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Spatial control of wettability is key to many applications of microfluidic devices, ranging from double emulsion generation to localized cell adhesion. A number of techniques, often based on masking, have been developed to produce spatially-resolved wettability patterns at the surface of poly(dimethylsiloxane) (PDMS) elastomers. A major impediment they face is the natural hydrophobic recovery of PDMS: hydrophilized PDMS surfaces tend to return to hydrophobicity with time, mainly because of diffusion of low molecular weight silicone species to the surface. Instead of trying to avoid this phenomenon, we propose in this work to take advantage of hydrophobic recovery to modulate spatially the surface wettability of PDMS. Because temperature speeds up the rate of hydrophobic recovery, we show that space-resolved hydrophobic patterns can be produced by locally heating a plasma-hydrophilized PDMS surface with microresistors. Importantly, local wettability is quantified in microchannels using a fluorescent probe. This "thermo-patterning" technique provides a simple route to in situ wettability patterning in closed PDMS chips, without requiring further surface chemistry.

An optically-induced thermal non-linear effect in a nematic liquid-crystal (E7) cell is evidenced through weak light-absorption by the ITO coating of an infrared pulsed femtosecond laser (m). Strong spatial self-phase modulation is generated, thus a multiple-ring pattern is observed in the far-field. The sign of the nonlinearity is changed depending on the laser polarization. The refractive index and thermal gradients are measured as a function of the laser intensity and we observe that the temperature can increase close to the nematic phase transition. The fidelity and stability of the process open new prospects for spatial shaping devices and delimits the operating wavelength range for ultrafast liquid-crystal based electro-optic application.

Among Super-Mirror (SM) polarizers, solid-state devices have many advantages. The most relevant is 5-10 times smaller length compared to air-gap polarizers allowing to apply stronger magnetic fields. An important condition for a good SM polarizer is the matching of the substrate SLD (Scattering Length Density) with the SM coating SLD for spin-down neutrons. For traditional Fe/Si SM on Si substrate, this SLD step is positive when a neutron goes from the substrate to the SM, which leads to a significant loss of the polarizer performance at small Q. Instead, we use single-crystal Sapphire/Quartz substrates. The latter show a negative SLD step for spin-down neutrons at the interface with Fe and, therefore, avoid the total reflection regime at small Q. To optimize the polarizer performance, we formulate the concept of Sapphire V-bender, perform ray-tracing simulations of Sapphire V-bender, compare results with those for traditional C-bender on Si, and study experimentally V-bender prototypes with different substrates. Our results show that the choice of substrate material, polarizer geometry and the strength and quality of magnetizing field have dramatic effect. In particular, we compare the performance of polarizer for the applied magnetic field strength of $50 mT$ and $300 mT$. Only the large field strength provides an excellent agreement between the simulated and measured polarization values. For the double-collision configuration, a record polarization $>0.999$ was obtained in the neutron wavelength band of $0.3-1.2 nm$ with only $1\%$ decrease at $2 nm$. Without any collimation, the polarization averaged over the full outgoing capture spectrum, $0.997$, was found to be equal to the value obtained previously only using a double polarizer in the "crossed" (X-SM) geometry. These results are applied in a full-scale polarizer for the PF1B instrument., Comment: 13 figures

While there has been substantial empirical work identifying factors that influence the contribution to, and use of open source software, we have as yet little theory that identifies the key constructs and relationships that would allow us to explain and predict how open source ecosystems function. What is needed is a clearly articulated and empirically validated theory of open source ecosystems. Such a theory should: $\bullet$ Explain why, how, and when key resources---primarily the work of developers---are attracted to or depart from a project or an ecosystem. $\bullet$ Explain why, how, and when projects and ecosystems move through a life cycle, from initiation, growth, maturity, and decline and death. $\bullet$ Explain how decisions about use are made, and how the cumulatively influence the socio-technical position of a project within an ecosystem, and the relations of ecosystems to each other.The remainder of this chapter provides a sketch of such a theory in the form of a set of propositions, which may form the foundation for future empirical work, Comment: Brian Fitzgerald; Audris Mockus; Minghui Zhou. Towards Engineering Free/Libre Open Source Software (FLOSS) Ecosystems for Impact and Sustainability, Springer, In press, Communications of NII Shonan Meetings, 978-981-13-7098-4. https://www.springer.com/gp/book/9789811370984#aboutBook

While the acoustic properties of solid foams have been abundantly characterized, sound propagation in liquid foams remains poorly understood. Recent studies have investigated the transmission of ultrasound through three-dimensional polydisperse liquid foams (Pierre et al., 2013, 2014, 2017). However, further progress requires to characterize the acoustic response of better controlled foam structures. In this work, we study experimentally the transmission of ultrasounds through a single layer of monodisperse bubbles generated by microfluidics techniques. In such a material, we show that the sound velocity is only sensitive to the gas phase. Nevertheless, the structure of the liquid network has to be taken into account through a transfer parameter analogous to the one in a layer of porous material. Finally, we observe that the attenuation cannot be explained by thermal dissipation alone, but is compatible with viscous dissipation in the gas pores of the monolayer.