Dynamics of a coefficient of friction during non-stationary sliding of a parabolic indenter on visco-elastic foundation

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 1783, 020041 (2016) and may be found at https://doi.org/10.1063/1.4966334.We have studied the coefficient of friction between a rigid parabolic indenter and a visco-elastic Kelvin foundation under step-wise change of sliding velocity. We have obtained analytical estimations for normal and tangential forces in a contact and their limiting values during transition process that occurs after a jump of sliding velocity. The results of numerical simulation are in good agreement with analytical estimates

A model of fretting wear in the contact of an axisymmetric indenter and a visco-elastic half-space

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 1683, 020040 (2015) and may be found at https://doi.org/10.1063/1.4932730.We propose a simple and efficient model of wear of axially symmetric bodies in contact with a visco-elastic foundation based on the method of dimensionality reduction. The results of simulation of wear of a parabolic indenter have been demonstrated. It has been shown that dissipation due to viscosity of a material leads to increase the size of the worn region of an indenter. The noted effect is conditioned with an increase of effective shear modulus of visco-elastic material under sufficiently high velocities of tangential loading. The model can be generalized to a wide range of materials with complex visco-elastic properties

Multidimensional Worldline Instantons

We extend the worldline instanton technique to compute the vacuum pair production rate for spatially inhomogeneous electric background fields, with the spatial inhomogeneity being genuinely two or three dimensional, both for the magnitude and direction of the electric field. Other techniques, such as WKB, have not been applied to such higher dimensional problems. Our method exploits the instanton dominance of the worldline path integral expression for the effective action.Comment: 22 pages, 13 figure

Schwinger Pair Creation of Particles and Strings

I shortly review the worldline instanton method for calculating Schwinger pair production rates in (i) one-loop QED (ii) multiloop QED and (iii) one-loop open string theory.Comment: 8 pages, 3 figures, talk given at XIV Mexican School of Particles and Fields, November 8 - 12, 2010, Morelia, Mexico, to appear in the conference proceeding

An Empirical Study of the Effectiveness of 'Forcing Diversity' Based on a Large Population of Diverse Programs

Use of diverse software components is a viable defence against common-mode failures in redundant softwarebased systems. Various forms of "Diversity-Seeking Decisions" (“DSDs”) can be applied to the process of developing, or procuring, redundant components, to improve the chances of the resulting components not failing on the same demands. An open question is how effective these decisions, and their combinations, are for achieving large enough reliability gains. Using a large population of software programs, we studied experimentally the effectiveness of specific "DSDs" (and their combinations) mandating differences between redundant components. Some of these combinations produced much better improvements in system probability of failure per demand (PFD) than "uncontrolled" diversity did. Yet, our findings suggest that the gains from such "DSDs" vary significantly between them and between the application problems studied. The relationship between DSDs and system PFD is complex and does not allow for simple universal rules (e.g. "the more diversity the better") to apply

Josephson and proximity effects on the surface of a topological insulator

We investigate Josephson and proximity effects on the surface of a topological insulator on which superconductors and a ferromagnet are deposited. The superconducting regions are described by the conventional BCS Hamiltonian, rather than the superconducting Dirac Hamiltonian. Junction interfaces are assumed to be dirty. We obtain analytical expressions of the Josephson current and the proximity-induced anomalous Green's function on the topological insulator. The dependence of the Josephson effect on the junction length, the temperature, the chemical potential and the magnetization is discussed. It is also shown that the proximity-induced pairing on the surface of a topological insulator includes even and odd frequency triplet pairings as well as a conventional s-wave one.Comment: 7 pages, 5 figure

Hygienic requirements of urban living environment in the Russian Federation and in Italy: a comparison

