At a time when other higher education institutions are closing or merging because of a decline in the supply of high school graduates, the Roux Institute is among a small but largely unnoticed number of new colleges that are opening. Some are focusing on high-demand disciplines such as technology, health and alternative energy. Others are serving the huge number of older, working Americans who never went to college or didn’t complete a degree. Still others are trying to remake higher education with new models that forgo top-heavy bureaucracies and expensive campuses — models that in some cases don’t look like conventional colleges at all.