The Effect of Particle Size on the Oxidation Resistance of a Nanoceria-Coated 304 Stainless Steel

In this work, the oxidation resistance of 304 stainless steel (SS) in the uncoated and nanoceria-coated conditions was investigated at 1073 K and 1273 K (800 °C and 1000 °C) under dry air conditions. It was found that nanoceria coatings with average particle sizes of 10 nm were effective enough to fully protect the 304 SS from oxidation. In particular, when the average nanoceria particle size in the coating was less than 5 nm, the coatings were highly efficient in hindering the oxidation susceptibility of the 304 SS. Improvements in the oxidation resistance of up to two orders of magnitude were experimentally found in this work. Finite elements were used in solving Fick’s Second Law using the Crank–Nicholson method in order to elucidate the active oxidation mechanisms in the bare and nanoceria-coated 304 SS. Oxygen penetration profiles across the scale were predicted suggesting that in the absence of a nanoceria coating, the oxygen concentration at a given scale depth is three times as high as in the nanoceria-coated samples. Moreover, kinetic simulations for scale growth through an exponential term containing a factor λ were satisfactory in predicting the experimental outcome on mass gain vs time. Ostwald-Ripening mechanisms were considered to be active during the dissolution of nanoceria particles. It was found that when average particle sizes fall below 5 nm in size, they tend to dissolve immediately, but the dissolution times become exceedingly long when the particle sizes increase above 10 nm.     

Acidity Loading Behavior in Coal-Mined Watersheds

In this paper, we propose a method (the Stoertz Water Quality Evaluation Method) to estimate the reduction in acidity load at mean annual discharge (l) in acid mine drainage impaired streams. For a given stream, acidity loading (L), defined as the product of measured acidity concentration and discharge (Q) for a range of streamflow conditions, is proportional to l and the ratio (Q_n) of Q and the mean daily discharge (Q), according to the following equations: L = l (Q/Q)^F = l Q_n ^F and log L = log l + F log Q_n, where F is a ‘flushing factor’ characterizing the stream loading behavior, such that F = 0 in pure dilution, F > 0 for flushing behavior, and F < 0 for sparing behavior. The assumed power-law relation between acidity load and discharge is supported by test cases. Acidity load at mean annual discharge can be a useful measure of the quantity of acid removed by mine drainage treatment, particularly where data for pre- and post-treatment cases can be compared. The proposed measure allows resource managers to assess and report the effectiveness of source control, passive treatment, and active treatment in alleviating acidity loads. This method can also be used to assess inputs of contamination to streams compared to pristine or background conditions.     

Effect of Copper and Nickel on the Transformation Kinetics of Austempered Ductile Iron

The kinetics of reaction occurring during the austempering treatment of ductile iron (DI) containing different additions of Cu and Ni was investigated in this work. DI bars were heat treated in an instrumented dilatometer in order to follow the exhibited transformation kinetics. The dilatometric results indicated that the addition of Cu alone did not have a significant effect on the incubation times for the austempering transformation. Also, the addition of both, Cu and Ni resulted in a significant effect on reducing the transformation rates. It was found that the austempering process is characterized by two clearly distinguished transformation stages. In the initial stage, the addition of Cu, and to a greater extent, additions of both Cu and Ni led to reductions in the transformation rates shifting the maximum transformation rate values toward longer times. The outcome of this work indicates that during the first stage of austempering, nucleation of the ferrite plates occurs via a diffusionless mechanism while their growth is diffusion controlled. Moreover, after the maximum in the transformation rate has been reached, the growth of ferrite plates becomes dominant with the rate-limiting step becoming the diffusion of C into the surrounding austenite. A qualitative model for the austempering transformation is proposed in this work to account for the experimental observations.     

Construction and Characterization of Dye-Sensitized Solar Cells

This work describes the development of solar cells manufactured with different natural dyes, with the purpose to determine their photoelectrochemical properties, employing for that virtual instrumentation. Data acquisitions and statistical process of the same, are realized through graphical programming software. The system has facilities for measurements, acquisitions and to see permanently in the computer display, information about the performance of the solar cells, as well as environmental parameters such as; temperature and the I-V characteristic curve of the solar cell. This monitoring system pretends to be part of a permanent station for monitoring variables of the manufactured solar cells.     

A parametric model for perceptual video quality estimation

In this paper, a parametric model is proposed which provides estimation for the perceived quality of video, coded with different codecs, at any bit rate and display format. The video quality metric used is one of the standardized Full Reference models in Recommendations ITU-T J.144 and ITU-R BT.1683. The proposed model is based on the video quality estimation described in Recommendation ITU-T G.1070, but incorporates different enhancements, allowing a much better estimation of the perceptual MOS values, especially in low bit rate ranges. The error obtained with the proposed model, regarding to the ITU models, is between the ITU algorithms error margins, according to the subjective tests developed by the VQEG. Studies were made for more than 1500 processed video clips, coded in MPEG-2 and H.264/AVC, in bit rate ranges from 50 kb/s to 12 Mb/s, in SD, VGA, CIF and QCIF display formats.     

Dynamic self-cleaning in gecko setae via digital hyperextension

Gecko toe pads show strong adhesion on various surfaces yet remain remarkably clean around everyday contaminants. An understanding of how geckos clean their toe pads while being in motion is essential for the elucidation of animal behaviours as well as the design of biomimetic devices with optimal performance. Here, we test the self-cleaning of geckos during locomotion. We provide, to our knowledge, the first evidence that geckos clean their feet through a unique dynamic self-cleaning mechanism via digital hyperextension. When walking naturally with hyperextension, geckos shed dirt from their toes twice as fast as they would if walking without hyperextension, returning their feet to nearly 80 per cent of their original stickiness in only four steps. Our dynamic model predicts that when setae suddenly release from the attached substrate, they generate enough inertial force to dislodge dirt particles from the attached spatulae. The predicted cleaning force on dirt particles significantly increases when the dynamic effect is included. The extraordinary design of gecko toe pads perfectly combines dynamic self-cleaning with repeated attachment/detachment, making gecko feet sticky yet clean. This work thus provides a new mechanism to be considered for biomimetic design of highly reuseable and reliable dry adhesives and devices.