replacement of a tractor is an influential factor affecting timely farm operation. the accurate prediction of repair and maintenance costs is essential to selection of a replacement model. this study used empirical data for 60 two-wheel drive (2wd) tractors from astan ghods-e razavi agroindustry. the types and numbers of tractors used were the massey ferguson 285 (17), fiat (10), john deere 314...

So many unexpected events can alter the course of a life. For me it was an illness. A few months after finishing my dermatology residency, I was diagnosed with a life-threatening blood disorder and would need a bone marrow transplant. Overnight I went from being a doctor to being a patient. And though I would metamorphose back again, I would never be the same, surely not the same doctor. Now 15...

or so members, created with this aim in mind. The result was an invitation to the first Pugwash Conference on Science and World Affairs in Nova Scotia in 1957, and a visit to Moscow (the first of 22) the following year. This in turn led to his appointment to President Eisenhower’s scientific advisory committee on nuclear arms control, and thence to those of Kennedy, Nixon and Carter. Doty made ...

John Avise was born and raised in Grand Rapids, Michigan. He earned a BS in fishery biology from the University of Michigan, an MA in zoology from the University of Texas, and a PhD in genetics from the University of California at Davis, before joining the faculty at the University of Georgia where he stayed for 30 years. In 2005, he took his current position: Distinguished Professor of Ecology...

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John Maynard Smith was one of the most original thinkers in evolutionary biology of the post neo-Darwinian synthesis age. He was able to define new problems with clarity and by doing so open up new research directions. He did this in a number of areas including game theory and evolution, the evolution of sex, animal behavior, evolutionary transitions and molecular evolution. Although he is best...

Frederick John Poynton was born at Kelston rectory, Bath, in 1869. On leaving Marlborough College he started his medical education at University College, Bristol, and continued it at St. Mary's Hospital where he won a scholarship in Anatomy and Physiology. He qualified in 1893, and rapidly showed the absorbing interest in children which largely determined his medical career. A disciple of Chead...