Hot Deformation Characteristics and Processing Map Analysis of Pre-Forged AZ80 Magnesium Alloy

Shi‑quan Huang,Ming Lu,Sheng‑lan Luo,Hai‑lin He,You‑ping Yi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

The hot deformation behavior of pre-forged AZ80 magnesium alloy is investigated by the isothermal compression tests attemperatures of 523–683 K and strain rates of 0.0001–0.1 s−1, and analyzed by the processing maps for guiding isothermaldie forging. Flow localization and even cracking occurs at low temperatures and high strain rates, where shear deformationdegree shows a positive correlation with the ��( ̇�� ) value. Two stability regions with high efficiency is found out by theprocessing maps. At common stability region with high temperatures and low strain rates, peak power dissipation efficiencydoes not represent optimum deformation condition as reported in other materials. A Z parameter criterion is introduced forparameters optimization. javascript:void(0); a new stability domain of 523–590 K and 0.0001–0.01 s−1 is observed, which istypical for fine microstructure composed of equiaxed clean α-Mg grains and big particles both about 1 μm (573 K/0.01 s−1).Super plasticity is speculated to occur at that condition.

Numerical investigation of two-phase flow characteristics in multiphase pump with split vane impellers

Yi Shi,Hongwu Zhu,Binbin Yin,Ruiting Xu,Jiate Zhang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.4

Multiphase pump is a cost-effective option for subsea oil and gas field development. The ability to handle different inlet gas volume fractions (GVFs) especially high inlet GVF is critical to the development of pump performance. In this study, the two-phase flow characteristics in normal impeller and split vane impeller at different inlet GVFs were investigated by steady numerical simulations. The gas distribution on blade-to-blade plane and meridional flow channel at different inlet GVFs were analyzed and compared. Gas accumulation area and movement characteristics of the gas-liquid flow in impeller flow passage were also pointed out by unsteady simulations. Experimental results of the pump differential pressure were compared with the numerical simulation results, to validate the accuracy of numerical simulation method. The flow characteristics in pump with modified impeller and its performance at different inlet GVFs were both compared with that of the normal impeller. The steady simulation results of normal impeller in different inlet GVFs show that gas concentrating area in the flow passage increases as inlet GVF grows. The unsteady simulation results indicate that gas pocket firstly occurs on the pressure side of impeller, then moves to the suction side in the middle area of blade and finally transfers to outlet of impeller and disappears. The errors between numerical simulation results and experiment data are below 10 %, which validated the feasibility of the numerical simulation method. Simulation results on the split vane impeller demonstrate that the gas accumulation area in flow passage of the modified impeller is dramatically decreased compared to that of the normal impeller. The performance of the modified impeller is generally better than the normal impeller especially in high inlet GVF conditions.

Surveillance of the progression and assessment of treatment endpoints for nonalcoholic steatohepatitis

Yi-Wen Shi,Jian-Gao Fan 대한간학회 2023 Clinical and Molecular Hepatology(대한간학회지) Vol.29 No.-

Nonalcoholic steatohepatitis (NASH) is an aggressive form of nonalcoholic fatty liver disease (NAFLD) characterized by steatosis-associated inflammation and liver injury. Without effective treatment or management, NASH can have life-threatening outcomes. Evaluation and identification of NASH patients at risk for adverse outcomes are therefore important. Key issues in screening NASH patients are the assessment of advanced fibrosis, differentiation of NASH from simple steatosis, and monitoring of dynamic changes during follow-up and treatment. Currently, NASH staging and evaluation of the effectiveness for drugs still rely on pathological diagnosis, despite sample error issues and the subjectivity associated with liver biopsy. Optimizing the pathological assessment of liver biopsy samples and developing noninvasive surrogate methods for accessible, accurate, and safe evaluation are therefore critical. Although noninvasive methods including elastography, serum soluble biomarkers, and combined models have been implemented in the last decade, noninvasive diagnostic measurements are not widely applied in clinical practice. More work remains to be done in establishing cost-effective strategies both for screening for at-risk NASH patients and identifying changes in disease severity. In this review, we summarize the current state of noninvasive methods for detecting steatosis, steatohepatitis, and fibrosis in patients with NASH, and discuss noninvasive assessments for screening at-risk patients with a focus on the characteristics that should be monitored at follow-up.

