Understanding water dynamics under the effect of climatic conditions is important to improve water sustainability over the medium-and long-term.Clay content can affect soil hydrothermal properties,and hence modify wat...Understanding water dynamics under the effect of climatic conditions is important to improve water sustainability over the medium-and long-term.Clay content can affect soil hydrothermal properties,and hence modify water and heat exchange between soil and atmosphere,e.g.evapotranspiration and infiltration.This work aims to develop a numerical approach to explore the influence of clay content on soil hydrothermal response to the timely climatic conditions in the Lake Chad region,Sahel Region of west-central Africa.The meteorological information at the studied points,i.e.points A and B with a clay content of 8.3%and 25%,during the year 2008 is collected from ERA5-Land hourly data.The numerical results allow for understanding the effect of clay content on the hydrothermal response of the surface soil layer.Specifically,the soil surface temperature under point A is lower than that under point B during the dry season due to the dominant effect of heat conduction.However,the converse tendency is observed during the wet season because of the combined effect of heat conduction and latent heat.The variations of soil volumetric water content are closely related to the timely interaction between the soil and atmosphere,in addition to the hydrothermal properties of soil.Moreover,the outcomes of this work improve the understanding of the heat and water dynamics under the effect of climatic conditions and clay content,and provide further insights into the potential water protection in arid and semi-arid regions in the future.展开更多
In fog, visibility is reduced. This reduction in visibility is measured by the meteorological optical range (MOR), which is important for studying human perception and various sensors in foggy conditions. The Cerema P...In fog, visibility is reduced. This reduction in visibility is measured by the meteorological optical range (MOR), which is important for studying human perception and various sensors in foggy conditions. The Cerema PAVIN Fog & Rain platform is capable of producing calibrated fog in order to better analyses it and understand its consequences. The problem is that the droplets produced by the platform are not large enough to resemble real fog. This can have a major impact on measurements since the interaction between electromagnetic waves and fog depends on the wavelength and diameter of the droplets. To remedy this, Cerema is building a new platform with new equipment capable of generating fog. This study analyses different nozzles and associated usage parameters such as the type of water used and the pressure used. The aim is to select the best nozzle with the associated parameters for producing large-diameter droplets and therefore more realistic fog.展开更多
A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate ...A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate solution, is developed in this work. After the samples were cured at room temperature under air for 28 d, they were analyzed by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, environmental scanning electron microscopy, mercury intrusion porosimetry, ^(27)Al and ^(29)Si nuclear magnetic resonance(NMR) spectroscopy, and compression testing to establish the relationship between microstructure and compressive strength. The XRD, FTIR, and ^(27)Al and ^(29)Si NMR analyses showed that the use of silica fume instead of alkali silicate solutions was feasible for manufacturing geopolymer cement. The Mk-based geopolymer with a silica fume content of 6 wt%(compared with those with 2% and 10%), corresponding to an SiO_2/Al_2O_3 molar ratio of 3.84, resulted in the highest compressive strength, which was explained on the basis of its high compactness with the smallest porosity. Silica fume improved the compressive strength by filling interstitial voids of the microstructure because of its fine particle size. In addition, an increase in the SiO_2/Al_2O_3 molar ratio, which is controlled by the addition of silica fume, to 4.09 led to a geopolymer with low compressive strength, accompanied by microstructures with high porosity. This high porosity, which is responsible for weaknesses in the specimen, is related to the amount of unreacted silica fume.展开更多
In continental and oceanic conditions, clay-rich deposits are characterised by the development of polygonal fracture systems（PFS）. PFS can increase the vertical permeability of clay-rich deposits（mean permeability ...In continental and oceanic conditions, clay-rich deposits are characterised by the development of polygonal fracture systems（PFS）. PFS can increase the vertical permeability of clay-rich deposits（mean permeability ≤10-16 m2） and are pathways for fluids. On continents, the width of PFS ranges from centimeters to hundreds of meters, while in oceanic contexts they are up to a few kilometers large. These structures are linked to water-solid separation during deposition, consolidation and complete fluid squeeze of the clay horizon. During the last few decades, modeling of melt migration in partially molten plastic rocks led to rigorous quantifications of two-phase flows with a particular emphasis on 2D and 3D induced flow structures. The numerical modeling shows that the melt migrates on distances almost equal to a few times the compaction length L that depends on permeability and viscosity. Consequently, polygonal structures in partially molten plastic rocks are resulted from the melt-rock separation and their sizes are proportional to L. Applying these results to fluid-solid separation in clay-rich horizons, we show that（1） centimetric to kilometric PFS are resulted from the dramatic increase of L during compaction and（2）, this process involves agglomerates with 100 μm to 1 mm size.展开更多
