A-level Mathematics Options – Views of Secondary-level Teachers

The A-level Mathematics qualification is based on a compulsory set of pure maths modules and a selection of applied maths modules with the pure maths representing two thirds of the assessment. The applied maths section includes mechanics, statistics and (sometimes) decision maths. A combination of mechanics and statistics tends to be the most popular choice by far. The current study aims to understand how maths teachers in secondary education make decisions regarding the curriculum options and offers useful insight to those currently designing the new A-level specifications.

Semi-structured interviews were conducted with A-level maths teachers representing 27 grammar schools across Northern Ireland. Teachers were generally in agreement regarding the importance of pure maths and the balance between pure and applied within the A-level maths curriculum. A wide variety of opinions existed concerning the applied options. While many believe that the basic mechanics-statistics (M1-S1) combination is most accessible, it was also noted that the M1-M2 combination fits neatly alongside A-level physics. Lack of resources, timetabling constraints and competition with other subjects in the curriculum hinder uptake of A-level Further Maths.

Teachers are very conscious of the need to obtain high grades to benefit both their pupils and the school’s reputation. The move to a linear assessment system in England while Northern Ireland retains the modular system is likely to cause some schools to review their choice of exam board although there is disagreement as to whether a modular or linear system is more advantageous for pupils. The upcoming change in the specification offers an opportunity to refresh the assessment also and reduce the number of leading questions. However, teachers note that there are serious issues with GCSE maths and these have implications for A-level.

The structure of an unconventional HD-GYP protein from Bdellovibrio reveals the roles of conserved residues in this class of cyclic-di-GMP phosphodiesterases

UNLABELLED: Cyclic-di-GMP is a near-ubiquitous bacterial second messenger that is important in localized signal transmission during the control of various processes, including virulence and switching between planktonic and biofilm-based lifestyles. Cyclic-di-GMP is synthesized by GGDEF diguanylate cyclases and hydrolyzed by EAL or HD-GYP phosphodiesterases, with each functional domain often appended to distinct sensory modules. HD-GYP domain proteins have resisted structural analysis, but here we present the first structural representative of this family (1.28 Å), obtained using the unusual Bd1817 HD-GYP protein from the predatory bacterium Bdellovibrio bacteriovorus. Bd1817 lacks the active-site tyrosine present in most HD-GYP family members yet remains an excellent model of their features, sharing 48% sequence similarity with the archetype RpfG. The protein structure is highly modular and thus provides a basis for delineating domain boundaries in other stimulus-dependent homologues. Conserved residues in the HD-GYP family cluster around a binuclear metal center, which is observed complexed to a molecule of phosphate, providing information on the mode of hydroxide ion attack on substrate. The fold and active site of the HD-GYP domain are different from those of EAL proteins, and restricted access to the active-site cleft is indicative of a different mode of activity regulation. The region encompassing the GYP motif has a novel conformation and is surface exposed and available for complexation with binding partners, including GGDEF proteins.

IMPORTANCE: It is becoming apparent that many bacteria use the signaling molecule cyclic-di-GMP to regulate a variety of processes, most notably, transitions between motility and sessility. Importantly, this regulation is central to several traits implicated in chronic disease (adhesion, biofilm formation, and virulence gene expression). The mechanisms of cyclic-di-GMP synthesis via GGDEF enzymes and hydrolysis via EAL enzymes have been suggested by the analysis of several crystal structures, but no information has been available to date for the unrelated HD-GYP class of hydrolases. Here we present the multidomain structure of an unusual member of the HD-GYP family from the predatory bacterium Bdellovibrio bacteriovorus and detail the features that distinguish it from the wider structural family of general HD fold hydrolases. The structure reveals how a binuclear iron center is formed from several conserved residues and provides a basis for understanding HD-GYP family sequence requirements for c-di-GMP hydrolysis.

