目的:应用斑点追踪成像技术对左束支起搏(left bundle branch pacing,LBBP)与希氏束起搏(His bundle pacing,HBP)患者起搏器植入1年后左心室收缩功能及同步性进行评价。方法:获取LBBP患者(40例)、HBP患者(40例)、对照组(40例)标准心尖...目的:应用斑点追踪成像技术对左束支起搏(left bundle branch pacing,LBBP)与希氏束起搏(His bundle pacing,HBP)患者起搏器植入1年后左心室收缩功能及同步性进行评价。方法:获取LBBP患者(40例)、HBP患者(40例)、对照组(40例)标准心尖四腔、三腔、两腔和短轴二尖瓣、心尖水平图像;分别测量和比较LBBP、HBP患者与对照组纵向、圆周和径向应变、纵向应变达峰时间弥散度(peak strain dispersion,PSD)、左室扭转、心室间机械延迟时间(interventricular mechanical delay time,IVMD);计算和比较圆周应变达峰时间标准差(standard deviation of time to peak circumferential strain,T-sd-CS)、径向应变达峰时间标准差(standard deviation of time to peak radial strain,T-sd-RS)。结果:HBP组短轴心尖平面T-sd-CS大于对照组,其余心室电活动及机械同步性参数与对照组无显著差异;LBBP组QRS波宽度大于HBP组和对照组(P<0.05);LBBP组短轴心尖平面T-sd-CS大于HBP组和对照组(P<0.05);LBBP组左室纵向PSD大于HBP组和对照组(P<0.05);各组间左心室短轴径向应变、T-sd-RS、纵向应变、扭转角度及IVMD比较均无统计学差异。结论:LBBP组与HBP组、对照组相比,左心室内同步性稍延迟;LBBP组与HBP组、对照组心肌收缩功能基本相近。展开更多
The special columnar jointed structure endows rocks with significant anisotropy,accurately grasping the strength and deformation properties of a columnar jointed rock mass(CJRM)under complex geological conditions is c...The special columnar jointed structure endows rocks with significant anisotropy,accurately grasping the strength and deformation properties of a columnar jointed rock mass(CJRM)under complex geological conditions is crucial for related engineering safety.Combined with the irregular jointed networks observed in the field,artificial irregular CJRM(ICJRM)samples with various inclination angles were prepared for triaxial tests.The results showed that the increase in confining pressure can enhance the ability of the ICJRM to resist deformation and failure,and reduce the deformation and strength anisotropic degrees.Considering the field stress situation,the engineering parts with an inclination angle of 30°−45°need to be taken seriously.Four typical failure modes were identified,and the sample with an inclination angle of 15°showed the same failure behavior as the field CJRM.Traditional and improved joint factor methods were used to establish empirical relationships for predicting the strength and deformation of CJRM under triaxial stress.Since the improved joint factor method can reflect the unique structure of CJRM,the predictive ability of the empirical relationship based on the improved method is better than that based on the traditional joint factor method.展开更多
Nanostructured BN and BN-Co films with Cu,Co,Au as the top electrodes,and Pt as the bottom electrodes were grown by magnetron sputtering.Both BN samples and BN-Co ones show bipolar resistive switching behaviors.For th...Nanostructured BN and BN-Co films with Cu,Co,Au as the top electrodes,and Pt as the bottom electrodes were grown by magnetron sputtering.Both BN samples and BN-Co ones show bipolar resistive switching behaviors.For the sample with active Cu as the top electrode,the formation and rupture of metallic Cu conductive filaments can explain the resistive switching behavior;for the other samples,the generation and annihilation of nitrogen vacancies under the electric stimuli may contribute to the occurrence of resistive switching.Taking advantage of the formed and broken Co-N bonds during resistive switching,the saturation magnetization of the BN-Co films can be modulated.Thus,it investigated the resistive switching behavior of BN and BN-Co materials in this work.Similar to that of oxide materials,the resistive switching behaviors of the nitrides may be attributed to the movement of cations or anions within the dielectric or electrodes during the application of voltage.Additionally,ion migration may lead to the formation or breaking of Co-N bonds,which can effectively regulate the magnetism of BN-Co materials.This study extends resistive switching materials to nitrides,enabling the regulation of magnetism along with resistance changes,thus providing insights for the design of novel voltage-controlled magnetic devices and achieving multi-functionality.展开更多
The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the i...The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the impact of vibration pretreatment temperature on the fiber weight content,microscopic morphology and mechanical properties of the composite laminates by using optical digital microscopy,universal tensile testing machine and thermo-gravimetric analyzer.Additionally,the combined mode of Bragg fiber grating sensor and temperature measurement fiber was employed to explore the effect of vibration pretreatment on the strain process during microwave curing.The study results revealed that the change in vibration pretreatment temperature had a slight impact on the fiber weight content when the vibration acceleration remained constant.The metallographic and interlaminar strength of the specimen formed at a vibration pretreatment temperature of 80℃ demonstrated a porosity of 0.414% and a 10.69% decrease in interlaminar shear strength compared to autoclave curing.Moreover,the introduction of the vibration energy field during the microwave curing process led to a significant reduction in residual strain in both the 0°and 90°fiber directions,when the laminate was cooled to 60℃.展开更多
