Export 657 results:
Sort by: Author Title Type [ Year  (Desc)]
2015
Barreto, J., D. Martins, Borges P. de Sousa, S. Kar, G. Bonfait, and I. Catarino Gas gap heat switch for a Cryogen-free magnet system., 2015.
Koerber, H., J. Xavier, P. P. Camanho, Y. E. Essa, and Martín F. de la Escalera. "High strain rate behaviour of 5-harness-satin weave fabric carbon-epoxy composite under compression and combined compression-shear loading." International Journal of Solids and Structures. 54 (2015): 172-182. AbstractWebsite

Abstract The strain rate dependent mechanical behaviour was studied for the common out-of-autoclave aerospace textile composite 5-harness-satin carbon�epoxy. End-loaded 15 � , 30 � and 45 � off-axis and 90 � compression tests were carried out at three different strain rate levels ( 4 � 10 - 4 s - 1 , 200 s - 1 and 1000 s - 1 ) to determine the effect of strain rate for transverse compression and combined transverse compression/in-plane shear loading. The dynamic tests were carried out on a split-Hopkinson pressure bar, where high speed photography and digital image correlation allowed a detailed study of the specimen deformation and failure process. Quasi-static reference tests were carried out on an electro-mechanical test machine using the same specimen type and a static \{DIC\} system. Pronounced strain rate effects on the axial stress�strain response were observed for all specimen types. Failure envelopes for the combined s 22 c - t 12 stress state were derived from the experimental data and compared with the maximum stress criterion, which appears well suited to approximate the experimental failure envelope at all strain rate levels. It was observed that the failure envelope was simply scaled up with increasing strain rate, while the overall shape was found to be strain rate independent.

Karlovich, Alexei Yu. "Maximally modulated singular integral operators and their applications to pseudodifferential operators on Banach function spaces." Function Spaces in Analysis. Contemporary Mathematics, 645. Ed. Krzysztof Jarosz. Providence, Rhode Island: American Mathematical Society, 2015. 165-178. Abstract

We prove that if the Hardy-Littlewood maximal operator is bounded on a separable Banach function space \(X(\mathbb{R}^n)\) and on its associate space \(X'(\mathbb{R}^n)\) and a maximally modulated Calderón-Zygmund singular integral operator \(T^{\Phi}\) is of weak type \((r,r)\) for all \(r\in(1,\infty)\), then \(T^{\Phi}\) extends to a bounded operator on \(X(\mathbb{R}^n)\). This theorem implies the boundedness of the maximally modulated Hilbert transform on variable Lebesgue spaces \(L^{p(\cdot)}(\mathbb{R})\) under natural assumptions on the variable exponent \(p:\mathbb{R}\to(1,\infty)\). Applications of the above result to the boundedness and compactness of pseudodifferential operators with \(L^\infty(\mathbb{R},V(\mathbb{R}))\)-symbols on variable Lebesgue spaces \(L^{p(\cdot)}(\mathbb{R})\) are considered. Here the Banach algebra \(L^\infty(\mathbb{R},V(\mathbb{R}))\) consists of all bounded measurable \(V(\mathbb{R})\)-valued functions on \(\mathbb{R}\) where \(V(\mathbb{R})\) is the Banach algebra of all functions of bounded total variation.

Kchaou, Omaya Bellaaj, Amin Sallem, Pedro Pereira, Mourad Fakhfakh, and Maria Helena Fino Multi-objective sensitivity-based optimization of analog circuits exploiting NSGA-II front ranking. Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design (SMACD). Istambul, Turkey: IEEE, 2015.
Passos, Fabio, Mouna Kotti, R. Gonzalez-Echevarria, M. H. Fino, E. Roca, R. Castro-Lopez, and F. V. Fernandez Physical vs. Surrogate Models of Passive RF Devices. 2015 IEEE International Symposium on Circuits and Systems. Lisbon: IEEE, 2015.
Karlovich, Alexei Yu. "The Stechkin inequality for Fourier multipliers on variable Lebesgue spaces." Mathematical Inequalities and Applications. 18.4 (2015): 1473-1481. Abstract

We prove the Stechkin inequality for Fourier multipliers on variable Lebesgue spaces under some natural assumptions on variable exponents.

