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Kim, Sung Kyun,Bhatia, Ravi,Kim, Tae-Ho,Seol, Daehee,Kim, Jung Ho,Kim, Hyun,Seung, Wanchul,Kim, Yunseok,Lee, Young Hee,Kim, Sang-Woo Elsevier 2016 Nano energy Vol.22 No.-
<P><B>Abstract</B></P> <P>Due to the interesting semiconducting and optical properties of transition metal dichalcogenides, they have received particular attention for novel electronics and optoelectronics. In addition it is expected that piezoelectric properties of two-dimensional (2D) layered materials are very useful to realize next generation mechanically powered transparent flexible charge-generating devices. Here we report directional dependent piezoelectric effects in chemical vapor deposition grown monolayer MoS<SUB>2</SUB> for flexible piezoelectric nanogenerators (NGs). It was found that the output power obtained from the NG with the armchair direction of MoS<SUB>2</SUB> is about two times higher than that from the NG with the zigzag direction of MoS<SUB>2</SUB> under the same strain of 0.48% and the strain velocity of 70mm/s. This study provides a new way to effectively harvest mechanical energy using novel flexible piezoelectric NGs based on 2D semiconducting piezoelectric MoS<SUB>2</SUB> for powering low power-consuming electronics and realizing self-powered sensors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Directional dependent piezoelectric effects in chemical vapor deposition (CVD) grown monolayer MoS<SUB>2</SUB> for flexible piezoelectric nanogenerators (NGs). </LI> <LI> Lateral piezoresponse force microscopy measurements revealed that the magnitude of the piezoelectric polarization in monolayer MoS<SUB>2</SUB> significantly depends on the atomic orientation axis of MoS<SUB>2</SUB>. </LI> <LI> Flexible piezoelectric NGs were successfully fabricated using the CVD-grown single-crystalline monolayer MoS<SUB>2</SUB> flakes. </LI> <LI> The output power obtained from the NG with the armchair direction of MoS<SUB>2</SUB> is about two times higher than the zigzag direction of MoS<SUB>2</SUB>. </LI> <LI> New effectively harvest mechanical energy using novel flexible piezoelectric NGs based on 2D semiconducting piezoelectric MoS<SUB>2</SUB> for powering low power-consuming devices and realizing self-powered electronics. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We report directional dependent piezoelectric effects in chemical vapor deposition grown monolayer MoS<SUB>2</SUB> for flexible piezoelectric nanogenerators. The output power obtained from the nanogenerator with the armchair direction of MoS<SUB>2</SUB> is about two times higher than that from the nanogenerator with the zigzag direction of MoS<SUB>2</SUB> under the same strain.</P> <P>[DISPLAY OMISSION]</P>
Automatic Frame Composition Using Histogram Based Graph Cut
Daehee Kim,Hyungtae Kim,Jinho Park,Donggyun Kim,Joonki Paik 보안공학연구지원센터 2015 International Journal of Multimedia and Ubiquitous Vol.10 No.1
In this paper, we present an automatic background composition method using histogram-based graph cut. The proposed method consists of four steps: i) initial label map generation, ii) label map update, iii) object extraction by segmentation, and iv) dynamic background composition. Since the proposed method can minimize the user interaction for generating the initial label map and updating, it is suitable for simple interaction using a low-speed processor and limited memory space. Experimental results show that the proposed method provides better segmentation results compared with existing state-of-the-art methods with significantly reduced computational complexity. The proposed automatic object segmentation and background composition method can be applied to video editing, video conference, and video contents creation using low-cost mobile devices such as smart phones, smart TVs, and tablet PCs.
Kim, Daehee,Oh, Jahwan,Jeon, Jieun,Lee, Junghyun The Institute of Electronics and Information Engin 2012 IEIE Transactions on Smart Processing & Computing Vol.1 No.3
This paper proposes an automatic object segmentation and background composition method for video communication over consumer mobile phones. The object regions were extracted based on the motion and color variance of the first two frames. To combine the motion and variance information, the Euclidean distance between the motion boundary pixel and the neighboring color variance edge pixels was calculated, and the nearest edge pixel was labeled to the object boundary. The labeling results were refined using the morphology for a more accurate and natural-looking boundary. The grow-cut segmentation algorithm begins in the expanded label map, where the inner and outer boundary belongs to the foreground and background, respectively. The segmented object region and a new background image stored a priori in the mobile phone was then composed. In the background composition process, the background motion was measured using the optical-flow, and the final result was synthesized by accurately locating the object region according to the motion information. This study can be considered an extended, improved version of the existing background composition algorithm by considering motion information in a video. The proposed segmentation algorithm reduces the computational complexity significantly by choosing the minimum resolution at each segmentation step. The experimental results showed that the proposed algorithm can generate a fast, accurate and natural-looking background composition.
