The effect of MnO4- and silver content on electrochemical behaviour of five commercial Pb-Ag alloy anodes was studied in acid zinc sulphate electrolyte with and without MnO4- ions at 38 °C during potential decay ...The effect of MnO4- and silver content on electrochemical behaviour of five commercial Pb-Ag alloy anodes was studied in acid zinc sulphate electrolyte with and without MnO4- ions at 38 °C during potential decay periods. When the anodes were immersed into acid zinc sulphate electrolyte without MnO4- ions, the Pb-0.72%Ag anode entered complete passivation state in the shortest time among the five anodes, followed by anodes Pb-0.67%Ag, Pb-0.60%Ag, Pb-0.58%Ag and Pb-0.29%Ag-0.1%Ca by measurement of open circuit potential. During immersion of the anodes, MnO4 ions accelerated the passivation and increased the corrosion current density of the anodes. After immersion in zinc electrolyte with MnO4-, the anode Pb-0.72%Ag had the best corrosion resistance, followed by anodes Pb-0.67%Ag, Pb-0.60%Ag, then the close anodes Pb-0.58%Ag and Pb-0.29%Ag-0.1%Ca by the electrochemical impedance spectroscopy （EIS） analysis.展开更多
The catalytic performance of two oxides coated anodes （OCSs） meshes and one OCA plate was investigated in a zinc electrowinning electrolyte at 38 ℃. Their electrochemical behaviors were compared with that of a conv...The catalytic performance of two oxides coated anodes （OCSs） meshes and one OCA plate was investigated in a zinc electrowinning electrolyte at 38 ℃. Their electrochemical behaviors were compared with that of a conventional Pb-0.7%Ag alloy anode. Electrochemical measurements such as cyclic voltammetric, galvanostatic, potentiodynamic, open-circuit potential （OCP） and in situ electrochemical noise measurements were considered. After 2 h of OCP test, the linear polarization shows that the corrosion current density of the Ti/（IrO2-Ta2O5） mesh electrode is the lowest （3.37μA/cm^2） among the three OCAs and shows excellent performance. Additionally, after 24 h of galvanostatic polarization at 50 mA/cm^2and 38 ℃, the Ti/MnO2mesh anode has the highest potential （1.799 V）, followed by the Ti/（IrO2-Ta2O5） plate （1.775 V） and Ti/（IrO2-Ta2O5） mesh （1.705 V） anodes. After 24 h of galvanostatic polarization followed by 16 h of decay, the linear polarization method confirms the sequence obtained after 2 h of OCP test, and the Ti/（IrO2-Ta2O5） mesh attains the lowest corrosion current density. The Ti/（IrO2-Ta2O5） mesh anode also shows better performance after 24 h of galvanostatic polarization with the overpotential lower than that of the conventional Pb-Ag anode by about 245 mV.展开更多
The most commonly used method for assessing the hydraulic erodibility of rock is Annandale's method.This method is based on a correlation between the erosive force of flowing water and the capacity of rock resista...The most commonly used method for assessing the hydraulic erodibility of rock is Annandale's method.This method is based on a correlation between the erosive force of flowing water and the capacity of rock resistance. This capacity is evaluated using Kirsten's index, which was initially developed to evaluate the excavatability of earth materials. For rocky material, this index is determined according to certain geomechanical factors related to intact rock and rock mass, such as compressive strength of intact rock, rock block size, discontinuity shear strength and relative block structure. To quantify the relative block structure, Kirsten(1982) developed a mathematical expression that accounts for the shape and orientation of the blocks relative to the direction of flow. Kirsten's initial concept for assessing the relative block structure considers that the geological formation is mainly fractured by two joint sets forming an orthogonally fractured system. An adjusted concept is proposed to determine the relative block structure when the fractured system is non-orthogonal where the angle between the planes of the two joint sets is greater or less than 90°. An analysis of the proposed relative block structure rating shows that considering a non-orthogonally fractured system has a significant effect on Kirsten's index and, as a consequence, on the assessment of the hydraulic erodibility of rock.展开更多
The daily operations in the mining industry are still a significant source of risk with regard to occupational safety and health(OS & H). Various research studies and statistical data world-wide show that the numb...The daily operations in the mining industry are still a significant source of risk with regard to occupational safety and health(OS & H). Various research studies and statistical data world-wide show that the number of serious injuries and fatalities still remains high despite substantial efforts the industry has put in recent years in decreasing those numbers. This paper argues that the next level of safety performance will have to consider a transition from coping solely with workplace dangers, to a more systemic model taking organizational risks in consideration. In this aspect, lessons learned from the nuclear industry may be useful, as organizational