2019备考SAT考试之阅读原文解析part3

>>SAT考试技巧：2019备考SAT考试之阅读原文解析part3

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Scientists Use Faux Fossils to Learn How Insect Colors Evolved

Scientists artificially age insects in a bid to learn how their colors evolved

By Lucas Laursen on June 1, 2013

On its way from flight to fossil, an ancient beetle's wings lost their color and then their form. Slow-baked and squished by sand, the glittering green wings darkened and turned blue, then indigo, then black.

That tale of an insect's life, death and fossilization sounds simple enough, but it took paleobiologist Maria McNamara years of painstaking work to piece together. The University of Bristol researcher wanted to know how ancient insects' warning signals, camouflage and mating displays evolved. Studying ordinary fossils tells only part of the story, since most fossilized insects are black today, probably because they lost their colors while buried underground.

McNamara and her team decided to work backward. They artificially aged modern beetle (shown above) and weevil wings to figure out how fossilization might affect color. They reported their results in Geology in April.

Fossilization is not a gentle process. To simulate it, McNamara left the insect wings in pond water for 18 months, then baked them at temperatures as high as 518 degrees Fahrenheit, hotter than most home ovens, and pressures almost 500 times the atmosphere's to simulate the crushing and heat that converts mud-trapped debris into subterranean stone fossils. The team found that the process broke up and thinned out the beetles' reflective shells, changing the wavelength of light that they reflect, from green to blue to black.

More important, they found that the weevils maintained color-producing structures known as photonic crystals, which could mean any fossil without these structures probably never had them. McNamara concludes that photonic crystals must have evolved recently, at least in weevils, because she examined three-million-year-old weevils that lacked them.

Some scientists disagree. Andrew Parker, an entomologist at the Natural History Museum in London, notes that “every fossil goes through a completely different process,” so it will be difficult to generalize lessons from one species or fossil to others. But he finds the idea tantalizing: “We can start to add up a picture and put together scenes of what life would have been like in color.”

This article was originally published with the title "Faux Fossils"

第二篇：

Quest for the Ideal or ‘Champion’ Photonic Crystal

Researchers are seeking photonic crystals as they aim to develop optical computers that run on light (photons) instead of electricity (electrons). Right now, light in near-infrared and visible wavelengths can carry data and communications through fiberoptic cables, but the data must be converted from light back to electricity before being processed in a computer.

The goal – still years away – is an ultrahigh-speed computer with optical integrated circuits or chips that run on light instead of electricity.

“You would be able to solve certain problems that we are not able to solve now,” Bartl says. “For certain problems, an optical computer could do in seconds what regular computers need years for.”

Researchers also are seeking ideal photonic crystals to amplify light and thus make solar cells more efficient, to capture light that would catalyze chemical reactions, and to generate tiny laser beams that would serve as light sources on optical chips.

“Photonic crystals are a new type of optical materials that manipulate light in non-classic ways,” Bartl says. Some colors of light can pass through a photonic crystal at various speeds, while other wavelengths are reflected as the crystal acts like a mirror.

Bartl says there are many proposals for how light could be manipulated and controlled in new ways by photonic crystals, “however we still lack the proper materials that would allow us to create ideal photonic crystals to manipulate visible light. A material like this doesn’t exist artificially or synthetically.”

The ideal photonic crystal – dubbed the “champion” crystal – was described by scientists elsewhere in 1990. They showed that the optimal photonic crystal – one that could manipulate light most efficiently – would have the same crystal structure as the lattice of carbon atoms in diamond. Diamonds cannot be used as photonic crystals because their atoms are packed too tightly together to manipulate visible light.

When made from an appropriate material, a diamond-like structure would create a large “photonic bandgap,” meaning the crystalline structure prevents the propagation of light of a certain range of wavelengths. Materials with such bandgaps are necessary if researchers are to engineer optical circuits that can manipulate visible light.

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