7,257 research outputs found
On the Intrinsic Locality Properties of Web Reference Streams
There has been considerable work done in the study of Web reference streams: sequences of requests for Web objects. In particular, many studies have looked at the locality properties of such streams, because of the impact of locality on the design and performance of caching and prefetching systems. However, a general framework for understanding why reference streams exhibit given locality properties has not yet emerged.
In this work we take a first step in this direction, based on viewing the Web as a set of reference streams that are transformed by Web components (clients, servers, and intermediaries). We propose a graph-based framework for describing this collection of streams and components. We identify three basic stream transformations that occur at nodes of the graph: aggregation, disaggregation and filtering, and we show how these transformations can be used to abstract the effects of different Web components on their associated reference streams. This view allows a structured approach to the analysis of why reference streams show given properties at different points in the Web.
Applying this approach to the study of locality requires good metrics for locality. These metrics must meet three criteria: 1) they must accurately capture temporal locality; 2) they must be independent of trace artifacts such as trace length; and 3) they must not involve manual procedures or model-based assumptions. We describe two metrics meeting these criteria that each capture a different kind of temporal locality in reference streams. The popularity component of temporal locality is captured by entropy, while the correlation component is captured by interreference coefficient of variation. We argue that these metrics are more natural and more useful than previously proposed metrics for temporal locality.
We use this framework to analyze a diverse set of Web reference traces. We find that this framework can shed light on how and why locality properties vary across different locations in the Web topology. For example, we find that filtering and aggregation have opposing effects on the popularity component of the temporal locality, which helps to explain why multilevel caching can be effective in the Web. Furthermore, we find that all transformations tend to diminish the correlation component of temporal locality, which has implications for the utility of different cache replacement policies at different points in the Web.National Science Foundation (ANI-9986397, ANI-0095988); CNPq-Brazi
Price linkages in pharmaceutical markets
A Work Project, presented as part of the requirements for the Award of a Masters Degree in Economics from the NOVA – School of Business and EconomicsThis paper studies the existing price linkage between generics and branded pharmaceuticals, in which the generic price must be a fraction of the latter. Using a vertical differentiation model, we look at the market equilibrium, the effects on the incentives for the brand producer to develop new products, and the possibility of predation by the brand producer over the generic firm. We find that the price linkage increases prices compared to no indexation and it may increase the incentives for the brand producer to expand its set of products. When prices are freely set, the branded firm may also want to expand a new product with a higher quality, but will prefer to remove the original one from the market. Predation may equally occur in both schemes but the price linkage may give fewer incentives for the branded firm to predate while compensating losses with a new drug
Optimization of wastewater quality in the Sines refinery
In order to address and resolve the wastewater contamination problem of the Sines refinery with the main objective of optimizing the quality of this stream and reducing the costs charged to the refinery, a dynamic mass balance was developed nd implemented for ammonia and polar oil and grease (O&G) contamination in the wastewater circuit.
The inadequate routing of sour gas from the sour water stripping unit and the kerosene caustic washing unit, were identified respectively as the major source of ammonia and polar substances present in the industrial wastewater effluent. For the O&G content, a predictive model was developed for the kerosene caustic washing unit, following the Projection to Latent Structures (PLS) approach. Comparison between analytical data for ammonia and polar O&G concentrations in refinery wastewater originating from the Dissolved Air Flotation (DAF) effluent and the model predictions of the dynamic mass balance calculations are in a very good agreement and highlights the dominant impact of the identified streams for the wastewater contamination levels. The ammonia contamination problem was solved by rerouting the sour gas through
an existing clogged line with ammonia salts due to a non-insulated line section, while for the O&G a dynamic mass balance was implemented as an online tool, which allows for prevision of possible contamination situations and taking the required preventive actions, and can also serve as a basis for establishing relationships between the O&G contamination in the refinery wastewater with the properties of the refined crude oils and the process operating conditions.
