The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. Ho...The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.展开更多
Using scanning tunneling spectroscopy, we studied the transition from tunneling regime to local point contact on the iron-based superconductor Ba0.6K0.4Fe2As2. By gradually reducing the junction resistance, a series o...Using scanning tunneling spectroscopy, we studied the transition from tunneling regime to local point contact on the iron-based superconductor Ba0.6K0.4Fe2As2. By gradually reducing the junction resistance, a series of spectra were obtained with the characteristics evolving from single-particle tunneling into Andreev reflection. The spectra can be well fitted to the modified Blonder–Tinkham–Klapwijk（BTK） model and exhibit significant changes of both spectral broadening and orbital selection due to the formation of point contact. The spatial resolution of the point contact was estimated to be several nanometers, providing a unique way to study the inhomogeneity of unconventional superconductors on such a scale.展开更多
This letter presents an analytical solution to the hydrodynamic lubrication of a circular point contact sliding over a flat surface with cavitation.The solution is found by solving the Reynolds equation with Reynolds ...This letter presents an analytical solution to the hydrodynamic lubrication of a circular point contact sliding over a flat surface with cavitation.The solution is found by solving the Reynolds equation with Reynolds boundary condition for cavitation.The cavitation boundary is shown to be straight lines directed 108.4°against the sliding direction.The result is experimentally verified in the limit of large values of viscosity,sliding velocity and radius of a spherical ball.The solution raises questions about the coupling between cavitation and film rupture and can be used as an independent check on the validity of numerical solutions.展开更多
An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state...An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state of the device reached up to 7.5meV, probably due to the hard wall confinement by using shallow electron gas and sharp point contact geometry. The two-dimensionM non-equilibrium shot noise contour map shows noise suppression characteristics in a wide range of bias voltage. Fano factor analysis indicates spin-polarized transport through a short quantum point contact.展开更多
Apart from usual quantization steps on the ballistic conductance of quasi-one-dimensional conductor, an additional plateau-like feature appears at a fraction of about 0.7 below the first conductance step in GaAs-based...Apart from usual quantization steps on the ballistic conductance of quasi-one-dimensional conductor, an additional plateau-like feature appears at a fraction of about 0.7 below the first conductance step in GaAs-based quantum point contacts (QPCs). Despite a tremendous amount of research on this anomalous feature, its origin remains still unclear. Here, a unique model of this anomaly is proposed relying on fundamental principles of quantum mechanics. It is noticed that just after opening a quasi-1D conducting channel in the QPC a single electron travels the channel at a time, and such electron can be—in principle—observed. The act of observation destroys superposition of spin states, in which the electron otherwise exists, and this suppresses their quantum interference. It is shown that then the QPC-conductance is reduced by a factor of 0.74. “Visibility” of electron is enhanced if the electron spends some time in the channel due to resonant transmission. Electron’s resonance can also explain an unusual temperature behavior of the anomaly as well as its recently discovered feature: oscillatory modulation as a function of the channel length and electrostatic potential. A recipe for experimental verification of the model is given.展开更多
Clearance not only affects the startup torque,rotation precision and stiffness of bearing,but also affects the load distribution,load-carrying capacity and life of bearing.A computational model in which the clearance ...Clearance not only affects the startup torque,rotation precision and stiffness of bearing,but also affects the load distribution,load-carrying capacity and life of bearing.A computational model in which the clearance of bearing is first included is presented for determining the contact force distribution and static load-carrying capacity of a double row four-point contact ball bearing which is subjected to the combined radial,axial and overturning moment loadings.The relation between the negative axial clearance and the contact force distribution is analyzed.The static load-carrying capacity curves are established,and the effects of the changes in negative axial clearance,curvature radius coefficient of raceway groove and initial contact angle on the static load-carrying capacity are analyzed.The results show that,with the increase in the absolute value of negative clearance,the maximum contact load decreases first and then increases.The clearance values in the range of 0.2 mme0 mm have little effect on the static load-carrying capacity of bearing.With the increase in the curvature radius coefficient of raceway groove and the decrease in the initial contact angle,the static load capacity of bearing decreases.展开更多
