Inundation Analysis of Coastal Area Considering Climate Change

Kim, Kyungtae,Kim, Yonsoo,Kim, Soojun,Choi, Changhyun,Kim, Hung Soo 한국방재학회 2015 한국방재학회 학술발표대회논문집 Vol.14 No.-

Future climate change is expected to raise the mean sea level of Korea by about 0.85m-1.29m. Consequently, flood damage in the coastal area would likewise increase and the scale of damage would also become much larger. Various researches have been conducted to efficiently respond to natural disasters caused by climate change. However, there haven’t been many researches related to the analysis and evaluation of coastal area flood vulnerability caused by the rise in sea level. Hence, this study selected Gilsan River basin, a branch of Geum River as the subject matter and tried to evaluate the effect of sea level rise caused by climate change on the coastal area and adjacent rivers. This study also calculated the change in water quantity in the coastal area by considering the sea level rise as well as the future precipitation according to climate change. It also prepared/compared the relevant flood inundation map. The study result showed that the overall flood level increased as the elevation of the water surface rose due to the rise in sea level. In addition, the extent of increase in flood level caused by sea level rise was greater at a location nearer the outlet and it was smaller at a place farther from the outlet. Based on this result, it could be verified that in coastal rivers, climate change can have an effect not only on the precipitation increase but also on the flood water level and flood inundation due to the rise in sea level. The result of this study could be used as basic data for creating technology that would assess the flood vulnerability of coastal urban regions and evaluate preventive measures for coastal disaster risks.

Flood Simulation and Economic Analysis Considering Stormwater Drainage Pumping Stations

Choi, Changhyun,Kim, Yonsoo,Kim, Soojun,Kim, Kyungtae,Kim, Hung Soo 한국방재학회 2015 한국방재학회 학술발표대회논문집 Vol.14 No.-

Global climate change has made natural disasters become large-scale, diversified, and concentrated, causing social and economic damages one after another. The frequency of natural disasters and the scale of subsequent damages are continuously increasing and more than 90% of damages are caused by rainfall, wind speed, and snowfall. In particular, flood damage accounts for the greatest percentage of damage, which prompts us to prepare necessary preventive measures. Flood damage caused by river inundation often occurred in the past. Recently, however, inland flood damages, such as the inundation of Gangnam Station in 2011 and 2012, caused by urbanization have been increasing, which makes it necessary to simulate flood inundation and calculate the damages while considering the effect of inland inundation as well as river inundation. Accordingly, this study analyzed the inland inundation reduction effect through a simulation of flood inundation utilizing flood pumping stations in Anyang River. An economic analysis was also conducted. In addition, this study prepared/compared the flow inundation map based on the existence and operation of flood pumping stations during a localized heavy rainfall event and tried to analyze the economic feasibility by comparing the expected flood damage and the cost of flood pumping stations using Multi-dimensional Flood Damage Assessment. Through this study, results will be provided as reference data for qualitative flood inundation simulation and economic analysis of the basin where natural discharge of direct runoff is impossible and compulsive drainage is taking place.

Intimate Freedom

Kyungtae KIM The Academy of Korean Studies 2018 Korea Journal Vol.58 No.2

Biodegradable, electro-active chitin nanofiber films for flexible piezoelectric transducers

Kim, Kyungtae,Ha, Minjeong,Choi, Byeongwook,Joo, Se Hun,Kang, Han Sol,Park, Ju Hyun,Gu, Bongjun,Park, Chanho,Park, Cheolmin,Kim, Jongbok,Kwak, Sang Kyu,Ko, Hyunhyub,Jin, Jungho,Kang, Seok Ju Elsevier 2018 Nano energy Vol.48 No.-

