211 research outputs found
Analytical and numerical solutions for a class of optimization problems in elasticity
The subject of topology optimization methods in structural de-
sign has increased rapidly since the publication of [?], where some ideas from
homogenization theory were put into practice. Since then, several engineering
applications have been developed successfully. However, in the literature, there
is a lack of analytical solutions, even for simple cases, which might help in the
validation of the numerical results. In this work, we develop analytical solu-
tions for simple minimum compliance problems, in the framework of elasticity
theory. We compare these analytical solutions with numerical results obtained
via an algorithm proposed in [?]
Thin waveguides with Robin boundary conditions
We consider the Laplace operator in a thin three dimensional tube with a
Robin type condition on its boundary and study, asymptotically, the spectrum of
such operator as the diameter of the tube's cross section becomes
infinitesimal. In contrast with the Dirichlet condition case, we evidence
different behaviors depending on a symmetry criterium for the fundamental mode
in the cross section. If that symmetry condition fails, then we prove the
localization of lower energy levels in the vicinity of the minimum point of a
suitable function on the tube's axis depending on the curvature and the
rotation angle. In the symmetric case, the behavior of lower energy modes is
shown to be ruled by a one dimensional Sturm-Liouville problem involving an
effective potential given in explicit form
Contabilidade Ambiental: divulgação de Informação
O presente artigo procura apresentar uma revisão da literatura sobre a temática da Contabilidade Ambiental na perspectiva da Divulgação.
Efectua-se o enquadramento teórico do tema como suporte para a problemática da motivação da Gestão para o relato ambiental e caracteriza-se o state of the art da divulgação ambiental no relatório anual a nível internacional com particular ênfase para os países onde este assunto tem merecido mais atenção.
Depois de apresentado o ponto da situação sobre a realidade portuguesa, antes e após a publicação da Directriz Contabilística nº29 – Matérias Ambientais, é efectuada uma abordagem sobre o papel que cabe aos auditores no processo de reporte de informação no domínio ambiental em face do impacte que estas matérias têm nas demonstrações financeiras
On the equilibrium of the egyptian game Senet
In this work we compute the probabilities of obtaining the values associated with the throwing of four rods in the Egyptian game Senet. Our purpose is to, among several sets of rules obtained by some historians and archeologists, deduce which ones provide the most balanced game. In the course of this study it was also possible to infer the most likely format for the rod’s cross section.publishersversionpublishe
Existence and uniqueness of solution to an adaptive elasticity model
International audienceIn this work we study the existence and unicity of solutions to an {\sl Adaptive Elasticity Model} applied to bone remodeling. Specifically, we consider the model derived by Cowin and Hegedus, directly from continuum mechanics theory. We use a fixed point argument in order to prove the existence of solutions and a straightforward adaptation of the Cowin and Nachlinger analysis in order to prove uniqueness
An open ocean record of the Toarcian oceanic anoxic event
Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic matter-rich sediments (black shales) and significant perturbations in the global carbon cycle. These perturbations are globally recorded in sediments as carbon isotope excursions irrespective of lithology and depositional environment. During the early Toarcian, black shales were deposited on the epi- and pericontinental shelves of Pangaea, and these sedimentary rocks are associated with a pronounced (ca. 7 ‰) negative (organic) carbon isotope excursion (CIE) which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the lower Toarcian is thought to represent an oceanic anoxic event (the T-OAE). If the T-OAE was indeed a global event, an isotopic expression of this event should be found beyond the epi- and pericontinental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (δ13Corg of lower Toarcian organic matter-rich cherts from Japan, deposited in the open Panthalassa Ocean, was analysed. The results show the presence of a major (>6 ‰) negative excursion in δ13Corg that, based on radiolarian biostratigraphy, is a correlative of the lower Toarcian negative CIE known from Pangaean epi- and pericontinental strata. A smaller negative excursion in δ13Corg (ca. 2 ‰) is recognized lower in the studied succession. This excursion may, within the current biostratigraphic resolution, represent the excursion recorded in European epicontinental successions close to the Pliensbachian/Toarcian boundary. These results from the open ocean realm suggest, in conjunction with other previously published datasets, that these Early Jurassic carbon cycle perturbations affected the active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric)
A new subsurface record of the Pliensbachian-Toarcian, Lower Jurassic, of Yorkshire
