摘要:

Neutron transmission and diffraction techniques are described with application to problems in nuclear physics, crystallography, magnetic scattering, physical structure of materials, and the liquid state. Experimental results for nuclear scattering amplitudes, positions of light atoms among heavy atoms, magnetic moment alignments in antiferromagnetic structures, and diffraction of neutrons by alkali metals in the liquid state are reported. The main features of the design and operation of the neutron diffraction spectrometer and the auxiliary equipment are given.

ISSN:0021-8979    

DOI:10.1063/1.1735331

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The operation of a wave‐type parametric amplifier may be thought of in terms of the force exerted by traveling discontinuities or reflecting elements on the waves present in the device. By invoking the principles of conservation of energy and momentum it is possible to understand in very simple terms certain limitations on the operation of such devices and to arrive very easily at certain general relations governing their behavior, including the Manley‐Rowe relation. It is proposed that for a guided wave the momentum per unit distance is the power divided by the product of the group and phase velocities.

ISSN:0021-8979    

DOI:10.1063/1.1735332

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Harmonic currents accompanying a fundamental space charge wave of current in a velocity modulated electron beam are found togrow with distanceeven though the peak amplitude of the fundamental current remains relatively constant.This effect was first noted in studying the results of a series of disk‐electron calculations. Subsequently, second harmonic growth was found experimentally using a sliding cavity setup. A physical explanation of this phenomenon is given.The harmonic growth can be interpreted as parametric amplification in which the finite electron beam acts as the nonlinear element, with the fundamental current providing the pump power.

ISSN:0021-8979    

DOI:10.1063/1.1735333

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A special technique for the accurate measurement of thermal conductivity is discussed. The method involves use of the Peltier heat to maintain a temperature gradient along the specimen. Straightforward measurements allow calculation of the absolute value of the thermoelectric power, thermal conductivity, and electrical resistivity. An especially useful feature of the method is that the thermoelectric figure of merit is given in terms of the ratio of two voltages. The theory is presented for the case in which the radiative heat transfer is important. The method has been tested experimentally at 300°K only, but analysis suggests that accurate measurements of thermal conductivity can be made by this technique on low thermal conductivity materials of small dimensions up to 1000°K.

ISSN:0021-8979    

DOI:10.1063/1.1735334

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The texture of 28 evaporated NiFe thin films, of various compositions, were determined by the Geiger counter x‐ray reflection technique. The grain orientation of the thin films is described by one of the following three textures; random, [111] fiber axis, or a [311] fiber axis. The development of a texture was influenced by the temperature of the substrate during deposition. The coercive force and the selectivity, which is a measure of the slope of the sides of the hysteresis loop, of the films were measured on a 60‐cycle hysteresis loop tracer. Only the selectivity was found to be related to the texture of the films. Films with a [311] fiber axis had a selectivity less than 0.5, while films with a [111] fiber axis had a selectivity of 0.5 or greater.

ISSN:0021-8979    

DOI:10.1063/1.1735335

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Single crystal &agr;‐iron whiskers have been used to study early stages in the oxidation of iron at high temperatures. Well defined oxide patterns are observed on clean iron surfaces and there are characteristic differences between the patterns on {100} and {110} faces. These differences tend to be eliminated if a natural oxide film is present before the high temperature oxidation is performed. Unusual mosaic oxide patterns which form on clean {100} iron surfaces are shown.

ISSN:0021-8979    

DOI:10.1063/1.1735336

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A model is presented for the high speed uniform rotational flux reversal of ferrite toroids. The magnetization is uniform in the sense that the components of magnetization in a cylindrical coordinate system are independent of position. Analysis of the model, to a very good approximation, leads to results identical with those obtained from uniform rotation in isotropic thin films. The minimum switching coefficient predicted by this model is 0.005 oe &mgr;sec. Experimental confirmation of a high speed switching mode in ferrite toroids is given. A toroid with a wire loop embedded in it was used to induce the proposed flux configuration. The switching coefficient and the extrapolated threshold field associated with the high speed mode have been found to decrease with increasing temperature.

ISSN:0021-8979    

DOI:10.1063/1.1735337

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

This paper presents a steady‐state theory for thein situcombustion of oil in an underground reservoir. The hydrodynamic, chemical, and thermal aspects are treated in their relation with each other. The major results are three criteria for successful forward burning. These criteria state the minimum values for the oil saturation, the carbon‐hydrogen ratio, and the volume flow rate.

ISSN:0021-8979    

DOI:10.1063/1.1735338

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

For photoconductors in which the dominant noise is generation‐recombination noise, it is shown that the signal‐to‐noise ratio is proportional toexp&bgr;Ei/2kTD, whereEiis the threshold response of the photoconductor,TDis its temperature, and &bgr; is a constant between unity and one‐half. If longer wavelength response is desired (smallerEi) without sacrificing signal‐to‐noise ratio, this can only be achieved by loweringTD. Similarly, for any givenEi, the generation‐recombination noise can be reduced to an arbitrarily low level by loweringTDsufficiently. Expressions are obtained for the optimum value ofEiunder typical operating conditions.

ISSN:0021-8979    

DOI:10.1063/1.1735339

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The conductivity of air ionized by injection of electrons at different altitudes is computed with the use of experimentally established collision cross sections of electrons in oxygen and nitrogen. The results, in the form of graphs, are compared with the usual, simpler formulas based upon the assumptions of (a) a constant collision frequency and (b) a constant mean free path. The departures are in excess of the experimental error in good conductivity measurements.

ISSN:0021-8979    

DOI:10.1063/1.1735340

出版商:AIP    

年代:1959

数据来源: AIP