They are three scientists – one from the Bronx and two from Queens – whose research may eventually prevent osteoporosis, help produce energy without pollution, and advance the regeneration of human tissue.

They are finalists in one of the premier science competitions in the country.

And they are in high school.

This year, three of the 18 national finalists for the annual Siemens Westinghouse Competition in Math, Science and Technology hail from the city. Another four finalists are from Long Island, meaning more than a third of the national finalists live in the New York metropolitan area.

The students, culled from more than 1,200 applicants, are competing this weekend in Washington for as much as $100,000 in scholarship money.

The finalists from the city are Samir Zaidi, 17, from the Riverdale section of the Bronx; Yonatan Schwab, 17, who lives in Hillcrest, Queens, and Taylor Bernheim, 16, from Holliswood, Queens.

Samir’s research began with his 81-year-old grandmother, who, like 8 million other American women, suffers from post-menopausal osteoporosis.

“I always saw my grandmother stooped over and I always wondered why,” said Samir, who is in his senior year at the Hackley School in Tarrytown.

Most research on osteoporosis focuses on low levels of estrogen in woman. In contrast, Samir advanced to the finals in the individual category by showing that high levels of a hormone produced in the pituitary gland, known as the follicle-stimulating hormone, lead to bone loss.

Yonatan began his investigation into making nanoparticles from palladium at the engineering department of the State University at Stony Brook with a classmate from Rambam Mesivta High School in Lawrence, Long Island, Yisrael Herzberg, 17.

What could be so important about nanoparticles from palladium that a high-school student would want to spend an entire summer staring through an electron microscope?

“We were very interested in hydrogen fuel cells,” said Yonatan, who, like his partner, speaks with the steady self-assuredness of a scientist. “We used a magnetometer to measure magnetic properties and found nanoparticles were more magnetic than regular palladium.”

The discovery was the high point of their research, the boys said. Because of their magnetic nature, the nanoparticles may eventually be used to process hydrogen fuel.

Taylor Bernheim, likewise, spent her summer at SUNY Stony Brook, where she met her research partner, Jessica Fields. Taylor, who is a junior at Ramaz Upper School on the Upper East Side, heard a lecture given by a biomedical engineer on new techniques to create viable tissues to use for organ transplants.

“And our brains started rolling,” she said.

After immersing themselves in the subject, they studied the way cells regenerate. As two high school students in a lab, they had an added challenge.

“People in huge laboratories are doing things with millions of dollars,” Taylor said. “We did this with very little.”

Using mainly polystyrene and silicon, the two produced a low-cost and effective method of directing tissue assembly on the microscopic level. Their research has potential implications for tissue engineering, medical implants, and cancer diagnosis, according to scientists who have judged their work.

“Our ultimate goal is to have it available in doctors’ offices and to make it the normal procedure [for diagnosing cancer] because it’s much less invasive,” Taylor said.

First, though, Taylor and the other finalists will have to defend their graduate-level work much like a Ph.D. student defends a thesis. First, there is a visual display, then a 12-minute oral presentation in front of experts. Finally, the students will have to answer questions to show they have a proper understanding of the concepts underlying their work.

“Once they get to the national level these students are working at a graduate level,” said a spokeswoman for Siemens Foundation, Marie Gentile. “In some cases, you will get a judge who will say this is the work of a Ph.D.”

New York has been well represented in past years. In 1999, Lisa Harris, who went to the Dalton School at the Upper East Side, won the top prize, for finding the DNA marker in cystic fibrosis by studying an orthodox Jewish community in Brooklyn, where the disease was found at a high rate. Last year’s top winner, Yin Li, who went to Stuyvesant High School, researched how memory works in the brain.