High-density triple-phase contact points for enhanced photocatalytic CO_(2) reduction to methanol

The efficiency of photocatalytic CO_(2) reduction reaction(PCRR)is restricted by the low solubility and mobility of CO_(2) in water,poor CO_(2) adsorption capacity of catalyst,and competition with hydrogen evolution reaction(HER).Recently,hydrophobic modification of the catalyst surface has been proposed as a potential solution to induce the formation of triple-phase contact points(TPCPs)of CO_(2)(gas phase),H_(2) O(liquid phase),and catalysts(solid phase)near the surface of the catalyst,enabling direct delivery of highly concentrated CO_(2) molecules to the active reaction sites,resulting in higher CO_(2) and lower H+surface concentrations.The TPCPs thus act as the ideal reaction points with enhanced PCRR and suppressed HER.However,the initial synthesis of triple-phase photocatalysts tends to possess a lower bulk density of TPCPs due to the simple structure leading to limited active points and CO_(2) adsorption sites.Here,based on constructing a hydrophobic hierarchical porous TiO_(2)(o-HPT)with interconnected macropores and mesopores structure,we have significantly increased the density of TPCPs in a unit volume of the photocatalyst.Compared with hydrophobic macroporous TiO_(2)(o-MacPT)or mesoporous TiO_(2)(o-MesPT),the o-HPT with increased TPCP density leads to enhanced photoactivity,enabling a high methanol production rate with 1111.5μmol g^(−1) h^(−1) from PCRR.These results emphasize the significance of high-density TPCPs design and propose a potential path for developing efficient PCRR systems.

Research on the influence of flexible wheelset rotation effect on wheel rail contact force

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.

A Novel Method of Nanocontact Fabrication for Andreev Reflection Measurement

A new method of nanocontact fabrication for Adreev reflection measurement based on the nanopore method using a SiN membrane with focused ion beam technique is presented. With this method, controllable, clean,tensionless nano-contacts for spin polarization probing can be obtained. Measurements of the fabricated samples show complicated spectral structures with a zero bias anomaly and dip structures from quasipartical interactions. A control sample of Co40Fe40B20 is measured with Nb tip method. None of the measured spectra can be explained satisfactorily by present theory. Further analysis of the contact interface and a more complete theory are needed to extract a reliable spin polarization message with the point contact Andreev reflection method.

Multi-point Contact of the High-speed Vehicle-turnout System Dynamics

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.

Transition from tunneling regime to local point contact realized on Ba0.6K0.4Fe2As2 surface

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.

ANALYSIS OF THE SINGULARITY FOR THE VERTICAL CONTACT PROBLEM OF LINE CRACK-INCLUSION

Taking the short-fiber composite materials as engineering back-ground, utilizing the existing basic solutions of single inclusion and single crack, the plane problem of vertical contact interactions between line crack and rigid line inclusion in infinite plane (matrix) from the viewpoint of crack fracture mechanics is studied. According to boundary conditions, a set of standard Cauchy-type singular integral equations of the problem is obtainable. Besides, singular indexes, stresses and stress intensity factors around the contact point are expressed. Numerical examples are given to provide references to engineering.

A solution to the hydrodynamic lubrication of a circular point contact sliding over a flat surface with cavitation

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.

Shot Noise Suppression in a Quantum Point Contact with Short Channel Length

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.

The 0.7-Anomaly in Quantum Point Contact;Many-Body or Single-Electron Effect?

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.

Nonlinear Properties of an Inhomogeneous Diode Structure in a Strong Microwave Field

Results of experimental investigation of detection (rectification) of high power X-band microwave signal in diodes of various design (semiconductor p-n-junction, point-contact, Schottky, Metal-Isolator-Metal—MIM) are reported. The maximum of the detected direct voltage V vs. power P of microwave signal and subsequent polarity reversal, previously found in MIM diodes in the optical and microwave bands, have found to be characteristic of all investigated diodes as well. After the reversal of polarity, this dependence comes linear, and the sign of the voltage corresponds to thermoEMF. In some diodes, the hysteresis on V(P) was observed. All 5 types of V(P) of MIM diodes (have made from different pairs of metals), reported earlier, were reproduced on same p-n-junction diode by variable external DC bias. These results joined with abnormal frequency cutoff forced to suggest that there is an unknown mechanism for direct flow of charge carriers (and for generate direct current) in the high-frequency electrical field, which differs from the conventional rectification.

Statistical evaluation of 571 GaAs quantum point contact transistors showing the 0.7 anomaly in quantized conductance using cryogenic on-chip multiplexing

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.

Modeling Method for Assembly Variation Propagation Taking Account of Form Error

The propagation of variations, such as fixture errors and datum errors resulting from assembly and machining processes, has been extensively studied. However, only a few studies that focus on form error propagation in assembly systems have been implemented. Machining errors, especially form errors, have great impact on assembly accuracy and accuracy stability of precision mechanical systems. With form errors being the research object, a method for calculating mating variation and specifying mating coordinate is proposed to improve the accuracy of the variation propagation model. Taking into account the form error of mating surfaces, the assembly variation propagation of a precision mechanical system is analyzed, and the brief derivation procedure of the variation propagation model is introduced afterwards. The variation propagation model involves a new concept of mating variation specified by the two mating surfaces. An innovative method, the difference surface search based method, is proposed to calculate the mating variation amongst the mating surfaces. The obtained mating variation is then utilized to specify the mating coordinate in the variation propagation model. Moreover, FEM is employed to simulate the contact state of the two mating surfaces to demonstrate effectiveness of the proposed method. Meanwhile, the mating variation and mating coordinate obtained are incorporated into the assembly variation propagation model, which is then verified by a following case study through a comparison between the calculated results and the experimental results. The comparing results indicate that the established model improves the prediction of assembly accuracy. The developed model enables the investigation of various fundamental issues in variation reduction, including variation analysis, process monitoring, accuracy prediction, and accuracy control.