The contact fatigue life of machine elements is affected by pitting, wear and so on, under heavier loading conditions. Increasing the fatigue life requires mainly the improvements of lubricating condition, operating c...The contact fatigue life of machine elements is affected by pitting, wear and so on, under heavier loading conditions. Increasing the fatigue life requires mainly the improvements of lubricating condition, operating condition and materials. In order to improve the lubricating condition, it is necessary to investigate the relation of the microscopic surface texturing and the contact modes of machine elements. In this paper, thus, the pressure and oil film thickness of the contact between sphere and the plate with 5 kinds surface texturing were calculated using a commercial software based on Reynolds equation. There was sufficient evidence to suggest that the dimple shape was the optimum texturing to increase the lubricating condition.展开更多
Themass production and the practical number of cryogenic quantum devices producible in a single chip are limited to the number of electrical contact pads and wiring of the cryostat or dilution refrigerator.It is,there...Themass production and the practical number of cryogenic quantum devices producible in a single chip are limited to the number of electrical contact pads and wiring of the cryostat or dilution refrigerator.It is,therefore,beneficial to contrast themeasurements of hundreds of devices fabricated in a single chip in one cooldown process to promote the scalability,integrability,reliability,and reproducibility of quantum devices and to save evaluation time,cost and energy.Here,we used a cryogenic on-chip multiplexer architecture and investigated the statistics of the 0.7 anomaly observed on the first three plateaus of the quantized conductance of semiconductor quantum point contact(QPC)transistors.Our single chips contain 256 split gate field-effect QPC transistors(QFET)each,with two 16-branch multiplexed source-drain and gate pads,allowing individual transistors to be selected,addressed and controlled through an electrostatic gate voltage process.A total of 1280 quantum transistors with nano-scale dimensions are patterned in 5 different chips of GaAs heterostructures.From the measurements of 571 functioning QFETs taken at temperatures T[1.4 K and T[40 mK,it is found that the spontaneous polarisation model and Kondo effect do not fit our results.Furthermore,some of the features in our data largely agreed with van Hove model with short-range interactions.Our approach provides further insight into the quantum mechanical properties and microscopic origin of the 0.7 anomaly in QFETs,paving the way for the development of semiconducting quantum circuits and integrated cryogenic electronics,for scalable quantum logic control,readout,synthesis,and processing applications.展开更多
Purpose-Under the high-speed operating conditions,the effects of wheelset elastic deformation on the wheel rail dynamic forces will become more notable compared to the low-speed condition.In order to meet different an...Purpose-Under the high-speed operating conditions,the effects of wheelset elastic deformation on the wheel rail dynamic forces will become more notable compared to the low-speed condition.In order to meet different analysis requirements and selecting appropriate models to analyzing the wheel rail interaction,it is crucial to understand the influence of wheelset flexibility on the wheel-rail dynamics under different speeds and track excitations condition.Design/methodology/approach-The wheel rail contact points solving method and vehicle dynamics equations considering wheelset flexibility in the trajectory body coordinate system were investigated in this paper.As for the wheel-rail contact forces,which is a particular force element in vehicle multibody system,a method for calculating the Jacobian matrix of the wheel-rail contact force is proposed to better couple the wheel-rail contact force calculation with the vehicle dynamics response calculation.Based on the flexible wheelset modeling approach in this paper,two vehicle dynamic models considering the wheelset as both elastic and rigid bodies are established,two kinds of track excitations,namely normal measured track irregularities and short-wave irregularities are used,wheel-rail geometric contact characteristic and wheel-rail contact forces in both time and frequency domains are compared with the two models in order to study the influence of flexible wheelset rotation effect on wheel rail contact force.Findings-Under normal track irregularity excitations,the amplitudes of vertical,longitudinal and lateral forces computed by the flexible wheelset model are smaller than those of the rigid wheelset model,and the virtual penetration and equivalent contact patch are also slightly smaller.For the flexible wheelset model,the wheel rail longitudinal and lateral creepages will also decrease.The higher the vehicle speed,the larger the differences in wheel-rail forces computed by the flexible and rigid wheelset model.Under track short-wave irregularity excitations,the vertical force amplitude computed by the flexible wheelset is also smaller than