Contact Configuration Research Articles

Decoupling activation volume via dynamic electron transfer in stress-driven chemical reactions

The activation volume, which quantifies the response of the chemical reactions to the applied stress, plays a central role in controlling the mechanochemical reactions for applications including lubricity, wear, and the topographic fabrication of the surfaces under stress. However, the physical interpretations of the activation volume remain scientifically intriguing and largely unexplored. Here, density functional theory calculations are used to investigate the general rules of charge transfer underlying activation volume in controlling the typically mechanochemical reaction process. It is found that the activation volume could be decoupled into the electronic contributions from interface chemistry and bulk physical deformation, which are commonly linear dependent on the contact pressure. Therefore, the activation volume may, indeed, be derived from the stress-driven charge transfer underlying cooperative competition between interfacial chemistry and the bulk region. This competition is related to the stiffness change from the bulk to slab. The magnitude of the stiffness change represents the degree to which the interface atoms modify the bulk properties, which is directly related to the contribution of different regions to the activation volume. This work may open up the understanding of the activation volume from dynamic electron transfer to engineer mechanochemical reactions, different from the existing insights into the geometric dimensionality of the contact configuration.

An Approach to Measure Slips in Friction Contacts Using a Self-Powered Sensor

The accumulation of small tangential slip will occur on the contact surfaces of components in mechanical structures when subjected to cyclic loadings, which will lead to system failure. However, the small tangential slip is difficult to measure directly. In this paper, a method for measuring the contact slip by using a self-powered displacement sensor based on triboelectric nanogenerator (TENG) is proposed, and the accuracy is verified by the finite element analysis (FEA). The contact slips for a flat-on-flat contact configuration are measured by this method. When the test piece is subjected to a cyclic tangential load with a frequency of 10Hz, the average obtained slip displacement of the test piece under single load cycle is less than 10μm. Then the finite element simulation of the contact configuration is carried out using software Abaqus 6.14. The analysis results are close to the test results, which verifies the effectiveness of the measurement method. Moreover, the slips of the flat-on-flat contact configuration under different frequency and amplitude of cyclic tangential load are investigated.

Towards the superlubricity of polymer–steel interfaces with ionic liquids and carbon nanotubes

Frictional losses are responsible for significant energy waste in many practical applications, and superlubricity with a coefficient of friction lower than 0.01 is the goal of tribologists. In this paper, metal-on-polymer contact was analysed and close to superlubricity conditions for this material configuration were explored. A new lubricant has been proposed hinge on the phosphorus-based ionic liquid and carbon nanotubes as thickeners. Additionally, carbon nanotube mesh was doped with copper nanoparticles that allowed for the close to superlubricity state in a mild steel/polymer contact configuration under low normal load conditions. The adsorption of phosphorus onto metallic and polymer surfaces has been reported in EDS analysis. The formulation of the new lubricant allowed for stable dispersion with a carbon nanotube content as low as 0.1% wt. The carbon nanotubes and Cu nanoparticles have been analysed using TEM and SEM imaging. A tribological test in a block-on-ring system has been carried out. The wear of material, topography, and surface free energy have been analysed along with SEM/EDS images to explore the underlying mechanisms of friction and wear.

Vertical PtOx/Pt/ β -Ga2O3 Schottky diodes with high permittivity dielectric field plate for low leakage and high breakdown voltage

