Source Of Friction Research Articles

Acoustic emission during the freezing of water or the melting of ice in aircraft

It is a frequently overlooked phenomenon that matter can produce sound emissions when undergoing a phase transition. The exact cause of this sound is until now not modeled and understood in depth, but it appears certain that sudden volume changes, cracks, friction, and other sources that occur during e.g. crystal decay/growth in melting/freezing processes must be considered. However, a generally accepted theory of the "sound of phase transitions" is lacking. In this paper we present a general introduction in this field. Besides the more fundamental aspects, the AE generation during the melting of ice can be used to detect the presence of this respective substance in technical structures. An interesting application is to detect the melting ice in aircraft. Adverse water accumulation, resulting from contamination and condensation, is regularly found in fuel tanks, and scheduled drainage procedures of this water after the melting of the ice are important to ensure the safety of systems and structures. A practical problem for drainage after flight is determining the right time to start the process. Beginning too early would mean that the remaining ice cannot be removed, and waiting too long presents an economic problem as it increases the aircraft's downtime. There is currently no technology that reports when all water has melted. To realize this goal acoustic sensors were attached to the skin of the tank walls, and the acoustic signals were intense enough to propagate through the aluminum sheets and coating and further analyzed. In this way, the completion of the melting of ice was determined by the time at which the acoustic emission stopped. We present measurements on a laboratory scale, the results from a climate chamber on relevant replica’s, and the outcome of a first campaign on an operational aircraft (Airbus A330).

Sliding on Slide-Ring Gels

Recent investigations have pointed to physical entanglements that greatly outnumber chemical crosslinks as key sources of energy dissipation and low friction in hydrogel networks. Slide-ring gels are an emerging class of hydrogels described by their mobile crosslinks, which are formed by rings topologically constrained to slide along linear polymer chains within the network. These materials have enjoyed decades of study by polymer chemists but have been underexplored by the tribology community. In this work, we synthesized a pseudo-rotaxane crosslinker from poly(ethylene glycol) diacrylate (PEG-diacrylate) and α-cyclodextrin-acrylate followed by hydrogel networks by connecting the sliding crosslinks with polyacrylamide chains. The mechanical and tribological properties of slide-ring hydrogels were investigated using a custom-built microtribometer. Slide-ring hydrogels exhibit unique behavior compared to conventional covalently crosslinked polyacrylamide hydrogels and offer a vast design space for future investigations.Graphical

Working Around the Clock: Temporal Distance, Intrafirm Communication, and Time Shifting of the Employee Workday

This paper examines the effects of temporal distance generated by time zone separation on communication in geographically distributed organizations. We build on prior research, which highlights time zone separation as a significant challenge, but argue that employees may time shift—move work-related communication to outside of regular business hours—to counteract temporal distance. We propose a theory in which employees’ tendency to time shift depends on the demands of their tasks and collaborative relationships and individuals’ ability to supply work outside of regular business hours. Analyzing communication-level data from 12,038 employees of a large multinational firm and using cities’ shifts to/from daylight saving time for identification, we find that temporal distance leads to sizable but smaller than expected reductions in volumes of rich, synchronous communication between employees. Consistent with our arguments, increased temporal distance significantly increases time shifting of work-related communication, especially among workers whose jobs are nonroutine and interactions in strong collaborative relationships. We further document that female employees and employees based in countries with stricter legal work hour limits engage in significantly less time-shifted communication. Our study improves understanding of a ubiquitous source of collaboration friction. It also sheds light on a potential source of inequities in workplace outcomes stemming from differences in individuals’ ability to work outside of regular business hours. Supplemental Material: The online appendix is available at https://doi.org/10.1287/orsc.2023.17558 .

Customer success managers' involvement in sales: Taxonomy, frictions, and implications

In recent years, several organizations have implemented customer success (CS) management to maximize customers' value in use. Despite the acknowledged benefits of CS management, challenges persist, particularly in understanding the involvement of CS managers in sales. Drawing from qualitative interviews with CS managers, this study reveals variability in CS managers' involvement in presales activities and responsibility for up- and cross-selling. These insights have led to the development of a taxonomy outlining different types of CS manager involvement in sales. This taxonomy provides more nuance to the analysis of CS managers' involvement in sales than previously assumed in the literature. Additionally, this research uncovers three CS manager-perceived sources of friction: short-term sales focus, conflicts over customer ownership, and poor handovers. These insights contribute to understanding the complexities of CS managers' involvement in sales and offer practical implications for improving alignment between both functions.

