Jo Feb 4, 2025
Nowadays NdFeB magnets are widely used in many applications such as electric two-wheelers, air conditioners, hybrid and electric cars, MRI scanners, wind generators, HDD, acoustic transducers, magnetic separators, etc. Thus, the global demand for NdFeB magnets is expected to continuously increase in the near future.
However, the supply of rare earth elements including neodymium, praseodymium and dysprosium for NdFeB magnets does not meet this growing demand, so rare earth elements are regarded as critical elements. Despite their criticality, less than 1% of rare earths are being recycled from end-of-life rare earth permanent magnets. Moreover, during the manufacturing process of NdFeB magnets, approximately 20~30% of rare earth alloy are lost and stockpiled as industrial waste. Therefore, development of an efficient recycling process for separation and recovery of rare earths from end-of-life products and magnet waste is an important issue.
Rare earth double sulfate precipitation is a traditional method for separation of rare earths from non-rare earths, which has advantages such as simple operation, low reagent cost, easy filtration of rare earth precipitates, high recovery of rare earths, etc. However, recovery of rare earths from NdFeB magnet waste by the rare earth double sulfate precipitation has not been reported.
Kim Sok Chol, a section head at the Faculty of Chemical Engineering, has succeeded in applying the rare earth double sulfate precipitation to the separation and recovery of rare earths from the solution obtained by leaching NdFeB magnet waste with sulfuric acid on a laboratory scale. He has also conducted a pilot plant test in order to investigate and optimize the various steps of the whole process for its application on an industrial scale.
The process includes leaching of NdFeB magnet waste by sulfuric acid, precipitation of rare earths in the form of double sulfate by sodium chloride, and conversion of rare earth double sulfates into hydroxides.
The yields of neodymium and dysprosium in the whole process were 92.3% and 90.8%, respectively. In the final rare earth hydroxides, the total rare earth oxides (TREO) content was 79.8%, where the contents of neodymium and dysprosium were 94.2% and 5.8%, respectively.
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Jo Feb 3, 2025
Selection of the optimal plan for maintaining the roadway affected by mining operations, when mining coal seams in weak rock formations with complex conditions of occurrence, has been studied a lot over the past decades, which has brought about many successes.
The optimal design of roadway maintenance plan requires a precise understanding of the mechanical properties of the surrounding rock mass, the interaction between the rock mass and the installed support system, and the stress distribution induced around the mining face and around the tunnel. Hence, researchers have been trying to solve the roadway maintenance problem by empirical methods such as mechanical, statistical and visual methods and numerical simulation analysis.
Empirical methods, where the complex mechanical interaction between rock mass and roof support is represented by simple equations, are supported by a large database, but they generally neglect the stress distribution generated by mining, the geological relationships of roof support management systems, and the interaction between the support system and the rock mass. On the other hand, numerical simulation analysis, which is dependent on the subjective experience of humans, cannot reflect well the nonlinear relationship between the factors affecting the stability of workings, and thus, it is not reliable for stability determination.
To solve this problem, researchers have used GA and ANN or their combination to establish nonlinear relationships, predict the displacement of the roadway influenced by the roadway depth, principal stress, drilling method, and rock load, and determine the displacement of the rock mass around roadway and the geological parameters for mining. This intelligent analysis method is very effective for its objectivity when evaluating the stability of roadways in a region of relatively regular coal seams. However, when the coal seams are in an irregular state and the roadway is strongly affected by mining operation, the nonlinear relationships between the factors should be taken into account for stability determination.
Pak Tae Song, a section head at the Faculty of Mining Engineering, has found the optimal maintenance scheme of roadways strongly affected by mining operation for nonlinear problems by combining ANN with high adaptive capacity and GA with strong adaptive optimization ability.
He applied a two-stage ANN-GA. First, he obtained the installation space and failure rate of the support from the combination of ANN and GA in the second stage. Then, he found the optimal roadway maintenance scheme from the combination of ANN and GA in the first stage.
After that, he compared the selected scheme with field observations. The results show that the scheme is effective in optimizing the maintenance system of workings, which is affected by the nonlinear relationship among mining geological parameters.
The ANN-GA method can be effectively applied to the study of the geo-mechanical behavior of rock mass affected by the uncertainty relations of qualitative and quantitative factors caused by mining operations.
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Jo Feb 1, 2025
February has two seasonal divisions of the year, ripchun and usu.
Ripchun, the first of the 24 seasonal divisions, signifies the opening of spring according to the lunar calendar. It usually falls around February 4th of the solar calendar.
From long ago, the Korean people used to greet ripchun, the first division of spring, with peculiar customs.
On the day, they tidied up their houses and some of them expressed their pleasure of greeting the spring in the diaries. In addition, they cooked some dishes with spring onion grown in a storage pit, leaf mustard, etc. scented with spring fragrance.
What is special about the customs related to farming around ripchun is that there were many ceremonies associated with oxen.
Usu is a term indicating the time when the snow melts and the spring rain starts to fall. It usually falls around February 18-20 of the solar calendar.
Ushering in usu, all the areas except the highlands in the north of our country start to thaw out. The peasants kept snowmelt in all pools and made haste with farming preparations.
In this season, our people used to play yut, tug-of-war, seesaw, kite-flying and other colorful folk games.
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Jo Jan 31, 2025
Image super-resolution (SR) is the process of artificially producing a high-resolution (HR) image from one or several low-resolution (LR) images. Image super-resolution techniques are based on interpolation, reconstruction and learning.
