73 research outputs found
The Development of Acoustical Communication in the Mallard (Anas Platyrhynchos)
Fesi ,es begin calling on the nest before the young hatch and calling increases as the time of exodus approaches. Female calls, on the nest, lire mainly in response to calls and movements of young. Females off the nest use a variety of calls and exercise complete control over the activity of the brood using mainly acoustical cues, Broody calls are significantly different between individual females and vary depending on. the situation. As young develop, female communication to and control over the brood decreases. Young are extremely vocal except when being brooded or when in alert positions. Contact calls are common and distress calls are rare. These calls arc end points of a graded system and intermediate calls occur. As young develop they become more independent and contact calls are eventually replaced by intention and aggressive calls. Development of the young is accompanied with a decrease in frequency (Hs) of the calls and a change in their structure to form a preliminary stroke and main note. Mult calls develop from the main note of con-tact calls by a decrease in its frequency below a threshold value and the addition of harmonics. During the juvenile to adult transition period, birds give juvenile, adult and intermediate calls. Juvenile calls were similar to those of adults by 18 to 19 weeks. By their first fall, birds are taking part in bouts of sexual displays and giving associated calls
Santos: Religious Folk Art of New Mexico, 1750 to 1850
This study was begun out of a sincere love for the art of the santos. It will cover the santos' beginnings in New Mexico around 1750 and discuss the historical causes for both the santos' rise to popularity and their later demise. This study will attempt to cover all of the factors that had an effect on their creation and style and to discuss what the santos' contribution to folk art in America might be.Housing, Design, and Consumer Resource
The statistics of triggered star formation: an overdensity of massive YSOs around Spitzer bubbles
We present a detailed statistical study of massive star formation in the
environment of 322 Spitzer mid-infrared bubbles by using the RMS survey for
massive Young Stellar Objects (YSOs). Using a combination of simple surface
density plots and a more sophisticated angular cross-correlation function
analysis we show that there is a statistically significant overdensity of RMS
YSOs towards the bubbles. There is a clear peak in the surface density and
angular cross-correlation function of YSOs projected against the rim of the
bubbles. By investigating the autocorrelation function of the RMS YSOs we show
that this is not due to intrinsic clustering of the RMS YSO sample. RMS YSOs
and Spitzer bubbles are essentially uncorrelated with each other beyond a
normalised angular distance of two bubble radii. The bubbles associated with
RMS YSOs tend to be both smaller and thinner than those that are not associated
with YSOs. We interpret this tendency to be due to an age effect, with YSOs
being preferentially found around smaller and younger bubbles. We find no
evidence to suggest that the YSOs associated with the bubbles are any more
luminous than the rest of the RMS YSO population, which suggests that the
triggering process does not produce a top heavy luminosity function or initial
mass function. We suggest that it is likely that the YSOs were triggered by the
expansion of the bubbles and estimate that the fraction of massive stars in the
Milky Way formed by this process could be between 14 and 30%.Comment: 12 pages, 8 figures. Accepted by MNRAS. This version incorporates
minor suggestions by the referee. A version with higher resolution Figure 1
is available upon reques
Throughflow centrality is a global indicator of the functional importance of species in ecosystems
To better understand and manage complex systems like ecosystems it is
critical to know the relative contribution of system components to system
functioning. Ecologists and social scientists have described many ways that
individuals can be important; This paper makes two key contributions to this
research area. First, it shows that throughflow, the total energy-matter
entering or exiting a system component, is a global indicator of the relative
contribution of the component to the whole system activity. It is global
because it includes the direct and indirect exchanges among community members.
