TGRS Observations of Positron Annihilation in Classical Novae

The TGRS experiment on board the Wind spacecraft has many advantages as a sky monitor --- broad field of view (~2 pi) centered on the south ecliptic pole), long life (1994-present), and stable low background and continuous coverage due to Wind's high altitude high eccentricity orbit. The Ge detector has sufficient energy resolution (3-4 keV at 511 keV) to resolve a cosmic positron annihilation line from the strong background annihilation line from beta-decays induced by cosmic ray impacts on the instrument, if the cosmic line is Doppler-shifted by this amount. Such lines (blueshifted) are predicted from nucleosynthesis in classical novae. We have searched the entire TGRS database for 1995-1997 for this line, with negative results. In principle such a search could yield an unbiased upper limit on the highly-uncertain Galactic nova rate. We carefully examined the times around the known nova events during this period, also with negative results. The upper limit on the nova line flux in a 6-hr interval is typically <3.8 E-3 photon/(cm2 s) at 4.6 sigma. We performed the same analysis for times around the outburst of Nova Vel 1999, obtaining a worse limit due to recent degradation of the detector response caused by cosmic ray induced damage.Comment: 5 pp. inc. 3 figs. Proc. 5th Compton Symposium (AIP Conf. Series), ed. M. McConnell, in pres

Time-modulated arrays with Haar wavelets

Time-modulated arrays (TMAs) can effectively perform beamsteering over the first positive harmonic pattern by applying progressively delayed versions of stair-step approximations of a sine waveform to the antenna excitations. In this letter, we consider synthesizing such stair-step sine approximations by means of Haar wavelets. Haar functions constitute a complete orthonormal set of rectangular waveforms, which have the ability to represent a given function with a high degree of accuracy using few constituent terms. Hence, when they are applied to the TMA synthesis, employing single-pole double-throw switches, such a feature leads to an excellent rejection level of the undesired harmonics as well as a bandwidth greater than that supported by conventional TMAs with on-off switches.Comment: 5 pages, 4 figures, Published in IEEE Antennas and Wireless Propagation Letter

Time-modulated multibeam phased arrays with periodic Nyquist pulses

We present a single sideband time-modulated multibeam phased array governed by periodic Nyquist pulsed signals. A Nyquist pulse is a physically realizable approach to the ideal sinc function. Hence, its low-pass spectrum suits particularly well for time-modulated arrays (TMAs) to perform harmonic beam steering. Contrarily to switched TMAs and standard solutions based on variable phase shifters, the performance and complexity of the proposed time modulation scheme is rather robust when increasing the number of multibeams.Comment: 4 pages, 4 figures, Published in IEEE Antennas and Wireless Propagation Letter

Unleashing the Potential of LTE for Next Generation Railway Communications

In an increasingly demanding marketplace that will put great strain on railway services, research on broadband wireless communication must continue to strive for improvement. Based on the mature narrowband GSM technology, Global System for Mobile Communications-Railways (GSM-R) has been deployed both for operational and voice communications. Although GSM-R fulfills the requirements of current railway services, it imposes limited capacity and high costs that restrict enhancements of operational efficiency, passenger security and transport quality. 4G Long Term Evolution (LTE) is expected to be the natural successor of GSM-R not only for its technical advantages and increasing performance, but also due to the current evolution of general-purpose communication systems. This paper examines the key features of LTE as well as its technical ability to support both the migration of current railway services and the provisioning of future ones.Comment: This is a portion of the ACCEPTED VERSION of the published document in: Kassab, M., Berbineau,M., Vinel, A., Jonsson, M., Garcia, F., Soler, J. (eds) Communication Technologies for Vehicles. Nets4Cars/Nets4Trains/Nets4Aircraft 2015. Lecture Notes in Computer Science, vol 9066. Springer, Cham. https://doi.org/10.1007/978-3-319-17765-6_1

La doctrina del purgatorio en el desarrollo teológico

El desarrollo teológico que ha acompañado a lo largo de los siglos la doctrina de la Iglesia acerca del purgatorio ha estado marcado por la propia vida de la Iglesia, por su culto, su liturgia y la reflexión creyente sobre las realidades últimas. Esta tesis de doctorado es el resultado de un amplio estudio sistemático del dogma del purgatorio y del desarrollo teológico en el que se apoya. Se tienen en cuenta la influencia de los diversos contextos históricos y culturales, las corrientes filosóficas y las categorías en las que se expresa la fe en las distintas lenguas. Todo ello influye en el quehacer teológico y marca con diversos matices la doctrina del purgatorio. El estudio de la teología sobre el purgatorio exige recorrer y contemplar un camino de reflexión a lo largo de dos milenios: en la Sagrada Escritura no hay una revelación explícita y detallada, lo que implica una reflexión según las categorías intelectuales-científicas de la época y según el nexus mysteriorum del que participa la escatología como parte de la fe de la Iglesia. En este desarrollo doctrinal destaca la segunda mitad del siglo XX como un tiempo particularmente fructífero; puede decirse que, desde la perspectiva del estudio de su desarrollo, en las últimas décadas la comprensión teológica del purgatorio ha supuesto una revisión y ha alcanzado una notable madurez.The theological development, which has accompanied the teaching of the Church on purgatory throughout the centuries, has been marked by the proper life of the Church—by her worship and liturgy— and by the reflection of the faithful concerning the Last Things. This doctoral thesis is a result of an extensive systematic investigation on the dogma of purgatory and the theological development on which the former is based. The thesis takes into account the influence of diverse historical and cultural contexts. All of them exert an influence on the theological work and mark the doctrine of purgatory with different nuances. The theological study on purgatory should go over and contemplate a path of reflection that spanned two millenniums: since the Sacred Scripture does not contain any explicit and detailed revelation concerning purgatory, the study requires a reflection in conformity with the intellectual-scientific categories of the epoch and with the nexus mysteriorum in which the eschatology— as a part of the Church’s faith—participates. In this doctrinal development, the second half of the twentieth century is a particularly fruitful period; it can be said that, from the standpoint of its development, the theological understanding of purgatory underwent a revision and reached a notable maturity in the last decades

The role of interfacial properties on the intralaminar and interlaminar damage behaviour of unidirectional composite laminates: Experimental characterization and multiscale modelling

The development of the latest generation of wide-body passenger aircraft has heralded a new era in the utilisation of carbon-fibre composite materials. One of the primary challenges facing future development programmes is the desire to reduce the extent of physical testing, required as part of the certification process, by adopting a ‘certification by simulation’ approach. A hierarchical bottom-up multiscale simulation scheme can be an efficient approach that takes advantage of the natural separation of length scales between different entities (fibre/matrix, ply, laminate and component) in composite structures. In this work, composites with various fibre/matrix and interlaminar interfacial properties were fabricated using an autoclave under curing pressures ranging from 0 to 0.8 MPa. The microstructure (mainly void content and spatial distribution) and the mechanical properties of the matrix and fibre/matrix interface were measured, the latter by means of nanoindentation tests in matrix pockets, and fibre push-in tests. In addition, the macroscopic interlaminar shear strength was determined by means of three-points bend tests on short beams. To understand the influence of interfacial properties on the intralaminar failure behaviour, a high-fidelity microscale computational model is presented to predict homogenized ply properties under shear loading. Predicted ply material parameters are then transferred to a mesoscale composite damage model to reveal the interaction between intralaminar and interlaminar damage behaviour of composite laminates