France has about one million kilometres of roads, 98% of which are managed by departments （the French Administrative Area Departement） and municipalities. Because of growing social expenditures, these local authorit...France has about one million kilometres of roads, 98% of which are managed by departments （the French Administrative Area Departement） and municipalities. Because of growing social expenditures, these local authorities are reducing credits for roads, which is leading to a reduction in the length of roads serviced annually, and an expected deterioration of roads generally. Faced with this problem, departmental and urban project designers in the eastern region of France have been meeting within the GEPUR （＂Gestion et Entretien du Patrimoine Urbain et Routier＂ or ＂Urban and Road Heritage Management and Maintenance＂） group since September 2012, to： firstly, develop a method for road network management and programming of assistance based on the experiences of each participant, a modular method depending on the size of the road network and adapted to the contracting authority; secondly, give technical legitimacy to the managers who will be applying the method. They will be able to more easily set up a constructive dialogue with the elected officials in charge of roads, and better justify the use of the credits requested. Two methodological guides will be published, one intended for departmental networks （2015）, the other for municipal networks in mid-2017. A white paper for elected officials has also been drafted. Ultimately, this experience will be extended throughout France.展开更多
A large amount of researches and studies have been recently performed by applying statistical and machine learning techniques for vibration-based damage detection. However, the global character inherent to the limited...A large amount of researches and studies have been recently performed by applying statistical and machine learning techniques for vibration-based damage detection. However, the global character inherent to the limited number of modal properties issued from operational modal analysis may be not appropriate for early-damage, which has generally a local character. The present paper aims at detecting this type of damage by using static SHM data and by assuming that early-damage produces dead load redistribution. To achieve this objective a data driven strategy is proposed, consisting of the combination of advanced statistical and machine learning methods such as principal component analysis, symbolic data analysis and cluster analysis. From this analysis it was observed that, under the noise levels measured on site, the proposed strategy is able to automatically detect stiffness reduction in stay cables reaching at least 1%.展开更多
基金the National Natural Science Foundation of China(Grant No.42207171).
文摘Understanding water dynamics under the effect of climatic conditions is important to improve water sustainability over the medium-and long-term.Clay content can affect soil hydrothermal properties,and hence modify water and heat exchange between soil and atmosphere,e.g.evapotranspiration and infiltration.This work aims to develop a numerical approach to explore the influence of clay content on soil hydrothermal response to the timely climatic conditions in the Lake Chad region,Sahel Region of west-central Africa.The meteorological information at the studied points,i.e.points A and B with a clay content of 8.3%and 25%,during the year 2008 is collected from ERA5-Land hourly data.The numerical results allow for understanding the effect of clay content on the hydrothermal response of the surface soil layer.Specifically,the soil surface temperature under point A is lower than that under point B during the dry season due to the dominant effect of heat conduction.However,the converse tendency is observed during the wet season because of the combined effect of heat conduction and latent heat.The variations of soil volumetric water content are closely related to the timely interaction between the soil and atmosphere,in addition to the hydrothermal properties of soil.Moreover,the outcomes of this work improve the understanding of the heat and water dynamics under the effect of climatic conditions and clay content,and provide further insights into the potential water protection in arid and semi-arid regions in the future.
文摘In fog, visibility is reduced. This reduction in visibility is measured by the meteorological optical range (MOR), which is important for studying human perception and various sensors in foggy conditions. The Cerema PAVIN Fog & Rain platform is capable of producing calibrated fog in order to better analyses it and understand its consequences. The problem is that the droplets produced by the platform are not large enough to resemble real fog. This can have a major impact on measurements since the interaction between electromagnetic waves and fog depends on the wavelength and diameter of the droplets. To remedy this, Cerema is building a new platform with new equipment capable of generating fog. This study analyses different nozzles and associated usage parameters such as the type of water used and the pressure used. The aim is to select the best nozzle with the associated parameters for producing large-diameter droplets and therefore more realistic fog.
