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O R Mattos - One of the best experts on this subject based on the ideXlab platform.
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hydrogen influence on fracture toughness of the weld metal in super duplex stainless steel uns s32750 welded with two different heat input
International Journal of Hydrogen Energy, 2015Co-Authors: Marcella Araujo Lage, Kioshy Santos De Assis, O R MattosAbstract:Abstract The super duplex stainless steels have a microstructure composed by two phases, ferrite (α) and austenite (γ). This dual microstructure improves simultaneously the mechanical and corrosion resistance properties. However, the welding of these steels is often a Critical Operation. The present work evaluated the fracture toughness through Critical tip open displacement (CTOD) tests of welded joints, with two different heat input, 1.1 kJ mm −1 and 2.0 kJ mm −1 . The steel used was a super duplex stainless steel (UNS S32750) in presence of hydrogen. The CTOD tests (according BS 7448-1 and BS 7448-2 standards) were performed in air and under different times of hydrogenation. The procedure of hydrogenation has been performed using cathodic potential of −1400 mV SCE by 96 and 360 h. The microstructural analysis allowed to determine relevant aspects (α/γ balance, inter austenitic spacing and γ morphology) and to compare with CTOD results. The results showed strong evidence that the reductions of CTOD values is related to differences in the γ 2 morphologies. Another important result was the high statistic dispersion in the measures of austenitic spacing, according DNV RP F112-08, which implies in low reliability of using this standard in presence of high anisotropy. The paper also aims to discuss and evaluate which is the best approach to hydrogenated duplex stainless steels: linear elastic fracture mechanics or elasto plastic fracture mechanics.
Mae Sexauer Gustin - One of the best experts on this subject based on the ideXlab platform.
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Dynamic flux chamber measurement of gaseous mercury emission fluxes over soils. Part 1: simulation of gaseous mercury emissions from soils using a two-resistance exchange interface model
Atmospheric Environment, 2002Co-Authors: Hong Zhang, Steve E. Lindberg, Alan F Vette, Mark O Barnett, Mae Sexauer GustinAbstract:Abstract A two-resistance exchange interface model (TREIM) was developed to simulate gaseous mercury (Hg) emissions from soils measured by dynamic flux chamber (DFC) Operations. The model is based on mass balance principles and a Hg air/soil exchange theory that considers the influence of flushing flow rate on Hg air/soil exchange. We used this model to examine the effect of the flushing flow rate and understand the optimum conditions for DFC measurements of Hg emission fluxes over soils. Our model simulations indicate that the flushing flow rate is a most Critical Operation condition. We recommend adoption of high flushing flow rates (e.g., ∼15–40 l min−1 for DFCs of common design) based on our simulation findings that underestimation of actual emission fluxes can occur at low flushing flow rates. The biased low fluxes are caused by suppression of emission potential resulting from internal accumulation of emitted Hg and by higher exchange resistance both at low flushing flow rates. This model provides a useful means for estimating maximum steady-state fluxes and soil air Hg concentrations and for adjustment of the fluxes measured under different operating conditions. The model also finds its value in understanding mechanical processes of Hg emissions from soils.
Henk A P Blom - One of the best experts on this subject based on the ideXlab platform.
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contrasting safety assessments of a runway incursion scenario event sequence analysis versus multi agent dynamic risk modelling
Reliability Engineering & System Safety, 2013Co-Authors: Sybert H Stroeve, Henk A P Blom, G J BakkerAbstract:In the safety literature it has been argued, that in a complex socio-technical system safety cannot be well analysed by event sequence based approaches, but requires to capture the complex interactions and performance variability of the socio-technical system. In order to evaluate the quantitative and practical consequences of these arguments, this study compares two approaches to assess accident risk of an example safety Critical sociotechnical system. It contrasts an event sequence based assessment with a multi-agent dynamic risk model (MA-DRM) based assessment, both of which are performed for a particular runway incursion scenario. The event sequence analysis uses the well-known event tree modelling formalism and the MA-DRM based approach combines agent based modelling, hybrid Petri nets and rare event Monte Carlo simulation. The comparison addresses qualitative and quantitative differences in the methods, attained risk levels, and in the prime factors influencing the safety of the Operation. The assessments show considerable differences in the accident risk implications of the performance of human operators and technical systems in the runway incursion scenario. In contrast with the event sequence based results, the MA-DRM based results show that the accident risk is not manifest from the performance of and relations between individual human operators and technical systems. Instead, the safety risk emerges from the totality of the performance and interactions in the agent based model of the safety Critical Operation considered, which coincides very well with the argumentation in the safety literature.
