• International Journal of Fluid Machinery and Systems
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• v.10 no.2
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• pp.176-188
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• 2017

The nozzle-flapper valves are widely applied as a pilot stage in aerospace and military system. A subject of the analysis presented in this work is to find out a reasonable range of null clearance between the nozzle and flapper. This paper has presented a numerical flow coefficient simulation. In every design point, a parameterized model is created for flow coefficient simulation and cavitation under different conditions with varying gap width and inlet pressure. Moreover, a new test device has been designed to measure the flow coefficient and for visualized cavitation. The numerical simulation and test results both indicate that cavitation intensity gets fierce initially and shrinks finally as the gap width varies from small to large. From the curve, the flow coefficient mostly has experienced three stages: linear throttle section, transition section and saturation section. The appropriate deflection of flapper is recommended to make the gap width drop into the linear throttle section. The flapper-nozzle null clearance is optionally recommended near the range of $D_N/16$. Finally through simulation it is also concluded that the inlet pressure plays a little role in the influence on the flow coefficient.

• Communications for Statistical Applications and Methods
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• v.2 no.1
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• pp.32-47
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• 1995

The coefficient of determination R/sup 2/, as the proprtation of by explained by a set of independent variavles x/sub 1/, x/sub 2, .cdots., x/sub k/ through a linear regression model, is a very useful tool in linear regression analysis. Suppose R/sup 2//sub yx/ is the coefficient of determination when y is regressed only on x/sub i/ alone. If the independent variables are correlaated, the sum, R/sup 2//sub {yx/sub 1/}/ +R/sup 2//sub {yx/sub 2/}/+.cdots.R/sup 2//sub {yx/sub k/}/, is not equal to R/sup 2/sub {yx/sub 1/x/sub 2/.cots.x/sub k/}/, where R/sup 2//sub {yx/sub 1/x/sub 2/.cdots.x/sub k/}/ is the coefficient of determination when y is regressed simultaneously on x/sub 1/, x/sub 2/,.cdots., x/sub k/. In this paper it is discussed that under what conditions the sum is greater than, equal to, or less than R/sup 2//sub {yx/sub 1/x/sub 2/.cdots.x/sub k/}/, and then the proofs for these conditions are given. Also illustrated examples are provided. In addition, we will discuss about inequality between R/sup 2//sub {yx/sub 1/x/sub 2/.cdots.x/sub k/}/ and the sum, R/sup 2//sub {yx/sub 1/}/+R/sup 2//sub {yx/sub 2/}/+.cdots.+R/sup 2//sub {yx/sub k/}/.

• Magazine of the Korean Society of Agricultural Engineers
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• v.18 no.4
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• pp.4242-4250
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• 1976

The determination of the pre-consolidation load known to have a great effect on the consolidation characteristics of the soil have been researched and discussed in detail by many other researchers. A study was undertaken to investigate and compare the effect of pre-consolidation loads on the coefficient of permeability and the consolidation characterisics of soil through the consolidation test on the three types of soil samples. The results of this study are follows; 1. Large compression index is dependent on initial void ratio of the sample being used and the pressure-void ratio curve shows a curved linear relationship in over-consolidated area but a linear relationship in normally consolidated area.2. Settlement-time curve is S-shaped where the pressure is larger than pre-consolidation load and regardless of over-burden pressure, it is a similar straight line respectively in the secondary consolidation area. 3. Primary consolidation ratio of the sample increases almost linearly with the increase of over-burden pressure but the coefficient of volume compressibility decreases linearly with the increase of it. 4. Time factor of a certain degree of consolidation increases with over-burden pressure but the coefficient of consolidation decreases with it in over-consolidated area. There is a linear relationship between them in normally consolidated area. 5. The void ratio of completion point of primary consolidation decreases linearly with over-burden pressure. 6. The coefficient of permeability of sample decreases linearly with over-burden pressure in normally consolidated area, also it increases linearly with increment of the void ratio of the sample.

• Journal of Astronomy and Space Sciences
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• v.38 no.1
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• pp.23-29
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• 2021

Utilizing a new version of the sunspot number and group sunspot number dataset available since 2015, we have statistically studied the relationship between solar activity parameters describing solar cycles and the slope of the linear relationship between the monthly sunspot numbers and the monthly number of active days in percentage (AD). As an effort of evaluating possibilities in use of the number of active days to predict solar activity, it is worthwhile to revisit and extend the analysis performed earlier. In calculating the Pearson's linear correlation coefficient r, the Spearman's rank-order correlation coefficient rs, and the Kendall's τ coefficient with the rejection probability, we have calculated the slope for a given solar cycle in three different ways, namely, by counting the spotless day that occurred during the ascending phase and the descending phase of the solar cycle separately, and during the period corresponding to solar minimum ± 2 years as well. We have found that the maximum solar sunspot number of a given solar cycle and the duration of the ascending phase are hardly correlated with the slope of a linear function of the monthly sunspot numbers and AD. On the other hand, the duration of a solar cycle is found to be marginally correlated with the slope with the rejection probabilities less than a couple of percent. We have also attempted to compare the relation of the monthly sunspot numbers with AD for the even and odd solar cycles. It is inconclusive, however, that the slopes of the linear relationship between the monthly group numbers and AD are subject to the even and odd solar cycles.

