An analysis of tortuosity for streamlines in porous media is presented by coupling the circle and square models. It is assulued that some particles in porous media do not overlap and that fluid in porous media is inco...An analysis of tortuosity for streamlines in porous media is presented by coupling the circle and square models. It is assulued that some particles in porous media do not overlap and that fluid in porous media is incompressible. The relationship between tortuosity and porosity is attained with different configurations by using a statistical method. In addition, the tortuosity fractal dimension is expressed as a function of porosity. Those correlations do not include any empirical constant. The percolation threshold and tortuosity fractal dimension threshold of porous media are also presented as： φc = 0.32, DT,： = 1.07. The predicted correlations of the tortuosity and the porosity agree well with the existing experimental and simulated results.展开更多
The numerical simulation using the multiple relaxation time lattice Boltzmann method （MRT-LBM） is carried out for the purpose of investigating the two-dimensional flow around three circular cylinders. Among these th...The numerical simulation using the multiple relaxation time lattice Boltzmann method （MRT-LBM） is carried out for the purpose of investigating the two-dimensional flow around three circular cylinders. Among these three circular cylinders, one of the three cylinders on which a forced in-line vibrating is used to do this research and attempt to find out the effects of the moving cylinder and the other two rigid cylinders on the wake characteristics and vortex formation. As a benchmark problem to discuss the problem of lift coefficient r.m.s for these cylinders with spacing ratios T/ D between other rigid side-by-side cylinders, and the calculation is carried out with two compared cases at Reynolds number of 100, two of the cylinders are rigid and the other one is an in-line vibrated cylinder lying downstream, in addition, forced vibrating amplitude and frequency are A/D = 0.5 and fv= 0.4 （where A is the forced amplitude, D is the cylinder diameter, and fv stands for the vibrating frequency, respectively）. The calculated results not only indicate that the spacing ratios T/D （T is the center-to-center spacing between the two upstream cylinders） have influence on the wake patterns and the formation of vortex shedding, but also analyze the lift coefficient r.m.s for the three cylinders with the spacing ratios S/D （where S is the center-to-center spacing between the center of upstream two side-by-side cylinders and downstream cylinder）.展开更多
Asymmetric tree-like branched networks are explored by geometric algorithms. Based on the network, an analysis of the thermal conductivity is presented. The relationship between effective thermal conductivity and geom...Asymmetric tree-like branched networks are explored by geometric algorithms. Based on the network, an analysis of the thermal conductivity is presented. The relationship between effective thermal conductivity and geometric structures is obtained by using the thermal-electrical analogy technique. In all studied cases, a clear behaviour is observed, where angle （δ,θ） among parent branching extended lines, branches and parameter of the geometric structures have stronger effects on the effective thermal conductivity. When the angle δ is fixed, the optical diameter ratio β＋ is dependent on angle θ. Moreover, γand m are not related to β＊. The longer the branch is, the smaller the effective thermal conductivity will be. It is also found that when the angle θ〈δ2, the higher the iteration m is, the lower the thermal conductivity will be and it tends to zero, otherwise, it is bigger than zero. When the diameter ratio β1 〈 0.707 and angle δ is bigger, the optimal k of the perfect ratio increases with the increase of the angle δ; when β1 〉 0.707, the optimal k decreases. In addition, the effective thermal conductivity is always less than that of single channel material. The present results also show that the effective thermal conductivity of the asymmetric tree-like branched networks does not obey Murray＇s law.展开更多
A tumour vascular network, characterized as an irregularly stochastic growth, is different from the normal vascular network. We systematieally analyse the dependence of the branching. It is found that anastomosis of t...A tumour vascular network, characterized as an irregularly stochastic growth, is different from the normal vascular network. We systematieally analyse the dependence of the branching. It is found that anastomosis of tumour on time is according to a number of tumour images, and both the fractal dimensions and multifractal spectra of the tumours are obtained. In the eases studied, the fractal dimensions of the tumour vascular network increase with time and the multifractal spectrum not only rises entirely but also shifts right. In addition, the best drug delivery stage is discussed according to the difference of the singularity exponent δα（δα = αmax - αmin）, which shows some change in the growth process of the tumour vascular network. A common underlying principle is obtained from our analysis along with previous results.展开更多
