The phrase "are kept flat" is correct and usable in written English.
It can be used when describing the state or condition of an object that is maintained in a flat position.
Example: "The documents are kept flat to prevent any creases or damage."
Alternatives: "are maintained flat" or "are stored flat".
The cisternal spacing is regulated by Climp63 (Shibata et al., 2010), which is proposed to be a luminal bridge, and the surface of the sheets are kept flat, likely by kinectin and p180, which scaffold the membrane as a rod-like structure (Shibata et al., 2010; Zhang and Hu, 2016).
It should be kept flat on a surface.
But then the state ran into fiscal trouble; funding was kept flat in 2009 and cut in 2010.
Under the collective bargaining agreements negotiated by unions for the clothing sector, wages were kept flat in 2011, while a rise of 1.3 percent was agreed to for 2012.
The dancers make extensive use of every part of the body except the instep: in general the foot is kept flat, bracing the leg in balance while the torso, arms and often the other leg move vividly through the air.
"If the BBC, as I think is very likely, has in the next two or three years to make cuts because of this settlement, they won't be because of some inadequacy on the BBC's part, they will be because the overall settlement isn't big enough," he told Radio 4's World at One. "How much has the BBC funding increased over the last few years – it's been kept flat.
The ear was kept flat on a microscope glass.
The mice were placed on a translatable X Y Z platform and the skin was kept flat with small clamping arms during treatment.
Meanwhile, the performances are kept deliberately flat.
The bucket of the excavator was kept almost flat during a real hoist swing.
The transmittance was kept almost flat from about 420 to 800 nm for all the curves, which indicated wide applications in the visible wavelength range.
