In order to provide more insights into the damage propagation composite wind turbine blades(blade)under cyclic fatigue loading,a stiffness degradation model for blade is proposed based on the full-scale fatigue testin...In order to provide more insights into the damage propagation composite wind turbine blades(blade)under cyclic fatigue loading,a stiffness degradation model for blade is proposed based on the full-scale fatigue testing of a blade.A novel non-linear fatigue damage accumulation model is proposed using the damage assessment theories of composite laminates for the first time.Then,a stiffness degradation model is established based on the correlation of fatigue damage and residual stiffness of the composite laminates.Finally,a stiffness degradation model for the blade is presented based on the full-scale fatigue testing.The scientific rationale of the proposed stiffness model of blade is verified by using full-scale fatigue test data of blade with a total length of 52.5 m.The results indicate that the proposed stiffness degradation model of the blade agrees well with the fatigue testing results of this blade.This work provides a basis for evaluating the fatigue damage and lifetime of blade under cyclic fatigue loading.展开更多
Background and objective:Liver stiffness measurement(LSM)may effectively correlate to the presence of liver fibrosis,but it is controversial to use for the prediction of clinical outcomes.Therefore,we aimed to evaluat...Background and objective:Liver stiffness measurement(LSM)may effectively correlate to the presence of liver fibrosis,but it is controversial to use for the prediction of clinical outcomes.Therefore,we aimed to evaluate the predictive value of liver stiffness for the regression of liver fibrosis.Methods:In this study,we collected data from a clinical cohort of patients who are received anti-virus therapies for 48 weeks.180 naive chronic hepatitis B(CHB)patients,who received paired LSM and liver biopsy with pre-and post-treatments were analyzed.Two methods(FibroScan and iLivTouch)test LSM.Result:The area under the receiver operating characteristics curve(AUROC)of changing LSM for fibrosis regression is higher in advanced fibrosis patients(F5/6)than in moderate fibrosis patients(F3/4)in both FibroScan(0.719,95%CI,0.590–0.848;P=0.003;vs 0.617,95%CI,0.379–0.856,P=0.282)and iLivTouch(0.707,95%CI,0.567–0.847;P=0.011;vs 0.583,95%CI,0.422–0.744;P=0.377).A higher kappa value was received in advanced stage than in moderate stage both in FibroScan(0.392,P=0.001 vs 0.265,P=0.053)and iLivTouch(0.326,P=0.019 vs 0.030,P=0.833).Cut-off set as 4.10 kPa(sen,69.4%;spe,73.9%)in FibroScan,as 4.25 kPa(sen,56.8%;spe,72.2%)in iLivTouch.Conclusion:The changing LSM can be used for predicting the liver fibrosis regression in advanced stage of CHB patients.展开更多
The failure behavior of the precast prestressed concrete T girder was investigated by destructive test and finite-element analysis,and the mid-span deflection,girder stiffness and the variation of the cross section st...The failure behavior of the precast prestressed concrete T girder was investigated by destructive test and finite-element analysis,and the mid-span deflection,girder stiffness and the variation of the cross section strain in the loading process were obtained,and the mechanical properties,mechanical behavior,elastic and plastic behavior and ultimate bearing capacity of T girder with large span were revealed.Furthermore,the relationship between the beam stiffness degradation,the neutral axis in cross-section,steel yielding and concrete cracking are investigated and analyzed.A method was proposed to predict the residual bearing capacity of a bridge based on the variation of the position of the cross section strain distribution and the section neutral axis,which provided a theoretical basis for predicting the stiffness detection and carrying capacity assessment of prestressed concrete beam.展开更多
In order to prevent unwanted excited vibrations and to secure better machining precision in large size heavy duty machine tools dynamic stiffness is one of the most desirable and critical properties. In the past decad...In order to prevent unwanted excited vibrations and to secure better machining precision in large size heavy duty machine tools dynamic stiffness is one of the most desirable and critical properties. In the past decades, many researches on machine tool stiffness test and evaluation methodology have been made. However any methodology for a Pin Turning Device (PTD), which is a special kind of turning lathe for machining big size crankshaft pins, is rarely found among them. This study proposes a test and evaluation process of stiffness of a PTD by measuring frequency response function at the tool center point (TCP). For conformance proving for the proposed methodology, stiffness of a PTD obtained by the proposed method with impact hammer test (IHT) has been compared with that determined by FEM.展开更多
Discrete element modelling is commonly used for particle-scale modelling of granular or particulate materials. Developing a DEM model requires the determination of a number of micro-structural parameters, including th...Discrete element modelling is commonly used for particle-scale modelling of granular or particulate materials. Developing a DEM model requires the determination of a number of micro-structural parameters, including the particle contact stiffness and the particle-particle friction. These parameters cannot easily be measured in the laboratory or directly related to measurable, physical material parameters. Therefore, a calibration process is typically used to determine the values for use in simulations of physical systems. This paper focuses on how to define the particle stiffness for the discrete element modelling in order to perform realistic simulations of granular materials in the case of linear contact model. For that, laboratory tests and numerical discrete element modelling of triaxial compression tests have been carried out on two different non-cohesive soils i.e. poorly graded fine sand and gap graded coarse sand. The results of experimental tests are used to calibrate the numerical model. It is found that the numerical results are qualitatively and quantitatively in good agreement with the laboratory tests results. Moreover, the results show that the stress dependent of soil behaviour can be reproduced well by assigning the particle stiffness as a function of the particle size particularly for gap graded soil.展开更多
Tensile stiffness of ocean dynamic power umbilical is an important design parameter for functional implementation and structural safety. A column with radial stiffness which is wound by helical steel wires is construc...Tensile stiffness of ocean dynamic power umbilical is an important design parameter for functional implementation and structural safety. A column with radial stiffness which is wound by helical steel wires is constructed to predict the tensile stiffness value of umbilicals in the paper. The relationship between the tension and axial deformation is expressed analytically so the radial contraction of the column is achieved in the relationship by use of a simple finite element method. With an agreement between the theoretical prediction and the tension test results, the method is proved to be simple and efficient for the estimation of tensile stiffness of the ocean dynamic power umbilical.展开更多
Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian ...Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases (or degradation degree increases) significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.展开更多
AIM To investigate changes in spleen stiffness measurements(SSMs) and other non-invasive tests(NITs) after treatment with direct-acting antivirals(DAAs) and identify predictors of SSM change after sustainedvirological...AIM To investigate changes in spleen stiffness measurements(SSMs) and other non-invasive tests(NITs) after treatment with direct-acting antivirals(DAAs) and identify predictors of SSM change after sustainedvirological response(SVR). METHODS We retrospectively analysed 146 advanced-chronic liver disease(ACLD) patients treated with DAA with available paired SSM at baseline and SVR24. Liver stiffness(LSM), spleen diameter(SD), platelet count(PLT) and liver stiffness-spleen diameter to platelet ratio score(LSPS) were also investigated. LSM ≥ 21 k Pa was used as a cut-off to rule-in clinically significant portal hypertension(CSPH). SSM reduction > 20% from baseline was defined as significant.RESULTS SSM significantly decreased at SVR24, in both patients with and without CSPH; in 44.8% of cases, SSM reduction was > 20%. LSPS significantly improved in the entire cohort at SVR24; SD and PLT changed significantly only in patients without CSPH. LSM significantly decreased in 65.7% of patients and also in 2/3 patients in whom SSM did not decrease. The independent predictor of decreased SSM was median relative change of LSM. CSPH persisted in 54.4% patients after SVR. Delta LSM and baseline SSM were independent factors associated with CSPH persistence.CONCLUSION SSM and other NITs significantly decrease after SVR, although differently according to the patient's clinical condition. SSM faithfully reflects changes in portal hypertension and could represent a useful NIT for the follow-up of these patients.展开更多
In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,ef...In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,effectively reduces the structural response in the case of relatively small story drifts,which occur during earthquakes.A predictive instantaneous optimal control algorithm is established for a SDOF structure equipped with an AVSD system Comparative shaking table tests of a 1/4 scale single story structural model with a full scale control device have been conducted.From the experimental and analytical results,it is shown that when compared to structures without control or with the active variable stiffness control alone, the suggested system exhibits higher efficiency in controlling the structural response,requires less energy input,operates with higher reliability,and can be manufactured at a lower cost and used in a wider range of engineering applications.展开更多
Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering.It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system.Previous studies...Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering.It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system.Previous studies have proposed some optimal rib parameters(e.g.rib spacing);unfortunately,the interface shear behaviors are generally ignored.Therefore,determination of radial stress and radial displacement on the bolt-grout interface using traditional pull-out tests is not possible.The load-bearing capacity and deformation capacity vary as bolt profiles differ,suggesting that the support effect of the bolting system can be enhanced by optimizing bolt profiles.The aim of this study is to investigate the effects of bolt profiles(with/without ribs,rib spacing,and rib height)on the shear behaviors between the rock bolt and grout material using direct shear tests.Thereby,systematic interfacial shear tests with different bolt profiles were performed under both constant normal load(CNL)and constant normal stiffness(CNS)boundary conditions.The results suggested that rib spacing has a more marked influence on the interface shear behavior than rib height does,in particular at the post-yield stage.The results could facilitate our understanding of bolt-grout interface shear behavior under CNS conditions,and optimize selection of rock bolts under in situ rock conditions.展开更多
Fractures of long bones are commonly treated with intramedullary (IM) nails and they have been shown to have a very high success rate. Recently we have concerns with the use of the newer IM nailing systems, that uses ...Fractures of long bones are commonly treated with intramedullary (IM) nails and they have been shown to have a very high success rate. Recently we have concerns with the use of the newer IM nailing systems, that uses longer cross screws, which have been developed with variation in implant designs. We believe that the newer implants provide less fracture stability, due to decreased stiffness of the IM nailing system. The aim of this study was to biomechanically determine the influence of the length of cross screw on the stiffness of the IM nailing system, using a composite model. Our test results confirmed our suspicion that the newer IM nailing system using longer cross screw-length is less stiff than traditional nailing systems using shorter cross screw length, during axial loading.展开更多
The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the e...The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the effect of pile−soil relative stiffness(K_(R)).This paper presents a series of 1-g cyclic tests aimed at improving understanding of the cyclic lateral responses of monopiles under different pile−soil systems.These systems are arranged by two model piles with different stiffness,including four different slenderness ratios(pile embedded length,L,normalized by diameter,D)under medium dense sand.The K_(R)-values are calculated by a previously proposed method considering the real soil stress level.The test results show that the lateral accumulation displacement increases significantly with the increment of the K_(R)-value,while the cyclic secant stiffness performs inversely.The maximum pile bending moment increases with the cycle number for the rigid pile−soil system,but shows a decreasing trend in the flexible system.For an uppermost concern,an empirical model is proposed to predict the accumulated displacement of arbitrary pile−soil systems by combining the results from this study with those from previous experimental investigations.The validity of the proposed model is demonstrated by 1-g and centrifuge tests.展开更多
BACKGROUND Assessment of liver reserve function(LRF)is essential for predicting the prognosis of patients with chronic liver disease(CLD)and determines the extent of liver resection in patients with hepatocellular car...BACKGROUND Assessment of liver reserve function(LRF)is essential for predicting the prognosis of patients with chronic liver disease(CLD)and determines the extent of liver resection in patients with hepatocellular carcinoma.AIM To establish noninvasive models for LRF assessment based on liver stiffness measurement(LSM)and to evaluate their clinical performance.METHODS A total of 360 patients with compensated CLD were retrospectively analyzed as the training cohort.The new predictive models were established through logistic regression analysis and were validated internally in a prospective cohort(132 patients).RESULTS Our study defined indocyanine green retention rate at 15 min(ICGR15)≥10%as mildly impaired LRF and ICGR15≥20%as severely impaired LRF.We constructed predictive models of LRF,named the mLPaM and sLPaM,which involved only LSM,prothrombin time international normalized ratio to albumin ratio(PTAR),age and model for end-stage liver disease(MELD).The area under the curve of the mLPaM model(0.855,0.872,respectively)and sLPaM model(0.869,0.876,respectively)were higher than that of the methods for MELD,albumin bilirubin grade and PTAR in the two cohorts,and their sensitivity and negative predictive value were the highest among these methods in the training cohort.In addition,the new models showed good sensitivity and accuracy for the diagnosis of LRF impairment in the validation cohort.CONCLUSION The new models had a good predictive performance for LRF and could replace the indocyanine green(ICG)clearance test,especially in patients who are unable to undergo ICG testing.展开更多
As an estimate for the in-situ spalling strength around massive underground excavations to moderately jointed brittle rocks, crack initiation stress marks the initiation of rock micro fracturing. It is crucial to accu...As an estimate for the in-situ spalling strength around massive underground excavations to moderately jointed brittle rocks, crack initiation stress marks the initiation of rock micro fracturing. It is crucial to accurately identify crack initiation stress level by proper method. In this study, confined compression tests of sandstone samples are used to examine the validity/applicability of proposed axial strain stiffness method. The results show that by highlighting the minuscule changes in stress-strain curve, the axial strain stiffness curve provided further insight into rock failure process and revealed five stages:(a) irregular fluctuation,(b) nearly horizontal regular fluctuation,(c) irregular fluctuation gradually decreasing to zero,(d) extreme fluctuation, and(e) near zero, which mainly correspond to five stages of stress–strain curve. The ratio of crack-initiation stress to peak strength determined using this approach is 0.44–0.51, similar to the ranges previously reported by other researchers. In this method, the key is to accurately detect the end point of the stage(b), "nearly horizontal regular fluctuation" characterized by a sudden change in axial strain stiffness curve, and the sudden change signifies crack initiation in rock sample. Finally, the research indicates that the axial strain stiffness curve can provide a mean to identify the crack-initiation stress thresholds in brittle rocks.展开更多
A damage detection method for complicated beam-like structures is proposed based on the subsection strain energy method (SSEM), and its applicability condition is introduced. For a beam with the continuously varying...A damage detection method for complicated beam-like structures is proposed based on the subsection strain energy method (SSEM), and its applicability condition is introduced. For a beam with the continuously varying fiexural stiffness and an edge crack, the SSEM is used to detect the crack location effectively by numerical modal shapes. As a complicated beam, the glass fiber-reinforced composite model of a wind turbine blade is studied based on an experimental modal analysis. The SSEM is used to calculate the damage index from the measured modal parameters and locate the damage position in the blade model successfully. The results indicate that the SSEM based on the modal shapes can be used to detect the damages in complicated beams or beam-like structures for engineering applications.展开更多
基金supported by the Science and Technology Programs of Gansu Province,China(Nos.21JR1RA248,20JR10RA264)the Young Scholars Science Foundation of Lanzhou Jiaotong University,China(Nos.2020039,2020017)the Special Funds for Guiding Local Scientific and Technological Development by the Central Government,China(No.22ZY1QA005)。
文摘In order to provide more insights into the damage propagation composite wind turbine blades(blade)under cyclic fatigue loading,a stiffness degradation model for blade is proposed based on the full-scale fatigue testing of a blade.A novel non-linear fatigue damage accumulation model is proposed using the damage assessment theories of composite laminates for the first time.Then,a stiffness degradation model is established based on the correlation of fatigue damage and residual stiffness of the composite laminates.Finally,a stiffness degradation model for the blade is presented based on the full-scale fatigue testing.The scientific rationale of the proposed stiffness model of blade is verified by using full-scale fatigue test data of blade with a total length of 52.5 m.The results indicate that the proposed stiffness degradation model of the blade agrees well with the fatigue testing results of this blade.This work provides a basis for evaluating the fatigue damage and lifetime of blade under cyclic fatigue loading.
基金supported by the National Science and Technology Major Project,The People’s Republic of China(2018ZX10302204,2014ZX10005001)the National Natural Science Foundation of China(81730109,82274305)。
文摘Background and objective:Liver stiffness measurement(LSM)may effectively correlate to the presence of liver fibrosis,but it is controversial to use for the prediction of clinical outcomes.Therefore,we aimed to evaluate the predictive value of liver stiffness for the regression of liver fibrosis.Methods:In this study,we collected data from a clinical cohort of patients who are received anti-virus therapies for 48 weeks.180 naive chronic hepatitis B(CHB)patients,who received paired LSM and liver biopsy with pre-and post-treatments were analyzed.Two methods(FibroScan and iLivTouch)test LSM.Result:The area under the receiver operating characteristics curve(AUROC)of changing LSM for fibrosis regression is higher in advanced fibrosis patients(F5/6)than in moderate fibrosis patients(F3/4)in both FibroScan(0.719,95%CI,0.590–0.848;P=0.003;vs 0.617,95%CI,0.379–0.856,P=0.282)and iLivTouch(0.707,95%CI,0.567–0.847;P=0.011;vs 0.583,95%CI,0.422–0.744;P=0.377).A higher kappa value was received in advanced stage than in moderate stage both in FibroScan(0.392,P=0.001 vs 0.265,P=0.053)and iLivTouch(0.326,P=0.019 vs 0.030,P=0.833).Cut-off set as 4.10 kPa(sen,69.4%;spe,73.9%)in FibroScan,as 4.25 kPa(sen,56.8%;spe,72.2%)in iLivTouch.Conclusion:The changing LSM can be used for predicting the liver fibrosis regression in advanced stage of CHB patients.
基金the support from the Program for Natural Science Foundation of Zhejiang Province(LY16E080006)National Natural Science Foundation of China(51378240)+1 种基金2015 Jiangsu provincial building energy saving and construction industry science and technology project2016 Jiangsu provincial construction industry modernization base project.
文摘The failure behavior of the precast prestressed concrete T girder was investigated by destructive test and finite-element analysis,and the mid-span deflection,girder stiffness and the variation of the cross section strain in the loading process were obtained,and the mechanical properties,mechanical behavior,elastic and plastic behavior and ultimate bearing capacity of T girder with large span were revealed.Furthermore,the relationship between the beam stiffness degradation,the neutral axis in cross-section,steel yielding and concrete cracking are investigated and analyzed.A method was proposed to predict the residual bearing capacity of a bridge based on the variation of the position of the cross section strain distribution and the section neutral axis,which provided a theoretical basis for predicting the stiffness detection and carrying capacity assessment of prestressed concrete beam.
文摘In order to prevent unwanted excited vibrations and to secure better machining precision in large size heavy duty machine tools dynamic stiffness is one of the most desirable and critical properties. In the past decades, many researches on machine tool stiffness test and evaluation methodology have been made. However any methodology for a Pin Turning Device (PTD), which is a special kind of turning lathe for machining big size crankshaft pins, is rarely found among them. This study proposes a test and evaluation process of stiffness of a PTD by measuring frequency response function at the tool center point (TCP). For conformance proving for the proposed methodology, stiffness of a PTD obtained by the proposed method with impact hammer test (IHT) has been compared with that determined by FEM.
文摘Discrete element modelling is commonly used for particle-scale modelling of granular or particulate materials. Developing a DEM model requires the determination of a number of micro-structural parameters, including the particle contact stiffness and the particle-particle friction. These parameters cannot easily be measured in the laboratory or directly related to measurable, physical material parameters. Therefore, a calibration process is typically used to determine the values for use in simulations of physical systems. This paper focuses on how to define the particle stiffness for the discrete element modelling in order to perform realistic simulations of granular materials in the case of linear contact model. For that, laboratory tests and numerical discrete element modelling of triaxial compression tests have been carried out on two different non-cohesive soils i.e. poorly graded fine sand and gap graded coarse sand. The results of experimental tests are used to calibrate the numerical model. It is found that the numerical results are qualitatively and quantitatively in good agreement with the laboratory tests results. Moreover, the results show that the stress dependent of soil behaviour can be reproduced well by assigning the particle stiffness as a function of the particle size particularly for gap graded soil.
基金financially supported by the National High Technology Research and Development Program of China(863 ProgramGrant No.2012AA09A212)+1 种基金the National Natural Science Foundation of China(Grant No.11372060)the China Postdoctoral Science Foundation(Grant No.20110491521)
文摘Tensile stiffness of ocean dynamic power umbilical is an important design parameter for functional implementation and structural safety. A column with radial stiffness which is wound by helical steel wires is constructed to predict the tensile stiffness value of umbilicals in the paper. The relationship between the tension and axial deformation is expressed analytically so the radial contraction of the column is achieved in the relationship by use of a simple finite element method. With an agreement between the theoretical prediction and the tension test results, the method is proved to be simple and efficient for the estimation of tensile stiffness of the ocean dynamic power umbilical.
基金supported bythe National Natural Science Foundation of China(Grant Nos.50579006,50639010 and 50909014)
文摘Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases (or degradation degree increases) significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.
