4,990 research outputs found
Performance of a 13-Stage Development Compressor for the J40-WE-24 Engine at Equivalent Speeds from 30 to 112 Percent of Design
The performance of a 13-stage development comressor for the J40-WE-24 engine has been determined at equivalent speeds from 30 to 112 percent of design. The design total-pressure ratio of 6.0 and the design weight flow of 164 pounds per second were not attained, An analysis was conducted to determine the reasons for the poor performance at the design and over-design speed. The analysis indicated that most of the difficulty could be attributed to the fact that the first stage was overcompromised to favor part-speed performance
Wheat and Feed Grains in the Great Plains and Northwest: Study Area Descriptions and State Statistical Summaries
The objectives are: (1) To determine individual farm-supply response for alternative product-price relationships and price levels with emphasis on wheat, feed grains, cotton and livestock (2) To estimate aggregate subregional and regional supply functions for major commodities (3) To provide guides for optimum farm organizations and adjustments and attendant adjustments by farm-related businesses and institutions in the Great Plains and Western States
The host galaxy of the z=2.4 radio-loud AGN MRC 0406-244 as seen by HST
We present multicolour Hubble Space Telescope images of the powerful z=2.4
radio galaxy MRC 0406-244 and model its complex morphology with several
components including a host galaxy, a point source, and extended nebular and
continuum emission. We suggest that the main progenitor of this radio galaxy
was a normal, albeit massive (M ~10^{11} solar masses), star-forming galaxy.
The optical stellar disc of the host galaxy is smooth and well described by a
S\'ersic profile, which argues against a recent major merger, however there is
also a point-source component which may be the remnant of a minor merger. The
half-light radius of the optical disc is constrained to lie in the range 3.5 to
8.2kpc, which is of similar size to coeval star forming galaxies.
Biconical shells of nebular emission and UV-bright continuum extend out from
the host galaxy along the radio jet axis, which is also the minor axis of the
host galaxy. The origin of the continuum emission is uncertain, but it is most
likely to be young stars or dust-scattered light from the AGN, and it is
possible that stars are forming from this material at a rate of
200^{+1420}_{-110} solar masses per year.Comment: Accepted for publication in MNRA
Semi-analytic model predictions of the galaxy population in protoclusters
We investigate the galaxy population in simulated protocluster regions using a semi-analytic model of galaxy formation, coupled to merger-trees extracted from N-body simulations. We select the most massive clusters at redshift z = 0 from our set of simulations, and follow their main progenitors back in time. The analysis shows that protocluster regions are dominated by central galaxies and their number decreases with time as many become satellites, clustering around the central object. In agreement with observations, we find an increasing velocity dispersion with cosmic time, the increase being faster for satellites. The analysis shows that protoclusters are very extended regions, 7320 Mpc at z 73 1. The fraction of galaxies in protocluster regions that are not progenitor of cluster galaxies varies with redshift, stellar mass and area considered. It is about 20-30 per cent for galaxies with stellar mass \u2dc109 M 99, while negligible for the most massive galaxies considered. Nevertheless, these objects have properties similar to those of progenitors. We investigate the building-up of the passive sequence in clusters, and find that their progenitors are on average always active at any redshift of interest of protoclusters. The main mechanism which quenches their star formation is the removal of the hot gas reservoir at the time of accretion. The later galaxies are accreted (become satellite), and the more the cold gas available, the longer the time spent as active. Central galaxies are active over all redshift range considered, although a non-negligible fraction of them become passive at redshift z < 1, due to strong feedback from active galactic nuclei
Hydrogen Two-Photon Continuum Emission from the Horseshoe Filament in NGC 1275
Far ultraviolet emission has been detected from a knot of Halpha emission in
the Horseshoe filament, far out in the NGC 1275 nebula. The flux detected
relative to the brightness of the Halpha line in the same spatial region is
very close to that expected from Hydrogen two-photon continuum emission in the
particle heating model of Ferland et al. (2009) if reddening internal to the
filaments is taken into account. We find no need to invoke other sources of far
ultraviolet emission such as hot stars or emission lines from CIV in
intermediate temperature gas to explain these data.Comment: 9 pages, 8 figures. Accepted for publication in MNRA
Electron Power-Law Spectra in Solar and Space Plasmas
Particles are accelerated to very high, non-thermal energies in solar and
space plasma environments. While energy spectra of accelerated electrons often
exhibit a power law, it remains unclear how electrons are accelerated to high
energies and what processes determine the power-law index . Here, we
review previous observations of the power-law index in a variety of
different plasma environments with a particular focus on sub-relativistic
electrons. It appears that in regions more closely related to magnetic
reconnection (such as the `above-the-looptop' solar hard X-ray source and the
plasma sheet in Earth's magnetotail), the spectra are typically soft ( 4). This is in contrast to the typically hard spectra ( 4) that are observed in coincidence with shocks. The difference
