Task-based occupational exposure assessment and particle number concentration: two important data resources to perform risk assessment for occupational exposure to particles

Environment monitoring has an important role in occupational exposure assessment. However, due to several factors is done with insufficient frequency and normally don��t give the necessary information to choose the most adequate safety measures to avoid or control exposure. Identifying all the tasks developed in each workplace and conducting a task-based exposure assessment help to refine the exposure characterization and reduce assessment errors. A task-based assessment can provide also a better evaluation of exposure variability, instead of assessing personal exposures using continuous 8-hour time weighted average measurements. Health effects related with exposure to particles have mainly been investigated with mass-measuring instruments or gravimetric analysis. However, more recently, there are some studies that support that size distribution and particle number concentration may have advantages over particle mass concentration for assessing the health effects of airborne particles. Several exposure assessments were performed in different occupational settings (bakery, grill house, cork industry and horse stable) and were applied these two resources: task-based exposure assessment and particle number concentration by size. The results showed interesting results: task-based approach applied permitted to identify the tasks with higher exposure to the smaller particles (0.3 ��m) in the different occupational settings. The data obtained allow more concrete and effective risk assessment and the identification of priorities for safety investments.

Improving a Cluster Based Directional Channel Model in Realistic Macro-Cell Environment

In this paper a realistic directional channel model that is an extension of the COST 273 channel model is presented. The model uses a cluster of scatterers and visibility region generation based strategy with increased realism, due to the introduction of terrain and clutter information. New approaches for path-loss prediction and line of sight modeling are considered, affecting the cluster path gain model implementation. The new model was implemented using terrain, clutter, street and user mobility information for the city of Lisbon, Portugal. Some of the model's outputs are presented, mainly path loss and small/large-scale fading statistics.

Phototransistor with nanocrystalline Si/amorphous Si bilayer channel

We report a field-effect phototransistor with a channel comprising a thin nanocrystalline silicon transport layer and a thicker hydrogenated amorphous silicon absorption layer. The semiconductor and dielectric layers were deposited by radio-frequency plasma enhanced chemical vapor deposition. The phototransistor with channel length of 24 microns and photosensitive area of 1.4 mm(2) shows an off-current of about 1 pA, and high photoconductive gain in the subthreshold region. Measurements of the quantum efficiency at different incident light intensities and biasing conditions, along with spectral-response characteristics, and threshold voltage stability characterization demonstrate the feasibility of the phototransistor for low light level detection.

Implementa����o de WDM com dispositivos semicondutores

Este trabalho utiliza uma estrutura pin empilhada, baseada numa liga de siliceto de carbono amorfo hidrogenado (a-Si:H e/ou a-SiC:H), que funciona como filtro ��ptico na zona vis��vel do espectro electromagn��tico. Pretende-se utilizar este dispositivo para realizar a demultiplexagem de sinais ��pticos e desenvolver um algoritmo que permita fazer o reconhecimento aut��nomo do sinal transmitido em cada canal. O objectivo desta tese visa implementar um algoritmo que permita o reconhecimento aut��nomo da informa����o transmitida por cada canal atrav��s da leitura da fotocorrente fornecida pelo dispositivo. O tema deste trabalho resulta das conclus��es de trabalhos anteriores, em que este dispositivo e outros de configura����o id��ntica foram analisados, de forma a explorar a sua utiliza����o na implementa����o da tecnologia WDM. Neste trabalho foram utilizados tr��s canais de transmiss��o (Azul ��� 470 nm, Verde ��� 525 nm e Vermelho ��� 626 nm) e v��rios tipos de radia����o de fundo. Foram realizadas medidas da resposta espectral e da resposta temporal da fotocorrente do dispositivo, em diferentes condi����es experimentais. Variou-se o comprimento de onda do canal e o comprimento de onda do fundo aplicado, mantendo-se constante a intensidade do canal e a frequ��ncia de transmiss��o. Os resultados obtidos permitiram aferir sobre a influ��ncia da presen��a da radia����o de fundo e da tens��o aplicada ao dispositivo, usando diferentes sequ��ncias de dados transmitidos nos v��rios canais. Verificou-se, que sob polariza����o inversa, a radia����o de fundo vermelho amplifica os valores de fotocorrente do canal azul e a radia����o de fundo azul amplifica o canal vermelho e verde. Para polariza����o directa, apenas a radia����o de fundo azul amplifica os valores de fotocorrente do canal vermelho. Enquanto para ambas as polariza����es, a radia����o de fundo verde, n��o tem uma grande influ��ncia nos restantes canais. Foram implementados dois algoritmos para proceder ao reconhecimento da informa����o de cada canal. Na primeira abordagem usou-se a informa����o contida nas medidas de fotocorrente geradas pelo dispositivo sob polariza����o inversa e directa. Pela compara����o das duas medidas desenvolveu-se e testou-se um algoritmo que permite o reconhecimento dos canais individuais. Numa segunda abordagem procedeu-se ao reconhecimento da informa����o de cada canal mas com aplica����o de radia����o de fundo, tendo-se usado a informa����o contida nas medidas de fotocorrente geradas pelo dispositivo sob polariza����o inversa sem aplica����o de radia����o de fundo com a informa����o contida nas medidas de fotocorrente geradas pelo dispositivo sob polariza����o inversa com aplica����o de radia����o de fundo. Pela compara����o destas duas medidas desenvolveu-se e testou-se o segundo algoritmo que permite o reconhecimento dos canais individuais com base na aplica����o de radia����o de fundo.

