10,206 research outputs found
Alternate islands of multiple isochronous chains in wave-particle interactions
We analyze the dynamics of a relativistic particle moving in a uniform
magnetic field and perturbed by a standing electrostatic wave. We show that a
pulsed wave produces an infinite number of perturbative terms with the same
winding number, which may generate islands in the same region of phase space.
As a consequence, the number of isochronous island chains varies as a function
of the wave parameters. We observe that in all the resonances, the number of
chains is related to the amplitude of the various resonant terms. We determine
analytically the position of the periodic points and the number of island
chains as a function of the wave number and wave period. Such information is
very important when one is concerned with regular particle acceleration, since
it is necessary to adjust the initial conditions of the particle to obtain the
maximum acceleration.Comment: Submitte
Exponential Distributions in a Mechanical Model for Earthquakes
We study statistical distributions in a mechanical model for an earthquake
fault introduced by Burridge and Knopoff [R. Burridge and L. Knopoff, {\sl
Bull. Seismol. Soc. Am.} {\bf 57}, 341 (1967)]. Our investigations on the size
(moment), time duration and number of blocks involved in an event show that
exponential distributions are found in a given range of the paramenter space.
This occurs when the two kinds of springs present in the model have the same,
or approximately the same, value for the elastic constants. Exponential
distributions have also been seen recently in an experimental system to model
earthquake-like dynamics [M. A. Rubio and J. Galeano, {\sl Phys. Rev. E} {\bf
50}, 1000 (1994)].Comment: 11 pages, uuencoded (submitted to Phys. Rev. E
Enraizamento de estaca de Tococa formicaria (Melastomataceae Juss), uma alternativa para acelerar o processo de restauração em matas ripárias.
Enraizamento de estacas de Miconia ibaguensis (Bonpl) Triana e Trembleya parviflora (Don) Cong. (MELASTOMACEAE).
Sobrevivência de espécies nativas do cerrado em experimento de restauração ecológica de mata ripária, Distrito Federal.
Sobrevivência inicial de mudas de espécies nativas de matas riparias em processo de restauração ecológica.
Revitalização do programa de gerenciamento de tratamento de resíduos químicos da Embrapa Pecuária Sudeste.
Restauração ecológica em matas ripárias: sobrevivência de espécies arbustivas e arbóreas nativas do cerrado.
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