Most debris flows occur in valleys of area smaller than 50 km2. While associated with a valley, debris flow is by no means a full-valley event but originates from parts of the valley, i.e., the tributary sources. We p...Most debris flows occur in valleys of area smaller than 50 km2. While associated with a valley, debris flow is by no means a full-valley event but originates from parts of the valley, i.e., the tributary sources. We propose that debris flow develops by extending from tributaries to the mainstream. The debris flow observed in the mainstream is the confluence of the tributary flows and the process of the confluence can be considered as a combination of the tributary elements. The frequency distribution of tributaries is found subject to the Weibull form (or its generalizations). And the same distribution form applies to the discharge of debris flow. Then the process of debris flow is related to the geometric structure of the valley. Moreover, viewed from a large scale of water system, all valleys are tributaries, which have been found to assume the same distribution. With each valley corresponding to a debris flow, the distribution can be taken as the frequency distribution of debris flow and therefore provides a quantitative description of the fact that debris flow is inclined to occur at valley of small size. Furthermore, different parameters appear in different regions, suggesting the regional differentials of debris flow potential. We can use the failure rate, instead of the size per se, to describe the risk of a valley of a given area. Finally we claim that the valleys of debris flow in different regions are in the similar episode of evolution.展开更多
Non-equilibrium fission has been described by diffusion model. In order to describe the diffusion process analytically, the analytical solution of Smoluchowski equation in harmonic oscillator potential is obtained. Th...Non-equilibrium fission has been described by diffusion model. In order to describe the diffusion process analytically, the analytical solution of Smoluchowski equation in harmonic oscillator potential is obtained. This analytical solution is able to describe the probability distribution and the diffusive current with the variable x and t. The results indicate that the probability distribution and the diffusive current are relevant to the initial distribution shape, initial position, and the nuclear temperature T; the time to reach the quasi-stationary state is proportional to friction coefficient beta, but is independent of the initial distribution status and the nuclear temperature T. The prerequisites of negative diffusive current are justified. This method provides an approach to describe the diffusion process for fissile process in complicated potentials analytically.展开更多
As an important role in the development of ITS, traffic assignment forecast is always the research focus. Based on the analysis of classic traffic assignment forecast models, an improved traffic assignment forecast mo...As an important role in the development of ITS, traffic assignment forecast is always the research focus. Based on the analysis of classic traffic assignment forecast models, an improved traffic assignment forecast model, multi-ways probability and capacity constraint (MPCC) is presented. Using the new traffic as- signment forecast model to forecast the traffic volume will improve the rationality and veracity of traffic as- signment forecast.展开更多
In this work, we propose a new model of evolution networks, which is based on the evolution of the traffic flow. In our method, the network growth does not take into account preferential attachment, and the attachment...In this work, we propose a new model of evolution networks, which is based on the evolution of the traffic flow. In our method, the network growth does not take into account preferential attachment, and the attachment of new node is independent of the degree of nodes. Our aim is that employing the theory of evolution network, we give a further understanding about the dynamical evolution of the traffic flow. We investigate the probability distributions and scaling properties of the proposed model The simulation results indicate that in the proposed model, the distribution of the output connections can be well described by scale-free distribution. Moreover, the distribution of the connections is largely related to the traffic flow states, such as the exponential distribution (i.e., the scale-free distribution) and random distribution etc.展开更多
To study the behavior of overlying strata and the likelihood of water inrush and quicksand with different mining sequences under an unconsolidated alluvium aquifer, a numerical model based on the fluid-solid coupling ...To study the behavior of overlying strata and the likelihood of water inrush and quicksand with different mining sequences under an unconsolidated alluvium aquifer, a numerical model based on the fluid-solid coupling theory was con- structed by FLAC3D. Simulation results revealed that the mining sequences had a significant influence on the seepage, dis- placement and failure characteristics of the overlying strata. In this kind of geological and hydrogeological conditions, the workface close to the outcrop of coal seam easily suffers from water inrush and quicksand during mining. In the simulation re- sults, the plastic zone, vertical displacement and pore water pressure in the overlying strata of the workface decrease more or less using the upward mining sequence than using the downward mining sequence. Therefore, the application of the upward mining sequence in the process of mining is preferential to prevent water inrush and quicksand.展开更多
