1,729 research outputs found
Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX
Direct sampling of neutral interstellar (NIS) atoms by the Interstellar
Boundary Explorer (IBEX) can potentially provide a complementary method for
studying element abundances in the Local Interstellar Cloud and processes in
the heliosphere interface.}{We set the stage for abundance-aimed in-depth
analysis of measurements of NIS He, Ne, and O by IBEX and determine systematic
differences between abundances derived from various calculation methods and
their uncertainties.}{Using a model of ionization rates of the NIS species in
the heliosphere, based on independent measurements of the solar wind and solar
EUV radiation, we develop a time-dependent method of calculating the survival
probabilities of NIS atoms from the termination shock (TS) of the solar wind to
IBEX. With them, we calculate densities of these species along the Earth's
orbit and simulate the fluxes of NIS species as observed by IBEX. We study
pairwise ratios of survival probabilities, densities and fluxes of NIS species
at IBEX to calculate correction factors for inferring the abundances at
TS.}{The analytic method to calculate the survival probabilities gives
acceptable results only for He and Ne during low solar activity. For the
remaining portions of the solar cycle, and at all times for O, a fully time
dependent model should be used. Electron impact ionization is surprisingly
important for NIS O. Interpreting the IBEX observations using the time
dependent model yields the LIC Ne/O abundance of . The uncertainty
is mostly due to uncertainties in the ionization rates and in the NIS gas flow
vector.}{The Ne/He, O/He and Ne/O ratios for survival probabilities, local
densities, and fluxes scaled to TS systematically differ and thus an analysis
based only on survival probabilities or densities is not recommended, except
the Ne/O abundance for observations at low solar activity.Comment: Astronomy & Astrophysics, in press. Language and editing corrections
implemente
Chemical approaches to carbon dioxide utilization for manned Mars missions
Use of resources available in situ is a critical enabling technology for a permanent human presence in space. A permanent presence on Mars, e.g., requires a large infrastructure to sustain life under hostile conditions. As a resource on Mars, atmospheric CO2 is as follows: abundant; available at all points on the surface; of known presence; chemically simple; and can be obtained by simple compression. Many studies focus on obtaining O2 and the various uses for O2 including life support and fuel; discussion of CO, the coproduct from CO2 fixation revolves around its uses as a fuel, being oxidized back to CO2. Several new proposals are studied for CO2 fixation through chemical, photochemical, and photoelectrochemical means. For example, the reduction of CO2 to hydrocarbons such as acetylene (C2H2) can be accomplished with H2. C2H2 has a theoretical vacuum specific impulse of approx. 375 secs. Potential uses were also studied of CO2, as obtained or further reduced to carbon, as a reducing agent in metal oxide processing to form metals or metal carbides for use as structural or power materials; the CO2 can be recycled to generate O2 and CO
Simulation of EAS properties on the basis of high energy interaction model deduced from the accelerator data
Calculations of extensive air showers in atmosphere were performed using formulae describing p-p and p-air nucleus interactions. The formulae fitted to the accelerator data were extrapolated taking the same trend up to 10 to the 16 eV. Above that energy it was assumed that the degree of scaling violating/alpha-parameter/ is saturating or even decreasing. The latter assumption follows from earlier work where it was found that without this restriction shower maxima at the highest energies are located too high in the atmosphere. Results of calculations have been compared with experimental data. The comparison was made separately for the curves obtained from the so called equal intensity cuts and for the Cerenkov data
- …