Partial Structure Factors of Liquid Na-K and Al-Mg Alloys(Physics)

Three partial structure factors S_(Q) have been evaluated from the scattered X-ray intensities of liquid Na-K and Al-Mg alloys assuming that the S_(Q) are independent of the relative abundance of the respective elements in the alloys. The functions S_(Q) and S_(Q) and the reduced radial distribution functions G_(r) and G_(r) obtained in this work are very similar to those observed in the respective pure liquid metals. In both cases, S_(Q) and G_(r) have maxima which lie in between those of the pure elements. From these results, liquid Na-K and Al-Mg alloys are interpreted as random mixing fluids. A comparison between the partial structure factors obtained in this work and those calculated from the hard sphere model was made. Adequate agreement was obtained on the low angle side of the first peak, but agreement on the whole pattern is not necessarily found. The electrical resistivity was calculated using Faber-Ziman\u27s theory and compared with experimental data

AMPTE/CCE‐SCATHA simultaneous observations of substorm‐associated magnetic fluctuations

This study examines substorm-associated magnetic field fluctuations observed by the AMPTE/CCE and SCATHA satellites in the near-Earth tail. Three tail reconfiguration events are selected, one event on August 28, 1986, and two consecutive events on August 30, 1986. The fractal analysis was applied to magnetic field measurements of each satellite. The result indicates that (1) the amplitude of the fluctuation of the north-south magnetic component is larger, though not overwhelmingly, than the amplitudes of the other two components and (2) the magnetic fluctuations do have a characteristic timescale, which is several times the proton gyroperiod. In the examined events the satellite separation was less than 10 times the proton gyroradius. Nevertheless, the comparison between the AMPTE/CCE and SCATHA observations indicates that (3) there was a noticeable time delay between the onsets of the magnetic fluctuations at the two satellite positions, which is too long to ascribe to the propagation of a fast magnetosonic wave, and (4) the coherence of the magnetic fluctuations was low in the August 28, 1986, event and the fluctuations had different characteristic timescales in the first event of August 30, 1986, whereas some similarities can be found for the second event of August 30, 1986. Result 1 indicates that perturbation electric currents associated with the magnetic fluctuations tend to flow parallel to the tail current sheet and are presumably related to the reduction of the tail current intensity. Results 2 and 3 suggest that the excitation of the magnetic fluctuations and therefore the trigger of the tail current disruption is a kinetic process in which ions play an important role. It is inferred from results 3 and 4 that the characteristic spatial scale of the associated instability is of the order of the proton gyroradius or even shorter, and therefore the tail current disruption is described as a system of chaotic filamentary electric currents. However, result 4 suggests that the nature of the tail current disruption can vary from event to event

Temperature dependence of current self-oscillations and electric field domains in sequential tunneling doped superlattices

We examine how the current--voltage characteristics of a doped weakly coupled superlattice depends on temperature. The drift velocity of a discrete drift model of sequential tunneling in a doped GaAs/AlAs superlattice is calculated as a function of temperature. Numerical simulations and theoretical arguments show that increasing temperature favors the appearance of current self-oscillations at the expense of static electric field domain formation. Our findings agree with available experimental evidence.Comment: 7 pages, 5 figure