Tribological behaviour of the low and high viscosity peek at various testing scales

Polyetheretherketone (PEEK) has become most attractive as a sliding bearing material in industrial applications, due to its excellent thermal stability, good friction and wear resistance. These properties promote the material to be used in so called high performance tribological applications. However, fundamental mechanisms governing friction and wear are not yet fully understood and neither is the influence of composition parameters. An important parameter is PEEK’s viscosity during injection moulding which is heated up to semi-solid state, between its glass transition and melting temperature. It is not known to what extent the injection viscosity, related to the applied temperature profile, affects subsequent tribological features. This paper studies the friction and wear performance of low and high viscosity PEEK under dry reciprocating sliding contact. The tests were performed with small and large scale specimens under pin-on-plate and flat-on-flat configuration, respectively; to determine the transitions in tribological behaviour at different scales and to identify the applications limits. Tests were carried out at controlled atmosphere with 25 °C and a relative humidity of 50%. Parameters such as contact pressures and sliding speed were limited at 10 MPa and 20 mm/s, respectively; post mortem analyses were carried out by means of 2-D surface topography and optical microscopy. The results show that PEEK injected at high viscosity exhibits a tribological performance with a relatively high coefficient of friction and high wear rate compare to PEEK injected at low viscosity

Multisystem proteinopathy due to a homozygous p.Arg159His VCP mutation : a tale of the unexpected

ObjectiveTo assess the clinical, radiologic, myopathologic, and proteomic findings in a patient manifesting a multisystem proteinopathy due to a homozygous valosin-containing protein gene (VCP) mutation previously reported to be pathogenic in the heterozygous state.MethodsWe studied a 36-year-old male index patient and his father, both presenting with progressive limb-girdle weakness. Muscle involvement was assessed by MRI and muscle biopsies. We performed whole-exome sequencing and Sanger sequencing for segregation analysis of the identified p.Arg159His VCP mutation. To dissect biological disease signatures, we applied state-of-the-art quantitative proteomics on muscle tissue of the index case, his father, 3 additional patients with VCP-related myopathy, and 3 control individuals.ResultsThe index patient, homozygous for the known p.Arg159His mutation in VCP, manifested a typical VCP-related myopathy phenotype, although with a markedly high creatine kinase value and a relatively early disease onset, and Paget disease of bone. The father exhibited a myopathy phenotype and discrete parkinsonism, and multiple deceased family members on the maternal side of the pedigree displayed a dementia, parkinsonism, or myopathy phenotype. Bioinformatic analysis of quantitative proteomic data revealed the degenerative nature of the disease, with evidence suggesting selective failure of muscle regeneration and stress granule dyshomeostasis.ConclusionWe report a patient showing a multisystem proteinopathy due to a homozygous VCP mutation. The patient manifests a severe phenotype, yet fundamental disease characteristics are preserved. Proteomic findings provide further insights into VCP-related pathomechanisms

Phanerozoic parasitism and marine metazoan diversity: Dilution versus amplification

Growing evidence suggests that biodiversity mediates parasite prevalence. We have compiled the first global database on occurrences and prevalence of marine parasitism throughout the Phanerozoic and assess the relationship with biodiversity to test if there is support for amplification or dilution of parasitism at the macroevolutionary scale. Median prevalence values by era are 5% for the Paleozoic, 4% for the Mesozoic, and a significant increase to 10% for the Cenozoic. We calculated period-level shareholder quorum sub-sampled (SQS) estimates of mean sampled diversity, three-timer (3T) origination rates, and 3T extinction rates for the most abundant host clades in the Paleobiology Database to compare to both occurrences of parasitism and the more informative parasite prevalence values. Generalized linear models (GLMs) of parasite occurrences and SQS diversity measures support both the amplification (all taxa pooled, crinoids and blastoids, and molluscs) and dilution hypotheses (arthropods, cnidarians, and bivalves). GLMs of prevalence and SQS diversity measures support the amplification hypothesis (all taxa pooled and molluscs). Though likely scale-dependent, parasitism has increased through the Phanerozoic and clear patterns primarily support the amplification of parasitism with biodiversity in the history of life. This article is part of the theme issue 'Infectious disease macroecology: parasite diversity and dynamics across the globe'

Quantitative analysis of suture lines in Carboniferous ammonoids

Two morphometric methods are applied and compared for the analysis of suture lines in Early Carboniferous ammonoids of the superfamilies Pericycloidea, Girtyoceratoidea and Goniatitoidea. We analysed (1) classic metric data (proportions of the width and depths or heights of lobes and saddles) using multivariate statistic methods and (2) outline data of the external lobe and the ventrolateral saddle of the same ammonoid taxa using the elliptic Fourier analysis. Both methods lead to similar results and simultaneously demonstrate ontogenetic and phylogenetic trends of these ammonoids. Our results are consistent with three previously suggested evolutionary patterns: (1) a general decrease of the amplitude of lobes and saddles, (2) a proportional widening of the external lobe and (3) a heightening of the median saddle.</p

