Intensity dependences of the nonlinear optical excitation of plasmons in graphene

Recently, we demonstrated an all-optical coupling scheme for plasmons, which takes advantage of the intrinsic nonlinear optical response of graphene. Frequency mixing using free-space, visible light pulses generates surface plasmons in a planar graphene sample, where the phase matching condition can define both the wavevector and energy of surface waves and intraband transitions. Here, we also show that the plasmon generation process is strongly intensity-dependent, with resonance features washed out for absorbed pulse fluences greater than 0.1 J m−2. This implies a subtle interplay between the nonlinear generation process and sample heating. We discuss these effects in terms of a non-equilibrium charge distribution using a two-temperature model.Peer ReviewedPostprint (author's final draft

Polymerized LB films imaged with a combined atomic force microscope-fluorescence microscope

The first results obtained with a new stand-alone atomic force microscope (AFM) integrated with a standard Zeiss optical fluorescence microscope are presented. The optical microscope allows location and selection of objects to be imaged with the high-resolution AFM. Furthermore, the combined microscope enables a direct comparison between features observed in the fluorescence microscope and those observed in the images obtained with the AFM, in air or under liquid. The cracks in polymerized Langmuir-Blodgett films of lO,l2-pentacosadiynoic acid as observed in the fluorescence microscope run parallel to one of the lattice directions of the crystal as revealed by molecular resolution images obtained with the AFM. The orientation of these cracks also coincides with the polarization direction of the fluorescent light, indicating that the cracks run along the polymer backbone. Ripple-like corrugations on a submicrometer scale have been observed, which may be due to mechanical stress created during the polymerization process

The Roles of Substrate vs Nonlocal Optical Nonlinearities in the Excitation of Surface Plasmons in Graphene

It has recently been demonstrated that difference frequency mixing (DFM) can generate surface plasmons in graphene [1]. Here, we present detailed calculations comparing the contributions to this effect from substrate and from graphene nonlinearities. Our calculations show that the substrate (quartz) nonlinearity gives rise to a surface plasmon intensity that is around twelve orders of magnitude smaller than that arising from the intrinsic graphene response. This surprisingly efficient intrinsic process, given the centrosymmetric structure of graphene, arises almost entirely due to non-local contributions to the second order optical nonlinearity of graphene

Project ExCEL: Web-based Scanning Electron Microscopy for K-12 Education

Project ExCEL (Extended Classroom for Enhanced Learning) brings the capabilities of scanning electron microscopy (SEM) into classrooms. University and industry personnel, working together, have developed a web-based interface to allow schools to control a modern SEM. The interface allows a user control of the operating parameters of the microscope, stage movement, and chemical analysis. Such total control is not available on any other system. Since Iowa State University (ISU) pioneered the idea of remote SEM for education, researchers have learned that providing teachers access to sophisticated equipment does not ensure that it will be used. Teachers are busy, and structured curriculums are not conducive for incorporating the SEM into classes. A lack of teacher knowledge of SEMs also discourages their use. To overcome these problems, College of Engineering and College of Education faculty are working together to train future teachers in the SEM. The web-based SEM is being used in education courses, and selected students (who receive additional training) prepare lesson plans and present their work to the class. In-service teachers receive instruction in the web-based SEM through workshops. By using this integrated approach, all science teachers in Iowa will eventually gain the confidence to use the SEM in their classrooms

Psychological support for ex-military families

There is a complex interaction between familial functioning and veteran mental health, with familial relationships often being affected. Family therapy is not routinely recommended or offered for veterans in the UK. This study used a narrative approach to explore the experiences of veterans and spouses having received family therapy. Specifically, this study aimed to explore what stories individuals in an ex-military family would tell of their experience of family therapy, what narrative themes occurred and what the perceived impact on familial relationships was following family therapy. Individual narrative interviews were conducted with four veterans and five spouses. Individual interviews were followed by joint couple interviews with two couples. Main findings suggested that typically veterans would tell a ‘romance’ story while spouses were more likely to tell a ‘tragedy’ or ‘epic’ story. Narrative themes occurring from veterans, spouses and couples included: family therapy helpful, lack of support, changes in veteran, impact of difficulties on family relationships and military culture and transitioning. Finally the study found that family therapy had positively impacted familial relationships, particularly highlighting improvements in couple communication and shared or alternative perspectives to be important. Limitations, clinical implications and future directions are discussed

