575 research outputs found
Baccharis nebularis (Asteraceae, Astereae): a new species of B. subgen. Tarchonanthoides sect. Curitybenses from the mountains of Southern Brazil.
Baccharis nebularis, a new species belonging to B. subgen. Tarchonanthoides sect. Curitybenses, is described, illustrated, and compared to B. chionolaenoides and B. curitybensis. A key for its identification is provided. The new species occurs in patches of cloud forest thickets mixed with high altitude tropical grasslands in the southern Brazilian mountains. Data on distribution and habitat, phenology, conservation status, as well as a list of specimens examined are also presented
Less is more. Adjusting the taxonomy of the polytypic: Mimosa setosa (Leguminosae, Mimosoid).
Resumo Mimosa setosa, em sua circunscrição atual, é uma espécie politípica que inclui quatro subespécies e oito variedades. Estudos filogenéticos recentes indicam que esses táxons infraespecíficos não formam um grupo monofilético. A análise morfológica de um conjunto de espécimes obtidos em diversos herbários, incluindo tipos e coletas recentes, associada à aplicação do Conceito Filogenético de espécie permite desmembrar M. setosa em seis diferentes espécies sem táxons infraespecíficos. Congruência entre dados filogenéticos, geografia e adoção do nível de espécie como a unidade mínima para descrição de táxons permite uma melhor comparação da diversidade biológica e uma circunscrição mais adequada dos táxons envolvidos no complexo M. setosa.</jats:p
Tetrads in SU(3) X SU(2) X U(1) Yang-Mills geometrodynamics
The relationship between gauge and gravity amounts to understanding
underlying new geometrical local structures. These structures are new tetrads
specially devised for Yang-Mills theories, Abelian and Non-Abelian in
four-dimensional Lorentzian spacetimes. In the present manuscript a new tetrad
is introduced for the Yang-Mills SU(3) X SU(2) X U(1) formulation. These new
tetrads establish a link between local groups of gauge transformations and
local groups of spacetime transformations. New theorems are proved regarding
isomorphisms between local internal SU(3) X SU(2) X U(1) groups and local
tensor products of spacetime LB1 and LB2 groups of transformations. The new
tetrads and the stress-energy tensor allow for the introduction of three new
local gauge invariant objects. Using these new gauge invariant objects and in
addition a new general local duality transformation, a new algorithm for the
gauge invariant diagonalization of the Yang-Mills stress-energy tensor is
developed.Comment: There is a new appendix. The unitary transformations by local SU(2)
subgroup elements of a local group coset representative is proved to be a new
local group coset representative. This proof is relevant to the study of the
memory of the local tetrad SU(3) generated gauge transformations. Therefore,
it is also relevant to the group theorems proved in the paper. arXiv admin
note: substantial text overlap with arXiv:gr-qc/060204
Equilibrium conditions of spinning test particles in Kerr-de Sitter spacetimes
Equilibrium conditions and spin dynamics of spinning test particles are
discussed in the stationary and axially symmetric Kerr-de Sitter black-hole or
naked-singularity spacetimes. The general equilibrium conditions are
established, but due to their great complexity, the detailed discussion of the
equilibrium conditions and spin dynamics is presented only in the simple and
most relevant cases of equilibrium positions in the equatorial plane and on the
symmetry axis of the spacetimes. It is shown that due to the combined effect of
the rotation of the source and the cosmic repulsion the equilibrium is spin
dependent in contrast to the spherically symmetric spacetimes. In the
equatorial plane, it is possible at the so-called static radius, where the
gravitational attraction is balanced by the cosmic repulsion, for the spinless
particles as well as for spinning particles with arbitrarily large
azimuthal-oriented spin or at any radius outside the ergosphere with a
specifically given spin orthogonal to the equatorial plane. On the symmetry
axis, the equilibrium is possible at any radius in the stationary region and is
given by an appropriately tuned spin directed along the axis. At the static
radii on the axis the spin of particles in equilibrium must vanish
On the propagation of jump discontinuities in relativistic cosmology
A recent dynamical formulation at derivative level \ptl^{3}g for fluid
spacetime geometries , that employs the concept
of evolution systems in first-order symmetric hyperbolic format, implies the
existence in the Weyl curvature branch of a set of timelike characteristic
3-surfaces associated with propagation speed |v| = \sfrac{1}{2} relative to
fluid-comoving observers. We show it is the physical role of the constraint
equations to prevent realisation of jump discontinuities in the derivatives of
the related initial data so that Weyl curvature modes propagating along these
3-surfaces cannot be activated. In addition we introduce a new, illustrative
first-order symmetric hyperbolic evolution system at derivative level
\ptl^{2}g for baryotropic perfect fluid cosmological models that are
invariant under the transformations of an Abelian isometry group.Comment: 19 pages, 1 table, REVTeX v3.1 (10pt), submitted for publication to
Physical Review D; added Report-No, corrected typo
A Characterisation of the Weylian Structure of Space-Time by Means of Low Velocity Tests
The compatibility axiom in Ehlers, Pirani and Schild's (EPS) constructive
axiomatics of the space-time geometry that uses light rays and freely falling
particles with high velocity, is replaced by several constructions with low
velocity particles only. For that purpose we describe in a space-time with a
conformal structure and an arbitrary path structure the radial acceleration, a
Coriolis acceleration and the zig-zag construction. Each of these quantities
give effects whose requirement to vanish can be taken as alternative version of
the compatibility axiom of EPS. The procedural advantage lies in the fact, that
one can make null-experiments and that one only needs low velocity particles to
test the compatibility axiom. We show in addition that Perlick's standard clock
can exist in a Weyl space only.Comment: to appear in Gen.Rel.Gra
Geodesic Deviation Equation in Bianchi Cosmologies
We present the Geodesic Deviation Equation (GDE) for the
Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation
for Bianchi type I model. We justify consider this cosmological model due to
the recent importance the Bianchi Models have as alternative models in
cosmology. The main property of these models, solutions of Einstein Field
Equations (EFE) is that they are homogeneous as the FRW model but they are not
isotropic. We can see this because they have a non-null Weyl tensor in the GDE.Comment: Submitted to Journal of Physics: Conference Series (JPCS), ERE200
On the Significance of the Weyl Curvature in a Relativistic Cosmological Model
The Weyl curvature includes the Newtonian field and an additional field, the
so-called anti-Newtonian. In this paper, we use the Bianchi and Ricci
identities to provide a set of constraints and propagations for the Weyl
fields. The temporal evolutions of propagations manifest explicit solutions of
gravitational waves. We see that models with purely Newtonian field are
inconsistent with relativistic models and obstruct sounding solutions.
Therefore, both fields are necessary for the nonlocal nature and radiative
solutions of gravitation.Comment: 15 pages, incorporating proof correction
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