The Progress of Research on Chinese Stabilized Fertilizer

Shi Yuanliang,Wang Lingli,Shi Xiaoyu,Li Jie,Sun Yi 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

On factorizations of the subgroups of self-homotopy equivalences

Yi-Yun Shi,Hao Zhao 대한수학회 2008 대한수학회지 Vol.45 No.4

For a pointed space X, the subgroups of self-homotopy equivalences Aut#N (X), Aut­Ω(X), Aut*(X) and Aut∑(X) are considered, where Aut#N (X) is the group of all self-homotopy classes f of X such that f# = id : πi(X) → πi(X) for all i ≤ N ≤ ∞, AutΩ­(X) is the group of all the above f such that ­Ωf = id; Aut*(X) is the group of all selfhomotopy classes g of X such that g* = id : Hi(X) → Hi(X) for all i ≤ ∞, Aut∑(X) is the group of all the above g such that ∑g = id. We will prove that AutΩ­(X₁×...×Xn) has two factorizations similar to those of Aut#N (X₁×...×Xn) in reference [10], and that Aut§(X₁∨...∨Xn), Aut*(X₁∨...∨ Xn) also have factorizations being dual to the former two cases respectively. For a pointed space X, the subgroups of self-homotopy equivalences Aut#N (X), Aut­Ω(X), Aut*(X) and Aut∑(X) are considered, where Aut#N (X) is the group of all self-homotopy classes f of X such that f# = id : πi(X) → πi(X) for all i ≤ N ≤ ∞, AutΩ­(X) is the group of all the above f such that ­Ωf = id; Aut*(X) is the group of all selfhomotopy classes g of X such that g* = id : Hi(X) → Hi(X) for all i ≤ ∞, Aut∑(X) is the group of all the above g such that ∑g = id. We will prove that AutΩ­(X₁×...×Xn) has two factorizations similar to those of Aut#N (X₁×...×Xn) in reference [10], and that Aut§(X₁∨...∨Xn), Aut*(X₁∨...∨ Xn) also have factorizations being dual to the former two cases respectively.

Channel Prediction Based on Non-Uniform Pilot Pattern for Mobile Massive MIMO Scenarios

Shi, Yi,Wang, Xianling,Jiang, Zhiyuan 한국통신학회 2023 Journal of communications and networks Vol.25 No.4

Massive multiple input multiple output (MIMO) isa broadly used technique that can provide numerous gains inspectral efficiency. However, the degradation of beamformingperformance due to outdated channel state information at thetransmitter side (CSIT) induced by the mobility of users hasbeen a significant problem waiting to be solved. It is reported thatsystem performance will decrease 50 percent even in a moderate30 km/h speed scenario. However, the CSI cannot be simplyreconstructed through interpolation in high mobility scenariosdue to the limitation of pilot density — the phenomenon is knownas “Doppler aliasing”. To address this, we propose a novel non-uniform pilot pattern that can provide more spectrum resolutioncompared with the uniform pilot currently used in most commu-nication protocols. Meanwhile, we maintain the density of pilotsin order not to sacrifice the payload resources. Based on the novelpilot setting, we propose two-channel prediction schemes withcompressive sensing and matrix completion methods. Simulationresults show our scheme can outperform deep learning-based andauto-regressive-based methods for about 15 percent in terms ofaverage throughput in the simulated channel generated from theCOST2100 channel model. To further verify the applicability,we apply our schemes in real channels measured from a channelsounding campaign, the proposed methods also achieve 5 percentgain which validates their superiority over conventional methods.

Multitarget tracking in cluttered environment for a multistatic passive radar system under the DAB/DVB network

Shi, Yi Fang,Park, Seung Hyo,Song, Taek Lyul Springer (Biomed Central Ltd.) 2017 EURASIP journal on advances in signal processing Vol.2017 No.1

