9,633 research outputs found
The Levi-Civita spacetime as a limiting case of the Gamma spacetime
It is shown that the Levi-Civita metric can be obtained from a family of the
Weyl metric, the Gamma metric, by taking the limit when the length of its
Newtonian image source tends to infinity. In this process a relationship
appears between two fundamental parameters of both metrics.Comment: LaTeX2e 17 page
Charge-density waves in one-dimensional Hubbard superlattices
We study the formation of charge density waves (CDW's) in one-dimensional
Hubbard superlattices, modeled by a repeated pattern of repulsive (U>0) and
free (U=0) sites. By means of Lanczos diagonalizations for the ground state, we
calculate the charge structure factor. Our results show that while the
superlattice structure affects the modulation of the charge density waves, the
periodicity can still be predicted through an effective density. We also show
that, for a fixed repulsive layer thickness, the periodicity of the CDW is an
oscillatory function of the free layer thickness.Comment: 4 pages, 4 figure
Effect of ABA and GA3 on protein mobilization in embryos and Cotyledons of angico (Anadenanthera peregrina (L.) sepg) seeds during germination.
In this work, a woody species [A. peregrina (L.) Speg.] was studied in order to observe the effect of ABA and GA3 at the biochemical level during the process of seed germination. Embryos incubated in sucrose solution containing ABA and/or GA3 were analyzed through SDS-PAGE to observe the mobilization pattern of storage proteins during the beginning of germination. Cotyledons isolated from seeds incubated in aqueous solutions containing ABA and/or GA3, were also analyzed through SDS-PAGE and by PAGE/Activity Gels (polyacrylamide gels copolymerized with substrate for enzymes) to observe the mobilization pattern of storage proteins and protease activity after the beginning of the germination. Results of these experiments show that ABA blocks protein mobilization by inhibiting protease activity in cotyledons. This inhibition is not sufficient to prevent germination showing that the effect of ABA on germination is not dependent on protease activity. The blockage of storage protein mobilization was also observed in embryos, but no protease activity inhibition was clearly detected. ABA was able to induce the synthesis of proteins in cotyledons but not in embryos. A polypeptide with an approximate molecular weight of 17 kD, was degraded within 6 hours in control embryos, but this degradation was blocked by ABA and GA3. Using the same concentrations of ABA and GA3 on embryos and cotyledons, the effect of ABA was counteracted by GA3 in embryos, but not in cotyledons. Although the effects of ABA and GA3 were not so different from those shown in the literature, the behavior of 17 kD-polypeptide contradicts these reports suggesting that specific studies should be performed
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