Institutional Friction and Policy Responsiveness: The Puzzle of Coalitional Fragmentation and Executive-Legislative Balance

Research on policy responsiveness to public opinion highlights differences owing to political institutions—both electoral and governmental. Electoral institutions that produce coalition governments tend to reduce responsiveness in between elections. Government institutions that divide powers horizontally, by contrast, appear to increase that responsiveness. These findings point to the role of institutional “friction” in shaping what governments do, though the two sources appear to produce different effects—one harmful and the other helpful. This paper explores this apparent contradiction. We revisit and clarify theoretical assumptions and outline alternative models of the effects of friction. Extending previous tests, now in 18 countries, we find clearer evidence supporting that earlier research and more firmly establish friction as the mechanism, particularly as regards the influence of electoral systems. The two institutional sources of friction appear to influence responsiveness in different ways, which has implications for politics and policy that we consider in the concluding section.

Ten simple rules for computational biologists collaborating with wet lab researchers.

Computational biologists are frequently engaged in collaborative data analysis with wet lab researchers. These interdisciplinary projects, as necessary as they are to the scientific endeavor, can be surprisingly challenging due to cultural differences in operations and values. In this Ten Simple Rules guide, we aim to help dry lab researchers identify sources of friction and provide actionable tools to facilitate respectful, open, transparent, and rewarding collaborations.

Examination of Pediatric Burn Incidence and the Impact of Social Determinants of Health in Florida.

Introduction Burn injuries are a major mechanism of trauma worldwide, caused by friction, cold, heat, radiation, chemical, or electric sources. Most often, burn injuries occur due to heat contact from hot liquids, solids, or fire, termed scald burns and flame burns, respectively. These types of injuries are complex and carry major injury and mortality risks, especially in pediatric populations. Burn trauma prevention has been a major focus in the US, with initiatives to increase public health outreach and safety measures. Unfortunately, children in socioeconomically disadvantaged situations may face these types of injuries at disproportionately higher rates, and we aim to highlight these disparities, if any, within our Florida community. Materials and methods This study was designed as a retrospective observational analysis using publicly available data from the Florida Health Community Health Assessment Resource Tool Set (CHARTS). Data was extracted for nonfatal burn injuries resulting in ED visits in the years 2018-2020. This data was limited to those ranging from 0 to 19 years old and converted to rates of burn injuries per 100,000. Sociodemographic details for each county were recorded from County Health Rankings & Roadmaps and compared with burn data in each respective county. Frequencies were generated for categorical data, and statistical analyses for burn rates and sociodemographic details were performed with a generalized linear model using a Poisson distribution and bivariate correlation for a p < 0.05. Results In Florida, the median annual burn rate per 100,000 was 136 (IQR: 96-179), with Jackson county holding the highest rate of 323 and Glades, Hardee, and Lafayette each holding a rate of 0. Of the 18 socioeconomic factors examined, a total of five were found to have no statistically significant effect on nonfatal burn injury ED visits: severe housing problems, percentage of Asians, teen births, percentage of children (<18 years) in poverty, and severe housing cost burden. The two most important factors to be found in nonfatal burn ED visits of pediatric patients were the percentage of those younger than 19 years old without health insurance and the average grade level performance of third-grader reading scores. When adjusting for the small sample size using Firth's bias-adjusted estimates and overdispersion, both reading scores and those without insurance play a significant role in pediatric burn injuries. For each increase in a single point in reading scores, the incidence rate ratio decreases by 97.1% (95% CI). For every percentage increase in children insured, there is a 28.8% decrease in pediatric burn injuries (95% CI). Conclusions This analysis highlights increased pediatric burn rates across multiple social determinants of health (SDOH) in all 67 Florida counties. The findings here demonstrate that there may continue to be a disproportionate distribution of burn rates among lower and higher sociodemographic areas. This study further highlights this trend within the Florida community, and continued research will be necessary to meet the needs of lower sociodemographic areas to improve burn rates in vulnerable populations, such as children, who are at increased risk of injury.

A novel efficient and robust treatment of the friction source term in 2D shallow water inundation models

The technological advancements of the last few decades have fostered the use of two-dimensional (2D) Shallow water Equations (SWE) flood simulations not only in academic research but also in practical real-world applications and territorial planning. The evaluation of flow resistance due to friction is crucial as it plays a relevant role in a variety of flow conditions. However, problems arise in dam-break and overland flow applications involving very small water depth because the time scale connected to the friction term may be much smaller than the hydrodynamic time scale. To cope with this issue, known as source term stiffness, an implicit treatment of the friction term is frequently adopted in Finite Volume (FV) numerical schemes, but there are cases (null roughness coefficient or null flow velocity) where a division by zero may occur during calculations, leading to a crash of the algorithm. Herein, we propose a reformulation of the implicit friction term that is general, more stable and computationally efficient (with a speed-up of approximately 3 times for the routine running the friction computation) than currently available approaches. The novel implicit method allows to manage special conditions with null roughness or null discharge, without resorting to ad-hoc thresholds, and can be easily implemented in existing schemes with pointwise friction treatment. The novel friction approach is implemented in a purposely simple FV numerical scheme (hydrostatic reconstruction to account for the bed slope terms, first-order accuracy in time and space) - to better focus on the friction term treatment - and it is validated against analytical, synthetic, laboratory and real-world case studies, showing promising capabilities.

