• Journal of the Korean Data and Information Science Society
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• 제22권6호
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• pp.1217-1222
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• 2011

In this paper, we show that any circular density can be closely approximated by an exponential family of distributions. Therefore we propose an exponential family of distributions as a new family of circular distributions, which is absolutely suitable to model any shape of circular distributions. In this family of circular distributions, the trigonometric moments are found to be the uniformly minimum variance unbiased estimators (UMVUEs) of the parameters of distribution. Simulation result and goodness of fit test using an asymmetric real data set show usefulness of the novel circular distribution.

• Journal of the Korean Data and Information Science Society
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• 제23권4호
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• pp.797-805
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• 2012

Many circular distributions are known to be not only asymmetric but also bimodal. Hidden truncation method of generating asymmetric distribution is applied to a bivariate circular distribution to generate an asymmetric circular distribution. While many other existing asymmetric circular distributions can only model an asymmetric data, this new circular model has great flexibility in terms of asymmetry and bi-modality. Some properties of the new model, such as the trigonometric moment generating function, and asymptotic inference about the truncation parameter are presented. Simulation and real data examples are provided at the end to demonstrate the utility of the novel distribution.

• Communications for Statistical Applications and Methods
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• 제19권4호
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• pp.527-536
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• 2012

In this paper we analyze the effect of circular variables such as wind direction, time and month on the ozone level. In particular, we examined the effect of wind direction by exploratory data analysis methods and provide the correlation and regression analyzes in the cases including all circular explanatory variables. In the analysis, we convert time and month variables to circular variables and analyze the effect of these variables on regression analysis; in addition, we also consider circular-circular regression. We used weather condition and air pollution data collected from Dongdaemoon district of Seoul in 2007.

• 한국공작기계학회논문집
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• 제13권5호
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• pp.1-6
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• 2004

Measurements of circular motion accuracy of NC lathe have achieved with ball bar systems proposed by Bryan, but the ball bar systems have ifluenced on the measuring data by way of the accuracy of the balls and the contacts of balls and bar seats. Therefore in this study, error data during of circular motion of ATC(Automatic Tool Changer) of NC lathe will be acquired by reading zx plane coordinates using two optical linear scales. Two optical linear scales of measuring unit are fixed on z-x plane of NC lathe, and the moving part is fixed to ATC and then is made to receive data of coordinates of the ATC at constant time intervals using tick pulses comming out from computer. And then, error data files of radial direction of circular motion are calculated with the data read, and the aspect of circular motion are modeled to plots, and are analysed by means of statistical treatments of circularity, means, standard deviations etc.

• Journal of the Korean Data and Information Science Society
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• 제22권5호
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• pp.961-966
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• 2011

Circular variables are those that have a period in its range. Their examples include direction of animal migration, and time of drug administration, just to mention a few. Statistical analysis of circular variables is quite different from that of linear variable due to its periodic nature. In this paper, the author proposes new circular regression models using geodesic lines on the surface of the sample space of the response and the predictor variables.

• 응용통계연구
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• 제25권4호
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• pp.651-659
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• 2012

In this paper we developed a statistical model for circular data with noises. In this case, model fitting by single circular model has a lack-of-fit problem. To overcome this problem, we consider some mixture models that include circular uniform distribution and apply an EM algorithm to estimate the parameters. Both von Mises and Wrapped skew normal distributions are considered in this paper. Simulation studies are executed to assess the suggested EM algorithms. Finally, we applied the suggested method to fit 2008 EHFRS(Epidemic Hemorrhagic Fever with Renal Syndrome) data provided by the KCDC(Korea Centers for Disease Control and Prevention).

• Journal of Welding and Joining
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• 제21권4호
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• pp.87-91
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• 2003

Effects of the circular and non-circular pad shapes on self-alignment in BGA soldering are predicted using Surface Evolver, and the calculated results are compared with experimental data. While the pad shape has minor effects on self-alignment in the vertical direction, self-alignment in the lateral direction depends on the pad direction and length ratio of the non-circular pad. Larger restoring force is obtained in the minor-axis direction than the major-axis direction, which suggests a possibility of reducing misalignment in the specific direction. The restoring force of the circular pad is between those of the non-circular pad in the major and minor-axis directions. The calculated results of Surface Evolver show reasonably good agreements with experimental data using the shear loading system.

• Journal of the Korean Data and Information Science Society
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• 제21권5호
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• pp.863-871
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• 2010

지금까지 원형자료의 적합에 대한 연구는 주로 von Mises, 겹친왜정규 분포를 비롯하여 주로 완만한 봉우리를 가지는 대칭 및 비대칭의 경우에 대해 수행되어 왔다. 본 논문에서는 뾰족한 봉우리를 가지며 정점을 중심으로 비대칭의 경향이 심한 첨봉형의 비대칭 원형자료에 대한 적합을 다루었다. 최근 Jammalamadaka와 Kozubowski (2003)가 소개한 겹친라플라스 분포와 그의 혼합분포를 중심으로 단봉형 및 다봉형의 원형자료에 대한 모형화 과정을 다루었다. 특히 혼합분포의 모수추정을 위해 EM 알고리즘을 사용하였으며, 모의실험을 통해 그 정확도를 확인하였다.

• International Journal of Fluid Machinery and Systems
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• 제10권1호
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• pp.63-75
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• 2017

Many axial fans have circular arc blades with constant thickness. It is still a challenging task to calculate their performance, i.e. to predict how large their pressure rise and pressure losses are. For this task a need for cascade data exists. Therefore, the designer needs a method which works quickly for design purposes. In the present contribution a design method for such cascades consisting of circular arc blades with constant thickness is described. It is based on a singularity method which is combined with a CFD-data-based flow loss model. The flow loss model uses CFD-data to predict the total pressure losses. An interpolation method for the CFD-data are applied and described in detail. Data of measurements are used to validate the CFD-data and parameter variations are conducted. The parameter variations include the variation of the camber angle, pitch chord ratio and the Reynolds number. Additionally, flow patterns of two dimensional cascades consisting of circular arc blades with constant thickness are shown.

• Communications for Statistical Applications and Methods
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• 제14권3호
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• pp.517-530
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• 2007

We studied a modelling process for unimodal and multimodal circular data by using von Mises and its mixture distribution. In particular we suggested EM algorithm to find ML estimates of the mixture model. Simulation results showed the suggested methods are very accurate. Applications to two kinds of real data sets are also included.