Neuronal growth, extension, branching, and formation of neural networks are markedly influenced by the extracellular matrix—a complex network composed of proteins and carbohydrates secreted by cells. In addition to p...Neuronal growth, extension, branching, and formation of neural networks are markedly influenced by the extracellular matrix—a complex network composed of proteins and carbohydrates secreted by cells. In addition to providing physical support for cells, the extracellular matrix also conveys critical mechanical stiffness cues. During the development of the nervous system, extracellular matrix stiffness plays a central role in guiding neuronal growth, particularly in the context of axonal extension, which is crucial for the formation of neural networks. In neural tissue engineering, manipulation of biomaterial stiffness is a promising strategy to provide a permissive environment for the repair and regeneration of injured nervous tissue. Recent research has fine-tuned synthetic biomaterials to fabricate scaffolds that closely replicate the stiffness profiles observed in the nervous system. In this review, we highlight the molecular mechanisms by which extracellular matrix stiffness regulates axonal growth and regeneration. We highlight the progress made in the development of stiffness-tunable biomaterials to emulate in vivo extracellular matrix environments, with an emphasis on their application in neural repair and regeneration, along with a discussion of the current limitations and future prospects. The exploration and optimization of the stiffness-tunable biomaterials has the potential to markedly advance the development of neural tissue engineering.展开更多
Quasi-zero stiffness(QZS)isolators have received considerable attention over the past years due to their outstanding vibration isolation performance in low-frequency bands.However,traditional mechanisms for achieving ...Quasi-zero stiffness(QZS)isolators have received considerable attention over the past years due to their outstanding vibration isolation performance in low-frequency bands.However,traditional mechanisms for achieving QZS suffer from low stiffness regions and significant nonlinear restoring forces with hardening characteristics,often struggling to withstand excitations with high amplitude.This paper presents a novel QZS vibration isolator that utilizes a more compact spring-rod mechanism(SRM)to provide primary negative stiffness.The nonlinearity of SRM is adjustable via altering the raceway of its spring-rod end,along with the compensatory force provided by the cam-roller mechanism so as to avoid complex nonlinear behaviors.The absolute zero stiffness can be achieved by a well-designed raceway curve with a concise mathematical expression.The nonlinear stiffness with softening properties can also be achieved by parameter adjustment.The study begins with the forcedisplacement relationship of the integrated mechanism first,followed by the design theory of the cam profile.The dynamic response and absolute displacement transmissibility of the isolation system are obtained based on the harmonic balance method.The experimental results show that the proposed vibration isolator maintains relatively low-dynamic stiffness even under non-ideal conditions,and exhibits enhanced vibration isolation performance compared to the corresponding linear isolator.展开更多
BACKGROUND The hepatic venous pressure gradient serves as a crucial parameter for assessing portal hypertension and predicting clinical decompensation in individuals with cirrhosis.However,owing to its invasive nature...BACKGROUND The hepatic venous pressure gradient serves as a crucial parameter for assessing portal hypertension and predicting clinical decompensation in individuals with cirrhosis.However,owing to its invasive nature,there has been growing interest in identifying noninvasive alternatives.Transient elastography offers a promising approach for measuring liver stiffness and spleen stiffness,which can help estimate the likelihood of decompensation in patients with chronic liver disease.AIM To investigate the predictive ability of the liver stiffness measurement(LSM)and spleen stiffness measurement(SSM)in conjunction with other noninvasive indicators for clinical decompensation in patients suffering from compensatory cirrhosis and portal hypertension.METHODS This study was a retrospective analysis of the clinical data of 200 patients who were diagnosed with viral cirrhosis and who received computed tomography,transient elastography,ultrasound,and endoscopic examinations at The Second Affiliated Hospital of Xi’an Jiaotong University between March 2020 and November 2022.Patient classification was performed in accordance with the Baveno VI consensus.The area under the curve was used to evaluate and compare the predictive accuracy across different patient groups.The diagnostic effectiveness of several models,including the liver stiffness-spleen diameter-platelet ratio,variceal risk index,aspartate aminotransferase-alanine aminotransferase ratio,Baveno Ⅵ criteria,and newly developed models,was assessed.Additionally,decision curve analysis was carried out across a range of threshold probabilities to evaluate the clinical utility of these predictive factors.RESULTS Univariate and multivariate analyses demonstrated that SSM,LSM,and the spleen length diameter(SLD)were linked to clinical decompensation in individuals with viral cirrhosis.On the basis of these findings,a predictive model was developed via logistic regression:Ln[P/(1-P)]=-4.969-0.279×SSM+0.348×LSM+0.272×SLD.The model exhibited strong performance,with an area under the curve of 0.944.At a cutoff value of 0.56,the sensitivity,specificity,positive predictive value,and negative predictive value for predicting clinical decompensation were 85.29%,88.89%,87.89%,and 86.47%,respectively.The newly developed model demonstrated enhanced accuracy in forecasting clinical decompensation among patients suffering from viral cirrhosis when compared to four previously established models.CONCLUSION Noninvasive models utilizing SSM,LSM,and SLD are effective in predicting clinical decompensation among patients with viral cirrhosis,thereby reducing the need for unnecessary hepatic venous pressure gradient testing.展开更多
