High spatial resolution measurements of NO₂ applying Topographic Target Light scattering-Differential Optical Absorption Spectroscopy (ToTaL-DOAS)

International audienceTomographic Target Light scattering ? Differential Optical Absorption Spectroscopy (ToTaL-DOAS), also called Target-DOAS, is a novel experimental procedure to retrieve trace gas concentrations present in the low atmosphere. Scattered sunlight (partially or totally) reflected from natural or artificial targets of similar albedo located at different distances is analyzed to retrieve the concentration of different trace gases like NO2, SO2 and others. We report high spatial resolution measurements of NO2 mixing ratios in the city of Montevideo (Uruguay) observing three buildings as targets with a Mini-DOAS instrument. Our instrument was 146 m apart from the first building, 196 m from the second and 286 m from the third one. All three buildings are located along a main Avenue. We obtain temporal variation of NO2 mixing ratios between 30 ppb and 65 ppb (±2 ppb). Our measurements demonstrate that ToTaL-DOAS measurements can be made over very short distances. In polluted air masses, the retrieved absorption signal was found to be strong enough to allow measurements over distances in the range of several ten meters, and achieve a spatial resolution of 50 m approximately

Gendelettre:De vormende jaren van Frans Erens, 1857-1893

Frans Erens (1857-1935) is regarded as "the Eighties man from Limburg," who took his own place within the Eighties Movement based on his origins, Catholic faith and international education. In 1884 he joined Flanor, the Amsterdam association that is considered the birthplace of the Eighties. Earlier, in Paris, he actively participated in the rise of the Symbolists. Gendelettre attempts to answer the intriguing question of how Erens' success in both Paris and Amsterdam can be explained and looks for that answer in his self-fashioning and the factors that contributed to it. The study also paints a picture of the world of letters at a crucial moment in the literary history of both countries, France and the Netherlands. Previously unreprinted texts by the author enrich this first scholarly biography of Frans Erens. Jean Frins (b. 1982) was accompanied in his writing by professors Mary Kemperink (University of Groningen) and Kees Snoek (Sorbonne Université Paris)

Tomographic MAX-DOAS observations of sun illuminated targets: a new technique providing well defined absorption paths in the boundary layer

A novel experimental procedure to measure the surface-near distribution of atmospheric trace gases using passive Multi-Axis-Differential Absorption Optical Spectroscopy (MAX-DOAS) is proposed. The idea consists of pointing the receiving telescope of the spectrometer to non-reflecting surfaces or to ‘bright’ targets placed at known distances from the measuring device, which are illuminated by sunlight. We show that the partial trace gas absorptions between the top of the atmosphere and the target can be easily removed from the measured total absorption. Thus it is possible to derive the average concentration of trace gases like e.g. NO2, HCHO, SO2, H2O, Glyoxal, BrO and others along the line of sight between the instrument and the target like for the well-known long-path DOAS observations (but with much less expense). If tomographic arrangements are used, even two- or three-dimensional trace gas distributions can be retrieved. The basic assumptions of the proposed method are confirmed by test measurements across the city of Heidelberg

Composition law for polarizers

The polarization process when polarizers act on an optical field is studied. We give examples for two kinds of polarizers. The first kind presents an anisotropic absorption - as in a polaroid film - and the second one is based on total reflection at the interface with a birefringent medium. Using the Stokes vector representation, we determine explicitly the trajectories of the wave light polarization during the polarization process. We find that such trajectories are not always geodesics of the Poincar\'e sphere as it is usually thought. Using the analogy between light polarization and special relativity, we find that the action of successive polarizers on the light wave polarization is equivalent to the action of a single resulting polarizer followed by a rotation achieved for example by a device with optical activity. We find a composition law for polarizers similar to the composition law for noncollinear velocities in special relativity. We define an angle equivalent to the relativistic Wigner angle which can be used to quantify the quality of two composed polarizers.Comment: 23 pages, 9 figures, accepted for publication in Physical Review

Differential Calcium Signaling by Cone Specific Guanylate Cyclase-Activating Proteins from the Zebrafish Retina

Zebrafish express in their retina a higher number of guanylate cyclase-activating proteins (zGCAPs) than mammalians pointing to more complex guanylate cyclase signaling systems. All six zGCAP isoforms show distinct and partial overlapping expression profiles in rods and cones. We determined critical Ca2+-dependent parameters of their functional properties using purified zGCAPs after heterologous expression in E.coli. Isoforms 1–4 were strong, 5 and 7 were weak activators of membrane bound guanylate cyclase. They further displayed different Ca2+-sensitivities of guanylate cyclase activation, which is half maximal either at a free Ca2+ around 30 nM (zGCAP1, 2 and 3) or around 400 nM (zGCAP4, 5 and 7). Zebrafish GCAP isoforms showed also differences in their Ca2+/Mg2+-dependent conformational changes and in the Ca2+-dependent monomer-dimer equilibrium. Direct Ca2+-binding revealed that all zGCAPs bound at least three Ca2+. The corresponding apparent affinity constants reflect binding of Ca2+ with high (≤100 nM), medium (0.1–5 µM) and/or low (≥5 µM) affinity, but were unique for each zGCAP isoform. Our data indicate a Ca2+-sensor system in zebrafish rod and cone cells supporting a Ca2+-relay model of differential zGCAP operation in these cells

Balancing wind energy and nature protection. From policy conflicts towards genuine sustainable development?

Contains fulltext : 134129.pdf (publisher's version ) (Open Access

Noot bij: ABRvS 18 februari 2015, TBR, 2015, 85 (Windturbines Moerdijk)

Item does not contain fulltext18 februari 201