Birthday photographs of the Golden Gate Bridge; to view or to buy

Birthday photographs of the Golden Gate Bridge

On an overcast day last month in Mesa, Ariz., an unusual vehicle, shaped like a flattened bullet, raced four times around a 5-mile circular track. On its fourth go-round, the racing car set a new world speed record for a land vehicle powered solely by direct energy from the sun. Taking 8 minutes, 28.628 seconds to complete the circuit, the GM Sunraycer traveled at an average speed of 35.227 miles per hour. This surpasses the previous record of 24.74 miles per hour set by a different vehicle in 1984. The circular course ensured that any wind or terrain effects would be canceled out.To test this postulated acceleration of natural erosion, a team of researchers last year began a careful study of sandstone deterioration at Mesa Verde National Park, where the Anasazi dwellings are located. For their project, the researchers used fragments of local sandstone to construct two test walls similar to those built by the Anasazi centuries before."Economically, one of the most serious effects of acid deposition is on materials," says James H. Gibson of Colorado State University in Ft. Collins. According to the Environmental Protection Agency (EPA), recent estimates of the annual cost of repairing or replacing structures damaged by acid deposition start at $5 billion and go up from there.But the stones may be eroding more quickly now than they were a few decades ago. Carried by wind or concentrated in rain and snow, air pollutants from several power plants and a nearby smelter continually wash over the site.Speed alone won't be enough to win the race, says Bruce McCristal of GM Hughes Electronics. "It's a test of durability and reliability,' he says.' "You need a good vehicle and some good luck.' Parts of the road are narrow, and much of it is roughly paved. The terrain varies from lush tropical forest and barren plateau in northern and central Australia to desert and mountains in south Australia. The GM team has only one car, but the team plans to bring along spare parts for just about any problem that could come up."We look at this thing as a really interesting scientific effort,' says McCristal. "Our motivation is to push some technologies along that we think are important to the future, and we're very interested in stimulating high-school and college students to get into technical fields [associated with automotive engineering].' The car demostrates advances in low-speed aerodynamics, high-efficiency batteries, lightweight motors and solar cells and panels.Even replacing mortar must be done carefully. If the replacement mortar is less porous than the bricks in a wall, the bricks will deteriorate faster than the mortar, says Charola. Instead, a more porous mortar should be used. In this way, the mortar rather than the brick will lose its strength first. It's usually cheaper to replace missing or cracked mortar than to rebuild a brick wall, she notes.Photo: Among the first across the bridgeon Pedestrian Day (May 27, 1937) were these three roller-skaters

Photo: Among the first across the bridgeon Pedestrian Day (May 27, 1937) were these three roller-skaters