• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.8
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• pp.759-769
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• 2013

Electronic equipment has been applied to virtually every area associated with commercial, industrial, and military applications. Specifically, electronics have been incorporated into avionics components installed in aircraft. This equipment is exposed to dynamic loads such as vibration, shock, and acceleration. Especially, avionics components installed in a helicopter are subjected to simultaneous sine and random base excitations. These are denoted as sine on random vibrations according to MIL-STD-810F, Method 514.5. In the past, isolators have been applied to avionics components to reduce vibration and shock. However, an isolator applied to an avionics component installed in a helicopter can amplify the vibration magnitude, and damage the chassis, circuit card assembly, and the isolator itself via resonance at low-frequency sinusoidal vibrations. The objective of this study is to investigate the dynamic characteristics of an avionics component installed in a helicopter and the structural dynamic modification of its tray plate without an isolator using both a finite element analysis and experiments. The structure is optimized by dynamic loads that are selected by comparing the vibration, shock, and acceleration loads using vibration and shock response spectra. A finite element model(FEM) was constructed using a simplified geometry and valid element types that reflect the dynamic characteristics. The FEM was verified by an experimental modal analysis. Design parameters were extracted and selected to modify the structural dynamics using topology optimization, and design of experiments(DOE). A prototype of a modified model was constructed and its feasibility was evaluated using an FEM and a performance test.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.3
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• pp.335-341
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• 2009

Statements of problem: Adequate bone quality and quantity were important to achieve initial stability and to prevent early failures. However there were few published data available regarding the actual effect of dimensional change in implant geometry on initial stability. Purpose: The purpose of the current study was to investigate the influence of diameter and length changes on initial stability of implants. Material and methods: Four types of dummy bone (D1, D2, D3 and D4) consisted of cortical and cancellous layers with different thickness were simulated. Implants which had similar surface area to each other ($3.5{\times}13.0-mm$, $4.0{\times}11.5-mm$, $4.5{\times}10.0-mm$, $5.0{\times}8.5-mm$) were inserted in dummy bones. Implant stability as a function of peak insertion torque and resonance frequency values were recorded for each implant. Results: 1. Bone quality was a major influential factor to achieve initial stability (P <.05). 2. In D1, D2 and D3 dummy bones, implant stability quotient values were not significantly different to each other (P >.05), however insertion torques were increased with wider and shorter implants (P <.05). 3. In D4 dummy bone, implant stability quotient values and insertion torques were decreased with wider and shorter implants (P <.05). Conclusion: From a point of view of initial stability, it is suggested that use of wide and short implant may be helpful in avoiding bone augmentation procedures in area of adequate bone quality.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.31 no.2
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• pp.136-142
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• 2009

Bone density in the recipient implant site seems to be an important factor for long term success of endosseous implants. Preoperative evaluation of bone density is very helpful to assist the clinician with the treatment planning of implant therapy. Accurate information on bone density will help the surgeon identify suitable implant sites, thereby improving the success rate of the procedure. Purpose; The aim of this study was to evaluate a correlation between bone density measured preoperatively with computerized tomography and histologically measured bone density by bone biopsy. Patients and methods; Twenty seven patients were selected. All the patients were in good health, with no systemic disorder and additional bone graft. Preoperatively the patients underwent CT scanning to evaluate Houmsfield Unit(HU). Each patients wore a surgical template for implant placement. During surgery 2mm in diameter and 6mm in length specimens were taken. Histomorphometric analysis was performed using digitalized image analysis software Axiovision 4.3. Also, the Resonance frequency analysis(RFA) and insertion torque values were recorded. Results; The highest histomorphometric values was found in the posterior mandible $32.3{\pm}3.8$, followed by $29.9{\pm}2.6$ for the posterior maxilla, $29.4{\pm}2.6$ for the anterior maxilla, $28.6{\pm}2.3$ for the anterior mandible(p=0.214). The hounsfield unit was $989.2{\pm}258.1$ in the posterior mandible, $845.0{\pm}241.5$ in the anterior maxilla, $744.5{\pm}92.6$ in the anterior mandible, $697.3{\pm}136.9$ in the posterior maxilla(p=0.045). This results may suggest that there are strong correlation between the histomorphometric values and hounsfield unit(r=0.760, p<0.05). The RF measurements were $81.9{\pm}2.4$ ISQ in the posterior mandible, $79.0{\pm}1.4$ ISQ in the anterior mandible, $78.3{\pm}4.6$ ISQ in the posterior maxilla, $76.5{\pm}5.0$ ISQ in the anterior maxilla(p=0.048). The insertion torque values was $43.2{\pm}4.2\;Ncm$ in the posterior mandible, $42.0{\pm}0.0\;Ncm$ in the anterior mandible, $41.3{\pm}4.1\;Ncm$ in the posterior maxilla, $40.8{\pm}3.8\;Ncm$ in the anterior maxilla(p=0.612). This results may suggest that there are statistical significance between the hounsfield unit and the insertion torque values(r=0.494, p<0.05), the histomorphometric values and the insertion torque values(r=0.689, p<0.05). But there was no correlation between histomorphometric values and ISQ. There was no statistical significance in age and gender effect on parameters. Conclusions; There was significant correlations between bone density and implant stability parameters. The bone density measurements using preoperative CT may help clinicians to predict primary stability before implant insertion, which is associated with implant survival rates.

