In this study,the typical Mg-14Gd-0.3Zr alloy was rolled at the high-temperature range of 450–500℃.The rolled Mg alloy plate with thickness of 30 mm exhibits an ultra-high ultimate tensile strength of 428 MPa and el...In this study,the typical Mg-14Gd-0.3Zr alloy was rolled at the high-temperature range of 450–500℃.The rolled Mg alloy plate with thickness of 30 mm exhibits an ultra-high ultimate tensile strength of 428 MPa and elongation of 3.4%,which has rarely been reported,and the strong fiber texture played a critical role in strengthening.The mechanisms underlying the evolution of texture during rolling were systematically investigated.At the early stage of rolling,alloys(450℃and 475℃)exhibited a[10.10]texture due to twinning assisted by Prismaticslipping.At 500℃,the alloy underwent nearly complete dynamic recrystallization(DRX)process.With increasing the rolling reduction,the DRX occurred in the whole temperature range,exhibiting the typical[10.10]–[11.20]double fiber texture.For continuous DRX,Prismaticdislocations accumulate to form grains with 30°[0001]grain boundaries,which exhibit a[10.10]fiber texture.During discontinuous DRX,Prismaticslip induced grain rotation around the[0001]axis,stabilizing either the<10.10>//RD(rolling direction)or<11.20>//RD orientations,leading to the formation of[10.10]–[11.20]double fiber texture.TEM observations confirmed that Prismaticdislocations can accumulate to form sub-grain lamellae,which gradually transform into high-angle grain boundaries by absorbing more Prismaticdislocations.First-principle calculation demonstrated that with increasing Gd content,the unstable stacking fault energy of prismatic slipping significantly decreases,promoting the activation of Prismaticslipping.These findings elucidate the critical role of twinning and Prismaticdislocations in texture evolution and the DRX process during thick plate rolling of the high-Gd content Mg-Gd-Zr alloy.展开更多
BACKGROUND Slipping rib syndrome(SRS)is caused by abnormal subluxation of floating ribs,resulting in chronic pain and possible tissue damage.Its prevalence is often overlooked,as it shares symptoms with other musculos...BACKGROUND Slipping rib syndrome(SRS)is caused by abnormal subluxation of floating ribs,resulting in chronic pain and possible tissue damage.Its prevalence is often overlooked,as it shares symptoms with other musculoskeletal conditions,and is more common in young females and athletes.Symptoms include pain along the lower rib margin,aggravated by trunk movements,deep breathing and coughing.Treatment usually starts conservatively with physiotherapy and analgesics.In severe cases,extrapleural rib resection may be required.CASE SUMMARY In April 2023,a 24-year-old woman presented with persistent right hemithorax pain in the eleventh rib for one year.Instrumental examinations,including ultrasonography and magnetic resonance imaging,were negative for abdominal and osteochondral abnormalities.The pain intensity,rated 8/10 on the numeric rating scale(NRS),remained unresponsive to pain therapy.After a careful literature review and discussion with the patient,we opted for a minimally invasive surgical approach.Under general anesthesia,a mini-thoracotomy was performed along the anterior course of the eleventh rib.After exposure,abnormal rib mobility was detected,which led to resection of the medial margin and anchoring to the overlying rib with nonabsorbable sutures.Histological examination revealed no abnormalities.The patient was discharged on the first postoperative day.Pain decreased significantly,reaching 1/10 on the NRS at one month.At 3 months,the patient had mild fluctuating pain(2/10)requiring occasional analgesics but did not interfere with daily activities.CONCLUSION Minimally invasive rib-preserving surgery effectively reduces pain and hospitalization time,offering a valid alternative to conventional rib resection for refractory SRS.展开更多
When the mobile robot performs certain motion tasks in complex environment, wheel slipping inevitably occurs due to the wet or icy road and other reasons, thus directly influences the motion control accuracy. To addre...When the mobile robot performs certain motion tasks in complex environment, wheel slipping inevitably occurs due to the wet or icy road and other reasons, thus directly influences the motion control accuracy. To address unknown wheel longitudinal slipping problem for mobile robot, a RBF neural network approach based on whole model approximation is presented. The real-time data acquisition of inertial measure unit(IMU), encoders and other sensors is employed to get the mobile robot’s position and orientation in the movement, which is applied to compensate the unknown bounds of the longitudinal slipping using the adaptive technique. Both the simulation and experimental results prove that the control scheme possesses good practical performance and realize the motion control with unknown longitudinal slipping.展开更多
In a system based on the phase lock loop（PLL）, a trade-off must be made between the tracking precision and the dynamic performance if constant parameters are adopted. To overcome this drawback, a new method called n...In a system based on the phase lock loop（PLL）, a trade-off must be made between the tracking precision and the dynamic performance if constant parameters are adopted. To overcome this drawback, a new method called no phase slipping adaptive bandwidth（NPS-AB） is proposed, which can adjust the loop bandwidth adaptively for different working conditions. As a result, both the tracking precision and the dynamic performance can be achieved concurrently. NPS-AB has two features to keep the loop stable： one is the capability of quick response to dynamics; the other is a series of additional constraints when the bandwidth is switched. Compared with other methods, there is no phase slipping during the adjustment process for NPS-AB. The phase integer ambiguity can be avoided and the phase value is kept valid. It is meaningful for carrier ranging systems. Simulation results show that NPS-AB can deal with sudden dynamics and keep the pseudo-range value stable in the entire dynamic process.展开更多
