摘要:

A study of the migration of Sr on W by a field electron emission technique revealed two modes. In the first mode, for &thgr;≥1, migration proceeds with a sharp boundary while in the second mode, &thgr;<1, no boundary is observed. The activation energy for the first mode was found to be 0.79±0.06 eV/atom, and the activation energy for the second mode was found to be 1.44±0.08 eV/atom.

ISSN:0021-8979    

DOI:10.1063/1.1713736

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A simple method is given for calculating the magnetic field components in or around any thick finite solenoid by superposition of fields of semi‐infinite solenoids with zero inner radius. Equations and graphs are presented for the field components of such semi‐infinite solenoids. From these graphs, the fields for solenoids of practical interest can be obtained with errors of less than a few percent. Greater accuracy is possible if numerical tables are used instead of graphs.

ISSN:0021-8979    

DOI:10.1063/1.1713737

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An expression of the thermodynamic potential is examined in terms of the primary and secondary pyroelectric coefficients of a poled ferroelectric ceramic. Anisotropic expansion and zero electric field conditions are assumed. The pyroelectric coefficient is applied to the composition, Pb(Zr0.95Ti0.05)O3(PZT 95/5) with 1 wt. % of Nb2O5, for which a complete set of elastic, piezoelectric, thermoelastic, and pyroelectric coefficients were determined. A value of −26.8×10−9C/cm2‐°C was found for the total pyroelectric coefficient of which +3.77×10−9was contributed towards the piezoelectric or secondary effect; therefore, −30.6×10−9C/cm2‐°C is reported for the primary pyroelectric coefficient for this material over the temperature range 25°–50°C.

ISSN:0021-8979    

DOI:10.1063/1.1713738

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Experimental results are presented which indicate that the Bauschinger effect is operative in cold‐worked SAE 1018 steel for the extreme strain rates (∼106/sec) associated with explosive loading. For approximately 20% prior tensile cold work the compressive dynamic yield stress for a propagation distance of 1.905 cm is about 8.8 kbars as compared to 15.7 kbars for annealed material. For heavily cold‐worked metals, which generally exhibit the Bauschinger effect, the results indicate that neglect of the Bauschinger effect under explosive loading conditions can lead to serious errors in the interpretation and extrapolation of experimental results. In the case of metals in annealed or slightly worked states, neglect of the Bauschinger effect in the elastic‐plastic model for shock loading and unloading may not be justified.

ISSN:0021-8979    

DOI:10.1063/1.1713739

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Densities of 35 diamonds have been determined by an improved high‐precision flotation method. The density varies from &rgr;25= 3.51477−3.51554 g/cm3. The average density of 35 samples is &rgr;25= 3.51532 g/cm3. The type I diamonds have higher density and narrower range than type II. Comparison with density computed from the lattice constant shows that type II diamonds contain either vacancies (voids) or impurities of lower atomic weight than carbon, or both, and that type I are contaminated by impurities of higher atomic weight than carbon. Computed nitrogen impurity concentration is in excellent agreement with that found by Kaiser and Bond.

ISSN:0021-8979    

DOI:10.1063/1.1713740

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Intense flash‐tube irradiation produces a brownish color in CaWO4:Nd, principally by absorption of wavelengths shorter than 300 m&mgr;. Initially, the photolytic optical absorption has a peak near 3.0 eV forE∥c, and at 3.0 eV forE⊥c. At 300°K, there is a fast partial decay of the optical absorption within a few hours followed by a slow subsequent decay which stabilizes within a few days. On approach to equilibrium, the initial 3.0‐eVE∥cpeak decomposes to two peaks at 2.5 and 3.0 eV. The absorption forE⊥cdiminishes with time, but the peak remains near 3.0 eV. The absorption coefficient forE∥cin this photolytic case is always about twice that forE⊥c. The photolytic coloring is removed by heating at 300°C for a few hours. It is unaffected by compensation of Nd with Na. Reduction of lightly doped CaWO4:Nd induces an optical absorption which peaks at 2.5 eV for bothE∥candE⊥c. For heavily doped CaWO4:Nd:Na, absorption peaks at 2.2 eV forE⊥cand 2.2 and 2.9 eV forE∥care produced. Thus, reduction and photolytic coloring have fairly similar spectra. The removal of reduction coloring requires 800°C heating in an oxidizing atmosphere, however. Pure CaWO4does not color in the bulk by either reduction or photolytic processes. The observations seem to point to an oxygen vacancy model with possible trapping of two electrons (perhaps an oxygen vacancy in conjunction with two W5+ions).

