12,355 research outputs found
Associação da seringueira com a cultura do cafĂ©, no municĂpio de Ouro Preto D'Oeste em RondĂŽnia.
bitstream/item/56619/1/PA-1540-0001.pd
Experimental investigation of quantum key distribution with position and momentum of photon pairs
We investigate the utility of Einstein-Podolsky-Rosen correlations of the
position and momentum of photon pairs from parametric down-conversion in the
implementation of a secure quantum key distribution protocol. We show that
security is guaranteed by the entanglement between downconverted pairs, and can
be checked by either direct comparison of Alice and Bob's measurement results
or evaluation of an inequality of the sort proposed by Mancini et al. (Phys.
Rev. Lett. 88, 120401 (2002)).Comment: 6 pages, 6 figures, subimitted for publicatio
Quantum key distribution with higher-order alphabets using spatially-encoded qudits
We propose and demonstrate a quantum key distribution scheme in higher-order
-dimensional alphabets using spatial degrees of freedom of photons. Our
implementation allows for the transmission of 4.56 bits per sifted photon,
while providing improved security: an intercept-resend attack on all photons
would induce an error rate of 0.47. Using our system, it should be possible to
send more than a byte of information per sifted photon.Comment: 4 pages, 5 figures. Replaced with published versio
Differential Density Statistics of Galaxy Distribution and the Luminosity Function
This paper uses data obtained from the galaxy luminosity function (LF) to
calculate two types of radial number densities statistics of the galaxy
distribution as discussed in Ribeiro (2005), namely the differential density
and the integral differential density . By applying the
theory advanced by Ribeiro and Stoeger (2003), which connects the relativistic
cosmology number counts with the astronomically derived LF, the differential
number counts are extracted from the LF and used to calculate both
and with various cosmological distance definitions,
namely the area distance, luminosity distance, galaxy area distance and
redshift distance. LF data are taken from the CNOC2 galaxy redshift survey and
and are calculated for two cosmological models:
Einstein-de Sitter and an , standard
cosmology. The results confirm the strong dependency of both statistics on the
distance definition, as predicted in Ribeiro (2005), as well as showing that
plots of and against the luminosity and redshift
distances indicate that the CNOC2 galaxy distribution follows a power law
pattern for redshifts higher than 0.1. These findings bring support to
Ribeiro's (2005) theoretical proposition that using different cosmological
distance measures in statistical analyses of galaxy surveys can lead to
significant ambiguity in drawing conclusions about the behavior of the observed
large scale distribution of galaxies.Comment: LaTeX, 37 pages, 6 tables, 10 figures. Accepted for publication in
"The Astrophysical Journal
Small Deviations from Gaussianity and The Galaxy Cluster Abundance Evolution
We raise the hypothesis that the density fluctuations field which originates
the growth of large scale structures is a combination of two or more
distributions. By applying the statistical analysis of finite mixture
distributions to a specific combination of Gaussian plus non-Gaussian random
fields, we studied the case where just a small departure from Gaussianity is
allowed. Our results suggest that even a very small level of non-Gaussianity
may introduce significant changes in the cluster abundance evolution rate.Comment: 10 pages with 2 figures, accepted for publication in Ap
The Apparent Fractal Conjecture: Scaling Features in Standard Cosmologies
This paper presents an analysis of the smoothness problem in cosmology by
focussing on the ambiguities originated in the simplifying hypotheses aimed at
observationally verifying if the large-scale distribution of galaxies is
homogeneous, and conjecturing that this distribution should follow a fractal
pattern in perturbed standard cosmologies. This is due to a geometrical effect,
appearing when certain types of average densities are calculated along the past
light cone. The paper starts reviewing the argument concerning the possibility
that the galaxy distribution follows such a scaling pattern, and the premises
behind the assumption that the spatial homogeneity of standard cosmology can be
observable. Next, it is argued that to discuss observable homogeneity one needs
to make a clear distinction between local and average relativistic densities,
and showing how the different distance definitions strongly affect them,
leading the various average densities to display asymptotically opposite
behaviours. Then the paper revisits Ribeiro's (1995: astro-ph/9910145) results,
showing that in a fully relativistic treatment some observational average
densities of the flat Friedmann model are not well defined at z ~ 0.1, implying
that at this range average densities behave in a fundamentally different manner
as compared to the linearity of the Hubble law, well valid for z < 1. This
conclusion brings into question the widespread assumption that relativistic
corrections can always be neglected at low z. It is also shown how some key
features of fractal cosmologies can be found in the Friedmann models. In view
of those findings, it is suggested that the so-called contradiction between the
cosmological principle, and the galaxy distribution forming an unlimited
fractal structure, may not exist.Comment: 30 pages, 2 figures, LaTeX. This paper is a follow-up to
gr-qc/9909093. Accepted for publication in "General Relativity and
Gravitation
Entropy and holography constraints for inhomogeneous universes
We calculated the entropy of a class of inhomogeneous dust universes.
Allowing spherical symmetry, we proposed a holographic principle by reflecting
all physical freedoms on the surface of the apparent horizon. In contrast to
flat homogeneous counterparts, the principle may break down in some models,
though these models are not quite realistic. We refined fractal parabolic
solutions to have a reasonable entropy value for the present observable
universe and found that the holographic principle always holds in the realistic
cases.Comment: 4 pages, revtex style, 3 figures in 8 eps-file
Growth and phosphorus absorption by common bean 'XodĂł' genotype under effect of glyphosate reduced rates.
Avaliou-se o efeito de subdoses de glyphosate no crescimento e na absorção de fĂłsforo (P) pelo feijoeiro comum (Phaseolus vulgaris L.) cv. XodĂł. O experimento foi conduzido em esquema fatorial 4 x 2 em blocos casualizados com quatro repetiçÔes, sendo o primeiro fator constituĂdo pelas subdoses de 0; 4,32; 8,64 e 12,96 g ha-1 de equivalente ĂĄcido (e.a.) de glyphosate e o segundo fator constituĂdo por doses de P no solo (50 e 250 mg dm-3). AvaliaçÔes foram realizadas 30 dias apĂłs a aplicação do glyphosate (DAA). A subdose de 12,96 g ha-1 estimulou o crescimento do feijoeiro comum cv. XodĂł, assim como aumentou o teor de P no ramo e o conteĂșdo de P na parte aĂ©rea das plantas
Frustration and sound attenuation in structural glasses
Three classes of harmonic disorder systems (Lennard-Jones like glasses,
percolators above threshold, and spring disordered lattices) have been
numerically investigated in order to clarify the effect of different types of
disorder on the mechanism of high frequency sound attenuation. We introduce the
concept of frustration in structural glasses as a measure of the internal
stress, and find a strong correlation between the degree of frustration and the
exponent alpha that characterizes the momentum dependence of the sound
attenuation . In particular, alpha decreases from
about d+1 in low-frustration systems (where d is the spectral dimension), to
about 2 for high frustration systems like the realistic glasses examined.Comment: Revtex, 4 pages including 4 figure
Noncommutative fields in three dimensions and mass generation
We apply the noncommutative fields method for gauge theory in three
dimensions where the Chern-Simons term is generated in the three-dimensional
electrodynamics. Under the same procedure, the Chern-Simons term is shown to be
cancelled in the Maxwell-Chern-Simons theory for the appropriate value of the
noncommutativity parameter. Hence the mutual interchange between
Maxwell-Chern-Simons theory and pure Maxwell theory turns out to be generated
within this method.Comment: Comments 5 pages, epl, version accepted for publication in
Europhysics Letter
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