At this article studies of nonlinear viscoelastic fluid with one internal tensor parameter flow between parallel planes under a constant pressure gradient, taking into account the slipping phenomenon on the boundary. ...At this article studies of nonlinear viscoelastic fluid with one internal tensor parameter flow between parallel planes under a constant pressure gradient, taking into account the slipping phenomenon on the boundary. Numerically depending found on the components of the stress tensor and the flow velocity of the pressure gradient and the distance to the wall, enabled us to explain the emergence of non-parabolic profile of the flow velocity of the polymeric melt.展开更多
Common effect of wave and slip of internal vehicles will make rolling of the roll-on ship serious. This is one of the important reasons for overturn of ro-ro ships. The multibody system with a floating base is compose...Common effect of wave and slip of internal vehicles will make rolling of the roll-on ship serious. This is one of the important reasons for overturn of ro-ro ships. The multibody system with a floating base is composed of ro-ro ship and slipping vehicles. Takes the rolling angle of the ship and the transverse displacements of the slipping vehicles on desk as freedoms. Making use of the analysis of apparent gravitation and apparent buoyancy, the wave rolling moment is derived. By means of dynamic method of multibody system, dynamic equations of the system are established. Taking a certain channel ferry as an example, a set of numerical calculation have been carried out for rolling response of the multibody system with a floating base of a ro-ro ship and displacements response of the slipping vehicles under common effect of free slipping vehicles and wave, and a conclusion has been drawn that the motion of the numerous free slipping heavy loads will trend to be synchronous under restraining of the side-wall bulkhead with time because of repeated collision.展开更多
When a block of dense sandy soil moves downhill, the shear-induced soil dilatancy along the basal shear boundary produces a negative value of excess pore pressure that increases the basal frictional resistance. Dilata...When a block of dense sandy soil moves downhill, the shear-induced soil dilatancy along the basal shear boundary produces a negative value of excess pore pressure that increases the basal frictional resistance. Dilatancy angle,Ψ, the degree to which the basal soil dilates due to the shear, normally evolves during slope failure. A study by other researchers shows that if Ψ is constant, the block of dense soil will remain stable(or unstable) sliding when the velocity-weakening rate of the basal friction coefficient of the block is small(or large) enough. Moreover, during unstable sliding processes, the block of dense soil exhibits "periodic" patterns of intermittent slipping. Here, we used a more efficient and accurate numerical scheme to revisit that study. We expanded their model by assuming Ψ evolves during slope failure. Consequently, we acquired completely different results. For instance, even though the velocity-weakening rate of the friction coefficient is fixed at the same smaller(or larger) value that those researchers use, the stable(or unstable) steady states of landslide they predict will inversely change to unstable(or stable) when Ψ decreases(or increases) with the increase of slide displacement to a value small(or large) enough. Particularly, in unstable processes, the soil block exhibits "aperiodic" styles of intermittent slipping, instead of "periodic". We found out that the stick states appearing later last longer(or shorter) in the case of decreasing(or increasing) Ψ. Moreover, because the basic states of landslides with impacts of dilatancy evolution are not steady nor periodic, traditional stability-analysis methods cannot be "directly" used to analyze the stability of such landslides. Here, we broke through this technical problem to a degree. We showed that combining a concept called "quasi-steady-state approximation" with a traditional stability-analysis technique can qualitatively predict the instability onset of the landslides. Through this study, we demonstrated that the combination of Chebyshev collocation(CC) and 4^(th)-order Runge-Kutta methods is more accurate and efficient than the numerical scheme those researchers use.展开更多
A nonlinear rotational motion model for n-pulley damped serpentine belt drive systems （SBDSs） was developed.The effects of the belt deflection along the contact arc of pulleys on the belt span tensions were consider...A nonlinear rotational motion model for n-pulley damped serpentine belt drive systems （SBDSs） was developed.The effects of the belt deflection along the contact arc of pulleys on the belt span tensions were considered.The methods for calculating the tensioner arm vibration and belt slipping on pulleys were introduced.The effects of belt damping on rotational vibration of tensioner arm and belt slipping on pulleys were studied.Numerical solutions for a 3-pulley SBDS indicate that the belt slipping at the steady states should be controlled to avoid belt slipping at transient states.The slip factors tend to decrease when the belt damping increases,and the possibility of the belt slipping can be controlled through adjusting the wrap angles of pulleys and the preload of the tensioner when the design parameters of SBDS remain constant.展开更多
