3,056 research outputs found
The Role of Subsidies in Promoting Italian Joint Ventures in Least Developed and Transition Economics.
Three dimensionality in the wake of the flow around a circular cylinder at Reynolds number 5000
The turbulent flow around a circular cylinder has been investigated at Re=5000Re=5000 using direct numerical simulations. Low frequency behavior, vortex undulation, vortex splitting, vortex dislocations and three dimensional flow within the wake were found to happen at this flow regime. In order to successfully capture the wake three dimensionality, different span-wise lengths were considered. It was found that a length LZ=2pDLZ=2pD was enough to capture this behavior, correctly predicting different aspects of the flow such as drag coefficient, Strouhal number and pressure and velocity distributions when compared to experimental values. Two instability mechanisms were found to coexist in the present case study: a global type instability originating in the shear layer, which shows a characteristic frequency, and a convective type instability that seems to be constantly present in the near wake. Characteristics of both types of instabilities are identified and discussed in detail. As suggested by Norberg, a resonance-type effect takes place in the vortex formation region, as the coexistence of both instability mechanisms result in distorted vortex tubes. However, vortex coherence is never lost within the wake.Peer ReviewedPostprint (author's final draft
Combined modelling and miniaturised characterisation of high-temperature forging in a nickel-based superalloy
Continuum models and miniaturised experiments are used to elucidate the high-temperature forgeability of the Ni-based superalloy Inconel 903. Uniaxial compression high temperature tests allow the derivation of an apparent activation energy and the strain rate sensitivity of the deformation process, and to propose a unified constitutive model that captures the underlying physics of deformation. Metallographic analysis is then used to elucidate changes in microstructure which arise during the deformation process; microstructure evolution models which define the changes in grain size and recrystallisation during high temperature compression are proposed. Miniaturised forging experiments in double-cone specimens validate the modelling approach under relevant forging conditions at different temperatures and deformation rates. Finally, the deformation behaviour of this material in an industrially relevant manufacturing scenario – the forging process of a turbine disc – is studied numerically
Optical Spectroscopy of X-Mega targets in the Carina Nebula - VI. FO 15: a new O-Type double-lined eclipsing binary
We report the discovery of a new O-type double-lined spectroscopic binary
with a short orbital period of 1.4 days. We find the primary component of this
binary, FO 15, to have an approximate spectral type O5.5Vz, i.e. a
Zero-Age-Main-Sequence star. The secondary appears to be of spectral type
O9.5V. We have performed a numerical model fit to the public ASAS photometry,
which shows that FO 15 is also an eclipsing binary. We find an orbital
inclination of ~ 80 deg. From a simultaneous light-curve and radial velocity
solution we find the masses and radii of the two components to be 30 +/- 1 and
16 +/- 1 solar masses and 7.5 +/- 0.5 and 5.3 +/- 0.5 solar radii. These radii,
and hence also the luminosities, are smaller than those of normal O-type stars,
but similar to recently born ZAMS O-type stars. The absolute magnitudes derived
from our analysis locate FO 15 at the same distance as Eta Carinae. From
Chandra and XMM X-ray images we also find that there are two close X-ray
sources, one coincident with FO 15 and another one without optical counterpart.
This latter seems to be a highly variable source, presumably due to a
pre-main-sequence stellar neighbour of FO 15.Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRAS.
Higher resolution version available at
http://lilen.fcaglp.unlp.edu.ar/papers2006.htm
Un modelo alternativo de gestión en las razas caninas autóctonas como base para su conservación
Experimental evidence for mantle drag in the Mediterranean
What forces control active deformation in the Central Mediterranean? Slab-pull has long been debated, but no other hypothesis has been generally accepted. Here we analyze the role of shear basal tractions.
