Sentence examples for has remained difficult from inspiring English sources

However, the problem of design of personal protection schemes has remained difficult since that time.

Treatment of non-healing wounds has remained difficult, in spite of better understanding of pathophysiologic principles.

In laboratory animals, however, the use of anxiety to predict alcohol preference has remained difficult.

Vaccines are one of the most effective interventions to improve public health, however, the generation of highly effective vaccines for many diseases has remained difficult.

Similar correlations between tick bites and meat allergies have recently been reported in Australia and Sweden, but establishing that the ticks are a definitive cause has remained difficult.

Various empirical and semiempirical flow resistance models have been developed during the past century; however, a universal flow resistance model for varying types of rivers has remained difficult to be achieved to date.

They said trading conditions since January had "remained difficult".

The distinctive boundaries and substantive concerns of this field, however, have remained difficult to discern.

As donated organs have remained difficult to procure, transplant operations have become safer and easier.

The general acknowledged, however, that Diyala Province had remained difficult to control because of continuing insurgent attacks.

Fundamentally, the topological physics arises from the geometric properties of quantum wavefunctions (e.g., Berry curvature, Berry connection, quantum metric, etc)., which have remained difficult to detect experimentally.