Paul Leroy

Compaction of quartz sands by pressure solution using a Cole‐Cole distribution of relaxation times

Stressed water-infiltrated silica rocks may deform by pervasive pressure solution transfer (PPST), which involves dissolution of the grain-to-grain contacts, transport by diffusion of the solute, and precipitation on the free surfaces of the grains. A fundamental question regarding this process is how to model rheological behavior at stresses and temperatures typical of the crust of the Earth. A Voigt-type poroviscoplastic model is modified by using a Cole-Cole distribution of relaxation times rather than a Dirac distribution used previously. The motivation of this choice is to account for the distribution of the grain size in the compaction of the porous aggregate assuming that this distribution obeys approximately a log normal distribution. This grain size distribution depends upon the initial grain size distribution and cataclasis in the early stage of compaction. We compared this modified viscoplastic model with the full set of experimental data obtained in various conditions of mean grain size, effective stress, and temperature by Niemeijer et al. (2002). These data provide tests of all aspects of the model, which can be considered to have no free parameters. We show the experiments of Niemeijer et al. (2002) on PPST are primarily diffusion-limited. The grain size distributions observed for three samples imply that the distribution of the relaxation time covers 5 orders of magnitude in grain size.

Induction Magnetometers Principle, Modeling and Ways of Improvement

This book provides an introductory overview of the research done in recent years in the area of magnetic sensors. The topics presented in this book range from fundamental theories and properties of magnets and their sensing applications in areas such as biomedicine, microelectromechanical systems, nano-satellites and pedestrian tracking. Written for the readers who wished to obtain a basic understanding of the research area as well as to explore other potential areas of applications for magnetic sensors, this book presents exciting developments in the field in a highly readable manner.

High magnetic field amplification for improving the sensitivity of Hall sensors

This paper describes the design of two magnetic concentrators that can be used to intensify the magnetic field in the active region of magnetic sensors, such as Hall sensors. The literature provides many examples of magnetic amplification, but magnetic gains never exceed 100 typically (Drljaca et al. 2001, Drljaca et al. 2002). We demonstrate that a larger magnetic field amplification (~1000 and even higher) can be achieved. Magnetic field amplification can even exceed the theoretical value fixed by the relative permeability of the material. Thus, the effective sensitivity of Hall sensors can be improved by at least three orders of magnitude by implementing them inside an especially tailored magnetic concentrator; noise-equivalent magnetic induction spectral density (National Electronics Manufacturing Initiative spectral density) down to 10 pT/radic(Hz) should be reached, using a good conditioning electronic

Combined airborne radio-instruments for ocean and land studies (CAROLS)

The CAROLS, L band radiometer, is built and designed as a copy of EMIRAD II radiometer of DTU team. It is a Correlation radiometer with direct sampling and fully polarimetric (i.e 4 Stockes). It will be used in conjunction with other airborne instruments (in particular the C-Band scatterometer (STORM) and IEEC GPS system, Infrared CIMEL radiometer, one visible camera), in coordination with in situ field campaigns for SMOS CAL/VAL. The instruments are implemented on board the French research airplane ATR42. A validation campaign with four flights was made over south west of France, Hourtin Lake and Bay of Biscay (Atlantic Ocean) in September 2007. In order to qualify the radiometer data, different types of aircraft movements were realized: circle flights, wing and nose wags. Simultaneously to flights, different ground measurements were made over continental surfaces and ocean. First results show a good quality of data over ocean surfaces. For continental surfaces, important Radio-Frequency Interferences (RFI) were observed over a large part of the studied region.

Carols Campaign, Scientific Data Analysis Results

The CAROLS L-band radiometer, which is built and designed as a copy of DTU EMIRAD II instrument will be used in conjunction with other airborne instruments (in particular the C-band scatterometer STORM) in coordination with in situ field campaigns for future SMOS CAL/VAL activities. A validation campaign with four flights was made over the South West of France and the Bay of Biscay (Atlantic Ocean) in September 2007. Different instrumented sites over ocean and land surfaces were covered. Moreover, in order to qualify the radiometric data, different types of aircraft maneuvers were performed over the ocean: circle flights, wing and nose wags. We present in this paper the first analysis of the data quality using these ocean measurements. We show a very good sensitivity of both channels.

Optimization of the Shape of Magnetic Field Concentrators to Improve the Sensitivity of Hall Sensors (Optimierung von Konzentratoren für magnetische Felder für die Steigerung der Empfindlichkeit bei Hallsensoren)

Summary This paper describes the design of a set of two magnetic concentrators which can be used to intensify the magnetic field in the active region of magnetic sensors, such as Hall sensors. Literature provides many examples of magnetic amplification, but magnetic gains never exceed 100 typically [1, 2]. We demonstrate that larger magnetic field amplification (∼1000 and even higher) can be achieved by implementing an appropriate geometry. Magnetic field amplification can even exceed the theoretical value fixed by the relative permeability of the material. Thus the effective sensitivity of Hall sensors can be improved by at least three orders of magnitude by implementing them inside especially tailored magnetic concentrators; noise-equivalent magnetic induction spectral density (NEMI spectral density) down to 10 pT/√Hz should be reached, using a good conditioning electronics. We present a formulation of our design process as an optimization problem and use it to find an optimum shape for the magnetic concentrators in a simple case.

Combined Airborne Radio-instruments for Ocean and Land Studies (CAROLS)

The CAROLS, L band radiometer, is built and designed as a copy of EMIRAD II radiometer of DTU team. It is a Correlation radiometer with direct sampling and fully polarimetric (i.e 4 Stockes). It will be used in conjunction with other airborne instruments (in particular the C-Band scatterometer (STORM) and IEEC GPS system, Infrared CIMEL radiometer, one visible camera), in coordination with in situ field campaigns for SMOS CAL/VAL. The instruments are implemented on board the French research airplane ATR42. A validation campaign with four flights was made over south west of France, Hourtin Lake and Bay of Biscay (Atlantic Ocean) in September 2007. In order to qualify the radiometer data, different types of aircraft movements were realized: circle flights, wing and nose wags. Simultaneously to flights, different ground measurements were made over continental surfaces and ocean. First results show a good quality of data over ocean surfaces. For continental surfaces, important Radio-Frequency Interferences (RFI) were observed over a large part of the studied region.