Indentation hardness
Hardness measurements quantify the resistance of a material to plastic deformation. Indentation hardness tests compose the majority of processes used to determine material hardness, and can be divided into two classes: "microindentation" and "macroindentation" tests. Microindentation tests typically have forces less than . Hardness, however, cannot be considered to be a fundamental material property. Classical hardness testing usually creates a number which can be used to provide a relative idea of material properties. As such, hardness can only offer a comparative idea of the material's resistance to plastic deformation since different hardness techniques have different scales.
Weighted correlation network analysis
Next, an adjacency matrix (network), formula_11, is used to quantify how strongly genes are connected to one another. formula_12 is defined by thresholding the co-expression similarity matrix formula_13 . 'Hard' thresholding (dichotomizing) the similarity measure formula_14 results in an unweighted gene co-expression network. Specifically an unweighted network adjacency is defined to be 1 if formula_15 and 0 otherwise.
Because hard thresholding encodes gene connections in a binary fashion, it can be sensitive to the choice of the threshold and result in the loss of co-expression information. The continuous nature of the co-expression information can be preserved by employing soft thresholding, which results in a weighted network. Specifically, WGCNA uses the following power function assess their connection strength: