• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.188.1-188.1
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• 2015

For present investigation Fe/MgO/Fe/Co multilayer stack is grown on Si substrate using e-beam evaporation in ultrahigh vacuum. This stack is irradiated perpendicularly by 120 MeV $Ag^{8+}$ at different fluences ranging from $1{\times}10^{11}$ to $1{\times}10^{13}ions/cm^2$ in high vacuum using 15UD Pelletron Accelerator at Inter University Accelerator Centre, New Delhi. Magnetic measurements carried out on pre and post irradiated stacks show significant changes in the shape of perpendicular hysteresis which is relevant with previous observation of re-orientation of magnetic moment along the direction of ion trajectory. However increase in plane squareness may be due to the modification of interface structure of stacks. X-ray reflectivity measurements show onset of interface roughness and interface mixing. X-ray diffraction measurements carried out using synchrotron radiation shows amorphous nature of MgO and Co layer in the stack. Peak corresponding body centered Fe [JCPDS-06-0696] is observed in X-ray diffraction pattern of pre and post irradiated stacks. Peak broadening shows granular nature of Fe layer. Estimated crystallite size is $22{\pm}1nm$ for pre-irradiated stack. Crystallite size first increases with irradiation then decreases. Structural quality of these stacks was further studied using transmission electron microscopic measurements. Thickness from these measurements are 54, 36, 23, 58 and 3 nm respectively for MgO, Fe, MgO, Fe+Co and Au layers in the stack. These measurements envisage poor crystallinity of different layers. Interfaces are not clear which indicate mixing at interface. With increase fluence mixing and diffusion was increased in the stack. X-ray absorption spectroscopic measurements carried out on these stacks show changes of Fe valence state after irradiation along with change of O(2p)-metal (3d) hybridized state. Valence state change predicts oxide formation at interface which causes enhanced in-plane magnetization.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.425-425
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• 2009

그라핀을 금속 촉매를 이용하여 상압 혹은 저진공 CVD로 성장할 경우 대형 기판을 쉽게 얻을 수 있으므로 최근 들어 금속 촉매를 이용한 CVD 기술이 재 각광받고 있다. 최근 MIT의 Jing Kong 그룹, Purdue 대학의 Yong P. Chen 그룹, 국내에서는 성균관대학에서 이에 대한 논문을 발표한 바 있다. CVD 방법의 가장 큰 장점은 그라핀 박막의 가장 큰 문제점 중 하나인 대형 기판에 매우 유리하다는 점이다. 본 연구에서는 결함 없는 대형 그라핀기판을 얻기위해 Si/$SiO_2$/Ni 박막위에 그라핀을 LPCVD로 성장하는 실험을 진행하였다. 우선 시료는 Si위에 $SiO_2$를 Sputtering으로 증착하였고, 그 위에 250nm, 300nm두께의 Ni 박막을 e-beam evaporator로 증착하였다. $0.5-1cm^2$ 크기의 샘플을 Thermal CVD 장비를 이용하여 그라핀을 성장하는 실험을 진행하였다. 성장 압력은 95 torr, 성장온도는 $800^{\circ}C$, $850^{\circ}C$, $900^{\circ}C$에서 Hydrocarbon ($C_2H_2$)을 5min, 10min으로 성장시간을 split하였다. Hydrocarbon을 흘리기 전에 Ni grain을 성장하기 위해 성장온도에서 30~60min정도 $H_2$분위기에서 Ni 산화막의 환원 및 어닐링을 진행하였다. 그림.1은 $850^{\circ}C$, 5분간 성장한 그라핀/Ni 샘플의 광학사진이다. 그림.2는 $850^{\circ}C$에서 5min, 10min 성장한 샘플의 Raman spectrum이다. (파장은 514.532nm). 850C 10min 샘플은 G>G' peak 이지만, 5min으로 성장한 샘플의 경우 G'>G peak 임을 알 수 있고, 따라서 5min의 조건에서는 층 두께가 4층 미만의 그라핀 박막을 얻을 수 있음을 보여준다. 또한 G' peak의 위치가 두께가 감소할수록 내려감을 확인할 수 있다. 다만 D peak가 실험한 대부분의 샘플에서 보여서 아직 성장한 그라핀의 결합이 많은 것으로 보인다. 이러한 이유는 성장온도가 낮은 것이 일차 원인으로 생각되며 박막의 균일도 향상과 결함을 줄이기 위한 추가적인 개선 실험을 진행 중이다.

