Effect of structural anisotropy on electrical and magnetic properties of polyaniline conducting films

It is shown that highly conducting films of polyaniline protonated with di-esters of sulfosuccinic and sulfophthalic acids which contain alkyl- or alkoxy-type substituents exhibit highly anisotropic structural, electrical and magnetic properties. The layered-like structure of these films can be described as consisting of polyaniline chains which are mainly oriented parallel to the plane of the film and form regular out-of-plane stacks. These stacks are separated by bilayers of the dopant anions. Accordingly, the main anisotropy observed for solution cast films implies in-plane and out-of-plane measurements. An electrical anisotropy of about 80 is found for the in-plane and out-of-plane electronic conductivities at 5 K. The temperature dependences of the in-plane and out-of-plane conductivities are qualitatively similar and have been fitted as a series combination of variable-range-hopping-type and power law contributions. A maximum is observed in the temperature dependence of the electrical anisotropy at low temperature. The films also show a clear anisotropy of magnetization whose temperature and field characteristics depend on the chemical structure of the dopant anion. © 2013 Elsevier B.V.

Effect of the composition on the thermal behaviour of the SrSn1-xTixO3 precursor prepared by the polymeric precursor method

Strontium stannate titanate Sr(Sn, Ti)O3 is a solid solution between strontium stannate (SrSnO3) and strontium titanate (SrTiO3). In the present study, it was synthesized at low temperature by the polymeric precursor method, derived from the Pechini process. The powders were calcined in oxygen atmosphere in order to eliminate organic matter and to decrease the amount of SrCO3 formed during the synthesis. The powders were annealed at different temperatures to crystallize the samples into perovskites-type structures. All the compositions were studied by thermogravimetry (TG) and differential thermal analysis (DTA), infrared spectroscopy (IR) and X-ray diffraction (XRD). The lattice former, Ti4+ and Sn4+, had a meaningful influence in the mass loss, without changing the profile of the TG curves. On the other hand, DTA curves were strongly modified with the Ti4+:Sn4+ proportion in the system indicating that intermediate compounds may be formed during the synthesis being eliminated at different temperature ranges, while SrCO3 elimination occurs at higher temperature as shown by XRD and IR spectra. © 2013 Akadémiai Kiadó, Budapest, Hungary.

Preparation and photoluminescence characteristics of In(OH) 3:xTb3+ obtained by Microwave-Assisted Hydrothermal method

Crystalline terbium-doped indium hydroxide structures were prepared by a rapid and efficient Microwave-Assisted Hydrothermal (MAH) method. Nanostructures were obtained at a low temperature. FE-SEM images confirm that these samples are composed of 3D nanostructures. XRD, optical diffuse reflectance and photoluminescence (PL) measurements were used to characterize the products. Emission spectra of terbium-doped indium hydroxide (In(OH)3:xTb 3+) samples under excitation (350.7 nm) presented broad band emission referent to the indium hydroxide matrix and 5D4 → 7F6, 5D4 → 7F 5, 5D4 → 7F4, and 5D4 → 7F3 terbium transitions at 495, 550, 590 and 627 nm, respectively. Relative intensities of the Tb 3+ emissions increased as the concentration of this ion increased from 0, 1, 2, 4 and 8 mol%, of Tb3+, but the luminescence is drastically quenched for the In(OH)3 matrix. © 2012 Elsevier B.V. All rights reserved.

