760 research outputs found
Modeling quarantine during epidemics and mass-testing using drones
No full textWe extend the classical SIR epidemic spread model by introducing the “quarantined” compartment. We solve (numerically) the differential equations that govern the extended model and quantify how quarantining “flattens the curve” for the proportion of infected population over time. Furthermore, we explore the potential of using drones to deliver tests, enabling mass-testing for the infection; we give a method to estimate the drone fleet needed to deliver the tests in a metropolitan area. Application of our models to COVID-19 spread in Sweden shows how the proposed methods could substantially decrease the peak number of infected people, almost without increasing the duration of the epidemic. © 2020 Sedov et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Evgeny Nikolaevich Sedov: a leading breeder of pome fruit crops in Russia
No full textAcad. Evgeny Nikolaevich Sedov, Doctor of Agricultural Sciences, Full Member of the Russian Academy of Agricultural Sciences, Full Member of the Russian Academy of Sciences, Professor, Scientist Emeritus, is an outstanding researcher and breeder, author of 90 apple and pear cultivars, founder of a scientific school specializing on priority trends in pome fruit breeding: – development of adaptable triploid apple cultivars with regular fruiting, high marketability of fruits, and increased self-fertility; – development of apple cultivars immune or highly resistant to scab; – development of triploid apple cultivars with immunity to scab; – development of columnar apple cultivars for super-intensive orchards and main technology elements for their cultivation; – development of apple cultivars with improved biochemical composition of fruits with higher content of ascorbic acid (vitamin C) and Р-active substances (vitamin Р)
Higher-gradient continua: The legacy of Piola, Mindlin, Sedov and Toupin and some future research perspectives
No full textSince the first studies dedicated to the mechanics of deformable bodies (by Euler, D'Alembert, Lagrange) the principle of virtual work (or virtual velocities) has been used to provide firm guidance to the formulation of novel theories. Gabrio Piola dedicated his scientific life to formulating a continuum theory in order to encompass a large class of deformation phenomena and was the first author to consider continua with non-local internal interactions and, as a particular case, higher-gradient continua. More recent followers of Piola (Mindlin, Sedov and then Richard Toupin) recognized the principle of virtual work (and its particular case, the principle of least action) as the (only!) firm foundation of continuum mechanics. Mindlin and Toupin managed to formulate a conceptual frame for continuum mechanics which is able to effectively model the complex behaviour of so-called architectured, advanced, multiscale or microstructured (meta)materials. Other postulation schemes, in contrast, do not seem able to be equally efficient. The present work aims to provide a historical and theoretical overview of the subject. Some research perspectives concerning this theoretical approach are outlined in the final section
Control of propagation of spatially localized polariton wave packets in a Bragg mirror with embedded quantum wells
No full textWe considered the nonlinear dynamics of Bragg polaritons in a specially designed stratified semiconductor structure with embedded quantum wells, which possesses a convex dispersion. The model for the ensemble of single periodically arranged quantum wells coupled with the Bragg photon fields has been developed. In particular, the generalized Gross-Pitaevskii equation with the non-parabolic dispersion has been obtained for the Bragg polariton wave function. We revealed a number of dynamical regimes for polariton wave packets resulting from competition of the convex dispersion and the repulsive nonlinearity effects. Among the regimes are spreading, breathing and soliton propagation. When the control parameters including the exciton-photon detuning, the matter-field coupling and the nonlinearity are manipulated, the dynamical regimes switch between themselves.</p
One-dimensional Tamm plasmons: Spatial confinement, propagation, and polarization properties
No full textTamm plasmons are confined optical states at the interface of a metal and a dielectric Bragg mirror. Unlike conventional surface plasmons, Tamm plasmons may be directly excited by an external light source in both TE and TM polarizations. Here we consider the one-dimensional propagation of Tamm plasmons under long and narrow metallic stripes deposited on top of a semiconductor Bragg mirror. The spatial confinement of the field imposed by the stripe and its impact on the structure and energy of Tamm modes are investigated. We show that the Tamm modes are coupled to surface plasmons arising at the stripe edges. These plasmons form an interference pattern close to the bottom surface of the stripe that involves modification of both the energy and loss rate for the Tamm mode. This phenomenon is pronounced only in the case of TE polarization of the Tamm mode. These findings pave the way to application of laterally confined Tamm plasmons in optical integrated circuits as well as to engineering potential traps for both Tamm modes and hybrid modes of Tamm plasmons and exciton polaritons with meV depth