Clemmensen, Lars B., Jesper Milàn, Jan Schulz Adolfssen, Eliza Jarl Estrup, Nicolai Frobøse, Nicole Klein, Octávio Mateus, and Oliver Wings. "The vertebrate-bearing Late Triassic Fleming Fjord Formation of central East Greenland revisited: stratigraphy, palaeoclimate and new palaeontological data." Geological Society, London, Special Publications. 434.1 (2015): 31-47. Abstractclemmensenetal2015greenland.pdfWebsite

In Late Triassic (Norian–Rhaetian) times, the Jameson Land Basin lay at 40° N on the northern part of the supercontinent Pangaea. This position placed the basin in a transition zone between the relatively dry interior of the supercontinent and its more humid periphery. Sedimentation in the Jameson Land Basin took place in a lake–mudflat system and was controlled by orbitally forced variations in precipitation. Vertebrate fossils have consistently been found in these lake deposits (Fleming Fjord Formation), and include fishes, dinosaurs, amphibians, turtles, aetosaurs and pterosaurs. Furthermore, the fauna includes mammaliaform teeth and skeletal material. New vertebrate fossils were found during a joint vertebrate palaeontological and sedimentological expedition to Jameson Land in 2012. These new finds include phytosaurs, a second stem testudinatan specimen and new material of sauropodomorph dinosaurs, including osteologically immature individuals. Phytosaurs are a group of predators common in the Late Triassic, but previously unreported from Greenland. The finding includes well-preserved partial skeletons that show the occurrence of four individuals of three size classes. The new finds support a late Norian–early Rhaetian age for the Fleming Fjord Formation, and add new information on the palaeogeographical and palaeolatitudinal distribution of Late Triassic faunal provinces.

Kauf, Thomas, Vitor Rosa, Christophe Fliedel, Roberto Pattacini, Naina Deibel, Teresa Aviles, Biprajit Sarkar, and Pierre Braunstein. "{Reactivity of TCNE and TCNQ derivatives of quinonoid zwitterions with Cu(I)}." {DALTON TRANSACTIONS}. {44} (2015): {5441-5450}. Abstract

{The reactions of TCNE- and TCNQ-functionalized (TCNE: tetracyanoethylene and TCNQ: 7,7', 8,8'-tetra-cyanoquinodimethane) zwitterionic benzoquinonemonoimines with a Cu(I)-BIAN complex (BIAN = bis-(o, o'-bisisopropylphenyl)acenaphthenequinonediimine) have been investigated and found to follow a diversity of interesting patterns. The complexes {[}Cu(BIAN)(NCMe)(L2)]BF4 (2) and {[}Cu(BIAN)(L2)(2)]BF4 (4) were obtained by reacting {[}Cu(BIAN)(NCMe) 2] BF4 (1) with one and two equivalents of L2, respectively. Following similar procedures, the complexes {[}Cu(BIAN)(NCMe)(L3)] BF4 (6) and {[}Cu(BIAN)(L3)(2)]BF4 (7) were obtained by reaction of 1 with L3. The reaction of 2 with 0.5 equiv. of 4,4'-bipyridine afforded {[}\{Cu(BIAN)-(L2)\}(2)(mu-4,4'-bipyridine)](BF4)(2) (3). The complexes were characterized by multinuclear NMR, IR and UV-Vis spectroscopic techniques, mass spectrometry, cyclic voltammetry and elemental analysis. The molecular structures of complexes 3 center dot 4CH(2)Cl(2) and 4 center dot CH2Cl2 were determined by single crystal X-ray diffraction. An unexpected coordination polymer {[}Cu(L2(-))(2)](infinity) (5) was also structurally characterized, which contains Cu(II) centres chelated by two N, O-bound ligands resulting from the monodeprotonation of L2.}

Klein, Hendrik, Jesper Milàn, Lars B. Clemmensen, Nicolaj Frobøse, Octávio Mateus, Nicole Klein, Jan S. Adolfssen, Eliza J. Estrup, and Oliver Wings. "Archosaur footprints (cf. Brachychirotherium) with unusual morphology from the Upper Triassic Fleming Fjord Formation (Norian–Rhaetian) of East Greenland." Geological Society, London, Special Publications. 434 (2015). AbstractWebsite

