All-optical processing systems based on semiconductor optical amplifiers

Nesta tese investigam-se e desenvolvem-se dispositivos para processamento integralmente óptico em redes com multiplexagem densa por divisão no comprimento de onda (DWDM). O principal objectivo das redes DWDM é transportar e distribuir um espectro óptico densamente multiplexado com sinais de débito binário ultra elevado, ao longo de centenas ou milhares de quilómetros de fibra óptica. Estes sinais devem ser transportados e encaminhados no domínio óptico de forma transparente, sem conversões óptico-eléctrico-ópticas (OEO), evitando as suas limitações e custos. A tecnologia baseada em amplificadores ópticos de semicondutor (SOA) é promissora graças aos seus efeitos não-lineares ultra-rápidos e eficientes, ao potencial para integração, reduzido consumo de potência e custos. Conversores de comprimento de onda são o elemento óptico básico para aumentar a capacidade da rede e evitar o bloqueio de comprimentos de onda. Neste trabalho, são estudados e analisados experimentalmente métodos para aumentar a largura de banda operacional de conversores de modulação cruzada de ganho (XGM), a fim de permitir a operação do SOA para além das suas limitações físicas. Conversão de um comprimento de onda, e conversão simultânea de múltiplos comprimentos de onda são testadas, usando interferómetros de Mach-Zehnder com SOA. As redes DWDM de alto débito binário requerem formatos de modulação optimizados, com elevada tolerância aos efeitos nefastos da fibra, e reduzida ocupação espectral. Para esse efeito, é vital desenvolver conversores integramente ópticos de formatos de modulação, a fim de permitir a interligação entre as redes já instaladas, que operam com modulação de intensidade, e as redes modernas, que utilizam formatos de modulação avançados. No âmbito deste trabalho é proposto um conversor integralmente óptico de formato entre modulação óptica de banda lateral dupla e modulação óptica de banda lateral residual; este é caracterizado através de simulação e experimentalmente. Adicionalmente, é proposto um conversor para formato de portadora suprimida, através de XGM e modulação cruzada de fase. A interligação entre as redes de transporte com débito binário ultra-elevado e as redes de acesso com débito binário reduzido requer conversão óptica de formato de impulso entre retorno-a-zero (RZ) e não-RZ. São aqui propostas e investigadas duas estruturas distintas: uma baseada em filtragem desalinhada do sinal convertido por XGM; uma segunda utiliza as dinâmicas do laser interno de um SOA com ganho limitado (GC-SOA). Regeneração integralmente óptica é essencial para reduzir os custos das redes. Dois esquemas distintos são utilizados para regeneração: uma estrutura baseada em MZI-SOA, e um método no qual o laser interno de um GC-SOA é modulado com o sinal distorcido a regenerar. A maioria dos esquemas referidos é testada experimentalmente a 40 Gb/s, com potencial para aplicação a débitos binários superiores, demonstrado que os SOA são uma tecnologia basilar para as redes ópticas do futuro.

Teachers’ reflections on non standard students work

One of the tasks of teaching (Ball, Thames, & Phelps, 2008) concerns the work of interpreting student error and evaluating alternative algorithms used by students. Teachers’ abilities to understand nonstandard student work affects their instructional decisions, the explanations they provide in the classroom, the way they guide their students, and how they conduct mathematical discussions. However, their knowledge or their perceptions of the knowledge may not correspond to the actual level of knowledge that will support flexibility and fluency in a mathematics classroom. In this paper, we focus on Norwegian and Portuguese teachers’ reflections when trying to give sense to students’ use of nonstandard subtraction algorithms and of the mathematics imbedded in such. By discussing teachers’ mathematical knowledge associated with these situations and revealed in their reflections, we can perceive the difficulties teachers have in making sense of students’ solutions that differ from those most commonly reached.

Accessing prospective early years’ teachers’ knowledge on fractions in order to design tasks for developing teachers’ MKT

Fractions is perhaps one of the most complex and difficult topics pupils explore in the early years of schooling. Difficulties in learning this topic may have its genesis in the fact that fractions comprise a multifaceted construct (Kieren, 1995) or can be conceived as being grounded in the instructional approaches employed to teach fractions (Behr, Harel, Post & Lesh, 1993). Thus, students’ limited understanding might be related to how their teachers understand and interpret fractions — it’s thus related with teachers’ knowledge and practice. Although there is a generalized agreement on teachers’ role on/for students learning, most research on fractions focus on students, leaving aside teachers’ role (and their knowledge on the topic). Thus, teachers’ training has in certain respects been left behind. We still know little about how teachers’ knowledge on fractions influences students’ broader view of mathematics, and its connection and evolution within and along schooling. Aimed at conceptualize ways of improving teachers’ knowledge, training and practices, it’s of fundamental importance to access the areas of knowledge (here conceived as mathematical knowledge for teaching (MKT) (Ball, Thames & Phelps, 2008) in which (prospective) teachers are more deficitaries.

