9,009 research outputs found
Resource Allocation for Secure Communications in Cooperative Cognitive Wireless Powered Communication Networks
We consider a cognitive wireless powered communication network (CWPCN)
sharing the spectrum with a primary network who faces security threats from
eavesdroppers (EAVs). We propose a new cooperative protocol for the wireless
powered secondary users (SU) to cooperate with the primary user (PU). In the
protocol, the SUs first harvest energy from the power signals transmitted by
the cognitive hybrid access point during the wireless power transfer (WPT)
phase, and then use the harvested energy to interfere with the EAVs and gain
transmission opportunities at the same time during the wireless information
transfer (WIT) phase. Taking the maximization of the SU ergodic rate as the
design objective, resource allocation algorithms based on the dual optimization
method and the block coordinate descent method are proposed for the cases of
perfect channel state information (CSI) and collusive/non-collusive EAVs under
the PU secrecy constraint. More PU favorable greedy algorithms aimed at
minimizing the PU secrecy outage probability are also proposed. We furthermore
consider the unknown EAVs' CSI case and propose an efficient algorithm to
improve the PU security performance. Extensive simulations show that our
proposed protocol and corresponding resource allocation algorithms can not only
let the SU gain transmission opportunities but also improve the PU security
performance even with unknown EAVs' CSI.Comment: Submitted to IEEE Systems Journal for possible publicatio
A Monge-Ampere Type Fully Nonlinear Equation on Hermitian Manifolds
We study a fully nonlinear equation of complex Monge-Ampere type on Hermitian
manifolds. We establish the a priori estimates for solutions of the equation up
to the second order derivatives with the help of a subsolution
Complex Monge-Ampere equations and totally real submanifolds
We study the Dirichlet problem for complex Monge-Ampere equations in
Hermitian manifolds with general (non-pseudoconvex) boundary. Our main result
extends the classical theorem of Caffarelli, Kohn, Nirenberg and Spruck in the
flat case. We also consider the equation on compact manifolds without boundary,
attempting to generalize Yau's theorems in the Kaehler case. As applications of
the main result we study some connections between the homogeneous complex
Monge-Ampere ({\em HCMA}) equation and totally real submanifolds, and a special
Dirichlet problem for the HCMA equation related to Donaldson's conjecture on
geodesics in the space of Kaehler metrics
The Dirichlet Problem for a Complex Monge-Ampere Type Equation on Hermitian Manifolds
We are concerned with fully nonlinear elliptic equations on complex manifolds
and search for technical tools to overcome difficulties in deriving a priori
estimates which arise due to the nontrivial torsion and curvature, as well as
the general (non-pseudoconvex) shape of the boundary. We present our methods,
which work for more general equations, by considering a specific equation which
resembles the complex Monge-Ampere equation in many ways but with crucial
differences. Our work is motivated by recent increasing interests in fully
nonlinear equations on complex manifolds from geometric problems.Comment: Revised version based on the referees' reports, we would like to
thank them for their helpful comment
Electromagnetic fields with electric and chiral magnetic conductivities in heavy ion collisions
We derive analytic formula for electric and magnetic fields produced by a
moving charged particle in a conducting medium with the electric conductivity
and the chiral magnetic conductivity . We use the Green
function method and assume that is much smaller than .
The compact algebraic expressions for electric and magnetic fields without any
integrals are obtained. They recover the Lienard-Wiechert formula at vanishing
conductivities. Exact numerical solutions are also found for any values of
and and are compared to analytic results. Both
numerical and analytic results agree very well for the scale of high energy
heavy ion collisions. The space-time profiles of electromagnetic fields in
non-central Au+Au collisions have been calculated based on these analytic
formula as well as exact numerical solutions.Comment: RevTex 4, 7 figures, 13 pages; section III-B has been re-written
using dimensionful variables to improve readability; added references and one
figur
Analytical Solution of Cross Polarization Dynamics
Cross polarization (CP) dynamics, which was remained unknown for five
decades, has been derived analytically in the zero- and double-quantum spaces.
The initial polarization in the double-quantum space is a constant of motion
under strong pulse condition (), while the
Hamiltonian in the zero-quantum space reduces to
under the Hartmann-Hahn match condition (). The time
dependent Hamilontian () in the zero-quantum space can
be expressed by average Hamiltonians. Since, only zero order average Hamiltonian needs to be
calculated, leading to an analytical solution of CP dynamics
Some rigidity results for complete manifolds with harmonic curvature
Let be an -dimensional complete Riemannian manifold
with harmonic curvature and positive Yamabe constant. Denote by and
the scalar curvature and the trace-free Riemannian curvature
tensor of , respectively. The main result of this paper states that
goes to zero uniformly at infinity if for , the
-norm of is finite. Moreover, If is positive, then
is compact. As applications, we prove that is isometric
to a spherical space form if for , is positive and the
-norm of is pinched in , where is an
explicit positive constant depending only on , and the Yamabe
constant.
In particular, we prove an -norm of pinching theorem
for complete, simply connected, locally conformally flat Riemannian -manifolds with constant negative scalar curvature.
We give an isolation theorem of the trace-free Ricci curvature tensor of
compact locally conformally flat Riemannian -manifolds with constant
positive scalar curvature, which improves Thereom 1.1 and Corollary 1 of E.
Hebey and M. Vaugon \cite{{HV}}. This rsult is sharped, and we can precisely
characterize the case of equality.Comment: We revise the older version, and add some content
An example of compact K\"ahler manifold with nonnegative quadratic bisectional curvature
We construct a compact K\"ahler manifold of nonnegative quadratic bisectional
curvature, which does not admit any K\"ahler metric of nonnegative orthogonal
bisectional curvature. The manifold is a 7-dimensional K\"ahler C-space with
second Betti number equal to 1, and its canonical metric is a K\"ahler-Einstein
metric of positive scalar curvatureComment: 11 page
Rigidity Theorem for integral pinched shrinking Ricci solitons
We prove that an -dimensional, , compact gradient shrinking Ricci
soliton satisfying a -pinching condition is isometric to a
quotient of the round , which improves the rigidity theorem given
by G. Catino (arXiv:1509.07416vl).Comment: arXiv admin note: text overlap with arXiv:1509.07416 by other author
Transverse Energy Production at RHIC
We study the mechanism of transverse energy (E_T) production in Au+Au
collisions at RHIC. The time evolution starting from the initial energy loss to
the final E_T production is closely examined in transport models. The
relationship between the experimentally measured E_T distribution and the
maximum energy density achieved is discussed.Comment: 5 pages, 4 figure
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