Search

Your search keyword '"Li, Hongfei"' showing total 2,233 results
Start Over Author "Li, Hongfei"
2,233 results on '"Li, Hongfei"'

102. Dielectric-electrolyte supercapacitors

Author

Dong, Shian, Gao, Weihang, Shi, Kunming, Kang, Qi, Xu, Zhenli, Yuan, Jinkai, Zhu, Yingke, Li, Hongfei, Chen, Jie, Jiang, Pingkai, Wu, Guangning, Wei, Qiulong, Qiu, Jieshan, Qian, Xiaoshi, and Huang, Xingyi

Published
2023
Full Text
View/download PDF

111. Electrospun Conjugated Polymer/Fullerene Hybrid Fibers: Photoactive Blends, Conductivity through Tunnelling-AFM, Light-Scattering, and Perspective for Their Use in Bulk-Heterojunction Organic Solar Cells

Author

Yang, Zhenhua, Moffa, Maria, Liu, Ying, Li, Hongfei, Persano, Luana, Camposeo, Andrea, Saija, Rosalba, Iatì, Maria Antonia, Maragò, Onofrio M., Pisignano, Dario, Nam, Chang-Yong, Zussman, Eyal, and Rafailovich, Miriam

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are prepared by electrospinning, and their properties assessed by scanning electron, atomic and lateral force, tunnelling, and confocal microscopy, as well as by attenuated total reflection Fourier transform-infrared spectroscopy, photoluminescence quantum yield and spatially-resolved fluorescence. Highlighted features include ribbon-shape of the realized fibers, and the persistence of a network serving as a template for heterogeneous active layers in solar cell devices. A set of favorable characteristics is evidenced in this way in terms of homogeneous charge transport behavior and formation of effective interfaces for diffusion and dissociation of photogenerated excitons. The interaction of the organic filaments with light, exhibiting specific light-scattering properties of the nanofibrous mat, might also contribute to spreading incident radiation across the active layers, thus potentially enhancing photovoltaic performance. This method might be applied to other electron donor-electron acceptor material systems for the fabrication of solar cell devices enhanced by nanofibrillar morphologies embedding conjugated polymers and fullerene compounds., Comment: 35 pages, 9 figures

Published
2018
Full Text
View/download PDF

112. Planting in ecologically solidified soil and its use

Author

Yang Yongdong, Liu Hai, Li Hongfei, Su Shengrui, and Liu Wanfeng

Subjects
loess slope, planting in solidified soil, soil stabilizer of consolid system, shear strength, effect evaluation, china, Geology, QE1-996.5
Abstract

Rainfall and surface water infiltration will affect the safety of loess slope. Ecological slope protection can protect and reinforce the surface layer of the slope by using the anchoring effect of plant root. In this study, the prevention and control technology of grass planting on loess slope in the solidified soil was studied. Heavy metal contents in the soil after addition of the stabilizer met the farmland standard at the end of the growth period. A comparison of the biomass data of different groups of solidified soil showed that the biological characteristics of plants had the best response at the mixture ratio of solidified soil of 0.86%. The shear strength of the root–soil composite increased by about 60% compared with that of plain soil at the mixture ratio of 0.86% stabilizer, and the permeability coefficient can be reduced by two orders of magnitude. Through the field engineering application, the ecological restoration test using loess soil solidified by consolid system with grass planting met the engineering requirements, with clear soil and water conservation benefits. Therefore, planting grass in solidified soil can effectively reduce the erosion of soil and improve the stability of the shallow slope.

Published
2022
Full Text
View/download PDF

135. Density functional simulations of defect behavior in oxides for applications in MOSFET and resistive memory

Author

Li, Hongfei and Robertson, John

Subjects
621.3815, DFT, Defect, MOSFET, ReRAM, Simulation, CASTEP, Oxide, Interface, Reliability, Stability, GeO2, IGZO, NBIS, SBH, Oxidation, Doping, Vacancy, Defect Diffusion, Fermi level pinning, TiO2, ZnO, Passivation, Scaling, First Principles, Ab initio, Molecular dynamics, MD, Hybrid functional, Screened Exchange, HSE, sX-LDA
Abstract

