48,435 research outputs found
Meson decay in a corrected model
Extensively applied to both light and heavy meson decay and standing as one
of the most successful strong decay models is the model, in which
pair production is the dominant mechanism. The pair production can
be obtained from the non-relativistic limit of a microscopic interaction
Hamiltonian involving Dirac quark fields. The evaluation of the decay amplitude
can be performed by a diagrammatic technique for drawing quark lines. In this
paper we use an alternative approach which consists in a mapping technique, the
Fock-Tani formalism, in order to obtain an effective Hamiltonian starting from
same microscopic interaction. An additional effect is manifest in this
formalism associated to the extended nature of mesons: bound-state corrections.
A corrected is obtained and applied, as an example, to
and decays.Comment: 3 figures. To appear in Physical Review
Properties of dust in the detached shells around U Ant, DR Ser, and V644 Sco
Understanding the properties of dust produced during the asymptotic giant
branch phase of stellar evolution is important for understanding the evolution
of stars and galaxies. Recent observations of the carbon AGB star R Scl have
shown that observations at far-infrared and submillimetre wavelengths can
effectively constrain the grain sizes in the shell, while the total mass
depends on the structure of the grains (solid vs. hollow or fluffy). We aim to
constrain the properties of the dust observed in the submillimetre in the
detached shells around the three carbon AGB stars U Ant, DR Ser, and V644 Sco,
and to investigate the constraints on the dust masses and grain sizes provided
by far-infrared and submm observations. We observed the carbon AGB stars U Ant,
DR Ser, and V644 Sco at 870 micron using LABOCA on APEX. Combined with
observations from the optical to far-infrared, we produced dust radiative
transfer models of the spectral energy distributions (SEDs) with contributions
from the stars, present-day mass-loss and detached shells. We tested the effect
of different total dust masses and grain sizes on the SED, and attempted to
consistently reproduce the SEDs from the optical to the submm. We derive dust
masses in the shells of a few 10e-5 Msun, assuming spherical, solid grains. The
best-fit grain radii are comparatively large, and indicate the presence of
grains between 0.1 micron-2 micron. The LABOCA observations suffer from
contamination from 12CO(3-2), and hence gives fluxes that are higher than the
predicted dust emission at submm wavelengths. We investigate the effect on the
best-fitting models by assuming different degrees of contamination and show
that far-infrared and submillimetre observations are important to constrain the
dust mass and grain sizes in the shells.Comment: Accepted by A&
A nonextensive insight to the stellar initial mass function
the present paper, we propose that the stellar initial mass distributions as
known as IMF are best fitted by -Weibulls that emerge within nonextensive
statistical mechanics. As a result, we show that the Salpeter's slope of
2.35 is replaced when a -Weibull distribution is used. Our results
point out that the nonextensive entropic index represents a new approach
for understanding the process of the star-forming and evolution of massive
stars.Comment: 5 pages, 2 figures, Accepted to EP
Avaliação de acesso, uso e manejo de água para consumo humano no Semiárido brasileiro.
Esse estudo avaliou a sustentabilidade do Programa Cisternas, quanto à sua implementação no semiárido nordestino, nas seguintes dimensões: a) cobertura do programa, b) localização, c) percepção quanto aos efeitos do programa sobre as condições de vida dos beneficiários; e d) condições e capacidade de manutenção das cisternas construídas. As informações sobre a avaliação são resultantes de entrevistas realizadas junto a 1.866 famílias beneficiárias. A condição de propriedade do domicílio, localização, acabamento, tipo de cobertura, tipo e forma de escoamento do banheiro, trabalho e indicadores de rendimento, permitiram afirmar que a população beneficiária do Programa Cisternas detém o perfil das famílias carentes da região. Outros resultados são: 98,76 % das famílias consideraram a cisterna muito importante e que houve melhoria na qualidade de vida (92,71 %), apesar de não ter influenciado sua renda (49,95 %). No entanto, poucos domicílios (± 21%), utilizam apenas a cisterna como forma de abastecimento para uso doméstico. Os demais utilizam, também, águas provenientes de outras fontes como açudes, barragens ou lagoas (30,92 %) e cacimba/ nascente (12,81 %). Quanto ao treinamento recebido para o uso e manejo correto das cisternas, 89,82 % dos entrevistados o consideraram adequado
- …