文摘A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate solution, is developed in this work. After the samples were cured at room temperature under air for 28 d, they were analyzed by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, environmental scanning electron microscopy, mercury intrusion porosimetry, ^(27)Al and ^(29)Si nuclear magnetic resonance(NMR) spectroscopy, and compression testing to establish the relationship between microstructure and compressive strength. The XRD, FTIR, and ^(27)Al and ^(29)Si NMR analyses showed that the use of silica fume instead of alkali silicate solutions was feasible for manufacturing geopolymer cement. The Mk-based geopolymer with a silica fume content of 6 wt%(compared with those with 2% and 10%), corresponding to an SiO_2/Al_2O_3 molar ratio of 3.84, resulted in the highest compressive strength, which was explained on the basis of its high compactness with the smallest porosity. Silica fume improved the compressive strength by filling interstitial voids of the microstructure because of its fine particle size. In addition, an increase in the SiO_2/Al_2O_3 molar ratio, which is controlled by the addition of silica fume, to 4.09 led to a geopolymer with low compressive strength, accompanied by microstructures with high porosity. This high porosity, which is responsible for weaknesses in the specimen, is related to the amount of unreacted silica fume.
基金support by the French Space Agency CNES,PNP(Programme National de Planétologie)TOSCA(Terre,Océan,Surfaces Continentales,Atmosphère)
文摘In continental and oceanic conditions, clay-rich deposits are characterised by the development of polygonal fracture systems（PFS）. PFS can increase the vertical permeability of clay-rich deposits（mean permeability ≤10-16 m2） and are pathways for fluids. On continents, the width of PFS ranges from centimeters to hundreds of meters, while in oceanic contexts they are up to a few kilometers large. These structures are linked to water-solid separation during deposition, consolidation and complete fluid squeeze of the clay horizon. During the last few decades, modeling of melt migration in partially molten plastic rocks led to rigorous quantifications of two-phase flows with a particular emphasis on 2D and 3D induced flow structures. The numerical modeling shows that the melt migrates on distances almost equal to a few times the compaction length L that depends on permeability and viscosity. Consequently, polygonal structures in partially molten plastic rocks are resulted from the melt-rock separation and their sizes are proportional to L. Applying these results to fluid-solid separation in clay-rich horizons, we show that（1） centimetric to kilometric PFS are resulted from the dramatic increase of L during compaction and（2）, this process involves agglomerates with 100 μm to 1 mm size.
文摘France has about one million kilometres of roads, 98% of which are managed by departments （the French Administrative Area Departement） and municipalities. Because of growing social expenditures, these local authorities are reducing credits for roads, which is leading to a reduction in the length of roads serviced annually, and an expected deterioration of roads generally. Faced with this problem, departmental and urban project designers in the eastern region of France have been meeting within the GEPUR （＂Gestion et Entretien du Patrimoine Urbain et Routier＂ or ＂Urban and Road Heritage Management and Maintenance＂） group since September 2012, to： firstly, develop a method for road network management and programming of assistance based on the experiences of each participant, a modular method depending on the size of the road network and adapted to the contracting authority; secondly, give technical legitimacy to the managers who will be applying the method. They will be able to more easily set up a constructive dialogue with the elected officials in charge of roads, and better justify the use of the credits requested. Two methodological guides will be published, one intended for departmental networks （2015）, the other for municipal networks in mid-2017. A white paper for elected officials has also been drafted. Ultimately, this experience will be extended throughout France.
文摘A large amount of researches and studies have been recently performed by applying statistical and machine learning techniques for vibration-based damage detection. However, the global character inherent to the limited number of modal properties issued from operational modal analysis may be not appropriate for early-damage, which has generally a local character. The present paper aims at detecting this type of damage by using static SHM data and by assuming that early-damage produces dead load redistribution. To achieve this objective a data driven strategy is proposed, consisting of the combination of advanced statistical and machine learning methods such as principal component analysis, symbolic data analysis and cluster analysis. From this analysis it was observed that, under the noise levels measured on site, the proposed strategy is able to automatically detect stiffness reduction in stay cables reaching at least 1%.