Inter-Domain Curriculum Learning for Domain Generalization
Daehee Kim(김대희),Youngjun Yoo(유영준),Inkyung Kim(김인경),Jaekoo Lee(이재구) 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.2
Despite the rapid advancements in deep learning, the appropriate performance is not guaranteed under domain-shift. This problem has been addressed through domain generalization (DG). In DG, decreasing the required computation is difficult to achieve because training should be performed multiple times to infer the average performance owing to the large deviation of performance. We propose inter-domain curriculum learning, a method that sequentially transforms easy-to-learn domain data to difficult-to-learn domain data. Quantitative experiments have demonstrated that the average performance increased by 1.08 points and the performance deviation is reduced. Moreover, the research cycle can be accelerated by reducing 16.7% of the computation.
Kim, Jihye,Kim, Minhyung,Jeong, Yoonjeong,Lee, Wook-bin,Park, Hyojin,Kwon, Ja-Young,Kim, Young-Myeong,Hwang, Daehee,Kwon, Young-Guen American Heart Association 2015 Arteriosclerosis, thrombosis, and vascular biology Vol.35 No.9
<P><B>Objective—</B></P><P>Modulating endothelial progenitor cells (EPCs) is essential for therapeutic angiogenesis, and thus various clinical trials involving EPCs are ongoing. However, the identification of environmental conditions and development of optimal methods are required to accelerate EPC-driven vasculogenesis.</P><P><B>Approach and Results—</B></P><P>We evaluated gene expression profiles of cord blood–derived EPCs and endothelial cells to identify the key factors in EPC→endothelial cell differentiation and to show that transforming growth factor-β family members contribute to EPC differentiation. The expression levels of activin receptor-like kinase 1 (ALK1) and its high-affinity ligand, bone morphogenetic protein 9 (BMP9) were markedly changed in EPC→endothelial cell differentiation. Interestingly, BMP9 induced EPC→endothelial cell differentiation and EPC incorporation into vessel-like structures by acting on ALK1 expressed on EPCs in vitro. BMP9 also induced neovascularization in mice with hindlimb ischemia by increasing vessel formation and the incorporation of EPCs into vessels. Conversely, neovascularization was impaired when ALK1 signaling was blocked. Furthermore, EPCs exposed to either short- or long-term BMP9 stimulation demonstrated these functions in EPC-mediated neovascularization.</P><P><B>Conclusions—</B></P><P>Collectively, our results indicated that BMP9/ALK1 augmented vasculogenesis and angiogenesis, and thereby enhanced neovascularization. Thus, we suggest that BMP9/ALK1 may improve the efficacy of EPC-based therapies for treating ischemic diseases.</P>
Secure and Efficient Time Synchronization for Border Surveillance Wireless Sensor Networks
KIM, Daehee,KANG, Sangwook,AN, Sunshin 'Institute of Electronics, Information and Communi 2016 IEICE transactions on fundamentals of electronics, Vol.ea99 No.1
<P>Time synchronization is of paramount importance in wireless sensor networks (WSNs) due to the inherent distributed characteristics of WSNs. Border surveillance WSNs, especially, require a highly secure and accurate time synchronization scheme to detect and track intruders. In this paper, we propose a Secure and Efficient Time synchronization scheme for Border surveillance WSNs (SETB) which meets the requirements of border surveillance WSNs while minimizing the resource usage. To accomplish this goal, we first define the performance and security requirements for time synchronization in border surveillance WSNs in detail. Then, we build our time synchronization scheme optimized for these requirements. By utilizing both heterogeneous WSNs and one-way key chains, SETB satisfies the requirements with much less overhead than existing schemes. Additionally, we introduce on-demand time synchronization, which implies that time synchronization is conducted only when an intruder enters the WSN, in order to reduce energy consumption. Finally, we propose a method of deploying time-source nodes to keep the synchronization error within the requirement. Our analysis shows that SETB not only satisfies the performance and security requirements, but also is highly efficient in terms of communication and computation overhead, thus minimizing energy consumption.</P>