• Tribology and Lubricants
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• 제23권6호
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• pp.278-282
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• 2007

Friction characteristics of a low-steel friction material were examined to investigate creep groan phenomena. The amount of three ingredients (steel fiber, $ZrSiO_4$, cashew) were changed to produce test specimens using a constrained mixture design. Tribological properties of the friction material specimens were obtained by using a 1/5 scale dynamometer. Results showed that the amount of three different ingredients strongly affected the level of friction coefficient and the difference between the static friction coefficient and the kinetic friction coefficient $({\Delta}{\mu}).\;ZrSiO_4$ and steel fiber tended to increase the average friction coefficient and aggravated the stick-slip phenomena suggesting high creep groan propensity. On the other hand, cashew tended to decrease average friction coefficient and ${\Delta}{\mu}$.

• 천문학회보
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• 제35권2호
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• pp.51.2-51.2
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• 2010

We have investigated 63 intense geomagnetic storms (Dst $\leq$ -100 nT) that occurred from 1998 to 2006. Using these events, we compared Dst forecast models: Burton et al. (1975), Fenrich and Luhmann (1998), O'Brien and McPherron (2000a), Wang et al. (2003), and Temerin and Li (2002, 2006) models. For comparison, we examined a linear correlation coefficient, RMS error, the difference of Dst minimum value (${\Delta}$peak), and the difference of Dst minimum time (${\Delta}$peak_time) between the observed and the predicted during geomagnetic storm period. As a result, we found that Temerin and Li model is mostly much better than other models. The model produces a linear correlation coefficient of 0.94, a RMS (Root Mean Square) error of 14.89 nT, a MAD (Mean Absolute Deviation) of ${\Delta}$peak of 12.54 nT, and a MAD of ${\Delta}$peak_time of 1.44 hour. Also, we classified storm events as five groups according to their interplanetary origin structures: 17 sMC events (IP shock and MC), 18 SH events (sheath field), 10 SH+MC events (Sheath field and MC), 8 CIR events, and 10 nonMC events (non-MC type ICME). We found that Temerin and Li model is also best for all structures. The RMS error and MAD of ${\Delta}$peak of their model depend on their associated interplanetary structures like; 19.1 nT and 16.7 nT for sMC, 12.5 nT and 7.8 nT for SH, 17.6 nT and 15.8 nT for SH+MC, 11.8 nT and 8.6 nT for CIR, and 11.9 nT and 10.5 nT for nonMC. One interesting thing is that MC-associated storms produce larger errors than the other-associated ones. Especially, the values of RMS error and MAD of ${\Delta}$peak of SH structure of Temerin and Li model are very lower than those of other models.

• 대한화학회지
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• 제43권4호
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• pp.456-460
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• 1999

메탄올 용매내에서 치환 피리딘류($3-CH_3,\;4-CH_3,\;H,\;3-Cl,\;3,4-(CH_3)_2,\;3,5-(CH_3)_2$)와 1-adamantyl fluoroformate의 반응속도를 여러 온도와 농도 조건에서 전도도 방법으로 측정하였다. 이들 반응속도상수로부터 활성화 파라미터(${\Delta}H^{\neq},\;{\Delta}S^{\neq}$)와 Hammett 반응상수(${\rho}$) 및 Bronsted 상관 계수(${\beta}$)를 구하였다. 이 때 ${\Delta}S^{\neq}$는 큰 음의 값을, ${\Delta}H^{\neq}$는 작은 양의 값을 얻었으며, 반응상수 ${\rho}$값과 상관 계수 ${\beta}$값은 각각 -4.15와 0.63이었다. 이러한 결과로부터 본 반응은 협동 치환 메카니즘으로 진행됨을 알 수 있었다.

• 한국산업보건학회지
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• 제23권2호
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• pp.65-74
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• 2013

Objectives: This study attempted to develop a method to measure ultra-trace lead concentrations in plasma using Inductively Coupled Plasma Mass Spectrometry(ICP-MS) and to test whether plasma lead can be used as a biomarker for the biological monitoring of exposure to lead. Methods: Lead concentrations in 160 plasma samples of field workers and 42 plasma samples from the control group were measured by ICP-MS. Blood zinc protophorphyrin(ZPP) concentrations and urinary ${\delta}$-aminolevulinic acid${\delta}-ALA$) were measured for correlation analysis with plasma lead. Results: The mean lead level in the plasma of the workers exposed to lead at work were 786.1 ng/L. Plasma lead levels were not correlated with blood ZPP or urinary ${\delta}-ALA$ concentrations. Otherwise, plasma lead levels showed a good correlation coefficient of 0.400 with blood lead levels, and their correlation coefficient had a better value of 0.552 for the non-smoking and drinking group. In the general population group which was not exposed to lead in the workplace and was considered the control group, the mean concentration of plasma lead was 123.1 ng/L. The plasma lead levels for the general population group showed a good correlation coefficient of 0.520 with blood ZPP and urinary ${\delta}-ALA$ concentrations.