In order to determine the relationship among energy consumption of rock and its fragmentation, dynamic strength and strain rate, granite, sandstone and limestone specimens were chosen and tested on large-diameter spli...In order to determine the relationship among energy consumption of rock and its fragmentation, dynamic strength and strain rate, granite, sandstone and limestone specimens were chosen and tested on large-diameter split Hopkinson pressure bar (SHPB) equipment with half-sine waveform loading at the strain rates ranging from 40 to 150 s- 1. With recorded signals, the energy consumption, strain rate and dynamic strength were analyzed. And the fragmentation behaviors of specimens were investigated. The experimental results show that the energy consumption density of rock increases linearly with the total incident energy. The energy consumption density is of an exponent relationship with the average size of rock fragments. The higher the energy consumption density, the more serious the fragmentation, and the better the gradation of fragments. The energy consumption density takes a good logarithm relationship with the dynamic strength of rock. The dynamic strength of rock increases with the increase of strain rate, indicating higher strain rate sensitivity.展开更多
Isothermal compression tests at temperatures from 1 273 to l 423 K and strain rates from 0.1 to 10 s-q were carried out to investigate the flow behaviors of Q420qE steel. Stress-strain data collected from the tests we...Isothermal compression tests at temperatures from 1 273 to l 423 K and strain rates from 0.1 to 10 s-q were carried out to investigate the flow behaviors of Q420qE steel. Stress-strain data collected from the tests were employed to establish the constitutive equation, in which the influence of strain was incorporated by considering the effect of strain on material constants Q, n, a, and lnA. The results show that the flow stress curves are dependent on the strain, strain rate and deformation temperature. They display typical dynamic recrystallization behavior and consist of three stages, i.e., hardening stage, softening stage and steady stage. The flow stress decreases with increasing the deformation temperature and decreasing the strain rate. In addition, the flow stress data predicted by the proposed constitutive model agree well with the corresponding experimental results, and the correlation coefficient and the average absolute relative error between them are 0.990 3 and 3.686%, respectively.展开更多
A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uni...A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uniaxial compression strength and elastic properties (elastic modulus and Poisson ratio) under different conditions and influence of pore fluid on them. When the loading strain rates are 10^(-5), 10^(-4) and 10^(-3)/s, uniaxial compression strengths of dry sandstones are 82.3, 126.6 and 141.6 MPa, respectively, and that of water saturated sandstones are 70.5, 108.3 and 124.1 MPa, respectively. The above results show that the uniaxial compression strength increases with the increase of strain rate, however, variation of softening coefficient is insignificant. Under monotonic loading condition, tangent modulus increases with an increment of stress (strain) to a maximum value at a certain stress level, beyond which it starts to decline. Under the partial cyclic loading during loading path condition, unloading or reloading modulus is larger than loading modulus, and unloading and reloading moduli are almost constants with respect to stress level, especially unloading modulus. Under the sine wave cyclic loading condition, tangent modulus and Poisson ratio display asymmetric 'X' shape with various strain, and the average unloading modulus is larger than the average loading modulus.展开更多
To investigate the effects of pressure on the hot isostatic pressing(HIP) process of a stainless steel powder,density distribution and deformation of the powder at four different applied pressure levels were predicted...To investigate the effects of pressure on the hot isostatic pressing(HIP) process of a stainless steel powder,density distribution and deformation of the powder at four different applied pressure levels were predicted and compared by using finite element method(FEM).Constitutive relations of porous compacts during HIP process were derived based on the yield criterion of porous metal materials.Thermo-mechanical coupling calculations were carried out by the MSC.Marc.Densification mechanisms were studied through evolutions of relative density,equivalent plastic strain and equivalent viscoplastic strain rate for compacts.The simulation results were also compared with experimental data.The results show that the densification rate and final density of compacts increase dramatically with the increase in the applied pressure level when it is below 100 MPa during HIP process,and the creep for compacts evolves into steady stage with the improvement of density.展开更多
