The Impact of Public Guarantees on Bank Risk Taking: Evidence from a Natural Experiment

In 2001, government guarantees for savings banks in Germany were removed following a law suit. We use this natural experiment to examine the effect of government guarantees on bank risk taking, using a large data set of matched bank/borrower information. The results suggest that banks whose government guarantee was removed reduced credit risk by cutting off the riskiest borrowers from credit. At the same time, the banks also increased interest rates on their remaining borrowers. The effects are economically large: the Z-Score of average borrowers increased by 7% and the average loan size declined by 13%. Remaining borrowers paid 57 basis points higher interest rates, despite their higher quality. Using a difference-in-differences approach we show that the effect is larger for banks that ex ante benefitted more from the guarantee. We show that both the credit quality of new customers improved (screening) and that the loans of existing riskier borrowers were less likely to be renewed (monitoring), after the removal of public guarantees. Public guarantees seem to be associated with substantial moral hazard effects.banking;public guarantees;credit risk;moral hazard

Contribution to advanced hot wire wind sensing

The thermal anemometry is a method which allows to estimate wind magnitude be the mean of measuring heat transfer to the ambient in a forced convection process. For Earth's atmosphere condition, this method is typically applied to the hot wires made of temperature dependent electrical conductor, typically platinum or tungsten, which working with overheat in reference to the ambient temperature estimate wind velocity. In case of the low pressure atmospheres, like this on Mars, the mean free path for molecules, due to the rarefied ambient conditions, is much bigger, Using hot wires designed for Earth in this conditions gives that heat exchange at macroscopic scale which does not to obey medium continuum model but rather reveals ballistic behavior Thus, instead of using hot wire, a structure of bigger dimension like hot films are usually propose for such a kind of application. The work included in this thesis is the contribution of the author Lukasz Kowalski to the goal of developing a new generation of wind sensors for the atmosphere of Mars. The work consists in the conception, design, simulation, manufacture and measurement of two novel types wind sensors based on thermal anemometers. The first kind of concept has been developed in this thesis by using hot silicon die made out of silicon wafer of approximate size: 1.5 x 1.5 x 0.5 mm with platinum resistances deposited on top in order to heat it and sense its temperature. These work was been a part of the bigger undertaking under the project name: "Colaboracíoon en el desarrollo de la estación medioambiental denominada REMS ". Inside the project REMS author of thesis was responsible for sensor shape development and concept validation of proposed geometry. Thermal-fluidical model of the device as well as characterization and behavior were analyzed for a simplified 2-D wind model for typical Martian atmospheric conditions. REMS was a Spanish contribution to the NASA mission MSL which has been a great success since rover Curiosity has landed on Mars on 8th August 2012 on Mars near to the Gale Crater location. Since then has been constantly running experiments on the Red Planet sending data to Earth for interpretation. From the experience and knowledge gained during REMS project, the author came out with an idea of the novel spherical sensor structure overcoming some fragility problems detected in the REMS wind sensor. The new 3-D wind sensor concept, besides this advantage, also provided a radical simplification of data post-processing providing comprehensive thermal model based on numerical simulation for any possible wind occurrence. This new device has been developed under Spanish Ministry of the Science and Innovation project: "Sensor de viento para la superficie de Marte para la mission Metnet''. This project, denominated as MEIGA, was a joint effort of many Spanish institution under leadership of Instituto Nacional de Tecnica Aeroespacial (INTA) for the development of space technology for Mars oriented application in a framework of upcoming space mission. To sum up, author's work include contributions to the development of two wind sensor concepts: 1. REMS wind sensor on board of the rover Curiosity in the surface of Mars since August 8th 2012 2. Spherical wind sensor concept developed in a course of MEIGA projec

Exploring high repetitivity remote sensing time series for mapping and monitoring natural habitats ; A new approach combining OBIA and k-partite graphs

International audienc

Forming Planetesimals in Solar and Extrasolar Nebulae

Planets are built from planetesimals: solids larger than a kilometer which grow by colliding pairwise. Planetesimals themselves are unlikely to form by two-body collisions; sub-km objects have gravitational fields individually too weak, and electrostatic attraction is too feeble for growth beyond a few cm. We review the possibility that planetesimals form when self-gravity brings together vast ensembles of small particles. Even when self-gravity is weak, aerodynamic processes can accumulate solids relative to gas, paving the way for gravitational collapse. Particles pile up as they drift radially inward. Gas turbulence stirs particles, but can also seed collapse by clumping them. While the feedback of solids on gas triggers vertical shear instabilities that obstruct self-gravity, this same feedback triggers streaming instabilities that strongly concentrate particles. Numerical simulations find that solids 10-100 cm in size gravitationally collapse in turbulent disks. We outline areas for progress, including the possibility that still smaller objects self-gravitate.Comment: To appear in Annual Reviews. This review is intended to be both current and pedagogical. Incorporates suggestions from the community; further comments welcome. v2: Single-space

