• 한국정보컨버전스학회:학술대회논문집
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• 2008.06a
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• pp.89-92
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• 2008

This study analyzed the status and causes for the dropouts of college based on the survey conducted among 14,210 freshmen attending D College, other than the supernumerary special selection, from 2001 through 2005. A significant difference was shown in all items of general characteristics. The dropout rate of women, generally selected and general high school graduated were higher than for men, specially selected and special high school graduated, respectively. The most dropouts were due to Not Return(40.16%), followed by Unenrolled(32.98%), Voluntary Leave(26.05%) and Expelled(0.81%) in order. In the distribution of the central tendency values measured from the entire subjects. the high school records and the days of absence showed a positive skewness. while the college records showed a negative skewness with the data mostly around a higher grade. The standard deviation indicating that the dropouts got the scores higher than those of the continuing students demonstrated that there was relatively insignificant difference in scores between two groups.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1648-1650
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• 1997

The effects of power frequency electric and magnetic fields have been a source of concern for many years. Electromagnetic fields can pose a theat to both signal system of electrified railways and human body around railways. It is believed that, though the electromagnetic fields do no serious harm to human health, they do induce biological effects. This paper estimates the electromagnetic fields near Kyeongbu high speed railways with numerical data. The charge simulation method and surface charge method are used to calculate the electric field of 2 dimensional power distribution lines and rails and magnetic field is calculated on the base of Biot-Sarart's law.

• Journal of Preventive Medicine and Public Health
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• v.4 no.1
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• pp.31-34
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• 1971

This study was conducted by the Dept. of Preventive Medicine, Kyung Hee University, School of Medicine as a preliminary test for the effects of Fluorine Compounds to the Plants from April through August, 1971. Fluorine was measured with Zirconium-Alizarine method and the following findings could be obtained: 1. Most high densities (25.7 pptm) was found around the industrial areas and lowest (19.3 pptm) around residential sections in Seoul. 2. Average density of Fluorine in the atmosphere of Seoul City was 22.3 pptm which can damage such plants as Pine, Strawberry, Peach and Grapes. 3. Fluorine contents (22.3 pptin) in Seoul area atmosphere shows about 4 times more than that of Cincinnati, Ohio, U. S. A.

• The korean journal of orthodontics
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• v.53 no.6
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• pp.345-357
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• 2023

Enamel demineralization represents the most prevalent complication arising from fixed orthodontic treatment. Its main etiology is the development of cariogenic biofilms formed around orthodontic appliances. Ordinarily, oral biofilms exist in a dynamic equilibrium with the host's defense mechanisms. However, the equilibrium can be disrupted by environmental changes, such as the introduction of a fixed orthodontic appliance, resulting in a shift in the biofilm's microbial composition from non-pathogenic to pathogenic. This alteration leads to an increased prevalence of cariogenic bacteria, notably mutans streptococci, within the biofilm. This article examines the relationships between oral biofilms and orthodontic appliances, with a particular focus on strategies for effectively managing oral biofilms to mitigate enamel demineralization around orthodontic appliances.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.5
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• pp.708-715
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• 1998

The shelter effect of a porous wind fence on a triangular prism was experimentally investigated in a circulating water channel. A porous fence of porosity .epsilon.=38.5% was installed in front of the prism model. The fence and prism model were embedded in a turbulent boundary layer. The instantaneous velocity fields around the fence and prism model were measured by using the instantaneous velocity fields around the fence and prism model were measured by using the 2-frame PTV(Particle Tracking Velocimetry) system. By installing the fence in front of the prism, the recirculation flow region decreases compared with that of no fence case. The porous fence also decreases the mean velocity, turbulent intensity and turbulent kinetic energy around the prism. Especially, at the top of the prism, the turbulent kinetic energy is about half of that without the fence.

