Temperature Imaging using Quadriwave Shearing Interferometry. Applications in Thermoplasmonics

International audienceThe use of illuminated gold nanoparticles as ideal nanosources of heat is the basis of numerous research activities and applications in physics, chemistry, biology and medicine. This field defines the area recently named Thermoplasmonics [1]. In most of the activities related to Thermoplasmonics, probing the temperature at the vicinity of the metal nanoparticles is not an easy task. In this context, we recently developed a novel optical microscopy technique, named TIQSI, aimed at mapping the temperature around plasmonic nanoparticles [2]. The approach is based on the measure of the thermal-induced variation of the refractive index surrounding the sources of heat. The TIQSI technique cumulates all the advantages a thermal microscopy technique may require: i) high resolution (diffraction limited), ii) high readout rate (less than one image per second), iii) high temperature sensitivity (<1°C), iv) large accessible temperature range, v) temperature can be measured without fluorescence labelling or any other kind of thermal probe, v) no need to use sophisticated devices such as heterodyne detection, acousto-optic modulator, spectrometer, etc, like previous thermal imaging techniques. In this presentation, we will first introduce the TIQSI technique, its principle and capabilities. We will then present several recent applications made it possible by this new thermal imaging technique. In particular, we shall explain how this technique have been already used to quantitatively measure the absorption cross section of gold nanoparticles [3] and graphene sheets, how it can be used to map the temperature in real time in living cells [4], how it can help to design temperature distributions at will at the microscale using gold nanoparticles [5,7], and how it can be used to investigate thermal-induced phenomena in hydro- dynamics and phase transitions [6]

Thermal Imaging of Nanostructures by Quantitative Optical Phase Analysis

International audienceWe introduce an optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner. Namely, the technique permits (i) mapping the temperature distribution around the source of heat, (ii) mapping the heat power density delivered by the source, and (iii) retrieving the absolute absorption cross section of light-absorbing structures. The technique is based on the measure of the thermal-induced refractive index variation of the medium surrounding the source of heat. The measurement is achieved using an association of a regular CCD camera along with a modified Hartmann diffraction grating. Such a simple association makes this technique straightforward to implement on any conventional microscope with its native broadband illumination conditions. We illustrate this technique on gold nanoparticles illuminated at their plasmonic resonance. The spatial resolution of this technique is diffraction limited, and temperature variations weaker than 1 K can be detected

Caracterisation de la productivite des aquiferes du socle de la region de l’extreme Nord, Cameroun

