High-performance supercapacitors using flexible and freestanding MnO_x/carbamide carbon nanofibers

Samuel, Edmund,Jo, Hong Seok,Joshi, Bhavana,Park, Hyun Goo,Kim, Yong Il,An, Seongpil,Swihart, Mark T.,Yun, Je Moon,Kim, Kwang Ho,Yoon, Sam S. Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.423 No.-

<P><B>Abstract</B></P> <P>We demonstrate the fabrication of a MnO<I> <SUB>x</SUB> </I>/carbamide carbon nanofiber (CCNF) composite consisting of MnO particles embedded in CCNFs as a highly flexible and freestanding electrode material for supercapacitors. A sacrificial polymer component, polymethylmethacrylate, included in the precursor solution, pyrolyzes during heating, resulting in pores in the fibers, some of which are filled by the MnO nanocrystals. Carbamide is added to control the size of the MnO<I> <SUB>x</SUB> </I> particles as well as to increase the carbon content of the composite and hence its conductivity. The X-ray diffraction and Raman spectra of the composite show that the MnO particles formed have low crystallinity. Transmission electron microscopy confirms that the MnO particles are distributed very uniformly over the CCNFs. Symmetric supercapacitors constructed using electrodes of this composite exhibit specific capacitances of 498F∙g<SUP>−1</SUP> at a scan rate of 10mV∙s<SUP>−1</SUP> and 271F∙g<SUP>−1</SUP> at a current density of 1A∙g<SUP>−1</SUP>. They also exhibit excellent long-term cycling performance, retaining 93% of their initial capacity after 5000 cycles of galvanostatic charging/discharging.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We successfully fabricated a novel flexible MnO/CCNF composite. </LI> <LI> Flexible MnO/CCNF showed excellent retention (93%) after 5000 cycles at 1Ag<SUP>−1</SUP>. </LI> <LI> MnO/CCNF composite demonstrated specific capacitance of 498Fg<SUP>−1</SUP> at a scan rate of 10mVs<SUP>−1</SUP>. </LI> <LI> Dynamic MnO particle formation controlled by using carbamide. </LI> </UL> </P>

Damping index of Doppler hepatic vein waveform to assess the severity of portal hypertension and response to propranolol in liver cirrhosis: a prospective nonrandomized study

Kim, Moon Young,Baik, Soon Koo,Park, Dong Hun,Lim, Dae Wook,Kim, Jae Woo,Kim, Hyun Soo,Kwon, Sang Ok,Kim, Young Ju,Chang, Sei Jin,Lee, Samuel S. Wiley-Blackwell Publishing 2007 Liver International Vol. No.

<P>Abstract</P><P>Background and Aims</P><P>Alterations in the Doppler hepatic vein (HV) waveform are associated with cirrhosis and portal hypertension. We prospectively evaluated the correlation between the extent of abnormal Doppler HV waveforms expressed as damping index (DI) and the hepatic venous pressure gradient (HVPG) and response to propranolol in patients with cirrhosis.</P><P>Material and Methods</P><P>In 76 patients with cirrhosis (69 men and seven women), both DI of Doppler HV waveform and HVPG were measured, and the relationship between them was analysed. DI was calculated by the minimum velocity/maximum velocity of the HV waveform. An HVPG>12 mmHg was defined as severe portal hypertension. In a subgroup of 19 patients receiving propranolol, changes in both DI and HVPG were evaluated after propranolol administration for 3 months. One author (S. K. B.) performed all DI of Doppler HV waveform studies.</P><P>Results</P><P>Abnormal HV waveforms were seen in 66 of 76 patients (86.8%). DI significantly correlated with the grade of HVPG, i.e. with higher HVPG increased DI was observed (<I>P</I><0.01). By logistic regression analysis, DI>0.6 was significantly more likely to be severe portal hypertension (odds ratio: 14.19, 95% confidence interval: 4.07–49.55). Receiver-operating characteristic curve according to the value of 0.6 of DI showed a sensitivity of 75.9% and a specificity of 81.8% for the presence of severe portal hypertension. In 19 patients of the propranolol subgroup, change of DI following propranolol treatment also significantly correlated with that of HVPG (<I>P</I><0.01).</P><P>Conclusions</P><P>Damping index of the HV waveform by Doppler ultrasonography might be a non-invasive supplementary tool in evaluating the severity of portal hypertension and in responding to propranolol in patients with liver cirrhosis.</P>

Flexible and freestanding core-shell SnO_<i>x</i>/carbon nanofiber mats for high-performance supercapacitors

