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Search Results: 1 - 10 of 28119 matches for " Kee Dong Yoon "
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NMR study on the stability of the magnetic ground state in MnCr${}_2$O${}_4$
Dong Young Yoon,Soonchil Lee,Yoon Seok Oh,Kee Hoon Kim
Physics , 2010, DOI: 10.1103/PhysRevB.82.094448
Abstract: The canting angles and fluctuation of the magnetic ion spins of spinel oxide MnCr${}_2$O${}_4$ were studied by nuclear magnetic resonance (NMR) at low temperatures, which has a collinear ferrimagnetic order below $T_C$ and a ferrimagnetic spiral order below $T_s < T_C$. Contrary to previous reports, only one spin canting angle of Cr ions was observed. The spin canting angles of Mn and Cr ions in the ferrimagnetic spiral obtained at a liquid-He temperature were $43\,^{\circ}$ and $110\,^{\circ}$, respectively. The nuclear spin-spin relaxation was determined by the Suhl-Nakamura interaction at low temperatures but the relaxation rate $T_2^{-1}$ increases rapidly as the temperature approaches $T_s$. This indicates that the fluctuation of the spiral component becomes faster as the temperature increases but not fast enough to leave an averaged hyperfine field to nuclei in the time scale of nuclear spin precession in the ferrimagnetic phase, which is on the order of $10^{-8}$ s. The spiral volume fraction measured for various temperatures reveals that the collinear and the spiral ferrimagnetic phases are mixed below the transition temperature of the spiral order. The temperature hysteresis in the volume fraction implies that this transition has first-order characteristics.
A Novel Source of Methylglyoxal and Glyoxal in Retina: Implications for Age-Related Macular Degeneration
Kee Dong Yoon, Kazunori Yamamoto, Keiko Ueda, Jilin Zhou, Janet R. Sparrow
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0041309
Abstract: Aging of retinal pigment epithelial (RPE) cells of the eye is marked by accumulations of bisretinoid fluorophores; two of the compounds within this lipofuscin mixture are A2E and all-trans-retinal dimer. These pigments are implicated in pathological mechanisms involved in some vision-threatening disorders including age-related macular degeneration (AMD). Studies have shown that bisretinoids are photosensitive compounds that undergo photooxidation and photodegradation when irradiated with short wavelength visible light. Utilizing ultra performance liquid chromatography (UPLC) with electrospray ionization mass spectrometry (ESI-MS) we demonstrate that photodegradation of A2E and all-trans-retinal dimer generates the dicarbonyls glyoxal (GO) and methylglyoxal (MG), that are known to modify proteins by advanced glycation endproduct (AGE) formation. By extracellular trapping with aminoguanidine, we established that these oxo-aldehydes are released from irradiated A2E-containing RPE cells. Enzyme-linked immunosorbant assays (ELISA) revealed that the substrate underlying A2E-containing RPE was AGE-modified after irradiation. This AGE deposition was suppressed by prior treatment of the cells with aminoguanidine. AGE-modification causes structural and functional impairment of proteins. In chronic diseases such as diabetes and atherosclerosis, MG and GO modify proteins by non-enzymatic glycation and oxidation reactions. AGE-modified proteins are also components of drusen, the sub-RPE deposits that confer increased risk of AMD onset. These results indicate that photodegraded RPE bisretinoid is likely to be a previously unknown source of MG and GO in the eye.
Estimation of the Effects of Air Pollutants on Tree Ring Growth in Black Pines (Pinus thunbergii)
Song, Young-Joo,Yoon-Dong Kim,Kee-Ryong Choi
Journal of Ecology and Field Biology , 2009,
Abstract: Tree-ring width analysis has been used to assess the effects of air pollution on tree growth aroundindustrial complexes. Our study was conducted to elucidate the effect of air pollutants on annual ring growthin black pines (Pinus thunbergii) of age 41~48 years around Ulsan Metropolitan City. The growth data wereanalyzed by multiple regression and the results are as follows: 1. The annual ring increment of black pinesincreased with tree age until age 40 years and then decreased gradually after age 40 years. 2. The incrementof annual ring width of black pines was affected more by precipitation and evapotranspiration than air temperature.An annual ring decline appeared in the years 1968~1983, when annual ring indices below zero wereobserved. Decreased annual ring growth during this period may have been due to air pollution. 3. The heavymetal with the strongest effect on annual ring growth of black pines in the experimental stand was lead (Pb).The concentration of lead in the stand was estimated as over 6 ppm. 4. The technique of tree-ring width analysismay be useful for estimation of the extent of pollution in forest areas near industrial complexes.
Realization of giant magnetoelectricity in helimagnets
Sae Hwan Chun,Yi Sheng Chai,Yoon Seok Oh,Deepshikha Jaiswal-Nagar,So Young Haam,Ingyu Kim,Bumsung Lee,Dong Hak Nam,Kyung-Tae Ko,Jae-Hoon Park,Jae-Ho Chung,Kee Hoon Kim
Physics , 2010, DOI: 10.1103/PhysRevLett.104.037204
Abstract: We show that low field magnetoelectric (ME) properties of helimagnets Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22 can be efficiently tailored by Al-substitution level. As x increases, the critical magnetic field for switching electric polarization is systematically reduced from ~1 T down to ~1 mT, and the ME susceptibility is greatly enhanced to reach a giant value of 2.0 x 10^4 ps/m at an optimum x = 0.08. We find that control of nontrivial orbital moment in the octahedral Fe sites through the Al-substitution is crucial for fine tuning of magnetic anisotropy and obtaining the conspicuously improved ME characteristics.
