• Computers and Concrete
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• v.25 no.2
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• pp.133-144
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• 2020

This paper aims to study vibration characteristics of chiral and zigzag double-walled carbon nanotubes entrenched on Donnell shell model. The Eringen's nonlocal elastic equations are being combined with Donnell shell theory to observe small scale response. Wave propagation is proposed technique to establish field equations of model subjected to four distinct end supports. A nonlocal model has been formulated to explore the frequency spectrum of both chiral and zigzag double-walled CNTs along with diversity of indices and nonlocal parameter. The significance of scale effect in relevance of length-to-diameter and thickness- to- radius ratios are discussed and displayed in detail. The numerical solution based on this nonlocal Donnell shell model can be further used to predict other frequency phenomena of double-walled and multi-walled CNTs.

• Wind and Structures
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• v.4 no.6
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• pp.495-504
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• 2001

With a newly developed multi-force-balance system(MFB), a twin-tower structure was studied for its wind-induced responses. The MFB system allowed the twin towers, which were linked structurally, to be treated as a single structural system with its corresponding modes of vibration involving coupled motions of the two towers. The towers were also studied using a more conventional force balance approach in which each tower was treated as an isolated structure, i.e., as though no structural link existed. Comparison of the results reveals how the wind loads between the towers are redistributed through the structural links and the modal couplings. The results suggest that although the structural links usually have beneficial impacts on wind-induced response, they may also play a negative role if the frequency ratios of pair modes are near 1.0.

• Structural Engineering and Mechanics
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• v.20 no.4
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• pp.435-450
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• 2005

Here, the dynamic instability characteristics of aero-thermo-mechanically stressed functionally graded plates are investigated using finite element procedure. Temperature field is assumed to be a uniform distribution over the plate surface and varied in thickness direction only. Material properties are assumed to be temperature dependent and graded in the thickness direction according to simple power law distribution. For the numerical illustrations, silicon nitride/stainless steel is considered as functionally graded material. The aerodynamic pressure is evaluated based on first-order high Mach number approximation to the linear potential flow theory. The boundaries of the instability region are obtained using the principle of Bolotin's method and are conveniently represented in the non-dimensional excitation frequency-load amplitude plane. The variation dynamic instability width is highlighted considering various parameters such as gradient index, temperature, aerodynamic and mechanical loads, thickness and aspect ratios, and boundary condition.

• Advances in concrete construction
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• v.10 no.6
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• pp.499-507
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• 2020

In current study, utilizing the Kelvin's theory with polynomial, exponential and trigonometric volume fraction laws for functionally graded cylindrical shell vibrations. Effects of different parameters for ratios of length- and height-to-radius and angular speed versus fundamental natural frequencies been determined for two categories of cylindrical shells with clamped-free edge condition. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing length-to-radius ratio. Moreover, on increasing the rotating speed, the backward frequencies increases and forward frequencies decreases. The frequencies are same when the cylinder is stationary. The frequencies increases and decreases on changing the constituent materials. The frequency results are verified with the earlier literature for the applicability of present model.

• Journal of Integrative Natural Science
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• v.13 no.4
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• pp.141-146
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• 2020

The purpose was to examine the factors related to subjective poor oral health in middle school and high school adolescents using data from '2019 Youth Health Behavior Online Survey'. Independent variables related to sociodemographic status and oral health related behaviors were the following:gender, grade, household economy, academic achievement, residence, frequency of daily and after lunch toothbrushing, smocking, alcohol,annual dental visit and preventive treatment. Almost all variables revealed a significant difference in poor oral health among boys and girls in school except resident area of girls and annual dental visit of boys. The odds ratios of subjective poor oral health were as follows:the highest ORs was subjective household economy and the second was frequency of daily toothbrushing in boys. The highest ORs was subjective household economy and the second was subjective academic achievement in girls.

• Advances in concrete construction
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• v.13 no.6
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• pp.451-459
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• 2022

In present study, the nonlocal Flügge shell model based is utilized to investigate the vibration characteristics of armchair and chiral single-walled carbon nanotubes with impact of small-scale effect subjected to two boundary supports. The wave propagation approach is employed to determine eigen frequencies for armchair and chiral tubes. The fundamental frequencies scrutinized with assorted aspect ratios by varying the bending rigidity. The raised in value of nonlocal parameter reduces the corresponding fundamental frequency. It is investigated with higher aspect ratio, the boundary conditions have a momentous influence on vibration of CNT. It is concluded that frequencies would increase by increasing of the bending rigidity. Solutions of the frequency equation have determined by writing in MATLAB coding.

