8,686 research outputs found
On the Influence of Informed Agents on Learning and Adaptation over Networks
Adaptive networks consist of a collection of agents with adaptation and
learning abilities. The agents interact with each other on a local level and
diffuse information across the network through their collaborations. In this
work, we consider two types of agents: informed agents and uninformed agents.
The former receive new data regularly and perform consultation and in-network
tasks, while the latter do not collect data and only participate in the
consultation tasks. We examine the performance of adaptive networks as a
function of the proportion of informed agents and their distribution in space.
The results reveal some interesting and surprising trade-offs between
convergence rate and mean-square performance. In particular, among other
results, it is shown that the performance of adaptive networks does not
necessarily improve with a larger proportion of informed agents. Instead, it is
established that the larger the proportion of informed agents is, the faster
the convergence rate of the network becomes albeit at the expense of some
deterioration in mean-square performance. The results further establish that
uninformed agents play an important role in determining the steady-state
performance of the network, and that it is preferable to keep some of the
highly connected agents uninformed. The arguments reveal an important interplay
among three factors: the number and distribution of informed agents in the
network, the convergence rate of the learning process, and the estimation
accuracy in steady-state. Expressions that quantify these relations are
derived, and simulations are included to support the theoretical findings. We
further apply the results to two models that are widely used to represent
behavior over complex networks, namely, the Erdos-Renyi and scale-free models.Comment: 35 pages, 8 figure
Diffusion Strategies Outperform Consensus Strategies for Distributed Estimation over Adaptive Networks
Adaptive networks consist of a collection of nodes with adaptation and
learning abilities. The nodes interact with each other on a local level and
diffuse information across the network to solve estimation and inference tasks
in a distributed manner. In this work, we compare the mean-square performance
of two main strategies for distributed estimation over networks: consensus
strategies and diffusion strategies. The analysis in the paper confirms that
under constant step-sizes, diffusion strategies allow information to diffuse
more thoroughly through the network and this property has a favorable effect on
the evolution of the network: diffusion networks are shown to converge faster
and reach lower mean-square deviation than consensus networks, and their
mean-square stability is insensitive to the choice of the combination weights.
In contrast, and surprisingly, it is shown that consensus networks can become
unstable even if all the individual nodes are stable and able to solve the
estimation task on their own. When this occurs, cooperation over the network
leads to a catastrophic failure of the estimation task. This phenomenon does
not occur for diffusion networks: we show that stability of the individual
nodes always ensures stability of the diffusion network irrespective of the
combination topology. Simulation results support the theoretical findings.Comment: 37 pages, 7 figures, To appear in IEEE Transactions on Signal
Processing, 201
Switchable valley functionalities of an junction in 2D semiconductors
We show that an junction in 2D semiconductors can flexibly
realize two basic valleytronic functions, i.e. valley filter and valley source,
with gate controlled switchability between the two. Upon carrier flux passing
through the junction, the valley filter and valley source functions are enabled
respectively by intra- and inter-valley scatterings, and the two functions
dominate respectively at small and large band-offset between the and
regions. It can be generally shown that, the valley filter effect has
an angular dependent polarity and vanishes under angular integration, by the
same constraint from time-reversal symmetry that leads to its absence in
one-dimension. These findings are demonstrated for monolayer transition metal
dichalcogenides and graphene using tight-binding calculations. We further show
that junction along chiral directions can concentrate the valley pump in an
angular interval largely separated from the bias direction, allowing efficient
havest of valley polarization in a cross-bar device
On the Erdos-Sos Conjecture for Graphs on n=k+4 Vertices
The Erd\H{o}s-S\'{o}s Conjecture states that if is a simple graph of
order with average degree more than then contains every tree of
order . In this paper, we prove that Erd\H{o}s-S\'{o}s Conjecture is true
for .Comment: 18 page
3次元アトムプローブ法を用いたシリコンデバイス中の不純物分布のナノスケール分析
Tohoku University永井康介課
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