Field Of Physics Research Articles

Laboratory-Scale Natural Gas Hydrate Extraction Numerical Simulation Under Phase Transition Effect

Phase transition in gas hydrate reservoirs has a significant effect on the fluid flow dynamic when performing test production, which should be carefully studied. This study systematically investigates the phase transition characteristics of natural gas hydrates during the depressurization extraction process through laboratory-scale numerical simulations. First, a laboratory-scale numerical simulation model is established with dimensions of 1 m × 1 m × 1 m. In the simulation, the nanoscale and microscale effect on phase transition is considered. Then, the analysis of how different sediment types and their properties affecting gas production dynamics is presented. The results show that hydrate dissociation and formation are significantly influenced by factors such as the pore scale, salinity, and water content. In particular, montmorillonite had the most significant effect, leading to a 525.25% increase in gas production, while the impact of silty soil was relatively smaller. The increase in salinity inhibited hydrate formation but promoted dissociation, resulting in a significant increase in gas production, especially when the salinity reached to 3.5%, where gas production increased by 590.21%. An increase in water content led to a significant decrease in production. Through monitoring temperature and pressure changes during the extraction process, the different physical fields are analyzed, providing important theoretical support and practical guidance for the efficient extraction of natural gas hydrates.

Perfect confinement of acoustic vortex by phase-gradient metacage

Abstract Acoustic wave isolation and noise reduction represent significant challenges in the field of physics and its various applications. Traditional noise control devices are often hampered by substantial size limitations and their operational efficacy is generally restricted to planar waveforms. In this work, we demonstrate the perfect confinement of acoustic vortex waves using an acoustic metacage consisting of phase-gradient metasurfaces. By leveraging the parity-reversed diffraction rule of the phase-gradient metasurfaces, the designed metacage exhibits remarkable capabilities for perfect confinement of acoustic vortex waves, showcasing robust performance even with source offsets. These findings present a promising strategy for the development of precise and adaptable acoustic confinement technologies.

Work-Related Low Back Pain Among Physical Therapists in the Makkah Region, Saudi Arabia: A Cross-Sectional Study

Background/Objectives: Low back pain (LBP) is a major work-related musculoskeletal disorder experienced globally, significantly limiting individuals’ daily activities and work performance. This study aimed to assess the prevalence of work-related LBP among physical therapists in the Makkah region of Saudi Arabia. Methods: A cross-sectional survey was conducted using an online self-reported questionnaire, which covered three domains: demographic information, history of LBP prior to joining the physical therapy field, and work-related LBP experienced during their current job. The questionnaire was distributed to 300 physical therapists in the Makkah region, yielding 151 responses. Data were analyzed to explore associations between LBP and various categorical and continuous factors. Results: Among the respondents, 78.1% reported experiencing LBP during their work as physical therapists, while 21.9% did not. Of those with LBP, 53.4% reported mild pain, 39.8% reported moderate pain, and smaller proportions reported severe pain (4.2%) or no pain (2.5%). Additionally, 52.5% of respondents with LBP indicated that it negatively affected their daily activities. Conclusions: Work-related LBP is highly prevalent among physical therapists in the Makkah region of Saudi Arabia, significantly impacting both patient care and the therapists’ daily functioning.

3D hydrogel-based salt resistant self-floating solar-driven interfacial evaporator with efficient water-lifting capacity for desalination

Solar desalination has been extensively researched as a promising way to address freshwater shortages. However, developing a salt resistant solar evaporator that can be easily extended and manufactured is still a challenge in practical applications. In this work, a 3D hydrogel-based salt resistant self-floating solar-driven interfacial evaporator with efficient water-lifting capacity was proposed using the prepared hydrogel with carbon black (CB) nanoparticles and extruded polystyrene (XPS) board as raw materials. The experimental results implied that the developed evaporator had the highest evaporation rate and evaporation efficiency at 0.05 g CB loading, which were 1.70 kg m-2h−1 and 92.8 % at a light intensity of 1 kW/m−2(−|-). Moreover, the evaporator also displayed prominent salt resistance in the evaporation of brine with high salinity and outstanding stability after 10 cycles. Significantly, the outdoor experiment demonstrated that 1 m2 evaporator can generate 5923.5 g freshwater per day, which was enough to meet the daily requirement of two adults for drinking water. In addition, the physical fields of the hydrogel with CB nanoparticles of the evaporator at evaporation equilibrium were simulated to analyze its long-term and high-performance operation capability. All in all, the 3D hydrogel-based salt resistant self-floating solar-driven interfacial evaporator with efficient water-lifting capacity presented an enormous application prospect in the field of solar desalination.

