A quoi servent les comités d'audit ? Un regard sur la recherche empirique

cahier de recherche n°2009-14 E2Résumé. Dans une optique disciplinaire de la gouvernance, cet article propose un cadre d'analyse des contributions du comité d'audit, en termes de qualité du processus d'audit d'une part (effets indirects), et de qualité de l'information financière publiée d'autre part (effets directs). Une revue approfondie de la recherche empirique nous permet alors d'évaluer les principaux leviers d'action des comités d'audit, ainsi que les conditions d'efficacité de ces organes. Dans les grandes lignes, il ressort qu'un comité d'audit indépendant contribue souvent à la qualité de l'audit externe et à la fiabilité des données comptables (avec des nuances) ; et que l'expertise financière du comité stimule la fiabilité du contrôle interne et la pertinence des états financiers. Indépendance et expertise apparaissent alors comme des attributs importants et complémentaires à l'efficacité du comité d'audit. Les limites et prolongements possibles de ce courant de recherche sont discutés

A quoi servent les comités d'audit ? Un regard sur la recherche empirique

Résumé. Dans une optique disciplinaire de la gouvernance, cet article propose un cadre d'analyse des contributions du comité d'audit, en termes de qualité du processus d'audit d'une part (effets indirects), et de qualité de l'information financière publiée d'autre part (effets directs). Une revue approfondie de la recherche empirique nous permet alors d'évaluer les principaux leviers d'action des comités d'audit, ainsi que les conditions d'efficacité de ces organes. Dans les grandes lignes, il ressort qu'un comité d'audit indépendant contribue souvent à la qualité de l'audit externe et à la fiabilité des données comptables (avec des nuances) ; et que l'expertise financière du comité stimule la fiabilité du contrôle interne et la pertinence des états financiers. Indépendance et expertise apparaissent alors comme des attributs importants et complémentaires à l'efficacité du comité d'audit. Les limites et prolongements possibles de ce courant de recherche sont discutés.Comité d'audit; gouvernance; audit externe; audit interne; qualité de l'audit; qualité de l'information financière

Using the de Haas-van Alphen effect to map out the closed three-dimensional Fermi surface of natural graphite

The Fermi surface of graphite has been mapped out using de Haas van Alphen (dHvA) measurements at low temperature with in-situ rotation. For tilt angles $\theta>60^{\circ}$ between the magnetic field and the c-axis, the majority electron and hole dHvA periods no longer follow the $\cos(\theta)$ behavior demonstrating that graphite has a 3 dimensional closed Fermi surface. The Fermi surface of graphite is accurately described by highly elongated ellipsoids. A comparison with the calculated Fermi surface suggests that the SWM trigonal warping parameter $\gamma_3$ is significantly larger than previously thought

Current-induced nuclear-spin activation in a two-dimensional electron gas

Electrically detected nuclear magnetic resonance was studied in detail in a two-dimensional electron gas as a function of current bias and temperature. We show that applying a relatively modest dc-current bias, I_dc ~ 0.5 microAmps, can induce a re-entrant and even enhanced nuclear spin signal compared with the signal obtained under similar thermal equilibrium conditions at zero current bias. Our observations suggest that dynamic nuclear spin polarization by small current flow is possible in a two-dimensional electron gas, allowing for easy manipulation of the nuclear spin by simple switching of a dc current.Comment: 5 pages, 3 fig

Colossal magnetoresistance in an ultra-clean weakly interacting 2D Fermi liquid

We report the observation of a new phenomenon of colossal magnetoresistance in a 40 nm wide GaAs quantum well in the presence of an external magnetic field applied parallel to the high-mobility 2D electron layer. In a strong magnetic field, the magnetoresistance is observed to increase by a factor of ~300 from 0 to 45T without the system undergoing any metal-insulator transition. We discuss how this colossal magnetoresistance effect cannot be attributed to the spin degree-of-freedom or localization physics, but most likely emanates from strong magneto-orbital coupling between the two-dimensional electron gas and the magnetic field. Our observation is consistent with a field-induced 2D-to-3D transition in the confined electronic system

Amp\`ere-Class Pulsed Field Emission from Carbon-Nanotube Cathodes in a Radiofrequency Resonator

Pulsed field emission from cold carbon-nanotube cathodes placed in a radiofrequency resonant cavity was observed. The cathodes were located on the backplate of a conventional $1+\frac{1}{2}$-cell resonant cavity operating at 1.3-GHz and resulted in the production of bunch train with maximum average current close to 0.7 Amp\`ere. The measured Fowler-Nordheim characteristic, transverse emittance, and pulse duration are presented and, when possible, compared to numerical simulations. The implications of our results to high-average-current electron sources are briefly discussed.Comment: 5 pages, 6 figures; submitted to Applied Physics Letter

Sub-picosecond compression by velocity bunching in a photo-injector

We present an experimental evidence of a bunch compression scheme that uses a traveling wave accelerating structure as a compressor. The bunch length issued from a laser-driven radio-frequency electron source was compressed by a factor >3 using an S-band traveling wave structure located immediately downstream from the electron source. Experimental data are found to be in good agreement with particle tracking simulations.Comment: 19 pages, 9 figures, submitted to Phys. Rev. Spec. Topics A&

Intrinsic Gap of the nu=5/2 Fractional Quantum Hall State

The fractional quantum Hall effect is observed at low field, in a regime where the cyclotron energy is smaller than the Coulomb interaction. The nu=5/2 excitation gap is measured to be 262+/-15 mK at ~2.6 T, in good agreement with previous measurements performed on samples with similar mobility, but with electronic density larger by a factor of two. The role of disorder on the nu=5/2 gap is examined. Comparison between experiment and theory indicates that a large discrepancy remains for the intrinsic gap extrapolated from the infinite mobility (zero disorder) limit. In contrast, no such large discrepancy is found for the nu=1/3 Laughlin state. The observation of the nu=5/2 state in the low-field regime implies that inclusion of non-perturbative Landau level mixing may be necessary to better understand the energetics of half-filled fractional quantum hall liquids.Comment: 5 pages, 4 figures; typo corrected, comment expande