Groundwater quality is pivotal for sustainable resource management,necessitating comprehen-sive investigation to safeguard this critical resource.This study introduces a novel methodology that inte-grates stiff diagra...Groundwater quality is pivotal for sustainable resource management,necessitating comprehen-sive investigation to safeguard this critical resource.This study introduces a novel methodology that inte-grates stiff diagrams,geostatistical analysis,and geometric computation to delineate the extent of a confined aquifer within the Chahrdoly aquifer,located west of Hamadan,Iran.For the first time,this approach combines these tools to map the boundaries of a confined aquifer based on hydrochemical characteristics.Stiff diagrams were used to calculate geometric parameters from groundwater chemistry data,followed by simulation using a linear model incorporating the semivariogram parameterγ(h).The Root Mean Square Error(RMSE)of the linear model was used to differentiate confined from unconfined aquifers based on hydrochemical signatures.Validation was conducted by generating a cross-sectional hydrogeological layer from well logs,confirming the presence of aquitard layers.The results successufully delineated the confined aquifer's extent,showing strong agreement with hydrogeological log data.By integrating stiff diagrams with semivariogram analysis,this study enhances the understanding of hydrochemical processes,offering a robust framework for groundwater resource identification and management.展开更多
The average stiffness performance indices throughout the workspace are commonly used as global stiffness performance indices to evaluate the overall stiffness performance of parallel mechanisms,which involves an analy...The average stiffness performance indices throughout the workspace are commonly used as global stiffness performance indices to evaluate the overall stiffness performance of parallel mechanisms,which involves an analysis of the stiffness performance of numerous discrete points in the workspace.This necessitates time-consuming and inefficient calculation,which is particularly pronounced in the optimization design stage of the mechanism,where the variations in the global stiffness performance indices versus various dimensional and structural parameters need to be analyzed.This paper presents a semi-analytical approach for stiffness modeling of the novel(R(RPS&RP))&2-UPS parallel mechanism(referred to as the Trifree mechanism)and proposes“local”stiffness performance indices as alternatives to global indices.Drawing on the screw theory,the Cartesian stiffness matrix of the Trifree mechanism is formulated explicitly by considering the compliances of all elastic elements and the over-constraint characteristics inherent in the mechanism.Based on the spherical motion pattern of the Trifree mechanism,four special reference configurations are extracted within the workspace.This yields“local”stiffness performance indices capable of accurately evaluating the overall stiffness performance of the mechanism and effectively improving the computational efficiency.The variations in global and“local”stiffness performance indices versus key design parameters are investigated.Furthermore,the proposed indices are applied to the Tricept and Trimule mechanisms.The results demonstrate that the proposed indices exhibit excellent computational accuracy and efficiency in evaluating the overall stiffness performance of these spherical parallel mechanisms.Moreover,the stiffness performance of the novel parallel mechanism investigated in this study closely resembles that of the well-known Tricept and Trimule mechanisms.This research proposes a semi-analytic stiffness model of the Trifree mechanism and“local”stiffness performance indices to evaluate the overall stiffness performance,thereby substantially improving the computational efficiency without sacrificing accuracy.展开更多
The contact stiffness of the tool-holder assembly interface affects the overall dynamic performance of the milling system.Currently,the contact parameters are primarily established by minimizing the frequency response...The contact stiffness of the tool-holder assembly interface affects the overall dynamic performance of the milling system.Currently,the contact parameters are primarily established by minimizing the frequency response in modal tests and through dynamic simulation results.However,alterations in the structure or material of the tool-holder system necessitate multiple modal tests,thereby increasing computational costs.This study aims to streamline the process of determining contact stiffness and enhance accuracy by developing an analytical model that considers tool-holder contact properties.Initially,the microstructure of the contact surface is characterized via fractal theory to determine its fractal parameters.Then the contact coefficient is introduced to precisely depict the area distribution function of the microcontact.Building upon this,a contact stiffness model is established which is verified by the modal tests.The test results indicate that utilizing this model can reduce the structural modal frequency calculation error to 0.56%.Finally,the Monte Carlo algorithm is employed to investigate the sensitivity of fractal parameters and radial interference on contact characteristics.The findings demonstrate that the fractal dimension has the greatest influence on the dynamic behavior of the tool-holder structure.This study proposes a milling tool-holder contact stiffness modeling method from a microscopic perspective,which offers sufficient computational accuracy to provide a theoretical basis for the selection of milling tool-holder structures in practical machining.展开更多