An explicit full-field expression of the Green's functions for anisotropic piezoeleetric bimateri- als with a slipping interface is derived.When the electro-elastic singularity reduces to a pray dislocation in dis...An explicit full-field expression of the Green's functions for anisotropic piezoeleetric bimateri- als with a slipping interface is derived.When the electro-elastic singularity reduces to a pray dislocation in displacement and electric potential,interaction energy,between the dislocation and the bimaterials is obtained explicitly while the generalized force on the disloeation is given in a real form whieh is also valid for degener- ate materials.The investigation demonstrates that the houndary conditions at lhe slipping interface between two piezoelectric materials will exert a prominent influence on the mobility of the dislocation.展开更多
Channel estimation is very important for MIMO (Multiple Input Multiple Output) OFDM (Or-thogonal Frequency Division Multiplexing) systems, but its precision is reduced due to the noise in channel. In this letter, circ...Channel estimation is very important for MIMO (Multiple Input Multiple Output) OFDM (Or-thogonal Frequency Division Multiplexing) systems, but its precision is reduced due to the noise in channel. In this letter, circularly slipping window is introduced to resist the noise. It can be proved by simulation that with the same channel model, optimal slipping window length is the same with different vehicle speed. MSE (Minimum Square Error) of channel is greatly reduced with circularly slipping window, and performance of the system is closed to that with correct channel estimation.展开更多
Based on the privious model,this paper discusses the effect of the compessed property of the weft on the weaving-resistance and picks slipping under unbalanced -shed.after giving a short description about the privious...Based on the privious model,this paper discusses the effect of the compessed property of the weft on the weaving-resistance and picks slipping under unbalanced -shed.after giving a short description about the privious work.The discussion is made.under both situation of constant- cloth- tension and variable- cloth- tension respectively.展开更多
Based on the observation of the deep bore cores sampled from the State of Cali-fornia, USA, preferred arranged particulate concentration belts were found in the ultra-slipping lamellae. And the same phenomenon was fou...Based on the observation of the deep bore cores sampled from the State of Cali-fornia, USA, preferred arranged particulate concentration belts were found in the ultra-slipping lamellae. And the same phenomenon was found again later in the bore cores from the petroleum basin in the Northern Shaanxi Province. It may be the product of the dynamic processes involv-ing tumbling, grinding and compresso-shearing functions, so the spherical particulates with ul-tra-size of nm and mm are called grinding grain. The formation of the grinding grains is related with the ductile-brittle deformation, the lateral pressure of the slipping, and the very low grade of dynamic metamorphism of the rocks. Based on the systematic analysis, it is indicated that some elements like Nb and Ta are enriched in the grinding grains in the granitic rocks because of the chemical differentiation, and that the slipping lamellae bearing grinding grains in mudstone with smear efficiency prove a perfect seal for oil and gas reservoirs. Meanwhile, the paper provides bases for the studies on the fast stick-slip movement and shear paradigm.展开更多
The minimum gripping force applied is expected to prevent objects from mechanical damage when an agricultural robot is applied to handle and manipulate fruits and vegetables.In this research,a sensitive slipping senso...The minimum gripping force applied is expected to prevent objects from mechanical damage when an agricultural robot is applied to handle and manipulate fruits and vegetables.In this research,a sensitive slipping sensor was developed with a piezo resistor to control the griping force of the agricultural robot.Firstly,an output of the slipping sensor was analyzed in a frequency domain by using a short time Fourier transform.Then rules for discriminating slipping signal from the output of a slipping sensor were proposed based on detail coefficients of discrete wavelet transform.Finally,a controller based on adaptive Neuro-Fuzzy inference system was developed to adjust the grasping force of the agricultural robot in real time.The detail coefficients and the normal gripping force were applied as input of the controller,and Fuzzy rules were simplified through subtractive clustering.With a two-finger end-effector of the agricultural robot,the experimental results showed that the slipping signal could be effectively extracted regardless of change in the normal gripping force,and the gripping force had been controlled successfully when grasping tomatoes and apples.This method was a promising way to optimize the gripping force of the agricultural robot grasping the fruits and vegetables.展开更多
An optical bandwidth analysis of a quantum-well （16 nm） transistor laser with 150-μm cavity length using a charge control model is reported in order to modify the quantum-well location through the base region. At c...An optical bandwidth analysis of a quantum-well （16 nm） transistor laser with 150-μm cavity length using a charge control model is reported in order to modify the quantum-well location through the base region. At constant bias current, the simulation shows significant enhancement in optical bandwidth due to moving the quantum well in the direction of collector-base junction. No remarkable resonance peak, limiting factor in laser diodes, is observed during this modification in transistor laser structure. The method can be utilized for transistor laser structure design.展开更多