Calibration of the modified Bartlett-Lewis model using global optimization techniques and alternative objective functions

The calibration of stochastic point process rainfall models, such as of the Bartlett-Lewis type, suffers from the presence of multiple local minima which local search algorithms usually fail to avoid. To meet this shortcoming, four relatively new global optimization methods are presented and tested for their ability to calibrate the Modified Bartlett-Lewis Model. The list of tested methods consists of: the Downhill Simplex Method, Simplex-Simulated Annealing, Particle Swarm Optimization and Shuffled Complex Evolution. The parameters of these algorithms are first optimized to ensure optimal performance, after which they are used for calibration of the Modified Bartlett-Lewis model. Furthermore, this paper addresses the choice of weights in the objective function. Three alternative weighing methods are compared to determine whether or not simulation results (obtained after calibration with the best optimization method) are influenced by the choice of weights

The impact of resource dependence of the mechanisms of life on the spatial population dynamics of an in silico microbial community

Biodiversity has a critical impact on ecosystem functionality and stability, and thus the current biodiversity crisis has motivated many studies of the mechanisms that sustain biodiversity, a notable example being non-transitive or cyclic competition. We therefore extend existing microscopic models of communities with cyclic competition by incorporating resource dependence in demographic processes, characteristics of natural systems often oversimplified or overlooked by modellers. The spatially explicit nature of our individual-based model of three interacting species results in the formation of stable spatial structures, which have significant effects on community functioning, in agreement with experimental observations of pattern formation in microbial communities. Published by AIP Publishing

Mapping mean total annual precipitation in Belgium, by investigating the scale of topographic control at the regional scale

Accurate precipitation maps are essential for ecological, environmental, element cycle and hydrological models that have a spatial output component. It is well known that topography has a major influence on the spatial distribution of precipitation and that increasing topographical complexity is associated with increased spatial heterogeneity in precipitation. This means that when mapping precipitation using classical interpolation techniques (e.g. regression, kriging, spline, inverse distance weighting, etc.), a climate measuring network with higher spatial density is needed in mountainous areas in order to obtain the same level of accuracy as compared to flatter regions. In this study, we present a mean total annual precipitation mapping technique that combines topographical information (i.e. elevation and slope orientation) with average total annual rain gauge data in order to overcome this problem. A unique feature of this paper is the identification of the scale at which topography influences the precipitation pattern as well as the direction of the dominant weather circulation. This method was applied for Belgium and surroundings and shows that the identification of the appropriate scale at which topographical obstacles impact precipitation is crucial in order to obtain reliable mean total annual precipitation maps. The dominant weather circulation is determined at 260°. Hence, this approach allows accurate mapping of mean annual precipitation patterns in regions characterized by rather high topographical complexity using a climate data network with a relatively low density and/or when more advanced precipitation measurement techniques, such as radar, aren't available, for example in the case of historical data

Best management practices to alleviate deep-seated compaction in asparagus (Asparagus officinalis) interrows (UK)

Field operations associated with UK asparagus production (re-ridging and intensive foot and vehicular trafficking of the wheelings) can result in severe deep-seated compaction in interrows, impacting on crop health and productivity. In this project, we investigate the long-term efficacy of a range of Best Management Practices (BMPs) targeted at preventing or remediating soil compaction in asparagus (Asparagus officinalis L.) interrows as compared to Conventional practice. BMPs included (1) companion crops - Rye (Sereale cecale L.), Mustard (Sinapis alba L.), (2) interrow surface mulch applications (straw mulch and PAS 100 compost in combination with shallow soil disturbance (SSD)), (3) modifications of the conventional tillage practice (re-ridging (R) or not ridging (NR) and applying SSD or not applying SSD) and (4) a zero-tillage option. In general, companion cropping had no effect on soil compaction or water infiltration rates as compared to the Conventional practice. Application and incorporation of straw mulch or PAS 100 compost however significantly reduced soil compaction of the interrows to >0.45 m beyond the working depth of the subsoiler (0.25 m). Composts and mulches in combination with SSD significantly reduce deep-seated compaction of the interrows within 3 years of annual application. Further, Conventional practice equivalent treatment (Bare soil No-SSD R) was associated with significantly higher PR values as compared to the zero-tillage (Bare soil No-SSD NR). These findings show that the extremely high levels of deep-seated compaction in interrows, associated with re-ridging, foot and vehicular traffic can be alleviated using surface mulches in combination with SSD