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Search Results: 1 - 10 of 9066 matches for " Kyung-Young Jhang "
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Evaluation of Ultrasonic Nonlinear Characteristics in Heat-Treated Aluminum Alloy (Al-Mg-Si-Cu)
JongBeom Kim,Kyung-Young Jhang
Advances in Materials Science and Engineering , 2013, DOI: 10.1155/2013/407846
Abstract: The nonlinear ultrasonic technique has been known to be more sensitive to minute variation of elastic properties in material than the conventional linear ultrasonic method. In this study, the ultrasonic nonlinear characteristics in the heat-treated aluminum alloy (Al-Mg-Si-Cu) have been evaluated. For this, the specimens were heat treated for various heating period up to 50 hours at three different heating temperatures: 250°C, 300°C, and 350°C. The ultrasonic nonlinear characteristics of each specimen were evaluated by measuring the ultrasonic nonlinear parameter β from the amplitudes of fundamental and second harmonic frequency components in the transmitted ultrasonic wave. After the ultrasonic test, tensile strengths and elongations were obtained by the tensile test to compare with the parameter β. The heating time showing a peak in the parameter β was identical to that showing critical change in the tensile strength and elongation, and such peak appeared at the earlier heating time in the higher heating temperature. These results suggest that the ultrasonic nonlinear parameter β can be used for monitoring the variations in elastic properties of aluminum alloys according to the heat treatment. 1. Introduction To evaluate material degradation, destructive tests such as tensile test, impact test, and bending test are commonly used. However, the destructive tests require preparation of specimens separately from the operating structures and the specimens cannot be reused after test. Therefore, in order to save time and cost, the nondestructive evaluation technique is preferred. Ultrasonic method is a common nondestructive method to evaluate the material degradation, since the propagation characteristics of ultrasonic wave is very closely associated with the elastic properties of material [1]. Generally, when the material is degraded, the elastic property of material will be changed, so that if we can monitor the change of elastic properties, then the degradation can be evaluated. For this purpose, most of ultrasonic methods measure the sound velocity or attenuation of amplitude: the linear elastic constant can be estimated by measuring the longitudinal wave velocity and the shear wave velocity [2]. Also, the correlation between the attenuation of ultrasonic wave and the microstructural change such as phase transformation or grain size growth has been reported [3]. And resonant frequency is dependent on the elastic properties of material as well. So, the linear elastic constant also can be estimated by using resonant frequency method [4]. Nevertheless,
Application of Macrofiber Composite for Smart Transducer of Lamb Wave Inspection
Gang Ren,Kyung-Young Jhang
Advances in Materials Science and Engineering , 2013, DOI: 10.1155/2013/281575
Abstract: Macrofiber composite (MFC) has been developed recently as a new type of smart material for piezoelectric transducers. It shows advantages over traditional piezoelectric ceramic materials (PZT) including the method of application, sensitivity, and cost. It can be embedded on the structure, which provides the possibility to monitor the structural health in real time. In this paper, the feasibility of this transducer for the Lamb wave inspection has been experimentally explored. A pair of MFC patches is bonded on a 2?mm thick aluminum plate, and it has been demonstrated that the dispersive characteristics of S0 and A0 modes, generated and detected by MFC patches, agreed well with the theory. The influence of the bonding condition of the transducer was also tested to show that rigid bonding is required to assure a high amplitude signal. In order to illustrate the performance of defect detection, an artificial defect fabricated on the surface of a specimen was inspected in the pitch-catch mode. The results showed that the MFC transducer is a promising Lamb wave transducer for nondestructive testing (NDT) and structural health monitoring (SHM). 