9 research outputs found
Cosmological evolution of interacting dark energy in Lorentz violation
The cosmological evolution of an interacting scalar field model in which the
scalar field interacts with dark matter, radiation, and baryon via Lorentz
violation is investigated. We propose a model of interaction through the
effective coupling . Using dynamical system analysis, we study the
linear dynamics of an interacting model and show that the dynamics of critical
points are completely controlled by two parameters. Some results can be
mentioned as follows. Firstly, the sequence of radiation, the dark matter, and
the scalar field dark energy exist and baryons are sub dominant. Secondly, the
model also allows the possibility of having a universe in the phantom phase
with constant potential. Thirdly, the effective gravitational constant varies
with respect to time through . In particular, we consider a simple
case where has a quadratic form and has a good agreement with the
modified CDM and quintessence models. Finally, we also calculate the
first post--Newtonian parameters for our model.Comment: 14 pages, published versio
Efeito de perĂodos de controle de plantas daninhas sobre o desenvolvimento inicial de plantas de eucalipto Effects of weed control periods on initial growth and development of eucalypt
O objetivo deste trabalho foi estudar os efeitos dos perĂodos de convivĂȘncia e de controle de Brachiaria decumbens sobre o desenvolvimento inicial de clones de Eucalyptus grandis x Eucalyptus urophylla. Para isso, um ensaio foi conduzido, no municĂpio de TrĂȘs Lagoas-MS, no perĂodo de janeiro a dezembro de 1997. Os tratamentos experimentais consistiram de diferentes Ă©pocas e perĂodos de convivĂȘncia das plantas daninhas na cultura do eucalipto. As Ă©pocas foram divididas em dois grupos. No primeiro, a convivĂȘncia se iniciava no transplante das mudas e era estendida atĂ© 28, 56, 84, 112, 140, 168, 224, 252 e 364 dias apĂłs. No segundo grupo, a convivĂȘncia se iniciava aos 0, 28, 56, 84, 112, 140, 168, 224 e 252 dias apĂłs o transplante e era estendida atĂ© o final de um ano. As principais plantas daninhas que ocorreram na ĂĄrea experimental foram Brachiaria decumbens e Spermacocea latifola. As plantas jovens de eucalipto foram bastante suscetĂveis Ă interferĂȘncia das plantas daninhas, apresentando um perĂodo anterior Ă interferĂȘncia inferior a 14-28 dias. Para assegurar o desenvolvimento da cultura, o perĂodo total de prevenção Ă interferĂȘncia foi de 140 dias, e o perĂodo crĂtico de prevenção Ă interferĂȘncia, de 14-28 a 140 dias apĂłs o transplante, considerando o Ăndice de 5% de redução em diĂąmetro.<br>A field trial was carried out in TrĂȘs Lagoas-MS, Brazil, from January to December of 1997, to study the effects of control and coexistence period of Brachiaria decumbens on the growth of Eucalyptus grandis x Eucalyptus urophylla clones. The experimental design was a complete randomized block design, with four replications. The treatments consisted of different periods of weed-eucalypt association. The periods were divided in two groups. In the first one, the weed-eucalypt coexistence initiated during the eucalypt transplanting, continuing up to 28, 56, 112, 140, 168, 224, 252 and 364 days after it. In the second group, the weed coexistence began at 0, 28, 56, 112, 140, 168, 224 and 252 days after the transplanting and ended 364 days later. The main infesting weeds were Brachiaria decumbens and Spermacocea latifola. The young eucalypt plants were very susceptible to weed interference. To assure normal crop development it was necessary to maintain a weed free period of 140 days after transplanting