• Smart Structures and Systems
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• v.17 no.6
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• pp.859-880
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• 2016

This study aims to establish an effective methodology for the detection of instant damages occurred in cable-stayed bridges with the measurements of cable vibration and structural temperatures. A transfer coefficient for the daily temperature variation and another for the long-term temperature variation are firstly determined to eliminate the environmental temperature effects from the cable force variation. Several thresholds corresponding to different levels of exceedance probability are then obtained to decide four upper criteria and four lower criteria for damage detection. With these criteria, the monitoring data for three stay cables of Ai-Lan Bridge are analyzed and compared to verify the proposed damage detection methodology. The simulated results to consider various damage scenarios unambiguously indicate that the damages with cable force changes larger than ${\pm}1%$ can be confidently detected. As for the required time to detect damage, it is found that the cases with ${\pm}2%$ of cable force change can be discovered in no more than 6 hours and those with ${\pm}1.5%$ of cable force change can be identified in at most 9 hours. This methodology is also investigated for more lightly monitored cases where only the air temperature measurement is available. Under such circumstances, the damages with cable force changes larger than ${\pm}1.5%$ can be detected within 12 hours. Even though not exhaustively reflecting the environmental temperature effects on the cable force variation, both the effective temperature and the air temperature can be considered as valid indices to eliminate these effects at high and low monitoring costs.

• Structural Monitoring and Maintenance
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• v.5 no.2
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• pp.243-260
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• 2018

Detection of damages in fibre reinforced plastic (FRP) composite structures is important from the safety and serviceability point of view. Usually, damage is realized as a local reduction of stiffness and if dynamic responses of the structure are sensitive enough to such changes in stiffness, then a well posed inverse problem can provide an efficient solution to the damage detection problem. Usually, such inverse problems are solved within the framework of pattern recognition. Support Vector Machine (SVM) Algorithm is one such methodology, which minimizes the weighted differences between the experimentally observed dynamic responses and those computed using the finite element model- by optimizing appropriately chosen parameters, such as stiffness. A damage detection strategy is hereby proposed using SVM which perform stepwise by first locating and then determining the severity of the damage. The SVM algorithm uses simulations of only a limited number of damage scenarios and trains the algorithm in such a way so as to detect damages at unknown locations by recognizing the pattern of changes in dynamic responses. A rectangular fiber reinforced plastic composite plate has been investigated both numerically and experimentally to observe the efficiency of the SVM algorithm for damage detection. Experimentally determined modal responses, such as natural frequencies and mode shapes are used as observable parameters. The results are encouraging since a high percentage of damage cases have been successfully determined using the proposed algorithm.

• Smart Structures and Systems
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• v.19 no.4
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• pp.393-402
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• 2017

Many vibration-based global damage detection methods attempt to extract modal parameters from vibration signals as the main structural features to detect damage. The local flexibility method is one promising method that requires only the first few fundamental modes to detect not only the location but also the extent of damage. Generally, the mode shapes in the lateral degree of freedom are extracted from lateral vibration signals and then used to detect damage for a beam structure. In this study, a new approach which employs the mode shapes in the rotary degree of freedom obtained from the macro-strain vibration signals to detect damage of a beam structure is proposed. In order to facilitate the application of mode shapes in the rotary degree of freedom for beam structures, the local flexibility method is modified and utilized. The proposed rotary approach is verified by numerical and experimental studies of simply supported beams. The results illustrate potential feasibility of the proposed new idea. Compared to the method that uses lateral measurements, the proposed rotary approach seems more robust to noise in the numerical cases considered. The sensor configuration could also be more flexible and customized for a beam structure. Primarily, the proposed approach seems more sensitive to damage when the damage is close to the supports of simply supported beams.

• Smart Structures and Systems
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• v.5 no.3
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• pp.291-316
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• 2009

Damage detection using structural classical deflection flexibility has received considerable attention due to the unique features of the flexibility in the last two decades. However, for relatively complex structures, most methods based on classical deflection flexibility fail to locate damage sites to the exact members. In this study, for structures whose members are dominated by axial forces, such as truss structures, a more feasible flexibility for damage detection is proposed, which is called the Axial Strain (AS) flexibility. It is synthesized from measured modal frequencies and axial strain mode shapes which are expressed in terms of translational mode shapes. A damage indicator based on AS flexibility is proposed. In addition, how to integrate the AS flexibility into the Damage Location Vector (DLV) approach (Bernal and Gunes 2004) to improve its performance of damage localization is presented. The methods based on AS flexbility localize multiple damages to the exact members and they are suitable for the cases where the baseline data of the intact structure is not available. The proposed methods are demonstrated by numerical simulations of a 14-bay planar truss and a five-story steel frame and experiments on a five-story steel frame.

• Structural Engineering and Mechanics
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• v.48 no.3
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• pp.291-308
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• 2013

Structural health monitoring is crucial to maintain the structural performance safely. Moreover, the Kullback-Leibler divergence (KLD) is applied usually to asset the similarity between different probability density functions in the pattern recognition. In this study, the KLD is employed to detect the damage. However the asymmetry of the KLD is a shortcoming for the damage detection, to overcoming this shortcoming, two other divergences and one statistic distribution are proposed. Then the damage identification by the KLD and its three descriptions from the symmetric point of view is investigated. In order to improve the reliability and accuracy of the four divergences, the gapped smoothing method (GSM) is adopted. On the basis of the damage index approach, the new damage index (DI) for detect damage more accurately based on the four divergences is developed. In the last, the grey relational coefficient and hypothesis test (GRCHT) is utilized to obtain the more precise damage identification results. Finally, a clear remarkable improvement can be observed. To demonstrate the feasibility and accuracy of the proposed method, examples of an isotropic beam with different damage scenarios are employed so as to check the present approaches numerically. The final results show that the developed approach successfully located the damaged region in all cases effect and accurately.

