摘要:

The magnetic flux distribution on the end faces of superconducting discs at 4.2°K has been observed by a Bitter pattern technique and compared with the metallurgical structure of the specimens. Second phase regions of CaPb3in two-phase lead-calcium alloys, compositional inhomogeneity in single-phase lead-indium alloys, and grain boundaries and surface scratches in V3Si are some of the features that give rise to flux pinning. The results suggest that the effectiveness of any pinning centre depends on its size in relation to the coherence length of the superconducting matrix and on the gradient of the Ginzberg-Landau parameter around the pinning centre.

ISSN:0031-8086    

DOI:10.1080/14786436808223198

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The Granato-Lücke theory of amplitude dependent internal friction contains a number of parameters, more than can be determined from an experiment. In a polycrystalline specimen all orientations of dislocations towards the external stress are equally probable, and an appropriate integration removes the orientation factors and the fractions of total dislocation length in these orientations. The vibrational entropy is allowed for, and an extension to higher amplitudes is used. In addition, a special experiment allows the determination of the break-away stress of a network length with a single pinning point. Thus the number of parameters is reduced sufficiently. The method is illustrated by an example.

ISSN:0031-8086    

DOI:10.1080/14786436808223199

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A summary is given of what is now known about the existence of localized states for electrons in three-dimensional disordered systems, and what can be conjectured about the behaviour of the conductivity at zero temperature when this is finite but small.

ISSN:0031-8086    

DOI:10.1080/14786436808223200

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The metal-insulator transition for donors in a semiconductor is examined in the light of the work of Kohn on the nature of the transition. Kohn's work predicts, for a rigid crystalline lattice, an infinite series of second-order transitions as the interatomic distance approaches the transition point. The original work of Mott on the transition suggested that it should be of the first order with a discontinuous change in the number of free electrons at T=0, unless the dielectric constant k could be shown to tend to infinity at the transition point. In this paper it is suggested that Kohn's theory may allow this to occur. The evidence from the behaviour of doped semiconductors is analysed; in this case the effect of the random (non-crystalline) distribution of the centres must be allowed for. It is suggested that Kohn's charge density waves must be replaced by random fluctuations of charge density, occurring near the transition point and due, as is the transition, to electron-electron interaction. The possibility that k should tend to infinity exists here as in Kohn's model. It appears therefore that the random distribution of the centres does not change the nature of the transition in any essential way, and that it is second order in either case.

ISSN:0031-8086    

DOI:10.1080/14786436808223201

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Calculations of the intensity of incoherent x-ray scattering (Iinc) from Si at small angles have been made using the full Waller-Hartree expression for comparison with the experimental results of Weinberg (1964). The agreement between calculation and experiment is poor for the entire angular range of the results (corresponding to q=(4π/λ)sinø/2 from 0.2 to 1.3 Å−1, where ø is the angle of scattering). Since Iincappears in the formulation of inelastic electron scattering by free atoms, it is pointed out that this formulation should be applied with caution to an interpretation of small-angle electron scattering by metal films.

ISSN:0031-8086    

DOI:10.1080/14786436808223202

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Stacking-fault tetrahedra in gold have been studied under conditions of persistent vacancy supersaturation produced by multiple quenching. Under such conditions the tetrahedral defects are found to be stable and to grow by absorbing vacancies.

ISSN:0031-8086    

DOI:10.1080/14786436808223203

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

By special technique of transmission electron microscopy a dislocation structure associated with shear mode fatigue crack growth is shown.

ISSN:0031-8086    

DOI:10.1080/14786436808223204

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The resistivity recovery after cold-work at -195°C of a set of Al-Zn alloys, with Zn content ranging from 0 to 3.99 wt. %, is investigated by isochronal annealing procedure. Results agree with a previously discussed recovery model assuming vacancy migration in stage III.

ISSN:0031-8086    

DOI:10.1080/14786436808223205

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Measurements of the Righi-Leduc effect have been performed on single crystals of pure aluminium at liquid helium temperatures. The results for the Righi-Leduc coefficient in the limit of high magnetic fields are in good agreement with the value predicted by the theory for metals with a closed Fermi surface.

ISSN:0031-8086    

DOI:10.1080/14786436808223206

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

ISSN:0031-8086    

DOI:10.1080/14786436808223207

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor