Computed tomography has been proven to be useful for non-destructive inspection of structures and materials. We build a three-dimensional imaging system with the photonically generated incoherent noise source and the ...Computed tomography has been proven to be useful for non-destructive inspection of structures and materials. We build a three-dimensional imaging system with the photonically generated incoherent noise source and the Schottky barrier diode detector in the terahertz frequency band (90–140GHz). Based on the computed tomography technique, the three-dimensional image of a ceramic sample is reconstructed successfully by stacking the slices at different heights. The imaging results not only indicate the ability of terahertz wave in the non-invasive sensing and non-destructive inspection applications, but also prove the effectiveness and superiority of the uni-traveling-carrier photodiode as a terahertz source in the imaging applications.展开更多
BACKGROUND There is evolving role of computed tomography coronary angiography(CTCA)in non-invasive evaluation of coronary artery abnormalities in children with Kawasaki disease(KD).Despite this,there is lack of data o...BACKGROUND There is evolving role of computed tomography coronary angiography(CTCA)in non-invasive evaluation of coronary artery abnormalities in children with Kawasaki disease(KD).Despite this,there is lack of data on radiation dose in this group of children undergoing CTCA.AIM To audit the radiation dose of CTCA in children with KD.METHODS Study(December 2013-February 2018)was performed on dual source CT scanner using adaptive prospective electrocardiography-triggering.The dose length product(DLP in milligray-centimeters-mGy.cm)was recorded.Effective radiation dose(millisieverts-mSv)was calculated by applying appropriate age adjusted conversion factors as per recommendations of International Commission on Radiological Protection.Radiation dose was compared across the groups(0-1,1-5,5-10,and>10 years).RESULTS Eighty-five children(71 boys,14 girls)with KD underwent CTCA.The median age was 5 years(range,2 mo-11 years).Median DLP and effective dose was 21 mGy.cm,interquartile ranges(IQR)=15(13,28)and 0.83 mSv,IQR=0.33(0.68,1.01)respectively.Mean DLP increased significantly across the age groups.Mean effective dose in infants(0.63 mSv)was significantly lower than the other age groups(1-5 years 0.85 mSv,5-10 years 1.04 mSv,and>10 years 1.38 mSv)(P<0.05).There was no significant difference in the effective dose between the other groups of children.All the CTCA studies were of diagnostic quality.No child required a repeat examination.CONCLUSION CTCA is feasible with submillisievert radiation dose in most children with KD.Thus,CTCA has the potential to be an important adjunctive imaging modality in children with KD.展开更多
The presence of Dirac delta function in differential equation can lead to a discontinuity,which may degrade the accuracy of related numerical methods.To improve the accuracy,a secondorder numerical method for elliptic...The presence of Dirac delta function in differential equation can lead to a discontinuity,which may degrade the accuracy of related numerical methods.To improve the accuracy,a secondorder numerical method for elliptic equations with singular sources is introduced by employing a local kernel flter.In this method,the discontinuous equation is convoluted with the kernel function to obtain a more regular one.Then the original equation is replaced by this fltered equation around the singular points,to obtain discrete numerical form.The unchanged equations at the other points are discretized by using a central difference scheme.1D and 2D examples are carried out to validate the correctness and accuracy of the present method.The results show that a second-order of accuracy can be obtained in the fltering framework with an appropriate integration rule.Furthermore,the present method does not need any jump condition,and also has extremely simple form that can be easily extended to high dimensional cases and complex geometry.展开更多
In this paper, a new method is applied to get the computation formula of partial coherence function. The main attention is paid to the computation formula of the partial coherence function with three and four signals....In this paper, a new method is applied to get the computation formula of partial coherence function. The main attention is paid to the computation formula of the partial coherence function with three and four signals. The advantages of the method discussed in the paper are clear in physical meaning and easy to compute at the end of the paper,the application of the method to the identification of an air compressor noise source is presented and the results are satisfactory.展开更多
Open source feld operation and manipulation(OpenFOAM)is one of the most prevalent open source computational fluid dynamics(CFD)software.It is very convenient for researchers to develop their own codes based on the...Open source feld operation and manipulation(OpenFOAM)is one of the most prevalent open source computational fluid dynamics(CFD)software.It is very convenient for researchers to develop their own codes based on the class library toolbox within OpenFOAM.In recent years,several density-based solvers within OpenFOAM for supersonic/hypersonic compressible flow are coming up.Although the capabilities of these solvers to capture shock wave have already been verifed by some researchers,these solvers still need to be validated comprehensively as commercial CFD software.In boundary layer where diffusion is the dominant transportation manner,the convective discrete schemes'capability to capture aerothermal variables,such as temperature and heat flux,is different from each other due to their own numerical dissipative characteristics and from viewpoint of this capability,these compressible solvers within OpenFOAM can be validated further.In this paper,frstly,the organizational architecture of density-based solvers within OpenFOAM is analyzed.Then,from the viewpoint of the capability to capture aerothermal variables,the numerical results of several typical geometrical felds predicted by these solvers are compared with both the outcome obtained from the commercial software Fastran and the experimental data.During the computing process,the Roe,AUSM+(Advection Upstream Splitting Method),and HLLC(Harten-Lax-van Leer-Contact)convective discrete schemes of which the spatial accuracy is 1st and 2nd order are utilized,respectively.The compared results show that the aerothermal variables are in agreement with results generated by Fastran and the experimental data even if the1st order spatial precision is implemented.Overall,the accuracy of these density-based solvers can meet the requirement of engineering and scientifc problems to capture aerothermal variables in diffusion boundary layer.展开更多
基金Supported by the Hundred Talents Program of Chinese Academy of Sciencesthe National Basic Research Program of China under Grant No 2014CB339803+2 种基金the Major National Development Project of Scientific Instrument and Equipment under Grant No2011YQ150021the National Natural Science Foundation of China under Grant Nos 61575214,61574155,61404149 and 61404150the Shanghai Municipal Commission of Science and Technology under Grant Nos 14530711300,15560722000 and 15ZR1447500
文摘Computed tomography has been proven to be useful for non-destructive inspection of structures and materials. We build a three-dimensional imaging system with the photonically generated incoherent noise source and the Schottky barrier diode detector in the terahertz frequency band (90–140GHz). Based on the computed tomography technique, the three-dimensional image of a ceramic sample is reconstructed successfully by stacking the slices at different heights. The imaging results not only indicate the ability of terahertz wave in the non-invasive sensing and non-destructive inspection applications, but also prove the effectiveness and superiority of the uni-traveling-carrier photodiode as a terahertz source in the imaging applications.
