I was born in Nås, Dalecarlia, Sweden, in 1931. I received the degree of "Civilingenjör" in Electrical Engineering from KTH (The Royal Institute of Technology) in Stockholm in 1955, the degree of MEE (Master of Electrical Engineering) from NYU (New York University) in 1962, the degree MS in Mathematics from the Courant Institute of NYU in 1965, and the degree of PhD in Mathematics, also from the Courant Institute of NYU in 1972. I was appointed Docent in Applied Mathematics at KTH in 1973. I worked at a Swedish Defence Research Organization from 1955 to 1960, at the Bell Telephone Laboratories in NJ, USA, from 1960 to 1974, and at the Department of Mathematics at KTH, Stockholm, from 1974 until retirement in 1996. After 1996 I have continued to be associated with the Department of Mathematics at KTH, where I work with research in biomathematics. My main concern has been with stochastic models in population biology. A list of my publications is found here.
SIS models (for susceptible-infected-susceptible) are used to study the spread of infection that does not lead to immunity in a population of hosts. I have studied the stochastic version of a SIS model in a monograph with the title "Extinction and Quasi-stationarity in the Stochastic Logistic SIS Model", Springer Lecture Notes in Mathematics #2022. It turns out that many of the results show different qualitative behaviors in different parameter regions. Access to a Maple module used for numerical evaluations, and a list of corrigenda are given here.
Moment closure methods are used to derive approximations of moments or cumulants of stochastic processes, and they have found a wide applicability. However, the methods are known to suffer from several weaknesses. Thus, both conditions for validity of the approximations and magnitudes of approximation errors are unknown. I have discovered that these and other weaknesses with moment closure methods can be eliminated by avoiding the ad-hoc assumptions that are associated with these methods. As a replacement I suggest a search for asymptotic approximations. An article with the title "An Alternative to Moment Closure" describes my new approach. It was published in Bulletin of Mathematical Biology, 2017. Essentially the same content can be found at arxiv:1707.03182.
Revised 2017-08-03.