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Pore size effect on the formation of polymer nanotubular structures within nanoporous templates
Cho, Y.,Lee, C.,Hong, J. Elsevier 2014 Colloids and surfaces. A, Physicochemical and engi Vol.443 No.-
Nanotubular structures have recently received much attention due to their potential applications in biosensors, drug delivery systems, electronic devices, and many others. The layer-by-layer (LbL) deposition technique on 3-dimensional templates has been one of the most popular methods for the formation of nanotubular structures. Any size, shape, and composition template can be utilized and the desired amount of various materials can be readily incorporated within the thin film geometry with nanoscale control. Therefore, the morphological features of those materials can easily be tuned by varying the structural properties of templates. However, LbL deposition within a confined geometry actually shows somewhat different results due to the geometrical restriction, which is still not fully understood so far. In the present study, in order to investigate such a template effect on the LbL process, we utilized a cylindrical nanoporous anodic aluminum oxide (AAO) structure as a template for the LbL process, yielding polymer nanotube structures. By varying the pore size of the porous templates, we determined the LbL process within porous structures was strongly governed by the geometrical characteristics of the utilized templates.
Enhanced energy harvesting based on surface morphology engineering of P(VDF-TrFE) film
Cho, Y.,Park, J.B.,Kim, B.S.,Lee, J.,Hong, W.K.,Park, I.K.,Jang, J.E.,Sohn, J.I.,Cha, S.,Kim, J.M. Elsevier 2015 Nano energy Vol.16 No.-
Polyvinylidene fluoride (PVDF) has great potential for its use as an energy harvesting material as it exhibits not only outstanding piezoelectric and electrostatic characteristics resulting from ferroelectric effects, but also remarkably robust stability against repeated mechanical stress compared to inorganic materials. We report enhanced performances of poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) based energy generators with wider range of selections of flexible substrates through a surface morphology engineering using solvent annealing method as the key technology for simple and cost-effective fabrication at room temperature. It is clearly revealed that a solvent annealed P(VDF-TrFE) film is crystallised at room temperature and that the surface morphology is changed from a rough surface into a smooth and flat surface with increasing annealing time. This surface morphology engineering results in 8 times enhanced output voltage and current of the energy generators because of well-aligned electrical dipoles. We also demonstrate a highly transparent and flexible energy generator by employing graphene electrodes with the solvent annealed P(VDF-TrFE) film, which can be effectively harvesting various mechanical energy sources.
Cho, Y.,Cole, R.,Ikaga, T.,Larsson, N.,Moro, A.,Rovers, R.,Shin, S. Sustainable Building Research Center 2010 International journal of sustainable building tech Vol.1 No.1
The purpose of the discussion is to enhance the understanding of importance of sustainable development in the industry and to expand the international relation on the technology of sustainable architecture. The theme of SB10 SEOUL conference, "Sustainable Building Assessment Technology and Strategies for Higher Education" is selected to expand the knowledge of the current condition and the direction of future in sustainable building assessment technology.
