The development of fracture around pre-existing cylindrical cavities in brittle rocks was examined using physical models and acoustic emission technique. The experimental results indicate that when granite blocks cont...The development of fracture around pre-existing cylindrical cavities in brittle rocks was examined using physical models and acoustic emission technique. The experimental results indicate that when granite blocks containing one pre-existing cylindrical cavity are loaded in uniaxial compression condition, the profiles of cracks around the cavity can be characterized by tensile cracking （splitting parallel to the axial compression direction） at the roof-floor, compressive crack at two side walls, and remote or secondary cracks at the perimeter of the cavity. Moreover, fracture around cavity is size-dependent. In granite blocks containing pre-existing half-length cylindrical cavities, compressive stress concentration is found to initiate at the two sidewalls and induce shear crack propagation and coalescence. In granite blocks containing multiple parallel cylindrical cavities, the adjacent cylindrical cavities can influence each other and the eventual failure mode is determined by the interaction of tensile, compressive and shear stresses. Experimental results show that both tensile and compressive stresses play an important role in fracture evolution process around cavities in brittle rocks.展开更多
The dynamic stress intensity factor (DSIF) and the scattering of SH wave by circle canyon and crack are studied with Green's function. In order to solve the problem, a suitable Green's function is constructed...The dynamic stress intensity factor (DSIF) and the scattering of SH wave by circle canyon and crack are studied with Green's function. In order to solve the problem, a suitable Green's function is constructed first, which is the solution of displacement fields for elastic half space with circle canyon under output plane harmonic line loading at horizontal surface. Then the integral equation for determining the unknown forces in the problem can be changed into the algebraic one and solved numerically so that crack DSIF can be determined. Last when the medium parameters are altered, the influence on the crack DSIF is discussed partially with the displacement between circle canyon and crack.展开更多
In order to obtain the reasonable undrained shear strength Su for geotechnical analyses of bridge foundations in Yangtze River floodplain clayey soils, a site-specific study is conducted using the imported piezocone p...In order to obtain the reasonable undrained shear strength Su for geotechnical analyses of bridge foundations in Yangtze River floodplain clayey soils, a site-specific study is conducted using the imported piezocone penetration test （CPTu） with dissipation phases at the Fourth Nanjing Yangtze River Bridge construction sites. Taking the values of Su from laboratory tests as references, several existing Su-predicted methods based on CPTu are compared and evaluated. To verify the presented cone factor Nk, additional test sites are selected and examined. The results show that the values of cone factors such as Nkt, Nke, and Nau, depend on the shear test mode and disturbance. Generally, the values of Nke show more scattering than those of Nkt and N△u. For the stratified and layered sediments of the Yangtze River floodplain, it is recommended using the net cone resistance qT to estimate Su and the preliminary cone factor values Nkt are from 7 to 16, with an average of 11. It is also confirmed that the CPTu test, as a new technique in site characterization, can present reasonable parameters for bridge foundations.展开更多
1 Introduction Isolated atrial septal defects （ASD） represent 7% of all cardiac anomalies and can present at any age. Adolescents and adults with simple congenital heart disease such as isolated atrial septal defec...1 Introduction Isolated atrial septal defects （ASD） represent 7% of all cardiac anomalies and can present at any age. Adolescents and adults with simple congenital heart disease such as isolated atrial septal defects are more likely to reach adult age without being diagnosed. Secundum ASD （sASD） is by far the most common type, occurring in 1/1500 live births, with 65% to 75% involving females, On the other hand, patent foramen ovale （PFO） represents an endemic variant in the normal population with a prevalence of 25%-27%. These two entities appear so different that is difficult to fred a conjunction ring： nevertheless we use the same philosophy for the treatment, Indeed, device-based closure has been proved to be effective in both settings.展开更多
