23,701 research outputs found
Collapse of Primordial Clouds
We present here studies of collapse of purely baryonic Population III objects
with masses ranging from to . A spherical Lagrangian
hydrodynamic code has been written to study the formation and evolution of the
primordial clouds, from the beginning of the recombination era () until the redshift when the collapse occurs. All the relevant processes
are included in the calculations, as well as, the expansion of the Universe. As
initial condition we take different values for the Hubble constant and for the
baryonic density parameter (considering however a purely baryonic Universe), as
well as different density perturbation spectra, in order to see their influence
on the behavior of the Population III objects evolution. We find, for example,
that the first mass that collapses is for ,
and with the mass scale . For
we obtain for the first
mass that collapses. The cooling-heating and photon drag processes have a key
role in the collapse of the clouds and in their thermal history. Our results
show, for example, that when we disregard the Compton cooling-heating, the
collapse of the objects with masses occurs earlier. On
the other hand, disregarding the photon drag process, the collapse occurs at a
higher redshift.Comment: 10 pages, MN plain TeX macros v1.6 file, 9 PS figures. Also available
at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES").
MNRAS in pres
Collapse of Primordial Clouds II. The Role of Dark Matter
In this article we extend the study performed in our previous article on the
collapse of primordial objects. We here analyze the behavior of the physical
parameters for clouds ranging from to . We
studied the dynamical evolution of these clouds in two ways: purely baryonic
clouds and clouds with non-baryonic dark matter included. We start the
calculations at the beginning of the recombination era, following the evolution
of the structure until the collapse (that we defined as the time when the
density contrast of the baryonic matter is greater than ). We analyze the
behavior of the several physical parameters of the clouds (as, e.g., the
density contrast and the velocities of the baryonic matter and the dark matter)
as a function of time and radial position in the cloud. In this study all
physical processes that are relevant to the dynamical evolution of the
primordial clouds, as for example photon-drag (due to the cosmic background
radiation), hydrogen molecular production, besides the expansion of the
Universe, are included in the calculations. In particular we find that the
clouds, with dark matter, collapse at higher redshift when we compare the
results with the purely baryonic models. As a general result we find that the
distribution of the non-baryonic dark matter is more concentrated than the
baryonic one. It is important to stress that we do not take into account the
putative virialization of the non-baryonic dark matter, we just follow the time
and spatial evolution of the cloud solving its hydrodynamical equations. We
studied also the role of the cooling-heating processes in the purely baryonic
clouds.Comment: 8 pages, MN plain TeX macros v1.6 file, 13 PS figures. Also available
at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES").
MNRAS in pres
The Noncommutative Doplicher-Fredenhagen-Roberts-Amorim Space
This work is an effort in order to compose a pedestrian review of the
recently elaborated Doplicher, Fredenhagen, Roberts and Amorim (DFRA)
noncommutative (NC) space which is a minimal extension of the DFR space. In
this DRFA space, the object of noncommutativity () is a
variable of the NC system and has a canonical conjugate momentum. The DFRA
formalism is constructed in an extended space-time with independent degrees of
freedom associated with the object of noncommutativity . A
consistent algebra involving the enlarged set of canonical operators is
described, which permits one to construct theories that are dynamically
invariant under the action of the rotation group. A consistent classical
mechanics formulation is analyzed in such a way that, under quantization, it
furnishes a NC quantum theory with interesting results. The Dirac formalism for
constrained Hamiltonian systems is considered and the object of
noncommutativity plays a fundamental role as an independent
quantity. It is also explained about the generalized Dirac equation issue, that
the fermionic field depends not only on the ordinary coordinates but on
as well. The dynamical symmetry content of such fermionic
theory is discussed, and we show that its action is invariant under . In the last part of this work we analyze the complex scalar fields using
this new framework. As said above, in a first quantized formalism,
and its canonical momentum are seen as
operators living in some Hilbert space. In a second quantized formalism
perspective, we show an explicit form for the extended Poincar\'e generators
and the same algebra is generated via generalized Heisenberg relations. We also
consider a source term and construct the general solution for the complex
scalar fields using the Green function technique
Possibilidades de avanço do melhoramento genético de cupuaçuzeiro, com a seleção de novas progênies.
Alterações nos níveis relativos de açúcares solúveis totais e de proteínas em plantas de milho infectadas com molicutes.
As doenças do milho causadas por molicutes (fitoplasma e espiroplasma) destacam-se em importância para a cultura, em conseqüência da alta incidência e dos prejuízos que causam à produção de grãos. Os molicutes infectam o floema das plantas; sendo assim, podem alterar a síntese de açúcares e proteínas. O objetivo deste trabalho foi verificar o efeito dos molicutes na síntese de açúcares solúveis totais e de proteínas em duas cultivares de milho. O experimento foi conduzido em vasos de plástico contendo 30 kg solo previamente analisado e adubado, com duas plantas por vaso. O delineamento experimental utilizado foi um fatorial 3 x 2 inteiramente casualizado, com seis repetições; sendo três inoculações (fitoplasma, espiroplasma e sadia) e duas cultivares (Dina 766 e BR 201). Trinta dias após a inoculação, foram realizadas medidas de temperatura foliar, umidade relativa, resistência estomática e transpiração. No estádio de grão leitoso, uma das plantas foi colhida e seccionada em três partes, para análise de açúcares solúveis totais, nutrientes e matéria seca. Foi realizada uma amostragem do internódio abaixo da primeira espiga e da folha bandeira, para determinação da atividade da peroxidase e do conteúdo proteíco. A planta restante foi conduzida até o final do ciclo, quando foram avaliados: número de espigas, peso de espigas e de grãos e matéria seca dos grãos. A análise de variância de todas as características avaliadas não detectou signifi-cância na interação cultivar x inoculação. Alguns parâmetros mostraram significância para cultivares, para inoculação ou para ambos. Açúcares solúveis, matéria seca, atividade da peroxidase e conteúdo protéico foram semelhantes em ambas as cultivares e nas inoculações. A resistência estomática foi maior para Dina 766 e nas plantas inoculadas por fitoplasma. A proliferação de espigas foi maior nas plantas inoculadas pelos molicutes que nas sadias. O peso de espigas e de grãos foi maior nas plantas sadias e com fitoplasma que naquelas infectadas por espiroplasma. Concentração de nutrientes e quantidade absorvida, em geral, foram semelhantes, excetuando P e Zn. Os molicutes não interferiram na concentração dos açúcares solúveis e no conteúdo proteíco total; entretanto, os dados de produtividade sugerem uma maior susceptibilidade das cultivares ao espiroplasma
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