that of the rigid wheelset.However,unlike the excitation case of measured track irregularity,under short-wave excitations,for the speed within the range of 200 to 350 km/h,the difference in the amplitude of the vertical force between the flexible and rigid wheelset models gradually decreases as the speed increase.This is partly due to the contribution of wheelset's elastic vibration under short-wave excitations.For low-frequency wheel-rail force analysis problems at speeds of 350 km/h and above,as well as high-frequency wheel-rail interaction analysis problems under various speed conditions,the flexible wheelset model will give results agrees better with the reality.Originality/value-This study provides reference for the modeling method of the flexible wheelset and the coupling method of wheel-rail contact force to the vehicle multibody dynamics system.Furthermore,by comparative research,the influence of wheelset flexibility and rotation on wheel-rail dynamic behavior are obtained,which is useful to the application scope of rigid and flexible wheelset models.展开更多
In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By emp...In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.展开更多
Ag/Ta_(2)O_(5)/CuO/Pt memristive devices with Ag point contacts at the interface exhibit forming-free and partial volatile analog resistive switching properties.Versatile synaptic functions,like the short-term plastic...Ag/Ta_(2)O_(5)/CuO/Pt memristive devices with Ag point contacts at the interface exhibit forming-free and partial volatile analog resistive switching properties.Versatile synaptic functions,like the short-term plasticity,the long-term potentiation and the paired-pulse facilitation,are emulated with these devices.The Ag point contacts in the Ta_(2)O_(5)layer are verified through transmission electron microscope(TEM)and X-ray photoelectron spectroscope(XPS).The Ag point contacts at the interface endow the device the transition from the electrochemical metallization mode to the valence change mode,and the analog resistive switching behavior and neuromorphic functions.This interface engineering of introducing point contacts at the interface provides a way for the development of neuromorphic devices with low power consumption.展开更多
The ride vibration of a tractor is affected mostly by the stiffness and damping coefficient of the seat suspension,cabin suspension,cabin rubber mounts,and rubber tires.However,in the case of rubber tractor tires,the ...The ride vibration of a tractor is affected mostly by the stiffness and damping coefficient of the seat suspension,cabin suspension,cabin rubber mounts,and rubber tires.However,in the case of rubber tractor tires,the stiffnesses and damping coefficients have not been researched adequately thus far,and it is not simple to measure these characteristics.In this study,a method for measuring and analyzing the stiffnesses and damping coefficients of rubber tractor tires,which were the input parameters for the tractor ride vibration simulation,was proposed.The cleat test,proposed in this study,did not require separate and complicated test equipment,unlike the conventional methods.The test was conducted simply by measuring acceleration under the driving conditions of the vehicle without detaching tires from the vehicle body or setting up additional test equipment.Based on the ground-vertical acceleration data obtained,the stiffness was calculated using the logarithmic decrement method,and the damping coefficient was calculated using least squares exponential curve fitting.The result of the cleat test indicated that the front tires had stiffnesses of 486.08-570.69 kN/m and damping coefficients of 4.02-4.52 kN·s/m;the rear tires had stiffnesses of 409.42-483.79 kN/m and damping coefficients of 2.21-2.67 kN·s/m.During the test,40 mm height cleats were installed on the track and the speed of the tractor was set to 7 and 10 km/h,which were the most common speeds during the operation.This study is meaningful in that it has presented a new method that improves the practicality of results,reduces cost,and simplifies the test process for measuring the stiffnesses and damping coefficients of rubber tractor tires.展开更多
Based on the mathematical model describing the third-order approximation of the cutter envelope surface according to one given cutter location(CL),a tool positioning strategy is proposed for efficiently machining free...Based on the mathematical model describing the third-order approximation of the cutter envelope surface according to one given cutter location(CL),a tool positioning strategy is proposed for efficiently machining free-form surfaces with non-ball-end cutters.The optimal CL is obtained by adjusting the inclination and tilt angles of the cutter until its envelope surface and the design surface have the third-order contact at the cutter contact(CC)point,which results in a wide machining strip.The strategy can handle the constraints of machine joint angle limits,global collision avoidance and tool path smoothness in a nature way,and can be applied to general rotary cutters and complex surfaces.Numerical examples demonstrate that the third-order point contact approach can improve the machining strip width greatly as compared with the recently reported second-order one.展开更多