Soft actuators are inherently flexible and compliant,traits that enhance their adaptability to diverse environments and tasks.However,their low structural stiffness can lead to unpredictable and uncontrollable complex...Soft actuators are inherently flexible and compliant,traits that enhance their adaptability to diverse environments and tasks.However,their low structural stiffness can lead to unpredictable and uncontrollable complex deformations when substantial force is required,compromising their load-bearing capacity.This work proposes a novel method that uses gecko setae-inspired adhesives as interlayer films to construct a layer jamming structure to adjust the stiffness of soft actuators.The mechanical behavior of a single tilted microcylinder was analyzed using the energy method to determine the adhesion force of the adhesives.The gecko-inspired adhesive was designed under the guidance of the adhesion force model.Testing under various loads and directions revealed that the tilted characteristic of microcylinders can enhance the adhesion force in its grasping direction.The adhesive demonstrated excellent adhesion performance compared to other typical adhesives.A tunable stiffness actuator using gecko setae-inspired adhesives(TSAGA),was developed with these adhesives serving as interlayer films.The stiffness model of TSAGA was derived by analyzing its axial compression force.The results of stiffness test indicate that the adhesives serve as interlayer films can adjust the stiffness in response to applied load.TSAGA was compared with other typical soft actuators in order to evaluate the stiffness performance,and the results indicate that TSAGA exhibits the highest stiffness and the widest tunable stiffness range.This demonstrates the superior performance of the setae-inspired adhesives as interlayer films in terms of stiffness adjustment.展开更多
This paper first analyzes the vibration environment at the spacecraft/launch vehicle(SC/LV)interface during the powered flight phase.Second,it proposes a method to enhance satellite panel stiffness.Satellite frequency...This paper first analyzes the vibration environment at the spacecraft/launch vehicle(SC/LV)interface during the powered flight phase.Second,it proposes a method to enhance satellite panel stiffness.Satellite frequency response analysis examines stiffness compatibility between the satellite(including its components)and the integrated launch stack.The environmental effect equivalence method then determines satellite ground verification test condi-tions.Ground test responses are compared with SC/LV coupling analysis results to ensure that ground tests envelope the coupling analysis results,confirming the adequacy of ground verification.展开更多
As a crucial component of intelligent chassis systems,air suspension significantly enhances driver comfort and vehicle stability.To further improve the adaptability of commercial vehicles to complex and variable road ...As a crucial component of intelligent chassis systems,air suspension significantly enhances driver comfort and vehicle stability.To further improve the adaptability of commercial vehicles to complex and variable road conditions,this paper proposes a linear motor active suspension with quasi-zero stiffness(QZS)air spring system.Firstly,a dynamic model of the linear motor active suspension with QZS air spring system is established.Secondly,considering the random uncertainties in the linear motor parameters due to manufacturing and environmental factors,a dynamic model and state equations incorporating these uncertainties are constructed using the polynomial chaos expansion(PCE)method.Then,based on H_(2) robust control theory and the Kalman filter,a state feedback control law is derived,accounting for the random parameter uncertainties.Finally,simulation and hardware-in-the-loop(HIL)experimental results demonstrate that the PCE-H_(2) robust controller not only provides better performance in terms of vehicle ride comfort compared to general H_(2) robust controller but also exhibits higher robustness to the effects of random uncertain parameters,resulting in more stable control performance.展开更多
Metabolic dysfunction-associated steatotic liver disease(MASLD)is the most widespread chronic liver disease signified by serious life-threatening conditions.The prevalence of MASLD increases along the growing prevalen...Metabolic dysfunction-associated steatotic liver disease(MASLD)is the most widespread chronic liver disease signified by serious life-threatening conditions.The prevalence of MASLD increases along the growing prevalence in obesity and metabolic syndrome.To minimize costs and complications,non-invasive diagnostic tools,including transient elastography(TE),were introduced for assessment of MASLD.TE measures liver stiffness(LS),a clinical marker for the diagnosis of liver fibrosis and cirrhosis.LS measurements are based on ultrasound wave imaging and quantification.Vibration-controlled TE,including FibroScan®,is commonly used TE methods which can accurately identify the degree of liver fibrosis and cirrhosis progression.TE was reported to predict the progression towards hepatocellular carcinoma,portal hypertension,and varices.However,the accuracy of LS diagnostics alone in patients with MASLD remains controversial.TE measurements have several limitations,including inadequate precision due to focal liver lesions,cholestasis,inflammation,and other pathological and anatomical factors which can lead to the stiffness variability.Overestimations of TE readings were reported in obese patients with body mass index(BMI)over 30 kg/m2,and older patients with ascites,diabetes,or hypertension.Not all MASLD patients have high BMI.The prevalence of obesity among MASLD patients varies worldwide,indicating the urgent need for comprehensive diagnostic tools.In patients with MASLD,improved diagnostic accuracy has been demonstrated by combining LS measurements with other blood test-based scores and simple clinical parameters(agile scores based on age,sex,platelet count,aminotransferases,and diabetes).This study reviews the limitations of TE-based diagnostics and discusses the combined scoring algorithm.In conclusion,the sequence of LS measurements along assessment of other important clinical markers is an effective,low-cost,reliable tool to identify and monitor fibrosis progression in MASLD.展开更多
