2,049 research outputs found
Cooling system for high speed aircraft
The system eliminates the necessity of shielding an aircraft airframe constructed of material such as aluminum. Cooling is accomplished by passing a coolant through the aircraft airframe, the coolant acting as a carrier to remove heat from the airframe. The coolant is circulated through a heat pump and a heat exchanger which together extract essentially all of the added heat from the coolant. The heat is transferred to the aircraft fuel system via the heat exchanger and the heat pump. The heat extracted from the coolant is utilized to power the heat pump. The heat pump has associated therewith power turbine mechanism which is also driven by the extracted heat. The power turbines are utilized to drive various aircraft subsystems, the compressor of the heat pump, and provide engine cooling
High heat flux actively cooled honeycomb sandwich structural panel for a hypersonic aircraft
The results of a program to design and fabricate an unshielded actively cooled structural panel for a hypersonic aircraft are presented. The design is an all-aluminum honeycomb sandwich with embedded cooling passages soldered to the inside of the outer moldline skin. The overall finding is that an actively cooled structure appears feasible for application on a hypersonic aircraft, but the fabrication process is complex and some material and manufacturing technology developments are required. Results from the program are summarized and supporting details are presented
Evaluation of a large capacity heat pump concept for active cooling of hypersonic aircraft structure
Results of engineering analyses assessing the conceptual feasibility of a large capacity heat pump for enhancing active cooling of hypersonic aircraft structure are presented. A unique heat pump arrangement which permits cooling the structure of a Mach 6 transport to aluminum temperatures without the aid of thermal shielding is described. The selected concept is compatible with the use of conventional refrigerants, with Freon R-11 selected as the preferred refrigerant. Condenser temperatures were limited to levels compatible with the use of conventional refrigerants by incorporating a unique multipass condenser design, which extracts mechanical energy from the hydrogen fuel, prior to each subsequent pass through the condenser. Results show that it is technically feasible to use a large capacity heat pump in lieu of external shielding. Additional analyses are required to optimally apply this concept
Design and fabrication of a radiative actively cooled honeycomb sandwich structural panel for a hypersonic aircraft
The panel assembly consisted of an external thermal protection system (metallic heat shields and insulation blankets) and an aluminum honeycomb structure. The structure was cooled to temperature 442K (300 F) by circulating a 60/40 mass solution of ethylene glycol and water through dee shaped coolant tubes nested in the honeycomb and adhesively bonded to the outer skin. Rene'41 heat shields were designed to sustain 5000 cycles of a uniform pressure of + or - 6.89kPa (+ or - 1.0 psi) and aerodynamic heating conditions equivalent to 136 kW sq m (12 Btu sq ft sec) to a 422K (300 F) surface temperature. High temperature flexible insulation blankets were encased in stainless steel foil to protect them from moisture and other potential contaminates. The aluminum actively cooled honeycomb sandwich structural panel was designed to sustain 5000 cycles of cyclic in-plane loading of + or - 210 kN/m (+ or - 1200 lbf/in.) combined with a uniform panel pressure of + or - 6.89 kPa (?1.0 psi)
An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly
We present an integrated study of star formation and galactic stellar mass
assembly from z=0.05-1.5 and galactic metallicity evolution from z=0.05-0.9
using a very large and highly spectroscopically complete sample selected by
rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit
Bruzual & Charlot (2003) models to compute the galactic stellar masses and
extinctions. We determine the expected formed stellar mass density growth rates
produced by star formation and compare them with the growth rates measured from
the formed stellar mass functions by mass interval. We show that the growth
rates match if the IMF is slightly increased from the Salpeter IMF at
intermediate masses (~10 solar masses). We investigate the evolution of galaxy
color, spectral type, and morphology with mass and redshift and the evolution
of mass with environment. We find that applying extinction corrections is
critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the
green valley are 24um sources, but after correcting for extinction, the bulk of
the 24um sources lie in the blue cloud. We find an evolution of the
metallicity-mass relation corresponding to a decrease of 0.21+/-0.03 dex
between the local value and the value at z=0.77 in the 1e10-1e11 solar mass
range. We use the metallicity evolution to estimate the gas mass of the
galaxies, which we compare with the galactic stellar mass assembly and star
formation histories. Overall, our measurements are consistent with a galaxy
evolution process dominated by episodic bursts of star formation and where star
formation in the most massive galaxies (>1e11 solar masses) ceases at z<1.5
because of gas starvation. (Abstract abridged)Comment: 48 pages, Accepted by the Astrophysical Journa
The Oxygen Abundance of Nearby Galaxies from Sloan Digital Sky Survey Spectra