Notwithstanding the fact that the problem of drill string buckling （Eulerian instability） inside the cylindrical cavity of an inclined bore-hole attracts attention of many specialists, it is far from completion. Thi...Notwithstanding the fact that the problem of drill string buckling （Eulerian instability） inside the cylindrical cavity of an inclined bore-hole attracts attention of many specialists, it is far from completion. This peculiarity can be explained by the complexity of its mathematic model which is described by singularly perturbed equations. Their solutions （eigen modes） have the shapes of boundary effects or buckles （harmonic wavelets） localized in zones of the bore-hole that are not specified in advance. Therefore, the problem should be stated in the domain of entire length of the drill string or in some separated part including an expected zone of its buckling. In the paper, a mathematic model for computer analysis of incipient buckling of a drill string in cylindrical channel of an inclined bore-hole is elaborated. The constitutive equation is deduced with allowance made for action of gravity, contact, and friction forces. Computer simulation of the drill string buckling is performed for different values of the bore-hole inclination angle, its length, friction coefficient, and clearance. The eigen values （critical loads） are found and modes of stability loss are constructed. The numerical results for the case when the inclination angle equals friction angle coincide with ones obtained analytically.展开更多
A mutual coupling suppression method is proposed for microstrip antenna array by cutting four small semi-circle annular apertures on the metal plate. The structure of antenna array is composed of 2 × 2 four eleme...A mutual coupling suppression method is proposed for microstrip antenna array by cutting four small semi-circle annular apertures on the metal plate. The structure of antenna array is composed of 2 × 2 four elements. The antenna consists of double layer dielectric, and it realizes circular polarization characteristics by cutting rectangular slot on circular patch in the direction of 45°, by using aperture coupling feeding and reverse feeding principle. There is 90＊ phase difference between adjacent antenna elements. Thus, it cuts off the coupling current field between the elements, suppresses the surface wave and reduces the mutual coupling by cutting four semi-circle annular apertures symmetrically on the metal plate. The simulation results show that after cutting four semi-circle annular apertures, the antenna array coupling coefficients decrease significantly, and the side and back lobe levels are suppressed effectively with the gain of antenna improved. So the proposed method is effective to suppress microstrip antenna array mutual coupling.展开更多
Objective Recently it has been suggested that, in patients with large patent foramen ovale （PFO） and atrial septal aneurysms （ASA）, a certain amount of left atrial （LA） dysfunction may be active as an alternate ...Objective Recently it has been suggested that, in patients with large patent foramen ovale （PFO） and atrial septal aneurysms （ASA）, a certain amount of left atrial （LA） dysfunction may be active as an alternate mechanism promoting arterial embolism. Following this hypothesis, elderly patients, being more susceptible to atrial chambers stiffness, should present a more severe LA dysfunction profile. We sought to evaluate the grade of LA dysfunction in elderly patients submitted to transcatheter PFO closure. Methods We retrospectively enrolled 28 consecutive patients with previous stroke （mean age 674-12.5 years, 18 females） referred to our centre for catheter-based PFO closure after recurrent stroke. Baseline values of LA passive and active emptying, LA conduit function, LA ejection fraction, and spontaneous echocontrast （SEC） in the LA and LA appendage were compared with those of 50 atrial fibrillation patients, as well as a sex/age/cardiac risk matched population of 70 healthy controls. Results Pre-closure elderly subjects demonstrated significantly greater reservoir function as well as passive and active emptying, with reduced conduit function and LA ejection fraction, when compared to healthy and younger patients. After closure in elderly patients, LAparameters did not return completely to the levels of healthy patients, whereas LA dysfunction in younger subjects returned normal. Conclusions This study suggests that elderly patients have more severe LA dysfunction than younger patients, which affects the LA remodelling after closure.展开更多