• Smart Structures and Systems
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• v.12 no.3_4
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• pp.427-440
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• 2013

A growing need has developed in the United States to obtain more specific knowledge on the structural integrity of infrastructure due to aging service lives, heavier and more frequent loading conditions, and durability issues. This need has spurred extensive research in the area of structural health monitoring over the past few decades. Several structural health monitoring techniques have been developed that are capable of locating damage in structures using modal strain energy of mode shapes. Typically in the past, bending strain energy has been used in these methods since it is a dominant vibrational mode in many structures and is easily measured. Additionally, there may be cases, such as pipes, shafts, or certain bridges, where structures exhibit significant torsional behavior as well. In this research, torsional strain energy is used to locate damage. The damage index method is used on two numerical models; a cantilevered steel pipe and a simply-supported steel plate girder bridge. Torsion damage indices are compared to bending damage indices to assess their effectiveness at locating damage. The torsion strain energy method is capable of accurately locating damage and providing additional valuable information to both of the structures' behaviors.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.43 no.5
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• pp.318-323
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• 2017

Objectives: Mandibular angle reduction or reduction genioplasty is a routine well-known facial contouring surgery that reduces the width of the lower face resulting in an oval shaped face. During the intraoral resection of the mandibular angle or chin using an oscillating saw, unexpected peripheral nerve damage including inferior alveolar nerve (IAN) damage could occur. This study analyzed cases of damaged IANs during facial contouring surgery, and asked what the basic standard of care in these medical litigation-involved cases should be. Materials and Methods: We retrospectively reviewed a total of 28 patients with IAN damage after mandibular contouring from August 2008 to July 2015. Most of the patients did not have an antipathy to medical staff because they wanted their faces to be ovoid shaped. We summarized three representative cases according to each patient's perceptions and different operation procedures under the approvement by the Institutional Review Board of Seoul National University. Results: Most of the patients did not want to receive any further operations not due to fear of an operation but because of the changes in their facial appearance. Thus, their fear may be due to a desire for a better perfect outcome, and to avoid unsolicited patient complaints related litigation. Conclusion: This article analyzed representative IAN cutting cases that occurred during mandibular contouring esthetic surgery and evaluated a questionnaire on the standard of care for the desired patient outcomes and the specialized surgeon's position with respect to legal liability.

• Journal of Korean Neurosurgical Society
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• v.55 no.1
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• pp.1-4
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• 2014

Objective : The case fatality rate of nonlesional intracerebral hemorrhage (n-ICH) was high and not changed. Knowing the causes is important to their prevention; however, the reasons have not been studied. The aims of this study were to determine the cause of death, to improve the clinical outcomes. Methods : We retrospectively analyzed consecutive cases of nonlesional intracerebral hemorrhage in a prospective stroke registry from January 2010 to December 2010. Results : Among 174 patients ($61.83{\pm}13.36$, 28-90 years), 29 patients (16.7%) died during hospitalization. Most common cause of death was initial neurological damage (41.4%, 12/29). Seventeen patients who survived the initial damage may then develop various potentially fatal complications. Except for death due to the initial neurological sequelae, death associated with immobilization (such as pneumonia or thromboembolic complication) was the most common in eight cases (8/17, 47.1%). However, death due to early rebleeding was not common and occurred in only 2 cases (2/17, 11.8%). Age, initial Glasgow Coma Scale, and diabetes mellitus were statistically significant factors influencing mortality (p<0.05). Conclusion : Mortality of n-ICH is still high. Initial neurological damage is the most important factor; however, non-neurological medical complications are a large part of case fatality. Most cases of death of patients who survived from the first bleeding were due to complications of immobilization. These findings have implications for clinical practice and planning of clinical trials. In addition, future conduct of a randomized study will be necessary in order to evaluate the benefits of early mobilization for prevention of immobilization related complications.

• Journal of Korea Society of Digital Industry and Information Management
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• v.13 no.1
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• pp.103-111
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• 2017

Recently, new variants of Ransomware are becoming a new security issue. Ransomware continues to evolve to avoid network of security solutions and extort users' information to demand Bitcoin using social engineering technique. Ransomware is damaging to users not only in Korea but also in all around the world. In this thesis, it will present research solution to prevent and cope from damage by new variants Ransomware, by studying on the types and damage cases of Ransomware that cause social problems. Ransomware which introduced in this paper, is the most issued malicious code in 2016, so it will evolve to a new and more powerful Ransomware which security officers cannot predict to gain profit. In this thesis, it proposes 4 methods to prevent the damage from the new variants of Ransomware to minimize the damage and infection from Ransomware. Most importantly, if user infected from Ransomware, it is very hard to recover. Thus, it is important that users understand the basic security rules and effort to prevent them from infection.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.4
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• pp.88-95
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• 2011

In this study, the deformation, stress, vibration, fatigue life and the probability of damage are analyzed at the pedal applied by the force of 300N. The maximum stress at the lower of pedal is shown as 20.801MPa. And the maximum displacement is 0.85mm at the maximum response frequency as 3800Hz. Among the cases of nonuniform fatigue loads, 'SAE bracket history' with the severest change of load becomes most unstable but 'Sample history' becomes most stable. In case of 'Sample history' with the average stress of 0 to $-10^{5}MPa$ and the amplitude stress of 0 to $10^{5}MPa$, the possibility of maximum damage becomes 0.6%. This stress state can be shown with 5 times more than the damage possibility of 'SAE bracket history' or 'SAE transmission'. The structural result of this study can be effectively improved with the design of pedal by investigating durability against its damage.