Variation-aware high-level DSP circuit design optimisation framework for FPGAs

The constant technology shrinking and the increasing demand for systems that operate under different power profiles with the maximum performance, have motivated the work in this thesis. Modern design tools that target FPGA devices take a conservative approach in the estimation of the maximum performance that can be achieved by a design when it is placed on a device, accounting for any variability in the fabrication process of the device. The work presented here takes a new view on the performance improvement of DSP designs by pushing them into the error-prone regime, as defined by the synthesis tools, and by investigating methodologies that reduce the impact of timing errors at the output of the system. In this work two novel error reduction techniques are proposed to address this problem. One is based on reduced-precision redundancy and the other on an error optimisation framework that uses information from a prior characterisation of the device. The first one is a generic architecture that is appended to existing arithmetic operators. The second defines the high-level parameters of the algorithm without using extra resources. Both of these methods allow to achieve graceful degradation whilst variation increases. A comparison of the new methods is laid against the existing methodologies, and conclusions drawn on the tradeoffs between their cost, in terms of resources and errors, and their benefits in terms of throughput. In some cases it is possible to double the performance of the design while still producing valid results.Open Acces

BIOLIF: Artrodese lombar intersomática - abordagem não instrumentada

Tese de doutoramento em MedicinaSpinal fusion (SF) is a surgical procedure conducted to promote bone growth in-between spinal segments, supported by fixation hardware, and complemented by bone graft or bone substitute. There are recognized risks and complications associated with instrumentation, such as damage to surrounding tissues, neurological deficits, material failure or migration and non-union. In this thesis, a novel approach is proposed based on the development of an adhesive, biodegradable and injectable foam, with the purpose to avoid instrumentation in SF. Carbon dioxide foaming was explored as processing methodology to generate, within physiologically compatible conditions, polycaprolactone (PCL) foams with morphological characteristics equivalent to those found in trabecular bone. A three-dimensional, mechanically stable and bioactive composite of PCL+βTCP+Dexamethasone was foamed at 45ºC and 5 MPa. This optimized PCL processing opened the possibility for creating a porous foam, delivered directly into the intervertebral space through a surgical tool designed and built for this purpose. The adhesive properties of PCL were further improved through modification with polydopamine (pDA) and polymethacrylic acid (pMAA). After tensile testing, PCL pDA pMAA material–bone interface remained intact at both ends (adhesivity significantly superior to non-modified PCL, p<0.05). Further in vitro assays confirmed the formulation as non-cytotoxic and bioactive (calcium phosphate (CaP) layer formation). Lastly, the surgical feasibility of PCL pDA pMAA foaming and its biological performance for non instrumented spinal fusion were assessed in a 6-month survival study using an interbody fusion porcine model. Segmental instrumented arthrodesis was used as control group. Minimally invasive in situ foaming of PCL pDA pMAA (BIOLIF) was technically achieved, leading to reduced surgical time (p<0.05) as compared to instrumentation. Animals in BIOLIF approach demonstrated no surgical complications and a higher mobility (p<0.05) at immediate post-op. Spinal fusion was determined by a set of assessments including: i) bone volume/ tissue volume percentage (BV/TV), superior in BIOLIF group (p<0.05); ii) reduced range of motion and increased stiffness of the treated spinal segment, equivalent in both groups; and iii) a relatively well-organized newly formed osseous structure identified by histological analysis at BIOLIF samples. As conclusion, the results obtained in this work could open a new perspective for lumbar instrumentation-free spinal fusion using biologic solutions.A artrodese da coluna vertebral é um procedimento cirúrgico que visa a indução de crescimento ósseo entre segmentos vertebrais, utilizando sistemas de fixação e suplementação com enxerto ósseo ou substituto sintético. São reconhecidos riscos e complicações associados à instrumentação, incluindo, danos nos tecidos circundantes, compromisso neurológico, risco de mobilização ou migração do material e pseudartrose. Nesta tese, é proposta uma nova abordagem, baseada no desenvolvimento de uma espuma adesiva, biodegradável e injetável, de forma de realizar artrodese intersomática lombar sem recurso a instrumentação. A tecnologia supercrítica/subcrítica foi explorada para a produção de uma espuma de policaprolactona (PCL), em condições fisiologicamente compatíveis, com características morfológicas equivalentes às encontradas no osso trabecular. Foi possível obter a 45ºC e 5 MPa, uma estrutura tridimensional de PCL+βTCP+Dexametasona mecanicamente estável e com propriedades bioativas. Estas condições tornaram possível a extrusão da espuma diretamente no espaço intersomático, através de um instrumento cirúrgico desenvolvido para esse efeito. As propriedades adesivas do PCL foram otimizadas através da modificação do polímero com polidopamina (pDA) e ácido polimetacrílico (pMAA), que se demonstrou significativamente mais adesivo do que o PCL p<0,05 em ensaios mecânicos de tração. As propriedades citocompatíveis e bioativas da formulação foram confirmadas em ensaios in vitro. Por fim, a exequibilidade cirúrgica da extrusão da espuma de PCL pDA pMAA, e o seu desempenho biológico, foram avaliados num estudo de sobrevida de 6 meses usando o porco doméstico como modelo animal. Como grupo de controlo foi realizada artrodese intersomática instrumentada. Foi tecnicamente possível efetuar extrusão in situ de PCL pDA pMAA (BIOLIF) por via minimamente invasiva, sendo o tempo de procedimento cirúrgico significativamente inferior (p<0,05) ao grupo da instrumentação. Os animais do grupo BIOLIF não demonstraram complicações cirúrgicas e apresentaram uma maior mobilidade (p<0,05) no pós-operatório imediato. A qualidade da artrodese foi avaliada por um conjunto de parâmetros: i) a relação volume ósseo/ volume total (BV/TV), superior no grupo BIOLIF (p<0,05); ii) a redução da amplitude de movimento e o aumento da rigidez do segmento vertebral intervencionado, equivalente em ambos os grupos; e iii) uma estrutura óssea recém-formada relativamente bem-organizada no grupo BIOLIF, identificada por análise histológica. Em conclusão, os resultados obtidos neste trabalho podem abrir uma nova perspectiva para a utilização de soluções biológicas como forma de realizar artrodese intersomática lombar sem recurso a instrumentação.Portuguese Foundation for Science and Technology (FCT) - projects UIDB/50026/2020 and UIDP/50026/2020

A wave of change: labor market and social security impacts of the EU refugee inflow

The recent massive inflow of refugees to the European Union (EU) raises a number of unanswered questions on the economic impact of this phenomenon. To examine these questions, we constructed an overlapping-generations model that describes the evolution of the skill premium and of the welfare benefit level in relevant European countries, in the aftermath of an inflow of asylum-seekers. In our simulation, relative wages of skilled workers increase between 8% and 11% in the period of the inflow; their subsequent time path is dependent on the initial skill premium. The entry of migrants creates a fiscal surplus of about 8%, which can finance higher welfare benefits in the subsequent periods. These effects are weaker in a scenario where refugees do not fully integrate into the labor market