The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechan...The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.展开更多
Top-k ranking of websites according to traffic volume is important for Internet Service Providers(ISPs) to understand network status and optimize network resources. However, the ranking result always has a big deviati...Top-k ranking of websites according to traffic volume is important for Internet Service Providers(ISPs) to understand network status and optimize network resources. However, the ranking result always has a big deviation with actual rank for the existence of unknown web traffic, which cannot be identified accurately under current techniques. In this paper, we introduce a novel method to approximate the actual rank. This method associates unknown web traffic with websites according to statistical probabilities. Then, we construct a probabilistic top-k query model to rank websites. We conduct several experiments by using real HTTP traffic traces collected from a commercial ISP covering an entire city in northern China. Experimental results show that the proposed techniques can reduce the deviation existing between the ground truth and the ranking results vastly. In addition, we find that the websites providing video service have higher ratio of unknown IP as well as higher ratio of unknown traffic than the websites providing text web page service. Specifically, we find that the top-3 video websites have more than 90% of unknown web traffic. All these findings are helpful for ISPs understanding network status and deploying Content Distributed Network(CDN).展开更多
This paper explores the diffeomorphism of a backward stochastic ordinary differential equation (BSDE) to a system of semi-linear backward stochastic partial differential equations (BSPDEs), under the inverse of a stoc...This paper explores the diffeomorphism of a backward stochastic ordinary differential equation (BSDE) to a system of semi-linear backward stochastic partial differential equations (BSPDEs), under the inverse of a stochastic flow generated by an ordinary stochastic differential equation (SDE). The author develops a new approach to BSPDEs and also provides some new results. The adapted solution of BSPDEs in terms of those of SDEs and BSDEs is constructed. This brings a new insight on BSPDEs, and leads to a probabilistic approach. As a consequence, the existence, uniqueness, and regularity results are obtained for the (classical, Sobolev, and distributional) solution of BSPDEs.The dimension of the space variable x is allowed to be arbitrary n, and BSPDEs are allowed to be nonlinear in both unknown variables, which implies that the BSPDEs may be nonlinear in the gradient. Due to the limitation of space, however, this paper concerns only classical solution of BSPDEs under some more restricted assumptions.展开更多
This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of 2–3 layers of densely packed spheres.In this study,we combined three the state-of-the-art technologi...This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of 2–3 layers of densely packed spheres.In this study,we combined three the state-of-the-art technologies,i.e.,the direct numerical simulation of turbulent flow,the combined finite-discrete element modelling of the deformation,movement and collision of the particles,and the immersed boundary method for the fluid-solid interaction.Here we verify our code by comparing the flow and particle statistical features with the published data and then present the hydrodynamic forces acting on a particle together with the particle coordinates and velocities,during a typical saltation.We found strong correlation between the abruptly decreasing particle stream-wise velocity and the increasing vertical velocity at collision,which indicates that the continuous saltation of large grain-size particles is controlled by collision parameters such as particle incident angle,local rough bed packing arrangement,and particle density,etc.This physical process is different from that of particle entrainment in which turbulence coherence structures play an important role.Probability distribution functions of several important saltation parameters and the relationships between them are presented.The results show that the saltating particles hitting the windward side of the bed particles are more likely to bounce off the rough bed than those hitting the leeside.Based on the above findings,saltation mechanisms of large grain-size particles in turbulent channel flow are presented.展开更多
