tl;dr emplace_back is often mistaken as a faster push_back, while it is in fact just a different tool. Do not blindly replace push_back by emplace_back, be careful of how you use emplace_back, since it can have unexpected consequences.
What is a strange attractor? The wikipedia article on attractors gives the following definition/explanation:
An attractor is called strange if it has a fractal structure. This is often the case when the dynamics on it are chaotic, but strange nonchaotic attractors also exist.