Complex Contact Research Articles

Data-driven modeling for complex contacting phenomena via improved neural networks considering link switches

Recent years saw tremendous developments of data-driven modeling in various engineering fields. As for the contact modeling between complex surfaces, the utilization of neural networks successfully eliminates the limitations encountered by the traditional physics-based contact modeling strategy. However, contrary to its increasingly extensive applications, very little attention has been paid to the role of network hyper-parameters in reducing the model redundancy and improving its training efficiency. In this work, a novel neural network considering link switches has been presented for the data-driven modeling of complex contact phenomena. In order to further boost its prediction performance, genetic algorithm (GA) is employed for the optimal settings of relevant hyper-parameters. An indoor experimental setup is utilized to demonstrate the effectiveness of the presented methodology. Comprehensive comparisons with the base models indicate the superiorities of the established locally-connected-neural-network-based contact force model for complex geometries.

Validation and evaluation of subject-specific finite element models of the pediatric knee

Finite element (FE) models have been widely used to investigate knee joint biomechanics. Most of these models have been developed to study adult knees, neglecting pediatric populations. In this study, an atlas-based approach was employed to develop subject-specific FE models of the knee for eight typically developing pediatric individuals. Initially, validation simulations were performed at four passive tibiofemoral joint (TFJ) flexion angles, and the resulting TFJ and patellofemoral joint (PFJ) kinematics were compared to corresponding patient-matched measurements derived from magnetic resonance imaging (MRI). A neuromusculoskeletal-(NMSK)-FE pipeline was then used to simulate knee biomechanics during stance phase of walking gait for each participant to evaluate model simulation of a common motor task. Validation simulations demonstrated minimal error and strong correlations between FE-predicted and MRI-measured TFJ and PFJ kinematics (ensemble average of root mean square errors < 5 mm for translations and < 4.1° for rotations). The FE-predicted kinematics were strongly correlated with published reports (ensemble average of Pearson's correlation coefficients (ρ) > 0.9 for translations and ρ > 0.8 for rotations), except for TFJ mediolateral translation and abduction/adduction rotation. For walking gait, NMSK-FE model-predicted knee kinematics, contact areas, and contact pressures were consistent with experimental reports from literature. The strong agreement between model predictions and experimental reports underscores the capability of sequentially linked NMSK-FE models to accurately predict pediatric knee kinematics, as well as complex contact pressure distributions across the TFJ articulations. These models hold promise as effective tools for parametric analyses, population-based clinical studies, and enhancing our understanding of various pediatric knee injury mechanisms. They also support intervention design and prediction of surgical outcomes in pediatric populations.

Numerical study on the effectiveness of directional well with multiple hydraulic slots for enhanced gas recovery in deep coal seam

Coalbed methane production failures through hydraulic fracturing in the Linxing gas field in China have encountered significant setbacks, hindering efforts to enhance the recovery of deep CBM reserves in the region. To address this challenge, we investigate the potential of directional wells with multiple hydraulic slots as a stimulation technology for deep coalbed methane extraction. This study presents two numerical models to evaluate the effectiveness of this technology. The first model is a continuum damage numerical model based on the Material Point Method, which simulates large deformations and complex contact behaviors induced by hydraulic slotting in the deep coal seam. The second model is a wellbore-pore coupling model to simulate the gas extraction process. We verified both numerical models against theoretical and experimental results. We conducted a case study in the Linxing gas field using these models. The investigation assessed stress relief, gas desorption, and permeability enhancement around a large deformed hydraulic slot, as well as the gas extraction performance of a directional well with multiple slots. The results indicate that (1) The Linxing gas recovery failure may be attributed to unsuccessful hydraulic fracturing based on the history matching analysis of field production; (2) Hydraulic slotting causes gradual compaction of the slot until full closure, and results in a rapid stress drop exceeding 7 MPa in the elliptical zone surrounding the slot, which is the large plastic damage zone; (3) The enhanced permeability in plastic zone exceeds ten times the natural coal permeability, leading to total gas desorption of 556 m3 from elastic and plastic zones; (4) Performance optimization can be achieved through reducing slot length and increasing slot width when using directional well with multiple slots. In summary, this research demonstrates the efficiency of directional wells with multiple slots in enhancing gas recovery from deep coal seams.