Enabling Extraordinary Rate Performance for Poorly Conductive Oxide Pseudocapacitors

Pseudocapacitive transition metal oxides(PTMOs)have the advantages of high areal capacitance and material density suitable for high-energy supercapacitor devices,but they are typically marred by insufficient rate performance,which in turn deteriorates cyclic stability at high current levels.Using the example of spinel manganese oxide,herein we demonstrate that a pseudocapacitive oxide electrode of remarkable rate performance and cyclic stability may be realized by adopting oxide nanocrystallites,which are derived based on a novel solution chemistry,and carbon additive(CA)nanoparticles with highly uniform of size distributions.Precisely controlling the particle morphology and size distribution of the active material and conductive additive(CA)in the nanometer range can maximize the density of active material-CA-electrolyte three-phase contact points,thus facilitating synchronized electron and cation flow for the completion of surface faradaic reactions.The resultant Mn3O4 pseudocapacitive electrode exhibits rate capability and cycle stability,including 60%capacity retention at 60 A g-1 and no capacity fade over 100000 cycles under dynamic current densities,far superior to the state-of-the-art PTMO electrodes.The electrode design strategy is in general applicable to pseudocapacitors containing poorly conductive active materials.

A grasp planning algorithm under uneven contact point distribution scenario for space non-cooperative target capture

The contact point configuration should be carefully chosen to ensure a stable capture,especially for the non-cooperative target capture mission using multi-armed spacecraft.In this work scenario,the contact points on the base and on the arms are distributed on the opposite side of the target.Otherwise,large forces will be needed.To cope with this problem,an uneven-oriented distribution union criterion is proposed.The union criterion contains a virtual symmetrical criterion and a geometry criterion.The virtual symmetrical contact point criterion is derived from the proof of the force closure principle using computational geometry to ensure a stable grasp,and the geometry criterion is calculated by the volume of the minimum polyhedron formed by the contact points to get a wide-range distribution.To further accelerate the optimization rate and enhance the global search ability,a line array modeling method and a continuous-discrete global search algorithm are proposed.The line array modeling method reduces the workload of calculating the descent direction and the gradient available,while the continuous-discrete global search algorithm reducing the optimization dimension.Then a highly efficient grasping is achieved and the corresponding contact point is calculated.Finally,an exhaustive verification is conducted to numerically analyze the disturbance resistance ability,and simulation results demonstrate the effectiveness of the proposed algorithms.

Research on Adjust Time of Premium

By considering economic strength and economic profit of insurance company, this paper presents a concept-contact point, and gives premium expectation adjust-time model which provides more practical significance for insurance company to make rational adjustment of premium. Finally, an illustration is given to show their application.

The Motion of a Sphere with Weak Nutation on a Rough Horizontal Plane

For the motion of a sphere on a rough horizontal plane, in the previous paper[1]the author aimed at providing approximate analytical solutions while the nutation is neglected,In this paper ,the control equations for the sphere with nutation have beendeduced on the basis of paper [1]. Through the medium of solving these equations,the conclusion for the velocity of contact point in paper [1]is still proved true for the case with nutation.What is more ,some interesting results are gained ,for example the ve-locity of centre and contact point is relative to the angular velocity of spin and nuta-tion the direction of velocity of centre and contact point is constant.Under the condi-tion which is supposed to be weak nutation,the approximate analytical solutions are obtained,so that the results of paper [1]is proved to be true.

Promising electroplating solution for facile fabrication of Cu quantum point contacts

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.

Forming-free artificial synapses with Ag point contacts at interface

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.

Investigation of point-contact Andreev reflection on magnetic Weyl semimetal Co3Sn2S2

Magnetic Weyl semimetals(WSMs)with broken time-reversal symmetry(TRS)hosting topological band structures are expected to provide an ideal platform for investigating topological superconductivity and spintronics.However,the experimental verification of magnetic WSMs is very challenging.Very recently,the kagome magnet Co3Sn2S2 was confirmed to be a magnetic WSM by both angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy and consequently has become the focus of great attention.This paper reports a point-contact Andreev-reflection spectroscopy(PCARS)investigation on the(001)surface and the side surface of the Co3Sn2S2 single crystals,respectively.The measurements from the sample’s(001)and side surfaces provide experimental evidence for transport spin polarization in the Co3Sn2S2 magnetic WSM.Furthermore,the superconducting proximity effect in the Co3Sn2S2 single crystal is successfully detected.The point-contact spectra(PCS)along the in-plane direction cannot be well fitted by theoretical models based on s-wave pairing,indicating that possible triplet p-wave superconductivity may be triggered at the interface,which paves the way for the future exploration of the topological superconductivity and Majorana states in broken TRS WSMs.

Direct observation of the impact of water droplets on oil replenishment in EHD lubricated contacts

Water is one of the most significant causes of lubrication failure.There is little research on the direct observation of the impact of water on lubrication properties.In this study,the influence of water on oil replenishment under different elastohydrodynamic(EHD)lubricating conditions is evaluated using optical interferometry and infrared microscopy,and a dimensionless criterion when water influences the film thickness is proposed.Evidence shows that the scour displacing effect and emulsification of water/oil are the main reasons for the reduction in film thickness.Once a water droplet enters an oil reservoir around the critical contact zone,it hardly moves away.This aggravates starvation,reduces the center film thickness of the contact,and leads to lubrication failure of the mechanical components.