• Journal of Photoscience
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• 제10권3호
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• pp.257-261
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• 2003

We have systematically studied the evolution of the photoluminescence(PL) tuning of porous silicon(PS) by electrochemical etching in various mixed electrolytes. The electrolytes employed as an etchants were mixtures of HF:CH$_3$COOH:HNO$_3$:C$_2$H$\_$5/OH solutions where the composition ratios (%) were varied from 10:1.98:0:88.02 to 10: 1.98:8.4:79.62 under constant concentration of HF and CH$_3$COOH with a total volume of 100 ml. Changes in the surface morphology of the samples caused by variations in the etching process were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). After samples are etched in various mixed electrolytes, FTIR analyses show that there is the non-photoluminescent state and the photoluminescent state simultaneously. The PL spectra show the PL tuning in the ranging from 560 to 700 nm with the increase of HNO$_3$ concentration. An analysis of the subsequent PL relaxation mechanism was carried out by time-correlated single photon counting (TCSPC) method. Based on experimental results, it is assumed that a red shift of the main PL peak position is related to the HNO$_3$ activated formation of silicon oxygen compounds. Therefore, the use of electrolyte mixtures with composition ratios can be obtained adequate and reproducible results for PL tuning.

• 한국군사과학기술학회지
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• 제14권3호
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• pp.509-516
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• 2011

In this paper, a ground penetrating radar(GPR) system is implemented for landmine detection. The performance of the GPR system is associated with the characteristics of local soil and buried target. The choice of the center frequency and the bandwidth of the GPR system are the key factors in the GPR system design. To detect a small and shallow target, the higher frequencies are needed for high depth resolution. We have been designed, fabricated and tested a new impulse generator using step recovery diodes. The measured impulse response has an amplitude of 6.2V and a pulse width of 250ps. The implemented GPR system has been tested real environmental conditions and has proved its ability to detect a small buried target.

• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.80-85
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• 2009

An experimental study of energy absorption and x-ray emission from ultrashort laser pulse irradiation of in-situ produced solid clusters has been performed. Silver clusters produced by a 30 mJ, 300 ps laser pulse were irradiated up to an intensity of $3{\times}10^{17}\;W/cm^2$ by a 70 mJ, 45 fs compressed laser pulse from the same Ti:sapphire laser. Absorption of the laser light exceeding 70% was observed, resulting in an x-ray yield (>1 keV) of ${\sim}60{\mu}J$ pulse. This may constitute a much simpler means of intense x-ray generation using ultrashort laser pulses as compared to the irradiation of structured / pre-deposited cluster targets, and it offers higher x-ray conversion efficiency than that from gas clusters and planar solid targets.

• 한국가스학회지
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• 제10권2호
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• pp.1-6
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• 2006

본 연구에서는 실내 오염물질인 포름알데히드가스를 제거하기위하여 $Pd/TiO_2$로 코팅한 극세 섬유에 광분해 효과를 제안하였다 광촉매 반응기는 사각박스(부피 2 l)내에 UV램프와 $Pd/TiO_2$로 코팅한 극세 섬유와 함께 장착하였다. 이 때 Langmuir-Heinshelwood의 반응속도와 흡착상수, 온도 및 농도 변화에 따른 전환을 그리고 습도변화와 오염가스($SO_2$) 혼합으로 인한 전환율의 영향을 조사하였다. 결과로서 속도상수(k)와 흡착상수($\beta$) 각각 114.94 ppmv/min, $0.0036ppmv^{-1}$을 얻었다. 또한 온도증가($40^{\circ}C{\sim}80^{\circ}C$)에 따른 포름알데히드가스 전환율이 약 20%로 감소하고 습도변화에 따른 전환율에서는 습도가 증가할수록 감소하는 경향을 보였다. 이외에 $SO_2$가스 혼입되어 있는 상태에서 전환율은 $SO_2$ 가스가 수분에 의한 이온의 영향으로 방해인자로 작용하는 것을 알 수 있었다.