1. Introduction With a view to enhance the safety and reliability in nondestructive evaluation (NDE), the development of highly efficient techniques for nondestructive damage detection or structural health monitoring is of vital significance [1]. Such SHM requires small, lightweight, cheap, and sensitive smart transducers to be embedded on the surface of the structure at affordable cost, especially in the aerospace field. In addition, the traditional PZT is not suitable for this situation because of limitations such as being monolithic, inflexible, and brittle. In order to make up for these limitations, a series of smart material transducers was developed in the past two decades. Piezoelectric films (PVDFs) have been used in SHM system [2–4]. Compared to the traditional PZT transducers, they have some advantages of durability and flexibility, but due to poor electromechanical coupling efficiency, they need greater actuation power in generation and heavy amplification in detection [5]. There are other transducers, including active fiber composites (AFCs) and macrofiber composites (MFCs) developed at NASA Langley Research Center, and these transducers avoid some of the limitations of PVDFs. AFCs and MFCs are composed of thin piezoceramic fibers sandwiched between layers of adhesive, electrodes, and a polyimide film [6]. These types of transducers produce higher force and strain than the typical monolithic piezoceramic
Crack Detection in Single-Crystalline Silicon Wafer Using Laser Generated Lamb Wave
Min-Kyoo Song,Kyung-Young Jhang
Advances in Materials Science and Engineering , 2013, DOI: 10.1155/2013/950791
Abstract: In the semiconductor industry, with increasing requirements for high performance, high capacity, high reliability, and compact components, the crack has been one of the most critical issues in accordance with the growing requirement of the wafer-thinning in recent years. Previous researchers presented the crack detection on the silicon wafers with the air-coupled ultrasonic method successfully. However, the high impedance mismatching will be the problem in the industrial field. In this paper, in order to detect the crack, we propose a laser generated Lamb wave method which is not only noncontact, but also reliable for the measurement. The laser-ultrasonic generator and the laser-interferometer are used as a transmitter and a receiver, respectively. We firstly verified the identification of S0 and A0 lamb wave modes and then conducted the crack detection under the thermoelastic regime. The experimental results showed that S0 and A0 modes of lamb wave were clearly generated and detected, and in the case of the crack detection, the estimated crack size by 6?dB drop method was almost equal to the actual crack size. So, the proposed method is expected to make it possible to detect the crack in the silicon wafer in the industrial fields. 1. Introduction Semiconductors have been applied to many fields including smart TVs, smart phones, smart PCs, automobiles, home appliances, and laptop computers. These fields have demanded that the semiconductor should be of high performance, high capacity, high reliability, small components, and low cost. Because of these demands, semiconductor fabrication processes have focused on the lithography for a nanometer-scaled line width. And especially, semiconductor packaging processes have focused on a few trends in recent years: multistacking components and thinner wafers [1–3]. The multistacking component implies that more chips have to be stacked up within the same size component for the high capacity, and the thinner wafer indicates that wafer thickness has to be very thin up to 30?μm for the multistacking component. Moreover, an attempt to change from 12 inch-wafers to 18 inch-wafers is recently going on, since larger wafers which are able to put more chips have impact on the yield improvement. Because of these trends that wafers are getting thinner and larger, silicon wafers are vulnerable to cracks during manufacturing. The cracks can also lead to the yield drop and reliability failure. Therefore, one of the most critical issues in the semiconductor packaging process is the crack. So, the online crack detection in silicon
Effects of Annealing and Removal of the Water-Soluble Fraction of Dry-Milled Rice Flour on the Texture of Cooked Rice Noodles  [PDF]
Soo Young Choi, Bong Kyung Koh
Food and Nutrition Sciences (FNS) , 2017, DOI: 10.4236/fns.2017.810064
Abstract: Rice noodles were prepared using dry-milled rice flours, which were treated by annealing and removing the water-soluble fraction to improve the quality of noodles without using chemical additives. The combined treatment (TC) with annealing and water-soluble fraction removal decreased the cooking losses for Goamibyeo but not for Chenmaai and Milyang260, which had soft kernels and contained less damaged starch than the hard kernel rice after milling. TC significantly reduced the hardness and adhesiveness of cooked noodles, and increased the cohesiveness according to the texture profile analysis. A sensory evaluation detected an increase in mouth feel firmness and elasticity of cooked TC noodles. These results indicate that annealing at room temperature for 3 h followed by the removal of the water-soluble fraction is effective for reducing the cooking losses and improving the textural properties of noodles made from rice flour with high starch damage.