The Ørsted Dal Member of the Upper Triassic Fleming Fjord Formation in East Greenland is well known for its rich vertebrate fauna, represented by numerous specimens of both body and ichnofossils. In particular, the footprints of theropod dinosaurs have been described. Recently, an international expedition discovered several slabs with 100 small chirotheriid pes and manus imprints (pes length 4–4.5 cm) in siliciclastic deposits of this unit. They show strong similarities with Brachychirotherium, a characteristic Upper Triassic ichnogenus with a global distribution. A peculiar feature in the Fleming Fjord specimens is the lack of a fifth digit, even in more deeply impressed imprints. Therefore, the specimens are assigned here tentatively to cf. Brachychirotherium. Possibly, this characteristic is related to the extremely small size and early ontogenetic stage of the trackmaker. The record from Greenland is the first evidence of this morphotype from the Fleming Fjord Formation. Candidate trackmakers are crocodylian stem group archosaurs; however, a distinct correlation with known osteological taxa from this unit is not currently possible. While the occurrence of sauropodomorph plateosaurs in the bone record links the Greenland assemblage more closer to that from the Germanic Basin of central Europe, here the described footprints suggest a Pangaea-wide exchange.Supplementary material: Three-dimensional model of cf. Brachychirotherium pes–manus set (from MGUH 31233b) from the Upper Triassic Fleming Fjord Formation (Norian–Rhaetian) of East Greenland as pdf, ply and jpg files (3D model created by Oliver Wings; photographs taken by Jesper Milàn) is available at https://doi.org/10.6084/m9.figshare.c.2133546

Araújo, João, Wolfram Bentz, and Janusz Konieczny. "The commuting graph of the symmetric inverse semigroup." Israel J. Math.. 207 (2015): 103-149. AbstractWebsite
n/a
Hansen, Bitten Bolvig, Jesper Milàn, Lars B. Clemmensen, Jan Schulz Adolfssen, Eliza Jarl Estrup, Nicole Klein, Octávio Mateus, and Oliver Wings. "Coprolites from the Late Triassic Kap Stewart Formation, Jameson Land, East Greenland: morphology, classification and prey inclusions." Geological Society, London, Special Publications. 434 (2015). AbstractWebsite

A large collection of vertebrate coprolites from black lacustrine shales in the Late Triassic (Rhaetian–Sinemurian) Kap Stewart Formation, East Greenland is examined with regard to internal and external morphology, prey inclusions, and possible relationships to the contemporary vertebrate fauna. A number of the coprolites were mineralogically examined by X-ray diffraction (XRD), showing the primary mineral composition to be apatite, clay minerals, carbonates and, occasionally, quartz in the form of secondary mineral grains. The coprolite assemblage shows multiple sizes and morphotypes of coprolites, and different types of prey inclusions, demonstrating that the coprolite assemblage originates from a variety of different producers.Supplementary material: A description of the size, shape, structure, texture, contents and preservation of the 328 specimens is available at https://doi.org/10.6084/m9.figshare.c.2134335

Koerber, H., J. Xavier, P. P. Camanho, Y. E. Essa, and Martín F. de la Escalera. "High strain rate behaviour of 5-harness-satin weave fabric carbon–epoxy composite under compression and combined compression–shear loading." International Journal of Solids and Structures. 54 (2015): 172-182. AbstractWebsite

Abstract The strain rate dependent mechanical behaviour was studied for the common out-of-autoclave aerospace textile composite 5-harness-satin carbon–epoxy. End-loaded 15 ° , 30 ° and 45 ° off-axis and 90 ° compression tests were carried out at three different strain rate levels ( 4 × 10 - 4 s - 1 , 200 s - 1 and 1000 s - 1 ) to determine the effect of strain rate for transverse compression and combined transverse compression/in-plane shear loading. The dynamic tests were carried out on a split-Hopkinson pressure bar, where high speed photography and digital image correlation allowed a detailed study of the specimen deformation and failure process. Quasi-static reference tests were carried out on an electro-mechanical test machine using the same specimen type and a static \{DIC\} system. Pronounced strain rate effects on the axial stress–strain response were observed for all specimen types. Failure envelopes for the combined σ 22 c - τ 12 stress state were derived from the experimental data and compared with the maximum stress criterion, which appears well suited to approximate the experimental failure envelope at all strain rate levels. It was observed that the failure envelope was simply scaled up with increasing strain rate, while the overall shape was found to be strain rate independent.

