73,640 research outputs found
Nonautonomous Hamiltonian Systems and Morales-Ramis Theory I. The Case
In this paper we present an approach towards the comprehensive analysis of
the non-integrability of differential equations in the form
which is analogous to Hamiltonian systems with 1+1/2 degree of freedom. In
particular, we analyze the non-integrability of some important families of
differential equations such as Painlev\'e II, Sitnikov and Hill-Schr\"odinger
equation.
We emphasize in Painlev\'e II, showing its non-integrability through three
different Hamiltonian systems, and also in Sitnikov in which two different
version including numerical results are shown. The main tool to study the
non-integrability of these kind of Hamiltonian systems is Morales-Ramis theory.
This paper is a very slight improvement of the talk with the almost-same title
delivered by the author in SIAM Conference on Applications of Dynamical Systems
2007.Comment: 15 pages without figures (19 pages and 6 figures in the published
version
Analytic Non-integrability in String Theory
Using analytic techniques developed for Hamiltonian dynamical systems we show
that a certain classical string configurations in AdS_5 x X_5 with X_5 in a
large class of Einstein spaces, is non-integrable. This answers the question of
integrability of string on such backgrounds in the negative. We consider a
string localized in the center of AdS_5 that winds around two circles in the
manifold X_5.Comment: 14 page
Synchrotron strain scanning for residual stress measurement in cold-drawn steel rods
Cold-drawn steel rods and wires retain significant residual stresses as a consequence of the manufacturing process. These residual stresses are known to be detrimental for the mechanical properties of the wires and their durability in aggressive environments. Steel makers are aware of the problem and have developed post-drawing processes to try and reduce the residual stresses on the wires. The present authors have studied this problem for a number of years and have performed a detailed characterization of the residual stress state inside cold-drawn rods, including both experimental and numerical techniques. High-energy synchrotron sources have been particularly useful for this research. The results have shown how residual stresses evolve as a consequence of cold-drawing and how they change with subsequent post-drawing treatments. The authors have been able to measure for the first time a complete residual strain profile along the diameter in both phases (ferrite and cementite) of a cold-drawn steel rod
Sustainable business models: integrating employees, customers and technology
This Special Issue of the Journal of Business & Industrial Marketing has the same title as the 23rd International Conference CBIM 2018 (June 18-20, 2018, Madrid, Spain) “Sustainable Business Models: Integrating Employees, Customers and Technology”. In this edition of International Conference, following a competitive blind review process, papers from 126 authors and 25 countries were ultimately accepted. The best papers of the Conference were invited to submit to this Special Issue and we were also open to direct submissions from other authors.
We present here the 17 accepted papers for publication in this Special Issue
Steady self-diffusion in classical gases
A steady self-diffusion process in a gas of hard spheres at equilibrium is
analyzed. The system exhibits a constant gradient of labeled particles. Neither
the concentration of these particles nor its gradient are assumed to be small.
It is shown that the Boltzmann-Enskog kinetic equation has an exact solution
describing the state. The hydrodynamic transport equation for the density of
labeled particles is derived, with an explicit expression for the involved
self-diffusion transport coefficient. Also an approximated expression for the
one-particle distribution function is obtained. The system does not exhibit any
kind of rheological effects. The theoretical predictions are compared with
numerical simulations using the direct simulation Monte Carlo method and a
quite good agreement is found
The shearing instability of a dilute granular mixture
The shearing instability of a dilute granular mixture composed of smooth
inelastic hard spheres or disks is investigated. By using the Navier-Stokes
hydrodynamic equations, it is shown that the scaled transversal velocity mode
exhibits a divergent behaviour, similarly to what happens in one-component
systems. The theoretical prediction for the critical size is compared with
direct Monte Carlo simulations of the Boltzmann equations describing the
system, and a good agreement is found. The total energy fluctuations in the
vicinity of the transition are shown to scale with the second moment of the
distribution. The scaling distribution function is the same as found in other
equilibrium and non-equilibrium phase transitions, suggesting the existence of
some kind of universality
Vibrated granular gas confined by a piston
The steady state of a vibrated granular gas confined by a movable piston on
the top is discussed. Particular attention is given to the hydrodynamic
boundary conditions to be used when solving the inelastic Navier-Stokes
equations. The relevance of an exact general condition relating the grain
fluxes approaching and moving away from each of the walls is emphasized. It is
shown how it can be used to get a consistent hydrodynamic description of the
boundaries. The obtained expressions for the fields do not contain any
undetermined parameter. Comparison of the theoretical predictions with
molecular dynamics simulation results is carried out, and a good agreement is
observed for low density and not too large inelasticity. A practical way of
introducing small finite density corrections to the dilute limit theory is
proposed, to improve the accuracy of the theory
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