• Smart Structures and Systems
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• v.33 no.3
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• pp.217-225
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• 2024

In this study, an electromagnetic dynamic vibration suppressor and energy harvester is designed and studied. In this system, a gear mechanism is used to convert the linear motion to continuous rotary motion. Governing equations of motion for the system are derived and validated using the experimental results. Effects of changing the main parameters of the presented system, such as mass ratio, stiffness ratio and gear ratio on the electro-mechanical behavior of system are investigated. Moreover, using so-called Weighted Cost Function, the optimum parameters of the system are obtained. Finally, it is shown that the presented electromagnetic dynamic vibration absorber not only can reduce the undesired vibration of the main system but also it can harvest acceptable electrical energy.

• Restorative Dentistry and Endodontics
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• v.41 no.3
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• pp.176-181
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• 2016

Objectives: This study aimed to compare two nickel-titanium systems (rotary vs. reciprocating) for their acceptance by undergraduate students who experienced nickel-titanium (NiTi) instruments for the first time. Materials and Methods: Eighty-one sophomore dental students were first taught on manual root canal preparation with stainless-steel files. After that, they were instructed on the use of ProTaper Universal system (PTU, Dentsply Maillefer), then the WaveOne (WO, Dentsply Maillefer). They practiced with each system on 2 extracted molars, before using those files to shape the buccal or mesial canals of additional first molars. A questionnaire was completed after using each file system, seeking students' perception about 'Ease of use', 'Flexibility', 'Cutting-efficiency', 'Screwing-effect', 'Feeling-safety', and 'Instrumentation-time' of the NiTi files, relative to stainless-steel instrumentation, on a 5-point Likert-type scale. They were also requested to indicate their preference between the two systems. Data was compared between groups using t-test, and with Chi-square test for correlation of each perception value with the preferred choice (p = 0.05). Results: Among the 81 students, 55 indicated their preferred file system as WO and 22 as PTU. All scores were greater than 4 (better) for both systems, compared with stainless-steel files, except for 'Screwing-effect' for PTU. The scores for WO in the categories of 'Flexibility', 'Screwing-effect', and 'Feeling-safety' were significantly higher scores than those of PTU. A significant association between the 'Screwing-effect' and students' preference for WO was observed. Conclusions: Novice operators preferred nickel-titanium instruments to stainless-steel, and majority of them opted for reciprocating file instead of continuous rotating system.

• Restorative Dentistry and Endodontics
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• v.43 no.1
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• pp.5.1-5.9
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• 2018

Objectives: This study evaluated the amount of remaining root canal filling materials after retreatment procedures performed by undergraduate students using manual, rotary, and reciprocating techniques through micro-computed tomographic analysis. The incidence of instrument fracture and the instrumentation time were also evaluated. Materials and Methods: Thirty maxillary single rooted teeth were prepared with Reciproc R25 files and filled with gutta-percha and AH Plus sealer by the continuous wave of condensation technique. Then, the specimens were assigned to 3 groups (n = 10), according to the retreatment technique used: manual, rotary, and reciprocating groups, which used K-file, Mtwo retreatment file, and Reciproc file, respectively. Retreatments were performed by undergraduate students. The sample was scanned after root canal filling and retreatment procedures, and the images of the canals were examined to quantify the amount of remaining filling material. The incidence of instrument fracture and the instrumentation time were recorded. Results: Remaining filling material was observed in all specimens regardless of the technique used. The mean volume of remaining material was significantly lower in the Reciproc group than in the manual K-file and Mtwo retreatment groups (p < 0.05). The time required to achieve a satisfactory removal of canal filling material and refinement was significantly lower in the Mtwo retreatment and Reciproc groups (p < 0.05) when compared to the manual K-file group. No instrument fracture was observed in any of the groups. Conclusions: Reciproc was the most effective instrument in the removal of canal fillings after retreatments performed by undergraduate students.