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safety risk assessment by monte carlo simulation of complex safety Critical Operations
SSS, 2006Co-Authors: Henk A P Blom, Sybert H Stroeve, Hans H De JongAbstract:This paper gives an overview of performing safety risk assessment of a safety Critical Operation with support of Monte Carlo (MC) simulation. The approach is outlined for an air traffic example involving aircraft departing from a runway, which is occasionally crossed by taxiing aircraft. At the airport considered, a Runway Incursion Alert System (RIAS) is installed to warn the air traffic controller in case of impending runway incursions. The paper explains the key issues to be mastered in performing a MC simulation supported safety risk assessment of this kind of Operation. To begin with, one has to develop an appropriate simulation model, and a sound way to speed up the MC simulation based on this model. Complementary, one has to validate the simulation model versus the real Operation, and the simulation supported approach has to be embedded within the safety risk assessment of the total Operation. For this application example MC simulation results are given and the way of feedback to the design of the Operation is outlined.
Cesnet Z S P O Zizkova - One of the best experts on this subject based on the ideXlab platform.
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Methodology for Fast Pattern Matching by Deterministic Finite Automaton with Perfect Hashing Ondrej Lengal
2020Co-Authors: Jan Kastil, Jan Korenek, Cesnet Z S P O ZizkovaAbstract:Abstract-As the speed of current computer networks increases, it is necessary to protect networks by security systems such as firewalls and Intrusion Detection Systems operating at multigigabit speeds. Pattern matching is the time-Critical Operation of current IDS on multigigabit networks. Regular expressions are often used to describe malicious network patterns. This paper deals with fast regular expression matching using the Deterministic Finite Automaton (DFA) with perfect hash function. We introduce decomposition of the problem on two parts: transformation of the input alphabet and usage of a fast DFA, and usage of perfect hashing to reduce space/speed tradeoff for DFA transition table
Marcella Araujo Lage - One of the best experts on this subject based on the ideXlab platform.
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hydrogen influence on fracture toughness of the weld metal in super duplex stainless steel uns s32750 welded with two different heat input
International Journal of Hydrogen Energy, 2015Co-Authors: Marcella Araujo Lage, Kioshy Santos De Assis, O R MattosAbstract:Abstract The super duplex stainless steels have a microstructure composed by two phases, ferrite (α) and austenite (γ). This dual microstructure improves simultaneously the mechanical and corrosion resistance properties. However, the welding of these steels is often a Critical Operation. The present work evaluated the fracture toughness through Critical tip open displacement (CTOD) tests of welded joints, with two different heat input, 1.1 kJ mm −1 and 2.0 kJ mm −1 . The steel used was a super duplex stainless steel (UNS S32750) in presence of hydrogen. The CTOD tests (according BS 7448-1 and BS 7448-2 standards) were performed in air and under different times of hydrogenation. The procedure of hydrogenation has been performed using cathodic potential of −1400 mV SCE by 96 and 360 h. The microstructural analysis allowed to determine relevant aspects (α/γ balance, inter austenitic spacing and γ morphology) and to compare with CTOD results. The results showed strong evidence that the reductions of CTOD values is related to differences in the γ 2 morphologies. Another important result was the high statistic dispersion in the measures of austenitic spacing, according DNV RP F112-08, which implies in low reliability of using this standard in presence of high anisotropy. The paper also aims to discuss and evaluate which is the best approach to hydrogenated duplex stainless steels: linear elastic fracture mechanics or elasto plastic fracture mechanics.