Contact Characteristics Research Articles

Numerical study on contact characteristics and sealing performance of rubber-bellows mechanical seals in ESPs

Purpose This study aims to evaluate the effects of the downhole environment and auxiliary rubber bellows on the contact mechanical characteristics and sealing performance of rubber-bellows mechanical seals (RBMS) in electric submersible pumps (ESPs), considering the elastic support of the rubber bellows, multi-field coupling effect and actual operating conditions. Design/methodology/approach A thermal-fluid-solid multi-field coupling numerical model for RBMS in ESPs is developed using the finite element analysis and influence coefficient method. Based on the contact mechanical characteristics of RBMS, the interactions of multiple physical fields between the sealing rings and lubricating oil are accounted for to assess the liquid lubrication state and sealing performance of RBMS in ESPs. Findings The findings indicate the anti-leakage effects of rubber bellows, the transition of lubrication state of the sealing end face and the evolution law of sealing performance with environmental pressure, axial compression amount and contact widths of rubber bellows. Originality/value This study innovatively proposes a multi-field numerical research method to reveal the impact of the downhole environment and rubber bellows on RBMS in ESPs. These findings contribute to a more comprehensive understanding of the sealing mechanism of RBMS and optimize the sealing design for ESPs in high-pressure environments. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2024-0369/

Modeling the impact of input credit access on farm performance and food nutrition: insights from smallholder rice farmers in Ghana

PurposeThis paper examines the nexus between input credit access, farm performance and food nutrition in Ghana.Design/methodology/approachUsing a random sample of 239 smallholder rice farmers, we utilized the endogenous switching regression model to address the self-selection issue and estimate the impact of input credit access on farm performance and food nutrition and further analyze the heterogenous impacts.FindingsThe results show that socioeconomic (age, education, sex, off-farm activity and farm size), institutional (extension contact and farmer-based organizations) characteristics and location variable significantly influence the decision to access input credit. After adjusting for both observed and unobserved factors, our findings reveal that access to input credit significantly improves rice yield, net profit and food nutrition of smallholder rice farmers in Ghana. Furthermore, results reveal that the effects of input credit access on rice yield, net profit and food nutrition are heterogeneous and subject to farmers’ propensity to access input credit. Specifically, we find that those with a higher inclination to access input credit experience larger positive impacts, indicating a positive selection process.Research limitations/implicationsAccess to agricultural input credit is essential for the adoption of modern and climate-smart technologies in agricultural production. However, the persistent lack of access to input credit hampers agricultural productivity and constrains investment in farm input resources in Sub-Saharan Africa. Our study calls for proper targeting of input credit interventions to incentivize the uptake of farm input credit such as improved seeds and fertilizers to improve overall crop production and achieve food security.Originality/valueThe study utilized rigorous econometric methods to analyze the impact of input credit access on smallholder rice farmers' farm performance and food nutrition in Ghana. The findings provide valuable guidance for policymakers and future research on agricultural development in Ghana.

Two-Dimensional Transition Metal Dichalcogenides: A Theory and Simulation Perspective.

Two-dimensional transition metal dichalcogenides (2D TMDs) are a promising class of functional materials for fundamental physics explorations and applications in next-generation electronics, catalysis, quantum technologies, and energy-related fields. Theory and simulations have played a pivotal role in recent advancements, from understanding physical properties and discovering new materials to elucidating synthesis processes and designing novel devices. The key has been developments in ab initio theory, deep learning, molecular dynamics, high-throughput computations, and multiscale methods. This review focuses on how theory and simulations have contributed to recent progress in 2D TMDs research, particularly in understanding properties of twisted moiré-based TMDs, predicting exotic quantum phases in TMD monolayers and heterostructures, understanding nucleation and growth processes in TMD synthesis, and comprehending electron transport and characteristics of different contacts in potential devices based on TMD heterostructures. The notable achievements provided by theory and simulations are highlighted, along with the challenges that need to be addressed. Although 2D TMDs have demonstrated potential and prototype devices have been created, we conclude by highlighting research areas that demand the most attention and how theory and simulation might address them and aid in attaining the true potential of 2D TMDs toward commercial device realizations.