Identifying the Influence of Channel Morphology on Physical Habitat Availability for Native Fish: Application to the Two-spined Blackfish (Gadopsis bispinosus) in the Cotter River, Australia.

The impact of channel morphology and flow on physical habitat availability for the two-spined blackfish (Gadopsis bispinosus) was assessed in the Cotter River, ACT, Australia. Physical habitat requirements for three life stages were identified based on previous field sampling in the Cotter River. Two sites were selected with contrasting channel morphology: Spur Hole, with a moderate gradient and runs and glides, and Vanity’s Crossing, with a steeper gradient, rapids, and fast-flowing pools. Physical Habitat Simulation System (PHABSIM) was used to simulate the flow v. physical habitat availability relationship for each life stage at both sites. Clear differences were apparent between sites, with Spur Hole characterised by increasing habitat with increasing flow and Vanity’s Crossing showing the opposite relationship. The nature of the channel morphology determined this difference, with Spur Hole characterised by marginal zones becoming inundated at higher flows and providing additional suitable physical habitat as discharge increases. Vanity’s Crossing does not contain similar marginal zones. Further analysis demonstrated that high water velocity was the most important factor limiting physical habitat availability at both sites. This approach demonstrates the importance of channel morphology in determining physical habitat availability and an alternative use of PHABSIM to highlight limiting factors for target species.

A Method For Producing Airborne Pollen Source Inventories: An Example of Ambrosia (Ragweed) on the Pannonian Plain

We present here a simple methodology for calculating species inventories for allergenic pollen that can be used by atmospheric transport models. Ragweed (Ambrosia) species distribution or infection level on the Pannonian Plain has been used as an example of how the methodology can be used. The Pannonian Plain is one of the three main regions in Europe recognized as being polluted by Ambrosia. The methodology relies on spatial variations in annual Ambrosia pollen counts, knowledge on ragweed ecology and detailed land cover information. The results of this analysis showed that some of the highest mean annual ragweed pollen concentrations were witnessed around Kecskemét in central Hungary and Novi Sad in northern Serbia. These areas are also the areas with the highest density of Ambrosia habitats. The resulting inventory can be entered into atmospheric transport models in combination with other components such as a phenological model and a model for daily pollen release, in order to simulate the movement of ragweed pollen from the Pannonian Plain. The methodology is likely to be generally applicable for creating inventories of species distribution of allergenic plants. The main requirement is availability of: detailed land cover information; pollen indexes; a list of the most important habitats; and a region of interest that is mainly influenced by local sources.

Ant genomics sheds light on the molecular regulation of social organization.

Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level.

Henley Bridge blueprints, 1939 [photocopies]

Four pages of photocopied blueprints of the Henley Bridge on the Queen Elizabeth Way in St. Catharines, Ontario. A note below the title indicates the bridge was opened by Her Majesty Queen Elizabeth on June 7, 1939. Three of the pages are part of the same blueprint and can be fit together to recreate the complete blueprint. The remaining page is an incomplete blueprint drawn by William Lyon Somerville, Architect, and dated March 24, 1939.

High-Speed Semiconductor Lasers based on Low-Dimensional Active Materials for Optical Telecommunication

