• Environmental and Resource Economics Review
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• v.13 no.2
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• pp.301-322
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• 2004

The current petroleum stockpiling by Korean government is based on the static concept of dead-stock. However, the recent changes in economic environment is requiring a transition to the dynamic concept of flow-stock. This study suggested selective trading strategies using basis of changing oil prices as an option for improving the economics of domestic strategic petroleum reserve (SPR), and quantitatively analyzed their effects. For this purpose, we tested the validity of selective trading strategies using the weekly spot and forwards prices of WTI for the period of October 1997 to August 2002. Summarizing the simulation results, the selective trading strategies would increase the expected values of profits and decrease their volatilities compared to those of traditional routine strategies. And, the adoption of trigger value could increase the improvements by the selective trading strategies. Based on the results, we suggest that, in order to improve the economics of domestic petroleum stockpiling, it is necessary to actively utilize the reserve facilities and the reserved petroleum with proper derivatives position.

• Journal of the Korean Society of Systems Engineering
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• v.12 no.1
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• pp.73-87
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• 2016

Combining power generation and water production by desalination is economically advantageous. Most desalination projects use fossil fuels as an energy source, and thus contribute to increased levels of greenhouse gases. Environmental concerns have spurred researchers to find new sources of energy for desalination plants. The coupling of nuclear power production with desalination is one of the best options to achieve growth with lower environmental impact. In this paper, we will per-form a sensitivity study of coupling nuclear power to various combinations of desalination technology: {1} thermal (MSF [Multi-Stage Flashing], MED [Multi-Effect Distillation], and MED-TVC [Multi-Effect Distillation with Thermal Vapour Compression]); {2} membrane RO [Reverse Osmosis]; and {3} hybrid (MSF-RO [Multi-Stage Flashing & Reverse Osmosis] and MED-RO [Multi-Effect Distillation & Reverse Osmosis]). The Korean designed reactor plant, the APR1400 will be modeled as the energy production facility. The economical evaluation will then be executed using the computer program DEEP (Desalination Economic Evaluation Program) as developed by the IAEA. The program has capabilities to model several types of nuclear and fossil power plants, nuclear and fossil heat sources, and thermal distillation and membrane desalination technologies. The output of DEEP includes levelized water and power costs, breakdowns of cost components, energy consumption, and net saleable power for any selected option. In this study, we will examine the APR1400 coupled with a desalination power plant in the Kingdom of Saudi Arabia (KSA) as a prototypical example. The KSA currently has approximately 20% of the installed worldwide capacity for seawater desalination. Utilities such as power and water are constructed and run by the government. Per state practice, economic evaluation for these utilities do not consider or apply interest or carrying cost. Therefore, in this paper the evaluation results will be based on two scenarios. The first one assumes the water utility is under direct government control and in this case the interest and discount rate will be set to zero. The second scenario will assume that the water utility is controlled by a private enterprise and in this case we will consider different values of interest and discount rates (4%, 8%, & 12%).

• Journal of Korean Neurosurgical Society
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• v.63 no.2
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• pp.218-227
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• 2020

Objective : To evaluate and compare the clinical and radiographic features of 25 patients with infectious spondylitis treated with anterior debridement and reconstruction using autogenous bone grafts vs. a metal cage with allogenic bone grafts. Methods : The study analyzed 25 patients diagnosed with infectious thoracolumbar spondylitis who underwent anterior radical debridement and reconstruction. Autogenous bone grafts were used in 13 patients (group 1), and a metal cage with allogenic bone grafts was used in 12 patients (group 2). Clinical outcomes were assessed by the visual analogue scale (VAS) scores and neurological status. Additionally, the serological results and the radiographic results using the sagittal Cobb angle were compared. Fusion was evaluated by computed tomography (CT) imaging at 24 months postoperatively. Results : Both groups showed a significant decrease in the postoperative mean VAS scores; however, only, group 1 patients showed a significantly higher VAS score than group 2 patients, 1 month postoperatively (p=0.002). The postoperative neurological status significantly improved. Elevated C-reactive protein levels and erythrocyte sedimentation rate values returned to normal limits at the 2-year follow-up without recurrent infection. No significant intergroup difference was observed in Cobb angle. Bony fusion was confirmed in all patients at CT 24 months postoperatively. Conclusion : Although the use of a metal cage with allogenic bone grafts for anterior column reconstruction remains controversial, our results suggest that it can be considered as an effective treatment of option for anterior column reconstruction in patients with infectious spondylitis.