Non-spherical Particle Modelling Approach in Discrete Element Method and its Validations

The discrete element method (DEM) is widely used for investigating the mechanical behaviours of complex physical system consisting of particles. In nature, the physical system such as rock and soil system, sand or flour are all composed of particles with different shapes. The particle shape can considerably influence nature characteristics in DEM simulation. Developing an effective particle shapes representation approach is a valuable task to improve the DEM modelling techniques. In this study, a super-quadrics function is introduced to represent the non-spherical particle shape. Furthermore, the corresponding contact detection and calculation algorithm named “deepest point method” is also explained to describe the complex contact relationships and calculate the contact forces between two irregular particles. At last, sandpile collapse simulations were conducted to validate the accuracy of the proposed approach. The numerical results indicate that the non-spherical particle modelling approach in this study can easily simulate most nature shape of particle system.

Integrating unsupervised language model with multi-view multiple sequence alignments for high-accuracy inter-chain contact prediction

Accurate identification of inter-chain contacts in the protein complex is critical to determine the corresponding 3D structures and understand the biological functions. We proposed a new deep learning method, ICCPred, to deduce the inter-chain contacts from the amino acid sequences of the protein complex. This pipeline was built on the designed deep residual network architecture, integrating the pre-trained language model with three multiple sequence alignments (MSAs) from different biological views. Experimental results on 709 non-redundant benchmarking protein complexes showed that the proposed ICCPred significantly increased inter-chain contact prediction accuracy compared to the state-of-the-art approaches. Detailed data analyses showed that the significant advantage of ICCPred lies in the utilization of pre-trained transformer language models which can effectively extract the complementary co-evolution diversity from three MSAs. Meanwhile, the designed deep residual network enhances the correlation between the co-evolution diversity and the patterns of inter-chain contacts. These results demonstrated a new avenue for high-accuracy deep-learning inter-chain contact prediction that is applicable to large-scale protein-protein interaction annotations from sequence alone.

An Analysis on Building Orientation and Occupants Satisfaction in Malaysia Low-Cost Housing

Thermal comfort is an important factor in ensuring a house's good thermal condition, affecting people’s productivity. People spend almost 90% of their time inside the house than outside. Since most people spend most of their time indoors, there is constant and complex contact between the inhabitants and their surroundings, affecting them physiologically and psychologically. Therefore, the thermal comfort in a residential building must be considered carefully. Several thermal comfort parameters need to be measured to understand the current indoor thermal situation of typical low-cost single-storey detached houses in Malaysia. This paper aims to identify the effects of the thermal comfort condition and orientation towards occupants’ satisfaction in low-cost detached houses. The research objective was achieved through questionnaire survey distribution to the respondents in low-cost detached houses in Bachok, Kelantan. Questionnaire survey has been distributed to occupants with different housing orientations: north, east, south, and west. A five-point Likert scale questionnaire was distributed face-to-face to 280 respondents occupying low-cost detached houses, and 233 (83%) were returned. The data gathered from the questionnaire were analysed using SPSS version 23. The finding on the occupants’ satisfaction towards thermal comfort condition indicates that their satisfaction depends on the orientation of the house and result for the last objective. There is a relationship between thermal comfort condition, building orientation, and occupants’ satisfaction. However, there is still a lack of research on the building orientation towards occupants’ satisfaction. Finally, it is hoped that this research can contribute to the thermal comfort knowledge, especially focusing on the occupants in low-cost housing.

Less Complex Contact Lens Required for a Patient With Keratoconus After Topography-Guided Photorefractive Keratectomy.

