• Research in Mathematical Education
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• v.2 no.1
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• pp.163-181
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• 1998

The paper deals with some aspects of early childhood geometry in the Czech Republic. Children's first geometrical experiences come from real life. In our opinion, there exist four types of geometrical experience which can be called the partition of space, the filling of space motion in space and the dimension of space. We distinguish three levels of the mathematical learning process: a spontaneous level, an operational level and a theoretical level.

• Research in Mathematical Education
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• v.1 no.2
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• pp.163-181
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• 1997

The paper deals with some aspects of early childhood geometry in the Czech Republic. Children's first geometrical experiences come from real life. In our opinion, there exist four types of geometrical experience which can be called the partition of space, the filling of space motion in space and the dimension of space. We distinguish three levels of the mathematical learning process: a spontaneous level, an operational level and a theoretical level.

• Journal of the Mineralogical Society of Korea
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• v.20 no.3
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• pp.165-173
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• 2007

The KAERI Underground Research Tunnel (KURT) located in KAERI (Korea Atomic Energy Research Institute) was recently constructed following the site investigation in 2003. Its dimension is 180 m in length, 6 m in width, and 6 m in height, and it has a horseshoe-like cross-sec-lion and is located in the ground to the depth of 90 m. When the tunnel was dug into the ground with 100 m in length, fresh rocks, weathered rocks and fracture-filling materials were taken and examined by mineralogical and chemical analyses. There are phyllosilicate minerals such as illite, smectite and chlorite including calcite, which are filling some faults and cracks of the KURT rock. The illite and smectite usually coexist in the fracture, where their content ratio is different according to which mineral is predominant. There are high concentrations of U and Th in the rocks coated with iron-oxides and filled with secondary materials as compared with those in the fresh rocks. It seems that the radionuclides, which are slowly leached from the parent rocks or exist as a dissolved form in the groundwater and hydrothermal solution, may have been migrated along the fractures and thereafter selectively sorbed and coprecipitated on the iron-oxides and the fracture-filling materials. These results will be very useful far the evaluation of environmental factors affecting the nuclides migration and retardation when long-term safety is considered to the geological disposal of high-level radioactive wastes in the future.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.3
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• pp.39-43
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• 2009

In this paper, the flow characteristics of underfill material driven by capillary action between flip-chip and substrate were investigated. Also, the effects of viscosity level and dispensing point of underfill on flow characteristics were investigated. Flip chip package size was $5mm{\times}5mm{\times}0.65^tmm$, the diameter of solder bump was 100 ${\mu}m$, and the pitch was 150 ${\mu}m$. It was full grid area-array type with 1024 I/Os. The glass substrate was used and the gap between the chip and substrate was 50 ${\mu}m$. For the experimental study, three different underfills with different viscous properties($2000{\sim}3700$ cps), and two different types of dispensing methods(center dot and edge dot) were used. The flow characteristics and filling time of underfill were investigated by using CCD camera. The results show that the edge flow was faster than center flow due to the edge effect, which was caused by the resistance of solder bumps. In case of edge dot dispensing type, the filling time was faster due to the large edge effect, compared to center dot dispensing type. Also, it was found that the underfill flow was faster and the filling time decreased as the viscosity level of underfill was decreased.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.75-85
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• 2010

The focus of this study is to evaluate the field applicability of the newly developed inorganic thixotropic-grout in various ways. In order to do this, the volume stability and the permeability of the inorganic thixotropic-grout have been measured and compared to the existing silica type grouts. In addition, the filling capability of the grout into the tail void has been evaluated through both an experiment with a miniature tail-void filling equipment and a test filling at the shield TBM construction site. The volume loss of the inorganic thixotropic-grout after a 14 day-curing under the atmosphere condition was appeared to be minimal. The excellent waterproofing ability of the inorganic thixotropic-grout was confirmed through a permeability test. The toxicity of the inorganic thixotropic-grout has been evaluated through a toxicity test of aquatic fishes (KS M 0111) and the pH value of the liquid eluviated from inorganic thixotropic-grout was measured as an average of 8.0 and a fatality rate of goldfish after 96 hours was 10% or so. The existence of harmful heavy metals in the liquid eluviated from the inorganic thixotropic-grout has been also examined through an atomic absorption spectroscopy (AAS) test. Any of harmful heavy metals were not detected and the detected level of $Cr^{6+}$ and Cd was far below the standard. Based on both an experiment with a miniature tail-void filling equipment and a test filling at the shield TBM construction site, the filling ability of inorganic thixotropic-grout into the tail void was proved to be excellent.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.4
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• pp.345-350
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• 2020

