2,702 research outputs found
The magnetic environment of the Orion-Eridanus superbubble as revealed by Planck
Using the 353-GHz polarization observations by the Planck satellite we
characterize the magnetic field in the Orion-Eridanus superbubble, a nearby
expanding structure that spans more than 1600 square degrees in the sky. We
identify a region of both low dispersion of polarization orientations and high
polarization fraction associated with the outer wall of the superbubble
identified in the most recent models of the large-scale shape of the region. We
use the Davis-Chandrasekhar-Fermi method to derive plane-of-the-sky magnetic
field strengths of tens of microGauss toward the southern edge of the bubble.
The comparison of these values with existing Zeeman splitting observations of
HI in emission suggests that the large-scale magnetic field in the region was
primarily shaped by the expanding superbubble.Comment: 7 pages, 8 figures. Accepted for publication as a Letter in A&A,
section 1. Letters to the Editor (08/12/2017
vertex from QCD sum rules
The form factors and the coupling constant of the vertex are
calculated using the QCD sum rules method. Three point correlation functions
are computed considering both and mesons off-shell and, after an
extrapolation of the QCDSR results, we obtain the coupling constant of the
vertex. We study the uncertainties in our result by calculating a third form
factor obtained when the is the off-shell meson, considering other
acceptable structures and computing the variations of the sum rules'
parameters. The form factors obtained have different behaviors but their
simultaneous extrapolations reach to the same value of the coupling constant
. We compare our result with other theoretical
estimates.Comment: 11 pages, 11 figure
Boundary layer separation in the surface quasi-geostrophic equations
Uniform potential vorticity flows are investigated. The evolution of surface potential temperature is studied in a two-dimensional oceanic model driven by a surface heating. The surface temperature plays the role of the vorticity, but the different relationship between the streamfunction and the advected scalar implies the formation of unidirectional free waves. Important distinctive features with respect to the standard homogeneous models are pointed out
Analysis of the vertex with the light-cone QCD sum rules
In this article, we analyze the vertex with the light-cone QCD
sum rules. The strong coupling constant is an important
parameter in evaluating the charmonium absorption cross sections in searching
for the quark-gluon plasmas. Our numerical value for the is
consistent with the prediction of the effective SU(4) symmetry and vector meson
dominance theory.Comment: 6 pages, 1 figure, revised versio
Coupling constants of and processes
We calculate the coupling constants of and vertices using
the QCD sum rules technique. We compare results obtained in the limit of SU(4)
symmetry and found that the symmetry is broken on the order of 40%.Comment: 4 pages, 3 ps figures. Talk presented in the 18 Workshop on Hadron
Interactions, IFUSP, Sao Paulo, Brazil, may 22-24 of 200
A QCD sum rules calculation of the strong coupling constant
In this work, we calculate the form factors and the coupling constant of the
strange-charmed vertex in the framework of the QCD sum rules
by studying their three-point correlation functions. All the possible off-shell
cases are considered, , and , resulting in three different
form factors. These form factors are extrapolated to the pole of their
respective off-shell mesons, giving the same coupling constant for the process.
Our final result for the coupling constant is .Comment: 17 pages, 4 figure
and vertices in a QCD Sum Rule approach
We calculate the strong form factors and coupling constants of
and vertices using the QCD sum rules technique. In each case we
have considered two different cases for the off-shell particle in the vertex:
the ligthest meson and one of the heavy mesons. The method gives the same
coupling constant for each vertex. When the results for different vertices are
compared, they show that the SU(4) symmetry is broken by around 40%.Comment: 10 pages, 8 figures. Submitted to Phys. Lett.
Gamma decay of pygmy states from inelastic scattering of ions
An overview of relevant results on the study of 1− states focusing on their excitation with nuclear probes is given. Results obtained for the 90Zr , 124Sn , and 208Pb nuclei using the (17O,17O′γ) reaction are compared with available data obtained with the (γ, γ′, and (p, p′) reactions. These comparisons allow to learn on the nature of the populated states, particularly the E1 states, whose isospin character is presently poorly known. The DWBA description of the data is discussed in terms of different form factors, standard collective form factor and form factors obtained by folding microscopically calculated transition densities. The relevant aspects related to the used theoretical approach are also presented. The main objective of the analyses is the extraction of the values of the fraction of the energy weighted sum rule strength for the isoscalar dipole excitation. For completeness, in all cases, the DWBA analysis was made also for the excitations of 2+ and 3− states
Herschel-ATLAS: statistical properties of Galactic cirrus in the GAMA-9 Hour Science Demonstration Phase Field
We study the spectral energy distribution (SED) and the power spectrum of Galactic cirrus emission observed in the 14 deg^2 Science Demonstration Phase field of the Herschel-ATLAS using Herschel and IRAS data from 100 to 500 μm. We compare the Spectral and Photometric Imaging Receiver (SPIRE) 250, 350 and 500 μm maps with IRAS 100-μm emission, binned in 6-arcmin pixels. We assume a modified blackbody SED with dust emissivity parameter β (F∝λ^(−β)) and a single dust temperature T_d, and find that the dust temperature and emissivity index varies over the science demonstration field as 10 < T_d < 25K and 1 < β < 4. The latter values are somewhat higher than the range of β often quoted in the literature (1 < β < 2). We estimate the mean values of these parameters to be T_d= 19.0 ± 2.4 K and β= 1.4 ± 0.4. In regions of bright cirrus emission, we find that the dust has similar temperatures with T_d = 18.0 ± 2.5 K, and similar values of β, ranging from 1.4 ± 0.5 to 1.9 ± 0.5. We show that T_d and β associated with diffuse cirrus emission are anti-correlated and can be described by the relationship: β(T_d) =NT^α_d with [N= 116 ± 38, α=−1.4 ± 0.1]. The strong correlation found in this analysis is not just limited to high-density clumps of cirrus emission as seen in previous studies, but is also seen in diffuse cirrus in low-density regions. To provide an independent measure of T_d and β, we obtain the angular power spectrum of the cirrus emission in the IRAS and SPIRE maps, which is consistent with a power spectrum of the form P(k) =P_0(k/k_0)^γ, where γ= 2.6 ± 0.2 for scales of 50–200 arcmin in the SPIRE maps. The cirrus rms fluctuation amplitude at angular scales of 100 arcmin is consistent with a modified blackbody SED with T_d 20.1 ± 0.9 K and β= 1.3 ± 0.2, in agreement with the values obtained above
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