132 research outputs found
Estudo morfológico de folhas de cupuaçu (Theobroma grandiflorum Schum.).
As folhas de Theobroma grandiflorum Schum. são morfologicamente descritas. A espécie apresenta elementos histológicos comuns para a família, destacando-se tipos de tricomas, estômatos e contornos das células epidérmicas em visão frontal. Empregou-se microscopia eletrônica de varredura para a caracterização de segmentos foliares jovens, onde ficou evidenciada a presença de tricomas estrelados nas superfícies adaxial e abaxial dos mesmos. As folhas de cupuaçu não apresentaram estômatos na superfície adaxial, sendo estes em número elevado na superfície abaxial, caracterizando-se como hipoestomáticas. As nervuras principais das folhas de cupuaçu apresentaram-se desprovidas de tricomas, com estômatos esparsamente distribuídos.bitstream/item/24661/1/bpd33-cupuacu.pd
Desenvolvimento de calos em explantes de cupuaçuzeiro (Theobroma grandiflorum schum.) em função da concentração de auxinas e do meio líquido.
Objetivou-se estudar o efeito da concentração de auxina e do meio líquido sobre o desenvolvimento de calos de cupuaçuzeiro. Segmentos de eixos embrionários e cotilédones, obtidos de frutos de cupuaçu dos tipos Mamorana e Redondo, foram cultivados em 4 meios de cultura diferentes: 1) meio MS (50%), suplementado com 2,4-D (1; 2; 4; 8 mg/L); 2) sais N6 (SIGMA) (4 g/L), acrescidos de 2,4-D (0; 2; 4 mg/L) e ANA (0; 3; 5 mg/L); 3) igual ao anterior, suplementado apenas com ANA (3 mg/L); e 4) meio MS, acrescido com ANA (1 mM). Calos com aspecto branco e brilhante foram observados em segmentos de eixos embrionários e cotilédones, cultivados nas menores concentrações de meio 1 (1 e 2 mg/L), enquanto nas maiores concentrações (4 e 8 mg/L) se observou a formação de calos e massa calosa branco-opaca, em eixos embrionários e em segmentos cotiledonares, estas estruturas tornaram-se escuras dentro de oito semanas. Usando o meio 2, um grande número de raízes foram formadas, enquanto o mesmo meio suplementado apenas com ANA (3; 5 mg/L) originou uma massa calosa. A combinação de ANA e 2,4-D, 3 e 2 mg/L, respectivamente, promoveu a formação de calos brancos e raízes. A transferência das culturas para meio líquido, sem regulador de crescimento, promoveu aumento de tamanho dos explantes e escurecimento dos mesmos. O cultivo desses explantes no meio 3 resultou no aparecimento de calos amarelos, com aspecto friável, que permaneceram com a mesma aparência no meio 4
The Efficiency of Gravitational Bremsstrahlung Production in the Collision of Two Schwarzschild Black Holes
We examine the efficiency of gravitational bremsstrahlung production in the
process of head-on collision of two boosted Schwarzschild black holes. We
constructed initial data for the characteristic initial value problem in
Robinson-Trautman spacetimes, that represent two instantaneously stationary
Schwarzschild black holes in motion towards each other with the same velocity.
The Robinson-Trautman equation was integrated for these initial data using a
numerical code based on the Galerkin method. The final resulting configuration
is a boosted black hole with Bondi mass greater than the sum of the individual
mass of each initial black hole. Two relevant aspects of the process are
presented. The first relates the efficiency of the energy extraction
by gravitational wave emission to the mass of the final black hole. This
relation is fitted by a distribution function of non-extensive thermostatistics
with entropic parameter ; the result extends and validates
analysis based on the linearized theory of gravitational wave emission. The
second is a typical bremsstrahlung angular pattern in the early period of
emission at the wave zone, a consequence of the deceleration of the black holes
as they coalesce; this pattern evolves to a quadrupole form for later times.Comment: 16 pages, 4 figures, to appear in Int. J. Modern Phys. D (2008
Embriogênese somática em tamareira.