In this report, we discuss contact lens (CL) fitting in a patient with a history of keratoconus (KC), before and after undergoing topography-guided photorefractive keratectomy (TG PRK). Before TG PRK, the patient failed multiple CL modalities and reported difficulty with his habitual CLs and inadequate spectacle-corrected visual acuity to perform his activities of daily living. In this case, a collaborative, comprehensive approach to visual management in a patient with KC was used, and after TG PRK was performed to improve his corneal contour and symmetry, our patient was fit with a standard soft CL and additionally had improved spectacle-corrected visual acuity.

Study of atypical particle flow and free surface evolution behaviour in stirred tanks

Stirred tanks are ideal vessels for material mixing reactions in the chemical sector. However, insufficient data on the complex contact collisions occurring inside these vessels hinder their appropriate design and utilization. This study employs a coupled discrete element method and volume of fluid method (DEM-VOF) to examine the evolutionary behaviour of atypical particle flow and free surface in stirred tanks. DEM is utilized to trace particle motion and interactions, while VOF is used to capture the phase interface between the gas and liquid phases. Simulations are conducted on three commonly used particle shapes-oblate ellipsoid, sphere, and prolate ellipsoid-varying their aspect ratios under the same volume of particles. The key results of the suspension, distribution, multiphase flow, and free surface behaviours in the stirred tanks were analysed. The results show that the suspension and distribution of the three particle shapes are not substantially different, with suspension stability primarily influenced. Notably, the suspension of oblate ellipsoid particles exhibits conspicuous fluctuations. Additionally, the particle shape influences the magnitude of turbulent kinetic energy in the paddle area, with oblate particles exhibiting the largest values and prolate ellipsoids the smallest values. The findings provide guidelines for designing and operating stirred tanks under optimal conditions.

Tunable, Wide-Temperature, and Macroscale Superlubricity Enabled by Nanoscale Van Der Waals Heterojunction-to-Homojunction Transformation.

Achieving macroscale superlubricity of van der Waals (vdW) nanopowders is particularly challenging, due to the difficulty in forming ordered junctions before friction and the friction-induced complex contact restructuration among multiple nanometer-sized junctions. Here, a facile way is reported to achieve vdW nanopowder-to-heterojunction conversion by graphene edge-oxygen (GEO) incorporation. The GEO effectively weakens the out-of-plane edge-edge and in-plane plane-edge states of the vdW nanopowder, leading to a coexistent structure of nanoscale homojunctions and heterojunctions on the grinding balls. When sliding on diamond-like carbon surfaces, the ball-supported structure governs macroscale superlubricity by heterojunction-to-homojunction transformation among the countless nanoscale junctions. Furthermore, the transformation guides the tunable design of superlubricity, achieving superlubricity (µ≈0.005) at wide ranges of load, velocity, and temperature (-200 to 300°C). Atomistic simulations reveal the GEO-enhanced conversion of vdW nanopowder to heterojunctions and demonstrate the heterojunction-to-homojunction transformation superlubricity mechanism. The findings are of significance for the macroscopic scale-up and engineering application of structural superlubricity.

A Robust Incipient Slip Detection Method With Vision-Based Tactile Sensor Based on Local Deformation Degree

Incipient slip detection is important for manipulators to achieve stable grasping. In order to make manipulators adapted to unstructured environments better and realize a wider range of applications, it is necessary to achieve incipient slip detection with robustness to object surface properties. In this paper, we propose a novel incipient slip detection method with vision-based tactile sensor. The method only uses sensor deformation data and does not need any information about the grasped object. In addition, it has the advantages of intuitive principles and a wide range of applicable working conditions. In this paper, the local deformation degree of the sensor is proved to be related to the stick/slip state at the corresponding location by kinematic aspects. Based on this, a method is proposed to select reference points in the stick region with local deformation degree. These reference points are used to fit the rigid motion of the contacted object and the slip field. Furthermore, an iterative algorithm is proposed to delineate the stick/slip region based on the characteristic of the slip field. Afterward, complex contact conditions are constructed through finite element simulation. Curved surfaces, discontinuous surfaces, and surfaces with multiple friction coefficients distribution are used to verify the correctness and superiority of the proposed method compared to other methods. Finally, the slip detection experimental bench is built, and our self-developed vision-based sensor is used to contact common objects with complex surface properties. Through the real slip detection experiments, the adaptability and good application prospects of this method are demonstrated.

