9,556 research outputs found
Resposta da aceroleira aos nutrientes nitrogênio, fósforo e potássio em latossolo amarelo do município de Castanhal-PA.
Does Quantum Cosmology Predict a Constant Dilatonic Field?
Quantum cosmology may permit to determine the initial conditions of the
Universe. In particular, it may select a specific model between many possible
classical models. In this work, we study a quantum cosmological model based on
the string effective action coupled to matter. The Schutz's formalism is
employed in the description of the fluid. A radiation fluid is considered. In
this way, a time coordinate may be identified and the Wheeler-DeWitt equation
reduces in the minisuperspace to a Schr\"odinger-like equation. It is shown
that, under some quite natural assumptions, the expectation values indicate a
null axionic field and a constant dilatonic field. At the same time the scale
factor exhibits a bounce revealing a singularity-free cosmological model. In
some cases, the mininum value of the scale factor can be related to the value
of gravitational coupling.Comment: Latex file, 14 page
Knowledge Acquisition by Networks of Interacting Agents in the Presence of Observation Errors
In this work we investigate knowledge acquisition as performed by multiple
agents interacting as they infer, under the presence of observation errors,
respective models of a complex system. We focus the specific case in which, at
each time step, each agent takes into account its current observation as well
as the average of the models of its neighbors. The agents are connected by a
network of interaction of Erd\H{o}s-Renyi or Barabasi-Albert type. First we
investigate situations in which one of the agents has a different probability
of observation error (higher or lower). It is shown that the influence of this
special agent over the quality of the models inferred by the rest of the
network can be substantial, varying linearly with the respective degree of the
agent with different estimation error. In case the degree of this agent is
taken as a respective fitness parameter, the effect of the different estimation
error is even more pronounced, becoming superlinear. To complement our
analysis, we provide the analytical solution of the overall behavior of the
system. We also investigate the knowledge acquisition dynamic when the agents
are grouped into communities. We verify that the inclusion of edges between
agents (within a community) having higher probability of observation error
promotes the loss of quality in the estimation of the agents in the other
communities.Comment: 10 pages, 7 figures. A working manuscrip
Singlet-triplet dispersion reveals additional frustration in the triangular dimer compound BaMnO
We present single crystal inelastic neutron scattering measurements of the
S=1 dimerized quasi-two-dimensional antiferromagnet BaMnO. The
singlet-triplet dispersion reveals nearest-neighbor and next-nearest-neighbor
ferromagnetic interactions between adjacent bilayers that compete against each
other. Although the inter-bilayer exchange is comparable to the intra-bilayer
exchange, this additional frustration reduces the effective coupling along the
c-axis and leads to a quasi-two dimensional behavior. In addition, the obtained
exchange values are able to reproduce the four critical fields in the phase
diagram.Comment: 4 pages, 3 color figures, submitted to an APS physical review journa
Regge Analysis of Diffractive and Leading Baryon Structure Functions from DIS
In this paper we present a combined analysis of the H1 data on leading baryon
and diffractive structure functions from DIS, which are handled as two
components of the same semi-inclusive process. The available structure function
data are analyzed in a series of fits in which three main exchanges are taking
into account: pomeron, reggeon and pion. For each of these contributions, Regge
factorization of the correspondent structure function is assumed. By this
procedure, we extract information about the interface between the diffractive,
pomeron-dominated, region and the leading proton spectrum, which is mostly
ruled by secondary exchanges. One of the main results is that the relative
reggeon contribution to the semi-inclusive structure function is much smaller
than the one obtained from a analysis of the diffractive structure function
alone.Comment: ps file, 22 pages, 5 figures. Totally revised version with major
changes, to appear in Physical Review
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