Hong C.,Ulsan College |
Shin K.-K.,Agency for Defense Development
Journal of Sound and Vibration | Year: 2010
This paper investigates a modeling technique of wall pressure fluctuations (WPF) due to turbulent boundary layer flows on a surface for finite element structural analysis. This study is motivated by critical issues of structural vibrations due to turbulent WPF over the surface of a body. The WPFs are characterized with random behavior in time and space. The temporal and spatial random behavior of the WPFs is mathematically expressed in the form of the auto- and cross-power spectral density functions (PSDF) in the frequency domain (e.g., Corcos Model). For finite element modeling of the random distributed fluctuations, the cross-PSDF is properly modeled over the finite element structural mesh. The quality of modeling of the cross-PSDF is directly affected by the structural mesh size. We first examine the maximum mesh size required for reliable finite element analysis. The reliability of the FEA results is confirmed by the theoretical results. It is found that the maximum mesh size should be determined under consideration of the spatial distribution of the cross-PSDF in addition to the representation of dynamic behavior of the structure in the frequency range of interest. It is also recognized that the requirement of the maximum mesh size is unrealistic in many practical cases. We then investigate practical modeling schemes under a realistic mesh size condition. We found that the WPF can be modeled without the exact consideration of cross-correlation if the power due to the wall pressure fluctuation can be properly compensated. This is owing to the feature of decreasing the crosscorrelation of WPFs at high frequencies and the fact that the WPF does weakly couple into the structural modes at high wavenumbers such that 2πf/Uc < kmax. The wall pressure fluctuations can therefore be modeled as uncorrelated loadings with power compensations. © 2009 Elsevier Ltd. All rights reserved.
Lee K.,Ulsan College |
Yoo H.,University of Ulsan |
Levermore G.J.,University of Manchester
Renewable Energy | Year: 2013
The measured data of global solar irradiation on a horizontal surface, the number of bright sunshine hours, and the amount of cloud cover for major cities of South Korea, during the period (1986-2005) are analyzed. Quality controls tests were carried out to eliminate spurious data and inaccurate measurements resulting from the cosine response error of the pyranometers. Accordingly, in six locations of South Korea where hourly global solar irradiation is currently measured, the hourly global solar irradiation was calculated using two Sunshine Fraction Radiation Model (SFRM) and a Cloud Cover Radiation Model (CRM), were compared and analyzed. Data for Ulsan, where hourly global solar irradiation is not currently measured, can be calculated from the data of the six other locations. The total solar irradiation on horizontal surfaces is separated into the beam and diffuses components. Empirical correlations for estimating the diffuse solar irradiation incident on horizontal surfaces have been proposed. The purpose of our work consists of predicting the solar irradiation on inclined surfaces based on horizontal measurements. To reach this goal, two studies were performed. They consisted of quantifying the accuracy of various well-known models. The first type of models calculated diffuse horizontal irradiations from global ones and the second type computed global irradiations on inclined planes from diffuse and global components on a horizontal surface. The proposed model can provide an alternative to building designers in estimating the solar irradiation on inclined surfaces where only the horizontal measurements are available. © 2013.
Foisal A.R.M.,University of Ulsan |
Hong C.,Ulsan College |
Chung G.-S.,University of Ulsan
Sensors and Actuators, A: Physical | Year: 2012
In this study, an array of four generators is designed and fabricated to demonstrate the possibility of harvesting energy from different environmental frequencies. The magnetic spring technique is used as a cantilever to scavenge energy from low frequency vibrations. Initially, a single frequency energy harvester is optimized in terms of the number of turns, coil width, and coil position. Finally, two configurations of a multi-generator are fabricated. In model A, four individual generators are placed side by side; whereas in model B, the generators are placed one above the other. The experimental results show that both models can operate in the 7-10 Hz frequency range. The power densities of model A and model B are 21.92 μW/cm 3 and 52.02 μW/cm 3, respectively, at an acceleration of 0.5 g. © 2012 Elsevier B.V. All rights reserved.
