The part of the sentence "difficult to be determined" is correct and usable in written English.
You would use this phrase to indicate that something is difficult or challenging to figure out or ascertain. For example, "The cause of the accident was difficult to be determined."
The distribution of elastic materials within a unit cell has significant effect on the band-gaps, which is extremely difficult to be determined without systematic synthesis method.
Bayesian model class selection is particularly useful for regression problems since the regression formula order is difficult to be determined solely by physics due to its empirical nature.
Forecasting the future, stability of personality and career issue in such circumstances are difficult to be determined and often remain enigmatic.
The paper introduces infrared thermography as a non-contact and non-destructive technique that conveniently offers the possibility of evaluating the energy-dissipating ability of soil, generally difficult to be determined using traditional techniques.
In this paper, some drawbacks of both the original independent component analysis (ICA) algorithm and the FastICA algorithm are analyzed as follows: the order of the independent components is difficult to be determined; because of using the Newtonian iteration, FastICA method often leads to local minimum solution, and the suitable source signals are not isolated.
A first critical issue is the correlation between the instantaneous cylinder gas composition and the composition of the exhaust flow: such a correlation, required by the 1d software, is very difficult to be determined by experiments, so that CFD-3D analyses remain the only reliable source of information.
Another difficult parameter to be determined is the pipe coefficient.
What's more difficult is determining whether to push in that direction.
It may be difficult to determine what is, or is not, an equivalent to a particular element of an invention.
But even with violent videos, it can be difficult to determine what is appropriate and what is not.
"It is difficult to determine what is reasonable and what is not reasonable when everything happens very quickly," he explained.
