Valve recession: From experiment to predictive model

Increasing demands on engine performance and cost reductions have meant that advances made in materials and production technology are often outpaced This frequently results in wear problems occurring with engine components. Few models exist for predicting wear, and consequently each wear problem has to be investigated, the cause isolated and remedial action taken. The objective of this work was to carry out experimental studies to investigate valve and seat insert wear mechanisms and use the test results to develop a recession prediction tool to assess the potential for valve recession and solve problems that occur more quickly. Experimental apparatus has been developed that is capable of providing a valid simulation of the wear of diesel automotive inlet valves and seats. Test methodologies developed have isolated the effects of impact and sliding. A semi-empirical wear model for predicting valve recession has been developed based on data gathered during the bench testing. A software program, RECESS, was developed to run the model. Model predictions are compared with engine dynamometer tests and bench tests. The model can be used to give a quantitative prediction of the valve recession to be expected with a particular material pair or a qualitative assessment of how parameters need to be altered in order to reduce recession. The valve recession model can be integrated into an industrial environment in order to help reduce costs and timescales involved in solving valve/seat wear problems

Friction and wear response of vegetable oils and their blends with mineral engine oil in a reciprocating sliding contact at severe contact conditions

Although many studies investigating the tribological performance of pure vegetable oils have been conducted, a better understanding of vegetable oil tribological performance at extreme conditions is still needed. Similarly, little work has been carried out to study the influence of the vegetable oils on the performance of a lubricant formed from a blend of vegetable oil and conventional mineral engine oil. This work presents the tribological performance of vegetable oils, and their blends with mineral oil, in a high temperature and contact pressure reciprocating contact. Palm and soybean based vegetable oils were mixed with a commercial mineral engine oil at a 1:1 ratio by volume. The conventional mineral oil was also tested to provide a benchmark. The pure palm oil exhibited lower friction than soybean oil, but for wear performance, this was reversed. The friction performance of the palm oil was competitive to that of the mineral engine oil. The mineral engine oil was far superior in wear resistance over both vegetable oils. When blended with mineral engine oil both vegetable oils demonstrated a reduction in coefficient of friction when compared to their pure oil states. An improvement in wear performance was observed for both a blend of palm oil and mineral engine oil (25% improvement) and that of soybean and mineral engine oil (27% improvement). This work shows that for palm oil and soybean oil, the performance of a blended oil is influenced by its vegetable oil component and that tribological characteristics of vegetable oils are dominant. That said, the significant limitation of these vegetable oils is their ability to provide a satisfactory level of wear resistance. It is suggested that any future work in this area should have a greater emphasis on the enhancement of wear resistance

Friction and wear response of vegetable oils and their blends with mineral engine oil in a reciprocating sliding contact at severe contact conditions

Although many studies investigating the tribological performance of pure vegetable oils have been conducted, a better understanding of vegetable oil tribological performance at extreme conditions is still needed. Similarly, little work has been carried out to study the influence of the vegetable oils on the performance of a lubricant formed from a blend of vegetable oil and conventional mineral engine oil. This work presents the tribological performance of vegetable oils, and their blends with mineral oil, in a high temperature and contact pressure reciprocating contact. Palm and soybean based vegetable oils were mixed with a commercial mineral engine oil at a 1:1 ratio by volume. The conventional mineral oil was also tested to provide a benchmark. The pure palm oil exhibited lower friction than soybean oil, but for wear performance, this was reversed. The friction performance of the palm oil was competitive to that of the mineral engine oil. The mineral engine oil was far superior in wear resistance over both vegetable oils. When blended with mineral engine oil both vegetable oils demonstrated a reduction in coefficient of friction when compared to their pure oil states. An improvement in wear performance was observed for both a blend of palm oil and mineral engine oil (25% improvement) and that of soybean and mineral engine oil (27% improvement). This work shows that for palm oil and soybean oil, the performance of a blended oil is influenced by its vegetable oil component and that tribological characteristics of vegetable oils are dominant. That said, the significant limitation of these vegetable oils is their ability to provide a satisfactory level of wear resistance. It is suggested that any future work in this area should have a greater emphasis on the enhancement of wear resistance

The recognition of collagen and triple-helical toolkit peptides by MMP-13: sequence specificity for binding and cleavage.

Remodeling of collagen by matrix metalloproteinases (MMPs) is crucial to tissue homeostasis and repair. MMP-13 is a collagenase with a substrate preference for collagen II over collagens I and III. It recognizes a specific, well-known site in the tropocollagen molecule where its binding locally perturbs the triple helix, allowing the catalytic domain of the active enzyme to cleave the collagen α chains sequentially, at Gly(775)-Leu(776) in collagen II. However, the specific residues upon which collagen recognition depends within and surrounding this locus have not been systematically mapped. Using our triple-helical peptide Collagen Toolkit libraries in solid-phase binding assays, we found that MMP-13 shows little affinity for Collagen Toolkit III, but binds selectively to two triple-helical peptides of Toolkit II. We have identified the residues required for the adhesion of both proMMP-13 and MMP-13 to one of these, Toolkit peptide II-44, which contains the canonical collagenase cleavage site. MMP-13 was unable to bind to a linear peptide of the same sequence as II-44. We also discovered a second binding site near the N terminus of collagen II (starting at helix residue 127) in Toolkit peptide II-8. The pattern of binding of the free hemopexin domain of MMP-13 was similar to that of the full-length enzyme, but the free catalytic subunit bound none of our peptides. The susceptibility of Toolkit peptides to proteolysis in solution was independent of the very specific recognition of immobilized peptides by MMP-13; the enzyme proved able to cleave a range of dissolved collagen peptides.This work was supported by a British Heart Foundation programme grant, RG/009/003/27122, and peptide synthesis, by grants from Medical Research Council and Wellcome Trust.This is the author accepted manuscript. The final version can be found on the publisher's website at: http://www.jbc.org/content/early/2014/07/09/jbc.M114.58344

