Jo Mar 29, 2024
In recent decades, temperature/pH dual responsive amphiphilic polymers have attracted the interest of researchers because they can perform certain functions by changing the hydrophilic hydrophobic balance in conformity with changes in the external environment. Therefore, these types of amphiphilic polymers are very useful, especially for drug delivery, tissue engineering, biotechnology, and related fields.
However, most of the temperature/pH dual responsive polymers are prepared using petroleum chemical monomers as the main raw material and their use has biocompatibility and toxicity problems. In recent years, many researchers have focused on biomass derivatives to improve the temperature/pH dual responsiveness of polymers.
Jong Kwang Hyok, a section head at the Faculty of Chemical Engineering, has synthesized a novel type of temperature-pH dual responsive amphiphilic hydrogel, PD(Hydroxyethyl starch(HES)-propynyl glycidylether(PGE)-2-dimethylamino ethanethiol (DMAET)- Triethoxyvinylsilane(TEVS)) and studied its characteristics.
First, HES, a hydrophilic polysaccharide, underwent etherification of hydroxyl groups in its glucose units with PGE and then click reaction between carbon-carbon triple bonds in PGE and thiol groups in DMAET, thereby possessing a hydrophilic-hydrophobic structure to be used for the preparation of PD, a temperature-pH dual responsive material, with pH-responsive tertiary amine groups. Next, it further became a dual responsive hydrogel through the formation of its internal network by TEVS.
He found that during the test experiments to use it as a drug carrier for oral delivery, the doxorubicin(DOX) release was ≤15% in acidic conditions in the stomach (pH < 2.0) and ≤94% in basic conditions in the small intestine, which ensures that it exhibits relatively good protective and release properties of drugs.
You can find the details in his paper “ Preparation of temperature-pH dual responsive hydrogel from hydroxyethyl starch for drug delivery” in “Colloid and Polymer Science” (SCI).
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Jo Mar 28, 2024
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique widely used in different wireless communication systems such as Digital Video Broadcasting (DVB), Digital Radio Mondiale (DRM), Wireless Local Area Network (WLAN), Long Term Evolution (LTE), etc.
But OFDM signals are prone to suffer from spectral spreading and in-band distortion due to the large envelope fluctuations.
As solutions to this problem, several methods have been presented. For reducing the signal envelope fluctuations without any in-band distortion, some methods such as Partial Transmit Sequence (PTS), Selected Mapping (SLM) and their hybrid techniques have been investigated, but they are in high computational complexity and need side information. Tone Reservation (TR) can reduce the signal envelope fluctuations significantly, but it does not use some subcarriers and depends on computationally intensive optimization. Systematic coding techniques are distortion-less methods, which can bound signal fluctuations but they require data rate compensation. As the simplest method, Amplitude Clipping could reduce the out-of-band radiation, but these non-linear techniques cause in-band distortion and the additional clipping noise compensation requires high computational complexity.
Among the presented methods, constellation extension based ACE would be one of the promising methods because ACE maintains the minimum Euclidean distance between symbols in a constellation and causes no reduction of BER performance and, especially, it does not require any side information. However, because the reduction performance of signal envelope fluctuations of ACE depends on the number of iterative computations, its computational complexity is usually very high. So, it is necessary to find an approach to maintain high reduction performance of signal envelope fluctuations and low computational complexity.
Jon Ji Hyon, a researcher at the Faculty of Communications, has proposed a novel ACE-DE approach to deal with this issue, where the anti-peak signal decomposition based double extension is applied to improving reduction performance of signal envelop fluctuations.
By using Fourier transform properties, an anti-peak signal is decomposed into 4 sub-signals in the time domain, and then recomposed via Second Order Cone Programming optimization. To realize the low computational complexity of ACE-DE, MPT algorithm is also proposed.
The simulation results show that ACE-DE with MPT outperforms other approaches in terms of CCDF, BER and OOB radiation.
For more information, please refer to his paper “Reduction of Signal Envelope Fluctuations in OFDM Systems Using ACE with Double Extension” in “Wireless Personal communications” (SCI).
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Jo Mar 26, 2024
Induction channel furnace (ICF) is widely used for melting, holding and casting metals and alloys in many processing industries because it has high overall efficiency, low electric power consumption and operation costs, better degassing and homogenization of melt and low oxide and slag formation. However, thermal stresses in the refractory lining caused by high temperature and flow of molten metal may cause premature erosion of the lining and failure of the inductor, and so it is difficult to repair the furnace. In addition, the furnace for steel melting often experiences shortened operating life and quicker needs for a repair cycle due to high temperature of molten metal and severe erosion of lining, so it is rarely used.
In order to solve these problems and make easy operation, it is important to improve the structure and to numerically simulate Joule heat generation and molten metal flow in the channel.
Song Hak Myong, a lecturer at the Mechanical Engineering Department, has designed a new type of channel of three-phase ICF for steel melting and investigated temperature distribution of the channel by a coupled simulation on the electromagnetism-heat-fluid using COMSOL Multiphysics 5.4.
ICF consists of molten metal bath and induction unit that is made up of iron core, inductor and channel. If one three-phase induction unit is fixed to the furnace body, it will lead to decrease in electrical unbalance and ease of furnace repair.
According to his simulation results, the optimal design parameters (with maximum S/N ratio) for three-phase ICF are as follows:
• Type of channel: Elliptic
• Dimensions of channel: 85×90 mm2
• Existence of protruding part: Yes
• Setting angle of channel: 30°
The local superheating temperature is relatively low (20.8–22.9K) and the maximum local superheating temperature is similar to the maximum local superheating temperature 33K in the channel of the twin channel induction furnaces.