Macroscopic Structural Analysis on a 10 kW Class Lab-Scale Process Heat Exchanger Prototype under a High-Temperature Gas Loop Condition  [PDF]
Kee-Nam Song, Sung-Deok Hong, Hong-Yoon Park
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.51A017
Abstract:

A PHE (Process Heat Exchanger) is a key component in transferring high-temperature heat generated from a VHTR (Very High Temperature Reactor) to a chemical reaction for the massive production of hydrogen. Last year, a 10 kW class lab-scale PHE prototype made of Hastelloy-X was manufactured at the Korea Atomic Energy Research Institute (KAERI), and a performance test of the PHE prototype is currently underway in a small-scale nitrogen gas loop at KAERI. The PHE prototype is composed of two kinds of flow plates: grooves 1.0 mm in diameter machined into the flow plate for the primary coolant, and waved channels bent into the flow plate for the secondary coolant. Inside the 10 kW class lab-scale PHE prototype, twenty flow plates for the primary and secondary coolants are stacked in turn. In this study, to understand the macroscopic structural behavior of the PHE prototype under the steady-state operating condition of the gas loop, high-temperature structural analyses on the 10 kW class lab-scale PHE prototype were performed for two extreme cases: in the event of contacting the flow plates together, and when not contacting them. The analysis results for the extreme cases were also compared.

An efficient and secure anonymous authentication scheme for mobile satellite communication systems
Yoon Eun-Jun,Yoo Kee-Young,Hong Jeong-Woo,Yoon Sang-Yoon
EURASIP Journal on Wireless Communications and Networking , 2011,
Abstract: This paper proposes a new efficient and secure anonymous authentication scheme for mobile satellite communication systems. Compared with the related schemes, the proposed scheme achieves the following three main advantages: (1) It is just based on a secure one-way hash function for avoiding complex computations for both mobile users and network control center (NCC), (2) it does not require sensitive verification table which may cause NCC to become an attractive target for numerous attacks (e.g., insertion attacks and stolen-verifier attacks), and (3) it provides higher security level (e.g., secure mutual authentication and key establishment, confidential communication, user's privacy, simple key management, and session key independence). As a result, the proposed scheme is very suitable for lightweight-device environments because of very low computation overload on the part of both mobile user and NCC.
A New Case of Turner Syndrome with Early Pubertal Development  [PDF]
Seok Ho Yoon, Dong Jun Lee, Son Moon Shin, So Young Yoon, Sung Won Park
International Journal of Clinical Medicine (IJCM) , 2016, DOI: 10.4236/ijcm.2016.75036
Abstract: Turner syndrome (TS) is a relatively common chromosomal disorder caused by complete or partial X monosomy. The most frequently observed karyotype, 45, X, arises more often by loss of the paternal X or Y chromosome in meiosis or in early embryogenesis than by loss of the maternal X chromosome. The main clinical features of TS are short stature, gonadal dysgenesis, and not to undergo pubertal development (e.g. primary amenorrhea). However, a few rare cases of TS have shown precocious puberty. Our case of a 9-year-old girl did not have any TS-specific clinical hallmarks, with the exception of short stature. She visited our clinic because of her pubertal development and short stature. In this report, we highlight the variability that can occur in patients with TS and emphasizes the need to carefully assess unusual growth patterns in any child, regardless of other underlying conditions.
On the Security of Signature Scheme with Message Recovery and Its Application
Eun-Jun Yoon,Kee-Young Yoo
International Journal of Network Security , 2006,
Abstract: In 2004, Sekhar proposed a new signature scheme with message recovery. Based on this signature scheme with message recovery, they also proposed a designated verifier signature scheme with non-repudiation of origin and a convertible designated verifier signature scheme with non-repudiation of origin. This paper, however, presents a security analysis where Sekhar's signature schemes are vulnerable to some forgery attacks. This means that any attacker can forge a signature for any message.
A Forgery Attack on A Low Computation Cost User Authentication Scheme
Eun-Jun Yoon,Kee-Young Yoo
International Journal of Network Security , 2006,
Abstract: In 2005, Lee-Lin-Chang proposed a low computation cost user authentication scheme for mobile communication. However, the current paper demonstrates the vulnerability of Lee-Lin-Chang's scheme to a forgery attack, where an attacker can easily masquerade other legal users to access the resources at a remote system and then presents an simple solution to isolate such a problem.
A Secure and Lightweight Approach for Routing Optimization in Mobile IPv6
Sehwa Song,Hyoung-Kee Choi,Jung-Yoon Kim
EURASIP Journal on Wireless Communications and Networking , 2009, DOI: 10.1155/2009/957690
Abstract: Mobility support is an essential part of IPv6 because we have recently seen sharp increases in the number of mobile users. A security weakness in mobility support has a direct consequence on the security of users because it obscures the distinction between devices and users. Unfortunately, a malicious and unauthenticated message in mobility support may open a security hole for intruders by supplying an easy mean to launch an attack that hijacks an ongoing session to a location chosen by the intruder. In this paper, we show how to thwart such a session hijacking attack by authenticating a suspicious message. Although much research has been directed toward addressing similar problems, we contend that our proposed protocol would outperform other proposals that have been advanced. This claim is based on observations that the proposed protocol has strengths such as light computational load, backward compatibility, and dependable operation. The results of in-depth performance evaluation show that our protocol achieves strong security and at the same time requires minimal computational overhead.
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