Polyhedral gold nanoparticles are of great current interest because of their unique optical and chemical properties which are attributable to their well-defined facets, corners, and size. While various polyhedral gold nanoparticles of different sizes mostly synthesized by the seed-mediated method have been reported, synthesis of gold cuboctahedra with tunable sizes still remains challenging. Here, we report for the first time a seedless method of synthesizing monodisperse gold cuboctahedra with finely tunable sizes ranging from 40 to 80 nm using cetyltrimethylammonium 4-vinylbenzoate (CTAVB) as a selective capping and mild reducing agent in the presence of a high concentration of HCl in aqueous solution. The HCl provides strong oxidative etching power to remove structural defects, resulting in single-crystal seeds, and significantly reduces the particle growth rate. This slow particle growth provides an easy and reliable way of tuning the particle size by stopping the reaction at different times and allowing sufficient time for the surface self-diffusion of Au atoms. Combined with the selective capping of {100} facets with CTA+, the surface self-diffusion of Au atoms from {111} to {100} facets is considered to be the key mechanism for the formation of Au cuboctahedra and their stable growth without morphological deformation.

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This paper is to explore how the neighborhood-unit concept, which had been initially promoted by North America and the United Kingdom, was adopted and utilized in the Asian cities of high-density developments, such as Seoul and Singapore from a walkability perspective. Among various environmental elements of walkability in a given neighborhood unit, 10 planning elements, as well as their configuration methods, were drawn from the review of the existing studies, which became an analytical framework for this paper. The findings of the analysis are as follows. First, there were similarities, yet also marked distinctions between the cases of Seoul and Singapore, on the one hand, and those in North America and the UK on the other, with respect to the configuration methods, categorized into four groups of typologies: 'Neighborhood Size', 'Neighborhood Structure', 'Neighborhood Network', and 'Neighborhood Facilities'. The differences largely resulted from the high-density developments in Seoul and Singapore. In the years since the 1990s, however, when the concept of sustainable development was strengthened, the configuration methods, related to 'Neighborhood Structure' and to 'Neighborhood Facilities' in most cases, were enhanced to suit more neighborhood walking. The initial concept of the neighborhood unit was actively modified to accommodate the high-density urban situations in Seoul and Singapore, having both positive and negative impacts on neighborhood walkability.