一些我认为对新托福很好价值的科学60秒听力.doc

一些我认为对新托福很好价值的科学60秒听力,准备靠新托福的同胞们,可以看看。
Why Paper Yellows As It Ages
As paper ages, oxidation changes molecules in cellulose so that they absorb some wavelengths of light and make the paper look yellow. Sophie Bushwick reports
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As it ages, white paper turns a distinctive yellow. But why? To find out, scientists artificially aged modern paper to reveal the changes on the molecular level. The research is in the journal Physical Review Letters. [A. Mosca Conte et al., "Role of Cellulose Oxidation in the Yellowing of Ancient Paper"]
For 48 days, three unbleached paper samples aged rapidly in reactors that simulated different environmental conditions. The researchers pared the artificially aged samples to the real deal: three pieces of paper crafted in 15th-century Europe. This technique allowed them to gauge the types and amounts of changes going on.
About 90 percent of the weight of old paper is cellulose, the sturdy material that makes up plant cell walls. But over time cellulose fibers oxidize. The process modifies parts of various molecules and turns them into what are call