You aren't using the past tense in those sentences; you're using the present perfect tense (has been observed; have been successfully validated). If you are referring to work that you did and are reporting on in this paper, you should be using the past tense.
The convention not to use "I" or "we" has led to a convention in scientific writing where verb tenses are used instead to convey some of this information. The simple past is used for the work that the authors did described in this paper, while the present perfect is used for research done by other people or in previous papers of the authors. (Since you're supposed to cite any previous research, these two cases aren't truly ambiguous.)
So for example:
Rocks have been collected from the moon. These rocks were prepared for electron microscopy and analyzed for signs of life.
Translation: somebody else collected rocks from the moon. We looked at them using an electron microscope to see whether we could see any evidence of life.
Rocks were collected from the moon. These rocks were prepared for electron microscopy and analyzed for signs of life.
Translation: we went to the moon and collected some rocks. We then looked at them using an electron microscope ...
See this document for more about tenses in scientific manuscripts where you avoid first person pronouns. I quote some relevant sentences:
The methods section should use the past tense because it is a report of what was done during the course of the study.
When referring to a previous study with results that are still relevant, use the present perfect tense.
(So if you're writing about somebody else's results that you show are incorrect, you should use the past tense.)