24,060 research outputs found
Effect of interaction strength on the evolution of cooperation
Cooperative behaviors are ubiquitous in nature,which is a puzzle to
evolutionary biology,because the defector always gains more benefit than the
cooperator,thus,the cooperator should decrease and vanish over time.This
typical "prisoners' dilemma" phenomenon has been widely researched in recent
years.The interaction strength between cooperators and defectors is introduced
in this paper(in human society,it can be understood as the tolerance of
cooperators).We find that only when the maximum interaction strength is between
two critical values,the cooperator and defector can coexist,otherwise, 1) if it
is greater than the upper value,the cooperator will vanish, 2) if it is less
than the lower value,a bistable state will appear
Secure Transmission to the Strong User with Optimal Power Allocation in NOMA
With non-orthogonal multiple access(NOMA), we tackle the maximization of the
secrecy rate for the strong user subject to a maximum allowable secrecy outage
probability, while guaranteeing a constraint on the transmission rate to the
weak user. For the first time, the dependence between the eavesdropper's
ability to conduct successive interference cancellation and her channel quality
is considered. We determine the optimal power allocation and the redundancy
rate, based on which the cost of security in terms of the reduction in the
strong user's secrecy rate is examined and the benefits of NOMA for secure
transmissions are explicitly revealed
On the minimal affinizations over the quantum affine algebras of type
In this paper, we study the minimal affinizations over the quantum affine
algebras of type by using the theory of cluster algebras. We show that
the -characters of a large family of minimal affinizations of type
satisfy some systems of equations. These equations correspond to mutation
equations of some cluster algebras. Furthermore, we show that the minimal
affinizations in these equations correspond to cluster variables in these
cluster algebras.Comment: arXiv admin note: substantial text overlap with arXiv:1501.00146,
arXiv:1502.0242
Upper bounds for bar visibility of subgraphs and n-vertex graphs
A -bar visibility representation of a graph assigns each vertex up to
horizontal bars in the plane so that two vertices are adjacent if and only if
some bar for one vertex can see some bar for the other via an unobstructed
vertical channel of positive width. The least such that has a -bar
visibility representation is the bar visibility number of , denoted by
. We show that if is a spanning subgraph of , then . It follows that when is an -vertex
graph. This improves the upper bound obtained by Chang et al. (SIAM J. Discrete
Math. 18 (2004) 462).Comment: 6 pages,1 figur
Beamforming Design and Power Allocation for Secure Transmission with NOMA
In this work, we propose a novel beamforming design to enhance physical layer
security of a non-orthogonal multiple access (NOMA) system with the aid of
artificial noise (AN). The proposed design uses two scalars to balance the
useful signal strength and interference at the strong and weak users, which is
a generalized version of the existing beamforming designs in the context of
physical layer security for NOMA. We determine the optimal power allocation
among useful signals and AN together with the two optimal beamforming scalars
in order to maximize the secrecy sum rate (SSR). Our asymptotic analysis in the
high signal-to-noise ratio regime provides an efficient and near-optimal
solution to optimizing the beamforming scalars and power allocation
coefficients. Our analysis indicates that it is not optimal to form a beam
towards either the strong user or the weak user in NOMA systems for security
enhancement. In addition, the asymptotically optimal power allocation informs
that, as the transmit power increases, more power should be allocated to the
weak user or AN signals, while the power allocated to the strong user keeps
constant. Our examination shows that the proposed novel beamforming design can
significantly outperform two benchmark schemes
On groups all of whose Haar graphs are Cayley graphs
A Cayley graph of a group is a finite simple graph such that
contains a subgroup isomorphic to acting regularly on
, while a Haar graph of is a finite simple bipartite graph
such that contains a subgroup isomorphic to
acting semiregularly on and the -orbits are equal to the
bipartite sets of . A Cayley graph is a Haar graph exactly when it is
bipartite, but no simple condition is known for a Haar graph to be a Cayley
graph. In this paper, we show that the groups and
are the only finite inner abelian groups all of whose Haar graphs are
Cayley graphs (a group is called inner abelian if it is non-abelian, but all of
its proper subgroups are abelian). As an application, it is also shown that
every non-solvable group has a Haar graph which is not a Cayley graph.Comment: 17 page
Gate voltage controlled thermoelectric figure of merit in three-dimensional topological insulator nanowires
The thermoelectric properties of the surface states in three-dimensional
topological insulator nanowires are studied. The Seebeck coefficients and
the dimensionless thermoelectrical figure of merit are obtained by using
the tight-binding Hamiltonian combining with the nonequilibrium Green's
function method. They are strongly dependent on the gate voltage and the
longitudinal and perpendicular magnetic fields. By changing the gate voltage or
magnetic fields, the values of and can be easily controlled. At the
zero magnetic fields and zero gate voltage, or at the large perpendicular
magnetic field and nonzero gate voltage, has the large value. Owing to the
electron-hole symmetry, is an odd function of the Fermi energy while
is an even function regardless of the magnetic fields. and show
peaks when the quantized transmission coefficient jumps from one plateau to
another. The highest peak appears while the Fermi energy is near the Dirac
point. At the zero perpendicular magnetic field and zero gate voltage, the
height of th peak of is and
for the longitudinal magnetic flux
and , respectively. Finally, we also study the
effect of disorder and find that and are robust against disorder. In
particular, the large value of can survive even if at the strong disorder.
These characteristics (that has the large value, is easily regulated, and
is robust against the disorder) are very beneficial for the application of the
thermoelectricity.Comment: 9 pages,10 figure
Energies and E1, M2 transition rates for Mo XXX
Based on relativistic wavefunctions from multiconfigurational
Dirac-Hartree-Fock (MCDHF) and configuration interaction calculations, energy
levels, radiative rates, and wavelengths are evaluated for all levels of
3s3p, 3s3p, 3s3d, 3p, 3s3p3d, 3p3d and 3s3d
configurations of Al-like Molybdenum ion (Mo XXX). Transition probabilities are
reported for E1 and M2 transitions from the ground level. The valence-valence
and core-valence correlation effects are accounted for in a systematic way.
Breit interactions and quantum electrodynamics effects are estimated in
subsequent relativistic configuration interaction calculations. Comparisons are
made with the available data in the literature and good agreement has been
found which confirms the reliability of our results.Comment: 13page
A nonlinear tracking algorithm with range-rate measurements based on unbiased measurement conversion
The three-dimensional CMKF-U with only position measurements is extended to
solve the nonlinear tracking problem with range-rate measurements in this
paper. A pseudo measurement is constructed by the product of range and
range-rate measurements to reduce the high nonlinearity of the range-rate
measurements with respect to the target state; then the mean and covariance of
the converted measurement errors are derived by the measurement conditioned
method, showing better consistency than the transitional nested conditioning
method; finally, the sequential filter was used to process the converted
position and range-rate measurements sequentially to reduce the approximation
error in the second-order EKF. Monte Carlo simulations show that the
performance of the new tracking algorithm is better than the traditional one
based on CMKF-D
Arc-transitive cyclic and dihedral covers of pentavalent symmetric graphs of order twice a prime
A regular cover of a connected graph is called {\em cyclic} or {\em dihedral}
if its transformation group is cyclic or dihedral respectively, and {\em
arc-transitive} (or {\em symmetric}) if the fibre-preserving automorphism
subgroup acts arc-transitively on the regular cover. In this paper, we give a
classification of arc-transitive cyclic and dihedral covers of a connected
pentavalent symmetric graph of order twice a prime. All those covers are
explicitly constructed as Cayley graphs on some groups, and their full
automorphism groups are determined
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