The Foreground and Background of Consciousness

This paper questions the tendency of philosophers, especially in the free will debate, to posit a certain experience of the self as introspectively obvious. It will attempt to demonstrate that introspection can create an experience of the self that is different from self-experience prior to introspection: hence, that introspection can distort self-experience. It will be argued that although there is room for the use of introspection in phenomenology and philosophy, this use should be continually questioned and open to re-examination. The concepts of a foreground and background will be introduced as a more productive way of understanding and visualising consciousness

Impact of oxidation on grease life in rolling bearings

In this paper the lubrication mechanism of lithium grease lubricated ball bearings in the bleed phase is described. Oxidation plays an important role and therefore grease life “in air” and grease life “in nitrogen” is studied in real bearings. It is shown that grease life is strongly dominated by oxidation but that this is by far not deterministic. Oxidation starts up at a certain time, the induction time, which is the point at which the anti-oxidants have been consumed. This induction time is a function of the bearing operational conditions and the oxygen concentration. Oxidation leads to loss of base oil and loss of lubricity, partly repaired by replenishment and oil release from the grease reservoirs (bleed)

Grease material properties from first principles thermodynamics

Thermodynamics has historically been used to derive characteristic material properties. In this study, fundamental thermodynamics is applied to grease. First-principle formulations of existing material properties—heat capacity and storage modulus—and new properties—thermal strain and stress coefficients, chemical resistance and thermo-chemical decay coefficient—are derived, some of which are experimentally determined. A new group of Maxwell relations is introduced by replacing the classical compression work (Formula presented.) with the grease shearing work (Formula presented.). The physical interpretations and implications of these properties on grease behaviour and performance are presented. Experimental measurements of the derived properties are performed in accordance with the theoretical formulations. Six different grease types are studied. Obtained results are shown to conform with anticipated, observed and established grease behaviours. The proposed properties can be used in grease performance and degradation analyses, as well as grease selection for lubrication applications.</p

On the Required Energy to Break Down the Thickener Structure of Lubricating Greases

The rheology of a conventional lithium-12 hydroxystearate bearing grease changes significantly when it is subjected to mechanical shear. Often this shear energy–along with the consequent entropy–is measured and used in engineering and thermodynamic models, leading to grease life models for predicting bearing seizure due to insufficiently thick film or loss of lubricity of the base oil/grease. In this degradation process, the bonds between the individual molecules, consisting mainly of the fairly weak van der Waals bonds and/or hydrogen bonds, are broken during this shearing process. In this article, we show that only a very small portion of the shear energy is needed to break these bonds and that the vast majority is dissipated as heat due to the lubricant viscosity, also known as viscous dissipation. We model the thickener as rod-shaped fibers, wherein the grease viscosity is reduced by a factor of 5 when the length of a fiber is reduced by a factor of 2.5. The energy needed to break the bonds between the molecules to shorten these fibers is 6 to 7 orders of magnitude smaller than the energy applied by shear. Hence, it is very difficult to measure this fiber structure breakage energy from grease shear aging experiments directly

Contribution of viscous shear to friction in cold rolling of low-carbon steel

This work shows that for temperatures, pressures and shear rates that are common in cold rolling of low-carbon steel, viscous shear stress significantly contributes to the total friction force. Experiments were carried out to validate the theory on lubricant film formation and elasto-hydrodynamic lubrication, both with laboratory scale tribometers and a semi-industrial pilot mill facility. These experiments showed that at high shear rates, that are common in cold rolling, the lubricant does not behave as a Newtonian fluid anymore; moreover the viscosity at high pressure cannot accurately be described by a simple exponential law. With the correct relations implemented in a rolling model, both rolling force and forward slip are predicted with good accuracy for hydrodynamically lubricated cold rolling experiments.</p