ISSN:0021-8979    

DOI:10.1063/1.1714914

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

This paper, consisting of three parts, describes investigations made with the objective of developing a simplified, practical microscope of the type which yields magnified images of transparent specimens with a resolving power superior to that of the best light microscopes. The first part deals with the general problem of design, including the electron gun and the imaging lenses. A later part will describe a completed instrument embodying many of the results of the investigations.

ISSN:0021-8979    

DOI:10.1063/1.1714924

出版商:AIP    

年代:1943

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1714915

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

Several techniques for producing surface replicas to be used in the transmission electron microscope are briefly discussed and compared on the basis of experience with them in this laboratory. A new two‐step replica process is described which utilizes molded polystyrene as the first replica and evaporated silica as the second, thin film replica. The high mobility of condensing silica vapor on polystyrene is pointed out and it is shown that such evaporated films tend to fill in small surface irregularities and so produce a replica of fine surface structure which appears to be reliable. A table is included which gives an idea of the amounts of silica required for several surfaces of different ``roughness'' to yield films that are of about the same quality for use in the electron microscope. Electron micrographs of replicas so prepared are exhibited illustrating some pearlitic structures in a 0.98 C, hot roll steel, precipitation in a Cu&sngbnd;Be alloy, and a calcite cleavage plane. Excellent resolution can be obtained in such replicas and a resolution of approximately 50A is demonstrated in the calcite cleavage plane.

ISSN:0021-8979    

DOI:10.1063/1.1714916

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

A method is shown whereby equations in trigonometric form and types of transcendental equations, which can be expanded into rapidly converging series, may be solved by a mechanical and graphical process. A mechanical and graphical method is also shown which effects the double summation of Fourier series used in the Patterson method for the determination of interatomic distances in crystals. Graphs are given to illustrate each of the processes discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714918

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

The rate of removal of mechanical strain should follow Maxwell's first‐order law, but for glasses it has been found that the rate is proportional to the square of the birefringence. The present paper explains this in terms of the structural picture of glass. During annealing the stress optical constant of the glass, as well as its viscosity, undergoes a continuous change. Birefringence, therefore, is not a correct measure of the stress, and the Adams‐Williamson findings are only apparently in contradiction to the classical derivation of Maxwell.

ISSN:0021-8979    

DOI:10.1063/1.1714919

出版商:AIP    

年代:1943

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1714920

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

A simple analytical treatment is developed for the differential equation(d2u/dt2)−&egr;(1−u2)×(du/dt)+u=0(van der Pol), in order to study the behavior of its solution assumed bounded in (0, ∞). It is shown, without any further assumption, that, if &egr;≪1,u(t) can be approximated closely, fort≧0, by a simple oscillation with amplitude 2. This is a more precise form of a statement due to van der Pol. It is further shown thatu2(t)+u′2(t)∼4, t≧0, 0<&egr;≪1. The method and results are then extended to the more general equation(d2u/dt2)−&egr;F(u)(du/dt)+u=0, in particular, forF(u)=1−u4, 1−2au−u2,a=constant, also to the non‐homogeneous equation(d2u/dt2)−&egr;F(u)(du/dt)+u=given function of t. The analytical results obtained in this paper show a remarkable agreement with those obtained for the same equations by mechanical means (on the differential analyzer).

ISSN:0021-8979    

DOI:10.1063/1.1714921

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

This report gives the results of attempts to produce a gaseous atmosphere in which the thermal conductivity increases with increasing ambient temperature much more rapidly than the normal, thereby causing a hot filament mounted in such an atmosphere to behave as if it had a negative temperature coefficient of resistance. There is also described a means of producing a gaseous atmosphere the thermal conductivity of whichdecreasesvery rapidly as the ambient temperature is increased, so that a hot filament mounted in such an atmosphere behaves as though it had a positive temperature coefficient of resistance three to four times as great as normal.

ISSN:0021-8979    

DOI:10.1063/1.1714922

出版商:AIP    

年代:1943

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1714923

出版商:AIP    

年代:1943

数据来源: AIP