Effects of Various Physical Field–Assisted Techniques and Combination Methods on Extraction of Flavonoids and Polyphenols From Angelica keiskei

ABSTRACTAngelica keiskei has been well documented as a promising resource rich in bioactive chemicals, especially flavonoids. Field‐assisted extraction and their hybrids have been proved to be advanced approaches for the efficient utilization of flavonoids compared to conventional extraction methods. The current study aims to optimize the extraction conditions of the flavonoids from A. keiskei through high‐pressure processing, ultrasound‐assisted extraction, and microwave‐assisted extraction. Furthermore, taking total flavonoid content, total phenolic content, and antioxidant activity as indexes, three combination methods, high‐pressure processing combined with ultrasound‐assisted extraction, high‐pressure processing combined with microwave‐assisted extraction, and ultrasound‐assisted extraction combined with microwave‐assisted extraction, were further investigated and compared to enhance the extraction efficiency. The results indicate that the A. keiskei extracts obtained by ultrasound‐assisted extraction combined with microwave‐assisted extraction have the optimal total flavonoid content (41.671 mg/g) and total phenolic content (12.071 mg/g), as well as the strongest antioxidant activity. Scanning electron microscopy analyses reflect that the ultrasound‐assisted extraction combined with microwave‐assisted extraction treatment imposed the most pronounced damage to A. keiskei, in which the particles were changed into the smaller size. In vitro experiments for A. keiskei extracts demonstrate that it can effectively inhibit α‐amylase and tyrosinase, suggesting its potential hypoglycemic and whitening activity. This study demonstrates that A. keiskei extracts may serve as a possible source of antioxidants, whereas ultrasound‐assisted extraction combined with microwave‐assisted extraction might represent an innovative and advantageous method for flavonoid extraction from A. keiskei.

Research on seismic characteristics of supercharged boiler based on measured boundary

Supercharged boilers are susceptible to seismic impact loads, which can cause severe structural responses and exceed their ultimate bearing capacity. Compared with the traditional simplified structural model for earthquake resistance research in cold state, this paper establishes a real and complete three-dimensional physical model of the supercharged boiler base, and uses the reverse calculation method to obtain the boundary conditions of the boiler based on the temperature of the experimental measurement points. The temperature field and pressure field of the boiler are reconstructed, combined with the coupling method of thermal mechanical solid multiple physical fields. Using time-domain data of peak acceleration in various directions under typical earthquakes as external input loads, this study explores the seismic characteristics of boilers in the X, Y, and Z directions using time-domain analysis methods, and clarifies the vibration response mechanism in the stress concentration area of the tube sheet. The results show that the measurement and simulation error of the temperature of the inner and outer walls of the drum is 0.10 %; The individual effects of thermal stress and mechanical stress account for 107.56 % and 66.46 % of the total stress, respectively. Thermal stress plays a dominant role, while mechanical stress produces impedance effects; Under the action of an earthquake, the tube sheet undergoes reciprocating oscillation motion, and the impedance effect generated by the flexibility of the tube bundle gradually attenuates. The local stress in the X and Y directions increases by 7.70–8.27 MPa, while the local stress concentration phenomenon occurs in the Z direction due to low damping and stiffness.

Lithium Deposition Mechanism under Different Thermal Conditions Unraveled via an Optimized Phase Field Model.