The scope of this work is the fundamental growth, tailoring and characterization of self-organized indium arsenide quantum dots (QDs) and their exploitation as active region for diode lasers emitting in the 1.55 µm range. This wavelength regime is especially interesting for long-haul telecommunications as optical fibers made from silica glass have the lowest optical absorption. Molecular Beam Epitaxy is utilized as fabrication technique for the quantum dots and laser structures. The results presented in this thesis depict the first experimental work for which this reactor was used at the University of Kassel. Most research in the field of self-organized quantum dots has been conducted in the InAs/GaAs material system. It can be seen as the model system of self-organized quantum dots, but is not suitable for the targeted emission wavelength. Light emission from this system at 1.55 µm is hard to accomplish. To stay as close as possible to existing processing technology, the In(AlGa)As/InP (100) material system is deployed. Depending on the epitaxial growth technique and growth parameters this system has the drawback of producing a wide range of nano species besides quantum dots. Best known are the elongated quantum dashes (QDash). Such structures are preferentially formed, if InAs is deposited on InP. This is related to the low lattice-mismatch of 3.2 %, which is less than half of the value in the InAs/GaAs system. The task of creating round-shaped and uniform QDs is rendered more complex considering exchange effects of arsenic and phosphorus as well as anisotropic effects on the surface that do not need to be dealt with in the InAs/GaAs case. While QDash structures haven been studied fundamentally as well as in laser structures, they do not represent the theoretical ideal case of a zero-dimensional material. Creating round-shaped quantum dots on the InP(100) substrate remains a challenging task. Details of the self-organization process are still unknown and the formation of the QDs is not fully understood yet. In the course of the experimental work a novel growth concept was discovered and analyzed that eases the fabrication of QDs. It is based on different crystal growth and ad-atom diffusion processes under supply of different modifications of the arsenic atmosphere in the MBE reactor. The reactor is equipped with special valved cracking effusion cells for arsenic and phosphorus. It represents an all-solid source configuration that does not rely on toxic gas supply. The cracking effusion cell are able to create different species of arsenic and phosphorus. This constitutes the basis of the growth concept. With this method round-shaped QD ensembles with superior optical properties and record-low photoluminescence linewidth were achieved. By systematically varying the growth parameters and working out a detailed analysis of the experimental data a range of parameter values, for which the formation of QDs is favored, was found. A qualitative explanation of the formation characteristics based on the surface migration of In ad-atoms is developed. Such tailored QDs are finally implemented as active region in a self-designed diode laser structure. A basic characterization of the static and temperature-dependent properties was carried out. The QD lasers exceed a reference quantum well laser in terms of inversion conditions and temperature-dependent characteristics. Pulsed output powers of several hundred milli watt were measured at room temperature. In particular, the lasers feature a high modal gain that even allowed cw-emission at room temperature of a processed ridge wave guide device as short as 340 µm with output powers of 17 mW. Modulation experiments performed at the Israel Institute of Technology (Technion) showed a complex behavior of the QDs in the laser cavity. Despite the fact that the laser structure is not fully optimized for a high-speed device, data transmission capabilities of 15 Gb/s combined with low noise were achieved. To the best of the author`s knowledge, this renders the lasers the fastest QD devices operating at 1.55 µm. The thesis starts with an introductory chapter that pronounces the advantages of optical fiber communication in general. Chapter 2 will introduce the fundamental knowledge that is necessary to understand the importance of the active region`s dimensions for the performance of a diode laser. The novel growth concept and its experimental analysis are presented in chapter 3. Chapter 4 finally contains the work on diode lasers.

Factores asociados a infección de fracturas abiertas de extremidades por accidentes de tránsito. Bogotá, 2012-2013

Los traumatismos por accidentes de tránsito, constituyen un problema de salud pública, a nivel mundial. Las lesiones más frecuentes son las fracturas de extremidades (84.3%). Las fracturas tienen un elevado riesgo de presentar infecciones, secuelas e incapacidades permanentes. Objetivo : Determinar si los factores asociados con la patología (lugar de fractura, clasificación de fractura, comorbilidades del paciente) y/o los factores relacionados con la atención médica (uso de profilaxis antibiótica diferente al protocolo institucional, tiempo prolongado para remisión, demoras en manejo quirúrgico) se asocian a mayor probabilidad de presentar infección de fracturas abiertas, en población mayor a 15 años, atendidos por accidente de tránsito, en una clínica de Bogotá de tercer nivel especializada en atención de SOAT, durante el período Octubre de 2012 a Octubre de 2013. Metodología: Estudio de casos y controles no apareado, relación 1:3, conformado por 43 casos (fracturas abiertas infectadas) y 129 controles (fracturas abiertas no infectadas). Resultados: La edad media de los casos fue de 39.42 +/- 16.82 años (med=36 años) y la edad media de los controles fue de 33.15 +/- 11.78 años (med=30 años). El 83.7% de los casos y el 78.3% de los controles corresponden al sexo masculino. Predominaron los accidentes en motocicleta en el 81.4% de los casos y el 86% de los controles. En el análisis bivariado se encuentra que la edad mayor a 50 años (p=0.042), una clasificación de la fractura grado IIIB o IIIC (p=0.02), cumplimiento del protocolo antibiótico institucional según el grado de fractura (p=0.014) y un tiempo mayor a 24 horas desde el momento del accidente al centro especializado en trauma (p=0.035) se asociaron significativamente con infección de la fractura abierta. En el análisis multivariado se encuentra únicamente que la clasificación de la fractura grado IIIB o IIIC se asocia con infección de la fractura OR 2.6 IC95% (1.187 – 5.781) (p=0.017). La duración de hospitalización fue mayor en los casos (32.37+/- 22.92 días, med=26 días) que en los controles (8.81 +/- 7.52 días, med=6 días) (p<0.001). El promedio de lavados quirúrgicos fue mayor en los casos (4.85±4.1, med=4.0) que en el grupo control (1.94±1.26, med=2) (p<0.001). Conclusiones: La infección posterior a una fractura abierta, implica costos elevados de atención con hospitalizaciones prolongadas y mayor frecuencia de intervenciones quirúrgicas como se evidencia en el presente estudio. Se debe fortalecer el sistema de remisión y contra remisión para acortar los tiempos de inicio de manejo especializado de los pacientes con fracturas abiertas. Se debe incentivar dentro de las instituciones, el cumplimiento de protocolos de profilaxis antibiótica según el grado de la fractura para disminuir el riesgo de complicación infecciosa.

