The effects of surface texture in reciprocating bearings

In recent years, interest in reducing friction in internal combustion engines has grown significantly. This has mainly been due to stricter regulatory standards, with emission targets set as low as 95g of CO2/km from 2020 onwards. As a result, motor vehicle manufacturers have been focusing investment on energy efficient technologies with the aim of reducing fuel consumption. As part of this drive, the reduction of friction between the piston rings and cylinder liners is gaining considerable attention. A potentially effective way of doing this is to apply laser texturing to piston liner surfaces. However, little is understood about the mechanisms by which pockets affect friction, primarily because of the lack of reliable experimental measurements. In this study, the influence of surface texture on film thickness and friction force was measured simultaneously in a convergent-divergent bearing under different lubrication regimes, closely replicating an automotive piston ring-bore conjunction. This was achieved using a reciprocating sliding test rig, designed to control all operating parameters with a high degree of accuracy. Various pocket shapes were assessed in order to understand the beneficial or detrimental effects of surface texture under various operating conditions. This showed unequivocally that pockets are able to reduce friction in the mixed regime and increase friction under full film conditions. After the optimum pocket shape had been determined, various spatial parameters (depth, breadth, separation) were tested, under different lubrication regimes, in order to characterise the influence of geometry. A key finding here is that optimum pocket geometry varies along the length of the stroke. Next, film thickness was measured using a modified version of the ultra-thin film optical interferometry approach. The results here agreed with the friction data by showing how pockets increase film thickness in the mixed and boundary regime and decrease film thickness in the full film regime. Furthermore, through transient measurements, a number of insights into mechanisms by which surface texture reduce or increase friction were obtained. In addition, cavitation in the ring-liner pairing was investigated, as well as various aspects of pocket behaviour, such as orientation, location relative to reversal and the influence of steady state versus transient sliding. Finally, wear tests were conducted under highly loaded conditions which led to an understanding of the interactions between laser surface texture and wear behaviour.Open Acces

Overview of the main incremental health care reforms introduced between 2014 and 2020 in Romania

Aim: On 2014 the Government of Romania has committed to improving health and health system through the implementation of the 2014–2020 National Health Strategy: Health for Prosperity. An official evaluation of the strategy implementation is not publicly available yet. This paper aims to provide an overview of the main incremental reforms taken during this period in Romania and to analyse the results from the perspective of the main Strategy goals. Methods: Information was collected from legislative documents, statistical and scientific publications. The main implemented or initiated incremental reforms, during the assessed period, were assigned to five main clusters: ”governance”, “resources for health”, “coverage and access”, “organization of health care”, “quality of care” and were analysed in accordance with the aim, the type, the implementation stage and the corresponding objectives of the Strategy. Results: The 2014–2020 National Health Strategy has definitely not reached all its objectives, but one sign of prosperity, is that based on 2019 per capita income (of $12,630) World Bank classified Romania, for the first time, as a high-income country. The health status of the population has increased in many aspects, yet Romanians’ health has still remained among the poorest in the European Union (EU). Conclusion:  Incremental reforms might be successful, but the small steps should be taken in a holistic approach, and should be tailored to specific needs. Previous strengthening health systems resilience and plans for overcoming possible risks and obstacles might ensure successful implementation. Assessments of the reforms might draw lessons that help policymakers in shaping further health policies and designing of next strategies

Appendicular mass – a rare form of tuberculosis

Tuberculosis is in the top 10 causes of death worldwide, being one of the most deadly infectious diseases. It is estimated that one of three people from the entire earth population has a latent infection with M tuberculosis. This aerobic bacterium possesses the ability to persist in host tissues for years and to begin replication once immunity declines. The lungs are most frequent site of infection as the Mycobacterium tuberculosis is carried by aerosol droplets and is commonly transmitted by respiratory route. The second way of transmission is by contaminated food. Intestinal contamination coexists with pulmonary tuberculosis and only 10% represent primitive enteric diseases. The ileocecal region is involved most frequently. Even in this context isolated appendicular involvement remains rare. We report the case of appendicular tuberculosis in a 17-year-old woman with no evidence of other location of disease elsewhere in the body

An adsorption chromatography assay to probe bulk particle transport through hydrogels

Biopolymer-based hydrogels such as mucus and the basal lamina play a key role in biology, where they control the exchange of material between different compartments. They also pose a barrier that needs to be overcome for successful drug delivery. Characterizing the permeability properties of such hydrogels is mandatory for the development of suitable drug delivery vectors and pharmaceutics. Here, we present an experimental method to measure bulk particle transport through hydrogels. We validate our assay by applying it to mucin hydrogels and show that the permeability properties of these mucin hydrogels can be modulated by polymer density and pH, in agreement with previous results obtained from single particle tracking. The method we present here is easy to handle, inexpensive, and high-throughput compatible. It is also a suitable platform for the design and screening of drugs that aim at modifying the barrier properties of hydrogels. This system can also aid in the characterization and development of synthetic gels for a range of biomedical applications.National Institutes of Health (U.S.) (Grant P50-GM068763)National Institutes of Health (U.S.) (Grant P30-ES002109

Transient experimental and modelling studies of laser-textured micro-grooved surfaces with a focus on piston-ring cylinder liner contacts