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.

Capacitive effects in pinpin photodiodes

The application of a-SiC:H/a-Si:H pinpin photodiodes for optoelectronic applications as a WDM demultiplexer device has been demonstrated useful in optical communications that use the WDM technique to encode multiple signals in the visible light range. This is required in short range optical communication applications, where for costs reasons the link is provided by Plastic Optical Fibers. Characterization of these devices has shown the presence of large photocapacitive effects. By superimposing background illumination to the pulsed channel the device behaves as a filter, producing signal attenuation, or as an amplifier, producing signal gain, depending on the channel/background wavelength combination. We present here results, obtained by numerical simulations, about the internal electric configuration of a-SiC:H/a-Si:H pinpin photodiode. These results address the explanation of the device functioning in the frequency domain to a wavelength tunable photo-capacitance due to the accumulation of space charge localized at the bottom diode that, according to the Shockley-Read-Hall model, it is mainly due to defect trapping. Experimental result about measurement of the photodiode capacitance under different conditions of illumination and applied bias will be also presented. The combination of these analyses permits the description of a wavelength controlled photo-capacitance that combined with the series and parallel resistance of the diodes may result in the explicit definition of cut off frequencies for frequency capacitive filters activated by the light background or an oscillatory resonance of photogenerated carriers between the two diodes. (C) 2013 Elsevier B.V. All rights reserved.

Caracteriza����o bidimensional de um canal r��dio Wimax

Com o crescimento previs��vel e exponencial das redes de comunica����es m��veis motivado pela mobilidade, flexibilidade e tamb��m comodidade do utilizador levam a que este se torne na fatia mais importante do mundo das telecomunica����es dos dias que correm. Assim �� importante estudar e caracterizar canais r��dio para as mais diversas gamas de frequ��ncias utilizadas nas mais variadas tecnologias. O objectivo principal desta disserta����o de Mestrado �� caracterizar um canal r��dio para a tecnologia sem fios Worldwide Inter-operability for Microwave Access (Wimax para as frequ��ncias de 3,5 GHz e 5 GHz) actualmente vista pela comunidade cient��fica como a tecnologia sem fios com maiores perspectivas de sucesso. Para tal, determinaram-se o Perfil de Atraso de Pot��ncia (PAP) e tamb��m a Pot��ncia em Fun����o da Dist��ncia (PFD) recorrendo ao m��todo computacional de simula����o Finite-Difference Time-Domain (FDTD). De forma a estudar e caracterizar o canal r��dio, em termos de desvanecimento relativo ao espalhamento de atraso, usaram-se dois m��todos alternativos que t��m como entrada o PAP. Para caracterizar o canal quanto ao desvanecimento baseado em espalhamento de Doppler, recorreu-se tamb��m a duas t��cnicas alternativas tendo como entrada o PFD. Em ambas as situa����es os dois m��todos alternativos convergiram para os mesmos resultados. A caracteriza����o �� feita em dois cen��rios diferentes: um em que consideramos que a maioria dos obst��culos s��o condutores el��ctricos perfeitos (CEP) e que passaremos a designar Cen��rio PEC, e um segundo cen��rio em que os obst��culos t��m propriedades electromagn��ticas diferentes, e que passar�� a ser designado por Cen��rio MIX. Em ambos os cen��rios de an��lise concluiu-se que o canal �� plano, lento e sem ISI.

Sistema WDM de 4 canais

Trabalho Final de Mestrado para obten����o do grau de Mestre em Engenharia de Electr��nica e Telecomunica����es

SiC pinpin photonic for linking the visible spectrum to the telecom gap

Expanding far beyond traditional applications at telecommunications wavelengths, the SiC photonic devices has recently proven its merits for working with visible range optical signals. Reconfigurable wavelength selectors are essential sub-systems for implementing reconfigurable WDM networks and optical signal processing. Visible range to telecom band spectral translation in SiC/Si can be accomplished using wavelength selector under appropriated optical bias, acting as reconfigurable active filters. In this paper we present a monolithically integrated wavelength selector based on a multilayer SiC/Si integrated optical filters that requires optical switches to select wavelengths. The selector filter is realized by using double pin/pin a-SiC:H photodetector with front and back biased optical gating elements. Red, green, blue and violet communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analyzed by reading out the generated photocurrent, under different background wavelengths applied either from the front or the back side. The backgrounds acts as channel selectors that selects one or more channels by splitting portions of the input multi-channel optical signals across the front and back photodiodes. The transfer characteristics effects due to changes in steady state light, irradiation side and frequency are presented. The relationship between the optical inputs and the digital output levels is established. (C) 2014 Elsevier B.V. All rights reserved.