The effects of artificial aging(T6)on the creep resistance with tensile stresses in the range of 50−80 MPa at 175℃were investigated for an extruded Mg−1.22Al−0.31Ca−0.44Mn(wt.%)alloy.The Guinier-Preston(G.P.)zones pr...The effects of artificial aging(T6)on the creep resistance with tensile stresses in the range of 50−80 MPa at 175℃were investigated for an extruded Mg−1.22Al−0.31Ca−0.44Mn(wt.%)alloy.The Guinier-Preston(G.P.)zones primarily precipitate in the sample aged at 200℃for 1 h(T6-200℃/1h),while the Al_(2)Ca phases mainly precipitate in the sample aged at 275℃for 8 h(T6-275℃/8h).The T6-200℃/1h sample exhibits excellent creep resistance,with a steady-state creep rate one order of magnitude lower than that of the T6-275℃/8h sample.The abnormally high stress exponent(~8.2)observed in the T6-200℃/1h sample is associated with the power-law breakdown mechanism.TEM analysis illuminates that the creep mechanism for the T6-200℃/1h sample is cross-slip between basal and prismatic dislocations,while the T6-275℃/8h sample exhibits a mixed mechanism of dislocation cross-slip and climb.Compared with the Al_(2)Ca phase,the dense G.P.zones effectively impede dislocation climb and glide during the creep process,demonstrating superior creep resistance of the T6-200℃/1h sample.展开更多
The effects of the Born repulsive force on the stability and dynamics of ultra-thin slipping films under the influences of intermolecular forces are investigated with bifurcation theory and numerical simulation. Resul...The effects of the Born repulsive force on the stability and dynamics of ultra-thin slipping films under the influences of intermolecular forces are investigated with bifurcation theory and numerical simulation. Results show that the repulsive force has a stabilizing effect on the development of perturbations, and can suppress the rupture process induced by the van der Waals attractive force. Although slippage will enhance the growth of disturbances, it does not have influence on the linear cutoff wave number and the final shape of the film thickness as time approaches to infinity.展开更多
Previous works were mainly concentrated on long-term average runoff alterations,and extreme temperatures and watershed conditions are little analyzed.In this study,we collected gauged river flow and meteorological dat...Previous works were mainly concentrated on long-term average runoff alterations,and extreme temperatures and watershed conditions are little analyzed.In this study,we collected gauged river flow and meteorological data time series from 1916 to 2015 and 1941 to 2015 across the contiguous United States(CONUS)for 188 catchments to investigate the temporal trends and spatial features of runoff changes at multi-time scales.We also analyzed the relationships between runoff changes and climatic factors.Median descriptive statistics and Budyko coupled climate elasticity methods were used to calculate runoff elasticity in each time scale.The original Mann-Kendall trend test was used to test their trend significance in four time-scale(11,20,40,and 60 a),respectively.The results show that the trend of runoff changes is more significant in high time scales;total changes are heterogeneous over CONUS.After the 1970s,increases of up to 27%decade-1 were mainly concentrated in the mid-northern regions.Maximum temperature and catchment characteristics are vital factors for runoff alteration;runoff changes are independent of rainfall,and wet regions tend to have lower changes.These findings could help develop better regional water resource planning and management.展开更多
The high-cycle fatigue fracture characteristics and damage mechanism of nickel-based single crystal superalloys at 850℃ was investigated.The results indicate that high-cycle fatigue cracks in single crystal superallo...The high-cycle fatigue fracture characteristics and damage mechanism of nickel-based single crystal superalloys at 850℃ was investigated.The results indicate that high-cycle fatigue cracks in single crystal superalloys generally originate from defect locations on the subsurface or interior of the specimen at 850℃.Under the condition of stress ratio R=0.05,as the fatigue load decreases,the high-cycle fatigue life gradually increases.The high-cycle fatigue fracture is mainly characterized by octahedral slip mechanism.At high stress and low lifespan,the fracture exhibits single or multiple slip surface features.Some fractures originate along a vertical small plane and then propagate along the{111}slip surface.At low stress and high lifespan,the fracture surface tend to alternate and expand along multiple slip planes after originating from subsurface or internal sources,exhibiting characteristics of multiple slip planes.Through electron backscatter diffraction and transmission electron microscope analysis,there is obvious oxidation behavior on the surface of the high-cycle fatigue fracture,and the fracture section is composed of oxidation layer,distortion layer,and matrix layer from the outside to the inside.Among them,the main components of the oxidation layer are oxides of Ni and Co.The distortion layer is mainly distributed in the form of elongated or short rod-shaped oxides of Al,Ta,and W.The matrix layer is a single crystal layer.Crack initiation and propagation mechanism were obtained by systematical analysis of a large number of highcycle fatigue fractures.In addition,the stress ratio of 0.05 is closer to the vibration mode of turbine blades during actual service,providing effective guidance for the study of failure and fracture mechanisms of turbine blades.展开更多
基金the National Key Research and Development Program(2023YFB3710903)the National Natural Science Foundation of China(U2167213)+1 种基金the Fundamental Research Funds for the Central Universities(N25GFZ006)the Xingliao Talent Plan Program(XLYC2203202).
