scientific american - 1994 03 - visiting yourself in the past

... grown. Copyright 1994 Scientific American, Inc. MARCH 1994 $3.95 In the deep Atlantic, Nautile hunts for clues to the forces that make continents drift. Visiting yourself in the past. Rewriting the genes. Information ... of the original miner- als in the peridotite. Some minerals, such as clinopyroxene, melt more easi- ly than do others and hence rapidly de- cre...

Ngày tải lên: 12/05/2014, 14:54

... ferrying the virus across the blood-brain barrier. Another main- tains the blood-brain barrier is some- how disrupted, permitting the entry of viral particles or infected cells. Once there, the virus ... call this the seeing-is-believing principle. T he true signiÞcance of the see- ing-is-believing principle was not revealed to me until 1985. One day in the spring of that ye...

Ngày tải lên: 12/05/2014, 14:49

... sur- rounding the Antarctic far inland. The three-million-year-old diatoms found by Harwood might also have been trans- ported from open sea into the Trans- antarctic Mountains, mingling with the much ... belching up gas now and then—or whether they result from the sound bouncing back and forth along the path between the source and the receiving instrument. Schlindwein and her...

Ngày tải lên: 12/05/2014, 15:02

... are versions of string theory that predict something like the menu of Þelds in- corporated in the Standard Model. But string theory has had no success- es yet in explaining or predicting any of the numerical ... their memories of running the maze. The ma- jor diÝerence was that the Þring was more rapid, as if the memories were be- ing run on fast-forward. The Þring oc- c...

Ngày tải lên: 12/05/2014, 14:58

... disease of rene- gade cells. Tissue from the uterine lin- ing proliferates in other areas of the body, such as the bladder, intestine or, in rare cases, the lung. How these cells reach the distant ... work- erÑby the purely domestic impact of the decline in productivity growth. I f foreign competition is neither the main villain in the decline of man- ufacturing nor...

Ngày tải lên: 12/05/2014, 14:54

... conditions. At the be- ginning of the race, the runners line up at the startÑthat is, they are well local- ized. Each one runs in one of the quan- tized Bohr orbits. During the initial laps, the runners ... how often it occurs. The standard neo-Dar- winian picture in evolution, in which mutation is the main engine for intro- ducing genetic novelty, has proved ex- treme...

Ngày tải lên: 12/05/2014, 14:56

... use. In a carÕs motor, pistons move through the cylinders, each dis- placing a certain volume. Expanding gas- es pushing on the piston produce pow- er. The combined volume for all the cyl- inders ... in the brain. Like the brain, the network must undergo a ÒtrainingÓ pro- cess. In the police network, input pro- cessors accept personnel information about an individual oÛc...

Ngày tải lên: 12/05/2014, 14:59

... in its wake. The ultra- violet glow detected by this instru- ment therefore outlines the shape of the sun’s wind. So far these mea- surements indicate that the solar wind is more intense in the ... links joining the lip- ids to one another, changing the color of the film to a reddish magenta. The sensitivity of the test scheme is limited mainly by the ability of the...

Ngày tải lên: 12/05/2014, 15:21

... responsible for feeling an itch. Examining anesthetized cats, they tracked the response of these neurons when itch- inducing histamine was ap- plied to the skin. The discov- ery, reported in the January Nature ... chronicling their way of life in a record-selling book and prizewinning documentaries. Napoleon Chagnon’s research catapulted the Yano- mamö into the limelight as t...

Ngày tải lên: 12/05/2014, 16:08

Ngày tải lên: 05/11/2012, 14:32