Sentence examples for it is usually very difficult from inspiring English sources

Besides, it is usually very difficult, if not impossible, to measure external excitations under the operation condition of a structure.

In most of the engineering applications it is usually very difficult if not impossible to model nonlinearity theoretically, especially for nonlinear effects stemming from structural connections.

However, it is usually very difficult to study the systems in a higher-dimensional space unless they can be reduced to a two-dimensional space.

However, because most of these chambers are designed to maintain a thermally stable environment for the cells under study, it is usually very difficult to use them to study temperature-dependent cellular events.

It is usually very difficult to assess the effectiveness of the RCM at its inception, when data is inadequate or when it is implemented on a large population of assets, especially when most of them are small in size as in the distribution systems.

In the physiotherapeutic practice it is usually very difficult to define the approach used.

This methodology, which has been field-tested and revised by the WHO, attempts to quantify information that is usually very difficult to quantify, and while it does not directly measure corruption itself, it serves the more useful purpose of identifying areas where key informants perceive that there are vulnerabilities to corruption in a consistent and systematic manner.

Compared with the existing results, the benefit of this method is that it can avoid the research of a common Lyapunov function which is usually very difficult, or even not possible.

Therefore, this method is usually very difficult to apply even for continuous-time switched linear systems [18, 19]; however, it becomes more complicated for switched nonlinear systems.

Unfortunately, the prior knowledge is usually very difficult to obtain.

The solution of these types of problems is usually very difficult due to their highly nonlinear, multidimensional and multimodal nature.