Equilibrium and non-equilibrium fluctuations in a glass-forming liquid

Glass-forming liquids display strong fluctuations -- dynamical heterogeneities -- near their glass transition. By numerically simulating a binary Weeks-Chandler-Andersen liquid and varying both temperature and timescale, we investigate the probability distributions of two kinds of local fluctuations in the non-equilibrium (aging) regime and in the equilibrium regime; and find them to be very similar in the two regimes and across temperatures. We also observe that, when appropriately rescaled, the integrated dynamic susceptibility is very weakly dependent on temperature and very similar in both regimes.Comment: v1: 5 pages, 4 figures v2: 5 pages, 4 figures. Now includes results at three temperatures, two of them above T_{MCT} and one below T_{MCT}; and more extensive discussion of connections to experiment

Mapping dynamical heterogeneity in structural glasses to correlated fluctuations of the time variables

Dynamical heterogeneities -- strong fluctuations near the glass transition -- are believed to be crucial to explain much of the glass transition phenomenology. One possible hypothesis for their origin is that they emerge from soft (Goldstone) modes associated with a broken continuous symmetry under time reparametrizations. To test this hypothesis, we use numerical simulation data from four glass-forming models to construct coarse grained observables that probe the dynamical heterogeneity, and decompose the fluctuations of these observables into two transverse components associated with the postulated time-fluctuation soft modes and a longitudinal component unrelated to them. We find that as temperature is lowered and timescales are increased, the time reparametrization fluctuations become increasingly dominant, and that their correlation volumes grow together with the correlation volumes of the dynamical heterogeneities, while the correlation volumes for longitudinal fluctuations remain small.Comment: v4: Detailed analysis of transverse and longitudinal parts. One figure removed, two added. v3: Explicit decomposition into transverse and longitudinal parts, discussion of correlation volumes. One more figure v2: Modified introduction and forma

Time reparametrization invariance in arbitrary range p-spin models: symmetric versus non-symmetric dynamics

We explore the existence of time reparametrization symmetry in p-spin models. Using the Martin-Siggia-Rose generating functional, we analytically probe the long-time dynamics. We perform a renormalization group analysis where we systematically integrate over short timescale fluctuations. We find three families of stable fixed points and study the symmetry of those fixed points with respect to time reparametrizations. One of those families is composed entirely of symmetric fixed points, which are associated with the low temperature dynamics. The other two families are composed entirely of non-symmetric fixed points. One of these two non-symmetric families corresponds to the high temperature dynamics. Time reparametrization symmetry is a continuous symmetry that is spontaneously broken in the glass state and we argue that this gives rise to the presence of Goldstone modes. We expect the Goldstone modes to determine the properties of fluctuations in the glass state, in particular predicting the presence of dynamical heterogeneity.Comment: v2: Extensively modified to discuss both high temperature (non-symmetric) and low temperature (symmetric) renormalization group fixed points. Now 16 pages with 1 figure. v1: 13 page

An appraisal of the thermal decomposition mechanisms of ILs as potential lubricants

Ionic liquid (IL) lubricants are rapidly seeing increased use as either base lubricants or additives for a wide range of functionalities. This study considers the thermal stability of the ILs with the emphasis being their use as potential lubricants. The effect of IL chemistry, including anion chain length, cation chain length, anion type, and cation type, on their thermal stability is studied. The decomposition mechanism as a function of time and temperature is considered. Five ILs are studied by utilising both thermogravimetric analysis (TGA) for the dynamic thermal decomposition and Fourier transform IR spectroscopy (FTIR) for the static thermal decomposition. For static thermal decomposition, both time and temperature are varied. The results show that the variation of IL chemistry directly influences their thermal stability. The increase of either cation or anion chain length decreases their thermal stability. Both anion and cation type have a significant influence on the thermal stability

Reactivity of oil‐soluble IL with silicon surface at elevated temperature

The reactivity of an oil‐miscible ionic liquid, phosphonium phosphate (PP), and the common anti‐wear additive zinc dialkyl dithio phosphate (ZDDP) with a solid surface at elevated temperature in the absence of any tribological motion is investigated. Understanding the thermal film build up, composition, and relative thickness will help in the understanding of lubrication mechanisms once tribological effects are introduced. Attenuated total reflection–Fourier transform infrared (ATR‐FTIR), scanning electron microscopy–energy dispersive spectroscopy (SEM‐EDS), and X‐ray photoelectron spectroscopy (XPS) are employed to characterise silicon surfaces before and after the experiments in terms of surface chemistry and surface morphology. The results show that both additives react with the silicon surface to produce thermal films. However, ZDDP forms a thicker film. PP reacts with the silicon and forms a thermal film, but the reaction rate is self‐limited such that an increase of time to 24 hours does not significantly increase the film thickness

Effect of Water on the Interfacial Mechanisms of the Tribofilms Formed by Zinc Dialkyl Dithiophosphate: Experimental and Analytical Study

Understanding the true interfacial mechanisms of the growth of the tribofilms generated by Zinc Dialkyl Dithiophosphate (ZDDP) is important because it is the most widely used anti-wear additive and there is legislative pressure to find efficient environmentally-friendly replacements. The main focus of this study is to investigate the effect of water on the interfacial mechanisms involved in the formation of the ZDDP tribofilms and correlate it to the chemical properties of the glassy polyphosphates. The effect of different parameters such as temperature, humidity, mixed-water in oil, load and rubbing time on the tribofilm formation and its durability has been studied experimentally and analytically using a Mini Traction Machine (MTM) with the Spacer Layer Interferometry Method (SLIM) attachment. The role of additive depletion on the pre-formed tribofilm thickness under mechanical stress has also been studied. Results show that physical parameters such as temperature, humidity and pressure significantly influence the tribofilm. X-ray Photoelectron Spectroscopy (XPS) analysis was carried out to assess the evolution of the chemical structure of the tribofilm during the test. The chemical analysis suggests that there are different chemical properties across the thickness of the tribofilm and these determine the durability characteristics. A humidity control system was designed and integrated with the Mini Traction Machine (MTM) and Spacer Layer Interferometry Method (SLIM) for the first time to evaluate the effect of relative humidity and the tribochemical changes on the tribological performance and tribofilm characteristics of boundary lubricated systems. One of the key aspects in this study is the use of continuous humidity control system, which can provide steady humid environment during the tribological tests. In the present study, the tribofilm thickness and wear results obtained experimentally were used to develop a semi-deterministic approach to implement the effect of humidity and mixed-water in wear prediction of boundary lubrication

National and Subnational Cardiovascular Diseases Mortality Attributable to Salt Consumption in Iran by Sex and Age From 1990 to 2016

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