Semi-Supervised Medical Image Segmentation with Co-Distribution Alignment

Medical image segmentation has made significant progress when a large amount of labeled data are available. However, annotating medical image segmentation datasets is expensive due to the requirement of professional skills. Additionally, classes are often unevenly distributed in medical images, which severely affects the classification performance on minority classes. To address these problems, this paper proposes Co-Distribution Alignment (Co-DA) for semi-supervised medical image segmentation. Specifically, Co-DA aligns marginal predictions on unlabeled data to marginal predictions on labeled data in a class-wise manner with two differently initialized models before using the pseudo-labels generated by one model to supervise the other. Besides, we design an over-expectation cross-entropy loss for filtering the unlabeled pixels to reduce noise in their pseudo-labels. Quantitative and qualitative experiments on three public datasets demonstrate that the proposed approach outperforms existing state-of-the-art semi-supervised medical image segmentation methods on both the 2D CaDIS dataset and the 3D LGE-MRI and ACDC datasets, achieving an mIoU of 0.8515 with only 24% labeled data on CaDIS, and a Dice score of 0.8824 and 0.8773 with only 20% data on LGE-MRI and ACDC, respectively.Comment: Paper appears in Bioengineering 2023, 10(7), 86

Heterobimetallic Catalysts for Ethylene Homo- and Co-Polymerization

Polyethylene (PE) is one of the most important plastics in the world. The incorporation of polar functional groups into PE, even in low concentrations, can dramatically improve its material properties. The discovery that late transition metal Ni and Pd complexes can promote the coordination-insertion copolymerization of ethylene and polar olefins was a major scientific breakthrough. Unfortunately, their catalytic activities are significantly reduced in the presence of polar monomers compared to in the presence of non-polar monomers. It is believed that the formation of metal-monomer chelated complexes prevents efficient copolymerization. As a new strategy to avoid coordination inhibition by polar monomers, we first designed a new class of mononuclear nickel complexes that have pedant polyethylene glycol (PEG) chains that can bind alkali metal ions. Solution titration studies by UV-vis absorption spectroscopy demonstrated that optimal metal binding is achieved by selecting the appropriate PEG chain length to match the size of the alkali ions. Upon the addition of the alkali salts, the resulting heterobimetallic nickel-alkali metal catalysts were found to be more active in ethylene polymerization, compared to their parent nickel catalysts. They also produced polymers with higher molecular weight and higher branching compared to in the absence of the alkali ions. To test our strategy on other molecular systems, we also designed cationic palladium phosphine-phosphonate complexes with secondary metal-binding PEG chains. Solution studies by 1H NMR spectroscopy showed that a 1:1 binding stoichiometry between Pd and alkali ions can be achieved. The structure of the palladium-sodium species was confirmed by X-ray crystallography. Our heterobimetallic complexes exhibit significant enhancement in catalytic activity and thermal stability compared to their parent monometallic catalysts. For the copolymerization of ethylene and acrylates, our heterobimetallic complexes also showed higher activity and produced copolymer with higher molecular weight. Mechanistic studies conducted by low-temperature NMR spectroscopy revealed that the addition of alkali ions can accelerate ethylene insertion by the palladium acrylate intermediate.Chemistry, Department o

Customizing Polyolefin Morphology by Selective Pairing of Alkali Ions with Nickel Phenoxyimine-Polyethylene Glycol Catalysts

In the present work, we have prepared nickel phenoxyimine-polyethylene glycol (PEG) catalysts with sterically bulky <i>N</i>-aryl substituents and investigated their ethylene homo- and copolymerization behavior. We have found that different nickel catalyst and alkali ion (Na⁺ or K⁺) combinations yielded polyethylene with different branching microstructures and molecular weights. Our heterobimetallic catalysts can copolymerize ethylene and nonpolar α-olefins with high activity but are strongly inhibited in the presence of polar vinyl olefins. We demonstrate that our heterobimetallic catalysts are significantly more stable in ethylene homopolymerization in comparison to conventional nickel phenoxyimine systems on the basis of time-dependent activity studies. This work showcases the versatility of Lewis acid tunable catalyst constructs to prepare customized polyolefins and suggests that similar design strategies could be applied to other catalyst systems

Fine-Tuning Nickel Phenoxyimine Olefin Polymerization Catalysts: Performance Boosting by Alkali Cations

To gain a better understanding of the influence of cationic additives on coordination–insertion polymerization and to leverage this knowledge in the construction of enhanced olefin polymerization catalysts, we have synthesized a new family of nickel phenoxyimine–polyethylene glycol complexes (<b>NiL0</b>, <b>NiL2</b>–<b>NiL4</b>) that form discrete molecular species with alkali metal ions (M⁺ = Li⁺, Na⁺, K⁺). Metal binding titration studies and structural characterization by X-ray crystallography provide evidence for the self-assembly of both 1:1 and 2:1 <b>NiL</b>:M⁺ species in solution, except for <b>NiL4</b>/Na⁺ which form only the 1:1 complex. It was found that upon treatment with a phosphine scavenger, these <b>NiL</b> complexes are active catalysts for ethylene polymerization. We demonstrate that the addition of M⁺ to <b>NiL</b> can result in up to a 20-fold increase in catalytic efficiency as well as enhancement in polymer molecular weight and branching frequency compared to the use of <b>NiL</b> without coadditives. To the best of our knowledge, this work provides the first systematic study of the effect of secondary metal ions on metal-catalyzed polymerization processes and offers a new general design strategy for developing the next generation of high performance olefin polymerization catalysts