Complex Antegrade Percutaneous Transhepatic and Retrograde Endoscopic Lithotripsy and Extraction

We report a clinical case of elimination of megacholedocholithiasis using complex antegrade percutaneous transhepatic and retrograde endoscopic contact electropulse lithotripsy and extraction. Since an attempt of antegrade extraction failed due to megacholedocholithiasis, the patient underwent complex contact electropulse lithotripsy followed by lithotripsy through antegrade and retrograde access, which made it possible to eliminate megacholedocholithiasis without the development of postoperative complications, restore the lumen of the bile ducts and ensure the possibility of subsequent planned surgical treatment of chronic calculous cholecystitis.

Identification of interbedded gas hydrate and free gas using amplitude versus offset forward modelling

AbstractThe complex contacts between gas hydrate and free gas have been confirmed by gas hydrate pilot production in the Pearl River Mouth Basin, South China Sea. The laminated clay silt reservoirs have high amplitude reflections which may be filled with different saturations of gas hydrates, free gas and the coexistence between gas hydrate and free gas. To distinguish the variations of amplitude reflections caused by different reservoirs properties below the bottom simulating reflection, we combine the forward modelling, pre‐stack gathers with different incident angles and well log analysis to conduct the seismic responses. A number of geological models are established with variable saturations and different interfaces between gas hydrate and free gas. First, we analyse the seismic and well log responses at Sites W11, W01 and W17 near the production test area. Then, we perform the forward modelling to quantify the differences among seismic reflections with different saturations, thickness, incident angles and strata dips in free gas‐ or gas hydrate‐bearing geological models. We extract the seismic amplitudes along the bottom simulating reflection and other layers to compare with the amplitudes generated from forward modelling. The results indicate that the inclined intervals below the bottom simulating reflection have high amplitude, continuous reflection and polarity reversal which may be caused by thin gas reservoir and the interlayered gas hydrate and free gas with different saturations. The top interfaces of the gas hydrate‐ and free gas‐bearing layers show typical Class III amplitude versus offset and exhibit high amplitude reflections at seismic data with near, mid and far‐incident angles, which are easy to distinguish. Seismic response of far‐incident angle can be used to identify the coexistence of gas hydrate and free gas.

Computational prediction of muscle synergy using a finite element framework for a musculoskeletal model on lower limb.

Previous studies have demonstrated that the central nervous system activates muscles in module patterns to reduce the complexity needed to control each muscle while producing a movement, which is referred to as muscle synergy. In previous musculoskeletal modeling-based muscle synergy analysis studies, as a result of simplification of the joints, a conventional rigid-body link musculoskeletal model failed to represent the physiological interactions of muscle activation and joint kinematics. However, the interaction between the muscle level and joint level that exists in vivo is an important relationship that influences the biomechanics and neurophysiology of the musculoskeletal system. In the present, a lower limb musculoskeletal model coupling a detailed representation of a joint including complex contact behavior and material representations was used for muscle synergy analysis using a decomposition method of non-negative matrix factorization (NMF). The complexity of the representation of a joint in a musculoskeletal system allows for the investigation of the physiological interactions in vivo on the musculoskeletal system, thereby facilitating the decomposition of the muscle synergy. Results indicated that, the activities of the 20 muscles on the lower limb during the stance phase of gait could be controlled by three muscle synergies, and total variance accounted for by synergies was 86.42%. The characterization of muscle synergy and musculoskeletal biomechanics is consistent with the results, thus explaining the formational mechanism of lower limb motions during gait through the reduction of the dimensions of control issues by muscle synergy and the central nervous system.