A novel engineered cementitious composite(ECC) was prepared with the complex binder of Portland cement and asphalt emulsion.By adjusting the amount of asphalt emulsion,different mixture proportions were adopted in exp...A novel engineered cementitious composite(ECC) was prepared with the complex binder of Portland cement and asphalt emulsion.By adjusting the amount of asphalt emulsion,different mixture proportions were adopted in experiments,including four-point bending test,compressive test,and scanning electric microscopy(SEM).The SEM observation was conducted to evaluate the contribution of polyvinyl alcohol(PVA) fiber and asphalt emulsion to the composite toughening mechanism.The tests results show that the most remarkable deflection-hardening behavior and saturated multiple cracking are achieved when the content of asphalt emulsion is 10%.However,excessive content of asphalt emulsion causes severe damages on the deformation behavior as well as loss in compressive strength of the mixture.SEM observation indicates that the influence of asphalt emulsion on the fiber/matrix interfacial property changes the dominant fiber failure type from rupture into pull-out mode,and thus causes beneficial effects for strain-hardening behavior.展开更多
It is of great significance for safety reason to obtain the triaxial compressive properties of cemented tailings backfill(CTB).The influence of cement content,curing age and confining pressure on strength and deformat...It is of great significance for safety reason to obtain the triaxial compressive properties of cemented tailings backfill(CTB).The influence of cement content,curing age and confining pressure on strength and deformation properties of CTB was examined and discussed.Results indicate that the triaxial compressive and deformation behavior of CTB is strongly affected by the cement content,curing age and confining pressure.The increase in cement content,curing age and confining pressure leads to a change in stress−strain behavior and an increase in the axial strain at failure and post-peak strength loss.The cohesion of CTB rises as the curing age and cement content increase.However,the enhancement in internal friction angle is trivial and negligible.It should be noted that the failure pattern of CTB samples in triaxial compression is mainly along a shear plane,the confining pressure restrains the lateral expansion and the bulging failure pattern is dominantly detected in CTB samples as curing age length and cement content increase.The results will help to better understand the triaxial mechanical and deformation behavior of CTB.展开更多
Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial co...Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally, based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular （CFST） stub colunms at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.展开更多
文摘目的:应用斑点追踪成像技术对左束支起搏(left bundle branch pacing,LBBP)与希氏束起搏(His bundle pacing,HBP)患者起搏器植入1年后左心室收缩功能及同步性进行评价。方法:获取LBBP患者(40例)、HBP患者(40例)、对照组(40例)标准心尖四腔、三腔、两腔和短轴二尖瓣、心尖水平图像;分别测量和比较LBBP、HBP患者与对照组纵向、圆周和径向应变、纵向应变达峰时间弥散度(peak strain dispersion,PSD)、左室扭转、心室间机械延迟时间(interventricular mechanical delay time,IVMD);计算和比较圆周应变达峰时间标准差(standard deviation of time to peak circumferential strain,T-sd-CS)、径向应变达峰时间标准差(standard deviation of time to peak radial strain,T-sd-RS)。结果:HBP组短轴心尖平面T-sd-CS大于对照组,其余心室电活动及机械同步性参数与对照组无显著差异;LBBP组QRS波宽度大于HBP组和对照组(P<0.05);LBBP组短轴心尖平面T-sd-CS大于HBP组和对照组(P<0.05);LBBP组左室纵向PSD大于HBP组和对照组(P<0.05);各组间左心室短轴径向应变、T-sd-RS、纵向应变、扭转角度及IVMD比较均无统计学差异。结论:LBBP组与HBP组、对照组相比,左心室内同步性稍延迟;LBBP组与HBP组、对照组心肌收缩功能基本相近。
基金Projects(42307192,41831278)supported by the National Natural Science Foundation of ChinaProject(CKWV20231175/KY)supported by the CRSRI Open Research Program,China。
文摘The special columnar jointed structure endows rocks with significant anisotropy,accurately grasping the strength and deformation properties of a columnar jointed rock mass(CJRM)under complex geological conditions is crucial for related engineering safety.Combined with the irregular jointed networks observed in the field,artificial irregular CJRM(ICJRM)samples with various inclination angles were prepared for triaxial tests.The results showed that the increase in confining pressure can enhance the ability of the ICJRM to resist deformation and failure,and reduce the deformation and strength anisotropic degrees.Considering the field stress situation,the engineering parts with an inclination angle of 30°−45°need to be taken seriously.Four typical failure modes were identified,and the sample with an inclination angle of 15°showed the same failure behavior as the field CJRM.Traditional and improved joint factor methods were used to establish empirical relationships for predicting the strength and deformation of CJRM under triaxial stress.Since the improved joint factor method can reflect the unique structure of CJRM,the predictive ability of the empirical relationship based on the improved method is better than that based on the traditional joint factor method.