EHL Traction Coefficient Is Not a Property of the Liquid Alone

Abstract The slow progress in prediction of elastohydrodynamic film thickness and friction may be attributed to the mistaken notion that a traction curve is equivalent to a rheological flow curve. A similar concept is being standardized by Society of Automotive Engineers (SAE) for the traction coefficient of aerospace oils. Four standards teach that traction coefficient is an inherent physical property of an oil and that full film traction does not depend upon the roller material and that there can be traction measurements which do not depend on the test rig. These traction coefficients are to be employed in models for thermal management analyses without the need for measuring primary properties. Through example calculations, using primary properties of a turbine oil, it is shown here that elastohydrodynamic lubrication (EHL) friction is not a property of the liquid alone, and that it depends on at least two contact characteristics as well; namely, the aspect ratio and scale. Within the tribology literature, there is much evidence of the dependence of EHL friction on other contact parameters as well that are not characteristic of the fluid.

Friction Performance of Three-Dimension Printed PEEK for Journal Bearing Application Under Grease Lubrication

Abstract Additive manufacturing revolutionizes component and part creation, offering unmatched flexibility and reducing production time. This innovation, especially significant with semicrystalline polymers like polyetheretherketone (PEEK) at high temperatures, expands applications, including sleeves and bushes. PEEK's mechanical and tribological properties make it an attractive long-term metal replacement. However, the 3D printed PEEK surface is pivotal, and the surface structure depends on infill density, which influences its response to sliding conditions, such as speed, load, and test duration. The PEEK structure's surface patterns facilitate lubricant accommodation, particularly during boundary lubrication tests, affecting the formation of a transfer layer. Surface properties directly impact friction in 3D printed PEEK against the counterbody. Lubrication decreases friction coefficients compared to dry conditions. Wear tests show that 3D printed PEEK parts outperform extruded rod samples, displaying superior wear resistance. Surface texture and properties directly affect contact characteristics and lubricant storage. In journal bearings, varying infill percentages create surface voids, efficiently accommodating polyalphaolefin (PAO)-based grease in PEEK-based applications where oil is not preferred for sliding operations.

Polymer-based Solid Electrolyte and Electrode/Electrolyte Interfacial Contact Characteristics Affecting Lithium-ion Battery Performance

Lithium-ion batteries (LIBs) are now embedded in peoples daily life usage including portable electronic devices and electric vehicles. The demand for further developed LIBs with better energy storage, energy transport, safety, etc. However, the commercial and conventional LIBs use liquid electrolyte widely. Although it provides excellent ionic conductivity, its poor mechanical strength often induces the growth of dendrite, which is often considered as the primary factor that causes short circuits, undesired side reactions, and reductions in energy capacity. To address these issues, polymer-based solid-state electrolytes (SSEs) were developed. It exhibits comprehensive properties and can cooperate with other materials to resolve their defects, creating various novel materials in different scenarios. This paper covers four commonly used polymers in the fabrication of SSEs and key parameters indicating their energy density and stability. It provides a brief introduction to the reader about the characteristics of varying polymer-based electrolytes, and how these characteristics, combined with interface contact, affect the overall battery performance.

Single-layer MoSeN – a synthetic Janus two-dimensional transition-metal compound grown by plasma-assisted molecular beam epitaxy

