The phrase "are periodically seen" is correct and usable in written English.
It can be used to describe something that appears or occurs at regular intervals.
Example: "In this region, certain species of birds are periodically seen during migration season."
Alternatives: "are occasionally observed" or "are regularly spotted".
After surgery patients were periodically seen at the Center, and Excess Weight Loss (EWL) was calculated at 2 years follow-up.
All participants were periodically seen (every 6 9 months) for routine medical examinations of glycemic control and chronic complications of diabetes.
The study participants were periodically seen at the diabetes clinic (every 6 12 months) for routine medical examinations of glycemic control, kidney function parameters, and chronic complications of diabetes.
The variability introduced in the colony response by the fluctuations with respect to the deterministic approach can also be observed in experiments under weak inducing conditions where the autoinducer concentration is periodically decreased (see Additional file 4: Figure S2).
However, it has been found that its genetic diversity is reduced periodically (see [12]), and this is associated with cluster transitions.
Similar to the NFs and NRs, the mesopores in the NEs are periodically ordered as can be seen by the HRTEM image (Fig. 3f) and the SAXS pattern (Fig. 4c).
It can be seen that the PS spheres are periodically arranged on the surface in a large scale area.
It is seen in this situation that χ and f are periodically oscillating along the z-axis.
At Breamore there is concern that an outflow from the pond could potentially allow fragments of the invasive plant into the nearby river Avon, which is why a team of volunteers is periodically to be seen waist deep in the cold, murky water, painstakingly pulling out the tendrils by hand.