Factors associated with obesity among Korean adolescents  [PDF]
Gyu Jin Heo, So Young Nam, Soo-Kyung Lee
Health (Health) , 2013, DOI: 10.4236/health.2013.58180
Abstract:

Obesity has been a great interest of public health. Studies simultaneously examining various factors associated with obesity among adolescents have been limited. Therefore, this study aimed to examine how various factors (socio-economic status, sex, age, diet, and physical activity) were simultaneously associated with obesity among Korean adolescents. This study analyzed two nationally representative datasets: 2008 Korea National Health and Nutrition Examination and Survey (KNHANES) and 2008 Korea Youth Risk Behavior Web-based Survey (KYRBWS). A total of 900 adolescents (12-18 year-old) in KNHANES and 74,451 adolescents in KYRBWS were included in statistical analyses with SPSS 19.0. Overweight (5.7%) and obesity (13.9%) rates were determined in KNHANES, and KYRBWS showed somewhat lower rates. No significant associations between the various factors and obesity were found in KNHANES. However, the analysis of KYRBWS confirmed higher obesity risk for boys, lower economic status, inferquent high-energy/low-nutrient type food consumption, practicing moderate-intensity physical activity less than five days per week, spending more than 2 hours sitting per day, and having tried exercise or diet for weight control (p < 0.05). The results from the two national datasets seemed to generally agree that many of the various obesity risk factors were important among Korean adolescents, although the associations were mostly not significant in KNHANES. It seemed that obese adolescents tried to practice good dietary behaviors, but not necessarily physical activity, known to reduce obesity risk. Obesity policies should continue to help adolescents achieve an active lifestyle and healthy eating behaviors.

The associations between socioeconomic status and obesity in Korean children from 1998 to 2009  [PDF]
So-Young Nam, Soo-Kyung Lee
Health (Health) , 2013, DOI: 10.4236/health.2013.511256
Abstract:

Increasing interests have been shown in associations between socioeconomic status (SES) and obesity in relation to health inequality. The research objectives were 1) to examine associations between SES and child obesity (including overweight) in Korea over 10 years and 2) to explore possible underlying mechanisms of relationships between SES and obesity. This study used the nationally representative data (KNHA-NES) from 1998, 2005, to 2009. Children (10-18 year-old) were grouped by household income (low, middle-low, middle-high and high) adjusted for the number of family members. Z-scores of height, weight, and BMI for each child were calculated from measured anthropometric data using the 2007 Korean national growth charts. No statistically significant associations were found, however, changes in association patterns were noted. The lower SES group showed shorter height as well as lighter weight among Korean children. More research should be conducted to understand the effects of socioeconomic status on child obesity.

 

Hierarchical Value Maps of Smart Phones, Portal Sites, and Social Network Services Based on User Involvement  [PDF]
Sang Hee Kwon, Min Kyung Cha, Seo Young Lee
Advances in Journalism and Communication (AJC) , 2015, DOI: 10.4236/ajc.2015.33007
Abstract: This study compares the hierarchical value maps (HVMs) for portal sites, smart phones, and social network services (SNSs) according to means-end chain theory. Means-end chain theory offers insights into how a media product satisfies the personal values of consumers. We derive the HVM for each media and investigate the effect of involvement on the HVM structure. A total of 424 individuals were queried for their opinions on the attributes, functional consequences, psychological consequences, and value of each media product through association pattern technique laddering. These elements constitute the value chain structure. Our findings show that the value of each media is determined by involvement levels. For each media, high-involvement user groups regard self-satisfaction as the most important value they aspire for. This study determines that different levels of involvement do not affect the relationships among the elements of the value chain. HVMs for smart phones, portal sites, and SNSs are focused on a special value. However, the level of involvement generally does not seem to alter the structures of HVMs.