• Restorative Dentistry and Endodontics
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• v.44 no.1
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• pp.9.1-9.9
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• 2019

Objectives: The aim of this study was to compare postoperative pain intensity after root canal treatment with One G (OG) vs. R-Pilot (RP) files used for glide path preparation. Materials and Methods: Ninety-three single-canaled mandibular premolar teeth with asymptomatic non-vital pulp were randomly assigned into 3 groups (n = 31): OG, RP, or without glide path (WGP). After creating the glide path, the root canals were prepared using sequential Mtwo rotary files to size 30/0.05. One endodontic specialist carried out single-visit endodontic treatment. The patients were asked to rate the severity of postoperative pain on a visual analogue scale at 24, 48, and 72 hours after the visit. They were also asked to record their intake of prescribed analgesics taken. The data were analyzed using the ${\chi}^2$, Friedman, Kruskal-Wallis, and Mann-Whitney U tests. Results: In all 3 groups, postoperative pain decreased significantly at each time interval (p < 0.05). At 24 hours, the OG group had less postoperative pain than the WGP group (p < 0.05). However, no significant difference was found between the RP group and the others. No statistically significant difference was found among the WGP, OG, and RP groups in postoperative pain intensity at 48 or 72 hours or in analgesic tablet intake at the 3 assessed time intervals. Conclusions: The OG group had less postoperative pain than the WGP group in the first 24 hours. The OG and RP systems were similar regarding postoperative pain intensity and analgesic intake.

• Restorative Dentistry and Endodontics
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• v.32 no.6
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• pp.491-497
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• 2007

The purpose of this study was to compare apical sealing ability of continuous wave canal filling technique according to various heat source plugging depths. Eighty one extracted human premolars with straight root were cleaned and shaped to size 35 using .06 taper rotary NiTi file. After cleansing and shaping, the teeth were divided into 5 groups following the heat source probing depths from the apex; 3, 4, 5, 6 and 7 mm. All specimens were filled using E&Q plus with #35/.06 tapered gutta-percha cone. The positive control teeth were not filled. All teeth were coated with nail varnish except the apical 1 mm around the apical foramen. Negative control teeth were completely sealed include the apical foramen. All specimens were immersed in 1% methylene blue solution for 72 hours. Then the specimens were sectioned horizontally at 1, 2 and 3 mm from the root apex. Each sectioned surface was photographed using a digital camera attached to the stereomicroscope at $12.5{\times}2.5$ fold magnification. All points at 1, 2 and 3 mm were summed as final score of one specimen. Statistical analysis of the collected data was performed. Under the condition of this study. there was no significant difference between the heat source plugging depths of 3, 4, 5, 6 and 7 mm in apical sealing ability. All of apical heat source plugging depth from 3 to 7 mm including Buchanan's protocol -from 5 to 7 mm- seems to be acceptable in clinical application.

• Journal of the Korea Organic Resources Recycling Association
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• v.16 no.3
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• pp.29-37
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• 2008

The objective of this research is to evaluate the optimum treatment methods for disposal sludge cake at different temperatures and periods of time. The disposal dehydrated sewage cake used in this study was obtained from N wastewater treatment plant in the P City. This system consists of continuous conveyer thermal dryer and pyrolysis. The continual conveyer thermal dryer was operated to evaluate the optimum conditions with temperature settings, ranges from 130 to $180^{\circ}C$, loading rates of 650~750 kg/hr and operating times of 110~120 minutes. The continual pyrolysis was also operated to evaluate the optimum conditions with temperature settings, ranges from 650 to $750^{\circ}C$, loading rates of 100~158 kg/hr and operating times of 20~40 minutes. The sewage sludge cake has a moisture content of 78~80% (wt) which decreased up to 1~3%(wt) resulted in breaking of cell wall after operating the continuous conveyer thermal dryer and pyrolysis. Important parameters which were operating times, moisture contents, loading rates, conveyer velocities and rotary velocities effects on the thermal kinetics and dynamics were investigated to evaluate the optimum conditions for the continual thermal dryer and pyrolysis.