Fixed-wing aircraft cannot maintain optimal aerodynamic performance at different flight speeds. As a type of morphing aircraft, the shear variable-sweep wing(SVSW) can dramatically improve its aerodynamic performance ...Fixed-wing aircraft cannot maintain optimal aerodynamic performance at different flight speeds. As a type of morphing aircraft, the shear variable-sweep wing(SVSW) can dramatically improve its aerodynamic performance by altering its shape to adapt to various flight conditions.In order to achieve smooth continuous shear deformation, SVSW's skin adopts a flexible composite skin design instead of traditional aluminum alloy materials. However, this also brings about the non-linear difficulty in stiffness modeling and calculation. In this research, a new SVSW design and efficient stiffness modeling method are proposed. Based on shear deformation theory, the flexible composite skin is equivalently modeled as diagonally arranged nonlinear springs, simulating the elastic force interaction between the skin and the mechanism. By shear loading tests of flexible composite skin, the accuracy of this flexible composite skin modeling method is verified. The SVSW stiffness model was established, and its accuracy was verified through static loading tests. The effects of root connection, sweep angles, and flexible composite skin on the SVSW stiffness are analyzed. Finally, considering three typical flight conditions of SVSW: low-speed flow(Ma = 0.3,Re = 5.82 × 10^(6)), transonic flow(Ma = 0.9, Re = 3.44 × 10^(6)), and supersonic flow(Ma = 3,Re = 7.51 × 10^(6)), the stiffness characteristics of SVSW under flight conditions were evaluated.The calculated results guide the application of SVSW.展开更多
Elastohydrodynamic lubrication(EHL)point contact occurs between two rough surfaces at the mesoscopic level,while the interaction of rough surfaces involves contact between asperities at the microscale level.In most ca...Elastohydrodynamic lubrication(EHL)point contact occurs between two rough surfaces at the mesoscopic level,while the interaction of rough surfaces involves contact between asperities at the microscale level.In most cases,the contact between asperities within an interface takes the form of lateral contact rather than peak contact.Regions devoid of contact asperities are filled with lubricating oil.However,conventional models often oversimplify lateral contact forms as interactions between asperities and a smooth,rigid plane.These simplifications fail to accurately represent the true contact conditions and can lead to inaccuracies in the analysis of EHL’s contact performance.To address this issue,we have developed a novel EHL interface model comprising two rough surfaces.This model allows us to explore the influence of asperity height,contact angle,and contact azimuth angle on EHL interface performance.展开更多
The extensive use of steel spring floating slab tracks has effectively addressed the challenge of alleviating the environmental vibrations induced by urban rail transit systems.However,under the combined action of tra...The extensive use of steel spring floating slab tracks has effectively addressed the challenge of alleviating the environmental vibrations induced by urban rail transit systems.However,under the combined action of train dynamic loads and complex environmental factors,problems,such as the fracture of steel spring vibration isolators and suspension vibrations induced by the uneven settlement of the base,often occur.The failure of isolator support stiffness is often hidden in its early stages and is challenging to identify by conventional detection methods.At the same time,it will aggravate the wheel-rail interaction,accelerate the deterioration of track structure,and even affect the driving safety.This study first establishes a detailed coupled train-floating slab track-foundation analytical model.Then the influence of the vibration isolator support stiffness failure on the dynamic indices of the floating slab track system response is analyzed.A set of defect identification methods that can detect the number of failed steel springs,severity of damage,and their location is proposed.Finally,an intelligent monitoring system for support stiffness of floating slab track is built by combining the density-based spatial clustering of applications with noise algorithm and statistical data analysis and is applied to a rail line in southern China.During a three-year monitoring campaign,a suspension failure and a fracture of a steel spring were each successfully detected and detailed failure information was obtained.Field investigation results were consistent with the damage identification results.After repair,the track structure dynamic response returned to the average pre-damage level and further deterioration had been arrested.The proposed damage identification methods and monitoring system provide an approach for intelligent identification of track structure support stiffness failures.展开更多
Continuum manipulators(CM)are soft and flexible manipulators with large numbers of degrees of freedom and can perform complex tasks in an unstructured environment.However,their deformability and compliance can deviate...Continuum manipulators(CM)are soft and flexible manipulators with large numbers of degrees of freedom and can perform complex tasks in an unstructured environment.However,their deformability and compliance can deviate distal tip under uncertain external interactions.To address this challenge,a novel tension-based control scheme has been proposed to modulate the stiffness of a tendon-driven CM,reducing the tip position errors caused by uncertain external forces.To minimize the tip position error,a virtual spring is positioned between the deviated and the desired tip positions.The proposed algorithm corrects the manipulator deviated tip position,improving tension distribution and stiffness profile,resulting in higher stiffness and better performance.The corresponding task space stiffness and condition numbers are also computed under different cases,indicating the effectiveness of the tension control scheme in modulating the manipulator's stiffness.Experimental validation conducted on an in-house developed prototype confirms the practical feasibility of the proposed approach.展开更多
