350,517 research outputs found
A practical experience with independent verification and validation
One approach to reducing software cost and increasing reliability is the use of an independent verification and validation (IV & V) methodology. The Software Engineering Laboratory (SEL) applied the IV & V methodology to two medium-size flight dynamics software development projects. Then, to measure the effectiveness of the IV & V approach, the SEL compared these two projects with two similar past projects, using measures like productivity, reliability, and maintain ablilty. Results indicated that the use of the IV & V methodology did not help the overall process nor improve the product in these cases
Leo IV & V - A possible dwarf galaxy pair ?
The last few years have seen the discovery of many faint and ultra-faint
dwarf spheroidal galaxies around the Milky Way. Among these is a pair of
satellites called Leo IV and Leo V. This pair is found at large distances from
the Milky Way (154 and 175 kpc respectively). The rather small difference in
radial distance, and the fact that they also show a close projected distance on
the sky, has led to the idea that we might be seeing a new pair of bound
galaxies - like the Magellanic Clouds. In this paper we investigate this
speculation by means of a simple integration code (confirming the results with
full N-body simulations). As the luminous mass of both faint dwarfs is far too
low to allow them to be bound, we simulate the pair assuming extended dark
matter haloes. Our results show that the minimum dark matter mass required for
the pair to be bound is rather high - ranging from 1.6 x 10^10 Msun to 5.4 x
10^10 Msun (within the virial radii). Computing the mass of dark matter within
a commonly adopted radius of 300 pc shows that our models are well within the
predicted range of dark matter content for satellites so faint. We therefore
conclude that it could be possible that the two galaxies constitute a bound
pair.Comment: 7 pages, 3 figures, accepted by A&
Modeling usual and unusual anisotropic spheres
In this paper, we study anisotropic spheres built from known static spherical
solutions. In particular, we are interested in the physical consequences of a
"small" departure from a physically sensible configuration. The obtained
solutions smoothly depend on free parameters. By setting these parameters to
zero, the starting seed solution is regained. We apply our procedure in detail
by taking as seed solutions the Florides metrics, and the Tolman IV solution.
We show that the chosen Tolman IV, and also Heint IIa Durg IV,V perfect fluid
solutions, can be used to generate a class of parametric solutions where the
anisotropic factor has features recalling boson stars. This is an indication
that boson stars could emerge by "perturbing" appropriately a perfect fluid
solution (at least for the seed metrics considered). Finally, starting with
Tolman IV, Heint IIa and Durg IV,V solutions, we build anisotropic
gravastar-like sources with the appropriate boundary conditions.Comment: Final version published in IJMP
Soft X-ray resonant scattering study of single-crystal LaSrMnO
Soft X-ray resonant scattering studies at the Mn - and
the La - edges of single-crystal LaSrMnO are
reported. At low temperatures, below K, energy scans
with a fixed momentum transfer at the \emph{A}-type antiferromagnetic (0 0 1)
reflection around the Mn -edges with incident linear
and polarizations show strong resonant enhancements. The
splitting of the energy spectra around the Mn -edges may
indicate the presence of a mixed valence state, e.g., Mn/Mn. The
relative intensities of the resonance and the clear shoulder-feature as well as
the strong incident and polarization dependences strongly
indicate its complex electronic origin. Unexpected enhancement of the charge
Bragg (0 0 2) reflection at the La -edges with
polarization has been observed up to 300 K, with an anomaly appearing around
the orbital-ordering transition temperature, K,
suggesting a strong coupling (competition) between them.Comment: Accepted by European Physical Journal
- …