20,034 research outputs found
Cristina Valdes: Pianist, in recital
Program listing performers and works performe
Composition of Near-Earth Asteroid (4179) Toutatis
Surface composition of near-Earth asteroid (4179) Toutatis is consistent with
an undifferentiated L-chondrite composition. This is inconsistent with early
observations that suggested high pyroxene iron content and a differentiated
body.Comment: 15 pages, 2 figures 1 table. Accepted for publication in Icaru
Phase Angle Effects on 3-micron Absorption Band on Ceres: Implications for Dawn Mission
Phase angle-induced spectral effects are important to characterize since they
affect spectral band parameters such as band depth and band center, and
therefore skew mineralogical interpretations of planetary bodies via
reflectance spectroscopy. Dwarf planet (1) Ceres is the next target of NASA's
Dawn mission, which is expected to arrive in March 2015. The visible and
near-infrared mapping spectrometer (VIR) onboard Dawn has the spatial and
spectral range to characterize the surface between 0.25-5.0 microns. Ceres has
an absorption feature at 3.0 microns due to hydroxyl- and/or water-bearing
minerals (e.g. Lebofsky et al. 1981, Rivkin et al. 2003). We analyzed phase
angle-induced spectral effects on the 3-micron absorption band on Ceres using
spectra measured with the long-wavelength cross-dispersed (LXD: 1.9-4.2
microns) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope
Facility (IRTF). Ceres LXD spectra were measured at different phase angles
ranging from 0.7o to 22o. We found that the band center slightly increases from
3.06 microns at lower phase angles (0.7o and 6o) to 3.07 microns at higher
phase angles (11 o and 22o), the band depth decreases by ~20% from lower phase
angles to higher phase angles, and the band area decreases by ~25% from lower
phase angles to higher phase angles. Our results will have implications for
constraining the abundance of OH on the surface of Ceres from VIR spectral
data, which will be acquired by Dawn starting spring 2015.Comment: 12 pages, 1 figure, 2 table
Adaptive Optics Imaging of IRAS 18276-1431: a bipolar pre-planetary nebula with circumstellar "searchlight beams" and "arcs"
We present high-angular resolution images of the post-AGB nebula
IRAS18276-1431 (also known as OH17.7-2.0) obtained with the Keck II Adaptive
Optics (AO) system in its Natural Guide Star (NGS) mode in the Kp, Lp, and Ms
near-infrared bands. We also present supporting optical F606W and F814W HST
images as well as interferometric observations of the 12CO(J=1-0), 13CO(J=1-0),
and 2.6mm continuum emission with OVRO. The envelope of IRAS18276-1431 displays
a clear bipolar morphology in our optical and NIR images with two lobes
separated by a dark waist and surrounded by a faint 4.5"x3.4" halo. Our Kp-band
image reveals two pairs of radial ``searchlight beams'' emerging from the
nebula center and several intersecting, arc-like features. From our CO data we
derive a mass of M>0.38[D/3kpc]^2 Msun and an expansion velocity v_exp=17km/s
for the molecular envelope. The density in the halo follows a radial power-law
proportional to r^-3, which is consistent with a mass-loss rate increasing with
time. Analysis of the NIR colors indicates the presence of a compact central
source of ~300-500K dust illuminating the nebula in addition to the central
star. Modeling of the thermal IR suggests a two-shell structure in the dust
envelope: 1) an outer shell with inner and outer radius R_in~1.6E16cm and
R_out>~1.25E17cm, dust temperature T_d~105-50K, and a mean mass-loss rate of
Mdot~1E-3Msun/yr; and 2) an inner shell with R_in~6.3E14cm, T_dust~500-105K,
and Mdot~3E-5Msun/yr. An additional population of big dust grains (radius
a>~0.4mm) with T_dust=150-20K and mass M_dust=(0.16-1.6)E-3 [D/3kpc]^2 Msun can
account for the observed sub-mm and mm flux excess. The mass of the envelope
enclosed within R_out=1.25E17cm derived from SED modeling is ~1[D/3kpc]^2 Msun.Comment: 46 pages, 14 figures, 3 tables, accepted for publication in ApJ.