• Journal of Radiation Protection and Research
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• v.28 no.3
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• pp.233-237
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• 2003

It has been known that ATM plays a central role in response of cells to ionizing radiation by enhancing DNA repair. We have investigated the feasibility of increasing radiosensitivity of tumor cells with the use of ATM inhibitors such as caffeine, pentoxifylline and wortmannin. Human colorectal cancer RKO.C cells and RKO-ATM cells (RKO cells overexpressing ATM) were used in the present study. The clonogenic cell survival in vitro indicated that RKO-ATM cells were markdely radioresistant than RKO.C cells. Treatment with 3 mM of caffeine significantly increased the radiosensitivity of cells, particulary the RKO-ATM cells, so that the radiosensitivity of RKO.C cells and RKO-ATM cells were almost similar. The radiation induced G2/M arrest in RKO-ATM cells was noticeably longer than that in RKO.C cells and caffeine treatment significantly reduced the length of the radiation induced G2/M arrest in both RKO.C and RKO-ATM cells. Pentoxifylline and wortmannin were also less effective than caffeine to radiosensitize RKO.C or RKO-ATM cells. However, wortmannin was more effective than caffeine against human lung adenocarcinoma A549 cells indicating the efficacy of ATM inhibitor to increase radiosensitivity is cell line dependent. For in vivo study, RKO.C cells were injected s.c. into the hind-leg of BALB/C-nuslc nude mice, and allowed to grow to 130mm3 tumor. The mice were i.p. injected with caffeine solution or saline and the tumors irradiated with 10 Gy of X-rays. The radiation induced growth delay was markedly increased by 1-2 mg/g of caffeine. It was concluded that caffeine increases radiosensitivity of tumor cells by inhibiting ATM kinase function, thereby inhibiting DNA repair, that occurs during the G2/M arrest after radiation.

• Journal of Physiology & Pathology in Korean Medicine
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• v.17 no.6
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• pp.1383-1392
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• 2003

Apoptosis is a morphologically and biochemically district form of cell death that occurs in many different cell types in a wide variety of organisms. Albizzia julibrissin belonging the family Leguminosae has been used for the treatment of contusion, sore throat, amnesia, and insomnia in oriental traditional medicine. This study investigates whether the water extract of A. julibrissin induce apoptotic cell death in Jurkat T-acute lymphoblastic leukemia (ALL) cells. Jurkat cells were increased inhibitions of cell viability in a concentration-dependent manner by A. julibrissin. This herbal medicine also caused apoptosis as measured by cell morphology and DNA fragmentation. The capability of A. julibrissin to induce apoptosis was associated with proteolytic cleavage of specific target proteins such as poly (ADP-ribose)polymerase (PARP) and beta-catenin proteins suggesting the possible involvement of caspases. Our result showed that Bcl-2 and Bax protein levels were not changed in all A. julibrissin-treated groups compared to control group. These results suggest that A. julibrissin-mediated apoptosis is independent with Bcl-2 related signaling pathway in this cells. The purpose of the present study is also to investigate the Effect of A. julibrissin on cell cycle progression. Our results showed that G1 checkpoint related gene products (cyclin D1, cyclin dependent kinase 4, retinoblastoma, E2F1) were decreased in their protein levels in a dose-dependent manners after treatment of the extract. These results indicate that the increase of apoptotic cell death by A. julibrissin may be due to the inhibition of cell cycle progression in wild type p53-lacking Jurkat cells.

