... Armagh Observatory, College Hill, Armagh BT61 9DG, +44 (0)28 3752 2928 . ... A numerical simulation of the Oort cloud is used to explain the observed orbital distributions and numbers of Jupiter-family and Halley-type short-period comets. ... Virtually all observed Halley-type comets and nearly half of observed Jupiter-family comets come from the Oort cloud, and initially (4.5 Gyr ago) from orbits concentrated near the outer planetary region. ...

Professor Yurij Shokin, born 1943, has been many years with the Computer Center and the Institute of Theoretical and Applied Mechanics (during the directorship of Academician N N Yanenko ) in Novosibirsk's scientific campus Akademgorodok and was director of the computer centre of the Soviet Academy of Sciences, Siberian Division, in Krasnoyarsk. ... He is an affiliate member of IFIP WG 2.5 and a member of the Russian Academy of Sciences. ... Russian Academy of Sciences . Siberian Division . ...