The influence of heterogeneity on mechanical and acoustic emission characteristics of rock specimen under uniaxial compress was studied with numerical simulation methods.Weibull distribution function was adopted to de...The influence of heterogeneity on mechanical and acoustic emission characteristics of rock specimen under uniaxial compress was studied with numerical simulation methods.Weibull distribution function was adopted to describe the mesoscopic heterogeneity of rocks.The failure process of heterogeneous rock specimen under uniaxial loading was simulated using FLAC 3D software.Five schemes were adopted to investigate the influence of heterogeneity.The results demonstrate that as the homogeneity increases,the peak strength and brittleness of rocks increase,and the macro elastic modulus improves as well.Heterogeneity has great influence on macro elastic modulus and strength when the homogeneity coefficient is less than 20.0.The volume expansion is not so obvious when the homogeneity increases.As the homogeneity coefficient increases the acoustic emissions modes change from swarm shock to main shock.When the homogeneity coefficient is high,the cumulative acoustic emission events-axial strain curve is gentle before the rock failure.The numerical results agree with the previously numerical results and earlier experimental measurements.展开更多
Non-equilibrium molecular dynamics simulations have been performed to investigate the effect of the cross-section shape on the thermal conductivity of argon nanowires. Some typical cross-section shapes, such as triang...Non-equilibrium molecular dynamics simulations have been performed to investigate the effect of the cross-section shape on the thermal conductivity of argon nanowires. Some typical cross-section shapes, such as triangle, square, pentagon, hexagon and circle, axe carefully explored. The simulation results show that with the same cross-sectional area of the regular polygons, tim thermal conductivities decrease with the reduction of the sides of the polygons, and the thermal conductivity of the circular nanowire is larger than those of the other polygonal ones. Phonon gas kinetic theory is used to analyse the phonon transport in nanowires, and the concept of equivalent diameter is proposed to illustrate the characteristic dimension of the none-circulax cross-section.展开更多
The importance of stochasticity in cellular processes is increasingly recognized in both theoretical andexperimental studies.General features of stochasticity in gene regulation and expression are briefly reviewed in ...The importance of stochasticity in cellular processes is increasingly recognized in both theoretical andexperimental studies.General features of stochasticity in gene regulation and expression are briefly reviewed in thisarticle,which include the main experimental phenomena,classification,quantization and regulation of noises.Thecorrelation and transmission of noise in cascade networks are analyzed further and the stochastic simulation methodsthat can capture effects of intrinsic and extrinsic noise are described.展开更多
Objective:To compare mini-probe endoscopic ultrasonography(MCUS)with computed tomography(CT)in pre-operative T and N staging of esophageal cancer,and to find out the MCUS parameters to judge lymph nodes metastasis for...Objective:To compare mini-probe endoscopic ultrasonography(MCUS)with computed tomography(CT)in pre-operative T and N staging of esophageal cancer,and to find out the MCUS parameters to judge lymph nodes metastasis for esophageal cancer.Methods:Thirty-five patients received both MCUS and CT preoperatively,on both of which the T and N stages were determined.The accuracy,sensitivity,specificity,positive predicting value and negative predicting value were compared with the postoperative pathological results.Results:The accuracy of MCUS was 85.7% in T staging and 85.7% and 80.0% in N staging by two different methods,which were 45.7% and 74.3%,respectively,by CT.Conclusion:MCUS is better than CT in preoperative staging for esophageal cancer.The ratio of short to long axis(S/L)combined with short axis is a useful way to determine lymph nodes metastasis.展开更多
This paper exploits the Rayleigh integral method to simulate the propagation of transmitted ultrasonic waves and received echoes through various media. Performed simulations study the effect of apodization using diffe...This paper exploits the Rayleigh integral method to simulate the propagation of transmitted ultrasonic waves and received echoes through various media. Performed simulations study the effect of apodization using different types of windows and the effect of medium properties on the reflections obtained. All estimations are done using the Rayleigh integral method simplified by the Fresnel approximation. Five different interfaces are considered： tissue-bone-tissue, tissue-fat-bone, fat-muscle-bone, air-fat-bone and water-fat-bone. The apodization simulations show that the hamming window is more efficient than the rectangular and triangular windows for obtaining a more consistent beam. In the second set of simulations, reflections are mapped with respect to the depth from which these reflections are generated. It demonstrates that the solid and water media allow for the attainment of echoes from deeper regions as compared to the air medium. Matlab is used as the simulation framework.展开更多
This paper presents a study where artificial neural networks are used as a curve fitting method applying measured data from an axial compressor test rig to predict the compressor map. Emphasis is on models for predict...This paper presents a study where artificial neural networks are used as a curve fitting method applying measured data from an axial compressor test rig to predict the compressor map. Emphasis is on models for prediction of pressure ratio, compressor mass flow and mechanical efficiency. Except for evaluation of interpolation and extrapolation capabilities, this study also investigates the effect of the design parameters such as number of neurons and size of training data. To reduce the effect of noise, the auto associative neural network has been applied for noise filtering of the data from the parameters used to calculate the efficiency. In summary, the results show that artificial neural network can be used for compressor map prediction, but it should be emphasized that the selection of data normalisation scale is crucial for the model where compressor mass flow is predicted. Furthermore, it is shown that the AANN （auto associative neural network） can be used to the reduce noise in measured data and thereby enhance the quality of the data.展开更多
基金Project(2007CB209407) supported by the National Basic Research Program of ChinaProject(50729904) supported by the National Natural Science Foundation of China
文摘The influence of heterogeneity on mechanical and acoustic emission characteristics of rock specimen under uniaxial compress was studied with numerical simulation methods.Weibull distribution function was adopted to describe the mesoscopic heterogeneity of rocks.The failure process of heterogeneous rock specimen under uniaxial loading was simulated using FLAC 3D software.Five schemes were adopted to investigate the influence of heterogeneity.The results demonstrate that as the homogeneity increases,the peak strength and brittleness of rocks increase,and the macro elastic modulus improves as well.Heterogeneity has great influence on macro elastic modulus and strength when the homogeneity coefficient is less than 20.0.The volume expansion is not so obvious when the homogeneity increases.As the homogeneity coefficient increases the acoustic emissions modes change from swarm shock to main shock.When the homogeneity coefficient is high,the cumulative acoustic emission events-axial strain curve is gentle before the rock failure.The numerical results agree with the previously numerical results and earlier experimental measurements.
