A self-healing Sn anode with an ultra-long cycle life for sodium-ion batteries

Kim, Changhyeon,Kim, Icpyo,Kim, Huihun,Sadan, Milan K.,Yeo, Hyewon,Cho, Gyubong,Ahn, Jaepyoung,Ahn, Jouhyeon,Ahn, Hyojun The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.45

<P>For a next-generation sodium battery to replace lithium ion batteries, it is essential to develop an anode with a long cycle life and high rate. Sn is considered to be an ideal candidate for the anode of sodium ion batteries. Here, we report a Sn anode that exhibits ultra-long-term cycle stability with a high capacity of 554 mA h g<SUP>−1</SUP> at 10C-rate for 5000 cycles. The optimized cell configuration consists of 1,2-dimethoxyethane as the electrolyte, a double separator including a nanoporous membrane, and a Sn anode with MWCNT as a conductive additive. Its capacity retention reaches up to 99.8% and its coulombic efficiency is near 100% for 5000 cycles. Surprisingly, we have discovered that the Sn powder exhibits a self-healing phenomenon during cycling. Sn is initially pulverized into a nanometer-sized powder, and then forms a three-dimensional porous coral-like structure in which ligament-shaped micrometer-sized Sn particles are connected with a low coordination number by room temperature sintering. The coral-like structure is mechanically stable towards volume change and electrically connected. The self-healing structure and mechanism provide a direction for the design of other electrodes with alloying mechanisms.</P>

Initial Discharge Behavior of an Ultra High Loading 3D Sulfur Cathode for a Room-Temperature Na/S Battery

Kim, Icpyo,Kim, Changhyeon,Kim, Huihun,Kim, Ki-Won,Ahn, Jou-Hyeon,Ahn, Hyo-Jun American Scientific Publishers 2018 Journal of Nanoscience and Nanotechnology Vol.18 No.9

Design of Simulator for Cloud Computing Infrastructure and Service

Changhyeon Kim,Junsang Kim,Won Joo Lee 보안공학연구지원센터 2014 International Journal of Smart Home Vol.8 No.6

Cloud computing that provides computational resource, platform and software as services is operated in cluster that is comprised of hundreds or thousands of servers. Thus, cloud computing providers may use various policies such as complex resource provisioning, allocation, configuration, and so on, to efficiently manage huge resources. In this environment, it is difficult to customize circumstance and to test and evaluate a hypothesis independently. To overcome these limitations, we provide SimCloudIS: simulator for cloud computing infrastructure and service. The SimCloudIS provides cloud system components such as the datacenter, host, VM, application, network and scheduling polices that are extendable and managed in independent layers. The network component supports packet based network communication which is based on the real network model, thereby facilitating simulation of internet based services. For evaluation, SimCloudIS provides a monitor that observes the status of all components and records them. The usefulness of SimCloudIS is demonstrated by involving a case study for dynamic allocation and relocation of VMs in a cloud environment and analyzing the result.

Inhibition of keratinocyte differentiation by cytosolic RNA sensor MDA5

( Changhyeon Kim ),( Dongkyun Hong ),( Mira Choi ),( Yullye Hwang ),( Jaekyung Lee ),( Young Lee ),( Youngjoon Seo ),( Changdeok Kim ),( Jeunghoon Lee ),( Sooil Kim ),( Youngho Lee ) 대한피부과학회 2020 대한피부과학회 학술발표대회집 Vol.72 No.1

Background: Psoriasis is a chronic inflammatory skin disease. The etiology of psoriasis is not fully understood, but the genetic background is considered to be the most important factor. To date, many psoriasis-related genes have been discovered, but the role of many important genes has not been well understood. Objectives: The purpose of this study is to uncover possible roles of MDA5 in psoriasis. Methods: Expression of MDA5 was investigated using immunohistochemistry. Then, MDA5 was overexpressed in keratinocytes using a recombinant adenovirus. Results: As a result of immunohistochemical staining, the expression of MDA5 was significantly increased in the epidermis of psoriasis compared to normal skin. Similarly, the expression of MDA5 was increased in imiquimodinduced psoriasiform dermatitis model. In cultured keratinocytes, TLR3 agonist poly(I:C) induced expression of MDA5 at both mRNA and protein levels. When MDA5 was overexpressed using a recombinant adenovirus, poly(I:C)- induced cytokine expression was significantly increased. Finally, MDA5 overexpression significantly inhibited calcium-induced differentiation of keratinocytes. Conclusion: These results suggest that MDA5 increases in psoriasis and negatively regulates keratinocyte differentiation.

