• Journal of the Korean Vacuum Society
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• v.21 no.2
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• pp.86-92
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• 2012

We have studied the effect of speed of deposited atom on morphology evolution during Glancing Angle Deposition (GLAD). Using Kinetic Monte Carlo simulation that incorporate molecular dynamics simulations, we have shown that the rough surface morphology became smoother as the speed of deposited atom is increased. The growth exponent ${\beta}$ change from 0.97 to 0.67 as the speed increase from ${\upsilon}_0$ to $10{\upsilon}_0$ in the case of GLAD. We also examined the effect of speed of deposited atom for the case of chemical vapor deposition (CVD) simulation. Compared to GLAD, the variation in scaling exponent ${\beta}$ is small but the speed of deposited atom also have considerable effect on growth morpholgy in the case of CVD.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.82-94
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• 2017

본 연구에서는 고분자의 해밀토니안을 Q-state Potts-Model로 근사하여, 2, 3차원 형태의 선형 고분자 시스템을 모사하고자 한다. 고분자 외부에서 힘이 작용하고 있는 경우와 아닌 경우에 대하여 전산모사 결과를 바탕으로 고분자의 크기의 경향성을 확인하였다. 그 결과, 흔히 사용되는 Flory's Theory와 달리 고분자의 대표적인 특성인 지수(exponent)에 대하여 더 유동적인 관계식을 얻어낼 수가 있었다. 이를 바탕으로, 고분자에서 흔히 사용되고 있는 scaling argument가 잘 적용되는지를 확인해보았으며, 그 결과 일부의 경우에서만 성립함을 확인할 수 있었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.2
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• pp.303-310
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• 2014

We show improved throughput scaling laws for an ultra-wide band (UWB) ad hoc network, in which n wireless nodes are randomly located. First, we consider the case where a modified hierarchical cooperation (HC) strategy is used. Then, in a dense network of unit area, our result indicates that the derived throughput scaling depends on the path-loss exponent ${\alpha}$ for certain operating regimes due to the power-limited characteristics. It also turns out that the HC protocol is dominant for 2 < ${\alpha}$ < 3 while using the nearest multihop (MH) routing leads to a higher throughput for ${\alpha}{\geq}3$. Second, the impact and benefits of infrastructure support are analyzed, where m base stations (BSs) are regularly placed in UWB networks. In this case, the derived throughput scaling depends on ${\alpha}$ due to the power-limited characteristics for all operating regimes. Furthermore, it is shown that the total throughput scales linearly with parameter m as m is larger than a certain level. Hence, the use of either HC or infrastructure is helpful in improving the throughput of UWB networks in some conditions.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1367-1372
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• 2007

Over the past decade, many computational researches have been performed to investigate quantitative relationships between load-displacement and material properties. But piling-up which causes errors to estimate mechanical material properties remains the most significant unresolved issue in nano-indentation test. This study has estimated quantitative aspects of the effects of material properties, especially work hardening exponent, on piling up/sinking in response of various materials. Using FE Analysis, piling up/sinking in response when material is indented by sharp indenter is investigated to evaluate the effects of material properties. From the FE analysis result, quantitative relationships between piling up/sinking in height and material properties is assessed using dimensional analysis which is used to define scaling variables and universal functions. And nano-indentaion test is performed to verify this relation on various materials. From the result of comparison with prediction from dimensional function and experiment, the work hardening exponent was found to have greater influence on the piling up/sinking in height during the nano-indentation than other material properties, such as elastic modulus and yield stress.

• Journal of the Korean Magnetics Society
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• v.25 no.6
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• pp.180-184
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• 2015

We have investigated the magnetization reversal behavior in ferromagnetic $Co_{0.5}Fe_{0.5}$ alloy films using the magneto-optical Kerr microscope capable of the direct observation of time-resolved domain patterns. Interestingly enough, as the sample thickness increases the magnetization reversal behavior becomes changed from a single domain wall motion to the random nucleations of domains. Also, from the stochastic analysis of the domain jump sizes during the domain wall motion, it was found that the magnetization reversal behavior in the samples shows the critical scaling behavior with the critical exponent of ${\tau}{\sim}1.33$.

