ISSN:0031-9228    

DOI:10.1063/1.2806730

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881986

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881990

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

To particle physicists, the electron is the quintessential example of an elementary particle: The highest energy experiments to date have revealed no evidence of any internal structure, no evidence that an electron is made up of some other, more fundamental components. But for condensed matter physicists studying the behavior of matter at low temperatures in semiconductor crystals, electrons can play by a different (although ultimately equivalent) set of rules. The fractional quantum Hall effect, for example, can be explained by invoking quasiparticles, which behave like distinct particles that each carry a fraction of an electron's charge. (On a more fundamental level, quasiparticles are collective excitations of interacting electrons.) Two recent experiments in Israel and France have added to the evidence that these quasiparticles exist.

ISSN:0031-9228    

DOI:10.1063/1.882050

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Akey question regarding high‐temperature superconductors has been the nature of the pairing state of the electrons responsible for the supercurrent: Do the electrons couple in an s‐wave state, as in conventional superconductors, or in a d‐wave state, specificallydx2−y2,whose wavefunction resembles a four‐leaf clover. The argument was largely settled in favor of d‐wave symmetry when several precise experiments were able to sense the phase of the electron‐pair wavefunction and found that it changed signs, suggestive of the alternating positive and negative lobes of the d‐wave clover leaf. But not all the evidence lined up: One study of the Josephson tunneling by Robert Dynes and his colleagues at the University of California, San Diego, simply wasn't compatible with a d‐wave interpretation.

ISSN:0031-9228    

DOI:10.1063/1.881991

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Unexpected behavior in a tunneling experiment on one of the high‐temperature superconductors has led the experimenters to conclude that they are seeing broken time‐reversal symmetry. The evidence, if confirmed, would indicate a violation of time reversal only at the surface, but it nevertheless has created a lot of interest, especially among theorists who predicted some type of symmetry breaking in unconventional superconductors even in the bulk.

ISSN:0031-9228    

DOI:10.1063/1.881992

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Four years ago, accelerator physicists at the Stanford Linear Accelerator Center (SLAC) began construction of the Next Linear Collider Test Accelerator (NLCTA), a 42‐meter‐long experimental prototype segment of what they call the “Next Linear Collider.” The NLC they hope to build early in the next century would be a face‐to‐face pair of 10‐km linacs firing electrons and positrons at each other with collision energies up to a TeV (1012electron volts).

ISSN:0031-9228    

DOI:10.1063/1.881993

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Unlike other major medical imaging methods, such as computed tomography, ultrasound, nuclear medicine and magnetic resonance imaging—all of which are digital—conventional x‐ray imaging remains a largely analog technology. Making the transition from analog to digital could bring several advantages to x‐ray imaging: Contrast and other aspects of image quality could be improved by means of image processing; radiological images could be compared more easily with those obtained from other imaging modalities; the electronic distribution of images within hospitals would make remote access and archiving possible; highly qualified personnel could service remote or poorly populated regions from a central facility by means of “teleradiology”; and radiologists could use computers more effectively to help with diagnosis—work that has already been initiated at the University of Chicago by Kunio Doi and his coworkers.

ISSN:0031-9228    

DOI:10.1063/1.881994

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Today the universe is characterized by a richness of complexity. Structure exists on scales from stars to superclusters of galaxies and beyond. Ordinary “baryonic” matter, in the form of protons, nuclei and their accompanying electrons, is found in stars, diffuse hot gas, cold gas and other forms; the admixture varies greatly with environment.

ISSN:0031-9228    

DOI:10.1063/1.881995

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

At first sight, nothing could be simpler than nuclear emulsions, those thin strips of film designed to trap the tracks of passing charged entities—nuclei, protons, electrons and the other objects that inaugurated the field of particle physics. But the method's seeming simplicity hides a complex history. Scientifically, emulsions posed myriad problems and required years of effort by a dedicated corps of emulsion physicists and chemists, who had to learn how to make the film sensitive to minimally ionizing particles, and how to store, process, dry and ultimately analyze the ramified skein of tracks. Developed in the 1930s by Marietta Blau, an Austrian physicist who fled her homeland following the Anschluss in March 1938, the nuclear emulsion method was taken over by Cecil Powell, who transformed it during the 1940s into a cottage industry, with female “scanners” and an international team of physicists and chemists. From Powell's laboratory in Bristol, England, the method migrated to the burgeoning, industrial‐scale accelerator centers at Berkeley and Brookhaven, until even there, emulsions were displaced by the mammoth bubble chambers of the 1950s and 1960s.

ISSN:0031-9228    

DOI:10.1063/1.881996

出版商:AIP    

年代:1997

数据来源: AIP