Further, throughflow is a special case of Hubbell status as defined in social
science. This recognition effectively joins the concepts, enabling ecologists
to use and build on the broader centrality research in network science. Second,
I characterize the distribution of throughflow in 45 empirically-based trophic
ecosystem models. Consistent with expectations, this analysis shows that a
small fraction of the system components are responsible for the majority of the
system activity. In 73% of the ecosystem models, 20% or less of the nodes
generate 80% or more of the total system throughflow. Four or fewer dominant
nodes are required to account for 50% of the total system activity. 121 of the
130 dominant nodes in the 45 ecosystem models could be classified as primary
producers, dead organic matter, or bacteria. Thus, throughflow centrality
indicates the rank power of the ecosystems components and shows the power
concentration in the primary production and decomposition cycle. Although these
results are specific to ecosystems, these techniques build on flow analysis
based on economic input-output analysis. Therefore these results should be
useful for ecosystem ecology, industrial ecology, the study of urban
metabolism, as well as other domains using input-output analysis.Comment: 7 figures, 2 table
A <i>Herschel</i> and BIMA study of the sequential star formation near the W 48A H II region
We present the results of Herschel HOBYS (Herschel imaging survey of OB Young Stellar objects) photometric mapping combined with Berkeley Illinois Maryland Association (BIMA) observations and additional archival data, and perform an in-depth study of the evolutionary phases of the star-forming clumps in W 48A and their surroundings. Age estimates for the compact sources were derived from bolometric luminosities and envelope masses, which were obtained from the dust continuum emission, and agree within an order of magnitude with age estimates from molecular line and radio data. The clumps in W 48A are linearly aligned by age (east-old to west-young): we find a ultra-compact (UC) H II region, a young stellar object (YSO) with class II methanol maser emission, a YSO with a massive outflow and finally the NH2D prestellar cores from Pillai et al. This remarkable positioning reflects the (star) formation history of the region. We find that it is unlikely that the star formation in the W 48A molecular cloud was triggered by the UC H II region and discuss the Aquila supershell expansion as a major influence on the evolution of W 48A. We conclude that the combination of Herschel continuum data with interferometric molecular line and radio continuum data is important to derive trustworthy age estimates and interpret the origin of large-scale structures through kinematic information
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Experimental Studies of Cavity and Core Flow Interactions With Application to Ultra-Compact Combustors
Reducing the weight and decreasing pressure losses of aviation gas turbine engines improves the thrust-to-weight ratio and improves efficiency. In ultra-compact combustors (UCC), engine length is reduced and pressure losses are decreased by merging a combustor with adjacent components using a systems engineering approach. High-pressure turbine inlet vanes can be placed in a combustor to form a UCC. In this work, experiments were performed to understand the performance and associated physics within a UCC. Experiments were performed using a combustor operating at pressures in the range of 520–1030 kPa (75–150 psia) and inlet temperature equal to 480–620 K (865 R–1120 R). The primary reaction zone is in a single trapped-vortex cavity where the equivalence ratio was varied from 0.7 to 1.8. Combustion efficiencies and NO[subscript x] emissions were measured and exit temperature profiles were obtained for various air loadings, cavity equivalence ratios, and configurations with and without representative turbine inlet vanes. A combined diffuser-flameholder (CDF) was used to study the interaction of cavity and core flows. Discrete jets of air immediately above the cavity result in the highest combustion efficiencies. The air jets reinforce the vortex structure within the cavity, as confirmed through coherent structure velocimetry of high-speed images. The combustor exit temperature profile is peaked away from the cavity when a CDF is used. Testing of a CDF with vanes showed that combustion efficiencies greater than 99.5% are possible for 0.8 ≤ Φ[subscript cavity] ≤ 1.8. Temperature profiles at the exit of the UCC with vanes agreed within 10% of the average value. Exit-averaged emission indices of NO[subscript x] ranged from 3.5 to 6.5 g/kg[subscript fuel] for all test conditions. Increasing the air loading enabled greater mass flow rates of fuel with equivalent combustion efficiencies. This corresponds to increased vortex strength within the cavity due to the greater momentum of the air driver jets
The environs of the HII region Gum31
We analyze the distribution of the interstellar matter in the environs of the
HII region Gum31, excited by the open cluster NGC3324, located in the complex
Carina region, with the aim of investigating the action of the massive stars on
the surrounding neutral material. We use neutral hydrogen 21-cm line data,
radio continuum images at 0.843, 2.4 and 4.9 GHz, 12CO(1-0) observations, and
IRAS and MSX infrared data. Adopting a distance of 3 kpc for the HII region and
the ionizing cluster, we derived an electron density of 33+/-3 cm^-3 and an
ionized mass of (3.3+/-1.1)x10^3 Mo based on the radio continuum data at 4.9
GHz. The HI 21-cm line images revealed an HI shell surrounding the HII region.