Abstract Two-dimensional (2D) nanomaterials hold immense application potentials such as in high-performance nano-electronics, and asymmetric 2D structures with inherent electric dipoles will extend the application promises. Yet synthesizing asymmetric 2D structures remains challenging. Herein, we report the first synthesis of single-layer (SL) hexagonal (H-) phase polar Janus MoSeN via nitrogen-plasma-assisted molecular beam epitaxy. This is a significant achievement given the incommensurate valence between Mo, Se, and N, and the inherent strain from the Janus architecture. Using an array of compositional and structural characterization methods, we establish the atomic configurations of the synthesized MoSeN SL, confirming that they are 2D Janus transition-metal chalcogen-nitrides rather than alloys. By employing density functional theory calculations and transport measurements, we explore the structural feasibility and offer insights into its electronic properties, demonstrating its metallic behavior with ohmic contact characteristics. Piezoresponse force microscopy measurements reveal vertical piezoelectricity and ferroelectric potentials from the Janus MoSeN SL. Therefore, it exhibits great potential for applications in, e.g. piezoelectric and ferroelectric devices, sensing technologies, and optoelectronic devices. This work not only addresses existing challenges in 2D nanomaterial research but also opens new avenues for the development of advanced functional materials.

Contact characteristics and reliability assessment for high-speed electrical connector based on artificial neural network surrogate modeling

Contact characteristics and reliability assessment for high-speed electrical connector based on artificial neural network surrogate modeling

Household transmission of SARS-CoV-2 in five US jurisdictions: Comparison of Delta and Omicron variants.

Households are a significant source of SARS-CoV-2 transmission, even during periods of low community-level spread. Comparing household transmission rates by SARS-CoV-2 variant may provide relevant information about current risks and prevention strategies. This investigation aimed to estimate differences in household transmission risk comparing the SARS-CoV-2 Delta and Omicron variants using data from contact tracing and interviews conducted from November 2021 through February 2022 in five U.S. public health jurisdictions (City of Chicago, Illinois; State of Connecticut; City of Milwaukee, Wisconsin; State of Maryland; and State of Utah). Generalized estimating equations were used to estimate attack rates and relative risks for index case and household contact characteristics. Data from 848 households, including 2,622 individuals (median household size = 3), were analyzed. Overall transmission risk was similar in households with Omicron (attack rate = 47.0%) compared to Delta variant (attack rate = 48.0%) circulation. In the multivariable model, a pattern of increased transmission risk was observed with increased time since a household contact's last COVID-19 vaccine dose in Delta households, although confidence intervals overlapped (0-3 months relative risk = 0.8, confidence interval: 0.5-1.2; 4-7 months relative risk = 1.3, 0.9-1.8; ≥8 months relative risk = 1.2, 0.7-1.8); no pattern was observed in Omicron households. Risk for household contacts of symptomatic index cases was twice that of household contacts of asymptomatic index cases (relative risk = 2.0, 95% confidence interval: 1.4-2.9), emphasizing the importance of symptom status, regardless of variant. Uniquely, this study adjusted risk estimates for several index case and household contact characteristics and demonstrates that few characteristics strongly dictate risk, likely reflecting the complexity of the biological and social factors which combine to impact SARS-CoV-2 transmission.

Numerical study on the evolution characteristics of contact and fluid flow in shear-induced rough joint

In order to investigate the influence of shear on contact characteristics and fluid flow evolution of rough rock fractures, a series of shear-flow tests were carried out by numerical experiments. Firstly, a sandstone specimen with a rough fracture was made in the laboratory, and the numerical model of the fracture was reconstructed in FLAC3D software. Experiments were conducted to investigate the depth of penetration of the fracture under different normal stress (1, 3, and 5 MPa) and shear displacement (2, 4, 6, 8, and 10 mm). By establishing the relationship between the shear direction and the apparent inclination of the fracture asperity, the effects on the asperity contact characteristics and seepage properties are explored. The results of the study indicated that the larger the normal stress the larger the surface contact section and the smaller the aperture, showing the opposite trend with increasing shear displacement. Positive apparent inclination distribution can effectively predict the location of shear damage during the shear process. Negative apparent dip implies that those regions increase permeability after shear, and decrease with increasing crack opening. Fracture seepage shows obvious nonlinear characteristics, where the nonlinear coefficients are 5–6 orders of magnitude larger than the linear coefficients. The critical Reynolds number Rec is used to distinguish the linear and nonlinear categories of fluid flow, and the calculated results show that the range of Rec is between 0.0081 and 0.11.3, and the Rec increases with shear displacement and decreases with normal stress.

