سلام. خسته نباشید
http://www.sciencedirect.com/science/article/pii/030891269091446Z
http://www.sciencedirect.com/science/article/pii/S016521250900119X
http://www.sciencedirect.com/science/article/pii/0584854782800426
http://www.sciencedirect.com/science/article/pii/S0010465584824765