The PLS model developed could be of great asset in both optimizing the existing and designing new refinery wastewater treatment units or reuse schemes. In order to find a possible treatment solution for the spent caustic problem, an on-site pilot plant experiments for NaOH recovery from the refinery kerosene caustic washing unit effluent using an alkaline-resistant nanofiltration (NF) polymeric membrane were performed in order to evaluate its applicability for treating these highly alkaline and contaminated streams. For a constant operating pressure and temperature and adequate operating conditions, 99.9% of oil and grease rejection and 97.7% of chemical oxygen demand (COD) rejection were observed. No noticeable membrane fouling or flux decrease were registered until a volume concentration factor of 3. These
results allow for NF permeate reuse instead of fresh caustic and for significant reduction of the wastewater contamination, which can result in savings of 1.5 M€ per year at the current prices for the largest Portuguese oil refinery. The capital investments needed for implementation of the required NF membrane system are less than 10% of those associated with the traditional wet air oxidation solution of the spent caustic problem. The operating costs are very similar, but can be less than half if reusing the NF concentrate in refinery pH control applications. The payback period was estimated to be 1.1 years. Overall, the pilot plant experimental results obtained and the process economic evaluation data indicate a very competitive solution through the proposed NF treatment process, which represents a highly promising alternative to
conventional and existing spent caustic treatment units
Ondas acopladas a convecção na região de África equatorial
Mestrado em Meteorologia e Oceanografia FísicaO clima da região da África equatorial é caracterizado por algumas das tempestades mais intensas associadas a convecção profunda. Esta convecção, na maior parte das vezes, deve-se a perturbações no campo do vento que se
propagam para Leste ou para Oeste com velocidades típicas. Estas perturbações podem ser estudadas através do modelo de águas pouco profundas, conforme sugerido por Matsuno (1966), facto que vem sendo comprovado por diversos estudos com base em dados observados.
Existem poucas publicações sobre as características de propagação de Sistemas Convectivos de Mesoescala (SCM) na região da África Equatorial. Porém, alguns dos estudos disponíveis revelaram que parte desses SCM é controlada por Ondas Equatoriais. Neste trabalho são analisados alguns dos aspectos dessas ondas,
que estarão associados à formação e propagação de SCM que afectam a região.
O período seleccionado para estudo inclui os meses de Março, Abril e Maio de 2012. Com base em dados simulados pelo Modelo WFR e dados OLR (Outgoing Longwave Radiation) das reanálises Era-Interim, identificaram-se eventos SCM e, através da análise da energia das ondas equatoriais e do campo da divergência da circulação projectada sobre essas ondas, foi possível identificar alguns eventos sugestivos da existência de acoplamento entre ondas equatoriais e sistemas convectivos. Identificaram-se eventos propagando-se para Oeste em associação
com ondas de Rossby-gravíticas mistas e ondas gravítico-inerciais. No período entre 10 e 15 de Abril, observou-se a propagação para Leste de um sistema convectivo de larga escala, acoplado a ondas de Kelvin.The climate of Africa Equatorial is characterized by some of the more intense storms associated with deep convection. This convection is most often due to disturbances in the wind field that propagates eastward or westward with typical speeds. These disturbances can be studied by the shallow water model, as suggested by Matsuno (1966), a fact that has been proven by several studies based on observed data.
There are few publications on the propagation characteristics of Mesoscale Convective Systems (MCS) in the Africa Equatorial region. However, some of the existent studies have shown that some of the MCS are controlled by Equatorial Waves. In this study, some aspects of these waves, which are associated with the formation and propagation of MCS affecting the region Equatorial Africa are analysed. The period selected for this study
involves the months of March, April and May 2012. Based on the data simulated by the WRF (Weather Research and Forecast) model, and on the OLR (Outgoing Longwave Radiation) of reanalysis ERA-Interim, it was possible to identify MCS events. By analysing the energy of equatorial waves and the divergence of the flow field projected on these waves, it was possible to identify some events suggesting the existence of equatorial waves coupled to the convection systems. The identified events include westward propagating SCMs associated with mixed Rossby-gravity waves and with westward propagating inertial gravity waves. It was also possible to identify a large-scale convection system propagating eastwards coupled with Kelvin waves in de period from 10 to 15 April
Metodologias para projeto mecânico ótimo de estruturas espaciais obtidas por fabrico aditivo
Additive Layer Manufacturing (ALM) is growing rapidly due to the unprecedented
design freedom. Thus, the structures' complexity can be drastically
increased without significant raises in costs. However, the economic viability
of ALM is strongly dependent on the full exploration of the referred
design freedom. In fact, the ALM is only cost-effective in highly customized
parts. Moreover, the mechanical behavior of materials processed via ALM
is an ongoing challenge due to defects, uncertainties in material characterization,
and verification methods. Thus, the goal of the present work is the
development of a robust methodology for the mechanical optimum design
of metallic space structures obtained from additive manufacturing. Thus,
two main tasks were established.
