Numerical simulation of sediment transport and bed evolution has become an important technique in the sediment research. In this article, a numerical model of suspended sediment transport was proposed, which was estab...Numerical simulation of sediment transport and bed evolution has become an important technique in the sediment research. In this article, a numerical model of suspended sediment transport was proposed, which was established in the vertical σ coordinate for fitting the free surface and bottom. In the research of the sediment transport, the predominant factors were found to be the eddy diffusion, the settling velocity, the bed condition and so on. By the aid of the model in the article, the contribution of the Rouse parameter to the vertical profile of sediment concentration was clarified, which was identical to the theoretical results. In the comparison of the numerical results with laboratory data, the agreement between experimental data and numerical results was reached except for some data. And the possible reasons for the disagreement were discussed.展开更多
The perovskite samples La1-x（Sr1-yKy）xMnO3 （y = 0.0, 0.2, 04, 0.6, 0.8） were prepared by the solid-state reaction method with comparatively low sintering tem- perature and with comparatively short sintering time, ...The perovskite samples La1-x（Sr1-yKy）xMnO3 （y = 0.0, 0.2, 04, 0.6, 0.8） were prepared by the solid-state reaction method with comparatively low sintering tem- perature and with comparatively short sintering time, and the electric transport property and temperature stability of MR of this system were studied. The p-T curves show the abnormal phenomenon that with the increase of K doping amount, resistivity increases, and the insulator-metal transition temperature decreases, which is because the influence of the occupation disorder degree of A-site ions σ2 on the electric transport property of perovskite manga- nites is larger than that of the radius of A-site ions （rA）. In the temperature range below 225 K, MR increases contin- uously with the decrease of temperature, which is the characteristic of low-field magnetoresistance; in the com- paratively wide temperature range near 250 K, the MR- T curves of all the samples are comparatively fiat, and the value of MR almost does not change with temperature, which shows the temperature stability of magnetoresis- tance, and can be explained by the competition between the low-field magnetoresistance induced by spin-dependent tunneling of surface phase and the intrinsic magnetoresis- tance of grain phase. The magnetoresistance value of the sample with y = 0.8 keeps at （7.92 ±0.36） % in the very wide temperature range of 225-275 K, and this is a goodreference for the preparation of this kind of sample with practical application value in the future.展开更多
The physical,mechanical properties and microstructures of three 2618 Aluminum alloys containing less than 0.046 wt.-%mischmetal have been studied.lt has been shown that the trace mischmetal has no obvious influence on...The physical,mechanical properties and microstructures of three 2618 Aluminum alloys containing less than 0.046 wt.-%mischmetal have been studied.lt has been shown that the trace mischmetal has no obvious influence on the physical properties of the.alloy,but can clearly improve plasticity and toughness,and slightly raise the thermal stability.展开更多
For positive integers j and k with j ≥ k, an L（j, k）-labeling of a graph G is an assignment of nonnegative integers to V（G） such that the difference between labels of adjacent vertices is at least j, and the diff...For positive integers j and k with j ≥ k, an L（j, k）-labeling of a graph G is an assignment of nonnegative integers to V（G） such that the difference between labels of adjacent vertices is at least j, and the difference between labels of vertices that are distance two apart is at least k. The span of an L（j, k）-labeling of a graph G is the difference between the maximum and minimum integers it uses. The λj, k-number of G is the minimum span taken over all L（j, k）-labelings of G. An m-（j, k）-circular labeling of a graph G is a function f ： V（G） →{0, 1, 2,..., m - 1} such that ｜f（u） - f（v）｜m ≥ j if u and v are adjacent; and ｜f（u） - f（v）｜m 〉 k ifu and v are at distance two, where ｜x｜m = min{｜xl｜, m-｜x｜}. The minimum integer m such that there exists an m-（j, k）-circular labeling of G is called the σj,k-number of G and is denoted by σj,k（G）. This paper determines the σ2,1-number of the Cartesian product of any three complete graphs.展开更多
In this paper,various aspects of the 2D and 3D nonlinear liquid sloshing problems in vertically excited containers have been studied numerically along with the help of a modified-transformation.Based on this new numer...In this paper,various aspects of the 2D and 3D nonlinear liquid sloshing problems in vertically excited containers have been studied numerically along with the help of a modified-transformation.Based on this new numerical algorithm,a numerical study on a regularly and randomly excited container in vertical direction was conducted utilizing four different cases： The first case was performed utilizing a 2D container with regular excitations.The next case examined a regularly excited 3D container with two different initial conditions for the liquid free surface,and finally,3D container with random excitation in the vertical direction.A grid independence study was performed along with a series of validation tests.An iteration error estimation method was used to stop the iterative solver（used for solving the discretized governing equations in the computational domain） upon reaching steady state of results at each time step.In the present case,this method was found to produce quite accurate results and to be more time efficient as compared to other conventional stopping procedures for iterative solvers.The results were validated with benchmark results.The wave elevation time history,phase plane diagram and surface plots represent the wave nonlinearity during its motion.展开更多
