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Due to the action of the scattering force, particles that are optically trapped at the surface of a waveguide are propelled in the direction of the light propagation. In this work, we demonstrate an original approach for creating tunable periodic arrays of optical traps along a few-mode silicon nanophotonic waveguide. We show how the near-field optical forces at the surface of the waveguide are periodically modulated when two guided modes with different propagation constants are simultaneously excited. The phenomenon is used to achieve stable trapping of a large number of dielectric particles or bacteria along a single waveguide. By controlling the light coupling conditions and the laser wavelength, we investigate several techniques for manipulating the trapped particles. Especially, we demonstrate that the period of the optical lattice can be finely tuned by adjusting the laser wavelength. This effect can be used to control the trap positions, and thus transport the trapped particles in both directions along the waveguide.

The growing number of drug-resistant bacterial infections worldwide is driving renewed interest in phage therapy. Based on the use of a personalized cocktail composed of highly specific bacterial viruses, this therapy relies on a range of tests on agar media to determine the most active phage on a given bacterial target (phage susceptibility testing), or to isolate new lytic phages from an environmental sample (enrichment of phage banks). However, these culture-based techniques are still solely interpreted through direct visual detection of plaques. The main objective of this work is to investigate computer-assisted methods in order to ease and accelerate diagnosis in phage therapy but also to study phage plaque growth kinetics. For this purpose, we designed a custom wide-field lensless imaging device, which allows continuous monitoring over a very large area sensor (3.3 cm2). Here we report bacterial susceptibility to Staphylococcus aureus phage in 3 hr and estimation of infectious titer in 8 hr 20 min. These are much shorter time-to-results than the 12 to 24 hours traditionally needed, since naked eye observation and counting of phage plaques is still the most widely used technique for susceptibility testing prior to phage therapy. Moreover, the continuous monitoring of the samples enables the study of plaque growth kinetics, which enables a deeper understanding of the interaction between phage and bacteria. Finally, thanks to the 4.3 μm resolution, we detect phage-resistant bacterial microcolonies of Klebsiella pneumoniae inside the boundaries of phage plaques and thus show that our prototype is also a suitable device to track phage resistance. Lensless imaging is therefore an all-in-one method that could easily be implemented in cost-effective and compact devices in phage laboratories to help with phage therapy diagnosis. [ABSTRACT FROM AUTHOR]

This study presents the first report comparing the efficiency of microspore culture, gynogenesis and durum wheat × maize crosses for haploid plant production from three durum wheat genotypes (Razzek, Karim and Jneh Khotifa). The results showed that the best induction, calli or embryos formation and plant regeneration rates for the three genotypes were obtained with gynogenesis (47.2, 7.6, 0.8%), followed by interspecific crosses (33.1, 1.7, 0.4%) and isolated microspore culture (8.2, 0.05, 0.01%). Interestingly, all plants regenerated by gynogenesis and durum wheat × maize crosses were green whereas all plants obtained by isolated microspore culture were albino. In the haploid production system, all steps of the process are important for the three methods. The critical steps that have greatly reduced the number of regenerated haploid plants were induction, embryogenesis and regeneration for microspore culture, forming and regeneration of calli or embryo and haploid regeneration for interspecific crosses and gynogenesis. Genotypes with good capacity of induction have not necessarily a good capacity of haploid plantlets regeneration and vice-versa. However, calli or embryos formation seems to be an indicator of the haploid production. Overall, Razzek showed a good ability to produce haploids using the three methods. Each haplomethod showed a specific advantage. Although gynogenesis is the less used method for durum wheat, it has proved to be a successful approach for green haploid plant production. [ABSTRACT FROM AUTHOR]

We study here the lateral evanescent coupling between photonic crystals cavities. The structure consists in two identical monomode Fabry–Perot nanocavities, integrated on silicon-on-insulator slot-waveguides (WG). Spectral and optical near field measurements were led and supported quantitatively by three dimensional simulations. It appears that this system produces a bimodal response: two resonances corresponding, respectively, to an even and odd mode. Particularly, the even case exhibits a field localization in the air slot inferior to λair/10. We demonstrate that merging a slotted WG structure with state-of-the-art nanocavities is a significant step toward an efficient air-slotted resonator. [ABSTRACT FROM AUTHOR]