implies that shocks are more efficient in producing a larger non-thermal
fraction of electron energies when compared to magnetic reconnection. A caveat
is that during active times in Earth's magnetotail, values seem
spatially uniform in the plasma sheet, while power-law distributions still
exist even in quiet times. The role of magnetotail reconnection in the electron
power-law formation could therefore be confounded with these background
conditions. Because different regions have been studied with different
instrumentations and methodologies, we point out a need for more systematic and
coordinated studies of power-law distributions for a better understanding of
possible scaling laws in particle acceleration as well as their universality.Comment: 67 pages, 15 figures; submitted to Space Science Reviews; comments
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A SINFONI view of flies in the Spiderweb: a galaxy cluster in the making
The environment of the high-z radio galaxy PKS 1138-262 at z~2.2 is a prime
example of a forming galaxy cluster. We use deep SINFONI data to perform a
detailed study of the kinematics of the galaxies within 60 kpc of the radio
core and we link this to the kinematics of the protocluster on the megaparsec
scale. Identification of optical emission lines shows that 11 galaxies are at
the redshift of the protocluster. The density of line emitters is more than an
order of magnitude higher in the core of the protocluster than the larger scale
environment. This implies a matter overdensity in the core of delta_m~70 which
is similar to the outskirts of local galaxy clusters. The velocity distribution
of the confirmed satellite galaxies shows a broad, double-peaked velocity
structure with sigma=1360+/-206 km/s. A similar broad, double-peaked
distribution was found in a previous study targeting the large scale
protocluster structure, indicating that a common process is acting on both
small and large scales. Including all spectroscopically confirmed protocluster
galaxies, a velocity dispersion of 1013+/-87 km/s is found. We show that the
protocluster has likely decoupled from the Hubble flow and is a dynamically
evolved structure. Comparison to the Millenium simulation indicates that the
protocluster velocity distribution is consistent with that of the most massive
haloes at z~2, but we rule out that the protocluster is a fully virialized
structure based on dynamical arguments and its X-ray luminosity. Comparison to
merging haloes in the Millennium simulation shows that the structure as
observed in and around the Spiderweb galaxy is best interpreted as being the
result of a merger between two massive haloes. We propose that this merger can
result in an increase in star formation and AGN activity in the protocluster
core and is possibly an important stage in the evolution of massive cD
galaxies.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Designing and Piloting a Tool for the Measurement of the Use of Pronunciation Learning Strategies
What appears to be indispensable to drive the field forward and ensure that research findings will be comparable across studies and provide a sound basis for feasible pedagogic proposals is to draw up a classification of PLS and design on that basis a valid and reliable data collection tool which could be employed to measure the use of these strategies in different groups of learners, correlate it with individual and contextual variables, and appraise the effects of training programs. In accordance with this rationale, the present paper represents an attempt to propose a tentative categorization of pronunciation learning strategies, adopting as a point of reference the existing taxonomies of strategic devices (i.e. O'Malley and Chamot 1990; Oxford 1990) and the instructional options teachers have at their disposal when dealing with elements of this language subsystem (e.g. Kelly 2000; Goodwin 2001). It also introduces a research instrument designed on the basis of the classification that shares a number of characteristics with Oxford's (1990) Strategy Inventory for Language Learning but, in contrast to it, includes both Likert-scale and open-ended items. The findings of a pilot study which involved 80 English Department students demonstrate that although the tool requires considerable refinement, it provides a useful point of departure for future research into PLS
The structure and evolution of a forming galaxy cluster at z = 1.62
We present a comprehensive picture of the Cl 0218.3−0510 protocluster at z = 1.623 across 10 comoving Mpc. Using filters that tightly bracket the Balmer and 4000 Å breaks of the protocluster galaxies we obtain precise photometric redshifts resulting in a protocluster galaxy sample that is 89 ± 5 per cent complete and has a contamination of only 12 ± 5 per cent. Both star-forming and quiescent protocluster galaxies are located, which allows us to map the structure of the forming cluster for the first time. The protocluster contains six galaxy groups, the largest of which is the nascent cluster. Only a small minority of the protocluster galaxies are in the nascent cluster (11 per cent) or in the other galaxy groups (22 per cent), as most protocluster galaxies reside between the groups. Unobscured star-forming galaxies predominantly reside between the protocluster’s groups, whereas red galaxies make up a large fraction of the groups’ galactic content, so observing the protocluster through only one of these types of galaxies results in a biased view of the protocluster’s structure. The structure of the protocluster reveals how much mass is available for the future growth of the cluster and we use the Millennium Simulation, scaled to a Planck cosmology, to predict that Cl 0218.3−0510 will evolve into a 2.7+3.9 −1.7 × 1014M cluster by the present day
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