5,434 research outputs found
Absorção via foliar de aminoácidos em mudas de videira cv. Thompson seedless em cultivo hidropônico.
Este trabalho teve por objetivo quantificar o teor de N proveniente dos aminoácidos, absorvidos via foliar, em mudas de videira da cultivar Thompson Seedless
Deep shower interpretation of the cosmic ray events observed in excess of the Greisen-Zatsepin-Kuzmin energy
We consider the possibility that the ultra-high-energy cosmic ray flux has a
small component of exotic particles which create showers much deeper in the
atmosphere than ordinary hadronic primaries. It is shown that applying the
conventional AGASA/HiRes/Auger data analysis procedures to such exotic events
results in large systematic biases in the energy spectrum measurement. SubGZK
exotic showers may be mis-reconstructed with much higher energies and mimick
superGZK events. Alternatively, superGZK exotic showers may elude detection by
conventional fluorescence analysis techniques.Comment: 22 pages, 5 figure
Neutrino Telescopes' Sensitivity to Dark Matter
The nature of the dark matter of the Universe is yet unknown and most likely
is connected with new physics. The search for its composition is under way
through direct and indirect detection. Fundamental physical aspects such as
energy threshold, geometry and location are taken into account to investigate
proposed neutrino telescopes of km^3 volume sensitivities to dark matter. These
sensitivities are just sufficient to test a few WIMP scenarios. Telescopes of
km^3 volume, such as IceCube, can definitely discover or exclude superheavy (M
> 10^10 GeV) Strong Interacting Massive Particles (Simpzillas). Smaller
neutrino telescopes such as ANTARES, AMANDA-II and NESTOR can probe a large
region of the Simpzilla parameter space.Comment: 28 pages, 9 figure
Fluctuating Dimension in a Discrete Model for Quantum Gravity Based on the Spectral Principle
The spectral principle of Connes and Chamseddine is used as a starting point
to define a discrete model for Euclidean quantum gravity. Instead of summing
over ordinary geometries, we consider the sum over generalized geometries where
topology, metric and dimension can fluctuate. The model describes the geometry
of spaces with a countable number of points, and is related to the Gaussian
unitary ensemble of Hermitian matrices. We show that this simple model has two
phases. The expectation value . Moreover, the
space-time dimension is a dynamical observable in our model, and plays
the role of an order parameter. The computation of is discussed and
an upper bound is found, .Comment: 10 pages, no figures. Third version: This new version emphasizes the
spectral principle rather than the spectral action. Title has been changed
accordingly. We also reformulated the computation of the dimension, and added
a new reference. To appear in Physical Review Letter
Identification and selection rules of the spin-wave eigen-modes in a normally magnetized nano-pillar
We report on a spectroscopic study of the spin-wave eigen-modes inside an
individual normally magnetized two layers circular nano-pillar
(PermalloyCopperPermalloy) by means of a Magnetic Resonance Force
Microscope (MRFM). We demonstrate that the observed spin-wave spectrum
critically depends on the method of excitation. While the spatially uniform
radio-frequency (RF) magnetic field excites only the axially symmetric modes
having azimuthal index , the RF current flowing through the
nano-pillar, creating a circular RF Oersted field, excites only the modes
having azimuthal index . Breaking the axial symmetry of the
nano-pillar, either by tilting the bias magnetic field or by making the pillar
shape elliptical, mixes different -index symmetries, which can be excited
simultaneously by the RF current. Experimental spectra are compared to
theoretical prediction using both analytical and numerical calculations. An
analysis of the influence of the static and dynamic dipolar coupling between
the nano-pillar magnetic layers on the mode spectrum is performed
Towards Spinfoam Cosmology
We compute the transition amplitude between coherent quantum-states of
geometry peaked on homogeneous isotropic metrics. We use the holomorphic
representations of loop quantum gravity and the
Kaminski-Kisielowski-Lewandowski generalization of the new vertex, and work at
first order in the vertex expansion, second order in the graph (multipole)
expansion, and first order in 1/volume. We show that the resulting amplitude is
in the kernel of a differential operator whose classical limit is the canonical
hamiltonian of a Friedmann-Robertson-Walker cosmology. This result is an
indication that the dynamics of loop quantum gravity defined by the new vertex
yields the Friedmann equation in the appropriate limit.Comment: 8 page
Atributos químicos de um Cambissolo háplico influenciados pela aplicação de resíduo de reciclagem de papel no solo.
Nesse sentido, o objetivo desse trabalho foi avaliar o efeito de resíduo de reciclagem de papel, aplicado em diferentes doses em Cambissolo Háplico com pH muito baixo, sobre alguns atributos químicos do solo. O resíduo de reciclagem de papel corrigiu a acidez do solo, bem como aumentou os teores de cálcio e fósforo, todavia reduziu os teores de manganês e incrementou os teores de sódio, em um Cambissolo Háplico muito ácido
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