Osteoblastoma del sacro. A propósito de dos casos clínicos.

El osteoblastoma es un tumor óseo primitivo de frecuente localización en los elementos posteriores de la columna vertebral, aunque raro en el sacro. Se presentan dos osteoblastomas del sacro, con un seguimiento medio de ocho años, tratados mediante resección intralesional que, sin morbilidad, deparó un excelente resultado. El curetaje sería un procedimiento de resección válido en osteoblastomas sacros no agresivos, si bien obliga a un seguimiento prolongado del paciente para vigilar la posibilidad de recidivas locales.Osteoblastoma is a primary neoplasm of bone fre- quently located in the posterior elements of the spine, alt- hough rarely affecting the sacrum. Two cases in this location are reported, with a mean follow-up of eight years, treated with an intralesional resection that, without any morbidity, has provided an excellent result. Curettage should be a valid re- section procedure for nonagressive osteoblastomas of the sacrum, although it makes necessary a long follow-up in or- der to watch over the possibility of a local recurrence

Wide range group delay tuning in lossy fiber ring resonators

22nd International Conference on Optical Fiber Sensors, OFS 2012, Beijing, China, 15-19 Oct. 2012We demonstrate theoretically and experimentally that a wide-range tuning of group delay values can be achieved in a\ud lossy fiber ring resonator. The tuning mechanism relies simply on varying the loss/coupling ratio in the resonator. This\ud simple structure may be used advantageously in different regimes for many sensing configurations, both for achieving\ud extremely high sensitivity enhancements (by working close to critical coupling, where the group index becomes\ud extremely large) or suppression of undesired refractive index effects (e.g. Kerr effect), by working in the under-coupled\ud regime

Modelado de estudiante en resolución de problemas a través de la dinámica de sistemas

Nuestra intención es utilizar un sistema tutorial inteligente (Arnau, Arevalillo-Herráez, González-Calero, 2014) para realizar la recogida de datos ligados a la destreza inicial del estudiante como resolutor de problemas aritméticos y poder construir un modelo de estudiante siguiendo la Teoría General de Sistemas. Esta teoría propone el uso de metodologías de carácter transdisciplinar que permitan construir modelos matemáticos con los que resolver problemas en el ámbito de los sistemas dinámicos complejos

Turning a low Q fiber resonator into a high-sensitivity displacement sensor using slow light concepts

High-Q resonators have been widely used for sensing purposes. High Q factors normally lead to sharp spectral peaks which accordingly provide a strong sensitivity in spectral interrogation methods. In this work we employ a low-Q ring resonator to develop a high sensitivity sub-micrometric resolution displacement sensor. We use the slow-light effects occurring close to the critical coupling regime to achieve high sensitivity in the device. By tuning the losses in the cavity close to the critical coupling, extremely high group delay variations can be achieved, which in turn introduce strong enhancements of the absorption of the structure. We first validate the concept using an Optical Vector Analyzer (OVA) and then we propose a simple functional scheme for achieving a low-cost interrogation of this kind of sensors.European CommissionMinisterio de Ciencia e InnovaciónComunidad de Madri

Fiber sensors for the high-speed railway environment

Specialty Optical Fibers 2014, Barcelona, Spain, 27–31 July 2014We review some recent work on fiber-optic sensors for the high-speed railway environment. In particular, we show convenient fiber-optic solutions for rail and wheel monitoring, perimeter security and catenary protection in changeover section

Special-purpose elements to impose Periodic Boundary Conditions for multiscale computational homogenization of composite materials with the explicit Finite Element Method

