The phrase "a challenge appears" is correct and usable in written English.
It can be used when indicating that a difficulty or obstacle has emerged in a situation or context.
Example: "As we progressed with the project, a challenge appears that we need to address immediately."
Alternatives: "a challenge arises" or "a challenge emerges".
As the number and diversity of new imaging techniques and their potential impact on science grows and diversifies, a serious challenge appears for a scientist, lab or even a department facility that wants to access and use new technology for their own research.
A greater challenge appears once the uncertainties of boundary conditions such as weather conditions, user demands and energy costs are taken into account.
A new challenge appears in deep space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays (GCR) since the missions are of long duration and the accumulated exposures can be high.
Another interesting version of a similar challenge appears on the r/trees sub-reddit.
Returning to limitations regarding the registry-based sampling frame that were illustrated exemplarily for Germany in this article, and to the definition of the term migrant, a major challenge appears to persist.
When a movie is more CG than it is real — think movies like Avatar or any of Pixar's stuff, where all or nearly all of the environment is rendered — a new challenge appears: the camera.
A particular challenge appears if variance components per se are the exposure variables of interest, for instance in studies of exposure variation [ 6, 7].
When an unforeseen challenge appears, do you immediately assume the worst case scenario will take place?
Women are staying in biomedical research beyond postgraduate training but a key career challenge appears to be promotion from lecturer to senior lecturer.
