3,541 research outputs found
Qualidade de sementes forrageiras de clima temperado.
Atual contexto do setor produtivo; Prejuízos decorrentes da baixa qualidade de sementes; Atributos da qualidade de sementes forrageiras.bitstream/item/61500/1/DT-119.pd
Particle Creation by a Moving Boundary with Robin Boundary Condition
We consider a massless scalar field in 1+1 dimensions satisfying a Robin
boundary condition (BC) at a non-relativistic moving boundary. We derive a
Bogoliubov transformation between input and output bosonic field operators,
which allows us to calculate the spectral distribution of created particles.
The cases of Dirichlet and Neumann BC may be obtained from our result as
limiting cases. These two limits yield the same spectrum, which turns out to be
an upper bound for the spectra derived for Robin BC. We show that the particle
emission effect can be considerably reduced (with respect to the
Dirichlet/Neumann case) by selecting a particular value for the oscillation
frequency of the boundary position
Dynamical Casimir effect with cylindrical waveguides
I consider the quantum electromagnetic field in a coaxial cylindrical
waveguide, such that the outer cylindrical surface has a time-dependent radius.
The field propagates parallel to the axis, inside the annular region between
the two cylindrical surfaces. When the mechanical frequency and the thickness
of the annular region are small enough, only Transverse Electromagnetic (TEM)
photons may be generated by the dynamical Casimir effect. The photon emission
rate is calculated in this regime, and compared with the case of parallel
plates in the limit of very short distances between the two cylindrical
surfaces. The proximity force approximation holds for the transition matrix
elements in this limit, but the emission rate scales quadratically with the
mechanical frequency, as opposed to the cubic dependence for parallel plates.Comment: 6 page
The Seyfert Population in the Local Universe
The magnitude-limited catalog of the Southern Sky Redshift Survey (SSRS2), is
used to characterize the properties of galaxies hosting Active Galactic Nuclei.
Using emission-line ratios, we identify a total of 162 (3%) Seyfert galaxies
out of the parent sample with 5399 galaxies. The sample contains 121 Seyfert 2
galaxies and 41 Seyfert 1. The SSRS2 Seyfert galaxies are predominantly in
spirals of types Sb and earlier, or in galaxies with perturbed appearance as
the result of strong interactions or mergers. Seyfert galaxies in this sample
are twice as common in barred hosts than the non-Seyferts. By assigning
galaxies to groups using a percolation algorithm we find that the Seyfert
galaxies in the SSRS2 are more likely to be found in binary systems, when
compared to galaxies in the SSRS2 parent sample. However, there is no
statistically significant difference between the Seyfert and SSRS2 parent
sample when systems with more than 2 galaxies are considered. The analysis of
the present sample suggests that there is a stronger correlation between the
presence of the AGN phenomenon with internal properties of galaxies
(morphology, presence of bar, luminosity) than with environmental effects
(local galaxy density, group velocity dispersion, nearest neighbor distance).Comment: 35 pages, 13 figures, Accepted to be publised in Astronomical Journa
Quantum radiation in a plane cavity with moving mirrors
We consider the electromagnetic vacuum field inside a perfect plane cavity
with moving mirrors, in the nonrelativistic approximation. We show that low
frequency photons are generated in pairs that satisfy simple properties
associated to the plane geometry. We calculate the photon generation rates for
each polarization as functions of the mechanical frequency by two independent
methods: on one hand from the analysis of the boundary conditions for moving
mirrors and with the aid of Green functions; and on the other hand by an
effective Hamiltonian approach. The angular and frequency spectra are discrete,
and emission rates for each allowed angular direction are obtained. We discuss
the dependence of the generation rates on the cavity length and show that the
effect is enhanced for short cavity lengths. We also compute the dissipative
force on the moving mirrors and show that it is related to the total radiated
energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review
Higher-Order Topological Insulators
Three-dimensional topological (crystalline) insulators are materials with an
insulating bulk, but conducting surface states which are topologically
protected by time-reversal (or spatial) symmetries. Here, we extend the notion
of three-dimensional topological insulators to systems that host no gapless
surface states, but exhibit topologically protected gapless hinge states. Their
topological character is protected by spatio-temporal symmetries, of which we
present two cases: (1) Chiral higher-order topological insulators protected by
the combination of time-reversal and a four-fold rotation symmetry. Their hinge
states are chiral modes and the bulk topology is -classified. (2)
Helical higher-order topological insulators protected by time-reversal and
mirror symmetries. Their hinge states come in Kramers pairs and the bulk
topology is -classified. We provide the topological invariants for
both cases. Furthermore we show that SnTe as well as surface-modified
BiTeI, BiSe, and BiTe are helical higher-order topological insulators and
propose a realistic experimental setup to detect the hinge states.Comment: 8 pages (4 figures) and 16 pages supplemental material (7 figures
Efeito do cultivo antecessor e do método de plantio no estabelecimento de um sementeiro de leguminosas forrageiras.
SIEPE. Online
Avaliação da lama de cal como material corretivo de solo.
O trabalho avaliou a lama de cal gerada pela Iguaçu Celulose, Papel, S.A., em Piraí do Sul, Paraná, como corretivo de solo e verificar se o material atende às exigências para ser considerado como tal. Para tanto, foram conduzidos ensaios para se avaliar o efeito desse subproduto na acidez do solo comparado ao carbonato de cálcio
Dynamical Casimir effect with Dirichlet and Neumann boundary conditions
We derive the radiation pressure force on a non-relativistic moving plate in
1+1 dimensions. We assume that a massless scalar field satisfies either
Dirichlet or Neumann boundary conditions (BC) at the instantaneous position of
the plate. We show that when the state of the field is invariant under time
translations, the results derived for Dirichlet and Neumann BC are equal. We
discuss the force for a thermal field state as an example for this case. On the
other hand, a coherent state introduces a phase reference, and the two types of
BC lead to different results.Comment: 12 page
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