Integrative analysis of chemo-transcriptomic profiles for drug-feature specific gene expression signatures

One of the major challenges in systems biology is to understand the complex responses of a biological system to external perturbations or internal signalling depending on its biological conditions. Genome-wide transcriptomic profiling of cellular systems under various chemical perturbations allows the manifestation of certain features of the chemicals through their transcriptomic expression profiles. The insights obtained may help to establish the connections between human diseases, associated genes and therapeutic drugs. The main objective of this study was to systematically analyse cellular gene expression data under various drug treatments to elucidate drug-feature specific transcriptomic signatures. We first extracted drug-related information (drug features) from the collected textual description of DrugBank entries using text-mining techniques. A novel statistical method employing orthogonal least square learning was proposed to obtain drug-feature-specific signatures by integrating gene expression with DrugBank data. To obtain robust signatures from noisy input datasets, a stringent ensemble approach was applied with the combination of three techniques: resampling, leave-one-out cross validation, and aggregation. The validation experiments showed that the proposed method has the capacity of extracting biologically meaningful drug-feature-specific gene expression signatures. It was also shown that most of signature genes are connected with common hub genes by regulatory network analysis. The common hub genes were further shown to be related to general drug metabolism by Gene Ontology analysis. Each set of genes has relatively few interactions with other sets, indicating the modular nature of each signature and its drug-feature-specificity. Based on Gene Ontology analysis, we also found that each set of drug feature (DF)-specific genes were indeed enriched in biological processes related to the drug feature. The results of these experiments demonstrated the pot- ntial of the method for predicting certain features of new drugs using their transcriptomic profiles, providing a useful methodological framework and a valuable resource for drug development and characterization.

Of no fixed form: The Irish Pavilion at Venice 2014 and beyond

This paper explores the theme of exhibiting architectural research through a particular example, the development of the Irish pavilion for the 14th architectural biennale, Venice 2014. Responding to Rem Koolhaas’s call to investigate the international absorption of modernity, the Irish pavilion became a research project that engaged with the development of the architectures of infrastructure in Ireland in the twentieth and twenty-first centuries. Central to this proposition was that infrastructure is simultaneously a technological and cultural construct, one that for Ireland occupied a critical position in the building of a new, independent post-colonial nation state, after 1921.

Presupposing infrastructure as consisting of both visible and invisible networks, the idea of a matrix become a central conceptual and visual tool in the curatorial and design process for the exhibition and pavilion. To begin with this was a two-dimensional grid used to identify and order what became described as a series of ten ‘infrastructural episodes’. These were determined chronologically across the decades between 1914 and 2014 and their spatial manifestations articulated in terms of scale: micro, meso and macro. At this point ten academics were approached as researchers. Their purpose was twofold, to establish the broader narratives around which the infrastructures developed and to scrutinise relevant archives for compelling visual material. Defining the meso scale as that of the building, the media unearthed was further filtered and edited according to a range of categories – filmic/image, territory, building detail, and model – which sought to communicate the relationship between the pieces of architecture and the larger systems to which they connect. New drawings realised by the design team further iterated these relationships, filling in gaps in the narrative by providing composite, strategic or detailed drawings.

Conceived as an open-ended and extendable matrix, the pavilion was influenced by a series of academic writings, curatorial practices, artworks and other installations including: Frederick Kiesler’s City of Space (1925), Eduardo Persico and Marcello Nizzoli’s Medaglio d’Oro room (1934), Sol Le Witt’s Incomplete Open Cubes (1974) and Rosalind Krauss’s seminal text ‘Grids’ (1979). A modular frame whose structural bays would each hold and present an ‘episode’, the pavilion became both a visual analogue of the unseen networks embodying infrastructural systems and a reflection on the predominance of framed structures within the buildings exhibited. Sharing the aspiration of adaptability of many of these schemes, its white-painted timber components are connected by easily-dismantled steel fixings. These and its modularity allow the structure to be both taken down and re-erected subsequently in different iterations. The pavilion itself is, therefore, imagined as essentially provisional and – as with infrastructure – as having no fixed form. Presenting archives and other material over time, the transparent nature of the space allowed these to overlap visually conveying the nested nature of infrastructural production. Pursuing a means to evoke the qualities of infrastructural space while conveying a historical narrative, the exhibition’s termination in the present is designed to provoke in the visitor, a perceptual extension of the matrix to engage with the future.

