111 research outputs found
Finite-Time Convergent Algorithms for Time-Varying Distributed Optimization
This paper focuses on finite-time (FT) convergent distributed algorithms for
solving time-varying distributed optimization (TVDO). The objective is to
minimize the sum of local time-varying cost functions subject to the possible
time-varying constraints by the coordination of multiple agents in finite time.
We first provide a unified approach for designing finite/fixed-time convergent
algorithms to solve centralized time-varying optimization, where an auxiliary
dynamics is introduced to achieve prescribed performance. Then, two classes of
TVDO are investigated included unconstrained distributed consensus optimization
and distributed optimal resource allocation problems (DORAP) with both
time-varying cost functions and coupled equation constraints. For the previous
one, based on nonsmooth analysis, a continuous-time distributed discontinuous
dynamics with FT convergence is proposed based on an extended zero-gradient-sum
method with a local auxiliary subsystem. Different from the existing methods,
the proposed algorithm does not require the initial state of each agent to be
the optimizer of the local cost function. Moreover, the provided algorithm has
a simpler structure without estimating the global information and can be used
for TVDO with nonidentical Hessians. Then, an FT convergent distributed
dynamics is further obtained for time-varying DORAP by dual transformation.
Particularly, the inverse of Hessians is not required from a dual perspective,
which reduces the computation complexity significantly. Finally, two numerical
examples are conducted to verify the proposed algorithms
DISA: A Dual Inexact Splitting Algorithm for Distributed Convex Composite Optimization
In this paper, we propose a novel Dual Inexact Splitting Algorithm (DISA) for
distributed convex composite optimization problems, where the local loss
function consists of a smooth term and a possibly nonsmooth term composed with
a linear mapping. DISA, for the first time, eliminates the dependence of the
convergent step-size range on the Euclidean norm of the linear mapping, while
inheriting the advantages of the classic Primal-Dual Proximal Splitting
Algorithm (PD-PSA): simple structure and easy implementation. This indicates
that DISA can be executed without prior knowledge of the norm, and tiny
step-sizes can be avoided when the norm is large. Additionally, we prove
sublinear and linear convergence rates of DISA under general convexity and
metric subregularity, respectively. Moreover, we provide a variant of DISA with
approximate proximal mapping and prove its global convergence and sublinear
convergence rate. Numerical experiments corroborate our theoretical analyses
and demonstrate a significant acceleration of DISA compared to existing
PD-PSAs
Fixed-Time Gradient Flows for Solving Constrained Optimization: A Unified Approach
The accelerated method in solving optimization problems has always been an
absorbing topic. Based on the fixed-time (FxT) stability of nonlinear dynamical
systems, we provide a unified approach for designing FxT gradient flows
(FxTGFs). First, a general class of nonlinear functions in designing FxTGFs is
provided. A unified method for designing first-order FxTGFs is shown under
PolyakL jasiewicz inequality assumption, a weaker condition than strong
convexity. When there exist both bounded and vanishing disturbances in the
gradient flow, a specific class of nonsmooth robust FxTGFs with disturbance
rejection is presented. Under the strict convexity assumption, Newton-based
FxTGFs is given and further extended to solve time-varying optimization.
Besides, the proposed FxTGFs are further used for solving equation-constrained
optimization. Moreover, an FxT proximal gradient flow with a wide range of
parameters is provided for solving nonsmooth composite optimization. To show
the effectiveness of various FxTGFs, the static regret analysis for several
typical FxTGFs are also provided in detail. Finally, the proposed FxTGFs are
applied to solve two network problems, i.e., the network consensus problem and
solving a system linear equations, respectively, from the respective of
optimization. Particularly, by choosing component-wisely sign-preserving
functions, these problems can be solved in a distributed way, which extends the
existing results. The accelerated convergence and robustness of the proposed
FxTGFs are validated in several numerical examples stemming from practical
applications
Structure, Mechanical and Electrochemical Properties of Thermally Reduced Graphene Oxide-poly (Vinyl Alcohol) Foams
Graphene oxide foams with a wide range of poly (vinyl alcohol) contents were synthesized by freeze casting, and then thermally reduced at 300ºC in argon atmosphere. Their thermal stability, microstructure, composition and chemical states of constituents, mechanical and electrical properties were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry, compressive testing and electrochemical analysis. The results indicated that the PVA content highly influenced the crystallinity and microstructure, resulting in different mechanical properties. After thermal reduction, not only graphene oxide was reduced to graphene, but also PVA was subjected to partial pyrolysis. With the increase of the PVA content, the intensity of the sp2 C-C bond decreased while the sp3 C-C bond increased. Although the mechanical properties decreased after thermal reduction, the composite foams still showed high cyclic structure stability up to 18 % compression strain. Meanwhile, the reduced foams exhibited high electrical conductivity. Applying as anodes in lithium ion battery, the initial discharge capacity for the foams can reach 1822 mA h g-1 and it remained more than 330 mA h g-1 after 50 cycles
Vanadium (V) bio-detoxification based on washing water of rice as microbial and carbon sources
Mining and smelting result in vanadium (V) being released into the environment. Biologically removing V(V) with washing water of rice (WWR) was investigated in this study. Over a 7-d trial, the V(V) removal efficiency increased with dosing washing water of rice dosage up to 56.6%. The results demonstrated that washing water of rice could be used as carbon and microbial sources for biologically reducing V(V). Using domesticated sludge as the inoculum could enhance V(V) detoxification performance, and 95.5% of V(V) was removed in the inoculated system for 5 d. Soluble V(V) was transformed into insoluble V(IV) (VO2), which could be further removed with precipitation. In addition to ABC transporters, a two-component system was also involved in V(V) reduction. The study confirmed that washing water of rice could be utilized for V(V) bio-detoxification
Performance Analysis of OFDM 60GHz System and SC-FDE 60GHz System
In this paper, the performance of 60GHz wireless communication system with SC and OFDM is studied, the models of OFDM 60GHz system and SC 60GHz frequency domain equalization (SC-FDE) system are established, and the bit error rate (BER) performance of OFDM 60GHz system and SC-FDE 60GHz system in 802.15.3c channels is compared. The simulation results show that SC-FDE 60GHz system has a slight advantage over OFDM system in line-of-sight (LOS) channels, while OFDM 60GHz system has a slight advantage over SC-FDE system in non-line-of-sight (NLOS) channels. For 60GHz system, OFDM 60GHz system has a slight advantage over SC-FDE system in overcoming multipath fading, but the performance of both is close whether in the LOS or NLOS case
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