2,744 research outputs found
Crisis de naturaleza y justicia en las sociedades de riesgo
Los niesgos ambientales en las sociedades actuales son un tópico de amplío debate, que derivan
de la consideración de los problemas incluidos en el cambio global que se manifiestan a nivel
biosférico como por ejemplo el aumento de los gases efecto invernadero, la disminución del
ozono estratosférico, o el incremento de nutrientes y contaminantes en los océanos y a nivel local
a través de cambios a pequeña escala en distintos lugares del planeta pero que sumados, también
constituyen un cambio global, como los cambios en los usos de la tierra, la fragmentación de los
ambientes, la pérdida de biodiversidad, las invasiones biológicas, o el incremento de los procesos
de desertificación. Estos riesgos constituyen la crisis de la naturaleza, que compromete la
supervivencia de todos los seres vivos, incluida nuestra especie
Spin-glass behaviour on random lattices
The ground-state phase diagram of an Ising spin-glass model on a random graph
with an arbitrary fraction of ferromagnetic interactions is analysed in the
presence of an external field. Using the replica method, and performing an
analysis of stability of the replica-symmetric solution, it is shown that
, correponding to an unbiased spin glass, is a singular point in the
phase diagram, separating a region with a spin-glass phase () from a
region with spin-glass, ferromagnetic, mixed, and paramagnetic phases
()
Processamento de umbu-cajá, variedade suprema, na forma de geleia dietética e convencional.
A umbu-cajazeira (Spondias sp.), pertencente à família Anarcadiaceae, é nativa das regiões semiáridas do Nordeste e encontra-se difundida principalmente entre os estados do Rio Grande do Norte, Ceará, Piauí, Pernambuco e Bahia (CARVALHO et al., 2008; NARAIN et al., 2007). Seus frutos apresentam pH que varia entre 2,4 a 3,0 e sabor ácido acentuado, que dificulta o seu consumo in natura (CARVALHO et al., 2008).bitstream/item/55928/1/CircularTecnica-102-1.pd
Isochronous island bifurcations driven by resonant magnetic perturbations in Tokamaks
Recent evidences show that heteroclinic bifurcations in magnetic islands may
be caused by the amplitude variation of resonant magnetic perturbations in
tokamaks. To investigate the onset of these bifurcations, we consider a large
aspect ratio tokamak with an ergodic limiter composed of two pairs of rings
that create external primary perturbations with two sets of wave numbers. An
individual pair produces hyperbolic and elliptic periodic points, and its
associated islands, that are consistent with the Poincar\'e-Birkhoff fixed
point theorem. However, for two pairs producing external perturbations resonant
on the same rational surface, we show that different configurations of
isochronous island chains may appear on phase space according to the amplitude
of the electric currents in each pair of the ergodic limiter. When one of the
electric currents increases, isochronous bifurcations take place and new
islands are created with the same winding number as the preceding islands. We
present examples of bifurcation sequences displaying (a) direct transitions
from the island chain configuration generated by one of the pairs to the
configuration produced by the other pair, and (b) transitions with intermediate
configurations produced by the limiter pairs coupling. Furthermore, we identify
shearless bifurcations inside some isochronous islands, originating
nonmonotonic local winding number profiles with associated shearless invariant
curves
- …