We demonstrate Schottky barrier engineering using PtOx/thin Pt Schottky contacts combined with edge termination using a high permittivity dielectric (ZrO2) field-plate for high-voltage vertical β-Ga2O3 diodes. A systematic study of baseline bare Pt/β-Ga2O3, PtOx/thin Pt/β-Ga2O3, and PtOx/β-Ga2O3 Schottky diode characteristics was performed, which revealed that the PtOx/thin Pt/β-Ga2O3 contact can combine the advantages of both PtOx and Pt, allowing better reverse blocking performance than plain metal Pt/β-Ga2O3 Schottky diodes and lower turn-on voltage than plain oxidized metal PtOx/β-Ga2O3 ones. Moreover, the thin Pt interlayer in the PtOx/thin Pt/β-Ga2O3 anode contact configuration, deposited by e-beam deposition, also provides plasma-free interface at the Schottky junction as opposed to the direct sputter deposited PtOx contacts of the PtOx/β-Ga2O3 diodes. We further implemented a high permittivity dielectric (ZrO2) field plate in PtOx/thin Pt/β-Ga2O3 diodes that assisted in edge-field management and enabled a breakdown voltage to ∼2.34 kV. These results indicate that the PtOx/thin Pt/β-Ga2O3 Schottky contact, combined with a high permittivity field-plate, will be promising to enable Schottky barrier engineering for high-performance and efficient vertical β-Ga2O3 power switches.

Face-to-face conducting mechanism enabled by Si-C bonds for binder free Si@CNTs electrode

The three-dimensional conductive network has been developed, creating a continuous pathway for Si anodes. Nonetheless, the weak physical contact between Si particles and the conducting network is prone to separation due to expansion stress and the solid electrolyte interface. This results in a rapid decline in cell cycling performance. Herein, we have developed a binder free Si@CNTs fibrous thin film structure using carbon nanotube (CNT) conducting networks through a high vacuum magnetic sputtering process of molecular reorganization. With Fourier Transform Infrared (FTIR), X-ray Photoelectron Spectroscopy (XPS) tests and density functional theory (DFT) calculations, we propose a strong “face-to-face” contact configuration based on Si-C bonds. The Si@CNTs film demonstrated stable mechanical and electrical properties even after repeated bending and stretching of up to 6%. In-situ transmission electron microscopy confirmed that the initial cycling volume expansion of the Si@CNTs fibers with Si-C bonds was only 58.33%. Furthermore, the full cell using Si@CNTs anode enabled stable high-rate cycling performance at 6C after 500 cycles. This innovative strategy redefines the conductive mode of CNTs with Si anodes.

EEG-based biomarkers for optimizing deep brain stimulation contact configuration in Parkinson's disease.

Subthalamic deep brain stimulation (STN-DBS) is a neurosurgical therapy to treat Parkinson's disease (PD). Optimal therapeutic outcomes are not achieved in all patients due to increased DBS technological complexity; programming time constraints; and delayed clinical response of some symptoms. To streamline the programming process, biomarkers could be used to accurately predict the most effective stimulation configuration. Therefore, we investigated if DBS-evoked potentials (EPs) combined with imaging to perform prediction analyses could predict the best contact configuration. In 10 patients, EPs were recorded in response to stimulation at 10 Hz for 50 s on each DBS-contact. In two patients, we recorded from both hemispheres, resulting in recordings from a total of 12 hemispheres. A monopolar review was performed by stimulating on each contact and measuring the therapeutic window. CT and MRI data were collected. Prediction models were created to assess how well the EPs and imaging could predict the best contact configuration. EPs at 3 ms and at 10 ms were recorded. The prediction models showed that EPs can be combined with imaging data to predict the best contact configuration and hence, significantly outperformed random contact selection during a monopolar review. EPs can predict the best contact configuration. Ultimately, these prediction tools could be implemented into daily practice to ease the DBS programming of PD patients.

Study on the fretting wear behaviour of AZ91/BLA MMCs and the implications that BLA has on that behaviour

