The phrase "are mainly characterized" is correct and usable in written English.
It can be used when describing the primary features or traits of a subject or object.
Example: "The species are mainly characterized by their vibrant colors and unique patterns."
Alternatives: "are primarily defined by" or "are chiefly marked by".
These counties, are mainly characterized by a conversion of forest areas and grassland areas.
These patterns are mainly characterized by the location, orientation and mechanism of the fault.
The lithofacies are mainly characterized by the presence of orbitolinid foraminifera, corals and rudist bivalves fauna.
Fluid flows in chemical engineering are mainly characterized by the coexistence of turbulent and non-turbulent fluids.
The meandering river sandstones are mainly characterized by lateral accretion shale beddings inside, with simple overlay-relationship in sand bodies.
Within the super-convergence domain, the compressional structures in the center of the South China Block are mainly characterized by shortening, thrusting and decollement.
Existing bone scaffolds are mainly characterized by complex porous designs whose shortcomings are a low level of permeability for growing tissue, and a difficult design customization.
Clays and clayey rocks are mainly characterized by a strong hydromechanical coupling and very low permeability leading to numerous difficulties when trying to study them experimentally.
The morphology and structure of as-prepared carbon-TiO2 nanotubes are mainly characterized by SEM, TEM, XRD, Raman spectroscopy, XPS and UV vis spectroscopy.
Various types of spectra described in this paper are mainly characterized by unusual spatial distributions of wave functions in the system under study.
The solidified microstructures are mainly characterized by α-Cu dendrites plus ζ phase which forms in the interdendritic areas within the whole undercooling regime.
