Surgical correction of scoliosis: Numerical analysis and optimization of the procedure

A previously developed model is used to numerically simulate real clinical cases of the surgical correction of scoliosis. This model consists of one-dimensional finite elements with spatial deformation in which (i) the column is represented by its axis; (ii) the vertebrae are assumed to be rigid; and (iii) the deformability of the column is concentrated in springs that connect the successive rigid elements. The metallic rods used for the surgical correction are modeled by beam elements with linear elastic behavior. To obtain the forces at the connections between the metallic rods and the vertebrae geometrically, non-linear finite element analyses are performed. The tightening sequence determines the magnitude of the forces applied to the patient column, and it is desirable to keep those forces as small as possible. In this study, a Genetic Algorithm optimization is applied to this model in order to determine the sequence that minimizes the corrective forces applied during the surgery. This amounts to find the optimal permutation of integers 1, ... , n, n being the number of vertebrae involved. As such, we are faced with a combinatorial optimization problem isomorph to the Traveling Salesman Problem. The fitness evaluation requires one computing intensive Finite Element Analysis per candidate solution and, thus, a parallel implementation of the Genetic Algorithm is developed.

Solvent effects on solution enthalpies of adamantyl derivatives

Solution enthalpies of 1-bromoadamantane, 1-adamantanol, and 2-adamantanone in a large set of protic and aprotic solvents are reported at 298.15 K. Solvent effects on the solution processes of these solutes are analyzed in terms of a modified TAKA equation, involving delta(cav) h (s) as the cavity term. The nature and magnitude of the major interactions which influence these processes are assessed and discussed in terms of the solutes' characteristics. New insights on the solution processes under scrutiny are presented.

Evaluating Tsunami Impact on the Gulf of Cadiz Coast (Northeast Atlantic).

The Gulf of Cadiz coasts are exposed to tsunamis. Emergency planning tools are now taking into account this fact, especially because a series of historical occurrences were strikingly significant, having left strong evidence behind, in the mareographic records, the geological evidence or simply the memory of the populations. The study area is a strip along the Algarve coast, south Portugal, an area known to have been heavily impacted by the 1 November 1755 event. In this study we use two different tsunami scenarios generated by the rupture of two thrust faults identified in the area, corresponding to 8.1-8.3 magnitude earthquakes. Tsunami propagation and inundation computation is performed using a non-linear shallow water code with bottom friction. Numerical modeling results are presented in terms of flow depth and current velocity with maximum values of 7 m and 8 m/s for inundation depth and flow speed, respectively. These results constitute a valuable tool for local authorities, emergency and decision planners to define the priority zones where tsunami mitigation measures must be implemented and to develop tsunami-resilient communities.

Laser scanned photodiodes (LSPs) for image sensing

An optimized ZnO:Al/a-pin SixC1-x:H/Al configuration for the laser scanned photodiode (LSP) imaging detector is proposed and the read-out parameters improved. The effect of the sensing element structure, cell configuration and light source flux are investigated and correlated with the sensor output characteristics. Data reveals that for sensors with wide band gap doped layers an increase on the image signal optimized to the blue is achieved with a dynamic range of two orders of magnitude, a responsivity of 6 mA W-1 and a sensitivity of 17 muW cm(-2) at 530 nm. The main output characteristics such as image responsivity, resolution, linearity and dynamic range were analyzed under reverse, forward and short circuit modes. The results show that the sensor performance can be optimized in short circuit mode. A trade-off between the scan time and the required resolution is needed since the spot size limits the resolution due to the cross-talk between dark and illuminated regions leading to blurring effects.

New p-i-n Si : H imager configuration for spatial resolution improvement

Amorphous glass/ZnO-Al/p(a-Si:H)/i(a-Si:H)/n(a-Si1-xCx:H)/Al imagers with different n-layer resistivities were produced by plasma enhanced chemical vapour deposition technique (PE-CVD). An image is projected onto the sensing element and leads to spatially confined depletion regions that can be readout by scanning the photodiode with a low-power modulated laser beam. The essence of the scheme is the analog readout, and the absence of semiconductor arrays or electrode potential manipulations to transfer the information coming from the transducer. The influence of the intensity of the optical image projected onto the sensor surface is correlated with the sensor output characteristics (sensitivity, linearity blooming, resolution and signal-to-noise ratio) are analysed for different material compositions (0.5 < x < 1). The results show that the responsivity and the spatial resolution are limited by the conductivity of the doped layers. An enhancement of one order of magnitude in the image intensity signal and on the spatial resolution are achieved at 0.2 mW cm(-2) light flux by decreasing the n-layer conductivity by the same amount. A physical model supported by electrical simulation gives insight into the image-sensing technique used.

Sensor element for a metal-insulator-semiconductor camera system (MISCam)

We discuss the operation of a new type of optical sensor (MISCam) based on a metal-insulator-semiconductor (MIS) structure. The operation principle relies on light-induced changes of the band bending and barrier height at the interface between semiconductor and insulator. An image is obtained from the quenching of the ac signal in analogy to the principle of the laser-scanned photodiode (LSP). Lateral resolution depends on the semiconductor material chosen. We have characterised the MIS structures by C-V, I-V, and spectral response measurements testing different types of insulators like a-Si3N4, SiO2, and AlN. The presence of slow interface charges allows for image memory. Colour sensors can be realised by controlling sign and magnitude of the electric fields in the base and the interface region.

Extreme Value Theory versus traditional GARCH approaches applied to financial data: a comparative evaluation

Although stock prices fluctuate, the variations are relatively small and are frequently assumed to be normal distributed on a large time scale. But sometimes these fluctuations can become determinant, especially when unforeseen large drops in asset prices are observed that could result in huge losses or even in market crashes. The evidence shows that these events happen far more often than would be expected under the generalized assumption of normal distributed financial returns. Thus it is crucial to properly model the distribution tails so as to be able to predict the frequency and magnitude of extreme stock price returns. In this paper we follow the approach suggested by McNeil and Frey (2000) and combine the GARCH-type models with the Extreme Value Theory (EVT) to estimate the tails of three financial index returns DJI,FTSE 100 and NIKKEI 225 representing three important financial areas in the world. Our results indicate that EVT-based conditional quantile estimates are much more accurate than those from conventional AR-GARCH models assuming normal or Student’s t-distribution innovations when doing out-of-sample estimation (within the insample estimation, this is so for the right tail of the distribution of returns).

CVD of CrO(2): Towards a lower temperature deposition process

The deposition of highly oriented a-axis CrO(2) films onto Al(2)O(3)(0001) by atmospheric pressure (AP)CVD at temperatures as low as 330 C is reported. Deposition rates strongly depend on the substrate temperature, whereas for film surface microstructures the dependence is mainly on film thickness. For the experimental conditions used in this work, CrO(2) growth kinetics are dominated by a surface reaction mechanism with an apparent activation energy of (121.0 +/- 4.3) kJ mol(-1). The magnitude and temperature dependence of the saturation magnetization, up to room temperature, is consistent with bulk measurements.

Desvio de posicionamento em radioterapia para patologias de cabeça e pescoço e próstata: revisão de literatura

Introdução – Numa era em que os tratamentos de Radioterapia Externa (RTE) exigem cada vez mais precisão, a utilização de imagem médica permitirá medir, quantificar e avaliar o impacto do erro provocado pela execução do tratamento ou pelos movimentos dos órgãos. Objetivo – Analisar os dados existentes na literatura acerca de desvios de posicionamento (DP) em patologias de cabeça e pescoço (CP) e próstata, medidos com Cone Beam Computed Tomography (CBCT) ou Electronic Portal Image Device (EPID). Metodologia – Para esta revisão da literatura foram pesquisados artigos recorrendo às bases de dados MEDLINE/PubMed e b-on. Foram incluídos artigos que reportassem DP em patologias CP e próstata medidos através de CBCT e EPID. Seguidamente foram aplicados critérios de validação, que permitiram a seleção dos estudos. Resultados – Após a análise de 35 artigos foram incluídos 13 estudos e validados 9 estudos. Para tumores CP, a média (μ) dos DP encontra-se entre 0,0 e 1,2mm, com um desvio padrão (σ) máximo de 1,3mm. Para patologias de próstata observa-se μDP compreendido entre 0,0 e 7,1mm, com σ máximo de 7,5mm. Discussão/Conclusão – Os DP em patologias CP são atribuídos, maioritariamente, aos efeitos secundários da RTE, como mucosite e dor, que afetam a deglutição e conduzem ao emagrecimento, contribuindo para a instabilidade da posição do doente durante o tratamento, aumentando as incertezas de posicionamento. Os movimentos da próstata devem-se principalmente às variações de preenchimento vesical, retal e gás intestinal. O desconhecimento dos DP afeta negativamente a precisão da RTE. É importante detetá-los e quantificá-los para calcular margens adequadas e a magnitude dos erros, aumentando a precisão da administração de RTE, incluindo o aumento da segurança do doente. - ABSTRACT - Background and Purpose – In an era where precision is an increasing necessity in external radiotherapy (RT), modern medical imaging techniques provide means for measuring, quantifying and evaluating the impact of treatment execution and movement error. The aim of this paper is to review the current literature on the quantification of setup deviations (SD) in patients with head and neck (H&N) or prostate tumors, using Cone Beam Computed Tomography (CBCT) or Electronic Portal Image Device (EPID). Methods – According to the study protocol, MEDLINE/PubMed and b-on databases were searched for trials, which were analyzed using selection criteria based on the quality of the articles. Results – After assessment of 35 papers, 13 studies were included in this analysis and nine were authenticated (6 for prostate and 3 for H&N tumors). The SD in the treatment of H&N cancer patients is in the interval of 0.1 to 1.2mm, whereas in prostate cancer this interval is 0.0 to 7.1mm. Discussion – The reproducibility of patient positioning is the biggest barrier for higher precision in RT, which is affected by geometrical uncertainty, positioning errors and inter or intra-fraction organ movement. There are random and systematic errors associated to patient positioning, introduced since the treatment planning phase or through physiological organ movement. Conclusion – The H&N SD are mostly assigned to the Radiotherapy adverse effects, like mucositis and pain, which affect swallowing and decrease secretions, contributing for the instability of patient positioning during RT treatment and increasing positioning uncertainties. Prostate motion is mainly related to the variation in bladder and rectal filling. Ignoring SD affects negatively the accuracy of RT. Therefore, detection and quantification of SD is crucial in order to calculate appropriate margins, the magnitude of error and to improve accuracy in RTE and patient safety.

IOPT Petri Net State Space Generation Algorithm with Maximal-Step Execution Semantics

This paper presents an algorithm to efficiently generate the state-space of systems specified using the IOPT Petri-net modeling formalism. IOPT nets are a non-autonomous Petri-net class, based on Place-Transition nets with an extended set of features designed to allow the rapid prototyping and synthesis of system controllers through an existing hardware-software co-design framework. To obtain coherent and deterministic operation, IOPT nets use a maximal-step execution semantics where, in a single execution step, all enabled transitions will fire simultaneously. This fact increases the resulting state-space complexity and can cause an arc "explosion" effect. Real-world applications, with several million states, will reach a higher order of magnitude number of arcs, leading to the need for high performance state-space generator algorithms. The proposed algorithm applies a compilation approach to read a PNML file containing one IOPT model and automatically generate an optimized C program to calculate the corresponding state-space.

Photodiode with nanocrystalline Si/amorphous Si absorber bilayer

This letter reports a near-ultraviolet/visible/near-infrared n(+)-n-i-delta(i)-p photodiode with an absorber comprising a nanocrystalline silicon n layer and a hydrogenated amorphous silicon i layer. Device modeling reveals that the dominant source of reverse dark current is deep defect states in the n layer, and its magnitude is controlled by the i layer thickness. The photodiode with the 900/400 nm thick n-i layers exhibits a reverse dark current density of 3nA/cm(2) at -1V. Donor concentration and diffusion length of holes in the n layer are estimated from the capacitance-voltage characteristics and from the bias dependence of long-wavelength response, respectively. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3660725]

Distribuição de sinais rádio e vídeo sobre fibra

As comunicações ópticas e as comunicações sem fios têm sofrido uma grande evolução ao longo das últimas décadas. Com o objectivo de juntar as vantagens de cada um dos sistemas surgiu o que se designa por rádio sobre fibra. Este sistema permite centralizar todo o processamento necessário num só local, na estação central, simplificando assim a estação base. Esta simplificação permite reduzir os custos de implementação e torna o sistema menos complexo. Esta dissertação de mestrado tem como objectivo principal estudar e simular um sistema que permite o envio de sinais vídeo e rádio pela fibra óptica para posterior difusão, utilizando o conceito de rádio sobre fibra. Os sinais enviados foram o LTE (Long Term Evolution), o UWB (Ultra WideBand) e o WiMAX (Worldwide Interoperability for Microwave Access). O primeiro disponibiliza o serviço de voz, o segundo disponibiliza o serviço de televisão e o último dá suporte à internet. Estes sinais foram modulados em OFDM (Orthogonal Frequency Division Multiplex), porque, posteriormente, estes sinais vão ser difundidos num ambiente sem fios e este tipo de modulação minimiza o efeito de multipercurso e da interferência intersimbólica. Com este estudo pretende-se verificar qual a viabilidade de um sistema que permite o envio de três sinais distintos simultaneamente (serviço Triple Play). Ao analisar os resultados deste sistema concluiu-se que a sua aplicabilidade pode apresentar algumas limitações, dependendo do tipo de modulação e do tipo de modulador que se utilize. Os moduladores ópticos utilizados foram o MZ (Mach-Zehnder) e o EA (Electro-Absorption). A qualidade do sinal recebido foi analisada com base no valor de EVM (Error Vector Magnitude). O primeiro modulador foi aquele que apresentou mais limitações, pois o desempenho do sistema é comprometido para distâncias superiores a 40 km e para potências de entrada inferiores a 0 dBm. Este tipo de sistema apresenta um EVM mais baixo quando a potência de entrada utilizada está entre 0 e 6 dBm. Se o modulador utilizado for o EA, o sistema apresenta um EVM mais baixo quando se utiliza um índice de modulação entre 20% e 30%, para uma potência de entrada entre 0 e 2 dBm.

Otimização do co-registo metabolismo-morfologia em estudos de PET/CT com 18F-DG de nódulos pulmonares: comparação de dois protocolos - 4D vs CT lento

Mestrado em Medicina Nuclear - Área de especialização: Tomografia por Emissão de Positrões.

Tsunamigenic earthquakes in the Gulf of Cadiz: fault model and recurrence

The Gulf of Cadiz, as part of the Azores-Gibraltar plate boundary, is recognized as a potential source of big earthquakes and tsunamis that may affect the bordering countries, as occurred on 1 November 1755. Preparing for the future, Portugal is establishing a national tsunami warning system in which the threat caused by any large-magnitude earthquake in the area is estimated from a comprehensive database of scenarios. In this paper we summarize the knowledge about the active tectonics in the Gulf of Cadiz and integrate the available seismological information in order to propose the generation model of destructive tsunamis to be applied in tsunami warnings. The fault model derived is then used to estimate the recurrence of large earthquakes using the fault slip rates obtained by Cunha et al. (2012) from thin-sheet neotectonic modelling. Finally we evaluate the consistency of seismicity rates derived from historical and instrumental catalogues with the convergence rates between Eurasia and Nubia given by plate kinematic models.

Optoelectronic Logic Functions Based on Reconfigurable SiC Multilayer Devices

WDM multilayered SiC/Si devices based on a-Si:H and a-SiC:H filter design are approached from a reconfigurable point of view. Results show that the devices, under appropriated optical bias, act as reconfigurable active filters that allow optical switching and optoelectronic logic functions development. Under front violet irradiation the magnitude of the red and green channels are amplified and the blue and violet reduced. Violet back irradiation cuts the red channel, slightly influences the magnitude of the green and blue ones and strongly amplifies de violet channel. This nonlinearity provides the possibility for selective removal of useless wavelengths. Particular attention is given to the amplification coefficient weights, which allow taking into account the wavelength background effects when a band needs to be filtered from a wider range of mixed signals, or when optical active filter gates are used to select and filter input signals to specific output ports in WDM communication systems. A truth table of an encoder that performs 8-to-1 multiplexer (MUX) function is presented.