Kowacz, M., M. Marchel, L. Juknaite, Jmss Esperanca, MJ Romao, AL Carvalho, and L. P. N. Rebelo. "Ionic-Liquid-Functionalized Mineral Particles for Protein Crystallization." Crystal Growth & Design. 15 (2015): 2994-3003. AbstractWebsite

Nucleation is a critical step determining the outcome of the entire crystallization process. Finding an effective nucleant for protein crystallization is of utmost importance for structural biology. The latter relies on good-quality crystals to solve the three-dimensional structures of macromolecules. In this study we show that crystalline barium sulfate (BaSO4) with an etched and/or ionic liquid (IL)-functionalized surface (1) can induce protein nucleation at concentrations well below the concentration needed to promote crystal growth under control conditions, (2) can shorten the nucleation time, (3) can increase the growth rate, and finally (4) may help to improve the protein crystal morphology. These effects were shown for lysozyme, RNase A, trypsin, proteinase K, myoglobin, and hemoglobin. Therefore, the use of BaSO4 particles enables us to reduce the amount of protein in crystallization trials and increases the chance of obtaining protein crystals of the desired quality. In the context of the underlying mechanism, it is shown that the protein-solid contact formation is governed by the interaction of the polar compartments of the biomacromolecule with the support. The tendency of a protein to concentrate near the solid surface is enhanced by both the hydrophobicity of the protein and that of the surface (tuned by the functionalizing IL). These mechanisms of interaction of biomacromolecules with inorganic hydrophilic solids correspond to the principles of amphiphilic IL-mineral interactions.

c Kiazadeh, A.a b, Salgueiro Branquinho Pinto Gomes Barquinha Martins Fortunato D. a R. a. "Operational stability of solution based zinc tin oxide/SiO2 thin film transistors under gate bias stress." APL Materials. 3 (2015). AbstractWebsite

In this study, we report solution-processed amorphous zinc tin oxide transistors exhibiting high operational stability under positive gate bias stress, translated by a recoverable threshold voltage shift of about 20% of total applied stress voltage. Under vacuum condition, the threshold voltage shift saturates showing that the gate-bias stress is limited by trap exhaustion or balance between trap filling and emptying mechanism. In ambient atmosphere, the threshold voltage shift no longer saturates, stability is degraded and the recovering process is impeded. We suggest that the trapping time during the stress and detrapping time in recovering are affected by oxygen adsorption/desorption processes. The time constants extracted from stretched exponential fitting curves are ∼106 s and 105 s in vacuum and air, respectively. © 2015 Author(s).

Xing, L., M. G. Lockley, D. Marty, J. Zhang, Y. Wang, H. Klein, R. T. McCrea, L. G. Buckley, M. Belvedere, O. Mateus, G. D. Gierli?ski, L. Piñuela, W. S. Persons, F. Wang, H. Ran, H. Dai, and X. Xie. "An ornithopod-dominated tracksite from the lower Cretaceous Jiaguan Formation (Barremian-Albian) of Qijiang, South-Central China: New discoveries, ichnotaxonomy, preservation and palaeoecology." PLoS ONE. 10 (2015). Abstract
n/a
Mottershead, J. E., M. Broggi, H. M. Gomes, Y. Govers, H. H. Khodaparast, M. Link, E. Patelli, and T. A. N. Silva Perspectives on model updating. ICEDyn2015 - International Conference on Structural Engineering Dynamics. Lagos, Portugal, 2015. Abstract
n/a
Mottershead, John E., Michael Link, Tiago A. N. Silva, Yves Govers, and Hamed Haddad Khodaparast The Sensitivity Method in Stochastic Model Updating. Eds. Jyoti K. Sinha. Vol. 23. Vibration Engineering and Technology of Machinery: Proceedings of VETOMAC X 2014, 23. University of Manchester, UK: Springer International Publishing, 2015. Abstract
n/a
Clemmensen, Lars B., Jesper Milàn, Jan Schulz Adolfssen, Eliza Jarl Estrup, Nicolai Frobøse, Nicole Klein, Octávio Mateus, and Oliver Wings. "The vertebrate-bearing Late Triassic Fleming Fjord Formation of central East Greenland revisited: stratigraphy, palaeoclimate and new palaeontological data." Geological Society, London, Special Publications. 434 (2015). AbstractWebsite