How can ridesharing be facilitated in car dependent practices? Insights from carless participants in organized leisure

This paper contributes a hitherto overlooked perspective on leisure practices-as-entities, and as performed by the carless, to understand and facilitate the conditions for related shared mobility. It identifies how organized car dependent leisure practices can be performed more sustainably by means of ridesharing. Applying a social practice perspective, car use is viewed as bundled with leisure practices. Drawing on in-depth interviews with 25 carless practitioners of scouting, orienteering, and children’s soccer in Sweden, we seek to determine the procedures and frictions of ridesharing, and how it can be facilitated. The findings show that ridesharing occurs and is mediated by digital tools in all three studied practices. Notable variations and sources of friction relate to whether ridesharing is collectively or individually coordinated, which is connected to the meanings and competences of the leisure practices themselves. The paper illustrates that, to facilitate ridesharing, competences beyond the management of digital tools are needed. More concretely, the promotion of ridesharing as part of a more formalized exchange within clubs and associations for organized leisure is suggested. Carless performers of car dependent practices illustrate potential “proto-practices” beyond the private car.

Visual investigation of static contact conditions at bolted joints

Accurate numerical models of physical systems are vital in engineering applications, and those for single components are generally accurate. However, there are significant errors in modelling the dynamics of bolted joints, which is a key source of friction in real-life systems, because existing experimental techniques are still far from offering sufficient understanding of the contact conditions of bolted joints. In the current study, static contact conditions of bolted joints are investigated with at least one component in the assembly being transparent. A novel visual identification method is proposed to (i) measure the clearance between plates in the vicinity of bolted joints and (ii) identify the contact conditions in receding contacts by applying a paste (known as Engineer’s blue) to the contact surface. The paste is thinner than most media applied in previous studies. Clearance results obtained by visual inspection are checked against micrometer profile tracing, and the contact regions predicted by the method are used to validate simulation results obtained from two contact mechanics algorithms. Difference between simulation and experiment is as low as 9% in terms of contact region diameters. Last but not least, the reproducibility of the method has been demonstrated, especially if the clearance is in the range of 2 to 5 μm.

A robust unstructured finite volume scheme for urban flash flood simulation: Duhok city as a case study

ABSTRACT A robust well-balanced finite volume scheme is proposed for simulating the flash floods due to rainfall-runoff process. The solver’s implementation on unstructured triangular meshes is based on a Godunov-type second-order upwind finite volume formulation, and Roe’s average scheme is used to determine the fluxes. The bed slope, friction and rainfall source terms are discretized using an upwind approach. The suggested algorithm uses the slope limiter and Hancock’s predictor-corrector method in order to secure numerical stability. The proposed model overwhelms the drawbacks of many commercial codes that use the finite difference, finite elements and finite volume in their scheme, especially in dealing with rapid change in topography. The prepared scheme solves the two-dimensional shallow water equations over a real topography of Hishkaro basin located in Duhok city in Kurdistan of Iraq where the variation of bed elevation reaches 717 m. The scheme is validated against real observed data in Duhok city provided by the Sewage directory. The data of five observation points over the study area were used to validate the code. The results showed that the max water level reaches 3.67, 2.12, 1.20, 0.67 and 0.3 m at observed points 3, 2, 4, 1 and 5, respectively.

Influence of Marangoni convection, viscous dissipation, and variable fluid viscosity of nanofluid flow on stretching surface analytical analysis

AbstractThe current research paper investigates the viscous dissipation, influence of Marangoni convection (MC), and the variable fluid viscosity of nanofluid flow on stretching surfaces. The flow system takes into account variable viscosity with the impact of MC. Furthermore, velocity and temperature slips at the stretching surface are also considered in this study. To convert a collection of NLPDE to a NODE, we applied appropriate transformations. We utilize Homotopy analysis method (HAM) to solve this set of equations. The effects of temperature, tangential, and radial velocities on numerical perceptions involving Marangoni convection, nanoparticle volume friction, porosity parameter, Eckert number (EN) and heat source input factors are shown. A physical description is used to simulate and evaluate the structures of flow features such as velocity and temperature profiles in response to changes in developing factors. Based on the given result, we can observe that the temperature profile increases as EN and the heat source parameter increase, and that the velocity profile decreases as MC increases and increases with the porosity parameter.

