Characterising the friction coefficient between rubber O-rings and a rigid surface under extreme pressures

Previous research into the friction behaviour of elastomers has typically focused on the effects of velocity, contact pressure, counter surface and lubrication on the coefficient of friction. O-ring type elastomer seals are common in many different industries. Friction plays a critical role during the setting and in service of these components. An experimental O-ring friction testing rig has been developed that can measure the effects of sliding speed and hydrostatic pressure on elastomer friction. Finite element analysis (FEA) packages can adopt fixed friction coefficients or ones that are pressure dependent. For the latter case, the dependence of the frictional behaviour is typically obtained from the instantaneous stress response at any given pressure and then related to the normal force response. The friction rig described in this paper uses industry standard dimensions for the O-ring gland, the pre-compression levels, extrusion gap size and pressure rating. The coefficient of friction is derived by dividing the measured friction force by the normal force, which was determined using an FEA modelling approach, as it could not be measured directly. Finally, a relationship between the frictional velocity and surface roughness is obtained in order to provide a frequency dependent Coefficient of Friction (CoF) that is easily translatable between surfaces

Cohesion and adhesion of nanoporous TiO2 coatings on titanium wires for photovoltaic applications

The working electrode of a dye-sensitized photovoltaic fiber is constituted of a porous TiO2 coated titanium wire. The cohesion and adhesion of such a brittle oxide coating on the ductile metal substrate are identified as crucial factors in maintaining photovoltaic efficiency during textile manufacture and weaving operations. The influence of coating thickness on these factors has been investigated in the present work. The tensile mechanical characterization with in situ microscopic observations shows that two damaging processes are involved. For the smaller thickness, loss of adherence appears to be at the interface and inside the coating bulk. Cracks become visible in a random distribution in size and density and do not cross the entire coating circumference. Large patches of coating are still anchored on the wire. For the larger thickness no cohesive rupture in the coating bulk has been observed. The loss of adherence appears at the interface closed to the cracks and grows rapidly as the strain increases. Numerical investigations based on the finite element method permit to analyze the distribution and the combination of radial interfacial stress and circumferential coating stress and their influence on the observed damage

Offshore methane detection and quantification from space using sun glint measurements with the GHGSat constellation

​​​​​​​The ability to detect and quantify methane emissions from offshore platforms is of considerable interest in providing actionable feedback to industrial operators. While satellites offer a distinctive advantage for remote sensing of offshore platforms which may otherwise be difficult to reach, offshore measurements of methane from satellite instruments in the shortwave infrared are challenging due to the low levels of diffuse sunlight reflected from water surfaces. Here, we use the GHGSat satellite constellation in a sun glint configuration to detect and quantify methane emissions from offshore targets around the world. We present a variety of examples of offshore methane plumes, including the largest single emission at (84 000 ± 24 000) kg h−1 observed by GHGSat from the Nord Stream 2 pipeline leak in 2022 and the smallest offshore emission measured from space at (180 ± 130) kg h−1 in the Gulf of Mexico. In addition, we provide an overview of the constellation's offshore measurement capabilities. We measure a median column precision of 2.1 % of the background methane column density and estimate a detection limit, from analytical modelling and orbital simulations, that varies between 160 and 600 kg h−1 depending on the latitude and season.</p

Changes in diad sequence distribution by preferential chain scission during the thermal hydrolysis of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Polyhydroxyalkanoates (PHAs) are microbial polyesters produced by many types of bacteria as an intracellular energy reserve material under substrate limiting conditions and in the presence of excessive carbon sources.¹ Poly((R)-3-hydroxybutyrate) (PHB), the most commonly used microbial polyester, was the first member of the PHA family to be discovered, and more than 150 other monomer units have been reported to date.2, 3 Poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate) (PHBHHx) is a copolymer in the PHA family that consists of randomly distributed (R)-3-hydroxybutyrate (HB) and (R)-3-hydroxyhexanoate (HHx) units.⁴ This type of copolymer exhibits improved mechanical properties and processability compared with those of PHB and poly((R)-3-hydroxyvalerate) (PHBV).⁵ PHBHHx copolymers are currently produced on a large scale and have proven to be biocompatible in clinical studies using mouse fibroblasts cells, and rabbit articular cartilage-derived chondrocytes.⁶ PHBHHx is a highly favorable copolymer of the PHB family due to its biodegradability, flexible mechanical properties and good melt processability

Performance on the Frontal Assessment Battery is sensitive to frontal lobe damage in stroke patients

Background: The Frontal Assessment Battery (FAB) is a brief battery of six neuropsychological tasks designed to assess frontal lobe function at bedside [Neurology 55:1621-1626, 2000]. The six FAB tasks explore cognitive and behavioral domains that are thought to be under the control of the frontal lobes, most notably conceptualization and abstract reasoning, lexical verbal fluency and mental flexibility, motor programming and executive control of action, self-regulation and resistance to interference, inhibitory control, and environmental autonomy. Methods: We examined the sensitivity of performance on the FAB to frontal lobe damage in right-hemisphere-damaged first-ever stroke patients based on voxel-based lesion-behavior mapping. Results: Voxel-based lesion-behavior mapping of FAB performance revealed that the integrity of the right anterior insula (BA13) is crucial for the FAB global composite score, for the FAB conceptualization score, as well as for the FAB inhibitory control score. Furthermore, the FAB conceptualization and mental flexibility scores were sensitive to damage of the right middle frontal gyrus (MFG; BA9). Finally, the FAB inhibitory control score was sensitive to damage of the right inferior frontal gyrus (IFG; BA44/45). Conclusions: These findings indicate that several FAB scores (including composite and item scores) provide valid measures of right hemispheric lateral frontal lobe dysfunction, specifically of focal lesions near the anterior insula, in the MFG and in the IFG

L 'Ulissipeade Poëme. Ou Les Calamités de Lisbonne, par le Tremblement de Terre, l'incendie & le reflux excessif de la Mer : Accompagné d'un Discours sur la Cause naturelle de cet effrayant Phoenomène

Par Un Spectateur De Ce Desastre.Autopsie nach Ex. der ULB DüsseldorfVorlageform der Veröffentlichungsangabe: Aux Dépens De L'Auteur. Par qui chaque Exemplaire sera signé.Mutmaßlicher Ercheinungsort ermittelt in: Barbier, Dictionnaire des ouvrages anonymes et pseudonymesHandsigniert: Ramie

The Effect of Thermal Ageing on the Fatigue Resistance of Hydrogenated Acrylonitrile Butadiene Rubber (HNBR) Compounds

Compounds incorporating hydrogenated acrylonitrile butadiene rubber (HNBR) are widely adopted in applications that operate under extreme conditions such as at high temperatures, often whilst in contact with oil and other chemicals. They also work effectively when subjected to high strains and high strain rates. The detailed mechanisms that allow these materials to perform so well under these specific conditions are not yet fully understood. In this study a high acrylonitrile (ACN) content HNBR is incorporated into four different rubber compounds that are subjected to different thermal ageing conditions to investigate their impact on fatigue crack growth resistance of the cured compound. The resulting compounds are subjected to detailed DSC, TGA and FTIR analysis to help understand the changes that take place in the compounds during ageing for the first time. Counterintuitively, in this work ageing under specific set of conditions can produce an increase in the fatigue crack resistance in some of the elastomer compounds and when this happens it is observed that this occurs when the HNBR compounds develop knottier tearing profiles. Analysis of the DSC, FTIR and TGA results confirm that during ageing there is a steady evolution of the some of the ingredients in the compound such as the processing oils and the plasticiser which appears to have a significant effect on the fatigue properties of the HNBR materials