ISSN:0031-9228    

DOI:10.1063/1.2806634

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881709

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881707

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

When Wolfgang Ketterle and his colleagues at MIT demonstrated an “atom laser” recently, the announcement excited the physics community and naturally grabbed the attention of the popular press. One essential property of a laser is, of course, its coherence, and the evidence provided by the MIT group is striking: Sharp interference fringes formed when two Bose–Einstein condensates from the same trap expanded and overlapped after being released from confinement. The fringes are reminiscent of the interference between coherent light waves emanating from a double slit. (See the figure below.)

ISSN:0031-9228    

DOI:10.1063/1.881708

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Everyone likes a bargain, and what could be better than two for the price of one? That's what researchers in Boulder, Colorado, must have figured when they snared not just one but two spin states of the rubidium atom in an ultracold trap and simultaneously formed overlapping Bose–Einstein condensates from them. The feat—accomplished by Eric Cornell, Carl Wieman and their colleagues at JILA, the University of Colorado and the National Institute of Standards and Technology in Boulder—gives a valuable tool to those interested in atomic collisions and their dependence on spin states, as well as to those interested in further exploration of interactions between and within condensates. As William Phillips of NIST in Gaithersburg, Maryland, points out, such a double condensate, of two different internal states of the same atom, is unlike anything seen in superfluid4He,a condensed‐matter Bose–Einstein condensate.

ISSN:0031-9228    

DOI:10.1063/1.881726

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

General relativity and quantum mechanics, two of the monumental achievements of 20th‐century physics, verified by experiment to unprecedented levels of accuracy, have long resisted physicists' attempts to combine them in a single comprehensive theory. In recent years much research in this area has focused on one central conundrum: how to describe the quantum physics of black holes.

ISSN:0031-9228    

DOI:10.1063/1.881727

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Has the time come to abandon hope of an astrophysical—as distinguished from particle‐theoretic—solution of the solar neutrino puzzle? Two recent papers espouse different positions on this important issue. In the 18 NovemberPhysical Review LettersWick Haxton (University of Washington) and Andrew Curnrning (a visiting undergraduate from Cambridge University), argued that there might still be an astrophysical explanation for the observed shortfall of8Bdecay neutrinos from the Sunandfor the even greater shortfall of solar neutrinos from electron capture by7Be:namely the slow mixing of3Hedown into the solar core. “This is a very speculative departure from the standard model of how the Sun works,” Haxton told us. “But we're all willing to carefully examine some rather exotic particlephysics solutions. So it may be equally important to explore unexpected solarphysics solutions.”

ISSN:0031-9228    

DOI:10.1063/1.881719

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Data security has become part of our everyday lives. For even the most banal transactions, a secure piece of identification—a passport, password, bank card, credit card, personal identification number or driver's permit—is often required. As those proofs of identity have become increasingly necessary in our complex world, they have also increased the opportunities for deception. Each year, US business spends many billions of dollars on information fraud, including forged credit cards. Many of those losses are passed onto the consumer. Each year, tens of millions of dollars in counterfeit US notes are seized worldwide. And counterfeit manufactured goods, such as computer chips and machine tools, are arriving on our shores in greater numbers than ever.

ISSN:0031-9228    

DOI:10.1063/1.881691

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The irreversibility of time is a topic generally associated with fundamental physics. Imaging techniques, on the other hand, are usually related to engineering sciences. Remarkably, however, these two domains can be fruitfully connected to yield many applications in medicine, undersea communications, hydrodynamics and material analysis, as well as elegant experiments in pure physics.

ISSN:0031-9228    

DOI:10.1063/1.881692

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thermoelectrics is an old field. In 1823, Thomas Seebeck discovered that a voltage drop appears across a sample that has a temperature gradient. This phenomenon provided the basis for thermocouples used for measuring temperature and for thermoelectric power generators. In 1838, Heinrich Lenz placed a drop of water on the junction of metal wires made of bismuth and antimony. Passing an electric current through the junction in one direction caused the water to freeze, and reversing the current caused the ice to quickly melt; thus thermoelectric refrigeration was demonstrated (figure 1).

ISSN:0031-9228    

DOI:10.1063/1.881752

出版商:AIP    

年代:1997

数据来源: AIP