摘要:

A general theory for treating magneto‐optic scattering (reflection and transmission) from multilayer structures comprised of magneto‐optic and dielectric materials is presented. The two principle assumptions are: (1) Only terms linear in the off‐diagonal element of the permittivity tensor are important. (2) The magnetic medium is optically lossy. The theory is cast in terms of the Fresnel reflection coefficients and the corresponding magneto‐optic reflection coefficients,rspandrps. The theory is illustrated by consideration of a dielectrically enhanced, thick magnetic film. Finally, a general formulation for scattering from a magneto‐optic medium with arbitrary orientation of the magnetization is also presented.

ISSN:0021-8979    

DOI:10.1063/1.1709738

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Ferroelectric potassium nitrate has been found, by a pulse‐testing technique, to show a threshold electric field, essentially invariant with duration, below which KNO3behaves as a completely elastic dielectric. Test results on several ferroelectric materials, all single crystals, are shown and compared to the results obtained from fused layers of KNO3. The technique for the detection of a threshold is described and the test circuit for obtaining the required data on change in charge vs applied step voltage is included. Finally, a precise time‐independent description of KNO3polarization reversal over the entire range of applied step fields is given by two empirically derived equations, each covering one side of threshold.

ISSN:0021-8979    

DOI:10.1063/1.1709739

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Electrical resistivity (&rgr;) of samples with different grain sizes, made from iron of three different purities (containing a maximum of 34, 79, and 2150 atomic ppm impurities, respectively), has been studied at 4.2°K in the presence of applied longitudinal magnetic fields up to 60 kOe. It has been found that the resistivity is influenced not only by impurities and magnetic domain arrangements but also by the grain‐boundary area per unit volume. The ratioR=&rgr;(300.0°K)/&rgr;min(4.2°K) varies from 2875 to 528 for the interfacial grain area range of 0 (single crystal) to 7.0 mm−1in the highest purity iron. (&rgr;minis the minimum in the resistivity measured as a function of the applied field at 4.2°K.) Due consideration of these large magnetic and grain‐boundary effects discloses a clearer correlation betweenRand purity.

ISSN:0021-8979    

DOI:10.1063/1.1709740

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The formation of fatgiue striations has been investigated by cycling oriented, cylindrical copper single crystals in torsion. Since in torsion of single crystals the applied stresses resolved on the slip systems vary as a function of azimuth, the stress on the cross‐slip system relative to that on the primary system varies with azimuthal position. The importance of cross slip to the formation of fatigue striations is tested by correlating the azimuthal position of fatigue striations with the stresses. It is concluded that a repeated cross slip mechanism will not account for fatigue striation formation.

ISSN:0021-8979    

DOI:10.1063/1.1709741

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

An analysis of the experimental evidence in Part I of this paper clearly indicates that for the case of copper crystals, striations in low‐amplitude fatigue are suppressed by strong slip on intersecting slip planes, including the cross slip system, but are formed by interactions between dislocations on the primary glide system with dislocations on another glide system sharing the same slip plane. This observation is in obvious contradiction toany theory based on cross slip of the primary dislocations alone, since cross slip combined with glide and climb allows every conceivable rearrangement of the dislocations but cannot change the Burgers vectors. A model for the mechanism of striation formation is therefore developed which takes into account that dislocations with at least two different Burgers vectors on the primary slip plane cooperate, according to the experimental evidence. It is proposed that striations consist of sequences of ``cells,'' forming pairs of dense dislocation networks parallel to the primary slip plane, separated by narrow channels almost free of dislocations and debris. The networks consist of almost equal surplusses of dislocations with the three ½ ⟨110⟩ Burgers vectors in the active {111} slip plane, representing more or less well‐developed twist boundaries with a greater or smaller neutral filling of other dislocations and debris. Once striations are formed, glide becomes concentrated in them and hardening proceeds at a much slower rate or comes to saturation. Extrusions and intrusions can arise in at least three different ways and it is believed that these mechanisms act singly or in combination, depending on conditions. It is shown that the model is in good accord with previous evidence. In particular, dislocation structures associated with striations in fatigued copper, observed by Laufer and Roberts, are very close to those described. A few simple numerical relationships are derived from the model which could be employed to test the theory presented. Much of the theory is believed to be applicable also to dislocation behavior in unidirectional work hardening of fcc single crystals.

