Effects of sulphate ($SO_{4}^{2-}$), nitrate ($NO_{3}^{-}$) and bicarbonate ($HCO_{3}^{-}$) ion additives on the morphological change of the pits formed on Inconel alloy 600 were investigated in 0.5M NaCl solution as functions of anion concentration and solution temperature using a potentiodynamic polarization experiment, a potentiostatic current transient technique, optical microscopy (OM) and image analysis method. As solution temperature increased, the value of pitting potential shifted to more negative values and the value of current density increased at any given anodic potential due to the decrease in the oxide film passivity. Potentiostatic current transients obtained above the pitting potential revealed that the anion addition to NaCl solution impeded the pitting process due to the competitive adsorption with $Cl^{-}$ ions. On the other hand, at 60 ˚ and 100 ℃, the addition of $SO_{4}^{2-}$ ions facilitates pitting corrosion. As a result, it is inferred that the addition of anions to NaCl solution has a inhibiting effect on pitting corrosion, while pitting corrosion is accelerated by $SO_{4}^{2-}$ ions in NaCl solution at elevated solution temperature. In addition, from the fact of the increase in the total charge consumed during the pitting process with rising solution temperature, it is realized that increasing solution temperature causes more serious pitting phenomena. After OM observation of the pits, the fractal dimension $D_{f}$ of the pits was determined as functions of solution temperature and anion concentration using perimeter area method. The value of $D_{f}$ of the pits increased with increasing solution temperature. This is caused by the increase in the ratio of perimeter to area at higher solution temperature, indicating the formation of pits with micro-branched shape. It was observed that the anion addition to NaCl solution reduced the value of $D_{f}$ of the pits. This means that anion additives diminish the ratio of pit perimeter to pit area due to the decrease in local attack on the specimen by competitive adsorption. In contrast, at 60 $^\circ$ and 100 $^\circ$C, the addition of $SO_{4}^{2-}$ ions raised the value of $D_{f}$, implying the increase in the local attack in the pits at elevated solution temperature. In addition, the degree of local attack on the specimen is discussed in terms of the change in mobility of anion additives and that in solubility of salt film formed on the specimen with respect to solution temperature.
전변동 크기(Total Variation norm)는 구하고자 하는 해가 연속함수가 아니라도 해의 가장자리 부분을 회복하기가 용이하기 때문에, Tikhonov 정규화를 통한 손상된 영상의 복원 문제를 푸는데 적합하다. 전변동(Total Variation)을 이용하여 noise를 제거하는 방법은 비선형 연립방정식으로 표현이 된다. 이 연립방정식을 풀기 위해 이 논문에서는 Newton 방법과 일반화된 Newton 방법을 사용한다.
