Top structure and basement will confront the risk of being damaged on account of large stress and strain fields incurred by differential uplift and settlement between inner column and diaphragm wall in top-down method...Top structure and basement will confront the risk of being damaged on account of large stress and strain fields incurred by differential uplift and settlement between inner column and diaphragm wall in top-down method. Top-down excavation of the Metro Line 10 in Shanghai was modeled with finite element analysis software ABAQUS and parameters of subsoil were obtained by inverse analysis. Based on the finite element model and parameters, changes in the following factors were made to find more effective methods to restrain differential uplift and settlement: length of diaphragm wall, thickness of jet-grouting reinforcement layer, ways of subsoil reinforcement, sequence of pit excavation, connection between slabs and diaphragm wall or column and width of pit. Several significant results are acquired. The longer the diaphragm wall is, the greater the differential uplift between column and diaphragm wall is. Rigidity of roof slab is in general not strong enough to keep diaphragm wall and column undergoing the same uplift during excavation; Uplift at head of column and differential uplift between column and diaphragm wall decrease when subsoil from-16.6 to-43 m in pit is reinforced through jet-grouting. But, as excavation proceeds to a lower level, benefit from soil reinforcement diminishes. During the process applying vertical load, the larger the depth of diaphragm wall is, the smaller the settlement is at head of column and diaphragm wall, and the greater the differential settlement is between column and diaphragm wall. When friction connection is implemented between column, diaphragm wall and floor slabs, uplifts at head of column and diaphragm wall are larger than those of the case when tie connection is implemented, and so does differential uplift between column and diaphragm wall. The maximum deflection of diaphragm wall decreases by 58% on account of soil reinforcement in pit. The maximum deflection of diaphragm wall decreases by 61.2% when friction connection is implemented instead of tie connection.展开更多
Top-down crack in asphalt pavements has been reported as a widespread mode of failure.A solid understanding of the mechanisms of crack growth is essential to predict pavement performance in the context of thickness de...Top-down crack in asphalt pavements has been reported as a widespread mode of failure.A solid understanding of the mechanisms of crack growth is essential to predict pavement performance in the context of thickness design,as well as in the design and optimization of mixtures.Using the coupled element free Galerkin (EFG) and finite element (FE) method,top-down crack propagation in asphalt pavements is numerically simulated on the basis of fracture mechanics.A parametric study is conducted to isolate the effects of overlay thickness and stiffness,base thickness and stiffness on top-down crack propagation in asphalt pavements.The results show that longitudinal wheel loads are disadvantageous to top-down crack because it increases the compound stress intensity factor (SIF) at the tip of top-down crack and shortens the crack path,and thus the fatigue life descends.The SIF experiences a process "sharply ascending—slowly descending—slowly ascending—sharply ascending again" with the crack propagating.The thicker the overlay or the base,the lower the SIF; the greater the overlay stiffness,the higher the SIF.The crack path is hardly affected by stiffness of the overlay and base.展开更多
This paper studies a new software project planning method under some actual project data in order to make software project plans more effective. From the perspective of system theory, our new method regards a software...This paper studies a new software project planning method under some actual project data in order to make software project plans more effective. From the perspective of system theory, our new method regards a software project plan as an associative unit for study. During a top-down estimation of a software project, Program Evaluation and Review Technique （PERT） method and analogy method are combined to estimate its size, then effort estimation and specific schedules are obtained according to distributions of the phase effort. This allows a set of practical and feasible planning methods to be constructed. Actual data indicate that this set of methods can lead to effective software project planning.展开更多
Climate change will bring huge risks to human society and the economy.Regional climate change risk assessment is an important basic analysis for addressing climate change,which can be expressed as a regional system of...Climate change will bring huge risks to human society and the economy.Regional climate change risk assessment is an important basic analysis for addressing climate change,which can be expressed as a regional system of comprehensive climate change risk.This study establishes regional systems of climate change risks under the proposed global warming targets.Results of this work are spatial patterns of climate change risks in China,indicated by the degree of climate change and the status of the risk receptors.Therefore,the risks show significant spatial differences.The high-risk regions are mainly distributed in East,South,and central China,while the medium-high risk regions are found in North and southwestern China.Under the 2℃warming target,more than 1/4 of China’s area would be at high and medium-high risk,which is more severe than under the 1.5℃warming target,and would extend to the western and northern regions.This work provides regional risk characteristics of climate change under different global warming targets as a foundation for dealing with climate change.展开更多
