Extinction calculations of multi-sphere polycrystalline graphitic clusters - A comparison with the 2175 AA peak and between a rigorous solution and discrete-dipole approximations

Certain dust particles in space are expected to appear as clusters of individual grains. The morphology of these clusters could be fractal or compact. In this paper we study the light scattering by compact and fractal polycrystalline graphitic clusters consisting of touching identical spheres. We compare three general methods for computing the extinction of the clusters in the wavelength range 0.1 - 100 micron, namely, a rigorous solution (Gerardy & Ausloos 1982) and two different discrete-dipole approximation methods -- MarCODES (Markel 1998) and DDSCAT (Draine & Flatau 1994). We consider clusters of N = 4, 7, 8, 27,32, 49, 108 and 343 particles of radii either 10 nm or 50 nm, arranged in three different geometries: open fractal (dimension D = 1.77), simple cubic and face-centred cubic. The rigorous solution shows that the extinction of the fractal clusters, with N < 50 and particle radii 10 nm, displays a peak within 2% of the location of the observed interstellar extinction peak at ~4.6 inverse micron; the smaller the cluster, the closer its peak gets to this value. By contrast, the peak in the extinction of the more compact clusters lie more than 4% from 4.6 inverse micron. At short wavelengths (0.1 - 0.5 micron), all the methods show that fractal clusters have markedly different extinction from those of non-fractal clusters. At wavelengths > 5 micron, the rigorous solution indicates that the extinction from fractal and compact clusters are of the same order of magnitude. It was only possible to compute fully converged results of the rigorous solution for the smaller clusters, due to computational limitations, however, we find that both discrete-dipole approximation methods overestimate the computed extinction of the smaller fractal clusters.Comment: Corrections added in accordance with suggestions by the referee. 12 pages, 12 figures. Accepted for publication in Astronomy & Astrophysic

Convolutional Goppa Codes

We define Convolutional Goppa Codes over algebraic curves and construct their corresponding dual codes. Examples over the projective line and over elliptic curves are described, obtaining in particular some Maximum-Distance Separable (MDS) convolutional codes.Comment: 8 pages, submitted to IEEE Trans. Inform. Theor

Defining, quantifying, and reporting intensity, dose, and dosage of neurorehabilitative interventions focusing on motor outcomes

INTRODUCTION Determining the minimal amount of therapy needed for positive neurorehabilitative outcomes is important for optimizing active treatment interventions to improve motor outcomes. However, there are various challenges when quantifying these relationships: first, several consensuses on the definition and usage of the terms intensity, dose, and dosage of motor interventions have been proposed, but there seems to be no agreement, and the terms are still used inconsistently. Second, randomized controlled trials frequently underreport items relevant to determining the intensity, dose, and dosage of the interventions. Third, there is no universal measure to quantify therapy intensity accurately. This "perspectives" paper aims to increase awareness of these topics among neurorehabilitation specialists. DEFINING QUANTIFYING AND REPORTING We searched the literature for definitions of intensity, dose, and dosage and adapted the ones we considered the most appropriate to fit the needs of neurorehabilitative interventions. Furthermore, we suggest refining the template for intervention description and replication (TIDieR) to enhance the reporting of randomized controlled trials. Finally, we performed a systematic literature search to provide a list of intensity measures and complemented these with some novel candidate measures. DISCUSSION The proposed definitions of intensity, dose, and dosage could improve the communication between neurorehabilitation specialists and the reporting of dose and dosage in interventional studies. Quantifying intensity is necessary to improve our understanding of the minimal intensity, dose, and dosage of therapy needed to improve motor outcomes in neurorehabilitation. We consider the lack of appropriate intensity measures a significant gap in knowledge requiring future research

Thermoelectric ceramic materials, and the quest to improve their performance

El pdf del artículo es la versión post-print.Peer Reviewe

Interstellar extinction by fractal polycrystalline graphite clusters?

Certain dust particles in space are expected to appear as clusters of individual grains. The morphology of these clusters could be fractal or compact. To determine how these structural features would affect the interpretation of the observed interstellar extinction peak at $\sim 4.6 \mu$m, we have calculated the extinction by compact and fractal polycrystalline graphite clusters consisting of touching identical spheres. We compare three general methods for computing the extinction of the clusters, namely, a rigorous solution and two different discrete-dipole approximation methods.Comment: 4 pages, 2 figures. Proceedings for the 6'th International Conference on Electromagnetic and Light Scattering by Non-spherical Particles, Marts 2002, Florid

Improvement of thermoelectric performances of Bi2Sr2Co1.8Ox textured materials by Pb addition using a polymer solution method

El pdf del artículo es la versión pre-print.Bi1.6Pb0.4Sr2Co1.8Ox ceramics have been prepared through a polymer solution method using polyethyleneimine. From these powders, bulk textured materials have been prepared using a melt growth technique. Microstructure has been observed by scanning electronic microscopy (SEM) which has shown that samples are mainly composed by the thermoelectric phase, with small amounts of secondary phases. Electrical resistivity measurements showed very small values nearly constant with temperature, whilst thermopower increases from room temperature to 650 °C. Power factor at 50 °C is about 0.15 mW/K2·m and 0.30 at 650 °C, which makes these ceramics good candidates for power generation applications. © 2012 Elsevier B.V. All rights reserved.This research has been supported by the Spanish Ministry of Science and Innovation-FEDER (Project MAT2008-00429) and by the Gobierno de Aragón (Consolidated Research Groups T12 and T87). Sh. Rasekh also acknowledges a JAE-PreDoc 2010 grant from CSIC.Peer Reviewe

Effect of Yb substitution in Bi-2212 ceramics prepared by laser floating zone technique

In the present work, the influence of Yb substitution for Bi on the structural, electrical and magnetic properties of textured Bi-2212 ceramics has been investigated. X-ray diffraction studies indicated that the major peaks correspond to the Bi-2212 phase. The SEM images clearly show that there is an increase in the number of secondary phases with raising Yb content while all samples maintain similar grain morphology. Magnetic analysis of all samples has been done by magnetic hysteresis measurements, indicating that an enhancement in the M-H loops is obtained by a low Yb doping. The critical current density of samples was calculated from the M-H curves by using Bean’s critical state model, indicating that sample with 0.05 Yb substitution possesses the highest Jc values.The authors wish to thank the Gobierno de Aragón and Fondo Social Europeo (Grupos de Investigacion Consolidados T12 and T87) and MINECO-FEDER (MAT2013-46505-C3-1-R) for financial support.Peer Reviewe