基金supported by the Natio`nal Natural Science Foundation of China,No. 81801241a grant from Sichuan Science and Technology Program,No. 2023NSFSC1578Scientific Research Projects of Southwest Medical University,No. 2022ZD002 (all to JX)。
文摘Neuronal growth, extension, branching, and formation of neural networks are markedly influenced by the extracellular matrix—a complex network composed of proteins and carbohydrates secreted by cells. In addition to providing physical support for cells, the extracellular matrix also conveys critical mechanical stiffness cues. During the development of the nervous system, extracellular matrix stiffness plays a central role in guiding neuronal growth, particularly in the context of axonal extension, which is crucial for the formation of neural networks. In neural tissue engineering, manipulation of biomaterial stiffness is a promising strategy to provide a permissive environment for the repair and regeneration of injured nervous tissue. Recent research has fine-tuned synthetic biomaterials to fabricate scaffolds that closely replicate the stiffness profiles observed in the nervous system. In this review, we highlight the molecular mechanisms by which extracellular matrix stiffness regulates axonal growth and regeneration. We highlight the progress made in the development of stiffness-tunable biomaterials to emulate in vivo extracellular matrix environments, with an emphasis on their application in neural repair and regeneration, along with a discussion of the current limitations and future prospects. The exploration and optimization of the stiffness-tunable biomaterials has the potential to markedly advance the development of neural tissue engineering.
基金supported by the National Natural Science Foundation of China(Grant No.11732006)the“Qinglan Project”of Jiangsu Higher Education Institutions.
文摘Quasi-zero stiffness(QZS)isolators have received considerable attention over the past years due to their outstanding vibration isolation performance in low-frequency bands.However,traditional mechanisms for achieving QZS suffer from low stiffness regions and significant nonlinear restoring forces with hardening characteristics,often struggling to withstand excitations with high amplitude.This paper presents a novel QZS vibration isolator that utilizes a more compact spring-rod mechanism(SRM)to provide primary negative stiffness.The nonlinearity of SRM is adjustable via altering the raceway of its spring-rod end,along with the compensatory force provided by the cam-roller mechanism so as to avoid complex nonlinear behaviors.The absolute zero stiffness can be achieved by a well-designed raceway curve with a concise mathematical expression.The nonlinear stiffness with softening properties can also be achieved by parameter adjustment.The study begins with the forcedisplacement relationship of the integrated mechanism first,followed by the design theory of the cam profile.The dynamic response and absolute displacement transmissibility of the isolation system are obtained based on the harmonic balance method.The experimental results show that the proposed vibration isolator maintains relatively low-dynamic stiffness even under non-ideal conditions,and exhibits enhanced vibration isolation performance compared to the corresponding linear isolator.
基金Supported by Xi’an Science and Technology Plan,No.23YXYJ0172.
文摘BACKGROUND The hepatic venous pressure gradient serves as a crucial parameter for assessing portal hypertension and predicting clinical decompensation in individuals with cirrhosis.However,owing to its invasive nature,there has been growing interest in identifying noninvasive alternatives.Transient elastography offers a promising approach for measuring liver stiffness and spleen stiffness,which can help estimate the likelihood of decompensation in patients with chronic liver disease.AIM To investigate the predictive ability of the liver stiffness measurement(LSM)and spleen stiffness measurement(SSM)in conjunction with other noninvasive indicators for clinical decompensation in patients suffering from compensatory cirrhosis and portal hypertension.METHODS This study was a retrospective analysis of the clinical data of 200 patients who were diagnosed with viral cirrhosis and who received computed tomography,transient elastography,ultrasound,and endoscopic examinations at The Second Affiliated Hospital of Xi’an Jiaotong University between March 2020 and November 2022.Patient classification was performed in accordance with the Baveno VI consensus.The area under the curve was used to evaluate and compare the predictive accuracy across different patient groups.The diagnostic effectiveness of several models,including the liver stiffness-spleen diameter-platelet ratio,variceal risk index,aspartate aminotransferase-alanine aminotransferase ratio,Baveno Ⅵ criteria,and newly developed models,was assessed.Additionally,decision curve analysis was carried out across a range of threshold probabilities to evaluate the clinical utility of these predictive factors.RESULTS Univariate and multivariate analyses demonstrated that SSM,LSM,and the spleen length diameter(SLD)were linked to clinical decompensation in individuals with viral cirrhosis.On the basis of these findings,a predictive model was developed via logistic regression:Ln[P/(1-P)]=-4.969-0.279×SSM+0.348×LSM+0.272×SLD.The model exhibited strong performance,with an area under the curve of 0.944.At a cutoff value of 0.56,the sensitivity,specificity,positive predictive value,and negative predictive value for predicting clinical decompensation were 85.29%,88.89%,87.89%,and 86.47%,respectively.The newly developed model demonstrated enhanced accuracy in forecasting clinical decompensation among patients suffering from viral cirrhosis when compared to four previously established models.CONCLUSION Noninvasive models utilizing SSM,LSM,and SLD are effective in predicting clinical decompensation among patients with viral cirrhosis,thereby reducing the need for unnecessary hepatic venous pressure gradient testing.