Due to their unique physical and chemical properties,two-dimensional(2D)boron nanosheets have received tremendous research attention and demonstrated substantial value in electronic devices,biomedicine,and energy conv...Due to their unique physical and chemical properties,two-dimensional(2D)boron nanosheets have received tremendous research attention and demonstrated substantial value in electronic devices,biomedicine,and energy conversion.In the preparation of boron nanosheets,compared with the bottom-up synthesis predominantly employed for electronics,the top-down synthesis route offers more facile and scalable production.In this mini-review,we mainly discuss the recent advances in the synthesis of boron nanosheets using the top-down strategy and the relevant applications in energy catalysis.Finally,inspired by our recent works on the novel applications of 2D silicon,we put forward prospects for designing boron nanosheets,providing insights into developing viable techniques for high-performance heterogeneous catalysis.展开更多
Two-dimensional(2D)covalent organic framework nanosheets(CONs)are attracting increasing research attention because of their unique properties derived from their ultrathin thickness,high surface-tovolume atomic ratio,a...Two-dimensional(2D)covalent organic framework nanosheets(CONs)are attracting increasing research attention because of their unique properties derived from their ultrathin thickness,high surface-tovolume atomic ratio,and extremely large surface area.2D CONs can provide high transport pathways for charge carriers(e.g.,electrons,holes and ions)through either the conjugated skeletons or the open channels.Therefore,they have shown great potential in energy related applications.In this review,we firstly introduce the recent developments and characteristics of 2D CONs by focusing on the two typical synthetic methods,i.e.,top-down and bottom-up methods.Then,the energy-related applications in energy storage and conversion of 2D CONs are summarized.Finally,we give our personal views on the challenges and perspectives for the future research of 2D CONs and their composites.展开更多
This paper discusses whether target costing(TC)is affected by the impacts of external circumstances and appears dynamic in real estate development industry.A case study was conducted and combined with literature revie...This paper discusses whether target costing(TC)is affected by the impacts of external circumstances and appears dynamic in real estate development industry.A case study was conducted and combined with literature reviews to test this proposition.The results of this paper show that the formula appears dynamic on the impacts of economic depression/recession,inflation,and change of governmental policy to assist the firms in the achievement of planned profits.TC,as a strategic profit management system in the industry,exhibits brisk utilization in a dynamic formula with more of a focus on value added to maintain fixed profits.It is different from the focus on cost reduction by a static formula in previous literatures.展开更多
Metal-organic framework(MOF)nanosheets and covalent organic framework(COF)nanosheets as emerging porous materials nanosheets have captured increasing attention owing to their attractive properties originating from the...Metal-organic framework(MOF)nanosheets and covalent organic framework(COF)nanosheets as emerging porous materials nanosheets have captured increasing attention owing to their attractive properties originating from the advantages of large lateral size,ultrathin thickness,tailorable physiochemical environment,flexibility and highly accessible active sites on surface,and the applications of them have been explored in a wide range of fields.Although MOF and COF nanosheets own many similar properties,their applications in various fields show significant differences,probably due to their different compositions and bonding modes.Hence,we summarize the recent progress of MOF and COF nanosheets by comparative analysis on their advantages and limitations in synthesis and applications,providing a more profound and full-scale perspective for researchers or beginners to understand this field.Herein,the categories of preparation methods of MOF and COF nanosheets are firstly discussed,including top-down and bottom-up methods.Secondly,the applications of MOF and COF nanosheets for separation,catalysis,sensing and energy storage are summarized.Finally,based on current achievements,we put forward our personal insights into the challenges and outlooks on the synthesis,characterizations,and promising applications for future research of MOF and COF nanosheets.展开更多
Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of th...Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of the Shanghai Center involved excavations in excess of 33-m-deep using the top-down method at a site underlain by thick deposits of marine soft clay. A retaining system was achieved by 50-m-deep diaphragm walls with six levels of struts. During construction, a comprehensive instrumentation program lasting 14 months was conducted to monitor the behaviors of this deep circular excavation. The following main items related to ground surface movements and deformations were collected： （1） walls and circumferential soils lateral movements; （2） peripheral soil deflection in layers and ground settlements; and （3） pit basal heave. The results from the field instrumentation showed that deflections of the site were strictly controlled and had no large movements that might lead to damage to the stability of the foundation pit. The field performance of another 21 cylindrical excavations in top-down method were collected to compare with this case through statistical analysis. In addition, numerical analyses were conducted to compare with the observed data. The extensively monitored data are characterized and analyzed in this paper.展开更多