Cha J.-D.,Korea University |
Kim J.-Y.,Ulsan College
Molecules | Year: 2012
Cryptomeria japonica D. Don (C. japonica) has been used in traditional medicines from Asia for a variety of indications, including liver ailments, and an antitussive, and for its antiulcer activities. We examined the cell viability and apoptosis of KB cells treated with C. japonica essential oil at several concentrations for 12 h by MTT assay, Hoechst-33258 dye staining, DNA fragmentation, flow cytometry (cell cycle), and Western blotting for mitochondria stress, activation of caspases, and poly (ADP-ribose) polymerase. The essential oil induced the apoptosis of KB cells in a dose-dependent manner, which was verified by DNA fragmentation, appearance of apoptotic bodies, and the sub-G1 ratio. The essential oil also induced rapid and transient caspase-3 activity and cleavage of PARP of the KB cells. Treating the cells with the oil also caused changes in the mitochondrial level of the Bcl-2 family proteins such as Bcl-2 and Bax, thereby inducing the release of cytochrome c into the cytosol. The essential oil of C. japonica may have potential as a cancer chemopreventive and therapeutic agent. © 2012 by the authors.
Cho H.C.,Ulsan College |
Fadali M.S.,University of Nevada, Reno
IEEE Transactions on Control Systems Technology | Year: 2011
This paper presents a new control approach for nonlinear network-induced time delay systems by combining online reset control, neural networks, and dynamic Bayesian networks. We use feedback linearization to construct a nominal control for the system then use reset control and a neural network to compensate for errors due to the time delay. Finally, we obtain a stochastic model of the Networked Control System (NCS) using a Dynamic Bayesian Network (DBN) and use it to design a predictive control. We apply our control methodology to a nonlinear inverted pendulum and evaluate its performance through numerical simulations. We also test our approach with real-time experiments on a dc motor-load NCS with wireless communication implemented using a Ubiquitous Sensor Network (USN). Both the simulation and experimental results demonstrate the efficacy of our control methodology. © 2010 IEEE.
Yu K.H.,Ulsan College
Nutrition Research and Practice | Year: 2011
Hemoglobin and zinc protoporphyrin (ZPP) tests are commonly used to screen for iron deficiency, but little research has been done to systematically evaluate the sensitivity and specificity of these two tests. The goal of this study was to evaluate the effectiveness of zinc protoporphyrin/heme (ZPP/H) ratio as a point-of-service screening test for iron deficiency among preschool-aged children by comparing the sensitivity and specificity of hemoglobin, ZPP/H ratio, and serum ferritin (SF). Also completed were assessments for the prevalence of anemia, iron deficiency (ID), and iron deficiency anemia (IDA) with indicators of ferritin models. This study was carried out with 95 children ages 3 to 6 y. Anthropometric measurements were assessed, and blood samples were analyzed for hemoglobin, SF, transferrin saturation (TS), and ZPP. Anemia was common and the prevalences of anemia, ID, and IDA were 14.7%, 12.6%, and 5.2%, respectively. The ZPP/H ratio was strongly and significantly correlated with hemoglobin. And ZPP/H ratio was a more sensitive test for ID than hemoglobin or SF measurement, correctly identifying more than twice as many iron-deficient children (sensitivity of 91.7%, compared to 41.7% for hemoglobin and SF). However, ZPP/H ratio had lower specificity (60.2%, compared to 89.1% for hemoglobin or 96.4% for SF) and resulted in the false identification of more subjects who actually were not iron deficient than did hemoglobin or SF. Low hemoglobin concentration is a late-stage indicator of ID, but ZPP/H ratio can detect ID at early stages and can be performed easily at a relatively low cost. Therefore, ZPP/H ratio can serve as a potential screening test for pre-anemic iron deficiency in community pediatric practices. © 2011 The Korean Nutrition Society and the Korean Society of Community Nutrition.
Jung H.,Yonsei University |
Kim D.,Ulsan College |
Kim H.,Yonsei University
Applied Surface Science | Year: 2014
The electrical and chemical properties of low pressure chemical vapor deposition (LP-CVD) Ga doped ZnO (ZnO:Ga) films were systematically investigated using Hall measurement and X-ray photoemission spectroscopy (XPS). Diethylzinc (DEZ) and O2 gas were used as precursor and reactant gas, respectively, and trimethyl gallium (TMGa) was used as a Ga doping source. Initially, the electrical properties of undoped LP-CVD ZnO films depending on the partial pressure of DEZ and O2 ratio were investigated using X-ray diffraction (XRD) by changing partial pressure of DEZ from 40 to 140 mTorr and that of O2 from 40 to 80 mTorr. The resistivity was reduced by Ga doping from 7.24 × 10-3 Ω cm for undoped ZnO to 2.05 × 10-3 Ω cm for Ga doped ZnO at the TMG pressure of 8 mTorr. The change of electric properties of Ga doped ZnO with varying the amount of Ga dopants was systematically discussed based on the structural crystallinity and chemical bonding configuration, analyzed by XRD and XPS, respectively. © 2014 Elsevier B.V. All rights reserved.