• Korean Journal of Materials Research
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• v.20 no.7
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• pp.392-400
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• 2010

The electrospinning process was established as a promising method to fabricate nano and micro-textured scaffolds for tissue engineering applications. A BCP-loaded PCL micro-textured scaffold thus can be a viable option. The biocompatibility as well as the mechanical properties of such scaffold materials should be optimized for this purpose. In this study, a composite scaffold of poly ($\varepsilon$-caprolactone) (PCL)-biphase calcium phosphate (BCP) was successfully fabricated by electrospinning. EDS and XRD data show successful loading of BCP nano particles in the PCL fibers. Morphological characterization of fibers shows that with a higher loaded BCP content the fiber surface was rougher and the diameter was approximately 1 to 7 ${\mu}m$. Tensile modulus and ultimate tensile stress reached their highest values in the PCL- 10 wt% BCP composite. When content of nano ceramic particles was low, they were dispersed in the fibers as reinforcements for the polymer matrix. However, at a high content of ceramic particles, the particles tend to agglomerate and lead to decreasing tensile modulus and ultimate stress of the PCL-BCP composite mats. Therefore, the use of nano BCP content for distribution in fiber polymer using BCP for reinforcement is limited. Tensile strain decreased with increasing content of BCP loading. From in vitro study using MG-63 osteoblast cells and L-929 fibroblast like cells, it was confirmed that electrospun PCL-BCP composite mats were biocompatible and that spreading behavior was good. As BCP content increased, the area of cell spreading on the surface of the mats also increased. Cells showed the best adherence on the surface of composite mats at 50 wt% BCP for both L-929 fibroblast-like cells and MG-63 osteoblast cell. PCL- BCP composites are a promising material for application in bone scaffolds.

• The Journal of Advanced Prosthodontics
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• v.3 no.4
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• pp.186-189
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• 2011

PURPOSE. Porcelain fused to metal (PFM) crowns provide the best treatment option for teeth that have a large or defective restoration. More than 20% of teeth with PFM crowns or bridges require non-surgical root canal treatment (NSRCT). This may be due to the effect of restorative procedures and the possible leakage of bacteria and or their by-products, which leads to the demise of the tooth pulp. Thus, this study was planned to compare the ability of the restorative materials to seal perforated PFM specimens. MATERIALS AND METHODS. The study evaluates the ability of amalgam, composite or compomer restorative materials to close perforated PFM specimen's in-vitro. Ninety PFM specimens were constructed using Ni-Cr alloys and feldspathic porcelain, and then they were divided into 3 groups: amalgam (A), composite + Exite adhesive bond (B) and compomer + Syntac adhesive bond (C). All the PFM samples were embedded in an acrylic block to provide complete sealing of the hole from the bottom side. After the aging period, each group was further divided into 3 equal subgroups according to the thermocycling period (one week for 70 cycles, one month for 300 cycles and three months for 900 cycles). Each subgroup was put into containers containing dye (Pelikan INK), one maintained at $5^{\circ}C$ and the other at $55^{\circ}C$, each cycle for 30 sec time. The data obtained was analyzed by SPSS, 2006 using one way ANOVA test and student t-test and significant difference level at (P<.01). RESULTS. The depth of dye penetration was measured at the interfaces of PFM and filling materials using Co-ordinate Vernier Microscope. The lowest levels of the dye penetration for the three groups, as well as subgroups were during the first week. The values of dye leakage had significantly increased by time intervals in subgroups A and C. CONCLUSION. It was seen that amalgam showed higher leakage than composite while compomer showed the lowest level of leakage.

