João Serra - Academia.edu (original) (raw)
Papers by João Serra
Materials Research Express, 2015
PROPAGAÇÃO DA ENERGIA SÍSMICA 46 47 A caracterização da acção sísmica envolve a estimativa da int... more PROPAGAÇÃO DA ENERGIA SÍSMICA 46 47 A caracterização da acção sísmica envolve a estimativa da intensidade, do conteúdo em
In order to assess hazard seismic scenarios for a region selected sites, seismic deaggregation wa... more In order to assess hazard seismic scenarios for a region selected sites, seismic deaggregation was evaluated applying a mixed model that uses (i) gross source zones to compute b_values and maximum magnitudes and (ii) geographically uniform bins to obtain seismic rates. Results are presented in terms of magnitude and geographical coordinates for the parishes of Lisbon County and surrounding areas. Once obtained the most likely scenarios that can affect the metropolitan region of Lisbon, seismic risk scenario was assessed weighting those scenarios with the geographic distribution of elements at risk in the region. The final risk scenario was the one that conducted to the higher total risk for the region in each considered return period. INTRODUCTION Studies on probabilistic seismic scenarios are important tools for civil protection emergency management and planning. In those studies, for a given region and reference time interval, the main objective is to identify the event, or group ...
RESUMO: São apresentados os aspectos relevantes das análises de riscos em barragens de aterro atr... more RESUMO: São apresentados os aspectos relevantes das análises de riscos em barragens de aterro através da metodologia qualitativa da FMEA. Procede-se à sua aplicação a uma barragem de aterro para a retenção de estéreis mineiros. Apresentam-se em detalhe, para o tapete drenante da barragem, as suas funcionalidades, os seus modos potenciais de rotura, as suas causas iniciadoras e os seus efeitos directos e nos vários elementos constituintes do sistema composto pela barragem e pela sua zona de influência. São ainda referidas as medidas disponíveis em obra para a detecção das causas ou dos modos de rotura e o controlo dos seus efeitos.
Risk analysis has been becoming increasingly important in the design of geotechnical works. Howev... more Risk analysis has been becoming increasingly important in the design of geotechnical works. However, due to the complexity often associated, its practical application is not as widespread as one would like. This paper aims at broader use of risk analysis in the design of urban tunnels and in particular for face stability problems. A simplified and straightforward methodology is suggested to estimate both variables of the risk, i.e. the probability of occurrence of an event and the resulting consequences. The probability of failure is computed with analytical solutions (limit equilibrium and lower bound theory) by means of a Monte Carlo probabilistic approach. The calculations account for geotechnical uncertainties (model and material properties), variability in the tunnel geometry, as well as for the external loads. Based on Poisson’s distribution and on inherent risk tolerance for a given reference length, classes of frequency are proposed. Consequence classes are also proposed bas...
This paper addresses the relevant aspects of risk analysis of embankment dams, through the qualit... more This paper addresses the relevant aspects of risk analysis of embankment dams, through the qualitative method of Failure Mode and Effects Analysis (FMEA). In particular the concepts, principles, assumptions and fundamental rules of FMEA are introduced. It proceeds to its application to a particular tailings dam (the Cerro do Lobo dam). The dam's system, composed with the embankment dam itself and its influence area, is first presented. The system is hierarchically structured into basic components with specific functionalities contributing to the functionality of the system. Next, the potential failures modes of each component are identified, as well as their corresponding root causes and immediate effects. It is evaluated the sequence effects progress through the successive parent subsystems until the final effects over the whole system are reached. Finally, the available measures in the field for detecting the rout cause of the components failure modes and for controlling their sequence of effects are also identified. Although FMEA application in large dam systems is a complex and time consuming process its outcome can be extremely useful. It allows the assessment and management of dam's major risks so that mitigations actions in an early stage can be optimized from the efficiency standpoint.
RESUMO -Neste artigo apresenta-se um enquadramento geral das análises de riscos em Geotecnia, per... more RESUMO -Neste artigo apresenta-se um enquadramento geral das análises de riscos em Geotecnia, perspectivando-se os seus objectivos e os respectivos domínios de aplicação. Referem-se, em pormenor, os seguintes métodos de análise de risco: análise dos modos de rotura e seus efeitos (FMEA) e análise dos modos de rotura, seus efeitos e sua criticalidade (FMECA). Aplicam-se a FMEA e a FMECA a uma barragem de aterro convencional para retenção de rejeitados. A utilização de análises de riscos em Geotecnia permite detectar, ou controlar atempadamente, os eventuais problemas e gerir os riscos, reduzindo-os, tão cedo e tão eficientemente, em termos de custos, quanto possível. Reconhecidas as vantagens das análises de riscos, admite-se que estas possam vir a desempenhar uma função central das actividades desenvolvidas em programas de segurança modernos de obras geotécnicas importantes.
