457 research outputs found
TEXES Observations of M Supergiants: Dynamics and Thermodynamics of Wind Acceleration
We have detected [Fe II] 17.94 um and 24.52 um emission from a sample of M
supergiants using TEXES on the IRTF. These low opacity emission lines are
resolved at R = 50, 000 and provide new diagnostics of the dynamics and
thermodynamics of the stellar wind acceleration zone. The [Fe II] lines, from
the first excited term, are sensitive to the warm plasma where energy is
deposited into the extended atmosphere to form the chromosphere and wind
outflow. These diagnostics complement previous KAO and ISO observations which
were sensitive to the cooler and more extended circumstellar envelopes. The
turbulent velocities, Vturb is about 12 to 13 km/s, observed in the [Fe II]
forbidden lines are found to be a common property of our sample, and are less
than that derived from the hotter chromospheric C II] 2325 Angstrom lines
observed in alpha Ori, where Vturb is about 17 to 19 km/s. For the first time,
we have dynamically resolved the motions of the dominant cool atmospheric
component discovered in alpha Ori from multi-wavelength radio interferometry by
Lim et al. (1998). Surprisingly, the emission centroids are quite Gaussian and
at rest with respect to the M supergiants. These constraints combined with
model calculations of the infrared emission line fluxes for alpha Ori imply
that the warm material has a low outflow velocity and is located close to the
star. We have also detected narrow [Fe I] 24.04 um emission that confirms that
Fe II is the dominant ionization state in alpha Ori's extended atmosphere.Comment: 79 pages including 10 figures and 2 appendices. Accepted by Ap
Study of Geometric Porosity on Static Stability and Drag Using Computational Fluid Dynamics for Rigid Parachute Shapes
This paper explores use of computational fluid dynamics to study the eect of geometric porosity on static stability and drag for NASA's Multi-Purpose Crew Vehicle main parachute. Both of these aerodynamic characteristics are of interest to in parachute design, and computational methods promise designers the ability to perform detailed parametric studies and other design iterations with a level of control previously unobtainable using ground or flight testing. The approach presented here uses a canopy structural analysis code to define the inflated parachute shapes on which structured computational grids are generated. These grids are used by the computational fluid dynamics code OVERFLOW and are modeled as rigid, impermeable bodies for this analysis. Comparisons to Apollo drop test data is shown as preliminary validation of the technique. Results include several parametric sweeps through design variables in order to better understand the trade between static stability and drag. Finally, designs that maximize static stability with a minimal loss in drag are suggested for further study in subscale ground and flight testing
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HDO And SO2 Thermal Mapping On Venus II. The So2 Spatial Distribution Above And Within The Clouds
Sulfur dioxide and water vapor, two key species of Venus photochemistry, are known to exhibit significant spatial and temporal variations above the cloud top. In particular, ground-based thermal imaging spectroscopy at high spectral resolution, achieved on Venus in January 2012, has shown evidence for strong SO2 variations on timescales shorter than a day. We have continued our observing campaign using the TEXES high-resolution imaging spectrometer at the NASA InfraRed Telescope Facility to map sulfur dioxide over the disk of Venus at two different wavelengths, 7 mu m (already used in the previous study) and 19 mu m. The 7 mu m radiation probes the top of the H2SO4 cloud, while the 19 mu m radiation probes a few kilometers below within the cloud. Observations took place on October 4 and 5, 2012. Both HDO and SO2 lines are identified in our 7-mu m spectra and SO2 is also easily identified at 19 mu m. The CO2 lines at 7 and 19 mu m are used to infer the thermal structure. An isothermal/inversion layer is present at high latitudes (above 60 N and S) in the polar collars, which was not detected in October 2012. The enhancement of the polar collar in October 2012 is probably due to the fact that the morning terminator is observed, while the January data probed the evening terminator. As observed in our previous run, the HDO map is relatively uniform over the disk of Venus, with a mean mixing ratio of about 1 ppm. In contrast, the SO2 maps at 19 mu m show intensity variations by a factor of about 2 over the disk within the cloud, less patchy than observed at the cloud top at 7 mu m. In addition, the SO2 maps seem to indicate significant temporal changes within an hour. There is evidence for a cutoff in the SO2 vertical distribution above the cloud top, also previously observed by SPICAV/SOIR aboard Venus Express and predicted by photochemical models.NASA NNX-08AE38AIRTF AST-0607312, AST-0708074Astronom
Multi-frequency high spectral resolution observations of HCN toward the circumstellar envelope of Y CVn
High spectral resolution observations toward the low mass-loss rate C-rich,
J-type AGB star Y CVn have been carried out at 7.5, 13.1 and 14.0 um with
SOFIA/EXES and IRTF/TEXES. Around 130 HCN and H13CN lines of bands v2, 2v2,
2v2-v2, 3v2-2v2, 3v2-v2, and 4v2-2v2 have been identified involving lower
levels with energies up to ~3900 K. These lines have been complemented with the
pure rotational lines J=1-0 and 3-2 of the vibrational states up to 2v2
acquired with the IRAM 30 m telescope, and with the continuum taken with ISO.