文摘AIM To investigate changes in spleen stiffness measurements(SSMs) and other non-invasive tests(NITs) after treatment with direct-acting antivirals(DAAs) and identify predictors of SSM change after sustainedvirological response(SVR). METHODS We retrospectively analysed 146 advanced-chronic liver disease(ACLD) patients treated with DAA with available paired SSM at baseline and SVR24. Liver stiffness(LSM), spleen diameter(SD), platelet count(PLT) and liver stiffness-spleen diameter to platelet ratio score(LSPS) were also investigated. LSM ≥ 21 k Pa was used as a cut-off to rule-in clinically significant portal hypertension(CSPH). SSM reduction > 20% from baseline was defined as significant.RESULTS SSM significantly decreased at SVR24, in both patients with and without CSPH; in 44.8% of cases, SSM reduction was > 20%. LSPS significantly improved in the entire cohort at SVR24; SD and PLT changed significantly only in patients without CSPH. LSM significantly decreased in 65.7% of patients and also in 2/3 patients in whom SSM did not decrease. The independent predictor of decreased SSM was median relative change of LSM. CSPH persisted in 54.4% patients after SVR. Delta LSM and baseline SSM were independent factors associated with CSPH persistence.CONCLUSION SSM and other NITs significantly decrease after SVR, although differently according to the patient's clinical condition. SSM faithfully reflects changes in portal hypertension and could represent a useful NIT for the follow-up of these patients.
文摘In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,effectively reduces the structural response in the case of relatively small story drifts,which occur during earthquakes.A predictive instantaneous optimal control algorithm is established for a SDOF structure equipped with an AVSD system Comparative shaking table tests of a 1/4 scale single story structural model with a full scale control device have been conducted.From the experimental and analytical results,it is shown that when compared to structures without control or with the active variable stiffness control alone, the suggested system exhibits higher efficiency in controlling the structural response,requires less energy input,operates with higher reliability,and can be manufactured at a lower cost and used in a wider range of engineering applications.
基金This study is supported by the key projects of the Yalong River Joint Fund of the National Natural Science Foundation of China(Grant No.U1865203)the National Key Research and Development Program of China(Grant Nos.2019YFC0605103,2019YFC0605100)the National Natural Science Foundation of China(Grant No.51279201).The partial support from the Youth Innovation Promotion Association CAS is gratefully acknowledged。
文摘Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering.It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system.Previous studies have proposed some optimal rib parameters(e.g.rib spacing);unfortunately,the interface shear behaviors are generally ignored.Therefore,determination of radial stress and radial displacement on the bolt-grout interface using traditional pull-out tests is not possible.The load-bearing capacity and deformation capacity vary as bolt profiles differ,suggesting that the support effect of the bolting system can be enhanced by optimizing bolt profiles.The aim of this study is to investigate the effects of bolt profiles(with/without ribs,rib spacing,and rib height)on the shear behaviors between the rock bolt and grout material using direct shear tests.Thereby,systematic interfacial shear tests with different bolt profiles were performed under both constant normal load(CNL)and constant normal stiffness(CNS)boundary conditions.The results suggested that rib spacing has a more marked influence on the interface shear behavior than rib height does,in particular at the post-yield stage.The results could facilitate our understanding of bolt-grout interface shear behavior under CNS conditions,and optimize selection of rock bolts under in situ rock conditions.
文摘Fractures of long bones are commonly treated with intramedullary (IM) nails and they have been shown to have a very high success rate. Recently we have concerns with the use of the newer IM nailing systems, that uses longer cross screws, which have been developed with variation in implant designs. We believe that the newer implants provide less fracture stability, due to decreased stiffness of the IM nailing system. The aim of this study was to biomechanically determine the influence of the length of cross screw on the stiffness of the IM nailing system, using a composite model. Our test results confirmed our suspicion that the newer IM nailing system using longer cross screw-length is less stiff than traditional nailing systems using shorter cross screw length, during axial loading.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.51808112,51878160,and 52078128)the Natural Science Foundation of Jiangsu Province(Grant No.BK20180155).