The core objective of this research is to develop an eco-friendly and cost-efficient engineering material termed “green composites.” These composites utilize waste bamboo leaf ash as a reinforcing element. Incorporating bamboo leaf ash into these composites offers several advantages due to its affordability, wide availability, and the presence of essential chemical compounds such as SiO2, CaO, TiO2, Al2O3, and others. Consequently, this investigation also examines the impact of bamboo leaf ash enriched with silica (referred to as BLA) on the fretting wear behaviour of Mg/BLA green composites. To create these composites, a bottom pouring stir casting setup was employed, with varying concentrations of BLA (1 wt% and 2 wt%) and reinforcement particles sized between 50 and 75 µm. The resulting cast products underwent machining in accordance with established testing standards and were subsequently polished using emery paper. These prepared samples were then subjected to testing in a fretting wear setup, utilizing a ball-on-flat contact configuration. The worn surfaces were thoroughly examined under a microscope, and data on the coefficient of friction were collected from the machine interface. The inclusion of BLA in the green composite enhanced the load-bearing capacity of the composite. Additionally, elements like CaO present in BLA acted as self-lubricating materials, resulting in a 21% reduction in the coefficient of friction and a 22% reduction in wear loss compared to the base alloy. The analysis of worn surfaces suggested that adhesive wear followed by oxidative and abrasive wear, were the predominant wear mechanisms in these green composites. Such environmentally-friendly materials with improved wear resistance properties have potential applications in situations prone to fretting wear.

A Simple Method to Measure the Contact Angle of Metal Droplets on Graphite

The determination of solid–liquid interfacial tension plays an important role in science and technology. Here, we propose a simple method to directly measure the contact angle between metal droplets and a graphite substrate for the determination of metal–graphite interfacial tension. The proposed method involves the synthesis of micro- and nanosized metal droplets on graphite by arc melting. Owing to its small volume, the rapid cooling of the prepared metal droplets on the graphite substrate leads to the freezing of equilibrium contact configuration after solidification. We observe that the measured contact angle between micro- and nanosized Au (or Ag) particles and the graphite substrate is almost size independent, even though the size of the particles synthesized herein is 1–3 orders of magnitude smaller than that studied in previous works. In addition, the interfacial tensions of Au and Ag on the step edges (edge plane) of graphite are found to be larger than that on the (0001) plane (basal plane). The proposed method provides a simple approach to determine the solid–liquid interfacial tension and may be effective in the study of interface related science and technology.

MSW pyro-gasification using high-temperature CO2 as gasifying agent: Influence of contact mode between CO2, char and volatiles on final products

The volatiles and char derived from municipal solid waste (MSW) pyrolysis can be catalytically reformed and gasified using high-temperature CO2 (HT-CO2) as gasifying agent and char as a catalyst simultaneously to obtain high quality synthesis gas, but the reactor's design for this purpose is still a question. In this research, the contact configuration between the HT-CO2, the volatile compounds, and the char from MSW pyrolysis were studied to understand the relevant reaction behaviors and to establish guidelines for the reactor’s design. Three contact modes were designed, including: M1, where volatiles and HT-CO2 contact first, then contact the char; M2, where volatiles, CO2, and char contact simultaneously at the bottom of the char layer; and M3, where CO2 contacts with the char first, then the volatiles contact in the middle of the char layer. The temperature evolution in the char layer, the yields and properties of the resultant combustible gases, used char, and tar were investigated. Experimental results revealed that the contact mode significantly affected the levels of char gasification and volatiles' reforming. For M1, intense thermal cracking of volatiles occurred and 65.41% of the input heat of HT-CO2 was consumed for thermal cracking, resulting in substantial carbon deposition and limited energy transfer from char to the synthesis gas. While, the char contacting HT-CO2 firstly in M3 improved its catalytic activity, causing 73.33 % of the input heat utilized for gasification and reforming; as a result, the maximum synthesis gas yield of 0.71 Nm3/kgMSW and gas energy ratio of 76.3 % were obtained respectively in M3 with the lowest tar yield of 5.45 %; additionally, the used char corresponded to the highest specific surface area of 10.12 m2/g. Ultimately, M3 is constructive and recommended, and the findings of this study offer helpful guidance for the design of pyro-gasification reactors.

