The mechanism of the direct process is still not well understood, despite much research.

In either case, I do not believe the actual mechanism is understood.

All mechanisms behind the process are not yet fully understood.

However, the mechanism behind this response is not fully understood.

I am not sure that the exact mechanism is well understood.

The mechanism that makes them soothing is not well understood, she said, though the results are clear.

The first goal seeks to understand mechanisms of learning using such tools.

However the mechanism by which this occurs is not fully understood.

The mechanism by which they affect fertility is not yet understood.

But the mechanism was poorly understood and did not always stand up to tests.