Role of nonlinear coupling and density fluctuations in magnetic-fluctuation-induced particle transport

Three-wave nonlinear coupling among spatial Fourier modes of density and magnetic fluctuations is directly measured in a magnetically confined toroidal plasma. Density fluctuations are observed to gain (lose) energy from (to) either equilibrium or fluctuating fields depending on the mode number. Experiments indicate that nonlinear interactions alter the phase relation between density and magnetic fluctuations, leading to strong particle transport.     

Local measurement of nonclassical ion heating during magnetic reconnection

Local ion temperature and flows are measured directly in the well-characterized reconnection layer of a laboratory plasma. The measurements indicate strongly that ions are heated due to reconnection and that more than half of the reconnected field energy is converted to ion thermal energy. Neither classical viscous damping of the observed sub-Alfvenic ion flows nor classical energy exchange with electrons is sufficient to account for the ion heating, suggesting the importance of nonclassical dissipation mechanisms in the reconnection layer.     

无机-有机杂化非线性光学晶体材料LAP和d-LAP晶体红外吸收边计算

根据双原子谐振子模型近似,提出了估算分子晶体材料红外吸收边的理论方法,然后利用超分子量子化学从头算,计算了L-精氨酸一水磷酸盐(LAP)晶体和氘化L-精氨酸一水磷酸盐(d-LAP)晶体单元超分子的红外振动光谱,其中LAP晶体超分子计算值与晶体红外光谱实验值吻合,表明超分子计算能有效地模拟无机-有机杂化非线性光学晶体的红外振动光谱。在归属了超分子重要基频线后,分析其红外强度,并估算了泛频频率。根据我们提出的方法,估算了这两种晶体的红外吸收边,结果与实验值较吻合。表明我们建议的理论方法是合理的。此外,通过计算表明,如果非线性光学晶体材料的红外吸收边是由与活泼H有关的伸缩振动泛频频率决定,那么活泼H的氘化是一种改善红外吸收边的有效途径。     

Measurement of the Majorana effect in a molecule using a switched magnetic field and quantum beat detection

By means of quantum beat spectroscopy we investigated the dynamics of magnetic moments associated with hyperfine levels in the molecule under “spin-flip conditions”. Oriented molecules in a cold beam were prepared by excitation with a circularly polarized laser pulse () in a weak magnetic field (). Subsequently, they were exposed to a rapid field inversion which left the magnetic moment in its initial orientation. The initially created coherences among the excited hf levels were conserved after field reversal and thus were explored to characterize the changes in the level structure due to this “Majorana spin-flip” process. Received: 4 February 1999     

Cancellation of Linearized Axion-Dilaton Self-Action Divergence in Strings

The force densities exerted on a localizedmaterial system by linearized interaction with fields ofaxionic and dilatonic type are shown to be describablevery generally by relatively simple expressions that are well behaved for fields of purelyexternal origin, but that will be subject to ultravioletdivergences requiring regularization for fields arisingfrom self-interaction in submanifold-supported brane-type systems. In theparticular case of a two-dimensionally supported, i.e.,string-type, system in an ordinary four-dimensionalbackground it is shown how the result of thisregularization is expressible in terms of the worldsheetcurvature vector K, and more particularlythat (contrary to what was suggested by early work onthis subject) for a string of Nambu-Goto type thedivergent contribution from the dilatonic self-action will always bedirected oppositely to its axionic counterpart. Thismakes it possible for the dilatonic and axionicdivergences entirely to cancel each other out (so that there is no need of a renormalization to getrid of infinities) when the relevantcoupling coefficents are related by the appropriateproportionality condition provided by the low-energylimit of superstring theory.     

Angular distribution of radiant intensity from sources of different degrees of spatial coherence

The relationship that exists between the state of coherence of a source and the angular distribution of the radiant intensity is investigated. It is found that the radiant intensity from a large, planar, statistically homogeneous source is related in a simple way to the Fourier transform of its degree of spatial coherence. This result is illustrated by curves that show the angular distribution of radiant intensity for gaussian correlated sources. The curves demonstrate in a striking way how spatial coherence of the source affects the directionality of a light beam that the source generates.     

A comparison of gas-phase,plasma, sputtering and beam-foil excitations

A comparison of relative populations of ZnI and ZnII levels excited in equilibrium plasma, sputtering, gas-phase single collision, and beam foil sources is presented, and includes data on the first reported excitation studies under single collision conditions for a (transition metal atom)-(transition metal ion) interaction. A search for continuum emission from atomic chromium, like that seen during sputtering of chromium metal, produced a negative result.     

An NRD-fed dielectric rod antenna for the short millimeter wave band

A simple E-plane tapered rectangular dielectric rod fed by NRD guide is used as a millimeter wave antenna. This class of aerial features attractive radiation patterns with relatively low sidelobes and moderate gain. The measured results show that such an antenna and mounting structure can be exploited as effective radiating element in the short millimeter wave frequency band.