Implicit and explicit schemes for energy-stable simulation of string vibrations with collisions: Refinement, analysis, and comparison

Collisions play an important role in the sound production mechanism of musical string instruments. Impactive contact modelling must therefore be incorporated in energy-stable time-stepping schemes for simulation and sound synthesis. Recently, explicit and linearly implicit schemes based on energy quadratisation have emerged as a means of numerical modelling of nonlinear string vibrations that avoids the need for iterative solvers, which significantly enhances the applicability to real-time sound synthesis. However when applied to modelling collisions, spurious oscillations and artefacts have been reported, which can be linked to the one-sided nature of the contact force. To investigate whether and how these limitations can be avoided, this paper proposes refined numerical scheme variants for both lumped and distributed contact configurations, and assesses their accuracy and efficiency. For reference, two nonlinearly implicit schemes are also included in the comparisons. Guaranteed correctness of the sign of the numerical contact force is proven for several of the scheme variants. Numerical experiments across three case studies indicate that each of the proposed schemes converges towards the exact solution, and that for sufficiently small time steps, explicit schemes generally perform well compared to implicit schemes.

Assessment of the Factors Influencing the Recording Performance of Circumneural Electrodes.

The quality of recorded peripheral nerve signals is decisive for their application in therapies. The electroneurogram can be recorded via implantable circumeural electrodes that are wrapped around the peripheral nerve. The shape and amplitude of the signal recorded by the electrode are influenced by the design and contact configuration of the electrode. In this paper, the impact of the number of contacts, contact size and electrical insulation to the outside is investigated to predict the single fiber action potential based on the measured impedance data.

HAp-Ti-6Al-4V Interface Fretting Wear Failure Prediction in Different Bio-lubricants using FEM

Plasma-sprayed hydroxyapatite (HAp) coated titanium alloy (Ti-6Al-4V) has been widely used as the material for artificial hip implants. However, studies have greatly challenged their long-time usage due to fretting wear behavior at the HAp-Ti-6Al-4V interface. Wear particles from the HAp coating may activate inflammation at surrounding organs, further leading to implant loosening, implant failures and even total hip replacement (THR) revision surgeries. Hence, present research aims to adopt the finite element methodology (FEM) in predicting fretting wear failure at the HAp-Ti-6Al-4V interface of uncemented hip implant femoral stem component under different body environments (bio-lubricants). A finite element (FE) model based on the half-cylinder on flat contact configuration subjected to actual mechanical and tribological properties under different bio-lubricants is developed with the modified Archard wear equation adopted to examine the fretting wear behavior through simulations. A parametric study is then conducted to evaluate the combined effects of different mechanical and tribological properties, including HAp coating thickness, bone elastic modulus and loading condition, under different bio-lubricants on the fretting wear behavior of HAp-Ti-6Al-4V interface. Lastly, single and multiple regression analyses are performed to formulate fretting wear predictive equation that acts as a fast-fretting wear failure prediction tool. The FE predicted results in this paper prove that the maximum wear depth at HAp-Ti-6Al-4V interface is promoted under lower coefficient of friction (COF), smaller HAp coating thickness, smaller bone elastic modulus and larger intensity of fatigue loading. The formulated predictive equations suggest a strong correlation between independent and dependent variables due to R-squared (R2) values being larger than 0.75 which guarantee goodness of fit.

Hydrogenated amorphous silicon high flux x-ray detectors for synchrotron microbeam radiation therapy

Objective. Microbeam radiation therapy (MRT) is an alternative emerging radiotherapy treatment modality which has demonstrated effective radioresistant tumour control while sparing surrounding healthy tissue in preclinical trials. This apparent selectivity is achieved through MRT combining ultra-high dose rates with micron-scale spatial fractionation of the delivered x-ray treatment field. Quality assurance dosimetry for MRT must therefore overcome a significant challenge, as detectors require both a high dynamic range and a high spatial resolution to perform accurately. Approach. In this work, a series of radiation hard a-Si:H diodes, with different thicknesses and carrier selective contact configurations, have been characterised for x-ray dosimetry and real-time beam monitoring applications in extremely high flux beamlines utilised for MRT at the Australian Synchrotron. Results. These devices displayed superior radiation hardness under constant high dose-rate irradiations on the order of 6000 Gy s−1, with a variation in response of 10% over a delivered dose range of approximately 600 kGy. Dose linearity of each detector to x-rays with a peak energy of 117 keV is reported, with sensitivities ranging from (2.74 ± 0.02) nC/Gy to (4.96 ± 0.02) nC/Gy. For detectors with 0.8 μm thick active a-Si:H layer, their operation in an edge-on orientation allows for the reconstruction of micron-size beam profiles (microbeams). The microbeams, with a nominal full-width-half-max of 50 μm and a peak-to-peak separation of 400 μm, were reconstructed with extreme accuracy. The full-width-half-max was observed as 55 ± 1 μm. Evaluation of the peak-to-valley dose ratio and dose-rate dependence of the devices, as well as an x-ray induced charge (XBIC) map of a single pixel is also reported. Significance. These devices based on novel a-Si:H technology possess a unique combination of accurate dosimetric performance and radiation resistance, making them an ideal candidate for x-ray dosimetry in high dose-rate environments such as FLASH and MRT.

