17,177 research outputs found
Two-orbital Systems with Crystal Field Splitting and Interorbital Hopping
The nondegenerate two-orbital Hubbard model is studied within the dynamic
mean-field theory to reveal the influence of two important factors, i.e.
crystal field splitting and interorbital hopping, on orbital selective Mott
transition (OSMT) and realistic compound CaSrRuO. A
distinctive feature of the optical conductivity of the two nondegenerate bands
is found in OSMT phase, where the metallic character of the wide band is
indicated by a nonzero Drude peak, while the insulating narrow band has its
Drude peak drop to zero in the mean time. We also find that the OSMT regime
expands profoundly with the increase of interorbital hopping integrals. On the
contrary, it is shown that large and negative level splitting of the two
orbitals diminishes the OSMT regime completely. Applying the present findings
to compound CaSrRuO, we demonstrate that in the doping
region from to 2.0, the negative level splitting is unfavorable to the
OSMT phase.Comment: 7 pages with 5 figure
Nonparametric Detection of Geometric Structures over Networks
Nonparametric detection of existence of an anomalous structure over a network
is investigated. Nodes corresponding to the anomalous structure (if one exists)
receive samples generated by a distribution q, which is different from a
distribution p generating samples for other nodes. If an anomalous structure
does not exist, all nodes receive samples generated by p. It is assumed that
the distributions p and q are arbitrary and unknown. The goal is to design
statistically consistent tests with probability of errors converging to zero as
the network size becomes asymptotically large. Kernel-based tests are proposed
based on maximum mean discrepancy that measures the distance between mean
embeddings of distributions into a reproducing kernel Hilbert space. Detection
of an anomalous interval over a line network is first studied. Sufficient
conditions on minimum and maximum sizes of candidate anomalous intervals are
characterized in order to guarantee the proposed test to be consistent. It is
also shown that certain necessary conditions must hold to guarantee any test to
be universally consistent. Comparison of sufficient and necessary conditions
yields that the proposed test is order-level optimal and nearly optimal
respectively in terms of minimum and maximum sizes of candidate anomalous
intervals. Generalization of the results to other networks is further
developed. Numerical results are provided to demonstrate the performance of the
proposed tests.Comment: Submitted for journal publication in November 2015. arXiv admin note:
text overlap with arXiv:1404.029
Secrecy Outage and Diversity Analysis of Cognitive Radio Systems
In this paper, we investigate the physical-layer security of a multi-user
multi-eavesdropper cognitive radio system, which is composed of multiple
cognitive users (CUs) transmitting to a common cognitive base station (CBS),
while multiple eavesdroppers may collaborate with each other or perform
independently in intercepting the CUs-CBS transmissions, which are called the
coordinated and uncoordinated eavesdroppers, respectively. Considering multiple
CUs available, we propose the round-robin scheduling as well as the optimal and
suboptimal user scheduling schemes for improving the security of CUs-CBS
transmissions against eavesdropping attacks. Specifically, the optimal user
scheduling is designed by assuming that the channel state information (CSI) of
all links from CUs to CBS, to primary user (PU) and to eavesdroppers are
available. By contrast, the suboptimal user scheduling only requires the CSI of
CUs-CBS links without the PU's and eavesdroppers' CSI. We derive closed-form
expressions of the secrecy outage probability of these three scheduling schemes
in the presence of the coordinated and uncoordinated eavesdroppers. We also
carry out the secrecy diversity analysis and show that the round-robin
scheduling achieves the diversity order of only one, whereas the optimal and
suboptimal scheduling schemes obtain the full secrecy diversity, no matter
whether the eavesdroppers collaborate or not. In addition, numerical secrecy
outage results demonstrate that for both the coordinated and uncoordinated
eavesdroppers, the optimal user scheduling achieves the best security
performance and the round-robin scheduling performs the worst. Finally, upon
increasing the number of CUs, the secrecy outage probabilities of the optimal
and suboptimal user scheduling schemes both improve significantly.Comment: 16 pages, 5 figures, accepted to appear, IEEE Journal on Selected
Areas in Communications, 201
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