Multi-Level Branched Regularization for Federated Learning

A critical challenge of federated learning is data heterogeneity and imbalance across clients, which leads to inconsistency between local networks and unstable convergence of global models. To alleviate the limitations, we propose a novel architectural regularization technique that constructs multiple auxiliary branches in each local model by grafting local and global subnetworks at several different levels and that learns the representations of the main pathway in the local model congruent to the auxiliary hybrid pathways via online knowledge distillation. The proposed technique is effective to robustify the global model even in the non-iid setting and is applicable to various federated learning frameworks conveniently without incurring extra communication costs. We perform comprehensive empirical studies and demonstrate remarkable performance gains in terms of accuracy and efficiency compared to existing methods. The source code is available at our project page.Comment: ICML 202

Communication-Efficient Federated Learning with Accelerated Client Gradient

Federated learning often suffers from slow and unstable convergence due to the heterogeneous characteristics of participating client datasets. Such a tendency is aggravated when the client participation ratio is low since the information collected from the clients has large variations. To address this challenge, we propose a simple but effective federated learning framework, which improves the consistency across clients and facilitates the convergence of the server model. This is achieved by making the server broadcast a global model with a lookahead gradient. This strategy enables the proposed approach to convey the projected global update information to participants effectively without additional client memory and extra communication costs. We also regularize local updates by aligning each client with the overshot global model to reduce bias and improve the stability of our algorithm. We provide the theoretical convergence rate of our algorithm and demonstrate remarkable performance gains in terms of accuracy and communication efficiency compared to the state-of-the-art methods, especially with low client participation rates. The source code is available at our project page.Comment: CVPR 202

ELECTROPHORETIC DISPLAYS WITH TUNABLE, ANGLE-INDEPENDENT COLOR

Electrophoretic displays (EPDs), which exploit the surface charge of microparticles to control their deposition, have become widely available in consumer electronics, such as e-readers and smartwatches. However, a full-color EPD has yet to be demonstrated and commercialized. Here, we demonstrate colloidal assemblies of engineered quasi-amorphous photonic materials, using pigmentary α-Fe2O3/SiO2 core/shell nanoparticles, exhibiting non- iridescent tunable colors which can be tuned electrophoretically. The observed colors result from combination of colloidal particle arrangements, giving rise to structural color, along with the inherent pigmentary color of the α-Fe2O3/SiO2 nanoparticles. Colloidal particle assemblies of α-Fe2O3/SiO2 core/shell nanoparticles, and therefore the resulting colors, can be manipulated by shell thickness, particle concentration and external electrical stimuli. Dynamic tunability of α-Fe2O3/SiO2 nanomaterials in the visible wavelengths is demonstrated using reversible electrophoretic deposition with a noticeable difference between transmitted and reflected colors. The distinct contrast generated can be exploited for tunable display applications. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-704082

In-situ USAXS/SAXS Investigation of Tunable Structural Color in Amorphous Photonic Crystals during Electrophoretic Deposition

Amorphous photonic crystals (APCs) formed via electrophoretic deposition (EPD) exhibit non-iridescent, angle-independent, structural colors believed to arise from changes in the particle-particle interactions and inter-particle spacing, representing a potential new paradigm for display technologies. However, inter-particle dynamics on nanometer length scales that govern (and enable control over) the displayed color, crystallinity, and other characteristics of the photonic structures, are not well understood. Unfortunately, typical lab-based characterization techniques such as SEM, TEM, and Computed Tomography (CT) are generally performed ex-situ once the sample deposit has been dried. In this work, in-situ USAXS/SAXS/WAXS studies of three-dimensional colloidal particle arrays (of varying particle size and concentration) were performed in order to identify their structural response to applied external electric fields. This data was compared to simultaneously acquired UV-Vis spectra to tie the overall electrically induced structure of the APCs directly to the observed changes in visible color. The structural evolution of the APCs provides new information regarding the correlation between nano-scale particle-particle interactions and the corresponding optical response. To our knowledge, there has been no other prior studies examining the structure of APCs during the application of an electric field. This novel, in-situ USAXS study has helped to gain a better fundamental understanding of how the properties of APCs can be controlled for the advancement of optical displays. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-725437-DRAF

Synthesis and luminescence properties of rare earth activated phosphors for near UV-emitting LEDs for efficacious generation of white light