Objetivou-se com este trabalho comparar o potencial de obtenção de propágulos de tamareira via embriogênese somática nas variedades Medjool, Zahidi, Deglet Nour, Khadrawy e Halawy, utilizando meio de cultura definido e em interação com luz vermelh
Gravitational Wave Emission from a Bounded Source: the Nonlinear Regime
We study the dynamics of a bounded gravitational collapsing configuration
emitting gravitational waves, where the exterior spacetime is described by
Robinson-Trautman geometries. The full nonlinear regime is examined by using
the Galerkin method that allows us to reduce the equations governing the
dynamics to a finite-dimensional dynamical system, after a proper truncation
procedure. Amongst the obtained results of the nonlinear evolution, one of the
most impressive is the fact that the distribution of the mass fraction
extracted by gravitational wave emission satisfies the distribution law of
nonextensive statistics and this result is independent of the initial
configurations considered.Comment: 3 page, 1 figure, proceedings of the X Marcel Grossmann Meeting 22-26
July, 2003, Rio de Janeir
Taub's plane-symmetric vacuum spacetime revisited
The gravitational properties of the {\em only} static plane-symmetric vacuum
solution of Einstein's field equations without cosmological term (Taub's
solution, for brevity) are presented: some already known properties (geodesics,
weak field limit and pertainment to the Schwarzschild family of spacetimes) are
reviewed in a physically much more transparent way, as well as new results
about its asymptotic structure, possible matchings and nature of the source are
furnished. The main results point to the fact that the solution must be
interpreted as representing the exterior gravitational field due to a {\em
negative} mass distribution, confirming previous statements to that effect in
the literature. Some analogies to Kasner's spatially homogeneous cosmological
model are also referred to.Comment: plain LaTex, four Postscript figure
Mass-Energy and Momentum Extraction by Gravitational Wave Emission in the Merger of Two Colliding Black Holes: The Non-Head-On Case
We examine numerically the post-merger regime of two Schwarzschild black
holes in non head-on collision. Our treatment is made in the realm of
non-axisymmetric Robinson-Trautman spacetimes which are appropriate for the
description of the system. Characteristic initial data for the system are
constructed and the Robinson-Trautman equation is integrated using a numerical
code based on the Galerkin spectral method. The collision is planar, restricted
to the plane determined by the directions of the two initial colliding black
holes, with the net momentum fluxes of gravitational waves confined to this
plane. We evaluate the efficiency of mass-energy extraction, the total energy
and momentum carried out by gravitational waves and the momentum distribution
of the remnant black hole. Our analysis is based on the Bondi-Sachs four
momentum conservation laws. Head-on collisions and orthogonal collisions
constitute, respectively, upper and lower bounds to the power emission and to
the efficiency of mass-energy extraction by gravitational waves. The momentum
extraction and the pattern of the momentum fluxes, as a function of the
incidence angle, are examined. The momentum extraction characterizes a regime
of strong deceleration of the system. The angular pattern of gravitational wave
signals is also examined. They are typically bremsstrahlung for early times
emission. Gravitational waves are also emitted outside the plane of collision
but this component has a zero net momentum flux. The relation between the
incidence angle of collision and the exit angle of the remnant closely
approximates a relation for inelastic collisions of classical particles in
Newtonian dynamics.Comment: 18 pages, 12 Figures, published with slight modifications in Phys.
Rev. D 85, 024003 (2012
Homoclinic chaos in the dynamics of a general Bianchi IX model
The dynamics of a general Bianchi IX model with three scale factors is
examined. The matter content of the model is assumed to be comoving dust plus a
positive cosmological constant. The model presents a critical point of
saddle-center-center type in the finite region of phase space. This critical
point engenders in the phase space dynamics the topology of stable and unstable
four dimensional tubes , where is a saddle direction and
is the manifold of unstable periodic orbits in the center-center sector.
A general characteristic of the dynamical flow is an oscillatory mode about
orbits of an invariant plane of the dynamics which contains the critical point
and a Friedmann-Robertson-Walker (FRW) singularity. We show that a pair of
tubes (one stable, one unstable) emerging from the neighborhood of the critical
point towards the FRW singularity have homoclinic transversal crossings. The
homoclinic intersection manifold has topology and is constituted
of homoclinic orbits which are bi-asymptotic to the center-center
manifold. This is an invariant signature of chaos in the model, and produces
chaotic sets in phase space. The model also presents an asymptotic DeSitter
attractor at infinity and initial conditions sets are shown to have fractal
basin boundaries connected to the escape into the DeSitter configuration
(escape into inflation), characterizing the critical point as a chaotic
scatterer.Comment: 11 pages, 6 ps figures. Accepted for publication in Phys. Rev.
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