517 research outputs found
Ichthyofauna assemblages from two unexplored Atlantic seamounts: Northwest Bank and João Valente Bank (Cape Verde archipelago)
Underwater censuses by divers were used to study the fish assemblages from two unexplored Atlantic
seamounts in the Cape Verde archipelago. Fifty three species of 27 families were recorded: 27 in Northwest Bank and
46 in João Valente Bank. Northwest Bank had dense schools, while João Valente Bank had higher species richness and
smaller schools. Both seamounts were dominated mainly by coastal species directly depending on seabed habitat (Demersal
or benthopelagic). Of the 53 fish species recorded, 22.6% were of continental African origin, while 9.4% and 5.7% were
endemic of the Cape Verde Islands and of the Macaronesia province, respectively. Most species (64.2%) had a very wide
biogeographic distribution: cosmopolitan (22.6%), amphi-Atlantic (28.3%) and Atlantic-Mediterranean (13.2%). Northwest
Bank and João Valente Bank may have a permanent fish community supported by various oceanographic-topographic
interactions. João Valente Bank seems more diverse, which is probably associated with algae cover and with a larger area
providing additional suitable and more varied habitats. The geographic proximity to the coast and the presence of oceanic
and/or oceanodromous species suggests that the upper part of these seamounts may act both as attraction points and as
“stepping-stones” for the dispersal of coastal species.info:eu-repo/semantics/publishedVersio
Modelação da furação de laminados por elementos finitos
Furação de estruturas em compósitos de matriz poliméricaO recurso ao Método de Elementos Finitos (MEF) para a simulação e estudo da maquinagem
tem vindo a merecer um interesse crescente. Neste trabalho comparam-se os resultados
experimentais obtidos usando diferentes brocas helicoidais com uma simulação numérica da
furação usando elementos sólidos tridimensionais do software ABAQUS® Explicit. Os
resultados obtidos mostram a aplicabilidade do modelo, nomeadamente no que respeita à
variação do principal parâmetro de corte no processo de furação – o avanço – e da
geometria da ferramenta. O desenvolvimento das forças axiais durante a furação está
directamente relacionado com a selecção dos parâmetros de corte e geometria de ferramenta
e contribui para a existência de danos na placa. Assim, a minimização destas forças permite
reduzir o risco de delaminação. Os resultados relativos à força para o início da delaminação
são comparados com modelos analíticos já conhecidos. Os resultados numéricos apresentam
uma concordância apreciável com os obtidos experimentalmente
The Domination Number of Grids
In this paper, we conclude the calculation of the domination number of all
grid graphs. Indeed, we prove Chang's conjecture saying that for
every , .Comment: 12 pages, 4 figure
Damage evaluation of drilled carbon/epoxy laminates based on area assessment methods
The characteristics of carbon fibre reinforced laminates had widened their use, from aerospace to domestic appliances. A common characteristic is the need of drilling for assembly purposes. It is known that a drilling process that reduces the drill thrust force can decrease the risk of delamination. In this work, delamination assessment methods based on radiographic data are compared and correlated with mechanical test results (bearing test)
Avaliação da delaminação após furação em compósitos laminados
As características excepcionais dos materiais compósitos de matriz polimérica têm
conduzido à sua crescente utilização em todos os domínios. A necessidade de ligar estas
peças entre si obriga à realização frequente de operações de furação que, embora
devidamente adaptada, pode provocar diferentes tipos de dano nas peças a ligar. Desses, o
dano mais grave é a delaminação pelas suas consequências na perda das propriedades
mecânicas. Neste trabalho é apresentado um estudo comparativo da extensão do dano em
função da geometria de ferramenta utilizada. Para tal as placas foram radiografadas após
furação e a imagem resultante segmentada para medição das áreas associadas. Os
resultados mostram a importância de uma adequada geometria de ferramenta na redução do
dano causado pela furação em compósitos laminados
Studies of lignin and polysaccharides recovery from kraft liquor for biotechnological applications
According to the biorefinery concept, this study has the objective of evaluating alternatives for
the valorization of all the kraft liquor fractions. This liquor consists mainly in lignin, cellulose and
hemicellulose. Currently, cellulose pulp industries recover the cooking chemicals by burning and
energy is introduced into the process. Sustainable development guidelines, regarding the costs
and wastes reduction and biotechnology principles may present new solutions for the production
of valuable products.
