Pusan National University
  • Busan, Busan, South Korea
Recent publications
In recent years, carbon nanotube (CNT) and metal oxide-based supercapacitor (SC) electrodes have shown remarkable enhancements in their electrochemical properties. In this study, we synthesized a NiO and NiO/3%f-CNT nanocomposite through the direct chemical co-precipitation method. The structural and morphological characteristics of the composite were analyzed using X-ray diffraction, scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscope, and energy-dispersive X-ray spectroscope. Additionally, we evaluated the electrochemical performance through cyclic voltammetry, galvanostatic charge-discharge, and electrical impedance spectroscopy. The NiO/3%f-CNT composite electrode revealed a specific capacitance of 390.74 F/g at 5 mV Na 2 SO 4 aqueous electrolyte. Furthermore, even after 5000 cycles, the NiO/3%f-CNT composite electrode displayed exceptional cyclic stability of 93.5% at 1 A/g, indicating its potential for long-term usage. Overall, our results demonstrated that the chemical co-precipitation synthesized nanocom-posite possesses superior electrochemical properties, making it a promising candidate for supercapacitor electrode material.
Microplastics (MPs) released from plastic products in daily life are present in the air and could be transported to freshwater environments along with rain. Recently, low-impact development (LID) facilities, such as permeable pavements, have been used to treat non-point source pollutants, including rainfall runoff. While runoff is treated by LID facilities, the periodic monitoring of MPs in rainfall and the efficiency of removal of MPs through LID facilities have rarely been investigated. Therefore, this case study focused on monitoring MPs in rainwater runoff and permeate from a permeable pavement in Busan, South Korea, thus evaluating the removal efficiency of MPs by a LID system. The initial rainfall runoff and permeate through the LID system were sampled, and the amounts, types, sizes, and shapes of MPs in the samples were analyzed using micro-Fourier Transform Infrared (FTIR) spectroscopy. The results showed that the distribution of MPs in the initial rainfall was affected by population in tested area. Polyethylene was the most common type of MPs in all the samples. Polyamide was only found in the LID samples because of the pollution caused by water flows and pavement materials. Fragment type MPs was most commonly observed and consisted of relatively small-sized (under 100 μm) particles. LID facilities were able to capture approximately 98% of MPs in the rainfall through a filtration process in the permeable pavement.
Oncolytic virotherapy (OVT) is a promising cancer treatment in which oncolytic viruses (OVs) act as immunostimulatory agents and selectively replicate and lyse tumor cells without harming normal tissues. OVs not only directly kill cancer cells but also boost anticancer systemic immunity. Genetic engineering of OVs can enhance their efficacy by including transgenes encoding cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), interferons (IFNs), tumor necrosis factor (TNF), and interleukins (ILs). Among these, IL-15 is a pleiotropic cytokine that plays an essential role in developing, activating, and promoting survival of T cells, natural killer (NK) cells, and NK-T cells. For stabilizing and enhancing the bioactivity of IL-15, IL-15 receptor subunit α (IL-15 Rα) can bind to IL-15 independently, form the IL-15/IL-15 Rα complex on the surface of activated monocytes, promote T cell survival, and mediate its signaling pathways.
Chemical mechanical polishing (CMP) is a global planarization process that effectively reduces the step height of patterns. Conventional mathematical models for predicting step height reduction in oxide CMP have been successful; however, a relatively large error is obtained when applied to copper CMP because of the effects of chemical factors on copper removal rate. This study focuses on temperature as a parameter and develops a modified semi-empirical model that considers its effects. The temperature function was obtained using experiments that measured the copper etching and removal amounts according to the temperature. The developed copper model had an error rate of less than 10 %, whereas the oxide model had an error rate of approximately 30 %, indicating that the model with temperature consideration is more effective in predicting copper CMP results.
