13,542 research outputs found
Embrapa Desenvolve novas ferramentas e gera perspectivas para o controle do Greening na citricultura brasileira.
bitstream/item/88151/1/2260001.pd
Embrapa Desenvolve novas ferramentas e gera perspectivas para o controle do Greening.
bitstream/item/88167/1/2320001.pd
On the thermal and double episode emissions in GRB 970828
Following the recent theoretical interpretation of GRB 090618 and GRB 101023,
we here interpret GRB 970828 in terms of a double episode emission: the first
episode, observed in the first 40 s of the emission, is interpreted as the
proto-black-hole emission; the second episode, observed after t+50 s, as a
canonical gamma ray burst. The transition between the two episodes marks the
black hole formation. The characteristics of the real GRB, in the second
episode, are an energy of erg, a
baryon load of and a bulk Lorentz factor at transparency
of . The clear analogy with GRB 090618 would require also in
GRB 970828 the presence of a possible supernova. We also infer that the GRB
exploded in an environment with a large average particle density part/cm and dense clouds characterized by typical dimensions
of cm and . Such an environment
is in line with the observed large column density absorption, which might have
darkened both the supernova emission and the GRB optical afterglow.Comment: 7 pages, 10 figures, submitted to Ap
Reconstrução 3D, visualização e cálculo de volume de frutas.
bitstream/CNPDIA-2009-09/11044/1/DOC31_2007.pd
Effects of quark family nonuniversality in SU(3)_c X SU(4)_L X U(1)_x models
Flavour changing neutral currents arise in the extension of the standard model because anomaly cancellation among the
fermion families requires one generation of quarks to transform differently
from the other two under the gauge group. In the weak basis the distinction
between quark families is meaningless. However, in the mass eigenstates basis,
the Cabibbo-Kobayashi-Maskawa mixing matrix motivates us to classify
left-handed quarks in families. In this sense there are, in principle, three
different assignments of quark weak eigenstates into mass eigenstates. In this
work, by using measurements at the Z-pole, atomic parity violation data and
experimental input from neutral meson mixing, we examine two different models
without exotic electric charges based on the 3-4-1 symmetry, and address the
effects of quark family nonuniversality on the bounds on the mixing angle
between two of the neutral currents present in the models and on the mass
scales and of the new neutral gauge bosons predicted by the
theory. The heaviest family of quarks must transform differently in order to
keep lower bounds on and as low as possible without
violating experimental constraints.Comment: 27 pages, 10 tables, 2 figures. Equation (19) and typos corrected.
Matches version to appear in Phys. Rev.
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