By using a thin-shell modeling technique, we generated a large number of models that span different sets of boundary conditions from the literature; we then explored acceptable ranges of model parameters. We computed residuals between model predictions and several datasets of stress directions, GPS measurements and tectonic stress regimes that have been produced in recent studies, and then compared the best models obtained in the presence of tractions with those obtained in the absence of tractions.
For all tested boundary conditions and all considered datasets, our results show that the only successful models are those with significant basal shear traction exerted by eastward mantle flow
Alloys-by-design:A low-modulus titanium alloy for additively manufactured biomedical implants
The performance of many metal biomedical implants – such as fusion cages for spines – is inherently limited by the mismatch of mechanical properties between the metal and the biological bone tissue it promotes. Here, an alloy design approach is used to isolate titanium alloy compositions for biocompatibility which exhibit a modulus of elasticity lower than the Ti-6Al-4V grade commonly employed for this application. Due to the interest in alloys for personalised medicine, additive manufacturability is also considered: compositions with low cracking susceptibility and with propensity for non-planar growth are identified. An optimal alloy composition is selected for selective laser melting, and its processability and mechanical properties tested. Additive manufacturing is used to engineer an heterogeneous microstructure with outstanding combined strength and ductility. Our results confirm the suitability of novel titanium alloys for lowering the stiffness towards that needed whilst being additively manufacturable and strong
Convolutional neural networks for the shape design of a magnetic core for material testing: Forward and inverse approaches
In this paper CNNs are used for solving an optimization problem with two different approaches: CNN is used as a surrogate model of the forward problem, inserted in an optimization loop governed by a genetic algorithm, in the first approach, while a CNN is trained for solving directly the inverse problem in the second approach. The case study is the shape design of a magnetic core used for material testing
Nestling diet and fledgling production of eurasian kestrels (Falco tinnunculus) in eastern Spain.
We studied 81 Eurasian kestrel (Falco tinnunculus) nests in the Alto Palancia region (Castel16n, eastern Spain) from 1982-87. Fledgling production was recorded in routine visits to the nests, and the diet was determined by pellet analysis. The mean date of laying was 8 May (N -- 24, SD -- 11.5), similar to that of populations breeding further north in Europe. On average, each successful pair produced four fledglings per year (N = 47, SD = 0.7, range = 2-5), and no significant differences in fledging success were found among years. Grasshoppers formed the bulk of the diet during the nestling period. Mammals and birds were scarcely represented. The number of fledglings per successful pair was similar to or higher than that reported from Finland, Germany, and England where voles are the main prey brought to the nestlings. We suggest that a relative abundance of insects, and reduced energy requirements for thermoregulation in Mediterranean areas allow kestrels to successfully feed their young mainly on insects, without reducing fledgling production in relation to populations where voles form the bulk of the nestling diet. Se estudiaron 81 nidos de cernícalo vulgar (Falco tinnunculus) en la comarca del Alto Palancia (Castel16n, Este de España) entre 1982-87. La producci6n de pollos se estudió mediante visitas periódicas a los nidos, y la dieta analizando las egagrópilas recolectadas durante el periodo de permanencia de los pollos en el nido. La fecha media de inicio de la puesta fue el 8 de Mayo (N -- 24, SD -- 11.5), similar a las observadas en otros países de Europa. Cada pareja con éxito produce una media de cuatro pollos por año (N -- 47, SD = 0.7, rango -- 2-5), no habiendo diferencias significativas entre años. Los saltamontes forman la base de la dieta durante el periodo estudiado, estando los mamíferos y las aves escasamente representados. La producción de pollos por pareja con éxito es similar o mayor a las obtenidas en Finlandia, Alemania e Inglaterra, donde los topillos forman la base de la dieta de los pollos. Se sugiere que una mayor disponibilidad de insectos, y una reducción de los requerimientos energéticos de los pollos en las áreas mediterráneas, permiten a los cernícalos alimentar a los pollos con una dieta basada en insectos sin reducir su productividad con respecto a poblaciones donde los mamíferos son la base de la dieta
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