摘要:

A method is described for the measurement of the thickness of thin films using the multiple beam interference techniques. Only simple equipment is required, but reduction of the order of interference to as low asonemakes possible the measurement of average thicknesses down to 10A. Applications have been made to evaporated films of six different metals and the method appears to be useful for all stable thin films in thicknesses up to several microns.Possible errors in the method and the precautions which may be taken to avoid them are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1699770

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The distribution in energy of Johnson noise pulses (random thermal voltages in a resistor) is derived and checked against pulse‐height measurements made with a linear amplifier and electronic counter. The following parameters are determined from the distribution function: (1) time of flight associated with a Lorentz mean free path, (2) the number of electrons which produce a pulse of a given height, and (3) the potential an electron falls through in a Lorentz mean free path.

ISSN:0021-8979    

DOI:10.1063/1.1699771

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A method is described which has been found useful to determine by application of the Reiner equation whether certain flow curves obtained with a concentric cylinder rotational viscometer indicate pseudoplastic or Bingham body types of flow.

ISSN:0021-8979    

DOI:10.1063/1.1699772

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The changing width of high angle Debye x‐ray diffraction lines from eutectiferous aluminum‐silicon alloys during thermal cycling as measured by a recording Geiger counter spectrometer is interpreted in terms of stresses resulting from the differences in thermal expansion of the microconstituents.

ISSN:0021-8979    

DOI:10.1063/1.1699773

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Published articles establish the fact that vibration or other inhomogeneous strain greatly increases the ability of a crystal to diffract x‐rays. The present article gives experimentally determined relations between integrated intensity and strain for the rather simple case of static bending. All measurements were made on quartz plates, but a wide range of geometrical and crystalline parameters was covered nevertheless. In some cases, the integrated intensity for extreme bending was more than 20 times that from the unbent crystal. An approximate theory is developed which agrees well enough with the measurements to serve as a means of computing the effects of other types of strain or of other combinations of crystalline parameters. A qualitative study of vibrating crystalline plates is also described briefly.

ISSN:0021-8979    

DOI:10.1063/1.1699774

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An evaluation has been made of some of the errors introduced into the electron diffraction of gases by failure of the sample to be localized, and by secondary and higher order scattering.The degree to which poor nozzle design may contribute to these factors was investigated experimentally by measurements of the pressure in the camera and absorption measurements of the main electron beam when a small volume of gas was allowed to expand into the camera; and theoretically for the cumulative effects of higher order scattering on the final picture. This evidence was complemented by density measurements on photographic plates taken under similar conditions. The effect of using liquid air cooled surfaces around the nozzle was tested.Of the nozzles tested, better ``image to background'' ratios were obtained with the ``hydrodynamic'' and ``comparison'' nozzles than with the ``conventional'' nozzle, but the gas must be admitted slowly enough so that less than about 10 percent of the main beam is appreciably scattered. The ``image to background'' ratios were always higher using adequate cooling on the condensing surfaces surrounding the nozzle. In the case of pressure and electron beam absorption measurements short exposures were advantageous, where secondary scattering was not directly considered, and high camera pumping speeds were always advantageous.On the basis of these results some general design suggestions for electron diffraction cameras, and requirements for good efficiency in nozzles can be made. A nozzle design is proposed which would reduce materially the errors normally encountered in electron diffraction work.

ISSN:0021-8979    

DOI:10.1063/1.1699775

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A shock tube has been set up at Cornell University to begin the study of two‐dimensional wave propagation. Pressure waves initiated by the shock itself were used to trigger the spark source for the schlieren flow‐observation system, to time the instant of exposure and to measure the strength (speed) of the shock waves. These techniques were employed to study the propagation of a wave in a converging channel. Fair agreement between the one‐dimensional method of characteristics and these experiments was obtained.

ISSN:0021-8979    

DOI:10.1063/1.1699776

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

In order to obtain a better understanding of the mechanism of coercive force in modern permanent magnets, magnetostriction measurements have been made on various alloys having coercive forces from 50 to 600 oersteds. The results can be summarized by discussing two types of alloys. First are the older carbonhardening permanent magnets, and for these alloys high coercive force and high magnetostriction occur together. Second are the newer carbon‐free permanent magnets and for these alloys high coercive force does not occur with high magnetostriction. In fact for the Mishima alloys having compositions near 29 percent nickel, 12.5 percent aluminum, and 58.5 percent iron, cooled at the rate of 3°C per second (coercive force 400 oersteds), the magnetostriction actually passes through zero. This is contrary to the classical strain theory of coercive force which states that the latter is proportional to the product of the magnetostriction and internal stress. To explain the mechanism of coercive force for these alloys it is necessary to resort to more recent theories.

ISSN:0021-8979    

DOI:10.1063/1.1699777

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The use of a reservoir of liquid to collect ribbons of thin sections as they are cut enables serial sections to be obtained and provides means for detecting variations in thickness. Reducing the effects of static friction and of external vibrations makes it possible to cut long series of sections 0.2&mgr; thick and uniform to better than five percent. Some observations which may throw some light on the mechanics of the cutting process are reported. Mounting the sections without any treatment is shown to be superior to any technique in which the embedding material is removed or replaced. It is shown that the technique provides sections in which a structural resolution of 200A is possible. The remaining artifacts introduced by the sectioning and mounting are easily recognized deformations which do not influence the interpretation.

ISSN:0021-8979    

DOI:10.1063/1.1699778

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The scattering of an arbitrary electromagnetic field by a conducting or non‐conducting obstacle is investigated. The differential equations and boundary conditions satisfied by the field are transformed into a pair of inhomogeneous linear integro‐differential equations forEandH. For an obstacle which is a thin shell of constant thicknessh, a formal procedure for obtaining a solution of these equations as power series inhis given. The lowest order term in this solution is the incident field. An explicit expression for the next term is found in the form of a surface integral. This integral is evaluated approximately by the method of stationary phase. The physical properties of the solution are examined in detail, and satisfactory agreement is found with many results previously obtained by other methods.

ISSN:0021-8979    

DOI:10.1063/1.1699779

出版商:AIP    

年代:1950

数据来源: AIP