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.

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

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

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.

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>

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

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.

ON FACTORIZATIONS OF THE SUBGROUPS OF SELF-HOMOTOPY EQUIVALENCES

Shi, Yi-Yun,Zhao, Hao Korean Mathematical Society 2008 대한수학회지 Vol.45 No.4

For a pointed space X, the subgroups of self-homotopy equivalences $Aut_{\sharp}_N(X)$, $Aut_{\Omega}(X)$, $Aut_*(X)$ and $Aut_{\Sigma}(X)$ are considered, where $Aut_{\sharp}_N(X)$ is the group of all self-homotopy classes f of X such that $f_{\sharp}=id\;:\;{\pi_i}(X){\rightarrow}{\pi_i}(X)$ for all $i{\leq}N{\leq}{\infty}$, $Aut_{\Omega}(X)$ is the group of all the above f such that ${\Omega}f=id;\;Aut_*(X)$ is the group of all self-homotopy classes g of X such that $g_*=id\;:\;H_i(X){\rightarrow}H_i(X)$ for all $i{\leq}{\infty}$, $Aut_{\Sigma}(X)$ is the group of all the above g such that ${\Sigma}g=id$. We will prove that $Aut_{\Omega}(X_1{\times}\cdots{\times}X_n)$ has two factorizations similar to those of $Aut_{\sharp}_N(X_1{\times}\cdots{\times}\;X_n)$ in reference [10], and that $Aut_{\Sigma}(X_1{\vee}\cdots{\vee}X_n)$, $Aut_*(X_1{\vee}\cdots{\vee}X_n)$ also have factorizations being dual to the former two cases respectively.

Characterization of Vaginal Microbiota Associated with Pregnancy Outcomes of Artificial Insemination in Dairy Cows

Shi-Yi Chen,Feilong Deng,Ming Zhang,Xian-Bo Jia,Song-Jia Lai 한국미생물·생명공학회 2020 Journal of microbiology and biotechnology Vol.30 No.6

The profitability of the dairy and beef industries is largely affected by the actually achieved reproductive efficiency. Although a large proportion of cows worldwide are bred by artificial insemination (AI) services, many potential factors affecting the outcome of pregnancy by AI remain to be addressed. In the present study, we investigated the vaginal microbiota by high-throughput sequencing of 16S rRNA gene and analyzed their association with differential pregnancy outcomes (i.e., pregnant vs. nonpregnant) of multiple AI services in dairy cows. Sequencing of the V3-V4 region totally produced 512,046 high-quality sequences that were computationally clustered into 2,584 operational taxonomic units (OTUs). All OTUs were taxonomically assigned to 10 bacterial phyla. There were statistically significant differences among the three AI service times (T1, T2 and T3) with respect to the Shannon index and number of observed OTUs (p < 0.05). Bray-Curtis distance-based PCoA analysis also revealed that T2 group could be significantly distinguished from T1 and T3. However, no significant difference between the pregnant and nonpregnant cows was found in confidence regarding both alpha diversity and beta diversity. These results could help us better understand the possible influence of vaginal microbial community on pregnancy outcomes of AI service in cows.

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.

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.