• 천문학회지
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• 제15권1호
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• pp.9-18
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• 1982

To derive the distributions of electron density, temperature and gas-phase metal abundances within the Orion Nebula, we have performed a non-LTE analysis to the radio observations of hydrogen recombination lines and continuum flux over the frequency range from 0.1GHz to 100GHz. We have explicitly included the thermal balance condition in our analysis, hence our derived distributions have their internal consistencies. This enables us to derive the radial distribution of Oxygen and Nitrogen. The gas-phase concentrations of these cooling agents show about the solar values at the very central part of the nebula, then, decrease slowly outward, and finally become about one quarter of the solar values in the outer extended envelope. Such an outward decrease is interpreted as an outward increase of dust concentrations in the Orion.

• Journal of Information Technology Applications and Management
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• 제9권1호
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• pp.27-44
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• 2002

Performance evaluations of database algorithms are usually conducted on a set of queries for a given test database. For more detailed evaluation results, it is often necessary to use different query workloads several times. Each query workload should reflect the querying patterns of the application domain in real world, which are non-uniform in the usage frequencies of attributes in queries of the workload for a given database. It is not trivial to generate many different query workloads manually, while considering non-uniform distributions of attributes'usage frequencies. In this paper we propose a technique to generate non-uniform distributions, which will help construct query workloads more efficiently. The proposed algorithm generates a query-attribute usage distribution based on given constraints on usage frequencies of attributes and qreries. The algorithm first allocates as many attributes to queries as Possible. Then it corrects the distribution by considering attributes and queries which are not within the given frequency constraints. We have implemented and tested the performance of the proposed algorithm, and found that the algorithm works well for various input constraints. The result of this work could be extended to help automatically generate SQL queries for various database performance benchmarking.

• 한국농공학회지
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• 제41권4호
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• pp.25-29
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• 1999

This study was conducted to derive optimal design floods by Gerneralized Extreme Value(GEV) and Weibull-3 distributions for the annual maximum series at ten watersheds along Han,Nagdong, Geum, Yeongsan and Seomjin reiver systems. Adequency for the analysis of flood data used in this study was established by the tests of Independence. Homogeneity , detection of Outlines, L-moments. Design flood sobtaine dby /methods of Moments and L-Moments using different methods for plotting positions in BEV and Weibull-3 distributions were compared by the Relative Mean Errors(RME) and Root MEan Square Errors(RMSE). The result wa found that design floods derived by the L-moments using the other formulas for plotting positions from the viewpoint of Relative Mean Errors and Root Mean Square Errors.

• 한국통신학회논문지
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• 제25권12A호
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• pp.1828-1835
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• 2000

In this paper, we analyzed the other-cell interference characteristics for various non-uniform traffic distributions and their effects on the capacity of multi-cell CDMA system. We consider three different traffic distributions, i.e., linear, exponential and Gaussian traffic distribution with distribution parameters. Changing the distribution parameter, we can obtain the center-focused distributions or uniform distributions for each model. From the results of other-cell interference calculation we can see that the other-cell interference decreases, as the user concentrates on the base station. Also using frequency reuse efficiency indicating the capacity reduction of a multi-cell system when compared to a single cell system, we evaluate the effect of traffic distribution on the reverse link CDMA capacity. For linear case, the capacity of multi-cell system is reduced to 0.637∼0.867 times that of single cell system. On the other hand, for both exponential and Gaussian cases, the capacity under a multi-cell environment is equal to 70∼100% of that under a single cell. Therefore, we conclude that the average capacity of multi-cell CDMA system are increased when users are likely to be at near the cell base station due to reduced total other-cell interference and decreased when users exist at near the cell edge regardless of traffic distribution models.

