On Feb.24,an annual butter sculpture show was held in Taer Monastery of Qinghai Province,which marks the Chinese Lanterm Festival.The butter sculptures are handmade by monks in shapes of Buddha figurines,trees,flowers...On Feb.24,an annual butter sculpture show was held in Taer Monastery of Qinghai Province,which marks the Chinese Lanterm Festival.The butter sculptures are handmade by monks in shapes of Buddha figurines,trees,flowers,birds and animals.展开更多
The bipartite Turán number of a graph H, denoted by ex(m,n;H), is the maximum number of edges in any bipartite graph G=(A,B;E(G))with | A |=mand | B |=nwhich does not contain H as a subgraph. Whenmin{ m,n }>2t...The bipartite Turán number of a graph H, denoted by ex(m,n;H), is the maximum number of edges in any bipartite graph G=(A,B;E(G))with | A |=mand | B |=nwhich does not contain H as a subgraph. Whenmin{ m,n }>2t, the problem of determining the value of ex(m,n;Km−t,n−t)has been solved by Balbuena et al. in 2007, whose proof focuses on the structural analysis of bipartite graphs. In this paper, we provide a new proof on the value of ex(m,n;Km−t,n−t)by virtue of algebra method with the tool of adjacency matrices of bipartite graphs, which is inspired by the method using { 0,1 }-matrices due to Zarankiewicz [Problem P 101. Colloquium Mathematicum, 2(1951), 301].展开更多
The Canton fans made in China have becometreasures in the world. As a product of theintegration of Chinese and Western culturesunder the background of trade between Chinaand the West in the 18th and 19th centuries,the...The Canton fans made in China have becometreasures in the world. As a product of theintegration of Chinese and Western culturesunder the background of trade between Chinaand the West in the 18th and 19th centuries,the Qing Dynasty Canton export fans bear thememory and charm of Chinese ivilization.展开更多
This study is concerned with 12-MW capacity turbochargers on diesel power generators. These are generators equipped with 18 cylinders. Our previous studies [1] showed that the processing of vibration signature collect...This study is concerned with 12-MW capacity turbochargers on diesel power generators. These are generators equipped with 18 cylinders. Our previous studies [1] showed that the processing of vibration signature collected from a power generator is very complex, insomuch the dominant vibration remains the one originating from explosion frequency in the diesel generator cylinders, with a fairly high number of cylinders. This vibration drowns out all other possible vibrations, which can expose defects. The study at hand is focused on turbochargers with 20,940 rpm, while the rotation speed in the diesel engine is 600 rpm only. With the turbocharger rotating at very high speed, it results in severe mechanical constraints on the rotor shaft in the turbocharger and its related organs (turbine blades). The wear of turbine blades can result in breakdowns in the turbocharger. This article is an attempt to early detect defaults in turbine blades based on vibration signature that can be experimentally determined. We noted in our investigations that a diesel engine and its turbochargers do not bear the same mechanic loads. While the diesel engine is the seat of violent shocks brought about by explosions in cylinders, the turbochargers are driven by the action of exhaust gas from explosions, without being affected by explosion shocks. The study found that explosion frequency in the diesel engine cylinders, which disrupted the vibration signals in the diesel engine and alternator, did not impact on the vibration signals in the turbocharger. We experimentally determined, following several campaigns of measurements, a vibration signature on the turbochargers under study, which corresponds to a defect in turbine blades.展开更多
Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional co- herent structures in the logarithmic region of the turbulent boundary layer in a water tunnel. The Reynolds number ...Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional co- herent structures in the logarithmic region of the turbulent boundary layer in a water tunnel. The Reynolds number based on momentum thickness is Reo = 2 460. The in- stantaneous velocity fields give evidence of hairpin vortices aligned in the streamwise direction forming very long zones of low speed fluid, which is flanked on either side by high- speed ones. Statistical support for the existence of hairpins is given by conditional averaged eddy within an increasing spanwise width as the distance from the wall increases, and the main vortex characteristic in different wall-normal re- gions can be reflected by comparing the proportion of ejec- tion and its contribution to Reynolds stress with that of sweep event. The pre-multiplied power spectra and two-point cor- relations indicate the presence of large-scale motions in the boundary layer, which are consistent with what have been termed very large scale motions （VLSMs）. The three dimen-sional spatial correlations of three components of veloc- ity further indicate that the elongated low-speed and high- speed regions will be accompanied by a counter-rotating roll modes, as the statistical imprint of hairpin packet structures, all of which together make up the characteristic of coherent structures in the logarithmic region of the turbulent boundary layer （TBL）.展开更多
文摘On Feb.24,an annual butter sculpture show was held in Taer Monastery of Qinghai Province,which marks the Chinese Lanterm Festival.The butter sculptures are handmade by monks in shapes of Buddha figurines,trees,flowers,birds and animals.