Kim W.H.,Ulsan College |
Park E.Y.,Jeonju University
Developmental Medicine and Child Neurology | Year: 2011
Aim: This study examined the causal relation between spasticity, weakness, gross motor function, and functional outcome (expressed as activity limitation) in children with cerebral palsy (CP) and tested models of functional outcome mediated by gross motor function. Method: Eighty-one children (50 males, 31 females) with CP were recruited for this cross-sectional study. Their mean age was 10 years 4 months (SD 1y 9mo). Strength was assessed using the Manual Muscle Test. Spasticity was assessed by the Modified Ashworth Scale. The Gross Motor Function Measure assessed gross motor function. The Functional Skills domain of the Pediatric Evaluation of Disability Inventory assessed functional outcome. Twenty-eight children (34.6%) had quadriplegia, 44 children (54.3%) had diplegia, and nine children (11.1%) had hemiplegia. Children were classified using the Gross Motor Function Classification System with 14 (17.3%) in level I, 9 (11.1%) in level II, 13 (16.0%) in level III, 5 (6.2%) in level IV, and 40 (49.4%) in level V. Results: The proposed path model showed good fit indices. The direct effects were significant between spasticity and gross motor function (β=-0.339), between strength and gross motor function (β=0.447), and between gross motor function and functional outcome (β=0.708). Spasticity had a significant negative indirect effect (β=-0.240) and strength had a significant positive indirect effect (β=0.317) on functional outcome through effects on gross motor function. Interpretation: Activity-based rather than impairment-based intervention is more important for reducing activity limitation in children with CP. The study established a base from which researchers can further develop a causal model between motor impairments and functional outcome. © The Authors. Journal compilation © Mac Keith Press 2010.
Yun K.-S.,Ulsan College
International Journal of Digital Content Technology and its Applications | Year: 2011
This article is a study to look for the module sequence in which the success rate of correction of a Korean spelling corrector is optimized for faulty phrases. The Korean spelling corrector consists of 18 modules, and each module performs unique corrective operations. The issue of optimization of the Korean spelling corrector has similar characteristics as those of Traveling Salesman Problem, coming under NP hard issue. In the issue of optimization of correction rate, unlike TSP, corrective operation of each module affect corrective operations of other modules. To cope with this complex problem, Generic Algorithm which is often utilized to solve optimization problems was used.
Shin C.,Pusan National University |
Hong C.,Ulsan College |
Jeong W.B.,Pusan National University
Journal of Sound and Vibration | Year: 2012
In this study, the active vibration control of clampedclamped beams using the acceleration feedback (AF) controller with a sensor/moment pair actuator configuration is investigated. The sensor/moment pair actuator is a non-collocated configuration, and it is the main source of instability in the direct velocity feedback control system. First, the AF controller with non-collocated sensor/moment pair actuator is numerically implemented for a clampedclamped beam. Then, to characterize and solve the instability problem of the AF controller, a parametric study is conducted. The design parameters (gain and damping ratio) are found to have significant effects on the stability and performance of the AF controller. Next, based on the characteristics of AF controllers, a multimode controllable single-input single-output (SISO) AF controller is considered. Three AF controllers are connected in parallel with the SISO architecture. Each controller is tuned to a different mode (in this case, the second, third and fourth modes). The design parameters are determined on the basis of the parametric study. The multimode AF controller with the selected design parameters has good stability and a high gain margin. Moreover, it reduces the vibration significantly. The vibration levels at the tuned modes are reduced by about 12 dB. Finally, the performance of the AF controller is verified by conducting an experiment. The vibration level of each controlled mode can be reduced by about 12 dB and this value is almost same as the theoretical result. © 2011 Elsevier Ltd All rights reserved.