Inequivalent embeddings of the Koras-Russell cubic threefold

The Koras-Russell threefold is the hypersurface X of the complex affine four-space defined by the equation x^2y+z^2+t^3+x=0. It is well-known that X is smooth contractible and rational but that it is not algebraically isomorphic to affine three-space. The main result of this article is to show that there exists another hypersurface Y of the affine four-space, which is isomorphic to X as an abstract variety, but such that there exists no algebraic automorphism of the ambient space which restricts to an isomorphism between X and Y. In other words, the two hypersurfaces are inequivalent. The proof of this result is based on the description of the automorphism group of X. We show in particular that all algebraic automorphisms of X extend to automorphisms of the ambient space

Pandemic Lockdown: The Role of Government Commitment

This note studies optimal lockdown policy in a model in which the government can limit a pandemic's impact via a lockdown at the cost of lower economic output. A government would like to commit to limit the extent of future lockdown in order to support more optimistic investor expectations in the present. However, such a commitment is not credible since investment decisions are sunk when the government makes the lockdown decision in the future. The commitment problem is more severe if lockdown is sufficiently effective at limiting disease spread or if the size of the susceptible population is sufficiently large. Credible rules that limit a government's ability to lock down the economy in the future can improve the efficiency of lockdown policy

Pandemic Lockdown: The Role of Government Commitment

This note studies optimal lockdown policy in a model in which the government can limit a pandemic's impact via a lockdown at the cost of lower economic output. A government would like to commit to limit the extent of future lockdown in order to support more optimistic investor expectations in the present. However, such a commitment is not credible since investment decisions are sunk when the government makes the lockdown decision in the future. The commitment problem is more severe if lockdown is sufficiently effective at limiting disease spread or if the size of the susceptible population is sufficiently large. Credible rules that limit a government's ability to lock down the economy in the future can improve the efficiency of lockdown policy

Émotions: vécu d'élèves de 3e et 4e HarmoS

Ce travail de recherche explore le thème des émotions, plus précisément celles de l’enfant. Un intérêt particulier est porté à quatre émotions de base, c’est-à-dire la joie, la tristesse, la peur et la colère. Les interviews de douze élèves issus de 3e et 4e HarmoS permettent de découvrir la perception qu’ils ont de ces émotions, la manière dont ils essaient de les gérer et s’ils les expriment librement ou non. En se basant sur le vécu de ces enfants, on découvre si ces derniers ressentent les quatre émotions choisies à l’école, quels en sont les déclencheurs et quelles aides ils souhaiteraient. Enfin, on remarque l’importance des émotions et à quel point on devrait, en tant qu’enseignant, aborder ce thème en classe et en tenir compte dans notre pédagogie

Optical-resolution photoacoustic imaging through thick tissue with a thin capillary as a dual optical-in acoustic-out waveguide

We demonstrate the ability to guide high-frequency photoacoustic waves through thick tissue with a water-filled silica-capillary (150 \mu m inner diameter and 30 mm long). An optical-resolution photoacoustic image of a 30 \mu m diameter absorbing nylon thread was obtained by guiding the acoustic waves in the capillary through a 3 cm thick fat layer. The transmission loss through the capillary was about -20 dB, much lower than the -120 dB acoustic attenuation through the fat layer. The overwhelming acoustic attenuation of high-frequency acoustic waves by biological tissue can therefore be avoided by the use of a small footprint capillary acoustic waveguide for remote detection. We finally demonstrate that the capillary can be used as a dual optical-in acoustic-out waveguide, paving the way for the development of minimally invasive optical-resolution photoacoustic endoscopes free of any acoustic or optical elements at their imaging tip

Molecular Photovoltaic Devices Mimic Photosynthesis

Photoinduced charge-transfer processes involving molecules adsorbed at interfaces are a fascinating topic which is presently attracting wide attention. Our investigations have focused on the identification of the factors that control the dynamics of such processes. The goal is to design molecular electronic devices that achieve efficient light-induced charge separation. Applications of similar systems in photochromic and electrochromic devices appear also feasible

A note on the consistency of Hybrid Eulerian/Lagrangian approach to multiphase flows

The aim of the present paper is to introduce and to discuss inconsistencies errors that may arise when Eulerian and Lagrangian models are coupled for the simulations of turbulent poly-dispersed two-phase flows. In these hydrid models, two turbulence models are in fact implicitely used at the same time and it is essential to check that they are consistent, in spite of their apparent different formulations. This issue appears in particular in the case of very-small particles, or tracer-limit particles, and it is shown that coupling inconsistent turbulence models (Eulerian and Lagrangian) can result in non-physical results, notably for second-order fluid velocity moments. This problem is illustrated by some computations for fluid particles in a turbulent channel flow using several coupling strategies.Comment: 14 pages, 3 figure

Molecular photovoltaics

Photoinduced charge transfer processes involving molecules adsorbed at interfaces are a fascinating topic which is presently attracting wide attention. Our investigations have focused on the identification of the factors that control the dynamics of such processes. The goal is to design molecular electronic devices that achieve efficient light-induced charge separation. Applications of similar systems in photochromic and electrochromic devices also appear feasible

Optical-resolution photoacoustic microscopy by use of a multimode fiber

We demonstrate Optical-Resolution Photoacoustic Microscopy (OR-PAM), where the optical field is focused and scanned using Digital Phase Conjugation (DPC) through a multimode fiber. The focus is scanned across the field of view using digital means, and the acoustic signal induced is collected by a transducer. Optical-resolution photoacoustic images of a knot made by two absorptive wires are obtained and we report on resolution smaller than 1.5{\mu}m across a 201{\mu}m by 201{\mu}m field of view. The use of a multimode optical fiber for the optical excitation part can pave the way for miniature endoscopes that can provide optical-resolution photoacoustic images at large optical depth.Comment: 10 pages, 3 figure

Descriptive Characteristics and Risk Factors for Trauma: An Evidence-Based Practice Project

This Evidence-Based Practice (EBP) project examined the following question: What are the perspectives, experiences, and self-reports of adult individuals, groups, or populations who have MCI or report problems with Functional Cognition (and / or their caregivers)