Repositório Institucional da Universidade de Aveiro
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A comparative analysis of energy dissipation and equivalent viscous damping of RC columns subjected to uniaxial and biaxial loading
No full textThe hysteretic behaviour of RC columns has been object of many experimental studies over the past
years. However, the majority of these studies are focused on unidirectional loading. An experimental program
was carried out where 24 columns were tested for different loading histories, under uniaxial and
biaxial conditions. The experimental results are presented in this paper and are discussed in terms of global
column behaviour, and particularly with regards to energy dissipation and damping capacity. The
energy dissipation capacity of the columns was evaluated in terms of cumulative dissipated energy, comparing
uniaxial and biaxial test results, and individual cycle dissipated energy. Ultimately, an equation
relating the normalised dissipated energy with the displacement ductility is proposed. The equivalent
viscous damping was analysed by comparing the uniaxial with biaxial test results, demonstrating the
high influence of the load path in the biaxial response of RC columns. Proposals for estimating the equivalent
viscous damping given by other authors are compared with the experimental results. Finally, simplified
expressions are proposed to estimate equivalent viscous damping in RC columns under biaxial
loading
Strategic planning in an uncertain business environment: the diffusion of scenario planning
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International buyer-supplier relationships, transfer of knowledge and local supplier's capability
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Problems of minimal and maximal aerodynamic resistance
No full textThis is a review of results recently obtained by the author, related to
problems of the body of minimal and maximal resistance. The cases of
purely translational motion, as well as (rotational & translational) motion are
considered. The notions of rough body and law of scattering on a body are
discussed. Connections with the Monge-Kantorovich problem of optimal
mass transportation are revealed, and applications to the Magnus effect and
retroreflectors are discussed
Experimental evaluation of strain shielding in distal femur in revision TKA
No full textTheoretical concerns about the use of cemented and press-fit stems in revision total knee arthroplasty (TKA) include stress shielding with adverse effects on prosthesis fixation. Radiological studies have showed distal femoral bone resorption after revision TKA. The revision with use of stems can place abnormal stresses. These stresses can promote the effect of bone stress shielding and may contribute to bone loss. Experimental quantification of strain shielding in the distal synthetic femur following TKA is the main purpose of the present study. Three different constructs of TKA were assessed. The first construct included a stemless femoral component. The other two included a press-fit and a cemented femoral stem. Cortical bone strains were measured experimentally with tri-axial strain gauges in synthetic femurs before and after in-vitro knee surgery. The difference between principal strains of implanted and intact femur was calculated for each strain gauge position. This study indicates that the use of stems in distal femur changes the distribution and magnitude of bone strains. The press-fit stem provoked relevant bone area ( stem length) subjected to strain shielding and also originated the highest reduction of strains in the distal region, which can potentially induce bone resorption. The stemless implanted femur produced minor bone strain changes relatively to the intact femur. The use of distal femur stems increases initial stability in the bone, but the observed reduction of strains in this region, relative to the intact femur, provokes strain shielding that can induce bone resorption and may compromise the long term implant stability
Vacuum casting with room temperature vulcanising rubber and aluminium moulds for rapid manufacturing of quality parts: a comparative study
No full textThe purpose of this study was to compare costs and
dimensional control parameters between same geometry
parts obtained by same prototyping techniques using
different material moulds. Vacuum casting was used to
obtain prototypes of a three-blade helix of a motor boat
propeller. Aluminium and room temperature vulcanising
(RTV) rubber moulds were manufactured and tested within
the study. Manufacturing costs and dimensional control
parameters were used within the comparison study.
For the dimensional deviation performance factor used,
no significant differences were observed relatively to the
dimensional control parameters measured. However, the
average deviations were smaller for the RTV rubber mould
prototype
Avaliação do comportamento da haste press-fit recta versus curva na revisão do componente femoral na ATJ
No full textO presente estudo teve como objectivo avaliar as diferenças
de estabilidade do componente femoral e as deformações no
osso aquando da revisão da artroplastia total joelho com hastes
press-fi t recta e curva. A análise relativa aos micromovimentos
e às deformações foi realizada por comparação entre os dois
modelos de haste mantendo todos os outros parâmetros idênticos,
utilizando, para o efeito, a aplicação de análise estrutural
(MEF) MARC Research Analysis (Palo Alto, CA, USA). Os
resultados obtidos revelaram que a utilização da haste curva
aumenta ligeiramente as deformações sobre o osso esponjoso
na interface osso-cimento do componente femoral assim como
os picos de deformação na zona da extremidade da haste. A
estabilidade proporcionada pela haste curva é ligeiramente inferior
à proporcionada pela haste recta. À luz dos resultados
numéricos obtidos, não existe vantagem adicional no uso de
hastes curvas em casos em que a anatomia do fémur permite a
utilização de uma haste recta.The aim of this study was to evaluate the load-sharing capacity,
bone strains and stability of the bone-cement interface under
the femoral component with straight and curved press-fi t femoral
stems. Th e diffi culties or unfeasible evaluation of these in vitro biomechanical
parameters makes the use of fi nite element (FE) models
one way forward to study these parameters. Two FE models were
developed. One with a straight stem and the other with a curved
stem, to compare the diff erent biomechanical parameters. Th e FE
results of load sharing and interface bone-cement stability under
the femoral component suggest identical load sharing capacity for
both stems, but the curved press-fi t stem reduces slightly the stability
at the bone-cement interafce under the femoral component
relatively to the straight stem. In light of these results, the use of a
curved stem does not present advantages relatively to the straight
design when the anatomic femur geometry is compatibly with the
implantation of a straight stem design
Неявный критерий оптимальности для задач выпуклого полубесконечного программирования
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O Bosque das Figuras Planas
No full textEste livro pretende levar as crianças a explorar a Matemática duma forma divertida e integrada com actividades do seu dia-a-dia, em particular com o prazer de ouvir contar histórias. Para isso, foram criadas histórias que giram em torno de um personagem bem conhecido, o Pinóquio. A acompanhar as histórias encontram-se actividades que levam as crianças a experimentar, a pensar e a encontrar respostas para os mais variados desafios.
Na primeira história Pinóquio é criado em computador, à imagem da sua criação em madeira por Carlo Collodi em 1881. Desta vez é gerado a partir de um programa gráfico utilizando figuras geométricas simples. Quando o boneco começa a falar faz perguntas sobre as figuras que o compõem. A esse propósito é levado a conhecer o Bosque das Figuras Planas onde vivem as figuras geométricas (planas) governadas por uma simpática rainha. Na segunda história, os habitantes do bosque juntam-se numa grande festa. Mas de repente, a rainha dá-se conta que desapareceram as figuras redondas. Que terá acontecido
Dynamic language modeling for European Portuguese
No full textThis paper reports on the work done on vocabulary and language model daily adaptation for a European Portuguese broadcast news transcription system. The proposed adaptation framework takes into consideration European Portuguese language characteristics, such as its high level of inflection and complex verbal system. A multi-pass speech recognition framework using contemporary written texts available daily on the Web is proposed. It uses morpho-syntactic knowledge (part-of-speech information) about an in-domain training corpus for daily selection of an optimal vocabulary. Using an information retrieval engine and the ASR hypotheses as query material, relevant documents are extracted from a dynamic and large-size dataset to generate a story-based language model. When applied to a daily and live closed-captioning system of live TV broadcasts, it was shown to be effective, with a relative reduction of out-of-vocabulary word rate (69%) and WER (12.0%) when compared to the results obtained by the baseline system with the same vocabulary size. (C) 2010 Elsevier Ltd. All rights reserved