Extreme Loads on an Oscillating Wave Surge Converter

A major difficulty in the design of full scale Wave Energy Converters is the need to design for two conflicting design criteria. In one instance devices must be designed to couple heavily to the incident wave force resulting in the efficient extraction of energy in small sea states, however devices must also be capable of withstanding the harsh conditions encountered during extreme seas. This paper presents an initial investigation of the extreme wave loading of a generic, surface-piercing, pitching flap-type device deployed in near shore wave conditions. Slamming of the flap is selected as the extreme load event for further investigation and the experimental methodologies employed are described. Preliminary results showing both local and global loading under such events are presented for the case of a flap tested in a 3-dimensional environment. Results are presented which show flap slamming effects on the pressures experienced on the front face of the flap.

Parker Morris and the Fordist House

6.00 pm. If people like watching T.V. while they are eating their evening meal, space for a low table is needed (Ministry of Housing and Local Government, Space in the Home, 1963, p. 4).

This paper re-examines the 1961 Parker Morris report on housing standards in Britain. It explores the origins, scope, text and iconography of the report and suggests that these not only express a particularly modernist conception of space but one which presupposed very specific economic conditions and geographies.

Also known as Homes for Today and Tomorrow Parker Morris attempted, through the application of scientific principles, to define the minimum living space standards needed to accommodate household activities. But while early modernist research into notions of existenzminimum were the work of avant-garde architects and thinkers, Homes for Today and Tomorrow and its sister design manual Space in the Home were commissioned by the British State. This normalization of scientific enquiry into space can be considered not only as a response to new conditions in the mass production of housing – economies of scale, prefabrication, system-building and modular coordination – but also to the post-war boom in consumer goods. In this, it is suggested that the domestic interior was assigned a key role as a privileged site of mass consumption as the production and micro-management of space in Britain became integral to the development of a planned national economy underpinned by Fordist principles. Parker Morris, therefore, sought to accommodate activities which were pre-determined not so much by traditional social or familial ties but rather by recently introduced commodities such as the television set, white goods, table tennis tables and train sets. This relationship between the domestic interior and the national economy are emblematized by the series of placeless and scale-less diagrams executed by Gordon Cullen in Space in the Home. Here, walls dissolve as space flows from inside to outside in a homogenized and ephemeral landscape whose limits are perhaps only the boundaries of the nation state and the circuits of capital.

In Britain, Parker Morris was the last explicit State-sponsored attempt to prescribe a normative spatial programme for national living. The calm neutral efficiency of family-life expressed in its diagrams was almost immediately problematised by the rise of 1960s counter-culture, the feminist movement and the oil crisis of 1972 which altered perhaps forever the spatial, temporal and economic conditions it had taken for granted. The debate on space-standards, however, continues.

Preoperative characteristics and compliance with follow-up after trabeculectomy surgery in rural southern China

Purpose: To evaluate preoperative characteristics and follow-up in rural China after trabeculectomy, the primary treatment for glaucoma there. Methods: Patients undergoing trabeculectomy at 14 rural hospitals in Guangdong and Guangxi Provinces and their doctors completed questionnaires concerning clinical and sociodemographic information, transportation, and knowledge and attitudes about glaucoma. Follow-up after surgery was assessed as cumulative score (1 week: 10 points, 2 weeks: 7 points, 1 month: 5 points). Results Among 212 eligible patients, mean preoperative presenting acuity in the operative eye was 6/120, with 61.3% (n=130) blind (≤6/60). Follow-up rates were 60.8% (129/212), 75.9% (161/212) and 26.9% (57/212) at 1 week, 2 weeks and 1 month, respectively. Patient predictors of poor follow-up included elementary education or less (OR=0.37, 95% CI 0.20 to 0.70, p=0.002), believing follow-up was not important (OR=0.62, 95% CI 0.41 to 0.94, p=0.02), lack of an accompanying person (OR=0.14, 95% CI 0.07 to 0.29, p<0.001), family annual income <US$800 (OR=0.28, 95% CI 0.11 to 0.72, p=0.008) and not requiring removal of scleral flap sutures postoperatively (OR=0.11, 95% CI 0.06 to 0.22, p<0.001). Age, sex, employment, travel distance/time/costs, patient preoperative clinical factors and physician factors were unassociated with follow-up. Conclusions: Follow-up after 2 weeks was inadequate to provide optimal clinical care, and surgery is being applied too late to avoid blindness in the majority of patients. Earlier surgery, support for return visits and better explanations of the importance of follow-up are needed. Directing all patients to return for possible scleral flap suture removal may be a valid strategy to improve follow-up.

