Origin of the negative differential resistance in the output characteristics of a picene-based thin-film transistor

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this work, we have fabricated and studied p-type picene thin-film transistors. Although the devices exhibited good electrical performance with high field-effect mobility (up to 1.3 cm2/V¿s) and on/off ratios above 105, the output electric characteristics of the devices exhibited a Negative Differential Resistance for higher drain-source voltage. Finally, a possible explanation for this phenomenon is developed.Peer ReviewedPostprint (author's final draft

Origin of passivation in hole-selective transition metal oxides for crystalline silicon heterojunction solar cells

Transition metal oxides (TMOs) have recently demonstrated to be a good alternative to boron/phosphorous doped layers in crystalline silicon heterojunction solar cells. In this work, the interface between n-type c-Si (n-Si) and three thermally evaporated TMOs (MoO3, WO3, and V2O5) was investigated by transmission electron microscopy, secondary ion-mass, and x-ray photoelectron spectroscopy. For the oxides studied, surface passivation of n-Si was attributed to an ultra-thin (1.9–2.8 nm) SiOx~1.5 interlayer formed by chemical reaction, leaving oxygen-deficient species (MoO, WO2, and VO2) as by-products. Carrier selectivity was also inferred from the inversion layer induced on the n-Si surface, a result of Fermi level alignment between two materials with dissimilar electrochemical potentials (work function difference ¿¿ = 1 eV). Therefore, the hole-selective and passivating functionality of these TMOs, in addition to their ambient temperature processing, could prove an effective means to lower the cost and simplify solar cell processing.Postprint (author's final draft

La noción de amistad en el " De adulatore et amico " de Plutarco

Sin resume

Do sunk exporting costs differ among markets? Evidence from Spanish manufacturing firms.

In this paper, we test the hypothesis of sunk exporting costs differing among markets. We use a sample of Spanish firms from Encuesta sobre Estrategias Empresariales (ESEE) for period 1991-2002. Our results confirm the importance of those sunk costs and demonstrate that they differ depending on the market they export to. Although most of the firms exports to developed markets, the costs to enter (and "to re-enter") are greater in those markets.Sunk costs, heterogeneity of firms, Regionalism.

Superior performance of V2O5 as hole selective contact over other transition metal oxides in silicon heterojunction solar cells

Transition metal oxides (TMOs) have recently been proved to efficiently serve as hole-selective contacts in crystalline silicon (c-Si) heterojunction solar cells. In the present work, two TMO/c-Si heterojunctions are explored using MoO3 (reference) and V2O5 as an alternative candidate. It has been found that V2O5 devices present larger (16% improvement) power conversion efficiency mainly due to their higher open-circuit voltage. While V2O5/c-Si devices with textured front surfaces exhibit larger short-circuit currents, it is also observed that flat solar cell architectures allow for passivation of the V2O5/n-Si interface, giving significant carrier lifetimes of 200 µs (equivalent to a surface recombination velocity of Seff ~140 cm s-1) as derived from impedance analysis. As a consequence, a significant open-circuit voltage of 662 mV is achieved. It is found that, at the TMO/c-Si contact, a TMO work function enhancement ¿FTMO occurs during the heterojunction formation with the consequent dipole layer enlargement ¿’=¿+¿FTMO. Our results provide new insights into the TMO/c-Si contact energetics, carrier transport across the interface and surface recombination allowing for further understanding of the nature of TMO/c-Si heterojunctions.Peer ReviewedPostprint (published version

Open access availability of Catalonia research output: Case analysis of the CERCA institution, 2011-2015

The open access availability of publications by Catalonia's CERCA research centres was analysed to determine the extent to which authors use open access journals, repositories, social networks and other websites to disseminate their research results. A sample of 3,730 journal articles published by authors from CERCA research centres between 2011 and 2015 and available on Web of Science (out of a total output of 44,423) was analysed to identify how many were available in open access, full-text format. The results revealed that 75,8% of the total (2,828 articles) had at least one version available in open access, but just 52% (1,940 articles) had at least one version available in either journals (whether pure or hybrid open access journals or those with embargo periods) or repositories, a finding that highlights the powerful role played by academic social networks in the sharp increase in open access availability. Of the 2,828 articles for which at least one open access version was found, a total of 9,868 copies were located. With respect to versions, the publisher's final version, i.e. the type formatted for publication by journal publishers, was found in 75,3% of cases. The number of articles published in open access journals (567) was very close to the number of articles published in hybrid journals or journals with embargo periods (624). Only 40,4% of the articles in the sample were located in repositories, being the subject repositories the heaviest used. Fifty percent of the articles (1,881 publications) were posted on academic social networks, the most popular of which were ResearchGate and Academia. According to thematic areas, all six areas (science, life sciences, medical and health sciences, engineering and architecture and humanities) exceeded 70% of articles in open access