Influence of calendering process on the structural mechanics and heat transfer characteristics of lithium-ion battery electrodes via DEM simulations

Elucidating the intricate correlation between calendering, structure, and performance is crucial to comprehending the relationship between performance parameters and process steps of lithium-ion batteries (LIBs). Discrete element method (DEM) simulations were adopted in this work to calculate the interparticle force and stress tensor under incremental calendering process conditions, which revealed the effect of the anisotropy of complex contact force network on the anisotropy of heat transfer within porous electrode. The thermal conductivity of electrode was predicted using porosity to characterize the process–structure–performance correlation. The comprehensive influence of contact number and contact area between particles and current collector determines the magnitude of interfacial thermal resistance and interfacial heat transfer coefficient. For the first time, this work quantitatively analyzed the structural mechanics and heat transfer mechanism during calendering process of porous electrodes, and the results indicate a promising way to optimize and design battery electrode structures.

COVID-19: Agent-based simulation-optimization to vaccine center location vaccine allocation problem

This article presents an agent-based simulation-optimization modeling and algorithmic framework to determine the optimal vaccine center location and vaccine allocation strategies under budget constraints during an epidemic outbreak. Both simulation and optimization models incorporate population health dynamics, such as susceptible (S), vaccinated (V), infected (I) and recovered (R), while their integrated utilization focuses on the COVID-19 vaccine allocation challenges. We first formulate a dynamic location–allocation Mixed-Integer Programming (MIP) model, which determines the optimal vaccination center locations and vaccines allocated to vaccination centers, pharmacies, and health centers in a multi-period setting in each region over a geographical location. We then extend the agent-based epidemiological simulation model of COVID-19 (Covasim) by adding new vaccination compartments representing people who take the first vaccine shot and the first two shots. The Covasim involves complex disease transmission contact networks, including households, schools, and workplaces, and demographics, such as age-based disease transmission parameters. We combine the extended Covasim with the vaccination center location-allocation MIP model into one single simulation-optimization framework, which works iteratively forward and backward in time to determine the optimal vaccine allocation under varying disease dynamics. The agent-based simulation captures the inherent uncertainty in disease progression and forecasts the refined number of susceptible individuals and infections for the current time period to be used as an input into the optimization. We calibrate, validate, and test our simulation-optimization vaccine allocation model using the COVID-19 data and vaccine distribution case study in New Jersey. The resulting insights support ongoing mass vaccination efforts to mitigate the impact of the pandemic on public health, while the simulation-optimization algorithmic framework could be generalized for other epidemics.

Bioinspired rapid self-replenishing liquid-infused surfaces for stable anti-adhesion of electrosurgical electrodes

Soft tissue adhesion on electrosurgical electrodes has been a significant concern in minimally invasive surgery. The liquid-infused surface (LIS) can effectively reduce the tissue adhesion on electrodes by constructing a lubricating interface. However, the tissue-cutting process involves a complex contact friction process and high temperature, resulting in lubricant depletion of LIS. Inspired by the rapid self-replenishment of liquid film on the peristome surface of Nepenthes, here, a novel self-replenishing liquid-infused surface (SR-LIS) is fabricated by the laser direct structuring method. SR-LIS consists of first-level microgrooves and second-level microcavities. The microcavities store lubricant for a long time and enhance the capillary force of microgrooves. The rapid self-replenishing lubricant of SR-LIS ensures that the cutting interface is composed of soft tissue-lubricant-steel, resulting in stable anti-adhesion. Soft tissue cutting experiments show that the SR-LIS could stably reduce tissue adhesion and tissue damage compared to LIS. The underlying mechanism is discussed, and further experiments conclude that the self-replenishing lubricant has the double action of lubrication and cooling. This novel structural design, preparation method, and the resulting surfaces have essential applications in electrosurgical electrodes and promote the development of slippery surfaces in various industries.

