3,085 research outputs found
The Electron Temperature Gradient in the Galactic Disk
We derive the electron temperature gradient in the Galactic disk using a
sample of HII regions that spans Galactocentric distances 0--17 kpc. The
electron temperature was calculated using high precision radio recombination
line and continuum observations for more than 100 HII regions. Nebular
Galactocentric distances were calculated in a consistent manner using the
radial velocities measured by our radio recombination line survey. The large
number of nebulae widely distributed over the Galactic disk together with the
uniformity of our data provide a secure estimate of the present electron
temperature gradient in the Milky Way. Because metals are the main coolants in
the photoionized gas, the electron temperature along the Galactic disk should
be directly related to the distribution of heavy elements in the Milky Way. Our
best estimate of the electron temperature gradient is derived from a sample of
76 sources for which we have the highest quality data. The present gradient in
electron temperature has a minimum at the Galactic Center and rises at a rate
of 287 +/- 46 K/kpc. There are no significant variations in the value of the
gradient as a function of Galactocentric radius or azimuth. The scatter we find
in the HII region electron temperatures at a given Galactocentric radius is not
due to observational error, but rather to intrinsic fluctuations in these
temperatures which are almost certainly due to fluctuations in the nebular
heavy element abundances. Comparing the HII region gradient with the much
steeper gradient found for planetary nebulae suggests that the electron
temperature gradient evolves with time, becoming flatter as a consequence of
the chemical evolution of the Milky Way's disk.Comment: 43 pages, 9 figures (accepted for publication in the ApJ
Carrier relaxation in GaAs v-groove quantum wires and the effects of localization
Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove
quantum wires (QWRs) with a large subband separation (46 meV). Signatures of
inhibited carrier relaxation mechanisms are seen in temperature-dependent
photoluminescence (PL) and photoluminescence-excitation (PLE) measurements; we
observe strong emission from the first excited state of the QWR below ~50 K.
This is attributed to reduced inter-subband relaxation via phonon scattering
between localized states. Theoretical calculations and experimental results
indicate that the pinch-off regions, which provide additional two-dimensional
confinement for the QWR structure, have a blocking effect on relaxation
mechanisms for certain structures within the v-groove. Time-resolved PL
measurements show that efficient carrier relaxation from excited QWR states
into the ground state, occurs only at temperatures > 30 K. Values for the low
temperature radiative lifetimes of the ground- and first excited-state excitons
have been obtained (340 ps and 160 ps respectively), and their corresponding
localization lengths along the wire estimated.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B Attempted to correct
corrupt figure
Mutations Of Androgen Receptor Gene In Brazilian Patients With Male Pseudohermaphroditism.
We describe the identification of point mutations in the androgen receptor gene in five Brazilian patients with female assignment and behavior. The eight exons of the gene were amplified by the polymerase chain reaction (PCR) and analyzed for single-strand conformation polymorphism (SSCP) to detect the mutations. Direct sequencing of the mutant PCR products demonstrated single transitions in three of these cases: G-->A in case 1, within exon C, changing codon 615 from Arg to His; G-->A in case 2, within exon E, changing codon 752 from Arg to Gln, and C-->T in case 3, within exon B, but without amino acid change.31775-
Virulência de isolados de Magnaporthe oryzae do trigo e poáceas invasoras.
Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel
Efeito das auxinas 2,4-D e TDZ na indução da embriogênese somática em Uncaria tomentosa a partir de ápice caulinar.
O objetivo desse trabalho foi avaliar o efeito das auxinas 2,4-D e TDZ na indução da embriogênese somática utilizando ápice caulinar de U. tomentosa
Virulência de isolados de Magnaporthe oryzae do trigo e poáceas invasoras.
Orientador: João Leodato Nunes Maciel
Embriogênese somática em Uncaria tomentosa a partir de folhas imaturas.
O objetivo desse trabalho foi induzir a embriogênese somática a partir de folhas imaturas de U. tomentosa de plântulas germinadas in vitro
Sulfur, Chlorine, & Argon Abundances in Planetary Nebulae. I: Observations and Abundances in a Northern Sample
This paper is the first of a series specifically studying the abundances of
sulfur, chlorine, and argon in Type II planetary nebulae (PNe) in the Galactic
disk. Ratios of S/O, Cl/O, and Ar/O constitute important tests of differential
nucleosynthesis of these elements and serve as strict constraints on massive
star yield predictions. We present new ground-based optical spectra extending
from 3600-9600 Angstroms for a sample of 19 Type II northern PNe. This range
includes the strong near infrared lines of [S III] 9069,9532, which allows us
to test extensively their effectiveness as sulfur abundance indicators. We also
introduce a new, model-tested ionization correction factor for sulfur. For the
present sample, we find average values of S/O=1.2E-2(+/- 0.71E-2),
Cl/O=3.3E-4(+/- 1.6E-4), and Ar/O=5.0E-3(+/- 1.9E-3).Comment: 44 pages, 6 figures. Accepted for publication in the Astrophysical
Journa
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