• Steel and Composite Structures
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• v.48 no.3
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• pp.293-303
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• 2023

In this paper, geometrically nonlinear free vibration analysis of Mindlin viscoelastic plates with various geometrical and material properties is studied based on the Von-Karman assumptions. A novel solution is proposed in which the nonlinear frequencies of time-dependent plates are predicted according to the nonlinear frequencies of plates not dependent on time. This method greatly reduces the cost of calculations. The viscoelastic properties obey the Boltzmann integral law with constant bulk modulus. The SHPC meshfree method is employed for spatial discretization. The Laplace transformation is used to convert equations from the time domain to the Laplace domain and vice versa. Solving the nonlinear complex eigenvalue problem in the Laplace-Carson domain numerically, the nonlinear frequencies, the nonlinear viscous damping frequencies, and the nonlinear damping ratios are verified and calculated for rectangular, skew, trapezoidal and circular plates with different boundary conditions and different material properties.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.5
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• pp.41-53
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• 2002

This study was conducted to derive the regional design rainfall by the regional frequency analysis based on the regionalization of the precipitation suggested by the first report of this project. According to the regions and consecutive durations, optimal design rainfalls were derived by the regional frequency analysis for L-moment in the second report of this project. Using the LH-moment ratios and Kolmogorov-Smirnov test, the optimal regional probability distribution was identified to be the Generalized extreme value (GEV) distribution among applied distributions. regional and at-site parameters of the GEV distribution were estimated by the linear combination of the higher probability weighted moments, LH-moment. Design rainfall using LH-moments following the consecutive duration were derived by the regional and at-site analysis using the observed and simulated data resulted from Monte Carlo techniques. Relative root-mean-square error (RRMSE), relative bias (RBIAS) and relative reduction (RR) in RRMSE for the design rainfall were computed and compared in the regional and at-site frequency analysis. Consequently, it was shown that the regional analysis can substantially more reduce the RRMSE, RBIAS and RR in RRMSE than at-site analysis in the prediction of design rainfall. Relative efficiency (RE) for an optimal order of L-moments was also computed by the methods of L, L1, L2, L3 and L4-moments for GEV distribution. It was found that the method of L-moments is more effective than the others for getting optimal design rainfall according to the regions and consecutive durations in the regional frequency analysis. Diagrams for the design rainfall derived by the regional frequency analysis using L-moments were drawn according to the regions and consecutive durations by GIS techniques.

• Journal of the Korean Society of Food Culture
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• v.23 no.6
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• pp.779-792
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• 2008

The consumption of a wide variety of food groups is considered one of the key components of nutritional adequacy. The 2005 Dietary Guidelines for Koreans includes the consumption of a variety of foods from diverse food groups as a component of a normal diet. A survey was conducted to evaluate the relationship between the dietary diversity of food groups and nutrient intake in elderly patients (age 65 and above) at a rural area in Korea (Inje). 296 subjects (111 male and 185 female) were probed in a 3 day 24-recall dietary survey. Subjects were grouped according to food group intake frequency, based on six food groups (grain, meat/fish/legume/egg, vegetable, fat/oil, dairy, fruit). Nutritional quality was evaluated according to the numbers of nutrients under EAR (Estimated Average Requirements), and MAR (mean adequacy ratios). The frequency of elderly subjects consuming a meat/fish/legumes/egg food group less than once per day was 29.4%. The frequency of elderly subjects consuming fat/oil food group less than once per day was 65.8%. The percentage of subjects who did not eat dairy food was 88.8%, and that of subjects who did not eat fruit was 57.5%. A stepwise multiple regression analysis was used to develop models relating nutritional quality to possible food group intake frequency factors. Using the number of nutrients under EAR as a dependent variable, the meat/fish/legume/egg food group intake frequency explained 9.9% of variance, followed by the grain group, fat/oil group, dairy group, and vegetable and fruit group (Model $R^2$=0.260). For mean nutrient adequacy ratio as a dependent variable, the model $R^2$ was 0.326. The results of this study suggest that a highly varied diet in elderly might be associated with better nutritional quality, as assessed by nutrient intake. Accordingly, dietary guidelines should take into consideration nutritional characteristics in order to improve intake from all major food groups and to provide a variety of foods in the diet.

• Journal of Biosystems Engineering
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• v.37 no.3
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• pp.192-200
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• 2012

Purpose: Aerial application of chemicals with an agricultural helicopter allows for precise and timely spraying and reduces working labor and pollution. An attitude controller for an agricultural helicopter would be helpful to aerial application operator. The objectives of this paper are to determine the transfer function models and to estimate the handling qualities of a bare-airframe model helicopter. Methods: Transfer functions of a model unmanned helicopter were estimated by using NAVFIT and DERIVID modules of the $CIFER^{(R)}$ program to the time history data of frequency sweep flight tests. Control inputs of the transfer functions were elevator, aileron, rudder and collective pitch stick positions and the outputs were resulting on-axis movements of the fuselage. Results: Minimum realization of the transfer functions for pitch rate output to elevator control input and roll rate output to aileron control input produced second order transfer functions with undamped natural frequencies around 3.0 Hz and damping ratios of 0.139 and 0.530, respectively. The equivalent time delays of the transfer functions ranged from 0.16 to 0.44 second. Sensitivity analysis of the proposed parameters allowed derivation of minimal realization of the transfer functions. Conclusions: Handling quality of the model helicopter was addressed based on the eigenvalues of the transfer functions, corresponding undamped natural frequencies with damping ratios. The equivalent time delays of the lateral-directional motion ranged from 0.16 to 0.44 second, longer than the 0.1 to 0.15 second requirement for well-controlled typical manned aerial vehicles.