文摘Nanostructured BN and BN-Co films with Cu,Co,Au as the top electrodes,and Pt as the bottom electrodes were grown by magnetron sputtering.Both BN samples and BN-Co ones show bipolar resistive switching behaviors.For the sample with active Cu as the top electrode,the formation and rupture of metallic Cu conductive filaments can explain the resistive switching behavior;for the other samples,the generation and annihilation of nitrogen vacancies under the electric stimuli may contribute to the occurrence of resistive switching.Taking advantage of the formed and broken Co-N bonds during resistive switching,the saturation magnetization of the BN-Co films can be modulated.Thus,it investigated the resistive switching behavior of BN and BN-Co materials in this work.Similar to that of oxide materials,the resistive switching behaviors of the nitrides may be attributed to the movement of cations or anions within the dielectric or electrodes during the application of voltage.Additionally,ion migration may lead to the formation or breaking of Co-N bonds,which can effectively regulate the magnetism of BN-Co materials.This study extends resistive switching materials to nitrides,enabling the regulation of magnetism along with resistance changes,thus providing insights for the design of novel voltage-controlled magnetic devices and achieving multi-functionality.
基金Projects(52175373,52005516)supported by the National Natural Science Foundation of ChinaProject(2018YFA0702800)supported by the National Key Basic Research Program,ChinaProject(ZZYJKT2021-03)supported by the State Key Laboratory of High Performance Complex Manufacturing,Central South University,China。
文摘The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the impact of vibration pretreatment temperature on the fiber weight content,microscopic morphology and mechanical properties of the composite laminates by using optical digital microscopy,universal tensile testing machine and thermo-gravimetric analyzer.Additionally,the combined mode of Bragg fiber grating sensor and temperature measurement fiber was employed to explore the effect of vibration pretreatment on the strain process during microwave curing.The study results revealed that the change in vibration pretreatment temperature had a slight impact on the fiber weight content when the vibration acceleration remained constant.The metallographic and interlaminar strength of the specimen formed at a vibration pretreatment temperature of 80℃ demonstrated a porosity of 0.414% and a 10.69% decrease in interlaminar shear strength compared to autoclave curing.Moreover,the introduction of the vibration energy field during the microwave curing process led to a significant reduction in residual strain in both the 0°and 90°fiber directions,when the laminate was cooled to 60℃.
基金Projects(50674107, 10472134, 50490274) supported by the National Natural Science Foundation of China
文摘In order to determine the relationship among energy consumption of rock and its fragmentation, dynamic strength and strain rate, granite, sandstone and limestone specimens were chosen and tested on large-diameter split Hopkinson pressure bar (SHPB) equipment with half-sine waveform loading at the strain rates ranging from 40 to 150 s- 1. With recorded signals, the energy consumption, strain rate and dynamic strength were analyzed. And the fragmentation behaviors of specimens were investigated. The experimental results show that the energy consumption density of rock increases linearly with the total incident energy. The energy consumption density is of an exponent relationship with the average size of rock fragments. The higher the energy consumption density, the more serious the fragmentation, and the better the gradation of fragments. The energy consumption density takes a good logarithm relationship with the dynamic strength of rock. The dynamic strength of rock increases with the increase of strain rate, indicating higher strain rate sensitivity.
基金Project(200804220021) supported by the Specialized Research Fund for Doctoral Program of Higher Education of China Project (Y2007F06) supported by the Natural Science Foundation of Shandong Province,China
文摘Isothermal compression tests at temperatures from 1 273 to l 423 K and strain rates from 0.1 to 10 s-q were carried out to investigate the flow behaviors of Q420qE steel. Stress-strain data collected from the tests were employed to establish the constitutive equation, in which the influence of strain was incorporated by considering the effect of strain on material constants Q, n, a, and lnA. The results show that the flow stress curves are dependent on the strain, strain rate and deformation temperature. They display typical dynamic recrystallization behavior and consist of three stages, i.e., hardening stage, softening stage and steady stage. The flow stress decreases with increasing the deformation temperature and decreasing the strain rate. In addition, the flow stress data predicted by the proposed constitutive model agree well with the corresponding experimental results, and the correlation coefficient and the average absolute relative error between them are 0.990 3 and 3.686%, respectively.