physica status solidi (c), 2014
ABSTRACT An inline optical CVD process operating at low temperature (<873 K) and at atmosp... more ABSTRACT An inline optical CVD process operating at low temperature (<873 K) and at atmospheric pressure is presented here to grow silicon films on top of crystalline, sintered silicon and pressed silicon powder substrates moving at constant speed (>10 mm/min) inside the furnace. Solid silicon substrates were laser textured to reduce the reflectivity, leveraging the growth rates. Laser patterning has a strong influence in the growth rate, reaching values up to 9 µm/min. Using pressed silicon powder substrates, growth rates increase dramatically to 40-90 µm/min. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c), 2014
A lot of research has been done to try to reduce the costs of solar cells by developing ribbon gr... more A lot of research has been done to try to reduce the costs of solar cells by developing ribbon growth techniques that bypass the ingot/wafering step. The SDS-Silicon on Dust Substrate process, here described, is a technique to produce ribbons directly from the gas phase. Test solar cells were fabricated on SDS ribbons as a demonstration of concept of this
IEEE Journal of Photovoltaics, 2014
The SLIM-cut technique provides a way to obtain thin silicon foils without a standard sawing step... more The SLIM-cut technique provides a way to obtain thin silicon foils without a standard sawing step, thus avoiding kerf losses. This process consists of three steps: depositing a stressinducing layer on top of the silicon surface; stress activation by heating and cooling, resulting in crack propagation in the silicon and detachment of a thin silicon layer; and a chemical cleaning to remove the stress-inducing layer. This paper describes a new stress activation method using Ag/Al and epoxy stress-inducing layers. The crack propagation is controlled along the sample length in order to avoid unwanted additional crack formation and interaction with other crack fronts. Silicon foils with thickness ranging between 50 and 130 μm were obtained with effective lifetimes between 1 and 81 μs.
Soil Dynamics and Earthquake Engineering, 2008
In this study, we simulate and compare ground motion shaking in the city of Lisbon and surroundin... more In this study, we simulate and compare ground motion shaking in the city of Lisbon and surrounding counties (metropolitan area of Lisbon (MAL)), using two possible earthquake models: the onshore source area of Lower Tagus Valley, M5.7 and M4.7 and the offshore source area, Marques de Pombal Fault, M7.6, one of the possible source of the 1755 Lisbon earthquake. The stochastic and a new hybrid stochastic-deterministic approach (DSM) are used in order to evaluate the ground shaking and to characterize its spatial variability. Results are presented in terms of response acceleration spectra (PSA) and peak ground acceleration (PGA) with respect to bedrock and surface. Site effects are evaluated by means of equivalent stochastic non-linear one-dimensional ground responses analysis, performed for a set of stratified soil profile units properly designed to cope with the soil site conditions of MAL region. A sensitive study is carried out using different input parameters and different approaches in order to give the basic information to evaluate the range of uncertainty in seismic scenarios. r
Semiconductor Science and Technology, 2010
A new method for boron bulk doping of silicon ribbons is developed. The method is based on the sp... more A new method for boron bulk doping of silicon ribbons is developed. The method is based on the spraying of the ribbons with a boric acid solution and is particularly suited for silicon ribbons that require a zone-melting recrystallization step. To analyse the quality of the material thus obtained, multicrystalline silicon samples doped with this doping process were used as substrate for solar cells and compared with solar cells made on commercial multicrystalline silicon wafers. The values obtained for the diffusion length and the IV curve parameters show that the method of doping with the boric acid solution is suitable to produce p-doped silicon ribbons for solar cell applications.
Journal of Crystal Growth, 2011
The sprayed boric acid (SBA) method for bulk doping of silicon ribbons is investigated. Experimen... more The sprayed boric acid (SBA) method for bulk doping of silicon ribbons is investigated. Experimental procedures and main results are reviewed. Computational fluid dynamics and experimental tests using partial spraying suggest the role of gas transported evaporated boron oxide to explain the boron incorporation profiles along the sample. The industrial applicability of the SBA method is discussed.
European Journal of Physics, 2004
The study of electromagnetic wave propagation in a coaxial cable can be a powerful approach to th... more The study of electromagnetic wave propagation in a coaxial cable can be a powerful approach to the study of waves at an undergraduate level. This study can explore different experimental situations, going from those where the finite velocity of propagation must be considered (distributed or transmission line behaviour), to those where this velocity may be considered infinite (lumped behaviour). We believe that the student observation of the existence of these two regimes can be important for the understanding of wave phenomena in general. In this work we show that this can be achieved using low-cost equipment and a set of quite simple experiments, such as the measurement of wave propagation velocity or the study of standing waves and resonance. The results obtained in a coherent set of selected experiments are discussed.