Finite element models were established to analyze the influence of soft filler on stress concentration for a rectangular plate with an elliptic hole in the center. The influence was quantified by means of stress conce...Finite element models were established to analyze the influence of soft filler on stress concentration for a rectangular plate with an elliptic hole in the center. The influence was quantified by means of stress concentration factor (SCF). Seven shape factors of the elliptic hole and three levels of elasticity modulus of the soft filler were considered. The reduction coefficient and sensitivity index of SCF are the two indicators in evaluating the influence of soft filler. It was found that the reduction coefficient of SCF increases significantly as the shape factor and the elasticity modulus of the filler increase, indicating that soft filler can reduce the concentrated stress effectively, especially when the shape factor is great. Analysis for the sensitivity index of SCF indicates that SCF is more sensitive to materials with small elasticity modulus than to materials with large one.展开更多
基金Projects(51004025,51174044)supported by the National Natural Science Foundation of ChinaProject(2011AA060400)supported by the National High-tech Research and Development Program of China+1 种基金Project(N120501003)supported by Ministry of Education of the People’s Republic of ChinaProject(LJQ2012024)supported by Department of Education of Liaoning Province,China
文摘The development of fracture around pre-existing cylindrical cavities in brittle rocks was examined using physical models and acoustic emission technique. The experimental results indicate that when granite blocks containing one pre-existing cylindrical cavity are loaded in uniaxial compression condition, the profiles of cracks around the cavity can be characterized by tensile cracking （splitting parallel to the axial compression direction） at the roof-floor, compressive crack at two side walls, and remote or secondary cracks at the perimeter of the cavity. Moreover, fracture around cavity is size-dependent. In granite blocks containing pre-existing half-length cylindrical cavities, compressive stress concentration is found to initiate at the two sidewalls and induce shear crack propagation and coalescence. In granite blocks containing multiple parallel cylindrical cavities, the adjacent cylindrical cavities can influence each other and the eventual failure mode is determined by the interaction of tensile, compressive and shear stresses. Experimental results show that both tensile and compressive stresses play an important role in fracture evolution process around cavities in brittle rocks.
文摘The dynamic stress intensity factor (DSIF) and the scattering of SH wave by circle canyon and crack are studied with Green's function. In order to solve the problem, a suitable Green's function is constructed first, which is the solution of displacement fields for elastic half space with circle canyon under output plane harmonic line loading at horizontal surface. Then the integral equation for determining the unknown forces in the problem can be changed into the algebraic one and solved numerically so that crack DSIF can be determined. Last when the medium parameters are altered, the influence on the crack DSIF is discussed partially with the displacement between circle canyon and crack.
基金The National Natural Science Foundation of China(No.40702047)
文摘In order to obtain the reasonable undrained shear strength Su for geotechnical analyses of bridge foundations in Yangtze River floodplain clayey soils, a site-specific study is conducted using the imported piezocone penetration test （CPTu） with dissipation phases at the Fourth Nanjing Yangtze River Bridge construction sites. Taking the values of Su from laboratory tests as references, several existing Su-predicted methods based on CPTu are compared and evaluated. To verify the presented cone factor Nk, additional test sites are selected and examined. The results show that the values of cone factors such as Nkt, Nke, and Nau, depend on the shear test mode and disturbance. Generally, the values of Nke show more scattering than those of Nkt and N△u. For the stratified and layered sediments of the Yangtze River floodplain, it is recommended using the net cone resistance qT to estimate Su and the preliminary cone factor values Nkt are from 7 to 16, with an average of 11. It is also confirmed that the CPTu test, as a new technique in site characterization, can present reasonable parameters for bridge foundations.
文摘1 Introduction Isolated atrial septal defects （ASD） represent 7% of all cardiac anomalies and can present at any age. Adolescents and adults with simple congenital heart disease such as isolated atrial septal defects are more likely to reach adult age without being diagnosed. Secundum ASD （sASD） is by far the most common type, occurring in 1/1500 live births, with 65% to 75% involving females, On the other hand, patent foramen ovale （PFO） represents an endemic variant in the normal population with a prevalence of 25%-27%. These two entities appear so different that is difficult to fred a conjunction ring： nevertheless we use the same philosophy for the treatment, Indeed, device-based closure has been proved to be effective in both settings.
