• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.7
• /
• pp.8-15
• /
• 2019

In this study, we synthesized a calcium sulfonate complex grease and a lithium complex grease to investigate their physical, rheological and tribological properties. The thermal stability of the calcium sulfonate was higher than $300^{\circ}C$ and the lithium complex grease was $245^{\circ}C$ in the dropping point test. In the grease viscosity measurement, the calcium sulfonate complex grease was measured as $7.0Pa{\cdot}s$ and the lithium complex grease was as $4.5Pa{\cdot}s$. Therefore, it was confirmed that the calcium sulfonate complex grease is superior to the lithium complex grease in terms of thermal stability and cohesiveness. In the 4-ball wear test, the calcium sulfonate complex grease was measured to be 0.43 mm and the lithium complex grease to 0.85 mm. In the 4-ball extreme pressure test, calcium sulfonate complex grease was measured as 620 kgf and the lithium complex grease was as 125 kgf. Therefore, it was confirmed that the calcium sulfonate complex grease is superior to the lithium complex grease in abrasion resistance and load-bearing property. It was found that the calcium sulfonate complex grease is more effective than the lithium complex grease in the lubrication at high temperature and high load.

• Applied Chemistry for Engineering
• /
• v.34 no.4
• /
• pp.434-443
• /
• 2023

We have investigated the performance improvement of grease by synthesizing calcium sulfonate grease as an alternative to lithium grease, which is widely used globally. Since the composition ratio of the grease, when manufactured, is usually 50% base oil and 50% thickener, using grease as a lubricant in a cryogenic environment is not encouraged due to its inferior low-temperature performance. In this study, we have synthesized three types of calcium sulfonate grease with paraffin oil and PAO-based base oil and thickener. Furthermore, lithium grease was synthesized via saponification with PAO-based base oil, lithium hydroxide, 12-hydroxystearic acid, and sebacic acid. We have measured low-temperature characteristics using a rheometer and low-temperature torque meter, and tribology characteristics were obtained using a four-ball lubricant tester and schwingung reibung verschleiß (SRV). As a result, the flow point of the calcium sulfonate grease synthesized with a PAO-based base oil and thickener was found to be -40℃, overcoming the existing calcium sulfonate grease's low-temperature limitation. Moreover, the synthesized calcium sulfonate grease showed low-temperature performance similar to that of lithium grease synthesized with PAO base oil, but superior anti-wear, extreme pressure, coefficient of friction, heat resistance, adhesion, and corrosion resistance. It is thus expected to commercially replace the existing lithium grease.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.50 no.4
• /
• pp.409-420
• /
• 2023

The purpose of this study is to analyze trends in the prevalence of dental caries and demand for dental caries treatment among children under 14 years old using Health Insurance Review and Assessment data. The analysis was conducted using treatment records from a random sample of approximately 1 million pediatric patients from a population that included all children and adolescents for each year from 2011 to 2020. In this study, the number of children diagnosed with K02 dental caries and the number of children receiving dental caries treatment across all ages have increased. However, the number of children aged 10 to 14 who received pulp treatment or extraction has decreased. In the National Survey of Children's Oral Health, the decay-missing-filled teeth index for 5- and 12-year-olds has stagnated or increased slightly, but the percentage of the population with active dental caries has decreased. Accessibility and local environments for dental caries treatment have generally improved compared to the past, but preventive dental care has stagnated over the past decade. Therefore, it is necessary to evaluate the effectiveness of oral health programs implemented in Korea to promote and prevent dental caries among children.

• Journal of Korea Foundry Society
• /
• v.44 no.1
• /
• pp.9-15
• /
• 2024

In this study, in order to improve the lifespan of parts made of manganese steel, manganese steel was cast by varying the amount of Ti added to the steel. In order to confirm the characteristics of the cast material, processing characteristics including tensile and surface characteristics and bearing ratio were investigated. It was confirmed that when the amount of Ti added to high manganese steel exceeds 0.5%, the strength of the alloy is improved due to grain refinement, and fine carbides are formed inside the steel. This results in increased resistance to surface wear compared to the alloy with only Mn added. There was no significant difference in the increase in tensile strength as the Ti content in manganese steel was increased. However, inclusion of Ti showed a small but greater effect on wear resistance compared to Mn, and the size and the distribution of carbides become coarse depending on the Ti content. and was evenly distributed. It was confirmed that the strength and surface properties of manganese steel can be improved by the addition of Ti to improve the lifespan of parts made with this steel. It was found that Ti is effective in developing materials with excellent wear resistance due to refinement of dendrite crystal grains. In the samples where Ti was added, the carbide appears to increase the resistance to surface roughness, and due to the nature of Mn steel, surface hardening begins to occur, which appears to extend the life.

• Journal of agricultural medicine and community health
• /
• v.29 no.1
• /
• pp.91-100
• /
• 2004

Objectives: This study was conducted to compare the present community health practitioners(CHPs)'s operating activities with their activity in 1989. Methods: Data were obtained two hundred seventy eight CHPs by self-administered questionnaire regarding duty traits, job satisfaction, and others. Results: The number of CHPs was 255 in 1989 and 224 in 2000. Age of CHPs in 2000 was much higher than that in 1989, and married women was 64.9% in 1989 and 95.9% in 2000. Both the primary duty of CHPs in 1989 and that in 2000 was medical service, and others(maternal health, infant health, family planning, and tuberculosis management, etc) are decreased in 2000, and community health service was added to duty of CHPs in 2000. 55% of CHPs in 1989 satisfied with their job, whereas about 80% of CHPs in 2000 satisfied with their job. The CHPs perceived that their primary necessary duty among requisite duty are medical practice(57.7%), health education(31.4%), and community health service(10.9%), in contrast, unnecessary duty are family planning(68.8%), tuberculosis management(11.1%), infant health(6.3%) maternal health(5.6%). Conclusions: These results suggest that there are such alteration of job satisfaction, needs and obstacles in duty traits of CHFs. These trend of duty traits are major issues to be caught for the health service in primary health post.

