Interest in terahertz (THz) systems and technology has grown significantly over the past 10 years for their potential in non-invasive imaging, sensing and high-data-rate wireless communication. Waves at THz frequencies present an alternative to x-rays for imaging through paper, cloth, wood, concrete, plastic and many other materials. In contrast to x-rays they are non-ionizing and therefore inherently safe. Applications of THz radiations range from nondestructive testing to medical imaging, security screening of objects and persons. Several groups have also considered using THz waves to transmit data in wireless communications. Wireless THz communications for which THz waves are the free-space carrier of data are recognized as the promising breakthrough solution to achieve data-rates up to 100 Gbps. THz imaging and wireless communication applications suffer, however, from the lack of fast and low-cost detectors operating at room temperature and in this work we show that graphene based plasma nanotransistors can be a good alternative. .Nanotransistors offer great prospect for the development of innovative THz detectors. The interest in using field-effect transistors for THz applications was initiated by the theoretical work of Dyakonov and Shur, who predicted that the nonlinear properties of the 2D plasma in the transistor channel can be used for detection of THz waves at frequencies significantly higher than the transistor cut-off frequency. Graphene field-effect nanotransistors were recently demonstrated showing maturity of graphene microelectronics. In this paper, we present extensive studies on first THz detectors based on monolayer and bilayer graphene field effect transistors. The specific detection sign reversal related to the graphene Dirac point change of electron to hole conductivity is clearly demonstrated. We show that the detectors consisting of a gated 2D massless fermion gas as rectifying element and an integrated coupling antenna achieve a responsivity above 1.2 V/W (1.3 mA/W) in photovoltage and photocurrent mode respectively, and a noise equivalent power below 2 10-9 W/Hz0.5 We show also that these detectors can operating as sensitive room-temperature broadband THz detectors in THz imaging systems. Feasibility of THz food industry quality control and agriculture watering control imagers using graphene nanotransitor sensors/detectors is demonstrated.

Relaxor ferroelectric perovskites are highly polarizable and can exhibit giant coupling between elastic strain and an applied electric field. Here, we report an in situ extended X-ray absorption fine structure (EXAFS) study of a PbZn1/3Nb2/3O3 (PZN) single crystal as a function of the electric field. We show that the strong dipoles in the NbO6 octahedra bonds are aligned along the four < 011 > directions close to the orientation of the electric field, while a small reversible polar shift occurs for Zn in the direction of the electric field, i.e., positive or negative. This reversible Zn-O polar shift is proposed to play an important role in both the "easy" switching of the ferroelectric polarization and the giant piezoelectric effect in PZN.

I'll review the current understanding of the low energy effective theory resulting from compactifications of Type II superstrings on Calabi-Yau manifolds. The effective action can be encoded into the metric on a moduli space which is known to receive quantum stringy corrections, both perturbative and non-perturbative. The description of instanton effects crucially relies on twistorial methods and points toward a deep relation to integrable structures.

Agricultural spraying involves atomizing a liquid stream through a hydraulic nozzle forming a liquid sheet, which is subsequently destabilized into droplets. Standard solution adjuvants as dilute oil-in-water emulsions are known to influence the spray drop size distribution. To elucidate the mechanisms causing the changes on the drop size distribution, we investigate the influence of emulsions on the destabilization mechanisms of liquid sheets. Model laboratory experiments based on the collision of a liquid drop on a small solid target are used to produce and visualize liquid sheets. With dilute oil-in-water emulsion, the liquid sheet is destabilized by the nucleation of holes in the sheet that perforate it during its expansion. The physico-chemical parameters of the emulsion, such as the emulsion concentration and the emulsion drop size distribution, are varied to rationalize their influence on the sheet destabilization mechanisms. The results obtained with the drop impact experiments are compared to the measurement of the spray drop size distribution. The very good correlation between the number of nucleation events and the volume fraction of small drops in the spray suggests that experiments on liquid sheet are appropriate model experiments to gain an understanding of the physical mechanisms governing the spray drop size distribution.

The collision of a liquid drop against a small target results in the formation of a thin liquid sheet that extends radially until it reaches a maximum diameter. The subsequent retraction is due to the air-liquid surface tension. We have used a time- and space-resolved technique to measure the thickness field of this class of liquid sheet, based on the grey level measurement of the image of a dyed liquid sheet recorded using a fast camera. This method enables a precise measurement of the thickness in the range (10 − 450) μm, with a temporal resolution equals to that of the camera. We have measured the evolution with time since impact, t, and radial position, r, of the thickness, h(r, t), for various drop volumes and impact velocities. Two asymptotic regimes for the expansion of the sheet are evidenced. The scalings of the thickness with t and r measured in the two regimes are those that were predicted in Rozhkov et al. (2004) fort the short-time regime and Villermaux & Bossa (2011) for the long time regime, but never experimentally measured before. Interestingly, our experimental data also evidence the existence of a maximum of the film thickness hmax(r) at a radial position rhmax (t) corresponding to the crossover of these two asymptotic regimes. The maximum moves with a constant velocity of the order of the drop impact velocity, as expected theoretically. Thanks to our visualization technique, we also evidence an azimuthal thickness modulation of the liquid sheets.