7,986 research outputs found
Cosmic-Ray Heating of Molecular Gas in the Nuclear Disk: Low Star Formation Efficiency
Understanding the processes occurring in the nuclear disk of our Galaxy is
interesting in its own right, as part of the Milky Way Galaxy, but also because
it is the closest galactic nucleus. It has been more than two decades since it
was recognized that the general phenomenon of higher gas temperature in the
inner few hundred parsecs by comparison with local clouds in the disk of the
Galaxy. This is one of the least understood characteristics of giant molecular
clouds having a much higher gas temperature than dust temperature in the inner
few degrees of the Galactic center. We propose that an enhanced flux of
cosmic-ray electrons, as evidenced recently by a number of studies, are
responsible for directly heating the gas clouds in the nuclear disk, elevating
the temperature of molecular gas ( 75K) above the dust temperature
( 20K). In addition we report the detection of nonthermal radio emission
from Sgr B2-F based on low-frequency GMRT and VLA observations. The higher
ionization fraction and thermal energy due to the impact of nonthermal
electrons in star forming sites have important implications in slowing down
star formation in the nuclear disk of our galaxy and nuclei of galaxies.Comment: 12 pages, one figure, ApJL (in press
On Vague Computers
Vagueness is something everyone is familiar with. In fact, most people think
that vagueness is closely related to language and exists only there. However,
vagueness is a property of the physical world. Quantum computers harness
superposition and entanglement to perform their computational tasks. Both
superposition and entanglement are vague processes. Thus quantum computers,
which process exact data without "exploiting" vagueness, are actually vague
computers
The Dirac point electron in zero-gravity Kerr--Newman spacetime
Dirac's wave equation for a point electron in the topologically nontrivial
maximal analytically extended electromagnetic Kerr--Newman spacetime is studied
in a zero-gravity limit; here, "zero-gravity" means , where is
Newton's constant of universal gravitation. The following results are obtained:
the formal Dirac Hamiltonian on the static spacelike slices is essentially
self-adjoint; the spectrum of the self-adjoint extension is symmetric about
zero, featuring a continuum with a gap about zero that, under two smallness
conditions, contains a point spectrum. Some of our results extend to a
generalization of the zero- Kerr--Newman spacetime with different
electric-monopole-to-magnetic-dipole-moment ratio.Comment: 49 pages, 17 figures; referee's comments implemented; the endnotes in
the published version appear as footnotes in this preprin
Pigment Melanin: Pattern for Iris Recognition
Recognition of iris based on Visible Light (VL) imaging is a difficult
problem because of the light reflection from the cornea. Nonetheless, pigment
melanin provides a rich feature source in VL, unavailable in Near-Infrared
(NIR) imaging. This is due to biological spectroscopy of eumelanin, a chemical
not stimulated in NIR. In this case, a plausible solution to observe such
patterns may be provided by an adaptive procedure using a variational technique
on the image histogram. To describe the patterns, a shape analysis method is
used to derive feature-code for each subject. An important question is how much
the melanin patterns, extracted from VL, are independent of iris texture in
NIR. With this question in mind, the present investigation proposes fusion of
features extracted from NIR and VL to boost the recognition performance. We
have collected our own database (UTIRIS) consisting of both NIR and VL images
of 158 eyes of 79 individuals. This investigation demonstrates that the
proposed algorithm is highly sensitive to the patterns of cromophores and
improves the iris recognition rate.Comment: To be Published on Special Issue on Biometrics, IEEE Transaction on
Instruments and Measurements, Volume 59, Issue number 4, April 201
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