• Clinical and Experimental Pediatrics
• /
• v.46 no.8
• /
• pp.784-788
• /
• 2003

Purpose : Perinatal asphyxia occurring in newborn is one of the major causes of acute mortality and chronic neurological disability in survivors. We have studied the relationship between early electroencephalography(EEG) findings and clinical course and neurologic outcome in severe asphyxiated neonates. Methods : Between the period of July 1999 and June 2002, 25 neonates who were diagnosed with severe perinatal asphyxia(1-minute Apgar score of ${\leq}3$ and initial pH is less than 7.2) at NICU in Dongsan Medical Center were enrolled. An EEG was recorded and analyzed within three days of life and divided into two groups - group 1(normal or focal change on EEG) and group 2(generalized abnormal EEG). Between the two groups, clinical courses and neurologic outcomes were compared. Results : Fifteen infants(60%) were group 1 and ten infants(40%) were group 2(polyspikes, burst-suppression, generalized low voltage). Associated maternal disease, days of hospitalization, need for ventilator support, delay of oral feeding and convulsion duration are significantly higher and longer in group 2. Also, poor neurologic outcome(expire, developmental delay) was significantly higher in group 2(60%) than group 1(13.3%). Conclusion : Thus, the early neonatal EEG in asphyxiated newborn can be a predictable diagnostic tool in assessment of neurologic outcome.

• Journal of Preventive Medicine and Public Health
• /
• v.9 no.1
• /
• pp.129-138
• /
• 1976

The causes and problems underlying deaths in perinatal period are often similar and might be expected to yield to same type of preventive measures. This is one of the reasons for attempting to develop a reporting of perinatal mortality and its related matters. This study aims at figuring out the biologic risk factors onto the perinatal death. Considering stillbirth and early neonatal mortality separately, considerable associations between stillbirth and reproductive history of women, are observed, ana it is found that prematurity is the the far most important factor in the early neonatal mortality.

• Korean Journal of Social Welfare
• /
• v.60 no.2
• /
• pp.77-98
• /
• 2008

For women living with mental illness, motherhood may be a normalizing life experiences and offers the opportunity to develop competencies in a major life roles. So, the main premise of this study that social contexts, social support of spouse and extended family, is very important for successful parenting of mothers with mental illness. Thus this study analyzes the impact of marital relationship and social support of networks on three dimensions of parenting competency(expression of love, encouragement of independence, rational discipline) when the socioeconomic(age, number of offsprings, subjective economic level) and disability variables(diagnosis, severity of symptoms, chronicity, frequencies of psychiatric admission) are controlled. This study conducted the survey with 145 mothers with schizophrenia and mood disorder. The major finding of the study are : i) Using step-wise multiple regression, marital relationship, social supports and economic level affect significantly on the expression of love. ii) Using step-wise multiple regression, the most powerful influenced factor on encouragement of independence is marital relationship. iii) Using step-wise multiple regression, diagnosis, severity of symptoms, chronicity and economic level affect significantly on the rational discipline. That is two dimensions of parenting competency, expression of love and encouragement of independence, can be explained well by social contexts variables(marital relationship, social support, economic level). But only rational discipline can be explain well by disability factors. In conclusion, this study recommends service providers to use family based comprehensive case management for the mothers with mental illness.

• The korean journal of orthodontics
• /
• v.37 no.6
• /
• pp.400-406
• /
• 2007

The purpose of this experimental study was to evaluate the effect of immediate orthodontic loading on the stability at the bone-implant interface of titanium miniscrews in a rabbit model. Methods: Forty titanium miniscrews (1.6 mm diameter, 8 mm length) were inserted in the tibiae of 10 rabbits. Twenty test group miniscrews were subjected to continuous orthodontic forces of 200g immediately after implantation for a period of 6 weeks. The remaining 20 control group miniscrews were left unloaded for the same follow-up interval. Removal torque values were recorded using a digital torque gauge. An independent t-test was performed. Results: All the miniscrews were stable, and exhibited no mobility or displacement throughout the experimental period. Histologically, miniscrews were well-integrated into bone. No statistically significant differences in removal torque data were found between the loaded test and the unloaded control groups. Conclusions: These findings suggest that titanium miniscrews can be used as anchoring units for orthodontic tooth movement immediately after insertion.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.22 no.4
• /
• pp.183-189
• /
• 2012

Surface treatments and their effects on high temperature properties for the Hastelloy X, which is a promising candidate alloy for high temperature heat-transport system, have been evaluated. For TiAlN and $Al_2O_3$ overlay coatings, the two different PVD (physical vapor deposition) methods using an arc discharge and a sputtering, were applied, respectively. In addition, a different surface treatment method of the diffusion coating by a pack cementation of Al (aluminiding) was also adopted in this study. To achieve enhanced thermal oxidation resistance at $1000^{\circ}C$ by suppressing the inhomogeneous formation of thick $Cr_2O_3$ crust at the surface region, a study for the surface modification methods on the morphological and structural properties of Hastelloy X substrates has been conducted. The structural and compositional properties of each sample were characterized before and after heat-treatment at $1000^{\circ}C$ under air and He environment. The results showed that the Al diffusion coating showed the more enhanced high temperature properties than the overlay coatings such as the suppressed thick $Cr_2O_3$ crust formation and lower wear loss.