Solid state white-emitting lighting devices based on LEDs outperform conventional light sources in terms of lifetime, durability, and luminous efficiency. Near UV-LEDs in combination with blue-, green-, and red-emitting phosphors show superior luminescence properties over the commercialized blue-emitting LED with yellow-emitting phosphors. However, phosphor development for near UV LEDs is a challenging problem and a vibrant area of research. In addition, using the proper synthesis technique is an important consideration in the development of phosphors. In this research, efficient blue-, green-yellow, red- emitting, and color tunable phosphors for near UV LEDs based white light are identified and prepared by various synthetic methods such as solid state reaction, sol-gel/ Pechini, co-precipitation, hydrothermal, combustion and spray-pyrolysis. Blue-emittingLiCaPO₄:Eu²⁺, Green/yellow- emitting (Ba,Sr)₂SiO₄:Eu²⁺, color tunable solid solutions of KSrPO₄₋(Ba,Ca)₂SiO₄:Eu²⁺, and red-emitting (Ba,Sr, Ca)₃MgSi₂O₈:Eu²⁺,Mn²⁺ show excellent excitation profile in the near UV region, high quantum efficiency, and good thermal stability for use in solid state lighting applications. In addition, different synthesis methods are analyzed and compared, with the goal of obtaining ideal phosphors, which should have not only have high luminous output but also optimal particle size (~150 - 400 nm) and spherical morphology. For Sr₂SiO₄:Eu²⁺, the sol-gel method appears to be the best method. For Ba₂SiO₄:Eu²⁺, the co- precipitation method is be the best. Lastly, the fabrication of core/SiO₂ shell particles alleviate surface defects and improve luminescence output and moisture stability of nano and micron sized phosphors. For nano- sized Y₂O₃:Eu³⁺, Y₂SiO₅:Ce³⁺,Tb³⁺, and (Ba,Sr)₂SiO₄, the luminescence emission intensity of the core/shell particles were significantly higher than that of bare cores. Additionally, the moisture stability is also improved by SiO₂ shells, the luminescence output of SiO₂ coated green emitting Ca₃SiO₄Cl₂:Eu²⁺ and blue emitting Ca₂PO₄Cl:Eu²⁺ phosphors is comparable to that of fresh phosphors although bare phosphors shows significant luminescence quenching after water exposur

Opportunities and Challenges for Nanoparticle Synthesis using Continuous Flow Systems: A Magnetite Nanocluster Case Study

In this study, we demonstrate a new high temperature flow synthesis system for magnetite nanoparticle clusters. We find that successful synthesis of nanoparticle clusters is dependent on residence time in the reaction chamber and linear flow speed. The long reaction times and elevated temperatures required, combined with the resulting slurry formed with successful magnetite nanocluster synthesis, made this reaction challenging to adapt to a flow system. However, proper design of a continuous flow synthesis platform and synthesis parameter control allows for the adoption of even difficult solvothermal synthesis processes. We discuss the importance of reaction pressure control and reaction duration for successful synthesis of magnetite nanoclusters and address opportunities and challenges associated with adopting solvothermal synthesis to continuous flow synthesis platforms.</div

Observation of Photoinduced Charge Transfer in Novel Luminescent CdSe Quantum Dot–CePO₄:Tb Metal Oxide Nanowire Composite Heterostructures

We report on the synthesis, structural characterization, and intrinsic charge transfer processes associated with novel luminescent zero-dimensional (0D) CdSe nanocrystal–one-dimensional (1D) CePO₄:Tb nanowire composite heterostructures. Specifically, ∼4 nm CdSe quantum dots (QDs) have been successfully anchored onto high-aspect ratio CePO₄:Tb nanowires, measuring ∼65 nm in diameter and ∼2 μm in length. Composite formation was confirmed by high-resolution transmission microscopy, energy-dispersive X-ray spectroscopy mapping, and confocal microscopy. Photoluminescence (PL) spectra, emission decay, and optical absorption of these nanoscale heterostructures were collected and compared with those of single, discrete CdSe QDs and CePO₄:Tb nanowires. We show that our composite heterostructure evinces both PL quenching and a shorter average lifetime as compared with unbound CdSe QDs and CePO₄:Tb nanowires. We propose that a photoinduced 0D–1D charge transfer process occurs between CdSe and CePO₄:Tb and that it represents the predominant mechanism, accounting for the observed PL quenching and shorter lifetimes noted in our composite heterostructures. Data are additionally explained in the context of the inherent energy level alignments of both CdSe QDs and CePO₄:Tb nanowires

Numerical and Experimental Analysis of the Shear Behavior of Ultrahigh-Performance Concrete Construction Joints

Shear performance of plain UHPC (ultrahigh-performance concrete) construction joints is studied in both experimental and analytical ways. In push-off tests, three different contact surfaces of the construction joint were considered, while the case without any joint was provided for the reference. Test results indicate that the geometry of contact surfaces greatly affects shear performance of the construction joint. With simplifying structural behavior of contact surfaces and UHPC substrate, the finite-element analysis model is developed for every case studied by utilizing the ABAQUS software and validated against the test results. Agreement between experimental and numerical simulation results is excellent especially in terms of displacement, strength, and failure mechanism. It is expected that the present work provides a basis for further study on reinforced UHPC construction joints

Electro-Optical Device with Tunable Transparency Using Colloidal Core/Shell Nanoparticles

Suspended particle devices (SPDs) adapted for controlling the transmission of electromagnetic radiation have become an area of considerable focus for smart window technology due to their desirable properties, such as instant and precise light control and cost-effectiveness. Here, we demonstrate a SPD with tunable transparency in the visible regime using colloidal assemblies of nanoparticles. The observed transparency using ZnS/SiO₂ core/shell colloidal nanoparticles is dynamically tunable in response to an external electric field with increased transparency when applied voltage increases. The observed transparency change is attributed to structural ordering of nanoparticle assemblies and thereby modifies the photonic band structures, as confirmed by the finite-difference time-domain simulations of Maxwell’s equations. The transparency of the device can also be manipulated by changing the particle size and the device thickness. In addition to transparency, structural colorations and their dynamic tunability are demonstrated using α-Fe₂O₃/SiO₂ core/shell nanomaterials, resulting from the combination of inherent optical properties of α-Fe₂O₃/SiO₂ nanomaterials and coloration due to their tunable structural particle assemblies in response to electric stimuli