Dans la zone de socle de la région de l’Extrême Nord du Cameroun, l’exploitation des ressources en eau souterraine permet de faire face au problème de l’alimentation en eau potable des populations rurales. Une meilleure connaissance de ces aquifères est nécessaire pour une bonne productivité. La présente étude a été effectué pour identifier les principaux paramètres hydrauliques essentiels dans la productivité des aquifères de ce socle. Pour ce faire, une compilation de données regroupant les fiches techniques de forage de même que les essais de pompage disponibles dans ce socle a été faite. Ces données concernent les paramètres tels que : le débit de forage (Q), la profondeur totale (Pt) et l’épaisseur d’altérites (EA). Les paramètres hydrauliques notamment la transmissivité (T) et le débit spécifique (Qs) ont été déterminés à partir de l’interprétation des essais de pompage issus des données des fiches. La transmissivité a été calculée par la méthode de Cooper Jacob avec les données de rabattement des ouvrages disponibles après l’arrêt du pompage lors de la remontée. Une analyse statistique de ces paramètres physiques et hydrauliques déterminés a été réalisée. Il ressort que les débits des forages oscillent entre 0,04 m³/h et 4 m³/h avec une moyenne de 1,66 m3/h. Les classes de débits très faible et faible représentent 74,57% des débits de forage de cette zone. Les forages productifs ont une profondeur totale comprise entre 30 et 75 m avec une épaisseur d’altérites qui varie entre 1m et 14 m. Les formations granitiques et métamorphiques semblent être productives, avec 47,46% des débits se trouvant dans la classe des débits faible à moyenne (Q e” 1m³/h). Les valeurs de transmissivité fluctuent entre 3x10-7 m²/s et 7,80x10-4 m²/s avec une moyenne de 5,03x10-5 m²/s. Elle illustre que les aquifères de socle de la région de l’Extrême Nord ont une faible fonction conductrice.Mots Clés: Productivité, aquifères, zone de socle, Extrême Nord, CamerounEnglish AbstractIn the socle zone of the extreme North region of Cameroon, the exploitation of groundwater resources makes it possible to cope with the problem of the supply of drinking water to rural populations. A better knowledge of these aquifers is necessary for good productivity. The present study was carried out to identify the main hydraulic parameters essential in the productivity of the aquifers of this socle zone. To do this, a compilation of data gathering the drilling data sheets as well as the pumping tests available in this socle was made. These data relate to parameters such as: flow of drilling (Q), total depth (Pt) and thickness of alterites (EA). The hydraulic parameters in particular the transmissivity (T) and specific flow rate (Qs) were determined from the interpretation of the pumping tests from the data the data sheets.The transmissivity was calculated by the Cooper Jacob method with the rabattement data of the works available after the stop of pumping at the time of the ride up. A statistical analysis of these parameters of given drillings and hydraulics was carried out. Borehole flow rates range from 0.04 m³ /h to 4 m³ / h with an average of 1.66 m3 / h. The very weak and weak flow classes account for 74.57% of the flow of drilling in this zone. The productive boreholes have a total depth of between 30 and 75 m with a thickness of alterites which varies between 1 m and 14 m. The granitic and metamorphic formations appear to be productive, with 47.46% of the flows in the low to medium flows class (Q e”1 m³ / h).Transmissivity values fluctuate between 3x10-7 m² / s and 7.80x10-4 m² / s with an average of 5.03x10-5 m² / s. It illustrates that the basement aquifers of the extreme North region have a weak conductive function.Keywords: Productivity, aquiferes, socle zone, Extreme North, Cameroo

Hydrogeological Characteristics of Shallow Hard Rock Aquifers in Yaounde (Cameroon, Central Africa)

The groundwater contained in the alterites is one of the main sources of water supply for many households in the city of Yaounde and its surroundings. Information from the field and laboratory studies was compiled and analyzed in order to understand the hydrogeological context of this superficial aquifer. Preliminary results show a staged morphology of the alteration mantle (regolith) of Yaounde migmatitic representative of the polyphase character of alteration processes observed in all granito-gneissic formations of the world. This mantle has a multilayer system whose soil sets could have a different hydrodynamic functioning. The values of the hydraulic conductivity have a normal distribution and vary over four orders of magnitude, attesting the variability of the hydraulic conductivity of the soft materials. The hydrometric and piezometric characteristics indicate that the aquifer has highly heterogeneous zones that would be related to the morphostructural character of the region. The δ18O mean values of the rain (−2.47‰) and shallow groundwater (−2.57‰) are not significantly different. They indicate that the recharge of the shallow aquifer of Yaounde Precambrian basement is recent and is done directly by infiltration of precipitation without any notable change due to evaporation

Evolutionary genetic dissection of human interferons

As revealed by population genetic analyses, different human interferon genes evolved under distinct selective constraints and signatures of positive selection vary according to geographic region, suggesting that some sequence changes may have conferred an advantage by increasing resistance to viral infection

The PLATO mission

PLATO (PLAnetary Transits and Oscillations of stars) is ESA’s M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2REarth) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5%, 10%, 10% for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO‘s target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile towards the end of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases

Quantitative absorption spectroscopy of nano-objects

International audienceWe report on an optical microscopy technique aimed at measuring the absolute absorption cross section of individual nanoparticles. It relies on the thermally induced variation of the refractive index of the surrounding medium subsequent to light absorption by the nanoparticle. The technique is illustrated on gold nanoparticles featuring a well-defined plasmonic resonance. Different plasmonic modes were evidenced and quantified. The simplicity and rapidity of the measurements make it possible to investigate absorption resonances of absorbing nanostructures and microstructures in a reasonable time frame. Furthermore, the experimental approach is simply based on the use of a wavefront analyzer, which is straightforward to implement on any conventional microscope