Centroidal Voronoi tessellations(CVTs) have become a useful tool in many applications ranging from geometric modeling,image and data analysis,and numerical partial differential equations,to problems in physics,astroph...Centroidal Voronoi tessellations(CVTs) have become a useful tool in many applications ranging from geometric modeling,image and data analysis,and numerical partial differential equations,to problems in physics,astrophysics,chemistry,and biology. In this paper,we briefly review the CVT concept and a few of its generalizations and well-known properties.We then present an overview of recent advances in both mathematical and computational studies and in practical applications of CVTs.Whenever possible,we point out some outstanding issues that still need investigating.展开更多
The little stiffness modulus, high voidage and long curing time has limited the use of CBEM＇s （cold bituminous emulsion mixtures） in road and highways to pavement experiencing low traffic. The aim of this study is ...The little stiffness modulus, high voidage and long curing time has limited the use of CBEM＇s （cold bituminous emulsion mixtures） in road and highways to pavement experiencing low traffic. The aim of this study is to improve the properties of gap graded CRA （cold rolled asphal0 containing OPC （ordinary portland cement） as filler by addition of a by-product material as an activator. OPC was added to the CRA as a replacement to the conventional mineral filler （0%-100%）, while LJMUA （Liverpool John Moores University Activator） was added as an additive in the range from 0%-3% by total mass of aggregate. Laboratory tests included stiffness modulus and uniaxial creep test to assess the mechanical properties. The results have shown a considerable improvement in the mechanical properties from the addition of LJMUA to the CRA containing OPC especially for the early life stiffness modulus that is the main disadvantage of the cold mixtures.展开更多
The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances （EPS） with unique morphologic features, such as stalks or sheaths, which can be regarded as geobiologi...The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances （EPS） with unique morphologic features, such as stalks or sheaths, which can be regarded as geobiological signatures. The Archean and early Palaeoproterozoic oceans were anoxic with high soluble Fe（Ⅱ） that were suggested to have been oxidized through the metabolism of Fe（II）-oxidizing bacteria. The precursor of the ultrafine hematite in banded iron formation （BIF）, e.g., ferrihy- drite, was suggested to be the mineral record of microbial Fe（Ⅱ）-oxidation at that time. However, both the biological materials and primary iron minerals were prone to being altered by diagenetic or low-grade metamorphic processes. This makes it diffi- cult to interpret the genesis of Precambrian BIFs. Here, we report experimental simulation on the effects of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe（Ⅱ）-oxidizing bacteria and their biomass. Stalks, sheaths, and iron oxide spheroidal aggregates are partially preserved after the 100 MPa/300℃ treatments, which indicates the mixed organic matters and iron oxides could survive the diagenetic or low-grade metamorphic processes. Some organic-mineral mixing structures carry information on microbial processes, though they appear similar to pseudomorphs of fossilized bacteria.展开更多
The problem of land ecological security directly threatens the sustainable development of many regions,and exploring the spatio-temporal characteristics of land ecological security is helpful for analyzing the land ec...The problem of land ecological security directly threatens the sustainable development of many regions,and exploring the spatio-temporal characteristics of land ecological security is helpful for analyzing the land ecological patterns between regions and over time.Based on the interpretation of remote sensing image data for Tianjin in 1980,2000,2010 and 2019,supported by software such as ArcGIS and GeoDa,the changes of land use in the study area are calculated by using the land use dynamic degree.Then,the land ecological security index and spatial autocorrelation analysis methods are used to study the spatial correlations and internal heterogeneity of land ecological security in each district in Tianjin.The results show that:(1)The land use of Tianjin has changed dramatically in the past 40 years:the building land has been expanding,while the farmland and barren have been shrinking continuously.(2)The overall level of land ecological security is in the high security area,and Jizhou District is the highest,while the Central areas and Binhai are low.(3)The spatial heterogeneity of land ecological security is not obvious,but the spatial agglomeration is strong.展开更多
Precipitation heterogeneity has a nontrivial influence on human life. Many studies have analyzed precipitation heterogeneity but none have proposed a systematic graded index for its evaluation, and therefore, its true...Precipitation heterogeneity has a nontrivial influence on human life. Many studies have analyzed precipitation heterogeneity but none have proposed a systematic graded index for its evaluation, and therefore, its true characteristics have not been expressed. After comparisons of various methods, the precipitation concentration degree(PCD) method was selected to study precipitation heterogeneity. In addition to the PCD, normal distribution functions, cumulative frequencies, and percentiles were used to establish a graded index for evaluating precipitation heterogeneity. A comprehensive evaluation of precipitation heterogeneity was performed, and its spatiotemporal variation in China from 1960 to 2013 was analyzed. The results indicated that(1) seven categories of precipitation heterogeneity were identified(high centralization, moderate centralization, mild centralization, normal, mild dispersion, moderate dispersion, and high dispersion) and(2) during the study period, the precipitation in more parts of China tended to be normal or dispersed, which is beneficial to human activities.展开更多
基金supported by the US Department of Energy Office of Science Climate Change Prediction Program through grant numbers DE-FG02-07ER64431 and DE-FG02-07ER64432the US National Science Foundation under grant numbers DMS-0609575 and DMS-0913491
文摘Centroidal Voronoi tessellations(CVTs) have become a useful tool in many applications ranging from geometric modeling,image and data analysis,and numerical partial differential equations,to problems in physics,astrophysics,chemistry,and biology. In this paper,we briefly review the CVT concept and a few of its generalizations and well-known properties.We then present an overview of recent advances in both mathematical and computational studies and in practical applications of CVTs.Whenever possible,we point out some outstanding issues that still need investigating.
