Microstructural Evolution of a High W Content Ni-Based Superalloy at γ′ Sub-Solvus Temperatures

Sigeng Zhou,Naicheng Sheng,Shijie Sun,Shigang Fan,Jinjiang Yu,Guichen Hou,Jinguo Li,Yizhou Zhou,Xiaofeng Sun 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.1

The evolution of γ′ phase and γ/γ′ eutectic during short-time heat treatment of the Ni-based superalloy with high W content,K416B are investigated. In this study, high temperature Differential Scanning Calorimetry (DSC) is employed to designthe heat treatment experiments and the precipitate temperature of secondary γ′ is found in the cooling curve. The standardcoarsening model is applied to figure out the coarsening rate constant of γ′ precipitate. On this basis, a novel method isproposed to predict the globularization time of γ phase in γ/γ′ eutectic during the heat treatment process. As holding temperatureincreases, more γ lamellae convert to platelets before reaching thermodynamic equilibrium. Electron microscopyobservations exhibit the boundary splitting and necking formation on the γ plate surface. Moreover, the dissolution kineticsof γ phase is quantitatively assessed by JMAK model. The volume fraction descends rapidly in the initial stage, and thenreach to a threshold. Above proposed approaches are validated via various heat treatment experiments.

Delay Tolerant Packet Forwarding Algorithm Based on Location Estimation for Micro Aerial Vehicle Networks

( Shiji Li ),( Guyu Hu ),( Youwei Ding ),( Yun Zhou ) 한국인터넷정보학회 2020 KSII Transactions on Internet and Information Syst Vol.14 No.3

In search and rescue mission, micro aerial vehicles (MAVs) are typically used to capture image and video from an aerial perspective and transfer the data to the ground station. Because of the power limitation, a cluster of MAVs are required for a large search area, hence an ad-hoc wireless network must be maintained to transfer data more conveniently and fast. However, the unstable link and the intermittent connectivity between the MAVs caused by MAVs’ movement may challenge the packet forwarding. This paper proposes a delay tolerant packet forwarding algorithm based on location estimation for MAV networks, called DTN_est algorithm. In the algorithm, ferrying MAVs are used to transmit data between MAVs and the ground station, and the locations of both searching MAVs and ferrying MAVs are estimated to compute the distances between the MAVs and destination. The MAV that is closest to the destination is selected greedy to forward packet. If a MAV cannot find the next hop MAV using the greedy strategy, the packets will be stored and re-forwarded once again in the next time slot. The experiment results show that the proposed DTN_est algorithm outperforms the typical DTN_geo algorithm in terms of packet delivery ratio and average routing hops.

Crack Detection of the Urban Underground Utility Tunnel Based on Residual Feature Pyramid Attention Network

Yuan Zhou,Chengwei Li,Shoubin Wang,Guili Peng,Shijie Ma,Zijian Yang,Yueyong Feng 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.7

The defect detection in the urban underground utility tunnel faces the challenges of low illuminance and large shadow region. The images collected have problems such as noise and uneven illumination, posing higher requirements for the image feature extraction ability of the network model. A residual feature pyramid attention network based on dense connections (RFPADNet) is proposed in the defect detection of the urban underground comprehensive pipe in this paper. The proposed network consists of three dense blocks, and each dense block uses four residual feature pyramid attention models (RFPAM) as the main feature extractors. Its focus is to utilize residual learning to obtain the fused multi-scale feature information. Soft mask branches are added to the multi-scale channels to enhance the network model's ability to extract positive features. The experimental results show that the network model proposed in this paper has a training accuracy of 97.50%. Compared with the existing network models, it could achieve better results in various test sets, which has good feasibility and practicality.

Investigation on the stability of periodic motions of a flexible rotor-bearing system with two unbalanced disks

Chaofeng Li,Shihua Zhou,Shijie Jiang,Hexing Yu,Bang-chun Wen 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.7

The stability of periodic motion of a rotor-bearing system with two unbalanced disks is analyzed based on a multi-degree of freedom(M-DOF) finite element model. Nonlinear effects of supporting oil-film and inertia distributions as well as shearing effect are taken intoaccount. Focusing on the more realistic FE method to study the stability of nonlinear rotor-bearing system with the influence of the eccentricityphase, the stability calculation of the M-DOF FE model is done by using the combination of Shooting method and Newmarkmethod. Experiments with a rotor-bearing test rig (two disks on a shaft with two bearings) are then performed and results are presented. Itis found that typical instability characteristic is successfully produced. Through comparisons between calculated results and measurements,it is shown that the combination of Shooting method and Newmark method in studying the M-DOF rotor-bearing system is useful,especially for the complex rotor-bearing system. In addition, altering eccentricity phase of the two disks can significantly influence instabilitytype and speed. When the two disks are out of phase, the occurring of oil whip is restrained effectively. It is suggested that a carefulexamination should be made in modeling more complex non-linear rotor-bearing system.