Numerical prediction of turbulent mixing can be divided into two subproblems: to predict the geometrical extent of a mixing region and to predict the mixing properties on an atomic or molecular scale, within the mixin...Numerical prediction of turbulent mixing can be divided into two subproblems: to predict the geometrical extent of a mixing region and to predict the mixing properties on an atomic or molecular scale, within the mixing region. The former goal suffices for some purposes, while important problems of chemical reactions(e.g. flames) and nuclear reactions depend critically on the second goal in addition to the first one. Here we review recent progress in establishing a conceptual reformulation of convergence, and we illustrate these concepts with a review of recent numerical studies addressing turbulence and mixing in the high Reynolds number limit. We review significant progress on the first goal, regarding the mixing region, and initial progress on the second goal, regarding atomic level mixing properties. New results concerning non-uniqueness of the infinite Reynolds number solutions and other consequences of a renormalization group point of view, to be published in detail elsewhere, are summarized here.The notion of stochastic convergence(of probability measures and probability distribution functions) replaces traditional pointwise convergence. The primary benefit of this idea is its increased stability relative to the statistical "noise" which characterizes turbulent flow. Our results also show that this modification of convergence, with sufficient mesh refinement, may not be needed. However, in practice, mesh refinement is seldom sufficient and the stochastic convergence concepts have a role.Related to this circle of ideas is the observation that turbulent mixing, in the limit of high Reynolds number, appears to be non-unique. Not only have multiple solutions been observed(and published) for identical problems, but simple physics based arguments and more refined arguments based on the renormalization group come to the same conclusion.Because of the non-uniqueness inherent in numerical models of high Reynolds number turbulence and mixing, we also include here numerical examples of validation. The algorithm we use here has two essential components. We depend on Front Tracking to allow accurate resolution of flows with sharp interfaces or steep gradients(concentration or thermal), as are common in turbulent mixing problems. The higher order and enhanced algorithms for interface tracking, both those already developed, and those proposed here, allow a high resolution and uniquely accurate description of sample mixing problems. Additionally, we depend on the use of dynamic subgrid scale models to set otherwise missing values for turbulent transport coefficients, a step that breaks the non-uniqueness.展开更多
基金the National Natural Science Foundation of China (Grant No.40771010 and No.40671025);the Innovation Project of IMHE, CAS (1100001062).
文摘Most debris flows occur in valleys of area smaller than 50 km2. While associated with a valley, debris flow is by no means a full-valley event but originates from parts of the valley, i.e., the tributary sources. We propose that debris flow develops by extending from tributaries to the mainstream. The debris flow observed in the mainstream is the confluence of the tributary flows and the process of the confluence can be considered as a combination of the tributary elements. The frequency distribution of tributaries is found subject to the Weibull form (or its generalizations). And the same distribution form applies to the discharge of debris flow. Then the process of debris flow is related to the geometric structure of the valley. Moreover, viewed from a large scale of water system, all valleys are tributaries, which have been found to assume the same distribution. With each valley corresponding to a debris flow, the distribution can be taken as the frequency distribution of debris flow and therefore provides a quantitative description of the fact that debris flow is inclined to occur at valley of small size. Furthermore, different parameters appear in different regions, suggesting the regional differentials of debris flow potential. We can use the failure rate, instead of the size per se, to describe the risk of a valley of a given area. Finally we claim that the valleys of debris flow in different regions are in the similar episode of evolution.
文摘Non-equilibrium fission has been described by diffusion model. In order to describe the diffusion process analytically, the analytical solution of Smoluchowski equation in harmonic oscillator potential is obtained. This analytical solution is able to describe the probability distribution and the diffusive current with the variable x and t. The results indicate that the probability distribution and the diffusive current are relevant to the initial distribution shape, initial position, and the nuclear temperature T; the time to reach the quasi-stationary state is proportional to friction coefficient beta, but is independent of the initial distribution status and the nuclear temperature T. The prerequisites of negative diffusive current are justified. This method provides an approach to describe the diffusion process for fissile process in complicated potentials analytically.
