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

Thermoelectric ceramic materials, and the quest to improve their performance

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

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

Decrease of Ca3Co4O9+δ thermal conductivity by Yb-doping

In this study, the effect of Yb-substitution on the structural, electrical and thermal transport properties of the CaCoO system has been investigated in the low temperature region (between 10 and 300 K). The resistivity of samples increases with raising the Yb-concentration in the system. All the samples show a metal-semiconductor transition below 85 K. In the analysis based on Strongly Correlated Fermi Liquid Model, an increased bandwidth and a reduced electronic correlation are found. It has also been found that the energy gap, E , value also decreases with Yb-substitution. The samples show positive thermoelectric power, indicating that dominant charge carriers are holes in all the samples. The thermoelectric power value decreases with Yb-substitution. From Mott equation, it is determined that the Fermi energy and hole concentration decrease in the Yb-susbtituted samples, compared to the undoped ones. Thermal conductivity, κ, is decreased in about 50% of the measured in undoped samples for the 0.01 and 0.03 Yb-doped samples at 300 K. Highest figure of merit, ZT, value is found to be 5.4 10 at 300 K for the unsubstituted sample and the ZT value decreases by the substitution.The authors wish to thank the MINECO-FEDER (Project MAT2013-46505-C3-1-R) and the Gobierno de Aragón and Fondo Social Europeo (Research Groups T12 and T87) for financial support.Peer Reviewe

Thermoelectric properties of directionally grown Bi2Ba2Co2Oδ/Ag composites: effect of annealing

Bi2Ba2Co2Oδ thermoelectric ceramics with Ag additions (0, 1, 3, and 5 wt%) have been successfully textured using the laser floating zone method. Microstructure has shown that samples are composed by thermoelectric grains, together with a high amount of secondary phases, and that 3 wt% Ag addition leads to the best grain orientation. These microstructural benefits have been reflected in the highest thermoelectric performances determined in these samples. It has also been found that annealing procedure leads to a drastic decrease of secondary phases amount and raises the oxygen content in the thermoelectric phase. These modifications are reflected in an important decrease of electrical resistivity, ρ (compared to the as-grown samples) without drastic modification of Seebeck coefficient, S. As a consequence, the highest thermoelectric performances, determined through the power factor, have been reached in the 3 wt% Ag textured and annealed samples in the whole measured temperature range. The maximum PF (=S/ρ) values at 650 °C determined in these samples are very close to the highest reported in single crystals or very low rate LFZ grown Bi2Ba2Co2Oδ compounds, making them very attractive for practical applications.This research has been supported by the Spanish MINECO-FEDER (MAT2013-46505-C3-1-R). The authors wish to thank the Gobierno de Aragón and Fondo Social Europeo (Consolidated Research Groups T87 and T12) for financial support.Peer Reviewe

Improved thermoelectric performances in textured Bi1.6Pb0.4Ba2Co2Oy/Ag composites

Bi1.6Pb0.4Ba2Co2Oy thermoelectric ceramics with small Ag additions (0, 1, 3, and 5 wt%) have been textured using the laser floating zone method. Microstructure has shown a slight decrease on the secondary phases content and a better grain alignment in Ag added samples. These microstructural features are reflected in the thermoelectric properties, which have shown a significant decrease of electrical resistivity, when the Ag content is raised. In spite of a corresponding decrease of Seebeck coefficient, all the Ag-containing samples possess higher Power Factor values than the Bi1.6Pb0.4Ba2Co2Oy ones. Moreover, the maximum Power Factor values (about 0.36 mW/K2.m at 650 °C) have been measured in Bi1.6Pb0.4Ba2Co2Oy+3 wt% Ag samples, which are the best results reported in this family of materials