The methodology of catchment extraction especially from regular grid digital elevation models (DEMs) is briefly reviewed. Then an efficient algorithm, which combines vector process and traditional neighbourhood raster...The methodology of catchment extraction especially from regular grid digital elevation models (DEMs) is briefly reviewed. Then an efficient algorithm, which combines vector process and traditional neighbourhood raster process, is designed for extracting the catchments and subcatchments from depressionless DEMs. The catchment area of each river in the grid DEM data is identified and delineated, then is divided into subcatchments as required. Compared to traditional processes, this method for identifying catchments focuses on the boundaries instead of the area inside the catchments and avoids the boundary intersection phenomena. Last, the algorithm is tested with a set of DEMs of different sizes, and the result proves that the computation efficiency and accuracy are better than existent methods.展开更多
The representation method of heterogeneous material information is one of the key technologies of heterogeneous object modeling, but almost all the existing methods cannot represent non-uniform rational B-spline （NU...The representation method of heterogeneous material information is one of the key technologies of heterogeneous object modeling, but almost all the existing methods cannot represent non-uniform rational B-spline （NURBS） entity. According to the characteristics of NURBS, a novel data structure, named NURBS material data structure, is proposed, in which the geometrical coordinates, weights and material coordinates of NURBS heterogene- ous objects can be represented simultaneously. Based on this data structure, both direct representation method and inverse construction method of heterogeneous NURBS objects are introduced. In the direct representation method, three forms of NURBS heterogeneous objects are introduced by giving the geometry and material information of con- trol points, among which the homogeneous coordinates form is employed for its brevity and easy programming. In the inverse construction method, continuous heterogeneous curves and surfaces can he obtained by interpolating discrete points and curves with specified material information. Some examples are given to show the effectiveness of the pro- posed methods.展开更多
Eu^2+/Eu^3+ mixed-valence couple co-doped material holds great potential for ratiometric temperature sensing owing to its different electronic configurations and electron-lattice interaction. Here, the correlation of ...Eu^2+/Eu^3+ mixed-valence couple co-doped material holds great potential for ratiometric temperature sensing owing to its different electronic configurations and electron-lattice interaction. Here, the correlation of nonstoichiometry in chemical composition, phase structures and luminescence propertis of Ca2 Al2 Si1-xO7:Eu is discussed, and controlled Eu^2+/Eu^3+ valence and tunable emission appear with decreasing Si content. It is found that the 2 Ca^2++ Si^4+←→ Eu^2++ Eu^3++ Al^3+ cosubstitution accounts for the structural stability and charge balance mechanism. Benefiting from the diverse thermal dependent emission behaviors of Eu^2+ and Eu^3+, Ca2 Al2 Si1-xO7:Eu thermometer exhibits excellent temperature sensing performances with the maximum absolute and relative sensitivity being 0.024 K-1(at 303 K) and 2.46% K-1(at 443 K) and good signal discriminability. We propose that the emission quenching of Eu^2+ is ascribed to 5 d electrons depopulation through Eu^2+/Eu^3+ intervalence charge transfer state, while the quenching of Eu^3+ comes from multiphonon relaxation. Our work demonstrates the potential of Ca2 Al2 Si1-xO7:Eu for noncontact optical thermometry, and also highlights mixed-valence europium-containing compounds toward temperature sensing.展开更多
Pulsar hulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar hulling pheno...Pulsar hulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar hulling phenomenon, by involving two key parameters, the nulling degree, X, which is defined as the angle in a rectangular coordinates for the numbers of nulling periods and bursting periods, and the nulling scale, N, which is defined as the effective length of the consecutive nulling periods and bursting periods. The nulling degree X can be calculated by tanX = Nnulling/Nbursting and the mean is related to the nulling fraction, while the nulling scale, N, is also a newly defined fundamental parameter which indicates how often the nulling occurs. We determined the distributions ofx and N for 10 pulsars by using the data in literature. We found that the nulling degree X indicates the relative length of nulling to that of bursting, and the nulling scale N is found to be related to the derivative of rotation frequency and hence the loss rate of rotational energy of pulsars. Their deviations reflect the randomness of the nulling process.展开更多
文摘The methodology of catchment extraction especially from regular grid digital elevation models (DEMs) is briefly reviewed. Then an efficient algorithm, which combines vector process and traditional neighbourhood raster process, is designed for extracting the catchments and subcatchments from depressionless DEMs. The catchment area of each river in the grid DEM data is identified and delineated, then is divided into subcatchments as required. Compared to traditional processes, this method for identifying catchments focuses on the boundaries instead of the area inside the catchments and avoids the boundary intersection phenomena. Last, the algorithm is tested with a set of DEMs of different sizes, and the result proves that the computation efficiency and accuracy are better than existent methods.