Subsurface Characterization and Revealing Geometry of the Baribis Fault in the Eastern Part of West Java Using Long-Offset Resistivity Tomography

The Baribis Fault is an important active fault in West Java, Indonesia. This fault has recently attracted the attention of many parties since some fault segments pass through densely populated areas, raising the risk of shallow earthquakes. The long-offset resistivity tomography method was applied to image the active Baribis Faults. This method clearly showed the subsurface geometry, including the contact characteristics of the Baribis Fault near the subsurface. The long-offset resistivity tomography surveys were acquired using multi-electrodes and multi-nodes, and the data acquisition was wirelessly controlled via a WiFi connection. The pole–dipole resistivity tomography image shows a 35∘ dip overhang structure of the Baribis thrust fault near the Jatigede area in Middle Eastern West Java, with a strike fault segment in a relative East–West direction. However, the other long-offset tomography images in northeastern West Java, near the Conggeang–Sumedang area, show the oblique thrust fault phenomena of the Baribis Fault with a strike in the Northeast–Southwest direction. The stress caused by the Cimandiri–Lembang regional strike–slip fault likely influences the dynamics of the Baribis Fault in the close area of Sumedang.

Modeling and test verification of variable cross-section contact behavior for spherical rollers during lapping process

Curved surface contact is widely used in the industry of bearing roller machining and shaft-hole connection, but there is no universal model to describe it. In order to study the contact problem between the spherical roller and the lapping sleeve, the existing cylindrical contact models were firstly compared and applied to the contact problem using slicing method, and a hybrid contact model was established. Based on Winkler's elastic foundation theory, a variable cross-section contact model was established and its analytical expression was obtained. Since the new model has no elastic half-space assumption, it can be used to solve conformal contact and non-conformal contact problems. Finally, the finite-element simulation results and the lapping test results show that compared with the hybrid contact model, the variable cross-section contact model can more accurately describe the static contact characteristics between the spherical roller and the lapping sleeve, and can provide a theoretical reference for roller machining and coordinated deformation of shaft-hole.

Mesh Stiffness and Dynamic Modeling and Analysis of Modified Straight Bevel Gears

Gear modification, which involves the removal of material from the theoretical surface to improve the contact characteristics of the gear face, is widely applied in gear vibration reduction and noise optimization design. This paper establishes a dynamic model of the straight bevel gear (SBG) transmission system to accurately and efficiently evaluate the effects of different modification strategies on the vibrational characteristics of SBGs. Initially, the time-varying meshing stiffness (TVMS) of standard SBGs was calculated, and methods such as the slicing method and deformation coordination equations were used to calculate the TVMS under tooth profile modification (TPM), Lead crown relief (LCR), and comprehensive modification (CM), which were then validated against finite element method (FEM) calculations. Subsequently, taking into account the impact of time-varying meshing point vectors and the degree of contact overlap, a finite element node dynamic model of the SBG transmission system was established. Finally, by comparing the dynamic characteristics under different modification conditions, the study further elucidates that selecting the appropriate modification method and amount according to different service scenarios is an effective means to suppress gear transmission vibration. This research provides a theoretical basis for the design of gear modification and vibration control for SBGs.

19.5%‐Efficiency Organic Solar Cells with High Thickness Tolerance and Exceptional Device Stability Enabled by TEMPO‐Functionalized Perylene Diimide as a Cathode Interface Layer

