摘要:

Analog‐computer studies are made on a variety of mixing and parametric effects in Josephson junctions. The predictions of the constant‐voltage model are compared with the more general behavior of a junction in a resistive circuit. A simple approximate method is developed for calculating frequency conversion efficiency and the matching condition for a junction operating in the oscillator mixer mode. A similar calculation is made for the second mode of operation, in which an external local oscillator is used. In either of these modes, frequency conversion gain is possible even in a purely resistive circuit. The conditions for parametric amplification without frequency conversion are also studied and it is found that gain occurs only when the self‐oscillation frequency is near the signal frequency.

ISSN:0021-8979    

DOI:10.1063/1.1662568

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Data are presented describing critical current densityJcas a function ofHa, applied magnetic field, for NbTi alloys containing between 22 and 38 at.% Nb. The effect onJc(Ha) of precipitation heat treatments between 275 and 565°C was studied in conjunction with cold area reductions up to 99.9%. The highest critical current densities,Jc(Ha), were in the range 1.0 to 3.6×105A/cm2at 3.0 T where most of the data were obtained. Critical temperature data are presented as a function of alloy composition and metallurgical preparation.

ISSN:0021-8979    

DOI:10.1063/1.1662569

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A rather general relation is derived between vertical accelerations of the train and cryogenic power dissipation due to ac currents induced in the superconducting suspension magnets. Our theoretical results account for the order of magnitude of the rather large losses observed in the Fuji Electric test vehicle, which used less than state‐of‐the‐art conductors. Even with parameters estimated to represent the best commercially available materials, however, it appears that these losses may be comparable with the total heat leak due to all other causes if the accelerations are as large as permitted by subjective human ride quality considerations. Empirical data on losses under appropriate conditions ofB, B˙, andI/Icmay be needed to ascertain whether improved materials will be required to avoid serious design constraints by cryogenic heating.

ISSN:0021-8979    

DOI:10.1063/1.1662570

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We present an improved method for calculating from ac susceptibility measurements the critical current densityJcand the surface shielding parameter &Dgr;Hin bulk cylindrical type‐II superconductors. As first developed by Bean, the method involves harmonic analysis of an expression for the voltage induced in a pickup coil around a specimen in an axial dc magnetic field with a small ac ripple field superimposed. Values ofJcobtained by Bean's analysis are suspect, in part because the analysis does not take account of surface shielding. Ullmaier modified Bean's calculation to remedy this defect. For simplicity he did not Fourier analyze the induced voltage, choosing instead to determineJcand &Dgr;Hby comparing experimental waveforms with his calculated voltage. This procedure permits only a qualitative indication of whether the data are consistent with the model. For generality, we have modified Ullmaier's calculation by removing the approximation that the depth of penetration of the ac field is small compared to the sample radius. The resulting expression for the induced voltageVis a complicated function ofJc, &Dgr;H, and the amplitude of the ripple fieldh0. A graphical procedure has been developed which not only extracts values ofJcand &Dgr;Hfrom plots of the amplitude of the third harmonic ofVvsh0, but also provides a check for consistency of the data with the model.

ISSN:0021-8979    

DOI:10.1063/1.1662571

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A method of measuring the uniaxial anisotropy of bubble materials is analyzed. The method consists of observing the in‐plane fieldH∥*at which a stripe domain pattern disappears. Calculations, based on a model with uniaxial anisotropy, are presented which give a relation betweenH∥*and the uniaxial anisotropy fieldHKfor different values of the characteristic magnetic length. It is shown thatH∥*is always smaller thanHKowing to the influence of the wall energy and the demagnetizing energy. The calculations are verified experimentally.

ISSN:0021-8979    

DOI:10.1063/1.1662572

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A method of evaluation of the directivity of gravitational wave (GW) radiators is given in the form of general equations applicable to most cases such as Weber's apparatus and the travelling wave (TW)‐type radiator (the latter proposed by one of the authors). Although it is not generally accepted now, Einstein's weak‐field theory is used for evaluating both near and distant fields. In a numerical example, using our general formula, the TW‐type radiator is considered and it is found that a half‐power angle width of ±5.3° is feasible using a crystal 30 cm in length. Intensity comparison is also made between the resonance vibrator and TW‐type radiators. Under reasonable assumptions, the radiated power of the latter is about 1023times larger than the former—that means 1040times higher intensity than the spinning rod first considered by Einstein as a GW source

ISSN:0021-8979    

DOI:10.1063/1.1662573

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An investigation of the time‐resolved gain of a volume‐excited TEA CO2laser amplifier is described. The amplitude and decay time of the small‐signal gain are obtained as a function of molecular gas flow ratio and input energy density.

ISSN:0021-8979    

DOI:10.1063/1.1662574

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In a recent issue of this journal Wellenstein, Frommhold, and Robertson identified two reasons for systematic error in microwave electron density measurements and described a calibration procedure to eliminate the error. In this paper, use of a polar gas for calibration purposes is recommended and the choice of suitable cavity modes for this measurement technique is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662575

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The condition for the amplification of the left‐hand polarized helicon wave in InSb subject to a parallel applied static electric field E0and magnetic field B0is derived from the dispersion relationship. It is shown that the helicon wave in InSb may be amplified in the range ofE0where Ohm's law is valid, provided that the value ofB0and the wave frequencyfare proper.

ISSN:0021-8979    

DOI:10.1063/1.1662576

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The morphology of copper precipitate colonies in silicon is determined completely by a dislocation climb and glide mechanism. Interstitial dislocation loops, originating from three‐dimensional nucleation centers are involved. Preferential climb in ⟨110⟩ directions of the ⟨100⟩ oriented edges of interstitial loops parallel to {110} planes and with b=⟨110⟩ determines the orientation of the colonies. The memory effect is ascribed to lattice defects which remain after complete out‐diffusion of the copper.

ISSN:0021-8979    

DOI:10.1063/1.1662577

出版商:AIP    

年代:1973

数据来源: AIP