It is one of the ways to prevent early erosion and expansion of refractory lining by local superheating in the channel and to increase its repair cycle.
The proposed method could be used for reducing manufacturing cost and regularizing operation through optimizing the parameters of induction furnace needed for aimed melting and flow.
If further information is needed, please refer to his paper “ Simulation on Temperature in Channel of Three-phase Induction Channel Furnace for Steel Melting Using COMSOL Multiphysics and Taguchi Method” in “International Journal of Metalcasting” (SCI).
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Jo Mar 23, 2024
As modern industrial processes become more complex with the development of technology, more advanced monitoring methodologies are required to keep high efficiency and safe operation. In order to improve monitoring performance, it is important to identify the operational phase of a process by evaluating all measurable variables comprehensively. Multiple operational characteristic that occurs in most industrial processes like chemical processes by their physical and chemical properties, variations in market requirement and product specification, catalyst degradation, etc. has become an important factor to be considered in process monitoring.
Since most multimode monitoring approaches with the mode-identification are only based on the similarity of process mean, the identification of transitions and faults is possible only after the cluster of process data should be formed or neighbour modes could be analyzed. Furthermore, mode-identification based approach seems to be inappropriate to monitoring of process with lots of modes not only because it requires a large amount of off-line data but also because its capability of adapting to unexpected states may not be acceptable.
Song Kwang Rim, a researcher at the Faculty of Automation Engineering, has proposed an online transition-identification based monitoring procedure for industrial process with multiple operational modes using process variability.
Firstly, he detected the change point in the dynamical behavior of multimode process by the log determinant of covariance matrix.
Second, based upon the analysis of the change behavior of process variability during transition and fault state, he developed new statistics to identify the transition.
Finally, he adopted an adaptive monitoring strategy to monitor multimode processes by the single model using the transition-identification.
Then, he conducted three case studies through TE benchmark to verify the usefulness and effectiveness of the proposed approach.
The result showed that the proposed approach has high ability to identify transitions and faults and to cope with the occurrence of new modes.
The details of this are found in his paper “Monitoring Industrial Processes with Multiple Operation Modes: a Transition-Identi¦cation Approach Based on Process Variability” in “Industrial & Engineering Chemistry Research” (SCI).
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Jo Mar 22, 2024
Numerical modeling and simulations of plasma is an indispensable means to overcome the technical limit in measuring plasma parameters, which has been performed by many researchers. Unlike conventional numerical modeling, lattice Boltzmann method (LBM) is a meso-scale scheme based on Boltzmann kinetic theory, which has some advantages such as relatively simple computational structure, easy handling on complex boundaries and possible parallel computation. Recently, the LBM has been widely used to simulate not only single phase flow but also multi-component and/or multi-phase thermal fluid transfer, electric and magnetic fields, acoustic fields and radiative transport. However, the previous models for plasma were limited to 2D schemes, so they were not enough to analyze 3D mechanism of arc dynamics.
Therefore, Kim Ju Song, a lecturer at the Faculty of Physical Engineering, has suggested a 3D lattice Boltzmann model to numerically simulate thermal fluid flow in non-transferred arc torch with swirl and validated its accuracy by comparing it with results in literature.
The Boltzmann model was built for local thermodynamic equilibrium. The boundary conditions were considered for both macro- and micro-parameters, and the curved boundaries were handled for the cathode and the anode.
The simulation results demonstrate that the maximal temperatures appear at positions downstream from cathode and the axial velocity profiles are remarkably different according to the swirl number and that the position in the maximal axial velocity shifts toward the cathode with increase in the swirl number.
For more information about it, please refer to his paper “Numerical Analysis for Argon Arc Plasma Jet Flow by Three-Dimensional Thermal Lattice Boltzmann Model” in “Bulletin of the Lebedev Physics Institute” (SCI).
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Jo Mar 20, 2024
Conventional approaches such as physical and chemical methods have been proposed for synthesis of metal nanoparticles. However, these are associated with the use of heavy equipment, huge amount of energy input, highly toxic and dangerous chemical compounds that cause biological hazards.
Apart from these, plant-mediated synthesis of metal nanoparticles seems to be very rapid, simple, dependable, non-toxic and ecofriendly.
Recently, great efforts have been made to use environmentally-friendly methods for the synthesis of silver (Ag) nanoparticles which have become a promising material in the recognition of ultrasensitive chemical and biological molecules owing to its low cost, high catalytic activity and noteworthy optical properties. Most plants used in green synthesis of Ag nanoparticles are medical herbs. The extracts of such medical herbs include several kinds of useful ingredients including polyphenol, protein and polysaccharide for reduction and stabilization of Ag nanoparticles.
Ri Yun Sik, a researcher at the Faculty of Materials Science and Technology, has investigated an eco-friendly route to the synthesis of Ag nanoparticles by extracts derived from Epimedium Koreanum Nakai leaves, which have been traditionally used as aphrodisiac and for low blood pressure, neurasthenia, infertility, impotence and amnesia, and their antibacterial properties and colorimetric sensing property on hydrogen peroxide.
As a result, he has found that the Ag nanoparticles he synthesized were small, nearly monodispersed and highly crystalline with face centered cubic structure and that these Ag nanoparticles show high antibacterial activity against bacteria such as E. coli and S. aureus. He has also proved that the degradation of Ag nanoparticles induced by catalytic decomposition of hydrogen peroxide causes a considerable change in the surface plasmon resonance absorbance with hydrogen peroxide concentration and that this sensor reaction has a very good sensitivity and a linear response over wide hydrogen peroxide concentration range of 10−6 to 10−1M hydrogen peroxide.
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