A novel nanoscale watermill for the unidirectional transport of water molecules through a curved single-walled carbon nanotube（SWNT） is proposed and explored by molecular dynamics simulations. In this nanoscale syst...A novel nanoscale watermill for the unidirectional transport of water molecules through a curved single-walled carbon nanotube（SWNT） is proposed and explored by molecular dynamics simulations. In this nanoscale system, a revolving charge is introduced to drive a water chain confined inside the SWNT, the charge and the tube together serving as a nano waterwheel and nano engine. A resonance-like phenomenon is found, and the revolving frequency of the charge plays a key role in pumping the water chain. The water flux across the SWNT increases with respect to the revolving frequency of the external charge and it reaches its maximum when the frequency is 4 THz. Correspondingly, the number of hydrogen bonds in the water chain inside the SWNT decreases dramatically as the frequency increases from 4 THz to 25 THz. The mechanism behind the resonance phenomenon has been investigated systematically. Our findings are helpful for the design of nanoscale fluidic devices and energy converters.展开更多
Fabrication of large-area atomically thin transition metal dichalcogenides is of critical importance for the preparation of new heterojunction-based devices.In this paper, we report the fabrication and optical investi...Fabrication of large-area atomically thin transition metal dichalcogenides is of critical importance for the preparation of new heterojunction-based devices.In this paper, we report the fabrication and optical investigation of large-scale chemical vapor deposition(CVD)-grown monolayer MoS2 and exfoliated few-layer GaS heterojunctions.As revealed by photoluminescence(PL) characterization, the as-fabricated heterojunctions demonstrated edge interaction between the two layers.The heterojunction was sensitive to annealing and showed increased interaction upon annealing at 300℃ under vacuum conditions, which led to changes in both the emission peak position and intensity resulting from the strong coupling interaction between the two layers.Low-temperature PL measurements further confirmed the strong coupling interaction.In addition, defect-related GaS luminescence was observed in our few-layer GaS, and the PL mapping provided evidence of edge interaction coupling between the two layers.These findings are interesting and provide the basis for creating new material systems with rich functionalities and novel physical effects.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.10932010,10972199,11005093,11072220, and 11079029)the Natural Science Foundation of Zhejiang Province of China (Grant No. Z6090556 and Y6100384)the Research Project for the Higher Educational Institutions of Inner Mongolia Autonomous Region (Grant No. NJZZ11284)
文摘An analysis of tortuosity for streamlines in porous media is presented by coupling the circle and square models. It is assulued that some particles in porous media do not overlap and that fluid in porous media is incompressible. The relationship between tortuosity and porosity is attained with different configurations by using a statistical method. In addition, the tortuosity fractal dimension is expressed as a function of porosity. Those correlations do not include any empirical constant. The percolation threshold and tortuosity fractal dimension threshold of porous media are also presented as： φc = 0.32, DT,： = 1.07. The predicted correlations of the tortuosity and the porosity agree well with the existing experimental and simulated results.
基金Support by the National Natural Science Foundation of China under Grant Nos.10932010 and 11072220the Natural Science Foundation of Zhejiang Province under Grant Nos.Y607425,Z6090556the Foundation Project for Youths of Zhijiang Normal University under Grant No.KJ20090102
文摘The numerical simulation using the multiple relaxation time lattice Boltzmann method （MRT-LBM） is carried out for the purpose of investigating the two-dimensional flow around three circular cylinders. Among these three circular cylinders, one of the three cylinders on which a forced in-line vibrating is used to do this research and attempt to find out the effects of the moving cylinder and the other two rigid cylinders on the wake characteristics and vortex formation. As a benchmark problem to discuss the problem of lift coefficient r.m.s for these cylinders with spacing ratios T/ D between other rigid side-by-side cylinders, and the calculation is carried out with two compared cases at Reynolds number of 100, two of the cylinders are rigid and the other one is an in-line vibrated cylinder lying downstream, in addition, forced vibrating amplitude and frequency are A/D = 0.5 and fv= 0.4 （where A is the forced amplitude, D is the cylinder diameter, and fv stands for the vibrating frequency, respectively）. The calculated results not only indicate that the spacing ratios T/D （T is the center-to-center spacing between the two upstream cylinders） have influence on the wake patterns and the formation of vortex shedding, but also analyze the lift coefficient r.m.s for the three cylinders with the spacing ratios S/D （where S is the center-to-center spacing between the center of upstream two side-by-side cylinders and downstream cylinder）.
