370 research outputs found
Avaliação da fertilidade de dois solos do Estado do Acre, em casa de vegetação.
Com uma imigração constante e crescente, a ocupação do estado do Acre tem sido feita em ritmo acelerado. Este crescimento desordenado tende a se agravar, na medida em que áreas que estão sendo ocupadas são, praticamente desconhecidas no tocante ao potencial dos solos, já que os estudos desta região se restringem, na maioria dos casos, a poucos trabalhos de revisão baseados em imagens de radar, ou seja, são informações apenas aproximadas. Assim. a UEPAE Rio Branco conduziu um experimento com o objetivo de avaliar a fertilidade de um Latossolo Vermelho Escuro (LE) e de um Podzólico Vermelho Amarelo (PV), e sugerir técnicas de manejo de adubação mais econômicas para estes solos, que ocorrem com frequência na região.bitstream/item/173383/1/1068.pd
Influência de aléias de leguminosas arbóreas na infestação de bicho-mineiro em cafeeiro.
O bicho-mineiro, Leucoptera coffeella (Guérin - Mèneville, 1842) (Lepidoptera: Lyonetiidae), é talvez a principal praga do cafeeiro (Coffea spp.) na atualidade, principalmente nas regiões de temperaturas mais elevadas e de maior déficit hídrico. Vários estudos indicam que a abundância e diversidade de insetos dentro de um campo podem estar intimamente relacionadas com a natureza da vegetação circundante. Considerando o exposto, foi objetivo deste trabalho observar o efeito de espécies de leguminosas arbóreas utilizadas como quebra-ventos (aléias) sobre os aspectos fitossanitários do cafeeiro. As leguminosas utilizadas foram: o Guandu (Cajanus cajan Millsp.), Bracatinga (Mimosa scabrella Benth.), Leucena (Leucaena leucocephala (Lam.) De Wit) e Acácia (Acacia mangium Willd.), plantadas perpendiculares ao sentido dos ventos predominantes. Os resultados parciais, obtidos em 2003, 2004, 2005 e 2006, mostram que a menor porcentagem de folhas com minas intactas foi observada nos cafeeiros sob Leucena e Guandu e também a menor porcentagem de minas predadas. Os cafeeiros sob Leucena e Guandu apresentaram nível de controle (NC) para o bicho-mineiro (30% de folhas minadas sem sinais de predação) no final de agosto enquanto que aqueles sob Acácia e Bracatinga foram semelhantes à testemunha e apresentaram NC bem mais cedo, no mês de junho
Controle de plantas invasoras em lavouras de café em formação no Estado do Acre.
A existência de áreas potenciais, ecologicamente favoráveis à cultura do café, levou o governo do estado do Acre a incluí-la, ao lado da seringueira e castanheira, como opção de cultivo nos projetos de colonização, em vários municípios acreanos. Além dos aspectos agronômicos favoráveis, confirmados pelas plantações existentes que, na grande maioria, são efetuados por pequenos produtores, a cultura do café é sócio-economicamente viável, com amplas possibilidades de êxito na região. O cafeeiro, como a maioria das culturas, é muito sensível a infestação e ocorrência natural de plantas daninhas que, devido às condições de umidade e temperatura da região, têm desenvolvimento exuberante, concorrendo com a cultura em nutrientes, água e luz. Não há dúvida de que o controle eficiente e econômico das plantas daninhas e um dos principais fatores de alta produção das culturas. De forma que o manejo adequado das plantas invasoras tem papel decisivo no rendimento da cultura e na redução do custo de produção. Ainda não existem métodos de controle na região reconhecidamente econômicos e eficientes para cafezais em formação.Com o objetivo de se estudar métodos de controle de plantas daninhas viáveis para a região, instalou-se no município de Rio Branco-AC, no km 14 da BR-364, na base física da UEPAE de Rio Branco, em lavoura de Catuaí Vermelho de seis meses de idade, plantada no espaçamento de 3,00 m x 2,00 m com duas plantas por cova, um ensaio de métodos de controle de plantas daninhas.bitstream/item/166122/1/1065.pd
Quantum cosmological perfect fluid models
Perfect fluid Friedmann-Robertson-Walker quantum cosmological models for an
arbitrary barotropic equation of state are constructed using
Schutz's variational formalism. In this approach the notion of time can be
recovered. By superposition of stationary states, finite-norm wave-packet
solutions to the Wheeler-DeWitt equation are found. The behaviour of the scale
factor is studied by applying the many-worlds and the ontological
interpretations of quantum mechanics. Singularity-free models are obtained for
.Comment: Latex file, 12 pages. New paragraphs in the Introduction and
Conclusion, and other minor corrections in the text and in some formulas.
Accepted for publication in General Relativity and Gravitatio
Modeling the quantum evolution of the universe through classical matter
It is well known that the canonical quantization of the
Friedmann-Lema\^itre-Robertson-Walker (FLRW) filled with a perfect fluid leads
to nonsingular universes which, for later times, behave as their classical
counterpart. This means that the expectation value of the scale factor
never vanishes and, as , we recover the classical expression for
the scale factor. In this paper, we show that such universes can be reproduced
by classical cosmology given that the universe is filled with an exotic matter.
