摘要:

Impedance measurements on scale models can be an extraordinarily simple and effective technique for comparing the lift and drag forces and the static and dynamic stabilities of various vehicle‐guideway configurations for levitation by motion‐induced eddy‐current repulsion. The real and imaginary components of the input impedance of an inductive circuit are a measure of its power loss and magnetic energy storage, and the gradient of that energy is magnetic force. As a demonstration of the technique, we have applied it to variations of the magneplane system being developed by the MIT‐Avco‐Raytheon group.

ISSN:0021-8979    

DOI:10.1063/1.1662272

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A theoretical expression for magnetic transition temperatures of binary rare‐earth alloys is proposed based on the similarity between the expressions of spin‐disorder resistivity and transition temperatures of pure rare‐earth metals. The proposed expression for the magnetic transition temperature for binary rare‐earth alloys iskTc (or Tp)=(−3&pgr;Z2)/EF&OHgr;2)&Sgr;Rn≠0&PHgr;(2KFR) × [x(1−x)Vab2 + xGa2(ga−1)2ja(ja+1)+(1−x)Gb2 (gb−1)2jb(jb+1)], where &PHgr;(2KFR)=(KFR×cosKFR‐ sinKFR)/(KFR)4and the other symbols have their usual meaning. The above expression is obtained from considering an equation for spin disorder resistivity given by Dekker. The experimental data of magnetic transition temperatures of Gd&sngbnd;Dy system have been used to test the validity of the proposed equation. The agreement between theory and experiment is reasonably good.

ISSN:0021-8979    

DOI:10.1063/1.1662273

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Transitions from the zero‐voltage to the voltage state have been directly measured on large (≃104&mgr;m2) Josephson junctions. By adjusting the current load, the switching times (10–90%) were varied from 60 to 400 psec. Good agreement was found between theoretical and experimental results. The times required to transfer current from junctions into superconductive inductances (10−11−10−10H) were also investigated. The switching times ranged from 300 to 550 psec and agreed basically with our simple theoretical model. To explain the details of the voltage developed during current transfer, self‐pumped junction resonances had to be invoked. Although these times are expected to be smaller in miniaturized devices, they represent to our knowledge the shortest times ever reported for circuits with a dissipation of less than 10−5W in continuous operation.

ISSN:0021-8979    

DOI:10.1063/1.1662274

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A quantitative theory for the magnetostriction due to exchange interactions in metals has been developed, based on the ideas of Zener. The theory is in good agreement with the measured values for pure nickel and iron, and it explains the anomalous thermal expansion in the iron‐nickel Invar alloys, as well as more complex alloys containing manganese and/or cobalt.

ISSN:0021-8979    

DOI:10.1063/1.1662275

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The effect of varying electron concentration on the magnetic ordering in the ternary intermetallic compounds DyCo3−xNix, DyFe3−xNix, HoCo3−xNix, HoFe3−xNix, with 0<x<3, has been investigated by saturation magnetization studies. The results show a filling of the Co and Fe bands and also a polarization of the 3dband of nickel. In the case of the Co compounds an additional contribution from the induced moment on cobalt by the rare‐earth exchange field is found to be important.

ISSN:0021-8979    

DOI:10.1063/1.1662276

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This work poses the control of an instability in the multiarm fluid pendulum as an optimal regulator problem. A linear set of equations describing the motion of fluid in the pendulum is developed and the analytical solution of the control problem is presented. An experiment of optimal stabilization on a two‐arm pendulum is discussed and compared with theoretical predictions. The optimal control requires only a slightly more complex feedback circuit, but it reduces considerably the energy put into the system.

ISSN:0021-8979    

DOI:10.1063/1.1662277

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

It is shown that insulating oils can be supercooled and that they exhibit a glass transition temperature and a secondary dielectric relaxation peak. The similarity in these properties between oils and polymers is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662278

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Chemically produced silver platelets were found to serve as ideal substrates for epitaxial experiments. The preparation, cleanliness, and perfection of these platelets are described and the epitaxial growth of iron on silver is discussed as an example. It is shown that iron deposits of average thickness as low as 1 Å may be detected via transmission electron diffraction, provided a sufficiently thin silver platelet is used as a substrate.

ISSN:0021-8979    

DOI:10.1063/1.1662279

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

It is shown that the true activation areaA*is less than the apparent activation areaB*, and the difference betweenA*andB*is calculated in terms of quantities obtainable in a tensile test. This result depends on the assumptions discussed in the paper, but represents a generalization of previous work in the sense that a sinusoidal stress field need not be assumed.

ISSN:0021-8979    

DOI:10.1063/1.1662280

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The Gru¨neisen parameters of some group‐V and group‐VI elements have been calculated from recent data on thermal expansion and compressibility and, theoretically, from the Morse function using a modification of Slater's method. These values agree mutually and with those estimated from the pressure variation of compressibility but differ severely from those estimated from log&thgr;‐logVplots.

ISSN:0021-8979    

DOI:10.1063/1.1662281

出版商:AIP    

年代:1973

数据来源: AIP