ISSN:0031-9228    

DOI:10.1063/1.2405447

出版商:AIP    

年代:1900

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.882955

出版商:AIP    

年代:1900

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.882956

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In high school chemistry experiments, it's easy to follow a chemical reaction: Mix the chemicals in a test tube, and watch for a change of color, fizzing, or some other sign of chemical transformation. But what do you do if you want to probe the spatial limits of chemistry—that is, to initiate and examine an individual chemical reaction? In a recent paper inScience, Wilson Ho of Cornell University and his graduate student Hyojune Lee provide an answer. By using a scanning tunneling microscope (STM), Ho and Lee combined atoms and molecules on a metal surface to make new molecules. But that's not all they accomplished. To confirm the chemical identity of their molecular creations, they measured the individual molecules' vibrational energies—again with the STM. “Their results are truly remarkable,” comments the University of Maryland's Ellen Williams, “not just creating the bonding, but also the single‐molecule spectroscopy.”

ISSN:0031-9228    

DOI:10.1063/1.882958

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Chalk up another one for the shell model…maybe its last one for a while. The model has had a long run in predicting which nuclei would have special stability compared to their neighboring isotopes because they had the right numbers of protons and neutrons—magic numbers—to completely fill the available shells, or energy levels. By now, experimenters have found about ten doubly magic nuclei (in which the numbers of protons and neutrons are both magic) but still sought one elusive holdout:48Ni.A group of researchers working at the Grande Acce´le´rateur National d'Ions Lourds (GANIL) in France has now produced this lightest of nickel's isotopes. (Two other isotopes of nickel are also doubly magic.)

ISSN:0031-9228    

DOI:10.1063/1.882959

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

By an improbable stroke of good fortune, the north‐polar region of Io, the innermost of Jupiter's four Galilean moons, was putting on an extraordinary volcanic display just as NASA's Galileo spacecraft flew by to take pictures on Thanksgiving Day last year. Because its proximity to Jupiter and its orbital resonance with two neighboring moons subject it to severe tidal flexing, Io turns out to be the most volcanically active body in the Solar System. (See the cover of this issue.)

ISSN:0031-9228    

DOI:10.1063/1.882960

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The usual potted history of the neutrino hypothesis that we find in textbooks goes something like this:Radioactivity—the spontaneous transformation of one element into another—produces &agr; particles, or &bgr; particles, or &ggr; rays. Experimental work on the energy of the electrons emitted in &bgr; decay began early in the 20th century, and the observations posed a problem: If there were only two bodies (the daughter nucleus and an electron) in the final state of a &bgr; decay, the conservation of energy and momentum would require that the spectrum of decay electrons must be monoenergetic. Thus, the observation of a continuous spectrum—electrons emitted with all energies from zero up to a maximum that depended on the radioactive element—cast doubt on both of these conservation laws. Or perhaps the electrons lost varying amounts of energy in escaping the radioactive substance, thus accounting for the continuous energy spectrum. But careful experiments showed that this was not the case. So the problem persisted. In the early 1930s, Wolfgang Pauli suggested that an undetected neutral particle of low mass was also emitted in &bgr; decay. Enrico Fermi dubbed this putative particle the “neutrino.” That solved the problem of the continuous spectrum, because, in a three‐body decay, the energy of the electron is no longer required to be unique. The energy and momentum conservation laws were saved.

ISSN:0031-9228    

DOI:10.1063/1.882961

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Cavitation—the formation of bubbles—is a familiar phenomenon. Whenever a liquid is agitated violently, there is a possibility that cavitation will occur (see, for example, figure 1). In the case of boat propellers or hydraulic machines, cavitation is a problem that engineers try to avoid. In other contexts, however, cavitation can be useful—as, for example, in ultrasonic cleaning devices.

ISSN:0031-9228    

DOI:10.1063/1.882962

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Let's meet tonight's lucky contestants, ladies and gentlemen, all ready to playGuess My Number, for the grand prize of “ONE MILLION DOLLARS!”

ISSN:0031-9228    

DOI:10.1063/1.882963

出版商:AIP    

年代:1900

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.882983

出版商:AIP    

年代:1900

数据来源: AIP