Graphene paper with controlled pore structure for high-performance cathodes in Li–O₂ batteries

Kim, Do Youb,Kim, Mokwon,Kim, Dong Wook,Suk, Jungdon,Park, Jung Jin,Park, O Ok,Kang, Yongku Elsevier 2016 Carbon Vol.100 No.-

<P>In non-aqueous Li-O-2 batteries, relatively large amounts of discharge products are formed on air cathodes. As such, the expansion of air cathodes is a critical issue that remains to be solved. Here, we report the fabrication of highly porous free-standing graphene paper by introducing macropores within the paper using polystyrene colloidal particles as a sacrificial template. The as-prepared macroporous graphene paper (mp-GP) have a large BrunauereEmmetteTeller (BET) surface area (ca. 373 m(2) g(-1)), a large pore volume (ca. 10.9 cm(3) g(-1)), and a high porosity (91.6%). Owing to the high surface area and large pore volume, the mp-GPs exhibit a high specific capacity of ca. 12,200 mAh g(-1) at a current density of 200 mA g(-1), as well as good rate capability, when used as an air cathode in a non-aqueous Li-O-2 battery. Moreover, the mp-GP shows good stability up to 100 and 78 cycles at a current density of 500 mA g(-1) and 2000 mA g(-1) respectively, with a limiting capacity of 1000 mAh g(-1). It is found that formation and decomposition of the discharge product, Li2O2, occur within the macropores, and thus, the mp-GP maintains its original structure without considerable expansion during cycling. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Nonparametric Bayesian analysis for multi-site hidden Markov model

Kim, Dal Ho,Jo, Aejung,Kim, Yongku Taylor Francis 2017 Communications in statistics. Simulation and compu Vol.46 No.6

<i>In-situ</i> preparation and unique electrochemical behavior of pore-embedding CoO/Co₃O₄ intermixed composite for Li⁺ rechargeable battery electrodes

Kim, Jin Kyu,Ju, Ji Young,Choi, Seul Ki,Unithrattil, Sanjith,Lee, Sun Sook,Kang, Yongku,Kim, Yongseon,Im, Won Bin,Choi, Sungho Elsevier 2018 Journal of Power Sources Vol.378 No.-

<P><B>Abstract</B></P> <P>Electrochemically active CoO/Co<SUB>3</SUB>O<SUB>4</SUB> co-existing microspheres with morphology-inherited porous particles is successfully synthesized via a simple solvothermal method. The as-prepared intermixed composite undergoes a monoxide CoO-preferred conversion reaction with an extremely enhanced capacity retention, ∼905 mA h g<SUP>−1</SUP> after 250 cycles for discharge state, which is 1.6 times higher than the conventional CoO<SUB>x</SUB>-based anodes. Moreover, stable catalytic behavior of the electrocatalysts in Li-air cathodes of the given composites is also demonstrated. We believe that the extraordinarily enhanced electrode performance might be due to the novel pore-tempered microspheres packed with double electrochemically active centers of the CoO/Co<SUB>3</SUB>O<SUB>4</SUB> composite effectively confine the detrimental volume exchange during the reversible cyclic reactions as well as the preserved multiple reactive sites for a reversible Li<SUP>+</SUP> ⇄ LiO<SUB>x</SUB> reaction, which is advantageous for advanced Li rechargeable battery.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>In-situ</I> growth of electrochemically active CoO/Co<SUB>3</SUB>O<SUB>4</SUB>composite for Li<SUP>+</SUP>ion. </LI> <LI> Unique electrochemical behavior of pore-embedding CoO/Co<SUB>3</SUB>O<SUB>4</SUB>spherical particles. </LI> <LI> Propose conceptual design of metal oxide composites for the novel electrodematerial. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Bootstrap methods for long-memory processes: a review

Kim, Young Min,Kim, Yongku The Korean Statistical Society 2017 Communications for statistical applications and me Vol.24 No.1

This manuscript summarized advances in bootstrap methods for long-range dependent time series data. The stationary linear long-memory process is briefly described, which is a target process for bootstrap methodologies on time-domain and frequency-domain in this review. We illustrate time-domain bootstrap under long-range dependence, moving or non-overlapping block bootstraps, and the autoregressive-sieve bootstrap. In particular, block bootstrap methodologies need an adjustment factor for the distribution estimation of the sample mean in contrast to applications to weak dependent time processes. However, the autoregressive-sieve bootstrap does not need any other modification for application to long-memory. The frequency domain bootstrap for Whittle estimation is provided using parametric spectral density estimates because there is no current nonparametric spectral density estimation method using a kernel function for the linear long-range dependent time process.

Stochastic precipitation modeling based on Korean historical data

Kim, Yongku,Kim, Hyeonjeong The Korean Data and Information Science Society 2012 한국데이터정보과학회지 Vol.23 No.6

Stochastic weather generators are commonly used to simulate time series of daily weather, especially precipitation amount. Recently, a generalized linear model (GLM) has been proposed as a convenient approach to fitting these weather generators. In this paper, a stochastic weather generator is considered to model the time series of daily precipitation at Seoul in South Korea. As a covariate, global temperature is introduced to relate long-term temporal scale predictor to short-term temporal predictands. One of the limitations of stochastic weather generators is a marked tendency to underestimate the observed interannual variance of monthly, seasonal, or annual total precipitation. To reduce this phenomenon, we incorporate time series of seasonal total precipitation in the GLM weather generator as covariates. It is veri ed that the addition of these covariates does not distort the performance of the weather generator in other respects.

