摘要:

In a sixth‐order solenoid of type I (or II), the field errors of second and fourth orders are compensated by a notch in the outer (or inner) cylindrical surface. The power efficiencyEF≡G/0.1792, where the Fabry factorGis defined in the same way as for an uncompensated cylindrical coil with the same least radius, and 0.1792 is the largest possible value ofGfor any such coil. The efficiency of a sixth‐order solenoid is defined to be ``near maximum'' whenEFhas a value no less than 98% of the maximum for any compensated coil of the same type and normalized volumeV. The 2% tolerance permits the choice of an experimental coil to be influenced by properties that may be more sensitive to changes in geometry than isEF. Coils of type I are relatively long, with a maximumEFof 0.692 atV≅200. In type II coils, the diameter often exceeds the length, and the maximumEFis 0.884 atV≅300. Separate tables withV1/2as argument list 100 solenoids of each type, with geometry, field strength,EF, and axial limits for field variations of 0.1% and 1.0%. All radial depths are so adjusted that the layer counts for the midplane and end sections are proportional to a pair of small integers. Though the 0.03% limits of a typical coil of type I could enclose the 1.0% limits of a type II coil of the same volume, the field error of the type II coil is less than 0.02% at the axial 1.0% limit of the same coil without the correcting notch.

ISSN:0021-8979    

DOI:10.1063/1.1658161

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Powder patterns of magnetic domains on various crystallographic surfaces of pure and doped hematite single crystals have been studied at room temperature and in the vicinity of the Morin transition. The observations below room temperature were made with an apparatus employing thermoelectric cooling modules. It was concluded that the domains were either slabs or cylinders of irregular transverse cross section with axes lying parallel to the basal plane. The domain walls were determined to be 180° ones. At the Morin transition, a light diffuse colloidal line is formed at the boundary between two phases, one weakly ferromagnetic and the other antiferromagnetic. On warming or cooling, the boundary sweeps across the crystal in a characteristic fashion.

ISSN:0021-8979    

DOI:10.1063/1.1658162

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The classical expression of the magnetoelastic energy of a monocrystal is transformed according to the most general rotation of the crystalline axes with respect to a given reference system. It is then possible to calculate the effect of a given stress on a polycrystalline material. It is shown that it is only for perfectly random crystallographic orientations that it is possible to cancel the ``macroscopic'' magnetostrictive effects of all the strains at the same composition for a magnetic alloy. If a cylindrical magnetic film with a preferential texture is made insensitive to an axial elongation, it will exhibit a magnetostrictive skew of its magnetic easy axis when the wire is twisted. The microscopic effects of stresses are also investigated in all cases: the so‐called ``isotropic stresses'' give a dispersion of the easy axis.

ISSN:0021-8979    

DOI:10.1063/1.1658163

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Magnetomechanical damping measurements are commonly made using wire specimens in a torsion pendulum. Twisting the cylindrical wires produces tensile stresses along a helix. An analytical study was made relating the direction of these stresses with the directions of the crystallographic axes assuming three different orientations of the crystal, ⟨100⟩, ⟨110⟩, and ⟨111⟩, along the axis of the wire. The results make it possible to calculate the correct magnetostriction values to be used in the mathematical model of magnetomechanical damping when there is preferred orientation in the specimens. Magnetostriction values are calculated over the temperature range of 78° to 300° K for iron, nickel, and an iron‐3.8% silicon alloy and these are compared with the magnetomechanical damping maxima in the same temperature range.

