4,686 research outputs found
Principal Boundary on Riemannian Manifolds
We consider the classification problem and focus on nonlinear methods for
classification on manifolds. For multivariate datasets lying on an embedded
nonlinear Riemannian manifold within the higher-dimensional ambient space, we
aim to acquire a classification boundary for the classes with labels, using the
intrinsic metric on the manifolds. Motivated by finding an optimal boundary
between the two classes, we invent a novel approach -- the principal boundary.
From the perspective of classification, the principal boundary is defined as an
optimal curve that moves in between the principal flows traced out from two
classes of data, and at any point on the boundary, it maximizes the margin
between the two classes. We estimate the boundary in quality with its
direction, supervised by the two principal flows. We show that the principal
boundary yields the usual decision boundary found by the support vector machine
in the sense that locally, the two boundaries coincide. Some optimality and
convergence properties of the random principal boundary and its population
counterpart are also shown. We illustrate how to find, use and interpret the
principal boundary with an application in real data.Comment: 31 pages,10 figure
Superfluidity and effective mass of magnetoexcitons in topological insulator bilayers: Effect of inter-Landau-level Coulomb interaction
The effective mass and superfluidity-normal phase transition temperature of
magnetoexcitons in topological insulator bilayers are theoretically
investigated. The intra-Landau-level Coulomb interaction is treated
perturbatively, from which the effective magnetoexciton mass is analytically
discussed. The inclusion of inter-Landau-level Coulomb interaction by more
exact numerical diagonalization of the Hamiltonian brings out important
modifications to magnetoexciton properties, which are specially characterized
by prominent reduction in the magnetoexciton effective mass and promotion in
the superfluidity-normal phase transition temperature at a wide range of
external parameters.Comment: 5.6 EPL pages, 4 figure
Coalitional Game Theoretic Approach for Cooperative Transmission in Vehicular Networks
Cooperative transmission in vehicular networks is studied by using
coalitional game and pricing in this paper. There are several vehicles and
roadside units (RSUs) in the networks. Each vehicle has a desire to transmit
with a certain probability, which represents its data burtiness. The RSUs can
enhance the vehicles' transmissions by cooperatively relaying the vehicles'
data. We consider two kinds of cooperations: cooperation among the vehicles and
cooperation between the vehicle and RSU. First, vehicles cooperate to avoid
interfering transmissions by scheduling the transmissions of the vehicles in
each coalition. Second, a RSU can join some coalition to cooperate the
transmissions of the vehicles in that coalition. Moreover, due to the mobility
of the vehicles, we introduce the notion of encounter between the vehicle and
RSU to indicate the availability of the relay in space. To stimulate the RSU's
cooperative relaying for the vehicles, the pricing mechanism is applied. A
non-transferable utility (NTU) game is developed to analyze the behaviors of
the vehicles and RSUs. The stability of the formulated game is studied.
Finally, we present and discuss the numerical results for the 2-vehicle and
2-RSU scenario, and the numerical results verify the theoretical analysis.Comment: accepted by IEEE ICC'1
A Cross-layer Perspective on Energy Harvesting Aided Green Communications over Fading Channels
We consider the power allocation of the physical layer and the buffer delay
of the upper application layer in energy harvesting green networks. The total
power required for reliable transmission includes the transmission power and
the circuit power. The harvested power (which is stored in a battery) and the
grid power constitute the power resource. The uncertainty of data generated
from the upper layer, the intermittence of the harvested energy, and the
variation of the fading channel are taken into account and described as
independent Markov processes. In each transmission, the transmitter decides the
transmission rate as well as the allocated power from the battery, and the rest
of the required power will be supplied by the power grid. The objective is to
find an allocation sequence of transmission rate and battery power to minimize
the long-term average buffer delay under the average grid power constraint. A
stochastic optimization problem is formulated accordingly to find such
transmission rate and battery power sequence. Furthermore, the optimization
problem is reformulated as a constrained MDP problem whose policy is a
two-dimensional vector with the transmission rate and the power allocation of
the battery as its elements. We prove that the optimal policy of the
constrained MDP can be obtained by solving the unconstrained MDP. Then we focus
on the analysis of the unconstrained average-cost MDP. The structural
properties of the average optimal policy are derived. Moreover, we discuss the
relations between elements of the two-dimensional policy. Next, based on the
theoretical analysis, the algorithm to find the constrained optimal policy is
presented for the finite state space scenario. In addition, heuristic policies
with low-complexity are given for the general state space. Finally, simulations
are performed under these policies to demonstrate the effectiveness
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