Optimization design of wireless charging system for autonomous robots based on magnetic resonance coupling

Wireless charging is the key technology to realize real autonomy of mobile robots. As the core part of wireless power transfer system, coupling mechanism including coupling coils and compensation topology is analyzed and optimized through simulations, to achieve stable and practical wireless charging suitable for ordinary robots. Multi-layer coil structure, especially double-layer coil is explored and selected to greatly enhance coupling performance, while shape of ferrite shielding goes through distributed optimization to guarantee coil fault tolerance and cost effectiveness. On the basis of optimized coils, primary compensation topology is analyzed to adopt composite LCL compensation, to stabilize operations of the primary side under variations of mutual inductance. Experimental results show the optimized system does make sense for wireless charging application for robots based on magnetic resonance coupling, to realize long-term autonomy of robots

Combination of Compensations and Multi-Parameter Coil for Efficiency Optimization of Inductive Power Transfer System

A loosely coupled inductive power transfer (IPT) system for industrial track applications has been researched in this paper. The IPT converter using primary Inductor-Capacitor-Inductor (LCL) network and secondary parallel-compensations is analyzed combined coil design for optimal operating efficiency. Accurate mathematical analytical model and expressions of self-inductance and mutual inductance are proposed to achieve coil parameters. Furthermore, the optimization process is performed combined with the proposed resonant compensations and coil parameters. The results are evaluated and discussed using finite element analysis (FEA). Finally, an experimental prototype is constructed to verify the proposed approach and the experimental results show that the optimization can be better applied to industrial track distributed IPT system

Analysis, design and implement of asymmetric coupled wireless power transfer systems for unmanned aerial vehicles

To solve the problem of short operating time of UAVs, this paper designs an asymmetric coupled wireless power transfer (WPT) system with optimized coupling structures and parameters, which effectively improves horizontal tolerance and performance for UAVs’ charging. Expressions of receiving power and transfer efficiency are derived to guide the design of parameters by modeling and analyzing the WPT systems. Structures and parameters of coupling coils are optimized to improve the quality factor and horizontal tolerance by simulations and comparison. System characteristics are further calculated and optimized with compensation topology. A prototype platform is implemented to verify the analysis and design, and experimental results show that it can achieve 64.87 W power transfer for UAVs with 57.94 % transfer efficiency, and the system is tolerant to horizontal misalignments of coupling coils. The analysis, design and implementation of asymmetric coupled WPT systems provides an important reference for the application of WPT technology in UAVs’ charging

Insights into substitution strategy towards thermodynamic and property regulation of chemically recyclable polymers

Abstract The development of chemically recyclable polymers serves as an attractive approach to address the global plastic pollution crisis. Monomer design principle is the key to achieving chemical recycling to monomer. Herein, we provide a systematic investigation to evaluate a range of substitution effects and structure−property relationships in the ɛ-caprolactone (CL) system. Thermodynamic and recyclability studies reveal that the substituent size and position could regulate their ceiling temperatures (T c). Impressively, M4 equipped with a tert-butyl group displays a T c of 241 °C. A series of spirocyclic acetal-functionalized CLs prepared by a facile two-step reaction undergo efficient ring-opening polymerization and subsequent depolymerization. The resulting polymers demonstrate various thermal properties and a transformation of the mechanical performance from brittleness to ductility. Notably, the toughness and ductility of P(M13) is comparable to the commodity plastic isotactic polypropylene. This comprehensive study is aimed to provide a guideline to the future monomer design towards chemically recyclable polymers

Generating New Cross‐Relaxation Pathways by Coating Prussian Blue on NaNdF 4

Cross-relaxation among sensitizers is commonly regarded as deleterious in fluorescent materials, although favorable in photothermal agents. Herein, we coated Prussian blue (PB) on NaNdF4 nanoparticles to fabricate core-shell nanocomplexes with new cross relaxation pathways between the ladder-like energy levels of Nd3+ ions and continuous energy band of PB. The photothermal conversion efficiency was improved exceptionally and the mechanism of the enhanced photothermal effect was investigated. In vivo photoacoustic imaging and photothermal therapy demonstrated the potential of the enhanced photothermal agents. Moreover, the concept of generating new cross-relaxation pathways between different materials is proposed to contribute to the design of all kinds of enhanced photothermal agents.Nanyang Technological UniversityThis work was financially supported by an NTU internal grant(M4081851), the National Basic Research Program of China(No.61805118 and 21674048), the Natural Science Founda-tion of Jiangsu Province of China (No.BK20171020), theChina Postdoctoral Science Foundation (No.2018T110488),and the open research fund of the Key Laboratory forOrganic Electronics and Information Displays