T3SiC2 bulks have been synthesized by infiltrating Si liquid into porous precursor pellets composed of solid Ti and C powders. Silicon pellets were placed at the bottom of the precursor pellets as the liquid source. T...T3SiC2 bulks have been synthesized by infiltrating Si liquid into porous precursor pellets composed of solid Ti and C powders. Silicon pellets were placed at the bottom of the precursor pellets as the liquid source. The starting compositions can be represented by the formula 3Ti + 2C + xSi, where x = 1.0, 1.2, 1.4 and 1.6, respectively. The phase formation and microstructure of the bulks were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrated that the Ti/C precursor pellet could only react with Si completely when the x value is 1.6. Large, a purity of above 95wt% Ti3SiC2 bulk of up to 50 mm in diameter was obtained by this method.展开更多
<div style="text-align:justify;"> Rainfall infiltration is a porous medium flow problem with variable saturation. Based on the theoretical analysis of the flow field, electrical conductivity of rocks, ...<div style="text-align:justify;"> Rainfall infiltration is a porous medium flow problem with variable saturation. Based on the theoretical analysis of the flow field, electrical conductivity of rocks, the electrical field, the paper simulates the coupling relationship between the water saturation in soil and the apparent resistivity distribution. It combines the Richards equation, the Archie formula and the Laplace equation. The experiment simulates the potential field data by the Wenner setting in electrical exploration on a two-layer geologic model with continuous rainfall during 5 days, which shows that the effective saturation in soil is increasing with the rainfall time, while the apparent resistivity is decreasing. This can provide a theoretical basis for the analyzing the rainfall infiltration and porosity of the soil by using high-density electrical method in the future. </div>展开更多
A finite difference (FD) model is proposed to simulate the chemical vapor infiltration (CVI) processes for fabrication of carbon carbon composites. With iterative operation of many discrete values, the FD based mode...A finite difference (FD) model is proposed to simulate the chemical vapor infiltration (CVI) processes for fabrication of carbon carbon composites. With iterative operation of many discrete values, the FD based model can be used to describe and analyze the real, continuous densification processing quantitatively. Many densification characteristics of carbon carbon composites can be predicated by modeling. The prediction results can be compared with experiment value directly, which shows its good ability for practical application. Special verification experiments are designed with Iso thermal CVI processing and slender cylindroid unidirectional C/C composites are prepared to verify the accuracy of the model. The modeling curve of density versus infiltration time is in good agreement with experiment values. According to modeling analysis, the effects of infiltration temperature and fiber volume fraction on densification are also discussed preliminarily. The conclusion obtained also accords with experiment or results in other literature, further approving the accuracy of the FD based model.展开更多
An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finit...An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finite-element method(FEM)-based models. The results show that the reactivation of old landslide deposit was triggered by the long-term leakage of diversion ditch before October 2012, and the reactivation was triggered again by the intense rainfall on 7-9 October 2012. The old cracks, which formed in the earlier reactivation of landslide, played a key role for the rainfall infiltration. They offered a preferential path for much more rainfall to infiltrate fast into deep soil, and caused wetting front to move down faster in landslide. The old slip zone with lower permeability was another important factor to cause the infiltrated water to accumulate and form a high pore water pressure above slip zone. Then the high pore water pressure decreased the shear strength of slip zone and triggered the reactivation of the old landslide deposit again.展开更多
