11,825 research outputs found
Advanced EVA system design requirements study
The results are presented of a study to identify specific criteria regarding space station extravehicular activity system (EVAS) hardware requirements. Key EVA design issues include maintainability, technology readiness, LSS volume vs. EVA time available, suit pressure/cabin pressure relationship and productivity effects, crew autonomy, integration of EVA as a program resource, and standardization of task interfaces. A variety of DOD EVA systems issues were taken into consideration. Recommendations include: (1) crew limitations, not hardware limitations; (2) capability to perform all of 15 generic missions; (3) 90 days on-orbit maintainability with 50 percent duty cycle as minimum; and (4) use by payload sponsors of JSC document 10615A plus a Generic Tool Kit and Specialized Tool Kit description. EVA baseline design requirements and criteria, including requirements of various subsystems, are outlined. Space station/EVA system interface requirements and EVA accommodations are discussed in the areas of atmosphere composition and pressure, communications, data management, logistics, safe haven, SS exterior and interior requirements, and SS airlock
Upper limits on the luminosity of the progenitor of type Ia supernova SN2014J
We analysed archival data of Chandra pre-explosion observations of the
position of SN2014J in M82. No X-ray source at this position was detected in
the data, and we calculated upper limits on the luminosities of the progenitor.
These upper limits allow us to firmly rule out an unobscured supersoft X-ray
source progenitor with a photospheric radius comparable to the radius of white
dwarf near the Chandrasekhar mass (~1.38 M_sun) and mass accretion rate in the
interval where stable nuclear burning can occur. However, due to a relatively
large hydrogen column density implied by optical observations of the supernova,
we cannot exclude a supersoft source with lower temperatures, kT < 80 eV. We
find that the supernova is located in the centre of a large structure of soft
diffuse emission, about 200 pc across. The mass, ~3x10^4 M_sun and short
cooling time of the gas, tau_cool ~ 8 Myrs, suggest that it is a
supernova-inflated super-bubble, associated with the region of recent star
formation. If SN2014J is indeed located inside the bubble, it likely belongs to
the prompt population of type Ia supernovae, with a delay time as short as ~ 50
Myrs. Finally, we analysed the one existing post-supernova Chandra observation
and placed upper limit of ~ (1-2) 10^37 erg/s on the X-ray luminosity of the
supernova itself.Comment: 8 pages, 6 figure
Advanced EVA system design requirements study: EVAS/space station system interface requirements
The definition of the Extravehicular Activity (EVA) systems interface requirements and accomodations for effective integration of a production EVA capability into the space station are contained. A description of the EVA systems for which the space station must provide the various interfaces and accomodations are provided. The discussion and analyses of the various space station areas in which the EVA interfaces are required and/or from which implications for EVA system design requirements are derived, are included. The rationale is provided for all EVAS mechanical, fluid, electrical, communications, and data system interfaces as well as exterior and interior requirements necessary to facilitate EVA operations. Results of the studies supporting these discussions are presented in the appendix
Interstellar H^+_3: possible detection of the 1_(10)→1_(11) transition of H_2D^+
An interstellar line has been detected in emission at the expected submillimeter wavelength of the 1_(10)→1_(11) transition of H_(2)D^+, the deuterated version of the primary ion (H^(+)_(3)) in the favored ion-molecule reaction scheme for interstellar gas phase chemistry. The strength of the line is in approximate agreement with the theoretically anticipated H_(2)D^+ abundance
Soft x-ray spectroscopy measurements of the p-like density of states of B in MgB2 and evidence for surface boron oxides on exposed surfaces
Soft X-ray absorption and fluorescence measurements are reported for the
K-edge of B in MgB2. The measurements confirm a high density of B
pxy(sigma)-states at the Fermi edge and extending to approximately 0.9 eV above
the edge. A strong resonance is observed in elastic scattering through a
core-exciton derived from out-of-plane pz(pi*)-states. Another strong
resonance, observed in both elastic and inelastic spectra, is identified as a
product of surface boron oxides.Comment: 7 pages total, 4 figures, submitted to Phys. Rev. Let
Airborne measurements of cloud-forming nuclei and aerosol particles in stabilized ground clouds produced by solid rocket booster firings
Airborne measurements of cloud volumes, ice nuclei and cloud condensation nuclei, liquid particles, and aerosol particles were obtained from stabilized ground clouds (SGCs) produced by Titan 3 launches at Kennedy Space Center, 20 August and 5 September 1977. The SGCs were bright, white, cumulus clouds early in their life and contained up to 3.5 g/m3 of liquid in micron to millimeter size droplets. The measured cloud volumes were 40 to 60 cu km five hours after launch. The SGCs contained high concentrations of cloud condensation nuclei active at 0.2%, 0.5%, and 1.0% supersaturation for periods of three to five hours. The SGCs also contained high concentrations of submicron particles. Three modes existed in the particle population: a 0.05 to 0.1 micron mode composed of aluminum-containing particles, a 0.2 to 0.8 micron mode, and a 2.0 to 10 micron mode composed of particles that contained primarily aluminum
Galaxy Formation with local photoionisation feedback I. Methods
We present a first study of the effect of local photoionising radiation on
gas cooling in smoothed particle hydrodynamics simulations of galaxy formation.
We explore the combined effect of ionising radiation from young and old stellar
populations. The method computes the effect of multiple radiative sources using
the same tree algorithm used for gravity, so it is computationally efficient
and well resolved. The method foregoes calculating absorption and scattering in
favour of a constant escape fraction for young stars to keep the calculation
efficient enough to simulate the entire evolution of a galaxy in a cosmological
context to the present day. This allows us to quantify the effect of the local
photoionisation feedback through the whole history of a galaxy`s formation. The
simulation of a Milky Way like galaxy using the local photoionisation model
forms ~ 40 % less stars than a simulation that only includes a standard uniform
background UV field. The local photoionisation model decreases star formation
by increasing the cooling time of the gas in the halo and increasing the
equilibrium temperature of dense gas in the disc. Coupling the local radiation
field to gas cooling from the halo provides a preventive feedback mechanism
which keeps the central disc light and produces slowly rising rotation curves
without resorting to extreme feedback mechanisms. These preliminary results
indicate that the effect of local photoionising sources is significant and
should not be ignored in models of galaxy formation.Comment: Accepted for Publication in MNRAS, 13 pages, 13 figure
Dynamics Of Australian Dairy-Food Supply Chain: Strategic Options For Participants In A Deregulated Environment
Following deregulation, participants in Australian dairy-food supply chains are confronted with a more complex and rapidly changing environment. In a study conducted between March 2002 and April 2003, major supermarkets emerged as the dominant power in chain development, with a trend towards greater interdependence and coordination between the chain participants. Future supply chain development will depend on the capabilities of the chain participants in operational and strategic management within the firm, and also in successfully negotiating linkages within the chains. In addition the organizational structures of both the firms and the chains need to be responsive to changing end-user needs and the dynamic business environment
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