Can news shocks account for the business-cycle dynamics of inventories?

The procyclicality of inventory investment is a central feature of US business cycles. As such, it provides a test for the recent literature on news shocks, which argues that anticipated changes in fundamentals are important sources of aggregate fluctuations. We show that, in a range of inventory models, anticipated shocks to fundamentals generate booms of a peculiar kind: consumption and investment increase, but inventories fall persistently. During these booms, production and inventory investment are dominated by intertemporal substitution, as firms satisfy sales out of inventory stock and delay production until the realization of the anticipated shock. This mechanism is surprisingly difficult to overturn. We derive analytical parameter restrictions which guarantee procyclical inventory dynamics in response to news shocks, and show that standard calibrations considered in the literature do not come close to satisfying the restrictions. Furthermore, the introduction of the frictions studied by the news literature, such as variable capacity utilization and adjustment costs, is not sufficient to restore the procyclicality of inventories. We use the models' restrictions on the comovement of sales and inventories to identify news shocks in postwar US data. We find that the identified shock leads to a diffusion in TFP, but has a short implementation lag and accounts for a small fraction of long-run movements in TFP, inventories and sales

Determination of physical properties of the asteroid (41) Daphne from interferometric observations in the thermal infrared

We describe interferometric observations of the asteroid (41) Daphne in the thermal infrared obtained with the Mid-Infrared Interferometric Instrument (MIDI) of the Very Large Telescope Interferometer (VLTI). We derived the size and the surface thermal properties of (41) Daphne by means of a thermophysical model (TPM), which is used for the interpretation of interferometric data for the first time. From our TPM analysis, we derived a volume equivalent diameter for (41) Daphne of 189 km, using a non-convex 3-D shape model derived from optical lightcurves and adaptive optics images (B. Carry, private communication). On the other hand, when using the convex shape of Kaasalainen et al. (2002. Icarus 159, 369-395) in our TPM analysis, the resulting volume equivalent diameter of (41) Daphne is between 194 and 209 km, depending on the surface roughness. The shape of the asteroid is used as an a priori information in our TPM analysis. No attempt is made to adjust the shape to the data. Only the size of the asteroid and its thermal parameters (albedo, thermal inertia and roughness) are adjusted to the data. We estimated our model systematic uncertainty to be of 4% and of 7% on the determination of the asteroid volume equivalent diameter depending on whether the non-convex or the convex shape is used, respectively. In terms of thermal properties, we derived a value of the surface thermal inertia smaller than 50 J m-2 s-0.5 K-1 and preferably in the range between 0 and 30 J m-2 s-0.5 K-1. Our TPM analysis also shows that Daphne has a moderate macroscopic surface roughness.Comment: 44 pages, 8 figures, 3 table

Essays in macroeonomics and corporate finance

This dissertation contains three essays in Macroeconomics and Corporate Finance. The first essay deals the implications of inventory investment for news-driven business cycles. The second essay looks at the connection between debt structure and investment at the firm level. The third essay proposes a macroeonomic model where firms choose simultaneously the composition and scale of their debt

Recherche et caractérisation d'exoplanètes par photométrie : développement et exploitation du projet ASTEP

