The influence of clearance on friction, lubrication and squeaking in large diameter metal-on-metal hip replacements

Large diameter metal-on-metal bearings (MOM) are becoming increasingly popular, addressing the needs of young and more active patients. Clinical data has shown excellent short-to-mid-term results, though incidences of transient squeaking have been noted between implantation and up to 2 years post-operative. Geometric design features, such as clearance, have been significant in influencing the performance of the bearings. Sets of MOM bearings with different clearances were investigated in this study using a hip friction simulator to examine the influence of clearance on friction, lubrication and squeaking. The friction factor was found to be highest in the largest clearance bearings under all test conditions. The incidence of squeaking was also highest in the large clearance bearings, with all bearings in this group squeaking throughout the study. A very low incidence of squeaking was observed in the other two clearance groups. The measured lubricating film was found to be lowest in the large clearance bearings. This study suggests that increasing the bearing clearance results in reduced lubricant film thickness, increased friction and an increased incidence of squeaking

Model and experiments to determine lubricant film formation and frictional torque in aircraft landing gear pin joints

Pin joints are found in many large articulating structures. They tend to be under high load and articulate slowly; so, the joints typically operate in the boundary or mixed lubrication regimes. This means that the operating torque depends on the respective proportions of liquid and solid contact between the joint mating faces. In this article, a mixed lubrication model of a grease-lubricated landing gear joint is established to determine a theoretical Stribeck curve, frictional torque and lubricant film thickness under different loads. Parameters describing pin joint working conditions, geometry, lubricant properties and pin/bush texture are used. The model can also predict the proportion of the load that is supported by contacting asperities and lubricant film. The changing proportions of these two parts indicate transformations between different lubrication regimes. Experiments on an instrumented pin joint have been carried out to compare with the predicted friction and torque performance. Theoretical calculation results show good consistency with experimental plots at high load. But under low load, the real friction between pin and bush is significantly lower than theoretical predictions

Transient Tribo-Dynamics of Thermo-Elastic Compliant High-Performance Piston Skirts

Advanced piston technology for motorsport applications is driven through development of lightweight pistons with preferentially compliant short partial skirts. The preferential compliance is achieved through structural stiffening, such that a greater entrainment wedge is achieved at the skirt’s bottom edge through thermo-elastic deformation, whilst better conforming contact geometry at the top of the skirt. In practice, the combination of some of these conditions is intended to improve the load-carrying capacity and reduce friction. The approach is fundamental to the underlying ethos of race and high-performance engine technology. Contact loads of the order of 5 kN and contact kinematics in the range 0–35 m/s result in harsh transient tribological conditions. Therefore, piston design requires detailed transient analysis, which integrates piston dynamics, thermo-elastic distortion and transient elastohydrodynamics. The paper provides such a detailed analysis as well as verification of the same using non-invasive ultrasonic-assisted lubricant film thickness measurement from a fired engine under normal operating conditions, an approach not hitherto reported in literature. Good agreement is noted between measured film thickness and predictions

Childhood Infections, Socioeconomic Status, and Adult Cardiometabolic Risk

BACKGROUND AND OBJECTIVES: Socioeconomic disadvantage throughout the life course is associated with increased risk of cardiometabolic diseases, but traditional risk factors do not fully account for the social gradient. We investigated the interactions between low socioeconomic status (SES) and infection in childhood and adverse cardiometabolic parameters in adulthood. METHODS: Participants from the Cardiovascular Risk in Young Finns Study, a cohort well phenotyped for childhood and adulthood cardiometabolic risk factors and socioeconomic parameters, were linked to lifetime hospitalization data from birth onward available from the Finnish National Hospital Registry. In those with complete data, we investigated relationships between infection-related hospitalization in childhood, SES, and childhood and adult cardiometabolic parameters. RESULTS: The study cohort consisted of 1015 participants (age range 3–18 years at baseline and 30–45 years at follow-up). In adults who were raised in below-median income families, childhood infection-related hospitalizations (at age 0–5 years) were significantly associated with higher adult BMI (β ± SE comparing those with 0 vs ≥1 hospitalizations 2.4 ± 0.8 kg/m2, P = .008), waist circumference (7.4 ± 2.3 cm, P = .004), and reduced brachial flow–mediated dilatation (−2.7 ± 0.9%, P = .002). No equivalent associations were observed in participants from higher-SES families. CONCLUSIONS: Infection was associated with worse cardiovascular risk factor profiles only in those from lower-SES families. Childhood infection may contribute to social gradients observed in adult cardiometabolic disease risk factors. These findings suggest reducing childhood infections, especially in socioeconomic disadvantaged children, may reduce the cardiometabolic disease burden in adults

Effect of different rubber materials on husking dynamics of paddy rice

The conventional way to husk rice is to pass it between two rubber rollers that are rotating with a surface speed differential. The resulting normal pressure and shear stress causes the husk to be peeled away from the kernel. The process is suited to high-rice flow rates, but is energy intensive and can result in considerable wear to the surfaces of the rollers. The operating parameters for machines of this design are usually determined and set empirically. In this article, some experiments and calculations had been carried out in order to explore the mechanisms involved in husking rice grains using this method. A simple sliding friction rig with load cell and high-speed camera was used to observe the mechanisms that occur during husking. The husking performance of different rubbers was compared for changes in the applied normal load. It was found that grains rotate between the rubber counterfaces on initial motion before being husked. In addition, harder rubbers were found to husk a higher proportion of entrained grains at lower applied normal load. By measuring the coefficient of friction between rice and rubber samples, the shear force required to husk a given percentage of grains could be calculated and was shown to be constant regardless of rubber type. Based on the mechanism seen in the high-speed video, it was evident that there was a limiting shear stress that was the governing factor over the husked ratio

