22,795 research outputs found
Design and performance of a high-pressure-ratio, highly loaded axial-flow transonic compressor space
A 50-cm-diam. axial-flow transonic compressor stage with multiple-circular-arc blades was designed and tested. At design speed, a rotor peak efficiency of 0.85 occurred at an equivalent weight flow of 29.3 kg/sec. Stage peak efficiency was 0.79 at 28.6 kg/sec. Stage total pressure ratio at peak efficiency was 1.84. The stall margin at design speed was 5 percent. Rotor and stator losses were higher than predicted. The stator choked at design flow
Effects of reset stators and a rotating, grooved stator hub on performance of a 1.92-pressure-ratio compressor stage
The overall performance and blade-element performance of a transonic fan stage are presented for two modified test configurations and are compared with the unmodified stage. Tests were conducted with reset stators 2 deg open and reset stators with a rotating grooved stator hub. Detailed radial and circumferential (behind stator) surveys of the flow conditions were made over the stable operating range at rotative speeds of 70, 90, and 100 percent of design speed. Reset stator blade tests indicated a small increase in stage efficiency, pressure ratio, and maximum weight flow at each speed. Performance with reset stators and a rotating, grooved stator hub resulted in an additional increase in stage efficiency and pressure ratio at all speeds. The rotating grooved stator hub reduced hub losses considerably
A New Brown Dwarf Desert? A Scarcity of Wide Ultracool Binaries
We present the results of a deep-imaging search for wide companions to
low-mass stars and brown dwarfs using NSFCam on IRTF. We searched a sample of
132 M7-L8 dwarfs to magnitude limits of and ,
corresponding to secondary-primary mass ratios of . No companions
were found with separations between 2{\arcsec} to 31{\arcsec} (40 AU
to 1000 AU). This null result implies a wide companion frequency below
2.3% at the 95% confidence level within the sensitivity limits of the survey.
Preliminary modeling efforts indicate that we could have detected 85% of
companions more massive than and 50% above .Comment: 27 pages, 8 figures, 3 tables: accepted to the Astronomical Journa
5-micron photometry of late-type dwarfs
We present narrowband-M photometry of nine low-mass dwarfs with spectral
types ranging from M2.5 to L0.5. Combining the (L'-M') colours derived from our
observations with data from the literature, we find colours consistent with a
Rayleigh-Jeans flux distribution for spectral types earlier than M5, but
enhanced F_3.8/F_4.7 flux ratios (negative (L'-M') colours) at later spectral
types. This probably reflects increased absorption at M' due to the CO
fundamental band. We compare our results against recent model predictions and
briefly discuss the implications.Comment: accepted for the Astronomical Journa
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A universal primer for isolation of fragments of a gene encoding phytoene desaturase for use in virus-induced gene silencing (VIGS) studies
We have been using Virus-Induced Gene Silencing (VIGS) to test the function of genes that are candidates for involvement in floral senescence. Although VIGS is a powerful tool for assaying the effects of gene silencing in plants, relatively few taxa have been studied using this approach, and most that have are in the Solanaceae. We typically use silencing of phytoene desaturase (PDS) in preliminary tests of the feasibility of using VIGS. Silencing this gene, whose product is involved in carotene biosynthesis, results in a characteristic photobleaching phenotype in the leaves. We have found that efficient silencing requires the use of fragments that are more than 90% homologous to the target gene. To simplify testing the effectiveness of VIGS in a range of species, we designed a set of universal primers to a region of the PDS gene that is highly conserved among species, and that therefore allows an investigator to isolate a fragment of the homologous PDS gene from the species of interest. We report the sequences of these primers and the results of VIGS experiments in horticultural species from the Asteraceae, Leguminosae, Balsaminaceae and Solanaceae
Radio signatures of solar energetic particles during the 23rd solar cycle
We present the association rates between solar energetic particles (SEPs) and
the radio emission signatures in the corona and IP space during the entire
solar cycle 23. We selected SEPs associated with X and M-class flares from the
visible solar hemisphere. All SEP events are also accompanied by coronal mass
ejections. Here, we focus on the correlation between the SEP events and the
appearance of radio type II, III and IV bursts on dynamic spectra. For this we
used the available radio data from ground-based stations and the Wind/WAVES
spacecraft. The associations are presented separately for SEP events
accompanying activity in the eastern and western solar hemisphere. We find the
highest association rate of SEP events to be with type III bursts, followed by
types II and IV. Whereas for types III and IV no longitudinal dependence is
noticed, these is a tendency for a higher SEP-association rate with type II
bursts in the eastern hemisphere. A comparison with reports from previous
studies is briefly discussed.Comment: http://adsabs.harvard.edu.ezproxy.obspm.fr/abs/2013CEAB...37..541
Trigonometric Parallaxes of Massive Star Forming Regions: VIII. G12.89+0.49, G15.03-0.68 (M17) and G27.36-0.16
We report trigonometric parallaxes for three massive star forming regions,
corresponding to distances of kpc for G12.89+0.49 (also
known as IRAS 18089-1732), kpc for G15.03-0.68 (in the
M17 region), and kpc for G27.36-0.16. Both G12.89+0.49 and
G15.03-0.68 are located in the Carina-Sagittarius spiral arm
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