Hydroxyproline Ring Pucker Causes Frustration of Helix Parameters in the Collagen Triple Helix.

Collagens, the most abundant proteins in mammals, are defined by their triple-helical structures and distinctive Gly-Xaa-Yaa repeating sequence, where Xaa is often proline and Yaa, hydroxyproline (Hyp/O). It is known that hydroxyproline in the Yaa position stabilises the triple helix, and that lack of proline hydroxylation in vivo leads to dysfunctional collagen extracellular matrix assembly, due to a range of factors such as a change in hydration properties. In addition, we note that in model peptides, when Yaa is unmodified proline, the Xaa proline has a strong propensity to adopt an endo ring conformation, whilst when Yaa is hydroxyproline, the Xaa proline adopts a range of endo and exo conformations. Here we use a combination of solid-state NMR spectroscopy and potential energy landscape modelling of synthetic triple-helical collagen peptides to understand this effect. We show that hydroxylation of the Yaa proline causes the Xaa proline ring conformation to become metastable, which in turn confers flexibility on the triple helix.The authors acknowledge BBSRC grant number BB/G021392/1 (MJD, DGR), EPSRC DTA studentship and Doctoral Prize (WYC), British Heart Foundation RG/09/003/27122 and PG/08/011/24416 (RWF, DB, DAS), Wellcome Trust 094470/Z/10/Z (RWF, DB, DAS), ERC and EPSRC (DJW).This is the final version of the article. It first appeared from NPG via http://dx.doi.org/10.1038/srep1255

Housing Affordability, Tenure and Mental Health in Australia and the United Kingdom: A Comparative Panel Analysis

The paper contributes insights into the role of tenure in modifying the relationship between housing affordability and health, using a cross-national comparison of similar post-industrial nations ? Australia and the United Kingdom ? with different tenure structures. The paper utilises longitudinal data from the Household, Income and Labour Dynamics in Australia Survey (HILDA) and British Household Panel Survey (BHPS) to examine change in the mental health of individuals associated with housing becoming unaffordable and considers modification by tenure. We present evidence that the role of tenure in the relationship between housing and health is context dependent and should not be unthinkingly generalised across nations. These findings suggest that the UK housing context offers a greater level of protection to tenants living in unaffordable housing when compared with Australia, and this finds expression in the mental health of the two populations. We conclude that Australian governments could improve the mental health of their economically vulnerable populations through more supportive housing policies

Hematopoietic Cell Transplantation in Patients With Primary Immune Regulatory Disorders (PIRD): A Primary Immune Deficiency Treatment Consortium (PIDTC) Survey.

Primary Immune Regulatory Disorders (PIRD) are an expanding group of diseases caused by gene defects in several different immune pathways, such as regulatory T cell function. Patients with PIRD develop clinical manifestations associated with diminished and exaggerated immune responses. Management of these patients is complicated; oftentimes immunosuppressive therapies are insufficient, and patients may require hematopoietic cell transplant (HCT) for treatment. Analysis of HCT data in PIRD patients have previously focused on a single gene defect. This study surveyed transplanted patients with a phenotypic clinical picture consistent with PIRD treated in 33 Primary Immune Deficiency Treatment Consortium centers and European centers. Our data showed that PIRD patients often had immunodeficient and autoimmune features affecting multiple organ systems. Transplantation resulted in resolution of disease manifestations in more than half of the patients with an overall 5-years survival of 67%. This study, the first to encompass disorders across the PIRD spectrum, highlights the need for further research in PIRD management

Friction and wear phenomena of vegetable oil based lubricants with additives at severe sliding wear conditions

The tribological responses of palm oil and soybean oil, combined with two commercial antiwear additives (zinc dialkyl dithiophosphate and boron compound), were investigated at a lubricant temperature of 100 °C and under severe contact conditions in a reciprocating sliding contact. The friction coefficient of palm oil with zinc dialkyl dithiophosphate was closest to the commercial mineral engine oil, with a 2% difference. The soybean oil with zinc dialkyl dithiophosphate produced a 57% improvement in wear resistance compared to its pure oil state. The existence of boron nitride in vegetable oils was only responsive in reduction of wear rather than friction. The response of commercial antiwear additives with vegetable oils showed a potential for the future improvement in the performance of vegetable oils