AIM: To investigate fat infiltration and volume of spino-pelvic muscles in adults spinal deformity(ASD) with magnetic resonance imaging(MRI) and 3D reconstructions.METHODS: Nineteen female ASD patients(mean age 60 ...AIM: To investigate fat infiltration and volume of spino-pelvic muscles in adults spinal deformity(ASD) with magnetic resonance imaging(MRI) and 3D reconstructions.METHODS: Nineteen female ASD patients(mean age 60 ± 13) were included prospectively and consecutively and had T1-weighted Turbo Spin Echo sequence MRIs with Dixon method from the proximal tibia up to T12 vertebra. The Dixon method permitted to evaluate the proportion of fat inside each muscle(fat-water ratio). In order to investigate the accuracy of the Dixon method for estimating fat vs water, the same MRI acquisition was performed on phantoms of four vials composed of different proportion of fat vs water. With Muscl'X software, 3D reconstructions of 17 muscles or group of muscles were obtained identifying the muscle's contour on a limited number of axial images [Deformation of parametric specific objects(DPSO) Method]. Musclar volume(Vmuscle), infiltrated fat volume(Vfat) and percentage of fat infiltration [Pfat, calculated as follow: Pfat = 100 ×(Vfat/Vmuscle)] were characterized by extensor or flexor function respectively for the spine, hip and knee and theirs relationship with demographic data were investigated. RESULTS: Phantom acquisition demonstrated a non linear relation between Dixon fat-water ratio and the real fat-water ratio. In order to correct the Dixon fatwater ratio, the non linear relation was approximated with a polynomial function of degree three using the phantom acquisition. On average, Pfat was 13.3% ± 5.3%. Muscles from the spinal extensor group had a Pfat significantly greater than the other muscles groups, and the largest variability(Pfat = 31.9% ± 13.8%, P < 0.001). Muscles from the hip extensor group ranked 2nd in terms of Pfat(14% ± 8%), and were significantly greater than those of the knee extensor(P = 0.030). Muscles from the knee extensor group demonstrated the least Pfat(12% ± 8%). They were also the only group with a significant correlation between Vmuscle and Pfat(r =-0.741, P < 0.001), however this correlation was lacking in the other groups. No correlation was found between the Vmuscle total and age or body mass index. Except for the spine flexors, Pfat was correlated with age. Vmuscle and Vfat distributions demonstrated that muscular degeneration impacted the spinal extensors most.CONCLUSION: Mechanisms of fat infiltration are not similar among the muscle groups. Degeneration impacted the spinal and hip extensors most, key muscles of the sagittal alignment.展开更多
In soil water infiltration problems,the basic control equation,i.e.,Richards equation is a nonlinear partial differential equation(PDE),and is difficult to solve.In this study,a finite difference lattice Boltzmann met...In soil water infiltration problems,the basic control equation,i.e.,Richards equation is a nonlinear partial differential equation(PDE),and is difficult to solve.In this study,a finite difference lattice Boltzmann method(FDLBM),in which the D1Q5 model is employed as the lattice layout scheme,is developed to solve the 1-D Richards equation with water content as the main variable in unsaturated soil.The relationship between the lattice Boltzmann equation(LBE)and the Richards equation is established using a multiscale expansion technique.Numerical examples show that LBM is suitable to solve Richards equation in unsaturated soil water infiltration problems.展开更多
The upper limit of the solid scatters density ns （x）, a key parameter for the simulation of flows in porous media with a gray Lattice Boltzmann Method, is studied by an analytical way for the infiltration Poiseuille...The upper limit of the solid scatters density ns （x）, a key parameter for the simulation of flows in porous media with a gray Lattice Boltzmann Method, is studied by an analytical way for the infiltration Poiseuille flow between two infinite parallel plates. Analyses of three different gray Lattice Boltzmann schemes, separately proposed by Gao and Sharma et al., Dardis and McCloskey, and Thorne and Sukop, indicate that the effective domain of Gao and Sharma＇s scheme is restricted to ns 〈 1/2√3≈0.289, Dardis and McCloskey＇s scheme is restricted to ns 〈 （√57-1）/28≈0.234, and that there is no extra restriction on ns（x） with Thorne and Sukop＇s scheme. These results are obtained for the dimensionless relaxation time τ= 1. The above analytical results are verified by our numerical simulations. The use of a gray LBM is further illustrated by simulating the flow at the interface of a porous medium. Simulation results yield velocity profiles which agree very well with Brinkman＇s prediction.展开更多