AbstractThe cathode interface material is pivotal for achieving excellent photovoltaic performance and device stability in organic solar cells (OSCs). However, currently, few interface materials can simultaneously satisfy multiple criteria such as low cost, high efficiency, insensitivity to film thickness, and good stability. To address this challenge, a novel perylene diimide (PDI) derivative, P‐C3T is designed and synthesized, by incorporating stable free radical unit TEMPO and polar quaternary ammonium salt as side chains. P‐C3T is facile to synthesize and cost‐effective, while also exhibiting good conductivity and excellent ohmic contact characteristics in OSCs. When utilized as the cathode interface material, the device based on D18:L8‐BO achieves a remarkable power conversion efficiency (PCE) of 19.52%, which is one of the highest levels reported for binary single‐junction OSCs. Notably, devices based on P‐C3T exhibit remarkable insensitivity to film thickness, with the PCE remaining at 95% of the initial efficiency even at a thickness of 40 nm. Furthermore, P‐C3T‐based OSCs demonstrate exceptional storage stability and improved light stability. In summary, with its high PCE, excellent thickness insensitivity, and good stability, P‐C3T is anticipated to be a promising candidate material for large‐area roll‐to‐roll processing of OSCs.

Characteristics of rolling interface lubrication considering contact surface textures in mixed lubrication

This study comprehensively utilizes the mixed lubrication theory and rolling deformation theory to establish a finite element stiffness contact model that considers the surface texture characteristics of the rolling interface. The dynamic explicit finite element analysis is used to obtain the deformed solid, and the turbulent equation is used to control the fluid boundary conditions. The bidirectional Fluid-Structure Interacton (FSI) ansysis is used to study the influence of surface roughness, surface textures, and rolling parameters such as rolling speed on the distribution of oil film pressure and contact characteristics during the rolling process. The results confirm that transverse texture reduces the friction coefficient and dynamic pressure by enhancing the trapping effect of rough peaks and facilitating the entrainment of the fluid film. Under the same textural conditions, the contact area decreases with increasing roughness while the friction coefficient increases. As the rolling speed increases, the rolling pressure decreases to a certain extent, and the contact area ratio will decrease; Lubricants with higher viscosity can effectively reduce the friction and rolling force at the rolling interface. We believe that the insights obtained from the numerical simulations provided in this reaserch will lay a theoretical foundation for subsequent research on plate shape control.

Thermoelastoplastic contact and charge characteristics of nonrotationally symmetric lunar dust particles

Thermoelastoplastic contact and charge characteristics of nonrotationally symmetric lunar dust particles

Characterization of aircraft landing impact loads: Effects on vertical tire-pavement contact characteristics and pavement performance

The comprehensive understanding of the mechanistic behavior of airport pavements under aircraft landing loads is essential for ensuring safety and durability. Addressing the limited understanding on the interaction between aircraft landing gear and airport pavement during landing, this study proposed a measurement method for the vertical dynamic contact characteristics of tire-pavement interface and internal dynamic responses based on a laboratory dynamic test device. This involved the experimental design and testing method for the dynamic characteristics of landing gear landing loads, utilizing the Tekscan pressure measurement system to evaluate the vertical dynamic contact characteristics between the aircraft tires and pavement during landing. Through comparative analysis with the static results, the study revealed the importance of landing load measurements for mechanical response analysis and durability design of airport pavements. Additionally, the study investigated the dynamic response of airport pavements under different simulated aircraft landing speeds and weights, and further quantified the impact effects of aircraft landing loads on airport pavements. The results show that the vertical tire-pavement contact characteristics under landing impact are significantly different from those under static conditions, and need to be considered. The proposed quantitative equations with acceptable good fitting effect provided more accurate and efficient vertical load inputs for numerical simulation and durability design of airport pavements, which laid the foundation for understanding the failure mechanisms of airport pavement and enhancing the safety of aircraft and airport operation.

