2,412 research outputs found
Elementary Teachers’ Ideologies On The Experience Of A Mixed-Race Student
With bi/multi-racial students existing within a nebulous racial categorization that has been historically defined to support an economic agenda, creating a positive self-identity for students in this group can be challenging. This article examined those challenges by exploring the reflections of elementary level teachers’ classroom practices and perceptions of the collective elementary educational experience of one bi-racial student in a southeastern U.S. public school
Synthesis of the Beryllium 3131A Spectral Region
The Beryllium spectral region of the Sun, Procyon and 4 stars in the open
cluster NGC6633 up to Teff = 7500K have been synthesised using ATLAS9 model
atmospheres and the MOOG spectral synthesis program.
The line list used for these syntheses has been modified from the ATLAS9 line
list to improve the quality of the fits in light of the improved opacities in
the new version of the MOOG code.
Significant changes have been made to the Mn I line at ATLAS9 wavelength
3131.037A and an OH line has been added at 3131.358A. In addition there are a
number of minor changes to gf-values throughout the synthesised region thus
improving the fit for the spectra across the temperature range considerably.Comment: 4 pages, 3 figures. To appear in the proceedings of the Workshop
"ATLAS 12 and related codes", Trieste, July 11-15, 200
Transition probabilities in OH A 2 sigma + - X 2 pi i: Bands with v prime = 0 and 1, v double prime = 0 to 4
Experimental results for relative vibrational band transition probabilities for v prime = 0 and 1, and v double prime = 0 to 4 in the A-X electronic system of OH are presented. The measurements, part of a larger set involving v prime = 0 to 4 and v double prime = 0 to 6, were made using spectrally dispersed laser-induced fluorescence (LIF) in the burnt gases of a flame. These Einstein coefficients will be useful in dynamics experiments for quantitative LIF determinations of OH radical concentrations in high v double prime
Lithium abundances from the 6104A line in cool Pleiades stars
Lithium abundances determined by spectral synthesis from both the 6708A
resonance line and the 6104 subordinate line are reported for 11 late-type
Pleiades stars, including spectra previously analysed by Russell (1996). We
report a 0.7 dex scatter in the abundances from 6708A, and a scatter at least
as large from the 6104A line. We find a reasonable correllation between the
6104A and 6708A Li abundances, although four stars have 6104A-determined
abundances which are significantly larger than the 6708-determined values, by
up to 0.5 dex, suggesting problems with the homogeneous, one-dimensional
atmospheres being used. We show that these discrepancies can be explained,
although probably not uniquely, by the presence of star spots with plausible
coverage fractions. The addition of spots does not significantly reduce the
apparent scatter in Li abundances, leaving open the possibility that at least
some of the spread is caused by real star-to-star differences in pre-main-
sequence Li depletion.Comment: 13 pages, 7 figures; Accepted by A&A 17/05/0
Competing Ordered Phases in URu2Si2: Hydrostatic Pressure and Re-substitution
A persistent kink in the pressure dependence of the \hidden order" (HO)
transition temperature of URu2-xRexSi2 is observed at a critical pressure Pc=15
kbar for 0 < x < 0.08. In URu2Si2, the kink at Pc is accompanied by the
destruction of superconductivity; a change in the magnitude of a spin
excitation gap, determined from electrical resistivity measurements; and a
complete gapping of a portion of the Fermi surface (FS), inferred from a change
in scattering and the competition between the HO state and superconductivity
for FS fraction
WIYN/Hydra Detection of Lithium Depletion in F Stars of the Young Open Cluster M35 and Implications for the Development of the Lithium Gap
We report discovery of significant depletion of Li on the surfaces of F dwarf
stars in the 150-Myr-old open cluster M35, analagous to a feature in the
700-Myr-old Hyades cluster that has been referred to as the ``Li gap.'' We have
caught the gap in the act of forming: using high resolution, high S/N,
WIYN/Hydra observations, we detect Li in all but a few M35 F stars; the maximum
depletion lies at least 0.6-0.8 dex below minimally depleted (or undepleted)
stars. The M35 Li depletion region, a) is quite wide, with clear depletion seen
from 6000K to 6700K or hotter; b) shows a significant dispersion in Li
abundance at all T_eff, even with stars of the same T_eff; and c) contains
undepleted stars (as well as depleted ones) in the (narrow) classical Hyades
gap region, which itself shows no undepleted stars. All of these M35 Li
depletion properties support rotationally-induced slow mixing as the primary
physical mechanism that forms the gap, and argues against other proposed
mechanisms, particularly diffusion and steady main sequence mass loss. When
viewed in the context of the M35 Li depletion properties, the Hyades Li gap may
well be wider than is usually recognized.Comment: 14 Pages, 3 figures. Accepted to ApJ Letter
Crustacean Hosts of the Pedunculate Barnacle Genus Octolasmis in the Northern Gulf of Mexico
A survey of live and preserved crustaceans from the northern portion of the Gulf of Mexico was conducted to investigate the colonization habits of the barnacle genus Octolasmis. In all, three crustacean orders (Decapoda, lsopoda, and Stomatopoda) comprising 43 families, 78 genera, and 122 species were surveyed. Octolasmis barnacles were observed to infest 14 families, 20 genera, and 27 species of the orders Decapoda and Isopoda. In order of decreasing frequency, the Octolasmis species encountered were O. lowei, O. forresti, O. hoehi, and O. aymonini geryonophila. The first two were found primarily in the gill chambers, the third was found mainly on external mouthparts, and the last was found exclusively on the external mouthparts, ventral pereonal and pleonal surfaces of the isopod, Bathynomus giganteus. The decapod families Pisidae and Portunidae had the highest rates of infestation, whereas the family Galatheidae (represented by six species) did not host Octolasmis. The order Stomatopoda, represented by two families (Lysiosquillidae and Squillidae), two genera, and seven species was also not infested with Octolasmis. Statistical tests confirm that octolasmids do not randomly occupy hosts, rather they appear to select a subset, generally the larger species of crustaceans
The Li Overabundance of J37: Diffusion or Accretion?