<P><B>Abstract</B></P> <P>Since the conventional fluorine-based electro-active polymers release toxic residues into the environment during their syntheses and decomposition processes, eco-friendly piezoelectric polymers are urgently demanded in the field of energy-related soft materials. Here, we derive a high-performance biodegradable chitin polymer from squid pen material and demonstrate its utility as a flexible piezoelectric material. The readily controlled ferroelectric chitin film confers excellent piezoelectricity under external mechanical pressure, resulting in comparable performance with that of conventional fluorine-based piezoelectric polymers. In particular, the sufficient piezoelectric behavior in chitin film allows us to not only realize a high-fidelity paper-type speaker and microphone that operates over a wide frequency range without significantly deteriorating the input and output sounds but also demonstrate transparent speaker consisting of AgNWs electrodes onto freestanding chitin film which also enables to resemble the original sound. Finally, the biodegradable chitin polymer can be successfully dissolved by chitinase enzyme within eight days without any toxic residues remained.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ferroelectric characteristic is confirmed by polarization measurement. </LI> <LI> β-chitin film enables to demonstrate high-fidelity paper-type speaker and microphone. </LI> <LI> The biodegradable nature of chitin film can be dissolved within eight days. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We present a novel biodegradable piezoelectric material from chitin material, the second-most abundant polysaccharide biopolymer. The decent polarization arising from the chitin molecules not only facilitates the piezoelectric response upon the external pressure but also generates the harmonic frequencies of the input music source. Moreover, the environmentally friendly chitin film can be completely dissolved in a water-based solution without generating toxic products.</P> <P>[DISPLAY OMISSION]</P>

Securing heap memory by data pointer encoding

Kim, Kyungtae,Pyo, Changwoo Elsevier 2012 Future generations computer systems Vol.28 No.8

<P><B>Abstract</B></P><P>Since pointer variables frequently cause programs to crash in unexpected ways, they often pose vulnerability abused as immediate or intermediate targets. Although code pointer attacks have been historically dominant, data pointer attacks are also recognized as realistic threats. This paper presents how to secure heap memory from data pointer attacks, in particular, heap overflow attacks. Our protection scheme encrypts the data pointers used for linking free chunks, and decrypts the pointers only before dereferencing. We also present a list structure with duplicate links that is harder to break than the conventional linked list structure. Our experiment shows that the proposed data pointer encoding is effective and has slightly better performance than the integrity check of link pointers in GNU’s standard C library.</P> <P><B>Research highlights</B></P><P>► Introduce the concept ”data pointer encoding”. ► Show how to protect heap space by data pointer encoding. ► Enhances the structure of free chunks of heap memory to make dual-linked lists for better security and detection. ► Present the experimental result using the GNU’s standard C library.</P>

Mechanical Snell's Law

KyungTae Kim,June-Haak Ee,Kyoung Hoon Kim,U-Rae Kim,이정일 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.4

We investigate the motion of a massive particle constrained to move along a path consisting of two line segments on a vertical plane under an arbitrary conservative force. By fixing the starting and end points of the track and varying the vertex horizontally, we find the least-time path. We define the angles of incidence and refraction similar to the refraction of a light ray. It is remarkable that the ratio of the sines of these angles is identical to the ratio of the average speeds on the two partial paths as long as the horizontal component of the conservative force vanishes.

Effects of chronic exposure to cefadroxil and cefradine on <i>Daphnia magna</i> and <i>Oryzias latipes</i>

Kim, Bokyung,Ji, Kyunghee,Kho, Younglim,Kim, Pan-Gyi,Park, Kyunghwa,Kim, Kyungtae,Kim, Youngsuk,Kim, Ki-Tae,Choi, Kyungho Pergamon Press 2017 Chemosphere Vol.185 No.-