On deviations from free-radial outflow in the inner coma of comet 67P/Churyumov–Gerasimenko

The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) onboard the European Space Agency's Rosetta spacecraft acquired images of comet 67P/Churyumov–Gerasimenko (67P) and its surrounding dust coma starting from May 2014 until September 2016. In this paper we present methods and results from analysis of OSIRIS images regarding the dust outflow in the innermost coma of 67P. The aim is to determine the global dust outflow behaviour and place constraints on physical processes affecting particles in the inner coma. We study the coma region right above the nucleus surface, spanning from the nucleus centre out to a distance of about 50 km comet centric distance (approximately 25 average comet radii). We primarily adopt an approach used by Thomas and Keller (1990) to study the dust outflow. We present the effects on azimuthally-averaged values of the dust reflectance of non-radial flow and non-point-source geometry, acceleration of dust particles, sublimation of icy dust particles after ejection from the surface, dust particle fragmentation, optical depth effects and the influence of gravitationally bound particles. All of these physical processes could modify the observed distribution of light scattered by the dust coma. In the image analysis, profiles of azimuthally averaged dust brightness as a function of impact parameter b (azimuthal average, “Ā-curve”) were fitted with a simple function that best fits the shape of our profile curves (f(b;u,v,w,z)=u/bv+wb+z). The analytical fit parameters (u, v, w, z), which hold the key information about the dust outflow behaviour, were saved in a comprehensive database. Through statistical analysis of these information, we show that the spatial distribution of dust follows free-radial outflow behaviour (i.e. force-free radial outflow with constant velocity) beyond distances larger than ∼11.9 km from the comet centre, which corresponds to a relative distance of about 6 average comet radii from the comet centre. Hence, we conclude that beyond this distance, and on average, fragmentation and gravitationally bound particles are negligible processes in determining the optically scattered light distribution in the innermost coma. Closer to the nucleus we observe dust outflow behaviour that deviates from free-radial outflow. A comparison of our result profiles with numerical models using a Direct Simulation Monte Carlo (DSMC) approach with dust particle distributions calculated using a test particle approach has been used to demonstrate the influence of a complex shape and particle acceleration on the azimuthal average profiles. We demonstrate that, while other effects such as fragmentation or sublimation of dust particles cannot be ruled out, acceleration of the dust particles and effects arising from the shape of the irregular nucleus (non-point source geometry) are sufficient to explain the observed dust outflow behaviour from image data analysis. As a by-product of this work, we have calculated “Afρ” values for the 1/r regime. We found a peak in the coma activity in terms of Afρ (normalised to a phase angle of 90°) of ∼210 cm 20 days after perihelion. Furthermore, based on simplified models of particle motion within bound orbits, it is shown that limits on the total cross-sectional area of bound particles might be derived through further analysis. An example is given

Gas outflow and dust transport of comet 67P/Churyumov-Gerasimenko

Because of the diurnal thermal cycle and the irregular shape of the nucleus, gas outflow of comet 67P/Churyumov-Gerasimenko could be highly anisotropic as indicated by the colliminated dust jet structures on the sunlit side. Based on the OSIRIS imaging observations of the outgassing effect, a simple model of surface sublimation can be constructed by taking into account the dependence on the solar insolation. With preliminary information on the time variability of the global gas production rate, a sequence of gas coma models can be generated at different epochs before and after perihelion. We also investigate different patterns of dust particle dynamics under the influences of nuclear rotation and gas drag. From these considerations, a consistent picture of the spatial distribution of dusty materials across the surface of comet 67P as it moves around the perihelion can be developed. It is found that because of the redeposition of the ejected dust from the Southern hemisphere to the Northern hemisphere during the southern summer season the Hapi region could gain up to 0.4 m while the Wosret region would lose up to 1.8 m of dust mantle per orbit

The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 au heliocentric distance range inbound

Context. The ESA Rosetta spacecraft, currently orbiting around cornet 67P/Churyumov-Gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments, particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution. Aims. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014. Methods. A Monte Carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from. Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately. Results. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is alpha = -3, instead of alpha = -2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 AU, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 AU. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment