• The Journal of Korean Academy of Prosthodontics
• /
• v.39 no.3
• /
• pp.260-272
• /
• 2001

All-ceramic restorations have had a more limited life expectancy than metal ceramic restorations because of their low strength. Their relatively lower strength and resistance to fracture have restricted the use of all-ceramic crowns to anterior applications where occlusal loads are lower. But there has been increasing interest in all-ceramic restorations because patients are primarily concerned with improved esthetics. Many efforts have been made to in prove the mechanical properties of dental ceramics. This study was designed to elucidate the influence of the luting agent on the strength of the Empress 2 crown (staining technique) cemented on human teeth. Seventy extracted human permanent molar teeth were chosen. Teeth were prepared for Empress 2 crowns with milling machine on a surveyor. A dental bur was placed in the mandrel that was positioned so that the long axis of the bur was perpendicular to the surveyor base. Dimensions of the Empress 2 crown preparation were $6^{\circ}$ taper on each side, $1.5{\pm}0.1mm$ shoulder margin, and 4mm crown height. The luting cements used in this study were as follow: 1. Uncemented 2. Zinc phosphate cements (Confi-Dental) 3. Conventional glass ionomer cement : Fuji 1 (GC) 4. Resin-modified glass ionomer cements : Fuji plus (GC) 5. Adhesive cements : Panavia F (Kuralay), Variolink II (Vivadent), Choice (Bisco). Fracture test using Instron. The crowns were loaded in compressive force to evaluate the effect of these cements on the breaking strength of these all-ceramic crowns. A steel ball with a diameter of 4mm was placed on the occlusal surface and load was applied to the steel ball by a cylindrical bolt with a crosshead speed of 0.5mm per minute until fracture occurred. The fractured surface was examined using Scanning Electron Microscopic Image (SEM) to discover the correlation between fracture strength and bonding capacity. Within the limitation of this in vitro study design, the results were as follows : 1. fomentations significantly increased the fracture resistance of Empress ceramic crowns compared to control. Uncemented (206.9 N): ZPC (812.9 N): Fuji 1 (879.5 N): Fuji Plus (937.7 N): Choice (1105.4 N): Variolink II (1221.1 N): Panavia F (1445.2 N). 2. Resin luting agent, treated by a silane bond enhancing agents, yielded a significant increase in fracture resistance. In some of the Panavia F group, a fracture extended into dentin. 3. According to SEM images of fractured Empress crowns, the stronger the bond at both interfaces(crown and die), the more fracture strength was acquired.

• Journal of Energy Engineering
• /
• v.22 no.2
• /
• pp.237-244
• /
• 2013

The engine oil is used for lubrication of various internal combustion engines. Recently, the vehicle and engine oil manufacture usually guarantee for oil change over 15000~20000 km mileage, but the most of driver usually change engine oil every 5000 km driving in korea. It can cause to raise environmental contamination by used engine oil and increase the cost of driving by frequently oil change. In this study, we investigate the various physical properties such as flash point, pour point, kinematic viscosity, cold cranking simulator characteristics, total acid number, four-ball test and concentration of metal component for fresh engine oil and used engine oil after real vehicle driving (5000 km, 10000 km). The result showed that the total acid number, wear scar diameter by four-ball test, Fe and Cu had increased than fresh engine oil, but 2 kind of used oil (5000 km and 10000km) had similar physical values and concentration of metal component.

• Journal of the Microelectronics and Packaging Society
• /
• v.10 no.1
• /
• pp.45-50
• /
• 2003

Global full 3D finite element analysis fatigue models are constructed for flip-chip BGA on system board to predict the creep fatigue life of solder joints during the thermal cycling test. The fatigue model applied is based on Darveaux's empirical equation approach with non-linear viscoplastic analysis of solder joints. The creep life was estimated the creep life as the variations of the four kinds of thermal cycling test conditions, pad structure, composition and size of solder ball. The shortest fatigue life was obtained at the thermal cycling test condition from $-65^{\circ}C$ to $150^{\circ}C$. It was increased about 3.5 times in comparison with that from $0^{\circ}C$ to $100^{\circ}C$. At the same conditions, the fatigue life of SMD structure as the change of pad structure increased about 5.7% as compared with NSMD structure. Consequently, it was confirmed that the fatigue life became short as the creep strain energy density increased in solder joint.

