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A．They all share common experiences.B．They all want to improve their English as soon a
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Somewhere in astronomer heaven, Percival Lowell must be smiling. A century after Lowell trained his telescope on Mars and claimed he saw canals built by intelligent beings, scientists are once again in the grip of the Red Planet's most seductive mystery—the possibility that life has existed there.
Did a microscopic race of Martians leave their traces inside a potato-size rock that fell on Antarctica 13,000 years ago？ Even as a new wave of Mars exploration begins this month— NASA's Mars Pathfinder lander arrives on July 4—researchers on Earth have begun a massive effort to answer that question, which has become one of the most controversial in science. No doubt Lowell, whose name has come to be synonymous with scientific wishful thinking, would want to know how it all turns out.
So will the hundreds of researchers who gathered in March at NASA's Johnson Space Center near Houston to attend the annual Lunar and Planetary Science Conference. Presentations at the meeting usually concern such topics as ancient lunar volcanism, or the icy satellites of Jupiter, or the surface composition of a distant asteroid. The subject of extraterrestrial life is rarely mentioned. This year, however, the star of the conference was the meteorite officially designated ALH84001: No less than 37 papers were devoted to it, and to the claims by a research team led by the space center's Dave McKay that the rock contains signs of ancient martian microbes.
The first reports of those claims last August jolted the small community of meteorite researchers. Some feared they were about to witness a scientific fiasco that would capsize not just the McKay team's careers, but their own. "We're all very dependent upon NASA," explains Alan Treiman of Houston's Lunar and Planetary Institute. "I was really worried that if this turned out to be (similar to the controversy over) cold fusion, that NASA was going to go down in disgrace. And that we were going to go with it." But it soon became clear that the debate about ALH84001 bears no resemblance to the one that sank cold fusion. Indeed, the McKay team's report in the journal Science won high praise from such respected scientists as Edward Anders, a University of Chicago professor who is considered the dean of meteorite science. He wrote that the work "sets a new standard for the study for the extraterrestrial materials."
At the same time, Anders and others have been critical to the way the McKay team interprets the three things it saw: first, molecules called PAHs (short for polycyclic aromatic hydrocarbons), which McKay and his colleagues believe were formed from the decay of simple organic matter; second, tiny crystals of iron oxide and iron sulfide, which the team says are identical to grains secreted by certain types of terrestrial bacteria; and finally oblong structures that the team tentatively calls fossil "nanobacteria." The strongly worded conclusion of the McKay team's report—that although each individual finding can be explained nonbiologically, taken together they represent compelling evidence for fossil life—strikes many scientists as wildly overreaching. UCLA's William Schopf, who pioneered the study of fossil bacteria on Earth, an effort fraught with false alarms, has summed up the attitude of many skeptics with a quote from Carl Sagan: "Extraordinary claims require extraordinary evidence."
Gathering evidence from ALH84001 has required a technological assault that Percival Lowell could never have imagined. Using electron microscopes and other state-of-the-art instruments, scientists have analyzed chips the size of rice grains, examining features measured in billionths of a meter (nanometers). At that scale, says McKay team member Chris Romanek of the University of Georgia, touring ALH84001 is "like walking in a jungle." Says the University of Tennesee's Harry McSween: "This is a complex rock. After all, it's 4.5 billion years old, and it's resided on mo
A．to the pointB．in not caseC．in any attemptD．with regard
In what way is the village shoemaker a “formidable figure”？
It may be the last book you'll ever buy. And certainly, from a practical standpoint, it will be the only book you'll ever need. No, it's not the Bible or some New Age tome promising enlightenment—although it would let you carry around both texts simultaneously. It's an electronic book—a single volume that could contain a library information or, if your tastes run toward what's current, every title on today's bestseller list. And when you're done with those, you could refill it with new titles.
Why an electronic book？ Computers can store a ton of data and their laptop companions make all that information portable. True enough. But laptops and similar portable information devices require a lot of power—and heavy batteries—to keep their LCD screens operating. And LCDs are not easy to read in the bright light of the sun.
Fact is, when it comes to portability, easy viewing, and low power requirements, it's hard to beat plain old paper. So let's make the ink electronic.
That's the deceptively simple premise behind a project currently coming to fruition at the Massachusetts Institute of Technology. Some hurdles—mostly having to do with large-scale manufacturing—remain, so it will be a few years before you see an electronic book for sale in stores. But the basic technology already exists, developed at the Institute's Media Lab by a team led by physicist Joe Jacobson.
Simply put, each page in an electronic book is coated with millions of microscopic particles encased in tiny capsules. Each of these microcapsules can respond independently to an electrical charge: Particles within the capsule moving to the rear appear dark while those moving toward the front look white. The direction in which the particles move depends upon whether a negative (dark) or positive (white) charge is applied. Each microcapsule is about 40 microns in size (that's a little less than half the thickness of a human hair).
The number of microcapsules used on a given page is enormous. For instance, about 1,000 micor-capsules might be used to create the letter "A" on this page. "The smaller the size of the letter, the more microcapsules you use," says Jacobson, "thereby improving resolution." The target is to have a "paper display" with a resolution higher than that offered by today's computer screens. More than static letters are at stake: Theoretically, the microcapsules could be programmed to "flip" rapidly between dark and white states, providing, for example, a sense of motion in a diagram showing how a car works.
Thanks to electronic ink, the book essentially typesets itself, receiving instructions for each page via electronics housed in the spine. From a power standpoint, this process makes the electronic book very efficient. Unlike an LCD screen, which uses power all the time, energy is no longer needed to view the electronic book's pages once they are typeset. Only a small battery would be required, as opposed to the large ones needed to power laptop computers and their LCDs.
Convenience, though, is still the main attraction—and that means more than simple portability. Because the information is in electronic form, it can be easily manipulated. You could, for instance, make the type larger for easier reading. Or you could make notes in the margin with a stylus, your observations being stored on tiny, removable flash-memory cards in the spine.
lt's likely that electronic books will come preloaded with a selection of titles. New titles could be made available through flash-memory cards, for example. Jacobson, though, thinks the Internet will be the delivery method of choice. Imagine browsing through an online bookstore like www. amazon, com and downloading a novel into your electronic book via the modem in its spine. Transmitting Moby Dick would take about a minute. You could download a few titles, so you'll have a few good read to choose from while you're relaxing at the beach. If
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