A bouncing ball model with two nonlinearities: a prototype for Fermi acceleration

Some dynamical properties of a bouncing ball model under the presence of an external force modelled by two nonlinear terms are studied. The description of the model is made by the use of a two-dimensional nonlinear measure-preserving map on the variable's velocity of the particle and time. We show that raising the straight of a control parameter which controls one of the nonlinearities, the positive Lyapunov exponent decreases in the average and suffers abrupt changes. We also show that for a specific range of control parameters, the model exhibits the phenomenon of Fermi acceleration. The explanation of both behaviours is given in terms of the shape of the external force and due to a discontinuity of the moving wall's velocity.

On Ti-18Si-6B and Ti-7.5Si-22.5B powder alloys prepared by high-energy ball milling and sintering

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of ball-milled low purity boron powder on the superconductivity of MgB2

MgB2 samples were prepared using as-supplied commercial 96% boron with strong crystalline phase and the same 96% boron (B) after ball milling. The effects of the properties of the starting B powder on the superconductivity were evaluated. We observed that samples using ball-milled 96% B, in comparison with the one made from the as-supplied 96% B, were character- ized by small grain size, broadened full width at half maximum (FWHM), and enhanced magnetic critical current density (J(c)). J(c) reached 2 x 10(3) Acm(-2) at 5 K and 8 T. The improved pinning of these samples seems to be caused by enhanced grain boundary pinning at high field.

Bulk and high-energy ball-milled Gd5Si2Ge2: Comparative study of magnetic and magnetocaloric properties

High-energy ball milling was employed to produce small particles of Gd5Si2Ge2. Magnetic and magnetocaloric properties of the ball-milled and bulk Gd5Si2Ge2 samples were investigated through the magnetization measurements. When compared to the bulk material, a significant decrease in saturation magnetization and magnetocaloric effect (-Delta S-max = 4 vs. 20 J/kgK for Delta H = 0-5 T) is observed even after the relatively short ball milling time of 4 h which produced particles with an average size of ca. 0.5 mu m. The ball-milled samples appear to loose a first-order structural transition, present in bulk Gd5Si2Ge2, and display a superparamagnetic behaviour below the corresponding Curie temperatures. (C) 2010 Elsevier Masson SAS. All rights reserved.

Histological study of resection arthroplasty with and without tendon ball interposition in dogs

We studied an experimental model of resection arthroplasty with or without tendon ball interposition in the wrist of dogs. Animals were divided into two groups. Animals in group A were treated by resection of the os carpi radiale with interposition of a ball made from the tendon of the extensor carpi radialis and the group B underwent bone resection alone. Animals were assessed 1, 6, 12 and 24 weeks after operation. In all of them the wrist joint was stable and had good mobility, allowing walking supported by the operated limb. In both groups biological material filled the cavity created by bone resection. A progressive repair process resulted in fibroplasia with areas of fibrocartilaginous metaplasia. The tendon ball showed complete ischaemic necrosis at the end of the first week, which delayed the healing process. © 1999 The British Society for Surgery of the Hand.

Consequences of quadratic frictional force on the one dimensional bouncing ball model

Some dynamical properties of the one dimensional Fermi accelerator model, under the presence of frictional force are studied. The frictional force is assumed as being proportional to the square particle's velocity. The problem is described by use of a two dimensional non linear mapping, therefore obtained via the solution of differential equations. We confirm that the model experiences contraction of the phase space area and in special, we characterized the behavior of the particle approaching an attracting fixed point. © 2007 American Institute of Physics.

The feigenbaumes δ for a high dissipative bouncing ball model

We have studied a dissipative version of a one-dimensional Fermi accelerator model. The dynamics of the model is described in terms of a two-dimensional, nonlinear area-contracting map. The dissipation is introduced via inelastic collisions of the particle with the walls and we consider the dynamics in the regime of high dissipation. For such a regime, the model exhibits a route to chaos known as period doubling and we obtain a constant along the bifurcations so called the Feigenbaum's number 8.

Use of high energy ball milling on the sintering optimization of alumina ceramics

In this work, the effect of the milling time on the densification of the alumina ceramics with or without 5wt.%Y 2O 3, is evaluated, using high-energy ball milling. The milling was performed with different times of 0, 2, 5 or 10 hours. All powders, milled at different times, were characterized by X-Ray Diffraction presenting a reduction of the crystalline degree and crystallite size as function of the milling time increasing. The powders were compacted by cold uniaxial pressing and sintered at 1550°C-60min. Green density of the compacts presented an increasing as function of the milling time and sintered samples presented evolution on the densification as function of the reduction of the crystallite size of the milled powders. © (2010) Trans Tech Publications.

Educative games and expositive lesson: Comparison of educational techniques on sitting posture

Introduction: Studies on education in health are important for the concretion of action of promotion of the health. Objective: To verify the changes of theoretical knowledge on sitting posture, evaluated at two moments (initial and final,) considering two programs of education (expositive lesson and operative groups). Methods: 75 pupils had been citizens, of both the sexes, three 4as series of a public school, evaluated previously (A1) on seated position; group 1 was submitted to a procedure of expositive education, the 2 educative games in the 2 and, the 3 to no intervention. After one week they had been reevaluated (A2). For the moments the test of Wilcoxon was applied and between the Kruskal groups Wallis. Results: In the comparison inside of the groups, of 2 and 3 they had presented increase in the number of rightness on position seated in the after-test, with statistical significant difference, whereas in the group has controlled, such fact did not occur. In the comparison between groups, at the first moment (A1), 2 groups e 3 had not presented significant difference statistical (p > 0,05), however, in as moment notices that it had difference statistics between the three groups (p < 0,01), being that the G3 presented minor frequency of errors (md = 5) in relation to the g2 (md = 8) and g1 (md = 10). Conclusions: It can be affirmed that educative techniques that supply information and promote debates and exchanges of experiences between the participants increase the possibilities of incorporation of the contents related to the sitting posture.

Effect of ball milling on structural and physicochemical characteristics of cassava and Peruvian carrot starches

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Some dynamical properties of a classical dissipative bouncing ball model with two nonlinearities

Some dynamical properties for a bouncing ball model are studied. We show that when dissipation is introduced the structure of the phase space is changed and attractors appear. Increasing the amount of dissipation, the edges of the basins of attraction of an attracting fixed point touch the chaotic attractor. Consequently the chaotic attractor and its basin of attraction are destroyed given place to a transient described by a power law with exponent -2. The parameter-space is also studied and we show that it presents a rich structure with infinite self-similar structures of shrimp-shape. © 2013 Elsevier B.V. All rights reserved.

Identificação dos ângulos do tornozelo do membro de suporte, distância entre o pé de apoio e a bola e velocidade de saída da bola em cobranças de pênalti no futebol

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Tormentas e inimigos: relações dialógicas entre a literatura de fantasia e os role playing games

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo de um depósito de argila ball clay de Tambaú (SP), para aplicação na indústria cerâmica de revestimentos

Pós-graduação em Geologia Regional - IGCE