<P><B>Abstract</B></P> <P>Cefadroxil and cefradine have frequently been detected in surface waters, however toxicological studies in aquatic organisms have mostly been limited to acute lethal effects. In the present study, endocrine disruption caused by cefadroxil and cefradine, and its underlying mechanism were investigated by chronic exposure of <I>Daphnia magna</I> (21 d) and <I>Oryzias latipes</I> (120 d). In medaka fish, the effects on growth, mortality, and reproduction, as well as on the levels of hormones and genes related to the hypothalamic-pituitary-gonad (HPG) axis, were investigated after 120 d exposure. In <I>D. magna</I>, the chronic effects on growth were observed at the highest concentration of 83.0 mg L<SUP>−1</SUP> cefadroxil and 80.8 mg L<SUP>−1</SUP> cefradine. The growth of juvenile fish was significantly impaired by exposure to cefradine. Following exposure to cefadroxil and cefradine for 120 d, sex-dependent changes in E2 hormones were observed and their levels were supported by the regulation of genes along the HPG axis. We found that chronic exposure to cefadroxil and cefradine impaired growth and reproduction in a freshwater invertebrate and fish, and altered the levels of sex hormones and genes associated with the HPG axis in fish.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cefadroxil and cefradine impaired growth in a freshwater invertebrate and a fish. </LI> <LI> Cephalosporin antibiotics altered gene transcriptions of the HPG axis in fish. </LI> <LI> Cefadroxil and cefradine modulated sex hormones and genes in a sex-dependent way. </LI> </UL> </P>

Strong contact coupling of neuronal growth cones with height-controlled vertical silicon nanocolumns

Kim, Seong-Min,Lee, Seyeong,Kim, Dongyoon,Kang, Dong-Hee,Yang, Kisuk,Cho, Seung-Woo,Lee, Jin Seok,Choi, Insung S.,Kang, Kyungtae,Yoon, Myung-Han SPRINGER SCIENCE + BUSINESS MEDIA 2018 NANO RESEARCH Vol.11 No.5

Gateway Strategies for VoIP Traffic over Wireless Multihop Networks

( Kyungtae Kim ),( Dragos Niculescu ),( Sangjin Hong ) 한국인터넷정보학회 2011 KSII Transactions on Internet and Information Syst Vol.5 No.1

When supporting both voice and TCP in a wireless multihop network, there are two conflicting goals: to protect the VoIP traffic, and to completely utilize the remaining capacity for TCP. We investigate the interaction between these two popular categories of traffic and find that conventional solution approaches, such as enhanced TCP variants, priority queues, bandwidth limitation, and traffic shaping do not always achieve the goals. TCP and VoIP traffic do not easily coexist because of TCP aggressiveness and data burstiness, and the (self-) interference nature of multihop traffic. We found that enhanced TCP variants fail to coexist with VoIP in the wireless multihop scenarios. Surprisingly, even priority schemes, including those built into the MAC such as RTS/CTS or 802.11e generally cannot protect voice, as they do not account for the interference outside communication range. We present VAGP (Voice Adaptive Gateway Pacer) - an adaptive bandwidth control algorithm at the access gateway that dynamically paces wired-to-wireless TCP data flows based on VoIP traffic status. VAGP continuously monitors the quality of VoIP flows at the gateway and controls the bandwidth used by TCP flows before entering the wireless multihop. To also maintain utilization and TCP performance, VAGP employs TCP specific mechanisms that suppress certain retransmissions across the wireless multihop. Compared to previous proposals for improving TCP over wireless multihop, we show that VAGP retains the end-to-end semantics of TCP, does not require modifications of endpoints, and works in a variety of conditions: different TCP variants, multiple flows, and internet delays, different patterns of interference, different multihop topologies, and different traffic patterns.

Detailed Balance of Thermalization Dynamics in Rydberg-Atom Quantum Simulators

Kim, Hyosub,Park, YeJe,Kim, Kyungtae,Sim, H.-S.,Ahn, Jaewook American Physical Society 2018 Physical Review Letters Vol.120 No.18

<P>Dynamics of large complex systems, such as relaxation towards equilibrium in classical statistical mechanics, often obeys a master equation that captures essential information from the complexities. Here, we find that thermalization of an isolated many-body quantum state can be described by a master equation. We observe sudden quench dynamics of quantum Ising-likc models implemented in our quantum simulator, defect-free single-atom tweezers in conjunction with Rydberg-atom interaction. Saturation of their local observables, a thermalization signature, obeys a master equation experimentally constructed by monitoring the occupation probabilities of prequench states and imposing the principle of the detailed balance. Our experiment agrees with theories and demonstrates the detailed balance in a thermalization dynamics that does not require coupling to baths or postulated randomness.</P>