환경 변화에 강인한 영상 항법 기술 동향

김창현(Changhyeon Kim),장영석(Youngseok Jang),김준하(Junha Kim),한영수(Youngsoo Han),김현진(H. Jin Kim) 제어로봇시스템학회 2022 제어·로봇·시스템학회 논문지 Vol.28 No.2

Visual navigation technology enables the pose of a robot to be estimated and the surrounding environment to be perceived using a vision sensor mounted on the robot. This technology is essential to autonomous driving systems in unmanned mobile vehicles and has been actively researched in visual odometry (VO) and visual simultaneous localization and mapping (vSLAM). Generally, the vision-based navigation algorithms perform data association and pose estimation under the assumption that the brightness of surrounding environments does not change over time and that the scene obtained from vision sensors is static. However, in realistic industrial sites or urban environments, the brightness of the environment varies, and dynamic objects such as workers and cars are present. These conditions may lead to a decline in the reliability and performance of visual navigation. Research on robust visual navigation under environmental variations, such as illumination changes and dynamic circumstances, has sought to solve this problem. This study proposes a state-of-the-art robust visual navigation system that is robust to illumination changes and dynamic environments. Moreover, our analysis and classification is based on the methodology used in each robust visual navigation.

An Ultra-low-power Mixed-mode Face Recognition Processor for Always-on User Authentication in Mobile Device

Ji-Hoon Kim,Changhyeon Kim,Kwantae Kim,Juhyoung Lee,Hoi-Jun Yoo,Joo-Young Kim 대한전자공학회 2020 Journal of semiconductor technology and science Vol.20 No.6

In this paper, we present an ultra-low-power analog-digital mixed-mode face recognition processor for user authentication in mobile devices. Unlike conventional face recognition processor architecture composed of an image sensor, high-resolution analog-to-digital converters (ADCs), and a digital signal processor, the proposed mixed-mode architecture removes the power-hungry ADCs and introduces an analog signal processor for processing the first layer of convolutional neural networks used by both face detection and face recognition as well as for performing ternary quantization. At the circuit level, we propose the reconfigurable readout circuit and exposure time-division scheme to integrate image sensor and analog signal processor without losing input data under various illumination conditions. We also propose the error-tolerant weighted-sum unit for analog convolution processing with only 15.09 uW power consumption. As a result, post-layout simulation results in 65 nm process demonstrate that the proposed mixed-mode face recognition processor has the total 0.205 mW power consumption while dissipating only 64 uW for always-on operation, which are 66.9% and 33.9% less than the state-of-the-art design.

Long-Term Isolation Elicits Depression and Anxiety-Related Behaviors by Reducing Oxytocin-Induced GABAergic Transmission in Central Amygdala

Han, Rafael T.,Kim, Young-Beom,Park, Eui-Ho,Kim, Jin Yong,Ryu, Changhyeon,Kim, Hye Y.,Lee, JaeHee,Pahk, Kisoo,Shanyu, Cui,Kim, Hyun,Back, Seung K.,Kim, Hee J.,Kim, Yang In,Na, Heung S. Frontiers Media S.A. 2018 Frontiers in molecular neuroscience Vol.11 No.-

<P>Isolation stress is a major risk factor for neuropsychiatric disorders such as depressive and anxiety disorders. However, the molecular mechanisms underlying isolation-induced neuropsychiatric disorders remain elusive. In the present study, we investigated the subcellular mechanisms by which long-term isolation elicits depression and anxiety-related behaviors in mice. First, we found that long-term isolation induced depression-related behaviors in the forced swimming test (FST) and the sucrose preference test, as well as anxiety-related behaviors in the elevated zero maze test (EZMT) and the open field test. Next, we showed that intracentral amygdala (CeA) injection of oxytocin (OXT), but not intracerebroventricular injection, attenuated isolation-induced depression and anxiety-related behaviors via oxytocin receptor (OXTR), not vasopressin-1a receptor (V1aR), in the FST and EZMT, respectively. Quantitative real-time polymerase chain reaction analysis revealed that after 5 weeks of isolation, mRNA transcription of OXTR in the CeA, but not that of V1aR, significantly decreased, whereas OXT and vasopressin mRNA transcription in the paraventricular nucleus of hypothalamus did not change significantly. Whole-cell patch clamping of acute brain slices demonstrated that the frequency of miniature inhibitory postsynaptic currents (mIPSCs) in CeA neurons, but not their amplitude, was lower in isolated mice than in group-housed mice. Notably, OXT treatment increased the mIPSC frequency in the CeA neurons, but to a lesser extent in the case of isolated mice than in that of group-housed mice via OXTR. Taken together, our findings suggest that long-term isolation down-regulates OXTR mRNA transcription and diminishes OXT-induced inhibitory synaptic transmission in the CeA and may contribute to the development of depression and anxiety-related behaviors in isolated mice through the enhancement of CeA activity.</P>