In this paper, the geometric properties of a pair of line contact surfaces are investigated. Then, based on the observation that the cutter envelope surface contacts with the cutter surface and design surface along th...In this paper, the geometric properties of a pair of line contact surfaces are investigated. Then, based on the observation that the cutter envelope surface contacts with the cutter surface and design surface along the characteristic curve and cutter contact (CC) path, respectively, a mathematical model describing the third-order approximation of the cutter envelope surface according to just one given cutter location (CL) is developed. It is shown that at the CC point both the normal curvature of the normal section of the cutter envelope surface and its derivative with respect to the arc length of the normal section can be determined by those of the cutter surface and design surface. This model characterizes the intrinsic relationship among the cutter surface, cutter envelope surface and design surface in the neighborhood of the CC point, and yields the mathematical foundation for optimally approximating the cutter envelope surface to the design surface by adjusting the cutter location.展开更多
Theoretical analysis and experimental measurement of the multiple dimples in thermal elastohydrodynamic lubrication (TEHL) point contacts have been carried out. Good agreement is found between the theoretical and expe...Theoretical analysis and experimental measurement of the multiple dimples in thermal elastohydrodynamic lubrication (TEHL) point contacts have been carried out. Good agreement is found between the theoretical and experimental results. A thermal multi-spike theory is proposed to explain the multi-dimple phenomena.展开更多
The numerical simulation of temperature distribution of point contacts in mixed lubrication is presented. The calculating includes two steps. First, temperature rises on two surfaces are obtained by a temperature inte...The numerical simulation of temperature distribution of point contacts in mixed lubrication is presented. The calculating includes two steps. First, temperature rises on two surfaces are obtained by a temperature integration method of transient point heat source. Second, the partition coefficients of heat flux are determined by matching the temperature of two surfaces. Similar to the calculation of elastic deformation, double linear interpolation function is used to get a better accuracy, and moving grid method is used to increase the efficiency of the computation. Due to the symmetry of influence coefficient matrix in the direction perpendicular to the velocity, storage and computational work are further reduced by 50%. Numerical samples validate the algorithm and program. The calculating results of the cases of smooth surface and isotropic sinusoidal surface are presented.展开更多
Micromagnetic simulation is employed to study the gyration motion of magnetic vortices in distinct permalloy nanodisks driven by a spin-polarized current. The critical current density for magnetic vortex gyration, eig...Micromagnetic simulation is employed to study the gyration motion of magnetic vortices in distinct permalloy nanodisks driven by a spin-polarized current. The critical current density for magnetic vortex gyration, eigenfrequency, trajectory, velocity and the time for a magnetic vortex to obtain the steady gyration are analyzed. Simulation results reveal that the magnetic vortices in larger and thinner nanodisks can achieve a lower-frequency gyration at a lower current density in a shorter time. However, the magnetic vortices in thicker nanodisks need a higher current density and longer time to attain steady gyration but with a higher eigenfrequency. We also find that the point-contact position exerts different influences on these parameters in different nanodisks, which contributes to the control of the magnetic vortex gyration. The conclusions of this paper can serve as a theoretical basis for designing nano-oscillators and microwave frequency modulators.展开更多
In this work,we discuss the origin of several anomalies present in the point-contact Andreev reflection spectra of（Li1-xFex）OHFeSe,LiTi2O4,and La2-xCexCuO4.While these features are similar to those stemming from int...In this work,we discuss the origin of several anomalies present in the point-contact Andreev reflection spectra of（Li1-xFex）OHFeSe,LiTi2O4,and La2-xCexCuO4.While these features are similar to those stemming from intrinsic superconducting properties,such as Andreev reflection,electron-boson coupling,multigap superconductivity,d-wave and p-wave pairing symmetry,they cannot be accounted for by the modified Blonder–Tinkham–Klapwijk（BTK） model,but require to consider critical current effects arising from the junction geometry.Our results point to the importance of tracking the evolution of the dips and peaks in the differential conductance as a function of the bias voltage,in order to correctly deduce the properties of the superconducting state.展开更多
基金supported by National Natural Science Foundation of China (Grant Nos. 51175032, U1134201)National Basic Research Program of China (973 Program, Grant No. 2011CD711104)
文摘The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.