The application of differential constraint method for the solution of non-homogeneous generalized Riemann problem

This paper reports the solution to the Non-homogeneous Riemann problem by applying the approach of differential constraint for the one-dimensional (1 − D) generalized Chaplygin gas equations with non-constant initial data. Here we take source term as a Coulomb type constant frictional term. We reduced the governing non-homogeneous model into a homogeneous one by introducing a new velocity variable. By virtue of this advantage of frictional type source term, we would easily determine the solution of reformulated homogeneous governing model. We have computed the differential constraint and its consistency conditions for the specified model. Moreover, we have derived here the compatibility condition between the governing model and the differential constraints. The solutions to generalized Riemann problem for the 1 − D Euler’s equation of governing gas model are obtained as well as for the smooth and non-constant initial conditions the comprehensive overview of the solutions is studied.

Axion inflation in the strong-backreaction regime: decay of the Anber-Sorbo solution

Axion inflation coupled to Abelian gauge fields via a Chern-Simons-like term of the form ϕFF~\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\phi F\\overset{\\sim }{F} $$\\end{document} represents an attractive inflationary model with a rich phenomenology, including the production of magnetic fields, black holes, gravitational waves, and the matter-antimatter asymmetry. In this work, we focus on a particular regime of axion inflation, the so-called Anber-Sorbo (AS) solution, in which the energy loss in the gauge-field production provides the dominant source of friction for the inflaton motion. We revisit the AS solution and confirm that it is unstable. Contrary to earlier numerical works that attempted to reach the AS solution starting from a regime of weak backreaction, we perform, for the first time, a numerical evolution starting directly from the regime of strong backreaction. Our analysis strongly suggests that, at least as long as one neglects spatial inhomogeneities in the inflaton field, the AS solution has no basin of attraction, not even a very small one that might have been missed in previous numerical studies. Our analysis employs an arsenal of analytical and numerical techniques, some established and some newly introduced, including (1) linear perturbation theory along the lines of ref. [1], (2) the gradient expansion formalism (GEF) developed in ref. [2], (3) a new linearized version of the GEF, and (4) the standard mode-by-mode approach in momentum space in combination with input from the GEF. All these methods yield consistent results confirming the instability of the AS solution, which renders the dynamics of axion inflation in the strong-backreaction regime even more interesting than previously believed.

Intensity analysis of frictional heat source during core tube sampling and drilling

AbstractCurrently, the heat generated during coal core tube sampling causes rapid gas desorption, leading to substantial measurement errors in laboratory gas content assessments. Reducing these errors requires studying frictional heat from core tube friction against the hole wall and coal core temperature rise. Combining the independently developed device to simulate the thermal effect of coring and the COMSOL finite element analysis software, the intensity of the frictional heat source during the core tube sampling and drilling process was analyzed under different coring depth and rotational speed conditions. The research results show that: At constant speed, frictional heat intensifies as the core depth increases. However, the rate of temperature rise decreases with increasing core depth; when the coring depth is constant, the frictional heat is proportional to the rotational speed. For example, at a depth of 140 m and a rotational speed of 120 r/min, the intensity of frictional heat generated by drilling is 2.21 ∗ 10E6J. Similarly, at 180 r/min, the strength is 2.28 ∗ 10E6J, and at 240 r/min, the strength reaches 3.65 ∗ 10E6J; Under certain conditions, core tube wall temperature will not rise indefinitely but will stabilize to a certain value.

Measuring the stasis: Punctuated equilibrium theory and partisan polarization

AbstractThe American policy process is characterized by a pattern known as “Punctuated Equilibrium,” manifesting as periods of stasis interspersed with large periods of change. Punctuated equilibrium suggests that friction in the policy process and uneven information processing result in a policy process that over‐ and underreacts to problems. Increasingly, American political institutions are also characterized by high levels of partisanship, which are rising steadily and represent one of many sources of institutional friction. We argue that with increased polarization, the policy process has become longer, exaggerating patterns of stasis and punctuation—the periods of stasis being more prolonged and punctuations less frequent. In sum, increased partisan polarization in Congress amplifies patterns of punctuated equilibrium. We test this theory using data from the Comparative Agendas Project on the federal budget and public laws, using kurtosis scores to measure the relative force of punctuations versus statis. We find increasingly leptokurtic distributions of budget changes from 1948 to 2020, but a decreasingly leptokurtic distribution of public law passage across the same time. These findings indicate that polarization has resulted in exaggerated patterns of punctuated equilibrium in the legislative process, and a tendency toward fewer, higher‐stakes public laws.

