Pitting corrosion with fractal porous structure often occurs on copper tubes used in heat exchangers of air-conditioning equipment, and this corrosion is called an ant-nest corrosion. Galvanostatic ...controlled EIS (G-EIS) was used to measure 3-dimensianal (3D) impedance during the formation of ant-nest corrosion on phosphorus deoxidized copper (pd-Cu). Instantaneous impedance at an arbitrary time after galvanostatic polarization was determined from the 3D impedance. The transmission line model (TLM) for fractal porous electrode was applied to detect a branched pore formation on pd-Cu electrode. Nyquist plot of instantaneous impedance at initial stage of ant-nest corrosion shows capacitive behavior and straight line of 45° angle against real axis in high frequency region, indicating that a porous structure was formed at the initial stage. The angle of straight line was varied from 45° to 22.5 and 11.25°, indicating the formation of branched and doble-branched porous structures, respectively.
The branched pitting corrosion often occurs on copper tubes used in heat-exchanger units in air-conditioners and leads to leakage of heat-exchanger fluid for several months. Figure 1 shows a ...photograph of this unique localized corrosion formed by galvanostatic polarization in the laboratory. The morphology is characterized by the fractal structure in which pits of several ten micro-m diameter are formed at copper surface and smaller pores are developed on the pit walls randomly. This localized corrosion has been reported with some names: ant-nest corrosion, formicary corrosion, unusual corrosion, branched pits and pinhole corrosion 1. It’s well known that the occurrence of this localized corrosion is related to trace phosphorus in copper and presence of low molecular weight carboxylic acid such as formic acid. However, the origin to form branched structure has not been clarified.
We reported an impedance method to analyze the branched (fractal) pore electrode with transmission line model (TLM) 2, 3. Impedance spectrum of simple cylinder pore electrode on Nyquist plane normally describes straight-line of 45 degree slope in the high frequency range. In the case of electrode with fractal pores, the slope of straight-line decreases depending on the fractal dimension 3. In this study, we employed this impedance analysis to investigate the initiation and growth of branched pores in ant-nest corrosion of copper.
References:
1 D. M. Bastidas, V. M. La Iglesia, E. Cano, S. Fajardo, and J. M. Bastidas,
J. Electrochem. Soc.
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155
, C578 (2008).
2 M. Itagaki, S. Suzuki, I. Shitanda, K. Watanabe, H. Nakazawa,
J. Power Sources
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161
, 415 (2007).
3 M. Itagaki, Y. Hatada, I. Shitanda, K. Watanabe,
Electrochim. Acta
,
55
, 6255 (2010).
Figure 1
Premise
Understanding the flower visitation history of individual pollinators is key in the study of pollination networks, but direct tracking is labor intensive and, more important, does not capture ...information about the previous interactions of an individual. Therefore, a protocol to detect most of the pollen species on the body surfaces of an individual pollinator could elucidate its flower visitation history.
Methods and Results
Under a microscope, we observed 6.0‐µL droplets from a sample solution (1.0 or 3.0 mL) containing pollen grains collected from individuals of six major pollinator functional groups. To clarify how many droplets need to be observed to detect all pollen species within the solution, we examined up to 10 droplets collected from each individual insect. Sample‐based rarefaction curve analyses of the data showed that we could detect ~90% of the pollen species and the plant–pollinator links in the networks by observing six droplets.
Conclusions
The rarefaction curve analysis for pollen‐on‐pollinator studies is a useful preliminary step for minimizing the time and labor required while maximizing the data on the flower visitation history of each individual pollinator and revealing any hidden flower–pollinator interactions.
During the last few decades, pine wilt disease has spread to cool-climate regions in Japan and, more recently, the potential risk of it spreading into the European midwest has also become a concern. ...In a coastal pine stand (84.7 ha) in Akita, near the northern limit of pine wilt disease in Japan, we investigated seasonal variations in the incidence of damage caused by the disease to trees and oviposition by the disease's insect vector, Monochamus alternatus, during a two-year period. Foliage discoloration occurred throughout each year, and its seasonal variation showed a bimodal pattern in Pinus thunbergii (a higher peak in May-June and a smaller peak in October) and a clear peak in June in P. densiflora, which differed from the patterns in seasonal variation seen for warm-climate regions. Oviposition scars by M. alternatus were found in 40-45% of the trees damaged each year. The percentage of trees that had oviposition scars was higher in P. thunbergii than in P. densiflora. This appeared to reflect the difference in seasonal discoloration pattern between the two species. Analysis of the oviposition risk showed that trees that exhibited discoloration starting between July and October had a significantly higher risk or significantly higher oviposition scar densities, particularly for those that became discolored between August and September (2.5-14.6-fold higher risk than during other months). Oviposition scar densities per damaged tree were similar within the period of higher oviposition risk. Considering both oviposition risks and scar densities, we concluded that trees with discoloration that become apparent between July and October are important targets for preventing the spread of pine wilt disease in Akita.
An experimental comparison of the recording density limits of three coding methods was performed to find the coding method most suitable for high density recording. We examined FM, MFM, and one of ...the so-called run-length-limited codes to which self-clocking and peak detection are applicable. In this paper, we call the last coding method "modified nonreturn to zero inverted" (MNRZI). The recording density limit was obtained for each method from measurement of the peak shift and signal to noise ratio for a given recording channel.
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