57,373 research outputs found
The class of n-entire operators
We introduce a classification of simple, regular, closed symmetric operators
with deficiency indices (1,1) according to a geometric criterion that extends
the classical notions of entire operators and entire operators in the
generalized sense due to M. G. Krein. We show that these classes of operators
have several distinctive properties, some of them related to the spectra of
their canonical selfadjoint extensions. In particular, we provide necessary and
sufficient conditions on the spectra of two canonical selfadjoint extensions of
an operator for it to belong to one of our classes. Our discussion is based on
some recent results in the theory of de Branges spaces.Comment: 33 pages. Typos corrected. Changes in the wording of Section 2.
References added. Examples added. arXiv admin note: text overlap with
arXiv:1104.476
Binary open clusters in the Milky Way: photometric and spectroscopic analysis of NGC 5617 and Trumpler 22
Using photometry and high resolution spectroscopy we investigate for the
first time the physical connection between the open clusters NGC 5617 and
Trumpler 22. Based on new CCD photometry we report their spatial proximity and
common age of ~70 Myr. Based on high resolution spectra collected using the
HERMES and UCLES spectrographs on the Anglo-Australian telescope, we present
radial velocities and abundances for Fe, Na, Mg, Al, Si, Ca and Ni. The
measured radial velocities are -38.63 +/-2.25 km/s for NGC 5617 and -38.46
+/-2.08 km/s for Trumpler 22. The mean metallicity of NGC 5617 was found to be
[Fe/H] =-0.18 +/-0.02 and for Trumpler 22 was found to be [Fe/H] = -0.17
+/-0.04. The two clusters share similar abundances across the other elements,
indicative of a common chemical enrichment history of these clusters. Together
with common motions and ages we confirm that NGC 5617 and Trumpler 22 are a
primordial binary cluster pair in the Milky Way.Comment: 7 pages, 3 figure, accepted by MNRA
Aquicultura: manejo e aproveitamento de efluentes.
Resumo: O trabalho aborda inicialmente o panorama atual da aquicultura mundial, enfatizando o crescimento da produção da ordem de 3,2% no período de 1961-2009, e da brasileira, na qual houve um incremento de 40% nas atividades aquícolas continentais durante os anos 2008-2010. No entanto, esta evolução numérica nem sempre foi acompanhada de práticas de manejo sustentáveis dos efluentes gerados, o que compromete a qualidade da água. Com o propósito de orientar na gestão sustentável da água utilizada nas atividades aquícolas, bem como dos resíduos gerados, são apresentados métodos de tratamento da água usada na produção, notadamente os naturais, como os biofiltros e aplicação de efluentes no solo (fertirrigação). A aquaponia ? integração da aquicultura com a hidroponia -, também é sugerida como prática possível para o uso mais eficiente da água na produção aquícola.bitstream/item/93537/1/Doc95.pd
Interplay between disorder, quantum and thermal fluctuations in ferromagnetic alloys: The case of UCu2Si(2-x)Ge(x)
We consider, theoretically and experimentally, the effects of structural
disorder, quantum and thermal fluctuations in the magnetic and transport
properties of certain ferromagnetic alloys.We study the particular case of
UCu2Si(2-x)Ge(x). The low temperature resistivity, rho(T,x), exhibits Fermi
liquid (FL) behavior as a function of temperature T for all values of x, which
can be interpreted as a result of the magnetic scattering of the conduction
electrons from the localized U spins. The residual resistivity, rho(0,x),
follows the behavior of a disordered binary alloy. The observed non-monotonic
dependence of the Curie temperature, Tc(x), with x can be explained within a
model of localized spins interacting with an electronic bath whose transport
properties cross-over from ballistic to diffusive regimes. Our results clearly
show that the Curie temperature of certain alloys can be enhanced due to the
interplay between quantum and thermal fluctuations with disorder.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Accelerating universe emergent from the landscape
We propose that the existence of the string landscape suggests the universe
can be in a quantum glass state, where an extremely large viscosity is
generated, and long distance dynamics slows down. At the same time, the short
distance dynamics is not altered due to the separation of time scales. This
scenario can help to understand some controversies in cosmology, for example
the natural existence of slow roll inflation and dark energy in the landscape,
the apparent smallness of the cosmological constant. We see also that moduli
stabilization is no longer necessary. We further identify the glass transition
point, where the viscosity diverges, as the location of the cosmic horizon. We
try to reconstruct the geometry of the accelerating universe from the structure
of the landscape, and find that the metric should have an infinite jump when
crossing the horizon. We predict that the static coordinate metric for dS space
breaks down outside the horizon.Comment: 20 pages, no figures, harvma
Efeito do óleo essencial de citronela sobre a mortalidade e oviposição do caruncho do feijão-caupi.
Resumo 0626
Horava-Lifshitz modifications of the Casimir effect
We study the modifications induced by spacetime anisotropy on the Casimir
effect in the case of two parallel plates. Nonperturbative and perturbative
regimes are analyzed. In the first case the Casimir force either vanishes or it
reverses its direction which, in any case, makes the proposal untenable. On the
other hand, the perturbative model enables us to incorporate appropriately the
effects of spacetime anisotropy.Comment: 6 pages, revtex
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