197 research outputs found
NIMASTEP: a software to modelize, study and analyze the dynamics of various small objects orbiting specific bodies
NIMASTEP is a dedicated numerical software developed by us, which allows one
to integrate the osculating motion (using cartesian coordinates) in a Newtonian
approach of an object considered as a point-mass orbiting a homogeneous central
body that rotates with a constant rate around its axis of smallest inertia. The
code can be applied to objects such as particles, artificial or natural
satellites or space debris. The central body can be either any terrestrial
planet of the solar system, any dwarf-planet, or even an asteroid. In addition,
very many perturbations can be taken into account, such as the combined
third-body attraction of the Sun, the Moon, or the planets, the direct solar
radiation pressure (with the central body shadow), the non-homogeneous
gravitational field caused by the non-sphericity of the central body, and even
some thrust forces. The simulations were performed using different integration
algorithms. Two additional tools were integrated in the software package; the
indicator of chaos MEGNO and the frequency analysis NAFF. NIMASTEP is designed
in a flexible modular style and allows one to (de)select very many options
without compromising the performance. It also allows one to easily add other
possibilities of use. The code has been validated through several tests such as
comparisons with numerical integrations made with other softwares or with
semi-analytical and analytical studies. The various possibilities of NIMASTEP
are described and explained and some tests of astrophysical interest are
presented. At present, the code is proprietary but it will be released for use
by the community in the near future. Information for contacting its authors and
(in the near future) for obtaining the software are available on the web site
http://www.fundp.ac.be/en/research/projects/page_view/10278201/Comment: Astronomy & Astrophysics - Received: 25 November 2011 / Accepted: 27
February 2012 -- 14 pages, 4 figure
Fine structure of excitons in CuO
Three experimental observations on 1s-excitons in CuO are not consistent
with the picture of the exciton as a simple hydrogenic bound state: the
energies of the 1s-excitons deviate from the Rydberg formula, the total exciton
mass exceeds the sum of the electron and hole effective masses, and the
triplet-state excitons lie above the singlet. Incorporating the band structure
of the material, we calculate the corrections to this simple picture arising
from the fact that the exciton Bohr radius is comparable to the lattice
constant. By means of a self-consistent variational calculation of the total
exciton mass as well as the ground-state energy of the singlet and the
triplet-state excitons, we find excellent agreement with experiment.Comment: Revised abstract; 10 pages, revtex, 3 figures available from G.
Kavoulakis, Physics Department, University of Illinois, Urban
BiVO4 based high k microwave dielectric materials: a review
The BiVO4material has attracted much attention in recent years due to its active photocatalytic properties under visible light, bright yellow color as a nontoxic pigment, and its high relative permittivity (ϵr) and Qf (quality factor, Q × resonant frequency, f) as a potential microwave dielectric ceramic. In this review, we introduce the origin, synthesis, crystal structure and phase transitions of the four polymorphic phases of BiVO4: orthorhombic (pucherite), zircon (dreyerite), scheelite monoclinic (clinobisvanite) and scheelite tetragonal. We then precis recent studies on doped BiVO4ceramics in terms of A site, B site and A/B site complex substitutions. Low sintering temperature (<800 °C) and high ϵrvalues could be obtained in some solid solution ceramics and near zero temperature coefficient of resonant frequency (TCF/τf) values could be achieved in layered or granulated particle composite ceramics. Besides, a series of temperature stable high ϵrmicrowave dielectric ceramics can also be obtained for many co-fired composite ceramics, such as BiVO4-TiO2, and BiVO4-TiO2-Bi2Ti4O11. The high ϵr, high Qf value, low sintering temperature and chemical compatibility with some base metals suggest that BiVO4-based materials are strong candidates for both LTCC and other microwave device applications in current 4G and future 5G technologies
The shepherd of Hermas and The gospel of truth of Valentinus : two early Christian perspectives on salvation
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