ISSN:0021-8979    

DOI:10.1063/1.1658164

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The effects of a dielectric overlayer on Kerr magneto‐optic properties in thick EuO films were examined. The dielectric film serves not only as a passivation layer, but also to increase the Kerr effects. A series of thin Eu2O3films were vacuum deposited on a thick EuO film, followed byin situmeasurements of the reflectivity and the transverse Kerr effects using a polarized light (with the electric field vector in the plane of incidence) at 45° angle of incidence in the wavelength region from 0.4 to 0.8 &mgr;. As the dielectric (Eu2O3) thickness increases the characteristic reflectance minimum of EuO shifts toward longer wavelengths, accompanied by decreasing reflectivity. This shift agrees well with calculated reflectances using optical constants of Eu2O3film and EuO. The minimum reflectance of ∼0.04% occurs at 0.675 &mgr; for a dielectric thickness of ∼500 Å. The transverse Kerr effects also depend strongly upon the dielectric thickness. The maximum Kerr effects occur at the wavelength of minimum reflectance For example, corresponding to the minimum reflectance of ∼0.04%, a maximum transverse Kerr effect of ∼+140% occurs at this wavelength. This value can be compared with ∼25% in bulk crystal at 0.575 &mgr; and ∼80% in thin EuO film on a mirror substrate at 0.525 &mgr;, which is the largest value reported in the literature. Preparations and optical properties of several other rare‐earth oxide films are also presented.

ISSN:0021-8979    

DOI:10.1063/1.1658165

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Twinning and detwinning in calcite were studied by means of selective etching and sound‐attenuation measurements in order to investigate dislocation behavior during these processes. Twinning was accompanied by an increase in attenuation caused by discontinuous dislocation multiplication in the twin lamella. During detwinning the attenuation changes were recovered by dislocation cluster formation and tangling. It was found that dislocation nucleation accompanies even elastic twinning in calcite and is probably responsible for various anelastic effects associated with it.

ISSN:0021-8979    

DOI:10.1063/1.1658166

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

We develop an analytical framework for the theory of plasticity in which the constitutive equations are single valued and which at the same time represents the proper physical concepts. A Coleman‐Gurtintype thermodynamics which utilizes internal state variables is used for the study of an elastic‐plastic substance. Quantities which are related to the dislocation motion and the dislocation arrangement in the material, play the role of the internal state variables in this thermodynamics. Rate‐independent plasticity is studied as a limiting case of the present theory. We illustrate the theory with a special case: a one‐dimensional, homogeneous, cyclic deformation of a rate‐independent elastic‐plastic body which exhibits a Bauschinger effect.

ISSN:0021-8979    

DOI:10.1063/1.1658167

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The theory of the effect of optical saturation upon the reflectance of a plane slab (irradiated by a linearly polarized monochromatic electromagnetic wave of constant amplitude at normal incidence) is developed. The absorbing centers within the slab are described by means of the density matrix, and the electromagnetic field is described by Maxwell's equations. For simplicity's sake, it is assumed that only two quantum states (characterized by a transition dipole moment &mgr; and relaxation timesT1andT2) at exact resonance with the electromagnetic wave are necessary to describe the absorption process. The coupling between waves travelling in opposite directions is provided by Fresnel reflection at the boundaries of the slab. Only the steady‐state solutions are found.

ISSN:0021-8979    

DOI:10.1063/1.1658168

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The drift of a small photoinjected sheet of free carriers can be used as a probe of the space charge and internal field distributions in the bulk of amorphous selenium films. We have found that unneutralized space charge can exist for long periods of time and can significantly affect the measurement of both drift mobility and deep trapping lifetimes. By deliberately creating bulk space charge, we can also examine some of the fatigue effects that arise when a selenium photoreceptor is not allowed to relax between large variations in applied field and exposure.

ISSN:0021-8979    

DOI:10.1063/1.1658169

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The role of impurities in a low‐pressure arc is theoretically investigated by use of a system of coupled rate equations. Some of the coefficients may be unknown; it is shown that by measuring a few parameters it is possible to obtain a set of equations at least equal in number to the number of unknown coefficients. The analysis is then particularized to the case when the introduction of the additive results in a perturbation sufficiently small that a linear treatment is applicable. This results in a system of seven linear equations, the left‐hand side of which is obtained by adding seven terms, each a product of aknowncoefficient times perturbation on a certain plasma parameter (population of an excited level, electron density, electric field, etc.) whereas the right‐hand side is linear in the pressure of the additive, the coefficient depending upon the characteristic properties of the additive.

ISSN:0021-8979    

DOI:10.1063/1.1658170

出版商:AIP    

年代:1969

数据来源: AIP