文摘The little stiffness modulus, high voidage and long curing time has limited the use of CBEM＇s （cold bituminous emulsion mixtures） in road and highways to pavement experiencing low traffic. The aim of this study is to improve the properties of gap graded CRA （cold rolled asphal0 containing OPC （ordinary portland cement） as filler by addition of a by-product material as an activator. OPC was added to the CRA as a replacement to the conventional mineral filler （0%-100%）, while LJMUA （Liverpool John Moores University Activator） was added as an additive in the range from 0%-3% by total mass of aggregate. Laboratory tests included stiffness modulus and uniaxial creep test to assess the mechanical properties. The results have shown a considerable improvement in the mechanical properties from the addition of LJMUA to the CRA containing OPC especially for the early life stiffness modulus that is the main disadvantage of the cold mixtures.
基金supported by General Research Fund from Hong Kong Research Grants Council (Grant No. HKU703412)
文摘The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances （EPS） with unique morphologic features, such as stalks or sheaths, which can be regarded as geobiological signatures. The Archean and early Palaeoproterozoic oceans were anoxic with high soluble Fe（Ⅱ） that were suggested to have been oxidized through the metabolism of Fe（II）-oxidizing bacteria. The precursor of the ultrafine hematite in banded iron formation （BIF）, e.g., ferrihy- drite, was suggested to be the mineral record of microbial Fe（Ⅱ）-oxidation at that time. However, both the biological materials and primary iron minerals were prone to being altered by diagenetic or low-grade metamorphic processes. This makes it diffi- cult to interpret the genesis of Precambrian BIFs. Here, we report experimental simulation on the effects of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe（Ⅱ）-oxidizing bacteria and their biomass. Stalks, sheaths, and iron oxide spheroidal aggregates are partially preserved after the 100 MPa/300℃ treatments, which indicates the mixed organic matters and iron oxides could survive the diagenetic or low-grade metamorphic processes. Some organic-mineral mixing structures carry information on microbial processes, though they appear similar to pseudomorphs of fossilized bacteria.
基金Tianjin Art and Science Planning Project(D16007)。
文摘The problem of land ecological security directly threatens the sustainable development of many regions,and exploring the spatio-temporal characteristics of land ecological security is helpful for analyzing the land ecological patterns between regions and over time.Based on the interpretation of remote sensing image data for Tianjin in 1980,2000,2010 and 2019,supported by software such as ArcGIS and GeoDa,the changes of land use in the study area are calculated by using the land use dynamic degree.Then,the land ecological security index and spatial autocorrelation analysis methods are used to study the spatial correlations and internal heterogeneity of land ecological security in each district in Tianjin.The results show that:(1)The land use of Tianjin has changed dramatically in the past 40 years:the building land has been expanding,while the farmland and barren have been shrinking continuously.(2)The overall level of land ecological security is in the high security area,and Jizhou District is the highest,while the Central areas and Binhai are low.(3)The spatial heterogeneity of land ecological security is not obvious,but the spatial agglomeration is strong.
基金National Natural Science Foundation of China,No.41171090National Social Science Foundation of China,No.14AZD094,No.14XSK019
文摘Precipitation heterogeneity has a nontrivial influence on human life. Many studies have analyzed precipitation heterogeneity but none have proposed a systematic graded index for its evaluation, and therefore, its true characteristics have not been expressed. After comparisons of various methods, the precipitation concentration degree(PCD) method was selected to study precipitation heterogeneity. In addition to the PCD, normal distribution functions, cumulative frequencies, and percentiles were used to establish a graded index for evaluating precipitation heterogeneity. A comprehensive evaluation of precipitation heterogeneity was performed, and its spatiotemporal variation in China from 1960 to 2013 was analyzed. The results indicated that(1) seven categories of precipitation heterogeneity were identified(high centralization, moderate centralization, mild centralization, normal, mild dispersion, moderate dispersion, and high dispersion) and(2) during the study period, the precipitation in more parts of China tended to be normal or dispersed, which is beneficial to human activities.