In the case of a perfect fluid, we find an implicit equation of state (EoS). We
then show that this single fluid with an implict EoS is equivalent to two
non-interacting fluids, one of them representing stiff matter with negative
energy density. In the case of two non-interacting scalar fields, one of them
of the phantom type, we find their potential energy. In both cases we find that
quantum mechanics changes completely the configuration of matter for small
values of time, by adding a fluid or a scalar field with negative energy
density. As time passes, the density of negative energy decreases and we
recover the ordinary content of the classical universe. The more the initial
wave function of the universe is concentrated around the classical big bang
singularity, the more it is necessary to add negative energy, since this type
of energy will be responsible for the removal of the classical singularity.Comment: updated version as accepted by Gen. Relativ. Gravi
Quantum Cosmology in Scalar-Tensor Theories With Non Minimal Coupling
Quantization in the minisuperspace of non minimal scalar-tensor theories
leads to a partial differential equation which is non separable. Through a
conformal transformation we can recast the Wheeler-DeWitt equation in an
integrable form, which corresponds to the minimal coupling case, whose general
solution is known. Performing the inverse conformal transformation in the
solution so found, we can construct the corresponding one in the original
frame. This procedure can also be employed with the bohmian trajectories. In
this way, we can study the classical limit of some solutions of this quantum
model. While the classical limit of these solutions occurs for small scale
factors in the Einstein's frame, it happens for small values of the scalar
field non minimally coupled to gravity in the Jordan's frame, which includes
large scale factors.Comment: latex, 18 page
Cold black holes and conformal continuations
We study Einstein gravity minimally coupled to a scalar field in a static,
spherically symmetric space-time in four dimensions. Black hole solutions are
shown to exist for a phantom scalar field whose kinetic energy is negative.
These ``scalar black holes'' have an infinite horizon area and zero Hawking
temperature and are termed ``cold black holes'' (CBHs). The relevant explicit
solutions are well-known in the massless case (the so-called anti-Fisher
solution), and we have found a particular example of a CBH with a nonzero
potential . All CBHs with are shown to behave
near the horizon quite similarly to those with a massless field. The above
solutions can be converted by a conformal transformation to Jordan frames of a
general class of scalar-tensor theories of gravity, but CBH horizons in one
frame are in many cases converted to singularities in the other, which gives
rise to a new type of conformal continuation.Comment: 15 pages, late
A comparative study of high-field diamagnetic fluctuations in deoxygenated YBa2Cu3O(7-x) and polycrystalline (Bi-Pb)2Sr2Ca3O(10)
We studied three single crystals of YBa2Cu3O{7-x} with Tc= 62.5, 52, and 41
K, and a textured specimen of (Bi-Pb)2Sr2Ca2Cu3O10 with Tc=108 K, for H//c
axis. The reversible data were interpreted in terms of 2D lowest-Landau-level
fluctuation theory. The data were fit well by the 2D LLL expression for
magnetization obtained by Tesanovic etal., producing reasonable values of kappa
but larger values of dHc2/dT. Universality was studied by obtaining a
simultaneous scaling of Y123 data and Bi2223. An expression for the 2D x-axis
LLL scaling factor used to obtain the simultaneous scaling was extracted from
theory, and compared with the experimental values. The comparison between the
values of the x-axis produced a deviation of 40% which suggests that the
hypothesis of universality of the 2D-LLL fluctuations is not supported by the
studied samples. We finaly observe that Y123 magnetization data for
temperatures above obbey a universal scaling obtained for the diamagnetic
fluctuation magnetization from a theory considering non-local field effects.
The same scaling was not obbeyed by the corresponding magnetization calculated
from the two-dimensional lowest-Landau-level theory.Comment: 7 pages 5 figures, accept in Journ. Low Temp. Phy
Dynamical Vacuum in Quantum Cosmology
By regarding the vacuum as a perfect fluid with equation of state p=-rho, de
Sitter's cosmological model is quantized. Our treatment differs from previous
ones in that it endows the vacuum with dynamical degrees of freedom. Instead of
being postulated from the start, the cosmological constant arises from the
degrees of freedom of the vacuum regarded as a dynamical entity, and a time
variable can be naturally introduced. Taking the scale factor as the sole
degree of freedom of the gravitational field, stationary and wave-packet
solutions to the Wheeler-DeWitt equation are found. It turns out that states of
the Universe with a definite value of the cosmological constant do not exist.
For the wave packets investigated, quantum effects are noticeable only for
small values of the scale factor, a classical regime being attained at
asymptotically large times.Comment: Latex, 19 pages, to appear in Gen. Rel. Gra
Understanding traditional and modern eating: The TEP10 framework
Across the world, there has been a movement from traditional to modern eating, including a movement of traditional eating patterns from their origin culture to new cultures, and the emergence of new foods and eating behaviors. This trend toward modern eating is of particular significance because traditional eating has been related to positive health outcomes and sustainability. Yet, there is no consensus on what constitutes traditional and modern eating. The present study provides a comprehensive compilation of the various facets that seem to make up traditional and modern eating. Specifically, 106 facets were mentioned in the previous literature and expert discussions, combining international and interdisciplinary perspectives. The present study provides a framework (the TEP10 framework) systematizing these 106 facets into two major dimensions, what and how people eat, and 12 subdimensions. Hence, focusing only on single facets of traditional and modern eating is an oversimplification of this complex phenomenon. Instead, the multidimensionality and interplay between different facets should be considered to gain a comprehensive understanding of the trends, consequences, and underlying factors of traditional and modern eating
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