The part of the sentence 'has been often observed' is correct and usable in written English.
You can use it to describe a phenomenon that is widely known, seen, or experienced often. For example: "The behavior of cats in response to a threatening presence has been often observed."
Acute stent recoil has been often observed following stent delivery balloon deflation in coronary arteries and the recoil rate varies by stent design.
As it has been often observed experimentally, small changes in geometry and functionality of a building-block can directly influence the morphology and stability of the resulting two-dimensional molecular assemblies.
The growing use of colour images may be credited to the increasing Persian influence upon ʿAbbāsid poetry, for the Persian poets were, as has been often observed, on the whole more disposed to visual than to acoustic imagery.
Under high-temperature annealing, the formation of interfacial SiO2 layer has been often observed [7].
This behavior has been often observed in root grown in soils poor in phosphorous [27].
The latter allows to overcome the performance inconsistency that has been often observed in previous fusion algorithms.
The optical textures, such as fan-shaped texture, parabolic focal conic texture and oily streaks, which have been often observed in smectics or columnar phases of lyotropic low-molecular-weight liquid crystals, were observed in the solutions above cc enclosed in between two glass slides.
In the case of the infill masonry panels, two principal mechanisms have been often observed.
Sequence variations at the 3' ends have been often observed in miRNA reads.
Indeed, small little bubbles of PFCl adherent to the retina have been often observed a long time after the removal [ 36].
Because the mutations of gene NOTCH1 have been often observed in human T-ALL, we decided to check the mutational status of NOTCH1 in our transgenic model.