White‐light detection from the visible to the near‐infrared (NIR) region is central to many applications such as high‐speed cameras, autonomous vehicles, and wearable electronics. While organic photodetectors (OPDs) are being developed for such applications, several challenges must be overcome to produce scalable high‐detectivity OPDs. This includes issues associated with low responsivity, narrow absorption range, and environmentally friendly device fabrication. Here, we report an OPD system processed from 2‐methyltetrahydrofuran (2‐MeTHF) sets a record in light detectivity, which is also comparable with commercially available silicon‐based photodiodes. The newly designed OPD has been employed in wearable devices to monitor heart rate and blood oxygen saturation. In achieving this, we also develop a framework for a detailed understanding of the structure‐processing‐property relationship in these OPDs. The BHJ thin films processed from 2‐MeTHF were characterized at different length scales with advanced techniques. The BHJ morphology exhibits optimal intermixing and phase separation of donor and acceptor moieties, which facilitates the charge generation and collection process. Benefitting from high charge carrier mobilities and a low shunt leakage current, our newly developed OPD exhibits a specific detectivity of above 10 ¹² Jones over 400–900 nm, which is higher than those of reference devices processed from chlorobenzene and ortho ‐xylene. This article is protected by copyright. All rights reserved
A structured sport environment is known to provide adequate conditions for the development and transfer of student-athletes’ life skills. However, recent research not only emphasizes the environment but also argues that the intentional effort of coaches such as life skills coaching is important. This study examines the role of coaches’ life skills coaching on the development and transfer of athletes’ life skills using a multilevel model. A total of 28 high school athletic teams (28 coaches, 291 student-athletes) were recruited to participate in the study, using cluster sampling. The life skills coaching of Level 2 (coaches) in sports were measured using the Korean version of the Coaching Life Skills in Sport Questionnaire (CLSS-Q). The life skills of the student-athletes at Level 1 were measured using the Life Skills Scale for Student-Athletes (LSSSA) and Korean version of Life Skills Transfer Survey (LSTS). Multilevel model analysis was conducted to analyze dyadic data. The result of analysis showed that three hypotheses were supported. Specifically, life skills development of student-athletes affected life skills transfer (Hypothesis 1), life skills coaching affected student-athletes’ life skills transfer (Hypothesis 2), and the interaction effect between life skills coaching and development affected life skills transfer of student-athletes (Hypothesis 3). We conclude that coaches should use intentional life skills coaching strategies to maximize student-athlete life skills development and transfer to daily life.
The effect of P2O5 as an additives that promote the phase separation and distribution of phosphorus in sodium borosilicate glass was investigated. We prepared various NBS1 glasses: (100-x)(0.17Na2O–0.29B2O3–0.54SiO2)–xP2O5 (x = 0, 3, 5, 7, and 10 wt%) and an NBS2P7 glass: 93(0.22Na2O–0.24B2O3–0.54SiO2)–7P2O5 (wt%). Phase separation was confirmed by scanning electron microscope (SEM) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). To understand the phase separation phenomenon, 31P, 11B and 29Si magic angle spinning nuclear magnetic resonance (MAS-NMR) analyses were performed. It was confirmed that phase separation was induced when the P2O5 content was great than 5 wt% in NBS1 glasses, together with a change in the mechanism of phase separation from droplet-type to spinodal-type with increasing P2O5 concentration. The phosphorus incorporated into the borate-rich phase and formed borophosphate units after phase separation. Additionally, the fraction of [BO4] units decreased with increasing P2O5 concentration. This phenomenon is expected to strongly influence the phase separation of sodium borosilicate glasses. In the NBS2P7 glass, no phase separation was observed owing to the high contents of P2O74− and PO43− units. These units were released from the borosilicate matrices to form Na4P2O7 crystalline phases.
Laser‐induced graphene (LIG) is a porous carbon nanomaterial that can be produced by irradiation of CO 2 laser directly on the polymer substrate under ambient conditions. LIG has many merits over conventional graphene, such as simple and fast synthesis, tunable structure and composition, high surface area and porosity, excellent electrical and thermal conductivity, and good flexibility and stability. These properties make LIG a promising material for energy applications, such as supercapacitors, batteries, fuel cells, and solar cells. In this review, we highlight the recent advances of LIG in energy materials, covering the fabrication methods, performance enhancement strategies, and device integration of LIG‐based electrodes and devices in the area of hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, zinc‐air batteries, and supercapacitors. This comprehensive review examines the potential of LIG for future sustainable and efficient energy material development, highlighting its versatility and multifunctionality in energy conversion.