基金Projects(51208071,51108312) supported by the National Natural Science Foundation of China
文摘Top structure and basement will confront the risk of being damaged on account of large stress and strain fields incurred by differential uplift and settlement between inner column and diaphragm wall in top-down method. Top-down excavation of the Metro Line 10 in Shanghai was modeled with finite element analysis software ABAQUS and parameters of subsoil were obtained by inverse analysis. Based on the finite element model and parameters, changes in the following factors were made to find more effective methods to restrain differential uplift and settlement: length of diaphragm wall, thickness of jet-grouting reinforcement layer, ways of subsoil reinforcement, sequence of pit excavation, connection between slabs and diaphragm wall or column and width of pit. Several significant results are acquired. The longer the diaphragm wall is, the greater the differential uplift between column and diaphragm wall is. Rigidity of roof slab is in general not strong enough to keep diaphragm wall and column undergoing the same uplift during excavation; Uplift at head of column and differential uplift between column and diaphragm wall decrease when subsoil from-16.6 to-43 m in pit is reinforced through jet-grouting. But, as excavation proceeds to a lower level, benefit from soil reinforcement diminishes. During the process applying vertical load, the larger the depth of diaphragm wall is, the smaller the settlement is at head of column and diaphragm wall, and the greater the differential settlement is between column and diaphragm wall. When friction connection is implemented between column, diaphragm wall and floor slabs, uplifts at head of column and diaphragm wall are larger than those of the case when tie connection is implemented, and so does differential uplift between column and diaphragm wall. The maximum deflection of diaphragm wall decreases by 58% on account of soil reinforcement in pit. The maximum deflection of diaphragm wall decreases by 61.2% when friction connection is implemented instead of tie connection.
基金Project (Nos. 50908093 and 50778077) supported by the National Natural Science Foundation of China
文摘Top-down crack in asphalt pavements has been reported as a widespread mode of failure.A solid understanding of the mechanisms of crack growth is essential to predict pavement performance in the context of thickness design,as well as in the design and optimization of mixtures.Using the coupled element free Galerkin (EFG) and finite element (FE) method,top-down crack propagation in asphalt pavements is numerically simulated on the basis of fracture mechanics.A parametric study is conducted to isolate the effects of overlay thickness and stiffness,base thickness and stiffness on top-down crack propagation in asphalt pavements.The results show that longitudinal wheel loads are disadvantageous to top-down crack because it increases the compound stress intensity factor (SIF) at the tip of top-down crack and shortens the crack path,and thus the fatigue life descends.The SIF experiences a process "sharply ascending—slowly descending—slowly ascending—sharply ascending again" with the crack propagating.The thicker the overlay or the base,the lower the SIF; the greater the overlay stiffness,the higher the SIF.The crack path is hardly affected by stiffness of the overlay and base.
文摘This paper studies a new software project planning method under some actual project data in order to make software project plans more effective. From the perspective of system theory, our new method regards a software project plan as an associative unit for study. During a top-down estimation of a software project, Program Evaluation and Review Technique （PERT） method and analogy method are combined to estimate its size, then effort estimation and specific schedules are obtained according to distributions of the phase effort. This allows a set of practical and feasible planning methods to be constructed. Actual data indicate that this set of methods can lead to effective software project planning.
基金The National Key R&D Program of China,No.2018YFC1509002The Strategic Priority Research Program of the Chinese Academy of Sciences,No.XDA19040304。
文摘Climate change will bring huge risks to human society and the economy.Regional climate change risk assessment is an important basic analysis for addressing climate change,which can be expressed as a regional system of comprehensive climate change risk.This study establishes regional systems of climate change risks under the proposed global warming targets.Results of this work are spatial patterns of climate change risks in China,indicated by the degree of climate change and the status of the risk receptors.Therefore,the risks show significant spatial differences.The high-risk regions are mainly distributed in East,South,and central China,while the medium-high risk regions are found in North and southwestern China.Under the 2℃warming target,more than 1/4 of China’s area would be at high and medium-high risk,which is more severe than under the 1.5℃warming target,and would extend to the western and northern regions.This work provides regional risk characteristics of climate change under different global warming targets as a foundation for dealing with climate change.
基金supported by the National Natural Science Foundation of China(No.52372233)the Fundamental Research Funds for the Central Universities(No.226-2022-00200),China.
