Jo Sep 24, 2025
Hazardous industrial wastewater usually contains many toxic heavy metals such as chromium, nickel, copper, zinc, lead, cadmium and mercury. The discharge of industrial wastewater containing such heavy metals without being treated not only destroys the ecological environment but also produces a negative effect when it enters animal or human bodies.
Chromium is one of the metals used in the industrial processes including stainless steel and alloy steel production, pulp production, electroplating, textile industry, metal refining, tanning, glass industry, petroleum refining, etc. Trivalent chromium existing in the waste water is generally produced from inorganic pigments, glass preparation, ceramics, etc., and it may be produced by reduction of hexavalent chromium in reducing atmosphere. Chromium ions are toxic heavy metal ions, which seriously contaminate soil and water. Therefore, it is very important to remove chromium ions in the wastewater before it is discharged into rivers or lakes.
Chromium, like other metals, can be treated in various ways such as chemical precipitation, ion exchange, membrane filtration, solvent extraction, electrochemical processes, biological methods and photo catalysis. Recently, adsorption method has been widely applied to wastewater treatment due to its simple operation and low cost.
Ri Kyong Hun, a researcher at the Faculty of Mining Engineering, has investigated the preparation of inorganic adsorbents for removing heavy metals from wastewater and other scientific and technological problems for efficient removal of chromium in wastewater by the adsorbents.
He worked on the synthesis of heavy metal adsorbents by low-temperature hydrothermal synthesis method to prepare nanocrystalline inorganic adsorbents (erdite) of 80nm in diameter and 100nm in length at 90℃ for 24h under the conditions of S/Fe > 3 and OH-/Fe > 20.
From the experiments to use the mother liquid back to the synthetic experiments, he has confirmed that a little addition of only Na2S·9H2O to the mother liquid makes it possible to effectively synthesize erdite. The removal efficiency of these sorbents for Cr(III) is above 99.8%.
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Jo Sep 23, 2025
Active disturbance rejection control (ADRC) is one of the notable disturbance and uncertainty estimation and attenuation techniques.
Kim Ho, dean of the Faculty of Automation Engineering, has proposed a method based on the maximum sensitivity index, with an attempt to solve the problems arising in the parameter tuning of ADRC.
Then, he has applied it to the temperature control of a water glass reaction tank subject to strong model uncertainties and disturbances.
First, he built a mathematical model of a water glass reaction tank by using the identification technique based on the step response signal, and designed a second-order linear active disturbance rejection controller based on it. Then, based on the maximum sensitivity index, he presented a formula of tuning the parameters of the second-order linear active disturbance rejection controller to achieve robustness, and verified its effectiveness using MATLAB.
As a result, he has concluded that the proposed formula is suitable when the non-delay is less than 0.3, and that time delay compensation techniques such as Smith predictor should be applied when the non-delay is more than 0.3 as the time delay is not negligible.
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Jo Sep 22, 2025
The Paleozoic erathem is important of all deposits in the earth’s crust, and they are widely distributed in many areas. Therefore, there have been many geological studies including stratigraphic, mineralogic, petrographic and mineral resources studies for Paleozoic erathem.
In our country, the Paleozoic Formations are distributed in the Pyongyang Basin, the Kaechon Basin and the Kowon Basin, where there are only lower layers because the upper layers are eroded. In Thaejawon Formation, the upper Formation of Kaechon Group, little extinct organisms and special resources have been found, unlike other Paleozoic erathem, and there have been fewer studies of these strata than other strata.
Jo Song Gil, a researcher at the Faculty of Earth Science and Technology, has conducted macrography, microscopic investigations, XRF and XRD on the lens bodies present at the top of lower Member of the Thaejawon Formation in the southern area of Jangansan syncline of Kaechon Basin, to elucidate the mineral petrographic characteristics and investigate the paleoenvironment.
He found out the elemental composition, mineral composition and lithological characteristics of the target layer and host rocks using an optical microscope, X-ray fluorescence (XRF) and X-ray diffraction (XRD). The target layer is a calcareous conglomerate lens, mostly similar to the host rock in mineral composition, with some differences in some contents and compositions. The target layer and its host rocks are deposited in the freshwater environment, and the paleosalinity of the calcareous conglomerate lens is higher than that of other strata. The redox potential of depositional environment in the target rock is higher than the host rock, and it was very dry when the target rock and its lower layer were formed.
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Jo Sep 21, 2025
The inverted pendulum system is one of the most widely-used experimental devices to verify the effectiveness of various control algorithms in the field of control engineering.
Despite being an unstable system, the inverted pendulum system is a very interesting control object with satisfactory controllability and observability that can be stabilized by one control variable.
Pak Se Yang, a researcher at the Science Engineering Institute, has designed a linear control system for the stabilization control of a flywheel inverted pendulum and applied it to an experimental device to evaluate its effectiveness.
First, he analytically derived the mathematical model of a flywheel inverted pendulum system and experimentally determined the parameter values of the model.
Next, he designed an augmented linear quadratic optimal controller as a robust controller considering the uncertainty of the model parameters and verified its control performance through semi-physical simulations. He designed a prototype experimental system and implemented a control program to experimentally verify that the theoretically designed control system actually stabilizes the system.
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Jo Sep 19, 2025
Carburization is a technological process for increasing the service life of steel by enhancing its abrasion resistance. However, carburization has low productivity because it takes a long time, and the increase in the carburizing temperature of low carbon steel to reduce carburization time causes coarsening of the prior austenite grains, which results in the decrease in the mechanical properties.
Kim Myong Gwon, a researcher at the Faculty of Materials Science and Technology, has simulated the phase constitutions of low alloy steel 18CrMn and Ti-and-Nb-microalloyed steel 18CrMnTiNb, and analyzed their microstructures and mechanical properties when they were carburized at high temperature.
The steel 18CrMnTiNb, which is microalloyed with 0.06% Ti and 0.06% Nb, has fine grain size after being carburized at 1 000℃. Its prior austenite grain size is less than 25μm. The experimental results show that high-temperature carburization of Ti-and-Nb microalloyed low carbon steels can significantly reduce the carburizing time and provide sufficient mechanical properties.
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Jo Sep 18, 2025
Graphene, like graphite, is a two-dimensional material of hexagonal structure of carbon. With excellent properties such as high electrical conductivity, thermal conductivity and permeability, it has been widely applied in advanced science and technology fields including graphene composites, electronic materials and energy storage materials.
Several oxidation-reduction methods that are commercially available worldwide are suitable for mass production of graphene, but due to the nature of the processing procedure, many functional groups exist in the prepared graphene, resulting in crystalline defects. In addition, the use of a large amount of strong oxidizing agents causes environmental pollution and the effects of the prepared graphene or graphene oxide on the human body must be considered.
The method of directly obtaining graphene from graphite using shockwave in isopropanol has a disadvantage of low yield, but it is environmentally friendly and nontoxic, so it has a great research value.
Ju Yong Chol, a section head at the Institute of Nano Science and Technology, has prepared few-layer graphene by suspending graphite in isopropanol and applying shockwave generated during pulsed discharge to it, and investigated the effects of charging voltage, capacitor and number of discharges on the number of layers and yield of graphene.
The effects of charging voltage and capacitor on the number of layers of graphene are almost similar. The number of discharges plays an important role in the yield of graphene.
He has analyzed various properties of the graphene prepared using Optics microscope, X-ray diffraction and Raman spectroscopy, and confirmed the presence of 3-6 layer graphene. The yield of graphene is 8%.
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