As one of the most important physical fields for battery operation, the regulatory effect of temperature on the growth of lithium dendrites should be studied. In this paper, we develop an optimized phase field model to explore the effect of temperature on the growth of Li dendrites in Li metal batteries. We incorporated full lithium deposition kinetics, including atom diffusion and solid electrolyte interface restriction on interface kinetics, into the model and revealed their significance in determining the transformation of the lithium deposition morphology from moss-like to dendrite-like. We found that a high temperature or dispersed hot spots are more conducive to stable battery operation than a low temperature or concentrated hot spots due to the enhanced diffusion kinetics at the high temperature and the more uniform temperature distribution of dispersed hot spots. We believe our work can provide a useful tool for further exploring the thermal effect on stable lithium metal battery operation.

More on unconstrained descriptions of higher spin massless particles

Here we suggest a new local action describing arbitrary integer spin-s massless particles in terms of only two symmetric fields φ and α of rank-s and (s−3) respectively. It is an unconstrained version of the Fronsdal theory where the double traceless constraint on the physical field is evaded via a rank-(s−4) Weyl like symmetry. The constrained higher spin diffeomorphism is enlarged to full diffeomorphism via the Stueckelberg field α through an appropriate field redefinition. After a partial gauge fixing where the Weyl symmetry is broken while preserving diffeomorphisms, the field equations reproduce, for arbitrary integer spin-s, diffeomorphism invariant equations of motion previously obtained via a truncation of the spectrum of the open bosonic string field theory in the tensionless limit. In the s=4 case we show that the functional integration over α leads to a unique nonlocal Weyl and diffeomorphism invariant action given only in terms of the physical field φ whose spectrum is confirmed via an analysis of the analytic structure of the spin-4 propagator for which we introduce a complete basis of projection and transition nonlocal differential operators. We also show that the elimination of α after the Weyl gauge fixing leads to a nonlocal diffeomorphism invariant action previously obtained in the literature. Published by the American Physical Society 2025

Thermal analysis of exciter rolling bearing based on heat flow coupling

Purpose This study aims to investigate the temperature rise characteristics of vibrating rolling bearings under the influence of the polarization force of unbalanced eccentric blocks. A thermal-fluid-solid mechanics coupled finite element model is established to analyze the effects of different loads and rotational speeds on bearing temperature to prevent overheating, wear and thermal damage. Design/methodology/approach A thermal-fluid-solid mechanics coupled finite element model of the vibrating rolling bearing is developed based on the principles of heat transfer. Finite element analysis software is used to conduct numerical simulations and study the temperature distribution of the bearing system under different loads and speeds. The model’s accuracy is verified by experimentally measuring the actual temperature of the bearing under the same working conditions. Findings This study successfully established a thermal-fluid-solid mechanics coupled finite element model of a vibrating rolling bearing, verifying its accuracy and reliability. The research results provide an essential reference for optimizing bearing design, preventing overheating and extending service life. Research limitations/implications By analyzing the temperature rise characteristics under various load and rotational speed conditions, the law governing the internal temperature distribution of bearings is revealed. This finding offers a theoretical foundation for comprehending the thermal behavior of bearings. Practical implications This study offers a scientific foundation for the maintenance and fault diagnosis of shaker rolling bearings, aiding in the timely identification and resolution of thermal damage issues. Through the optimization of bearing design and usage conditions, the equipment’s lifespan can be prolonged, maintenance expenses can be minimized and production efficiency can be enhanced. Originality/value A thermal-fluid-solid mechanics coupled finite element model of a vibrating rolling bearing was established, considering the interaction of multiple physical fields. The influence of the polarization force from the unbalanced eccentric block on the bearing temperature is analyzed in detail, which is close to the actual working conditions. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2024-0396/

Discovering emergent connections in quantum physics research via dynamic word embeddings