文摘In this study,the typical Mg-14Gd-0.3Zr alloy was rolled at the high-temperature range of 450–500℃.The rolled Mg alloy plate with thickness of 30 mm exhibits an ultra-high ultimate tensile strength of 428 MPa and elongation of 3.4%,which has rarely been reported,and the strong fiber texture played a critical role in strengthening.The mechanisms underlying the evolution of texture during rolling were systematically investigated.At the early stage of rolling,alloys(450℃and 475℃)exhibited a[10.10]texture due to twinning assisted by Prismaticslipping.At 500℃,the alloy underwent nearly complete dynamic recrystallization(DRX)process.With increasing the rolling reduction,the DRX occurred in the whole temperature range,exhibiting the typical[10.10]–[11.20]double fiber texture.For continuous DRX,Prismaticdislocations accumulate to form grains with 30°[0001]grain boundaries,which exhibit a[10.10]fiber texture.During discontinuous DRX,Prismaticslip induced grain rotation around the[0001]axis,stabilizing either the<10.10>//RD(rolling direction)or<11.20>//RD orientations,leading to the formation of[10.10]–[11.20]double fiber texture.TEM observations confirmed that Prismaticdislocations can accumulate to form sub-grain lamellae,which gradually transform into high-angle grain boundaries by absorbing more Prismaticdislocations.First-principle calculation demonstrated that with increasing Gd content,the unstable stacking fault energy of prismatic slipping significantly decreases,promoting the activation of Prismaticslipping.These findings elucidate the critical role of twinning and Prismaticdislocations in texture evolution and the DRX process during thick plate rolling of the high-Gd content Mg-Gd-Zr alloy.
文摘BACKGROUND Slipping rib syndrome(SRS)is caused by abnormal subluxation of floating ribs,resulting in chronic pain and possible tissue damage.Its prevalence is often overlooked,as it shares symptoms with other musculoskeletal conditions,and is more common in young females and athletes.Symptoms include pain along the lower rib margin,aggravated by trunk movements,deep breathing and coughing.Treatment usually starts conservatively with physiotherapy and analgesics.In severe cases,extrapleural rib resection may be required.CASE SUMMARY In April 2023,a 24-year-old woman presented with persistent right hemithorax pain in the eleventh rib for one year.Instrumental examinations,including ultrasonography and magnetic resonance imaging,were negative for abdominal and osteochondral abnormalities.The pain intensity,rated 8/10 on the numeric rating scale(NRS),remained unresponsive to pain therapy.After a careful literature review and discussion with the patient,we opted for a minimally invasive surgical approach.Under general anesthesia,a mini-thoracotomy was performed along the anterior course of the eleventh rib.After exposure,abnormal rib mobility was detected,which led to resection of the medial margin and anchoring to the overlying rib with nonabsorbable sutures.Histological examination revealed no abnormalities.The patient was discharged on the first postoperative day.Pain decreased significantly,reaching 1/10 on the NRS at one month.At 3 months,the patient had mild fluctuating pain(2/10)requiring occasional analgesics but did not interfere with daily activities.CONCLUSION Minimally invasive rib-preserving surgery effectively reduces pain and hospitalization time,offering a valid alternative to conventional rib resection for refractory SRS.
