A new spin has been put on the old equation, e=mc2.

James Yorke, a University of Maryland mathematics and physics professor, is now using this equation to track the growth phase of the HIV and AIDS epidemic.

Yorke presented the 2006 Russell Marker Lectures in the Mathematical Sciences from April 3 to April 6 at Penn State. These annual lectures are presented in astronomy and astrophysics, the chemical sciences, evolutionary biology, genetic engineering, the mathematical sciences and physics.

The Eberly College of Science sponsored the four free lectures that concerned the issues of the HIV/AIDS epidemic, the differences in DNA among species and evolution.

On April 4, before an audience of about 60 people in McAllister building, Yorke explained how he and his co-collaborators, Brandy Rapatski and Frederick Suppe, use this equation in their studies.

"I figured most people would remember this equation easily," Yorke said.

In their version of this equation, 'e' equals the ratio of active core men to women, 'm' equals the ratio of infectiousness of men to that of women and 'c' equals the number of core men and women infected to date.

"The core people are the promiscuous people with multiple partners," Yorke said. "You're not supposed to say promiscuous, but I don't know any other term."

His lecture entitled "Describing the Exponential Growth of the HIV Epidemic" explored the implications of semen infectivity and estimates for understanding the untreated heterosexual population.

"However, there are no assumptions that men are more active than women," Yorke said.

He said there are three stages to the HIV epidemic. Stage one lasts about six months and during this stage people often exhibit flu-like symptoms. Stage two typically lasts seven years; however, it has been known to last as long as 20 years. Stage three usually lasts three years, with the last year of this stage being AIDS.

Yorke uses these three stages to determine which stage people are most infectious.

Stage one has a high level of infectivity; stage two has a relatively low level of infectivity, and stage three is more infectious or at least the same as stage one, Yorke said.

"For women, we don't have evidence of when they are infectious. We can only guess that they are the same as men; high, low, high," Yorke said.

Rolf Ryham (graduate-mathematics) said the lecture explained illness using mathematical terms.

"You can go very far using simple mathematics while using serious questions," he said.

Vivek Srikrishnan (graduate-mathematics) said he also had a positive view of the lecture.

"It shows to start with the simplest model and see where it goes from there," he said.