• 천문학회보
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• 제37권1호
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• pp.58.1-58.1
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• 2012

We present a comprehensive re-analysis of stellar photometric variability in the field of open cluster M37, using our new high-precision light curves. This dataset provides a rare opportunity to explore different types of variability between short (-minutes) and long (-one month) time-scales. To investigate the variability properties of -30,000 objects, we developed new algorithms for detecting periodic, aperiodic, and sporadic variability in their light curves. About 7.5% (2,284) of the total sample exhibits convincing variations that are induced by flares, pulsations, eclipses, starspots and, in some cases, unknown causes. The benefits of our new photometry and analysis package are evident. The discovery rate of new variables is increased by 63% in comparison with the existing catalog of variables, and 51 previously identified variables were found to be false positives resulting from time-dependent systematic effects. Based on extended and improved catalog of variables, we will review the basic properties (e.g., periodicity, amplitude, type) of the variability and how different they are for different spectral types and for cluster memberships.

• 충청수학회지
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• 제26권3호
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• pp.625-630
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• 2013

In this paper, we define an extension $f^*:[a,b]{\rightarrow}\mathbb{R}$ of a function $f^*:[a,b]_{\mathbb{T}}{\rightarrow}\mathbb{R}$ for a time scale $\mathbb{T}$ and show that $f$ is Henstock delta integrable on $[a,b]_{\mathbb{T}}$ if and only if $f^*$ is Henstock integrable on $[a, b]$.

• 플랜트 저널
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• 제7권3호
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• pp.48-64
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• 2011

In this work, risks in EPC project for overseas power plant projects are analyzed and risk management methods are suggested to reduce cost and to shorten time. 79% of risks occurred in the engineering phase for S project located in South-East Asia. The impact scales of risks on major project objectives which are cost, time, scope, and quality are analyzed as 3.5, 3.8, 2.7, and 3.7, respectively. The level of impact scales is very similar to each other except the impact scale of scope. The risk management methods suggested in this study have to be applied at the appropriate time to manage risks effectively. After that, risks are managed continuously by monitoring.

• Journal of applied mathematics & informatics
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• 제29권1_2호
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• pp.279-292
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• 2011

In this paper, we consider anti-periodic solutions of the following BAM neural networks with multiple delays on time scales: $$\{{x^\Delta_i(t)=-a_i(t)e_i(x_i(t))+{\sum\limits^m_{j=1}}c_{ji}(t)f_j(y_j(t-{\tau}_{ji}))+I_i(t),\atop y^\Delta_j(t)=-b_j(t)h_j(y_j(t))+{\sum\limits^n_{i=1}}d_{ij}(t)g_i(x_i(t-{\delta}_{ij}))+J_j(t),}\$$ where i = 1, 2, ..., n,j = 1, 2, ..., m. Using some analysis skills and Lyapunov method, some sufficient conditions on the existence and exponential stability of the anti-periodic solution to the above system are established.

• 대한수학회논문집
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• 제26권3호
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• pp.499-513
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• 2011

By using the Riccati transformation technique, we study the oscillation and asymptotic behavior for the third-order nonlinear delay dynamic equations $(c(t)(p(t)x^{\Delta}(t))^{\Delta})^{\Delta}+q(t)f(x({\tau}(t)))=0$ on a time scale T, where c(t), p(t) and q(t) are real-valued positive rd-continuous functions defined on $\mathbb{T}$. We establish some new sufficient conditions which ensure that every solution oscillates or converges to zero. Our oscillation results are essentially new. Some examples are considered to illustrate the main results.

• EDISON SW 활용 경진대회 논문집
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• 제6회(2017년)
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• pp.39-45
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• 2017

We present a Brownian dynamics simulation study on the diffusion of a neutral tracer particle confined in a regularly crosslinked polymer network, especially, when the tracer size is comparable to the mesh size of the network. Polymer networks with different mesh sizes are prepared and compressed to the extent that the total polymer densities become the same. Irrespective of the network mesh size, the tracer diffusion in the networks is slowed down, showing the subdiffusion on intermediate time scales followed by the normal diffusion at long times. However, the confinement effect on the tracer diffusion becomes more significant when network strands are tightly stretched with smaller mesh size. The time scales of dynamic transitions are analyzed in terms of the probability distribution of time-correlated particle displacements.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1307-1316
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• 1998

Engine turbulences obtained by LDV measurement near the compression TDC was analyzed by the classic turbulence theory. Turbulences were quantified by a cycle resolved analysis and processed to reveal integral time scale and length scale. Three different definitions were applied to obtain the turbulence time scales and then compared each others. The classic turbulence theory with the several assumptions for engine application proven to be very efficient for understanding engine turbulence in this study. It was found that the integral length scale is strongly affected and increased by tumble flow.

• 항공우주시스템공학회지
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• 제13권5호
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• pp.9-15
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• 2019

In this paper, dynamic analysis of a nonlinear active vibration absorber is conducted with a time delay acceleration feedback to suppress the vibration of a nonlinear single degree of freedom primary system. The primary system consisting of linear and nonlinear cubic springs, mass, and damper is subjected to the multi-harmonic hard excitation with a parametric excitation. It is proposed to reduce the vibration of the primary system and the absorber by using a lead zirconate titanate (PZT) stack actuator in series with a spring in the absorber which configures as an active vibration absorber. The method of multiple scales (MMS) is used to obtain the approximate solution of the system under the internal resonance, subharmonic, superharmonic, and principal parametric resonance conditions simultaneously. Frequency and time responses of the system are investigated considering a delay in the feedback for the various parameters of the absorber configuration and controlling force.

• Korean Journal of Mathematics
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• 제27권1호
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• pp.119-129
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• 2019

Balance function is one of the joint factors to determine fall in risk theory. It helps to moderate the progression and riskiness of falls for detecting balance and fall risk factors. Nevertheless, the objective measures for balance function require expensive equipment with the assessment of any expertise. We establish the existence and uniqueness of a multi-order fractional differential equations based on ${\psi}$-Hilfer operator on time scales with balance function. This class describes the dynamic of time scales derivative. Our tool is based on the Schauder fixed point theorem. Here, sufficient conditions for Ulam-stability are given.

• 충청수학회지
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• 제25권2호
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• pp.349-357
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• 2012

In this paper we introduce the C-delta integral which generalize the McShane delta integral and investigate some properties of these integrals.