Noninformative priors for the between-group variance in the unbalanced one-way random effects model with heterogeneous error variances

Kim, Dal Ho,Lee, Woo Dong,Kang, Sang Gil,Kim, Yongku Informa UK (Taylor Francis) 2019 JOURNAL OF STATISTICAL COMPUTATION AND SIMULATION Vol.89 No.10

Flexible binder-free graphene paper cathodes for high-performance Li-O₂ batteries

Kim, Do Youb,Kim, Mokwon,Kim, Dong Wook,Suk, Jungdon,Park, O Ok,Kang, Yongku Elsevier 2015 Carbon Vol.93 No.-

<P><B>Abstract</B></P> <P>In this study, free-standing porous graphene papers for high-capacity and reversible Li-O<SUB>2</SUB> battery cathodes are investigated. The graphene paper-like films were fabricated by the assembling of graphene nanoplatelets (GNPs) with the aid of graphene oxides (GOs) as a stabilizer, using a vacuum-assisted filtration method. By using GOs as a stabilizer, the GNP/GO films were fabricated with a paper-like form and they exhibited a highly wrinkled and disordered morphology. Moreover, the use of GNPs as a basic material eliminated the need for a post-annealing to recover the intrinsic electrical conductivity of graphene sheets. Subsequently, the GNP/GO paper could be directly used as a Li-O<SUB>2</SUB> battery cathode without any conducting additives and binders. The GNP/GO paper electrode showed a much higher discharge capacity in comparison to the reduced-GO paper and commercially available carbon papers. We also found that toroidal Li<SUB>2</SUB>O<SUB>2</SUB> mainly nucleated and grew on discharge, and decomposed on charge with a relatively high O<SUB>2</SUB> evolution/consumption efficiency of 87%. However, a large number of Li<SUB>2</SUB>O<SUB>2</SUB> particles grew inside the GNP/GO paper electrode, resulting in severe volume expansion of the electrode. This volume expansion could be the primary reason for the capacity fading on cycling.</P>

Neuroprotection in Schizophrenia and Its Therapeutic Implications

YongKu Kim,KyoungSae Na 대한신경정신의학회 2017 PSYCHIATRY INVESTIGATION Vol.14 No.4

Schizophrenia is a chronic and debilitating mental disorder. The persisting negative and cognitive symptoms that are unresponsive to pharmacotherapy reveal the impairment of neuroprotective aspects of schizophrenia. In this review, of the several neuroprotective factors, we mainly focused on neuroinflammation, neurogenesis, and oxidative stress. We conducted a narrative and selective review. Neuroinflammation is mainly mediated by pro-inflammatory cytokines and microglia. Unlike peripheral inflammatory responses, neuroinflammation has a role in various neuronal activities such as neurotransmission neurogenesis. The cross-talk between neuroinflammation and neurogenesis usually has beneficial effects in the CNS under physiological conditions. However, uncontrolled and chronic neuroinflammation exert detrimental effects such as neuronal loss, inhibited neurogenesis, and excessive oxidative stress. Neurogenesis is also a major component of neuroprotection. Adult neurogenesis mainly occurs in the hippocampal region, which has an important role in memory formation and processing. Impaired neurogenesis and an ineffective response to antipsychotics may be thought to indicate a deteriorating course of schizophrenia. Oxidative stress and excessive dopaminergic neurotransmission may create a vicious cycle and consequently disturb NMDA receptor-mediated glutamatergic neurotransmission. Based on the current evidences, several neuroprotective therapeutic approaches have been reported to be efficacious for improving psychopathology, but further longitudinal and large-sample based studies are needed.

Nonparametric Bayesian modeling for monotonicity in catch ratio

Kim, Dal Ho,Ryu, Hyunnam,Kim, Yongku Informa UK (TaylorFrancis) 2018 Communications in statistics. Simulation and compu Vol.47 No.4

<P>This article proposes nonparametric Bayesian approaches to monotone function estimation. This approach uses a hierarchical Bayes framework and a characterization of stick-breaking process that allows unconstrained estimation of the monotone function. In order to avoid the limitation of parametric modeling, a general class of prior distributions, called stick-breaking priors, is considered. It accommodates much more flexible forms and can easily deal with skewness, multimodality, etc., of the dependent variable response. The proposed approach is incorporated to model the catch ratio based on automatic weather station (AWS) data.</P>

Lactobacillus rhamnosus CBT-LR5 Improves Lipid Metabolism by Enhancing Vitamin Absorption

Kim Dong-Jin,Kim Tai Yeub,Yoon Yeo-Sang,Ryu Yongku,Chung Myung Jun 한국미생물·생명공학회 2022 한국미생물·생명공학회지 Vol.50 No.4

Probiotics provide a symbiotic relationship and beneficial effects by balancing the human intestinal microbiota. The relationships between microbiota changes and various diseases may predict health abnormalities and diseases. Treatment with vitamins and probiotics is one therapeutic approach. To evaluate the effect of probiotics on vitamin absorption, we chose Lactobacillus rhamnosus CBT-LR5 treatment, which has resistance to vitamin C-inducible toxicity, with vitamins in high-fat diet (HFD)-induced obesity models. CBT-LR5 affected the absorption of micronutrients, such as ionic minerals and water-soluble vitamins. An increase in vitamin C absorption by CBT-LR5 enhanced the antioxidant response in HFD-induced obesity models. Increased vitamin B absorption by CBT-LR5 regulated lipid metabolism in HFD-induced obesity models. These favorable effects of CBT-LR5 on the absorption of vitamins should be investigated as candidate therapeutic target treatments for metabolic diseases.