基金Supported by Scientific and Innovation Research Funds for the Beijing University of Posts and Telecommunications(Grant No.2017RC22)
文摘When the mobile robot performs certain motion tasks in complex environment, wheel slipping inevitably occurs due to the wet or icy road and other reasons, thus directly influences the motion control accuracy. To address unknown wheel longitudinal slipping problem for mobile robot, a RBF neural network approach based on whole model approximation is presented. The real-time data acquisition of inertial measure unit(IMU), encoders and other sensors is employed to get the mobile robot’s position and orientation in the movement, which is applied to compensate the unknown bounds of the longitudinal slipping using the adaptive technique. Both the simulation and experimental results prove that the control scheme possesses good practical performance and realize the motion control with unknown longitudinal slipping.
文摘In a system based on the phase lock loop（PLL）, a trade-off must be made between the tracking precision and the dynamic performance if constant parameters are adopted. To overcome this drawback, a new method called no phase slipping adaptive bandwidth（NPS-AB） is proposed, which can adjust the loop bandwidth adaptively for different working conditions. As a result, both the tracking precision and the dynamic performance can be achieved concurrently. NPS-AB has two features to keep the loop stable： one is the capability of quick response to dynamics; the other is a series of additional constraints when the bandwidth is switched. Compared with other methods, there is no phase slipping during the adjustment process for NPS-AB. The phase integer ambiguity can be avoided and the phase value is kept valid. It is meaningful for carrier ranging systems. Simulation results show that NPS-AB can deal with sudden dynamics and keep the pseudo-range value stable in the entire dynamic process.
文摘At this article studies of nonlinear viscoelastic fluid with one internal tensor parameter flow between parallel planes under a constant pressure gradient, taking into account the slipping phenomenon on the boundary. Numerically depending found on the components of the stress tensor and the flow velocity of the pressure gradient and the distance to the wall, enabled us to explain the emergence of non-parabolic profile of the flow velocity of the polymeric melt.
基金Project supported by the National Natural Science Foundation of China (No.50309018)
文摘Common effect of wave and slip of internal vehicles will make rolling of the roll-on ship serious. This is one of the important reasons for overturn of ro-ro ships. The multibody system with a floating base is composed of ro-ro ship and slipping vehicles. Takes the rolling angle of the ship and the transverse displacements of the slipping vehicles on desk as freedoms. Making use of the analysis of apparent gravitation and apparent buoyancy, the wave rolling moment is derived. By means of dynamic method of multibody system, dynamic equations of the system are established. Taking a certain channel ferry as an example, a set of numerical calculation have been carried out for rolling response of the multibody system with a floating base of a ro-ro ship and displacements response of the slipping vehicles under common effect of free slipping vehicles and wave, and a conclusion has been drawn that the motion of the numerous free slipping heavy loads will trend to be synchronous under restraining of the side-wall bulkhead with time because of repeated collision.
基金financial support with the Grant No. MOST 105-2911-I-006-301
文摘When a block of dense sandy soil moves downhill, the shear-induced soil dilatancy along the basal shear boundary produces a negative value of excess pore pressure that increases the basal frictional resistance. Dilatancy angle,Ψ, the degree to which the basal soil dilates due to the shear, normally evolves during slope failure. A study by other researchers shows that if Ψ is constant, the block of dense soil will remain stable(or unstable) sliding when the velocity-weakening rate of the basal friction coefficient of the block is small(or large) enough. Moreover, during unstable sliding processes, the block of dense soil exhibits "periodic" patterns of intermittent slipping. Here, we used a more efficient and accurate numerical scheme to revisit that study. We expanded their model by assuming Ψ evolves during slope failure. Consequently, we acquired completely different results. For instance, even though the velocity-weakening rate of the friction coefficient is fixed at the same smaller(or larger) value that those researchers use, the stable(or unstable) steady states of landslide they predict will inversely change to unstable(or stable) when Ψ decreases(or increases) with the increase of slide displacement to a value small(or large) enough. Particularly, in unstable processes, the soil block exhibits "aperiodic" styles of intermittent slipping, instead of "periodic". We found out that the stick states appearing later last longer(or shorter) in the case of decreasing(or increasing) Ψ. Moreover, because the basic states of landslides with impacts of dilatancy evolution are not steady nor periodic, traditional stability-analysis methods cannot be "directly" used to analyze the stability of such landslides. Here, we broke through this technical problem to a degree. We showed that combining a concept called "quasi-steady-state approximation" with a traditional stability-analysis technique can qualitatively predict the instability onset of the landslides. Through this study, we demonstrated that the combination of Chebyshev collocation(CC) and 4^(th)-order Runge-Kutta methods is more accurate and efficient than the numerical scheme those researchers use.