• Korean Journal of Soil Science and Fertilizer
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• v.45 no.1
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• pp.93-97
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• 2012

This study was conducted to evaluate the efficiency of various inorganic and organic materials to improve physical properties of soil. Saline sodic soil (saturation percentage = 40.36%, $EC_e=5.15dS\;m^{-1}$, $pH_s=8.70$, $SAR=18.84(m\;mol\;L^{-1})^{1/2}$, bulk density =$1.49Mg\;m^{-3}$) was collected, brought to wire house and filled in pots after laboratory analysis for various parameters. Different sources of organic nutrients like farm manure (FM), press mud, compost, poultry manure and sesbania green manure were analyzed for their chemical composition. The experiment comprised of 12 treatments replicated thrice; $T_1$: control (recommended NPK), $T_2:{\frac{1}{2}}$ recommended NPK, $T_3$: FM at 1.5% by soil weight, $T_4$: pressmud at 1.5% by soil weight, $T_5$: compost at 1.5% by soil weight, $T_6$: poultry manure at 1.5% by soil weight, $T_7$: sesbania green manure at 1.5% by soil weight, $T_8:T_2$ + FM at 0.75% by soil weight, $T_9:T_2$ + pressmud at 0.75% by soil weight, $T_{10}:T_2$ + compost at 0.75% by soil weight, $T_{11}:T_2$ + poultry manure at 0.75% by soil weight, $T_{12}:T_2$ + sesbania green manure at 0.75% by soil weight. These treatments were applied using completely randomized (CR) design and appropriate time was given to decompose these organic nutritional sources. Seeds of wheat cultivar Sahar-2006 were sown. After harvesting the wheat, soil samples were collected from each pot and analyzed for various physical properties like bulk density, porosity and saturation percentage. An improvement in physical properties (bulk density, porosity and saturation percentage) of soil was noticed with the application of various organic nutritional sources but role of compost alone ($T_5$) remained prominent.

• Asian-Australasian Journal of Animal Sciences
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• v.24 no.9
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• pp.1268-1273
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• 2011

The present study was conducted to determine a feasible method of protein concentrate extraction from rice bran (RBPC) and its effect as a substitution for skim milk in early weaning pig diets. An investigation to extract protein concentrate from full fat rice bran was undertaken to determine the best ratio of water and rice bran, the amount of NaOH and a HCl solvent to use in a simple paddle-type mixer with modified spinning to produce RBPC. The results stated that the best ratio for water mixing in the RBPC extraction process was 1:5 with 20 g NaOH and 30 min in a paddle-type mixer at 300 rpm. A mix of 250 ml 0.2 N HCl was optimum for neutralization and protein precipitation. After the fluid was spun out with a washing machine, the sediment was left for 12-14 hours to complete the filtration. One kilogram of rice bran could produce an average of 324.5 gram RBPC and it contained 3.40% ash, 496.48 kcal of GE/100 gram, 1.94% crude fiber, 28.20% ether extract, 7.64% moisture and 16.66% crude protein, respectively. A total of 45 crossbred piglets, weaned at 3 weeks of age were allotted into control diet (A) and dietary treatments formulated with a four different rates of RBPC substitution for skim milk at a percentage of 25 (B), 50 (C), 77 (D) and 100 (E) respectively, in a randomized complete block (RCB) design. All piglets had free access to feed and water until 8 week of age when the experiment ended. Feed intake, average daily gain, growth rate and feed efficiency were not affected by dietary treatments. Blood test parameters after completion of the growth trial indicated normal health. Even though the mean of cell hemoglobin concentration was significantly different between treatments (p<0.05) it was still within the normal range. The cost difference for BW gain of 100% RBPC substituted for skim milk in the weaning diet was approximately 35% lower than that of the control and the relative cost of production was 96.67, 92.85, 70.75 and 64.48% lower for the replacement of 25, 50, 75 and 100% of skim milk respectively. These results implied that this technology is feasible for use by small scale farmers to improve their self-reliance.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.105.2-105.2
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• 2011