• The Korean Journal of Applied Statistics
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• v.4 no.2
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• pp.117-127
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• 1991

Coefficient of determination $R^2$ is most frequently used descriptive measure in practical use of linear regression analysis. But there have been controversies on defining this measure in the cases of linear regression without the intercept, weighted linear regression and robust linear regression. Several authors such as Kvalseth(1985) and Willet and Singer(1988) proposed many variations of $R^2$ to meet the situations. However, theire measures are not satisfactory due to the lack of a universal principle. In this study, we propose a unfied approach to defining the coefficient of determination $R^2$ using the concept of likelihood distance. This new measure is in good accordance with typical $R^2$ in linear regression and, moreover, can be applied to nonlinear regression models and generalized linear models such as logit and log-linear models.

• Journal of Korea Foundry Society
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• v.17 no.1
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• pp.36-50
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• 1997

Invar-type austenitic cast irons are being used as low thermal expansive materials because of its good low thermal expansion characteristics and castability despite its low hardness. The effects of alloying elements such as Cr, Ti, V, and Mo on hardness and linear thermal expansion coefficient of the invar-type austenitic cast irons were investigated. A combined use of V and Mo addition was found to be the most effective for the improvement of hardness without causing an increase in the thermal expansion coefficient. With a combined addition of 4.6wt%V and 3.8wt%Mo, the hardness increased up to 180HB and the thermal expansion coefficient was kept at a relatively low value of $4.6{\times}10^{-6}/^{\circ}C$ in the temperature range from room to $250^{\circ}C$.

• Steel and Composite Structures
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• v.6 no.5
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• pp.401-415
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• 2006

Based on a non-linear model taking into account flexural-torsional couplings, analytical solutions are derived for lateral buckling of simply supported I beams under some representative load cases. A closed form is established for lateral buckling moments. It accounts for bending distribution, load height application and pre-buckling deflections. Coefficients $C_1$ and $C_2$ affected to these parameters are then derived. Regard to well known linear stability solutions, these coefficients are not constant but depend on another coefficient $k_1$ that represents the pre-buckling deflection effects. In numerical simulations, shell elements are used in mesh process. The buckling loads are achieved from solutions of eigenvalue problem and by bifurcations observed on non linear equilibrium paths. It is proved that both the buckling loads derived from linear stability and eigenvalue problem lead to poor results, especially for I sections with large flanges for which the behaviour is predominated by pre-buckling deflection and the coefficient $k_1$ is large. The proposed solutions are in good agreement with numerical bifurcations observed on non linear equilibrium paths.

• Journal of the Korean Society of Radiology
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• v.16 no.6
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• pp.771-778
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• 2022

The purpose of this study is to present a method of measuring noise by the percentage of effective line attenuation coefficient of water that can be used for quality control of CT image noise using AAPM CT performance phantom in clinical practice. In the CT images obtained by scanning the AAPM CT performance phantom with a 120 kVp CT X-ray beam, the mean CT number was measured for each pin and water in the CT number linearity insert part. The effective energy was determined as the photon energy with the largest correlation coefficient from the correlation coefficients of the linear regression analysis of the measured mean CT number for each pin and water and the linear attenuation coefficient for each photon energy. And for water and acrylic, the contrast scale was calculated as 0.000188 cm^-1 · HU^-1 from the measured mean CT number and effective line attenuation coefficient. Using the calculated contrast scale, the effective line attenuation coefficient of water, and the standard deviation measured in the water of the alignment pin part of the AAPM CT performance phantom, The noise measurement value by the percentage of effective line attenuation coefficient of water obtained 0.31 ~ 0.52% in the range of 100 ~ 300 mAs.

• Journal of Engineering Education Research
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• v.16 no.2
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• pp.24-30
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• 2013

This paper deals with the measurement theory and technique of linear expansion coefficient for solid material using Michelson interferometer. The Michelson interferometer produces interference fringes by splitting a beam of monochromatic light so that one beam strikes a fixed mirror and the other a movable mirror. When the reflected beams are brought back together, an interference pattern results. Precise distance measurements until a quarter of wave length can be made with the Michelson interferometer by moving the mirror and counting the interference fringes which move by a photo diode. This paper represents the application of Michelson interferometer for measuring infinitesimal length system and shows the measurement method of linear expansion coefficients for various materials like copper, aluminum and iron. the results are good agreement with theoretical value within margin of error for each materials.

• Journal of the Korean Statistical Society
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• v.7 no.2
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• pp.95-98
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• 1978

This note deals with the estimations of the variance of a normal distribution $N(\theta,c\theta^2)$ where c, the square of coefficient of variation is assumed to be known. This amounts to the estimation of $\theta^2$. The minimum variance estimator among all unbiased estimators linear in $\bar{x}^2$ and $s^2$ where $\bar{x}$ and $s^2$ are the sample mean and variance, respectively, and the minimum risk estimator in the class of all estimators linear in $\bar{x}^2$ and $s^2$ are obtained. It is shown that the suggested estimators are BAN.