Electro-optic polymers for high speed modulators

Different electro-optic polymer systems are analyzed with respect to their electro-optic activity, glass transition temperature (Tg) and photodefinable properties. The polymers tested are polysulfone (PS) and polycarbonate (PC). The electro-optic chromophore, tricyanovinylidenediphenylaminobenzene (TCVDPA),which was reported to have a highest photochemical stability [1] has been employed in the current work. Modified TCVDPA with bulky side groups has been synthesized, and a doubling of the electro-optic coefficient (r33) compared to the unmodified TCVDPA has been shown. The plasticizing effect of the chromophore, has been reduced by attaching it to the polymer backbone. SU8 (passive) and PC-TCVDPA (active) channel waveguides were fabricated by photodefinition technique and the passive waveguide losses were measured to be 5 dB/cm at 1550 nm

Photodefinable electro-optic polymers for high speed modulators

We present a series of polymeric electro-optic (EO) materials based on the tricyanovinylidenediphenylaminobenzene (TCVDPA) chromophore which exhibits an exceptionally high photostability combined with a high EO activity. The EO properties of these derivatives are given and the best result was obtained with the di-tBut derivative 2, which showed a nearly doubling effect of $r_{33}$ (14 pm/V to 25 pm/V), while increasing the concentration from 25 wt% to 37.5 wt%. A microring resonator design was made based on the PC-TCVDPA system. Waveguides were fabricated by photodefinition of inverted ridges in VSC, a negative epoxy based photoresist with low refractive index

Photodefinition of channel waveguide in electro-optic polymer

Polymers with optically active nonlinear chromophores have been shown to have a promising future in low cost and high speed electro–optic device applications. However, a main question of concern is the photochemical stability of the chromophores for long term application. The chromophore TCVDPA with a benzene bridge between a tricyanovinyl acceptor and an amino donor has been reported to have high photochemical stability combined with high electro-optic activity. In the current work direct waveguide definition of the host polymer SU-8, a negative photoresist, containing this chromophore by masked UV exposure followed by development, has been demonstrated. This was possible by utilizing the chromophore low absorption window in the UV region that allows crosslinking of the host polymer by exposing to UV light followed by thermal curing

Geomorphological hazard and tourist vulnerability along Portofino Park trails (Italy)

International audienceThe many trails existing in the coastal area of Portofino Promontory are used by tourists for trekking or as pathways to small villages and beaches. The aim of this paper is to define geomorphological hazard and tourist vulnerability in this area, within the framework of the management and planning of hiking activities in Portofino Natural Park. In particular, processes triggered by gravity, running waters and wave motion, affecting the slopes and the cliff, are considered. The typology of the trails and trail maintenance are also taken into account in relation to weather conditions that can make the excursion routes dangerous for tourists. In conclusion, an operative model is applied for the definition of possible risk scenarios. This model is founded on an inventory and the quantification of geomorphological hazards and tourist vulnerability, in comparison with trail rescue data. The model can be applied to other environments and tourist areas

Development of Protective Clothing against Nanoparticle Based on Electrospun Nanofibers

In this paper, the development of efficient protective clothing against nanoparticulate aerosols is presented. Nanofibrous mats of polyamide 6 (PA6) were deposited onto a nonwoven viscose substrate by electrospinning technique. The influence of electrospinning parameters, including solution concentration, viscosity, and conductivity, was studied for the production of nonwovens with controlled fiber diameter showing a size distribution ranging from 66 to 195 nm. By varying several process parameters, textiles with different thickness of the nanofiber layer and thus air permeability were obtained. A hot-press lamination process using a thermoplastic resin as glue was applied to improve the adhesion of the nanofiber layer onto the textile support. After 1500 cycles of repeated compression and torsion, the nanofiber layer was still firmly attached to the support, while mechanical damage is visible in some areas. The penetration of NaCl particles with diameter ranging from 15 to 300 nm through the electrospun textiles was found to be strongly dependent on nanofiber layer thickness. A really thin nanofiber coating provides up to 80% retention of 20 nm size particles and over 50% retention of 200 nm size nanoparticles. Increasing the thickness of the nanofiber mat, the filtration efficiency was increased to over 99% along the whole nanoparticle range. The results obtained highlight the potential of nanofibers in the development of efficient personal protective equipments against nanoparticles.The financial support of this work was provided by MICINN (Spanish Ministry of Science and Innovation) and ERDF (European Regional Development Fund) (ref.: PSE-420000-2008–003), and ACC1´O (Catalan Business Competitiveness Support Agency

The extended structure of the dwarf irregular galaxies Sextans A and Sextans B. Signatures of tidal distortion in the outskirts of the Local Group

We present a detailed study of the stellar and HI structure of the dwarf irregular galaxies SextansA and SextansB, members of the NGC3109 association. We use newly obtained deep (r~26.5) and wide field g,r photometry to extend the Surface Brightness (SB) profiles of the two galaxies down to mu_V~ 31.0 mag/arcsec^2. We find that both galaxies are significantly more extended than what previously traced with surface photometry, out to ~4 kpc from their centers along their major axis. Older stars are found to have more extended distribution with respect to younger populations. We obtain the first estimate of the mean metallicity for the old stars in SexB, from the color distribution of the Red Giant Branch, =-1.6. The SB profiles show significant changes of slope and cannot be fitted with a single Sersic model. Both galaxies have HI discs as massive as their respective stellar components. In both cases the HI discs display solid-body rotation with maximum amplitude of ~50 km/s (albeit with significant uncertainty due to the poorly constrained inclination), implying a dynamical mass ~10^{9}~M_sun, a mass-to-light ratio M/L_V~25 and a dark-to-barionic mass ratio of ~10. The distribution of the stellar components is more extended than the gaseous disc in both galaxies. We find that the main, approximately round-shaped, stellar body of Sex~A is surrounded by an elongated low-SB stellar halo that can be interpreted as a tidal tail, similar to that found in another member of the same association (Antlia). We discuss these, as well as other evidences of tidal disturbance, in the framework of a past passage of the NGC3109 association close to the Milky Way, that has been hypothesized by several authors and is also supported by the recently discovered filamentary configuration of the association itself.Comment: Accepted for publication by A&A. PdfLateX, 16 pages, 11 figures, 2 appendice

High-resolution lightning detection and possible relationship with rainfall events over the Central Mediterranean area

Lightning activity is usually associated with precipitations events and represents a possible indicator of climate change, even contributing to its increase with the production of NOx gases. The study of lightning activity on long temporal periods is crucial for fields related to atmospheric phenomena from intense rain-related hazard processes to long-term climate changes. This study focuses on 19 years of lightning-activity data, recorded from Italian Lightning Detection Network SIRF, part of the European network EUCLID (European Cooperation for Lightning Detection). Preliminary analysis was dedicated to the spatial and temporal assessment of lightning through detection in the Central Mediterranean area, focusing on yearly and monthly data. Temporal and spatial features have been analyzed, measuring clustering through the application of global Moran’s I statistics and spatial local autocorrelation; a Mann–Kendall trend test was performed on monthly series aggregating the original data on a 5 × 5 km cell. A local statistically significant trend emerged from the analysis, suggesting a possible linkage between surface warming and lightning activity