Energy-Efficient DNN Processor on Embedded Systems for Spontaneous Human-Robot Interaction

Kim, Changhyeon,Yoo, Hoi-Jun The Institute of Semiconductor Engineers 2021 Journal of semiconductor engineering Vol.2 No.2

Recently, deep neural networks (DNNs) are actively used for action control so that an autonomous system, such as the robot, can perform human-like behaviors and operations. Unlike recognition tasks, the real-time operation is essential in action control, and it is too slow to use remote learning on a server communicating through a network. New learning techniques, such as reinforcement learning (RL), are needed to determine and select the correct robot behavior locally. In this paper, we propose an energy-efficient DNN processor with a LUT-based processing engine and near-zero skipper. A CNN-based facial emotion recognition and an RNN-based emotional dialogue generation model is integrated for natural HRI system and tested with the proposed processor. It supports 1b to 16b variable weight bit precision with and 57.6% and 28.5% lower energy consumption than conventional MAC arithmetic units for 1b and 16b weight precision. Also, the near-zero skipper reduces 36% of MAC operation and consumes 28% lower energy consumption for facial emotion recognition tasks. Implemented in 65nm CMOS process, the proposed processor occupies 1784×1784 um2 areas and dissipates 0.28 mW and 34.4 mW at 1fps and 30fps facial emotion recognition tasks.

Sodium Polysulfides during Charge/Discharge of the Room-Temperature Na/S Battery Using TEGDME Electrolyte

Kim, Icpyo,Park, Jin-Young,Kim, ChangHyeon,Park, Jin-Woo,Ahn, Jae-Pyoung,Ahn, Jou-Hyeon,Kim, Ki-Won,Ahn, Hyo-Jun The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.5

<P>The charge-discharge process of the room-temperature Na/S battery is studied using the Na/S cell with tetraethylene glycol dimethyl ether (TEGDME) and the solid electrolyte. The solid electrolyte is a barrier for chemical mass transport between the anode and the cathode. The sodium polysulfides as reaction products in TEGDME could therefore be investigated without interference from the anode side. During discharge, the color of the TEGDME electrolyte changes from transparent to brown, yellowish-green, and then back to transparent, and in the reverse order during charge. The first three colors are well-matched with those of prepared TEGDME solutions of Na2Sn (6 <= n <= 8), Na2S4 and Na2S, respectively. The solubility of sodium polysulfides (Na2Sn, 1 <= n <= 8) in TEGDME are measured systematically. The dissolution of sodium polysulfides is found to depend on the molar concentration of sulfur. The optimized Na/S cell using activated carbon delivers a high capacity of 1070 mAh g(-1) at the first discharge, and remains at 782 mAh g(-1) after 37 cycles. It also shows good rate capability with a discharge capacity of 569 mAh g(-1) at 1/2 C. The coulombic efficiency is nearly 100% after the 5th cycle. (C) 2016 The Electrochemical Society. All rights reserved.</P>

A Resource Reduction Scheme with Low Migration Frequency for Virtual Machines on a Cloud Cluster

( Changhyeon Kim ),( Wonjoo Lee ),( Changho Jeon ) 한국인터넷정보학회 2013 KSII Transactions on Internet and Information Syst Vol.7 No.6

A method is proposed to reduce excess resources from a virtual machine(VM) while avoiding subsequent migrations for a computer cluster that provides cloud service. The proposed scheme cuts down on the resources of a VM based on the probability that migration may occur after a reduction. First, it finds a VM that can be scaled down by analyzing the history of the resource usage. Then, the migration probability is calculated as a function of the VM resource usage trend and the trend error. Finally, the amount of resources needed to eliminate from an underutilized VM is determined such that the migration probability after the resource reduction is less than or equal to an acceptable migration probability. The acceptable migration probability, to be set by the cloud service provider, is a criterion to assign a weight to the resource reduction either to prevent VM migrations or to enhance VM utilization. The results of simulation show that the proposed scheme lowers migration frequency by 31.6~60.8% depending on the consistency of resource demand while losing VM utilization by 9.1~21.5% compared to other known approaches, such as the static and the prediction-based methods. It is also verified that the proposed scheme extends the elapsed time before the first occurrence of migration after resource reduction 1.1~2.3-fold. In addition, changes in migration frequency and VM utilization are analyzed with varying acceptable migration probabilities and the consistency of resource demand patterns. It is expected that the analysis results can help service providers choose a right value of the acceptable migration probability under various environments having different migration costs and operational costs.