基金supported by the National Natural Science Foundation of China(Grant Nos.11574372 and 11322432)the“Strategic Priority Research Program(B)”of the Chinese Academy of Sciences(Grant No.XDB07020300)
文摘Using scanning tunneling spectroscopy, we studied the transition from tunneling regime to local point contact on the iron-based superconductor Ba0.6K0.4Fe2As2. By gradually reducing the junction resistance, a series of spectra were obtained with the characteristics evolving from single-particle tunneling into Andreev reflection. The spectra can be well fitted to the modified Blonder–Tinkham–Klapwijk（BTK） model and exhibit significant changes of both spectral broadening and orbital selection due to the formation of point contact. The spatial resolution of the point contact was estimated to be several nanometers, providing a unique way to study the inhomogeneity of unconventional superconductors on such a scale.
基金supported by the Swedish Foundation for Strategic Research(SSF)
文摘This letter presents an analytical solution to the hydrodynamic lubrication of a circular point contact sliding over a flat surface with cavitation.The solution is found by solving the Reynolds equation with Reynolds boundary condition for cavitation.The cavitation boundary is shown to be straight lines directed 108.4°against the sliding direction.The result is experimentally verified in the limit of large values of viscosity,sliding velocity and radius of a spherical ball.The solution raises questions about the coupling between cavitation and film rupture and can be used as an independent check on the validity of numerical solutions.
基金Supported by the Basic Science Research Program through the National Research Foundation of Korea under Grant No 2011-0004949
文摘An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state of the device reached up to 7.5meV, probably due to the hard wall confinement by using shallow electron gas and sharp point contact geometry. The two-dimensionM non-equilibrium shot noise contour map shows noise suppression characteristics in a wide range of bias voltage. Fano factor analysis indicates spin-polarized transport through a short quantum point contact.
文摘Apart from usual quantization steps on the ballistic conductance of quasi-one-dimensional conductor, an additional plateau-like feature appears at a fraction of about 0.7 below the first conductance step in GaAs-based quantum point contacts (QPCs). Despite a tremendous amount of research on this anomalous feature, its origin remains still unclear. Here, a unique model of this anomaly is proposed relying on fundamental principles of quantum mechanics. It is noticed that just after opening a quasi-1D conducting channel in the QPC a single electron travels the channel at a time, and such electron can be—in principle—observed. The act of observation destroys superposition of spin states, in which the electron otherwise exists, and this suppresses their quantum interference. It is shown that then the QPC-conductance is reduced by a factor of 0.74. “Visibility” of electron is enhanced if the electron spends some time in the channel due to resonant transmission. Electron’s resonance can also explain an unusual temperature behavior of the anomaly as well as its recently discovered feature: oscillatory modulation as a function of the channel length and electrostatic potential. A recipe for experimental verification of the model is given.
基金supported by NSFC(51105131)Excellent Youth Foundation of Henan Scientific Committee(124100510002)Creative Talent Foundation in University of Henan Province(2011HASTIT016)
文摘Clearance not only affects the startup torque,rotation precision and stiffness of bearing,but also affects the load distribution,load-carrying capacity and life of bearing.A computational model in which the clearance of bearing is first included is presented for determining the contact force distribution and static load-carrying capacity of a double row four-point contact ball bearing which is subjected to the combined radial,axial and overturning moment loadings.The relation between the negative axial clearance and the contact force distribution is analyzed.The static load-carrying capacity curves are established,and the effects of the changes in negative axial clearance,curvature radius coefficient of raceway groove and initial contact angle on the static load-carrying capacity are analyzed.The results show that,with the increase in the absolute value of negative clearance,the maximum contact load decreases first and then increases.The clearance values in the range of 0.2 mme0 mm have little effect on the static load-carrying capacity of bearing.With the increase in the curvature radius coefficient of raceway groove and the decrease in the initial contact angle,the static load capacity of bearing decreases.
文摘The contact fatigue life of machine elements is affected by pitting, wear and so on, under heavier loading conditions. Increasing the fatigue life requires mainly the improvements of lubricating condition, operating condition and materials. In order to improve the lubricating condition, it is necessary to investigate the relation of the microscopic surface texturing and the contact modes of machine elements. In this paper, thus, the pressure and oil film thickness of the contact between sphere and the plate with 5 kinds surface texturing were calculated using a commercial software based on Reynolds equation. There was sufficient evidence to suggest that the dimple shape was the optimum texturing to increase the lubricating condition.