Polycrystalline Si–Al–C–O fibers with high mechanical properties at high temperatures are mainly manufactured through oxidation curing. The polymer-derived SiC fibers fabricated by chemical vapor curing have difficulty in densification due to the additional decomposition of the crosslinking agent above 1400 °C. In this study, the structural and elemental evolution of polycrystalline SiC ceramics prepared through a novel route was analyzed, and then polycrystalline Si–Al–C–O fibers were simply fabricated based on these results. In the polyaluminocarbosilane modified with blending method, aluminum not only remained until 1800 °C but also served as a sintering aid. In addition, the excess carbon exhibited a graphitic-like structure as C=O and C=C bonds were introduced from the ligands of Al(acac)3. The iodine impurity was released together with SiO and CO gas up to 1600 °C. As a result, polycrystalline SiC fibers composed of β-SiC crystals and graphitic-like carbon exhibited densification behaviors.
Cubic boron arsenide (c-BAs), a semiconducting material with ultra-high thermal conductivity and carrier mobilities, has been studied using first-principles calculation. This study examined the elastic and optoelectronic properties of c-BAs. The challenge of subphase boron (B) formation in bulk form owing to the volatile nature of arsenic (As) makes it mandatory to calculate its optoelectronic properties, by producing vacancies and antisite defects with BAs (As atom on a B site) and AsB (B atom on an As site). The mechanical properties including bulk (B), shear (G) moduli, and Poison’s ratio of all the systems were studied. It was found that mechanical instability of the structure is observed for the overall vacancy creation, arsenic substitution, and mutual antisite defects. Further, pristine c-BAs showed an indirect bandgap of 1.48 eV. Defect formation reduces the bandgap and shifts the absorption peaks, which improves the overall optoelectronic properties of the host material. In addition, B vacancy formation shows the maximum optical absorption and reflectivity and low energy loss, suggesting its potential applications for optoelectronic devices. The obtained anticipated data from this study is for the optoelectronic and elastic properties of c-BAs, for the device applications in photonics and electronics. In this paper, the elastic and optoelectronic properties of the pristine and defected c-BAs were systematically investigated using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA). The SIESTA program uses pseudopotentials in the norm-conserving nonlocal forms and pseudo-atomic orbital (PAO) basis set with a double-zeta potential (DZP) which are fundamental for calculating the Hamiltonian and overlap matrices in O(N) operations.
This study proposes a new actuator for a haptic controller that has a wider bandwidth than that of the prototype. The acceleration on the dummy jig of the prototype is analyzed using the electromagnetic-mechanical coupling method and verified using the experimental results. Several new designs have been proposed to provide higher accelerations on the dummy jig and a wider bandwidth. The new magnetic circuit, called the “sandwich” structure, includes one top plate, two permanent magnets, and two yokes. Response surface methodology is employed to perform the optimal analysis to find the maximum force factor while maintaining a magnet volume similar to that of the prototype. The predicted values (force factor and magnet volume) are confirmed by analysis results of the optimal type. Compared with the prototype, the optimal type has a higher force factor (77.74%) and 417.24% improvement in bandwidth with the same outer dimensions.
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5,636 members
Yoon-Ho Choi
  • School of Computer Science and Engineering
Subpiramaniyam Sivakumar
  • Department of Bioenvironmental Energy
Arulkumar Nagappan
  • College of Medicine
Selvam Ayarpadikkannan
  • Department of Biological Sciences
Ramesh Kumar Chitumalla
  • Department of Nanoenergy Engineering
Busandaehak-ro 63beon-gil, 609-735, Busan, Busan, South Korea