화비정질 실리콘의 빛에 의한 노화현상 (light-induced degradation; LID)은 이미 1977년 보고된 Staebler-Wronski 효과에 의해서 확인된 바 있다. 이는 비정질 실리콘이 빛에 노출될 때, 이미 포함되어 있는 수소원자가 빛 에너지에 의해서 이동하게 되고, 이로 인해서 생성 또는 소멸되는 댕글링 본드 때문에 일어난다. 특히, 일상적인 태양광의 노출 하에서 태양전지의 장시간 성능을 예측하는데 물리적인 이해의 부족 및 기술 환경적인 어려움이 있고, 이러한 요인들은 안정된 태양전지를 개발하는데 장해요인으로 나타난다. 그러므로 비정질 실리콘 태양전지가 장시간 태양광에 노출되어 시간이 지남에 따라서 "성능이 어떻게 변하는지?" 그리고 "이에 대한 원인은 무엇인지?" 등은 여전히 과학적으로 풀어야할 숙제로 남아있다. 본 논문에서는 비정질 실리콘으로 구성된 태양전지가 태양광에 노출될 때 시간이 지남에 따라서 (1) 성능이 어떻게 변하는지, (2) LID의 변화는 언제 안정화되는지, 그리고 (3) 성능변화에 대한 원인은 무엇인지에 대해서 논의한다. 본 논문은 장시간 빛에 노출되는 비정질 실리콘 태양전지의 성능예측에 관해서 연구하였다. 결함밀도의 운동학적 모형을 통해서 태양광 노출에 대한 태양전지 성능변화를 예측하는데 초점을 맞추었고, 이를 위해서 태양전지에 조사되는 태양광 세기, 주변온도, 등이 고려되었다. 특히, 전하운반자의 수명이 결함밀도에 의해서 결정되기 때문에 비정질 실리콘 태양전지의 빛에 대한 노화현상 (LID)이 확장지수함수 (stretched-exponential) 완화법칙을 따르는 결함밀도에 의해서 물리적으로 설명된다. 한편 이와 같은 물리적 계산의 유용성을 확인하기 위해서 동일한 태양전지에 대해서 AMPS-1D 컴퓨터 프로그램을 사용하였고, 이를 통해서 비정질 실리콘 태양전지의 빛에 대한 노화현상을 물리적 및 정량적으로 이해하였다. 본 연구에 적용되는 태양전지는 비정질 실리콘으로 구성된 pin 구조 (glass/$SnO_2$/a-SiC:H:B/a-Si:H/a-Si:H:P/ITO)로서 다음과 같은 특성을 갖는다: 에너지 띠간격~1.72 eV, 두께~400 nm, 내부전위~1.05 V, 초기 fill factor~0.71, 초기 단락전류~16.4 mA/$cm^2$, 초기 개방전압 0.90 V, 초기 변환효율 10.6 %. 우리는 이와 같은 연구를 통해서 과학적으로 비정질 실리콘의 빛에 의한 노화현상을 이해하고, 기술적으로 효율 및 경제성이 높은 태양전지의 개발에 도전한다.

• Journal of Biomedical Engineering Research
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• v.38 no.1
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• pp.9-15
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• 2017

