1,489 research outputs found
Resolving the electron temperature discrepancies in HII Regions and Planetary Nebulae: kappa-distributed electrons
The measurement of electron temperatures and metallicities in H ii regions
and Planetary Nebulae (PNe) has-for several decades-presented a problem:
results obtained using different techniques disagree. What it worse, they
disagree consistently. There have been numerous attempts to explain these
discrepancies, but none has provided a satisfactory solution to the problem. In
this paper, we explore the possibility that electrons in H ii regions and PNe
depart from a Maxwell-Boltzmann equilibrium energy distribution. We adopt a
"kappa-distribution" for the electron energies. Such distributions are widely
found in Solar System plasmas, where they can be directly measured. This simple
assumption is able to explain the temperature and metallicity discrepancies in
H ii regions and PNe arising from the different measurement techniques. We find
that the energy distribution does not need to depart dramatically from an
equilibrium distribution. From an examination of data from Hii regions and PNe
it appears that kappa ~ 10 is sufficient to encompass nearly all objects. We
argue that the kappa-distribution offers an important new insight into the
physics of gaseous nebulae, both in the Milky Way and elsewhere, and one that
promises significantly more accurate estimates of temperature and metallicity
in these regions.Comment: 16 pages, 11 figures, 2 tables, published in Ap
Handedness, Health and Cognitive Development: Evidence from Children in the NLSY
Using data from the US National Longitudinal Survey of Youth, and fitting family fixed-effects models of child health and cognitive development, we test if left-handed children do significantly worse than their right-handed counterparts. The health measures cover both physical and mental health, and the cognitive development test scores span (1) Memory, (2) Vocabulary, (3) Mathematics, (4) Reading and (5) Comprehension. We find that while left-handed children have a significantly higher probability of suffering an injury needing medical attention, there is no difference in their experience of illness or poor mental health. We also find that left-handed children have significantly lower cognitive development test scores than right-handed children for all areas of development with the exception of reading. Moreover, the left-handedness disadvantage is larger for boys than girls, and remains roughly constant as children grow older for most outcomes. We also find that the probability of a child being left-handed is not related to the socioeconomic characteristics of the family, such as income or maternal education. All these results tend to support a difference in brain functioning or neurological explanation for handedness differentials rather than one based on left-handed children living in a right-handed world.handedness, children, health, cognitive development, family fixed-effects
Metal-poor dwarf galaxies in the SIGRID galaxy sample. I. HII region observations and chemical abundances
In this paper we present the results of observations of seventeen HII regions
in thirteen galaxies from the SIGRID sample of isolated gas rich irregular
dwarf galaxies. The spectra of all but one of the galaxies exhibit the auroral
[OIII] 4363A line, from which we calculate the electron temperature, Te, and
gas-phase oxygen abundance. Five of the objects are blue compact dwarf (BCD)
galaxies, of which four have not previously been analysed spectroscopically. We
include one unusual galaxy which exhibits no evidence of the [NII]
{\lambda}{\lambda} 6548,6584A lines, suggesting a particularly low metallicity
(< Zsolar/30). We compare the electron temperature based abundances with those
derived using eight of the new strong line diagnostics presented by Dopita et
al. (2013). Using a method derived from first principles for calculating total
oxygen abundance, we show that the discrepancy between the Te-based and strong
line gas-phase abundances have now been reduced to within ~0.07 dex. The
chemical abundances are consistent with what is expected from the
luminosity-metallicity relation. We derive estimates of the electron densities
and find them to be between ~5 and ~100 cm-3. We find no evidence for a
nitrogen plateau for objects in this sample with metallicities 0.5 > Zsolar >
0.15.Comment: 46 pages, 15 figures, 6 tables, 1 appendix. Accepted for publication
in the Astrophysical Journa
International Journal of Molecular Science Best Paper Award 2014
International Journal of Molecular Science is instituting an annual award to recognize outstanding papers in the area of chemistry, molecular physics and molecular biology published in International Journal of Molecular Science. We are pleased to announce the third "International Journal of Molecular Science Best Paper Award" for 2014 [1,2]. Nominations were made by the Section Editors-in-Chief of International Journal of Molecular Science from all papers published in 2010
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