• Korean Journal of Biological Psychiatry
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• v.19 no.1
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• pp.65-69
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• 2012

Objectives : Much is still unknown about the neurophysiological mechanisms or dynamics of the sleep onset process. Detrended fluctuation analysis (DFA) is a new tool for the analysis of electroencephalography (EEG) that may give us additional information about electrophysiological changes. The purpose of this study is to analyze long-range correlations of electroencephalographic signals by DFA and their changes in the sleep onset process. Methods : Thirty channel EEG was recorded in 61 healthy subjects (male:female=34:27, age=$27.2{\pm}3.0$ years). The scaling exponents, alpha, were calculated by DFA and compared between four kinds of 30s sleep-wakefulness states such as wakefulness, transition period, early sleep, and late sleep (stage 1). These four states were selected by the distribution of alpha and theta waves in O1 and O2 electrodes. Results : The scaling exponents, alpha, were significantly different in the four states during sleep onset periods, and also varied with the thirty leads. The interaction between the sleep states and the leads was significant. The means (${\pm}$ standard deviation) of alphas for the states were 0.94 (${\pm}0.12$), 0.98 (${\pm}0.12$), 1.10 (${\pm}0.10$), 1.07 (${\pm}0.07$) in the wakefulness, transitional period, early sleep and late sleep state respectively. The mean alpha of anterior fifteen leads was greater than that of posterior fifteen leads, and the two regions showed the different pattern of changes of the alpha during the sleep onset periods. Conclusions : The characteristic findings in the sleep onset period were the increasing pattern of scaling exponent of DFA, and the pattern was slightly but significantly different between fronto-temporal and parieto-occipital regions. It suggests that the long-range correlations of EEG have a tendency of increasing from wakefulness to early sleep, but anterior and posterior brain regions have different dynamical process. DFA, one of the nonlinear analytical methods for time series, may be a useful tool for the investigation of the sleep onset period.

• Journal of the Korean Ceramic Society
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• v.28 no.4
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• pp.329-337
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• 1991

The Ni-MgO composites were prepared by coprecipitation of NiO-MgO solid solutions and their selective reduction in a hydrogen atmosphere. We report on the measurements of both ac conductivity $\sigma$ ($\omega$, f) and dielectric constant $textsc{k}$'($\omega$, f) for the Ni-MgO composites in the frequency range from 10 Hz to 10 MHz at room temperature. The frequency exponents of conductivity and dielectric constant, x and y, are found to be x=0.98$\pm$0.05 and y=0.05$\pm$0.01. These results are in good agreement with a general scaling relation $\chi$-y=1, although these values are different from the theoretical predications. The dielectric constant exponent ($textsc{k}$' f-fc -s) is found to be s=0.62$\pm$0.07 with estimated percolation threshold fc=0.20$\pm$0.02.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.306-306
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• 2018

일반적으로 경향성 분석은 연최대강우량으로부터 산정하고 있으나 본 연구에서는 강우자료 이외의 자료를 이용하여 경향성 분석을 하고자 한다. 이를 위해 국내에서 가장 신뢰할 수 있는 기상청 산하의 강우량으로부터 연최대강우량을 추출하고 월단위인 월별 스케일 지수를 추정하였다. 비교를 위해 경향성 분석 방법 중 가장 널리 사용되고 있는 Mann-Kendall (MK) 분석을 사용하였고, 추가적으로 MK 분석의 단점을 보완할 수 있는 the block bootstrap-based MK (BBS-MK) 분석을 적용하였다. 연최대강우량을 이용한 경향성 분석 결과는 홍수기 기간에 해당하는 7월부터 10월까지의 경향성은 뚜렷하게 나타나지 않았다. 그러나 스케일 지수에 대한 경향성 분석 결과에서는 몇몇 지점에서 감소 또는 증가하는 경향을 보이는 강우 지점들을 확인할 수 있었다. 따라서 경향성 분석을 위해서는 연최대강우량뿐만이 아니라 다양한 인자를 이용한 경향성 분석이 필요함을 확인하였다.

• Journal of the Korean Magnetics Society
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• v.19 no.5
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• pp.176-179
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• 2009

We report a direct observation of Barkhausen avalanches in 50-nm Fe film, using a magneto-optical microscope magnetometer, capable of time-resolved domain observation. The time-resolved domain-evolution patterns exhibit that the occurrence of Barkhausen jump is random with respect to interval, size, and location. From the repetitive measurements more than 1000 times, we found that the probability distribution of Barkhausen jump size follows a power-law distribution and the critical exponent reveals the value of 1.14 $\pm$ 0.03.

• 한국해양학회지
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• v.29 no.4
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• pp.392-401
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• 1994

We examined the temporal characteristics of the oceanic eddy diffusion at 5 coastal regions of Korea by measuring the separation distances of multiple drifters released simultaneously at the same by the GPS and Decca transponder system. The observed variance of separation distance, for the time scales from minutes to hours, is proportional to t/SUP m/ with scaling exponent m between 1.2 and 2.0. The observed Lagrangian trajectories of drifters show fractal characteristics instead of random walk or Brown motion. As an effort toward a development of a realistic model of the oceanic eddy diffusion, we simulated the Lagrangian trajectories of drifters by fractional Brown motion (FBM) model. The observed variances of drifter separations can be generated by the FBM process provided the Hurst exponent is the same as the observed one. We further showed that the observed power law in the variance of drifter separations cannot be simulated with an ordinary Brown motion or random walk process.