97 research outputs found
Population adaptation for genetic algorithm-based cognitive radios
Abstract — Genetic algorithms are best suited for optimization problems involving large search spaces. The problem space encountered when optimizing the transmission parameters of an agile or cognitive radio for a given wireless environment and set of performance objectives can become prohibitively large due to the high number of parameters and their many possible values. Recent research has demonstrated that genetic algorithms are a viable implementation technique for cognitive radio engines. However, the time required for the genetic algorithms to come to a solution substantionally increases as the system complexity grows. In this paper, we present a population adaptation technique for genetic algorithms that takes advantage of the information from previous cognition cycles in order to reduce the time required to reach an optimal decision. Our simulation results demonstrate that the amount of information from the previous cognition cycle can be determined from the environmental variation factor (EVF), which represents the amount of change in the environment parameters since the previous cognition cycle. I
Antimagnetic rotation and sudden change of electric quadrupole transition strength in 143Eu
Lifetimes of the states in the quadrupole structure in 143Eu have been
measured using the Doppler shift attenuation method as well as parity of the
states in the sequence has been firmly identified from polarization measurement
using the Indian National Gamma Array. The decreasing trends of the deduced
quadrupole transition strength B(E2) with spin, along with increasing J (2)
/B(E2) values before band crossing, conclusively establish the origin of these
states as arising out of antimagnetic rotation. The abrupt increase in the
B(E2) values after the band crossing in the quadrupole band, a novel feature
observed in the present experiment, may indicates the crossing of different
shears configurations resulting in re-opening of shears structure. The results
are well reproduced by numerical calculation within the framework of
semi-classical geometric model.Comment: 6 pages, 4 postscript figure
Effect of neutron alignments on the structure of Tl 197
The excited states of 197Tl have been studied via 19 Au(4He, 4n)197 Tl reaction at a beam energy of 50 MeV from the K-130 cyclotron at the Variable Energy Cyclotron Centre (VECC). The γ rays were detected using the VECC array for Nuclear Spectroscopy (VENUS) with six Compton-suppressed clover HPGe detectors. An improved level scheme of
197
Tl has been proposed from this work, which has been extended to 5.1 MeV of excitation energy and 39/2
ℏ of spin from the placement of 28 new γ-ray transitions. Band crossings in the known one- and three-quasiparticle (qp) bands have been identified for the first time in this work. Two new bands, based on 3-qp and 5-qp configurations, have been observed for the first time in this nucleus; both of which are identified as the magnetic rotational (MR) in nature. The excitation energies of these bands are similar to that of the doubly degenerate bands observed for the similar 3-qp and 5-qp configurations in
195 Tl. These indicate a transition from an aplanar geometry of the neutron, proton, and the core angular momentum vectors to a planar one for neutron number
N≥116 in Tl isotopes. The total Routhian surface calculations suggest a change in shape from oblate for the 1-qp configuration to a near-spherical one for the 3- and 5-qp configurations. This is consistent with the observed MR nature of the bands with multi-qp configuration. The MR bands are well reproduced by a model calculations in the frame work of the shears mechanism with the principal axis cranking.One of the authors (H.P.) is grateful
for the support from the Ramanujan Fellowship Research
Grant under SERB-DST Grant No. SB/S2/RJN-031/2016
Shape evolution in the rapidly rotating Gd nucleus
Ground state band of Gd has been investigated following their
population in the Sn(Cl,~p2n)Gd reaction at 195
MeV of beam energy using a large array of Compton suppressed HPGe clovers as
the detection setup. Apart from other spectroscopic measurements, level
lifetimes of the states have been extracted using the Doppler Shift Attenuation
Method. Extracted quadrupole moment along with the pairing independent cranked
Nilsson-Strutinsky model calculations for the quadrupole band reveal that the
nucleus preferably attains triaxiality with = -30. The
calculation though shows a slight possibility of rotation around the longest
possible principal axis at high spin 30 which is beyond the scope
of the present experiment
Measurements and Analysis of Secondary User Device Effects on Digital Television Receivers
This is the published version. Copyright © 2009 Newman et al.This article presents results from a study of the potential effects of secondary users operating in unoccupied television spectrum. Television spectrum is known within the wireless communications community as being underutilized, making it a prime candidate for dynamic spectrum access. The proposed use of this open spectrum has prompted questions concerning the quantity of available channel space that could be used without negative impact on consumers who view digital television broadcasts and the viability of secondary use of open channels immediately adjacent to a digital television broadcast channel. In this work, we investigate secondary device operation in the channels directly adjacent to a desired television channel, and the effects upon a selection of consumer digital television (DTV) receivers. Our observations strongly suggest that secondary users could operate "White Space Devices" (WSDs) in unoccupied channel bandwidth directly adjacent to a desired digital television (DTV) channel, with no observable adverse impact upon the reception of the desired channel content
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