The use of stationary waterjet for the removal of coating material from the substrate is investigated analytically and experimentally. In the analysis, the cleaning width as a function of standoff distance, water pressure, and nozzle radius is derived by considering the structure of waterjet and the cleaning mechanism. Also derived are the relations of the optimal cleaning standoff distance and maximum cleaning width to the critical cleaning standoff distance, and how the water pressure and nozzle radius affect this critical standoff distance. These derived analytical relations are verified with experimental results.

In this study, we investigated the age difference in numeral recognition and calculation in one group of school-aged children (n = 38) and one of undergraduate students (n = 26) using the event-related potential (ERP) methods. Consistent with previous reports, the age difference was significant in behavioral results. Both numeral recognition and calculation elicited a negativity peaking at about 170-280 ms (N2) and a positivity peaking at 200-470 ms (pSW) in raw ERPs, and a difference potential (dN3) between 360 and 450 ms. The difference between the two age groups indicated that more attention resources were devoted to arithmetical tasks in school-aged children, and that school-aged children and undergraduate students appear to use different strategies to solve arithmetical problems. The analysis of frontal negativity suggested that numeral recognition and mental calculation impose greater load on working memory and executive function in schoolchildren than in undergraduate students. The topography data determined that the parietal regions were responsible for arithmetical function in humans, and there was an age-related difference in the area of cerebral activation.

A mathematical model of cleaning with moving waterjet is established by considering the structure of waterjet and applying Springer’s semi-empirical model on material erosion due to impact of water droplets. Based on this model, the cleaning width as a function of travel speed, standoff distance, water pressure, and nozzle radius is derived. Also derived is the relation of the critical cleaning standoff distance to travel speed, water pressure, and nozzle radius. The validity of the derived relations is verified by conducting moving waterjet experiments with varied cleaning system parameters.

The objective of this work is to investigate the cognitive development of semantic process and arithmetic calculation in childhood using event-related potential tools. Sixty children of three age groups (8-, 9-and 11-year-old groups)