Development of a new mechano-chemical model in boundary lubrication

A newly developed tribochemical model based on thermodynamics of interfaces and kinetics of tribochemical reactions is implemented in a contact mechanics simulation and the results are validated against experimental results. The model considers both mechanical and thermal activation of tribochemical reactions instead of former thermal activation theories. The model considers tribofilm removal and is able to capture the tribofilm behaviour during the experiment. The aim of this work is to implement tribochemistry into deterministic modelling of boundary lubrication and study the effect of tribofilms in reducing friction or wear. A new contact mechanics model considering normal and tangential forces in boundary lubrication is developed for two real rough steel surfaces. The model is developed for real tribological systems and is flexible to different laboratory experiments. Tribochemistry (e.g. tribofilm formation and removal) and also mechanical properties are considered in this model. The amount of wear is calculated using a modified Archard’s wear equation accounting for local tribofilm thickness and its mechanical properties. This model can be used for monitoring the tribofilm growth on rough surfaces and also the real time surface roughness as well as changes in the λ ratio. This model enables the observation of in-situ tribofilm thickness and surface coverage and helps in better understanding the real mechanisms of wear

Cardiorespiratory hysteresis during incremental high altitude ascent-descent quantifies the magnitude of ventilatory acclimatization

Maintenance of arterial blood gases is achieved through sophisticated regulation of ventilation, mediated by central and peripheral chemoreflexes. Respiratory chemoreflexes are important during exposure to high altitude due to the competing influence of hypoxia and hypoxic hyperventilation‐mediated hypocapnia on steady‐state ventilatory drive. Inter‐individual variability exists in ventilatory acclimatization to high altitude, potentially affecting the development of acute mountain sickness (AMS). We aimed to quantify ventilatory acclimatization to high altitude by comparing differential ascent and descent values (i.e. hysteresis) in steady‐state cardiorespiratory variables. We hypothesized that (a) the hysteresis area formed by cardiorespiratory variables during ascent and descent would quantify the magnitude of ventilatory acclimatization, and (b) larger hysteresis areas would be associated with lower AMS symptom scores during ascent. In 25 healthy, Diamox‐free trekkers ascending to and descending from 5160 m, cardiorespiratory hysteresis was measured in the pressure of end‐tidal (PET)CO2, peripheral oxygen saturation (SpO2), minute ventilation (V̇E), chemoreceptor stimulus index (SI; PETCO2/SpO2) and the calculated steady‐state chemoreflex drive (SS‐CD; V̇E/SI) using portable devices (capnograph, peripheral pulse oximeter and respirometer, respectively). AMS symptoms were assessed daily using the Lake Louise Questionnaire. We found that (a) ascent‐descent hysteresis was present in all cardiorespiratory variables, (b) SS‐CD is a valid metric for tracking ventilatory acclimatization to high altitude and (c) highest AMS scores during ascent were significantly, moderately and inversely‐correlated to SS‐CD hysteresis magnitude (rs = ‐0.408, P = 0.043). We propose that ascent‐descent hysteresis is a novel and feasible way to quantify ventilatory acclimatization in trekkers during high altitude exposure