To investigate the thermal stability of ceramic-matrix composites,three kinds of C/C−ZrC−SiC composites with different Zr/Si molar ratios were synthesized by reactive melt infiltration.Employing region labeling method...To investigate the thermal stability of ceramic-matrix composites,three kinds of C/C−ZrC−SiC composites with different Zr/Si molar ratios were synthesized by reactive melt infiltration.Employing region labeling method,the high-temperature thermal stability of the composites was systematically studied by changing the temperature and holding time of thermal treatment.Results show that the mass loss rate of low Si composites has a growth trend with increasing temperature,and a crystal transformation from β-SiC toα-SiC occurs in the composites.In the calibrated area,SiC phase experiences Ostwald ripening and volume change with location migration,while ZrC phase experiences a re-sintering process with diffusion.Moreover,it is found that increasing temperature has a more obvious effect on the thermal stability than extending holding time,which is mainly attributed to the faster diffusion rate of atoms.展开更多
通过文献计量法,基于中国知网(CNKI)和Web of Science(WOS)数据库中2000—2023年有关污水地下渗滤系统(SWIS)的270篇文献,利用VOSviewer和CiteSpace软件绘制发文机构合作图谱、作者合作网络图谱以及关键词共现分析图谱,旨在探究地下渗...通过文献计量法,基于中国知网(CNKI)和Web of Science(WOS)数据库中2000—2023年有关污水地下渗滤系统(SWIS)的270篇文献,利用VOSviewer和CiteSpace软件绘制发文机构合作图谱、作者合作网络图谱以及关键词共现分析图谱,旨在探究地下渗滤的合作网络、研究现状及核心热点。研究表明,地下渗滤相关的发表量呈现先增后减的趋势,反映了该技术自21世纪以来的发展历程和学术关注度的变化。此外,发文作者和机构的合作图谱展现了学术交流和合作研究的活跃态势,辽宁省的高校和科研院所之间合作较为密切。关键词分析发现当前研究热点集中于填料优化、水力负荷调控、污染物去除效率提升及微生物群落作用4个方向。展开更多
The chemical vapor infiltration process in fabrication of carbon-carbon composites is highly inefficient and requires long processing time. These limitations add considerably to the cost of fabrication and restrict th...The chemical vapor infiltration process in fabrication of carbon-carbon composites is highly inefficient and requires long processing time. These limitations add considerably to the cost of fabrication and restrict the application of this material. Efforts have been made to study the CVI process in fabrication of carbon-carbon composites by computer simulation and predict the process parameters, density, porosity, etc. According to the characteristics of CVI process, the basis principle of FEM and mass transport, the finite element model has been established. Incremental finite element equations and the elemental stiffness matrices have been derived for the first time. The finite element program developed by the authors has been used to simulate the ICVI process in fabrication of carbon-carbon composites. Computer color display of simulated results can express the densification and distributions of density and porosity in preform clearly. The influence of process parameters on the densification of preform has been analyzed. The numerically simulated and experimental results give a good agreement.展开更多
Some Swedish school buildings built in the 1960s and 1970s experience indoor air quality problems,where the contaminants are suspected to come from the crawl space underneath the building.The poor indoor air quality c...Some Swedish school buildings built in the 1960s and 1970s experience indoor air quality problems,where the contaminants are suspected to come from the crawl space underneath the building.The poor indoor air quality causes discomfort among pupils and teachers.Installing an exhaust fan to maintain a negative pressure difference in the crawl space relative to indoors or increasing the ventilation in the classroom are two examples of common measures taken to improve the indoor air quality.However,these measures are not always effective,and sometimes the school building has to be demolished.The relation between pressure distribution,contaminant concentration in the classroom,outdoor temperature,wind,mechanical ventilation,and air leakage distribution is complex.A better understanding of these relations is crucial for making decisions on the most efficient measure to improve the indoor air quality.In this paper,a model for contaminant infiltration from the crawl space is used together with the Monte Carlo method to study these relations.Simulations are performed for several cases where different building shapes,building orientations,shielding conditions,and geographical locations are simulated.Results show,for example,that for a building with an imbalanced ventilation system,air is leaking from the crawl space to the classroom for the majority of cases and that concentration levels in the classroom are usually the highest during mild and calm days.展开更多
基金National Basic Research Program of China (2011CBA00102)National Natural Science Foundation of China (50672077)
文摘T3SiC2 bulks have been synthesized by infiltrating Si liquid into porous precursor pellets composed of solid Ti and C powders. Silicon pellets were placed at the bottom of the precursor pellets as the liquid source. The starting compositions can be represented by the formula 3Ti + 2C + xSi, where x = 1.0, 1.2, 1.4 and 1.6, respectively. The phase formation and microstructure of the bulks were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrated that the Ti/C precursor pellet could only react with Si completely when the x value is 1.6. Large, a purity of above 95wt% Ti3SiC2 bulk of up to 50 mm in diameter was obtained by this method.