文摘The bipartite Turán number of a graph H, denoted by ex(m,n;H), is the maximum number of edges in any bipartite graph G=(A,B;E(G))with | A |=mand | B |=nwhich does not contain H as a subgraph. Whenmin{ m,n }>2t, the problem of determining the value of ex(m,n;Km−t,n−t)has been solved by Balbuena et al. in 2007, whose proof focuses on the structural analysis of bipartite graphs. In this paper, we provide a new proof on the value of ex(m,n;Km−t,n−t)by virtue of algebra method with the tool of adjacency matrices of bipartite graphs, which is inspired by the method using { 0,1 }-matrices due to Zarankiewicz [Problem P 101. Colloquium Mathematicum, 2(1951), 301].
文摘The Canton fans made in China have becometreasures in the world. As a product of theintegration of Chinese and Western culturesunder the background of trade between Chinaand the West in the 18th and 19th centuries,the Qing Dynasty Canton export fans bear thememory and charm of Chinese ivilization.
文摘目的:探讨Bite Turbo应用于自锁矫治技术中治疗青少年深覆牙合的效果。方法:纳入江门市新会区第二人民医院2020年1月至2021年1月期间收治的70例青少年深覆牙合患者作为研究对象,根据电脑生成随机数字表法分为两组,对照组35例给予3M自锁矫治器+平面导板治疗,观察组35例给予3M自锁矫治器+Bite Turbo治疗。观察并比较两组治疗后的颌骨改变情况及上颌牙齿位置与角度测量结果。结果:治疗后,两组的下齿槽座角(SNB角)、上齿槽座角(SNA角)、上下齿槽座角(ANB角)均较治疗前减小,且观察组均小于对照组(P<0.05)。治疗后,两组的Apg线至上中切牙切缘的垂直距离(Apg-U1距)、上中切牙缘至NA连线垂直距离(U1-NA距)、翼上颌裂后缘至上颌磨牙远中邻面垂直距离(Ptm-U6距)均较治疗前缩小,且观察组均小于对照组(P<0.05)。结论:在采用自锁矫治技术治疗青少年深覆牙合时,应用Bite Tur bo可有效改善牙齿形态,调整上颌牙齿的位置与角度。
文摘This study is concerned with 12-MW capacity turbochargers on diesel power generators. These are generators equipped with 18 cylinders. Our previous studies [1] showed that the processing of vibration signature collected from a power generator is very complex, insomuch the dominant vibration remains the one originating from explosion frequency in the diesel generator cylinders, with a fairly high number of cylinders. This vibration drowns out all other possible vibrations, which can expose defects. The study at hand is focused on turbochargers with 20,940 rpm, while the rotation speed in the diesel engine is 600 rpm only. With the turbocharger rotating at very high speed, it results in severe mechanical constraints on the rotor shaft in the turbocharger and its related organs (turbine blades). The wear of turbine blades can result in breakdowns in the turbocharger. This article is an attempt to early detect defaults in turbine blades based on vibration signature that can be experimentally determined. We noted in our investigations that a diesel engine and its turbochargers do not bear the same mechanic loads. While the diesel engine is the seat of violent shocks brought about by explosions in cylinders, the turbochargers are driven by the action of exhaust gas from explosions, without being affected by explosion shocks. The study found that explosion frequency in the diesel engine cylinders, which disrupted the vibration signals in the diesel engine and alternator, did not impact on the vibration signals in the turbocharger. We experimentally determined, following several campaigns of measurements, a vibration signature on the turbochargers under study, which corresponds to a defect in turbine blades.
基金supported by the National Natural Science Foundation of China (10832001 and 10872145)the State Key Laboratory of Nonlinear Mechanics,Institute of Mechanics,Chinese Academy of Sciences
文摘Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional co- herent structures in the logarithmic region of the turbulent boundary layer in a water tunnel. The Reynolds number based on momentum thickness is Reo = 2 460. The in- stantaneous velocity fields give evidence of hairpin vortices aligned in the streamwise direction forming very long zones of low speed fluid, which is flanked on either side by high- speed ones. Statistical support for the existence of hairpins is given by conditional averaged eddy within an increasing spanwise width as the distance from the wall increases, and the main vortex characteristic in different wall-normal re- gions can be reflected by comparing the proportion of ejec- tion and its contribution to Reynolds stress with that of sweep event. The pre-multiplied power spectra and two-point cor- relations indicate the presence of large-scale motions in the boundary layer, which are consistent with what have been termed very large scale motions （VLSMs）. The three dimen-sional spatial correlations of three components of veloc- ity further indicate that the elongated low-speed and high- speed regions will be accompanied by a counter-rotating roll modes, as the statistical imprint of hairpin packet structures, all of which together make up the characteristic of coherent structures in the logarithmic region of the turbulent boundary layer （TBL）.