ISSN:0021-8979    

DOI:10.1063/1.1709742

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Electrical resistivity and x‐ray studies were performed on a series of cerium samples, each of which contained in solution a 2‐at.% addition of one of the other rare earths (except promethium and ytterbium). The resistivity measurements showed that the amount of double hcp &bgr; phase formed at low temperatures varied in accord with the solute species present, the maximum amounts of &bgr; being associated with the solutes at the ends of the rare‐earth series and the minimum with those near the center of the series. The anomalously strong &bgr;‐forming tendency of the europium solute is explainable on the basis of atomic‐size and valence effects. The x‐ray studies revealed a varying tendency toward extrinsic stacking‐fault formation, which correlates with the trend in &bgr;‐phase formation. This correlation is attributed to the fact that both &bgr; cerium and extrinsic faults in fcc &ggr; cerium exhibit ABAC stacking of close‐packed planes. It is proposed that the observed trends in ABAC stacking stability are dependent on the number of unpaired 4felectrons of the solute atoms, with the stability being least when the number of these magnetic electrons is greatest.

ISSN:0021-8979    

DOI:10.1063/1.1709743

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The room temperature optical properties of single crystal MgF2were determined in the 4.1 eV–10.9 eV energy range, from transmission and near‐normal‐incidence reflectance measurements, and in the 11.0 eV–27.5 eV range, from reflectance measurements made at various angles of incidence. Sharp structure in the reflectance spectra of single crystal MgF2is associated with an exciton transition at 11.8 eV. Broader structure at higher energies is associated with an interband transition at 20.8 eV. The energy‐loss function for volume plasmons has a maximum at 24.5 eV which agrees well with the theoretical value. In addition, the optical properties of an evaporated film were determined in the range 11.0 eV to 29.5 eV, but structure in the reflectance spectrum is not as well defined. However, there is fair agreement with previously published optical constants of evaporated MgF2.

ISSN:0021-8979    

DOI:10.1063/1.1709744

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

In a giant‐pulse laser rod an inhomogeneous excess inversion across the rod diameter will lead to a non‐uniform growth rate of the photon avalanche, when the transverse modes are not tightly coupled. For a model inversion distribution the resulting giant‐pulse elongation is calculated. The radial time dispersion can be compensated by a radius‐dependent resonator feedback or by transverse mode coupling. The influence of thermal resonator curvature on the decoupling of transverse modes is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1709745

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A statistical model for the reflection of scalar plane waves from a rough surface leads to a plane wave in the direction of specular reflection and to a contribution with a finite angular spread about that direction, depending on the tangential correlation of the surface asperities. Based upon on this result, a new semiclassical model, which satisfies the requirement of flux conservation, is proposed for the boundary condition for the distribution function of the size effect in the electrical conductivity. In the absence of correlation, the resultant expression replaces the constant specularity parameterpof Fuchs by the function exp[−(4&pgr;(h/&lgr;) cos&thgr;0)2] with &thgr;0the angle of the electron wave vector with the surface normal. Correlation produces an additional forward component within the diffuse contribution. Numerical results of the size effect for zero correlation are compared to the Fuchs model as well as a more recent model, and show a different thickness dependence for thin samples. The effect of correlation is to add to the conductivity, as a result of the diffuse contribution whose velocity has a finite expectation value in the direction of the current.

ISSN:0021-8979    

DOI:10.1063/1.1709746

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Surfaces shown by x‐ray diffraction measurements after fabrication to be TaB2, ZrC, Mo2C, MoSi2, TaSi2, and WSi2were subjected to vacuum thermionic work function and thermal stability measurements. Subsequent x‐ray diffraction stoichiometry checks showed that only ZrC and Mo2C remained stable after many hours at thermionic emission temperatures. TaB2decomposed to TaB+B when a diffusion barrier of TaC was provided under the TaB2; the three disilicides decomposed to lower silicon content silicides. The vacuum work functions measured after outgassing were TaB2(4.32 eV), ZrC(3.70 eV), Mo2C(4.74 eV), MoSi2(4.73 eV), TaSi2(4.71 eV), and WSi2(4.62 eV), subject to some temperature dependencies, as described.

ISSN:0021-8979    

DOI:10.1063/1.1709747

出版商:AIP    

年代:1967

数据来源: AIP