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Could engineers have known ahead of time exactly how much pressure the levees protecting New Orleans could withstand? Is it possible to predict when and under what conditions material wear and tear will become critical, causing planes to crash or bridges to collapse? A study by Weizmann Institute scientists takes a new and original approach to the study of how materials fracture and split.
When force is applied to a material - such as a rock hitting a pane of glass - a crack starts to form in the interior layers of that material. In the glass, the force of the striking rock causes the fracture to progress through the material with gradually increasing speed until the glass splits apart. The path the forming crack follows and the direction it takes are influenced by the nature of the force and by its shape. As cracking continues, microscopic ridges form along the advancing front of the crack and the fracture path repeatedly branches, creating a lightning bolt or herringbone pattern.
Physicists attempting to find a formula for the dynamics of cracking to allow them to predict how a crack will advance in a given material have faced a serious obstacle in pinning down the fundamental directionality of the cracking process. From any given angle of observation or starting point of measurement, a crack will look different and yield different results. Scientists worldwide have experimented with cracking, but until now no one has managed to come up with a method for analyzing the progression of a forming crack.
Prof. Itamar Procaccia and research students Eran Bouchbinder and Shani Sela of the Rehovot institute's chemical physics department set out to find a way of analyzing data from experiments that would avoid the direction problem. First, they divided the cracks' ridged surfaces into mathematically-determined sectors. For each sector they were able to measure and evaluate different aspects of the crack's formation and to assign it simple directional properties. After some complex data analysis of the combined information from all sectors, the team found their method allowed them to gain a deeper understanding of the process of cracking, no matter which direction the measurements started from. The team then applied the method to plastic, glass and metal.
From the concrete in dams and buildings to the metal alloys and composites in airplane wings and car windshields, many of the materials we depend on are subject to cracking. The team's method will give engineers and materials scientists new tools to understand how these materials act under different stresses, to predict how and when microscopic or internal fractures might become life-threatening, or to improve these materials to make them more resistant to cracks' formation .
A DOG'S LIFE GETSBETTER
It wasn't publicized other than by word of mouth, and still the University of Wisconsin-Madison School of Veterinary Medicine was overwhelmed with requests. Since 1998, the school's oncology department has been producing an anti-cancer vaccine for dogs diagnosed with melanoma. Though it is still an experimental treatment, dog owners from all over the US have wanted to participate in the study on the remote chance that this would help their pet.
"Not all dogs respond to this treatment," cautions Ilene Kurzman, a researcher in the veterinary medical school's oncology section. "But those that do seem to do quite well." Melanoma, the equivalent of one form of skin cancer in humans, is very aggressive in dogs. It usually manifests itself in or around the mouth or toes. Despite conventional treatment, 75% of dogs with oral melanoma die within a year.
But about 40% of dogs with a melanoma tumor responded to a vaccine created from actual melanoma tumor cells; in 12.5% of the treated dogs, the tumor disappeared. While the current results are promising, funding limitations reduce the program's ability to take the next step in improving the vaccine, Kurzman says. The vaccine is created from dog melanoma cells grown in the lab, with the cells treated so they can no longer divide. DNA is then inserted into these cells which directs them to secrete an immune stimulant. This combination of cells and stimulant, when administered as an injection, has been shown to help the immune system fight melanoma cells. Dogs that first had surgery for melanoma and then received vaccine lived cancer-free for approximately twice as long as dogs ithat did not receive the vaccine.
"It's the closest thing to a miracle I've ever seen," says Maggie Hoefling of Largo, Florida. Following vaccine therapy, her 14-year-old beagle, Mack, not only lived an additional two years, but thrived - and that's after their veterinarian gave Mack only four months to live.
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