Broadband telecom transparency of semiconductor-coated metal nanowires: more transparent than glass

Metallic nanowires (NW) coated with a high permittivity dielectric are proposed as means to strongly reduce the light scattering of the conducting NW, rendering them transparent at infrared wavelengths of interest in telecommunications. Based on a simple, universal law derived from electrostatics arguments, we find appropriate parameters to reduce the scattering efficiency of hybrid metal-dielectric NW by up to three orders of magnitude as compared with the scattering efficiency of the homogeneous metallic NW. We show that metal@dielectric structures are much more robust against fabrication imperfections than analogous dielectric@metal ones. The bandwidth of the transparent region entirely covers the near IR telecommunications range. Although this effect is optimum at normal incidence and for a given polarization, rigorous theoretical and numerical calculations reveal that transparency is robust against changes in polarization and angle of incidence, and also holds for relatively dense periodic or random arrangements. A wealth of applications based on metal-NWs may benefit from such invisibility

Nanostructural differences in pectic polymers isolated from strawberry fruits with low expression levels of pectate lyase or polygalacturonase genes

Our research group has obtained transgenic strawberry plants expressing antisense sequences of either a pectate lyase (APEL lines) [1] or a polygalacturonase gene (APG lines) [2]. Both genes encode ripening-specific endo-pectinases with a common target, deesterified homogalacturonans, but each enzyme act by a different mechanism and pH range. Ripe fruits from both transgenic genotypes were significantly firmer than control, being APG fruits on average 25% firmer than APEL fruits. Cell wall analysis of both transgenic genotypes indicated that pectin fractions extracted with CDTA and sodium carbonate were significantly modified in transgenic fruits [2,3]. To gain insight in the role of these pectinases in pectin disassembly during ripening, CDTA and Na2CO3 pectins have been analyzed by atomic force microscopy (AFM). APEL and APG CDTA pectins had similar contour lengths but both were significantly longer than control. Similarly, APG carbonate chains were longer than control, showing APEL carbonate chains an intermediate length. Furthermore, transgenic pectins displayed a more complex branching pattern and a higher number of micellar aggregates, especially in the sodium carbonate fractions of APG samples. Acid hydrolysis of carbonate pectins reduced the number of micellar aggregates. AFM analyses confirm that the inhibition of both pectinases reduces pectin disassembly, and also suggest that each pectinase acts on specific pectin domains. Particularly, polygalacturonase silencing induces more significant pectin modifications, nicely correlated with the firmer phenotype of APG fruits, than the down-regulation of pectate lyase

Correlations between reflected and transmitted intensity patterns emerging from opaque disordered media

The propagation of monochromatic light through a scattering medium produces speckle patterns in reflection and transmission, and the apparent randomness of these patterns prevents direct imaging through thick turbid media. Yet, since elastic multiple scattering is fundamentally a linear and deterministic process, information is not lost but distributed among many degrees of freedom that can be resolved and manipulated. Here we demonstrate experimentally that the reflected and transmitted speckle patterns are correlated, even for opaque media with thickness much larger than the transport mean free path, proving that information survives the multiple scattering process and can be recovered. The existence of mutual information between the two sides of a scattering medium opens up new possibilities for the control of transmitted light without any feedback from the target side, but using only information gathered from the reflected speckle.Comment: 6 pages, 4 figure

The Spanish universities in Twitter: Messages, contents and publics

En apenas un lustro, el uso de Twitter se ha generalizado entre las universidades españolas. El 97,4 por ciento de ellas dispone de perfil institucional en esta red social, caracterizada por la brevedad de sus mensajes y la posibilidad de acceder a la información sin necesidad de ser usuario. El empleo de Twitter por parte de las universidades presenta características bien definidas, como pone de manifiesto este trabajo: público preferentemente estudiantil, contenidos relacionados sobre todo con la docencia y la extensión universitaria, y poca atención a la actividad investigadora.The use of Twitter has become widespread among the Spanish universities since five years ago. The 97.4 per cent of them have got an institutional profile in this social network, whose most prominent properties are the brevity of their messages and the easiness to access to the information for all the users. This study demonstrates that the use of Twitter by the Spanish universities shows some clear characteristics: messages orientated to the students, contents connected with educational and cultural activities and lack of information about university research

Microstructural study of the deformation zones around a penetrating coned tip in silty soil

The change in soil microstructure around the penetrating probe during a cone penetration test is investigated. Backscattered electron images of polished thin sections prepared from frozen samples at the end of penetration are used. The images have a spatial resolution of 0.4 µm/pixel that allow a clear identification of grains and pore spaces. The statistical distribution of the change of particles orientation is analyzed for the zones around the cone tip and the shaft. Quantitative analysis of the change in porosity near the penetrating object is investigated. An increase in porosity and a decrease in the anisotropy of particle orientations from the cone and further out confirm that the soil deformation during CPTU in silt is a combination of compaction and dilative behavior that might influence the pore pressure distribution during penetration

Microstructural study of the deformation zones during cone penetration in silt at variable penetration rates

During conventional cone penetration testing in silt, the soil will normally be partially drained. If the penetration rate varies, time for drainage is altered and therefore the measured cone resistance and pore pressure will change. This paper studies the change in soil microstructure around the probe during cone penetration carried out at different penetration rates to investigate the failure mechanism and the processes controlling drainage in silt. Backscattered electron images of polished thin sections prepared from frozen samples at the end of penetration were used. Making use of advanced image processing techniques, the statistical distribution of particle orientations and the local porosity were investigated for the zones around the cone tip and the shaft. The spatial distribution of the measured microscale parameters in the region near the probe indicates that the soil deformation during CPTU in silt leads to the formation of both contractive and dilative zones. The macro response of the material, presented by the pore pressure and the cone penetration resistance measured during the test, results from the competition between these zones during penetration, which is shown to be dependent on the penetration rate