• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.3
• /
• pp.498-502
• /
• 1998

Sintering phenomena at refractory temperature ranges, from $1400^{\circ}C$ to $1700^{\circ}C$, of the pure spinel $(MgAl_2O_4)$ are analysed and compared to the experimental data from other researchers in terms of grain size(G), density($\rho$), and activation energy(Q). The grain size and relative density relationships for the spinels present very similar trends. They exhibit two distinct regions, an intermediate sintering stage to about the 85~90% density level and what appears to be the final stage sintering region above that transition-density level. The activation energy in terms of the grain size (G) and density ($\rho$) is determined to be 670$\pm$48 (kJ/mol) in this spinel and about 590 kJ/mol for the overall temperature range in other's spinel. These values are close to other published data, 360 to 580 kJ/mol.

• Journal of the Korean Ceramic Society
• /
• v.39 no.3
• /
• pp.294-298
• /
• 2002

Polycrystalline $La_{2.1}Sr_{1.9}Mn_3O_{10}$ with layered perovskite structure have been successfully synthesized and investigated with respect to their thermoelectric, electric and magnetic properties. The large magnetoresistance (MR) effect with $-{\Delta}{\rho}/{\rho}_0$ of ∼120% at 0.85T was observed in a wide temperature range below a cusp temperature in resistivity of about 120K, which is well below the magnetic $T_C$. At high temperature, a singnificant difference between the activation energy deduced from the electrical resistivity and thermoelectric power, a characteristic of small polaron, is observed. All of the experimental data can be well explained on the basis of the small polaron model.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.1
• /
• pp.151-159
• /
• 1998

Elelctrical properties of $BaTiO_3$ were characterized with addition of $Y_2O_3, CaO,SiO_2$ and Mn to develope the composition of PTC thermistor suitable as a current limiting device for automobile motor system. With the addition of 0.2 mol% $Y_{2}O_3$ to $BaTiO_3$, the minimum resistance of 16.5 ${\Omega}{\cdot}$cm was obtained at room temperature. $(Ba_{0.996}Y_{0.004})TiO_3$ exibited a minimum resistance of 50${\Omega}{\cdot}$cm with addition of 1.6 mol% $SiO_2$. The grain size of $(Ba_{0.996}Y_{0.004})TiO_3$ decreased from 34.95 ${\mu}$m to 13.4 ${\mu}$m and thus breakdown voltage could be improved by changing the composition as $(Ba_{0.996}Y_{0.004}Ca_{0.05}) TiO_3$ with substition of 5 mol% Ca into Basites. When 0.04 mol% Mn was added, the optimum PTCR properties could be obtained : the resistivity at room temperature and ${\rho}_{max}/{\rho}_{min}$ were 30~40${\Omega}{\cdot}$cm and $1.5{\times}10^5$ respectively.

• Journal of Korean Society of Transportation
• /
• v.26 no.1
• /
• pp.113-126
• /
• 2008

This research aims to explore the effects of multicollinearity on the reliability and goodness of fit of logit model. To investigate the effects of multicollinearity on the multinominal logit model, numerical experiments are performed. The exploratory variables(attributes of utility functions) which have a certain degree of correlations from (rho=) 0.0 to (rho=) 0.9 are generated and rho-squares and t-statistics which are the indices of goodness of fit and reliability of logit model are traced. From the well designed numerical experiments, following findings are validated : 1) When a new exploratory variable is added, some of rho-squares increase while the others decrease. 2) The higher relations between generic variables lead a logit model worse with respect to goodness of fit. 3) Multicollinearity has a tendency to produce over-evaluated parameters. 4) The reliability of the estimated parameter has a tendency to decrease when the correlations between attributes are high. These results suggest that we have to examine the existence of multicollinearity and perform the proper treatments to diminish multicollinearity when we develop logit model.

• Journal of the Korea Concrete Institute
• /
• v.17 no.1 s.85
• /
• pp.59-68
• /
• 2005

This paper as Part II of the present study deals with the verification of the new truss model that has been conceptually derived and formulated in Part I. Since the model includes the arch coefficient-$\alpha$, the characteristics of this coefficient are examined, and it appears that the coefficient-$\alpha$ is a function of a/d, $\rho$ and $\rho_v$ After transforming the model Into a sectional approach, the formula for predicting the stirrup stress, the longitudinal steel force, and ultimate shear strength are derived. Then, the equations are applied to the test specimens available in literatures, and the predicted values are shown to be in excellent agreement with the experimental results.