Computerized key of the genus genus Laimaphelenchus Fuchs, 1937

The Order Aphelenchida contains several genera of economic importance, namely Aphelenchoides and Bursaphelenchus. Nematode species belonging to these 2 genera frequently co-habit with other genera such as Laimaphelenchus. It is therefore important to clearly distinguish them, as well as understand the group´s biodiversity. A computerized, or e-key, for the genus Laimaphelenchus Fuchs has been developed in the BiKey Identification system (Dianov & Lobanov, 1996-2004). The e-key includes 14 species and 34 characters (from 2 to 6 character states each). It also includes the built-in algorithm ranging characters according their diagnostic values to minimize the number of the diagnosis steps (average number of steps is 2.7; values are re-calculated at each step). The most important characters (as calculated by BiKey) are: length of posterior branch of the female genital system; excretory pore position; vulval anterior flap shape; number pairs of mail tale papillae; male bursa shape (ventral view); number of tail tip setae in female; female tail tip stub shape; presence of mucro on tail tip in male. Key is pictorial (image-operating), multientry, as other BiKey products.

Bursaphelenchus antoniae sp. n. (Nematoda: Parasitaphelenchidae) associated with Hylobius sp. from Pinus pinaster in Portugal

Bursaphelenchus antoniae sp. n. is described and illustrated. Dauer juveniles were isolated from the body of the large pine weevil, Hylobius sp., collected from maritime pine (Pinus pinaster) stumps, in Portugal. Bursaphelenchus antoniae sp. n. was reared and maintained in P. pinaster wood segments and on Petri dish cultures of the fungi Botrytis cinerea and Monilinia fructicola. The new species is characterised by a relatively small body length of ca 583 μm (females) and 578 μm (males), a lateral field with two incisures, presence of a small vulval flap and a conoid female tail with a rounded or pointed terminus. Males have stout spicules with a disc-like cucullus and seven caudal papillae arranged as a single midventral precloacal papilla, one precloacal pair and two postcloacal pairs. In the character of the lateral field, B. antoniae sp. n. comes close to B. abietinus, B. rainulfi and B. hylobianum, whilst spicule characters place it within the piniperdae-group sensu Ryss et al. Morphologically, B. antoniae sp. n. is closest to B. hylobianum; the spicules of these two species having flattened, wing-like, alae on the distal third of the lamina. Bursaphelenchus antoniae sp. n. is distinguished from B. hylobianum on the arrangement of the caudal papillae (two vs three pairs). ITS-RFLP profiles and the failure to hybridise support the separation of the two species. Phylogenetic analysis of the new species, based on the 18S rDNA sequence, supports the inclusion of this new species in the B. hylobianum-group sensu Braasch. Sequence analysis of the 28S rDNA D2/D3 domain did not place the new species in a definite group.

Bursaphelenchus Fuchs, 1937 (Nematoda: Parasitaphelenchidae) species associated with Pinus species in northern Turkey

A survey for Bursaphelenchus nematodes, associated with different conifer trees, was conducted in several forest areas in the northern regions of Turkey. Only pine trees (Pinus nigra, P. pinaster and P. sylvestris) yielded Bursaphelenchus specimens. Nematodes were identified using several morphological diagnostic characters of the genus (male spicule structure, number of lateral incisures, number and distribution of the male papillae, presence of female vulval flap), and confirmed by using RFLP analysis of the internal transcriber spacer (ITS) regions of ribosomal DNA. Three different species were identified from several sampled areas, namely B. mucronatus, B. pinophilus and B. sexdentati, representing a first report of the last two species for Turkey. The association of B. pinophilus with black pine (P. nigra) is herein reported for the first time.