基金Sponsored by the National Natural Science Foundation of China(50975091)Science Fund of State Key Laboratory of Automotive Safety and Energy(KF10162)
文摘A nonlinear rotational motion model for n-pulley damped serpentine belt drive systems （SBDSs） was developed.The effects of the belt deflection along the contact arc of pulleys on the belt span tensions were considered.The methods for calculating the tensioner arm vibration and belt slipping on pulleys were introduced.The effects of belt damping on rotational vibration of tensioner arm and belt slipping on pulleys were studied.Numerical solutions for a 3-pulley SBDS indicate that the belt slipping at the steady states should be controlled to avoid belt slipping at transient states.The slip factors tend to decrease when the belt damping increases,and the possibility of the belt slipping can be controlled through adjusting the wrap angles of pulleys and the preload of the tensioner when the design parameters of SBDS remain constant.
基金the National Natural Science Foundation of China (No.59635140)
文摘An explicit full-field expression of the Green's functions for anisotropic piezoeleetric bimateri- als with a slipping interface is derived.When the electro-elastic singularity reduces to a pray dislocation in displacement and electric potential,interaction energy,between the dislocation and the bimaterials is obtained explicitly while the generalized force on the disloeation is given in a real form whieh is also valid for degener- ate materials.The investigation demonstrates that the houndary conditions at lhe slipping interface between two piezoelectric materials will exert a prominent influence on the mobility of the dislocation.
文摘Channel estimation is very important for MIMO (Multiple Input Multiple Output) OFDM (Or-thogonal Frequency Division Multiplexing) systems, but its precision is reduced due to the noise in channel. In this letter, circularly slipping window is introduced to resist the noise. It can be proved by simulation that with the same channel model, optimal slipping window length is the same with different vehicle speed. MSE (Minimum Square Error) of channel is greatly reduced with circularly slipping window, and performance of the system is closed to that with correct channel estimation.
文摘Based on the privious model,this paper discusses the effect of the compessed property of the weft on the weaving-resistance and picks slipping under unbalanced -shed.after giving a short description about the privious work.The discussion is made.under both situation of constant- cloth- tension and variable- cloth- tension respectively.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 40173001, 40003002 and 40172072) the State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation.
文摘Based on the observation of the deep bore cores sampled from the State of Cali-fornia, USA, preferred arranged particulate concentration belts were found in the ultra-slipping lamellae. And the same phenomenon was found again later in the bore cores from the petroleum basin in the Northern Shaanxi Province. It may be the product of the dynamic processes involv-ing tumbling, grinding and compresso-shearing functions, so the spherical particulates with ul-tra-size of nm and mm are called grinding grain. The formation of the grinding grains is related with the ductile-brittle deformation, the lateral pressure of the slipping, and the very low grade of dynamic metamorphism of the rocks. Based on the systematic analysis, it is indicated that some elements like Nb and Ta are enriched in the grinding grains in the granitic rocks because of the chemical differentiation, and that the slipping lamellae bearing grinding grains in mudstone with smear efficiency prove a perfect seal for oil and gas reservoirs. Meanwhile, the paper provides bases for the studies on the fast stick-slip movement and shear paradigm.
基金This work was supported by the Key Research and Development Program of Jiangsu(Grant No.BE2017370)the National Natural Science Foundation of China(Grant No.31471419)the Natural Science Funds of Jiangsu(Grant No.BK20140729).
文摘The minimum gripping force applied is expected to prevent objects from mechanical damage when an agricultural robot is applied to handle and manipulate fruits and vegetables.In this research,a sensitive slipping sensor was developed with a piezo resistor to control the griping force of the agricultural robot.Firstly,an output of the slipping sensor was analyzed in a frequency domain by using a short time Fourier transform.Then rules for discriminating slipping signal from the output of a slipping sensor were proposed based on detail coefficients of discrete wavelet transform.Finally,a controller based on adaptive Neuro-Fuzzy inference system was developed to adjust the grasping force of the agricultural robot in real time.The detail coefficients and the normal gripping force were applied as input of the controller,and Fuzzy rules were simplified through subtractive clustering.With a two-finger end-effector of the agricultural robot,the experimental results showed that the slipping signal could be effectively extracted regardless of change in the normal gripping force,and the gripping force had been controlled successfully when grasping tomatoes and apples.This method was a promising way to optimize the gripping force of the agricultural robot grasping the fruits and vegetables.
文摘An optical bandwidth analysis of a quantum-well （16 nm） transistor laser with 150-μm cavity length using a charge control model is reported in order to modify the quantum-well location through the base region. At constant bias current, the simulation shows significant enhancement in optical bandwidth due to moving the quantum well in the direction of collector-base junction. No remarkable resonance peak, limiting factor in laser diodes, is observed during this modification in transistor laser structure. The method can be utilized for transistor laser structure design.