ISSN:0021-8979    

DOI:10.1063/1.1713741

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The present report extends resistance fluctuation studies in the current‐induced intermediate state to the intermediate state induced by the application of an external magnetic field. Evidence for the existence of resistance levels is again found for both directions of the superconducting transition. The resistance levels are interpreted in terms of superconducting domains. The number of levels consequently represents the number of superconducting domains present and the difference &Dgr;Rbetween the two successive resistance levels correspond to a spread of the normal phase over a length &Dgr;lof a specimen. The transition time between two successive resistance levels is identified as the time of collapse of a domain. The observed transition times for soft superconductors are compared with the theory of propagation of a normal phase boundary and some conclusions on the structure of the intermediate state are presented.

ISSN:0021-8979    

DOI:10.1063/1.1713742

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The magnetic ripple of thin films with uniaxial anisotropy is calculated for the field and the magnetization lying along the easy and the hard direction of the uniaxial anisotropy. For small dispersion of the direction of magnetization, the variational principle, applied to all energy terms including the exchange, crystalline anisotropy, uniaxial anisotropy, magnetostriction, magnetostatic, and stray field energies, yields a Bessel's differential equation. Its solutions (cylindrical functions) describe the two‐dimensional magnetic ripple of the film. Along the mean direction of the magnetization the fluctuations of the magnetization vector are much greater than perpendicular to it. In the first case these fluctuations are coupled by exchange forces, and in the second case by the stray field. The dispersion of the magnetization depends on the dispersion of the anisotropy, on the magnetic constants of the film, on the thickness of the film, and on the applied field. The theory is able to explain the image of the ripple observed by the electron microscope and to explain the variation of the ripple quantitatively, if the applied field is varied. The estimation of the mean magnetization dispersion agrees with the experimental data of Fuller and Hale. The statements of the theory concerning the mean wavelength &lgr; of the ripple for the mean direction of magnetization along the easy axis&lgr;L=2&pgr;A12Ku−12(hL+1)−12,and along the hard axis&lgr;s=2&pgr;A12Ku−12(hs−1)12,are verified by experimental observations. (A is the exchange constant,Kuthe uniaxial anisotropy constant,hL=HL/Hkis the reduced field along the easy axis,hs=Hs/Hkis the reduced field along the hard axis.) The calculated domain width, occuring at magnetization reversal along the hard axis, is in good agreement with the experiments of Middelhoek, Feldtkeller, and Smith. The domain splitting is fine at a great dispersion of the anisotropy axis and is less fine at smaller dispersions. The smallest domain width of 80–20 Permalloy films is of the order of 2 &mgr;.Furthermore the theory gives a new method for the determination of the anisotropy field strengthHk.

ISSN:0021-8979    

DOI:10.1063/1.1713743

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The optical Faraday rotation and magnetic susceptibility of cerous phosphate glass of concentration Ce2O3·2.67 P2O5has been studied as a function of temperature. The Verdet constant exhibits the same temperature dependence as the magnetic susceptibility, consistent with the theory formulated by Van Vleck and Hebb.

ISSN:0021-8979    

DOI:10.1063/1.1713744

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

This paper determines the field and current distribution in a high‐field, superconducting material in sheet form, where the applied magnetic field is parallel to the sheet. The distributions are obtained from a critical state equation and Maxwell's equations, and determined for the two cases of absence or presence of a net transport current in the material.The field distributions are used to determine the magnetization of the material as a function of applied magnetic field, with the short‐sample current‐carrying capacity as a parameter. The zero transport current magnetization curves show good agreement in general shape with those experimentally observed. The analysis indicates a reduction in magnetization with increasing transport current.

ISSN:0021-8979    

DOI:10.1063/1.1713745

出版商:AIP    

年代:1964

数据来源: AIP