• Structural Engineering and Mechanics
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• v.27 no.6
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• pp.713-739
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• 2007

Nowadays computers can perform symbolic computations in addition to mere number crunching operations for which they were originally designed. Symbolic computation opens up exciting possibilities in Structural Mechanics and engineering. Classical areas have been increasingly neglected due to the advent of computers as well as general purpose finite element software. But now, classical analysis has reemerged as an attractive computer option due to the capabilities of symbolic computation. The repetitive cycles of simultaneous - equation sets required by the finite element technique can be eliminated by solving a single set in symbolic form, thus generating a truly closed-form solution. This consequently saves in data preparation, storage and execution time. The power of Symbolic computation is demonstrated by six examples by applying symbolic computation 1) to solve coupled shear wall 2) to generate beam element matrices 3) to find the natural frequency of a shear frame using transfer matrix method 4) to find the stresses of a plate subjected to in-plane loading using Levy's approach 5) to draw the influence surface for deflection of an isotropic plate simply supported on all sides 6) to get dynamic equilibrium equations from Lagrange equation. This paper also presents yet another computationally efficient and accurate numerical method which is based on the concept of derivative of a function expressed as a weighted linear sum of the function values at all the mesh points. Again this method is applied to solve the problems of 1) coupled shear wall 2) lateral buckling of thin-walled beams due to moment gradient 3) buckling of a column and 4) static and buckling analysis of circular plates of uniform or non-uniform thickness. The numerical results obtained are compared with those available in existing literature in order to verify their accuracy.

• Korean Journal of Plant Taxonomy
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• v.46 no.3
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• pp.273-282
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• 2016

The establishment of a DNA barcode database at the regional scale and assessments of the utility of DNA barcodes are crucial for conservation biology and for the sustainable utilization of biological resources. Schisandraceae is a small family consisting of ca. 45 species. It contains many economically important species, such as Schisandra chinensis, which is widely used as a source in tonic beverages and in oriental medicine. In Korea, three species, S. chinensis, S. repanda, and Kadsura japonica, are distributed. We evaluated the level of variation of the DNA sequences of rbcL, matK, and the ITS regions from 13 accessions representing the distributional range of the three species. The three DNA barcode regions were easily amplified and sequenced. The minimum values of the interspecific genetic distances among S. chinensis, S. repanda, and K. japonica either separately or in combination are 4- to 23-fold higher than the maximum value of the intraspecific distance, showing that there is a clear DNA barcoding gap in the regions for Korean Schisandraceae. Phylogenetic analyses of the three DNA barcode regions, separately and simultaneously, indicate that all of the DNA barcode regions are useful for identifying a species of Schisandraceae in Korea. The distinctiveness of the three species of Schisandraceae was also supported at the species level when Chinese and Japanese populations were added. The results of this study indicate that three concatenated regions constitute the best option for DNA barcoding in Schisandraceae in Korea.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.1
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• pp.107-118
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• 2007