Progress in the use of scanning electron microscopy (SEM) applied to the taxonomy of the genus Bursaphelenchus (Nematoda: Parasitaphelenchidae)

The scanning electron microscope (SEM) has been a major tool in detailed morphological observations of plant parasitic nematodes during the last 30 years, efficiently complementing light microscopical (LM) studies. Nematodes are extremely difficult to observe and characterize due to their small size (aprox. 1 mm long) and paucity of morphological characters, so detailed surface observations of several organs and nematode regions are of the highest value. Among plant parasitic nematodes, one of the most devastating species is the “pinewood nematode” (PWN), Bursaphelenchus xylophilus, which has been a major problem for forest species, and in particular pines, in Asia (Japan, China, Korea) and has been recently detected in the European Union (Portugal). B. xylophilus belongs to a closely related, morphologically similar group of species, within the genus Bursaphelenchus, and designated by the “xylophilus group”. SEM has become a crucial tool in observing several genital characters of males and females, such as male genital papillae, male copulatory spicules, female vulval flap and female genital papillae.s In this presentation, we will show how SEM has been utilized to observe and characterize the shape of the vulval flap, the presence/ absence of papillae near the flap, and confirm the presence and the arrangement of the male genital papillae. LM is also used in this work to show its value as a complementary tool to SEM, in both genital characteristics and other, general, characters of the genus Bursaphelenchus, such as the male bursa and cephalic region.

On lattices from combinatorial game theory modularity and a representation theorem: Finite case

We show that a self-generated set of combinatorial games, S, may not be hereditarily closed but, strong self-generation and hereditary closure are equivalent in the universe of short games. In [13], the question “Is there a set which will give an on-distributive but modular lattice?” appears. A useful necessary condition for the existence of a finite non-distributive modular L(S) is proved. We show the existence of S such that L(S) is modular and not distributive, exhibiting the first known example. More, we prove a Representation Theorem with Games that allows the generation of all finite lattices in game context. Finally, a computational tool for drawing lattices of games is presented.

Endocrine disruption in the terrestrial isopod porcellio scaber

Nas últimas décadas tem-se assistido a uma preocupação crescente relativamente às possíveis consequências da exposição a compostosxenóbioticos capazes de modular ou causar disrupção do sistema endócrino, os denominados Compostos Disruptores Endócrinos (CDEs). A maioria dos estudos efectuados tem-se centrado principalmente nos efeitos dos CDEs em vertebrados, enquanto que os seus efeitos em invertebrados têmsido negligenciados, embora este grupo represente mais de 95% de todas asespécies animais. Isópodes como o Porcellio scaber, combinam características associadas às mudas e aos processos reprodutivos mediados por mecanismos endócrinosconhecidos com um modo de vida terrestre, tornando-os potenciais espécies sentinela para estudos de disrupção endócrina (DE) em ambientes terrestres. Neste estudo, isópodes machos adultos, machos e fêmeas juvenis e casais foram expostos a concentrações crescentes dedois CDEs, vinclozolina (Vz) e bisfenol A (BPA). Testou-se a hipótese nula que a Vz e o BPA não interferem com o desenvolvimento e reprodução deste isópode terrestre. Foi investigadaa possível ligação entre os efeitos causados pelos compostos propostos e DE assim como a ligação a outros potenciais mecanismos de toxicidade.Parâmetros como concentração de 20-hidroxiecdisona (20E), muda, crescimento, rácios sexuais ediversos parâmetros reprodutivos foram estudados. Adicionalmente, de modo a estudar os alvos moleculares destes tóxicos, analisou-se a expressão proteica do intestino, hepatopâncreas e testículos do isópode após exposição aos químicos. Os resultados demonstram que a Vz e o BPA estimulam o aumento dos níveis de 20E de um modo dependente da dose. Excepção feita para a concentração mais baixa de BPA testada (10 mg/kg solo), para a qual concentrações significativamente mais altas de 20E foram determinadas, sugerindo a ocorrência dos “efeitos de baixas doses típicos de DE” já demonstrados por outros autores. O BPA também distorceu o rácio sexual favorecendo asfêmeas na concentração mais baixa. A mortalidade devido à ecdise incompleta foi relacionada com o hiper-ecdisonismo nas concentrações mais elevadas de Vz. Mais ainda, a Vz tende a atrasar a muda e o BPA a induzi-la. Não obstante, ambos os compostos provocam toxicidade no desenvolvimento,uma vez que foi encontrada uma diminuição generalizada nos parâmetros de crescimento. Os juvenis mostraram ser mais sensíveis à exposição aos tóxicos que os adultos. Estes compostos provocaram ainda toxicidade reprodutiva, com um decréscimo generalizado do “output” reprodutivo. A toxicidadecausada pelos ecdisteróides e o seu papel na síntese de vitelogenina são alguns dos factores chave que poderão influenciar negativamente a reprodução.A Vz e o BPA afectaram a expressão de proteínas envolvidas nometabolismo energético e induziram várias respostas de stress. Interferiram ainda com proteínas intimamente ligadas com o sucesso reprodutivo. Conclui-se assim,que ambos os CDEs propostos provocam toxicidade nodesenvolvimento e na reprodução de P. scaber, tendo sido evidenciada umaligação a DE. Alvos moleculares de natureza não-endócrina foram também revelados, através da expressão diferencial de algumas proteínaspreviamente descritas para invertebrados aquáticos e mesmo alguns vertebrados.

