160 research outputs found
On Stability and Convergence of Distributed Filters
Recent years have bore witness to the proliferation of distributed filtering
techniques, where a collection of agents communicating over an ad-hoc network
aim to collaboratively estimate and track the state of a system. These
techniques form the enabling technology of modern multi-agent systems and have
gained great importance in the engineering community. Although most distributed
filtering techniques come with a set of stability and convergence criteria, the
conditions imposed are found to be unnecessarily restrictive. The paradigm of
stability and convergence in distributed filtering is revised in this
manuscript. Accordingly, a general distributed filter is constructed and its
estimation error dynamics is formulated. The conducted analysis demonstrates
that conditions for achieving stable filtering operations are the same as those
required in the centralized filtering setting. Finally, the concepts are
demonstrated in a Kalman filtering framework and validated using simulation
examples
Personalized Graph Federated Learning with Differential Privacy
This paper presents a personalized graph federated learning (PGFL) framework
in which distributedly connected servers and their respective edge devices
collaboratively learn device or cluster-specific models while maintaining the
privacy of every individual device. The proposed approach exploits similarities
among different models to provide a more relevant experience for each device,
even in situations with diverse data distributions and disproportionate
datasets. Furthermore, to ensure a secure and efficient approach to
collaborative personalized learning, we study a variant of the PGFL
implementation that utilizes differential privacy, specifically
zero-concentrated differential privacy, where a noise sequence perturbs model
exchanges. Our mathematical analysis shows that the proposed privacy-preserving
PGFL algorithm converges to the optimal cluster-specific solution for each
cluster in linear time. It also shows that exploiting similarities among
clusters leads to an alternative output whose distance to the original solution
is bounded, and that this bound can be adjusted by modifying the algorithm's
hyperparameters. Further, our analysis shows that the algorithm ensures local
differential privacy for all clients in terms of zero-concentrated differential
privacy. Finally, the performance of the proposed PGFL algorithm is examined by
performing numerical experiments in the context of regression and
classification using synthetic data and the MNIST dataset
Asynchronous Online Federated Learning with Reduced Communication Requirements
Online federated learning (FL) enables geographically distributed devices to
learn a global shared model from locally available streaming data. Most online
FL literature considers a best-case scenario regarding the participating
clients and the communication channels. However, these assumptions are often
not met in real-world applications. Asynchronous settings can reflect a more
realistic environment, such as heterogeneous client participation due to
available computational power and battery constraints, as well as delays caused
by communication channels or straggler devices. Further, in most applications,
energy efficiency must be taken into consideration. Using the principles of
partial-sharing-based communications, we propose a communication-efficient
asynchronous online federated learning (PAO-Fed) strategy. By reducing the
communication overhead of the participants, the proposed method renders
participation in the learning task more accessible and efficient. In addition,
the proposed aggregation mechanism accounts for random participation, handles
delayed updates and mitigates their effect on accuracy. We prove the first and
second-order convergence of the proposed PAO-Fed method and obtain an
expression for its steady-state mean square deviation. Finally, we conduct
comprehensive simulations to study the performance of the proposed method on
both synthetic and real-life datasets. The simulations reveal that in
asynchronous settings, the proposed PAO-Fed is able to achieve the same
convergence properties as that of the online federated stochastic gradient
while reducing the communication overhead by 98 percent.Comment: A conference precursor of this work appears in the 2022 IEEE IC
Quantum Cellular Neural Networks
We have previously proposed a way of using coupled quantum dots to construct
digital computing elements - quantum-dot cellular automata (QCA). Here we
consider a different approach to using coupled quantum-dot cells in an
architecture which, rather that reproducing Boolean logic, uses a physical
near-neighbor connectivity to construct an analog Cellular Neural Network
(CNN).Comment: 7 pages including 3 figure
Crystallization of Adenylylsulfate Reductase from Desulfovibrio gigas: A Strategy Based on Controlled Protein Oligomerization
Adenylylsulfate reductase (adenosine 5′-phosphosulfate reductase, APS reductase or APSR, E.C.1.8.99.2) catalyzes the conversion of APS to sulfite in dissimilatory sulfate reduction. APSR was isolated and purified directly from massive anaerobically grown Desulfovibrio gigas, a strict anaerobe, for structure and function investigation. Oligomerization of APSR to form dimers–α_2β_2, tetramers–α_4β_4, hexamers–α_6β_6, and larger oligomers was observed during purification of the protein. Dynamic light scattering and ultracentrifugation revealed that the addition of adenosine monophosphate (AMP) or adenosine 5′-phosphosulfate (APS) disrupts the oligomerization, indicating that AMP or APS binding to the APSR dissociates the inactive hexamers into functional dimers. Treatment of APSR with β-mercaptoethanol decreased the enzyme size from a hexamer to a dimer, probably by disrupting the disulfide Cys156—Cys162 toward the C-terminus of the β-subunit. Alignment of the APSR sequences from D. gigas and A. fulgidus revealed the largest differences in this region of the β-subunit, with the D. gigas APSR containing 16 additional amino acids with the Cys156—Cys162 disulfide. Studies in a pH gradient showed that the diameter of the APSR decreased progressively with acidic pH. To crystallize the APSR for structure determination, we optimized conditions to generate a homogeneous and stable form of APSR by combining dynamic light scattering, ultracentrifugation, and electron paramagnetic resonance methods to analyze the various oligomeric states of the enzyme in varied environments
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