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Yuming Qi,Tengwu He,Miaolin Feng 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7
Adding nanotwins to a metal could be a way to effectively improve its strength without suppressing its tensile ductility, whichsuggests that their unique nanostructure may alter microstructure evolution and deformation mechanisms. In this work, weperform a molecular dynamics-based tension simulation of two-dimension (2D) polycrystalline copper (Cu) with embeddednanotwins under uniaxial stress conditions. The results of MD-simulation reveal that the spacing of the twin boundarieshad a significant effect on the mechanical properties of nanotwinned materials. Specifically, an irregular relationship isfound between the twin boundary spacing ( DT ) and the strength of the material. It exhibits that the peak stress reached amaximum at DT = 12.5 nm and decreased thereafter with increasing average DT . However, flow stress reaches a maximumat a critical value of DT = 7 nm. According to the analysis of microstructure evolution, the presence of nanotwins hinder themotion of partial dislocations and stacking faults, and the stress-concentrated region leads to the transition from coherenttwin boundaries to incoherency. The stress-concentrated region locates in the step of incoherent would release the intrinsicstacking faults responsible for the formation of hierarchical contraction nanotwins stacking faults which efficiently improvesthe strength of Cu. In addition, as the tension proceeds, some samples begin to display the secondary twinning. This workwill be helpful for further investigation the nucleation and evolution of 2D nanotwinned metals and for formulating effectivestrength criteria for 2D nanotwinned metals.
COMPLETE MONOTONICITY OF A DIFFERENCE BETWEEN THE EXPONENTIAL AND TRIGAMMA FUNCTIONS
Feng Qi,Xiao-Jing Zhang 한국수학교육학회 2014 純粹 및 應用數學 Vol.21 No.2
In the paper, by directly verifying an inequality which gives a lowerbound for the first order modified Bessel function of the first kind, the authors supplya new proof for the complete monotonicity of a difference between the exponentialfunction e^(1/t) and the trigamma function ψ'(t) on (0, ∞).
Four logarithmically completely monotonic functions involving gamma function
Feng Qi,Da-Wei Niu,Jian Cao,Shou-Xin Chen 대한수학회 2008 대한수학회지 Vol.45 No.2
In this paper, two classes of functions, involving a parameter and the classical Euler gamma function, and two functions, involving the classical Euler gamma function, are verified to be logarithmically completely monotonic in (-½, ∞) or (0, ∞); some inequalities involving the classical Euler gamma function are deduced and compared with those originating from certain problems of traffic flow, due to J. Wendel and A. Laforgia, and relating to the well known Stirling’s formula. In this paper, two classes of functions, involving a parameter and the classical Euler gamma function, and two functions, involving the classical Euler gamma function, are verified to be logarithmically completely monotonic in (-½, ∞) or (0, ∞); some inequalities involving the classical Euler gamma function are deduced and compared with those originating from certain problems of traffic flow, due to J. Wendel and A. Laforgia, and relating to the well known Stirling’s formula.
Research on Network Defense Graph Model in Network Security
Feng Qi,Haili Xu 보안공학연구지원센터 2016 International Journal of Security and Its Applicat Vol.10 No.11
Security analysis and attack-defense modeling are effective method to identify the vulnerabilities of information systems for proactive defense. The attack graph model reflects only attack actions and system state changes, without considering the perspective of the defenders. To assess the network information system and comprehensively show attack and defense strategies and theirs cost, a defense graph model is proposed. Compared with the attack graph, the model makes some improvements. Defense graph will be mapped to the attack and defense game model, in order to provide a basis for active defense policy decision. What’s more, a generation algorithm of defense graph is proposed. A representative example is provided to illustrate our models and generation algorithm.
OME PROPERTIES OF THE BERNOULLI NUMBERS OF THE SECOND KIND AND THEIR GENERATING FUNCTION
Qi, Feng,Zhao, Jiao-Lian Korean Mathematical Society 2018 대한수학회보 Vol.55 No.6
In the paper, the authors find a common solution to three series of differential equations related to the generating function of the Bernoulli numbers of the second kind and present a recurrence relation, an explicit formula in terms of the Stirling numbers of the first kind, and a determinantal expression for the Bernoulli numbers of the second kind.
Feng Qi,Xiao-Jing Zhang 대한수학회 2015 대한수학회보 Vol.52 No.3
In the paper, the authors discover an integral representation, some inequalities, and complete monotonicity of the Bernoulli numbers of the second kind.
Qi Feng Li,Chen Guang Liu,김재창 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.1
The synthesis of thiophene from the reaction of n-Butanol and carbon disulfide was performed in a fixedbed reactor in the presence of promoted chromia on γ-alumina. A high selectivity to thiophene (87%) and a long lifetime of the catalyst (55 hour) was obtained at 450℃with a 1 : 6 n-Butanol to carbon disulfide molar ratio and LHSV 1 h−1 over γ-Al2O3 promoted by 7% K2CO3 with 15% Cr2O3 loaded. The catalytic behavior of these catalysts can be attributed to their dual-functional acidity and dehydrogenating and cyclized properties.
FOUR LOGARITHMICALLY COMPLETELY MONOTONIC FUNCTIONS INVOLVING GAMMA FUNCTION
Qi, Feng,Niu, Da-Wei,Cao, Jian,Chen, Shou-Xin Korean Mathematical Society 2008 대한수학회지 Vol.45 No.2
In this paper, two classes of functions, involving a parameter and the classical Euler gamma function, and two functions, involving the classical Euler gamma function, are verified to be logarithmically completely monotonic in $(-\frac{1}{2},\infty)$ or $(0,\infty)$; some inequalities involving the classical Euler gamma function are deduced and compared with those originating from certain problems of traffic flow, due to J. Wendel and A. Laforgia, and relating to the well known Stirling's formula.
SOME LOGARITHMICALLY COMPLETELY MONOTONIC FUNCTIONS RELATED TO THE GAMMA FUNCTION
Qi, Feng,Guo, Bai-Ni Korean Mathematical Society 2010 대한수학회지 Vol.47 No.6
In this article, the logarithmically complete monotonicity of some functions such as $\frac{1}{[\Gamma(x+1)]^{1/x}$, $\frac{[\Gamma(x+1)]^{1/x}}{x^\alpha}$, $\frac{[\Gamma(x+1)]^{1/x}}{(x+1)^\alpha}$ and $\frac{[\Gamma(x+\alpha+1)]^{1/(x+\alpha})}{[\Gamma(x+1)^{1/x}}$ for $\alpha{\in}\mathbb{R}$ on ($-1,\infty$) or ($0,\infty$) are obtained, some known results are recovered, extended and generalized. Moreover, some basic properties of the logarithmically completely monotonic functions are established.