Micro-Raman spectroscopy was used to characterize the rust formed on 1008 carbon steel exposed to marine test sites in Hawaii. Besides lepidocrocite in the outer rust layers and goethite in the inner rust layers, akaganeite was detected on all samples due to the presence of Cl − and increased in quantity in the rust layer with increasing Cl − deposition rate. The presence of Cl − did not affect the corrosion rate of carbon steel when the Cl − deposition rate was lower than a threshold of approximately 75 mg/m 2 /day, but significantly increased the corrosion rate when the Cl − deposition rate was higher than the threshold. This is likely due to akaganeite being a sink for Cl − by incorporating it into its tunnel structure when salt deposition is below a certain level. Once the akaganeite is saturated with Cl − and the akaganeite cannot take up any more Cl − , free Cl − can be available to accelerate corrosion at anodic sites.

Corrosion initiation on steel from predeposited NaCl particles was observed in situ using an optical microscope. Corrosion did not initiate from small droplets (D,y45 mm) formed by the deliquescence of predeposited NaCl particles upon exposing to high humidity (RH.80%). Corrosion occurred under larger NaCl droplets and was accompanied by the formation of secondary droplets outside of the perimeter of the initial droplets. Sometimes, corrosion that initiated from the large NaCl droplets propagated in the form of filiform corrosion. Elemental mapping using energy dispersive X-ray analysis showed that Cl was concentrated at the filament tip, while Na migrated to the outside region of the secondary droplets. Under large NaCl droplets, there was evidence that corrosion initiated from slag based inclusions.

In this paper, we propose a region-of-interest (ROI) based HEVC coding approach for conversational videos, with a novel hierarchical perception model of face (HP model), to improve the perceived visual quality of state-of-the-art HEVC standard. In contrast to the previous ROI-based video coding approaches, this novel HP model allows the unequal importance of facial features (e.g., the eyes and mouth) within the facial region, by generating a pixel-wise weight map. Benefitting from such a perception model, the adaptive coding tree unit (CTU) partition structure is developed to alleviate the encoding complexity of HEVC, without any degradation of the visual quality in facial regions, especially in the regions of facial features. Subsequently, for the rate control in HEVC a weight-based unified rate-quantization (URQ) scheme, instead of the conventional pixel-based URQ scheme, is proposed to adaptively adjust the value of quantization parameter (QP). Such an adaptive adjustment of QPs is capable of allocating more bits to the face/facial features with respect to our HP model, and as a result, the visual quality of face, in particular facial features, can be enhanced for conversational HEVC coding. Finally, the experimental results show that the perceived visual quality of our approach is greatly improved, with even less encoding time, for conversational video coding on the HEVC platform.

The study of NaCl particle-induced atmospheric corrosion is facilitated by in situ Raman spectroscopic analysis through real time identification of corrosion products. Droplet formation on carbon steel by the deliquescence of pre-deposited NaCl particles that were exposed to high relative humidity (RH) (>80%), and corrosion initiation under the droplets were observed using an optical microscope. Pitting initiated within several minutes under the NaCl droplets. In situ and ex situ Raman spectra from the various rust species that formed during the corrosion process show that green rust (GR) formed close to the corrosion pit (i.e., anodic site) while lepidocrocite (γ-FeOOH) clusters precipitated outside of the GR region. A small amount of magnetite (Fe3O4) was also detected, mostly in the transitional region from GR to lepidocrocite. Upon exposure to an ambient atmosphere, GR transformed to lepidocrocite. This study confirms that the initial rust formed in NaCl particle-induced marine atmospheric corrosion of carbon steel is GR and lepidocrocite. While revealing the initiation mechanisms of NaCl particle-induced marine atmospheric corrosion of carbon steel, this study also provides insights for future studies involving wet-dry cycle exposures, which are more akin to the real atmospheric corrosion process.

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