This paper presents a comparison between the results from numerical modelling and experiments to shed light on the mechanisms by which surface texture can reduce friction when applied to an automotive cylinder liner. In this configuration, textured features move relative to th e piston-liner conjunction and to account for this our approach is to focus on the transient friction response to individual pockets as they pass through, and then leave, the sliding contact. The numerical approach is based on the averaged Reynolds’ equat ion with the Patir & Cheng’s flow factors and the p- θ Elrod- Adams mass-conserving cavitation model. The contact pressures that arises from the asperity interactions are solved simultaneously to the fluid flow solution using the Greenwood and Tripp method. The experimental data is produced using a pin-on -disc set up, in which laser textured pockets have been applied to the disc specimen. Under certain conditions in the mixed and boundary lubrication regime s, both model and experimental results show i ) an increase in friction as the pocket enters the contact, followed by ii ) a sharp decrease as the pocket leaves the contact, and then iii ) a gradual decay back to the pre-entrainment value. From the evidence obtained for the first time from the proposed combined modelling and experimental investigation conducted under carefully controlled conditions, w e suggest that these three stages occur due to the following mechanisms: i ) a reduction in fluid pressure due to the increased inlet gap, ii ) inlet suction as the cavitated fluid within the pocket draws lubricant into the contact, and iii ) film thickness decay as oil is squeezed out of the contact. The interplay of these three mechanisms is shown to control the response of micro-textured surfaces under all lubrication regimes

Radio Frequency Magnetron Sputter Deposition as a Tool for Surface Modification of Medical Implants

The resent advances in radio frequency (RF)‐magnetron sputtering of hydroxyapatite films are reviewed and challenges posed. The principles underlying RF‐magnetron sputtering used to prepare calcium phosphate‐based, mainly hydroxyapatite coatings, are discussed in this chapter. The fundamental characteristic of the RF‐magnetron sputtering is an energy input into the growing film. In order to tailor the film properties, one has to adjust the energy input into the substrate depending on the desired film properties. The effect of different deposition control parameters, such as deposition time, substrate temperature, and substrate biasing on the hydroxyapatite (HA) film properties is discussed

There and (slowly) back again: Entropy-driven hysteresis in a model of DNA overstretching

When pulled along its axis, double-stranded DNA elongates abruptly at a force of about 65 pN. Two physical pictures have been developed to describe this overstretched state. The first proposes that strong forces induce a phase transition to a molten state consisting of unhybridized single strands. The second picture instead introduces an elongated hybridized phase, called S-DNA, structurally and thermodynamically distinct from standard B-DNA. Little thermodynamic evidence exists to discriminate directly between these competing pictures. Here we show that within a microscopic model of DNA we can distinguish between the dynamics associated with each. In experiment, considerable hysteresis in a cycle of stretching and shortening develops as temperature is increased. Since there are few possible causes of hysteresis in a system whose extent is appreciable in only one dimension, such behavior offers a discriminating test of the two pictures of overstretching. Most experiments are performed upon nicked DNA, permitting the detachment (`unpeeling') of strands. We show that the long-wavelength progression of the unpeeled front generates hysteresis, the character of which agrees with experiment only if we assume the existence of S-DNA. We also show that internal melting (distinct from unpeeling) can generate hysteresis, the degree of which is strongly dependent upon the nonextensive loop entropy of single-stranded DNA.Comment: 18 pages, 10 figure

Experimental validation of a mixed-lubrication regime model for textured piston-ring-liner contacts

Recent experiments have shown that automotive piston-liner friction may be reduced by up to 50 % if the surface of the liner is laser textured with certain configurations of micro-pockets. It is important to model this behavior to understand and optimize the friction reduction mechanisms that are occurring. However, until now, very few models that predict the lubrication performance of textured surfaces have been successfully validated against experimental data. This is because of the requirement for them to: (1) reproduce experimental configurations with a certain degree of fidelity, (2) conserve mass properly, and (3) account for transient, boundary lubrication conditions. To address this, the current paper presents a comparison between the results from a numerical model, which fulfils these criteria, and an experimental test rig operating under the same conditions. The mathematical modeling is based on the averaged Reynolds’ equation with Patir and Cheng’s flow factors and the p − θ Elrod–Adams mass-conserving cavitation model. Simultaneously to the fluid flow solution, the contact pressures that arise from the asperity interactions are also included into the calculations through the well-known stochastic Greenwood and Tripp model for rough contacts. The experimental data is produced using a reciprocating tribometer, whose contact conditions are closely controlled and accurately mimic those found in an automotive piston–liner conjunction. Data is presented in terms of friction force versus stroke angle, and the similarities and differences between the model and experiment are discussed

Corrosion and tribological performance of quasi-stoichiometric titanium containing carbo-nitride coatings

Zr, Nb and Si doped TiCN coatings, with (C+N)/(metal + Si) ratios of approximately 1, were deposited on stainless steel and Si wafer substrates using a cathodic arc technique in a mixture of N2 and CH4 gases. The coatings were comparatively analysed for elemental and phase composition, adhesion, anticorrosive properties and tribological performance at ambient and 250 °C. Zr, Nb and Si alloying contents in the coatings were in the range 2.9–9.6 at.%. All the coatings exhibited f.c.c. solid solution structures and had a 〈111〉 preferred orientation. In the adhesion tests conducted, critical loads ranged from 20 to 30 N, indicative of a good adhesion to substrate materials. The Ti based coatings with Nb or Si alloying elements proved to be resistant to corrosive attack in 3.5% NaCl and of these coatings the TiNbCN was found to have the best corrosion resistance. TiCN exhibited the best tribological performance at 250 °C, while at ambient temperatures it was TiNbCN. Abrasive and oxidative wear was found to be the main wear mechanism for all of the coatings. Of the tested coatings, TiNbCN coatings would be the most suitable candidate for severe service (high temperature, corrosive, etc.) applications