• 한국재료학회지
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• 제16권8호
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• pp.466-472
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• 2006

The electrical, dielectric properties, and its stability of ZPCCL-based varistors were investigated for different sintering temperatures in the range of $1230{\sim}1300^{\circ}C$. As the sintering temperatures increased, the varistor voltage decreased in the range of $777.9{\sim}108$ V/mm, the nonlinear coefficient decreased in the range of $77.9{\sim}7.1$, and the leakage current increased in the range of $0.3{\sim}50.6\;{\mu}A$. The stability of electrical and dielectric characteristics was obtained from sintering temperature of $1260^{\circ}C$. the varistors sintered at $1260^{\circ}C$ marked the high electrical and dielectric stability, with $%{\Delta}{V_{1mA}=+1.9%,\;%{\Delta}{\alpha}=-10.6%,\;%{\Delta}I_L=+20%\;and\;%{\Delta}tan\;{\delta}=+9.9%$ for DC accelerated aging stress state of $0.95V_{1mA}/150^{\circ}C$/24 h.

• 대한화학회지
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• 제7권4호
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• pp.264-270
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• 1963

前報에서 誘導한 置換基效果 一般關係式은 溶媒組成에 따르는 常數, Y를 potential energy 項에 代置함으로서 solvolysis 反應에 適用할 수가 있다. 新方程式, $\Delta{\Delta}H^\neq=a'Y+b\Delta{\Delta}S^\neq$, 의 適用性은 文獻에 報告된 35個反應에 對한 直線關係를 調査해 봄으로서 檢討하였다. 結果로 平均 相關係數 0.977을 얻었고, 따라서 이 方程式이 solvolysis反應에 一般的으로 適用됨을 밝혔고, 또 Grunwald-Winstein의 式이 지니는 몇몇 難點을 解決할 수가 있음을 알 수 있었다. enthalypy-entopy 直線效果는 外部 enthalpy와 外部 entropy에 限한 것이며, 嚴格히 말해서 外部 enthalpy entropy 直線效果임을 强調하였다.

• 한국환경과학회지
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• 제11권12호
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• pp.1195-1204
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• 2002

We calculated dose rate using radiative transfer equations to consider radiative processes distinctly. The dose rate at Pohang(36°02'N, 129°23'E) was calculated using measured ozone and meteorological data and two-stream approximations(quadrature, Eddington, delta Eddington, PIFM(practical improved flux method), discrete ordinate, delta discrete ordinate) are used in solving equation. The purpose of this study is to determine the most compatible radiative transfer approximation for simulating the radiative and photochemical processes of atmosphere through comparision between calculated and measured values. Dose rate of the biologically effective irradiance in the region 0.28-0.32 U m showed the highest value when quadrature and Eddington was used and lower value on condition that delta scaling was applied. Correlation coefficient between dose rate at surface using radiation transfer equation and measured UV-B at Pohang was 0.78, 0.79 and 0.81 when delta Eddington, PIFM and delta discrete ordinate were used. Also, in case of above approximations were used, MBE(Mean Bias Error) was within -0.3MED/30min and RMBE(Relative Mean Bias Error) was below 10% between 1200 LST and 1400 LST Approximations which are compatible in estimating radiative process are delta Eddington, PIFM and delta discrete ordinate. Especially, in case that radiative process is considered more detail, delta discrete ordinate increased the number of stream is proper.

• Korean Journal of Mathematics
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• 제15권2호
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• pp.171-176
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• 2007

The purpose of this paper is to study harmonic univalent mappings defined in ${\Delta}=\{z:{\mid}z{\mid}>1\}$ that map ${\infty}$ to ${\infty}$. Some coefficient estimates are obtained in a normalized class of mappings.

• Journal of Biosystems Engineering
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• 제21권4호
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• pp.436-448
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• 1996

An earth tube soil air heat exchange system was designed, installed and operated as a single pass heat exchanger to utilize the geothermal energy as an natural energy source. This study was undertaken to investigate the potential of the heating and cooling, energy gain, heat exchange efficiency and coefficient of performance of the system. The system consisted of 30m in length and 30cm in diameter polyethylene pipes buried 2m deep in soil. Maximum heating and cooling performance were 2.51㎾ and 1.26㎾ at the air mass rate of 21cmm. Energy gain and coefficient of performance were the function of temperature difference between outside air and soil temperature. They were expressed as Q=0.33$ imes$$Delta T_{max}$+0.134(㎾) for energy gain and COP=0.44$ imes$$Delta T_{max}$+0.178 for coefficient of performance with correlation factor of 0.95. The mean of heat exchange efficiencies was 85.6%.

• Geomechanics and Engineering
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• 제11권4호
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• pp.515-530
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• 2016

In this paper, five different quantitative parameters were proposed for the characterization of the primary roughness which is the component of surface morphology that prevails during large strike-slip faults of more than 50 m. These parameters are mostly the anisotropic properties of rock surface morphology at various scales: (i) coefficient ($k_a$) and degree (${\delta}_a$) of apparent structural anisotropy of surface; (ii) coefficient ($k_r$) and degree (${\delta}_r$) of real structural anisotropy of surface; (iii) surface anisotropy function P(${\varphi}$); and (iv) degree of surface waviness ($W_s$). The coefficient and degree of apparent structural anisotropy allow qualifying the anisotropy/isotropy of a discontinuity according to a classification into four classes: anisotropic, moderately anisotropic/isotropic and isotropic. The coefficient and degree of real structural anisotropy of surface captures directly the actual surface anisotropy using geostatistical method. The anisotropy function predicts directional geometric properties of a surface of discontinuity from measurements in two orthogonal directions. These predicted data may subsequently be used to highlight the anisotropy/isotropy of the surface (radar plot). The degree of surface waviness allows qualifying the undulation of anisotropic surfaces. The proposed quantitative parameters allows their application at both lab and field scales.