文摘Groundwater quality is pivotal for sustainable resource management,necessitating comprehen-sive investigation to safeguard this critical resource.This study introduces a novel methodology that inte-grates stiff diagrams,geostatistical analysis,and geometric computation to delineate the extent of a confined aquifer within the Chahrdoly aquifer,located west of Hamadan,Iran.For the first time,this approach combines these tools to map the boundaries of a confined aquifer based on hydrochemical characteristics.Stiff diagrams were used to calculate geometric parameters from groundwater chemistry data,followed by simulation using a linear model incorporating the semivariogram parameterγ(h).The Root Mean Square Error(RMSE)of the linear model was used to differentiate confined from unconfined aquifers based on hydrochemical signatures.Validation was conducted by generating a cross-sectional hydrogeological layer from well logs,confirming the presence of aquitard layers.The results successufully delineated the confined aquifer's extent,showing strong agreement with hydrogeological log data.By integrating stiff diagrams with semivariogram analysis,this study enhances the understanding of hydrochemical processes,offering a robust framework for groundwater resource identification and management.
基金Supported by National High-quality Development Project of China(Grant No.2340STCZB193).
文摘The average stiffness performance indices throughout the workspace are commonly used as global stiffness performance indices to evaluate the overall stiffness performance of parallel mechanisms,which involves an analysis of the stiffness performance of numerous discrete points in the workspace.This necessitates time-consuming and inefficient calculation,which is particularly pronounced in the optimization design stage of the mechanism,where the variations in the global stiffness performance indices versus various dimensional and structural parameters need to be analyzed.This paper presents a semi-analytical approach for stiffness modeling of the novel(R(RPS&RP))&2-UPS parallel mechanism(referred to as the Trifree mechanism)and proposes“local”stiffness performance indices as alternatives to global indices.Drawing on the screw theory,the Cartesian stiffness matrix of the Trifree mechanism is formulated explicitly by considering the compliances of all elastic elements and the over-constraint characteristics inherent in the mechanism.Based on the spherical motion pattern of the Trifree mechanism,four special reference configurations are extracted within the workspace.This yields“local”stiffness performance indices capable of accurately evaluating the overall stiffness performance of the mechanism and effectively improving the computational efficiency.The variations in global and“local”stiffness performance indices versus key design parameters are investigated.Furthermore,the proposed indices are applied to the Tricept and Trimule mechanisms.The results demonstrate that the proposed indices exhibit excellent computational accuracy and efficiency in evaluating the overall stiffness performance of these spherical parallel mechanisms.Moreover,the stiffness performance of the novel parallel mechanism investigated in this study closely resembles that of the well-known Tricept and Trimule mechanisms.This research proposes a semi-analytic stiffness model of the Trifree mechanism and“local”stiffness performance indices to evaluate the overall stiffness performance,thereby substantially improving the computational efficiency without sacrificing accuracy.
基金Supported by National Science and Technology Major Project of China(Grant No.J2019-VII-0001-0141).
文摘The contact stiffness of the tool-holder assembly interface affects the overall dynamic performance of the milling system.Currently,the contact parameters are primarily established by minimizing the frequency response in modal tests and through dynamic simulation results.However,alterations in the structure or material of the tool-holder system necessitate multiple modal tests,thereby increasing computational costs.This study aims to streamline the process of determining contact stiffness and enhance accuracy by developing an analytical model that considers tool-holder contact properties.Initially,the microstructure of the contact surface is characterized via fractal theory to determine its fractal parameters.Then the contact coefficient is introduced to precisely depict the area distribution function of the microcontact.Building upon this,a contact stiffness model is established which is verified by the modal tests.The test results indicate that utilizing this model can reduce the structural modal frequency calculation error to 0.56%.Finally,the Monte Carlo algorithm is employed to investigate the sensitivity of fractal parameters and radial interference on contact characteristics.The findings demonstrate that the fractal dimension has the greatest influence on the dynamic behavior of the tool-holder structure.This study proposes a milling tool-holder contact stiffness modeling method from a microscopic perspective,which offers sufficient computational accuracy to provide a theoretical basis for the selection of milling tool-holder structures in practical machining.
基金supported by Jiangsu Special Project for Frontier Leading Base Technology(Grant Nos.BK20192004)Fundamental Research Funds for Central Universities(Grant Nos.B240201190)+3 种基金Changzhou Social Development Science and Technology Support Project(Grant Nos.CE20225037)Changzhou Science and Technology Project(Grant Nos.CM20223014)Suzhou Key Industrial Technology Innovation Forward-Looking Application Research Project(Grant Nos.SYG202143)Changzhou Science and Technology Project(Grant Nos.CJ20241061).