A novel methodology is presented to introduce Periodic Boundary Conditions (PBC) on periodic Representative Volume Elements (RVE) in Finite Element (FE) solvers based on dynamic explicit time integration. This implementation aims at overcoming the difficulties of the explicit FE method in dealing with standard PBC. The proposed approach is based on the implementation of a user-defined element, named a Periodic Boundary Condition Element (PBCE), that enforces the periodicity between periodic nodes through a spring-mass-dashpot system. The methodology is demonstrated in the multiscale simulation of composite materials. Two showcases are presented: one at the scale of computational micromechanics, and another one at the level of computational mesomechanics. The first case demonstrates that the proposed PBCE allows the homogenization of composite ply properties through the explicit FE method with increased efficiency and similar reliability with respect to the equivalent implicit simulations with traditional PBC. The second case demonstrates that the PBCE coupled with Periodic Laminate Elements (PLE) can effectively be applied to the computational homogenization of elastic and strength properties of entire laminates taking into account highly nonlinear effects. Both cases motivate the application of the methodology in multiscale virtual testing in support of the building-block certification of composite materials.The research leading to this publication was supported by the European Community FP7 Programme through project MAAXIMUS (grant agreement 213371) and by the Spanish Ministry of Industry, Economy and Competitiveness (MINECO) through project HYDTCOMP (grant MAT2015-69491-C03-02). C.S. Lopes also acknowledges the support of MINECO through the Ramón y Cajal fellowship (grant RYC-2013-14271). The authors are grateful to Prof. Ignacio Romero for his helpful insights on this research

Multiscale modelling of thermoplastic woven fabric composites: From micromechanics to mesomechanics

The mechanical properties of woven composites can be predicted by using a multiscale modelling approach. The starting point to its application is the microscale (the level of fibres, matrix and interfaces), that allows the computation of the homogenised behaviour of the yarn. The aim of this work was to predict the yarn-level behaviour of a thermoplastic-based woven composite in order to allow the formulation of a representative constitutive model that can be used to predict ply properties at the mesoscale. To accomplish this purpose, an in situ characterisation of the microconstituents was carried out. This served to generate inputs for three different representative volume element (RVE) models that allowed predicting the yarn longitudinal, transverse and shear responses. These mechanical characteristics allowed the determination of homogenised yarn constitutive behaviour which was found to be characterised by significant non-linearity until failure, specially in transverse and shear directions.The research leading to the developments described received funding of the project ADVANSEAT; a collaborative R&D project led by Grupo Antolín, and partially supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO). C.S. Lopes also acknowledges the support of MINECO through the Ramón y Cajal fellowship (RYC-2013-14271)

Phase-sensitive optical time domain reflectometer assisted by first-order raman amplification for distributed vibration sensing over >100 km

In this study, the authors present an experimental and theoretical description of the use of first order Raman amplification to improve the performance of a Phase-sensitive optical time domain reflectometer (φ OTDR) when used for vibration measurements over very long distances. A special emphasis is given to the noise which is carefully characterized and minimized along the setup. A semiconductor optical amplifier and an optical switch are used to greatly decrease the intra-band coherent noise of the setup and balanced detection is used to minimize the effects of RIN transferred from the Raman pumps. The sensor was able to detect vibrations of up to 250 Hz (close to the limits set by the time of flight of light pulses) with a resolution of 10 m in a range of 125 km. To achieve the above performance, no post-processing was required in the φOTDR signal. The evolution of the φOTDR signal along the fiber is also shown to have a good agreement with the theoretical model.European CommissionMinisterio de Economía y CompetitividadComunidad de Madri

Computational micromechanics of fiber kinking in unidirectional FRP under different environmental conditions

The determination of ply properties of Fiber Reinforced Polymers (FRP) for particular operational environmental conditions in aeronautical applications is mandatory in order to fulfill current industry stringent certification requirements. However, the traditional experimental approach requires massive investments of resources and time. From the behaviour obtained experimentally, constitutive equations including failure criteria are then devised to be used in the design of FRP structures. The ply longitudinal behaviour under compression is generally the most difficult to measure and characterize. In this work, an alternative coupled experimental-computational micromechanics approach is proposed to determine the longitudinal compression properties of unidirectional FRP plies under different environmental conditions. This methodology includes experimental characterization of matrix and fiber/matrix interface, combined with numerical simulations of realistic microstructures. The interface decohesion is simulated using cohesive-frictional interactions. A pressure dependent, elasto-plastic model that includes tensile damage is employed to capture the matrix nonlinear behaviour. The numerical predictions match the experimentally-obtained ply properties available in the literature in a remarkable way and suggest that virtual ply property characterization is a mature and reliable approach to conduct screening of materials.The authors would like to acknowledge the support provided by AIRBUS SAS through the project SIMSCREEN (Simulation for Screening Composite Materials Properties). Additionally, C.S. Lopes acknowledges the support of the Spanish Ministry of Economy and Competitiveness (RYC-2013-14271) through the Ramón y Cajal program. The collaboration with NASA Langley Research Center in some aspects of this work is also acknowledged