• Journal of radiological science and technology
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• v.28 no.3
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• pp.219-226
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• 2005

By analyzing the severally clinical characteristics such as the prevalence by gender and age, and the developmental region, and the developmental factor in terms of vertebral compression fracture, which was diagnosed by MRI(Magnetic Resonance Imaging), the following conclusions were obtained. 1. The general characteristics in 183 research subjects, were 70 men (38.0%) and 113 women (62.0%), and aged from the minimum 16 years old to the maximum 84 years old. 2. Among 183 persons with abnormal findings in vertebral compression fracture, the single compression fracture was included 111 persons (60.7%) with 38 men (34.0%) and 73 women (66.0%), and women in their 60s were largest with 32 persons. 3. As the multiple compression fracture was included 72 persons (39.3%) among 183 research subjects, and as the incidence had 182 cases, this is what classified the case in which one person with abnormal findings has the compression fracture at the levels with more than one, and there were 70 cases (38.0%) in men and 112 cases (62.0%) in women, and it is being indicated the large frequency in women in their 60s and in their 70s. 4. The developmental regions in the single compression fracture and the multiple compression fracture, were generated about 70% of the whole at $T11{\sim}L2$. 5. In terms of the prevalence by cause for compression fracture in 183 whole subjects, it was largest with 41.4% in the fracture caused by trauma in case of men, and with 70.0% in what was caused by the osteoporosis in case of women, and as for a case that combined men and women, it was largest with 56.8% in the vertebral compression fracture caused by osteoporosis.

• Journal of the Korean Child Neurology Society
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• v.26 no.4
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• pp.197-204
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• 2018

Purpose: West syndrome is a severe form of age-specific epilepsy that typically affects infants younger than 2 years of age with mitochondrial disease. We aimed to examine age-specific characteristics of the syndrome in these patients. Methods: We retrospectively analyzed 54 patients with West syndrome diagnosed with mitochondrial disease between March 2006 and March 2016. We compared treatment strategies and diagnostic and clinical variables between patients with early-onset (<6 months of age) and late-onset (${\geq}6$ months of age) seizures. Results: Seizure was the first symptom in 30 (90.9%) and 13 (65%) patients of the early-onset and late-onset groups, respectively (P=0.046). Delayed development was observed in 3 (9.1%) and 7 (35%) patients of the early-onset and late-onset groups, respectively (P=0.023). Lactate levels were normal in 17 patients (55%) of the early-onset group and 5 (25%) of the late-onset group (P=0.036), while initial brain magnetic resonance imaging (MRI) findings were normal in 23 (67.6%) and 8 (40%) patients of the early-onset and late-onset groups, respectively. Final MRI findings were abnormal in 32 patients (94.1%) of the early-onset group and 18 (90%) of the late-onset group (P=0.036). Although ketogenic diets reduced seizure frequency in both groups, the difference was not significant. Conclusion: There is no significant difference in epilepsy-related variables when patients are divided based on a cut-off age of 6 months. However, differences in the first symptom at onset and MRI findings were observed. Although lactate levels were not of significant diagnostic value in the early-onset group, they may be in the late-onset group.

• Sleep Medicine and Psychophysiology
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• v.5 no.1
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• pp.54-70
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• 1998

Objectives : The purpose of this study is to evaluate the role of structural and functional changes of the brain in the pathophysiology of schizophrenia. Methods : The authors measured the regions of interest on the magnetic resonance imaging of the brain in 20 patients with paranoid schizophrenia(15 men and 5 women) and 23 control subjects(15 men and 8 women). We also assessed the neurocognitive functions with the Wisconsin Card Sorting Test, the Benton Neuropsychological Assessment, and the Weschler IQ test-Korean version, soft neurologic signs, and psychiatric symptoms in the patient group. Results : In the patient group, all ventricles and basal ganglia including caudate nucleus and globus pallidus were significantly enlarged. Although there were no significant differences between the two groups in the values of right frontal lobe and left temporal lobe, there was a tendency of decrease in the values of right frontal lobe and left temporal lobe. There were significant positive correlations between the values of ventricles and the frequency of previous hospitalization. However, there were no significant correlations between other values of regions of interest and clinical data. The value of the right frontal lobe was significantly correlated with the score of soft neurologic signs, which is suggestive of the neurodevelopmental abnormalities. There were significant correlations between the value of frontal lobe and the scores of the various subscales of Benton Neuropsychiatric Inventory. In contrast, the value of left amygdala and putamen showed significant correlation with the score of verbal IQ on the Weschler IQ test. Structural changes of the temporal lobe areas were related with the positive and general symptom scores on PANSS, while those of the basal ganglia were related with the negative symptom scores. Conclusions : These results suggest that the structural changes of the brain in the patients with schizophrenia show the dual process, which is suggestive that the enlarged ventricle show the neurodegenerative process, while enlarged basal ganglia, and shrinked right frontal and left temporal lobe show the neurodevelopmental abnormalities. Among these changes, structural changes of the frontal lobe related with various neuropsychological deficits, while those of left temporal lobe related with language abnormality. Relative to the relation between structural changes and psychiatric symptoms, structural changes of the temporal lobe areas were related with the positive and general symptoms, while those of the basal ganglia were related with the negative symptoms.