Cho, Y.,Kim, S.,Pyo, S.,Park, Y.S.,Kim, S.J.,Yun, H.,Do, J. Pergamon Press 2010 Polyhedron Vol.29 No.9
The solvothermal synthesis and crystal structures of two new lead(II) compounds, bis(ethylenediamine)lead(II) chloride, Pb(en)<SUB>2</SUB>l<SUB>2</SUB> and mono(ethylenediamine)lead(II) chloride, Pb(en)Cl<SUB>2</SUB>, are reported. A detailed comparison of the two structures is given. In 1, the Pb(II) center is coordinated by two chlorine atoms and four nitrogen atoms from three en ligands, which act as either chelating or bridging ligands, allowing links to other Pb(II) centers. This creates an infinite linear chain of Pb(en)<SUB>2</SUB>l<SUB>2</SUB> In 2, the Pb(II) center is chelated by one en ligand and is coordinated by six chlorine atoms, including two unusually weak Pb-Cl bonds (>3.5A) connected through μ<SUB>2</SUB> and μ<SUB>4</SUB>Cl to build a neutral layer of Pb(en)Cl<SUB>2</SUB>units. Complex 1 contains a hemidirected Pb(II), while complex 2 has a (pseudo-)hemidirected Pb(II). TGA and high-temperature controlled powder-XRD studies show that compound 1 decomposes to compound 2 near 150<SUP>o</SUP>, and finally to PbCl<SUB>2</SUB>above 320<SUP>o</SUP>
Adaptive live streaming system performance of MMT and DASH over a deployed LTE network
Cho, Y.,Park, S.,Kim, K.,Suh, D.Y. IET 2016 Electronics letters Vol.52 No.13
<P>Moving Picture Expert Group (MPEG) media transport and dynamic adaptive streaming over Hypertext Transfer Protocol are compared, which have been standardised by the MPEG for internet-based video services. Their performances as adaptive live streaming systems are evaluated over a deployed long term evolution network. The results provide their operational limitations and optimal operation parameters to improve resource usage and the quality of the users' experience.</P>
Miniaturised dual-band implantable antenna for wireless biotelemetry
Cho, Y.,Yoo, H. IET 2016 Electronics letters Vol.52 No.12
<P>A miniaturised implantable antenna with dual-band operation the Medical Implant Communications Service (MICS) (402-405 MHz) and Industrial, Scientific, and Medical (ISM) (2400.0-2483.5 MHz) bands is presented. The size of the proposed antenna is 31.5 mm(3) (8.75 mm x 7.2 mm x 0.5 mm) which is the smallest size compared to previous implantable antennas. A serpentine-shaped radiating patch and open-end slot placed on the ground plane are used for miniaturisation. The performance of the antenna was evaluated from measurements and is based on good agreement with simulations.</P>
Challenges of organic rice farming in Jeonnam Province, Korea
Cho, Y.,Nicholas, P.,Lee, J. Korean Association of Organic Agriculture 2011 韓國有機農業學會誌 Vol.19 No.S
The production practices, productivity and economic performance of organic and non-chemical rice farming were compared in Jeonnam Province, Korea. Korean organic rice farming showed a lack of use of resistant varieties and rotational cropping systems as well as less use of farm wastes and a high dependency upon external inputs. When compared with no-chemical rice production practices very little differences were found. However, organic rice farming showed 15% to 18% higher profits than no-chemical farming even though the productivity was arguably similar between the two farming types. This may encourage more farmers to convert to organic production rather than non-chemical farming as the farming practices are very similar, thereby resulting in increased supply of organic products and decreased prices for organic rice near future. There is a need to more greatly differentiate organic farming practices and products from those of no-chemical farming.
Cho, Y.,Song, S.,Lim, S.,Kim, J.,Park, C.,Kim, H. Royal Society of Chemistry 2017 Physical chemistry chemical physics Vol.19 No.10
<P>Although upconversion phosphors have been widely used in nanomedicine, laser engineering, bioimaging, and solar cell technology, the upconversion luminescence mechanism of the phosphors has been fiercely debated. A comprehensive understanding of upconversion photophysics has been significantly impeded because the number of photons incorporated in the process in different competitive pathways could not be resolved. Few convincing results to estimate the contribution of each of the two-, three-, and four-photon channels of near-infrared (NIR) energy have been reported in yielding upconverted visible luminescence. In this study, we present the energy upconversion process occurring in NaYF4: Yb3+, Er3+ phosphors as a function of excitation frequency and power density. We investigated the upconversion mechanism of lanthanide phosphors by comparing UV/VIS one-photon excitation spectra and NIR multi-photon spectra. A detailed analysis of minor transitions in one-photon spectra and luminescence decay enables us to assign electronic origins of individual bands in multi-photon upconversion luminescence and provides characteristic transitions representing the corresponding upconversion channel. Furthermore, we estimated the quantitative contribution of multiple channels with respect to irradiation power and excitation energy.</P>