• The Korean Journal of Nuclear Medicine
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• v.22 no.1
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• pp.27-31
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• 1988

In Graves' disease, changes in orbital tissue and structure are casued by inflammatory infiltation, which induces increase of capillary permeability and breakdown of blood-tissue barriers. Using the uptake of $^{99m}Tc-DTPA$ in inflammatory lesion, Eye/Brain radioactivity ratios in brain scintigraphy were evaluated in 15 normal controls and 40 Graves' patients. The results were as follows; 1) Eye/Brain radioactivity ratio was significantly higher in Graves' ophthalmopthy group than in control group (p < 0.005). 2) In Graves' ophthalmopathy, Eye/Brain radioactivity ratio was significantly higher in active (progressive) group than in inactive (non-progressive) group (p < 0.05). 3) There was no correlation between class of ATA classification of Graves' ophthalmopathy and Eye/Brain radioactivity ratio. 4) There was no correlation between Eye/Brain radioactivity ratio and serum activity of TBII. In conclusion, Eye/Brain radioactivity ratio using $^{99m}Tc-DTPA$ brain scintigraphy may be useful to determine the activity of Graves' ophthalmopathy and whether treatment of Graves' ophthalmopathy is necessary or not.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.455-463
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• 2000

In order to develop nondestructive techniques for the quantitative estimation of creep damage a series of crept copper samples were prepared and their ultrasonic velocities were measured. Velocities measured in three directions with respect to the loading axis decreased nonlinearly and their anisotropy increased as a function of creep-induced porosity. A progressive damage model was described to explain the void-velocity relationship, including the anisotropy. The comparison of modeling study showed that the creep voids evolved from sphere toward flat oblate spheroid with its minor axis aligned along the stress direction. This model allowed us to determine the average aspect ratio of voids for a given porosity content. A novel technique, the back propagation neural network (BPNN), was applied for estimating the porosity content due to the creep damage. The measured velocities were used to train the BP classifier, and its accuracy was tested on another set of creep samples containing 0 to 0.7 % void content. When the void aspect ratio was used as input parameter together with the velocity data, the NN algorithm provided much better estimation of void content.

• Structural Engineering and Mechanics
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• v.61 no.6
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• pp.755-763
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• 2017

In this study, the susceptibility of different symmetric steel buildings with dual frame system to Progressive Collapse (PC) was assessed. Some ten-story dual frame systems with different type of braced frames (concentrically and eccentrically braced frames) were considered. In addition, numbers and locations of braced bays were investigated (two and three braced bays in exterior frames) to quantitatively find out its effect on PC resistance. An Alternate Path Method (APM) with a linear static analysis was carried out based on General Services Administration (GSA 2003) guidelines. Maximum Demand Capacity Ratio (DCR) for the elements (beams and columns) with highest DCRs ($DCR_{moment}$ and $DCR_{shear}$) is given in tables. The results showed that the three braced bays with concentric braced frames especially X-braced and inverted V-braced frame systems had a lower susceptibility and greater resistance to PC. Also, the results represented that the beams were more critical than columns against PC after the removal of column.

• Steel and Composite Structures
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• v.25 no.5
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• pp.617-624
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• 2017

In this study, a new empirical method is presented to obtain Dynamic Increase Factor (DIF) in nonlinear static analysis of structures against sudden removal of a gravity load-bearing element. In this method, DIF is defined as a function of minimum ratio of difference between maximum moment capacity ($M_u$) and moment demand ($M_d$) to plastic moment capacity ($M_p$) under unamplified gravity loads of elements. This function determines the residual strength of a damaged building before amplified gravity loads. For each column removal location, a nonlinear dynamic analysis and a step-by-step nonlinear static analysis are carried out and the modified empirical DIF formulas are derived, which correspond to the ratio min $[(M_u-M_d)/M_p]$ of beams in the bays immediately adjacent to the removed column, and at all floors above it. Therefore, the new DIF can be used with nonlinear static analysis instead of nonlinear dynamic analysis to assess the progressive collapse potential of a moment frame structure. The proposed DIF formulas can estimate the real residual strength of a structure based on critical member.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.1
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• pp.57-70
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• 2012

This article presents a numerical investigation concerning the effect of two kinds of axially progressing internal flows (namely, upward and downward) on fluid.structure interaction (FSI) dynamics about a marine riser model which is subject to external shear current. The CAE technology behind the current research is a proposed FSI solution, which combines structural analysis software with CFD technology together. Efficiency validation for the CFD software was carried out first. It has been proved that the result from numerical simulations agrees well with the observation from relating model test cases in which the fluidity of internal flow is ignorable. After verifying the numerical code accuracy, simulations are conducted to study the vibration response that attributes to the internal progressive flow. It is found that the existence of internal flow does play an important role in determining the vibration mode (/dominant frequency) and the magnitude of instantaneous vibration amplitude. Since asymmetric curvature along the riser span emerges in the case of external shear current, the centrifugal and Coriolis accelerations owing to up- and downward internal progressive flows play different roles in determining the fluid.structure interaction response. The discrepancy between them becomes distinct, when the velocity ratio of internal flow against external shear current is relatively high.

• Proceedings of the KOSOMBE Conference
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• v.1991 no.11
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• pp.48-53
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• 1991

The discrete cosine transform (DCT)-based progressive and hierarchical coding schemes developed by the International Standardization Organization (ISO) Joint Photographic Experts Groups (JPEG) are implemented and evaluated for the application of medical image communication. For a series of head sections of magnetic resonance images, a compression ratio of about 10 is obtained by the algorithm without noticeable image degradation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.3
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• pp.211-216
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• 2008

Recently a lot of researches have been conducted on the progressive collapse of structures which is the total collapse of structures initiated by localized damage. Most of the previous studies on the field of progressive collapse have followed deterministic approach without considering uncertainty involved in design variables, which results in unknown reliability of the analysis results. In this study the sensitivity analyses are carried out with design variables such as yield strength, live load, damping ratio, and elastic modulus on the vertical deflection of the joint from which a column is suddenly removed. The Monte Calro simulation, tornado diagram method, and the first order second moment method(FOSM) are applied for the sensitivity study. According to the nonlinear static analysis results, the vertical deflection is most affected by the variation of yield strength of beams. The nonlinear dynamic analyses show that the behaviour of model structures is highly sensitive to variation of the yield strength of beams and the structural damping ratio.

• International Journal of High-Rise Buildings
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• v.7 no.4
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• pp.375-387
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• 2018

This paper presents a review on progressive collapse mechanism of steel framed buildings exposed to fire. The influence of load ratios, strength of structural members (beam, column, slab, connection), fire scenarios, bracing systems, fire protections on the collapse mode and collapse time of structures is comprehensively reviewed. It is found that the key influencing factors include load ratio, fire scenario, bracing layout and fire protection. The application of strong beams, high load ratios, multi-compartment fires will lead to global downward collapse which is undesirable. The catenary action in beams and tensile membrane action in slabs contribute to the enhancement of structural collapse resistance, leading to a ductile collapse mechanism. It is recommended to increase the reinforcement ratio in the sagging and hogging region of slabs to not only enhance the tensile membrane action in the slab, but to prevent the failure of beam-to-column connections. It is also found that a frame may collapse in the cooling phase of compartment fires or under travelling fires. This is because that the steel members may experience maximum temperatures and maximum displacements under these two fire scenarios. An edge bay fire is more prone to induce the collapse of structures than a central bay fire. The progressive collapse of buildings can be effectively prevented by using bracing systems and fire protections. A combination of horizontal and vertical bracing systems as well as increasing the strength and stiffness of bracing members is recommended to enhance the collapse resistance. A protected frame dose not collapse immediately after the local failure but experiences a relatively long withstanding period of at least 60 mins. It is suggested to use three-dimensional models for accurate predictions of whether, when and how a structure collapses under various fire scenarios.

• Journal of Korean Neurosurgical Society
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• v.59 no.4
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• pp.346-351
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• 2016

Objective : Early progressive infarction (EPI) is frequently observed and related to poor functional outcome in patients with middle cerebral artery (MCA) infarction caused by MCA occlusion. We evaluated the perfusion parameters of magnetic resonance imaging (MRI) as a predictor of EPI. Methods : We retrospectively analyzed patients with acute MCA territory infarction caused by MCA occlusion. EPI was defined as a National Institutes of Health Stroke Scale increment ${\geq}2$ points during 24 hours despite receiving standard treatment. Regional parameter ratios, such as cerebral blood flow and volume (rCBV) ratio (ipsilateral value/contralateral value) on perfusion MRI were analyzed to investigate the association with EPI. Results : Sixty-four patients were enrolled in total. EPI was present in 18 (28%) subjects and all EPI occurred within 3 days after hospitalization. Diabetes mellitus, rCBV ratio and regional time to peak (rTTP) ratio showed statically significant differences in both groups. Multi-variate analysis indicated that history of diabetes mellitus [odds ratio (OR), 6.13; 95% confidence interval (CI), 1.55-24.24] and a low rCBV ratio (rCBV, <0.85; OR, 6.57; 95% CI, 1.4-30.27) was significantly correlated with EPI. Conclusion : The incidence of EPI is considerable in patients with acute MCA territory infarction caused by MCA occlusion. We suggest that rCBV ratio is a useful neuro-imaging parameter to predict EPI.

• Earthquakes and Structures
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• v.7 no.4
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• pp.587-607
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• 2014

Progressive collapse, which is referred to as the collapse of the entire building under local damages, is a common failure mode happened by earthquakes. The collapse process highly depends on the whole structural system. Since, asymmetry of the building plan leads to the local damage concentration; it may intensify the progressive collapse mechanism of asymmetric buildings. In this research the progressive collapse of regular and irregular 6-story RC ordinary moment resisting frame buildings are studied in the presence of the earthquake loads. Collapse process and collapse propagation are investigated using nonlinear time history analyses (NLTHA) in buildings with 5%, 15% and 25% mass asymmetry with respect to the number of collapsed hinges and story drifts criteria. Results show that increasing the value of mass eccentricity makes the asymmetric buildings become unstable earlier and in the early stages with lower number of the collapsed hinges. So, with increasing the mass eccentricity in building, instability and collapse of the entire building occurs earlier, with lower potential of the progressive collapse. It is also demonstrated that with increasing the mass asymmetry the decreasing trend of the number of collapsed beam and column hinges is approximately similar to the decreasing trend in the average story drifts of the mass centers and stiff edges. So, as an alternative to a much difficult-to-calculate local response parameter of the number of collapsed hinges, the story drift, as a global response parameter, measures the potential of progressive collapse more easily.