4,589 research outputs found
Investigation of Three Low-temperature-ratio Combustor Configurations in a 48-inch-diameter Ram-jet Engine
A preliminary evaluation was made of three types of combustor configurations in a 48-inch-diameter ram-jet engine to determine the one with the greatest promise of ultimately achieving efficient and stable combustion at low fuel-air rations and low combustor-inlet pressure. The combustor configurations evaluated include (1) a can-piloted configuration using a gutter-type flame holder with can-type pilot burners for stability, (2) an annular-piloted configuration using a gutter-type flame holder with an annular pilot burner to provide stability and to serve as a flow divider for confined fuel-air mixing, and (3) a can-type configuration using a flow divider for confined fuel-air mixing. No modifications were made to optimize the performance of any configuration. On the basis of this preliminary evaluation at an inlet-air temperature of about 990 degrees R, the annular-piloted combustor configuration appeared to have the greatest promise of permitting combustion efficiencies in excess of 0.90 at low fuel-air ratio with combustor-inlet pressures as low as 700 pounds per square foot absolute
Interferometric Constraints on Quantum Geometrical Shear Noise Correlations
Final measurements and analysis are reported from the first-generation
Holometer, the first instrument capable of measuring correlated variations in
space-time position at strain noise power spectral densities smaller than a
Planck time. The apparatus consists of two co-located, but independent and
isolated, 40 m power-recycled Michelson interferometers, whose outputs are
cross-correlated to 25 MHz. The data are sensitive to correlations of
differential position across the apparatus over a broad band of frequencies up
to and exceeding the inverse light crossing time, 7.6 MHz. By measuring with
Planck precision the correlation of position variations at spacelike
separations, the Holometer searches for faint, irreducible correlated position
noise backgrounds predicted by some models of quantum space-time geometry. The
first-generation optical layout is sensitive to quantum geometrical noise
correlations with shear symmetry---those that can be interpreted as a
fundamental noncommutativity of space-time position in orthogonal directions.
General experimental constraints are placed on parameters of a set of models of
spatial shear noise correlations, with a sensitivity that exceeds the
Planck-scale holographic information bound on position states by a large
factor. This result significantly extends the upper limits placed on models of
directional noncommutativity by currently operating gravitational wave
observatories.Comment: Matches the journal accepted versio
The "Solar Model Problem" Solved by the Abundance of Neon in Stars of the Local Cosmos
The interior structure of the Sun can be studied with great accuracy using
observations of its oscillations, similar to seismology of the Earth. Precise
agreement between helioseismological measurements and predictions of
theoretical solar models has been a triumph of modern astrophysics (Bahcall et
al. 2005). However, a recent downward revision by 25-35% of the solar
abundances of light elements such as C, N, O and Ne (Asplund et al. 2004) has
broken this accordance: models adopting the new abundances incorrectly predict
the depth of the convection zone, the depth profiles of sound speed and
density, and the helium abundance (Basu Antia 2004, Bahcall et al. 2005). The
discrepancies are far beyond the uncertainties in either the data or the model
predictions (Bahcall et al. 2005b). Here we report on neon abundances relative
to oxygen measured in a sample of nearby solar-like stars from their X-ray
spectra. They are all very similar and substantially larger than the recently
revised solar value. The neon abundance in the Sun is quite poorly determined.
If the Ne/O abundance in these stars is adopted for the Sun the models are
brought back into agreement with helioseismology measurements (Antia Basu 2005,
Bahcall et al. 2005c).Comment: 13 pages, 3 Figure
The Abundances of Nitrogen and Oxygen in Damped Lyman Alpha Systems
We take a fresh look at the abundance of nitrogen in DLAs with oxygen
abundances between 1/10 and 1/100 of solar. This is a metallicity regime poorly
sampled in the local universe and where QSO absorbers may hold clues to both
the nucleosynthetic origin of N and the chemical evolution of high redshift
galaxies. We combine new VLT UVES observations with others from the literature
to form a sample of 10 DLAs in which the abundances of N and of one of the two
alpha-capture elements O or S have been measured. We confirm earlier reports
that the (N/O) ratio exhibits a larger range of values than other ratios of
heavy elements in DLAs; however, all 10 DLAs fall in the region of the (N/O)
vs. (O/H) plot delimited by the primary and secondary levels of nitrogen
production. Our results provide empirical evidence in support of the proposal
that intermediate mass stars (with masses less than 7 solar masses) are the
main source of primary nitrogen, so that its release into the ISM lags behind
that of oxygen, which is produced by Type II SNae. A high proportion (40%) of
the DLAs in our sample have apparently not yet attained the full primary level