文摘As an important role in the development of ITS, traffic assignment forecast is always the research focus. Based on the analysis of classic traffic assignment forecast models, an improved traffic assignment forecast model, multi-ways probability and capacity constraint (MPCC) is presented. Using the new traffic as- signment forecast model to forecast the traffic volume will improve the rationality and veracity of traffic as- signment forecast.
基金The project supported by National Natural Science Foundations of China under Grant Nos and Technology Foundation of Beijing Jiaotong University under Grant No. 2004SM026 70471088 and 70225005 and Che Science.
文摘In this work, we propose a new model of evolution networks, which is based on the evolution of the traffic flow. In our method, the network growth does not take into account preferential attachment, and the attachment of new node is independent of the degree of nodes. Our aim is that employing the theory of evolution network, we give a further understanding about the dynamical evolution of the traffic flow. We investigate the probability distributions and scaling properties of the proposed model The simulation results indicate that in the proposed model, the distribution of the output connections can be well described by scale-free distribution. Moreover, the distribution of the connections is largely related to the traffic flow states, such as the exponential distribution (i.e., the scale-free distribution) and random distribution etc.
文摘To study the behavior of overlying strata and the likelihood of water inrush and quicksand with different mining sequences under an unconsolidated alluvium aquifer, a numerical model based on the fluid-solid coupling theory was con- structed by FLAC3D. Simulation results revealed that the mining sequences had a significant influence on the seepage, dis- placement and failure characteristics of the overlying strata. In this kind of geological and hydrogeological conditions, the workface close to the outcrop of coal seam easily suffers from water inrush and quicksand during mining. In the simulation re- sults, the plastic zone, vertical displacement and pore water pressure in the overlying strata of the workface decrease more or less using the upward mining sequence than using the downward mining sequence. Therefore, the application of the upward mining sequence in the process of mining is preferential to prevent water inrush and quicksand.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50708030 and 90815021)
文摘The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.
基金supported by 111 Project of China under Grant No.B08004
文摘Top-k ranking of websites according to traffic volume is important for Internet Service Providers(ISPs) to understand network status and optimize network resources. However, the ranking result always has a big deviation with actual rank for the existence of unknown web traffic, which cannot be identified accurately under current techniques. In this paper, we introduce a novel method to approximate the actual rank. This method associates unknown web traffic with websites according to statistical probabilities. Then, we construct a probabilistic top-k query model to rank websites. We conduct several experiments by using real HTTP traffic traces collected from a commercial ISP covering an entire city in northern China. Experimental results show that the proposed techniques can reduce the deviation existing between the ground truth and the ranking results vastly. In addition, we find that the websites providing video service have higher ratio of unknown IP as well as higher ratio of unknown traffic than the websites providing text web page service. Specifically, we find that the top-3 video websites have more than 90% of unknown web traffic. All these findings are helpful for ISPs understanding network status and deploying Content Distributed Network(CDN).
基金Project supported by the National Natural Science Foundation of China (No.10325101, No.101310310)the Science Foundation of the Ministry of Education of China (No. 20030246004).
文摘This paper explores the diffeomorphism of a backward stochastic ordinary differential equation (BSDE) to a system of semi-linear backward stochastic partial differential equations (BSPDEs), under the inverse of a stochastic flow generated by an ordinary stochastic differential equation (SDE). The author develops a new approach to BSPDEs and also provides some new results. The adapted solution of BSPDEs in terms of those of SDEs and BSDEs is constructed. This brings a new insight on BSPDEs, and leads to a probabilistic approach. As a consequence, the existence, uniqueness, and regularity results are obtained for the (classical, Sobolev, and distributional) solution of BSPDEs.The dimension of the space variable x is allowed to be arbitrary n, and BSPDEs are allowed to be nonlinear in both unknown variables, which implies that the BSPDEs may be nonlinear in the gradient. Due to the limitation of space, however, this paper concerns only classical solution of BSPDEs under some more restricted assumptions.
