Sanghun Park

High quality graphene nanosheets were fabricated within 1 min by solid-state microwave irradiation of a mixture of graphite oxide and graphene nanosheets under a hydrogen atmosphere. The graphene nanosheets in the mixture acted as an effective microwave susceptor under microwave irradiation synthesis, and could provide sufficiently rapid heating for the effective exfoliation of graphite oxide. A hydrogen containing atmosphere played important roles in improving the quality of the graphene nanosh

In order to improve the efficiency of energy conversion for a photovoltaic (PV) system, a soft-switching boost converter using a simple auxiliary resonant circuit, which is composed of an auxiliary switch, a diode, a resonant inductor, and a resonant capacitor, is adopted in this paper. The conventional boost converter decreases the efficiency because of hard switching, which generates losses when the switches are turned on/off. During this interval, all switches in the adopted circuit perform z

Providing effective motivational support is a critical determinant of a successful online distance learning experience for students in higher education. In this study, we examined how students’ academic level and use of 8 motivational regulation strategies influence 3 types of student engagement: behavioral engagement, emotional engagement, and cognitive engagement. A total of 95 undergraduate and graduate students enrolled in online courses in 4-year universities in the United States participat

High Resolution Image Download MS PowerPoint Slide To take full advantage of graphene in macroscale devices, it is important to integrate two-dimensional graphene nanosheets into a micro/macrosized structure that can fully utilize graphene’s nanoscale characteristics. To this end, we developed a novel spray-assisted self-assembly process to create a spherically integrated graphene microstructure (graphene microsphere) using a high-temperature organic solvent in a manner reminiscent of deep-fryin

A new soft-switching boost converter is proposed in this paper. The conventional boost converter generates switching losses at turn on and off, and this causes a reduction in the whole system's efficiency. The proposed boost converter utilizes a soft-switching method using an auxiliary circuit with a resonant inductor and capacitor, auxiliary switch, and diodes. Therefore, the proposed soft-switching boost converter reduces switching losses more than the conventional hard-switching converter. Th

Narrowing genioplasty, either as a single procedure or in combination with mandible reduction, makes the lower face appear slender and produces a more feminine contour.

Abstract In this study, we investigated an energy harvesting effect of tensile stress using piezoelectric polymers and flexible electrodes. A chemical-vapor-deposition grown graphene film was transferred onto both sides of the PVDF and P(VDF-TrFE) films simultaneously by means of a conventional wet chemical method. Output voltage induced by sound waves was measured and analyzed when a mechanical tension was applied to the device. Another energy harvester was made with a metallic electrode, where

Abstract Among other things, battery electrodes need to display large absolute capacities coupled with high rate performance. However, enhancing areal capacity, for example via increased electrode thickness, results in reductions in rate performance. The basis for this negative correlation has not been studied in a quantitative fashion. Here, a semiempirical model is used to analyze capacity versus rate data for electrodes fabricated from a number of materials, each measured at various thickness

Introduction The use of animated pedagogical agents in multimedia learning environments has increased as new technologies have made them more accessible (Gholson & Craig, 2002; Johnson, Rickel, & Lester, 2000). Pedagogical agents are animated life-like characters enabled with speech, gesture, movement, and human-like behaviors (Sweller, Ayres, & Kalyuga, 2011) and designed to facilitate learning in multimedia learning environments (Johnson et al., 2000). Pedagogical agents can embody different p