The phrase "a certain gap" is correct and usable in written English.
You can use it when referring to an unspecified but known amount of space between two things. For example, "There is a certain gap between our understanding of the issue and the action needed to solve it."
Poor Richard became a very rich Richard before very long, and a certain gap began to open up between the public perception of Franklin and the man himself.
As always with his addresses focused on domestic issues, there was a certain gap between the Russia he was describing and the reality.
As the downstream cylinder was shifted upstream, the base suction exhibited a critical fall at a certain gap for different levels off the wake centerline.
After four decades of the intensive studies of the soil-structure interaction (SSI) effects in the field of the NPP seismic analysis there is a certain gap between the SSI specialists and civil engineers.
We all felt there was a certain gap in our education, so we all scrambled back to the 20s and 30s to figure out how Charlie Patton did this, or Robert Johnson, who, after all, was and still probably is the supremo.
However, there is still a certain gap between our country and the advanced countries in Europe and America in such aspects as the material variety of SWHE, the diversity of heat exchange tube specification, the application of numerical simulation technology in design and the inspection and repair technology of high pressure SWHE etc.
There is a, let's say, certain gap (1,000,000 miles) between reasonable people and football-only fans here, believe me.
Gap patterns 1, 2, 3, and 8 typically resulted in only one to four subalignments, while gap patterns 6, 9, and 10 typically resulted in a much larger number; thus, certain gap patterns are intrinsically more likely to see an improvement under SIA than others.
Moreover, while the mutant forms of Rab1 and Rab35 were poor substrates for certain GAP proteins, a GAP protein called RUTBC3 could bind to and act upon mutant Rab5 protein, similar to previous reports from other groups (see, e.g., Pan et al., 2006).
A downward lift is observed at certain gap ratios in rod-generated boundary layers, and an explanation of this downward lift is given.
As shown in Fig. 10, welded details in the manufacturing process have a certain assembly gap (or plate space) between flange and web, and the main parameters of the assembly gap are the gap width q and the gap length p. Large assembly gap is easy to cause large shrinkage deformation of the weld and the waste of flux material [17].