Optical nonlinearity in Tandem SI-C photodetectors

The behavior of tandem pin heterojunctions based on a-SiC: H alloys is investigated under different optical and electrical bias conditions. The devices are optimized to act as optically selective wavelength filters. Depending on the device configuration (optical gaps, thickness, sequence of cells in the stack structure) and on the applied voltage (positive or negative) and optical bias (wavelength, intensity, frequency) it is possible to combine the wavelength discrimination function with the self amplification of the signal. This wavelength nonlinearity allows the amplification or the rejection of a weak signal-impulse. The device works as an active tunable optical filter for wavelength selection and can be used as an add/drop multiplexer (ADM) which enables data to enter and leave an optical network bit stream without having to demultiplex the stream. Results show that, even under weak transient input signals, the background wavelength controls the output signal. This nonlinearity, due to the transient asymmetrical light penetration of the input channels across the device together with the modification on the electrical field profile due to the optical bias, allows tuning an input channel without demultiplexing the stream. This high optical nonlinearity makes the optimized devices attractive for the amplification of all optical signals. Transfer characteristics effects due to changes in steady state light, control d.c. voltage and applied light pulses are presented. Based on the experimental results and device configuration an optoelectronic model is developed. The transfer characteristics effects due to changes in steady state light, dc control voltage or applied light pulses are simulated and compared with the experimental data. A good agreement was achieved.

The impact of the 2008 and 2010 financial crises on international stock markets : contagion and long memory

Nesta tese estudamos os efeitos de cont��gio financeiro e de mem��ria longa causados pelas crises financeiras de 2008 e 2010 em alguns mercados acionistas internacionais. A tese �� composta por tr��s ensaios interligados. No Ensaio 1, recorremos �� teoria das c��pulas para testar a exist��ncia de cont��gio e revelar os canais ���investor induced��� de transmiss��o da crise de 2008 aos mercados da B��lgica, Fran��a, Holanda e Portugal (grupo NYSE Euronext). Conclu��mos que existe cont��gio nestes mercados, que o canal ���portfolio rebalancing��� �� o mecanismo mais importante de transmiss��o da crise, e que o fen��meno ���flight to quality��� est�� presente nos mercados. No Ensaio 2, usando novamente modelos de c��pulas, avaliamos os efeitos de cont��gio provocados pelo mercado acionista grego nos mercados do grupo NYSE Euronext, no contexto da crise de 2010. Os resultados obtidos sugerem que durante a crise de 2010 apenas o mercado portugu��s foi objeto de cont��gio; al��m disso, conclui-se que os efeitos de cont��gio provocados pela crise de 2008 s��o claramente superiores aos efeitos provocados pela crise de 2010. No Ensaio 3, abordamos o tema da mem��ria longa atrav��s do estudo do expoente de Hurst dos mercados acionistas da B��lgica, E.U.A., Fran��a, Gr��cia, Holanda, Jap��o, Reino Unido e Portugal. Verificamos que as propriedades de mem��ria longa dos mercados foram afetadas pelas crises, especialmente a de 2008 ��� que aumentou a mem��ria longa dos mercados e tornou-os mais persistentes. Finalmente, usando c��pulas mais uma vez, verificamos que as crises provocaram, em geral, um aumento na correla����o entre os expoentes de Hurst locais dos mercados foco das crises (E.U.A. e Gr��cia) e os expoentes de Hurst locais dos outros mercados da amostra, sugerindo que o expoente de Hurst pode ser utilizado para detetar efeitos de cont��gio financeiro. Em s��ntese, os resultados desta tese sugerem que comparativamente com per��odos de acalmia, os per��odos de crises financeiras tendem a provocar inefici��ncia nos mercados acionistas e a conduzi-los na dire����o da persist��ncia e do cont��gio financeiro.

Distributed controllers modeling through Petri nets with multi-asynchronous-channels

This paper proposes the concept of multi-asynchronous-channel for Petri nets. Petri nets extended with multi-asynchronous-channels and time-domains support the specification of distributed controllers, where each controller has a synchronous execution but the global system is asynchronous (globally-asynchronous locally-synchronous systems). Each multi-asynchronous-channel specify the interaction between two or more distributed controllers. These channels, together with the time-domain concept, ensure the creation of network-independent models to support implementations using heterogeneous communication networks. The created models support not only the systems documentation but also their validation and implementation through simulation tools, verification tools, and automatic code generators. An application example illustrates the use of a Petri net class extended with the proposed channels. �� 2015 IEEE.