7,638 research outputs found
Tripropellant engine study
The potential for converting the space shuttle main engine (SSME) to a dual-fuel, dual-mode engine using LOX/hydrocarbon propellants in mode 1 and LOX/H2 in mode 2 was examined. Various engine system concepts were formulated that included staged combustion and gas generator turbine power cycles, and LOX/RP-1, LOX/CH4, and LOX/C3H8 mode 1 propellants. Both oxidizer and fuel regenerative cooling were considered. All of the SSME major components were examined to determine their adaptability to the candidate dual-fuel engines
High-pressure LOX/CH4 injector program
Two injector types, either coaxial or impinging elements, for high pressure LOX/CH4 operation with an existing 40K chamber are examined. A comparison is presented. The detailed fabrication drawings and supporting analysis are presented
Deteriorative Influences Upon the Morale of the British 21st Army Group in the Shadow of Operation ‘Market Garden’.
Operation ‘Market Garden’ was initiated by Allied forces on the 17th September
1944, ending on the 25th of the same month. Up until that point of the Second World War, it
was the largest airborne landing to have ever been undertaken. The main aim of Operation
‘Market Garden’ was to open up an invasion route for the Allied forces into the north of
Germany from the Netherlands. In order to do this, the operation sought to capture and
cross a number of bridges over a series of rivers and canals, including the Rhine and the
Maas. The first part of this operation - ‘Market’ - involved the landing of paratroopers in
proximity to these bridges in order to capture and secure, awaiting part two of the
operation. ‘Garden’ involved the movement of heavier units from Belgium, up through the
Netherlands, relieving the units holding these bridges (See Source 0.01, 0.02, 0.03)
High-resolution Spectroscopy of Extremely Metal-poor Stars in the Least Evolved Galaxies: Leo IV
We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H] = –3.2, adding to the rapidly growing sample of extremely metal-poor (EMP) stars being identified in Milky Way satellite galaxies. The star is enhanced in the α elements Mg, Ca, and Ti by ~0.3 dex, very similar to the typical Milky Way halo abundance pattern. All of the light and iron-peak elements follow the trends established by EMP halo stars, but the neutron-capture elements Ba and Sr are significantly underabundant. These results are quite similar to those found for stars in the ultra-faint dwarfs Ursa Major II, Coma Berenices, Boötes I, and Hercules, suggesting that the chemical evolution of the lowest-luminosity galaxies may be universal. The abundance pattern we observe is consistent with predictions for nucleosynthesis from a Population III supernova explosion. The extremely low metallicity of this star also supports the idea that a significant fraction (≳10%) of the stars in the faintest dwarfs have metallicities below [Fe/H] = –3.0
Formation and structural characterization of Ni nanoparticles embedded in SiOâ‚‚
Face-centered cubic Ni nanoparticles were formed in SiOâ‚‚ by ion implantation and thermal annealing. Small-angle x-ray scattering in conjunction with transmission electron microscopy was used to determine the nanoparticle size as a function of annealing temperature, whereas the local atomic structure was measured with x-ray absorption spectroscopy. The influence of finite-size effects on the nanoparticle structural properties was readily apparent and included a decrease in coordination number and bond length and an increase in structural disorder for decreasing nanoparticle size. Such results are consistent with the non-negligible surface-to-volume ratio characteristic of nanoparticles. In addition, temperature-dependent x-ray absorption spectroscopy measurements showed the mean vibrational frequency (as obtained from the Einstein temperature) decreased with decreasing nanoparticle size. This reduction was attributed to the greater influence of the loosely bound, under-coordinated surface atoms prevailing over the effects of capillary pressure, the former enhancing the low frequency modes of the vibrational density of statesThis work was financially supported by the Australian
Synchrotron and the Australian Research Council with access to equipment provided by the Australian Nanofabrication
Facility
Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor
Current cosmological models indicate that the Milky Way's stellar halo was
assembled from many smaller systems. Based on the apparent absence of the most
metal-poor stars in present-day dwarf galaxies, recent studies claimed that the
true Galactic building blocks must have been vastly different from the
surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in
the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt
on this conclusion. However, verification of the iron-deficiency and
measurements of additional elements, such as the alpha-element Mg, are
mandatory for demonstrating that the same type of stars produced the metals
found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars
be conclusively linked to early stellar halo assembly. Here we report
high-resolution spectroscopic abundances for 11 elements in S1020549,
confirming the iron abundance of less than 1/4000th that of the Sun, and
showing that the overall abundance pattern mirrors that seen in low-metallicity
halo stars, including the alpha-elements. Such chemical similarity indicates
that the systems destroyed to form the halo billions of years ago were not
fundamentally different from the progenitors of present-day dwarfs, and
suggests that the early chemical enrichment of all galaxies may be nearly
identical.Comment: 16 pages, including 2 figures. Accepted for publication in Nature. It
is embargoed for discussion in the press until formal publication in Natur
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