摘要:

A method of computing demagnetizing factors using a resistance network analog or an electrolytic tank has been devised, and the demagnetizing factors for spheres, rods, disks, and tubes have been computed for the case &mgr; = ∞. When the size of the model on the analog is appropriate, the value obtained for a sphere is within 1% of the theoretical value of ⅓. Although the demagnetizing factor is not a precise concept for rods, disks, or tubes, in which the induced magnetization is not uniform, this term is often used for convenience. In this paper, the ``ballistic demagnetizing factor'' (defined in terms of the mean magnetization over the median cross section of the object) is considered. The values obtained for rods and disks are compared with those found in the literature, principally with Bozorth and Chapin's compiled values. Typical results are 0.37 (0.47), 0.223(0.27), 0.117(0.14), and 0.052 (0.056) for (L/d) = ½, 1, 2, and 4, respectively, where (L/d) denotes the length‐to‐diameter ratio and the values in the brackets are the previously used values. The axial nonuniformity of the magnetization in rods and tubes is also measured and discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714495

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Nonlinear rf effects in plasmas are discussed in this paper. It is shown that the strong type of harmonic generation mechanism is due to the equation of motion for the plasma electrons being nonlinear, as is the relationship between current and velocity. A theory of plasma harmonic generators and parametric oscillators is given. Input reaction is taken into account and it is shown that a resonance at the output frequency tends to lead to high efficiency. Such a resonance is the electrostatic resonance of a plasma sphere. Experiments carried out with a small spherical rf discharge are described. A 25% conversion efficiency to the second harmonic of anS‐band signal has been obtained. Measurements have been made up to the seventh harmonic. For maximum efficiency a plasma resonance at the harmonic of interest is required. By tuning the system to be resonant at half the input frequency, parametric oscillations were obtained at this frequency, thus proving that the nonlinearity must be of a reactive type. It is believed this is the first time that parametric oscillations have been observed in a plasma.

ISSN:0021-8979    

DOI:10.1063/1.1714496

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

We have measured the absolute Raman scattering cross section for the 1345‐cm−1shifted Stokes line in nitrobenzene using a ruby laser. We have also measured the efficiency of conversion of radiation from a giant pulse ruby laser into stimulated Raman scattered radiation for this line. We have found that the average intensity needed to produce a given conversion is one or two orders of magnitude less than that predicted by the theory of Hellwarth using our measured cross section. We discuss some possible explanations for this disagreement.

ISSN:0021-8979    

DOI:10.1063/1.1714497

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The stability of extended dislocation barriers in face‐centered cubic metals is determined using the theory of anisotropic elasticity. It is found that the results typically differ from the isotropic elasticity solution by 25%, but the difference can in special cases amount to as much as a factor of four. The anisotropic results are in qualitative agreement with earlier isotropic results in predicting the relative strength of the barriers to dislocation glide. The results suggest that the measurement of barrier extension should provide the most accurate available means of estimating the stacking‐fault energy in fcc metals.

ISSN:0021-8979    

DOI:10.1063/1.1714498

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The possibility of generating high‐frequency acoustic waves by illuminating the negative end of a cadmium sulfide rod with light of periodically varying intensity exists. The strains produced and the acoustic gain present under different conditions of drift current and resistivity are calculated for three decades of frequency.

ISSN:0021-8979    

DOI:10.1063/1.1714499

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Thermal radiation from a fully ionized gas near the plasma frequency is investigated theoretically with consideration given to boundary effects. It is shown that the emission spectrum is a relatively complicated function of frequency, temperature, density, and geometry, but that the absorption spectrum can be approximated by a simple function of the three parameters representing frequency, collisions, and geometry. The sensitivity of the absorption curve to these parameters is investigated, and the results are used to interpret recently measured infrared radiation from a theta pinch.

ISSN:0021-8979    

DOI:10.1063/1.1714500

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Steady‐state creep of polycrystalline sodium choride having grain size stabilized by the addition of an aluminum oxide dispersion and containing about 4% porosity was investigated at 740°C over a range of grain sizes from 65–130 &mgr; and at stresses from 2.1–8.4 kg/cm2. Deformation was viscous (strain rate directly proportional to stress) at a rate in good agreement with the Nabarro—Herring equation, assuming the deformation rate to be limited by chlorine ion diffusion. Grain‐size dependence and absolute creep rates were satisfactorily predicted with Laurent and Be´nard's diffusion data, including the influence of grain size on diffusion coefficients.

ISSN:0021-8979    

DOI:10.1063/1.1714501

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

On the basis of a small‐signal, one‐dimensional analysis, a set of basic macroscopic differential equations, governing the fluctuations in quantities such as the electron‐beam temperature, the mean velocity, and the current density, has been derived by taking moments of the Liouville equation with respect to the velocity variable. This set of differential equations expresses the conservations of charge, momentum, and energy, and is valid for an arbitrary amount of velocity spreading and includes the effect of heat conduction.A system of differential equations, governing the correlation among the fluctuations in the mean velocity, current density, and beam temperature, is also derived. The relationship among the various noise parameters along the electron beam is obtained in the form of a system of differential equations whose solution gives detailed information on the variation of the noisiness parameter along the beam. The solution of the system of differential equations thus derived is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714502

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

By extending the optical and magneto‐optical measurements of the insulating ferromagnet CrBr3(hexagonal layer structure,Tc=36°K, and 4&pgr;Ms=3520 G) beyond the absorption band edge near 22 000 cm−1with reflection techniques, three absorption bands representing the &pgr; and &sgr; processes of electron transfer transitions and an internal transition of Cr3+have been observed. The room‐temperature dielectric constant was measured by means of an ellipsometer. The &sgr; process and the internal transitions give rise to the two absorption bands at 24 310 cm−1and 29 580 cm−1with oscillator strengths of 0.30 and 1.61, respectively. They account for most of the dielectric constant. While the &pgr; process is too weak to be resolved in the dielectric constant data, it accounts for the main peak of the normal incidence polar Kerr rotation at 1.5°K of 3.5° at 23 500 cm−1. The &sgr; process accounts for the relatively sharp negative peak in the Kerr rotation of −2.5° at 26 700 cm−1. The data further suggest that the &pgr; process component of the off‐diagonal element of the electric polarizability tensor has opposite sign to the &sgr; process and the internal transitions.

ISSN:0021-8979    

DOI:10.1063/1.1714503

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An analysis is presented of the propagation of magnetoelastic waves in transversely magnetized rods. Efficiencies for longitudinal wave‐spin wave and shear wave‐spin wave conversion are evaluated for the case of a [1¯10] rod magnetized along [111]. A longitudinal to shear wave converter in yttrium iron garnet is discussed which is estimated to have 20‐dB conversion efficiency at 3 Gc/sec.

ISSN:0021-8979    

DOI:10.1063/1.1714504

出版商:AIP    

年代:1965

数据来源: AIP