• International Journal of Oral Biology
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• 제39권4호
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• pp.169-176
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• 2014

A positional scanning synthetic peptide combinatorial library (PS-SCL) was screened in order to identify antimicrobial peptides against the cariogenic oral bacteria, Streptococcus mutans. Activity against Streptococcus gordonii and Aggregatibacter actinomycetemcomitans was also examined. The library was comprised of six sub-libraries with the format $O_{(1-6)}XXXXX-NH_2$, where O represents one of 19 amino acids (excluding cysteine) and X represents equimolar mixture of these. Each sub-library was tested for antimicrobial activity against S. mutans and evaluated for antimicrobial activity against S. gordonii and A. actinomycetemcomitans. The effect of peptides was observed using transmission electron microscopy (TEM). Two semi-mixture peptides, RXXXXN-$NH_2$ (pep-1) and WXXXXN-$NH_2$ (pep-2), and one positioned peptide, RRRWRN-$NH_2$ (pep-3), were identified. Pep-1 and pep-2 showed significant antimicrobial activity against Gram positive bacteria (S. mutans and S. gordonii), but not against Gram negative bacteria (A. actinomycetemcomitans). However, pep-3 showed very low antimicrobial activity against all three bacteria. Pep-3 did not form an amphiphilic ${\alpha}$-helix, which is a required structure for most antimicrobial peptides. Pep-1 and pep-2 were able to disrupt the membrane of S. mutans. Small libraries of biochemically-constrained peptides can be used to generate antimicrobial peptides against S. mutans and other oral microbes. Peptides derived from such libraries may be candidate antimicrobial agents for the treatment of oral microorganisms.

• 환경생물
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• 제30권3호
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• pp.210-218
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• 2012

일반적으로 많이 양식되는 방사무늬김(Porphyra yezoensis Ueda)에 대하여 방사무늬김 엽체의 형태적 특성, 탄소 및 질소 성분의 농도, 안정동위원소 비값, 광합성 효율을 방사무늬김 양식이 이루어 지고 있는 남서해역에서 조사를 하였다. 방사무늬김의 형태적 특성에 대해서 살펴보면 평균 엽장은 11.6~16.3 (13.8) cm, 평균 엽폭은 4.6~6.3 (5.4) cm이었고, 단위면적당 방사무늬김 엽체의 평균 엽중량은 $1.1{\sim}2.6(1.86)g\;DW\;m^{-2}$이었다. 단위면적당 Chl a 농도는 2.18~17.77 (평균 9.65) mg DW Chl a $m^{-2}$이었다. 방사무늬김의 탄소 농도는 $201{\sim}317(240)mg\;DW\;g^{-1}$이었고, 질소 농도는 $39.8{\sim}50.0(43.5)mg\;DW\;g^{-1}$이었으며, C/N비는 5.0~6.7 (5.5)이었다. 방사무늬김의 방사성 안정동위원소비 중에서 탄소 안정동위원소 비는 ${\delta}^{13}C$=-25.6‰ 에서 ${\delta}^{13}C$=-24.0‰ (평균 -24.7‰)의 값을 보였고, 질소 안정동위원소 비는 ${\delta}^{15}N$=1.3‰ 에서 ${\delta}^{15}N$=4.1‰ (평균 2.1‰)의 값을 보였다. PAM에 의한 해조류의 광합성 특성은 광합성 활동의 지시자로서 사용될 수 있다. 우리는 Diving-PAM을 이용하여 각 정점 해조류인 방사무늬김의 광합성율을 분석하였다. 최대양자수율은 0.46~0.55 (평균 0.52)로서 최대 양자수율의 변동은 정점간 큰 차이는 없었다. 최대상대전자전달률은 4.71~5.84 (평균 5.33) ${\mu}mol\;electrons\;m^{-2}\;s^{-1}$ 로서 최대양자수율과 비슷한 분포를 보였다. 기울기 (${\alpha}$)는 0.027~0.045 (평균 0.036)을 보였고, 전자전달을 위한 포화광은 지역에 따라서 일부 차이를 보였으나 $139{\sim}180(156){\mu}mol\;photons\;m^{-2}\;s^{-1}$이었다. 남서해역 방사무늬김 엽체의 탄소 및 질소 농도와 광합성 효율은 지역에 따른 큰 차이는 보이지 않았다. 광합성 특성은 낮은 최대양자수율과 최대 상대전자전달률로 인한 낮은 광합성 효율이 나타났다.

• 한국환경과학회지
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• 제18권12호
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• pp.1361-1368
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• 2009

The effects of $Cd^{2+}$ ions on the Chl a fluorescence of 5 hydrophytes (e.g. Lemna, Salvinia, Ricciocarp, Nymph, Typha plants) were investigated in order to select $Cd^{2+}$-sensitive plant species and to get informations on physiological responses of plants to $Cd^{2+}$ stress. Lemna plants were most sensitive to cadmium stress, while Nymph plants were tolerant. However, in all $Cd^{2+}$-treated plants, Fv/Fm, the maximum photochemical efficiency of PS II, decreased in proportion to the increase of $Cd^{2+}$ concentration and treatment time. The Chl a fluorescence transient O-J-I-P was also considerably affected by $Cd^{2+}$ ions; the fluorescence yield decreased consid- erably in steps J, I and P in $Cd^{2+}$ treated plants, although it followed a typical polyphasic rise in non-treated plants. In Lemna plants, the functional parameters, ABS/CS, TRo/CS와 ETo/CS and RC/CS, decreased in proportion to the increase of $Cd^{2+}$ concentration, while N, Mo and Kn increased. The structural parameters, ${\Phi}po$, ${\Phi}po$/($1-{\Phi}po$), Plabs, SFlabs, Kp and RC/ABS, also decreased according to the increase of $Cd^{2+}$ concentration. Consequently, Lemna plants will be useful as a experimental model system to investigate responses of plants. And several functional or structural parameters could be applied to determine quantitatively the physiological states of plants under stresses.

