• 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.

• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.229-237
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• 2012

Phosphorus was incorporated into Co/$Al_2O_3$ catalyst for FTS by impregnating an acidic precursor, phosphoric acid, in ${\gamma}-Al_2O_3$ support to improve the mechanical strength, the hydrothermal stability of the catalyst particle, and the catalytic performance as well. Surface characterization techniques such as FT-IR revealed that $AlPO_4$ phase was generated on the surface of the P-modified catalyst. The addition of phosphorus was found to alleviate the interaction between cobalt and alumina surface, and to increase reducibility of catalyst. The catalytic activity such as $C_{5+}$ productivity and turnover frequency (TOF) was calculated to evaluate catalytic performance. The influence of calcination temperature of the $Al_2O_3$ containing 2 wt.% P on the catalytic performance was also investigated. Through hydrothermal stability test and XRD analysis, the P-modified catalyst had strong resistant to the pressurized and hot $H_2O$. The mechanical strength of the P-modified catalyst was also examined through an in-house fluidized-bed vessel, and it was found that the catalyst fragmentation could be successfully suppressed with P. Taken as a whole, the best performance was shown to be at 1~2 wt.% P in alumina and at the calcination temperature of $500^{\circ}C$.

• Korea journal of population studies
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• v.11 no.1
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• pp.159-184
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• 1988

Race and ethnicity are important factors which influence the elderIy's residential adjustment behaviors, although it is unclear whether this reflects influences unrelated to race and ethnlcity. Culturally, the norm of family supportoften obseved among various minority ethnic groups is likely to provide flexible family suppof for the elderIy. Economically, the life-long hardship ofminority groups is likely to force them to maintain extended family living arrangements simply to reduce expenses via economies of scale. Thecontroversy about the economic need versus the cultural prescription forextended living arrangements remains unresoIved because it fails to articulatethe meaning of family supports among many disadvantaged groups.This study aims to test previous economic and cultural arguments, byexamining ethnic differences iu the eiderIy's responsiveness to their health andeconomic problems. Two hypotheses about cultural influences on the elderly's resideutiai adjustment are examined. First, do elderly minorities receive famiiysupporis for longer periods when they are poor if economic and health status\ulcorner Second, do elderiy minorities receive family supports more often when their health status declines\ulcorner Using the Longitudinal Suvey on Aging from 1984 to 1990. this study employs Markovian multi-state life tables, and discrete and contonuous competing hazard analyses for the transition in living arrangements. The main results provide substantial evidence against the cultural resource thesis. Elderly minorities experience more frequent transition between living alone and living with relatives than white elderly persons when group differences in the extent of mortality and insititutionalization are controlled. The shorter timf of living alone among elderly monorities stems from their greater likehood of joining relatives as well as greater mortality and attrition rates than elderly whites. Coresidence of elderly whites with their relatives is more likely to occur in response to their needs for health care than of elderly whites. it implies that instability. not flezibility. characterrizes elderly minorities living arrangements.