We have derived the oxygen abundance for a sample of nearby galaxies in the
Data Release 5 of the Sloan Digital Sky Survey (SDSS) which possess at least
two independent spectra of one or several HII regions with a detected
[OIII]4363 auroral line. Since, for nearby galaxies, the [OII]3727 nebular line
is out of the observed wavelength range, we propose a method to derive (O/H)_ff
abundances using the classic Te method coupled with the ff relation. (O/H)_7325
abundances have also been determined, based on the [OII]7320,7330 line
intensities, and using a small modification of the standard Te method. The
(O/H)_ff and (O/H)_7325 abundances have been derived with both the one- and
two-dimensional t_2 - t_3 relations. It was found that the (O/H)_ff abundances
derived with the parametric two-dimensional t_2 - t_3 relation are most
reliable. Oxygen abundances have been determined in 29 nearby galaxies, based
on 84 individual abundance determinations in HII regions. Because of our
selection methods, the metallicity of our galaxies lies in the narrow range 8.2
< 12 + log (O/H) < 8.4. The radial distribution of oxygen abundances in the
disk of the spiral galaxy NGC 4490 is determined for the first time.Comment: 39 pages, 10 figures, 4 tables, accepted for publication in the
Astrophysical Journa
Stellar and gaseous abundances in M82
The near infrared (IR) absorption spectra of starburst galaxies show several
atomic and molecular lines from red supergiants which can be used to infer
reliable stellar abundances. The metals locked in stars give a picture of the
galaxy metallicity prior to the last burst of star formation. The enrichment of
the new generation of stars born in the last burst can be traced by measuring
the hot gas in the X-rays. For the first time detailed stellar abundances in
the nuclear region of the starburst galaxy M82 have been obtained. They are
compared with those of the hot gas as derived from an accurate re-analysis of
the XMM and Chandra nuclear X-ray spectra. The cool stars and the hot gas
suggest [Fe/H]=-0.35+/-0.2 dex, and an overall [Si,Mg/Fe] enhancement by 0.4
and 0.5 dex, respectively. This is consistent with a major chemical enrichment
by SNe II explosions in recursive bursts on short timescales. Oxygen is more
puzzling to interpret since it is enhanced by 0.3 dex in stars and depleted by
0.2 dex in the hot gas. None of the standard enrichment scenarios can fully
explain such a behavior when compared with the other alpha-elements.Comment: APJ, in pres
Evidence for Solar Metallicities in Massive Star-forming Galaxies at z>~2
We present results of near-IR spectroscopic measurements of 7 star-forming
galaxies at 2.1<z<2.5. Drawn from a large spectroscopic survey of galaxies
photometrically pre-selected by their U_nGR colors to lie at z~2, these
galaxies were chosen for their bright rest-frame optical luminosities
(K_s<=20.0). Most strikingly, the majority of the sample of 7 galaxies exhibit
[NII]/Ha nebular emission line ratios indicative of at least solar HII region
metallicities, at a lookback time of 10.5 Gyr. The broadband colors of the
K_s-bright sample indicate that most have been forming stars for more than a
Gyr at z~2, and have already formed stellar masses in excess of 10^11 Msun. The
descendants of these galaxies in the local universe are most likely metal-rich
and massive spiral and elliptical galaxies, while plausible progenitors for
them can be found among the population of z~3 Lyman Break Galaxies. While the
K_s-bright z~2 galaxies appear to be highly evolved systems, their large Ha
luminosities and uncorrected Ha star-formation rates of 24-60 Msun/yr indicate
that active star formation is still ongoing. The luminous UV-selected objects
presented here comprise more than half of the high-redshift (z>1.5) tails of
current K-band-selected samples such as the K20 and Gemini Deep Deep surveys.Comment: 15 pages including 5 figures. Accepted for publication in Ap
The oxygen abundance calibrations and N/O abundance ratios of ~40,000 SDSS star-forming galaxies
Using a large sample of 38,478 star-forming galaxies selected from the Second
Data Release of the Sloan Digital Sky Survey database (SDSS-DR2), we derive
analytical calibrations for oxygen abundances from several
metallicity-sensitive emission-line ratios: [N II]/H_alpha, [O III]/[N II], [N
II]/[O II], [N II]/[S II], [S II]/H_alpha, and [O III]/H_beta. This consistent
set of strong-line oxygen abundance calibrations will be useful for future
abundance studies. Among these calibrations, [N II]/[O II] is the best for
metal-rich galaxies due to its independence on ionization parameter and low
scatter. Dust extinction must be considered properly at first. These
calibrations are more suitable for metal-rich galaxies (8.4<12+log(O/H)<9.3),
and for the nuclear regions of galaxies. The observed relations are consistent
with those expected from the photoionization models of Kewley & Dopita (2002).
However, most of the observational data spread in a range of ionization
parameter q from 1*10^7 to 8*10^7 cm s^{-1}, corresponding to logU= -3.5 to
-2.5, narrower than that suggested by the models. We also estimate the (N/O)
abundance ratios of this large sample of galaxies, and these are consistent
with the combination of a "primary" and a dominant "secondary" components of
nitrogen.Comment: 17 pages, 10 figures, 1 table. ApJ in pres
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