Figures 12 & 13 in low resolution. Full resolution versions are available
upon request to the first autho
Teaching formulaic sequences in an English-language class: The effects of explicit instruction versus coursebook instruction
This study investigates the relative effectiveness of different teaching approaches
on the learning of formulaic sequences. Three comparisons were made in this
study: the effects of explicit teaching of formulaic sequences versus teaching embedded
in traditional coursebook instruction, the effects of the degree of salience
of the sequences in the coursebook on learning, and the effects of explicit teaching
of formulaic sequences with context versus teaching without context. Sixtynine
formulaic sequences occurring in an English as a Foreign Language (EFL)
coursebook were selected for the study. The participants were 60 low-proficiency
university students majoring in technology in Vietnam. Participants were quasirandomly
assigned to one of three groups: control, no-context learning, and
sentence-context learning. Learning was measured by two multiple-choice tests
of receptive knowledge of form and meaning. Findings indicated that although
explicit instruction was effective, the degree of salience in traditional coursebook
instruction had no significant effects on learning formulaic sequences. Explicit
teaching combined with incidental exposure to formulaic sequences in the
coursebook was superior to the traditional coursebook instruction approach in the
classroom setting. Furthermore, the results from explicit instruction with context
sentences did not differ significantly from those of instruction without context.
Explanations for the findings and pedagogical applications are offered
Proposal to study transitions
It is proposed to clear some of the puzzles of B decay to the broad
states by studying the corresponding decay with strange
states at LHCb. Interpretation of the results
should be easier due to the narrowness of the state.Comment: 21 page
Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta
The detection of olivine on Vesta is interesting because it may provide
critical insights into planetary differentiation early in our Solar System's
history. Ground-based and Hubble Space Telescope (HST) observations of asteroid
(4) Vesta have suggested the presence of olivine on the surface. These
observations were reinforced by the discovery of olivine-rich HED meteorites
from Vesta in recent years. However, analysis of data from NASA's Dawn
spacecraft has shown that this olivine-bearing unit is actually impact melt in
the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed
during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole,
further complicated this picture. Ammannito et al., (2013a) reported the
discovery of local scale olivine-rich units in the form of excavated material
from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. Here
we explore alternative sources for the olivine in the northern hemisphere of
Vesta by reanalyzing the data from the VIR instrument using laboratory spectral
measurements of meteorites. We suggest that these olivine exposures could be
explained by the delivery of olivine-rich exogenic material. Based on our
spectral band parameters analysis, the lack of correlation between the location
of these olivine-rich terrains and possible mantle-excavating events, and
supported by observations of HED meteorites, we propose that a probable source
for olivine seen in the northern hemisphere are remnants of impactors made of
olivine-rich meteorites. Best match suggests these units are HED material mixed
with either ordinary chondrites, or with some olivine-dominated meteorites such
as R-chondrites.Comment: 62 pages, 12 figures, 4 tables; Icarus, Available online 30 January
2015, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2015.01.01
Nitrate metabolism in tobacco leaves overexpressing Arabidopsis nitrite reductase
AbstractPrimary nitrogen assimilation in plants includes the reduction of nitrite to ammonium in the chloroplasts by the enzyme nitrite reductase (NiR EC:1.7.7.1) or in the plastids of non-photosynthetic organs. Here we report on a study overexpressing the Arabidopsis thaliana NiR (AtNiR) gene in tobacco plants under the control of a constitutive promoter (CERV â Carnation Etched Ring Virus). The aim was to overexpress AtNiR in an attempt to alter the level of residual nitrite in the leaf which can act as precursor to the formation of nitrosamines. The impact of increasing the activity of AtNiR produced an increase in leaf protein and a stay-green phenotype in the primary transformed AtNiR population. Investigation of the T1 homozygous population demonstrated elevated nitrate reductase (NR) activity, reductions in leaf nitrite and nitrate and the amino acids proline, glutamine and glutamate. Chlorophyl content of the transgenic lines was increased, as evidenced by the stay-green phenotype. This reveals the importance of NiR in primary nitrogen assimilation and how modification of this key enzyme affects both the nitrogen and carbon metabolism of tobacco plants
- âŠ