文摘<div style="text-align:justify;"> Rainfall infiltration is a porous medium flow problem with variable saturation. Based on the theoretical analysis of the flow field, electrical conductivity of rocks, the electrical field, the paper simulates the coupling relationship between the water saturation in soil and the apparent resistivity distribution. It combines the Richards equation, the Archie formula and the Laplace equation. The experiment simulates the potential field data by the Wenner setting in electrical exploration on a two-layer geologic model with continuous rainfall during 5 days, which shows that the effective saturation in soil is increasing with the rainfall time, while the apparent resistivity is decreasing. This can provide a theoretical basis for the analyzing the rainfall infiltration and porosity of the soil by using high-density electrical method in the future. </div>
文摘A finite difference (FD) model is proposed to simulate the chemical vapor infiltration (CVI) processes for fabrication of carbon carbon composites. With iterative operation of many discrete values, the FD based model can be used to describe and analyze the real, continuous densification processing quantitatively. Many densification characteristics of carbon carbon composites can be predicated by modeling. The prediction results can be compared with experiment value directly, which shows its good ability for practical application. Special verification experiments are designed with Iso thermal CVI processing and slender cylindroid unidirectional C/C composites are prepared to verify the accuracy of the model. The modeling curve of density versus infiltration time is in good agreement with experiment values. According to modeling analysis, the effects of infiltration temperature and fiber volume fraction on densification are also discussed preliminarily. The conclusion obtained also accords with experiment or results in other literature, further approving the accuracy of the FD based model.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41472274, 41672300)Independent Subject Foundation of SKLGP (SKLGP2017Z010)
文摘An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finite-element method(FEM)-based models. The results show that the reactivation of old landslide deposit was triggered by the long-term leakage of diversion ditch before October 2012, and the reactivation was triggered again by the intense rainfall on 7-9 October 2012. The old cracks, which formed in the earlier reactivation of landslide, played a key role for the rainfall infiltration. They offered a preferential path for much more rainfall to infiltrate fast into deep soil, and caused wetting front to move down faster in landslide. The old slip zone with lower permeability was another important factor to cause the infiltrated water to accumulate and form a high pore water pressure above slip zone. Then the high pore water pressure decreased the shear strength of slip zone and triggered the reactivation of the old landslide deposit again.
