377 research outputs found
Anatoly Kuznetsov, Author of Babi Yar: The History of the Book and the Fate of the Author
No full textThis Introduction to the special issue devoted to Anatoly Kuznetsov, author of Babi Yar: A Document in the Form of a Novel, dwells on the different aspects of the book’s importance, surveys the life of the author as intertwined with the history of this book, suggests a way of reading his other work in the light of Babi Yar, and notes the contributions of the articles collected in this issue
Molecular size and local stiffness of molecular bottle brushes by Monte Carlo simulations
No full textModeling of comb polymers with a high branching density
No full textBranched macromolecules are currently of great scientific interest. They are formed by a backbone carrying many closely spaced linear arms, and their most important property consists on their backbone stiffness due to the large branching density. From this property, one can reasonably expect lyotropic behaviour of these systems in solution and adsorbed on a surface. These molecules have a cylindrical shape and a characteristic size that ranges from a few nanometers (radius of their circular section) to hundreds of nanometers (contour length). Little is known at present about the nature of the backbone stiffness and its dependence on the monomers excluded volume and on the stereochemical constraints. The availability of high-performance computers allowed us to apply the Metropolis Monte Carlo algorithm to a coarse-grained model to describe bottle-brushes in a diluted solution or adsorbed on a surface. Accurate results are obtained for the value of the Flory exponent, the persistence length and the distribution functions of the distances between the monomers
The role of high vorticity structures in development of Kolmogorov turbulent spectra in inviscid flow
No full textThis work is aimed for understanding nonlinear mechanisms at early stages of turbulence, when the flow is not yet affected by viscosity. Based on numerical simulations of the 3D incompressible Euler equations with generic large-scale initial conditions, we show that the exponential growth of vorticity developing in thin vortex sheets (pancake structures) leads to formation of Kolmogorov energy spectrum in fully inviscid flow. This direct observation yields the decoupling of the finite-time blowup problem from the Kolmogorov theory of turbulence. We demonstrate that the pancake structures have self-similar dynamics and evolve according to the scaling law W(t) ~ l(t)^(-2/3) for the local vorticity maximums W(t) and the transverse pancake scales l(t). Then, we argue that the energy spectrum requires an increasing number of such structures developing densely through the Kolmogorov range of wavenumbers, in good agreement with numerical data
Codimension-two singularities on the stability boundary in 2D Filippov systems
No full textBifurcation theory provides powerful tools for the analysis of the dynamics of openloop
or closed-loop nonlinear control systems. These systems are Filippov (or piecewise smooth)
when the dynamics depends discontinuously on the state, for example as a consequence relay
feedback actions. In this paper we contribute to the analysis of codimension-two bifurcations in
Filippov systems by reporting some results on the equilibrium bifurcations of 2D systems that
involve a sliding limit cycle. There are only two such local bifurcations: a degenerate boundary
focus that we call homoclinic boundary focus; and the boundary Hopf. We address both of them,
and provide the complete set of curves that exist around such codimension-two bifurcation
points. Existing numerical software can be used to exploit these results for the analysis of the
stability boundaries of nonlinear piecewise smooth control systems. In the final part of this
paper, we discuss a 2D Filippov system modelling an ecosystem subject to on-off harvesting
control that exhibits both codimension-two bifurcations
Travelling wave solutions of generalized coupled Zakharov–Kuznetsov and dispersive long wave equations
No full textAbstractIn this manuscript, we constructed different form of new exact solutions of generalized coupled Zakharov–Kuznetsov and dispersive long wave equations by utilizing the modified extended direct algebraic method. New exact traveling wave solutions for both equations are obtained in the form of soliton, periodic, bright, and dark solitary wave solutions. There are many applications of the present traveling wave solutions in physics and furthermore, a wide class of coupled nonlinear evolution equations can be solved by this method
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