Materials Research Express, 2015
PROPAGAÇÃO DA ENERGIA SÍSMICA 46 47 A caracterização da acção sísmica envolve a estimativa da int... more PROPAGAÇÃO DA ENERGIA SÍSMICA 46 47 A caracterização da acção sísmica envolve a estimativa da intensidade, do conteúdo em
In order to assess hazard seismic scenarios for a region selected sites, seismic deaggregation wa... more In order to assess hazard seismic scenarios for a region selected sites, seismic deaggregation was evaluated applying a mixed model that uses (i) gross source zones to compute b_values and maximum magnitudes and (ii) geographically uniform bins to obtain seismic rates. Results are presented in terms of magnitude and geographical coordinates for the parishes of Lisbon County and surrounding areas. Once obtained the most likely scenarios that can affect the metropolitan region of Lisbon, seismic risk scenario was assessed weighting those scenarios with the geographic distribution of elements at risk in the region. The final risk scenario was the one that conducted to the higher total risk for the region in each considered return period. INTRODUCTION Studies on probabilistic seismic scenarios are important tools for civil protection emergency management and planning. In those studies, for a given region and reference time interval, the main objective is to identify the event, or group ...
RESUMO: São apresentados os aspectos relevantes das análises de riscos em barragens de aterro atr... more RESUMO: São apresentados os aspectos relevantes das análises de riscos em barragens de aterro através da metodologia qualitativa da FMEA. Procede-se à sua aplicação a uma barragem de aterro para a retenção de estéreis mineiros. Apresentam-se em detalhe, para o tapete drenante da barragem, as suas funcionalidades, os seus modos potenciais de rotura, as suas causas iniciadoras e os seus efeitos directos e nos vários elementos constituintes do sistema composto pela barragem e pela sua zona de influência. São ainda referidas as medidas disponíveis em obra para a detecção das causas ou dos modos de rotura e o controlo dos seus efeitos.
Risk analysis has been becoming increasingly important in the design of geotechnical works. Howev... more Risk analysis has been becoming increasingly important in the design of geotechnical works. However, due to the complexity often associated, its practical application is not as widespread as one would like. This paper aims at broader use of risk analysis in the design of urban tunnels and in particular for face stability problems. A simplified and straightforward methodology is suggested to estimate both variables of the risk, i.e. the probability of occurrence of an event and the resulting consequences. The probability of failure is computed with analytical solutions (limit equilibrium and lower bound theory) by means of a Monte Carlo probabilistic approach. The calculations account for geotechnical uncertainties (model and material properties), variability in the tunnel geometry, as well as for the external loads. Based on Poisson’s distribution and on inherent risk tolerance for a given reference length, classes of frequency are proposed. Consequence classes are also proposed bas...
This paper addresses the relevant aspects of risk analysis of embankment dams, through the qualit... more This paper addresses the relevant aspects of risk analysis of embankment dams, through the qualitative method of Failure Mode and Effects Analysis (FMEA). In particular the concepts, principles, assumptions and fundamental rules of FMEA are introduced. It proceeds to its application to a particular tailings dam (the Cerro do Lobo dam). The dam's system, composed with the embankment dam itself and its influence area, is first presented. The system is hierarchically structured into basic components with specific functionalities contributing to the functionality of the system. Next, the potential failures modes of each component are identified, as well as their corresponding root causes and immediate effects. It is evaluated the sequence effects progress through the successive parent subsystems until the final effects over the whole system are reached. Finally, the available measures in the field for detecting the rout cause of the components failure modes and for controlling their sequence of effects are also identified. Although FMEA application in large dam systems is a complex and time consuming process its outcome can be extremely useful. It allows the assessment and management of dam's major risks so that mitigations actions in an early stage can be optimized from the efficiency standpoint.
RESUMO -Neste artigo apresenta-se um enquadramento geral das análises de riscos em Geotecnia, per... more RESUMO -Neste artigo apresenta-se um enquadramento geral das análises de riscos em Geotecnia, perspectivando-se os seus objectivos e os respectivos domínios de aplicação. Referem-se, em pormenor, os seguintes métodos de análise de risco: análise dos modos de rotura e seus efeitos (FMEA) e análise dos modos de rotura, seus efeitos e sua criticalidade (FMECA). Aplicam-se a FMEA e a FMECA a uma barragem de aterro convencional para retenção de rejeitados. A utilização de análises de riscos em Geotecnia permite detectar, ou controlar atempadamente, os eventuais problemas e gerir os riscos, reduzindo-os, tão cedo e tão eficientemente, em termos de custos, quanto possível. Reconhecidas as vantagens das análises de riscos, admite-se que estas possam vir a desempenhar uma função central das actividades desenvolvidas em programas de segurança modernos de obras geotécnicas importantes.
