• Journal of Korean Neurosurgical Society
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• v.62 no.1
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• pp.10-26
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• 2019

Magnetic resonance-guided focused ultrasound (MRgFUS) is an emerging new technology with considerable potential to treat various neurological diseases. With refinement of ultrasound transducer technology and integration with magnetic resonance imaging guidance, transcranial sonication of precise cerebral targets has become a therapeutic option. Intensity is a key determinant of ultrasound effects. High-intensity focused ultrasound can produce targeted lesions via thermal ablation of tissue. MRgFUS-mediated stereotactic ablation is non-invasive, incision-free, and confers immediate therapeutic effects. Since the US Food and Drug Administration approval of MRgFUS in 2016 for unilateral thalamotomy in medication-refractory essential tremor, studies on novel indications such as Parkinson's disease, psychiatric disease, and brain tumors are underway. MRgFUS is also used in the context of blood-brain barrier (BBB) opening at low intensities, in combination with intravenously-administered microbubbles. Preclinical studies show that MRgFUS-mediated BBB opening safely enhances the delivery of targeted chemotherapeutic agents to the brain and improves tumor control as well as survival. In addition, BBB opening has been shown to activate the innate immune system in animal models of Alzheimer's disease. Amyloid plaque clearance and promotion of neurogenesis in these studies suggest that MRgFUS-mediated BBB opening may be a new paradigm for neurodegenerative disease treatment in the future. Here, we review the current status of preclinical and clinical trials of MRgFUS-mediated thermal ablation and BBB opening, described their mechanisms of action, and discuss future prospects.

• Korean Journal of Metals and Materials
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• v.46 no.5
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• pp.296-303
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• 2008

Hydrogen permeation through dense palladium-based membranes has attracted the attention of many scientists largely due to their unmatched potential as hydrogen-selective membranes for membrane reactor applications. Although it is well known that the permeation mechanism of hydrogen through Pd involves various processes such as dissociative adsorption, transitions to and from the bulk Pd, diffusion within Pd, and recombinative desorption, it is still unclear which process mainly limits hydrogen permeation at a given temperature and hydrogen partial pressure. In this study, we report an all-electron density-functional theory study of hydrogen permeation through Pd membrane (using VASP code). Especially, we focus on the variation of the energy barrier of the penetration process from the surface to the bulk with hydrogen coverage, which means the large reduction of the fracture stress in the brittle crack propagation considering Griffith's criterion. It is also found that the penetration energy barrier from the surface to the bulk largely decreases so that it almost vanishes at the coverage 1.25, which means that the penetration process cannot be the rate determining process.

• Geomechanics and Engineering
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• v.35 no.1
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• pp.13-27
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• 2023

The model production for large-scale (lateral length ≥ 2.0 m) capillary barrier (CB) model tests is time and cost-intensive. To address these limitations, the framework of a small-scale CB (SSCB) model test under the lateral no-flow condition has been established. In this study, to validate the experimental methodology of the SSCB model test, a series of seepage analyses on the SSCB model test and engineered slopes in the same and additional test conditions was performed. First, the seepage behavior and diversion length (L_D) of the CB system were investigated under three rainfall conditions. In the seepage analysis for the engineered slopes with different slope angles and sand layer thicknesses, the L_D increased with the increase in the slope angle and sand layer thickness, although the increase rate of the L_D with the sand layer thickness exhibited an upper limit. The L_D values from the seepage analysis agreed well with the results estimated from the laboratory SSCB mode test. Therefore, it can be concluded that the experimental methodology of the SSCB model test is one of the promising alternatives to efficiently evaluate the water-shielding performance of the CB system for an engineered slope.

• Advances in aircraft and spacecraft science
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• v.4 no.1
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• pp.37-52
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• 2017

Gas turbines operating in dusty or sandy environment polluted with micron-sized solid particles are highly prone to blade surface erosion damage in compressor stages and molten sand attack in the hot-sections of turbine stages. Commercial/Military fixed-wing aircraft engines and helicopter engines often have to operate over sandy terrains in the middle eastern countries or in volcanic zones; on the other hand gas turbines in marine applications are subjected to salt spray, while the coal-burning industrial power generation turbines are subjected to fly-ash. The presence of solid particles in the working fluid medium has an adverse effect on the durability of these engines as well as performance. Typical turbine blade damages include blade coating wear, sand glazing, Calcia-Magnesia-Alumina-Silicate (CMAS) attack, oxidation, plugged cooling holes, all of which can cause rapid performance deterioration including loss of aircraft. The focus of this research work is to simulate particle-surface kinetic interaction on typical turbomachinery material targets using non-linear dynamic impact analysis. The objective of this research is to understand the interfacial kinetic behaviors that can provide insights into the physics of particle interactions and to enable leap ahead technologies in material choices and to develop sand-phobic thermal barrier coatings for turbine blades. This paper outlines the research efforts at the U.S Army Research Laboratory to come up with novel turbine blade multifunctional protective coatings that are sand-phobic, sand impact wear resistant, as well as have very low thermal conductivity for improved performance of future gas turbine engines. The research scope includes development of protective coatings for both nickel-based super alloys and ceramic matrix composites.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.131-138
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• 2009

A simulation-optimization model is developed for development of groundwater and control of a saltwater wedge for protecting over-exploiting freshwater pumping wells. To achieve the goal an objective function is developed for three types of wells: freshwater pumping, freshwater injection and saltwater pumping. Integrity of groundwater environment is accounted for by including three indices. Illustrative cross-sectional examples show that both types of barriers can protect freshwater pumping wells from saltwater intrusion. A barrier well operating at the same rate located anywhere within a certain reach can protect a pumping well. However, the location of the reach appears to contradict the common practice of barrier placements. Consideration of the groundwater environment yields a unique optimal location for barrier wells.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.3
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• pp.203-212
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• 2010

In this paper, we present an analytical model for the first eigen energy level ($E_0$) of the carriers in the inversion layer in present generation MOSFETs, having ultrathin gate oxides and high substrate doping concentrations. Commonly used approaches to evaluate $E_0$ make either or both of the following two assumptions: one is that the barrier height at the oxide-semiconductor interface is infinite (with the consequence that the wave function at this interface is forced to zero), while the other is the triangular potential well approximation within the semiconductor (resulting in a constant electric field throughout the semiconductor, equal to the surface electric field). Obviously, both these assumptions are wrong, however, in order to correctly account for these two effects, one needs to solve Schrodinger and Poisson equations simultaneously, with the approach turning numerical and computationally intensive. In this work, we have derived a closed-form analytical expression for $E_0$, with due considerations for both the assumptions mentioned above. In order to account for the finite barrier height at the oxide-semiconductor interface, we have used the asymptotic approximations of the Airy function integrals to find the wave functions at the oxide and the semiconductor. Then, by applying the boundary condition at the oxide-semiconductor interface, we developed the model for $E_0$. With regard to the second assumption, we proposed the inclusion of a fitting parameter in the wellknown effective electric field model. The results matched very well with those obtained from Li's model. Another unique contribution of this work is to explicitly account for the finite oxide-semiconductor barrier height, which none of the reported works considered.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.76
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• pp.147-166
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• 2017

There is a growing interest on entrepreneurship for undergraduate students to enhance their employment ratio because they have big difficulty in getting a job in Korea as well as Vietnam. Currently, on-line business is booming because customers feel convenience in approaching on-line store. Therefore, this study has explored identifying the factors to affect entrepreneurial intention of being e-commerce trader for the undergraduates in Korean universities as well as Vietnam universities. In addition to this, the study has also investigated the difference of the results between Korea and Vietnam. The results of the study are as follows ; First, entrepreneurial knowledge affects positively on entrepreneurial intention for being e-commerce trader. Second, employment barrier also affects positively on entrepreneurial intention for being e-commerce trader. Third, social perception on entrepreneurship mediates the relationship between employment barrier and entrepreneurial intention for being e-commerce trader. Lastly, the level of entrepreneurial intention for vietnam undergraduate students shows higher than that of Korean undergraduate students. Since there was lack of recognition as to the importance for entrepreneurial intention of being e-commerce trader in Korea, Korean government can refer to the results of this survey and implement the related policies to enhance related entrepreneurial intention. This indicates that when it comes to the establishment of new ventures in Korea, entrepreneurial education has been the focus of interest such as making business plan, setting up strategy, marketing the products etc. In this regard, this research is expected to be used for the development for the future policies to boost youth entrepreneurship in Korea.

• Journal of Powder Materials
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• v.22 no.6
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• pp.420-425
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• 2015

Rare-earth zirconates, such as lanthanum zirconates and gadolinium zirconates, have been intensively investigated due to their excellent properties of low thermal conductivity as well as chemical stability at high temperature, which can make these materials ones of the most promising candidates for next-generation thermal barrier coating applications. In this study, three compositions, lanthanum/gadolinium zirconates with reduced rare-earth contents from stoichiometric $RE_2Zr_2O_7$ compositions, are fabricated via solid state reaction as well as sintering at $1600^{\circ}C$ for 4 hrs. The phase formation, microstructure, and thermo-physical properties of three oxide ceramics are examined. In particular, each oxide ceramics exhibits composite structures between pyrochlore and fluorite phases. The potential of lanthanum/gadolinium zirconate ceramics for TBC applications is also discussed.

• 대한공업교육학회지
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• v.38 no.2
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• pp.218-239
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• 2013

This study aims to understand the status of mandatory military service planning and career barrier recognition as well as to analyze the difference between how students perceive mandatory military service as a potential barrier to their future careers(career barrier recognition) and career preparation behavior by the mandatory military service planning level among male college students. For the purpose, inquiries for the subject were set up as follows. 1. What are the levels of mandatory military service planning and career barrier recognition? 2. Is there a difference in career barrier recognition depending on the level of mandatory military service planning? 3. Is there a difference in career preparation behaviour depending on the level of mandatory military service planning? This study found out the level of mandatory military service, military barrier recognition and career preparation behavior of 284 male students from 4 universities in Daejeon and Chungnam area. Along with that, descriptive statistic, correlation analysis and t-test were conducted with SPSS 17.0 program The results of this study are as follows: First, 79.2% of male students have higher mandatory military service planning than the average value. Meanwhile, considering 3 sub-factors of mandatory military service planning, the ratio of those with high scores in practicality is lower than importance and concreteness. Based on this, it is assumable that they have a low perception for practical and concrete behaviors such as data collection in mandatory military service planning, which indicates their awareness has not developed into concrete behaviors even though they recognize the importance of planning. Also 73.9% of male students responded higher career barrier recognition than the average value shows that they recognize mandatory military service as a barrier relatively highly. Especially, those who answered "Very much" (7 scores) for every inquiry in career barrier recognition accounted for 16.9%, which forms the biggest group. and considering the response by each inquiry, it is ascertained that they consider the absence by mandatory military service time or military service as the biggest difficulty. Second, the difference in career barrier recognition between the top 30% and bottom 30% of mandatory military service planning is not statistically significant. However, in terms of importance and the sub-factor of mandatory military service planning, a significant inter-group difference in career barrier recognition is shown. In other words, to join the military is recognized as an obstacle in their career barrier recognition regardless of the mandatory military service planning level. Also, a group which considers the importance of the mandatory military service planning highly recognizes the military as the bigger obstacle compared to the other groups which are not considered in this way. Third, the difference in career barrier recognition between the top 30% and the bottom 30% of the mandatory military service planning is statistically significant. The need of mandatory military service planning is marked by the fact that those with a high level of mandatory military service planning show stronger career barrier recognition than those without plans. Through the study, the need of mandatory military service planning is suggested to both male students and career consultants considering the mandatory military service from a perspective of career based on Korean reality. Also, as precedent studies on pre-inducted men can be hardly found currently, this study is significant in accumulating empirical data about mandatory military service, a unique characteristic of the Korean career development process.

• Journal of Veterinary Clinics
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• v.27 no.2
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• pp.142-146
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• 2010

The purpose of this study is to establish experimental canine skin barrier disruption model in dog. The study was designed to investigate the predictive properties of acetone damage using as effect parameters transepidermal water loss (TEWL) and stratum corneum (SC) hydration. To compare the structures of SC intercellular lipids in normal and acetone damaged skin, TEM observations were performed. Six clinically normal, male Beagles without dermatological problems were chosen for this study. Acetone damage was performed at 48hrs after clipping. Efficacy measurements for TEWL and skin hydration were performed before ($t_1$) and after ($t_2$) damage in a temperature- and humidity-controlled room ($2{0\sim}22^{\circ}C$, 50-60%). TEWL and SC hydration values were decreased in the acetone damaged model compared with non damaged skin. In TEM observation of acetone damaged sample, the intercellular lipid lamellae exhibit abnormal and incomplete structure compared with those of normal skin. It seems that acetone damage would be one of canine skin epidermal barrier disruption model for the study of canine atopic dermatitis (AD) as well as dry skin in veterinary dermatology research.