Multilayer optimization in radio resource allocation for the packet transmission in wireless networks

Na última década tem-se assistido a um crescimento exponencial das redes de comunicações sem fios, nomeadamente no que se refere a taxa de penetração do serviço prestado e na implementação de novas infra-estruturas em todo o globo. É ponto assente neste momento que esta tendência irá não só continuar como se fortalecer devido à convergência que é esperada entre as redes móveis sem fio e a disponibilização de serviços de banda larga para a rede Internet fixa, numa evolução para um paradigma de uma arquitectura integrada e baseada em serviços e aplicações IP. Por este motivo, as comunicações móveis sem fios irão ter um papel fundamental no desenvolvimento da sociedade de informação a médio e longo prazos. A estratégia seguida no projecto e implementação das redes móveis celulares da actual geração (2G e 3G) foi a da estratificação da sua arquitectura protocolar numa estrutura modular em camadas estanques, onde cada camada do modelo é responsável pela implementação de um conjunto de funcionalidades. Neste modelo a comunicação dá-se apenas entre camadas adjacentes através de primitivas de comunicação pré-estabelecidas. Este modelo de arquitectura resulta numa mais fácil implementação e introdução de novas funcionalidades na rede. Entretanto, o facto das camadas inferiores do modelo protocolar não utilizarem informação disponibilizada pelas camadas superiores, e vice-versa acarreta uma degradação no desempenho do sistema. Este paradigma é particularmente importante quando sistemas de antenas múltiplas são implementados (sistemas MIMO). Sistemas de antenas múltiplas introduzem um grau adicional de liberdade no que respeita a atribuição de recursos rádio: o domínio espacial. Contrariamente a atribuição de recursos no domínio do tempo e da frequência, no domínio espacial os recursos rádio mapeados no domínio espacial não podem ser assumidos como sendo completamente ortogonais, devido a interferência resultante do facto de vários terminais transmitirem no mesmo canal e/ou slots temporais mas em feixes espaciais diferentes. Sendo assim, a disponibilidade de informação relativa ao estado dos recursos rádio às camadas superiores do modelo protocolar é de fundamental importância na satisfação dos critérios de qualidade de serviço exigidos. Uma forma eficiente de gestão dos recursos rádio exige a implementação de algoritmos de agendamento de pacotes de baixo grau de complexidade, que definem os níveis de prioridade no acesso a esses recursos por base dos utilizadores com base na informação disponibilizada quer pelas camadas inferiores quer pelas camadas superiores do modelo. Este novo paradigma de comunicação, designado por cross-layer resulta na maximização da capacidade de transporte de dados por parte do canal rádio móvel, bem como a satisfação dos requisitos de qualidade de serviço derivados a partir da camada de aplicação do modelo. Na sua elaboração, procurou-se que o standard IEEE 802.16e, conhecido por Mobile WiMAX respeitasse as especificações associadas aos sistemas móveis celulares de quarta geração. A arquitectura escalonável, o baixo custo de implementação e as elevadas taxas de transmissão de dados resultam num processo de multiplexagem de dados e valores baixos no atraso decorrente da transmissão de pacotes, os quais são atributos fundamentais para a disponibilização de serviços de banda larga. Da mesma forma a comunicação orientada à comutação de pacotes, inenente na camada de acesso ao meio, é totalmente compatível com as exigências em termos da qualidade de serviço dessas aplicações. Sendo assim, o Mobile WiMAX parece satisfazer os requisitos exigentes das redes móveis de quarta geração. Nesta tese procede-se à investigação, projecto e implementação de algoritmos de encaminhamento de pacotes tendo em vista a eficiente gestão do conjunto de recursos rádio nos domínios do tempo, frequência e espacial das redes móveis celulares, tendo como caso prático as redes móveis celulares suportadas no standard IEEE802.16e. Os algoritmos propostos combinam métricas provenientes da camada física bem como os requisitos de qualidade de serviço das camadas superiores, de acordo com a arquitectura de redes baseadas no paradigma do cross-layer. O desempenho desses algoritmos é analisado a partir de simulações efectuadas por um simulador de sistema, numa plataforma que implementa as camadas física e de acesso ao meio do standard IEEE802.16e.