The first task is related to the mechanical characterization of a Ti6Al4V
alloy, processed via Selective Laser Melting (SLM). Therefore, an experimental
testing campaign of Ti6Al4V samples is presented using homogeneous
macroscopic testing (tensile, compression, density, hardness, and
fatigue) and microscopic testing (defects detection via microcomputed tomography).
These samples show better static properties than the other
counterparts, obtained by traditional manufacturing processes. However,
the repeatability of the SLM samples is still a challenge (particularly in its
fatigue behavior) and more testing is needed. Furthermore, these campaigns
are expensive and, consequently, more information per test is required. With
the development of full-field measurement methods, material model calibration
strategies call upon the use of heterogeneous testing specimens. In the
scope of this work, an indirect TO methodology is presented, being capable
of designing a wide range of different heterogeneous specimens. Then, a
stress states performance indicator is also presented to help the selection of
the most promising geometry.
The second task is related to the definition of the engineering cycle for
ALM structures in its mains phases: (i) design for ALM, (ii) bridging between
Topology Optimization (TO) and ALM, (iii) process simulation and
structural verification, and (iv) manufacturing. Concerning the first phase,
ALM provides great geometric freedom however, there are some design limitations.
Therefore, a systematic design methodology is presented, being
based on a topology optimization algorithm capable of incorporating the
main ALM design limitations (minimum member size and overhang angle).
Furthermore, the non-trivial task of bridging between TO and the final
smooth geometry is also studied (second phase). The referred task uses a
Laplacian smoothing algorithm, which is based on the new concept of mutable
diffusion. This new concept shows better properties than the classic
algorithms, giving promising results. Furthermore, a new volume constraint
is presented, which exhibits a less detrimental impact on the chosen structural indicators. Regarding the remaining phases, these were analyzed via
industrial case studies. For instance, process simulation can provide crucial
insight into the optimum manufacturing direction and might dictate the
difference between success and failure upon manufacturing.
The impact of this Ph.D. is related with some improvements in (i) the
characterization of ALM-produced materials as well as the geometry of the
specimens used for their characterization; and in (ii) the engineering cycle
of ALM structures, allowing higher efficiency in the structural solutions for
the space industry with lower costs.O uso do fabrico aditivo por camadas está a crescer a um elevado ritmo
devido À elevada liberdade de projeto de estruturas. Assim, a complexidade
das estruturas pode ser aumentada significativamente sem incrementos significativos nos custos. Todavia, a viabilidade económica do fabrico aditivo
por camadas é fortemente dependente de uma exploração inteligente da
liberdade de projeto estrutural. Na verdade, o fabrico aditivo por camadas
só é rentável em peças de elevada complexidade e valor acrescentado. Adicionalmente,
o comportamento mecânico de materiais processados através
do fabrico aditivo por camadas é ainda um desafio por resolver devido à
existência de defeitos, incertezas na caracterização de materiais e nos seus
métodos de velicação. Deste modo, o objetivo deste trabalho é o desenvolvimento
de uma metodologia robusta que permita o projeto mecânico
ótimo de estruturas obtidas por fabrico aditivo para a indústria espacial.
Para isso, foram estabelecidas duas tarefas principais.