• Restorative Dentistry and Endodontics
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• v.48 no.2
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• pp.15.1-15.7
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• 2023

Objectives: This study evaluated the efficiency of WaveOne Primary files (Dentsply Sirona) for removing root canal fillings with 2 types of movement: reciprocating (RCP) and continuous counterclockwise rotation (CCR). Materials and Methods: Twenty mandibular incisors were prepared with a RCP instrument (25.08) and filled using the Tagger hybrid obturation technique. The teeth were retreated with a WaveOne Primary file and randomly allocated to 2 experimental retreatment groups (n = 10) according to movement type: RCP and CCR. The root canals were emptied of filling material in the first 3 steps of insertion, until reaching the working length. The timing of retreatment and procedure errors were recorded for all samples. The specimens were scanned before and after the retreatment procedure with micro-computed tomography to calculate the percentage and volume (mm³) of the residual filling material. The results were statistically evaluated using paired and independent t-tests, with a significance level set at 5%. Results: No significant difference was found in the timing of filling removal between the groups, with a mean of 322 seconds (RCP) and 327 seconds (CCR) (p < 0.05). There were 6 instrument fractures: 1 in a RCP motion file and 5 in continuous rotation files. The volumes of residual filling material were similar (9.94% for RCP and 15.94% for CCR; p > 0.05). Conclusions: The WaveOne Primary files used in retreatment performed similarly in both RCP and CCR movements. Neither movement type completely removed the obturation material, but the RCP movement provided greater safety.

• Clean Technology
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• v.15 no.3
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• pp.186-193
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• 2009

The characteristics of product materials obtained from thermal degradation of low-qualify pyrolytic oil were investigated in this study. The reactants were produced by pyrolysis of mixed plastic waste with film type in a commercial rotary kiln reaction system. The properties of reactants were measured by elemental analysis, calorimetry analysis and SIMDIST analyst. The result of degradation experiments with different reaction temperature programs was discussed through product yields, cumulative yields and production rates of oil products. The multi-step reaction temperature program resulted in higher yields of product oils and lower yields of residues than one-step reaction temperature program. The product characteristics such as production yield and the rate of oil products etc. were influenced by reaction temperature program in the continuous thermal degradation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.24-29
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• 2003

Deep sea water has cold temperature, abundant nutrients and minerals, and good water quality that is pathogen-free and stable. Compared with surface water, deep sea water contains more nutrition salt, such as nitrogen and phosphor. Moreover, if has the good balance of minerals. Because of the ability of the spray drying process to produce a free-flowing power considering of spherical particles with a well-defined size distribution and the rapid drying times for heat-sensitive material, spray drying is attractive for a wide range of applications spray drying is a unique unit operation in which powders are produced from a liquid feed in a single processing step. Key component of the process are atomizer, spray chamber. Design of spray chamber should be based on the atomizer type, the production rate, and the particle size required. Because of the complex processes taking place during spray drying, traditional design method are based on pilot-plant tests and empirical scale-up rules. Modern technique such as CFD have a role to play in design and troubleshooting.

• Structural Engineering and Mechanics
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• v.1 no.1
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• pp.87-102
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• 1993

A $C^{\circ}$ continuous finite element formulation of a higher order displacement theory is presented for predicting linear and geometrically non-linear in the sense of von Karman transient responses of composite and sandwich plates. The displacement model accounts for non-linear cubic variation of tangential displacement components through the thickness of the laminate and the theory requires no shear correction coefficients. In the time domain, the explicit central difference integrator is used in conjunction with the special mass matrix diagonalization scheme which conserves the total mass of the element and included effects due to rotary inertia terms. The parametric effects of the time step, finite element mesh, lamination scheme and orthotropy on the linear and geometrically non-linear responses are investigated. Numerical results for central transverse deflection, stresses and stress resultants are presented for square/rectangular composite and sandwich plates under various boundary conditions and loadings and these are compared with the results from other sources. Some new results are also tabulated for future reference.