ISSN:0031-9228    

DOI:10.1063/1.2806691

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881877

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881878

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

For years, a debate has raged among Earth scientists about the convection within our planet's thick mantle. Most researchers agree that the 3000 km thick mantle is divided into an upper region and a lower region by an interface at a depth of about 660 km where the mantle materials undergo an isochemical phase change. But they differ as to whether this seismic discontinuity is a barrier to convection.

ISSN:0031-9228    

DOI:10.1063/1.881853

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

These five images are probability distributions for quantum states of light, as measured by a group at the University of Konstanz in Germany. The top distribution is a coherent state and the other four are a variety of squeezed states.

ISSN:0031-9228    

DOI:10.1063/1.881854

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

At the Lawrence Berkeley National Laboratory, Ron Scanlan and colleagues are investigating the use of brittle superconducting cable to create accelerator bending magnets significantly stronger than those designed for the abandoned Superconducting Super Collider (SSC) and CERN's much‐anticipated Large Hadron Collider (LHC). With the 1‐meter‐long prototype dipole magnet shown here end‐on, the group recently achieved a record bending field of 13.5 tesla in the 5 cm beam aperture visible at the center.

ISSN:0031-9228    

DOI:10.1063/1.881880

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

New studies are revealing the dynamics of the Earth's deep interior to a degree that could hardly be imagined even a few years ago. A combination of geophysical observations (mostly seismological, geomagnetic and geodetic) and new laboratory and computational results has revolutionized our ability to understand what happens at the core of our planet.

ISSN:0031-9228    

DOI:10.1063/1.881885

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

It is through photosynthesis that Earth's biosphere derives its energy from sunlight. Photosynthetic organisms—plants, algae and photosynthetic bacteria—have developed efficient systems to harvest the light of the Sun and to use its energy to drive their metabolic reactions, such as the reduction of carbon dioxide to sugar. The ubiquitous green color of plants is testimony to the key molecular participant in the light harvesting of plants, chlorophyll. More hidden in this respect, but no less widespread, is a second participating molecule, carotenoid. In green leaves, the color of the carotenoids is masked by the much more abundant chlorophylls, whereas in ripe tomatoes or the petals of yellow flowers, the carotenoids predominate. Chlorophyll molecules exist in slightly different chemical structures in various photosynthetic organisms, as chlorophyllaorbin plants or algae, and as bacteriochlorophyllaorbin photosynthetic bacteria. Molecules such as chlorophyll and carotenoid that absorb light and impart color to living matter and other materials are called pigments.

ISSN:0031-9228    

DOI:10.1063/1.881879

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The quest to measure temperature accurately began in ancient Greece with the invention of the thermoscope—an open, oil‐inglass device that was the forebear of the familiar, sealed, liquid‐in‐glass thermometer. Since that time, many new types of thermometer have been invented to serve contemporary science and commerce. The two extremes of temperature will, however, always remain out of reach of our devices. The highest temperature attained by a physical phenomenon, that of the universe at its birth, is certainly beyond our measurement capabilities, although not our ability to estimate—on the order of1023kelvin. The third law of thermodynamics forbids experiments from ever reaching the lower limit, absolute zero, although they may approach it arbitrarily closely.

ISSN:0031-9228    

DOI:10.1063/1.881886

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881958

出版商:AIP    

年代:1997

数据来源: AIP