learning processes are believed to be more universal than the technologies in which they are used. With the notable exception of major accidents, organizational performance has not received all the attention it deserves. A key element for reaching the next level of performance is to include organizational factors in low level events analyses, and approach the management as a risk control system. These factors will then appear not only in the event analysis,but in supervision activities, audits, change management and the like. Many recent event analyses across various industries have shown that organizational factors play a key role in creating conditions for triggering major accidents(aviation, railway transportation, nuclear industry, oil exploitation, mining, etc.).In this paper, a perspective that may be used in supervisory activities, self-assessments and minor events investigations, is presented. When ingrained in an organizational culture, such perspective has the highest potential for continuous safety improvement.展开更多
The electric field required for stable propagation of a positive streamer along an ice surface was investigated by measuring the currents associated with the streamer discharge.The influence of the surface properties,...The electric field required for stable propagation of a positive streamer along an ice surface was investigated by measuring the currents associated with the streamer discharge.The influence of the surface properties,namely the existence of a water film on the ice surface and surface contamination,was analyzed.Results showed that in the presence of an ice surface,except in case of low conductive surface,streamers propagate stably with an external field lower than that generally measured for propagation in air alone(approximately 5 kV/cm).For higher contamination levels,the stability field was found to be slightly influenced by the temperature,while for lower contamination levels,it decreased significantly with an increase in temperature.展开更多
Specimens of the forest species such as Pentaclethra macrophylla, Petersianthus macrocarpus, Pycnanthus angolensis and Terminalia superba have been sampled from LUKI Biosphere reserve in the Democratic Republic of the...Specimens of the forest species such as Pentaclethra macrophylla, Petersianthus macrocarpus, Pycnanthus angolensis and Terminalia superba have been sampled from LUKI Biosphere reserve in the Democratic Republic of the Congo in order to determine their wood density with the perspective to decarbonisation. These parameters have been found out experimentally utilizing a drying technique in an oven including techniques of immersion in an Erlenmeyer full of water. The corresponding results indicated that the four species wood density is respectively 0.85, 0.80, 0.77 and 0.51. These preliminary results will be useful in our ongoing project on carbon dioxide absorption capacity of Congo rainforest tree species.展开更多
A micromechanical model, based on the FEA (finite element analysis), was developed to estimate the influence of hydrogen pressure on short crack behaviour. Morphology of voids has important connotations in the develop...A micromechanical model, based on the FEA (finite element analysis), was developed to estimate the influence of hydrogen pressure on short crack behaviour. Morphology of voids has important connotations in the development of the model. Stress intensity factor was calculated for different crack geometries under hydrogen pressure. The analysis indicates that the form factor of a crack emerging from a round void will be less affected by trapped hydrogen pressure-compared to an elongated void. This analysis reinforces the beneficial effect of inclusion shape control in reducing significantly the detrimental effect of hydrogen.展开更多
The intent of this paper is to propose an engineering approach to estimate the stress intensity factor of a micro crack emerging from an inclusion in relation with the morphology of the inclusion and its relative stif...The intent of this paper is to propose an engineering approach to estimate the stress intensity factor of a micro crack emerging from an inclusion in relation with the morphology of the inclusion and its relative stiffness with the matrix. A micromechanical model, based on the FEA (finite element analysis) of the behavior of cracks initiated at micro structural features such as inclusions, has been developed using LEFM (Linear Elastic Fracture Mechanics) to predict the stress intensity factor of a micro crack emerging from an inclusion. Morphology of inclusions has important connotations in the development of the analysis. Stress intensity factor has been estimated from the FEA model for different crack geometries. Metallographic analysis of inclusions has been carried out to evaluate the typical inclusion geometry. It also suggests that micro cracks less than 1?μm behave differently than larger cracks.展开更多
