28,428 research outputs found
Modelling a Particle Detector in Field Theory
Particle detector models allow to give an operational definition to the
particle content of a given quantum state of a field theory. The commonly
adopted Unruh-DeWitt type of detector is known to undergo temporary transitions
to excited states even when at rest and in the Minkowski vacuum. We argue that
real detectors do not feature this property, as the configuration "detector in
its ground state + vacuum of the field" is generally a stable bound state of
the underlying fundamental theory (e.g. the ground state-hydrogen atom in a
suitable QED with electrons and protons) in the non-accelerated case. As a
concrete example, we study a local relativistic field theory where a stable
particle can capture a light quantum and form a quasi-stable state. As
expected, to such a stable particle correspond energy eigenstates of the full
theory, as is shown explicitly by using a dressed particle formalism at first
order in perturbation theory. We derive an effective model of detector (at
rest) where the stable particle and the quasi-stable configurations correspond
to the two internal levels, "ground" and "excited", of the detector.Comment: 13 pages, references added, final versio
Efeito de micorrizas arbusculares sobre o crescimento e nutriĆ§Ć£o mineral de Brachiaria brizantha c.v Marandu.
O efeito da inoculaĆ§Ć£o de micorrizas arbusculares (MA) sobre o crescimento ...., foi avaliado sob condiƧƵes de casa-de-vegetaĆ§Ć£o. Foram avaliados oito espĆ©cies de MA: Glomus mossaea, G. fasciculatum, G. etunicatum, G. macrocarpum, Gigaspora margarita, Scutellospora heterogama, Acaulospora laevis e A. muricata.bitstream/item/67179/1/FOL-5289-5879id-.pd
Redshift-Distance Survey of Early-Type Galaxies. IV. Dipoles of the Velocity Field
We use the recently completed redshift-distance survey of nearby early-type
galaxies (ENEAR) to measure the dipole component of the peculiar velocity field
to a depth of cz ~ 6000 km/s. The sample consists of 1145 galaxies brighter
than m_B=14.5 and cz < 7000 km/s, uniformly distributed over the whole sky, and
129 fainter cluster galaxies within the same volume. Most of the Dn-sigma
distances were obtained from new spectroscopic and photometric observations
conducted by this project, ensuring the homogeneity of the data over the whole
sky. These 1274 galaxies are objectively assigned to 696 objects -- 282
groups/clusters and 414 isolated galaxies. We find that within a volume of
radius ~ 6000 km/s, the best-fitting bulk flow has an amplitude of |vbulk| =220
+/- 42 km/s in the CMB restframe, pointing towards l=304 +/- 16 degrees, b=25
+/- 11 degrees. The error in the amplitude includes statistical, sampling and
possible systematic errors. This solution is in excellent agreement with that
obtained by the SFI Tully-Fisher survey. Our results suggest that most of the
motion of the Local Group is due to fluctuations within 6000 km/s, in contrast
to recent claims of large amplitude bulk motions on larger scales.Comment: 11 pages, 2 figures, ApJL, accepted (updated results; matches
accepted version
Efeito de micorrizas arbusculares e adubaĆ§Ć£o com fosfato de rocha em Sesbania sesban.
No presente trabalho avaliou-se os efeitos da inoculaĆ§Ć£o de MA e da aplicaĆ§Ć£o de fosfato de rocha sobre o rendimento de forragem e composiĆ§Ć£o quĆmica de Sesbania sesban.bitstream/item/60899/1/COT-194-micorrizasarburscular....pd
InoculaĆ§Ć£o de micorrizas arbusculares em Sesbania sesban.
Este trabalho teve como objetivo avaliar o efeito da inoculaĆ§Ć£o de micorrizas arbusculares sobre a produĆ§Ć£o de biomassa e composiĆ§Ć£o quĆmica de Sesbania sesban
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