2,032 research outputs found
Break up of returning plasma after the 7 June 2011 filament eruption by Rayleigh-Taylor instabilities
A prominence eruption on 7 June 2011 produced spectacular curtains of plasma
falling through the lower corona. At the solar surface they created an
incredible display of extreme ultraviolet brightenings. The aim is to identify
and analyze some of the local instabilities which produce structure in the
falling plasma. The structures were investigated using SDO/AIA 171A and 193A
images in which the falling plasma appeared dark against the bright coronal
emission. Several instances of the Rayleigh-Taylor instability were
investigated. In two cases the Alfven velocity associated with the dense plasma
could be estimated from the separation of the Rayleigh-Taylor fingers. A second
type of feature, which has the appearance of self-similar branching horns, is
also discussed.Comment: 6 pages, 7 figures, submitted A&A. Movies are at
http://www.mps.mpg.de/data/outgoing/innes/arcs_movie.avi and
http://www.mps.mpg.de/data/outgoing/innes/horns_movie.av
Obsidian Artifacts from East Texas Archaeological Sites
Obsidian artifacts are one of the few material culture remains on East Texas sites that provide direct evidence of distant links between East Texasâs native American peoples and native American communities in the Southwest or the Northwestern Plains. Other such material culture items include marine shells from the Gulf of California, turquoise from New Mexico sources, and sherds from ceramic vessels made in the Puebloan Southwest. Such artifacts, however, are rarely recovered in East Texas archaeological sites. In this article, we summarize the available information on obsidian artifacts from East Texas archaeological sites, much of it gathered from Hesterâs Texas Obsidian Project (TOP), including obsidian source data when it is available
Effects of Alcohol and Expectancy Upon Episodic Memory in Individuals Reporting Alcoholic Blackouts
In a within-subject placebo design, 10 heavy drinkers reporting alcoholic blackouts showed significant decrements in episodic memory when receiving alcohol but not on days when a placebo was given. Parallel deficits were observed on recall and recognition measures. On placebo days, self-ratings of intoxication were related to the degree of observed performance decrement. Memory deficits appear to be primarily pharmacologic rather than expectancy effects of drinking
People See Political Opponents as More Stupid Than Evil
Affective polarization is a rising threat to political discourse and democracy. Public figures have expressed that "conservatives think liberals are stupid, and liberals think conservatives are evil." However, four studies (N = 1,660)-including a representative sample-reveal evidence that both sides view political opponents as more unintelligent than immoral. Perceiving the other side as "more stupid than evil" occurs both in general judgments (Studies 1, 3, and 4) and regarding specific issues (Study 2). Study 4 also examines "meta-perceptions" of how Democrats and Republicans disparage one another, revealing that people correctly perceive that both Democrats and Republicans see each other as more unintelligent than immoral, although they exaggerate the extent of this negativity. These studies clarify the way everyday partisans view each other, an important step in designing effective interventions to reduce political animosity
A VLA Search for Water Masers in Six HII Regions: Tracers of Triggered Low-Mass Star Formation
We present a search for water maser emission at 22 GHz associated with young
low-mass protostars in six HII regions -- M16, M20, NGC 2264, NGC 6357, S125,
and S140. The survey was conducted with the NRAO Very Large Array from 2000 to
2002. For several of these HII regions, ours are the first high-resolution
observations of water masers. We detected 16 water masers: eight in M16, four
in M20, three in S140, and one in NGC 2264. All but one of these were
previously undetected. No maser emission was detected from NGC 6357 or S125.
There are two principle results to our study. (1) The distribution of water
masers in M16 and M20 does not appear to be random but instead is concentrated
in a layer of compressed gas within a few tenths of a parsec of the ionization
front. (2) Significantly fewer masers are seen in the observed fields than
expected based on other indications of ongoing star formation, indicating that
the maser-exciting lifetime of protostars is much shorter in HII regions than
in regions of isolated star formation. Both of these results confirm
predictions of a scenario in which star formation is first triggered by shocks
driven in advance of ionization fronts, and then truncated approximately 10^5
years later when the region is overrun by the ionization front.Comment: 30 pages, 20 figures, 3 tables. Accepted for publication by ApJ. Full
resolution figures and PS and PDF versions with full-res figures available at
http://eagle.la.asu.edu/healy/preprints/hhc0
Molecular excitation in the Eagle nebula's fingers
Context: The M16 nebula is a relatively nearby Hii region, powered by O stars
from the open cluster NGC 6611, which borders to a Giant Molecular Cloud.