Local governments' dependence on tobacco tax revenue: a deterrent to tobacco control in the Republic of Korea
Do,Young Kyung; Park,Kidong;
Bulletin of the World Health Organization , 2009, DOI: 10.1590/S0042-96862009000900013
Abstract: objective: to investigate, in the republic of korea, whether local governments' participation in an anti-smoking programme supported by the national health promotion fund in 2002-2003 was related to the percentage of local tax revenue comprised by the tobacco consumption tax (tct). methods: using financial and administrative data on 163 municipalities, the authors estimated logit models of local governments' participation in the anti-smoking programme as a function of the proportion of local tax revenue that came from the tct and a set of control variables, namely local socioeconomic characteristics and the size of the staff in the local public health centre (phc). findings: local governments that derived a greater percentage of their local tax revenue from the tct, particularly those that ranked in the upper fourth in terms of this percentage, were less likely to participate in the anti-smoking programme. insufficient staff in the phc was also found to be associated with lower participation in the anti-smoking programme. conclusion: local governments' dependence on revenue from the tct may be a deterrent to tobacco control in the republic of korea.
The Expression of Matrix Metalloproteinases and Tissue Inhibitors of Metalloproteinases in Idiopathic Interstitisal Pneumonia  [PDF]
Ji Young Shin, Yu Jin Kim, Sun Young Kyung, Seung Yeon Ha, Sung Hwan Jeong
Open Journal of Respiratory Diseases (OJRD) , 2014, DOI: 10.4236/ojrd.2014.43014
Abstract:
Background: Idiopathic interstitial pneumonia is characterized by fibroblast proliferation and extracellular matrix (ECM) accumulation. Matrix metalloproteases (MMPs) and tissue inhibitors of metalloproteases (TIMPs) have been shown to regulate remodeling of the ECM, which indicates that they are important factors in the process of lung fibrosis. Therefore, we evaluated the expression of MMPs and TIMPs in tissues obtained from patients with idiopathic interstitial pneumonia and control tissues. Methods: Thirty-seven patients who were diagnosed with IIP (22: IPF, 13: NSIP, 2: COP) and 5 controls were enrolled in this study. The MMP-2 and -9 activity in lung tissue obtained from these patients was analyzed using gelatin zymography and the levels of TIMP-1 and -2 were measured by western blotting. We also evaluated the expression of MMP-2 and -9, as well as that of TIMP-1 and -2 in lung tissue using immunohistochemistry. Results: The levels of MMP-2 and MMP-9 were significantly increased in patients with IPF compared to those with NSIP and COP. The activities of TIMP-1 and -2 were also higher in patients with IPF than NSIP/COP patients and control subjects. There were no significant differences observed in the activities of MMPs and TIMPs obtained from patients with NSIP/COP and control subjects. The immunohistochemical analysis showed that TIMP-2 and MMP-2 were strongly stained at the fibroblasts of the fibroblastic foci in patients with IPF. Conclusions: These results suggest that over-expression of gelatinases and TIMPs in patients with IPF are important factors in the irreversible fibrosis that is associated with lung parenchyma.
A mechanism for magnetic field stochastization and energy release during an edge pedestal collapse
Tongnyeol Rhee,Sung Sik Kim,Hogun Jhang,Gun Young Park,Raghvendra Singh
Physics , 2014, DOI: 10.1088/0029-5515/55/3/032004
Abstract: On the basis of three-dimensional nonlinear magnetohydrodynamic simulations, we propose a new dynamical process leading to the stochastization of magnetic fields during an edge pedestal collapse. Primary tearing modes are shown to grow by extracting kinetic energy of unstable ballooning modes, eventually leading to the island overlap. Secondary tearing modes, which are generated through a coherent nonlinear interaction between adjacent ballooning modes, play a key role in this process, mediating the energy transfer between primary ballooning and tearing modes. Explicit calculations of the parallel energy loss through the stochastic field lines show that it can be a likely dominant energy loss mechanism during an edge pedestal collapse.
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