eyeball. 1  Photoreceptors are the cells in the retina that respond to light. Their distinguishing feature is the presence of large amounts of tightly packed membrane that contains the photopigment rhodopsin or a related molecule.
In chemical analysis,  matrix refers to the components of a sample other than the analyte of interest. The matrix can have a considerable effect on the way the analysis is conducted and the quality of the results obtained; such effects are called matrix effects. For example, the ionic strength of the solution can have an effect on the activity coefficients of the analytes.
Rectangular Matrix (a.k.a. Data Matrix) The base data type in PASSaGE is the rectangular matrix (also called a data matrix; these terms are used interchangeably throughout the manual). These matrices may have any number of rows and columns, containing either numeric or text values. These data matrices generally have two forms.