Effects of α-Si₃N₄ seeds and sintering additives on properties of porous silicon nitride ceramics fabricated by carbothermal reduction

Yuan Lu,Ji-Qiang Gao,Jian-feng Yang 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.6

In this paper, porous Si3N4 ceramics were fabricated by carbothermal reduction between silicon dioxide and carbon [1]. The influences of α-Si3N4 seeds and sintering additives on the microstructure and mechanical properties of porous Si3N4 ceremics were investigated. XRD analysis proved the complete formation of a single-phase β-Si3N4. SEM analysis showed that the resultant porous Si3N4 ceramics had a fine microstructure and a uniform pore structure. The sintered sample with Lu2O3 as sintering additive showed finer, higher aspect ratio β-Si3N4 grains. The addition of Eu2O3 accelerated the densification of porous Si3N4 ceramics, decreased the porosity and increased the flexural strength. The addition of α-Si3N4 seeds accelerated the formation of the α-Si3N4 phase at a low temperature and the α-β phase transformation process at a high temperature. With an increase in the α-Si3N4 seeds content, the porosity decreased, and the flexural strength increased accordingly. In this paper, porous Si3N4 ceramics were fabricated by carbothermal reduction between silicon dioxide and carbon [1]. The influences of α-Si3N4 seeds and sintering additives on the microstructure and mechanical properties of porous Si3N4 ceremics were investigated. XRD analysis proved the complete formation of a single-phase β-Si3N4. SEM analysis showed that the resultant porous Si3N4 ceramics had a fine microstructure and a uniform pore structure. The sintered sample with Lu2O3 as sintering additive showed finer, higher aspect ratio β-Si3N4 grains. The addition of Eu2O3 accelerated the densification of porous Si3N4 ceramics, decreased the porosity and increased the flexural strength. The addition of α-Si3N4 seeds accelerated the formation of the α-Si3N4 phase at a low temperature and the α-β phase transformation process at a high temperature. With an increase in the α-Si3N4 seeds content, the porosity decreased, and the flexural strength increased accordingly.

Delay Dependent Local Stabilization Conditions for Time-delay Nonlinear Discrete-time Systems Using Takagi-Sugeno Models

Luís F. P. Silva,Valter J. S. Leite,Eugênio B. Castelan,Gang Feng 제어·로봇·시스템학회 2018 International Journal of Control, Automation, and Vol.16 No.3

We propose convex conditions for stabilization of nonlinear discrete-time systems with time-varying delay in states through a fuzzy Takagi-Sugeno (T-S) modeling. These conditions are developed from a fuzzy Lyapunov-Krasovskii function and they are formulated in terms of linear matrix inequalities (LMIs). The results can be applied to a class of nonlinear systems that can be exactly represented by T-S fuzzy models inside a specific region called the region of validity. As a consequence, we need to provide an estimate of the set of safe initial conditions called the region of attraction such that the closed-loop trajectories starting in this set are assured to remain in the region of validity and to converge asymptotically to the origin. The estimate of the region of attraction is done with the aid of two sets: one dealing with the current state, and the other concerning the delayed states. Then, we can obtain the feedback fuzzy control law depending on the current state, xk, and the maximum delayed state vector, xk-d. It is shown that such a control law can locally stabilize the nonlinear discrete-time system at the origin. We also develop convex optimization procedures for the computation of the fuzzy control gains that maximize the estimates of the region of attraction. We present two examples to demonstrate the efficiency of the developed approach and to compare it with other approaches in the literature.

Nonlinear tribo-dynamic model of helicopter mid-reducer system under light loss of lubrication

Feng-xia Lu,Xuechen Cao,He-yun Bao,Rupeng Zhu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.11

When the helicopter tail transmission system loses oil due to damage, the system needs to persist for 30 minutes. Therefore, the nonlinear tribo-dynamics model of the helicopter intermediate reducer (HIR) is established, which is coupled with the loss of oil lubrication. To simulate condition of the HIR system under the loss of lubrication (LOL), this study begins by establishing a complete HIR system CFD model, and analyse the lubrication of the gear tooth surface and the oil churning/windage under different lubrication conditions. Then, a coupled model based on the result of the CFD is proposed to calculate the coefficient of friction (COF) under the condition of light loss of lubrication (LLOL). The results show that COF gradually decreases first and then increases rapidly.

NORMAL FAMILIES AND SHARED HOLOMORPHIC FUNCTIONS

Lu, Feng Korean Mathematical Society 2012 대한수학회보 Vol.49 No.1

In this paper, we study the problem of normal families and deduce some results, which improve and generalize several related theorems obtained by Pang [7], Fang and Xu [3], L$\ddot{u}$, Xu, and Yi [6]. Mean-while, some examples are given to show the sharpness of our results.

<i>Plasmodium ovale curtisi</i> and <i>Plasmodium ovale wallikeri</i> in Chinese travelers: Prevalence of novel genotypes of circumsporozoite protein in the African continent

Lu, Feng,Ahmed, Md Atique,Xu, Simin,Xu, Sui,Han, Jin-Hee,Liu, Qianyan,Chen, Jing,Zhu, Guoding,Zhou, Huayun,Cao, Jun,Han, Eun-Taek ELSEVIER 2019 INFECTION GENETICS AND EVOLUTION Vol.70 No.-

<P><B>Abstract</B></P> <P>Imported malaria due to <I>Plasmodium ovale curtisi</I> and <I>P</I>. <I>ovale wallikeri</I> infections from African countries has increased recently (2011–2014) in Chinese travelers. We report novel genotypes, their prevalence and the predominant haplotypes of <I>P</I>. <I>ovale curtisi</I> and <I>P</I>. <I>ovale wallikeri</I> circumsporozoite protein (CSP) from 20 African countries in Chinese travelers. These genotypes should be considered while designing a CSP-based vaccine against <I>P</I>. <I>ovale</I> malaria.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This is the first to report the <I>csp</I> genotypes and their heterogeneity for <I>P. ovale curtisi</I> and <I>P. ovale wallikeri</I> parasites from African countries. </LI> <LI> Ten <I>csp</I> genotypes of <I>P</I>. <I>ovale curtisi</I> and 13 <I>csp</I> genotypes of <I>P</I>. <I>ovale wallikeri</I> based on the arrangement of central repeat motifs were found. </LI> <LI> Fifteen <I>csp</I> haplotypes of <I>P</I>. <I>ovale curtisi</I> and 10 <I>csp</I> haplotypes of <I>P</I>. <I>ovale wallikeri</I> on central repeat motifs were identified. </LI> <LI> These genotypes should be considered while designing a CSP-based vaccine against <I>P</I>. <I>ovale</I> malaria. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Parameter design method for the heat transfer performance of a fan-driven gearbox under planetary gear opening and oil-return conditions

Feng-xia Lu,Lijuan Yuan,Zhiqiang Zhao,Chun-lei Wang,He-yun Bao 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.9

On the basis of the computational fluid dynamics (CFD) method, this study calculates the surface convective heat transfer coefficients of the sun gear, planetary gear, ring gear, and bearing before and after the opening of the planetary gear of a fan-driven gearbox. A numerical fitting method is used to establish the calculation model of the convective heat transfer coefficients of the sun gear, planetary gear, ring gear, and bearing under the open-hole oilreturn condition. The convective heat transfer coefficients of each element are compared before and after the hole is bored, and the design method for the gearbox parameters with the objective of heat transfer performance is proposed. Result shows that the convective heat transfer coefficients of each element are increased after oil is returned from the hole of the planetary gear, and the change rate of the convective heat transfer coefficient of the raceway in the planetary gear bearing is the highest. When the aperture of the planetary gear is 7 mm and the number of holes is four, the heat transfer performance of the gearbox is the best. The maximum error between the convection heat transfer coefficient fitting formula value and the CFD simulation calculation result is 1.0558 %.

A NOTE ON THE BRÜCK CONJECTURE

Lu, Feng Korean Mathematical Society 2011 대한수학회보 Vol.48 No.5

In 1996, Br$\ddot{u}$ck studied the relation between f and f' if an entire function f shares one value a CM with its first derivative f' and posed the famous Br$\ddot{u}$ck conjecture. In this work, we generalize the value a in the Br$\ddot{u}$ck conjecture to a small function ${\alpha}$. Meanwhile, we prove that the Br$\ddot{u}$ck conjecture holds for a class of meromorphic functions.

THE BRÜCK CONJECTURE AND ENTIRE FUNCTIONS SHARING POLYNOMIALS WITH THEIR κ-TH DERIVATIVES

Lu, Feng,Yi, Hongxun Korean Mathematical Society 2011 대한수학회지 Vol.48 No.3

The purpose of this paper is twofold. The first is to establish a uniqueness theorem for entire function sharing two polynomials with its ${\kappa}$-th derivative, by using the theory of normal families. Meanwhile, the theorem generalizes some related results of Rubel and Yang and of Li and Yi. Several examples are provided to show the conditions are necessary. The second is to generalize the Br$\"{u}$-ck conjecture with the idea of sharing polynomial.

Optimization Model of Reliable Data Storage in Cloud Environment Using Genetic Algorithm

Feng Liu,Haitao Wu,Xiaochun Lu,Xiyang Liu 보안공학연구지원센터 2014 International Journal of Grid and Distributed Comp Vol.7 No.6

Massive data storage is one of the great challenges for cloud computing service, and reliable storage of sensitive data directly affects quality of storage service. In this paper, based on analysis of data storage process in cloud environment, the cost of massive data storage is considered to be comprised of data storage price, data migration and communication; and the storage reliability consists of data transmission reliability and hardware dependability. A multi-objective optimization model for reliable massive storage is proposed, in which storage cost and reliability are the objectives. Then, a genetic algorithm for solving the model is designed. Finally, experimental results indicate that the proposed model is positive and effective.

Entire Functions That Share One Value With Their Derivatives

Lu, Feng,Xu, Junfeng Department of Mathematics 2007 Kyungpook mathematical journal Vol.47 No.3

In the paper, we use the theory of normal family to study the problem on entire function that share a finite non-zero value with their derivatives and prove a uniqueness theorem which improve the result of J.P. Wang and H.X. Yi.