Higher-gradient continua: The legacy of Piola, Mindlin, Sedov and Toupin and some future research perspectives
No full textSince the first studies dedicated to the mechanics of deformable bodies (by Euler, D’Alembert, Lagrange) the principle of virtual work (or virtual velocities) has been used to provide firm guidance to the formulation of novel theories. Gabrio Piola dedicated his scientific life to formulating a continuum theory in order to encompass a large class of deformation phenomena and was the first author to consider continua with non-local internal interactions and, as a particular case, higher-gradient continua. More recent followers of Piola (Mindlin, Sedov and then Richard Toupin) recognized the principle of virtual work (and its particular case, the principle of least action) as the (only!) firm foundation of continuum mechanics. Mindlin and Toupin managed to formulate a conceptual frame for continuum mechanics which is able to effectively model the complex behaviour of so-called architectured, advanced, multiscale or microstructured (meta)materials. Other postulation schemes, in contrast, do not seem able to be equally efficient. The present work aims to provide a historical and theoretical overview of the subject. Some research perspectives concerning this theoretical approach are outlined in the final section
Nonlinear dynamics of railway wheelsets incorporating randomness
No full textThe thesis is to investigate the dynamic behavior of a single-axle railway wheelset and identify its chaotic behavior by means of time history, phase portrait, Lyapunov exponents, information dimension, bifurcation diagram and control strategy. The thesis has its analytical and computational components. For the analytical component, several mathematical models of a single-axle rail vehicle wheelset are presented in order to compare their features for similarities and differences. These models present different contact theories of creep force, and have different parametric values. In addition, Model III does not consider gravitational stiffnesses and gyroscopic couple. As a result, directly comparing simulation results of these models makes it difficult to interpret results and to draw conclusions. Therefore, these models need to be expanded so that issues can be isolated and investigated accordingly
Modern lessons’ construction based on the taxonomy of pedagogical objectives and the multiple intelligences theory
No full text© 2019, Emerald Publishing Limited. Purpose: Currently, teachers meet difficulties when design the modern classes so that they respond to the requirements of new educational standards. Thus, the purpose of this paper is to justify the algorithm for applying the “foundations” for designing modern classes of different types and varied subject areas. Design/methodology/approach: The author coordinates the “foundations” of constructing modern occupations in various subject areas on the example of lessons for children mastering the basic level of preparation and higher one. As the basis for building classes in modern conditions, the author considers the taxonomy of the pedagogical goals of B. Bloom and G. Gardner’s theory of multiple intelligences (MI). Findings: The taxonomy of pedagogical goals can be one of the key foundations in the design of modern occupations of various types; the theory of MI – in the construction of classes of different subject areas. As examples for the argumentation, the author used the educational technologies of “problem education” and “project education.” Practical implications: This study is a modest contribution to didactics (the science of theories and learning technologies). The results of the research actualize the work of B. Bloom and G. Gardner in the context of modern requirements for the results and content of education in general and vocational schools. The main provisions of the paper should supplement a number of such works where the solution of modern problems in education is built on the traditions and innovations balance. Originality/value: The algorithm of applying the “foundations” in the modern studies’ planning can be used for lessons of various types and different subject areas. Further, research can be built in the context of interpreting the algorithm and testing its effectiveness using examples of other educational technologies
Effect of character, value, and sequence of overloads on the fatigue crack growth in 2024-T3 aluminum alloy
No full text- …