文摘Soft actuators are inherently flexible and compliant,traits that enhance their adaptability to diverse environments and tasks.However,their low structural stiffness can lead to unpredictable and uncontrollable complex deformations when substantial force is required,compromising their load-bearing capacity.This work proposes a novel method that uses gecko setae-inspired adhesives as interlayer films to construct a layer jamming structure to adjust the stiffness of soft actuators.The mechanical behavior of a single tilted microcylinder was analyzed using the energy method to determine the adhesion force of the adhesives.The gecko-inspired adhesive was designed under the guidance of the adhesion force model.Testing under various loads and directions revealed that the tilted characteristic of microcylinders can enhance the adhesion force in its grasping direction.The adhesive demonstrated excellent adhesion performance compared to other typical adhesives.A tunable stiffness actuator using gecko setae-inspired adhesives(TSAGA),was developed with these adhesives serving as interlayer films.The stiffness model of TSAGA was derived by analyzing its axial compression force.The results of stiffness test indicate that the adhesives serve as interlayer films can adjust the stiffness in response to applied load.TSAGA was compared with other typical soft actuators in order to evaluate the stiffness performance,and the results indicate that TSAGA exhibits the highest stiffness and the widest tunable stiffness range.This demonstrates the superior performance of the setae-inspired adhesives as interlayer films in terms of stiffness adjustment.
文摘This paper first analyzes the vibration environment at the spacecraft/launch vehicle(SC/LV)interface during the powered flight phase.Second,it proposes a method to enhance satellite panel stiffness.Satellite frequency response analysis examines stiffness compatibility between the satellite(including its components)and the integrated launch stack.The environmental effect equivalence method then determines satellite ground verification test condi-tions.Ground test responses are compared with SC/LV coupling analysis results to ensure that ground tests envelope the coupling analysis results,confirming the adequacy of ground verification.
基金Supported by National Natural Science Foundation of China(Grant No.51875256)Open Platform Fund of Human Institute of Technology(Grant No.KFA22009).
文摘As a crucial component of intelligent chassis systems,air suspension significantly enhances driver comfort and vehicle stability.To further improve the adaptability of commercial vehicles to complex and variable road conditions,this paper proposes a linear motor active suspension with quasi-zero stiffness(QZS)air spring system.Firstly,a dynamic model of the linear motor active suspension with QZS air spring system is established.Secondly,considering the random uncertainties in the linear motor parameters due to manufacturing and environmental factors,a dynamic model and state equations incorporating these uncertainties are constructed using the polynomial chaos expansion(PCE)method.Then,based on H_(2) robust control theory and the Kalman filter,a state feedback control law is derived,accounting for the random parameter uncertainties.Finally,simulation and hardware-in-the-loop(HIL)experimental results demonstrate that the PCE-H_(2) robust controller not only provides better performance in terms of vehicle ride comfort compared to general H_(2) robust controller but also exhibits higher robustness to the effects of random uncertain parameters,resulting in more stable control performance.
文摘Metabolic dysfunction-associated steatotic liver disease(MASLD)is the most widespread chronic liver disease signified by serious life-threatening conditions.The prevalence of MASLD increases along the growing prevalence in obesity and metabolic syndrome.To minimize costs and complications,non-invasive diagnostic tools,including transient elastography(TE),were introduced for assessment of MASLD.TE measures liver stiffness(LS),a clinical marker for the diagnosis of liver fibrosis and cirrhosis.LS measurements are based on ultrasound wave imaging and quantification.Vibration-controlled TE,including FibroScan®,is commonly used TE methods which can accurately identify the degree of liver fibrosis and cirrhosis progression.TE was reported to predict the progression towards hepatocellular carcinoma,portal hypertension,and varices.However,the accuracy of LS diagnostics alone in patients with MASLD remains controversial.TE measurements have several limitations,including inadequate precision due to focal liver lesions,cholestasis,inflammation,and other pathological and anatomical factors which can lead to the stiffness variability.Overestimations of TE readings were reported in obese patients with body mass index(BMI)over 30 kg/m2,and older patients with ascites,diabetes,or hypertension.Not all MASLD patients have high BMI.The prevalence of obesity among MASLD patients varies worldwide,indicating the urgent need for comprehensive diagnostic tools.In patients with MASLD,improved diagnostic accuracy has been demonstrated by combining LS measurements with other blood test-based scores and simple clinical parameters(agile scores based on age,sex,platelet count,aminotransferases,and diabetes).This study reviews the limitations of TE-based diagnostics and discusses the combined scoring algorithm.In conclusion,the sequence of LS measurements along assessment of other important clinical markers is an effective,low-cost,reliable tool to identify and monitor fibrosis progression in MASLD.
基金Supported by the National Nature Science Foundation of China(Grant No.52192631 and No.52105013).
