37,664 research outputs found
Impact of Power Allocation and Antenna Directivity in the Capacity of a Multiuser Cognitive Ad Hoc Network
This paper studies the benefits that power control and antenna directivity can bring to the capacity of a multiuser cognitive radio network. The main objective is to optimize the secondary network sum rate under the capacity constraint of the primary network. Exploiting location awareness, antenna directivity, and the power control capability, the cognitive radio ad hoc network can broaden its coverage and improve capacity. Computer simulations show that by employing the proposed method the system performance is significantly enhanced compared to conventional fixed power allocation
Constraining non-minimally coupled tachyon fields by Noether symmetry
A model for a spatially flat homogeneous and isotropic Universe whose
gravitational sources are a pressureless matter field and a tachyon field
non-minimally coupled to the gravitational field is analyzed. Noether symmetry
is used to find the expressions for the potential density and for the coupling
function, and it is shown that both must be exponential functions of the
tachyon field. Two cosmological solutions are investigated: (i) for the early
Universe whose only source of the gravitational field is a non-minimally
coupled tachyon field which behaves as an inflaton and leads to an exponential
accelerated expansion and (ii) for the late Universe whose gravitational
sources are a pressureless matter field and a non-minimally coupled tachyon
field which plays the role of dark energy and is the responsible of the
decelerated-accelerated transition period.Comment: 11 pages, 5 figures. Version accepted for publication in Classical
and Quantum Gravit
Crystallization, data collection and data processing of maltose-binding protein (MalE) from the phytopathogen Xanthomonas axonopodis pv. citri
Maltose-binding protein is the periplasmic component of the ABC transporter
responsible for the uptake of maltose/maltodextrins. The Xanthomonas axonopodis
pv. citri maltose-binding protein MalE has been crystallized at 293 Kusing
the hanging-drop vapour-diffusion method. The crystal belonged to the
primitive hexagonal space group P6_122, with unit-cell parameters a = 123.59,
b = 123.59, c = 304.20 Å, and contained two molecules in the asymetric unit. It
diffracted to 2.24 Å resolution
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