The photometry of transits is a powerful method to detect and characterize exoplanets. The Concordia base in Dome C, Antarctica, is an extremely promising site for photometric astronomy due to the 3-month long night during the Antarctic winter and very favorable weather conditions. The ASTEP project (Antarctic Search for Transiting ExoPlanets) is a pilot project to discover and characterize transiting planets and understand the limits of visible photometry from the Concordia site. The project is divided into two phases : ASTEP South, a fixed 10 cm refractor, and ASTEP 400, a pointable 40 cm telescope. This thesis is dedicated to the development and exploitation of the ASTEP project. A photometric simulator is built to identify the noise sources affecting the photometry, such as seeing and PSF (Point Spread Function) variations. The simulator is used to choose the ASTEP CCD cameras. These cameras are tested and characterized. We then focus on ASTEP South. The instrument is composed of a fixed 10 cm refractor and a CCD camera inside a heated box, pointing continuously a 3.88°x3.88° field of view centered on the celestial south pole. The observation strategy is validated, and the various parts of the instrument are chosen. The observation parameters are defined from an analysis of the crowding in the field of view and tests on the sky. ASTEP South has functionned almost continuously during the 2008, 2009, and 2010 winters. A preliminary analysis leads to the qualification of Dome C for photometry : the fraction of excellent weather for photometric observations is between 56.3 and 68.4 % for the 2008 winter, and between 59.4 et 72.7 % for the 2009 winter. This is better than large observatories located in temperate sites. Lightcurves are then extracted for the 8000 stars in the field. The reduction pipeline is under improvement to reach a precision high enough to search for transit signals of exoplanets. The heart of the project, ASTEP 400, is a 40 cm telescope entirely designed and built to perform high precision photometry under the extreme conditions of the Antarctic winter. The optical, mechanical, and thermal studies, as well as sofware development led by the ASTEP team members are presented. We focus in particular on the photometric and guiding simulations, performed during this thesis. After test observations at the Nice Observatory, ASTEP 400 is installed at Concordia during the 2010 summer campaign. The telescope has functionned nominally since the first observations. The photometric precision we obtain is equivalent to that of 1.5 to 2 meter telescopes located in temperate sites. Besides, 1-month long continuous observations of known transiting planets yield a precision of 200 ppm, better than any other ground-based photometric observations in the visible. As a result, we put an upper limit on the secondary transit depth, and thus on the brightness temperature in the visible of these planets. In parallel, the follow-up of microlensing alerts with ASTEP 400 is performed in complement to observations with other telescopes, and leads to the detection of brown dwarf or planetary companions. The fact that ASTEP 400 has fonctionned nominally during all the 2010 winter, and the very high quality of the data, are a strong confirmation of the potential of Dome C for the search and characterization of transiting exoplanets, and for photometry in the visible in general.La photométrie des transits est une méthode puissante pour la détection et la caractérisation des exoplanètes. Le Dôme C, en Antarctique, est un site extrêmement prometteur pour les observations photométriques, grâce à une nuit continue de 3 mois durant l'hiver austral et des conditions atmosphériques très favorables. Le projet ASTEP (Antarctic Search for Transiting ExoPlanets) vise à détecter et caractériser des planètes en transit, ainsi qu'à déterminer les limites de la photométrie dans le visible depuis la station Concordia, au Dôme C. Il se divise en deux phases : ASTEP Sud, un instrument fixe de 10 cm, et ASTEP 400, un télescope pointable de 40 cm. Le travail présenté dans cette thèse est dédié au développement et à l'exploitation du projet ASTEP. Un simulateur photométrique est élaboré, et permet d'identifier les sources de bruit affectant la photométrie, telles que les variations de seeing ou de la forme des PSF (Point Spread Function). Des simulations aboutissent au choix des caméras CCD d'ASTEP. Ces caméras sont alors testées et caractérisées. On présente ensuite ASTEP Sud, un instrument fixe composé d'une lunette de 10 cm et d'une caméra CCD dans une enceinte chauffée, qui pointe en permanence un champ de 3.88°x3.88° centré sur le pôle sud céleste. La stratégie d'observation est validée, et les différents éléments de l'instrument sont choisis. Les paramètres d'observation sont définis à partir d'une étude de la contamination et des tests sur le ciel. ASTEP Sud a fonctionné quasiment en continu durant les hivers 2008, 2009 et 2010. L'analyse préliminaire des données permet de qualifier le Dôme C pour la photométrie : la fraction de temps excellent pour les observations photométriques est comprise entre 56.3 et 68.4 % pour l'hiver 2008 et entre 59.4 et 72.7 % pour l'hiver 2009, ce qui est meilleur que dans les grands observatoires des régions tempérées. Les courbes de lumière des 8000 étoiles du champ sont extraites. Le traitement est en cours d'amélioration pour atteindre une précision permettant d'identifier la signature de transits d'exoplanètes. Le coeur du projet, ASTEP 400, est un télescope de 40 cm entièrement conçu et développé dans le but d'effectuer des observations photométriques de qualité dans les conditions extrêmes de l'hiver antarctique. On présente les différentes études menées par les membres de l'équipe ASTEP (études optiques, mécaniques, thermiques, développement logiciel) ; en particulier, on détaille les simulations photométriques et l'étude du guidage. Après des observations de test à l'Observatoire de Nice, ASTEP 400 est installé à Concordia durant la campagne d'été 2010. Le fonctionnement du télescope est nominal dès le début des observations. La précision photométrique obtenue est équivalente à celle de télescopes de 1.5 à 2 m situés dans des sites tempérés. De plus, l'observation continue pendant 1 mois de planètes à transits connues permet d'atteindre une précision de 200 ppm, inégalée pour des observations photométriques dans le visible depuis le sol. On obtient ainsi une limite supérieure sur la profondeur du transit secondaire, et donc sur la température de brillance de ces planètes dans le visible. En parallèle, le suivi d'alertes microlentilles avec ASTEP 400 permet de compléter les données d'autres télescopes, et de participer à la détection d'objets de type naine brune ou planétaire. Le fonctionnement nominal d'ASTEP 400 durant tout l'hiver 2010 et la qualité des données obtenues confirment le potentiel du Dôme C pour la recherche et la caractérisation de planètes en transits, et pour la photométrie dans le visible en général

