465 research outputs found
A finite element model using a unified formulation for the analysis of viscoelastic sandwich laminates
In this paper we present a layerwise finite element model for the analysis of sandwich laminated plates with a viscoelastic core and laminated anisotropic face layers. The stiffness and mass matrices of the element are obtained by Carrera's Unified Formulation (CUF). The dynamic problem is solved in the frequency domain with viscoelastic frequency-dependent material properties for the core. The dynamic behaviour of the model is compared with solutions found in the literature, including experimental data
Quantifying the impact of variability in railway bridge asset management
Bridge asset management is often a challenging and complicated task due to the diversity, multitude and variation of bridge configurations. Much research has been carried out in the field of asset management which has resulted in a wealth of models to help with the decision making process. However, often these models oversimplify the process, resulting in a decision making tool that trivialises the complexity of the decisions. The purpose of this study was to ascertain what the main sources of variability are in the process and then quantify the impact of them in terms of the Whole Life-Cycle Cost (WLCC). The study focuses on human-induced variability to ensure the results are directly influenceable by bridge portfolio managers. The sources of variability identified include misdiagnoses of defects as well as imperfect repairs and variability in costs, all of which are aspects that bridge portfolio managers are exposed to. The sources of variability are quantified and then incorporated into an existing railway bridge WLCC model, established in a previous study, which uses a flexible Petri-Net (PN) approach which is able to incorporate the complex logic and probabilistic aspects. The model itself is able to replicate some of the more complicated decisions which have to be made in bridge asset management, especially those which influence the decisions around rehabilitation. The resulting model, enhanced with the probabilistic variability, is able to reveal the impact of variability on the asset condition, WLCC and even understand where operational complexities are occurring within the system. Incorporating human-induced variability into any model will inevitably increase the financial and operational burden predicted by the model, however, recognising and modelling these aspects is a crucial step in providing bridge portfolio managers a more robust and accurate decision making tool which can more accurately replicate the real world system
Effects of starch/polycaprolactone-based blends for spinal cord injury regeneration in neurons/glial cells viability and proliferation
Spinal cord injury (SCI) leads to drastic alterations on the quality of life of afflicted individuals. With the advent of Tissue Engineering and Regenerative Medicine where approaches combining biomaterials, cells and growth factors are used, one can envisage novel strategies that can adequately tackle this problem. The objective of this study was to evaluate a blend of starch with poly(ε-caprolactone) (SPCL) aimed to be used for the development of scaffolds spinal cord injury (SCI) repair. SPCL linear parallel filaments were deposited on polystyrene coverslips and assays were carried out using primary cultures of hippocampal neurons and glial cells. Light and fluorescence microscopy observations revealed that both cell populations were not negatively affected by the SPCL-based biomaterial. MTS and total protein quantification indicated that both cell viability and proliferation rates were similar to controls. Both neurons and astrocytes occasionally contacted the surface of SPCL filaments through their dendrites and cytoplasmatic processes, respectively, while microglial cells were unable to do so. Using single cell [Ca2+ ]i imaging, hippocampal neurons were observed growing within the patterned channels and were functional as assessed by the response to a 30 mM KCl stimulus. The present data demonstrated that SPCL-based blends are potentially suitable for the development of scaffolds in SCI regenerative medicine.Portuguese Foundation for Science and Technology through funds from POCTI and/or FEDER programs (Funding to ICVS, 3B's Research Group and post doctoral fellowship to A.J. Salgado-SFRH/BPD/17595/2004)
Vacuum solutions of the gravitational field equations in the brane world model
We consider some classes of solutions of the static, spherically symmetric
gravitational field equations in the vacuum in the brane world scenario, in
which our Universe is a three-brane embedded in a higher dimensional
space-time. The vacuum field equations on the brane are reduced to a system of
two ordinary differential equations, which describe all the geometric
properties of the vacuum as functions of the dark pressure and dark radiation
terms (the projections of the Weyl curvature of the bulk, generating non-local
brane stresses). Several classes of exact solutions of the vacuum gravitational
field equations on the brane are derived. In the particular case of a vanishing
dark pressure the integration of the field equations can be reduced to the
integration of an Abel type equation. A perturbative procedure, based on the
iterative solution of an integral equation, is also developed for this case.
Brane vacuums with particular symmetries are investigated by using Lie group
techniques. In the case of a static vacuum brane admitting a one-parameter
group of conformal motions the exact solution of the field equations can be
found, with the functional form of the dark radiation and pressure terms
uniquely fixed by the symmetry. The requirement of the invariance of the field
equations with respect to the quasi-homologous group of transformations also
imposes a unique, linear proportionality relation between the dark energy and
dark pressure. A homology theorem for the static, spherically symmetric
gravitational field equations in the vacuum on the brane is also proven.Comment: 13 pages, no figures, to appear in PR
Report of the 2006 ICCAT workshop for bluefin tuna direct ageing
This report provides the presentations, discussions and conclusions from the ICCAT bluefin
tuna workshop for direct ageing held in Santander, Spain, in April 2006. The report
summarizes the ageing criteria used in the past and the agreements on future age determination
based on otoliths, vertebrae and spines. Advantages and disadvantages of each calcified
structure for ageing and border interpretation were discussed. It was considered that bluefin
tuna age interpretation becomes very difficult from age ten onwards using the whole vertebra
and the spine sections methods, but this last technique continues to be useful for older ages.
Otolith sections can be used for the whole age range. Participants agreed that none of these
three structures could be excluded from routine ageing because otoliths are not easily
available. Age estimations within the same structure and between different structures of the
same specimen were compared for several readers. Better precision was found between spine
readers compared to vertebra and otolith readers. Good age agreement was also achieved
between readers of spines and vertebrae from the same bluefin for ages less than 12 years.