From the perspective of high-temperature applications,materials with excellent high-temperature mechanical properties are always desirable.The present work demonstrates that the binder-free nanopolycrystalline WC cera...From the perspective of high-temperature applications,materials with excellent high-temperature mechanical properties are always desirable.The present work demonstrates that the binder-free nanopolycrystalline WC ceramic with an average grain size of 103 nm obtained by high-pressure and hightemperature sintering exhibits excellent mechanical properties at both room temperature and high temperature up to 1000℃.Specifically,the binder-free nanopolycrystalline WC ceramic still maintains a considerably high Vicker hardness H_(V)of 23.4 GPa at 1000℃,which is only 22%lower than the room temperature H_(V).This outstanding thermo-mechanical stability is superior to that of typical technical ceramics,e.g.SiC,Si_(3)N_(4),Al_(2)O_(3),etc.Nanocrystalline grains with many dislocations,numerous low-energy,highly stableΣ2 grain boundaries,and a relatively low thermal expansion coefficient,are responsible for the observed outstanding high-temperature mechanical properties.展开更多
Let G be a connected graph of order n. The rainbow connection number rc（G） of G was introduced by Chartrand et al. Chandran et al. used the minimum degree of G and obtained an upper bound that rc（G） 〈_ 3n/（ δ...Let G be a connected graph of order n. The rainbow connection number rc（G） of G was introduced by Chartrand et al. Chandran et al. used the minimum degree of G and obtained an upper bound that rc（G） 〈_ 3n/（ δ＋ 1） - 3, which is tight up to additive factors. In this paper, we use the minimum degree-sum a2 6n of G to obtain a better bound rc（G） _〈 - 8, especially when is small （constant） but a2 is large （linear in n）.展开更多
文摘Numerical simulation of sediment transport and bed evolution has become an important technique in the sediment research. In this article, a numerical model of suspended sediment transport was proposed, which was established in the vertical σ coordinate for fitting the free surface and bottom. In the research of the sediment transport, the predominant factors were found to be the eddy diffusion, the settling velocity, the bed condition and so on. By the aid of the model in the article, the contribution of the Rouse parameter to the vertical profile of sediment concentration was clarified, which was identical to the theoretical results. In the comparison of the numerical results with laboratory data, the agreement between experimental data and numerical results was reached except for some data. And the possible reasons for the disagreement were discussed.
基金financially supported by the National Natural Science Foundation of China (No. 19934003)the Key Program of Natural Science Foundation of Anhui Province (Nos. KJ2011A259 and KJ2013A245)+1 种基金the Program of Professors and Doctors' Research Startup Foundation of Suzhou College (Nos. 2011jb01 and 2011jb02)the Program of Cultivating Base of Anhui Key Laboratory of Spintronics and Nano-materials Research (No. 2012YKF09)
文摘The perovskite samples La1-x（Sr1-yKy）xMnO3 （y = 0.0, 0.2, 04, 0.6, 0.8） were prepared by the solid-state reaction method with comparatively low sintering tem- perature and with comparatively short sintering time, and the electric transport property and temperature stability of MR of this system were studied. The p-T curves show the abnormal phenomenon that with the increase of K doping amount, resistivity increases, and the insulator-metal transition temperature decreases, which is because the influence of the occupation disorder degree of A-site ions σ2 on the electric transport property of perovskite manga- nites is larger than that of the radius of A-site ions （rA）. In the temperature range below 225 K, MR increases contin- uously with the decrease of temperature, which is the characteristic of low-field magnetoresistance; in the com- paratively wide temperature range near 250 K, the MR- T curves of all the samples are comparatively fiat, and the value of MR almost does not change with temperature, which shows the temperature stability of magnetoresis- tance, and can be explained by the competition between the low-field magnetoresistance induced by spin-dependent tunneling of surface phase and the intrinsic magnetoresis- tance of grain phase. The magnetoresistance value of the sample with y = 0.8 keeps at （7.92 ±0.36） % in the very wide temperature range of 225-275 K, and this is a goodreference for the preparation of this kind of sample with practical application value in the future.