Multiplex-GAM: genome-wide identification of chromatin contacts yields insights overlooked by Hi-C

Technology for measuring 3D genome topology is increasingly important for studying gene regulation, for genome assembly and for mapping of genome rearrangements. Hi-C and other ligation-based methods have become routine but have specific biases. Here, we develop multiplex-GAM, a faster and more affordable version of genome architecture mapping (GAM), a ligation-free technique that maps chromatin contacts genome-wide. We perform a detailed comparison of multiplex-GAM and Hi-C using mouse embryonic stem cells. When examining the strongest contacts detected by either method, we find that only one-third of these are shared. The strongest contacts specifically found in GAM often involve ‘active’ regions, including many transcribed genes and super-enhancers, whereas in Hi-C they more often contain ‘inactive’ regions. Our work shows that active genomic regions are involved in extensive complex contacts that are currently underestimated in ligation-based approaches, and highlights the need for orthogonal advances in genome-wide contact mapping technologies.

Contact holes in vertical electrode structures analyzed by voltage contrast-SEM and conducting AFM

Soaring demands of multi-stacked memory devices request urgent development of backside contact electrode technologies, such as high aspect ratio etching, metallization, and inspection methods. Especially the complex metal contact process should be monitored for each manufacturing step to filter the defective samples and to maintain the high yield of production. Among the inspection methods for detecting the electrical connections, there is voltage contrast (VC)-SEM and conducting AFM (C-AFM). In this report, we investigated the two inspection methods for testing designed samples with different contact hole states. The VC-SEM data shows the contrast variation at the contact holes, from which one may discern the contact status with an optimum voltage. The C-AFM results clearly demonstrate a finite electrical current in the connected contact, while a negligible current in the disconnected one. Finally, we discuss insights of using the two methods for analyzing the contact hole technologies with high aspect ratios.

Numerical modelling of cold-formed steel built-up columns

Built-up cold-formed steel structural members can provide technically and economically advantageous solutions in cold-formed steel construction. However, there is a need for a deeper understanding of their stability behaviour, and this paper demonstrates that detailed, accurate and reliable finite element models provide an excellent means to achieve this. Apart from the typical issues to be considered in the high-fidelity modelling of thin-walled members, which include geometric and material nonlinearity, element type, mesh density, and the modelling of imperfections and boundary conditions, the paper focuses on two additional complications which arise in built-up members: the modelling of connectors, and contact between constituent parts. A number of alternative techniques to model connector behaviour are investigated and their effect on the predictions of the ultimate capacity quantified by benchmarking against experimental data. Various successful strategies to mitigate stubborn convergence problems, which almost inevitable originate when modelling complex contact problems, are also presented. It is demonstrated, however, that the inclusion of contact as a model feature does not have a significant effect on the predicted capacity in the majority of the considered cases, with its influence typically remaining limited below 10%. The validated models were further used in parametric studies which showed that once the connector spacing is short enough to prevent global instabilities of the component sections between connector points, its effect on the ultimate capacity of the built-up column is very small within the practical range of connector spacings. Modelling connector lines as continuous longitudinal constraints tying surfaces together, on the other hand, is bound to significantly overestimate the capacity.

Impact of Chromatin 3D-Organization on Promoter–Superenhancer Interactions in Embryonic Stem vs Cancer Cells

The interaction of enhancers and superenhancers (SE) with promoters is functionally significant for the regulation of gene expression. Pattern of these interactions plays a key role in various processes, such as differentiation, malignant transformation, etc. In order to quantify the relationship between 3D chromatin organization and promoter–SE contacts, a computational analysis of chromatin conformations near the murine Nanog pluripotency gene was performed for normal embryonic stem (mESC) and lymphoma (CH12LX) cells. Using biophysical modeling approach, the following parameters of the promoter–SE interactions were identified: the distribution of distances between the Nanog promoter and the SEs, the frequency of contacts with one and several SEs simultaneously. In normal mESC expressing Nanog, the frequency of contacts of promoters with SEs is higher than in cancer cells, and complex contacts with two or more SEs are more frequent. The modelling reveals a small subpopulation of cancer cells, where the promoter contacts simultaneously three SEs. The predicted subpopulation of cancer cells with multiple promoter–SE contacts may be predisposed to increased stemness and hypothetically be considered as a reservoir for generation of cancer stem cells.