• Journal of Ship and Ocean Technology
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• v.5 no.4
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• pp.29-43
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• 2001

In this paper, free surface flows around an advancing two-dimensional rectangular cylinder piercing the free surface are studied using numerical and experimental methods. Especially, wave breaking phenomenon around the cylinder is treated in detail. A series of numerical simulations and experiments were performed for the purpose of comparison. For the numerical simulations, a finite difference method was adopted with a rectangular grid system, and the variation of the free surface was computed by the marker density method. The computational results are compared with the experiments. It is confirmed that the present numerical method is useful for the numerical simulation of nonlinear free surface waves around a piercing body.

• JSTS:Journal of Semiconductor Technology and Science
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• v.12 no.3
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• pp.360-369
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• 2012

The causes of showing different subthreshold slopes (SS) in programmed and erased states for two different charge trap flash (CTF) memory devices, SONOS type flash memory with gate-all-around (GAA) structure and TANOS type NAND flash memory with planar structure were investigated. To analyze the difference in SSs, TCAD simulation and low-frequency noise (LFN) measurement were fulfilled. The device simulation was performed to compare SSs considering the gate electric field effect to the channel and to check the localized trapped charge distribution effect in nitride layer while the comparison of noise power spectrum was carried out to inspect the generation of interface traps ($N_{IT}$). When each cell in the measured two memory devices is erased, the normalized LFN power is increased by one order of magnitude, which is attributed to the generation of $N_{IT}$ originated by the movement of hydrogen species ($h^*$) from the interface. As a result, the SS is degraded for the GAA SONOS memory device when erased where the $N_{IT}$ generation is a prominent factor. However, the TANOS memory cell is relatively immune to the SS degradation effect induced by the generated $N_{IT}$.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.37 no.6
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• pp.483-489
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• 2011

Introduction: This study examined the cumulative resorption of implants placed in a severely atrophic mandible and analyzed the radiologic bone resorption in the marginal bone, after an autogenous bone graft including both block and particulates that had been harvested from the ramus and iliac crest. Materials and Methods: A retrospective study was performed on patients who had bone grafts for augmentation followed by implant installation in the mandible area from 2003 to 2008. Twelve patients (6 men and 6 women) who received 34 implants in the augmented sites were evaluated. Cumulative radiologic resorption around the implants was measured immediately, 3 months, 6 months and 12 months after implant installation surgery. Results: The installed implant in grafted bone showed 0.84 mm marginal bone resorption after 3 months and 50% total cumulative resorption after 1 year. The mean marginal bone resorption around the implant installed in the grafted bone was 0.44 mm after 3 months, 0.52 mm after 1 year, after which it stabilized. The implant survival rate was 97% (failed implant was 1/34). Marginal bone resorption of the installed implant in the autogenous onlay block bone grafts was 0.98 mm after 3 months, which was significantly higher than that of a particulated bone graft (0.74 mm) (P <0.05). Conclusion: An autogenous graft including block type and particulate type is a predictable procedure for the use of dental implants in a severely atrophic mandible. Implant placement in augmented areas show a relatively high survival and minimal bone loss, as revealed by a radiologic evaluation.

• Journal of Periodontal and Implant Science
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• v.42 no.1
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• pp.20-24
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• 2012

Purpose: The purpose of this study was to evaluate the soft tissue and bone change around two adjacent implants in onestage implant surgery. Methods: Eleven subjects (7 males, 4 females) who were needed placement of 2 adjacent implants in the molar area were included. The two implants were placed with the platform at the level of the alveolar crest. The interproximal bone between the 2 implants was not covered with gingiva. After surgery, an alginate impression was taken to record the gingival shape and radiographs were taken to evaluate implant placement. Using a master cast, the gingival height was measured at baseline, 4 weeks, and 12 weeks. In the radiograph, the alveolar bone level was measured at the mesial and distal side of both implants at baseline and 12 weeks. Results: The exposed bone was covered with gingiva at both 4 and 12 weeks. Loss of alveolar bone around implants was found in all areas. The alveolar bone level in the exposed bone area did not differ from that in the non-exposed area. Conclusions: This study showed that the alveolar bone level and gingival height around 2 adjacent implants in the exposed bone area did not differ from that in unexposed bone area.