Diagnostics by means of the linear discriminant function X = ∑pi=1bixi requires a knowledge of all the p symptoms that are arguments of this function. However, some responses are…
Abstract
Diagnostics by means of the linear discriminant function X = ∑pi=1bixi requires a knowledge of all the p symptoms that are arguments of this function. However, some responses are often missing. One may overcome this difficulty by constructing two acceptance zones whose boundaries depend on the number of the utilized symptoms. One of the two alternatives is accepted if the “incomplete” sum Xp−j = ∑p−ji=1bixi, j being the symptom number counted from the end of the list, crosses one of the boundaries. Otherwise the next symptom must be enlisted. Formulae defining the boundaries of the acceptance zones and the percentage of the patients whose diagnosis requires not more than p‐j symptoms are given. When the sum Xp−1 remains in the indifferent zone one may obtain the full discriminant function by replacing the missing data xi with the mean value xi. The increase of the probability of misclassification due to this procedure is calculated.
Lina Si, Yan Pan, Xiaoqing Zhang, Jie Wang, Jia Yao, Yanjie Wang, Fengbin Liu and Feng He
This paper aims to clarify the effects of metallic nanoparticles (NPs) additives and room temperature ionic liquids (ILs) on the tribological performance of electric contacts.
Abstract
Purpose
This paper aims to clarify the effects of metallic nanoparticles (NPs) additives and room temperature ionic liquids (ILs) on the tribological performance of electric contacts.
Design/methodology/approach
Tribological properties of copper (Cu) and silver (Ag) NPs as lubricant additives in different lubricants of ILs or polyalphaolefin (PAO) oils under applied electric currents were investigated. After tribological tests, morphologies of worn surfaces were observed; meanwhile, lubrication and anti-wear properties were analyzed.
Findings
The mixture solution of the IL and Cu NPs showed desirable lubrication and anti-wear properties due to the reduction of electrocorrosion and the enhancement of rolling effects of particles in the contact region. The anti-wear performance of Cu NPs is better than that of Ag NPs due to the difference in the particle size. The PAO oil with the Cu NPs additives showed poor lubrication properties due to the low solubility of the particles in the oil. When the direction of applied current was changed, the friction of the lubricant with better conductivity was more stable in the variation trend.
Originality/value
This paper begins with a study of tribological properties of Cu and Ag NPs as lubricant additives in different lubricants of IL or PAO oils under applied electric currents. The authors then propose several methods and possible solutions which could be implemented to improve the tribological performance of electric contacts.
Details
Keywords
Zhongkai Shen, Shaojun Li, Zhenpeng Wu, Bowen Dong, Wenyan Luo and Liangcai Zeng
This study aims to investigate the effects of irregular groove textures on the friction and wear performance of sliding contact surfaces. These textures possess multiple depths…
Abstract
Purpose
This study aims to investigate the effects of irregular groove textures on the friction and wear performance of sliding contact surfaces. These textures possess multiple depths and asymmetrical features. To optimize the irregular groove texture structure of the sliding contact surface, an adaptive genetic algorithm was used for research and optimization purposes.
Design/methodology/approach
Using adaptive genetic algorithm as an optimization tool, numerical simulations were conducted on surface textures by establishing a dimensionless form of the Reynolds equation and setting appropriate boundary conditions. An adaptive genetic algorithm program in MATLAB was established. Genetic iterative methods were used to calculate the optimal texture structure. Genetic individuals were selected through fitness comparison. The depth of the groove texture is gradually adjusted through genetic crossover, mutation, and mutation operations. The optimal groove structure was ultimately obtained by comparing the bearing capacity and pressure of different generations of micro-convex bodies.
Findings
After about 100 generations of iteration, the distribution of grooved textures became relatively stable, and after about 320 generations, the depth and distribution of groove textures reached their optimal structure. At this stage, irregular texture structures can support more loads by forming oil films. Compared with regular textures, the friction coefficient of irregular textures decreased by nearly 47.01%, while the carrying capacity of lubricating oil films increased by 54.57%. The research results show that irregular texture structures have better lubrication characteristics and can effectively improve the friction performance of component surfaces.
Originality/value
Surface textures can enhance the friction and lubrication performance of metal surfaces, improving the mechanical performance and lifespan of components. However, surface texture processing is challenging, as it often requires multiple experimental comparisons to determine the optimal texture structure, resulting in high trial-and-error costs. By using an adaptive genetic algorithm as an optimization tool, the optimal surface groove structure can be obtained through simulation and modeling, effectively saving costs in the process.
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Qingshun Bai, Wanmin Guo, Yuhao Dou, Xin He, Shun Liu and Yongbo Guo
The purpose of this paper is to reveal the mechanism of graphene low-temperature friction and provide a theoretical basis for the application of graphene.
Abstract
Purpose
The purpose of this paper is to reveal the mechanism of graphene low-temperature friction and provide a theoretical basis for the application of graphene.
Design/methodology/approach
A probe etching model of graphene on the copper substrate was established to obtain the friction pattern of graphene with different layers in the temperature interval from 100 to 300 K. The friction mechanism was also explained from a microscopic perspective based on thermal lubrication theory. Low-temperature friction experiments of graphene were carried out by atomic force microscopy to further verify the graphene low-temperature friction law.
Findings
Graphene nanofriction experiments were conducted at 230–300 K. Based on this, more detailed simulation studies were performed. It is found that the combined effect of thermolubricity and thermal fluctuations affects the variation of friction. For monolayer graphene, thermolubricity is the main influence, and friction decreases with increasing temperature. For multilayer graphene, thermal fluctuations gradually become the main influencing factor as the temperature rises, and the overall friction becomes larger with increasing temperature.
Originality/value
Graphene with excellent mechanical properties provides a new way to reduce the frictional wear of metallic materials in low-temperature environments. The friction laws and mechanisms of graphene in low-temperature environments are of great significance for the expansion of graphene application environments.