• KCI Concrete Journal
• /
• v.13 no.2
• /
• pp.10-18
• /
• 2001

The spectral analysis of surface waves (SASW) method, which is an in-situ seismic technique, has mainly been developed and used for many years to determine the stiffness profile of layered media (such as asphalt concrete and layered soils) in an infinite half-space. This paper presents a modified experimental technique for nondestructive evaluation of in-place cement mortar compressive strength in single-layer concrete slabs of rather a finite thickness through a correlation to surface wave velocity. This correlation can be used in the quality control of early age cement mortar structures and in evaluating the integrity of structural members where the infinite half space condition is not met. In the proposed SASW field test, the surface of the structural members is subjected to an impact, using a 12 mm steel ball, to generate surface wave energy at various frequencies. Two accelerometer receivers detect the energy transmitted through the medium. By digitizing the analog receiver outputs, and recording the signals for spectral analysis, surface wave velocities can be identified. Modifications to the SASW method includes the reduction of boundary reflections as adopted on the surface waves before the point where the reflected compression waves reach the receivers. In this study, the correlation between the surface wave velocity and the compressive strength of cement mortar is developed using one 36"x36"x4"(91.44$\times$91.44$\times$91.44 cm) cement mortar slab of 2,000 psi (140 kgf/$\textrm{cm}^2$) and two 36"x36"x4"(91.44$\times$91.44$\times$91.44 cm) cement mortar slabs of 3,000 psi (210 kgf/$\textrm{cm}^2$).

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.4
• /
• pp.409-416
• /
• 2012

Recently, surface modification technology is of importance to improve the wear resistance and the corrosive resistance for high accurate mechanical parts such as LM guide, Ball Screw and Roller Bearing etc., Those has generally featured on rolling contact mechanism to improve not only the wear and the friction, but also the accuracy and the corrosion performances. For surface modifications of high accurate mechanical parts, normally thermal spray, PVD, CVD and E.P. processes have been used with many materials such as DLC, raydent, W, Ni, Ti etc. Diamondlike carbon (DLC) films possess a combination of attractive properties and have been largely employed to modify the tribological behaviors such as friction, wear, corrosion, fretting fatigue, biocompatibility, etc. However, for rolling contact mechanism mechanical parts DLC films are needed to study for commercial benefit. Rolling contact mechanism has features on effects of cyclic motions and stresses, and also not simply sliding motions. The papers focused on the performance test of wear and corrosive resistance according to Me-DLC film thickness. And also, its thickness effect of wear analysis was carried out through the simulation of the maximum shear stress under the rolling contact surface. As the results, Me-DLC films have more potential to improve the wear resistance for high precision mechanical parts than raydent films.

• Tribology and Lubricants
• /
• v.31 no.4
• /
• pp.183-188
• /
• 2015

This paper presents the experimental effects of lubricant with nanodiamond particles in sliding friction. In order to improve the performance of lubricants many additives are used, such as MoS₂, cadmium chloride, indium, sulfides, and phosphides. These additives are harmful to human health and to the environment, so alternatives are necessary. One such alternative is nanodiamond powder, which has a large surface area. In order to investigate the effect of nanodiamonds in lubricants under sliding friction, they are dispersed in the lubricant at a variety of concentrations (0 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, and 1 wt%) using the matrix synthesis method. Friction and wear tests are performed according to the ASTM G99 method using a pin-on-disc tester at room temperature. The specimens used in this experiment are AISI 52100 ball bearings and AISI 1020 steel discs. During the test, lubricant mixed with nanodiamond is supplied constantly to keep the two bodies separated by a lubricant film. To maintain boundary lubrication, the speed is set to 0.18 m/s and a load of 294 N is applied to the disc through the pin. Results are recorded by using workbench software over the test duration of 10 minutes. Experimental results show that when the concentration of nanodiamond increases, the coefficient of friction decreases. However, above a nanodiamond concentration of 0.5 wt%, both the coefficient of friction and wear volume increase. From this experiment, the optimum concentration of nanodiamond showing a minimum coefficient of friction of 0.09 and minimum wear volume of 0.82 nm² was 0.5 wt%.

• Journal of the Korean Society of Physical Medicine
• /
• v.13 no.4
• /
• pp.85-94
• /
• 2018

PURPOSE: This study was conducted to determine the effects of therapeutic exercise on range of motion (ROM), the manual muscle test (MMT), functional movement screen (FMS) and radiological evaluation in a youth football player with football-specific anterior pelvic tilt (APT). METHODS: The subject of this case report was a 12-year-old youth football player, who presented with football-specific APT. Therapeutic exercise consisted of hamstring stretch, prone hip extension, abdominal crunch, bridging with isometric hip abduction, plank exercise with posterior tilt and posterior pelvic tilting exercise using a swiss-ball for 40 min/day, twice a week for 8-weeks. ROM, MMT, FMS (deep squat, hurdle step, inline lunge, shoulder mobility, active straight-leg raise, rotary stability and trunk stability push-up) and radiographs (lumbar lordotic and sacral horizontal angle) were analyzed before and after week 8 of therapeutic exercise. RESULTS: The ROM, MMT, and FMS increased and the lumbar lordotic angle and sacral horizontal angle improved after 8-weeks of therapeutic exercise. CONCLUSION: The results of this case report suggest that therapeutic exercise improves ROM, MMT and radiography associated parameters in youth football players with football-specific APT. These findings have clinical implications for therapeutic exercise in youth football players with football-specific APT.

