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Synthesis of Monoclinic Potassium Niobate Nanowires That Are Stable at Room Temperature
Kim, Seungwook,Lee, Ju-Hyuck,Lee, Jaeyeon,Kim, Sang-Woo,Kim, Myung Hwa,Park, Sungnam,Chung, Haegeun,Kim, Yong-Il,Kim, Woong American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.1
<P>We report the synthesis of KNbO<SUB>3</SUB> nanowires (NWs) with a monoclinic phase, a phase not observed in bulk KNbO<SUB>3</SUB> materials. The monoclinic NWs can be synthesized via a hydrothermal method using metallic Nb as a precursor. The NWs are metastable, and thermal treatment at ∼450 °C changed the monoclinic phase into the orthorhombic phase, which is the most stable phase of KNbO<SUB>3</SUB> at room temperature. Furthermore, we fabricated energy-harvesting nanogenerators by vertically aligning the NWs on SrTiO<SUB>3</SUB> substrates. The monoclinic NWs showed significantly better energy conversion characteristics than orthorhombic NWs. Moreover, the frequency-doubling efficiency of the monoclinic NWs was ∼3 times higher than that of orthorhombic NWs. This work may contribute to the synthesis of materials with new crystalline structures and hence improve the properties of the materials for various applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-1/ja308209m/production/images/medium/ja-2012-08209m_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja308209m'>ACS Electronic Supporting Info</A></P>
Seungwook Kim,Han Suk Choi,Dong Sup kim,Laxmi Prasad Thapa,Sang Jun Lee,Sung Bong Kim,Jaehoon Cho,박철환 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.12
The enzyme cellobiose dehydrogenase (CDH), with high ability of electron transport, has been widely used in enzymatic fuel cells or biosensors. In this study, the cellobiose dehydrogenase gene from Phanerochaete chrysosporium KCCM 60256 was amplified and expressed in the methylotrophic yeast Pichia pastoris X-33. The recombinant enzyme (PcCDH) was purified using a metal affinity chromatography under non-denaturing conditions. The purified enzyme was analyzed by SDS-PAGE, confirming a corresponding band about 100 kDa. The enzyme activity of this purified PcCDH was determined as 1,845U/L (65mg/L protein). The enzyme showed the maximum activity at pH 4.5 and high activity in broad ranges of temperature from 30 oC to 60 oC. Moreover, the application of PcCDH to enzymatic fuel cell (EFC) was demonstrated. Lactose was used as the substrate in the EFC system; anode and cathode were immobilized with PcCDH and laccase, respectively. The cell’s open circuit voltage and maximum power density of the EFC system were, respectively, determined as 0.435 V and 314 μW/cm2 (at 0.247 V) with 10 mM lactose.
Kim, Seungwook,Kim, Min-Seop,Lee, Chiho,Park, Sungnam,Cho, Won Il,Kim, Woong Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.709 No.-
<P><B>Abstract</B></P> <P>Fundamentals in materials science are often based on understanding the relationships between the structures and properties of materials. Recently, our group reported on potassium niobate (KNbO<SUB>3</SUB>) nanowires with a metastable monoclinic phase that has never been observed before in bulk materials. In this paper, we report on the unique phase transition behaviors of these monoclinic nanowires and describe how their nonlinear optical properties are correlated with structural changes. The metastable monoclinic nanowires exhibit phase transition behaviors that are distinct from those of thermodynamically stable orthorhombic nanowires. The monoclinic nanowires undergo two phase transitions: monoclinic to tetragonal at 120 °C and tetragonal to cubic at 380 °C. In contrast, orthorhombic nanowires undergo phase transitions from orthorhombic to tetragonal and from tetragonal to cubic at 130 °C and 330 °C, respectively. The monoclinic and orthorhombic nanowires were found to exhibit clearly distinguishable variations in the second harmonic generation (SHG) intensity with variations in temperature. We show that the tetragonal structures derived from the monoclinic and orthorhombic phases are clearly different. The tetragonal phase derived