• Toxicological Research
• /
• v.25 no.4
• /
• pp.217-224
• /
• 2009

Inhaled inorganic dusts such as coal can cause inflammation and fibrosis in the lung called pneumoconiosis. Chronic inflammatory process in the lung is associated with various cytokines and reactive oxygen species (ROS) formation. Expression of some cytokines mediates inflammation and leads to tissue damage or fibrosis. The aim of the present study was to compare the levels of blood cytokines interleukin (IL)-$1\beta$, IL-6, IL-8, tumor necrosis factor (TNF)-$\alpha$ and monocyte chemoatlractant protein (MCP)-1 among 124 subjects (control 38 and pneumoconiosis patient 86) with category of chest x-ray according to International Labor Organization (ILO) classification. The levels of serum IL-8 (p= 0.003), TNF-$\alpha$ (p=0.026), and MCP-1 (p=0.010) of pneumoconiosis patients were higher than those of subjects with the control. The level of serum IL-8 in the severe group with the small opacity (ILO category II or III) was higher than that of the control (p=0.035). There was significant correlation between the profusion of radiological findings with small opacity and serum levels of IL-$1\beta$(rho=0.218, p<0.05), IL-8 (rho=0.224, p<0.05), TNF-$\alpha$ (rho=0.306, p<0.01), and MCP-1 (rho=0.213, p<0.01). The serum levels of IL-6 and IL-8, however, did not show significant difference between pneumoconiosis patients and the control. There was no significant correlation between serum levels of measured cytokines and other associated variables such as lung function, age, BMI, and exposure period of dusts. Future studies will be required to investigate the cytokine profile that is present in pneumoconiosis patient using lung specific specimens such as bronchoalveolar lavage fluid (BALF), exhaled breath condensate, and lung tissue.

• Journal of Food Hygiene and Safety
• /
• v.16 no.1
• /
• pp.53-60
• /
• 2001

A study has been carried out to estimate the average daily intakes of sorbates, benzoates, and and esters of $\rho$-hydroxybenzoic acid commonly used in Korea. The estimation of daily intakes was based on individual dietary intakes in “National Health and Nutrition Survey in 1998”and the the contents of preservatives from 264 samples. Estimated daily intakes(EDI) of sorbates, benzoates, esters of $\rho$-hydroxybenzoic acid were 0.22, 0.015, and 0.004 mg/kg bw/day, respectively. When assuming the standard body weight of 55 kg for Korean, ratios to acceptable daily intake (ADI) of sorbates, benzoates, and esters of $\rho$-hydroxybenzoic acid were 0.88, 0.30, and 0.04%, respectively.

• The Journal of the Korea Contents Association
• /
• v.13 no.6
• /
• pp.300-308
• /
• 2013

The purpose of this study was to explore the level of anger and social support and to identify factors affecting anger in elderly women. This was a cross-sectional descriptive survey. A convenience sample of 155 elderly women was recruited from two senior welfare centers and three nursing homes in J city. Data were collected from June 15 to July 15, 2010 through interviews using a structured questionnaire. Data were analyzed with descriptive statistics, independent t-test, one-way ANOVA, Pearson's correlation coefficient, and multiple linear regression using the SPSS WIN 18.0 program. The level of social support and anger was 3.73 and 2.72 out of 5, respectively. Anger was statistically significantly different according to type of residence (B=0.21, t=2.42, ${\rho}$=.017), psychiatric medication (B=0.66, t=4.93, ${\rho}$ <.001), physical medication (B=0.41, t=4.22, ${\rho}$ <.001), and evaluation support (B=-0.15, t=-3.00, ${\rho}$=.004), and these accounted 33.0% of anger. Providing proper information and developing social support program would be useful for managing anger of elderly women.

• The Korean Journal of Physiology and Pharmacology
• /
• v.22 no.6
• /
• pp.697-703
• /
• 2018

Myoblast fusion depends on mitochondrial integrity and intracellular $Ca^{2+}$ signaling regulated by various ion channels. In this study, we investigated the ionic currents associated with $[Ca^{2+}]_i$ regulation in normal and mitochondrial DNA-depleted(${\rho}0$) L6 myoblasts. The ${\rho}0$ myoblasts showed impaired myotube formation. The inwardly rectifying $K^+$ current ($I_{Kir}$) was largely decreased with reduced expression of KIR2.1, whereas the voltage-operated $Ca^{2+}$ channel and $Ca^{2+}$-activated $K^+$ channel currents were intact. Sustained inhibition of mitochondrial electron transport by antimycin A treatment (24 h) also decreased the $I_{Kir}$. The ${\rho}0$ myoblasts showed depolarized resting membrane potential and higher basal $[Ca^{2+}]_i$. Our results demonstrated the specific downregulation of $I_{Kir}$ by dysfunctional mitochondria. The resultant depolarization and altered $Ca^{2+}$ signaling might be associated with impaired myoblast fusion in ${\rho}0$ myoblasts.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.9 no.1
• /
• pp.1-7
• /
• 1976

1) The decrease in strength of netting twines at the knot may be regarded to be due mainly to the frictional force acting on the tip of the knot. The knot strength T may be given by $$T=\frac{T_0}{1+{\mu}\frac{s}{\rho}\varrho^{\mu\theta}$$ were $T_0$ is the tensile strength of unknotted netting twines, $\mu$ the coefficient of friction beween two netting twines forming a knot, s the contact length between the tip and the netting twine compressing it, $\rho$ the radius of curvature of the compressing, and $\theta$ the angle at which the compressing rubs with another one in the vicinity of the opposite tip. 2) Knots are arranged in order of strength as follows : the reef knot pulled lengthwise $\risingdotseq$ the trawler knot pulled breadtwise the reef knot pulled breadthwise.