DEM modeling direct shearing behavior of sand considering anti-rotation of particle

Considering anti-rotation of sand particles, two-dimensional Discrete Element Method (DEM) has been employed to reproduce direct shear behaviors of sand with different particle distribution sizes, so as to explore effects of anti-rotation of particle on responses of stress-displacement and dilatancy, the evolution law of shear stress, coordination number and vertical displacement of sand samples, and analyze the contact force chain, contact fabric and porosity of the samples after shearing.The results show that the anti-rotation ability of sand is enhanced, the torque of overcoming the relative rotation between particles is increased, and the peak shear stress, dilatancy and porosity in the middle of the sample are increased; with the increase of the anti-rotation coefficient, the coordination number decreases more obviously. The proportion of the contact number in the direction of 100°–160° to the total contact number decreases with the increase of the anti-rotation coefficient. The elliptical shape of the contact configuration becomes more flat, and the anisotropy of the contact force chain is more obvious; compared with fine sand, the coarse sand has greater shear capacity, more obvious dilatancy and larger porosity in the middle of the sample.The maximum minimum particle size ratio of the sample becomes larger, so that the shear strength of the sample is reduced, and the dilatancy is also weak.

Optimum Contact Configurations for Quasi-One-Dimensional Phosphorene Nanodevices.

We employ atomistic quantum transport simulations based on non-equilibrium Green's function (NEGF) formalism of quasi-one-dimensional (quasi-1D) phosphorene, or phosphorene nanoribbons (PNRs), to explore routes towards minimizing contact resistance (RC) in devices based on such nanostructures. The impact of PNR width scaling from ~5.5 nm down to ~0.5 nm, different hybrid edge-and-top metal contact configurations, and various metal-channel interaction strengths on the transfer length and RC is studied in detail. We demonstrate that optimum metals and top-contact lengths exist and depend on PNR width, which is a consequence of resonant transport and broadening effects. We find that moderately interacting metals and nearly edge contacts are optimum only for wider PNRs and phosphorene, providing a minimum RC of ~280 Ωμm. Surprisingly, ultra-narrow PNRs benefit from weakly interacting metals combined with long top contacts that lead to an added RC of only ~2 Ωμm in the 0.49 nm wide quasi-1D phosphorene nanodevice.

Friction in Adhesive Contacts: Experiment and Simulation

An experimental study of the process of friction between a steel spherical indenter and a soft elastic elastomer, with a strongly pronounced adhesive interaction between the surfaces of the contacting bodies, is presented. We consider sliding of the indenter at low speed (quasi-static contact) for different indentation depths. The forces, displacements and contact configuration as functions of time were recorded. The most important finding is that under conditions of uni-lateral continuous sliding, the tangential stress in the contact area remains constant and independent on the indentation depth and details of loading. We suggest a simple numerical model in which the elastic substrate is considered as a simple elastic layer (thus reminding a two-dimensional elastic foundation), although with in-plane elastic interactions. It is found that this model leads to the dynamic scenarios which qualitatively resemble the experimentally observed behavior of the considered system.

Multi-scale optical simulation of crystalline silicon solar cells by combining ray and wave optics.

