• Korean Journal of Child Studies
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• v.33 no.5
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• pp.19-35
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• 2012

The purposes of this study were to investigate how children's categorization differs in object categorical hierarchy and to examine whether these aspects were different according to the children's age of 18 months, 24 months, 30 months. The participants consisted of 120 young children aged 18 months, 24 months, and 30 months from 31 child-care centers located in middle-income regions of Seoul and Kyonggi Province. The major findings were as follows : First, all the children from all three age groups could consistently differentiate the superordinates; however, they could not consistently differentiate basic categories. Second, 24 month appears to be a critical change period in category development. Third, as the children become older, they are able to acquire more knowledge regarding categories. These results suggested that the advent of ordering, in terms of basic categories as well as superordinates which occurred around the age of 24 month, was confirmed in category development.

• Computers and Concrete
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• v.6 no.2
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• pp.133-153
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• 2009

Discrete element modeling (DEM) in concrete technology is concerned with design and use of models that constitute a schematization of reality with operational potentials. This paper discusses the material science principles governing the design of DEM systems and evaluates the consequences for their operational potentials. It surveys the two families in physical discrete element modeling in concrete technology, only touching upon probabilistic DEM concepts as alternatives. Many common DEM systems are based on random sequential addition (RSA) procedures; their operational potentials are limited to low configuration-sensitivity features of material structure, underlying material performance characteristics of low structure-sensitivity. The second family of DEM systems employs concurrent algorithms, involving particle interaction mechanisms. Static and dynamic solutions are realized to solve particle overlap. This second family offers a far more realistic schematization of reality as to particle configuration. The operational potentials of this family involve valid approaches to structure-sensitive mechanical or durability properties. Illustrative 2D examples of fresh cement particle packing and pore formation during maturation are elaborated to demonstrate this. Mainstream fields of present day and expected application of DEM are sketched. Violation of the scientific knowledge of to day underlying these operational potentials will give rise to unreliable solutions.