基金financial support from EPSRC,UK.the China Scholarship Council(CSC)for its financial support.
文摘Themass production and the practical number of cryogenic quantum devices producible in a single chip are limited to the number of electrical contact pads and wiring of the cryostat or dilution refrigerator.It is,therefore,beneficial to contrast themeasurements of hundreds of devices fabricated in a single chip in one cooldown process to promote the scalability,integrability,reliability,and reproducibility of quantum devices and to save evaluation time,cost and energy.Here,we used a cryogenic on-chip multiplexer architecture and investigated the statistics of the 0.7 anomaly observed on the first three plateaus of the quantized conductance of semiconductor quantum point contact(QPC)transistors.Our single chips contain 256 split gate field-effect QPC transistors(QFET)each,with two 16-branch multiplexed source-drain and gate pads,allowing individual transistors to be selected,addressed and controlled through an electrostatic gate voltage process.A total of 1280 quantum transistors with nano-scale dimensions are patterned in 5 different chips of GaAs heterostructures.From the measurements of 571 functioning QFETs taken at temperatures T[1.4 K and T[40 mK,it is found that the spontaneous polarisation model and Kondo effect do not fit our results.Furthermore,some of the features in our data largely agreed with van Hove model with short-range interactions.Our approach provides further insight into the quantum mechanical properties and microscopic origin of the 0.7 anomaly in QFETs,paving the way for the development of semiconducting quantum circuits and integrated cryogenic electronics,for scalable quantum logic control,readout,synthesis,and processing applications.
基金China National Railway Group Science and Technology Program(N2022J009)China Academy of Railway Sciences Group Co.,Ltd.Program(2021YJ036).
文摘Purpose-Under the high-speed operating conditions,the effects of wheelset elastic deformation on the wheel rail dynamic forces will become more notable compared to the low-speed condition.In order to meet different analysis requirements and selecting appropriate models to analyzing the wheel rail interaction,it is crucial to understand the influence of wheelset flexibility on the wheel-rail dynamics under different speeds and track excitations condition.Design/methodology/approach-The wheel rail contact points solving method and vehicle dynamics equations considering wheelset flexibility in the trajectory body coordinate system were investigated in this paper.As for the wheel-rail contact forces,which is a particular force element in vehicle multibody system,a method for calculating the Jacobian matrix of the wheel-rail contact force is proposed to better couple the wheel-rail contact force calculation with the vehicle dynamics response calculation.Based on the flexible wheelset modeling approach in this paper,two vehicle dynamic models considering the wheelset as both elastic and rigid bodies are established,two kinds of track excitations,namely normal measured track irregularities and short-wave irregularities are used,wheel-rail geometric contact characteristic and wheel-rail contact forces in both time and frequency domains are compared with the two models in order to study the influence of flexible wheelset rotation effect on wheel rail contact force.Findings-Under normal track irregularity excitations,the amplitudes of vertical,longitudinal and lateral forces computed by the flexible wheelset model are smaller than those of the rigid wheelset model,and the virtual penetration and equivalent contact patch are also slightly smaller.For the flexible wheelset model,the wheel rail longitudinal and lateral creepages will also decrease.The higher the vehicle speed,the larger the differences in wheel-rail forces computed by the flexible and rigid wheelset model.Under track short-wave irregularity excitations,the vertical force amplitude computed by the flexible wheelset is also smaller than that of the rigid wheelset.However,unlike the excitation case of measured track irregularity,under short-wave excitations,for the speed within the range of 200 to 350 km/h,the difference in the amplitude of the vertical force between the flexible and rigid wheelset models gradually decreases as the speed increase.This is partly due to the contribution of wheelset's elastic vibration under short-wave excitations.For low-frequency wheel-rail force analysis problems at speeds of 350 km/h and above,as well as high-frequency wheel-rail interaction analysis problems under various speed conditions,the flexible wheelset model will give results agrees better with the reality.Originality/value-This study provides reference for the modeling method of the flexible wheelset and the coupling method of wheel-rail contact force to the vehicle multibody dynamics system.Furthermore,by comparative research,the influence of wheelset flexibility and rotation on wheel-rail dynamic behavior are obtained,which is useful to the application scope of rigid and flexible wheelset models.
