The growth conditions to achieve group-III-nitride nanocolumns and nanocolumnar heterostructures by plasma-assisted molecular beam epitaxy are studied. The evolution of the nanocolumnar morphology with the growth conditions is determined for (Ga,Al)N and (In,Ga)N nanocolumns. The mechanisms behind the nanocolumnar growth under high N-rich conditions are clarified in the sense that no seeding or catalysts are required, as it is the case in the vapour-liquid-solid model that applies to most nanocolumns grown by metal organic chemical vapour deposition, either with group-III nitrides, II -VI or III -V compounds. Some examples of nanocolumnar heterostructures are given, like quantum disks and cylindrical nanocavities. Preliminary results on the growth of arrays of ordered GaN nanocolumns are reported.

A polarization insensitive technique for highly efficient coupling between SOI waveguides and high mode field diameter single-mode fibers is reported. The proposed coupling structure is based on an inverted taper structure coupled to a fiber-adapted waveguide. The fiber-adapted waveguide is made by using the SiO(2) layer under the Si waveguiding layer of the SOI wafer thus avoiding the use of extra materials such as polymers. The proposed coupling structure is aimed for being integrated with V-groove auto-alignment techniques. Coupling losses of 3.5dB and 3.7dB to 8mum mode field diameter single-mode fibers have been estimated by means of 3D-BPM simulations for TE and TM polarizations respectively and a 1550nm input signal wavelength.

The influence of the relative position of Ag metallic nanoparticles (Ag MNPs) embedded in a 100 nm SiO x Antireflection Coating (ARC) for specular polished c-Si substrates is studied. It is demonstrated that this Plasmonic ARC (PARC) can achieve lower average reflectivities than the optimised SiO x ARC. This has been done for different sizes of Ag nanoparticles. An alternative for PECVD to encapsulate Ag MNPs with SiO x is presented, avoiding the risk of metallic contamination in the reactor chamber as well as its effect on the size and shape of the self-aggregated Ag MNP. It is demonstrated, however, that this PARC is not suitable for silicon solar cells as a substitute for traditional ARC because it presents a high loss related with Fano destructive interference. V C 2013 AIP Publishing LLC.

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The flow of internally deposited radioisotope particles inside the body of people exposed to inhalation, ingestion, injection or other ways is usually evaluated using compartmental models (see Sanchez & Lopez-Fidalgo, (2003, and Lopez-Fidalgo & Sanchez, 2005). The International Commission on Radiological Protection (ICRP, 1994) describes the model of the human respiratory tract, represented by two main regions. One of these, the thoracic region (lungs) is divided into different compartments. The retention in the lungs is given by a large combination of ratios of exponential sums depending on time. The aim of this work is to provide optimal times for making bioassays when there has been an accidental radioactivity intake and there is interest in estimating it. In this paper, a large two-parameter model is studied and a simplified model is proposed in order to obtain optimal designs in a more suitable way. Local c-optimal designs for the main parameters are obtained using the results of Lopez-Fidalgo & Rodriguez-Diaz, 2004). Efficiencies for all the computed designs are provided and compared.Bioassays, biokinetic models, design efficiencies, initial deposition factors, radioactivity retention,