基金supported by the National Natural Science Foundation of China (Nos. 52175322, 52271031)the Natural Science Foundation of Jilin Province, China (No. SKL202302015)。
文摘The effects of artificial aging(T6)on the creep resistance with tensile stresses in the range of 50−80 MPa at 175℃were investigated for an extruded Mg−1.22Al−0.31Ca−0.44Mn(wt.%)alloy.The Guinier-Preston(G.P.)zones primarily precipitate in the sample aged at 200℃for 1 h(T6-200℃/1h),while the Al_(2)Ca phases mainly precipitate in the sample aged at 275℃for 8 h(T6-275℃/8h).The T6-200℃/1h sample exhibits excellent creep resistance,with a steady-state creep rate one order of magnitude lower than that of the T6-275℃/8h sample.The abnormally high stress exponent(~8.2)observed in the T6-200℃/1h sample is associated with the power-law breakdown mechanism.TEM analysis illuminates that the creep mechanism for the T6-200℃/1h sample is cross-slip between basal and prismatic dislocations,while the T6-275℃/8h sample exhibits a mixed mechanism of dislocation cross-slip and climb.Compared with the Al_(2)Ca phase,the dense G.P.zones effectively impede dislocation climb and glide during the creep process,demonstrating superior creep resistance of the T6-200℃/1h sample.
基金Project supported by the National Natural Science Foundation of China (Grant No:10472062 ) and Shanghai Leading Academic Discipline Project (Grant No: Y0103 ).
文摘The effects of the Born repulsive force on the stability and dynamics of ultra-thin slipping films under the influences of intermolecular forces are investigated with bifurcation theory and numerical simulation. Results show that the repulsive force has a stabilizing effect on the development of perturbations, and can suppress the rupture process induced by the van der Waals attractive force. Although slippage will enhance the growth of disturbances, it does not have influence on the linear cutoff wave number and the final shape of the film thickness as time approaches to infinity.
基金supported by National Key R&D Program of China(No.2018YFC0407303)“Young Talents”Project of Northeast Agricultural University(No.20QC13)the Natural Science Foundation of Heilongjiang Province of China(No.E2017009)。
文摘Previous works were mainly concentrated on long-term average runoff alterations,and extreme temperatures and watershed conditions are little analyzed.In this study,we collected gauged river flow and meteorological data time series from 1916 to 2015 and 1941 to 2015 across the contiguous United States(CONUS)for 188 catchments to investigate the temporal trends and spatial features of runoff changes at multi-time scales.We also analyzed the relationships between runoff changes and climatic factors.Median descriptive statistics and Budyko coupled climate elasticity methods were used to calculate runoff elasticity in each time scale.The original Mann-Kendall trend test was used to test their trend significance in four time-scale(11,20,40,and 60 a),respectively.The results show that the trend of runoff changes is more significant in high time scales;total changes are heterogeneous over CONUS.After the 1970s,increases of up to 27%decade-1 were mainly concentrated in the mid-northern regions.Maximum temperature and catchment characteristics are vital factors for runoff alteration;runoff changes are independent of rainfall,and wet regions tend to have lower changes.These findings could help develop better regional water resource planning and management.
基金National Science and Technology Major Project(J2019-VI-0022-0138)。
文摘The high-cycle fatigue fracture characteristics and damage mechanism of nickel-based single crystal superalloys at 850℃ was investigated.The results indicate that high-cycle fatigue cracks in single crystal superalloys generally originate from defect locations on the subsurface or interior of the specimen at 850℃.Under the condition of stress ratio R=0.05,as the fatigue load decreases,the high-cycle fatigue life gradually increases.The high-cycle fatigue fracture is mainly characterized by octahedral slip mechanism.At high stress and low lifespan,the fracture exhibits single or multiple slip surface features.Some fractures originate along a vertical small plane and then propagate along the{111}slip surface.At low stress and high lifespan,the fracture surface tend to alternate and expand along multiple slip planes after originating from subsurface or internal sources,exhibiting characteristics of multiple slip planes.Through electron backscatter diffraction and transmission electron microscope analysis,there is obvious oxidation behavior on the surface of the high-cycle fatigue fracture,and the fracture section is composed of oxidation layer,distortion layer,and matrix layer from the outside to the inside.Among them,the main components of the oxidation layer are oxides of Ni and Co.The distortion layer is mainly distributed in the form of elongated or short rod-shaped oxides of Al,Ta,and W.The matrix layer is a single crystal layer.Crack initiation and propagation mechanism were obtained by systematical analysis of a large number of highcycle fatigue fractures.In addition,the stress ratio of 0.05 is closer to the vibration mode of turbine blades during actual service,providing effective guidance for the study of failure and fracture mechanisms of turbine blades.