Ginsenoside Rh2 reduces m6A RNA methylation in cancer via the KIF26B-SRF positive feedback loop

Chunmei Hu,Linhan Yang,Yi Wang,Shijie Zhou,Jing Luo,Yi Gu 고려인삼학회 2021 Journal of Ginseng Research Vol.45 No.6

Background: The underlying mechanisms of the potential tumor-suppressive effects of ginsenoside Rh2are complex. N6-methyladenosine (m6A) RNA methylation is usually dysregulated in cancer. This studyexplored the regulatory effect of ginsenoside Rh2 on m6A RNA methylation in cancer. Methods: m6A RNA quantification and gene-specific m6A RIP-qPCR assays were applied to assess totaland gene-specific m6A RNA levels. Co-immunoprecipitation, fractionation western blotting, andimmunofluorescence staining were performed to detect protein interactions and distribution. QRT-PCR,dual-luciferase, and ChIP-qPCR assays were conducted to check the transcriptional regulation. Results: Ginsenoside Rh2 reduces m6A RNA methylation and KIF26B expression in a dose-dependentmanner in some cancers. KIF26B interacts with ZC3H13 and CBLL1 in the cytoplasm of cancer cellsand enhances their nuclear distribution. KIF26B inhibition reduces m6A RNA methylation level in cancercells. SRF bound to the KIF26B promoter and activated its transcription. SRF mRNA m6A abundancesignificantly decreased upon KIF26B silencing. SRF knockdown suppressed cancer cell proliferation andgrowth both in vitro and in vivo, the effect of which was partly rescued by KIF26B overexpression. Conclusion: ginsenoside Rh2 reduces m6A RNA methylation via downregulating KIF26B expression insome cancer cells. KIF26B elevates m6A RNA methylation via enhancing ZC3H13/CBLL1 nuclear localization. KIF26B-SRF forms a positive feedback loop facilitating tumor growth.

Effect of Sulfur on Microstructures and Solidification Characteristics of a Nickel-Base Single Crystal Superalloy

Shaofeng Chen,Naicheng Sheng,Shigang Fan,Shijie Sun,Guichen Hou,Jinguo Li,Lirong Liu,Yizhou Zhou,Xiaofeng Sun 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.12

The effects of sulfur on the microstructures and solidification characteristics of a second-generation single crystal superalloywere clarified through optical microscope (OM), scanning electron microscope (SEM), differential scanning calorimetry(DSC) and electron probe microanalysis (EPMA). When sulfur was added to the alloy, the area fraction of theeutectic and microporosity decreased with the area fraction of MC carbides increasing. The γ / γ’ eutectic morphologychanged from mosaic + fan + coarse γ’ to mosaic + fan as the sulfur content increased, and very few γ / γ’ eutectic wasfound in the alloy with the highest sulfur content. Moreover, sulfur tended to segregate at the interdendritic regions andform Hf / Cr- rich sulfides, which were adjacent to the carbides or eutectic. This work not only uncovers some sulfideswrapped by eutectic or carbides, but also presents the solidification sequence of the interdendritic regions in high sulfurcontent alloy was discussed.

Facile synthesis of AgPt nano-pompons for efficient methanol oxidation: Morphology control and DFT study on stability enhancement

Tao Shao,Dehong Bai,Mingzhu Qiu,Yu Li,Qiankun Zhang,Ziyu Xue,Shijie He,Dongxia Zhang,Xibin Zhou 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.108 No.-

Facile synthesis of more dendritic and uniform Pt-based nanostructures with carbon materials couldgreatly reduce cost and increase Pt utilization for methanol oxidation reaction (MOR) in direct methanolfuel cell (DMFC). This study reports a novel one-pot method to fabricate AgPt nano-pompons (AgPt NPs)with the guidance of N-GQDs through AA reduce the precursor of Ag and Pt. Morphology characterizationdescribes N-GQDs as morphology guiding and dispersing agents to regulate the dendrite formation ofnano-pompons. Under the optimized conditions, the AgPt NPs (Ag1Pt2) display above 11 times improvementin electrocatalytic activity and higher stability for the MOR compared with Pt/C catalysts. Densityfunction theory (DFT) studies prove that the introduction of Ag can greatly enhance the adsorption of COon Pt and promote the transformation of CO to COOH. The facile synthetic method and excellent MORperformance endow AgPt NPs with great application prospect in DMFCs as an anode catalyst.