24,622 research outputs found
The young massive stellar cluster associated to RCW121
We report NIR broad and narrow band photometric observations in the direction
of the IRAS17149-3916 source that reveal the presence of a young cluster of
massive stars embedded in an HII region coincident with RCW121. These
observations, together with published radio data, MSX and Spitzer images were
used to determine some of the physical parameters of the region. We found 96
cluster member candidates in an area of about 1.5 x 2.0 square arcmin, 30% of
them showing excess emission in the NIR. IRS 1, the strongest source in the
cluster with an estimated spectral type of O5V-O6V ZAMS based on the
color-magnitude diagram, is probably the main ionizing source of the HII region
detected at radio wavelengths. Using the integrated Brgamma and the 5 GHz flux
densities, we derived a mean visual extinction AV=5.49 magnitudes. From the
observed size of the Brgamma extended emission, we calculated the emission
measure E and the electron density ne, characteristic of compact HII regions.Comment: 18 pages, 8 figures, accepted for publication on AJ (February/2006
Fractal analysis of weld defect patterns obtained by radiographic tests
This paper presents a fractal analysis of radiographic patterns obtained from
specimens with three types of inserted welding defects: lack of fusion, lack of
penetration, and porosity. The study focused on patterns of carbon steel beads
from radiographs of the International Institute of Welding (IIW). The
radiographs were scanned using a greyscale with 256 levels, and the fractal
features of the surfaces constructed from the radiographic images were
characterized by means of Hurst, detrended-fluctuation, and minimal-cover
analyses. A Karhunen-Loeve transformation was then used to classify the curves
obtained from the fractal analyses of the various images, and a study of the
classification errors was performed. The obtained results indicate that fractal
analyses can be an effective additional tool for pattern recognition of weld
defects in radiographic tests.Comment: 7 pages, 2 figures. To appear AIP Conference Proceedings - QNDE 200
Potencial de radão em setores da Zona de Ossa Morena
O radão é considerado a maior fonte de exposição a radiação ionizante dentro de habitações, motivo pelo qual é essencial conhecer a sua distribuição espacial. Este trabalho tem como objetivo o estudo do potencial de radão de rochas aflorantes na Zona de Ossa Morena (ZOM). Para tal, foram colhidas 132 amostras nos principais setores da ZOM. Os resultados obtidos demonstram a enorme variabilidade das propriedades radiológicas e físicas nas litologias analisadas. As atividades de 226Ra e de radão são, em média, inferiores nas rochas calco-silicatadas e rochas ígneas básicas e ultrabásicas e superiores nas rochas graníticas e sienitos. Os metassedimentos, rochas de alto grau metamórfico, granodioritos, dioritos e tonalitos apresentam atividades de 226Ra e de radão intermédias e similares entre si. A porosidade, que determina a capacidade de migração de radão no meio, é superior nos metassedimentos e inferior nas rochas ígneas, independentemente do seu caráter
Vanishing Viscosity Limits and Boundary Layers for Circularly Symmetric 2D Flows
We continue the work of Lopes Filho, Mazzucato and Nussenzveig Lopes [LMN],
on the vanishing viscosity limit of circularly symmetric viscous flow in a disk
with rotating boundary, shown there to converge to the inviscid limit in
-norm as long as the prescribed angular velocity of the
boundary has bounded total variation. Here we establish convergence in stronger
and -Sobolev spaces, allow for more singular angular velocities
, and address the issue of analyzing the behavior of the boundary
layer. This includes an analysis of concentration of vorticity in the vanishing
viscosity limit. We also consider such flows on an annulus, whose two boundary
components rotate independently.
[LMN] Lopes Filho, M. C., Mazzucato, A. L. and Nussenzveig Lopes, H. J.,
Vanishing viscosity limit for incompressible flow inside a rotating circle,
preprint 2006
Development of liquid xenon detectors for medical imaging
In the present paper, we report on our developments of liquid xenon detectors
for medical imaging, positron emission tomography and single photon imaging, in
particular. The results of the studies of several photon detectors
(photomultiplier tubes and large area avalanche photodiode) suitable for
detection of xenon scintillation are also briefly described.Comment: 13 pages, 5 figures, presented on the International Workshop on
Techniques and Applications of Xenon Detectors (Xenon01), ICRR, Univ. of
Tokyo, Kashiwa, Japan, December 3-4, 2001 (submitted to proceedings
On the Solution of the Number-Projected Hartree-Fock-Bogoliubov Equations
The numerical solution of the recently formulated number-projected
Hartree-Fock-Bogoliubov equations is studied in an exactly soluble
cranked-deformed shell model Hamiltonian. It is found that the solution of
these number-projected equations involve similar numerical effort as that of
bare HFB. We consider that this is a significant progress in the mean-field
studies of the quantum many-body systems. The results of the projected
calculations are shown to be in almost complete agreement with the exact
solutions of the model Hamiltonian. The phase transition obtained in the HFB
theory as a function of the rotational frequency is shown to be smeared out
with the projection.Comment: RevTeX, 11 pages, 3 figures. To be published in a special edition of
Physics of Atomic Nuclei (former Sov. J. Nucl. Phys.) dedicated to the 90th
birthday of A.B. Migda
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