Introduzione/scopo. La pianificazione urbana tende a contenere e regolamentare la crescita urbana consentendo uno sviluppo sostenibile a livello ambientale, sociale e sanitario. Nel presente lavoro gli autori hanno confrontato i quadri normativi della Federazione Russ e dell’Italia ponendo particolare attenzione agli aspetti urbani degli spazi abitativi. Metodo. Considerando la ponderosa produzione normativa nei due paesi, il lavoro ha preso in esame le normative a livello nazionale per l’Italia e federale per la Russia, tenendo principalmente conto dei seguenti aspetti: strumenti di pianificazione urbana e protezione ambientale e sanitaria degli spazi abitativi. Risultati. I problemi relativi alla sicurezza igienico-sanitaria dell’ambiente di vita in Russia sono essenzialmente riconducibili a due sistemi normativi (SNiP e SanPiN), mentre in Italia rientrano nel D.M. 05/07/1975. I principi fondamentali della pianificazione urbana in Russia sono dettati da una norma federale, mentre in Italia sono recepiti nel Piano Regolatore Generale (PRG) comunale e nei diversi regolamenti locali, dove si riasriassume tutta la normativa sovraordinata. Gli aspetti legati alla qualità ambientale, infine, in entrambi i paesi sono disciplinati da varie leggi specifiche (federali e statali); un articolato sistema di norme che tengono conto dei potenziali impatti sulla salute e sull’ambiente Conclusioni. Gli autori ritengono che dovrebbero essere sviluppati, specialmente in Italia che si trova nettamente più indietro da questo punto di vista, strumenti normativi chiari e aggiornati aventi per oggetto l’igiene degli edifici e degli ambienti urbani, basati sulle più recenti acquisizioni di letteratura scientifica internazionale nell’intento di garantire i più alti standard in materia di tutela della Salute Pubblica.Aim. Urban planning tries to contain and regulate the uncontrolled growth of cities, encouraging their sustainable development at environmental, social and health levels. In the present work, the authors compare the regulatory frameworks of the Russian Federation and of Italy, with particular attention paid to the urban aspects of living spaces. Method. Considering the extant normative production in the two countries, the authors examine national legislation for Italy and federal legislation for Russia, mainly taking into account the following aspects: urban planning tools and environmental and sanitary protection of living spaces. Results. Hygienic-sanitary requirements regarding living environment in Russia are essentially expressed by two regulatory systems (SNiP and SanPiN), while in Italy they are regulated by the D.M. 07/05/1975. The main principles of urban planning in Russia are expressed by federal standards, while in Italy they are incorporated in the Municipal General Plan (PRG) and in the various local regulations, where all the superordinate regulations are summarized. Finally, aspects related to environmental quality in both countries are governed by various specific laws (federal and state); a complex system of rules that take into account potential impacts on health and the environment. Conclusions. The authors reckon that clear and updated regulatory tools should be developed, especially in Italy that lags behind, regarding the building and urban hygiene, relying on the most recent acquisitions of international scientific literature in order to guarantee the highest standards in Public Health safeguard

Affine Toric SL(2)-embeddings

In 1973 V.L.Popov classified affine SL(2)-embeddings. He proved that a locally transitive SL(2)-action on a normal affine three-dimensional variety X is uniquely determined by a pair (p/q, r), where 0<p/q<=1 is an uncancelled fraction and r is a positive integer. Here r is the order of the stabilizer of a generic point. In this paper we show that the variety X is toric, i.e. admits a locally transitive action of an algebraic torus, if and only if r is divisible by q-p. To do this we prove the following necessary and sufficient condition for an affine G/H-embedding to be toric. Suppose X is a normal affine variety, G is a simply connected semisimple algebraic group acting regularly on X, H is a closed subgroup of G such that the character group $\mathfrak{X}(H)$ is finite and G/H -> X is a dense open equivariant embedding. Then X is toric if and only if there exist a quasitorus T and a $(G\times T)$-module V such that $X\stackrel{G}{\cong} V//T$. The key role in the proof plays D. Cox's construction.Comment: 16 page

Dynamically assisted Schwinger mechanism

We study electron-positron pair creation {from} the Dirac vacuum induced by a strong and slowly varying electric field (Schwinger effect) which is superimposed by a weak and rapidly changing electromagnetic field (dynamical pair creation). In the sub-critical regime where both mechanisms separately are strongly suppressed, their combined impact yields a pair creation rate which is {dramatically} enhanced. Intuitively speaking, the strong electric field lowers the threshold for dynamical particle creation -- or, alternatively, the fast electromagnetic field generates additional seeds for the Schwinger mechanism. These findings could be relevant for planned ultra-high intensity lasers.Comment: 4 pages, 2 figure

Noncentrosymmetric plasmon modes and giant terahertz photocurrent in a two-dimensional plasmonic crystal

We introduce and theoretically study the plasmon-photogalvanic effect in the planar noncentrosymmetric plasmonic crystal containing a homogeneous two-dimensional electron system gated by a periodic metal grating with an asymmetric unit cell. The plasmon-photogalvanic DC current arises due to the two-dimensional electron drag by the noncentrosymmetric plasmon modes excited under normal incidence of terahertz radiation. We show that the collective plasmon modes of the planar plasmonic crystal become strongly noncentrosymmetric in the weak coupling regime of their anticrossing. Large plasmon wavevector (which is typically by two-three orders of magnitude greater than the terahertz photon wavevector) along with strong near-field enhancement at the plasmon resonance make the plasmonic drag a much stronger effect compared to the photon drag observed in conventional two-dimensional electron systems.Comment: 9 pages, 10 figures, submitted to Physical Review