Running Climate Models On The NERC Cluster Grid Using G-Rex

Compute grids are used widely in many areas of environmental science, but there has been limited uptake of grid computing by the climate modelling community, partly because the characteristics of many climate models make them difficult to use with popular grid middleware systems. In particular, climate models usually produce large volumes of output data, and running them usually involves complicated workflows implemented as shell scripts. For example, NEMO (Smith et al. 2008) is a state-of-the-art ocean model that is used currently for operational ocean forecasting in France, and will soon be used in the UK for both ocean forecasting and climate modelling. On a typical modern cluster, a particular one year global ocean simulation at 1-degree resolution takes about three hours when running on 40 processors, and produces roughly 20 GB of output as 50000 separate files. 50-year simulations are common, during which the model is resubmitted as a new job after each year. Running NEMO relies on a set of complicated shell scripts and command utilities for data pre-processing and post-processing prior to job resubmission. Grid Remote Execution (G-Rex) is a pure Java grid middleware system that allows scientific applications to be deployed as Web services on remote computer systems, and then launched and controlled as if they are running on the user's own computer. Although G-Rex is general purpose middleware it has two key features that make it particularly suitable for remote execution of climate models: (1) Output from the model is transferred back to the user while the run is in progress to prevent it from accumulating on the remote system and to allow the user to monitor the model; (2) The client component is a command-line program that can easily be incorporated into existing model work-flow scripts. G-Rex has a REST (Fielding, 2000) architectural style, which allows client programs to be very simple and lightweight and allows users to interact with model runs using only a basic HTTP client (such as a Web browser or the curl utility) if they wish. This design also allows for new client interfaces to be developed in other programming languages with relatively little effort. The G-Rex server is a standard Web application that runs inside a servlet container such as Apache Tomcat and is therefore easy to install and maintain by system administrators. G-Rex is employed as the middleware for the NERC1 Cluster Grid, a small grid of HPC2 clusters belonging to collaborating NERC research institutes. Currently the NEMO (Smith et al. 2008) and POLCOMS (Holt et al, 2008) ocean models are installed, and there are plans to install the Hadley Centre’s HadCM3 model for use in the decadal climate prediction project GCEP (Haines et al., 2008). The science projects involving NEMO on the Grid have a particular focus on data assimilation (Smith et al. 2008), a technique that involves constraining model simulations with observations. The POLCOMS model will play an important part in the GCOMS project (Holt et al, 2008), which aims to simulate the world’s coastal oceans. A typical use of G-Rex by a scientist to run a climate model on the NERC Cluster Grid proceeds as follows :(1) The scientist prepares input files on his or her local machine. (2) Using information provided by the Grid’s Ganglia3 monitoring system, the scientist selects an appropriate compute resource. (3) The scientist runs the relevant workflow script on his or her local machine. This is unmodified except that calls to run the model (e.g. with “mpirun”) are simply replaced with calls to "GRexRun" (4) The G-Rex middleware automatically handles the uploading of input files to the remote resource, and the downloading of output files back to the user, including their deletion from the remote system, during the run. (5) The scientist monitors the output files, using familiar analysis and visualization tools on his or her own local machine. G-Rex is well suited to climate modelling because it addresses many of the middleware usability issues that have led to limited uptake of grid computing by climate scientists. It is a lightweight, low-impact and easy-to-install solution that is currently designed for use in relatively small grids such as the NERC Cluster Grid. A current topic of research is the use of G-Rex as an easy-to-use front-end to larger-scale Grid resources such as the UK National Grid service.