Sliding contacts in laminar flow regimes have been investigated extensively in recent years. The results indicate the possibility to increase load carrying capacity in a slider bearing for more than 10% with the addit...Sliding contacts in laminar flow regimes have been investigated extensively in recent years. The results indicate the possibility to increase load carrying capacity in a slider bearing for more than 10% with the addition of dimples. Parametric studies have been performed to determine optimal size and position, with emphasis in the optimal shape and position of the dimple for an operating condition. In this article, the numerical analysis of a 2D textured slider bearing with a dimple is initially considered with an isothermal laminar fluid. Position, depth, width and convergence ratio are optimized, the results demonstrate the importance of the width and convergence ratio to increase load. Then, the numerical analysis of a 3D textured slider bearing with fore-region and extended channels at the outlet and on the sides of a pad is considered. The simulations are also carried out for a laminar isothermal flow. Three dimples are considered and their depth is optimized.展开更多
Variations in droplet wettability affect localized corrosion during scanning electrochemical cell microscopy(SECCM)on stainless steel.The droplet dynamics are influenced by stainless-steel micro-structural features an...Variations in droplet wettability affect localized corrosion during scanning electrochemical cell microscopy(SECCM)on stainless steel.The droplet dynamics are influenced by stainless-steel micro-structural features and surface conditions-such as surface roughness,inclusions,and the addition of an oil layer.As opposed to previous work on aluminum alloys,droplet spreading is promoted by oil immersion,which leads to an increase in the cathodic currents.Rougher surfaces hinder droplet spreading,largely due to the droplet pinning effect,and exhibit higher pitting corrosion incidences compared to smoother surfaces.Moreover,the presence of inclusions intensifies pitting initiation and constrains the landing area(droplet size).We report that while the landing area does not affect the number of metastable pits,small landing areas lead to a high probability of stable pitting.展开更多
This paper presents a security constrained unit commitment(SCUC)suitable for power systems with a large share of wind energy.The deterministic spinning reserve requirement is supplemented by an adjustable fraction of ...This paper presents a security constrained unit commitment(SCUC)suitable for power systems with a large share of wind energy.The deterministic spinning reserve requirement is supplemented by an adjustable fraction of the expected shortfall from the supply of wind electric generators(WEGs),computed using the stochastic feature of wind and loosely represented in the security constraint with scenarios.The optimization tool commits and dispatches generating units while simultaneously determining the geographical procurement of the required spinning reserve as well as load-following ramping reserve,by mixed integer quadratic programming(MIQP).Case studies are used to investigate various effects of grid integration on reducing the overall operation costs associated with more wind power in the system.展开更多
We study the generation of nonlinear plasma wake fields by intense laser pulses,using an Eulerian code for the numerical solution of the fully relativistic onedimensional(1D)Vlasov-Maxwell equations.The examination of...We study the generation of nonlinear plasma wake fields by intense laser pulses,using an Eulerian code for the numerical solution of the fully relativistic onedimensional(1D)Vlasov-Maxwell equations.The examination of the phase-space of the distribution function allows to study without numerical noise aspects of the particle acceleration by the wake-field generated by intense laser pulses,in the very low density regions of the phase-space.We study the effect of the thermal spread on the existence of accelerated beams,and we compare between results obtained from a circularly polarized wave and a linearly polarized wave.展开更多
基金Project(RDCPJ346365-06)supported by the Natural Sciences and Engineering Research Council of CanadaProject(51208193)supported by the National Natural Science Foundation of ChinaProject(11jj6034)supported by the Hunan Provincial Natural Science Foundation
文摘The effect of MnO4- and silver content on electrochemical behaviour of five commercial Pb-Ag alloy anodes was studied in acid zinc sulphate electrolyte with and without MnO4- ions at 38 °C during potential decay periods. When the anodes were immersed into acid zinc sulphate electrolyte without MnO4- ions, the Pb-0.72%Ag anode entered complete passivation state in the shortest time among the five anodes, followed by anodes Pb-0.67%Ag, Pb-0.60%Ag, Pb-0.58%Ag and Pb-0.29%Ag-0.1%Ca by measurement of open circuit potential. During immersion of the anodes, MnO4 ions accelerated the passivation and increased the corrosion current density of the anodes. After immersion in zinc electrolyte with MnO4-, the anode Pb-0.72%Ag had the best corrosion resistance, followed by anodes Pb-0.67%Ag, Pb-0.60%Ag, then the close anodes Pb-0.58%Ag and Pb-0.29%Ag-0.1%Ca by the electrochemical impedance spectroscopy （EIS） analysis.