In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633,
an iron poor analogue of the better studied Hyades and Praecepe open clusters,
was announced. This unique star was thought to be the smoking gun for the
action of diffusion, models of which predict a narrow "Li-peak" at
approximately the correct temperature. However, with more detailed studies into
J37s abundance pattern this star provides firm evidence for the accretion of
planetesimals or other material from the circumstellar environment of new born
stars.
Thanks to the specific predictions made about the behaviour of Be abundances,
(the most striking of which being no Be in super-Li-rich dwarfs subject to
diffusion) the opposing diffusion/accretion predictions can be tested.
Initial modelling of the Be line indicates that J37 is as Be rich as it is Li
rich; log N(Be) = 2.25 +/- 0.25, and so is broadly consistent with an
accretion-fuelled enhancement. However, that both Li and Be are enhanced by
much more than the iron-peak elements (as determined in previous studies)
suggests that diffusion also plays a role in increasing the abundances of Li
and Be specifically.
Furthermore, a new data set from the UVES/UT2 combination has allowed the
elemental abundance of Iron to be measured, and the set of preliminary stellar
parameters determined; Teff ~ 7340 K, log g ~ 4.1, microturbulence ~ 4.3 km/s,
[Fe/H] ~ 0.50. This again provides distinct evidence for the effects of
accretion in J37 and requires a new synthesis of the Be doublet.Comment: 5 pages, 2 figures. Poster presented at IAU Symposium 224 "The A Star
Puzzle", 7-13 July 2004, Poprad, Slovaki
Beryllium Enhancement as Evidence for Accretion in a Lithium-Rich F Dwarf
The early F dwarf star ``J37'' in the open cluster NGC6633 shows an unusual
pattern of photospheric abundances, including an order of magnitude enhancement
of lithium and iron-peak elements, but an under-abundance of carbon. As a
consequence of its thin convection zone these anomalies have been attributed to
either radiative diffusion or the accretion of hydrogen-depleted material. By
comparing high resolution VLT/UVES spectra of J37 (and other F stars in NGC
6633) with syntheses of the Be ii doublet region at 3131 Ang, we establish that
J37 also has a Be abundance (A(Be)=3.0+/-0.5) that is at least ten times the
cosmic value. This contradicts radiative diffusion models that produce a Li
over-abundance, as they also predict photospheric Be depletion. Instead, since
Be is a highly refractory element, it supports the notion that J37 is the first
clear example of a star that has accreted volatile-depleted material with a
composition similar to chondritic meteorites, although some diffusion may be
necessary to explain the low C and O abundances.Comment: Accepted for publication in MNRAS letters, 5 page
Antiferromagnetic critical pressure in URu2Si2 under hydrostatic conditions
The onset of antiferromagnetic order in URu2Si2 has been studied via neutron
diffraction in a helium pressure medium, which most closely approximates
hydrostatic conditions. The antiferromagnetic critical pressure is 0.80 GPa,
considerably higher than values previously reported. Complementary electrical
resistivity measurements imply that the hidden order-antiferromagnetic
bicritical point far exceeds 1.02 GPa. Moreover, the redefined
pressure-temperature phase diagram suggests that the superconducting and
antiferromagnetic phase boundaries actually meet at a common critical pressure
at zero temperature.Comment: 5 pgs, 4 figs; AFM ordered moment revised to 0.5 muB, added and
corrected citations and reference
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