The short drying times of spray paints are of great benefit in some applications, and this property allows for painting over almost immediately. However, this fast-drying process precludes following it using conventional techniques. In a previous article, we used the dynamic speckle to follow the drying process of solvent-based and water-based paints with relatively long drying times, and recently we developed alternative speckle contrast methods to characterize faster processes. This article presents the application of these methods using dynamic speckle techniques to study the drying of a spray paint. Activity image display is also included. M any industrial processes involve the coating of substrates with thin layers of paint to protect and/or decorate them and to impart desirable properties such as gloss, adhesion, magnetic properties, etc., and new coating products are continually being developed for other specific uses. The coating process involves the application of paint using a wide variety of applicators such as brushes, spray guns, roll coaters, extrusion dies, etc. Drying is part of the coating process and, therefore, the knowledge of the drying process has practical applications. For example, it is very important to establish the shortest time necessary for drying of the first layer before the application of the second layer.After applying paint, the initial drying process consists of a constant slope falling period of loss of mass. 1 In that period, the coating behaves as if it were a pool of solvent. There is always solvent on the surface of the coating and the rate of evaporation of drying is controlled solely by factors external to the coating. The geometry, air velocity, air temperature, and solvent level in the drying air and any source of heat are the most important factors. In some cases, the constant rate period may be absent and all the drying occurs in the falling rate period. Different paint formulations behave in different ways. For example, in waterborne coatings most of the drying takes place in the constant rate period, and in solventborne coatings the constant rate period is short or even nonexistent. Spray paint is a paint product in an aerosol. There are different types including general spray paint, car enamel, vehicle rim spray paint, galvanizing spray paint, hobby and decorative spray paint, marking spray paint, sealant spray, and radiator paint. Spray paint is, therefore, a very useful type of paint application and the drying process is an important issue. In a previous article 2 we used dynamic speckle interferometry (DSI) to study the drying process of waterborne and solventborne paints, where the drying times were long enough to follow the process properly. However, faster drying processes like those found in spray paint applications were not possible to follow. In this article, we used a similar laser speckle technique to characterize faster drying processes. Before describing the new method used here, we will briefly discuss the origin of the speckle phenomenon.When a cohe...
Highly ordered dimple arrays that give rise to bright structural colours with a rainbow distribution have been fabricated by means of etidronic acid anodising and subsequent selective oxide dissolution. High-purity aluminium samples were anodised at 270 V and 313 K and after removing the alumina porous film, highly ordered structures were obtained with two different cell diameters, namely 701 ± 43 and 655 ± 36 nm. These highly ordered near-subwavelength structures fabricated on the aluminium surface induced an optical effect for surface colorisation that could be predicted by interferometric equations. The generated angle-dependent colours were investigated. The mathematically predicted colours agree well with the reflected measured colours.
The modelling of many complex systems is usually approached by directed networks where nodes and connections represent the elements of the system and their interactions respectively. The degree-assortativity, which is the tendency of nodes to link to nodes of similar degree, has four components in the digraphs case. In comparison with the undirected graph case, the degree-assortativity of digraphs has not been well studied despite the potential effects that it has to constraint or influence the structural and dynamical properties of a network. Thus, we have considered a random directed network and numerically trained the assortativity profiles of the four components (in–out; out–in; in–in; out–out) by applying degree-preserving rewiring, but we interestingly found that the widely used two-swap method is severely limited. In consequence, we used a much powerful and rather forgotten three-swap method capable to achieve all different assortativities configurations of the given initial random graphs. Secondly, we characterized the obtained networks in relation to other common structural properties such as path length and algebraic connectivity. Finally, by simulating and analysing a dynamical process on the network, we have found that certain profiles cause the network to exhibit enhanced sensitivity to small perturbations without losing their stability.
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