Caracterización de las almazaras cooperativas catalanas

En el presente artículo hemos tratado de analizar las características de las almazaras cooperativas catalanas con la finalidad de destacar no solamente sus elementos más importantes de gestión sino también sus principales debilidades. Las cooperativas se consideran instrumentos útiles para acometer políticas de desarrollo económico y bienestar social. A pesar de ello hay un gran debate abierto acerca de la eficiencia de estas organizaciones, que plantean el interrogante de si están en condiciones de competir con éxito en una economía cada vez más abierta, liberalizada y global. A través de las encuestas que hemos realizado al conjunto de las cooperativas oleícolas de Catalunya, hemos podido averiguar sus características distintivas, así como las principales desventajas y problemas a los que se enfrentan. Creemos puede ser de interés analizar las características de estas organizaciones, que tanto desde el punto de vista organizativo como de recursos humanos, como financiero, las hace diferentes de otro tipo de organizaciones pero que sin embargo, han de hacer frente a un mercado cada día más exigente y competitivo.In this article we analyze the features of the catalane olive oil mills cooperatives. The purpose is not only stand out the most important elements, but pointing out as well its main weaknesses. Cooperatives are considered a useful tool to deploy economic development policies and social welfare. In spite of this, there is an open debate about the efficiency of these organizations to operate in a global and liberalized economy. Analyzing the received questionnaires from the cooperatives of Catalonia, we find out their distinctive features and disadvantages and problems they face. We think it will be interesting to find out the differences between cooperatives and other organizations that compete in the same market. These differences are detected in several aspects as the leadership style, financing system o human resource policies.Dans l’article présent nous avons essayé d’analyser les caractéristiques des moulins à huile coopératifs catalans dans le but de pas seulement détacher ses éléments les plus importants de gestion mais aussi ses faiblesses principales. Les coopératives se considèrent comme instruments utiles pour attaquer politiques d’un développement économique et d’un bien-être social. Malgré cela il y a un grand débat ouvert au sujet de l’efficacité de ces organisations, qui posent la question de s’ils sont dans des conditions de rivaliser avec succès en économie de plus en plus ouverte, libéralisée et globale. A travers des enquêtes que nous avons réalisées à l’ensemble des coopératives oleícolas de Catalunya, nous avons pu vérifier ses caractéristiques distinctives, ainsi que les désavantages principaux et les problèmes aunxquels ils s’affrontent. Nous croyons qu’il pert être d’un intérêt d¡analyser les caractéristiques de ces organisations que du point de vue organisant et de recours humains comme financier, il les rend différentes d’autre type d’organisations mais que cependant, ils ont à faire face pa un marché chaque jour plus exigeant et compétitive

Agro-Industrial Waste as Potential Heavy Metal Adsorbents and Subsequent Safe Disposal of Spent Adsorbents

Water pollution is an environmental problem that affects the ecosystem and living beings. Adsorption is one of the best technologies for the removal of heavy metals. Since waste recovery is the basis of the Circular Economy, agro-industrial waste is emerging as low-cost adsorbents for these pollutants from wastewater. Residues of pine sawdust, sunflower seed hulls and corn residues mix were evaluated as adsorbents of synthetic aqueous solutions of Ni(II), Zn(II) and Cd(II). These residues were characterized to determine their structure and composition, and to understand the adsorption mechanism. Adsorption efficiencies and capacities for the adsorbents and adsorbates were determined and compared. From the obtained results, it is possible to affirm that all biomasses used are good alternatives to the synthetic materials, with adsorption efficiencies greater than 50%. The order of adsorption was Cd > Zn > Ni. At the concentration range checked, adsorption efficiencies decreased in sawdust when a mixture of all metals together was considered (as present in real sewage). Finally, the heavy metals were immobilized, with efficiencies over 88.5%, in clay ceramics (as brick's precursors). This procedure would help to minimize the contamination that could be generated by the disposal of spent adsorbents, rarely explored in the literature

Bioactive compounds (phytoestrogens) recovery from Larrea tridentata leaves by solvents extraction

Methanol, ethanol, and acetone at four different concentrations (90%, 70%, 50%, and 30% v/v) were used for extraction of phytoestrogens (nordihydroguaiaretic acid (NDGA), kaempferol, and quercetin) from Larrea tridentata leaves. Besides the phytoestrogens extraction, the antioxidant potential, and the contents of total phenols, flavonoids, and protein in the produced extracts were also determined. The solvent and concentration used for extraction strongly affected the phytoestrogens recovery. The highest NDGA, quercetin, and kaempferol contents (46.96 ± 3.39, 10.46 ± 1.01, and 87.00 ± 6.43 mg/g DW plant, respectively) were recovered using 90% (v/v) methanol. All the produced extracts showed antioxidant capacity, but those obtained using 70% and 90% (v/v) methanol had significantly higher (p < 0.05) FRAP (ferric reducing antioxidant power) values (2.55 ± 0.09 and 2.73 ± 0.11 mM FE(II)/g DW plant, respectively) than the remaining ones. Extract produced by using 90% (v/v) methanol contained also the highest contents of total flavonoids (19.29 ± 0.79 mg QE/g DW plant) and protein (131.84 ± 6.23 mg/g DW plant), and elevated total phenols concentration (263.60 ± 25.78 mg GAE/g DW plant).The authors gratefully acknowledge FCT (Contract/Grant Nos: SFRH/BD/40439/2007 and SFRH/BPD/38212/2007) for financial support of this work

Physicochemical characterization and extraction of bioactive compound from Larrea tridentata leaves

Este resumo faz parte de: Book of abstracts of the Meeting of the Institute for Biotechnology and Bioengineering, 2, Braga, Portugal, 2010. A versão completa do livro de atas está disponível em: http://hdl.handle.net/1822/1096