Abstract As the field of quantum physics evolves, researchers naturally form subgroups focusing on specialized problems. 
While this encourages in-depth exploration, it can limit the exchange of ideas across structurally similar problems in different subfields. 
To encourage cross-talk among these different specialized areas, data-driven approaches using machine learning have recently shown promise to uncover meaningful connections between research concepts, promoting cross-disciplinary innovation.
Current state-of-the-art approaches represent concepts using knowledge graphs and frame the task as a link prediction problem, where connections between concepts are explicitly modeled.
In this work, we introduce a novel approach based on dynamic word embeddings for concept combination prediction. 
Unlike knowledge graphs, our method captures implicit relationships between concepts, can be learned in a fully unsupervised manner, and encodes a broader spectrum of information. 
We demonstrate that this representation enables accurate predictions about the co-occurrence of concepts within research abstracts over time.
To validate the effectiveness of our approach, we provide a comprehensive benchmark against existing methods and offer insights into the interpretability of these embeddings, particularly in the context of quantum physics research. 
Our findings suggest that this representation offers a more flexible and informative way of modeling conceptual relationships in scientific literature.

Association between the attentional network efficiency and change of direction speed ability in young male Indian footballers

IntroductionInteractions between cognitive functions and sports-specific motor actions are crucial for strategic sports performance. Change of direction speed (CODS) is an essential motor ability required for rapid positional maneuvering in football. Although CODS lacks perceptual judgment and anticipatory elements of higher-level cognition, its connection with fundamental cognitive abilities cannot be undermined. The attentional networks is the basis of the fundamental cognitive abilities controlling complex behavior. The present study aimed to investigate the association between CODS ability and the efficiency of alerting, orienting, and executive components of the attentional networks, and decision-making in footballers.MethodsSeventy-eight male footballers (age: 15.4 ± 0.87 years, BMI: 19.4 ± 1.98 kg/m2) during pre-season completed a battery of field tests comprising Illinois agility test (IAT), 30 m sprint, standing broad jump, and Yo-Yo test. Attentional network components and decision-making ability were tested in the participants with computerized Attentional Network Test-Interactions (ANT-I) and choice reaction time (CRT) tasks in the laboratory set-up. A 2(alerting) ×3 (orienting) ×2 (executive) repeated measures ANOVA tested interactions between the attentional network components. Partial correlation was conducted between the physical (field tests) and cognitive test scores adjusted for age and BMI.ResultsCODS ability measured with IAT was significantly correlated [r = +0.507 (large), p < 0.05] with the executive control network only, nor with alerting [r = −0.039 (trivial), p > 0.05] and orienting [r = + 0.051 (trivial), p > 0.05] networks and neither the CRT task performance [r = −0.011 (trivial), p > 0.05].DiscussionA strong positive association between executive control and preplanned CODS indicates better interference control by the attentional network. The later may be a factor for faster CODS execution in young footballers. Hence, it may be concluded that better CODS ability is possibly an outcome of innate competence in executive control of the attentional network in young male footballers. These findings attempted to fill the knowledge gap by highlighting the importance of the attentional network functions in modulating CODS ability. The outcomes can benefit football training by implementing ANT-I test in sports-specific settings and for screening purposes. However in the future, a large-scale study including female footballers is required to strengthen this claim further.

Acoustic interaction of submerged thin-shell structures considering seabed reflection effects

This paper presents a novel approach for simulating acoustic-shell interaction, specifically focusing on seabed reflection effects. The interaction between acoustic waves and shell vibration is crucial in various engineering applications, particularly in underwater acoustics and ocean engineering. The study employs the finite element method (FEM) with Kirchhoff-Love shell elements to numerically analyze thin-shell vibrations. The boundary element method (BEM) is applied to simulate exterior acoustic fields and seabed reflections, using half-space fundamental solutions. The FEM and BEM are coupled to model the interaction between acoustic waves and shell vibration. Furthermore, the FEM-BEM approach is implemented within an isogeometric analysis (IGA) framework, where the basis functions used for geometric modeling also discretize the physical fields. This ensures geometric exactness, eliminates meshing, and enables the use of Kirchhoff-Love shell theory with high-order continuous fields. The coupled FEM-BEM system is accelerated using the fast multipole method (FMM), which reduces computational time and memory storage. Numerical examples demonstrate the effectiveness and efficiency of the proposed algorithm in simulating acoustic-shell interaction with seabed reflection.