Gestão de qualidade de serviço baseada em políticas

A evolução observada nas redes de comunicações durante a última década traduziu-se na diversificação de serviços que utilizam a rede, no aumento das taxas de transferência e na massificação da utilização de serviços de acesso à Internet e de comunicações celulares. Durante esta década, várias organizações, das quais se destacam os operadores de telecomunicações, têm dedicado consideráveis esforços no sentido de definir e normalizar arquitecturas de redes de próxima geração. A principal característica deste tipo de rede reside no facto de possuir uma arquitectura modular capaz de fornecer serviços multimédia a clientes de uma rede de acesso com características tecnológicas heterogéneas. Os trabalhos de normalização das arquitecturas de rede NGN têm-se limitado, até ao momento, a especificar detalhes relativos ao funcionamento da rede não tendo ainda sido definida a arquitectura de gestão. Em termos de tecnologias de gestão de redes, foram propostos nas últimas duas décadas novos paradigmas de gestão, novos modelos de dados, novos protocolos de transporte e várias linguagens de definição de informação de gestão. Os modelos de dados têm vindo a ser enriquecidos, os protocolos são mais flexíveis e poderosos, as soluções de gestão oferecem interoperabilidade acrescida e as linguagens permitem definir formatos de configuração mais ricos. Simultaneamente tem crescido a complexidade das soluções de gestão, aumentado a sobrecarga causada pelo aumento de complexidade nos equipamentos bem como nas plataformas computacionais que suportam os sistemas de gestão. O presente trabalho propõe uma solução de gestão para redes NGN capaz de gerir os recursos de rede garantindo Qualidade de Serviço. A solução de gestão proposta inclui uma plataforma de execução de políticas que utiliza os eventos ocorridos na rede para empreender acções de configuração, autonomizando o processo de gestão. Inclui uma avaliação da complexidade de várias tecnologias de gestão estudando a sobrecarga causada pela tecnologia tanto no processo de gestão como na operação da rede. É ainda estudada a escalabilidade das várias tecnologias e analisado o seu comportamento num cenário da rede de um operador de telecomunicações. O trabalho propõe ainda uma metodologia de configuração integrada dos elementos de gestão, através de uma interface de configuração amigável para o administrador do sistema.