physica status solidi (c), 2014
ABSTRACT An inline optical CVD process operating at low temperature (<873 K) and at atmosp... more ABSTRACT An inline optical CVD process operating at low temperature (<873 K) and at atmospheric pressure is presented here to grow silicon films on top of crystalline, sintered silicon and pressed silicon powder substrates moving at constant speed (>10 mm/min) inside the furnace. Solid silicon substrates were laser textured to reduce the reflectivity, leveraging the growth rates. Laser patterning has a strong influence in the growth rate, reaching values up to 9 µm/min. Using pressed silicon powder substrates, growth rates increase dramatically to 40-90 µm/min. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c), 2014
A lot of research has been done to try to reduce the costs of solar cells by developing ribbon gr... more A lot of research has been done to try to reduce the costs of solar cells by developing ribbon growth techniques that bypass the ingot/wafering step. The SDS-Silicon on Dust Substrate process, here described, is a technique to produce ribbons directly from the gas phase. Test solar cells were fabricated on SDS ribbons as a demonstration of concept of this
IEEE Journal of Photovoltaics, 2014
The SLIM-cut technique provides a way to obtain thin silicon foils without a standard sawing step... more The SLIM-cut technique provides a way to obtain thin silicon foils without a standard sawing step, thus avoiding kerf losses. This process consists of three steps: depositing a stressinducing layer on top of the silicon surface; stress activation by heating and cooling, resulting in crack propagation in the silicon and detachment of a thin silicon layer; and a chemical cleaning to remove the stress-inducing layer. This paper describes a new stress activation method using Ag/Al and epoxy stress-inducing layers. The crack propagation is controlled along the sample length in order to avoid unwanted additional crack formation and interaction with other crack fronts. Silicon foils with thickness ranging between 50 and 130 μm were obtained with effective lifetimes between 1 and 81 μs.
Soil Dynamics and Earthquake Engineering, 2008
In this study, we simulate and compare ground motion shaking in the city of Lisbon and surroundin... more In this study, we simulate and compare ground motion shaking in the city of Lisbon and surrounding counties (metropolitan area of Lisbon (MAL)), using two possible earthquake models: the onshore source area of Lower Tagus Valley, M5.7 and M4.7 and the offshore source area, Marques de Pombal Fault, M7.6, one of the possible source of the 1755 Lisbon earthquake. The stochastic and a new hybrid stochastic-deterministic approach (DSM) are used in order to evaluate the ground shaking and to characterize its spatial variability. Results are presented in terms of response acceleration spectra (PSA) and peak ground acceleration (PGA) with respect to bedrock and surface. Site effects are evaluated by means of equivalent stochastic non-linear one-dimensional ground responses analysis, performed for a set of stratified soil profile units properly designed to cope with the soil site conditions of MAL region. A sensitive study is carried out using different input parameters and different approaches in order to give the basic information to evaluate the range of uncertainty in seismic scenarios. r
Semiconductor Science and Technology, 2010
A new method for boron bulk doping of silicon ribbons is developed. The method is based on the sp... more A new method for boron bulk doping of silicon ribbons is developed. The method is based on the spraying of the ribbons with a boric acid solution and is particularly suited for silicon ribbons that require a zone-melting recrystallization step. To analyse the quality of the material thus obtained, multicrystalline silicon samples doped with this doping process were used as substrate for solar cells and compared with solar cells made on commercial multicrystalline silicon wafers. The values obtained for the diffusion length and the IV curve parameters show that the method of doping with the boric acid solution is suitable to produce p-doped silicon ribbons for solar cell applications.
Journal of Crystal Growth, 2011
The sprayed boric acid (SBA) method for bulk doping of silicon ribbons is investigated. Experimen... more The sprayed boric acid (SBA) method for bulk doping of silicon ribbons is investigated. Experimental procedures and main results are reviewed. Computational fluid dynamics and experimental tests using partial spraying suggest the role of gas transported evaporated boron oxide to explain the boron incorporation profiles along the sample. The industrial applicability of the SBA method is discussed.
European Journal of Physics, 2004
The study of electromagnetic wave propagation in a coaxial cable can be a powerful approach to th... more The study of electromagnetic wave propagation in a coaxial cable can be a powerful approach to the study of waves at an undergraduate level. This study can explore different experimental situations, going from those where the finite velocity of propagation must be considered (distributed or transmission line behaviour), to those where this velocity may be considered infinite (lumped behaviour). We believe that the student observation of the existence of these two regimes can be important for the understanding of wave phenomena in general. In this work we show that this can be achieved using low-cost equipment and a set of quite simple experiments, such as the measurement of wave propagation velocity or the study of standing waves and resonance. The results obtained in a coherent set of selected experiments are discussed.