基金Project(Z110510) supported by Opening Research Foundation of the Chinese Academy of Sciences Key Laboratory of Rock and Soil MechanicsProject(20060390473) supported by China Postdoctoral Science FoudationProject(40172084) supported by the National Natural Science Foundation of China
文摘A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uniaxial compression strength and elastic properties (elastic modulus and Poisson ratio) under different conditions and influence of pore fluid on them. When the loading strain rates are 10^(-5), 10^(-4) and 10^(-3)/s, uniaxial compression strengths of dry sandstones are 82.3, 126.6 and 141.6 MPa, respectively, and that of water saturated sandstones are 70.5, 108.3 and 124.1 MPa, respectively. The above results show that the uniaxial compression strength increases with the increase of strain rate, however, variation of softening coefficient is insignificant. Under monotonic loading condition, tangent modulus increases with an increment of stress (strain) to a maximum value at a certain stress level, beyond which it starts to decline. Under the partial cyclic loading during loading path condition, unloading or reloading modulus is larger than loading modulus, and unloading and reloading moduli are almost constants with respect to stress level, especially unloading modulus. Under the sine wave cyclic loading condition, tangent modulus and Poisson ratio display asymmetric 'X' shape with various strain, and the average unloading modulus is larger than the average loading modulus.
基金Project(2007AA03Z115) supported by the National High Technology Research and Development Program of ChinaProject(2009ZX04005-041-03) supported by the National Science and Technology Major Program of ChinaProject(2010MS046) supported by the Independent Fund of Huazhong University of Science and Technology,China
文摘To investigate the effects of pressure on the hot isostatic pressing(HIP) process of a stainless steel powder,density distribution and deformation of the powder at four different applied pressure levels were predicted and compared by using finite element method(FEM).Constitutive relations of porous compacts during HIP process were derived based on the yield criterion of porous metal materials.Thermo-mechanical coupling calculations were carried out by the MSC.Marc.Densification mechanisms were studied through evolutions of relative density,equivalent plastic strain and equivalent viscoplastic strain rate for compacts.The simulation results were also compared with experimental data.The results show that the densification rate and final density of compacts increase dramatically with the increase in the applied pressure level when it is below 100 MPa during HIP process,and the creep for compacts evolves into steady stage with the improvement of density.
基金Project(2011BAE27B04)supported by the National Key Technology R&D Program of ChinaProjects(CHD2011TD003,CHD2011ZD017)supported by the Special Fund for Basic Scientific Research of Central Colleges in Chang’an University,China
文摘A novel engineered cementitious composite(ECC) was prepared with the complex binder of Portland cement and asphalt emulsion.By adjusting the amount of asphalt emulsion,different mixture proportions were adopted in experiments,including four-point bending test,compressive test,and scanning electric microscopy(SEM).The SEM observation was conducted to evaluate the contribution of polyvinyl alcohol(PVA) fiber and asphalt emulsion to the composite toughening mechanism.The tests results show that the most remarkable deflection-hardening behavior and saturated multiple cracking are achieved when the content of asphalt emulsion is 10%.However,excessive content of asphalt emulsion causes severe damages on the deformation behavior as well as loss in compressive strength of the mixture.SEM observation indicates that the influence of asphalt emulsion on the fiber/matrix interfacial property changes the dominant fiber failure type from rupture into pull-out mode,and thus causes beneficial effects for strain-hardening behavior.
基金Projects(2018YFC0808403,2018YFE0123000)supported by the National Key Technologies Research&Development Program of ChinaProject(800015Z1185)supported by the Yueqi Young Scholar Project,ChinaProject(2020YJSNY04)supported by the Fundamental Research Funds for the Central Universities,China。
文摘It is of great significance for safety reason to obtain the triaxial compressive properties of cemented tailings backfill(CTB).The influence of cement content,curing age and confining pressure on strength and deformation properties of CTB was examined and discussed.Results indicate that the triaxial compressive and deformation behavior of CTB is strongly affected by the cement content,curing age and confining pressure.The increase in cement content,curing age and confining pressure leads to a change in stress−strain behavior and an increase in the axial strain at failure and post-peak strength loss.The cohesion of CTB rises as the curing age and cement content increase.However,the enhancement in internal friction angle is trivial and negligible.It should be noted that the failure pattern of CTB samples in triaxial compression is mainly along a shear plane,the confining pressure restrains the lateral expansion and the bulging failure pattern is dominantly detected in CTB samples as curing age length and cement content increase.The results will help to better understand the triaxial mechanical and deformation behavior of CTB.
基金Projects(50438020 50578162) supported by the National Natural Sceince Foundation of China
文摘Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally, based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular （CFST） stub colunms at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.