Samuel, Edmund,Joshi, Bhavana,Jo, Hong Seok,Kim, Yong Il,Swihart, Mark T.,Yun, Je Moon,Kim, Kwang Ho,Yoon, Sam S. ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.728 No.-

<P><B>Abstract</B></P> <P>We demonstrate the fabrication of core-shell SnO<SUB> <I>x</I> </SUB>/carbon nanofiber (CNF) composite mats via single-nozzle one-step electrospinning for use as flexible freestanding electrodes in supercapacitors. The freestanding and flexible nature of the composites is essential for their use in lightweight, portable, and foldable electronic devices and eliminates the need for a separate current collector. We fully characterized the structural and morphological properties of the SnO<SUB> <I>x</I> </SUB>/CNF mats and optimized the SnO<SUB> <I>x</I> </SUB> to CNF precursor ratio. The optimized SnO<SUB> <I>x</I> </SUB>/CNF-based symmetric supercapacitor exhibited a capacitance of 289 F·g<SUP>−1</SUP> at a scan rate of 10 mV·s<SUP>−1</SUP>. Moreover, it retained more than 88% of its initial capacitance after 5000 cycles, highlighting the long-term stability of supercapacitors based on these SnO<SUB> <I>x</I> </SUB>/CNF mats.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A core-shell-structured SnO<SUB>x</SUB>/CNF composite mat electrodes were synthesized by single-nozzle-electrospinning. </LI> <LI> The core-shell composite is highly flexible and freestanding. </LI> <LI> Capacitors using these electrodes had specific capacitance of up to 289 F·g<SUP>−1</SUP> at a scan rate of 10 mV·s<SUP>−1</SUP>. </LI> <LI> Specific capacitance at a current density of 100 mA·g<SUP>−1</SUP> reached 273 F·g<SUP>−1</SUP>. </LI> </UL> </P>

Carbon nanofibers decorated with FeO<i> _x </i> nanoparticles as a flexible electrode material for symmetric supercapacitors

Samuel, Edmund,Joshi, Bhavana,Jo, Hong Seok,Kim, Yong Il,An, Seongpil,Swihart, Mark T.,Yun, Je Moon,Kim, Kwang Ho,Yoon, Sam S. Elsevier 2017 Chemical Engineering Journal Vol. No.

<P><B>Abstract</B></P> <P>We have produced flexible, freestanding, and light weight mats of FeO<I> <SUB>x</SUB> </I>-decorated carbon nanofibers (CNFs) and demonstrated their use in supercapacitors with high energy and power density and excellent long term capacitance retention. Highly flexible carbon-iron oxide nanofibers were synthesized by electrospinning a solution of polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and iron acetylacetonate (FeAcAc), followed by annealing to carbonize the PAN, pyrolyze the PMMA to produce pores, and convert FeAcAc to FeO nanoparticles. The morphology of the FeO<I> <SUB>x</SUB> </I>/CNF composite was determined by scanning and transmission electron microscopies, which showed that the embedded FeO<I> <SUB>x</SUB> </I> nanoparticles were well distributed in the CNF electrode. We employed cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy to evaluate the electrochemical performance of symmetric supercapacitors prepared from the FeO<I> <SUB>x</SUB> </I>/CNF composite. The supercapacitors exhibited high specific capacitance (427F·g<SUP>−1</SUP> at 10mV·s<SUP>−1</SUP> and 436F·g<SUP>−1</SUP> at 1A·g<SUP>−1</SUP> in the optimal case) and good stability, retaining 89% of their initial capacitance after 5000 cycles at a current density of 1A·g<SUP>−1</SUP>. The optimal device achieved an energy density of 167Wh·kg<SUP>−1</SUP> at a power density of 0.75kW·kg<SUP>−1</SUP>, and an energy density of 66Wh·kg<SUP>−1</SUP> at a power density of 7.5kW·kg<SUP>−1</SUP>. These combinations of energy and power densities can meet the needs of many emerging supercapacitor applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly flexible FeO<SUB>x</SUB>-carbon nanocomposite nanofibers were fabricated. </LI> <LI> Freestanding FeO<I> <SUB>x</SUB> </I>-CNF showed excellent retention (89%) after 5000 cycles at 1A·g<SUP>−1</SUP>. </LI> <LI> A FeO<SUB>x</SUB>/CNF-based supercapacitor provides 436F·g<SUP>−1</SUP> of capacitance at 1A·g<SUP>−1</SUP>. </LI> <LI> Excellent uniform decoration of CNF with FeO<SUB>x</SUB> was demonstrated. </LI> </UL> </P>

