7,179 research outputs found
The Matrix Element Method and QCD Radiation
The matrix element method (MEM) has been extensively used for the analysis of
top-quark and W-boson physics at the Tevatron, but in general without dedicated
treatment of initial state QCD radiation. At the LHC, the increased center of
mass energy leads to a significant increase in the amount of QCD radiation,
which makes it mandatory to carefully account for its effects. We here present
several methods for inclusion of QCD radiation effects in the MEM, and apply
them to mass determination in the presence of multiple invisible particles in
the final state. We demonstrate significantly improved results compared to the
standard treatment.Comment: 15 pp; v2: references and some clarifications added; v3: discussion
of NLO effects, version published in PR
Dono, donos ou posseiros? A difícil tarefa de identificar a propriedade de recursos genéticos.
Nos últimos anos, após a Convenção da Diversidade Biológica, em 1992 e, principalmente após a entrada em vigor da medida provisória de 2001 (BRASIL, 1992), que criou o Conselho do Patrimônio Genético e toda uma legislação de acesso a recursos genéticos; conhecimento tradicional associado e; repartição de benefícios, cabe apresentar neste momento dois exemplos concretos da dificuldade de se legislar em temas como propriedade de recursos genéticos. Os exemplos apresentados são frutos de depoimentos informais de dois caciques do Parque Indígena do Xingu, comentando sobre algumas espécies/ variedades de plantas cultivadas que manejam em suas aldeias, relatados a seguir.bitstream/CENARGEN/28445/1/cot163.pd
Gravitational Model of High Energy Particles in a Collimated Jet
Observations suggest that relativistic particles play a fundamental role in
the dynamics of jets emerging from active galactic nuclei as well as in their
interaction with the intracluster medium. However, no general consensus exists
concerning the acceleration mechanism of those high energy particles. A
gravitational acceleration mechanism is here proposed, in which particles
leaving precise regions within the ergosphere of a rotating supermassive black
hole produce a highly collimated flow. These particles follow unbound geodesics
which are asymptotically parallel to the spin axis of the black hole and are
characterized by the energy , the Carter constant and zero
angular momentum of the component . If environmental effects are
neglected, the present model predicts at distances of about 140 kpc from the
ergosphere the presence of electrons with energies around 9.4 GeV. The present
mechanism can also accelerate protons up to the highest energies observed in
cosmic rays by the present experiments.Comment: 27 pages and 5 figures. Accepted for publication in Astrophysical
Journal. arXiv admin note: text overlap with arXiv:1011.654
Imagery and long-slit spectroscopy of the Polar-Ring Galaxy AM2020-504
Interactions between galaxies are very common. There are special kinds of
interactions that produce systems called Polar Ring Galaxies (PRGs), composed
by a lenticular, elliptical, or spiral host galaxy, surrounded by a ring of
stars and gas, orbiting in an approximately polar plane. The present work aims
to study AM2020-504, a PRG with an elliptical host galaxy, and a narrow and
well defined ring, probably formed by accretion of material from a donor
galaxy, collected by the host galaxy. Our observational study was based on BVRI
broad band imagery as well as longslit spectroscopy in the wavelenght range
4100--8600\AA, performed at the 1.6m telescope at the Observat\'orio do Pico
dos Dias (OPD), Brazil. We estimated a redshift of z= 0.01683, corresponding a
heliocentric radial velocity of 5045 +/-23 km/s. The (B-R) color map shows that
the ring is bluer than the host galaxy, indicating that the ring is a younger
structure. Standard diagnostic diagrams were used to classify the main ionizing
source of selected emission-line regions (nucleus, host galaxy and ring). It
turns out that the ring regions are mainly ionized by massive stars while the
nucleus presents AGN characteristics. Using two empirical methods, we found
oxygen abundances for the HII regions located in the ring in the range
12+log(O/H)=8.3-8.8 dex, the presence of an oxygen gradient across the ring,
and that AM2020-504 follows the metallicity-luminosity relation of spiral
galaxies. These results support the accretion scenario for this object and
rules out cold accretion as source for the HI gas in the polar ring
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