Optical simulations allow the evaluation of the absorption, reflection, and transmission of each functional layer of solar cells and, therefore, are of great importance for the design of high-efficiency crystalline silicon (c-Si) solar cells. Here, a multi-scale simulation method (MSM) based on ray and wave optics is proposed to investigate the optical characteristics of c-Si solar cells. The ray and wave optical methods are first independently employed on inverted pyramid glass sheets, where the latter one can describe the size-dependent interfacial scattering characteristics more accurately. Then the optical properties of a c-Si solar cell with a tunnel oxide passivated carrier-selective contact configuration are studied by employing the MSM, where scattering at the interfaces is acquired by a finite-difference time-domain method (wave optics). Since the MSM can accurately simulate optical modes such as the Rayleigh anomaly, Bloch mode, and Mie resonances, the reflection and transmission spectra of the whole device are in good agreement with the measured data. The proposed MSM has proven to be accurate for structures with functional thin films, which can be extended to hybrid tandem devices with top-level cells consisting of stacks of layers with similar dimensions.

SOCIAL DISTANCE AND VIETNAMESE TRADITIONAL ART DECORATION

The goal of this analysis is to apply the Systemic Functional Linguistics theory (SFL) to analyze social distance and visual sign in the context of Vietnamese art decoration. Based on the concept of social semiotics, social distance between interactants in this analysis is analyzed through a register description of tenor system within the context of situation. From a social point of view, this analysis applies the five lines of human thought based on Bogardus divided into motivational relevancies, including (i) human life, (ii) the natural world, (iii) mythology, (iv) philosophy, (v) religion, and (vi) culture and tradition, to describe the relationship between context of situation and meaning interpretation of Vietnamese traditional art decoration. The findings suggest that social distance generally plays an important role among interactants through Vietnamese traditional art decoration and functional meaning interpretation. The findings further suggest that the tenor system reflects some levels of social distance through a configuration of power, contact, and affective involvement of language usage. As a result, the levels of social distance could be realized by functional and social meaning interpretation, called socio-functional meaning system, through three perspectives: (i) art interpretation and art appreciation, (ii) social beliefs, faiths, and respect, and (iii) features and properties of art decoration. Some benefits of this study can be applied to other fields of human communication such as film, advertising, and art aesthetics.

Ionic liquid lubricants of PLA. New self-lubricating (PLA+ionic liquid) materials

Friction coefficients and wear rates of polylactic acid (PLA)-stainless steel pair have been determined under two different contact configurations using four aprotic imidazolium and a bio-based protic ammonium ionic liquid (IL) lubricants. Under rotational pin-on-disk, all ILs reduce friction coefficient in more than one order of magnitude and prevent wear. Under linear reciprocating sliding, the best performance is found for the halogen-free protic ammonium IL, with the highest viscosity and lower contact angle values. New (PLA+IL) materials have been obtained and excellent self-lubricating performance has been found for those with a porous surface. Results are discussed upon the basis of rheology, contact angles, surface topography and electron microscopy (SEM/EDX) studies.

Structural transitions in jammed asymmetric bidisperse granular packings

We study the local structural changes along the jamming transitions in asymmetric bidisperse granular packings. The local structure of the packing is assessed by the contact orientational order, tilde{Q}_{ell }, that quantifies the contribution of each contact configuration (Large–Large, Small–Small, Large–Small, Small–Large) in the jammed structure. The partial values of tilde{Q}_{ell } are calculated with respect to known ordered lattices that are fixed by the size ratio, delta , of the particles. We find that the packing undergoes a structural transition at phi _J, manifested by a sudden jump in the partial tilde{Q}_{ell }. Each contact configuration contributes to the jammed structure in a different way, changing with delta and concentration of small particles, X_{textrm{S}}. The results show not only that the packing undergoes a structural change upon jamming, but also that bidisperse packings exhibit local HCP and FCC structures also found in monodisperse packings. This suggests that the jammed structure of bidisperse systems is inherently endowed with local structural order. These results are relevant in understanding how the arrangement of particles determines the strength of bidisperse granular packings.Graphic abstract