A primeira tarefa está relacionada com a caracterização mecânica da liga
Ti6Al4V, processada através da fusão seletiva a laser. Portanto, foi realizado
uma campanha de testes experimentais com provetes da liga Ti6Al4V
composta por testes macroscópicos homogéneos (tração, compressão, densidade,
dureza e fadiga) e testes microscópicos (deteção de defeitos usando
uma análise com recurso à tomografia microcomputorizada). Foi
verificado que estas amostras exibem melhor propriedades estáticas que
amostras idênticas produzidas através de processos tradicionais. Contudo,
a sua repetibilidade ainda é um desafio (particularmente o comportamento
à fadiga), sendo necessário mais testes. Adicionalmente, estas campanhas
experimentais são onerosas e, consequentemente, é crítico obter mais informação por cada teste realizado. Dado o desenvolvimento dos métodos de
medição full-field, as estratégias de calibração de modelos de material propiciam
o uso de provetes heterogéneos em testes mecânicos. No ^âmbito deste
trabalho apresenta-se uma metodologia de otimização topológica indireta
capaz de projetar uma grande variedade de provetes heterógenos. Posteriormente
apresenta-se um indicador de desempenho baseado na quantidade
de estados de tensão para selecionar o provete mais promissor.
A segunda tarefa está relacionada com a definição do ciclo de engenharia
para o fabrico aditivo por camadas de estruturas metálicas nas suas fases
principais: (i) projeto para fabrico aditivo por camadas, (ii) transição entre
a otimização topológica e o fabrico aditivo por camadas, (iii) simulação do
seu processo de fabrico e sua verificação estrutural e (iv) fabrico. Relativamente
à primeira fase, o fabrico aditivo por camadas proporciona uma
grande liberdade geométrica, contudo existe limitações ao design. Portanto
é apresentada uma metodologia de projeto sistemática, baseada num algoritmo
de otimização topológica capaz de incorporar as principais limitações
de projeto do fabrico aditivo por camadas tais como a espessura mínima
e ângulo do material sem suporte. Adicionalmente, a tarefa complexa de
efetuar a transição entre os resultados da otimização topológica e uma
geometria final suave também é objeto de estudo. A tarefa anteriormente
referida baseia-se na suavização Laplaciana que por sua vez se baseia no
novo conceito de difusão mutável. Este novo conceito apresenta melhores
e mais promissores resultados que os algoritmos clássicos. Adicionalmente,
é apresentado uma nova restrição de volume que proporciona um menor
impacto nos indicadores estruturais escolhidos. Relativamente às restantes
fases, estas são analisadas através de casos de estudo industriais. A título
exemplar, a simulação do processo de fabrico pode fornecer informações
crucias para a escolha da direção de fabrico que, por sua vez, pode ditar a
diferença entre o sucesso ou o insucesso durante o fabrico.
O impacto deste trabalho está relacionado com melhorias na (i) caracterização de materiais produzidos através de fabrico aditivo por camadas assim
como nas geometrias de provetes usados durante a sua caracterização e no
(ii) ciclo de projeto em engenharia de estruturas obtidas através do fabrico
aditivo por camadas, permitindo soluções estruturais com maior eficiência
e menor custo para indústria espacial.Programa Doutoral em Engenharia Mecânic
What Internal and External consequences to expect?
UID/CPO/04627/2013publishersversionpublishe
Training to practice: Importance of Self-Care Theory in Nursing Process for improving care
Em 1991, Dorothea Orem definiu o
autocuidado na sua Teoria do Défice do
Autocuidado de Enfermagem. Assim, para a
teórica, autocuidado “é o desempenho ou a
prática de actividades que os indivíduos realizam
em seu benefício para manter a vida, a saúde e
o bem-estar.” Este autocuidado é universal por
abranger todos os aspectos vivenciais, não se
restringindo às actividades de vida diária e às
instrumentais. Orem desenvolveu o seu projecto
em três teorias inter-relacionadas, que são: a
Teoria do Autocuidado, que descreve o porquê e
como as pessoas cuidam de si próprias; a Teoria
do Défice de Autocuidado, que descreve e
explica a razão pela qual as pessoas podem ser
ajudadas através da enfermagem; e a Teoria dos
Sistemas de Enfermagem, que descreve e
explica as relações que têm de ser criadas e
mantidas para que se produza enfermagem
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