文摘Due to their unique physical and chemical properties,two-dimensional(2D)boron nanosheets have received tremendous research attention and demonstrated substantial value in electronic devices,biomedicine,and energy conversion.In the preparation of boron nanosheets,compared with the bottom-up synthesis predominantly employed for electronics,the top-down synthesis route offers more facile and scalable production.In this mini-review,we mainly discuss the recent advances in the synthesis of boron nanosheets using the top-down strategy and the relevant applications in energy catalysis.Finally,inspired by our recent works on the novel applications of 2D silicon,we put forward prospects for designing boron nanosheets,providing insights into developing viable techniques for high-performance heterogeneous catalysis.
基金the Class D of Qianjiang Talent Program(No.ZD20011250001)the start-up grant(No.2019125016829)in Zhejiang University of Technology+1 种基金the financial support from the funding of"Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang"(No.2020R01002)the financial support from the National Natural Science Foundation of China(No.51907173)。
文摘Two-dimensional(2D)covalent organic framework nanosheets(CONs)are attracting increasing research attention because of their unique properties derived from their ultrathin thickness,high surface-tovolume atomic ratio,and extremely large surface area.2D CONs can provide high transport pathways for charge carriers(e.g.,electrons,holes and ions)through either the conjugated skeletons or the open channels.Therefore,they have shown great potential in energy related applications.In this review,we firstly introduce the recent developments and characteristics of 2D CONs by focusing on the two typical synthetic methods,i.e.,top-down and bottom-up methods.Then,the energy-related applications in energy storage and conversion of 2D CONs are summarized.Finally,we give our personal views on the challenges and perspectives for the future research of 2D CONs and their composites.
文摘This paper discusses whether target costing(TC)is affected by the impacts of external circumstances and appears dynamic in real estate development industry.A case study was conducted and combined with literature reviews to test this proposition.The results of this paper show that the formula appears dynamic on the impacts of economic depression/recession,inflation,and change of governmental policy to assist the firms in the achievement of planned profits.TC,as a strategic profit management system in the industry,exhibits brisk utilization in a dynamic formula with more of a focus on value added to maintain fixed profits.It is different from the focus on cost reduction by a static formula in previous literatures.
基金the National Natural Science Foundation of China for Distinguished Young Scholars(No.21625401)the National Natural Science Foundation of China(Nos.21727808,21971114).
文摘Metal-organic framework(MOF)nanosheets and covalent organic framework(COF)nanosheets as emerging porous materials nanosheets have captured increasing attention owing to their attractive properties originating from the advantages of large lateral size,ultrathin thickness,tailorable physiochemical environment,flexibility and highly accessible active sites on surface,and the applications of them have been explored in a wide range of fields.Although MOF and COF nanosheets own many similar properties,their applications in various fields show significant differences,probably due to their different compositions and bonding modes.Hence,we summarize the recent progress of MOF and COF nanosheets by comparative analysis on their advantages and limitations in synthesis and applications,providing a more profound and full-scale perspective for researchers or beginners to understand this field.Herein,the categories of preparation methods of MOF and COF nanosheets are firstly discussed,including top-down and bottom-up methods.Secondly,the applications of MOF and COF nanosheets for separation,catalysis,sensing and energy storage are summarized.Finally,based on current achievements,we put forward our personal insights into the challenges and outlooks on the synthesis,characterizations,and promising applications for future research of MOF and COF nanosheets.
基金This paper is supported by National Natural Science Foundation of China （Grant No. 51768065）. The field monitoring measurements used in this paper were made available to the writers through the efforts of many organizations and individuals involved with the construction and inspection of the foundation pit of the Shanghai Center project. Special thanks to SGIDI for facilitating access to field data, In addition, the writers would like to acknowledge the support of Ms. Yashuang Bai and Mr. Yuxia Ji for data compilation and figures processing. Any views and opinions expressed in this case study are those of the writers and do not necessarily represent the views of the organizations or other individuals responsible for the design and construction of this project,
文摘Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of the Shanghai Center involved excavations in excess of 33-m-deep using the top-down method at a site underlain by thick deposits of marine soft clay. A retaining system was achieved by 50-m-deep diaphragm walls with six levels of struts. During construction, a comprehensive instrumentation program lasting 14 months was conducted to monitor the behaviors of this deep circular excavation. The following main items related to ground surface movements and deformations were collected： （1） walls and circumferential soils lateral movements; （2） peripheral soil deflection in layers and ground settlements; and （3） pit basal heave. The results from the field instrumentation showed that deflections of the site were strictly controlled and had no large movements that might lead to damage to the stability of the foundation pit. The field performance of another 21 cylindrical excavations in top-down method were collected to compare with this case through statistical analysis. In addition, numerical analyses were conducted to compare with the observed data. The extensively monitored data are characterized and analyzed in this paper.