• The Journal of Korean Academy of Prosthodontics
• /
• v.51 no.4
• /
• pp.284-291
• /
• 2013

Purpose: This study compared fracture strength and fracture modes between metal wire reinforcement and glass fiber reinforcement in repaired maxillary complete denture. Materials and methods: In this study, fracture was reproduced on center of maxillary complete dentures and the denture was repaired with auto-polymerizing resin. The experimental groups (n = 10) were subjected to the following condition: without reinforcing material (control group), reinforcing with metal wire (W group), reinforcing with glass fiber pre-impregnated with light-curing resin (SES MESH, INNO Dental Co., Yeoncheon, Korea, G group). The fracture strength and fracture modes of a maxillary complete denture were tested using Instron test machine (Instron Co., Canton, MA, USA) at a 5.0 mm/min crosshead speed. The flexure load was applied to center of denture with a 20 mm diameter ball attachment. When fracture occurred, the fracture mode was classified based on fracture lines. The Kruskal-wallis test and the Mann-whitney U test were performed to identify statistical differences at ${\alpha}=.05$. Results: W group showed the highest value of fracture strength, there was no significant difference (P>.05) between control group and G group. Control group and W group showed anteroposterior fracture mainly, group W showed adhesive fracture of denture base and reinforcing material. Conclusion: In limitation of this study, the glass fiber did not improve the fracture strength of repaired maxillary complete denture, and adhesive failure was occurred along the lines of glass fiber.

• 한국노년학
• /
• v.28 no.4
• /
• pp.953-968
• /
• 2008

This research was performed to recognize anxiety level of older people, to find out anxiety level after or before regular exercises, and to find out how much anxiety level could be lowered by the sports activities. This research selected a population among the students who enrolled at sport activity classes (e, g., physical exercises, gate ball, volume dance) at L, S, J, Y (a), Y (b), D older people college located in Seoul and Gyoenggi area. 200 of the population were chosen as candidates by convenience sampling, nonprobability sampling. Considering the age of the candidates, total 200 cases were collected by using two methods (survey and interview) simultaneously. The data assessment was made by SPSS 12.0 Version. Error tolerance in statistics is .05. The data was analyzed by using frequency analysis, paired t-test and independent t-test. After analyzing anxiety awareness level after and before regular exercises, anxiety of older people are classified by four factors. First, anxiety for loss is 3.756 (M=3.756) before exercises, while 1.942 (M=1.942) after exercises. Second, fear for aging is 3.443 before exercises and 2.243 after exercises. Third, anxiety for physical appearance is 3.253 before exercises and 2.310 after exercises. Finally, anxiety caused by psychological insecurity is 3.060 before exercises, while 1.666 after exercises. Error of tolerance for all factors falls within .001. Anxiety score after exercises is lower than that of before exercises for every factor as well. As a result, regular physical exercises appeared to reduce anxiety level of older people.

• Journal of Korean Physical Therapy Science
• /
• v.24 no.1
• /
• pp.1-13
• /
• 2017

Purpose: The objective of this study was compare the effect of core muscle strengthening between core exercise on stable surface and core exercise on unstable surface. Methods: Thirty-nine adults participated in this study and were randomly allocated to three groups. The stable surface exercise group and unstable surface exercise groups practiced core muscle training for $3{\times}30minute$ sessions over a 4-week period. The control group did not received therapeutic intervention except pre and post test. The following clinical tools were used to assess core muscle strength and balance: Side Plank Test, Trunk Flexion Test, Balance Error Scoring Test, Core Muscle Stength & Stability Test. Results: The stable surface exercise group showed significant improvement in trunk muscle strength of anterolateral part as revealed by the Side Plank Test and Trunk flexion Test(p<.05). The unstable surface exercise group showed significant improvement in trunk muscle strength of anterolateral part and balance ability as revealed by the Balance Error Scoring Test and Core Muscle Strength & Stability Test(p<.05). Conclusion: The results of this study, both core exercise on stable surface and core exercise on unstable surface induced core muscle strengthening and balance ability. Expecially core exercise on unstable surface more effective to core muscle strengthening and balance ability.