<P>The target tracking using multistatic passive radar in a digital audio/video broadcast (DAB/DVB) network with illuminators of opportunity faces two main challenges: the first challenge is that one has to solve the measurement-to-illuminator association ambiguity in addition to the conventional association ambiguity between the measurements and targets, which introduces a significantly complex three-dimensional (3-D) data association problem among the target-measurement illuminator, this is because all the illuminators transmit the same carrier frequency signals and signals transmitted by different illuminators but reflected via the same target become indistinguishable; the other challenge is that only the bistatic range and range-rate measurements are available while the angle information is unavailable or of very poor quality. In this paper, the authors propose a new target tracking algorithm directly in three-dimensional (3-D) Cartesian coordinates with the capability of track management using the probability of target existence as a track quality measure. The proposed algorithm is termed sequential processing-joint integrated probabilistic data association (SP-JIPDA), which applies the modified sequential processing technique to resolve the additional association ambiguity between measurements and illuminators. The SP-JIPDA algorithm sequentially operates the JIPDA tracker to update each track for each illuminator with all the measurements in the common measurement set at each time. For reasons of fair comparison, the existing modified joint probabilistic data association (MJPDA) algorithm that addresses the 3-D data association problem via 'supertargets' using gate grouping and provides tracks directly in 3-D Cartesian coordinates, is enhanced by incorporating the probability of target existence as an effective track quality measure for track management. Both algorithms deal with nonlinear observations using the extended Kalman filtering. A simulation study is performed to verify the superiority of the proposed SP-JIPDA algorithm over the MJIPDA in this multistatic passive radar system.</P>

Enhanced Electrochemical Properties of Surface Modified LiMn₂O₄ by Li-Fe Composites for Rechargeable Lithium Ion Batteries

Shi, Jin-Yi,Yi, Cheol-Woo,Liang, Lianhua,Kim, Keon Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.2

The surface modified $LiMn_2O_4$ materials with Li-Fe composites were prepared by a sol-gel method to improve the electrochemical performance of $LiMn_2O_4$ and were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and transmission electron microscopy (TEM)-EDS. XRD results indicate that all the samples (modified and pristine samples) have cubic spinel structures, and XRD, XPS, and TEM-EDS data reveal the formation of $Li(Li_xFe_xMn_{2-2x})O_4$ solid solution on the surface of particles. For the electrochemical properties, the modified material demonstrated dramatically enhanced reversibility and stability even at elevated temperature. These improvements are attributed to the formation of the solid solution, and thus-formed solid solution phase on the surface of $LiMn_2O_4$ particle reduces the dissolution of Mn ion and suppresses the Jahn-Teller effect.

인터넷쇼핑이 고객만족의 구매의도에 미치는 영향에 관한 연구 -중국 시장 중심으로-

( Shi Yi Yao ) 한국인터넷비즈니스학회 2014 인터넷비지니스연구 Vol.15 No.1

인터넷 쇼핑이 새로운 유통 채널이 되었고, 왕성히 발전하기 때문에 연구할 가치가 있다. 이 논문은 인터넷 쇼핑의 편리성, 저렴한 가격, 만족도, 고객의 재구매 의도.가 연구되었다. 이 연구를 위하여 샘플링으로 240부 설문 조사지를 발부하였다. 그 다음에 spss20.0으로 연구 분석하였다. 연구 방법은 성과 분석, 신뢰도 분석, 공동 분석, 회귀 분석으로 인터넷 쇼핑의 편리성, 저렴한 가격, 만족도, 고객의 재구매 의도를 확인하였다. 이 연구의 중요성은 고객의 구매력의 영향을 미치는 4 가지 요소를 분석을 하는 것이다. 연구결과는 인터넷 쇼핑의 큰 잠재력을 보여주었다. 결론으로, 인터넷쇼핑이 고객만족의 구매의도에 많은 영향을 미치는 것으로 조사되었다. Internet shopping is worth studying since it has become a new distribution channel and its booming development. Through research described in this paper: the convenience of internet shopping, low price, pleasure and diversity impact to the customers`re-purchase intent. This study examined a random sample of 240 copies of questionnaires. And use spss20.0 research and analysis. By using the following study methods: result analysis, reliability analysis, mutual analysis and regression analysis, proved that, the convenience of internet shopping, low price, pleasure and diversity produced positive impact to the customers` re-purchase intent. The significance of this study is analyzing the impact the customers` purchasing power by the four factors of internet shopping motivation. And the result shows great potential of internet shopping. In conclusion of this study will contribute to growth in the network market, so that flourish the emerging distribution channels.

An Investigation of LiFePO₄/Poly(3,4-ethylenedioxythiophene) Composite Cathode Materials for Lithium-Ion Batteries

Shi, Jin-Yi,Yi, Cheol-Woo,Kim, Keon Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.9