Preliminary results from radiocarbon assays on otoliths were presented at the workshop and
gave promising outcomes for bluefin tuna age validation. Also, these suggested that bluefin
tuna can live longer than had previously been established and that a review is needed of the
currently used asymptotic size and growth rate for both stocks. Another important contribution
of the workshop was a manual for age interpretation.Le présent rapport recueille les présentations, discussions et conclusions de l’Atelier de
l’ICCAT chargé de la détermination directe de l’âge du thon rouge, tenu à Santander
(Espagne) au mois d’avril 2006. Le rapport résume les critères employés par le passé pour
interpréter l’âge et les accords pour la détermination future de l’âge à partir des otolithes,
vertèbres et épines. L’Atelier a discuté des avantages et des inconvénients de chaque structure
calcifiée pour déterminer l’âge et l’interprétation du type de bord. On a abordé la difficulté de
l’interprétation de l’âge des thons de plus de 10 ans au moyen de la vertèbre entière et des
sections des épines, bien que cette dernière méthode continue d’être utile pour les âges
avancés. Les sections d’otolithes peuvent être employées pour toute la gamme d’âges. Les
participants ont convenu qu’aucune de ces trois structures ne doit être exclue pour
l’interprétation de l’âge parce qu’il n’est pas toujours possible d’obtenir des otolithes. On a
comparé les lectures de l’âge à l’intérieur de la même structure et entre différentes structures
du même exemplaire pour divers lecteurs. On a obtenu une plus grande précision parmi les
lecteurs d’épines que parmi les lecteurs de vertèbres et d’otolithes. On a également obtenu un
bon accord entre les lecteurs d’épines et de vertèbres originaires du même exemplaire pour les
âges inférieurs à 12 ans. Les résultats préliminaires des essais de radiocarbone dans les
otolithes ont été présentés à l’Atelier, offrant de bonnes perspectives pour son utilisation dans la validation de l’âge. Ces résultats indiquent aussi que le thon rouge a une plus grande
longévité que ce qui avait été auparavant établi et qu’il est nécessaire de réviser la longueur
asymptotique et le taux de croissance actuellement utilisés. L’élaboration d’un manuel aux fins
de l’interprétation de l’âge a constitué une autre contribution importante de l’Atelier.Este informe recoge las presentaciones, discusiones y conclusiones del congreso de ICCAT
para la determinación directa de la edad de atún rojo, celebrado en Santander, España, en
abril de 2006. El informe resume los criterios empleados en el pasado para interpretar la edad
y los acuerdos para la determinación futura de la edad a partir de otolitos, vértebras y espinas.
Se discutieron las ventajas y los inconvenientes de cada estructura calcificada para determinar
la edad y la interpretación del tipo borde. Se planteó la dificultad en la interpretación de la
edad de atunes mayores de 10 años utilizando la vértebra entera y las secciones de espinas, no
obstante este último método continúa siendo útil para edades mayores. Las secciones de
otolitos pueden ser empleadas para todo el rango de edades. Los participantes acordaron que
ninguna de estas tres estructuras deben excluirse para la interpretación de la edad porque no
siempre es posible obtener los otolitos. Se compararon las lecturas de edad dentro de la misma
estructura y entre diferentes estructuras del mismo ejemplar para varios lectores. Se obtuvo
una mayor precisión entre lectores de espinas comparada con las obtenidas por los lectores de
vértebras y otolitos. También se obtuvo un buen acuerdo entre lectores de espinas y vértebras
procedentes del mismo ejemplar para edades menores de 12 años. Los resultados preliminares
de las pruebas de radiocarbono en otolitos fueron presentados en el congreso, proporcionando
buenas expectativas para su uso en la validación de la edad. Estos resultados también indican
que el atún rojo es más longevo de lo que se consideraba y que es necesaria una revisión de la
longitud asintótica y de la tasa de crecimiento empleadas actualmente. Otra importante
contribución del congreso fue la elaboración de un manual para la interpretación de la edad
Demagnetization via Nucleation of the Nonequilibrium Metastable Phase in a Model of Disorder
We study both analytically and numerically metastability and nucleation in a
two-dimensional nonequilibrium Ising ferromagnet. Canonical equilibrium is
dynamically impeded by a weak random perturbation which models homogeneous
disorder of undetermined source. We present a simple theoretical description,
in perfect agreement with Monte Carlo simulations, assuming that the decay of
the nonequilibrium metastable state is due, as in equilibrium, to the
competition between the surface and the bulk. This suggests one to accept a
nonequilibrium "free-energy" at a mesoscopic/cluster level, and it ensues a
nonequilibrium "surface tension" with some peculiar low-T behavior. We
illustrate the occurrence of intriguing nonequilibrium phenomena, including:
(i) Noise-enhanced stabilization of nonequilibrium metastable states; (ii)
reentrance of the limit of metastability under strong nonequilibrium
conditions; and (iii) resonant propagation of domain walls. The cooperative
behavior of our system may also be understood in terms of a Langevin equation
with additive and multiplicative noises. We also studied metastability in the
case of open boundaries as it may correspond to a magnetic nanoparticle. We
then observe burst-like relaxation at low T, triggered by the additional
surface randomness, with scale-free avalanches which closely resemble the type
of relaxation reported for many complex systems. We show that this results from
the superposition of many demagnetization events, each with a well- defined
scale which is determined by the curvature of the domain wall at which it
originates. This is an example of (apparent) scale invariance in a
nonequilibrium setting which is not to be associated with any familiar kind of
criticality.Comment: 26 pages, 22 figure
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
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