In recent times, learning-based super-resolution algorithms are widely used. In learning-based super-resolution algorithms, HR image is obtained from a single LR image using training database. In these algorithms, the priori information is derived from the training database.
Ro Mi Ha, a lecturer at the Faculty of Information Science and Technology, has proposed a learning-based image super-resolution for a single LR image using discrete wavelet transform (DWT) and Gaussian mixture model (GMM).
In this method, if a low resolution (LR) input image and a database consisting of low and high resolution images are given, a high-resolution image for the input image is obtained by learning of the high-frequency details from the database. Then, high-frequency details of an HR image are described as wavelet coefficients at finer scale using DWT. The conversion function for obtaining the finer wavelet coefficients of an HR image from the coarse wavelet coefficients of an LR image is set as a weighted linear transformation using GMM.
She has demonstrated the effectiveness of the proposed method by conducting some experiments on gray images.
The proposed method can be used in applications such as remote surveillance where the memory, the transmission bandwidth and the camera performance are the main constraints.
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Jo Jan 30, 2025
The electrode support arm is the key component of an electric furnace, which supports the electrode, conducts electrical energy from the transformer through the electrode to the furnace, and produces a strong arc current within the furnace material to raise the temperature of the weld pool. The electrode support arm is usually mounted on the brace, and its front end holds the electrode by the gripper to keep it in position at the electrode center circle during the lift process.
During the operation, a high-temperature arc with a large power output is formed between the extremes of electrodes and the weld pool, which can cause intense electromagnetic oscillation of the electrode support arm. Therefore, the electrode support arm should have great strength and low resistance value. In modern electric furnaces, the secondary bus on the furnace body is retrofitted from the former copper tube bus to the copper-steel conductive electrode arm and aluminum conductive arm. To manufacture the copper-steel conductive electrode arm of a 5-ton ultrahigh power (UHP) electric furnace, a copper plate is welded around the steel structure and a cooling water pipe with a rectangular cross-section is formed on its bottom surface to cool the heat generated when the high current flows through the copper plate.
So far, many studies have been published on the cooling systems in the furnace body and furnace ceiling, but no mention has been made on the cooling in the electrode support arm section. The reason lies in the fact that Joule heat generated in the conductive arm is too small and only recently has the bimetallic conductive arm been widely used. However, during the reducing operation of the electric furnace, the temperature of the furnace should be raised to the maximum, so the operation is carried out without ventilation. Therefore, the convective heat transfer by this flue gas must be considered because the gas ambient temperature around the electrode support arm increases to about 700K.
Ri Sim Hyok, a researcher at the Faculty of Metal Engineering, has analyzed the temperature distribution of the copper-steel conductive electrode arm of UHP electric furnace, determined the geometry of the cooling water pipeline to minimize the cooling water consumption, while keeping the temperature of the conductive copper plate within the acceptable range (50℃), and determined the consumption amount of cooling water.
He analyzed the current flow in the bimetallic conductive arm using Maxwell software and found that the current flows only into the copper plate. Then, he simulated the temperature distribution of the bimetallic conductive arm during the reducing stroke with ANSYS FLUENT. After that, he simulated the temperature changes of the conductive copper plate and the cooling water, and verified the results with the experimental data obtained in situ.
The results show that the cooling water flow rate of 1 to 1.5kg/s and the 6-stroke pipeline guarantee the minimum consumption of cooling water while keeping the temperature of the copper plate bus of the copper-steel conductive electrode arm within the acceptable range.
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Jo Jan 29, 2025
A text can be represented by a vector of binary weights indicating the presence or absence of terms inside documents. Therefore, the correlation of terms is quantified by the frequency of co-occurrence or the internal product of the index term vector, but it has the limitation that it does not capture the joint relationship. As each element of the binary document vector is set to be 0 or 1, 0 and 1 are dealt with quantitatively and methods of multidimensional incidence tables and various statistics are used.
Maximum entropy is one method applicable to such problems, and it can represent a variety of models depending on which interaction terms are involved. The maximum entropy model is the basic principle of the maximum entropy classifier, and it constructs a model for all known factors and excludes the unknown factors. The basic characteristic is that the features are independent of each other, so the features useful to the final classification can be added freely, regardless of mutual influence.
The maximum entropy model with constraints on binary features is widely used in natural language processing, speaker identification, information retrieval, text filtering, machine translation, etc.
In lexeme equivocality removal using maximum entropy, when the context, i.e., neighboring words are given, the probability of each outcome (each meaning of the target word) is estimated and the variance of the neighboring words for each meaning is used to compute the probability. Either log-linear (log-linear) model or exponential (exponential) model is used to combine features. However, where the dependence structure between variables using maximum entropy is included, except for the relationship where the joint probability is zero, which would reduce the computational effort in training and prediction still remains a challenge.
Pak Il Chol, a researcher at the Faculty of Information Science and Technology, has proposed a joint distribution estimation method via marginal distribution constraint based on the maximum entropy principle in document data represented by binary weight vectors, and how to apply it to document classification and ranking. The proposed method allows determination of the target joint distribution using the marginal distribution obtained from the given data as a constraint. He has also proposed a method to search for the maximum dimension of the marginal distribution, except for the case of marginal probability 0.
The simulation results show that the proposed method for classification through marginal distribution estimation underperforms the simple Bayesian approach assuming conditional independence when the dataset size is small, but outperforms the simple Bayesian approach when the dataset size gets larger. He has also found that the ranking shows an improvement of about 4% in MAP over the two-valued independent retrieval model.
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