Multi-gap superconductivity in a BaFe1.84Co0.16As2 film from optical measurements at terahertz frequencies

We measured the THz reflectance properties of a high quality epitaxial thin film of the Fe-based superconductor BaFe$_{1.84}$Co$_{0.16}$As$_2$ with T$_c$=22.5 K. The film was grown by pulsed laser deposition on a DyScO$_3$ substrate with an epitaxial SrTiO$_3$ intermediate layer. The measured $R_S/R_N$ spectrum, i.e. the reflectivity ratio between the superconducting and normal state reflectance, provides clear evidence of a superconducting gap $\Delta_A$ close to 15 cm$^{-1}$. A detailed data analysis shows that a two-band, two-gap model is absolutely necessary to obtain a good description of the measured $R_S/R_N$ spectrum. The low-energy $\Delta_A$ gap results to be well determined ($\Delta_A$=15.5$\pm$0.5 cm$^{-1}$), while the value of the high-energy gap $\Delta_B$ is more uncertain ($\Delta_B$=55$\pm$7 cm$^{-1}$). Our results provide evidence of a nodeless isotropic double-gap scenario, with the presence of two optical gaps corresponding to 2$\Delta/kT_c$ values close to 2 and 7.Comment: Published Versio

Fitting the integrated Spectral Energy Distributions of Galaxies

Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details ofdust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics & Space Scienc

Global conformal anomaly in N=2 string

We show the existence of a global anomaly in the one-loop graphs of N=2 string theory, defined by sewing tree amplitudes, unless spacetime supersymmetry is imposed. The anomaly is responsible for the non-vanishing maximally helicity violating amplitudes. The supersymmetric completion of the N=2 string spectrum is formulated by extending the previous cohomological analysis with an external spin factor; the target space-time spin-statistics of these individual fields in a selfdual background are compatible with previous cohomological analysis as fields of arbitrary spin may be bosonized into one another. We further analyze duality relations between the open and closed string amplitudes and demonstrate this in the supersymmetric extension of the target space-time theory through the insertion of zero-momentum operators.Comment: 29 pages, LaTeX, one figur

Canadian Imaging And Sampling Technology For Studying Marine Benthic Habitat And Biological Communities

No abstracts are to be cited without prior reference to the author.The systematic mapping of marine benthic habitat and biological communities requires specialized oceanographic instrumentation. During the past ten years, as part of research programs investigating the effects of mobile fishing gear and offshore hydrocarbon development, Canadian scientists and engineers have developed a suite of tools for imaging and sampling seabed habitats over different spatial scales. Towcam is a towed vehicle which collects continuous but low-resolution video imagery of the seabed over a large area (i.e. 1-10 km transects). Campod is an instrumented tripod equipped with two video cameras and a 35-mm camera with 250-frame capacity. It is deployed while the ship is on station, or slowly drifting, and collects both general reconnaissance video and high-resolution imagery from a small area of the seabed. A hydraulically operated videograb, which uses the same conductor cable and winch as Campod, collects sediment and organisms from an area of 0.5 m2. Video cameras allow the operator to select the exact area of seabed to sample and to ensure that the grab closes properly. These three instruments are briefly described and examples of their application on the continental shelf off eastern Canada provided. These and comparable tools used by other ICES countries, when used in conjunction with acoustic survey tools (multibeam, seismic, sidescan, RoxAnn, QTCview, etc.), make possible the classification and mapping of marine benthic habitat and biological communities over large areas