from the monoclinic phase has higher spontaneous polarization and exhibits higher SHG intensity than the other tetragonal phase. Our analysis can be extended to explain the size-dependent properties of KNbO<SUB>3</SUB>. We calculated the spontaneous polarizations of the various phases based on the structural data and show how to use them to explain the above-mentioned structure–property relationships. The results of this study have important implications for both fundamental understanding and technological applications of metastable nanomaterials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Metastable monoclinic KNbO<SUB>3</SUB> nanowires exhibit unique phase transition behaviors. </LI> <LI> Tetragonal phases derived from monoclinic and orthorhombic phases are different. </LI> <LI> Intensity of second harmonic generation is strongly correlated to structural change. </LI> <LI> Spontaneous polarization explains the structure-dependent optical properties. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Young-Jun Kim,Hyo-Eun Kim,Seok-Hoon Kim,Jun-Seok Park,Seungwook Paek,Lee-Sup Kim IEEE 2012 IEEE transactions on very large scale integration Vol.20 No.9
<P>We embed special function units (SFUs) in homogeneous stream processors (SPs) within a graphics processing unit (GPU), to improve its performance in running modern programmable shaders, which make poor use of a single-instruction multiple-data (SIMD) architecture. We also compact instructions, so as to reduce the size of the instruction memory, and reduce area requirements by using a partial SFU in SPs, and a lookup table which is shared between multiple SFUs. The result is an increase of 88% in utilization and a reduction in the normalized area-delay product of 27%, compared to a baseline SIMD architecture. We verified our architecture on an field-programmable gate-array evaluation platform with an ARM9 host processor and a full 3-D graphics pipeline.</P>
Development of an integrated breeding platform for data-driven crop improvement
Yeisoo Yu(Yeisoo Yu),SeungWook Lee(SeungWook Lee),Suhyeon Park(Suhyeon Park),Changyuel Lee(Changyuel Lee),Youngsil Kim(Youngsil Kim),Daegyu Kim(Daegyu Kim),Seok Jae Yun(Seok Jae Yun),Dae Kwan Kim(Da 한국육종학회 2023 한국육종학회 공동학술발표집 Vol.2023 No.-
Kim, Seungwook 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 1996 기초과학연구 Vol.4 No.-
A pseudometric is a generalization of a metric where the reflexive property and symmetry, triangularity are satisfied. In this paper we study the topologies generated by a pseudometric. The main result are the sufficient and necessary conditions for the pseudometrization theorems.
Hybrid Temperature Sensor Network for Area-Efficient On-Chip Thermal Map Sensing
Seungwook Paek,Wongyu Shin,Jaeyoung Lee,Hyo-Eun Kim,Jun-Seok Park,Lee-Sup Kim IEEE 2015 IEEE journal of solid-state circuits Vol.50 No.2
<P>Spatial thermal distribution of a chip is an essential information for dynamic thermal management. To get a rich thermal map, the sensor area is required to be reduced radically. However, squeezing the sensor size is about to face its physical limitation. In this background, we propose an area-efficient thermal sensing technique: hybrid temperature sensor network. The proposed sensor architecture fully exploits the spatial low-pass filtering effect of thermal systems, which implies that most of the thermal information resides in very low spatial frequency region. Our on-chip sensor network consists of a small number of accurate thermal sensors and a large number of tiny relative thermal sensors, responsible for low and high spatial frequency thermal information respectively. By combining these sensor readouts, a thermal map upsampler synthesizes a higher spatial resolution thermal map with a proposed guided upsampling algorithm.</P>
ON THE SEMI CONTINUOUS FUNCTIONS WITH THE OPEN PROPERTY
Kim, Seungwook The Kangwon-Kyungki Mathematical Society 2005 한국수학논문집 Vol.13 No.2
Some of the generalized continuous functions and their basic properties are introduced in concern with the cover theory. The open property of a function is a crucial tool for the survey of this area.