基金Project(RDCPJ 428402)supported by the Natural Sciences and Engineering Research Council of Canada
文摘The catalytic performance of two oxides coated anodes （OCSs） meshes and one OCA plate was investigated in a zinc electrowinning electrolyte at 38 ℃. Their electrochemical behaviors were compared with that of a conventional Pb-0.7%Ag alloy anode. Electrochemical measurements such as cyclic voltammetric, galvanostatic, potentiodynamic, open-circuit potential （OCP） and in situ electrochemical noise measurements were considered. After 2 h of OCP test, the linear polarization shows that the corrosion current density of the Ti/（IrO2-Ta2O5） mesh electrode is the lowest （3.37μA/cm^2） among the three OCAs and shows excellent performance. Additionally, after 24 h of galvanostatic polarization at 50 mA/cm^2and 38 ℃, the Ti/MnO2mesh anode has the highest potential （1.799 V）, followed by the Ti/（IrO2-Ta2O5） plate （1.775 V） and Ti/（IrO2-Ta2O5） mesh （1.705 V） anodes. After 24 h of galvanostatic polarization followed by 16 h of decay, the linear polarization method confirms the sequence obtained after 2 h of OCP test, and the Ti/（IrO2-Ta2O5） mesh attains the lowest corrosion current density. The Ti/（IrO2-Ta2O5） mesh anode also shows better performance after 24 h of galvanostatic polarization with the overpotential lower than that of the conventional Pb-Ag anode by about 245 mV.
基金the organizations that have funded this project:the Natural Sciences and Engineering Research Council of Canada(Grant No.498020-16)Hydro-Quebec(NC-525700)Mitacs Accelerate Program(Grant Ref.IT10008)
文摘The most commonly used method for assessing the hydraulic erodibility of rock is Annandale's method.This method is based on a correlation between the erosive force of flowing water and the capacity of rock resistance. This capacity is evaluated using Kirsten's index, which was initially developed to evaluate the excavatability of earth materials. For rocky material, this index is determined according to certain geomechanical factors related to intact rock and rock mass, such as compressive strength of intact rock, rock block size, discontinuity shear strength and relative block structure. To quantify the relative block structure, Kirsten(1982) developed a mathematical expression that accounts for the shape and orientation of the blocks relative to the direction of flow. Kirsten's initial concept for assessing the relative block structure considers that the geological formation is mainly fractured by two joint sets forming an orthogonally fractured system. An adjusted concept is proposed to determine the relative block structure when the fractured system is non-orthogonal where the angle between the planes of the two joint sets is greater or less than 90°. An analysis of the proposed relative block structure rating shows that considering a non-orthogonally fractured system has a significant effect on Kirsten's index and, as a consequence, on the assessment of the hydraulic erodibility of rock.
文摘The daily operations in the mining industry are still a significant source of risk with regard to occupational safety and health(OS & H). Various research studies and statistical data world-wide show that the number of serious injuries and fatalities still remains high despite substantial efforts the industry has put in recent years in decreasing those numbers. This paper argues that the next level of safety performance will have to consider a transition from coping solely with workplace dangers, to a more systemic model taking organizational risks in consideration. In this aspect, lessons learned from the nuclear industry may be useful, as organizational learning processes are believed to be more universal than the technologies in which they are used. With the notable exception of major accidents, organizational performance has not received all the attention it deserves. A key element for reaching the next level of performance is to include organizational factors in low level events analyses, and approach the management as a risk control system. These factors will then appear not only in the event analysis,but in supervision activities, audits, change management and the like. Many recent event analyses across various industries have shown that organizational factors play a key role in creating conditions for triggering major accidents(aviation, railway transportation, nuclear industry, oil exploitation, mining, etc.).In this paper, a perspective that may be used in supervisory activities, self-assessments and minor events investigations, is presented. When ingrained in an organizational culture, such perspective has the highest potential for continuous safety improvement.
文摘The electric field required for stable propagation of a positive streamer along an ice surface was investigated by measuring the currents associated with the streamer discharge.The influence of the surface properties,namely the existence of a water film on the ice surface and surface contamination,was analyzed.Results showed that in the presence of an ice surface,except in case of low conductive surface,streamers propagate stably with an external field lower than that generally measured for propagation in air alone(approximately 5 kV/cm).For higher contamination levels,the stability field was found to be slightly influenced by the temperature,while for lower contamination levels,it decreased significantly with an increase in temperature.
文摘Specimens of the forest species such as Pentaclethra macrophylla, Petersianthus macrocarpus, Pycnanthus angolensis and Terminalia superba have been sampled from LUKI Biosphere reserve in the Democratic Republic of the Congo in order to determine their wood density with the perspective to decarbonisation. These parameters have been found out experimentally utilizing a drying technique in an oven including techniques of immersion in an Erlenmeyer full of water. The corresponding results indicated that the four species wood density is respectively 0.85, 0.80, 0.77 and 0.51. These preliminary results will be useful in our ongoing project on carbon dioxide absorption capacity of Congo rainforest tree species.
