• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.48 no.2
• /
• pp.174-179
• /
• 2012

A new absorption material, cellulose sponge soaked in cement, was made for anechoic water tank and its acoustical properties were investigated by pulse methods. The sound absorption coefficient a (dB/cm) of the material was obtained in the frequency range of 40~120kHz from the echo reduction ER (dB) and insertion loss IL (dB) data. The result was averagely 1.8dB/cm higher than the sound absorption coefficient a (dB/cm) of cork-filled rubber which is one of the most effective absorption materials. The wedge (1.2~5.0cm long) type absorption tiles were made with this new material. The echo reduction ER (dB) of the absorption tile with 5.0cm wedge measured in water tank was higher than 20dB in the experimental frequency range.

• Journal of Ocean Engineering and Technology
• /
• v.26 no.2
• /
• pp.39-47
• /
• 2012

The objective of this study was to develop a strength prediction model using a polynomial regression analysis based on the experimental results obtained from ninety samples. As the results of a correlation analysis between various mixing factors and unconfined compressive strength using SPSS (statistical package for the social sciences), the governing factors in the strength of lightweight soil were found to be the crumb rubber content, bottom ash content,and water-cement ratio. After selecting the governing factors affecting the strength through the correlation analysis, a strength prediction model, which consisted of the selected governing factors, was developed using the polynomial regression analysis. The strengths calculated from the proposed model were similar to those resulting from laboratory tests (R2=87.5%). Therefore, the proposed model can be used to predict the strength of lightweight mixtures with various mixing ratios without time-consuming experimental tests.

• Journal of Korean society of Dental Hygiene
• /
• v.4 no.2
• /
• pp.277-291
• /
• 2004

The purpose of this study is to analyze the dental hygienists' overall performance in operative restoration and the clinical performance in operative restoration according to dental hygienists' career and to provide basic data for establishing the appropriate range of dental hygienists' work. Subjects of this study are 339 dental hygienists working at dental clinic and hospital nationwide, selected by their working place, career, type of clinic, and location of clinical institution. The distribution of people who responded to the survey shows that 81 belong to beginner level(less than 2 years since entering clinic), 115 intermediate level(2 to 3 years since entering clinic), 81 higher level(4 to 5 years since entering clinic) and 62 advanced level(more than 6 years since their entering clinic). In terms of the types of clinical institution, 178 belong to dental clinics and 161 belong to dental hospitals. The survey used in this study are focused on perception about clinical performance in operative dentistry and adequacy of the work. Operative dentistry consists of operative restoration and endodontic therapy. The operative restoration consists of 15 categories such as patient welcoming, examination and diagnosis, planning of treatment, anesthesia, control of moisture, cavity preparation, pulp protection, matrix band application, amalgam filling, resin filling, glass ionomer cement filling, abrasive strip removal, rubber dam removal, bite check and polishing, patient education, and arrangement. The reliability was Cronbach's Alpha .9453. SPSS 10.0 for Windows was used to analyze the responses. One way ANOVA was utilized to verify the differences in the dental hygienists' job performance in operative restoration and their job performance according to career. When significant difference was found. Duncan multi comparison post hoc was done. To sum up the results of this study, patient welcoming look the first place in the operative restoration. It was followed by patient education, examination and diagnosis, introducing treatment plan, resin filling, glass ionomer cement filling, amalgam filling, bite check and polishing, anesthesia, pulp protection, control of moisture, abrasive strip removal, cavity preparation, matrix band application, rubber dam removal, and anesthesia. In terms of the clinical performance by career, there were significant differences in 19 activities such as medical eraluation, oral examination, patient charting, intra oral readio graphs, firm developing fixing mounting, curing light gun, education of attention content after operation. Based on the results of this study, the specific range of operative restoration for dental hygienists should be focused on providing basic data for dentists' diagnosis, alleviation of fear and aching accompanied by injection and anesthesia, data providing for dentists' decision of anesthesia degree, and maximization of control of moisture.

• Journal of dental hygiene science
• /
• v.23 no.1
• /
• pp.1-12
• /
• 2023

Background: This study aimed to identify the present level and needs of clinical dental hygienists and to present the Borich needs assessment and the locus for focus model as integrated priorities. Methods: The participants of this study were dental hygienists working in dental clinics (hospitals). The final data of the 194 participants were analyzed using frequency analysis and a paired sample t-test. To analyze the need for clinical dental hygienists to perform work, the Borich priority determination formula was used. The x-y plane consisting of four quadrants was used to analyze the need using the locus for focus model, which helps to determine the priority while showing visual effects. Results: "Scaling" was the highest required level for clinical dental hygienists, and "panorama taking" was the highest present level. The priorities of educational needs were systematically and visually derived from dental hygienists who were currently working through the Borich needs assessment and the locus for focus model for each task performed in the clinical field. Through the priorities of these two models, a total of 13 items appeared in the common high-level area; "oral health care (disability)," "oral health care (systemic disease)," "applying a rubber dam," "professional mechanical tooth cleaning," "root planing," "taking vital signs," "medication counseling," "wire cutting," "removing cement after removing band/bracket," "delivering bracket," "preparing mini-screw implantation," "dental insurance claim," and "patient reception." Conclusion: Based on the results, the department of dental hygiene should maintain and improve the standardized clinical practice curriculum and clinical dental hygienists' practical skills and contribute to the realization of the legal scope of dental hygienists, reflecting the requirements of clinical fields.

• International Journal of Highway Engineering
• /
• v.8 no.3 s.29
• /
• pp.39-48
• /
• 2006

A laboratory investigation was conducted wherein smooth, rounded, siliceous river gravel aggregates were coated with fine-grained polyethylene, carpet co-product, or cement + styrene butadiene rubber latex and used to prepare hot mix asphalt concrete specimens. Only the coarse (+ No.4) aggregates were coated. The concept was that the coatings would enhance surface roughness of the aggregates and, thus, produce asphalt mixtures with superior engineering properties. Hot mix asphalt specimens were prepared and evaluated using several standard and non-standard test procedures. Based on experiences during the coating processes and analyses of these limited test results, the following was concluded: All three aggregate coating materials increased Hveem and Marshall stability, tensile strength, and resilient modulus(stiffness). These findings are indicative of improved resistance to rutting and cracking in hot mix asphalt pavements prepared using coated gravel aggregates in comparison to similar uncoated gravel aggregates.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.24 no.5
• /
• pp.61-68
• /
• 2020

In this study, the international standard ISO TS 16774 Part 3 Test Method for Water (wash out) Resistance and KS F 4935 ｢Sealant Injection type for water leakage maintenance of adhesive flexible rubber asphalt series｣, which are standardized as a quality control method of injection type repair materials used for water leakage cracks in underground concrete structures, are currently used in Korea. As a result, considering the performance criteria of "mass change rate -0.1%" stipulated in KS F 4935, the remaining 13 types repair materials, excluding RG-2 of synthetic rubber and UG-1 of urethane, need to be reviewed for stabilization of the loss resistance due to the flow of ground water. The results of this study are determined to be available as a basic indicator for the selection of repair materials used for cracks in concrete structures. In addition, it is expected that the results of this study can be utilized as reference data that can be reflected in the improvement of the quality of repair materials that will be researched and developed later.

• Journal of Ocean Engineering and Technology
• /
• v.26 no.3
• /
• pp.39-45
• /
• 2012

This paper investigates the strength characteristics and stress-strain behaviors of waste fishing net (WFN)-added lightweight soil. The lightweight soil, which consisted of dredged soil, crumb rubber, and cement, was reinforced with WFN in order to increase its shear strength. Glue treated WFN was also added to lightweight soil to improve the interlocking between the soil mixture and WFN. Three kinds of test specimens were prepared: unreinforced lightweight soil, reinforced lightweight soil without glue treatment, and reinforced lightweight soil with glue treatment. Several series of laboratory tests were carried out, including flow value tests, unconfined compression tests, and SEM analyses. From the experimental results, it was found that the peak strength of the reinforced lightweight soil with glue treatment was increased by the increased interlocking between the soil mixture and WFN, which was induced from the bonding effect. The stress-strain relation of the reinforced lightweight soil, irrespective of the glue treatment, showed a more ductile behavior than that of the unreinforced lightweight soil.

• Elastomers and Composites
• /
• v.33 no.4
• /
• pp.290-296
• /
• 1998

Recycling of waste tire has been limited and very simple, few applications have been observed. This study introduces a new elastic and permeable pavement made of scrap tire. Experimental results showed that key factors affecting the compressive strength were the size of scrap tire, size of aggregate, amounts and property of binder. Also, the water permeability depended on the size of aggregate and scrap tire. The compressive strength and water permeability of the samples were 1.4 and 116 times higher than those of the conventional porous cement concrete, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.3
• /
• pp.1385-1390
• /
• 2012

Couple of laboratory for controlled low strength materials with bottom ash and recycled in-situ soil have been carried out. The optimum mix ratios for 4 cases with flowability and unconfined compressive strength were determined. The optimim mixing ratios were 25 to 45% of insitu soil, 30% of bottom ash, 10 to 20% of fly ash, 0 to 3% of crumb rubber, 3% of cement and 22% of water. Each mixture was satisfied the standard specification, minimum 20cm of flowability and 127 kPa of unconfined compressive strength. Two different curling methods, at room temperature and wet condition, were adopted. The average secant modulus(E50) was 0.07 to 0.08 * $q_u$. The compressive strength at wet condition showed 10% larger than at room temperature. The range of internal friction angle and cohesion for mixtures were 36.5o to 46.6o and 49.1 to 180 kPa, respectively. The mixture with crumb rubber(case 4) showed higher choesion and lower internal friction angle than the others. The pH of all the mixtures was over 12 which is strong alkine.

• Journal of the Korea Concrete Institute
• /
• v.15 no.6
• /
• pp.888-893
• /
• 2003

The purpose of this study is to make clear the durability of the polymer films formed in the autoclaved polymer-modified mortars and concretes. The polymer films prepared with polymer dispersions such as a styrene-butadiene rubber (SBR) latex, a poly (ethylene-vinyl acetate)(EVA) emulsion and a polyacrylic ester (PAE) emulsion for polymeric admixtures are exposed to autoclaving at 18$0^{\circ}C$ in temperature and 1.01 MPa in vapor pressure, and subjected to tensile test and infrared spectroscopy. The durability of the polymer films is evaluated from the application of autoclaving to the polymer films under saturated Ca(OH)$_2$ solution immersion causes no degradation for SBR films and a significant degradation due to the saponification of the polymers for EVA and PAE films. Accordingly, in the application of autoclaving to polymer-modified mortars and concretes, it is suggested that SBR-modified mortars and concretes are hardly degraded but EVA- and PAE-modified mortars and concretes are markedly degraded by the saponification of the polymers.