Rainfall and runoff water quality of the Pang and Lambourn, tributaries of the River Thames, south-eastern England

The water quality of rainfall and runoff is described for two catchments of two tributaries of the River Thames, the Pang and Lambourn. Rainfall chemistry is variable and concentrations of most determinands decrease with increasing volume of catch probably due to 'wash out' processes. Two rainfall sites have been monitored, one for each catchment. The rainfall site on the Lambourn shows higher chemical concentrations than the one for the Pang which probably reflects higher amounts of local inputs from agricultural activity, Rainfall quality data at a long-term rainfall site on the Pang (UK National Air Quality Archive) shows chemistries similar to that for the Lambourn site. but with some clear differences. Rainfall chemistries show considerable variation on an event-to-event basis. Average water quality concentrations and flow-weighted concentrations as well as fluxes vary across the sites, typically by about 30%. Stream chemistry is much less variable due to the main Source of water coming from aquifer sources of high storage. The relationship between rainfall and runoff chemistry at the catchment outlet is described in terms of the relative proportions of atmospheric and within-catchment sources. Remarkably, in view of the quantity of agricultural and sewage inputs to the streams, the catchments appear to be retaining both P and N.

Effects of dietary fat modification on skeletal muscle fatty acid handling in the metabolic syndrome

Objective: In the metabolic syndrome (MetS), increased fat storage in ‘nonadipose’ tissues such as skeletal muscle may be related to insulin resistance (‘lipid overflow’ hypothesis). The objective of this study was to examine the effects of dietary fat modification on the capacity of skeletal muscle to handle dietary and endogenous fatty acids (FAs). Subjects and Methods: In total, 29 men with the MetS were randomly assigned to one of four diets for 12 weeks: a high-fat saturated fat diet (HSFA, n=6), a high-fat monounsaturated fat diet (HMUFA, n=7) and two low-fat high-complex carbohydrate diets supplemented with (LFHCCn−3, n=8) or without (LFHCC, n=8) 1.24 g per day docosahexaenoic and eicosapentaenoic acid. Fasting and postprandial skeletal muscle FA handling was examined by measuring arteriovenous concentration differences across the forearm muscle. [2H2]-palmitate was infused intravenously to label endogenous triacylglycerol (TAG) and free fatty acids in the circulation and subjects received a high-fat mixed meal (2.6 MJ, 61 energy% fat) containing [U-13C]-palmitate to label chylomicron-TAG. Results: Postprandial circulating TAG concentrations were significantly lower after dietary intervention in the LFHCCn−3 group compared to the HSFA group (ΔiAUC −139±67 vs 167±70 μmol l−1 min−1, P=0.009), together with decreased concentrations of [U-13C]-labeled TAG, representing dietary FA. Fasting TAG clearance across forearm muscle was decreased on the HSFA diet, whereas no differences were observed in postprandial forearm muscle FA handling between diets. Conclusion: Chronic manipulation of dietary fat quantity and quality did not affect forearm muscle FA handling in men with the MetS. Postprandial TAG concentrations decreased on the LFHCCn−3 diet, which could be (partly) explained by lower concentration of dietary FA in the circulation.

Means, motive and opportunity? Disentangling client influence on performance measurement appraisals

This paper investigates the extent to which clients were able to influence performance measurement appraisals during the downturn in commercial property markets that began in the UK during the second half of 2007. The sharp change in market sentiment produced speculation that different client categories were attempting to influence their appraisers in different ways. In particular, it was recognised that the requirement for open-ended funds to meet redemptions gave them strong incentives to ensure that their asset values were marked down to market. Using data supplied by Investment Property Databank, we demonstrate that, indeed, unlisted open ended funds experienced sharper drops in capital values than other fund types in the second half of 2007, after the market turning point. These differences are statistically significant and cannot simply be explained by differences in portfolio composition. Client influence on appraisal forms one possible explanation of the results observed: the different pressures on fund managers resulting in different appraisal outcomes.