Statement of problem: Implant-type distractor uses a removable distraction device that has an appearance similar to that of a dental implant and utilizes many of the same techniques for placement as are used for dental implants. Material and method: In this study, 48 implant type titanium distractors were inserted into the osteotomized alveolar bone of 12 beagle dogs. After a 7-day latency period, the alveolar bone was augmented by 5mm vertically at a rate of 1.0 mm/day. The dogs were sacrificed after 4weeks, 8weeks and 12 weeks for radiographic, histologic, and histomorphometric analysis. Result: Copper equivalent value showed significant difference between 4 weeks and the other weeks(8, 12 weeks)(p<0.05). But there was no significant difference between maxillary and mandibular groups. In the bone to metal contact analysis, there was a significant difference between 4 weeks and 12 weeks(p<0.05). On the contrary, there was no significant difference between maxilla and mandible. The bone area showed significantly higher values in 12 weeks compared to 4 weeks(p<0.05). Histologically mineralization began at the host bone margins. At 12 weeks, increasing accumulation of $Ca^{++}$ element was confirmed. Conclusion: From the results above, the new bone formation was increased according to consolidation period. Especially there was significant difference between 4 weeks and 12 weeks(p<0.05). Implant type distractors used in this study to augment vertical ridge defect may prove to be a clinically useful treatment option in selected cases.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.7
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• pp.3185-3189
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• 2014

Background: Breast cancer evolution and tumor progression are controlled by complex interactions between steroid receptors and growth factor receptor signaling. Aberrant growth factor receptor signaling can augment or suppress estrogen receptor function in hormone-dependent breast cancer cells. Thus, we aimed to investigate antitumor effects of sorafenib and lapatinib alone and in combination on MCF-7 breast cancer cells. Materials and Methods: Cytotoxicity of the sorafenib and lapatinib was tested in MCF-7 cells by XTT assays. 50, 25, 12.5 and $6.25{\mu}M$ concentrations of sorafenib and 200, 100, 50 and $25{\mu}M$ concentrations of lapatinib were administered alone and in combination. Results were evaluated as absorbance at 450nM and $IC_{50}$ values are calculated according to the absorbance data Results: Both sorafenib and lapatinib showed concentration dependent cytotoxic effects on MCF-7 cells. Sorafenib exerted cytotoxic effects with an $IC_{50}$ value of $32.0{\mu}M$; in contrast with lapatinib the $IC_{50}$ was $136.6{\mu}M$. When sorafenib and lapatinib combined, lapatinib increased cytotoxic effects of sorafenib at its ineffective concentrations. Also at the concentrations where both drugs had cytotoxic effects, combination show strong anticancer effects and killed approximately 70 percent of breast cancer cells. Conclusions: Combinations of tyrosine kinase inhibitors and cytotoxic agents or molecular targeted therapy has been successful for many types of cancer. The present study shows that both sorafenib and lapatinib alone are effective in the treatment of breast cancer. Also a combination of these two agents may be a promising therapeutic option in treatment of breast cancer.

• Development and Reproduction
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• v.22 no.2
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• pp.133-142
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• 2018

Patients with type II diabetes mellitus are more susceptible to colorectal cancer (CRC) incidence than non-diabetics. The anti-diabetic drug metformin is most commonly prescribed for the treatment of this disease and has recently shown antitumor effect in preclinical studies. The aberrant mutational activation in the components of RAS/RAF/MEK/ERK and PI3K/AKT/mTOR signaling pathway is very frequently observed in CRC. We previously reported that metformin inhibits the phosphorylation of ERK and BEZ235, a dual inhibitor of PI3K and mTOR, has anti-tumor activity against HCT15 CRC cells harboring mutations of KRAS and PIK3CA. Therefore, we hypothesized that simultaneous inhibition of two pathways by combining metformin with BEZ235 could be more effective in the suppression of proliferation than single agent treatment in HCT15 CRC cells. Here, we investigated the combinatory effect of metformin and BEZ235 on the cell survival in HCT15 CRC cells. Our study shows that both of the two signaling pathways can be blocked by this combinational strategy: metformin suppressed both pathways by inhibiting the phosphorylation of ERK, 4E-BP1 and S6, and BEZ235 suppressed PI3K/AKT/mTOR pathway by reducing the phosphorylation of 4E-BP1 and S6. This combination treatment synergistically reduced cell viability. The combination index (CI) values ranged from 0.44 to 0.88, indicating synergism for the combination. These results offer a preclinical rationale for the potential therapeutic option for the treatment of CRC.