CHINA’S CONFLICT-MANAGEMENT APPROACH TO THE NUCLEAR STANDOFF ON THE KOREAN PENINSULA

Samuel S. Kim 경남대학교 극동문제연구소 2006 ASIAN PERSPECTIVE Vol.30 No.1

This article provides an analysis and assessment of China’s uncharacteristically proactive conflict-management (CM) diplomacy in the U.S.-North Korea (DPRK) nuclear standoff on the Korean peninsula from 2002 to 2005. In the first of four sections, the focus is on the global context and conditions that gave rise to CM studies as a new field of international relations research in the West. The second section argues that three proximate and underlying causes—greater danger, greater stakes, and greater leverage—catapulted Beijing into the terra incognita of CM leadership role. The third section examines the shift in China’s role as well as the style and substance of this approach. The fourth section critically evaluates the possibilities and limitations of China’s conflict-management diplomacy for the resolution of the U.S.-DPRK nuclear standoff. The conclusion is a brief assessment of future prospects for establishing a more peaceful and prosperous regional order in Northeast Asia either through the ongoing Six Party Talks or through some permanent Northeast Asian security regime coming out of the success or failure of the six-party process.

Nationalism and Globalization in South Korea’s Foreign Policy

Samuel S,Kim 신아시아연구소(구 신아세아질서연구회) 2007 신아세아 Vol.14 No.3

An examination of Korea’s foreign policy in the post-Cold War era quickly encounters a double paradox: globalization and nationalism. This paper provides an analysis and assessment of how Korea is coping with these twin pressures of globalization from without and above and nationalism from within and below, with a particular focus on the dynamics of national identity. A consideration of the interplay between national identity and globalization may develop an alternative conceptual framework to facilitate a synthetic interactive explanation of the thinking and practice of globalization in post-Cold War Korean foreign policy. Globalization as a political strategy developed from Kim Young Sam’s segyehwa drive through Kim Dae June’s “intormationization” to Roh Moo-hyun’s FTA drive. These policy themes then played out in the appropriation of globalization for national-identity purposes, especially in relation to the great powers of Northeast Asia. The nexus of globalization and national identity can be seen particularly in Korea’s relations with Japan, China, and the United States. In the end, Korea’s growing integration into the regional and global systems, aided and abetted by the forces of globalization, has a paradoxical relationship with nationalism, as both remain moving targets that force Korea to adapt to the changing circumstances of Korea’s nationalized and globalized “intermestic politics.”

THE DIALECTICS OF CHINA'S NORTH KOREA POLICY IN A CHANGING POST-COLD WAR WORLD

Kim,Samuel S. The Institute for Far Eastern Studies Kyungnam Uni 1994 ASIAN PERSPECTIVE Vol.18 No.2

Will Seoul's Sunshine Policy also Rise in Beijing? : A Chinese Perspective

Kim, Samuel S. Yonsei University Press 1999 Kim Dae-jung Government and Sunshine Policy Vol.- No.1

China’s Tortuous Return to Great Power Status

Samuel S. Kim 동아시아재단 2013 Global Asia Vol.8 No.4

Assessment of the integrity of human oocytes retrieved from cryopreserved ovarian tissue after xenotransplantation

Samuel Kim, S.,Kang, Hee Gyu,Kim, Nam Hyung,Lee, Hoi Chang,Lee, Hyang Heun Oxford University Press 2005 Human reproduction Vol.20 No.9

<P>BACKGROUND: Previous studies showed that immature oocytes stored in ovarian tissue could develop to the mature stage after transplantation. However, the quality and competency of the oocytes developed in xenografted ovarian tissue have never been investigated. As a pilot study to investigate this uncharted issue, we evaluated microtubule organization and chromatin configuration of human oocytes harvested from xenografted frozen–thawed ovarian tissue. METHODS: Frozen–thawed human ovarian tissue was transplanted into severe combined immunodeficient mice. All animals were stimulated with gonadotrophin from 20 weeks after transplantation. Grafts were recovered 36 h after hCG administration. The oocytes were retrieved from the antral follicles (>2 mm diameter), cultured <I>in vitro</I>, stained for microtubule and chromatin localization. RESULTS: Five oocytes from 21 female mice and seven oocytes from nine male mice were retrieved. Immunocytochemical examinations of these oocytes after <I>in vitro</I> maturation revealed only two developed to the metaphase II stage. Most oocytes were between prophase and metaphase with abnormal microtubule organization and chromatin configuration. CONCLUSIONS: Immature oocytes in stored human ovarian tissue can grow to maturity in host animals after xenotransplantation. Retrieval of oocytes from the xenograft can be carried out and is reproducible. However, many oocytes, grown in host animals and further matured <I>in vitro</I>, showed aberrant microtubule organization and chromatin patterns.</P>