文摘BACKGROUND There is evolving role of computed tomography coronary angiography(CTCA)in non-invasive evaluation of coronary artery abnormalities in children with Kawasaki disease(KD).Despite this,there is lack of data on radiation dose in this group of children undergoing CTCA.AIM To audit the radiation dose of CTCA in children with KD.METHODS Study(December 2013-February 2018)was performed on dual source CT scanner using adaptive prospective electrocardiography-triggering.The dose length product(DLP in milligray-centimeters-mGy.cm)was recorded.Effective radiation dose(millisieverts-mSv)was calculated by applying appropriate age adjusted conversion factors as per recommendations of International Commission on Radiological Protection.Radiation dose was compared across the groups(0-1,1-5,5-10,and>10 years).RESULTS Eighty-five children(71 boys,14 girls)with KD underwent CTCA.The median age was 5 years(range,2 mo-11 years).Median DLP and effective dose was 21 mGy.cm,interquartile ranges(IQR)=15(13,28)and 0.83 mSv,IQR=0.33(0.68,1.01)respectively.Mean DLP increased significantly across the age groups.Mean effective dose in infants(0.63 mSv)was significantly lower than the other age groups(1-5 years 0.85 mSv,5-10 years 1.04 mSv,and>10 years 1.38 mSv)(P<0.05).There was no significant difference in the effective dose between the other groups of children.All the CTCA studies were of diagnostic quality.No child required a repeat examination.CONCLUSION CTCA is feasible with submillisievert radiation dose in most children with KD.Thus,CTCA has the potential to be an important adjunctive imaging modality in children with KD.
基金supported by the National Natural Science Foundation in China(Grant Nos.51076006,11202013)BUAA SJP ‘‘111’’ Program(Grant No.B08009)+1 种基金the National Basic Research Program of China(2012CB720200)the Open Research Fund of MOE Key Lab-oratory of High-speed Railway Engineering,Southwest Jiao-tong University and the European Community’s Seventh Framework Program(FP7/2007-2013)under Grant agreement 225967‘‘NextMuSE’’
文摘The presence of Dirac delta function in differential equation can lead to a discontinuity,which may degrade the accuracy of related numerical methods.To improve the accuracy,a secondorder numerical method for elliptic equations with singular sources is introduced by employing a local kernel flter.In this method,the discontinuous equation is convoluted with the kernel function to obtain a more regular one.Then the original equation is replaced by this fltered equation around the singular points,to obtain discrete numerical form.The unchanged equations at the other points are discretized by using a central difference scheme.1D and 2D examples are carried out to validate the correctness and accuracy of the present method.The results show that a second-order of accuracy can be obtained in the fltering framework with an appropriate integration rule.Furthermore,the present method does not need any jump condition,and also has extremely simple form that can be easily extended to high dimensional cases and complex geometry.
文摘In this paper, a new method is applied to get the computation formula of partial coherence function. The main attention is paid to the computation formula of the partial coherence function with three and four signals. The advantages of the method discussed in the paper are clear in physical meaning and easy to compute at the end of the paper,the application of the method to the identification of an air compressor noise source is presented and the results are satisfactory.
基金supported by the National Natural Science Foundation of China(Grant Nos.51176038,51121004)
文摘Open source feld operation and manipulation(OpenFOAM)is one of the most prevalent open source computational fluid dynamics(CFD)software.It is very convenient for researchers to develop their own codes based on the class library toolbox within OpenFOAM.In recent years,several density-based solvers within OpenFOAM for supersonic/hypersonic compressible flow are coming up.Although the capabilities of these solvers to capture shock wave have already been verifed by some researchers,these solvers still need to be validated comprehensively as commercial CFD software.In boundary layer where diffusion is the dominant transportation manner,the convective discrete schemes'capability to capture aerothermal variables,such as temperature and heat flux,is different from each other due to their own numerical dissipative characteristics and from viewpoint of this capability,these compressible solvers within OpenFOAM can be validated further.In this paper,frstly,the organizational architecture of density-based solvers within OpenFOAM is analyzed.Then,from the viewpoint of the capability to capture aerothermal variables,the numerical results of several typical geometrical felds predicted by these solvers are compared with both the outcome obtained from the commercial software Fastran and the experimental data.During the computing process,the Roe,AUSM+(Advection Upstream Splitting Method),and HLLC(Harten-Lax-van Leer-Contact)convective discrete schemes of which the spatial accuracy is 1st and 2nd order are utilized,respectively.The compared results show that the aerothermal variables are in agreement with results generated by Fastran and the experimental data even if the1st order spatial precision is implemented.Overall,the accuracy of these density-based solvers can meet the requirement of engineering and scientifc problems to capture aerothermal variables in diffusion boundary layer.