Here, we describe the upper Pliensbachian to middle Toarcian stratigraphy of the Dove's Nest borehole, which was drilled near Whitby, North Yorkshire, in 2013. The core represents a single, continuous vertical section through unweathered, immature Lower Jurassic sedimentary rocks. The thickness of the Lias Group formations in the Dove's Nest core is approximately the same as that exposed along the North Yorkshire coast between Hawsker Bottoms and Whitby. The studied succession consists of epeiric-neritic sediments and comprises cross-laminated very fine sandstones, (oolitic) ironstones, and argillaceous mudstones. Dark argillaceous mudstone is the dominant lithology. These sediments were deposited in the Cleveland Basin, a more subsident area of an epeiric sea, the Laurasian Sea. We present a set of geochemical data that includes organic carbon isotope ratios (δ13Corg) and total organic carbon (TOC). The δ13Corg record contains a negative excursion across the Pliensbachian–Toarcian boundary and another in the lower Toarcian that corresponds to the Toarcian Oceanic Anoxic Event (T-OAE). Below the T-OAE negative excursion, δ13Corg values are less 13C-depleted than above it. We find no evidence of a long-term δ13Corg positive excursion. TOC values below the T-OAE negative excursion are lower than above it. Sedimentary evidence suggests that, during much of the Pliensbachian–Toarcian interval, the seafloor of the Cleveland Basin was above storm wave-base and that storm-driven bottom currents were responsible for much sediment erosion, transport, and redeposition during the interval of oceanic anoxia. The abrupt shifts observed in the δ13Corg record (lower Toarcian) are likely to reflect the impact of erosion by storms on the morphology of the δ13C record of the T-OAE
Characterisation and modelling of transient transport through dense membranes using on-line mass spectrometry
European KBBE FP7 project (262632)
PTDC/MAT109973/2009Abstract: This work presents a methodology for characterising solute transport through pervaporation membranes or, more generally, through dense membranes, in the whole transient regime. A real-time characterisation of transport through dense membrane is obtained by using on-line mass spectrometry (MS) monitoring, which allows to acquire the concentration of solutes in the permeate compartment with time intervals of 2 seconds (and lower if required). Time-dependent diffusion coefficients, D(t), were calculated for the whole operation period, including the initial transient period. Based on these values it is possible to infer about the relevance of solute-membrane interactions and rearrangement of the membrane structure due to the presence of permeant solutes. Finally, based on the information acquired, a mathematical model was developed in order to obtain solute concentration profiles inside the membrane and their evolvement along time.authorsversionpublishe
A regional ocean circulation model for the mid-Cretaceous North Atlantic Basin: implications for black shale formation
High concentrations of organic matter accumulated in marine sediments during Oceanic Anoxic Events (OAEs) in the Cretaceous. Model studies examining these events invariably make use of global ocean circulation models. In this study, a regional model for the North Atlantic Basin during OAE2 at the Cenomanian-Turonian boundary has been developed. A first order check of the results has been performed by comparison with the results of a recent global Cenomanian CCSM3 run, from which boundary and initial conditions were obtained. The regional model is able to maintain tracer patterns and to produce velocity patterns similar to the global model. The sensitivity of the basin tracer and circulation patterns to changes in the geometry of the connections with the global ocean is examined with three experiments with different bathymetries near the sponges. Different geometries turn out to have little effect on tracer distribution, but do affect circulation and upwelling patterns. The regional model is also used to test the hypothesis that ocean circulation may have been behind the deposition of black shales during OAEs. Three scenarios are tested which are thought to represent pre-OAE, OAE and post-OAE situations. Model results confirm that Pacific intermediate inflow together with coastal upwelling could have enhanced primary production during OAE2. A low sea level in the pre-OAE scenario could have inhibited large scale black shale formation, as could have the opening of the Equatorial Atlantic Seaway in the post-OAE scenario
Lithological controls on the deformation mechanisms operating within carbonate-hosted faults during the seismic cycle
A significant proportion of moderate-large earthquakes, plus aftershocks, nucleate within and propagate through upper-crustal carbonate-dominated sequences, where the effects of lithological variations on fault behaviour are poorly understood. The Gubbio fault is an active (1984, Ms = 5.2) normal fault in Italy, hosted in Mesozoic–Cenozoic limestones and interbedded marls. Fault core domains derived from limestone at the studied outcrop are characterised by fractures/hydrofractures and breccias and host a number of localised (<1.5 mm wide) principal slip zones (PSZs). The majority of displacement of up to 230 m is concentrated in these PSZs, which comprise cataclasites, gouges, and calcite veins. Degassing bubbles, ‘quenched’ calcite, and the transformation of smectite to illite, are also observed within PSZs, implying frictional heating and seismic slip. In contrast, marl-rich domains exhibit distributed shear planes bounding a continuous and pervasive foliation, defined by phyllosilicate-rich pressure-solution seams. Microstructures in the seams include folds/kinks of phyllosilicates and pressure shadows around clasts, consistent with aseismic fault creep. A model is proposed for the behaviour of lithologically complex carbonate-hosted faults during the seismic cycle, whereby limestone-dominated fault core domains behave in a predominantly seismic manner, whereas phyllosilicate-rich domains behave in a predominantly aseismic manner
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