文摘A micromechanical model, based on the FEA (finite element analysis), was developed to estimate the influence of hydrogen pressure on short crack behaviour. Morphology of voids has important connotations in the development of the model. Stress intensity factor was calculated for different crack geometries under hydrogen pressure. The analysis indicates that the form factor of a crack emerging from a round void will be less affected by trapped hydrogen pressure-compared to an elongated void. This analysis reinforces the beneficial effect of inclusion shape control in reducing significantly the detrimental effect of hydrogen.
文摘The intent of this paper is to propose an engineering approach to estimate the stress intensity factor of a micro crack emerging from an inclusion in relation with the morphology of the inclusion and its relative stiffness with the matrix. A micromechanical model, based on the FEA (finite element analysis) of the behavior of cracks initiated at micro structural features such as inclusions, has been developed using LEFM (Linear Elastic Fracture Mechanics) to predict the stress intensity factor of a micro crack emerging from an inclusion. Morphology of inclusions has important connotations in the development of the analysis. Stress intensity factor has been estimated from the FEA model for different crack geometries. Metallographic analysis of inclusions has been carried out to evaluate the typical inclusion geometry. It also suggests that micro cracks less than 1?μm behave differently than larger cracks.
文摘Sliding contacts in laminar flow regimes have been investigated extensively in recent years. The results indicate the possibility to increase load carrying capacity in a slider bearing for more than 10% with the addition of dimples. Parametric studies have been performed to determine optimal size and position, with emphasis in the optimal shape and position of the dimple for an operating condition. In this article, the numerical analysis of a 2D textured slider bearing with a dimple is initially considered with an isothermal laminar fluid. Position, depth, width and convergence ratio are optimized, the results demonstrate the importance of the width and convergence ratio to increase load. Then, the numerical analysis of a 3D textured slider bearing with fore-region and extended channels at the outlet and on the sides of a pad is considered. The simulations are also carried out for a laminar isothermal flow. Three dimples are considered and their depth is optimized.
基金supported by NSERC CRD 2020-04609,Hydro-Quebec Research Institute(IREQ),and Fonds de recherche du Quebec−Nature et technologies(FRQNT)for doctoral scholarship No.333966(S.R.Y.).
文摘Variations in droplet wettability affect localized corrosion during scanning electrochemical cell microscopy(SECCM)on stainless steel.The droplet dynamics are influenced by stainless-steel micro-structural features and surface conditions-such as surface roughness,inclusions,and the addition of an oil layer.As opposed to previous work on aluminum alloys,droplet spreading is promoted by oil immersion,which leads to an increase in the cathodic currents.Rougher surfaces hinder droplet spreading,largely due to the droplet pinning effect,and exhibit higher pitting corrosion incidences compared to smoother surfaces.Moreover,the presence of inclusions intensifies pitting initiation and constrains the landing area(droplet size).We report that while the landing area does not affect the number of metastable pits,small landing areas lead to a high probability of stable pitting.
文摘This paper presents a security constrained unit commitment(SCUC)suitable for power systems with a large share of wind energy.The deterministic spinning reserve requirement is supplemented by an adjustable fraction of the expected shortfall from the supply of wind electric generators(WEGs),computed using the stochastic feature of wind and loosely represented in the security constraint with scenarios.The optimization tool commits and dispatches generating units while simultaneously determining the geographical procurement of the required spinning reserve as well as load-following ramping reserve,by mixed integer quadratic programming(MIQP).Case studies are used to investigate various effects of grid integration on reducing the overall operation costs associated with more wind power in the system.
基金The constant support and interest of Dr.Andr´e Besner is gratefully acknowledged。
文摘We study the generation of nonlinear plasma wake fields by intense laser pulses,using an Eulerian code for the numerical solution of the fully relativistic onedimensional(1D)Vlasov-Maxwell equations.The examination of the phase-space of the distribution function allows to study without numerical noise aspects of the particle acceleration by the wake-field generated by intense laser pulses,in the very low density regions of the phase-space.We study the effect of the thermal spread on the existence of accelerated beams,and we compare between results obtained from a circularly polarized wave and a linearly polarized wave.