In Late Triassic (Norian–Rhaetian) times, the Jameson Land Basin lay at 40° N on the northern part of the supercontinent Pangaea. This position placed the basin in a transition zone between the relatively dry interior of the supercontinent and its more humid periphery. Sedimentation in the Jameson Land Basin took place in a lake–mudflat system and was controlled by orbitally forced variations in precipitation. Vertebrate fossils have consistently been found in these lake deposits (Fleming Fjord Formation), and include fishes, dinosaurs, amphibians, turtles, aetosaurs and pterosaurs. Furthermore, the fauna includes mammaliaform teeth and skeletal material. New vertebrate fossils were found during a joint vertebrate palaeontological and sedimentological expedition to Jameson Land in 2012. These new finds include phytosaurs, a second stem testudinatan specimen and new material of sauropodomorph dinosaurs, including osteologically immature individuals. Phytosaurs are a group of predators common in the Late Triassic, but previously unreported from Greenland. The finding includes well-preserved partial skeletons that show the occurrence of four individuals of three size classes. The new finds support a late Norian–early Rhaetian age for the Fleming Fjord Formation, and add new information on the palaeogeographical and palaeolatitudinal distribution of Late Triassic faunal provinces.

Kololuoma, Terho, Jaakko Leppäniemi, Himadri Majumdar, Rita Branquinho, Elena Herbei-Valcu, Viorica Musat, Rodrigo Martins, Elvira Fortunato, and Ari Alastalo. "{Gravure printed sol–gel derived AlOOH hybrid nanocomposite thin films for printed electronics}." J. Mater. Chem. C. 3 (2015): 1776-1786. AbstractWebsite

We report a sol-gel approach to fabricate aluminum-oxy-hydroxide (AlOOH) -based inks for gravure printing of high-dielectric-constant nanocomposite films. By reacting 3-glycidoxypropyl- trimethoxysilane (GPTS) with aluminum-oxide-hydroxide (AlOOH) nanoparticles under constant bead milling, inks suitable for gravure printing were obtained. The calculated relative dielectric constant based on measured capacitances and film thicknesses for the gravure-printed GPTS:AlOOH nanocomposite varied between 7 and 11 at a 10 kHz frequency. The dielectric constant depended on the mixing ratio of the composite and was found to follow the Maxwell-Garnett ternary-system mixing rule indicating presence of micro/nanopores that affect the electrical properties of the fabricated films. Increasing leakage current with increasing AlOOH content was observed. High leakage current was reduced by printing two-layer films. The double-layered gravure-coated films exhibited similar capacitance density but clearly lower leakage current and less electrical breakdowns in comparison to single-layered films having comparable film compositions and film thicknesses. The best composite yielded a capacitance density of 109 ± 2 pF/mm2 at the 10 kHz frequency and a leakage current density of 60 ± 20 µA/cm2 at 0.5 MV/cm electric field as a single layer. The calculated relative dielectric constant at the 10 kHz frequency for this composition was 11.2 ± 0.5. Introduction

Kiazadeh, Asal, Daniela Salgueiro, Rita Branquinho, Joana Pinto, Henrique L. Gomes, Pedro Barquinha, Rodrigo Martins, and Elvira Fortunato. "{Operational stability of solution based zinc tin oxide/SiO2 thin film transistors under gate bias stress}." APL Materials. 3 (2015): 062804. AbstractWebsite

In this study, we report solution-processed amorphous zinc tin oxide transistors exhibiting high operational stability under positive gate bias stress, translated by a recoverable threshold voltage shift of about 20{%} of total applied stress voltage. Under vacuum condition, the threshold voltage shift saturates showing that the gate-bias stress is limited by trap exhaustion or balance between trap filling and emptying mechanism. In ambient atmosphere, the threshold voltage shift no longer saturates, stability is degraded and the recovering process is impeded. We suggest that the trapping time during the stress and detrapping time in recovering are affected by oxygen adsorption/desorption processes. The time constants extracted from stretched exponential fitting curves are ≈106 s and 105 s in vacuum and air, respectively.