文摘Non-equilibrium molecular dynamics simulations have been performed to investigate the effect of the cross-section shape on the thermal conductivity of argon nanowires. Some typical cross-section shapes, such as triangle, square, pentagon, hexagon and circle, axe carefully explored. The simulation results show that with the same cross-sectional area of the regular polygons, tim thermal conductivities decrease with the reduction of the sides of the polygons, and the thermal conductivity of the circular nanowire is larger than those of the other polygonal ones. Phonon gas kinetic theory is used to analyse the phonon transport in nanowires, and the concept of equivalent diameter is proposed to illustrate the characteristic dimension of the none-circulax cross-section.
基金Supported by the Ministry of Science and Technology of China under Grant No. 2012CB934001the National Natural Science Foundation of China under Grant No. 10975019+1 种基金the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Personnel of China under Grant No. MOP2006138the Fundamental Research Funds for the Central Universities, and Y1515530U1
文摘The importance of stochasticity in cellular processes is increasingly recognized in both theoretical andexperimental studies.General features of stochasticity in gene regulation and expression are briefly reviewed in thisarticle,which include the main experimental phenomena,classification,quantization and regulation of noises.Thecorrelation and transmission of noise in cascade networks are analyzed further and the stochastic simulation methodsthat can capture effects of intrinsic and extrinsic noise are described.
文摘Objective:To compare mini-probe endoscopic ultrasonography(MCUS)with computed tomography(CT)in pre-operative T and N staging of esophageal cancer,and to find out the MCUS parameters to judge lymph nodes metastasis for esophageal cancer.Methods:Thirty-five patients received both MCUS and CT preoperatively,on both of which the T and N stages were determined.The accuracy,sensitivity,specificity,positive predicting value and negative predicting value were compared with the postoperative pathological results.Results:The accuracy of MCUS was 85.7% in T staging and 85.7% and 80.0% in N staging by two different methods,which were 45.7% and 74.3%,respectively,by CT.Conclusion:MCUS is better than CT in preoperative staging for esophageal cancer.The ratio of short to long axis(S/L)combined with short axis is a useful way to determine lymph nodes metastasis.
文摘This paper exploits the Rayleigh integral method to simulate the propagation of transmitted ultrasonic waves and received echoes through various media. Performed simulations study the effect of apodization using different types of windows and the effect of medium properties on the reflections obtained. All estimations are done using the Rayleigh integral method simplified by the Fresnel approximation. Five different interfaces are considered： tissue-bone-tissue, tissue-fat-bone, fat-muscle-bone, air-fat-bone and water-fat-bone. The apodization simulations show that the hamming window is more efficient than the rectangular and triangular windows for obtaining a more consistent beam. In the second set of simulations, reflections are mapped with respect to the depth from which these reflections are generated. It demonstrates that the solid and water media allow for the attainment of echoes from deeper regions as compared to the air medium. Matlab is used as the simulation framework.
文摘This paper presents a study where artificial neural networks are used as a curve fitting method applying measured data from an axial compressor test rig to predict the compressor map. Emphasis is on models for prediction of pressure ratio, compressor mass flow and mechanical efficiency. Except for evaluation of interpolation and extrapolation capabilities, this study also investigates the effect of the design parameters such as number of neurons and size of training data. To reduce the effect of noise, the auto associative neural network has been applied for noise filtering of the data from the parameters used to calculate the efficiency. In summary, the results show that artificial neural network can be used for compressor map prediction, but it should be emphasized that the selection of data normalisation scale is crucial for the model where compressor mass flow is predicted. Furthermore, it is shown that the AANN （auto associative neural network） can be used to the reduce noise in measured data and thereby enhance the quality of the data.
