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Modelling Martian dust storms: feedbacks between dust and atmospheric circulation at a hierarchy of scales
We employ numerical models of Mars at spatial scales ranging from global to a few metres in order to investigate both the impact of increasing dust loading on atmospheric circulations and the role of different atmospheric circulation components on dust lifting, transport and on dust storm decay
Analytical computation of the off-axis Effective Area of grazing incidence X-ray mirrors
Focusing mirrors for X-ray telescopes in grazing incidence, introduced in the
70s, are characterized in terms of their performance by their imaging quality
and effective area, which in turn determines their sensitivity. Even though the
on-axis effective area is assumed in general to characterize the collecting
power of an X-ray optic, the telescope capability of imaging extended X-ray
sources is also determined by the variation in its effective area with the
off-axis angle. [...] The complex task of designing optics for future X-ray
telescopes entails detailed computations of both imaging quality and effective
area on- and off-axis. Because of their apparent complexity, both aspects have
been, so far, treated by using ray-tracing routines aimed at simulating the
interaction of X-ray photons with the reflecting surfaces of a given focusing
system. Although this approach has been widely exploited and proven to be
effective, it would also be attractive to regard the same problem from an
analytical viewpoint, to assess an optical design of an X-ray optical module
with a simpler calculation than a ray-tracing routine. [...] We have developed
useful analytical formulae for the off-axis effective area of a
double-reflection mirror in the double cone approximation, requiring only an
integration and the standard routines to calculate the X-ray coating
reflectivity for a given incidence angle. [...] Algebraic expressions are
provided for the mirror geometric area, as a function of the off-axis angle.
Finally, the results of the analytical computations presented here are
validated by comparison with the corresponding predictions of a ray-tracing
code.Comment: 12 pages, 11 figures, accepted for publication in "Astronomy &
Astrophysics", section "Instruments, observational techniques, and data
processing". Updated version after grammatical revision and typos correctio
Surface smoothness requirements for the mirrors of the IXO X-ray telescope
The International X-ray Observatory (IXO) is a very ambitious mission, aimed
at the X-ray observation of the early Universe. This makes IXO extremely
demanding in terms of effective area and angular resolution. In particular, the
HEW requirement below 10 keV is 5 arcsec Half-Energy Width (HEW). At higher
photon energies, the HEW is expected to increase, and the angular resolution to
be correspondingly degraded, due to the increasing relevance of the X-ray
scattering off the reflecting surfaces. Therefore, the HEW up to 40 keV is
required to be better than 30 arcsec, even though the IXO goal is to achieve an
angular resolution as close as possible to 5 arcsec also at this energy. To
this end, the roughness of the reflecting surfaces has to not exceed a
tolerance, expressed in terms of a surface roughness PSD
(Power-Spectral-Density). In this work we provide such tolerances by simulating
the HEW scattering term for IXO, assuming a specific configuration for the
optical module and different hypotheses on the PSD of mirrors
Chemical characterization and economic evaluation of the coal fly ash pre-washing and carbonation process
In the present laboratory-scale study, the combination of washing and carbonation processes was examined to evaluate the feasibility to reduce the environmental impact of coal power plants. Three different washing solutions (tap, distilled and sea water) were used to pre-treat coal fly ash and the corresponding effect on direct gas-solid carbonation and final metal leaching was evaluated. Finally, a preliminary economic evaluation of the process was performed. In terms of captured CO2, the results have shown that significant amounts can be captured, although, as expected, the leaching of soluble salts in water such as Ca and Mg reduce the CO2 uptake. In terms of heavy metal's leaching, the application of pre-washing and carbonation treatment significantly affected the metal immobilization on the final residue. The pre-washing with sea water allowed to reach a sensible improvement since only selenium, chlorides and sulphates resulted outside the range for disposing of the carbonated residue in landfill for non-hazardous waste
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