Numerical tools in particle physics

In this paper, I stress the role of the numerical tools for any theoretical predictions in the field of particle physics due to the difficult and complex computation of the different observable related to the different processes. Being one of the contributors to the program Phantom, I chose it as a prototype to shed light on the main features of the Monte Carlo event generators and how they work. I tried to keep the presentation as simple as possible, avoiding as many technical difficulties as possible, to make this short review accessible to a large number of undergraduate students. It can serve as a good starting point with plenty of references for those who want to deepen their knowledge in the subject.

Comparative analysis of purine release in ostrich meat under different food heating techniques

Abstract Ostrich meat has attracted significant attention as an appealing substitute for traditional red meat, particularly due to its abundant protein content, minimal fat content, and wide array of vital nutrients. However, concerns remain regarding the purine content of ostrich meat and its implications for human health, particularly in relation to conditions such as hyperuricemia and gout. This study focused on ostrich meat, an increasingly popular emerging ‘red meat’ ingredient, and investigated the effects of three types of single physical field processing (steam, microwave, and infrared) as well as their combinations in dual and triple physical field processing on purine content in ostrich meat. The results indicated that both dual and triple physical field combinations significantly reduced purine content in ostrich meat (p < 0.001). Compared with fresh ostrich meat, dual physical field processing (steam + infrared) and triple physical field processing achieved the greatest reductions in purine content, by 43.34% and 45.12%, respectively. Furthermore, the impact of processing on purine content after simulated digestion was assessed. The results revealed significant variations in purine content among different processing methods, which have implications for the nutritional quality and safety of processed ostrich meat products. Understanding these effects is crucial for optimizing processing methods and promoting the development of healthier meat products with reduced purine content.

The spectral analysis of the state parameters of technical systems in the regular and damaged states

It is noted that reaction of bearing elements of structures and engineering components to service loadings, impacts of physical fields and corrosive environments is initiation not only fields of stresses and strains, but also fields of damages. At the same time depending on conditions of a loading and environment various mechanisms of accumulation of damages and fracture which indicators are essential changes in spectra of a response of technical systems to different impacts are realized. The analysis of parameters of a state of such systems by registration of spectral characteristics of service processes allows to carry out estimations of levels of their damage in rather full degree. On the basis of results of research of service states of technical systems on spectral diagnostic parameters approaches to the analysis of amplitude-frequency characteristicses of their actual states both in the regular allowed states, and upon transition to dangerous states owing to accumulation in them of dangerous service damages are offered. At the same time criteria of transition of technical systems from regular in emergency and catastrophic states at accumulation of critical limits of damage are formulated. Examples of the dispersed initiation of microcracks in material of structures parts at a cyclic deformation with their propagation in the main fractures, and also examples of the analysis of dynamic states on vibration spectra of a response of simple and compound technical systems with the crack which arose in them and with existence of defects are given. At the same time the possibility of obtaining initial computation and experimental information on parameters of a stress-strain state and damage of installation with use of methods of the spectral analysis of a response of a compound structure to vibration impact as a result of initiation of damage of its separate parts is shown. Results of such spectral analysis can be used for diagnostics and monitoring of conditions of regular service of high-loaded installations of a technosphere and transition of their states to limit emergency and catastrophic in relation to objects of power engineerings, space-rocket and aircraft equipment.

A Descriptive Study on Interconnection Networks for Parallel Computing and Algorithm Models in Parallel Computing

In parallel computing, Interconnection networks are very crucial for efficient communication among all processors within a similar system. Parallel computing has become a crucial topic in the concern of computer science and also it is revealed to be critical when researching in high performance. The evolution of computer architectures towards an improved number of nodes, where parallelism could be the approach to option for speeding up an algorithm within the last few decades. Efficient data transfer between processors is an essential component in any large scale parallel computation. Motivated by the growing interest in parallel computers, a significant amount of theoretical research has been devoted to the area of interconnection networks for parallel computers, most of it to the packet routing (or store-and-forward) model of communication. We survey some of the major developments in this field, and discuss several new alternative models of communication, In many large scale applications, communication time dominates the execution time of the whole parallel computation. Thus, the performance of a large scale parallel computer is highly correlated with the efficiency of its network and communication algorithm. The combination of processing units build a model of computation (circuits) has gained an essential place in the area of high performance computing (HPC) due to its configuration and considerable processing supremacy that is parallel, series, etc. The aim of the Presenting this paper is study on the idea of parallel computing and its programming models and also explore some theoretical and technical concepts which can be often needed to understand the Interconnection network. In particular, we show how this technology is new in assisting the field of computational physics, especially when the issue is data parallel. In the real-life example of parallel computing, there are two queues to get a ticket of anything; if two cashiers are giving tickets to 2 persons simultaneously, it helps to save time as well as reduce complexity