基金supported by a Marie Curie International Incoming Fellowship within the seventh European Community Framework Programme(Grant No.PIIF-GA-2009-236457)the financial support of the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51321065)+2 种基金Programme of Introducing Talents of Discipline to Universities(Grant No.B14012)National Natural Science Foundation of China(Grant Nos.50809047 and 51009105)Natural Science Foundation of Tianjin(Grant No.12JCQNJC02600)
文摘This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of 2–3 layers of densely packed spheres.In this study,we combined three the state-of-the-art technologies,i.e.,the direct numerical simulation of turbulent flow,the combined finite-discrete element modelling of the deformation,movement and collision of the particles,and the immersed boundary method for the fluid-solid interaction.Here we verify our code by comparing the flow and particle statistical features with the published data and then present the hydrodynamic forces acting on a particle together with the particle coordinates and velocities,during a typical saltation.We found strong correlation between the abruptly decreasing particle stream-wise velocity and the increasing vertical velocity at collision,which indicates that the continuous saltation of large grain-size particles is controlled by collision parameters such as particle incident angle,local rough bed packing arrangement,and particle density,etc.This physical process is different from that of particle entrainment in which turbulence coherence structures play an important role.Probability distribution functions of several important saltation parameters and the relationships between them are presented.The results show that the saltating particles hitting the windward side of the bed particles are more likely to bounce off the rough bed than those hitting the leeside.Based on the above findings,saltation mechanisms of large grain-size particles in turbulent channel flow are presented.
基金supported in part by the Nuclear Energy University Program of the Department of Energy,project NEUP-09-349,Battelle Energy Alliance LLC 00088495(subaward with DOE as prime sponsor),Leland Stanford Junior University 2175022040367A(subaward with DOE asprime sponsor),Army Research Office W911NF0910306This research used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory,which is supported by the Office of Science of the U.S.Department of Energy under contract DE-AC02-06CH11357.Stony Brook University Preprint number SUNYSB-AMS-12-04
文摘Numerical prediction of turbulent mixing can be divided into two subproblems: to predict the geometrical extent of a mixing region and to predict the mixing properties on an atomic or molecular scale, within the mixing region. The former goal suffices for some purposes, while important problems of chemical reactions(e.g. flames) and nuclear reactions depend critically on the second goal in addition to the first one. Here we review recent progress in establishing a conceptual reformulation of convergence, and we illustrate these concepts with a review of recent numerical studies addressing turbulence and mixing in the high Reynolds number limit. We review significant progress on the first goal, regarding the mixing region, and initial progress on the second goal, regarding atomic level mixing properties. New results concerning non-uniqueness of the infinite Reynolds number solutions and other consequences of a renormalization group point of view, to be published in detail elsewhere, are summarized here.The notion of stochastic convergence(of probability measures and probability distribution functions) replaces traditional pointwise convergence. The primary benefit of this idea is its increased stability relative to the statistical "noise" which characterizes turbulent flow. Our results also show that this modification of convergence, with sufficient mesh refinement, may not be needed. However, in practice, mesh refinement is seldom sufficient and the stochastic convergence concepts have a role.Related to this circle of ideas is the observation that turbulent mixing, in the limit of high Reynolds number, appears to be non-unique. Not only have multiple solutions been observed(and published) for identical problems, but simple physics based arguments and more refined arguments based on the renormalization group come to the same conclusion.Because of the non-uniqueness inherent in numerical models of high Reynolds number turbulence and mixing, we also include here numerical examples of validation. The algorithm we use here has two essential components. We depend on Front Tracking to allow accurate resolution of flows with sharp interfaces or steep gradients(concentration or thermal), as are common in turbulent mixing problems. The higher order and enhanced algorithms for interface tracking, both those already developed, and those proposed here, allow a high resolution and uniquely accurate description of sample mixing problems. Additionally, we depend on the use of dynamic subgrid scale models to set otherwise missing values for turbulent transport coefficients, a step that breaks the non-uniqueness.