• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.4
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• pp.405-417
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• 2010

Previous studies have already shown that mouthguard is effective in protecting jaw bone, teeth and oral tissue against sports trauma. However, other than severe trauma, repetitive force, such as disorders like clenching, cause teeth or oral tissue damage. These kinds of disorders usually present pathologic attrition in the posterior teeth, resorption in alveolar bone, loss of teeth and destruction of occlusion. Wearing a mouthguard is believed to be effective in preventing these disorders. But its effect is not examined thoroughly enough. The purpose of this study is to identify whether mouthguard is effective in reducing strain caused by clenching. Mandibular first molars in the normal occlusal relationship without any history of dental treatment were chosen. Biaxial type strain gauge was placed on the buccal surface of the tooth. Having maximum occlusal force, measured by load cell, as a standard, clenching intensity were divided into three stages; moment of slightly tooth contact, medium bite force (50% of maximum bite force), maximum bite force. Strain occurring in dentition in each stage with and without mouthguard was measured. Changes in strain (on dentition) between each stage and difference in strain, between with or without mouthguard were recorded by PCD-300 analyzer and PCD-30 soft ware. The data was statistically analyzed by Wilcoxon signed rank test. The following results were drawn; Without mouthguard, strain given on dentition increased as the clenching force increased. With mouthguard, strain given on dentition also increased as the clenching force increased. With mouthguard, strain decreased, in all cases of clenching force stages. Data on the moment of slightly tooth contact stage, had no statistical significance. However, with mouthguard, 50-90% of decrease in strain could be obtained in maximum occlusal force, compared to the group without mouthguard. Mouthguard decreased the strain on the dentition, caused by clenching. Therefore, mouthguard seems to be effective in preventing damage on dentition, by acting against clenching, which occurs both consciously and unconsciously during sports activities.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.3
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• pp.39-55
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• 1992

In this research, a Three Level Decomposition technique has been developed for configuration design optimization of truss structures. In the first level, as design variables, behavior variables are used and the strain energy has been treated as the cost function to be maximized so that the truss structure can absorb maximum energy. For design constraint of the optimal design problem, allowable stress, buckling stress, and displacement under multi-loading conditions are considered. In the second level, design problem is formulated using the cross-sectional area as the design variable and the weight of the truss structure as the cost function. As for the design constraint, the equilibrium equation with the optimal displacement obtained in the first level is used. In the third level, the nodal point coordinates of the truss structure are used as coordinating variable and the weight has been taken as the cost function. An advantage of the Three Level Decomposition technique is that the first and second level design problems are simple because they are linear programming problems. Moreover, the method is efficient because it is not necessary to carry out time consuming structural analysis and techniques for sensitivity analysis during the design optimization process. By treating the nodal point coordinates as design variables, the third level becomes unconstrained optimal design problems which is easier to solve. Moreover, by using different convergence criteria at each level of design problem, improved convergence can be obtained. The proposed technique has been tested using four different truss structures to yield almost identical optimum designs in the literature with efficient convergence rate regardless of constraint types and configuration of truss structures.

• Membrane Journal
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• v.19 no.3
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• pp.252-260
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• 2009

The effects of the treatment of an acidic solution at pH 2 on polyacrylonitrile ultrafiltration (UF) membranes were investigated using a circular cross-flow filtration bench with a membrane module. A substantial reduction in the membrane permeability was observed after 80 hours' treatment of the acidic solution. In addition, the analyses of the sample solutions by ultraviolet/visible absorption spectroscopy and gas chromatography/mass spectrometry (GC/MS), which were taken from the feed tank as a function of the treatment time, showed that a new organic compound was produced in the course of the treatment. From a thorough search of the mass spectral library we presumed the new compound to be 1,6-dioxacyclododecane-7,12-dione (DCD), one of the well-known additives for polyurethane. Based on further experimental results, including the scanning electron microscope (SEM) images and the solid-state NMR spectra of the membranes used for the treatment of the acidic solution, we suggested that the decrease of the permeate flux resulted not from the deformation of the membranes, but from the fouling by DCD eluted from the polyurethane tubes in the filtration bench during the treatment. Those results imply that the reactivity to an acidic solution of the parts comprising the filtration bench is as important as that of the membranes themselves for effective treatments of acidic solutions, for efficient chemical cleaning by strong acids, and also in determining the pH limit of the solutions that can be treated by the membranes.

• Journal of the Mineralogical Society of Korea
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• v.22 no.3
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• pp.241-248
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• 2009

Kaolinite was synthesized from amorphous $SiO_2$ and $Al(OH)_3{\cdot}xH_{2}O$ as starting materials by hydrothermal reaction conducted at $250^{\circ}C$ and $30\;kg/cm^2$. The acidity of the solution was adjusted at pH 2. The synthesized kaolinite was characterized by XRD, IR, NMR, FE-SEM, TEM and EDS to clarify the formational process according to the reaction time from 2 to 36 hours. X-ray diffraction patterns showed after 2 h of reaction time, the starting material amorphous $Al(OH)_3{\cdot}xH_{2}O$ transformed to boehmite (AlOOH) and after the reaction time 5 h, the peaks of boehmite were observed to be absent thereby indicating the crystal structure is partially destructed. Kaolinite formation was identified in the product obtained after 10 h of reaction and the peak intensity of kaolinite increased further with reaction time. The results of TGA and DTA revealed that the principal feature of kaolinite trace are well resolved. TGA results showed 13 wt% amount of weight loss and DTA analysis showed that exothermic peak of boehmite observed at $258^{\circ}C$ was decreased gradually and after 10 h of reaction time, it was disappeared. After 5 h of the reaction time, the exothermicpeak of transformation to spinel phase was observed and the peak intensiy increased with reaction time. The results of FT-IR suggested a highly ordered kaolinite was obtained after 36 hours of reaction. It was identified by the characteristic hydroxide group bands positioned at 3,696, 3670, 3653 and $3620\;cm^{-1}$. The development of the hydroxyl stretching between 3696 and $3620\;cm^{-1}$, depends on the degree of order and crystalline perfection. TEM results showed that after 15 h reaction time, curved platy kaolinite was observed as growing of (001) plane and after 36 h, the morphology of synthetic kaolinite exhibited platy crystal with partial polygonal outlines.

• (The) Research of the performance art and culture
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• no.18
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• pp.257-282
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• 2009

Le $th{\acute{e}}{\hat{t}}re$ musical en $Cor{\acute{e}}e$ est devenu aujourd'hui une mode. Beaucoup parlent de musical, mais beaucoup de musicals sont $mont{\acute{e}}s$ sur la $sc{\grave{e}}ne$ sans des recherches $n{\acute{e}}cessaires$ suffisantes. C'est pour cette raison que la plupart des spectacles musicaux qui sont $cr{\acute{e}}es$ en $Cor{\acute{e}}e$ sont $destin{\acute{e}}s$ en faillite $d{\grave{e}}s$ la naissance. D'ailleurs les musicals $liscenci{\acute{e}}s$ par $l^{\prime}Am{\acute{e}}rique$, la France qui sont $mont{\acute{e}}s$ sur la $sc{\grave{e}}ne$ de $Cor{\acute{e}}e$ aujourd'hui sont assez pour nuire le $march{\acute{e}}$ $cor{\acute{e}}en$ $constitu{\acute{e}}$ autour de musical. Quels sont donc les $probl{\grave{e}}mes$ que posent les musicals $liscenci{\acute{e}}s$? $Premi{\grave{e}}rement$ ils encouragent la mime, pas la $cr{\acute{e}}ation$. En d'autre terme, les musicals $liscenci{\acute{e}}s$ que les $Cor{\acute{e}}ens$ montent sur la $sc{\grave{e}}ne$ ne sont pas les $cr{\acute{e}}ations$ propres chez les $Cor{\acute{e}}ens$, par contre, ces derniers sont $demand{\acute{e}}s$ de suivre ${\grave{a}}$ la mot les indications $dict{\acute{e}}es$ par le droit d'auteur. Les $cr{\acute{e}}ateurs$ $cor{\acute{e}}ens$ ne sont pas libres de $cr{\acute{e}}ation$. $Deuxi{\grave{e}}mement$ les musicals ${\grave{a}}$ la mode ont pouvoir de $d{\acute{e}}truire$ la $diversit{\acute{e}}$ de l'homme. L'homme se $caract{\grave{e}}rise$ par la $diversit{\acute{e}}$ et se $diff{\grave{e}}re$ l'un par rapport ${\grave{a}}$ l'autre. C'est l'essence de l'homme. Tous sont $diff{\acute{e}}rents$. Pourtant le musical qui $r{\grave{e}}gne$ sur tous genres de spectacles d'aujourd'hui de $Cor{\acute{e}}e$ ne laisse pas vivre d'autres genres de spectacles, la danse, le $th{\acute{e}}{\hat{a}}tre$, etc. Seul le musical est $compt{\acute{e}}$. $Troisi{\grave{e}}mement$ le musical ne peut pas nier $compl{\grave{e}}tement$ son origine commerciale. En fait le musical est devenu une chose important depuis des investigations immenses par le gouvernement $d^{\prime}Am{\acute{e}}rique$ pour donner des travails aux gens. Donc, $d{\grave{e}}s$ le $d{\acute{e}}but$, il n'y avait pas de $consid{\acute{e}}rations$ artistiques dans et sur le musical. Comme c'est par le commerce que le musical est $r{\acute{e}}pandu$, s'il y aura un $probl{\grave{e}}me$ quelconque, il est $tr{\grave{e}}s$ possible qu'on cherche ${\grave{a}}$ $r{\acute{e}}soudre$ le $probl{\grave{e}}me$ par la vue de commerce. En comprenant les $probl{\grave{e}}mes$ $mentionn{\acute{e}}s$ $l{\grave{a}}$-dessus, il faut $pr{\acute{e}}parer$ le changement de $march{\acute{e}}$ $cor{\acute{e}}enne$ de musical. Le moyen le plus $su{\hat{r}}$ de se $pr{\acute{e}}parer$ est de trouver la $r{\acute{e}}solution$ dans la culture. Pourtant cette $derni{\grave{e}}re$ ne signifie pas la tradition comme $c^{\prime}{\acute{e}}tait$ le cas $jusqu^{\prime}{\grave{a}}$ aujourd'hui, car les $Cor{\acute{e}}ens$ ne sont pas ${\acute{e}}duqu{\acute{e}}s$ par cette $derni{\grave{e}}re$. La $modernit{\acute{e}}$, disons occidentale, traverse la $Cor{\acute{e}}e$. Donc, la signification du mot 'culture' doit ${\hat{e}}tre$ $bas{\acute{e}}e$ sur la tradition et la $modernit{\acute{e}}$ en $m{\hat{e}}me$ temps.