基金Project supported by the State Key Development Program for Basic Research of China (Grant No 2006CB708612)the National Natural Science Foundation of China (Grant No 10572130)the Natural Science Foundation of Zhejiang Province, China (Grant No Y607425)
文摘Asymmetric tree-like branched networks are explored by geometric algorithms. Based on the network, an analysis of the thermal conductivity is presented. The relationship between effective thermal conductivity and geometric structures is obtained by using the thermal-electrical analogy technique. In all studied cases, a clear behaviour is observed, where angle （δ,θ） among parent branching extended lines, branches and parameter of the geometric structures have stronger effects on the effective thermal conductivity. When the angle δ is fixed, the optical diameter ratio β＋ is dependent on angle θ. Moreover, γand m are not related to β＊. The longer the branch is, the smaller the effective thermal conductivity will be. It is also found that when the angle θ〈δ2, the higher the iteration m is, the lower the thermal conductivity will be and it tends to zero, otherwise, it is bigger than zero. When the diameter ratio β1 〈 0.707 and angle δ is bigger, the optimal k of the perfect ratio increases with the increase of the angle δ; when β1 〉 0.707, the optimal k decreases. In addition, the effective thermal conductivity is always less than that of single channel material. The present results also show that the effective thermal conductivity of the asymmetric tree-like branched networks does not obey Murray＇s law.
基金Supported by the National Basic Research Programme of China under Grant No 2006CB708612, the Natural Science Foundation for Young Scientists of Zhejiang Province Grant No RC02096, the National Natural Science Foundation of China under Grant No 10572130, and the Natural Science Foundation of Zhejiang Province under Grant No Y607425.
文摘A tumour vascular network, characterized as an irregularly stochastic growth, is different from the normal vascular network. We systematieally analyse the dependence of the branching. It is found that anastomosis of tumour on time is according to a number of tumour images, and both the fractal dimensions and multifractal spectra of the tumours are obtained. In the eases studied, the fractal dimensions of the tumour vascular network increase with time and the multifractal spectrum not only rises entirely but also shifts right. In addition, the best drug delivery stage is discussed according to the difference of the singularity exponent δα（δα = αmax - αmin）, which shows some change in the growth process of the tumour vascular network. A common underlying principle is obtained from our analysis along with previous results.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11005093 and 61274099)the Research Fund of Education Department of Zhejiang Province,China(Grant No.Y201223336)+2 种基金the Zhejiang Provincial Science and Technology Key Innovation Team,China(Grant No.2011R50012)the Key Laboratory of Zhejiang Province,China(Grant No.2013E10022)the Hong Kong Polytechnic University,China(Grant No.G-YL41)
文摘A novel nanoscale watermill for the unidirectional transport of water molecules through a curved single-walled carbon nanotube（SWNT） is proposed and explored by molecular dynamics simulations. In this nanoscale system, a revolving charge is introduced to drive a water chain confined inside the SWNT, the charge and the tube together serving as a nano waterwheel and nano engine. A resonance-like phenomenon is found, and the revolving frequency of the charge plays a key role in pumping the water chain. The water flux across the SWNT increases with respect to the revolving frequency of the external charge and it reaches its maximum when the frequency is 4 THz. Correspondingly, the number of hydrogen bonds in the water chain inside the SWNT decreases dramatically as the frequency increases from 4 THz to 25 THz. The mechanism behind the resonance phenomenon has been investigated systematically. Our findings are helpful for the design of nanoscale fluidic devices and energy converters.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11104250,61274099,and 11774313)the Science Technology Department of Zhejiang Province,China(Grant No.2012C21007)+1 种基金Zhejiang Province Innovation Team,China(Grant No.2011R50012)Zhejiang Provincial Natural Science Foundation,China(Grant No.LY17A040003)
文摘Fabrication of large-area atomically thin transition metal dichalcogenides is of critical importance for the preparation of new heterojunction-based devices.In this paper, we report the fabrication and optical investigation of large-scale chemical vapor deposition(CVD)-grown monolayer MoS2 and exfoliated few-layer GaS heterojunctions.As revealed by photoluminescence(PL) characterization, the as-fabricated heterojunctions demonstrated edge interaction between the two layers.The heterojunction was sensitive to annealing and showed increased interaction upon annealing at 300℃ under vacuum conditions, which led to changes in both the emission peak position and intensity resulting from the strong coupling interaction between the two layers.Low-temperature PL measurements further confirmed the strong coupling interaction.In addition, defect-related GaS luminescence was observed in our few-layer GaS, and the PL mapping provided evidence of edge interaction coupling between the two layers.These findings are interesting and provide the basis for creating new material systems with rich functionalities and novel physical effects.