The HI structure is 10.0+/-1.7 pc in radius, has a neutral mass of 1500+/-500
Mo, and is expanding at 11 km/s. The associated molecular gas amounts to
1.1+/-0.5)x10^5 Mo, being its volume density of about 350 cm^3. This molecular
shell could represent the remains of the cloud where the young open cluster
NGC3324 was born or could have originated by the shock front associated with
the HII region. The difference between the ambient density and the electron
density of the HII region suggests that the HII region is expanding. The
distributions of the ionized and molecular material, along with that of the
emission in the MSX band A, suggest that a photodissociation region has
developed at the interface between the ionized and molecular gas. The
characteristics of a relatively large number of the IRAS, MSX, and 2MASS point
sources projected onto the molecular envelope are compatible with protostellar
candidates, showing the presence of active star forming regions. Very probably,
the expansion of the HII region has triggered stellar formation in the
molecular shell
Wild Bird Influenza Survey, Canada, 2005
Of 4,268 wild ducks sampled in Canada in 2005, real-time reverse transcriptase–PCR detected influenza A matrix protein (M1) gene sequence in 37% and H5 gene sequence in 5%. Mallards accounted for 61% of samples, 73% of M1-positive ducks, and 90% of H5-positive ducks. Ducks hatched in 2005 accounted for 80% of the sample
The G305 star-forming complex: Embedded Massive Star Formation Discovered by Herschel Hi-GAL
We present a Herschel far-infrared study towards the rich massive star-
forming complex G305, utilising PACS 70, 160 {\mu}m and SPIRE 250, 350, and 500
{\mu}m observations from the Hi-GAL survey of the Galactic plane. The focus of
this study is to identify the embedded massive star-forming population within
G305, by combining far-infrared data with radio continuum, H2O maser, methanol
maser, MIPS, and Red MSX Source survey data available from previous studies. By
applying a frequentist technique we are able to identify a sample of the most
likely associations within our multi-wavelength dataset, that can then be
identified from the derived properties obtained from fitted spectral energy
distributions (SEDs). By SED modelling using both a simple modified blackbody
and fitting to a comprehensive grid of model SEDs, some 16 candidate
associations are identified as embedded massive star-forming regions. We derive
a two-selection colour criterion from this sample of log(F70/F500)\geq 1 and
log(F160/F350)\geq 1.6 to identify an additional 31 embedded massive star
candidates with no associated star-formation tracers. Using this result we can
build a picture of the present day star-formation of the complex, and by
extrapolating an initial mass function, suggest a current population of \approx
2 \times 10^4 young stellar objects (YSOs) present, corresponding to a star
formation rate (SFR) of 0.01-0.02 M\odot yr^-1. Comparing this resolved star
formation rate, to extragalactic star formation rate tracers (based on the
Kennicutt-Schmidt relation), we find the star formation activity is
underestimated by a factor of \geq 2 in comparison to the SFR derived from the
YSO population.Comment: Accepted by MNRAS, 16 pages, 8 figures, 3 table
Ionization compression impact on dense gas distribution and star formation: probability density functions around H II regions as seen by <i>Herschel</i>
Aims. Ionization feedback should impact the probability distribution function (PDF) of the column density of cold dust around the ionized gas. We aim to quantify this effect and discuss its potential link to the core and initial mass function (CMF/IMF).
Methods. We used Herschel column density maps of several regions observed within the HOBYS key program in a systematic way: M 16, the Rosette and Vela C molecular clouds, and the RCW 120 H II region. We computed the PDFs in concentric disks around the main ionizing sources, determined their properties, and discuss the effect of ionization pressure on the distribution of the column density.
Results. We fitted the column density PDFs of all clouds with two lognormal distributions, since they present a "double-peak" or an enlarged shape in the PDF. Our interpretation is that the lowest part of the column density distribution describes the turbulent molecular gas, while the second peak corresponds to a compression zone induced by the expansion of the ionized gas into the turbulent molecular cloud. Such a double peak is not visible for all clouds associated with ionization fronts, but it depends on the relative importance of ionization pressure and turbulent ram pressure. A power-law tail is present for higher column densities, which are generally ascribed to the effect of gravity. The condensations at the edge of the ionized gas have a steep compressed radial profile, sometimes recognizable in the flattening of the power-law tail. This could lead to an unambiguous criterion that is able to disentangle triggered star formation from pre-existing star formation.
Conclusions. In the context of the gravo-turbulent scenario for the origin of the CMF/IMF, the double-peaked or enlarged shape of the PDF may affect the formation of objects at both the low-mass and the high-mass ends of the CMF/IMF. In particular, a broader PDF is required by the gravo-turbulent scenario to fit the IMF properly with a reasonable initial Mach number for the molecular cloud. Since other physical processes (e.g., the equation of state and the variations among the core properties) have already been said to broaden the PDF, the relative importance of the different effects remains an open question
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