sense the quantum effects of 2D materials or quantum systems. Indeed, quantum dot-like behaviour is reported on free-standing graphene monolayer where electrons charging and discharging events are observed and dissipation maps show Coulomb rings. In addition to that, the band filling of twisted bilayer graphene at the magic angle twist and a signature of potential orbital ferromagnetic behaviour for the band filling equal to 3ns/4 was investigated. Last, the transition between ferromagnetic to paramagnetic phase in a molybdenum disulfate monolayer was investigated and revealed a linear dependence of the magnetic susceptibility as suggested by theoretical studies

Bayesian Lower Bounds for Dense or Sparse (Outlier) Noise in the RMT Framework

Robust estimation is an important and timely research subject. In this paper, we investigate performance lower bounds on the mean-square-error (MSE) of any estimator for the Bayesian linear model, corrupted by a noise distributed according to an i.i.d. Student's t-distribution. This class of prior parametrized by its degree of freedom is relevant to modelize either dense or sparse (accounting for outliers) noise. Using the hierarchical Normal-Gamma representation of the Student's t-distribution, the Van Trees' Bayesian Cram\'er-Rao bound (BCRB) on the amplitude parameters is derived. Furthermore, the random matrix theory (RMT) framework is assumed, i.e., the number of measurements and the number of unknown parameters grow jointly to infinity with an asymptotic finite ratio. Using some powerful results from the RMT, closed-form expressions of the BCRB are derived and studied. Finally, we propose a framework to fairly compare two models corrupted by noises with different degrees of freedom for a fixed common target signal-to-noise ratio (SNR). In particular, we focus our effort on the comparison of the BCRBs associated with two models corrupted by a sparse noise promoting outliers and a dense (Gaussian) noise, respectively