29,318 research outputs found
Captures of Hot and Warm Sterile Antineutrino Dark Matter on EC-decaying Ho-163 Nuclei
Capturing low-energy electron antineutrinos on radioactive Ho-163 nuclei,
which decay into Dy-163 via electron capture (EC), is a noteworthy opportunity
to detect relic sterile antineutrinos. Such hypothetical particles are more or
less implied by current experimental and cosmological data, and they might be a
part of hot dark matter or a candidate for warm dark matter in the Universe.
Using the isotope Ho-163 as a target and assuming reasonable active-sterile
antineutrino mixing angles, we calculate the capture rate of relic electron
antineutrinos against the corresponding EC-decay background in the presence of
sterile antineutrinos at the sub-eV or keV mass scale. We show that the
signature of hot or warm sterile antineutrino dark matter should in principle
be observable, provided the target is big enough and the energy resolution is
good enough.Comment: 16 pages, 6 figures, more discussions and references added. To appear
in JCA
Multiple-Level Power Allocation Strategy for Secondary Users in Cognitive Radio Networks
In this paper, we propose a multiple-level power allocation strategy for the
secondary user (SU) in cognitive radio (CR) networks. Different from the
conventional strategies, where SU either stays silent or transmit with a
constant/binary power depending on the busy/idle status of the primary user
(PU), the proposed strategy allows SU to choose different power levels
according to a carefully designed function of the receiving energy. The way of
the power level selection is optimized to maximize the achievable rate of SU
under the constraints of average transmit power at SU and average interference
power at PU. Simulation results demonstrate that the proposed strategy can
significantly improve the performance of SU compared to the conventional
strategies.Comment: 12 page
Volume integrals associated with the inhomegeneous Helmholtz equation. Part 2: Cylindrical region; rectangular region
Results are presented for volume integrals associated with the Helmholtz operator, nabla(2) + alpha(2), for the cases of a finite cylindrical region and a region of rectangular parallelepiped. By using appropriate Taylor series expansions and multinomial theorem, these volume integrals are obtained in series form for regions r r' and r 4', where r and r' are distances from the origin to the point of observation and source, respectively. When the wave number approaches zero, the results reduce directly to the potentials of variable densities
On the propagation of plane waves above an impedance surface
The propagation of grazing incidence plane waves along a finite impedance boundary is investigated. A solution of the semi-infinite problem, where a harmonic motion, parallel to the boundary, is imposed along a line perpendicular to the boundary, is obtained. This solution consists of quasiplane waves, waves moving parallel to the boundary with amplitude and phase variations perpendicular to the boundary. Several approximations to the full solution are considered
Optimization of scale-free network for random failures
It has been found that the networks with scale-free distribution are very
resilient to random failures. The purpose of this work is to determine the
network design guideline which maximize the network robustness to random
failures with the average number of links per node of the network is constant.
The optimal value of the distribution exponent and the minimum connectivity to
different network size are given in this paper. Finally, the optimization
strategy how to improve the evolving network robustness is given.Comment: 6 pages, 1 figur
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