基金Acknowledgements This work was supported by the National Natural Science Foundation of China （Nos. 21503179, 21403181, 61573295, 21522508, 21673195, 21533006, and 61071010）, the National Basic Research Program of China （No. 2015CB932300）, the Natural Science Foundation of Fujian Province （No. 2016J05162）, the Fundamental Research Funds for the Central Universities in China （Xiamen University, Nos. 20720170035 and 20720160092）, and the Young Thousand Talent Project of China.
文摘In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.
基金This work is supported by the National Natural Science Foundation of China(Grant No.51772112,U1832116 and 51372094)Fundamental Research Funds for the Central Universities(HUST:2016YXZD058).
文摘Ag/Ta_(2)O_(5)/CuO/Pt memristive devices with Ag point contacts at the interface exhibit forming-free and partial volatile analog resistive switching properties.Versatile synaptic functions,like the short-term plasticity,the long-term potentiation and the paired-pulse facilitation,are emulated with these devices.The Ag point contacts in the Ta_(2)O_(5)layer are verified through transmission electron microscope(TEM)and X-ray photoelectron spectroscope(XPS).The Ag point contacts at the interface endow the device the transition from the electrochemical metallization mode to the valence change mode,and the analog resistive switching behavior and neuromorphic functions.This interface engineering of introducing point contacts at the interface provides a way for the development of neuromorphic devices with low power consumption.
基金This research was supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(Grant No.2019R1F1A1059712).
文摘The ride vibration of a tractor is affected mostly by the stiffness and damping coefficient of the seat suspension,cabin suspension,cabin rubber mounts,and rubber tires.However,in the case of rubber tractor tires,the stiffnesses and damping coefficients have not been researched adequately thus far,and it is not simple to measure these characteristics.In this study,a method for measuring and analyzing the stiffnesses and damping coefficients of rubber tractor tires,which were the input parameters for the tractor ride vibration simulation,was proposed.The cleat test,proposed in this study,did not require separate and complicated test equipment,unlike the conventional methods.The test was conducted simply by measuring acceleration under the driving conditions of the vehicle without detaching tires from the vehicle body or setting up additional test equipment.Based on the ground-vertical acceleration data obtained,the stiffness was calculated using the logarithmic decrement method,and the damping coefficient was calculated using least squares exponential curve fitting.The result of the cleat test indicated that the front tires had stiffnesses of 486.08-570.69 kN/m and damping coefficients of 4.02-4.52 kN·s/m;the rear tires had stiffnesses of 409.42-483.79 kN/m and damping coefficients of 2.21-2.67 kN·s/m.During the test,40 mm height cleats were installed on the track and the speed of the tractor was set to 7 and 10 km/h,which were the most common speeds during the operation.This study is meaningful in that it has presented a new method that improves the practicality of results,reduces cost,and simplifies the test process for measuring the stiffnesses and damping coefficients of rubber tractor tires.
基金supported by the National Natural Science Foundation of China(Grant Nos.50835004,50775147)the National Basic Research Program of China("973"Program)(Grant No.2005CB724103)the Science&Technology Commission of Shanghai Municipality(Grant No.07JC14028)
文摘Based on the mathematical model describing the third-order approximation of the cutter envelope surface according to one given cutter location(CL),a tool positioning strategy is proposed for efficiently machining free-form surfaces with non-ball-end cutters.The optimal CL is obtained by adjusting the inclination and tilt angles of the cutter until its envelope surface and the design surface have the third-order contact at the cutter contact(CC)point,which results in a wide machining strip.The strategy can handle the constraints of machine joint angle limits,global collision avoidance and tool path smoothness in a nature way,and can be applied to general rotary cutters and complex surfaces.Numerical examples demonstrate that the third-order point contact approach can improve the machining strip width greatly as compared with the recently reported second-order one.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50835004, 50775147)the National Basic Research Program of China ("973" Program) (Grant No. 2005CB724103)the Science & Technology Commission of Shanghai Municipality (Grant No. 07JC14028)
文摘In this paper, the geometric properties of a pair of line contact surfaces are investigated. Then, based on the observation that the cutter envelope surface contacts with the cutter surface and design surface along the characteristic curve and cutter contact (CC) path, respectively, a mathematical model describing the third-order approximation of the cutter envelope surface according to just one given cutter location (CL) is developed. It is shown that at the CC point both the normal curvature of the normal section of the cutter envelope surface and its derivative with respect to the arc length of the normal section can be determined by those of the cutter surface and design surface. This model characterizes the intrinsic relationship among the cutter surface, cutter envelope surface and design surface in the neighborhood of the CC point, and yields the mathematical foundation for optimally approximating the cutter envelope surface to the design surface by adjusting the cutter location.