文摘The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the effect of pile−soil relative stiffness(K_(R)).This paper presents a series of 1-g cyclic tests aimed at improving understanding of the cyclic lateral responses of monopiles under different pile−soil systems.These systems are arranged by two model piles with different stiffness,including four different slenderness ratios(pile embedded length,L,normalized by diameter,D)under medium dense sand.The K_(R)-values are calculated by a previously proposed method considering the real soil stress level.The test results show that the lateral accumulation displacement increases significantly with the increment of the K_(R)-value,while the cyclic secant stiffness performs inversely.The maximum pile bending moment increases with the cycle number for the rigid pile−soil system,but shows a decreasing trend in the flexible system.For an uppermost concern,an empirical model is proposed to predict the accumulated displacement of arbitrary pile−soil systems by combining the results from this study with those from previous experimental investigations.The validity of the proposed model is demonstrated by 1-g and centrifuge tests.
基金Startup Fund for Scientific Research of Fujian Medical University,No.2018QH1052Fujian Health Research Talents Training Program,No.2019-1-42.
文摘BACKGROUND Assessment of liver reserve function(LRF)is essential for predicting the prognosis of patients with chronic liver disease(CLD)and determines the extent of liver resection in patients with hepatocellular carcinoma.AIM To establish noninvasive models for LRF assessment based on liver stiffness measurement(LSM)and to evaluate their clinical performance.METHODS A total of 360 patients with compensated CLD were retrospectively analyzed as the training cohort.The new predictive models were established through logistic regression analysis and were validated internally in a prospective cohort(132 patients).RESULTS Our study defined indocyanine green retention rate at 15 min(ICGR15)≥10%as mildly impaired LRF and ICGR15≥20%as severely impaired LRF.We constructed predictive models of LRF,named the mLPaM and sLPaM,which involved only LSM,prothrombin time international normalized ratio to albumin ratio(PTAR),age and model for end-stage liver disease(MELD).The area under the curve of the mLPaM model(0.855,0.872,respectively)and sLPaM model(0.869,0.876,respectively)were higher than that of the methods for MELD,albumin bilirubin grade and PTAR in the two cohorts,and their sensitivity and negative predictive value were the highest among these methods in the training cohort.In addition,the new models showed good sensitivity and accuracy for the diagnosis of LRF impairment in the validation cohort.CONCLUSION The new models had a good predictive performance for LRF and could replace the indocyanine green(ICG)clearance test,especially in patients who are unable to undergo ICG testing.
基金supported by the National Natural Science Foundation of China(Grants No.41772329,41572283 and 41230635)the funding of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection(Nos.SKLGP2017Z001 and SKLGP2013Z004)supported by the Funding of Science and Technology Office of Sichuan Province(Grants No.2015JQ0020 and 2017TD0018)
文摘As an estimate for the in-situ spalling strength around massive underground excavations to moderately jointed brittle rocks, crack initiation stress marks the initiation of rock micro fracturing. It is crucial to accurately identify crack initiation stress level by proper method. In this study, confined compression tests of sandstone samples are used to examine the validity/applicability of proposed axial strain stiffness method. The results show that by highlighting the minuscule changes in stress-strain curve, the axial strain stiffness curve provided further insight into rock failure process and revealed five stages:(a) irregular fluctuation,(b) nearly horizontal regular fluctuation,(c) irregular fluctuation gradually decreasing to zero,(d) extreme fluctuation, and(e) near zero, which mainly correspond to five stages of stress–strain curve. The ratio of crack-initiation stress to peak strength determined using this approach is 0.44–0.51, similar to the ranges previously reported by other researchers. In this method, the key is to accurately detect the end point of the stage(b), "nearly horizontal regular fluctuation" characterized by a sudden change in axial strain stiffness curve, and the sudden change signifies crack initiation in rock sample. Finally, the research indicates that the axial strain stiffness curve can provide a mean to identify the crack-initiation stress thresholds in brittle rocks.
基金supported by the National Basic Research Program of China (973 Program)(No. 2007CB714603)
文摘A damage detection method for complicated beam-like structures is proposed based on the subsection strain energy method (SSEM), and its applicability condition is introduced. For a beam with the continuously varying fiexural stiffness and an edge crack, the SSEM is used to detect the crack location effectively by numerical modal shapes. As a complicated beam, the glass fiber-reinforced composite model of a wind turbine blade is studied based on an experimental modal analysis. The SSEM is used to calculate the damage index from the measured modal parameters and locate the damage position in the blade model successfully. The results indicate that the SSEM based on the modal shapes can be used to detect the damages in complicated beams or beam-like structures for engineering applications.