We have analyzed the data with a ro-vibrational diagram and a code which models
the absorption and emission of the circumstellar envelope of an AGB star. The
continuum is produced by the star with a small contribution from dust grains
comprising warm to hot SiC and cold amorphous carbon. The HCN abundance
distribution seems to be anisotropic. The ejected gas is accelerated up to the
terminal velocity (~8 km/s) from the photosphere to ~3R* but there is evidence
of higher velocities (>9-10 km/s) beyond this region. In the vicinity of Y CVn,
the line widths are as high as ~10 km/s, which implies a maximum turbulent
velocity of 6 km/s or the existence of other physical mechanisms probably
related to matter ejection that involve higher gas expansion velocities than
expected. HCN is rotationally and vibrationally out of LTE throughout the whole
envelope. A difference of about 1500 K in the rotational temperature at the
photosphere is needed to explain the observations at 7.5 and 13-14 um. Our
analysis finds a total HCN column density that ranges from ~2.1E+18 to 3.5E+18
cm^{-2}, an abundance with respect to H2 of 3.5E-05 to 1.3E-04, and a 12C/13C
isotopic ratio of ~2.5 throughout the whole envelope.Comment: 24 pages, 11 figures, 3 tables, accepted for publication in A&
Robin sequence: what the multidisciplinary approach can do
Robin sequence (RS) is a commonly encountered triad of micrognathia, glossoptosis, and airway obstruction, with or without a cleft palate. The management of airway obstruction is of paramount importance, and multiple reviews and retrospective series outline the diagnosis and treatment of RS. This article focuses on the multidisciplinary nature of RS and the specialists’ contributions and thought processes regarding the management of the RS child from birth to skeletal maturity. This review demonstrates that the care of these children extends far beyond the acute airway obstruction and that thorough monitoring and appropriate intervention are required to help them achieve optimal outcomes
The Basics of American Government
Newly revised, The Basics of American Government offers a comprehensive overview of the American political system for students taking introductory courses in American national government and combines the best aspects of both a traditional textbook and a reader. The Basics of American Government is a collaborative effort among eight current and one former faculty members in the Department of Political Science & Criminal Justice at the University of North Georgia. Most of its chapters offer a piece of original scholarship as a case study bolstering the material in the chapter. Additionally, most chapters present a civic engagement-type exercise and discussion questions that are challenging and engaging, and help foster student participation in the political system. The purpose of this book is to offer a no-frills, low-cost, yet comprehensive overview of the American political system for students taking introductory courses in American national government.
A print version of this book is available for $27.99.
