Observing angular deviations in light beam reflection via weak measurements

An optical analog of the quantum weak measurement scheme proved to be very useful for the observation of optical beam shifts. Here we adapt the weak value amplification method for the observation of the angular Goos-Hanchen shift. We observe this effect in the case of external air-dielectric reflection, the more fundamental case in which it occurs.We show that weak measurements allow for a faithful amplification of the effect at any angle of incidence, even at the Brewster angle of incidence

Sliding drops across alternating hydrophobic and hydrophilic stripes

We perform a joint numerical and experimental study to systematically characterize the motion of 30 μl drops of pure water and of ethanol in water solutions, sliding over a periodic array of alternating hydrophobic and hydrophilic stripes with a large wettability contrast and a typical width of hundreds of microns. The fraction of the hydrophobic areas has been varied from about 20% to 80%. The effects of the heterogeneous patterning can be described by a renormalized value of the critical Bond number, i.e., the critical dimensionless force needed to depin the drop before it starts to move. Close to the critical Bond number we observe a jerky motion characterized by an evident stick-slip dynamics. As a result, dissipation is strongly localized in time, and the mean velocity of the drops can easily decrease by an order of magnitude compared to the sliding on the homogeneous surface. Lattice Boltzmann numerical simulations are crucial for disclosing to what extent the sliding dynamics can be deduced from the computed balance of capillary, viscous, and body forces by varying the Bond number, the surface composition, and the liquid viscosity. Beyond the critical Bond number, we characterize both experimentally and numerically the dissipation inside the droplet by studying the relation between the average velocity and the applied volume forces

Stick-Slip Sliding of Water Drops on Chemically Heterogeneous Surfaces

We present a comprehensive study of water drops sliding down chemically heterogeneous surfaces formed by a periodic pattern of alternating hydrophobic and hydrophilic stripes. Drops are found to undergo a stick-slip motion whose average speed is an order of magnitude smaller than that measured on a homogeneous surface having the same static contact angle. This motion is the result of the periodic deformations of the drop interface when crossing the stripes. Numerical simulations confirm this view and are used to elucidate the principles underlying the experimental observations

Resgate de germoplasma de Stylosanthes em áreas do semi-árido baiano.

O bioma caatinga apresenta uma paisagem bastante diversificada, na qual se destaca principalmente a família guminosae.Algumas espécies de leguminosas têm potencial para serem empregadas na alimentação animal, permitindo o pastoreio direto ou, sendo conservada, na forma de feno ou silagem. Entre as diversas leguminosas existentes em ambientes tropicais e subtropicais, destaca-se o gênero Stylosanthes. Neste, a maioria das espécies constituintes são perenes, dotadas de um potente sistema radicular, resistente à seca e apresentando boa adaptação a solos de baixa fertilidade. Para enriquecimento do banco de germoplasma de espécies forrageiras da Universidade Estadual de Feira de Santana, no estado da Bahia, foram realizadas expedições para coleta de acessos de Stylosanthes, com os dados de passaporte registrados em caderneta de coleta, com as principais informações tais como latitude e longitude, tipo de solo, de vegetação, dentre outros. Foram feitas exsicatas e os acessos coletados, após a triagem dos frutos e manejo de sementes, foram armazenados em um banco de sementes e acondicionados em potes herméticos com sílica gel; as exsicatas foram depositadas no herbário da Universidade Estadual de Feira de Santana ? HUEFS, onde estão sendo identificados por especialistas. Dentre os 57 acessos coletados, foram identificados cinco espécies, havendo diferenças de cor de sementes e tipo de planta prostrada ou ereta

LiNbO3 integrated system for opto-microfluidic sensing

International audience; In this work, we realized and tested an integrated opto-microfluidics platform entirely made on lithium niobate (LiNbO3) crystals, able to detect the single droplet passage and estimate its size without the need of any imaging processing. It is based on the coupling of a self-aligned integrated optical stage, made of an array of optical waveguides, to a microfluidic circuit such as a T-junction or Cross-junction engraved in the same substrate. The platform presented high quality performances in terms of optical triggering, reproducibility and stability in time, allowing in real-time data analysis. The comparison with standard approaches using microscopes and fast camera imagining acquisition and relative post-processing, showed an increased capability better than 50%. The demonstrated feasibility of integration of these two stages will allow the realization of a Lab-On-a-Chip on a monolithic substrate of lithium niobate, exploiting its multiple applications for manipulation of droplets