ISSN:0031-9228    

DOI:10.1063/1.2808689

出版商:AIP    

年代:1994

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808690

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In the wake of the cancellation of the $11 billion Superconducting Super Collider, another big‐ticket physics facility is seeking its fortunes with Congress. The supplicant is the Advanced Neutron Source, a $2.9 billion research reactor designed at Oak Ridge National Laboratory to provide at least five times the neutron flux of any existing facility and support up to 1000 users per year, conducting experiments in material, biological, condensed‐matter and chemical physics. The 1994 Nobel Prize in Physics was just awarded for the type of studies that would be done at the ANS: The Royal Swedish Academy of Sciences gave the prize to Bertram N. Brockhouse of McMaster University in Hamilton, Ontario, and Clifford Shull of MIT for “pioneering contributions to the development of neutron‐scattering techniques for studies of condensed matter.”

ISSN:0031-9228    

DOI:10.1063/1.2808691

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Recently there have been some interesting developments at HERA, the Hadron‐Electron Ring Accelerator that wends its circular way for 6 kilometers beneath the streets and parks of Hamburg. Since the fall of 1992 this uniquely asymmetric pair of storage rings has been providing experimenters with collisions between 820‐GeV protons and 30‐GeV electrons. (SeePHYSICS TODAYMarch 1992, page 21.) Since July, however, HERA has been running with positrons instead of electrons, and will continue to do so at least until the end of 1995. And more importantly, the circulating HERA positron (or electron) beam can now be longitudinally polarized at will. That's an important first: No other electron storage ring has ever achieved longitudinal polarization.

ISSN:0031-9228    

DOI:10.1063/1.2808692

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

If you have ever lived in an apartment and had overhead neighbors, you have probably been anoyed by the noise they made just walking. This can be a problem even in luxury condominiums designed with acoustic privacy in mind. Now we know why.

ISSN:0031-9228    

DOI:10.1063/1.2808693

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Planet Earth is too small. Our activities as a species are constrained by our environment in more complex and subtle ways than we understood only a few decades ago. We have been living within fences and only now have found these fences. What a loss of innocence!

ISSN:0031-9228    

DOI:10.1063/1.881422

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Humans are greatly perturbing the global nitrogen cycle. Perhaps the best evidence for this perturbation comes from air trapped in layers of quasipermanent ice in the Arctic and the Antarctic. Ice cores taken from these two polar regions give us a 2000‐year record of the Earth's atmospheric composition. This record indicates a striking constancy in nitrous oxide concentrations, at approximately 285 parts per billion, for nearly 1500 years. (See figure 2.) Since about 1600 AD, however, nitrous oxide concentrations have been increasing, and the present‐day atmospheric burden of this gas is greater than at any other time in the past two millennia. Furthermore, nitrous oxide concentrations continue to increase, currently at a rate of about 0.3&percent; per year. These variations indicate that many nitrogen flows are now larger than in preindustrial times, and other evidence suggests that human activity is responsible. (See figure 1.).

ISSN:0031-9228    

DOI:10.1063/1.881423

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The balance between incoming solar radiation and outgoing infrared radiation determines to a significant degree the Earth's climate. Clouds play a major role in determining the net radiative balance, so any change in cloud coverage or optical properties leads to a new climate state. To study the present and future climate states, the most comprehensive numerical tools currently available are global climate models. A major challenge in these models of Earth's environment is an accurate representation of clouds. (See figure 1.)

ISSN:0031-9228    

DOI:10.1063/1.881424

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The ocean is a mysterious place. As terrestrial creatures, we are familiar with a small volume of relatively warm ocean water near the surface. The deep ocean is not so familiar. Isolated from the thermal energy of the Sun and the mechanical energy of atmospheric winds, the deep ocean is completely dark and filled with near‐freezing water. Yet the deep ocean is far from stagnant. Radioactive tracer measurements show that the ocean's circulation brings its interior water into contact with the atmosphere every 600 years or so.

ISSN:0031-9228    

DOI:10.1063/1.881425

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Fossil fuel combustion, the technology on which the world relies most heavily for power generation, heating and transportation, was adopted long before its environmental burdens had been fully recognized. The results of our recent efforts to mitigate these environmental costs are perceptible, but still modest and very costly. Despite the use of sulfur scrubbers, acid rain remains a serious regional threat, especially with the increased use of lowquality coals. Catalytic converters have reduced nitrogen oxide and carbon monoxide emissions from automobiles in some countries, but the poor air quality of many of the world's urban areas nonetheless constitutes a severe health threat. New, more efficient power plants and automobiles generate less carbon dioxide per unit of useful energy than did their predecessors, but atmospheric carbon dioxide concentrations continue to rise, intensifying the threat of global warming. Despite our diligent efforts, a major strategic shift in energy production may be required to achieve more than incremental and perhaps inadequate advances. What is needed is an energy conversion technology that is inherently clean, efficient and compatible with renewable energy sources.

ISSN:0031-9228    

DOI:10.1063/1.881426

出版商:AIP    

年代:1994

数据来源: AIP