文摘Notwithstanding the fact that the problem of drill string buckling （Eulerian instability） inside the cylindrical cavity of an inclined bore-hole attracts attention of many specialists, it is far from completion. This peculiarity can be explained by the complexity of its mathematic model which is described by singularly perturbed equations. Their solutions （eigen modes） have the shapes of boundary effects or buckles （harmonic wavelets） localized in zones of the bore-hole that are not specified in advance. Therefore, the problem should be stated in the domain of entire length of the drill string or in some separated part including an expected zone of its buckling. In the paper, a mathematic model for computer analysis of incipient buckling of a drill string in cylindrical channel of an inclined bore-hole is elaborated. The constitutive equation is deduced with allowance made for action of gravity, contact, and friction forces. Computer simulation of the drill string buckling is performed for different values of the bore-hole inclination angle, its length, friction coefficient, and clearance. The eigen values （critical loads） are found and modes of stability loss are constructed. The numerical results for the case when the inclination angle equals friction angle coincide with ones obtained analytically.
基金Qingdao Basic Research of Science and Technology Plan Projects(No.13-1-4-132-jch)
文摘A mutual coupling suppression method is proposed for microstrip antenna array by cutting four small semi-circle annular apertures on the metal plate. The structure of antenna array is composed of 2 × 2 four elements. The antenna consists of double layer dielectric, and it realizes circular polarization characteristics by cutting rectangular slot on circular patch in the direction of 45°, by using aperture coupling feeding and reverse feeding principle. There is 90＊ phase difference between adjacent antenna elements. Thus, it cuts off the coupling current field between the elements, suppresses the surface wave and reduces the mutual coupling by cutting four semi-circle annular apertures symmetrically on the metal plate. The simulation results show that after cutting four semi-circle annular apertures, the antenna array coupling coefficients decrease significantly, and the side and back lobe levels are suppressed effectively with the gain of antenna improved. So the proposed method is effective to suppress microstrip antenna array mutual coupling.
文摘Objective Recently it has been suggested that, in patients with large patent foramen ovale （PFO） and atrial septal aneurysms （ASA）, a certain amount of left atrial （LA） dysfunction may be active as an alternate mechanism promoting arterial embolism. Following this hypothesis, elderly patients, being more susceptible to atrial chambers stiffness, should present a more severe LA dysfunction profile. We sought to evaluate the grade of LA dysfunction in elderly patients submitted to transcatheter PFO closure. Methods We retrospectively enrolled 28 consecutive patients with previous stroke （mean age 674-12.5 years, 18 females） referred to our centre for catheter-based PFO closure after recurrent stroke. Baseline values of LA passive and active emptying, LA conduit function, LA ejection fraction, and spontaneous echocontrast （SEC） in the LA and LA appendage were compared with those of 50 atrial fibrillation patients, as well as a sex/age/cardiac risk matched population of 70 healthy controls. Results Pre-closure elderly subjects demonstrated significantly greater reservoir function as well as passive and active emptying, with reduced conduit function and LA ejection fraction, when compared to healthy and younger patients. After closure in elderly patients, LAparameters did not return completely to the levels of healthy patients, whereas LA dysfunction in younger subjects returned normal. Conclusions This study suggests that elderly patients have more severe LA dysfunction than younger patients, which affects the LA remodelling after closure.
基金Supported by National Natural Science Foundation of China (No. 50878142)
文摘Finite element models were established to analyze the influence of soft filler on stress concentration for a rectangular plate with an elliptic hole in the center. The influence was quantified by means of stress concentration factor (SCF). Seven shape factors of the elliptic hole and three levels of elasticity modulus of the soft filler were considered. The reduction coefficient and sensitivity index of SCF are the two indicators in evaluating the influence of soft filler. It was found that the reduction coefficient of SCF increases significantly as the shape factor and the elasticity modulus of the filler increase, indicating that soft filler can reduce the concentrated stress effectively, especially when the shape factor is great. Analysis for the sensitivity index of SCF indicates that SCF is more sensitive to materials with small elasticity modulus than to materials with large one.