Contact the University of North Georgia Press for details and ordering information. [email protected] | 706-864-1556https://digitalcommons.northgeorgia.edu/books/1004/thumbnail.jp
Trends in stream nitrogen concentrations for forested reference catchments across the USA
To examine whether stream nitrogen concentrations in forested reference catchments have changed over time and if patterns were consistent across the USA, we synthesized up to 44 yr of data collected from 22 catchments at seven USDA Forest Service Experimental Forests. Trends in stream nitrogen presented high spatial variability both among catchments at a site and among sites across the USA. We found both increasing and decreasing trends in monthly flow-weighted stream nitrate and ammonium concentrations. At a subset of the catchments, we found that the length and period of analysis influenced whether trends were positive, negative or non-significant. Trends also differed among neighboring catchments within several Experimental Forests, suggesting the importance of catchment-specific factors in determining nutrient exports. Over the longest time periods, trends were more consistent among catchments within sites, although there are fewer long-term records for analysis. These findings highlight the critical value of long-term, uninterrupted stream chemistry monitoring at a network of sites across the USA to elucidate patterns of change in nutrient concentrations at minimally disturbed forested sites
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Language support for immigrant children: a study of state schools in the UK and US
In recent decades, immigrants, refugees and asylum seekers have sought a new way of life in large numbers, often leaving their countries of origin behind in search of places that offer a better way of life. The purpose of this study was to investigate how elementary and middle school students in state schools in Reading, England (primarily speakers of Asian languages), and Richmond, Virginia (primarily speakers of Spanish), were supported academically, when most children’s first language was not English. The authors were interested in exploring whether or not there were cultural or structural differences in the way each country helped or hindered these students as they progressed through the school systems. Three UK schools in a district of approximately 100,000 and three US schools in a district of approximately 250,000 were the focus of this exploration from 2000 to 2003. Findings indicated that there were cultural and legislative differences and similarities. Teachers and administrators in both countries attempted to provide services with limited and sometimes diminishing resources. Community support varied based on resources, attitudes toward various ethnic groups, and the coping strategies adopted by these groups in their new environments. Marked differences appeared with regard to the manner in which assessments took place and how the results were made available to the public
Enhanced CH absorption within Jupiter's southern auroral oval from Juno UVS observations
Reflected sunlight observations from the Ultraviolet Spectrograph (UVS) on
the Juno spacecraft were used to study the distribution of acetylene
(CH) at Jupiter's south pole. We find that the shape of the CH
absorption feature varies significantly across the polar region, and this can
be used to infer spatial variability in the CH abundance. There is a
localized region of enhanced CH absorption which coincides with the
location of Jupiter's southern polar aurora; the CH abundance poleward
of the auroral oval is a factor of 3 higher than adjacent quiescent,
non-auroral longitudes. This builds on previous infrared studies which found
enhanced CH abundances within the northern auroral oval. This suggests
that Jupiter's upper-atmosphere chemistry is being strongly influenced by the
influx of charged auroral particles and demonstrates the necessity of
developing ion-neutral photochemical models of Jupiter's polar regions.Comment: Accepted in JGR: Planet
Possible Transient Luminous Events observed in Jupiter's upper atmosphere
11 transient bright flashes were detected in Jupiter's atmosphere using the
UVS instrument on the Juno spacecraft. These bright flashes are only observed
in a single spin of the spacecraft and their brightness decays exponentially
with time, with a duration of ~1.4 ms. The spectra are dominated by H2 Lyman
band emission and based on the level of atmospheric absorption, we estimate a
source altitude of 260 km above the 1-bar level. Based on these
characteristics, we suggest that these are observations of Transient Luminous
Events (TLEs) in Jupiter's upper atmosphere. In particular, we suggest that
these are elves, sprites or sprite halos, three types of TLEs that occur in the
Earth's upper atmosphere in response to tropospheric lightning strikes. This is
supported by visible light imaging, which shows cloud features typical of
lightning source regions at the locations of several of the bright flashes.
TLEs have previously only been observed on Earth, although theoretical and
experimental work has predicted that they should also be present on Jupiter.Comment: Accepted in JGR: Planets. 28 pages, 8 figure
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