基金Supported by National Natural Science Foundation of China (No. 60973079)Natural Science Foundation of Hebei Province (No. E2006000039)
文摘The representation method of heterogeneous material information is one of the key technologies of heterogeneous object modeling, but almost all the existing methods cannot represent non-uniform rational B-spline （NURBS） entity. According to the characteristics of NURBS, a novel data structure, named NURBS material data structure, is proposed, in which the geometrical coordinates, weights and material coordinates of NURBS heterogene- ous objects can be represented simultaneously. Based on this data structure, both direct representation method and inverse construction method of heterogeneous NURBS objects are introduced. In the direct representation method, three forms of NURBS heterogeneous objects are introduced by giving the geometry and material information of con- trol points, among which the homogeneous coordinates form is employed for its brevity and easy programming. In the inverse construction method, continuous heterogeneous curves and surfaces can he obtained by interpolating discrete points and curves with specified material information. Some examples are given to show the effectiveness of the pro- posed methods.
基金supported by the National Natural Science Foundation of China (51722202, 51972118 and 51572023)the Guangdong Provincial Science & Technology Project (2018A050506004)Innovation Projects of Department of Education of Guangdong Province (2018KQNCX265)
文摘Eu^2+/Eu^3+ mixed-valence couple co-doped material holds great potential for ratiometric temperature sensing owing to its different electronic configurations and electron-lattice interaction. Here, the correlation of nonstoichiometry in chemical composition, phase structures and luminescence propertis of Ca2 Al2 Si1-xO7:Eu is discussed, and controlled Eu^2+/Eu^3+ valence and tunable emission appear with decreasing Si content. It is found that the 2 Ca^2++ Si^4+←→ Eu^2++ Eu^3++ Al^3+ cosubstitution accounts for the structural stability and charge balance mechanism. Benefiting from the diverse thermal dependent emission behaviors of Eu^2+ and Eu^3+, Ca2 Al2 Si1-xO7:Eu thermometer exhibits excellent temperature sensing performances with the maximum absolute and relative sensitivity being 0.024 K-1(at 303 K) and 2.46% K-1(at 443 K) and good signal discriminability. We propose that the emission quenching of Eu^2+ is ascribed to 5 d electrons depopulation through Eu^2+/Eu^3+ intervalence charge transfer state, while the quenching of Eu^3+ comes from multiphonon relaxation. Our work demonstrates the potential of Ca2 Al2 Si1-xO7:Eu for noncontact optical thermometry, and also highlights mixed-valence europium-containing compounds toward temperature sensing.
基金supported by China Ministry of Science and Technology(Grant No.2013CB837900)the National Natural Science Foundationof China(Grant Nos.10833003,11003023,11273029 and 11261140641)
文摘Pulsar hulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar hulling phenomenon, by involving two key parameters, the nulling degree, X, which is defined as the angle in a rectangular coordinates for the numbers of nulling periods and bursting periods, and the nulling scale, N, which is defined as the effective length of the consecutive nulling periods and bursting periods. The nulling degree X can be calculated by tanX = Nnulling/Nbursting and the mean is related to the nulling fraction, while the nulling scale, N, is also a newly defined fundamental parameter which indicates how often the nulling occurs. We determined the distributions ofx and N for 10 pulsars by using the data in literature. We found that the nulling degree X indicates the relative length of nulling to that of bursting, and the nulling scale N is found to be related to the derivative of rotation frequency and hence the loss rate of rotational energy of pulsars. Their deviations reflect the randomness of the nulling process.
