A criterion theorem of having no finite coverings for a finitely generated module M over a semisimple ring R is given. 对半单环上有限生成左模给出一个无有限覆盖的判定定理。
Numerical simulation shows that the two erbium-doped fiber ring lasers can be well synchronized if the strengths of delay feedback and injection are suitable. 数值模拟表明,在合适的反馈和注入条件下,两个单环掺铒光纤激光器能够达到混沌同步。