• 대한기계학회논문집B
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• 제32권9호
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• pp.683-694
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• 2008

The performance and durability of Polymer Electrolyte Fuel Cells (PEFCs) are strongly influenced by the uniformity of current density, temperature, species distributions inside a cell In order to obtain uniform distributions in them, the optimal design of flowfield must be a key factor. In this paper, the numerical study of land/channel flowfield optimizations is performed, using a multi-dimensional, multi-phase, non-isothermal PEFC model. Numerical simulations reveal more uniform current density and HFR(High Frequency Resistance) distributions and thus better PEFC performance with narrower land/channel width where the less severe oxygen depletion effect near the land region and more uniform contact resistance variation along the in-plane direction are achieved. The present study elucidates detailed effects of land/channel width and assist in identifying optimal flow-field design strategies for the operation of PEFCs.

• Structural Engineering and Mechanics
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• 제71권5호
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• pp.485-502
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• 2019

In this research, the nonlinear static, buckling and vibration analysis of viscoelastic micro-composite beam reinforced by various distributions of boron nitrid nanotube (BNNT) with initial geometrical imperfection by modified strain gradient theory (MSGT) using finite element method (FEM) are presented. The various distributions of BNNT are considered as UD, FG-V and FG-X and also, the extended rule of mixture is used to estimate the properties of micro-composite beam. The components of stress are dependent to mechanical, electrical and thermal terms and calculated using piezoelasticity theory. Then, the kinematic equations of micro-composite beam using the displacement fields are obtained. The governing equations of motion are derived using energy method and Hamilton's principle based on MSGT. Then, using FEM, these equations are solved. Finally the effects of different parameters such as initial geometrical imperfection, various distributions of nanotube, damping coefficient, piezoelectric constant, slenderness ratio, Winkler spring constant, Pasternak shear constant, various boundary conditions and three material length scale parameters on the behavior of nonlinear static, buckling and vibration of micro-composite beam are investigated. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of micro-composite beam increases and thus the non-dimensional nonlinear frequency of the micro structure reduces gradually.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.506-512
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• 1997

Ultrasonic knives have been successfully used for the surgery of many medical fields. However, the conventional ultrasonic knives for surgical operation cannot be controlled its resonant frequency. So if the material to cut has different characteristic impedance then different ultrasonic knife will be needed. Because the optimum driving frequency of ultrasonic knife is different by characteristic impedance of material. In this work, using a frequency variable ultrasonic transducer made of multi-layered PZT vibrator, a frequency controllable ultrasonic knife will be suggested. The design and computation principles will be also derived. For this work, firstly, the characteristics of this ultrasonic knife will be analyzed by transmission line model equivalent circuit, and the free admittance characteristics and vibrational velocity distributions will be obtained. Secondly, we will design and make the frequency controllable electrical oscillator for driving this ultrasonic knife.

• 한국해안·해양공학회논문집
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• 제28권3호
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• pp.171-176
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• 2016

기온과 수온의 분포형태는 발생빈도의 양상을 결정하는 기본적이고 필수적인 정보이다. 또한 기후변화에 의한 기온과 수온의 장기변화 양상 파악에 유용하다. 기온과 수온의 전형적인 분포형태는 다수의 첨두(mode)를 가지는 형태로 일반적으로 널리 사용되는 정규분포로 표현하기에는 한계가 있다. 본 연구에서는 Gaussian 혼합함수와 Kernel 분포함수를 보다 기온과 수온의 보다 적합한 분포함수 형태로 제안한다. 제안된 분포함수를 우리나라 연안 기온과 수온자료를 이용하여 추정-평가한 결과, 관측 자료의 분포는 꼬리 영역에서 크게 차이를 보이고 있는 것으로 파악되었다. 높은 수온영역과 낮은 기온 영역에서 꼬리 영역이 길게 나타나고 있다. 또한 본 연구에서 제안한 분포함수 추정 및 비교는 기온과 수온의 상호 변동관계 및 장기적인 변동양상을 파악할 수 있다. 그러나 평균 기온 및 수온 그리고 정규분포 함수 형태로는 이러한 변화 양상의 파악은 크게 제한되고 있다.