Radiation from these hot stars has sculpted columns of dense obscuring material
on a few arcmin scales. The interface between these pillars and the hot ionised
medium provides a textbook example of a Photodissociation Region (PDR).
Aims: To constrain the physical conditions of the atomic and molecular
material with submillimeter spectroscopic observations.
Methods: We used the APEX submillimeter telescope to map a ~3'x3' region in
the CO J=3-2, 4-3 and 7-6 rotational lines, and a subregion in atomic carbon
lines. We also observed C18O(3-2) and CO(7-6) with longer integrations on five
peaks found in the CO(3-2) map. The large scale structure of the pillars is
derived from the molecular lines' emission distribution. We estimate the
magnitude of the velocity gradient at the tips of the pillars and use LVG
modelling to constrain their densities and temperatures. Excitation
temperatures and carbon column densities are derived from the atomic carbon
lines.
Results: The atomic carbon lines are optically thin and excitation
temperatures are of order 60 K to 100 K, well consistent with observations of
other Hii region-molecular cloud interfaces. We derive somewhat lower
temperatures from the CO line ratios, of order 40 K. The Ci/CO ratio is around
0.1 at the fingers tips.Comment: 4 pages, APEX A&A special issue, accepte
X-rays and Protostars in the Trifid Nebula
The Trifid Nebula is a young HII region recently rediscovered as a
"pre-Orion" star forming region, containing protostars undergoing violent mass
ejections visible in optical jets as seen in images from the Infrared Space
Observatory and the Hubble Space Telescope. We report the first X-ray
observations of the Trifid nebula using ROSAT and ASCA. The ROSAT image shows a
dozen X-ray sources, with the brightest X-ray source being the O7 star, HD
164492, which provides most of the ionization in the nebula. We also identify
85 T Tauri star and young, massive star candidates from near-infrared colors
using the JHKs color-color diagram from the Two Micron All Sky Survey (2MASS).
Ten X-ray sources have counterpart near-infrared sources. The 2MASS stars and
X-ray sources suggest there are potentially numerous protostars in the young
HII region of the Trifid. ASCA moderate resolution spectroscopy of the
brightest source shows hard emission up to 10 keV with a clearly detected Fe K
line. The best model fit is a two-temperature (T = 1.2x10^6 K and 39x10^6 K)
thermal model with additional warm absorbing media. The hotter component has an
unusually high temperature for either an O star or an HII region; a typical
Galactic HII region could not be the primary source for such hot temperature
plasma and the Fe XXV line emission. We suggest that the hotter component
originates in either the interaction of the wind with another object (a
companion star or a dense region of the nebula) or from flares from deeply
embedded young stars.Comment: Accepted in ApJ (Oct, 20 issue, 2001
Risk factors for head injury events in professional rugby union: a video analysis of 464 head injury events to inform proposed injury prevention strategies
OBJECTIVES: The tackle is responsible for the majority of head injuries during rugby union. In order to address head injury risk, risk factors during the tackle must first be identified. This study analysed tackle characteristics in the professional game in order to inform potential interventions. METHODS: 464 tackles resulting in a head injury assessment (HIA) were analysed in detail, with tackle type, direction, speed, acceleration, nature of head contact and player body position the characteristics of interest. RESULTS: Propensity to cause an HIA was significantly greater for active shoulder tackles, front-on tackles, high speeder tackles and an accelerating tackler. Head contact between a tackler's head and ball carrier's head or shoulder was significantly more likely to cause an HIA than contact below the level of the shoulder (incident rate ratio (IRR) 4.25, 95%-CI 3.38 to 5.35). The tackler experiences the majority (78%) of HIAs when head-to-head contact occurs. An upright tackler was 1.5 times more likely to experience an HIA than a bent at the waist tackler (IRR 1.44, 95% CI 1.18 to 1.76). CONCLUSIONS: This study confirms that energy transfer in the tackle is a risk factor for head injury, since direction, type and speed all influence HIA propensity. The study provides evidence that body position and the height of tackles should be a focus for interventions, since lowering height and adopting a bent at the waist body position is associated with reduced risk for both tacklers and ball carriers. To this end, World Rugby has implemented law change based on the present data
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