of N enrichment; this finding may be an indication that the metallicity regime
we are studying preferentially picks out galaxies which have only recently
condensed out of the IGM and begun forming stars. Alternatively, the delay in
the release of N following an episode of star formation may increase with
decreasing metallicity, if stars of progressively lower masses than 4 solar
masses can synthesize N in their hotter interiors.Comment: 17 pages, LaTeX, 7 Postscript Figures. Accepted for publication in
Astronomy & Astrophysic
Cumulative impacts on the peoples of the Nez Perce, Yakama, Umatilla, and Warm Springs Indian reservations from construction and operation of U.S. Army Corps of Engineers' dams in the Columbia River basin upstream of Bonneville Dam, inclusive
Sexuality and Affection among Elderly German Men and Women in Long-Term Relationships: Results of a Prospective Population-Based Study
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.The study was funded by the German Federal Ministry for Families, Senior Citizens, Women and Youth (AZ 314-1722-102/16; AZ 301-1720-295/2), the Ministry for Science, Research and Art Baden-Württemberg, and the University of Rostock (FORUN 989020; 889048)
Retreatment of Patients Nonresponsive to Pegylated Interferon and Ribavirin with Daily High-Dose Consensus Interferon
Background. Current treatment of chronic hepatitis C with pegylated interferon and ribavirin has the ability to eliminate viral infection in about half of the patients treated. Therapeutic options, for those with remaining chronic hepatitis, will remain limited until
novel antivirals become available in the future. Consensus interferon is currently available and has demonstrated clinical efficacy with superior invitro antiviral activity, but the maximum tolerated dose is not defined. Methods. We assessed the efficacy of daily high-dose (24 ug) consensus interferon with weight-based (1000–1200 mg daily) ribavirin in HCV genotype 1-infected non-responder patients. Results. Six adverse events were documented in five patients, and the trial was terminated with no subject achieving viral clearance. Conclusions. The occurrence of serious adverse events effectively defined the upper limit of acceptable dose, while also revealing that this dose did not offer enhanced sustained viral clearance
The young active star SAO 51891 (V383 Lac)
Our aim is investigating surface inhomogeneities of the young late-type star
SAO51891, from photosphere to upper chromosphere, analyzing contemporaneous
high-resolution spectra and broad-band photometry. The FOCES@CAHA spectral
range is used to determine spectral classification and derive vsini and Vrad.
The Li abundance is measured to estimate the age. The BVRIJHKs bands are used
to construct the SED. The variations of our BV fluxes and Teff are used to
infer the presence of photospheric spots and observe their behavior over time.
The chromospheric activity is studied applying the spectral subtraction
technique to Halpha, CaII H&K, Heps, and CaII IRT lines. We find SAO51891 to be
a young K0-1V star with Li abundance close to the Pleiades upper envelope,
confirming its youth (~100 Myr), also inferred from its kinematical membership
to the Local Association. We detect no IR excess from SED analysis, and
rotational modulation of luminosity, Teff, CaII, and Heps total fluxes. A spot
model with two active regions, ~240 K cooler than the surrounding photosphere,
fits our light/Teff curves, and reproduces the small-amplitude Vrad variations.
The anti-correlation of light curves and chromospheric diagnostics indicates
plages spatially associated with spots. The large amplitude observed in the
Heps-flux curve suggests that this line is very sensitive to the plage
presence. Finally, SAO51891 is a young active star, lacking significant amounts
of circumstellar dust or any evidence for low mass companions. The spots turn
out to be larger and warmer than those in less active MS stars. The Vrad
variation produced by spots has an amplitude comparable with those induced by
Jupiter-mass planets orbiting close to the star. SAO51891 is a good example of
star where the detection of planets may be hampered by the high activity level.Comment: 16 pages, 12 figures, 7 tables, accepted by Astronomy and
Astrophysics; abstract here was shortene
Fluor-schorl, a new member of the tourmaline supergroup, and new data on schorl from the cotype localities
Fluor-schorl, NaFe^(2+) _3Al_6Si_6O_(18)(BO_3)_3(OH)_3F, is a new mineral species of the tourmaline supergroup from alluvial tin deposits near Steinberg, Zschorlau, Erzgebirge (Saxonian Ore Mountains), Saxony, Germany, and from pegmatites near Grasstein (area from Mittewald to Sachsenklemme), Trentino, South Tyrol, Italy. Fluor-schorl was formed as a pneumatolytic phase and in high-temperature hydrothermal veins in granitic pegmatites. Crystals are black (pale brownish to pale greyish-bluish, if distance (r^2 = 0.93). This correlation indicates that Fe^(2+)-rich tourmalines from the investigated localities clearly tend to have a F-rich or F-dominant composition. A further strong positive correlation (r^2 = 0.82) exists between the refined F content and the Y–W (F,OH) distance, and the latter may be used to quickly estimate the F content
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