Recently, flexible cages have been introduced in an attempt to absorb and reduce the abnormal load transfer along the anterior parts of the spine. They are designed to be used with the pedicle screw systems to allow some mobility at the index level while containing ROM at the adjacent level. In this study, a finite element (FE) study was performed to assess biomechanical efficacies of the flexible cage when combined with pedicle screws with flexible rods. The post-operated models were constructed by modifying the L4-5 of a previously-validated 3-D FE model of the intact lumbar spine (L2-S1): (1) Type 1, flexible cage only; (2) Type 2, pedicle screws with flexible rods; (3) Type 3, interbody fusion cage plus pedicle screws with rigid rods; (4) Type 4, interbody fusion cage plus Type 2; (5) Type 5, Type 1 plus Type 2. Flexion/extension of 10 Nm with a compressive follower load of 400N was applied. As compared to the Type 3 (62~65%) and Type 4 (59~62%), Type 5 (53~55%) was able to limit the motion at the operated level effectively, despite moderate reduction at the adjacent level. It was also able to shift the load back to the anterior portions of the spine thus relieving excessively high posterior load transfer and to reduce stress on the endplate by absorbing the load with its flexible shape design features. The likelihood of component failure of flexble cage remained less than 30% regardless of loading conditions when combined with pedicle screws with flexible rods. Our study demonstrated that flexible cages when combined with posterior dynamic system may help reduce subsidence of cage and degeneration process at the adjacent levels while effectively providing stability at the operated level.

• Clinical and Experimental Pediatrics
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• v.49 no.10
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• pp.1100-1105
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• 2006

Purpose : Because NELL2 expression is strictly restricted only in neurons in developing and post-differentiated neural tissues, it is thought to be involved in the neuronal differentiation during development and in the maintenance of neuronal physiology in the post-differentiated neurons. In this study, we examined whether NELL2 is involved in the regulation of cell cycle and apoptosis in the hippocampal neuroprogenitor HiB5 cells. Methods : Effects of NELL2 on the cultured HiB5 cell numbers, DNA fragmentation, and proteins involved in the regulation of the cell cycle were measured. Results : NELL2 induced a decrease in cell numbers and an increase in G1 phase arrest. Moreover, transfection of NELL2 resulted in an increase of DNA fragmentation that shows an evidence of apoptosis. Contents of proteins involved in the regulation of cell cycle were also changed by transfection of NELL2 expression vectors. Conclusion : This study suggests that NELL2 plays an important role in the regulation of cell cycle and apoptosis of neurons.

• Journal of Microbiology and Biotechnology
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• v.20 no.2
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• pp.301-310
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• 2010

Bacillus subtilis strains produce a broad spectrum of bioactive peptides. The lipopeptide surfactin belongs to one well-known class, which includes amphiphilic membrane-active biosurfactants and peptide antibiotics. Both the srfA promoter and the ComP-ComA signal transduction system are an important part of the factor that results in the production of surfactin. Bs-M49, obtained by means of low-energy ion implantation in wild-type Bs-916, produced significantly lower levels of surfactin, and had no obvious effects against R. solani. Occasionally, we found strain Bs-M49 decreased spore formation and the development of competence. Blast comparison of the sequences from Bs-916 and M49 indicate that there is no difference in the srfA operon promoter PsrfA, but there are differences in the coding sequence of the comA gene. These differences result in three missense mutations within the M49 ComA protein. RT-PCR analyses results showed that the expression levels of selected genes involved in competence and sporulation in both the wild-type Bs-916 and mutant M49 strains were significantly different. When we integrated the comA ORF into the chromosome of M49 at the amyE locus, M49 restored hemolytic activity and antifungal activity. Then, HPLC analyses results also showed the comA-complemented strain had a similar ability to produce surf actin with wild-type strain Bs-916. These data suggested that the mutation of three key amino acids in ComA greatly affected the biological activity of Bacillus subtilis. ComA protein 3D structure prediction and motif search prediction indicated that ComA has two obvious motifs common to response regulator proteins, which are the N-terminal response regulator receiver motif and the C-terminal helix-turn-helix motif. The three residues in the ComA N-terminal portion may be involved in phosphorylation activation mechanism. These structural prediction results implicate that three mutated residues in the ComA protein may play an important role in the formation of a salt-bridge to the phosphoryl group keeping active conformation to subsequent regulation of the expression of downstream genes.