基金Supported by International Spine Study Group and ParisTech BiomecAM chair program on subject-specific musculoskeletal modeling,with the support of Proteor,Covea,Société Général,ParisTech and Yves Cotrel Foundation
文摘AIM: To investigate fat infiltration and volume of spino-pelvic muscles in adults spinal deformity(ASD) with magnetic resonance imaging(MRI) and 3D reconstructions.METHODS: Nineteen female ASD patients(mean age 60 ± 13) were included prospectively and consecutively and had T1-weighted Turbo Spin Echo sequence MRIs with Dixon method from the proximal tibia up to T12 vertebra. The Dixon method permitted to evaluate the proportion of fat inside each muscle(fat-water ratio). In order to investigate the accuracy of the Dixon method for estimating fat vs water, the same MRI acquisition was performed on phantoms of four vials composed of different proportion of fat vs water. With Muscl'X software, 3D reconstructions of 17 muscles or group of muscles were obtained identifying the muscle's contour on a limited number of axial images [Deformation of parametric specific objects(DPSO) Method]. Musclar volume(Vmuscle), infiltrated fat volume(Vfat) and percentage of fat infiltration [Pfat, calculated as follow: Pfat = 100 ×(Vfat/Vmuscle)] were characterized by extensor or flexor function respectively for the spine, hip and knee and theirs relationship with demographic data were investigated. RESULTS: Phantom acquisition demonstrated a non linear relation between Dixon fat-water ratio and the real fat-water ratio. In order to correct the Dixon fatwater ratio, the non linear relation was approximated with a polynomial function of degree three using the phantom acquisition. On average, Pfat was 13.3% ± 5.3%. Muscles from the spinal extensor group had a Pfat significantly greater than the other muscles groups, and the largest variability(Pfat = 31.9% ± 13.8%, P < 0.001). Muscles from the hip extensor group ranked 2nd in terms of Pfat(14% ± 8%), and were significantly greater than those of the knee extensor(P = 0.030). Muscles from the knee extensor group demonstrated the least Pfat(12% ± 8%). They were also the only group with a significant correlation between Vmuscle and Pfat(r =-0.741, P < 0.001), however this correlation was lacking in the other groups. No correlation was found between the Vmuscle total and age or body mass index. Except for the spine flexors, Pfat was correlated with age. Vmuscle and Vfat distributions demonstrated that muscular degeneration impacted the spinal extensors most.CONCLUSION: Mechanisms of fat infiltration are not similar among the muscle groups. Degeneration impacted the spinal and hip extensors most, key muscles of the sagittal alignment.
基金Project supported by the National Natural Science Foundation of China(Grant No.12461084)supported by the Natural Science Foundation of Ningxia(Grant No.2023AAC02049)+3 种基金the Graduate Innovation Program of North Minzu University(Grant No.YCX24072)the Science and Technology Innovation Team of Water Resource Efficient Applications and Ecological Remediation(Grant No.2024CXTD015)the Innovation Team of North Minzu University(Grant No.2022PT_S02)the Leading Personnel of State Ethnic Affairs Commission,China(Grant No.113114000706).
文摘In soil water infiltration problems,the basic control equation,i.e.,Richards equation is a nonlinear partial differential equation(PDE),and is difficult to solve.In this study,a finite difference lattice Boltzmann method(FDLBM),in which the D1Q5 model is employed as the lattice layout scheme,is developed to solve the 1-D Richards equation with water content as the main variable in unsaturated soil.The relationship between the lattice Boltzmann equation(LBE)and the Richards equation is established using a multiscale expansion technique.Numerical examples show that LBM is suitable to solve Richards equation in unsaturated soil water infiltration problems.
基金the National Natural Science Foundation of China(10772097)
文摘The upper limit of the solid scatters density ns （x）, a key parameter for the simulation of flows in porous media with a gray Lattice Boltzmann Method, is studied by an analytical way for the infiltration Poiseuille flow between two infinite parallel plates. Analyses of three different gray Lattice Boltzmann schemes, separately proposed by Gao and Sharma et al., Dardis and McCloskey, and Thorne and Sukop, indicate that the effective domain of Gao and Sharma＇s scheme is restricted to ns 〈 1/2√3≈0.289, Dardis and McCloskey＇s scheme is restricted to ns 〈 （√57-1）/28≈0.234, and that there is no extra restriction on ns（x） with Thorne and Sukop＇s scheme. These results are obtained for the dimensionless relaxation time τ= 1. The above analytical results are verified by our numerical simulations. The use of a gray LBM is further illustrated by simulating the flow at the interface of a porous medium. Simulation results yield velocity profiles which agree very well with Brinkman＇s prediction.