In this study, two methods for the polysaccharides extraction, in three different pH conditions,
are presented. The only difference between these methods is the solvent applied: ethanol and
1,4‐dioxane. All the samples were maintained 24 h at 298 K. After a filtration step, the solid
fraction resultant from the ethanol treatment had a carbohydrate content of 40.51%, 44.64% and
49.53%, for pH values of 3, 4 and 6, respectively. The treatment with 1,4‐dioxane, reached the
following values: 21.17%, 18.41% and 29.73% for the same pH values. These results were
obtained with HPLC analysis after polysaccharides hydrolysis. Three unknown peaks were
detected that we considered to be sugar derivative compounds. Thus, the polysaccharides
contents, for both treatments, might actually be superior.
Concerning to the product purity, the ethanol extraction revealed to be the less efficient. The
lignin content in the solid fraction, ranged between 28% and 31%, with 1,4‐dioxane extraction,
and between 40% and 50%, with ethanol.
The lignin molecular weight was determined with GPC, after and before liquor pH lowering.
Thereby, for pH 6, pH 4 and pH 3 the obtained MWs were: 2376 Da, 1477 Da and 3705 Da,
respectively. The molecular weight increase may be due to the lignin repolymerization. These
results suggest that the polysaccharides recovery and lignin molecular weight may be related. As
the molecular weight increases or decreases, the polysaccharides percentage presents the same
behavior, regardless of the product purity. The data obtained after FT‐IR analysis suggested that
there was no significant modifications on lignin structure.
Summarizing, these preliminary results indicate that there is a possibility of recovering the kraft
liquor´s polysaccharide while the residual lignin can still be used for burning to energy recovery.Erasmus Mundus ‐ ISAC ProgramFundação para a Ciência e a Tecnologia (FCT)Millipore BrazilConselho Nacional de Desenvolvimento Científico e Tecnológico Brazil - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CNPq‐CAPES
Tool geometry evaluation for carbon reinforced composite laminates
The use of composite laminates in complex structures has increased significantly.
However, there are still some issues when considering their use, mainly related with
machining, leading to some difficulties and lack of acceptance. In this work, a
methodology to evaluate drill geometry and feed rate based on thrust force and
delamination extension is presented
Avaliação de ferramentas na furação de laminados compósitos
Drilling of polymeric matrix composite structuresThe development of cutting tools becomes a challenge to the industry of composite materials to obtain high
quality holes, minimizing damage. This work aims to examine the influence of various parameters such as feed rate and tool
geometry on thrust forces developed during drilling operations and on the extent of damage.
In this work, a comparative study of tool geometry with the aim of reducing the associated damage during drilling process
is presented. In the end a good combination of tool geometry and drilling parameters based on experimental work will be
presented.O desenvolvimento de ferramentas de corte torna-se um desafio à indústria de materiais compósitos, na obtenção
de furos de elevada qualidade, minimizando o dano. Este trabalho visa analisar a influência de vários parâmetros, tais como
o avanço e a geometria de ferramenta, nas forças desenvolvidas durante a furação e na extensão do dano.
Neste artigo é apresentado um estudo comparativo de geometrias de broca com o objectivo de reduzir o dano associado à
furação, que permitirá determinar qual a melhor selecção de parâmetros de furação, atendendo às diferentes geometrias de
ferramenta
Integration of particles of different sizes in a hydrothermal process for the pre-treatment of agro-industrial residues such as wheat straw
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