Exploring soliton and soliton-type solutions to the modified Camassa-Holm and Schrödinger-Hirota equations: An analytical approach

Abstract In this work, we investigate the solitary wave solutions of two nonlinear evolution equations (NLEEs): the modified Camassa-Holm (MCH) equation and the Schrödinger-Hirota (SH) equation. Both are widely used, especially in fluid dynamics, nonlinear optics, and quantum mechanics. We analytically extract solitary wave solutions to the considered equations by applying the (G'⁄((G'+G+A)))-expansion method which enhances the understanding of wave dynamics in various fields of mathematical physics and engineering. The graphical representations of the obtained results of these two equations for certain values are shown in 3D, 2D, contour, and density plot diagrams, all of which are of the soliton types with one compacton, one anti-flat kink-shaped, one anti-bell-shaped, and one parabolic-shaped soliton. Moreover, we analyze the role of non-algebraic functions, specifically exponential and trigonometric functions, in characterizing the intricate waveforms and their stability properties. We systematically explore the applicability of the chosen expansion method, demonstrating its effectiveness in generating explicit solutions and examining the conditions under which these solitary wave phenomena arise. The novel findings contribute new analytical insights into these classical equations and pave the way for future research into the complex behaviors exhibited by nonlinear wave interactions.

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/

Development of the NUCLEUS Detector to Explore Coherent Elastic Neutrino-Nucleus Scattering

The NUCLEUS experiment, currently being commissioned at the Technical University of Munich, is designed to observe coherent elastic neutrino-nucleus scattering (CEνNS) from reactor neutrinos and measure its cross-section with a percent-level precision at recoil energies below 100 eV. As a Standard Model process, CEνNS provides a unique probe into neutrino properties, potential new physics, and background suppression techniques relevant to dark matter experiments. The experiment utilizes gram-scale cryogenic calorimeters operating at 10 mK with an energy threshold of 20 eV. Situated at a shallow overburden of 3 m of water equivalent, the experimental site necessitates an advanced shielding strategy combining active vetoes and passive layers to reduce background rates to approximately 100counts/(kg·day·keV), as confirmed by full setup simulations. The commissioning phase has successfully demonstrated the stable operation of the cryogenic target detectors, achieving baseline resolutions below 10 eV, and the integration of the various shielding systems. Following this milestone, the experiment is set to transition to the EdF Chooz B nuclear reactor in France in 2025, where it will enable precise measurements of CEνNS, contributing to the understanding of neutrino interactions and advancing the field of astroparticle physics.

Coupled modelling and analysis of lubrication-wear evolution of textured piston/cylinder pair in high-pressure common rail pumps

Abstract Surface texturing is an important approach to enhance fluid lubrication performance and reduce friction and wear. Research on the surface texturing of the piston/cylinder pair considering various characteristics such as multi-physical fields and the evolution of friction and wear is still insufficient. The novelty of this work aims to establish a coupled numerical simulation model considering the coupling effect of multiple physical fields, wear of the cylinder bore and surface texture, and determine the effective surface texture parameters to improve the friction performance of the mechanical components of high-pressure common rail pump. The influence of surface texture on friction and wear characteristics and the evolution of lubrication-wear under different geometric cases were in-depth investigated, and the action mechanism of surface texture on lubrication and wear was revealed. Through numerical analysis, optimal parameters were identified that significantly reduce the friction coefficient and wear amount, offering practical insights for mitigating friction and wear in mechanical systems.