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Navarro-Fuster V.,University of Alicante | Calzado E.M.,University of Alicante | Boj P.G.,University of Alicante | Quintana J.A.,University of Alicante | And 7 more authors.
Applied Physics Letters | Year: 2010

An efficient, low-cost, and highly photostable second-order distributed feedback (DFB) laser, fabricated by thermal nanoimprint lithography and based on a polymer active film containing a perylenediimide derivative, is reported. It shows a photostability half-life of 3.1× 105 pump pulses (>8 h), when pumped at the same spot of the film. This value is the highest reported to date for organic DFB lasers measured under ambient conditions. The device emits at 573 nm, matching the second low-loss transmission window of poly(methylmethacrylate) (460-590 nm), thus offering potential for applications in data communications based on polymer optical fibers. © 2010 American Institute of Physics.

Verdia P.,University of Vigo | Hernaiz M.,Tekniker | Gonzalez E.J.,University of Porto | Macedo E.A.,University of Porto | And 2 more authors.
Journal of Chemical Thermodynamics | Year: 2014

The knowledge of the physical properties of ionic liquids is of high importance in order to evaluate their potential applicability for a given purpose. In the last few years, ionic liquids have been proposed as promising solvents for extractive desulfurization of fuels. Among them, recent studies have shown that ionic liquids derived from pyridinium affords excellent S-compounds removal capacity. In this work, the thermal analysis of five ionic liquids derived from pyridinium cation polysubstituted with different alkyl chains was carried out by Differencial Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA). Furthermore, the density, speed of sound, refractive index and dynamic viscosity for all the pure ionic liquids were also measured from T = (298.15 to 343.15) K. The effect of the number of cation alkyl chains, their length, and their position on the pyridinium ring, on the ionic liquid physical properties is also analyzed and discussed. © 2013 Elsevier Ltd. All rights reserved.

Belforte G.,Polytechnic University of Turin | Conte M.,Tekniker | Mazza L.,Polytechnic University of Turin | Raparelli T.,Polytechnic University of Turin | Visconte C.,Polytechnic University of Turin
WIT Transactions on Engineering Sciences | Year: 2010

The sealing efficiency and the extent of the friction force in an elastomeric seal - scounterpart sliding contact depend highly on the contact characteristics at the interface. In particular, a deep knowledge of the interface contact pressure is needed. The work herein described deals with the design of a new test bench for an indirect contact pressure measurement. In particular, the radial force exerted by a rod seal sliding on a sensor-equipped portion of a cylinder rod is measured; during the seal displacement, the contact area between the seal and the sensorequipped rod increases, so that the radial force trend during time can be acquired. Taking the sliding velocity at a low constant value, contact pressure can be indirectly computed by differentiating the force signal. This way it is possible to perform measurements without introducing a third body between the seal and its counterpart, so avoiding any modification of the contact surface. Initially, the test bench working principle is described, highlighting all critical aspects related to the radial force transmission from the seal to the load sensor; subsequently, the test bench requirements were defined. Finally, the design solution was presented. © 2010 WIT Press.

Axinte D.A.,Rolls-Royce | Allen J.M.,Rolls-Royce | Anderson R.,Rolls-Royce | Dane I.,Rolls-Royce | And 2 more authors.
CIRP Annals - Manufacturing Technology | Year: 2011

The paper reports on the development, calibration and exploitation of a novel configuration of parallel kinematic platform, Free-leg Hexapod (FreeHex), on which the base (fixed) platform has been removed; thus, each leg can be individually positioned on workpiece surfaces of non-flat geometries. To enable the utilisation of FreeHex as a miniature machine tool, calibration methods (to reference the platform against the workpiece), work volume calculations, and collision assessment procedures have been developed. The concept of this novel miniature machine tool was demonstrated by generating standard test pieces as well as freeform surfaces followed by accuracy assessments. © 2011 CIRP.

Gomez-Acedo E.,Tekniker | Olarra A.,Tekniker | Lopez De La Calle L.N.,EHU UPV
International Journal of Advanced Manufacturing Technology | Year: 2012

In this paper, a method specially designed for the assessment of repeatability and accuracy of large machine tools is proposed, along with results for a large gantry-type milling machine, recorded in a medium-term period. For this purpose, temperatures were recorded and a metrological frame was used along with inductive sensors in the tool tip, performing repetitive measurements. As initial results, origin, weight and influence of every heat source on this kind of machines were found. Afterwards, high precision measurements of thermal deformations were obtained. Mechanism of errors was found, discerning between main thermal error in the vertical Z-axis and secondary error in longitudinal X-axis towards out of the plane of the gantry bridge. Finally, a finite element model was developed which showed main thermal behavior identified experimentally. This will permit to make simulations of the thermal response of the machine and to choose machining strategies for future parts. Proposed methodology was therefore proved satisfactory for thermal characterization of this kind of big machine tools. This knowledge will make possible to improve thermal design of machines and to develop error compensation procedures. This method can also be applied on workshop conditions for recalibration purposes. © Springer-Verlag London Limited 2012.