Compiling Linguistic Constraints into Finite State Automata

International audienceThis paper deals with linguistic constraints encoded in the form of (binary) tables, generally called lexicon-grammar tables. We describe a unified method to compile sets of tables of linguistic constraints into Finite State Automata. This method has been practically implemented in the linguistic platform Unitex

Un nouvel indicateur intégré d’évaluation des dégâts occasionnés aux grappes par des bioagresseurs majeurs au vignoble

Communication faite au cours du colloque DinABio2013, 13 et 14 novembre 2013; Tours, FranceAn original and integrative evaluation indicator has been developed to quantify the cumulated damage from major pests and diseases affecting grape bunches: downy mildew, powdery mildew, gray mould and tortricid moths. It made it possible to estimate the associated crop losses and to relate them to the plant protection strategy in different modes of production (organic farming, in-transition, conventional). Thus, overall plant losses were higher in 2012 than in 2011. The in-transition growers’ strategy, with reduced copper doses but increased numbers of sprays, led to a 20% increase in average severity on bunches (essentially due to Downy mildew). The more pragmatic approach of experienced organic growers and conventional ones (higher doses and fewer sprays) reduced the yield losses. The proposed indicator is used for two purposes, i) evaluating the quantitative losses due to pest attacksand ii) differentiating them from other non-pest ones. A more detailed analysis including the impact on performance will be achieved and published soon.Un indicateur d’évaluation, l’IEDG (Indicateur d’Evaluation des Dégâts sur Grappes), a été mis au point pour quantifier les dégâts cumulés dus aux principaux bioagresseurs affectant les grappes de raisin : mildiou, oïdium, pourriture grise et tordeuses. Il permet d’estimer la perte de récolte imputable au cortège parasitaire et de faire le lien avec la stratégie phytosanitaire adoptée (caractérisée ici par l’IFT) et le mode de production (AB, conversion, conventionnel). Ainsi, les pertes sanitaires ont été supérieures en 2012 par rapport à 2011. La stratégie phytosanitaire des viticulteurs en conversion, basée sur des réductions de dose de cuivre de près de 80% et des passages plus nombreux dans les parcelles, n’a pas été efficiente en 2012 avec des sévérités proches de 20% sur grappe, essentiellement dues au mildiou. L’utilisation de doses d’applications supérieures et moins de passages dans les parcelles limite les dommages chez les autres viticulteurs. L’indicateur proposé permet d’évaluer les pertes quantitatives générées par les attaques de bioagresseurs et de les différencier des autres pertes non parasitaires. Une analyse plus fine incluant l’effet région et l’impact sur le rendement devra être réalisée

VEGF preconditioning leads to stem cell remodeling and attenuates age-related decay of adult hippocampal neurogenesis

Several factors are known to enhance adult hippocampal neurogenesis but a factor capable of inducing a long-lasting neurogenic enhancement that attenuates age-related neurogenic decay has not been described. Here, we studied hippocampal neurogenesis following conditional VEGF induction in the adult brain and showed that a short episode of VEGF exposure withdrawn shortly after the generation of durable new vessels (but not under conditions where newly made vessels failed to persist) is sufficient for neurogenesis to proceed at a markedly elevated level for many months later. Continual neurogenic increase over several months was not accompanied by accelerated exhaustion of the neuronal stem cell (NSC) reserve, thereby allowing neurogenesis to proceed at a markedly elevated rate also in old mice. Neurogenic enhancement by VEGF preconditioning was, in part, attributed to rescue of age-related NSC quiescence. Remarkably, VEGF caused extensive NSC remodelling manifested in transition of the enigmatic NSC terminal arbor onto long cytoplasmic processes engaging with and spreading over even remote blood vessels, a configuration reminiscent of early postnatal "juvenile" NSCs. Together, these findings suggest that VEGF preconditioning might be harnessed for long-term neurogenic enhancement despite continued exposure to an "aged" systemic milieu