diamond

Ancient Chinese people may have used diamonds to polish their stone axes to mirrorlike finishes, according to a new analysis. Other than pushing back by several thousand years the date for the first known use of diamonds, the findings also suggest that Neolithic Chinese societies were more technologically advanced than previous studies had shown.

Some sections of the ax surfaces are almost as smooth as some silicon wafers used to make computer chips, says Peter Lu, a physicist at Harvard University. "Somehow, Stone Age people . . . were able to make something smooth enough that you could pattern a circuit on it," he says. In an attempt to discover how the polishing was done, Lu obtained four ceremonial burial axes from the tombs of two Neolithic Chinese societies—the Liangzhu culture and the Sanxingcun culture—that once inhabited parts of southern China near what is now Shanghai. The stone axes had been dated by others to between 4000 and 2500 B.C.http://ljsheehan.livejournal.com

To determine what kind of stone the axes were made of, Lu used X-ray diffraction, scanning electron microscopy, and electron microprobe analysis. These techniques enabled him to determine the axes' chemical composition as well as the crystal structure of the stones' minerals. He found that all four axes were composed primarily of three minerals, the most abundant one being the aluminum oxide called corundum, which is the stuff of rubies and sapphires. Corundum's presence was a surprise, says Lu.

It's the second-hardest mineral on Earth; only diamond is harder. Lu reasoned therefore that the only mineral strong enough to polish a corundum-rich ax would have been diamond. "Everyone thought the ancient Chinese were using quartz" for their polishing, he says. Quartz, however, is too soft to buff corundum into a shine.http://ljsheehan.livejournal.com

To test his theory, Lu conducted a series of polishing experiments on one of the burial axes. Using a diamond saw, he sliced the ax parallel to the polished surface and then buffed the new surfaces with commercial polishing equipment using three abrasives: diamond, corundum, and quartz.

Lu quantified the smoothness achieved with each abrasive by using an atomic force microscope to measure nanoscale features on all the samples' surfaces. Only the diamond-polished sample closely matched the smoothness of the ancient surface, he reports in the February Archaeometry.

There are two known diamond deposits within 300 kilometers of the burial sites, a distance that could have been traversed by Neolithic people, Lu notes.

"Lu and his colleagues are the first to seriously address the question of what abrasives were used [in Neolithic China]," says Janet Douglas, a conservation scientist at the Smithsonian Institution in Washington, D.C. The new work also indicates that ancient Chinese artisans could have used diamond to work jade into thousands of smooth, gleaming objects, she says.

Lu also wonders whether Neolithic societies polished jade with diamond, since it would have been a more efficient abrasive than quartz.

report

When it comes to pain control, a dose of positive thinking goes a long way, according to researchers who have found that many of the same brain areas that respond to severe pain also respond to mere expectations of pain. This commonality provides a neural route for the mind to quell pain and could explain the pain-fighting power of placebos, the scientists say.

"Pain emerges from the interaction between signals coming from an injured body region and cognitive information unique to each individual, such as expectations about what that pain will feel like," says neuroscientist Robert C. Coghill of Wake Forest University School of Medicine in Winston-Salem, N.C. He and his coworkers report their results in the Sept. 6 Proceedings of the National Academy of Sciences.

For their study, Coghill and his colleagues recruited 10 volunteers, ages 24 to 46, and fitted each with a device that delivered heat pulses to the lower right leg. In a training session, the researchers taught participants to expect one of three intensities of painful heat, depending on the delay between a tone and the jolt. A 7-second interval signaled heat that caused mild pain, a 15-second wait heralded heat that produced moderate pain, and a 30-second gap indicated heat resulting in pronounced pain. http://www.soulcast.com/Louis_J_Sheehan_Esquire_1

Each heat pulse lasted for 20 seconds, and none burned or damaged the skin.

A day or two after training, each participant completed 30 heat-pulse trials while a functional magnetic resonance imaging scanner measured blood flow throughout the brain. On about one-third of the trials, the researchers switched the timing signals for upcoming pain amounts so that volunteers received heat pulses that were either of higher or lower intensity than they expected.

As the magnitude of expected pain increased, brain regions associated with learning, memory, emotion, and tactile sensation became more active. Areas of neural activation measured while volunteers actually experienced pain largely corresponded to areas activated by the expectation.

When participants received the most-painful heat after expecting only moderately painful jolts, the intensity of their self-reported pain fell by 28 percent compared with trials in which they both expected and experienced the severe pain.

These expectations of less pain yielded about as much relief from physical pain as researchers had previously reported for morphine, Coghill says. The new study adds to a growing body of evidence that placebos work via the brain mechanisms underlying pain (SN: 9/3/05, p. 157: Available to subscribers at http://www.sciencenews.org/articles/20050903/note13.asp).

In contrast, expectations of harsher heat pulses than were actually delivered didn't magnify volunteers' self-reported pain. The researchers plan to examine potential effects of negative expectations more closely in pessimists, whose personalities may predispose them to pain sensitivity. http://www.soulcast.com/Louis_J_Sheehan_Esquire_1

The new report "underscores the biological fact that pain is not merely a passive response to tissue damage or potential tissue damage," remarks neuroscientist Donald D. Price of the University of Florida's College of Dentistry in Gainesville. "Its magnitude is partly determined by ongoing expectations."

The work opens the door to exploring purely psychological interventions to prepare patients for painful medical treatments by recasting their expectations of what's in store, Coghill notes.