Martinez-Perdiguero J.,Tekniker | Etxebarria J.,University of the Basque Country | Folcia C.L.,University of the Basque Country | Ortega J.,University of the Basque Country | And 2 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

Three bent-core liquid-crystal compounds presenting the unusual columnar B1 to tilted polar smectic (Sm-CP or B2) phase transition are studied through small-angle x-ray diffraction on aligned samples. The well-established character of the smectic phase helps to characterize the structural changes during the transition. A mechanism for this transition is proposed, which accounts for the low enthalpy usually observed in this process. The B1 phase is found to possess a great degree of lamellarization, with pseudosmectic ferroelectric layers along the crystallographic (11) planes. As a consequence of these observations a distribution of the block polarizations in the columnar structure is proposed. © 2010 The American Physical Society.

De Las Cuevas F.,University of Navarra | Reis M.,University of Lisbon | Ferraiuolo A.,CSM | Pratolongo G.,DUFERCO La Louviere | And 3 more authors.
Advanced Materials Research | Year: 2010

Hot rolled, laboratory-cast, TWIP steel samples (5.4 mm thick) of 22% Mn - 0.6% C (in mass-%) were cold rolled to different reductions (from 40 % to 70 %) and subsequently isothermally annealed for various times at temperatures ranging from 450° C to 1100° C. The evolution of recrystallization and grain growth was followed by control of the softening kinetics complemented by metallographic, OIM and microtexture observations. A map of the recovery, recrystallization and grain growth in the temperature-time space was obtained. In all instances, the grain size at the end of recrystallization was very fine, D ≤ 2 μm and larger grain sizes were the result of grain growth. A range of grain sizes 2 μm ≤ D ≤ 50 μm was covered by the grain growth experiments. A phenomenological grain growth equation that is useful for the annealing control of this steel was derived from the measurements. © (2010) Trans Tech Publications.

Tosello G.,Technical University of Denmark | Hansen H.N.,Technical University of Denmark | Gasparin S.,Technical University of Denmark | Albajez J.A.,University of Zaragoza | Esmoris J.I.,TEKNIKER
CIRP Annals - Manufacturing Technology | Year: 2012

Limited tool life of nickel mould inserts represents an issue for the mass-production of polymer optics with complex micro three-dimensional geometries by injection moulding. TiN coating was applied to a nickel insert for the injection moulding of polycarbonate micro Fresnel lenses. Surface wear was monitored at different intervals during production on different tool locations. 3D micro optical dimensional microscopy, surface replica technique and SEM-EDS were employed to characterize wear of the micro features. Results showed wear decreasing at higher distance from the gate. After 24,500 moulding cycles the measured height reduction of 23 μm high ribs was on the order of 400-1000 nm. © 2012 CIRP.

Arnaiz A.,TEKNIKER | Ferreiro S.,TEKNIKER | Buderath M.,Airbus
Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability | Year: 2010

This paper details a new decision support that adds a proactive function to the actual line aircraft maintenance turn-around-time (TAT) process, where next-flight decisions are assisted by the health assessment function of the integrated vehicle health management (IVHM) of an aircraft. The 'operational risk assessment' concept appears an extended function supported on the IVHM information for calculating and evaluating the operational risk for aircraft and fleet operations. It creates or reshapes maintenance plans based on predictions of the future maintenance relevant events (e.g. component-degradation-driven repair or replacement events) and its impact on the operational planning of the aircraft/fleet. 'Operational risk assessment' makes it possible to turn the scheduled line maintenance into a proactively defined maintenance. The paper also illustrates the first step involved in this approach: 'condition view' function, which is responsible for the provision of the remaining useful life (RUL) prediction of a health managed component. This function provides the basis for the operational risk estimation on the aircraft in order to identify maintenance actions that can be deferred.

Sedano A.,MTOI | Sancibrian R.,University of Cantabria | De Juan A.,University of Cantabria | Viadero F.,University of Cantabria | Egaa F.,Tekniker
Mathematical Problems in Engineering | Year: 2012

A hybrid optimization approach for the design of linkages is presented. The method is applied to the dimensional synthesis of mechanism and combines the merits of both stochastic and deterministic optimization. The stochastic optimization approach is based on a real-valued evolutionary algorithm (EA) and is used for extensive exploration of the design variable space when searching for the best linkage. The deterministic approach uses a local optimization technique to improve the efficiency by reducing the high CPU time that EA techniques require in this kind of applications. To that end, the deterministic approach is implemented in the evolutionary algorithm in two stages. The first stage is the fitness evaluation where the deterministic approach is used to obtain an effective new error estimator. In the second stage the deterministic approach refines the solution provided by the evolutionary part of the algorithm. The new error estimator enables the evaluation of the different individuals in each generation, avoiding the removal of well-adapted linkages that other methods would not detect. The efficiency, robustness, and accuracy of the proposed method are tested for the design of a mechanism in two examples. Copyright © 2012 A. Sedano et al.

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