The european project NURISP for nuclear reactor simulation

The NURISP project aims at developing the European NURESIM reference simulation platform [1] for nuclear reactor. A first version of NURESIM was delivered in 2008. 22 organizations from 14 European countries contribute to the further development of this platform. NURISP also includes a User’s Group (UG) whose members are not NURISP partners and come from the industrial nuclear sector or European and non-European R&D labs. Users can benefit from the use of the NURESIM platform, methods, results and modules and they provide concrete input and feedback on the use of these elements

Advanced multi-physics simulation for reactor safety in the framework of the NURESAFE project

Since some years, there is a worldwide trend to move towards “higher-fidelity” simulation techniques in reactor analysis. One of the main objectives of the research in this area is to enhance the prediction capability of the computations used for safety demonstration of the current LWR nuclear power plants through the dynamic 3D coupling of the codes simulating the different physics of the problem into a common multi-physics simulation scheme. In this context, the NURESAFE European project aims at delivering to the European stakeholders an advanced and reliable software capacity usable for safety analysis needs of present and future LWR reactors and developing a high level of expertise in Europe in the proper use of the most recent simulation tools including uncertainty assessment to quantify the margins toward feared phenomena occurring during an accident. This software capacity is based on the NURESIM European simulation platform created during FP6 NURESIM project which includes advanced core physics, two-phase thermal–hydraulics, fuel modeling and multi-scale and multi-physics features together with sensitivity and uncertainty tools. These physics are fully integrated into the platform in order to provide a standardized state-of-the-art code system to support safety analysis of current and evolving LWRs

Thermalizing a telescope in Antarctica: Analysis of ASTEP observations

The installation and operation of a telescope in Antarctica represent particular challenges, in particular the requirement to operate at extremely cold temperatures, to cope with rapid temperature fluctuations and to prevent frosting. Heating of electronic subsystems is a necessity, but solutions must be found to avoid the turbulence induced by temperature fluctua- tions on the optical paths. ASTEP 400 is a 40 cm Newton telescope installed at the Concordia station, Dome C since 2010 for photometric observations of fields of stars and their exoplanets. While the telescope is designed to spread star light on several pixels to maximize photometric stability, we show that it is nonetheless sensitive to the extreme variations of the seeing at the ground level (between about 0.1 and 5 arcsec) and to temperature fluctuations between --30 degrees C and --80 degrees C. We analyze both day-time and night-time observations and obtain the magnitude of the seeing caused by the mirrors, dome and camera. The most important effect arises from the heating of the primary mirror which gives rise to a mirror seeing of 0.23 arcsec K--1 . We propose solutions to mitigate these effects.Comment: Appears in Astronomical Notes / Astronomische Nachrichten, Wiley-VCH Verlag, 2015, pp.1-2