• Ocean Systems Engineering
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• 제9권3호
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• pp.287-328
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• 2019

Comprehensive understanding of the flood risk assessments via frequency analysis often demands multivariate designs under the different notations of return periods. Flood is a tri-variate random consequence, which often pointing the unreliability of univariate return period and demands for the joint dependency construction by accounting its multiple intercorrelated flood vectors i.e., flood peak, volume & durations. Selecting the most parsimonious probability functions for demonstrating univariate flood marginals distributions is often a mandatory pre-processing desire before the establishment of joint dependency. Especially under copulas methodology, which often allows the practitioner to model univariate marginals separately from their joint constructions. Parametric density approximations often hypothesized that the random samples must follow some specific or predefine probability density functions, which usually defines different estimates especially in the tail of distributions. Concentrations of the upper tail often seem interesting during flood modelling also, no evidence exhibited in favours of any fixed distributions, which often characterized through the trial and error procedure based on goodness-of-fit measures. On another side, model performance evaluations and selections of best-fitted distributions often demand precise investigations via comparing the relative sample reproducing capabilities otherwise, inconsistencies might reveal uncertainty. Also, the strength & weakness of different fitness statistics usually vary and having different extent during demonstrating gaps and dispensary among fitted distributions. In this literature, selections efforts of marginal distributions of flood variables are incorporated by employing an interactive set of parametric functions for event-based (or Block annual maxima) samples over the 50-years continuously-distributed streamflow characteristics for the Kelantan River basin at Gulliemard Bridge, Malaysia. Model fitness criteria are examined based on the degree of agreements between cumulative empirical and theoretical probabilities. Both the analytical as well as graphically visual inspections are undertaken to strengthen much decisive evidence in favour of best-fitted probability density.

• 한국수자원학회논문집
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• 제39권10호
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• pp.891-904
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• 2006

합리적인 수공구조물의 설계를 위해서 확률강우량의 산정은 필수적이며, 확률 강우량을 산정하는 기법은 크게 지점빈도해석과 지역빈도해석으로 구분 지을 수 있다 이 중에서 지역빈도해석은 지점의 부족한 강우자료를 보완하기 위해서 L-모멘트로 확률분포형의 매개변수를 추정하고, 강우 계열의 동질성이 검정된 자료를 빈도분석하여 확률 강우량을 결정하는 기법이다. 이와 같은 지역빈도해석 기법은 매개변수를 선형조합하여 확률분포형의 종류와 크기 및 형상을 결정하여 확률 강우량을 산정하게 된다. 여기서 각 지점별 강우 자료들이 동질성 검정을 통과하였다 하더라도 지점별로 최적의 분포형이 다를 수 있으나, 부족한 강우자료를 보완하기 위해서 동일한 분포형을 따르는 것으로 가정하고 빈도해석을 수행하게 된다. 그러므로 지역빈도해석기법은 확률 분포형을 가정하고 강우자료를 적용하는 과정에서 기존에 매개변수적 빈도해석의 약점을 갖게 된다 따라서 본 연구에서는 변동핵밀도 함수를 동질성이 확보된 강우자료에 적용하여 빈도해석을 수행함으로써 기존의 빈도해석이 가지는 약점을 극복하고자 하였다. 본 연구에서는 기상청에서 관리하는 16개 강우관측소의 강우자료를 수집하여 매년최대 연강우량 계열을 구성해 지점빈도해석과 지역빈도해석을 수행하였다. 지점빈도해석은 매개변수적 기법과 비매개변수적 기법을 모두 적용하였으며, 지역빈도채석은 Index Flood 기법과 L-모멘트 기법을 적용하였다. 또한 변동핵밀도함수를 지역빈도해석에 적용하였으며, 각 기법별로 산정된 확률강우량을 비교 분석하였다.