The role of hierarchical morphologies in the superior gas sensing performance of CuO-based chemiresistors

The development of gas sensors with innovative designs and advanced functional materials has attracted considerable scientific interest given their potential for addressing important technological challenges. This work presents new insight towards the development of high-performance p-type semiconductor gas sensors. Gas sensor test devices, based on copper (II) oxide (CuO) with innovative and unique designs (urchin-like, fiber-like, and nanorods), are prepared by a microwave-assisted synthesis method. The crystalline composition, surface area, porosity, and morphological characteristics are studied by X-ray powder diffraction, nitrogen adsorption isotherms, field-emission scanning electron microscopy and high-resolution transmission electron microscopy. Gas sensor measurements, performed simultaneously on multiple samples, show that morphology can have a substantial influence on gas sensor performance. An assembly of urchin-like structures is found to be most effective for hydrogen detection in the range of parts-per-million at 200 °C with 300-fold larger response than the previously best reported values for semiconducting CuO hydrogen gas sensors. These results show that morphology plays an important role in the gas sensing performance of CuO and can be effectively applied in the further development of gas sensors based on p-type semiconductors. High-performance gas sensors based on CuO hierarchical morphologies with in situ gas sensor comparison are reported. Urchin-like morphologies with high hydrogen sensitivity and selectivity that show chemical and thermal stability and low temperature operation are analyzed. The role of morphological influences in p-type gas sensor materials is discussed. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Annual reproductive cycle of males of the flat-faced fruit-eating bat, Artibeus planirostris (Chiroptera: Phyllostomidae)

Artibeus planirostris is an endemic species of Phyllostomid bat from the Neotropical region. Some studies have indicated that it exhibits seasonal bimodal polyestry; however, others postulate that it may be able to produce young at any time during the year. Thus, the aim of this study was to evaluate the annual variations in testicular and epididymal parameters of this species in southeast Brazil and try to understand how the reproduction of this species is regulated in this environment. Sixty mature male specimens, collected between June 2009 and May 2010, were submitted to morphometric and immunohistochemical analysis. Our study showed that A. planirostris presented a continuously active pattern of spermatogenesis throughout the year, presenting spermatozoa inside its cauda epididymis in all months, but with two pronounced peaks of spermatogenic production, one in September and other in February. We propose that the males developed these two peaks in order to produce sufficient sperm for the reproduction in a harem system and to synchronize with the female reproductive cycle, which had a bimodal polyestric pattern. Control of this variation is directly linked to the expression of the androgen receptor (AR) in Sertoli cells and to serum testosterone levels, which appear to synchronize to establish these two peaks. In the months preceding the two peaks, the testis have a higher expression of the AR, which possibly stimulates the increase in PCNA, and drives a gradual increase in the testicular parameters. Taken together the results suggest that if sperm storage happens in this species, it is of short duration. © 2013 Elsevier Inc.

O modelo 'hydrotime' pode descrever a resposta de sementes de feijão comum (phaseolus vulgaris l.) à temperatura e potenciais de água reduzidos

Germination parameters of the response to temperature and water potential from four common bean (Phaseolus vulgaris) lines based on thermal-time and hydrotime concepts were estimated to verify to what extent they can predict germination under different thermal and water conditions. The cultivars IPR Uirapuru and IAPAR 81 (drought-tolerant), and Grauna and Carioca (not tolerant) were used. The isothermal assays were performed in a temperature gradient block, and the assays with different osmotic potentials (PEG 6000) were performed in germination chambers. Seeds from drought-tolerant cultivars spent less time to germinate at supra-optimum temperatures than non-tolerant ones, and the cultivar Uirapuru (drought-tolerant) germinated faster in response to reduced Ψ and low temperatures. The parameter Ψb(50) did not discriminate between drought-tolerant and non-tolerant lines at the infraoptimum temperature range, but it can be used to identify drought-tolerant lines at high temperatures. In general, the hydrotime model reproduced the actual germination data relatively well, chiefly at higher temperatures. This study evidenced that the hydrotime model can be used to describe the germination of common bean seeds under reduced water potentials, and as a screening tool for drought-tolerant bean genotypes.