文摘The physical,mechanical properties and microstructures of three 2618 Aluminum alloys containing less than 0.046 wt.-%mischmetal have been studied.lt has been shown that the trace mischmetal has no obvious influence on the physical properties of the.alloy,but can clearly improve plasticity and toughness,and slightly raise the thermal stability.
基金Foundation item： the National Natural Science Foundation of China （No. 10671033） the Science Foundation of Southeast University （No. XJ0607230） the Natural Science Foundation of Nantong University （No. 08Z003）.
文摘For positive integers j and k with j ≥ k, an L（j, k）-labeling of a graph G is an assignment of nonnegative integers to V（G） such that the difference between labels of adjacent vertices is at least j, and the difference between labels of vertices that are distance two apart is at least k. The span of an L（j, k）-labeling of a graph G is the difference between the maximum and minimum integers it uses. The λj, k-number of G is the minimum span taken over all L（j, k）-labelings of G. An m-（j, k）-circular labeling of a graph G is a function f ： V（G） →{0, 1, 2,..., m - 1} such that ｜f（u） - f（v）｜m ≥ j if u and v are adjacent; and ｜f（u） - f（v）｜m 〉 k ifu and v are at distance two, where ｜x｜m = min{｜xl｜, m-｜x｜}. The minimum integer m such that there exists an m-（j, k）-circular labeling of G is called the σj,k-number of G and is denoted by σj,k（G）. This paper determines the σ2,1-number of the Cartesian product of any three complete graphs.
文摘In this paper,various aspects of the 2D and 3D nonlinear liquid sloshing problems in vertically excited containers have been studied numerically along with the help of a modified-transformation.Based on this new numerical algorithm,a numerical study on a regularly and randomly excited container in vertical direction was conducted utilizing four different cases： The first case was performed utilizing a 2D container with regular excitations.The next case examined a regularly excited 3D container with two different initial conditions for the liquid free surface,and finally,3D container with random excitation in the vertical direction.A grid independence study was performed along with a series of validation tests.An iteration error estimation method was used to stop the iterative solver（used for solving the discretized governing equations in the computational domain） upon reaching steady state of results at each time step.In the present case,this method was found to produce quite accurate results and to be more time efficient as compared to other conventional stopping procedures for iterative solvers.The results were validated with benchmark results.The wave elevation time history,phase plane diagram and surface plots represent the wave nonlinearity during its motion.
基金supported by the National Key R&D Program of China(Grant No.2018YFA0305900)the Natural Science Basic Research Program of Shaanxi Province(Grant No.2020JQ870)+2 种基金the National Natural Science Foundation of China(Nos.52090020,U20A20238,51772260,91963203,51525205)NSF for Distinguished Young Scholars of Hebei Province of China(E2018203349)the China Postdoctoral Science Foundation(2017M620097)。
文摘From the perspective of high-temperature applications,materials with excellent high-temperature mechanical properties are always desirable.The present work demonstrates that the binder-free nanopolycrystalline WC ceramic with an average grain size of 103 nm obtained by high-pressure and hightemperature sintering exhibits excellent mechanical properties at both room temperature and high temperature up to 1000℃.Specifically,the binder-free nanopolycrystalline WC ceramic still maintains a considerably high Vicker hardness H_(V)of 23.4 GPa at 1000℃,which is only 22%lower than the room temperature H_(V).This outstanding thermo-mechanical stability is superior to that of typical technical ceramics,e.g.SiC,Si_(3)N_(4),Al_(2)O_(3),etc.Nanocrystalline grains with many dislocations,numerous low-energy,highly stableΣ2 grain boundaries,and a relatively low thermal expansion coefficient,are responsible for the observed outstanding high-temperature mechanical properties.
基金Supported by the National Natural Science Foundation of China(No.11071130)the Fundamental Research Funds for the Central Universities
文摘Let G be a connected graph of order n. The rainbow connection number rc（G） of G was introduced by Chartrand et al. Chandran et al. used the minimum degree of G and obtained an upper bound that rc（G） 〈_ 3n/（ δ＋ 1） - 3, which is tight up to additive factors. In this paper, we use the minimum degree-sum a2 6n of G to obtain a better bound rc（G） _〈 - 8, especially when is small （constant） but a2 is large （linear in n）.
