TRIBOINFORMATICS: MACHINE LEARNING METHODS FOR FRICTIONAL INSTABILITIES

The study of friction is traditionally a data-driven area with many experimental data and phenomenological models governing structure-property relationships. Triboinformatics is a new area combining Tribology with Machine Learning (ML) and Artificial Intelligence (AI) methods, which can help to establish correlations in data on friction and wear. This is particularly relevant to unstable motion, where deterministic models are difficult to build. There are several types of friction-induced instabilities including those caused by the velocity dependency of dry friction, coupling of friction with another process (wear, heat generation, etc.), the elastic Adams instabilities, and others. The onset of sliding is also an unstable process. ML/AI methods, such as Topological Data Analysis and various ML algorithms, which have been already used for various aspects of data analysis on friction, can be applied also to the frictional instabilities

An introduction to superhydrophobicity

This paper is derived from a training session prepared for COST P21. It is intended as an introduction to superhydrophobicity to scientists who may not work in this area of physics or to students. Superhydrophobicity is an effect where roughness and hydrophobicity combine to generate unusually hydrophobic surfaces, causing water to bounce and roll off as if it were mercury and is used by plants and animals to repel water, stay clean and sometimes even to breathe. The effect is also known as The Lotus Effect® and Ultrahydrophobicity. In this paper we introduce many of the theories used, some of the methods used to generate surfaces and then describe some of the implications of the effect

Not by Firkowicz's Fault: Daniel Chwolson's Comic Blunders in Research of Hebrew Epigraphy of the Crimea and Caucasus, and their Impact on Jewish Studies in Russia

Daniel Chwolson (1819-1911) made a huge impact upon the research of Hebrew epigraphy from the Crimea and Caucasus. Despite that, his role in the more-than-a-century-long controversy regarding Crimean Hebrew tomb inscriptions has not been well studied. Chwolson, at first, adopted Abraham Firkowicz's forgeries, and then quickly realized his mistake; however, he could not back up. The criticism by both Abraham Harkavy and German Hebraists questioned Chwolson's scholarly qualifications and integrity. Consequently, the interference of political pressure into the academic argument resulted in the prevailing of the scholarly flawed opinion. We revisit the interpretation of these findings by Russian, Jewish, Karaite and Georgian historians in the 19th and 20th centuries. During the Soviet period, Jewish Studies in the USSR were in neglect and nobody seriously studied the whole complex of the inscriptions from the South of Russia / the Soviet Union. The remnants of the scholarly community were hypnotized by Chwolson's authority, who was the teacher of their teachers' teachers. At the same time, Western scholars did not have access to these materials and/or lacked the understanding of the broader context, and thus a number of erroneous Chwolson's conclusion have entered academic literature for decades

Self-assembled levitating clusters of water droplets: pattern-formation and stability

Water forms ordered hexagonally symmetric structures (snow crystals) in its solid state, however not as liquid. Typically, mists and clouds are composed of randomly moving small droplets lacking any ordered structure. Self-organized hexagonally patterned microdroplet clusters over locally heated water surfaces have been recently observed. However, many aspects of the phenomenon are far from being well understood including what determines droplets size, arrangement, and the distance between them. Here we show that the Voronoi entropy of the cluster tends to decrease indicating to their selforganization, while coupling of thermal effects and mechanical forces controls the stability of the clusters. We explain the balance of the long-range attraction and repulsion forces which stabilizes the cluster patterns and established the range of parameters, for which the clusters are stable. The cluster is a dissipative structure similar to self-organized Rayleigh–Bénard convective cells. Microdroplet formation plays a role in a variety effects from mist and clouds to aerosols. We anticipate that the discovery of the droplet cluster phenomenon and its explanation will provide new insights on the fundamental physical and chemical processes such as microdroplet role in reaction catalysis in nature as well as new tools for aerosol analysis and microfluidic applications

Oil as a Lubricant in the Ancient Middle East

There is a significant interest toward the history of tribology in both engineering and historical communities. However, there is a gap between engineers and historians in their approach to the topic, and existing literature sometimes overlooks various cultural influences, in particular, oriental ones, which affected the tribological science and technology. We consider the early history of lubrication and show that while the evidences of usage of lubricants (water, gypsum, and animal fats) in Ancient Egypt in 2nd-3rd millennia BC are hypothetic, rather than established facts, the Hebrew Bible contains earliest records of using oil as a lubricant. In particular, the account of rubbing the shield of King Saul (11th century BC) is discussed as well as other similar cases. These findings allow us to better understand the universal nature of history of science and technology as a multicultural phenomenon

Ternary Logic of Motion to Resolve Kinematic Frictional Paradoxes

Paradoxes of dry friction were discovered by Painlevé in 1895 and caused a controversy on whether the Coulomb–Amontons laws of dry friction are compatible with the Newtonian mechanics of the rigid bodies. Various resolutions of the paradoxes have been suggested including the abandonment of the model of rigid bodies and modifications of the law of friction. For compliant (elastic) bodies, the Painlevé paradoxes may correspond to the friction-induced instabilities. Here we investigate another possibility to resolve the paradoxes: the introduction of the three-value logic. We interpret the three states of a frictional system as either rest-motion-paradox or as rest-stable motion-unstable motion depending on whether a rigid or compliant system is investigated. We further relate the ternary logic approach with the entropic stability criteria for a frictional system and with the study of ultraslow sliding friction (intermediate between the rest and motion or between stick and slip)