Schuster, Christian S., Seweryn Morawiec, Manuel J. Mendes, Maddalena Patrini, Emiliano R. Martins, Liam Lewis, Isodiana Crupi, and Thomas F. Krauss. "{Plasmonic and diffractive nanostructures for light trapping - an experimental comparison}." Optica. 2 (2015): 194-200. AbstractWebsite

Metal nanoparticles and diffractive nanostructures are widely studied for enhancing light trapping efficiency in thin-film solar cells. Both have achieved high performance enhancements, but there are very few direct comparisons between the two. Also, it is difficult to accurately determine the parasitic absorption of metal nanoparticles. Here, we assess the light trapping efficiencies of both approaches in an identical absorber configuration. We use a 240 nm thick amorphous silicon slab as the absorber layer and either a quasi-random supercell diffractive nanostructure or a layer of self-assembled metal nanoparticles for light trapping. Both the plasmonic and diffractive structures strongly enhance the absorption in the red/near-infrared regime. At longer wavelengths, however, parasitic absorption becomes evident in the metal nanoparticles, which reduces the overall performance of the plasmonic approach. We have formulated a simple analytical model to assess the parasitic absorption and effective reflectivity of a plasmonic reflector and to demonstrate good agreement with the experimental data.

Branquinho, Rita, Daniela Salgueiro, Ana Santa, Asal Kiazadeh, Pedro Barquinha, LuÍs Pereira, Rodrigo Martins, and Elvira Fortunato. "{Towards environmental friendly solution- based ZTO / AlO x TFTs}." Semicond. Sci. Technol.. 30 (2015): 024007. AbstractWebsite

Solution based deposition has been recently considered as a viable option for low-cost flexible electronics. In this context research efforts have been increasingly centred on the development of suitable solution-processed materials for oxide based transistors. Nevertheless, the majority of synthetic routes reported require the use of toxic organic solvents. In this work we report on a new environmental friendly solution combustion synthesis route, using ethanol as solvent, for the preparation of indium/gallium free amorphous zinc-tin oxide (ZTO) thin film transistors (TFTs) including AlOx gate dielectric. The decomposition of ZTO and AlOx precursor solutions, electrical characterization and stability of solution processed ZTO/AlOx TFTs under gate-bias stress, in both air and vacuum atmosphere, were investigated. The devices demonstrated low hysteresis ($Δ$V = 0.23 V), close to zero turn on voltage, low threshold voltage (VT = 0.36 V) and a saturation mobility of 0.8 cm2 V−1 s−1 at low operation voltages. Ethanol based ZTO/AlOx TFTs are a promising alternative for applications in disposable, low cost and environmental friendly electronics.

2014
Valtchev, Stanimir, Joana Almeida, Jorge P. Teixeira, and Ben J. Klaassens. "Conversion of wind-induced vibrations into electricity." 2014 {IEEE} 36th International Telecommunications Energy Conference ({INTELEC}). Institute of Electrical {&} Electronics Engineers ({IEEE}), 2014. Abstract
n/a
Valtchev, Stanimir, Rui Neves-Medeiros, Anastassia Krusteva, George Gigov, and Plamen Avramov. "A wireless energy transceiver based on induction heating equipment." 2014 16th International Power Electronics and Motion Control Conference and Exposition. Institute of Electrical {&} Electronics Engineers ({IEEE}), 2014. Abstract
n/a
Katriel, Jacob, J. P. Marques, P. Indelicato, A. M. Costa, M. C. Martins, J. P. Santos, and F. Parente. "Approach towards the critical charge of some excited states of the Be isoelectronic series." Physical Review A. 90 (2014): 052519-5. AbstractWebsite
n/a