A novel LTCC electrochemical cell construction and characterization: A detection compartment for portable devices

In this work we described for the first time the construction of a 25 μL electrochemical cell from low temperature co-fired ceramic (LTCC) material and carbon screen-printed electrode applicable in portable devices. Firstly, a carbon screen-printed electrode was prepared and characterized by cyclic voltammetry and scanning electron microscopy. Afterwards carbon polymeric film and metal pastes were dropped into the LTCC cell cavities in order to determine the device electrodes, and this arrangement was also electrochemically characterized. The great advantage of this promising device is the simple construction method and its widespread applicability in reusable portable devices. © 2013 The Royal Society of Chemistry.

Evolution of the South Atlantic passive continental margin in southern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

The area between São Paulo and Porto Alegre in southeastern Brazil plays a key area to understand and quantify the evolution of the South Atlantic passive continental margin (SAPCM) in Brazil. In this contribution, we present new thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons from metamorphic, sedimentary and intrusive rocks. The zircon fission-track ages range between 108.4 (15.0) and 539.9 (68.4). Ma, the zircon (U-Th-Sm)/He ages between 72.9 (5.8) and 525.1(2.4). Ma, whereas the apatite fission-track ages range between 40.0 (5.3) and 134.7 (8.0). Ma, and the apatite (U-Th-Sm)/He ages between 32.1 (1.5) and 93.0 (2.5). Ma. The spatial distribution of these ages shows three distinct blocks with a different evolution cut by old fracture zones. While the central block exhibits an old stable block, the Northern and especially the Southern block underwent complex post-rift exhumation. The sample of the Northern block shows two distinct cooling phases in the Upper Cretaceous and the Paleogene to Neogene. After sedimentation of the Permian sandstones the samples of the Central block were never heated up over 100. °C with a following moderate to fast cooling phase in Cretaceous to Eocene time and a fast cooling between Oligocene to Miocene. The five thermal models obtained in the Southern block indicate a complex evolution with three cooling phases. The exhumation events of the three blocks correspond with the Paraná-Etendekka event, the alkaline intrusions due to the Trinidad hotspot, and the evolution of the continental rift basins in SE Brazil and are, therefore, most likely to be the major force for the post-rift evolution of the passive continental margin in SE Brazil, which therefore corresponds to the three main phases of the Andean orogeny. © 2013 Elsevier B.V.

Properties of individual YBCO layers in a two-layered design for energy-efficient digital data cables

We are developing two-layered Yttrium Barium Copper Oxide (YBCO) thin film structures for energy efficient data links for superconducting electronics and present the results of their property measurements. High temperature superconductors (HTS) are advantageous for the implementation of energy-efficient cables interconnecting low temperature superconductor-based circuits and other cryogenic electronics circuits at higher temperature stages. The advantages of the HTS cables come from their low loss and low dispersion properties, allowing ballistic transfer of low power signals with very high bandwidth, low heat conduction and negligible inter-line crosstalk. The microstrip line cable geometry for typical materials is a two-layered film, in which the two superconducting layers are separated by an insulation layer with a minimized permittivity. We have made a proof of concept design of two YBCO films grown by pulsed laser deposition and then assembled into a sandwich with uniform insulating interlayer of tens of micrometers thick. We report on results obtained from such systems assembled in different ways. Structural and electromagnetic properties have been examined on individual films and on the corresponding sandwich composite. © 2013 IEEE.

Ecofisiologia de morfotipos reto e espiralado de Cylindrospermopsis raciborskii (Cyanobacteria) em condições controladas

Pós-graduação em Ciências Biológicas (Biologia Vegetal) - IBRC

Investigação comparativa das propriedades estruturais do diboreto de magnésio dopado com compostos de carbono

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Avaliação de maçã Royal Gala revestida com filme de quitosana durante o período de pós-colheita

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação energética da secagem combinada de milho na região de Pedrinhas Paulista, SP

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Análises técnica e energética da secagem combinada no processamento de casulo do bicho-da-seda de Bombyx Mori L

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Estudos das propriedades ópticas e térmicas dos xerogéis de sílica dopados com Rodamina B

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)