Effect of different rubber materials on husking dynamics of paddy rice

The conventional way to husk rice is to pass it between two rubber rollers that are rotating with a surface speed differential. The resulting normal pressure and shear stress causes the husk to be peeled away from the kernel. The process is suited to high-rice flow rates, but is energy intensive and can result in considerable wear to the surfaces of the rollers. The operating parameters for machines of this design are usually determined and set empirically. In this article, some experiments and calculations had been carried out in order to explore the mechanisms involved in husking rice grains using this method. A simple sliding friction rig with load cell and high-speed camera was used to observe the mechanisms that occur during husking. The husking performance of different rubbers was compared for changes in the applied normal load. It was found that grains rotate between the rubber counterfaces on initial motion before being husked. In addition, harder rubbers were found to husk a higher proportion of entrained grains at lower applied normal load. By measuring the coefficient of friction between rice and rubber samples, the shear force required to husk a given percentage of grains could be calculated and was shown to be constant regardless of rubber type. Based on the mechanism seen in the high-speed video, it was evident that there was a limiting shear stress that was the governing factor over the husked ratio

Socioeconomic position Is associated with carotid intima-media thickness in mid-childhood: The longitudinal study of Australian children

Background: Lower socioeconomic position (SEP) predicts higher cardiovascular risk in adults. Few studies differentiate between neighborhood and family SEP or have repeated measures through childhood, which would inform understanding of potential mechanisms and the timing of interventions. We investigated whether neighborhood and family SEP, measured biennially from ages 0 to 1 year onward, was associated with carotid intima-media thickness (IMT) at ages 11 to 12 years.Methods and Results: Data were obtained from 1477 families participating in the Child Health CheckPoint study, nested within the Longitudinal Study of Australian Children. Disadvantaged family and neighborhood SEP was cross-sectionally associated with thicker maximum carotid IMT in separate univariable linear regression models. Associations with family SEP were not attenuated in multivariable analyses, and associations with neighborhood SEP were attenuated only in models adjusted for family SEP. The difference in maximum carotid IMT between the highest and lowest family SEP quartile measured at ages 10 to 11 years was 10.7 μm (95% CI, 3.4-18.0; P=0.004), adjusted for age, sex, pubertal status, passive smoking exposure, body mass index, blood pressure, and arterial lumen diameter. In longitudinal analyses, family SEP measured as early as age 2 to 3 years was associated with maximum carotid IMT at ages 11 to 12 years (difference between highest and lowest quartile: 8.5 μm; 95% CI, 1.3-15.8; P=0.02). No associations were observed between SEP and mean carotid IMT.Conclusions: We report a robust association between lower SEP in early childhood and carotid IMT in mid-childhood. Further investigation of mechanisms may inform pediatric cardiovascular risk assessment and prevention strategies

Socioeconomic Position Is Associated With Carotid Intima-Media Thickness in Mid-Childhood: The Longitudinal Study of Australian Children

Background Lower socioeconomic position (SEP) predicts higher cardiovascular risk in adults. Few studies differentiate between neighborhood and family SEP or have repeated measures through childhood, which would inform understanding of potential mechanisms and the timing of interventions. We investigated whether neighborhood and family SEP, measured biennially from ages 0 to 1 year onward, was associated with carotid intima–media thickness (IMT) at ages 11 to 12 years.Methods and Results Data were obtained from 1477 families participating in the Child Health CheckPoint study, nested within the Longitudinal Study of Australian Children. Disadvantaged family and neighborhood SEP was cross‐sectionally associated with thicker maximum carotid IMT in separate univariable linear regression models. Associations with family SEP were not attenuated in multivariable analyses, and associations with neighborhood SEP were attenuated only in models adjusted for family SEP. The difference in maximum carotid IMT between the highest and lowest family SEP quartile measured at ages 10 to 11 years was 10.7 μm (95% CI, 3.4–18.0; P=0.004), adjusted for age, sex, pubertal status, passive smoking exposure, body mass index, blood pressure, and arterial lumen diameter. In longitudinal analyses, family SEP measured as early as age 2 to 3 years was associated with maximum carotid IMT at ages 11 to 12 years (difference between highest and lowest quartile: 8.5 μm; 95% CI, 1.3–15.8; P=0.02). No associations were observed between SEP and mean carotid IMT.Conclusions We report a robust association between lower SEP in early childhood and carotid IMT in mid‐childhood. Further investigation of mechanisms may inform pediatric cardiovascular risk assessment and prevention strategies.</ul

Strong interface-induced spin-orbit coupling in graphene on WS2

Interfacial interactions allow the electronic properties of graphene to be modified, as recently demonstrated by the appearance of satellite Dirac cones in the band structure of graphene on hexagonal boron nitride (hBN) substrates. Ongoing research strives to explore interfacial interactions in a broader class of materials in order to engineer targeted electronic properties. Here we show that at an interface with a tungsten disulfide (WS2) substrate, the strength of the spin-orbit interaction (SOI) in graphene is very strongly enhanced. The induced SOI leads to a pronounced low-temperature weak anti-localization (WAL) effect, from which we determine the spin-relaxation time. We find that spin-relaxation time in graphene is two-to-three orders of magnitude smaller on WS2 than on SiO2 or hBN, and that it is comparable to the intervalley scattering time. To interpret our findings we have performed first-principle electronic structure calculations, which both confirm that carriers in graphene-on-WS2 experience a strong SOI and allow us to extract a spin-dependent low-energy effective Hamiltonian. Our analysis further shows that the use of WS2 substrates opens a possible new route to access topological states of matter in graphene-based systems.Comment: Originally submitted version in compliance with editorial guidelines. Final version with expanded discussion of the relation between theory and experiments to be published in Nature Communication