基金This work was supported partly by the Visiting Scholar Foundation of the Laboratories ofColleges Universities of the Ministry of Education+1 种基金 People's Republic of China partly by the Satellite Venture Business Laboratory of Kyushu Institute of Tech
文摘Theoretical analysis and experimental measurement of the multiple dimples in thermal elastohydrodynamic lubrication (TEHL) point contacts have been carried out. Good agreement is found between the theoretical and experimental results. A thermal multi-spike theory is proposed to explain the multi-dimple phenomena.
文摘The numerical simulation of temperature distribution of point contacts in mixed lubrication is presented. The calculating includes two steps. First, temperature rises on two surfaces are obtained by a temperature integration method of transient point heat source. Second, the partition coefficients of heat flux are determined by matching the temperature of two surfaces. Similar to the calculation of elastic deformation, double linear interpolation function is used to get a better accuracy, and moving grid method is used to increase the efficiency of the computation. Due to the symmetry of influence coefficient matrix in the direction perpendicular to the velocity, storage and computational work are further reduced by 50%. Numerical samples validate the algorithm and program. The calculating results of the cases of smooth surface and isotropic sinusoidal surface are presented.
基金Project supported by the Thirteenth Five-Year Program for Science and Technology of Education Department of Jilin Province,China(Grant No.JJKH20191007KJ)the Program for Development of Science and Technology of Siping City,China(Grant No.2016063)
文摘Micromagnetic simulation is employed to study the gyration motion of magnetic vortices in distinct permalloy nanodisks driven by a spin-polarized current. The critical current density for magnetic vortex gyration, eigenfrequency, trajectory, velocity and the time for a magnetic vortex to obtain the steady gyration are analyzed. Simulation results reveal that the magnetic vortices in larger and thinner nanodisks can achieve a lower-frequency gyration at a lower current density in a shorter time. However, the magnetic vortices in thicker nanodisks need a higher current density and longer time to attain steady gyration but with a higher eigenfrequency. We also find that the point-contact position exerts different influences on these parameters in different nanodisks, which contributes to the control of the magnetic vortex gyration. The conclusions of this paper can serve as a theoretical basis for designing nano-oscillators and microwave frequency modulators.
基金Project supported by the National Key Basic Research Program of China(Grant Nos.2015CB921000,2016YFA0300301,and 2017YFA0302902)the National Natural Science Foundation of China(Grant Nos.11674374 and 1474338)+5 种基金the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant No.QYZDB-SSW-SLH008)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB07020100 and XDB07030200)the Beijing Municipal Science and Technology Project(Grant No.Z161100002116011)the Fonds de la Recherche Scientifique–FNRS and the ARC Grant 13/18-08 for Concerted Research Actions,financed by the French Community of Belgium(Wallonia-Brussels Federation)Jérémy Brisbois acknowledges the support from F.R.S.–FNRS(Research Fellowship)The work of Alejandro V Silhanek is partially supported by PDR T.0106.16 of the F.R.S.–FNRS
文摘In this work,we discuss the origin of several anomalies present in the point-contact Andreev reflection spectra of（Li1-xFex）OHFeSe,LiTi2O4,and La2-xCexCuO4.While these features are similar to those stemming from intrinsic superconducting properties,such as Andreev reflection,electron-boson coupling,multigap superconductivity,d-wave and p-wave pairing symmetry,they cannot be accounted for by the modified Blonder–Tinkham–Klapwijk（BTK） model,but require to consider critical current effects arising from the junction geometry.Our results point to the importance of tracking the evolution of the dips and peaks in the differential conductance as a function of the bias voltage,in order to correctly deduce the properties of the superconducting state.
