Beautiful flowers and memorial greeting cards our mothers are given on Mother’s Day are associated with a touching story.
One day in September, Juche 101 (2012), the respected Comrade Kim Jong Un visited ...
One day the respected Comrade Kim Jong Un visited Mirim Riding Club with its completion just ahead.
Wherever he went, he repeatedly expressed great satisfaction, feeling delighted beyond measure at the wonderful scene ...
Mining Method Selection (MMS) is the first and the most critical problem in mine design, and it depends on some parameters such as geometric and geological features and economic factors.
The ultimate goals of mining method selection are maximizing profit, enhancing mining recovery rate and providing a safe mining environment.
Selection of an appropriate mining method is a complex task that requires consideration of many technical, economic, social, and historical factors.
Pak Myong Chun, a section head at the Faculty of Mining Engineering, determined the factors affecting MMS with the help of some mining experts, and selected the most suitable mining method using the hesitant fuzzy group decision-making (HFGDM) and technique for order performance by similarity to the ideal solution (TOPSIS). These factors included type of deposit, slope of deposit, thickness of orebody, depth below the surface, grade distribution, hanging wall Rock Mass Rating (RMR), footwall RMR, ore body RMR, recovery, capital cost, mining cost, annual productivity, and environmental impact.
Firstly, he proposed a group decision-making (GDM) method to determine the weights of several attributes based on the score function with decision-makers’ weights, in which the n-dimensional hesitant fuzzy environment takes the form of hesitant fuzzy sets (HFS). Then, he calculated the weights of these factors using the HFGDM method. He compared seven mining methods for an apatite mine to select the optimal mining method using the TOPSIS method.
The results showed that the sub-level stoping method with priority of 0.811 3 was the best for the studied mine.
Generally, least squares (LS) method treats only random errors of observation vector in adjustment function models. However, both observation vector and elements of coefficient matrix of an adjustment function model contain random errors. Therefore, the adjustment result of least square method does not guarantee a global-optimal solution.
Since total least square (TLS) method takes into account both random errors of observation vector and coefficient matrix based on an errors-in-variables (EIV) model, it is possible to improve the accuracy more than the result by LS method. TLS method has been further systematically developed and widely applied to many science and engineering problems, namely some practical problems, such as those in signal processing, statistical calculation and regression analysis.
Kim Jung Hyang, a researcher at the Faculty of Earth Science and Technology, has described a parameter adjustment method based on Weighted Total Least Square (WTLS) method and verified effectiveness of this method through application in simulated network. He has shown its advantage in comparison with classical LS and TLS methods.
The results show that the WTLS method based on an EIV model can further improve the accuracy of adjustment results as it handles simultaneously all kinds of random errors involved in the observation system.
In the environmental protection and petroleum industries, advanced technologies for separating water and oil are essential. Selective separation of oil and water is an important means of oil and water separation, and superoleophilic and superoleophobic properties of microstructure surface in water have attracted attentions of many researchers. Contact angle is greatly affected by interactions between the liquid and the solid and by chemical characteristics and roughness of a solid surface. For a certain solid surface, surface roughness is a key factor in controlling contact angle.
Contact angle is usually used for study of wetting phenomenon while wetting equations connect experimental measurement variables and wetting phenomenon. Wettability phenomenon can be theoretically explained by wettability equation.
Previous numerical simulations on static contact angle and dynamic contact angle of droplets on surfaces were mainly directed to water droplets in the air. Two-dimensional numerical simulations were used to study static and dynamic properties of water droplets in the air. Numerical simulations on static contact angles and dynamic contact angles of oil droplets in water were rarely found.
Choe Hyon Chol, a researcher at the Faculty of Mechanical Science and Technology, has conducted a 3-dimensional numerical simulation on the underwater apparent contact angle of oil droplets on the microstructure-textured surface by VOF method.
The results are as follows.
The height of a microstructure layer on the surface is an important variable that affects the wettability of a solid surface. When the surface of material is oleophobic in water, an increased microstructure height increases roughness factor, apparent contact angle of an oil droplet and oleophobic nature of surface. When the surface of material is oleophilic in water, an increased microstructure height reduces apparent contact angle and makes the surface more oleophilic.