Hydrogen is an green energy without pollution. Recently, fuel cell electric vehicle has been commercialized, and many studies have been conducted on hydrogen tanks for vehicles. The hydrogen tank for vehicles can be charged up to 70 MPa pressure. In this study, the change in filling time, pressure, and temperature for each hydrogen level in a 59 L hydrogen tank was predicted by numerical analysis. The injected hydrogen has the properties of real gas, the temperature is -40℃, and the mass flow rate is injected into the tank at 35 g/s. The initial tank internal temperature is 25℃. Realizable k-epsilon turbulence model was used for numerical analysis. As a result of numerical analysis, it was predicted that the temperature, charging time, and the mass of injected hydrogen increased as the residual capacity of hydrogen is smaller.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.9
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• pp.3835-3840
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• 2012

Nanoimprint lithography (NIL) is an emerging technology enabling cost-effective and high-throughput nanofabrication. Recently a lot of research for the nanoimprint have been carried out, but almost are about merely experimental result relating to the material operation and the imprint fabrication, and numerical analysis relating to the understanding of the imprint process with R&D level. In this paper, the viscoelasticity analysis model is developed using the finite element method. With this model, the filling process and residual layer formation in nanoimprint are analyzed, which is evaluated by a nanoimprint experiment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9A
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• pp.998-1004
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• 2004

In this paper we propose a discrete bit-loading algorithm that maximizes the transmit bit rate using the channel information. to optimize the performance of the very high-speed digital subscriber line(VDSL) system under the constraint of a maximum transmit power for each user. When the power level of crosstalk is high, the power allocation of a user changes the crosstalk experienced by the other users in the same binder. In this case, the performance of DSL modems can be improved by jointly considering the bit and power allocation of all users Simulation results shows that the proposed method improves the performance compared With that of iterative water-filling method.

• Restorative Dentistry and Endodontics
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• v.49 no.2
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• pp.16.1-16.10
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• 2024

Objectives: This cross-sectional study evaluated the prevalence of apical periodontitis (AP) and the technical quality of root canal fillings in an adult Kuwaiti subpopulation using cone-beam computed tomography (CBCT) images. Materials and Methods: Two experienced examiners analyzed 250 CBCT images obtained from Kuwaiti patients aged 15-65 years who attended government dental specialist clinics between January 2019 and September 2020. The assessment followed the radiographic scoring criteria proposed by De Moor for periapical status and the technical quality of root canal filling. Chi-square and Fisher's exact tests were used for statistical analysis, with significance level set at p < 0.05. Results: Among the 2,762 examined teeth, 191 (6.91%) exhibited radiographic signs of AP, and 176 (6.37%) had undergone root canal filling. AP prevalence in root canal-treated teeth was 32.38%, with a significant difference between males and females. Most of the endodontically treated teeth exhibited adequate root canal filling (71.5%). Conclusions: The study demonstrated a comparable prevalence of AP and satisfactory execution of root canal treatment compared to similar studies in different countries.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.142-142
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• 2017

Wheat (Triticum asetivum L.) is one of the major grain crops worldwide. The reduced productivity ascribed by adverse environment is increasing the risk of food security. Wheat cultivars have been actively released by public side since 1960s in Korea. Each variety has been developed for superior regional adaptation, pest resistance and mostly high yield. Heat stress tolerance is one of the major parameters that threaten wheat production in Korea. Heat stress during grain filling period has been conceived as critical level and directly influences on wheat production. We evaluated 11 common wheat cultivars ("Baegjoong", "Dajung", "Goso", "Hanbaek", "Jokyoung", "Joeun", "Jopum", "Keumgang", "Olgeuru", "Sinmichal", "Uri") that were exposed to abnormally high temperature during the grain filling period. Each plant was grown well in a pot containing "Sunshine #4" soil in controlled phytotron facility set on $20^{\circ}C$ and 16 h photoperiod. At 9 day-after-anthesis (DAA9), plants were subjected to a gradual increase in temperature from $20^{\circ}C$ to $33^{\circ}C$ and maintained constantly at $33^{\circ}C$ for 5 days. After the treatment, plants were subjected to gradual decrease to normal temperature ($20^{\circ}C$) and continue to grow till harvest. Seeds were harvested from each tiller/plant. Total chlorophyll contents decrease level as well as grain parameters were measured to evaluate varietal tolerance to heat stress. We also divide each spike into five regions and evaluate grain characteristics among the regions in each spike. The obtained results allow us to classify cultivars for heat stress tolerance. The pedigree information showed that typical wheat lines provide either tolerance or susceptible trait to their off-springs, which enable breeders to develop heat stress tolerance wheat by appropriate parental choice.