摘要:

A method is developed for the determination of the effective dissociation potential (Vd) of an alkali compound used as a seed in the low‐temperature and high‐pressure working fluid of a magnetohydrodynamic (MHD) generator. For a simple compound like potassium chloride (KCl)Vdcan be derived directly by measuring the ion density in the plasma from the current‐voltage characteristics observed in MHD generator. For complex seed compounds like potassium sulphate (K2SO4), the method leads to an effectiveVdas referred to an assumed dissociation reaction. Additional experimental information as to the specific radical involved would be required to establish the true dissociation energy. In the experiments presented here, the working gas is argon at atmospheric pressure and the temperature ranges from 2000° to 3000°K. In the temperature range used and for KCl undergoing the reaction KCl&rlarr2;K+Cl, the actual dissociation potentialVdis found to be 3.6±0.4 eV. For K2SO4the assumed dissociation reaction, K2SO4&rlarr2;2K+S+4O leads to the effectiveVd=10.7±3.1 eV.

ISSN:0021-8979    

DOI:10.1063/1.1659409

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A phenomenological description of excess noise in a nonequilibrium system is presented. The development involves two basic physical ideas. Firstly, the excess noise is ascribed to the fluctuation of the local reference level to which equilibrium and other white fluctuations are compared. Secondly, it is assumed that excess low‐frequency noise involves a nonlinear process. This implies the noise power in different frequency regions are coupled. A further simple assumption requires the integral of the power spectral density over specially chosen intervals to be a constant. This leads to a 1/fspectrum for the power spectral density. Possible generalizations that provide for other spectral laws are also mentioned.

ISSN:0021-8979    

DOI:10.1063/1.1659410

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In the production of a hollow inviscid cylinder, it is necessary to maintain an internal pressure to prevent collapse. If this pressure is too low, collapse ensues. The process of collapse is herein examined and equations are given which enable the shape of the initially cylindrical surfaces to be calculated. This collapse mechanism is compared with that arising from capillary instability.

ISSN:0021-8979    

DOI:10.1063/1.1659411

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Laser‐induced optical index damage in LiNbO3and other pyroelectrics of ABO3structure is discussed in the light of recent results of stoichiometry investigations. The damage is attributed to the presence ofB‐excess stacking‐fault defects. The dc photovoltaic effect in LiNbO3as well as the detailed spatial distribution of refractive‐index variation is explained in terms of photoinduced variation of the macroscopic spontaneous polarization density. This variation results in a polarization charge‐density distribution, and an approximately compensatory space‐charge distribution. The index damage results from the polarization‐based electrooptic effect.

ISSN:0021-8979    

DOI:10.1063/1.1659412

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The minimum propagating current, the velocity of propagation, and the temperature rise in semistabilized superconducting wires with and without insulation have been measured by heat pulse tests in magnetic fields up to 70 kG. These experiments have shown that insulated wire can be more stable under external heat perturbation than bare wire and that its temperature rise after quenching is slower. The tests also show that the velocity of propagation is strongly affected, at any current level, by the cooling conditions and by even a very thin surface coating on the wire.

ISSN:0021-8979    

DOI:10.1063/1.1659413

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A stability analysis is presented for the superconducting levitron stabilized partly by feedback and partly by magnetic coupling to metal plates placed symmetrically above and below the current ring. The system is so designed that eddy currents in the plates provide sufficient damping to limit the velocity of the ring to safe values in case of loss of control. The magnetic field associated with the feedback system must diffuse through the plates, which tends to handicap the feedback process and complicate the stability analysis. While levitated current rings stabilized by feedback normally require a component of stabilizing current proportional to the ring velocity to produce artificial damping, the present system is found to be stable without such a velocity‐dependent component.

ISSN:0021-8979    

DOI:10.1063/1.1659414

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

It is shown that photoluminescent and electroluminescent decay times are equal in a wide variety of red‐emitting GaP diodes grown by liquid‐phase epitaxy. In general, the luminescent decay times depend strongly on the Zn concentration in the bulkpregion. For high Zn concentrations (≥5×1017cm−3) the decay times vary approximately inversely with Zn concentration. The equality of the photoluminescent and electroluminescent decay times for the wide variation of decay times and Zn concentrations provides additional evidence that the luminescence occurs in the bulk Zn‐ and O‐dopedpregion.

ISSN:0021-8979    

DOI:10.1063/1.1659415

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The rate equations for green fluorescence of the Yb3+&sngbnd;Er3+doubly doped quantum counter are solved for the case of an infrared pump at the Yb3+2F7/2−2F5/2transition. The successive transfer of excitation from two Yb3+ions to the Er3+produces green emission from the Er3+4S3/2level. The increase of the4S3/2lifetime with increasing Yb3+concentration in Na0.5(Y, Yb, Er)0.5WO4confirms the consecutive transfer model of Auzel. Emission from Er3+in a solid solution of divalent cation tungstates or molybdates (having the scheelite structure) under long‐wave ultraviolet excitation is proportional to the inverse of the cation‐anion separation, and hence the binding energy. The emission under infrared excitation is relatively independent of this separation.

ISSN:0021-8979    

DOI:10.1063/1.1659416

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The internal‐stress‐distribution model of magnetomechanical hysteresis is extended to a calculation of the &Dgr;Eeffect, the irreversible low‐field permeability, and temperature‐dependent magnetomechanical damping. The calculation of the strain dependence of the &Dgr;Eeffect agrees well with experimental results for Fe‐7.65% Ge. The model for permeability yields results for the product &lgr;&sgr;i(&lgr;=magnetostriction, &sgr;i=average internal stress) in reasonable agreement with values from the Becker‐Kersten model for reversible initial permeability &mgr;0and coercive forceHc. The temperature‐dependent damping observed in Ni by Roberts and Barrand is ascribed to an increase in domain‐wall thickness as anistropy decreases. The model gives reasonable agreement with the measured temperature dependence.

ISSN:0021-8979    

DOI:10.1063/1.1659417

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The method, which was previously proposed by the authors, of locating the magnetic‐field axis has been applied to measure the misalignment of the axes of a uniform magnetic field produced by a solenoidal coil and of a periodic one produced by a permanent‐magnet stack. In the former the tilt of field axis has been detected with a resolution of the order of 10−3rad. In the latter the displacement of the field axis has been detected with a resolution of the order of 10−2mm, which is equal to about one part in 103of the inner diameter of magnets. It has been found experimentally that even a slight local misalignment considerably influences electron‐beam transmission.

ISSN:0021-8979    

DOI:10.1063/1.1659418

出版商:AIP    

年代:1970

数据来源: AIP