Silicon-on-insulator slot waveguides are studied by scanning near-field optical microscopy. Images of the standing wave pattern were established experimentally and compared with numerical simulations. Fourier analysis along the propagation direction reveals noticeable frequencies both on the experiment and the computation that could be related not only to the guided mode but also to beating phenomena between the coupled waveguides. Finally, light confinement above the slot is directly visualized with a subwavelength resolution and is compared with the expected field distribution. [ABSTRACT FROM AUTHOR]

The optical near field of a high-Q and ultrasmall volume photonic crystal nanocavity is visualized with a subwavelength resolution by using a scanning near-field optical microscope (SNOM) operating at the same time in collection-scanning mode and in interaction-scanning mode. It is shown that the nanocavity resonant mode is selectively visualized by using the SNOM interaction-scanning mode while the whole electromagnetic field surrounding the nanocavity is probed using the SNOM collection-scanning mode. The different optical near-field images are compared in light of a three-dimensional numerical analysis and we demonstrate an unexpected mode coupling at the cavity resonance. [ABSTRACT FROM AUTHOR]

A história do Ensino Superior francês contemporâneo foi objeto, desde os anos 1970, de importantes trabalhos franceses e estrangeiros, mas está ainda longe de suscitar tanto interesse quanto outros segmentos do ensino. Este artigo apresenta um panorama crítico da pesquisa nesta área e propõe uma periodização dos contextos de produção e das temáticas dominantes, ao mesmo tempo em que reflete acerca das causas deste pequeno interesse. A apresentação dos estudos em curso permite sugerir as orientações para os próximos anos e conduz ao desenvolvimento de uma abordagem global da questão

In this paper, we study the influence of fabrication uncertainties on silicon-on-insulator optical nanosystems performances. The considered structure consists in near-field coupled twin nanobeam cavities. We have performed experiments on a given population of samples, and noticeable changes in light propagation and localization were observed. Thanks to an analytic coupled-mode-based method supported by three-dimensional numerical computations, we quantitatively explain these experimental observations. We have indeed noticed that a few percent variation of the system nominal dimensions is enough to significandy change the optical coupling conditions between the cavities. Particularly, we show that, under specific conditions, light can stay locked in one of the two cavities. This result highlights the issues of reproducibihty and reliabihty concerning future industrial application, hke nano-optical electromechanical systems. [ABSTRACT FROM AUTHOR]

Abstract: While optical near-field microscopy techniques have been devoted to mapping the electromagnetic fields down to the Raleigh limit, an exciting challenge is now to use near-field probes to manipulate in situ the properties of these electromagnetic fields. Here we report the resonance tuning and therefore switching of an ultra-low volume solid state resonator by evanescent interaction with a nanometric dielectric tip. By modelling the tip-nanocavity interaction, we demonstrate that a lossless interaction regime can be achieved in which the tip behaves as a pure optical path length modulator. To cite this article: B. Cluzel et al., C. R. Physique 9 (2008). [Copyright &y& Elsevier]

Abstract: In Triticum turgidum subsp. durum (Desf.) Husn., the utilization of in vitro anther culture is hampered by the very high frequency of albinism of the regenerated plants reaching in most cases 100%. Only in vitro ovary culture or intergeneric crosses with maize produce gynogenetic green haploid and doubled haploid plants. This paper is concerned with another very interesting method of androgenetic doubled haploid plant production, the in vitro isolated microspore culture. It is shown that this method, associated with cold alone or cold plus mannitol pre-treatments, of the spikes kept within their sheath leaves, during different times, have significant positive effects, not only on embryo production, but also on chlorophyllian plant regeneration. All pre-treatments and control taken together, a total of 16 490 embryos was obtained from microspores of two T. durum varieties, among which 9320 embryos were transferred to regeneration medium and developed 150 chlorophyllian plants. Thus a long-term (five weeks) 4 °C cold pre-treatment of the microspores could be promising for green regeneration in durum wheat. To cite this article: Z. Labbani et al., C. R. Biologies 328 (2005). [Copyright &y& Elsevier]