Interface dipole evolution from the hybrid coupling between nitrogen-doped carbon quantum dots and polyethylenimine featuring the electron transport thin layer at Al/Si interfaces

The assessment of electron transport layer (ETL) for rear-contact engineering of silicon (Si) based optoelectronics has been considered as one of the critical challenges that leverage the performance improvement and device reliability. In this work, the hybrid design of ETL, obtained from the solution-processed nitrogen-doped carbon quantum dots (NCQDs) incorporated with organic polyethylenimine (PEI) demonstrates the feasible contact characteristics for the modification of Si/Al contacts, which greatly facilitates the transport and collection of photoexcited electrons in the Si-based optoelectronics. The aspects of microstructures, functional groups, chemical features, interfacial characteristics and band structures of NCQD/PEI are explicated, visualizing that the evolution of interface dipoles mediated by the overall outcome of physisorption and chemisorption effects, modifies the surface potential difference and results in the explicit reduction of the Al work function from 4.3 eV for pristine Al to 3.23 eV based on the optimized constitutional design (0.10 % NCQD in PEI). These findings are practically employed on the Si-based hybrid solar cells at Si/Al interfaces, fulfilling the conversion-efficiency improvement by 30.9 % compared with reference cells without ETL employment, which are experimentally interpreted by the efficient electron transport across the Si/Al heterojunction and charge collection.

Topological Insulator Bismuth-Antimony Alloy Contact for Two-Dimensional Semiconductor Based Electronics

Two-dimensional (2D) semiconductors are considered as the most promising candidate for channel materials in next-generation electronic devices owing to their atomically thin nature [1]. In order to minimize the overall chip size, it is imperative to reduce both the channel length and the contact area of the devices. However, the reduction in contact area inevitably leads to an increase in the contact resistance (RC), and recent studies have been devoted to solving this problem. In particular, the significant achievements in reducing the RC to near quantum limits in 2D semiconductor based field-effect transistors (FET) were reported using semi-metal as bismuth (Bi) and antimony (Sb) as contact metals [2,3]. In spite of these advancements, research on the scaling-down of the metal contact with the exploration of alternative contact materials to shrink overall chip footprint remains limited.To overcome these limitations, we propose the topological insulator (TI) as a contact metal for 2D-based electronics. TI is known to enable electron transport without backscattering at the surfaces owing to its unique surface band structures [4]. Result from these properties, the RC increase with a contact area reduction is lower compared to conventional metals, indicating high potential for TIs as an interconnector in extreme scaling regimes [5]. Additionally, the Dirac cone band structure on TIs surface [6] is expected to suppress metal-induced gap states (MIGS) similar to semi-metal contacts [2-3].In this study, a 2D semiconductor FETs was fabricated with Bi-Sb alloy as the electrode material. Bi-Sb alloys are known to exhibit the TI phase with Sb composition ranging from 7% to 22% [7]. A 20 nm thick Ti-phase Bi-Sb alloy was synthesized using molecular beam epitaxy (MBE) on exfoliated MoS2 flakes with pre-patterned contact areas using a standard e-beam lithography process. The device was then completed by capping the TI contacts with gold. A systematic investigation of the electrical properties of the device showed that the on-current with the contact of the Ti-phase Bi-Sb alloy is enhanced compared to the bismuth-only configuration. Through this research, we aim to improve the contact characteristic of 2D based electronics in nano-scale regimes, and provide insights that can contribute to the development and commercialization of next-generation electronic devices.

Early Findings of Helpline Inquiries From Youth and Young Adults With Concerns About Their Sexual Thoughts, Behaviors, and Experiences.

Most self-reported victims of child sexual abuse are harmed by peers or known older youth with the average age of first-time sexual perpetration being between 11 and 16 years. In this retrospective review of inquiries made to the WhatsOK helpline over an 18.5-month period, we examine the characteristics of contacts to a helpline for youth with questions about their sexual interests and behaviors. Data were collected from pre-set questions on age, primary reason for contact, timing of inquiry relative to other help-seeking, and timing relative to harm caused. Most inquiries came from youth aged 14 to 21 (57.7%) via email (54.4%). Over half (54.6%) had or were at risk to cause sexual harm. The second most common reason to contact (17.4%) was about general sexual health topics. The majority sought help prior to seeking out other external professional resources (54%). This study provides proof of concept that youth are willing to seek out help for their (and others') sexual interests and behaviors, highlighting the critical need for prevention strategies targeting youth with potentially concerning sexual behaviors.