基金supported by the National Natural Science Foundation of China(No.U19A2099)the CAS Key Laboratory of Carbon Materials,China(No.KLCMKFJJ2005)the Fund of Aerospace Research Institute of Material and Processing Technology,China(No.6142906200108).
文摘To investigate the thermal stability of ceramic-matrix composites,three kinds of C/C−ZrC−SiC composites with different Zr/Si molar ratios were synthesized by reactive melt infiltration.Employing region labeling method,the high-temperature thermal stability of the composites was systematically studied by changing the temperature and holding time of thermal treatment.Results show that the mass loss rate of low Si composites has a growth trend with increasing temperature,and a crystal transformation from β-SiC toα-SiC occurs in the composites.In the calibrated area,SiC phase experiences Ostwald ripening and volume change with location migration,while ZrC phase experiences a re-sintering process with diffusion.Moreover,it is found that increasing temperature has a more obvious effect on the thermal stability than extending holding time,which is mainly attributed to the faster diffusion rate of atoms.
文摘通过文献计量法,基于中国知网(CNKI)和Web of Science(WOS)数据库中2000—2023年有关污水地下渗滤系统(SWIS)的270篇文献,利用VOSviewer和CiteSpace软件绘制发文机构合作图谱、作者合作网络图谱以及关键词共现分析图谱,旨在探究地下渗滤的合作网络、研究现状及核心热点。研究表明,地下渗滤相关的发表量呈现先增后减的趋势,反映了该技术自21世纪以来的发展历程和学术关注度的变化。此外,发文作者和机构的合作图谱展现了学术交流和合作研究的活跃态势,辽宁省的高校和科研院所之间合作较为密切。关键词分析发现当前研究热点集中于填料优化、水力负荷调控、污染物去除效率提升及微生物群落作用4个方向。
文摘The chemical vapor infiltration process in fabrication of carbon-carbon composites is highly inefficient and requires long processing time. These limitations add considerably to the cost of fabrication and restrict the application of this material. Efforts have been made to study the CVI process in fabrication of carbon-carbon composites by computer simulation and predict the process parameters, density, porosity, etc. According to the characteristics of CVI process, the basis principle of FEM and mass transport, the finite element model has been established. Incremental finite element equations and the elemental stiffness matrices have been derived for the first time. The finite element program developed by the authors has been used to simulate the ICVI process in fabrication of carbon-carbon composites. Computer color display of simulated results can express the densification and distributions of density and porosity in preform clearly. The influence of process parameters on the densification of preform has been analyzed. The numerically simulated and experimental results give a good agreement.
基金The project has been funded by FORMAS,the Swedish Research Council for Environment,Agricultural Sciences and Spatial Planning and supported by Gothenburg Premises Administration.
文摘Some Swedish school buildings built in the 1960s and 1970s experience indoor air quality problems,where the contaminants are suspected to come from the crawl space underneath the building.The poor indoor air quality causes discomfort among pupils and teachers.Installing an exhaust fan to maintain a negative pressure difference in the crawl space relative to indoors or increasing the ventilation in the classroom are two examples of common measures taken to improve the indoor air quality.However,these measures are not always effective,and sometimes the school building has to be demolished.The relation between pressure distribution,contaminant concentration in the classroom,outdoor temperature,wind,mechanical ventilation,and air leakage distribution is complex.A better understanding of these relations is crucial for making decisions on the most efficient measure to improve the indoor air quality.In this paper,a model for contaminant infiltration from the crawl space is used together with the Monte Carlo method to study these relations.Simulations are performed for several cases where different building shapes,building orientations,shielding conditions,and geographical locations are simulated.Results show,for example,that for a building with an imbalanced ventilation system,air is leaking from the crawl space to the classroom for the majority of cases and that concentration levels in the classroom are usually the highest during mild and calm days.