A well-balanced and positivity-preserving numerical model for overland flow under vegetation effects

In this study, we used the depth-averaged shallow water equations for modeling flows through vegetation field. The vegetation effects on flow are modeled using Morison’s equation taking into account drag and inertia forces which depend on both vegetation and flow properties. We compute and compare different formulations for the stem drag coefficient based on the Froude number or the vegetation volume fraction. Vegetation-induced turbulence is taken into account by adding diffusion terms in the momentum equations. The resulting system of equations is solved using a well-balanced and positivity preserving finite volume method to guarantee the balance between the flux and bed topography source terms, and the positivity of the computed water depth. In our approach, the drag force and bed friction source terms are combined into a unified form. We propose to discretize the obtained term using an implicit temporal method where an analytical technique is used. Special discretization techniques are used for the inertia force and turbulent diffusion terms. Numerical simulations are performed to validate the accuracy of the proposed numerical model. We investigate and compare different formulations for the stem drag coefficient in the vegetation model. Our results confirm the capability of the proposed numerical model for simulating overland flows under vegetation effects.

Market response to environmental social and governance performance: A global analysis

Market remediation of the cost of externalities depends on the market’s ability to read and interpret environmental, social, and governance (ESG) reporting. This study is designed to estimate the market reaction to ESG performance using a comprehensive dataset of 5038 firms from 73 countries for 2016–2021. Overall, we found an asymmetric response highlighting ESG as a source of friction for market efficiency. We further conducted a geographical analysis and found that the results are biased toward different regions. The European Union market indicators exhibited a negative association, which is consistent for each model. This symmetric behavior authenticates EU initiatives for the internalization of ESG factors. In comparison, this behavior is asymmetric for the Americas, Asia, and the Oceanian and African capital markets. The results are robust to alternative econometric methodologies and each pillar of ESG disclosure.

Effect of alumina content on the thermal, mechanical and tribological properties of resin‐based friction materials

AbstractTo investigate the effect of alumina on the thermal, mechanical, and tribological properties of resin‐based friction materials, five friction materials with different alumina contents were prepared by the hot press molding process. The experimental results showed denser friction materials possessed higher hardness, while compressive strength and compression modulus dropped as alumina decreased. Friction material with 6 wt% alumina exhibited outstanding impact strength and great heat resistance. It also showed excellent friction stability, with a maximum mean coefficient of friction (COF) steady between 0.408 and 0.425 at various braking speeds. The wear resistance of friction materials had a positive relationship with the stability of the COF, and the greater the stability of the COF, the better the wear resistance and the lower the corresponding wear rate. The morphology of the worn surface indicated multiple sources of friction at different braking speeds, and large areas of dense friction films were beneficial to stabilizing the COF and reducing the wear rate.Highlights The sample with 6 wt% alumina showed excellent heat resistance, with a residual value of 83.5% at 800°C. The highest compressive strength and compression modulus were achieved in the sample with 8 wt% alumina. The sample containing 6 wt% alumina exhibited the highest COF and the lowest wear rate. The maximum subsurface temperature of the friction materials basically rose as braking speed increased. Large areas of dense friction films were beneficial to stabilizing the COF and reducing the wear rate.

Separating method for multi-source vibration signals in ultra-weak fiber Bragg grating distributed acoustic sensors

Mixing multi-source vibration signals presents a major challenge in target recognition in distributed fiber optic acoustic sensor systems. This article proposes a deep learning method for separating ultra-weak fiber Bragg grating (UW-FBG) distributed acoustic sensor (DAS) multi-source signals. An experimental setup is constructed to create vibration environments for knocking, fan vibration, and steel pipe friction. The UW-FBG DAS system is used to collect single-source vibration signals, as well as two-source and three-source mixed vibration signals. First, a wavelet denoising algorithm is used to preprocess the data. Second, the datasets are constructed for simulated mixed signals and measured mixed signals. The Conv-TasNet deep learning network is utilized to separate DAS vibration signals. Results demonstrate that the proposed method can separate mixed signals of vibration, fan, and steel pipe friction sources, obtaining the corresponding time–frequency entropy similarity of 97.5%, 92.8% and 90.2%, and compared with commonly used multi-source signal separation methods, it has advantages in separation performance and separation time, and exhibits good robustness in different signal environments. This finding the efficacy of the separation method and provides a valuable solution for DAS multi-source signal separation problems in complex environments.