• Bulletin of the Korean Chemical Society
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• 제26권9호
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• pp.1369-1380
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• 2005

The reaction of methyl radical with iodine molecule on an attractive potential energy surface is studied by classical trajectory procedures. The reaction occurs over a wide range of impact parameters with the majority of reactive events occurring in the backward rebound region on a subpicosecond scale. A small fraction of reactive events take place in the forward hemisphere on a longer time scale. The ensemble average of reaction times is 0.36 ps. The occurrence of reactive events is strongly favored when the incident radical and the target molecule align in the neighborhood of collinear geometry. Since the rotational velocity of I2 is slow, the preferential occurrence of reactive events at the collinear configuration of $CH_3{\ldots}I{\ldots}$I leads to the reaction exhibiting an anisotropic dependence on the orientation of $I_2$. During the collision, there is a rapid flow of energy from the $H_3C{\ldots}$I interaction to the I-I bond. The $CH_3I$ translation and $H_3C$-I vibration share nearly all the energy released in the reaction, and the distribution of the vibrational energy is statistical. The reaction probability is $\cong$0.4 at the $CH_3$ and I2 temperatures maintained at 1000 K and 300 K, respectively. The probability is weakly dependent on the $CH_3\;and\;I_2$ temperatures between 300 K and 1500 K.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2005년도 가을 학술발표논문집 Vol.32 No.2 (1)
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• pp.391-393
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• 2005

최근 유비쿼터스 네트워크 환경을 구축하기 위해 많은 무선 통신 기술들이 등장하였다. 그 중 무선랜 기술은 쉬운 설치와 저렴한 비용 덕에 폭발적인 보급이 이루어 겼다. IEEE 802.11 표준을 기반으로 만들어진 무선랜은 여러 개의 전송속도를 지원한다. 대표적으로 802.11b는 1, 2, 5.5, 11MbPs의 4가지 전송속도를 지원한다. 낮은 전송속도로 전송을 하면 패킷 전송시간은 증가하지만 비트 에러율은 감소된다. 각각의 전송속도에 따라 다른 패킷 전송 성공률을 갖게 된다. 한 무선랜 AP에 연결된 노드들은 각자 자신의 처리율을 최대화할 수 있는 전송속도를 결정하여 사용하게 된다. 이러한 상황은 전체 시스템 성능에는 문제를 발생시킬 수 있다. 본 논문에서는 각자의 전송속도를 각자가 결정하는 것이 전체 시스템 성능에 문제를 발생시키는 경우를 보이고, 그것을 해결하기 위해 AP가 각 노드의 전송속도를 결정하는 기법을 제안한다. 나아가 무선랜에서의 문제점인 Performance Anomaly 현상을 해결하고, [3]에서 언급된 Inefficient Equilibria 현상도 막아본다.

• 한국응용과학기술학회지
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• 제8권1호
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• pp.69-78
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• 1991

Frog legs were stored before and after 30, 60, 90, 120 days at $-30^{\circ}C$ and $-70^{\circ}C$. The amounts of triglycerides, glycolipide and phospholipids by TLC and composition of fatty acids by GC were shown in this experiment, there fore, I have got these following results. 1. The amount of PL in frog legs consisted of 80% of the total lipids before storage. As the days of storage was longer, the amount of TG was increased, while PL and GL were decreased. 2. TG and ES & HC were composed of 66% to 77% of the neutral lipids composition before storage. As the days of storage was longer, the amount of MG, DG. FFA and ES & HC were increased, while FS and TG were decreased. 3. PE and PC were composed of 78% to 81% of the phospholipids composition before storage. As the days of storage was longer, the amount of FA and PS were increased, while PC and PE were decreased. 4. The composition of fatty acids in neutral lipids of frozen frog legs at $-30^{\circ}C$, 120 days was studied, Capric acid. Stearic acid, Behnic acid. Oleic acid and Linoleic acid were increased as compared with initial neutral lipids.