文摘Fixed-wing aircraft cannot maintain optimal aerodynamic performance at different flight speeds. As a type of morphing aircraft, the shear variable-sweep wing(SVSW) can dramatically improve its aerodynamic performance by altering its shape to adapt to various flight conditions.In order to achieve smooth continuous shear deformation, SVSW's skin adopts a flexible composite skin design instead of traditional aluminum alloy materials. However, this also brings about the non-linear difficulty in stiffness modeling and calculation. In this research, a new SVSW design and efficient stiffness modeling method are proposed. Based on shear deformation theory, the flexible composite skin is equivalently modeled as diagonally arranged nonlinear springs, simulating the elastic force interaction between the skin and the mechanism. By shear loading tests of flexible composite skin, the accuracy of this flexible composite skin modeling method is verified. The SVSW stiffness model was established, and its accuracy was verified through static loading tests. The effects of root connection, sweep angles, and flexible composite skin on the SVSW stiffness are analyzed. Finally, considering three typical flight conditions of SVSW: low-speed flow(Ma = 0.3,Re = 5.82 × 10^(6)), transonic flow(Ma = 0.9, Re = 3.44 × 10^(6)), and supersonic flow(Ma = 3,Re = 7.51 × 10^(6)), the stiffness characteristics of SVSW under flight conditions were evaluated.The calculated results guide the application of SVSW.
基金supported by the National Natural Science Foundation of China(No.52005401,No.52375127)the Cultivation Scientific Research Project of Panzhihua University(2021PY001)+1 种基金the Opening Project of Material Corrosion and Protection Key Laboratory of Sichuan province(2022CL15)the Project for Science and Technology Plan of Henan Province(212102210445).
文摘Elastohydrodynamic lubrication(EHL)point contact occurs between two rough surfaces at the mesoscopic level,while the interaction of rough surfaces involves contact between asperities at the microscale level.In most cases,the contact between asperities within an interface takes the form of lateral contact rather than peak contact.Regions devoid of contact asperities are filled with lubricating oil.However,conventional models often oversimplify lateral contact forms as interactions between asperities and a smooth,rigid plane.These simplifications fail to accurately represent the true contact conditions and can lead to inaccuracies in the analysis of EHL’s contact performance.To address this issue,we have developed a novel EHL interface model comprising two rough surfaces.This model allows us to explore the influence of asperity height,contact angle,and contact azimuth angle on EHL interface performance.
基金This work is supported by the National Natural Science Foundation of China(Nos.51978585 and 52008264)the Applied Basic Research Programs of Science and Technology Commission Foundation of Sichuan Province(No.2020YJ0214)+1 种基金the Foundation of High-speed Rail Joint Fund Key Projects of Basic Research(No.U1734207)the Foundation of National Engineering Laboratory for Digital Construction Evaluation Technology of Urban Rail Transit,China(No.2023JZ01).
文摘The extensive use of steel spring floating slab tracks has effectively addressed the challenge of alleviating the environmental vibrations induced by urban rail transit systems.However,under the combined action of train dynamic loads and complex environmental factors,problems,such as the fracture of steel spring vibration isolators and suspension vibrations induced by the uneven settlement of the base,often occur.The failure of isolator support stiffness is often hidden in its early stages and is challenging to identify by conventional detection methods.At the same time,it will aggravate the wheel-rail interaction,accelerate the deterioration of track structure,and even affect the driving safety.This study first establishes a detailed coupled train-floating slab track-foundation analytical model.Then the influence of the vibration isolator support stiffness failure on the dynamic indices of the floating slab track system response is analyzed.A set of defect identification methods that can detect the number of failed steel springs,severity of damage,and their location is proposed.Finally,an intelligent monitoring system for support stiffness of floating slab track is built by combining the density-based spatial clustering of applications with noise algorithm and statistical data analysis and is applied to a rail line in southern China.During a three-year monitoring campaign,a suspension failure and a fracture of a steel spring were each successfully detected and detailed failure information was obtained.Field investigation results were consistent with the damage identification results.After repair,the track structure dynamic response returned to the average pre-damage level and further deterioration had been arrested.The proposed damage identification methods and monitoring system provide an approach for intelligent identification of track structure support stiffness failures.
文摘Continuum manipulators(CM)are soft and flexible manipulators with large numbers of degrees of freedom and can perform complex tasks in an unstructured environment.However,their deformability and compliance can deviate distal tip under uncertain external interactions.To address this challenge,a novel tension-based control scheme has been proposed to modulate the stiffness of a tendon-driven CM,reducing the tip position errors caused by uncertain external forces.To minimize the tip position error,a virtual spring is positioned between the deviated and the desired tip positions.The proposed algorithm corrects the manipulator deviated tip position,improving tension distribution and stiffness profile,resulting in higher stiffness and better performance.The corresponding task space stiffness and condition numbers are also computed under different cases,indicating the effectiveness of the tension control scheme in modulating the manipulator's stiffness.Experimental validation conducted on an in-house developed prototype confirms the practical feasibility of the proposed approach.