Defects in the functional oxides play an important role in electronic devices like metal oxide semiconductor field effect transistors (MOSFETs) and resistive random-access memories (ReRAMs). The continuous scaling of CMOS has brought the Si MOSFET to its physical technology limit and the replacement of Si channel with Ge channel is required. However, the performance of Ge MOSFETs suffers from Ge/oxide interface quality and reliability problems, which originates from the charge traps and defect states in the oxide or at the Ge/oxide interface. The sub-oxide layers composed of GeII states at the Ge/GeO2 interface seems unavoidable with normal passivation methods like hydrogen treatment, which has poor electrical properties and is related to the reliability problem. On the other hand, ReRAM works by formation and rupture of O vacancy conducting filaments, while how this process happens in atomic scale remains unclear. In this thesis, density functional theory is applied to investigate the defect behaviours in oxides to address existing issues in these electronic devices. In chapter 3, the amorphous atomic structure of doped GeO2 and Ge/GeO2 interface networks are investigated to explain the improved MOSFET reliability observed in experiments. The reliability improvement has been attributed to the passivation of valence alternation pair (VAP) type O deficiency defects by doped rare earth metals. In chapter 4, the oxidation mechanism of GeO2 is investigated by transition state simulation of the intrinsic defect diffusion in the network. It is proposed that GeO2 is oxidized from the Ge substrate through lattice O interstitial diffusion, which is different from SiO2 which is oxidized by O2 molecule diffusion. This new mechanism fully explains the strange isotope tracer experimental results in the literature. In chapter 5, the Fermi level pinning effect is explored for metal semiconductor electrical contacts in Ge MOSFETs. It is found that germanides show much weaker Fermi level pinning than normal metal on top of Ge, which is well explained by the interfacial dangling bond states. These results are important to tune Schottky barrier heights (SBHs) for n-type contacts on Ge for use on Ge high mobility substrates in future CMOS devices. In chapter 6, we investigate the surface and subsurface O vacancy defects in three kinds of stable TiO2 surfaces. The low formation energy under O poor conditions and the +2 charge state being the most stable O vacancy are beneficial to the formation and rupture of conducting filament in ReRAM, which makes TiO2 a good candidate for ReRAM materials. In chapter 7, we investigate hydrogen behaviour in amorphous ZnO. It is found that hydrogen exists as hydrogen pairs trapped at oxygen vacancies and forms Zn-H bonds. This is different from that in c-ZnO, where H acts as shallow donors. The O vacancy/2H complex defect has got defect states in the lower gap region, which is proposed to be the origin of the negative bias light induced stress instability.

Published
2018
Full Text
View/download PDF

140. Tea Bud Detection Model in a Real Picking Environment Based on an Improved YOLOv5.

Author

Li, Hongfei, Kong, Min, and Shi, Yun

Subjects
*DEEP learning, *SPRING, *TEA, *BUDS, *PYRAMIDS
Abstract

The detection of tea bud targets is the foundation of automated picking of premium tea. This article proposes a high-performance tea bud detection model to address issues such as complex environments, small target tea buds, and blurry device focus in tea bud detection. During the spring tea-picking stage, we collect tea bud images from mountainous tea gardens and annotate them. YOLOv5 tea is an improvement based on YOLOv5, which uses the efficient Simplified Spatial Pyramid Pooling Fast (SimSPPF) in the backbone for easy deployment on tea bud-picking equipment. The neck network adopts the Bidirectional Feature Pyramid Network (BiFPN) structure. It fully integrates deep and shallow feature information, achieving the effect of fusing features at different scales and improving the detection accuracy of focused fuzzy tea buds. It replaces the independent CBS convolution module in traditional neck networks with Omni-Dimensional Dynamic Convolution (ODConv), processing different weights from spatial size, input channel, output channel, and convolution kernel to improve the detection of small targets and occluded tea buds. The experimental results show that the improved model has improved precision, recall, and mean average precision by 4.4%, 2.3%, and 3.2%, respectively, compared to the initial model, and the inference speed of the model has also been improved. This study has theoretical and practical significance for tea bud harvesting in complex environments. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

141. Issues in cox proportional hazards model with unequal randomization.

Author

Li, Hongfei, Li, Qian H., Tian, Chuan, and Hou, Kevin

Subjects
*FALSE positive error, *JENSEN'S inequality, *PROPORTIONAL hazards models, *REGRESSION analysis, *INFERENTIAL statistics, *PRAGMATICS
Abstract

The article discusses issues related to the Cox proportional hazards model with unequal randomization in clinical trials. It explains how unequal randomization ratios can impact the estimation and statistical inference of treatment effects, leading to bias and type I error inflation, especially with limited sample sizes. The article provides theoretical insights, simulation results, and practical guidance for study design when using the Cox PH model in analyses with unequal randomization. It emphasizes the importance of considering bias and type I error inflation when choosing randomization ratios and sample sizes, advocating for 1-sided hypotheses and cautioning against 2-sided hypotheses in drug development and evaluation. [Extracted from the article]

Published
2024
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results