scientific american - 1993 09 - special issue - life, death, and the immune system

... Number 3 52 64 72 80 SPECIAL ISSUE Life, Death and the Immune System Sir Gustav J. V. Nossal How the Immune System Develops Irving L. Weissman and Max D. Cooper How the Immune System Recognizes ... the activity of B cells, other T cells and oth- er parts of the immune system. Once formed, cells of both types mi- grate to the spleen, lymph nodes and in...

Ngày tải lên: 12/05/2014, 14:50

... river sand and then some plastic sheeting and then more sand and a lot of boulders on top to keep the animals oÝ and the Maasai oÝ.Ó But acacia trees took root and grew down among the tracks and ... expansion. A nother theory, the steady state the- ory, also succeeds in accounting for the expansion and homogen- eity of the universe. In 1946 three phys- icists in...

Ngày tải lên: 12/05/2014, 14:58

... howev- er, the consuming issues are not statisti- cal and political but personal and med- ical. What are the latest findings about how cancer develops and becomes le- thal? What is the most up-to-date ... is —de- pending on your point of view —either the ultimate guarantee of privacy from snoopers or the stock-in- trade of Internet-savvy terrorists, drug smugglers and other v...

Ngày tải lên: 12/05/2014, 15:15

... edifice. In the case of the World Trade Center, which was a state-of -the- art design in the late 1960s, the steel-mesh exterior skeleton was highly robust, but the steel-truss floor fram- ing turned ... fragile, and the cen- tral core was not designed to handle signi - cant lateral (sideways) loads, Thornton ex- plains. When the planes hit the towers, they knocked out man...

Ngày tải lên: 12/05/2014, 16:14

... pro- posed second-generation system known as Computer-Assisted Passenger Pre-Screening, or CAPPS II. In terms of the variety of in- formation, the sys- tem goes much fur- ther than the 1.0 ver- sion and ... understanding of other cultures and the fact that data mining is only as successful as the mind-set that pro- duces the search criteria allows it to be, he fa- vors a ris...

Ngày tải lên: 12/05/2014, 16:18

... most of their travel time on the ground. The Past and Future of Global Mobility Scientific American October 1997 61 The Authors ANDREAS SCHAFER and DAVID VICTOR col- laborate on long-term and large-scale ... bicycles, ships and the new steam-, electric- and gas-pow- ered automobiles. “If there are faults” with cars, the editors concluded, “only time is wanted to make t...

Ngày tải lên: 12/05/2014, 15:30

... need to under- stand their relationship with the environment,Ó Gonzalez says. Some of the tribes live in the for- est during the rainy sea- son, some during the dry season, and they all have slightly ... such small-time cus- tomers for bootleg CFCs: their com- petitors. The agency has set up an 800 number as a tip line and has been pass- ing on leads to the IRS. ÒItÕs a dog-...

Ngày tải lên: 12/05/2014, 15:02

... declines as the reefs get farther away from two centersÑone in the Indo-Pa- ciÞc and the other in the Caribbean. The outlines of a map marking plum- meting diversity coincide with the con- tours ... 4,400 12-BILLION-YEAR- OLD AGE TRACK 15-BILLION-YEAR- OLD AGE TRACK NGC 288 NGC 362 Copyright 1992 Scientific American, Inc. means that within the halo the only re- maining m...

Ngày tải lên: 12/05/2014, 14:48

... protects the sample from the heat, to the surface of the superconduc- tor. There they decorate the regions where the magnet- ic-flux lines pass through the surface. The iron parti- cles “stick” to the ... logged land. They bring with them little ability to protect the fragile ecosystem. Their small-scale logging, charcoal produc- tion and slash -and- burn farming often c...

Ngày tải lên: 12/05/2014, 14:48

... radar and laser altimeter, which together can determine the thick- ness of the ice and the nature of the underlying rock. With Robin E. Bell of the Lamont-Doherty Geological Obser- vatory, the co-leader ... the tension and comparing the re- sults with those from the other craft. Copyright 1993 Scientific American, Inc. A t its best, the immune system is the...

Ngày tải lên: 12/05/2014, 14:49