摘要:

In investigations of lubricated sliding friction between two crossed cylinders it is found that for hard, smooth surfaces the friction force is a straight‐line function of the applied load, although this line does not generally pass through the origin. The slope of this line defines a friction coefficient, designated as the incremental frictionf&Dgr;, which is thought to have certain advantages in the study of non‐fluid lubricated friction. It is obviously independent of the load. It is found to be independent of viscous fluid effects and hence permits investigation of non‐fluid friction at reasonable speeds. In spite of being devoid of any viscous component, it is found in a great many cases to decrease with increasing speed,U, over at least part of the range, and this variation often appears to be a linear function of the logarithm of the speed. The curve off&Dgr;vs.lnUseems to be characteristic of the chemical structure of the lubricant and of the rubbing surfaces. It is not contended that viscous effects are absent under the conditions of these experiments but simply that the value off&Dgr;, which is not thetotalfriction coefficient, does not, because of its method of determination, include such effects.

ISSN:0021-8979    

DOI:10.1063/1.1698240

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The fundamental optical problem encountered in three‐dimensional photoelasticity is that of the propagation of light in a heterogeneous, aeolotropic medium. Although there is an extensive literature on the homogeneous, aeolotropic medium and the heterogeneous, isotropic medium, only a few special cases of the combined problem have been studied from the point of view of Maxwell's electromagnetic equations. With regard to approximate treatments, the most general is that of F. Neumann (1841), derived from purely kinematical considerations. In the present paper the passage from Maxwell's to Neumann's equations is executed and the nature and order of magnitude of the necessary approximations are disclosed. During the passage, there are discovered a pair of equations, of relatively simple form, which open the way to a variety of new solutions in closed form and reveal the essential parameter upon which the optical phenomena depend.

ISSN:0021-8979    

DOI:10.1063/1.1698241

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Measurements of the absorption coefficients are made with a double crystal spectrometer in the parallel position, placing the sample between the two crystals, and between the second crystal and the chamber. In the first position the beam is cut down by the ordinary absorption and also by the power going into small‐angle scattering; in the second position it is cut down only by the ordinary absorption. The difference in the two measured absorption coefficients gives directly the total power in small‐angle scattering. From the latter, an average spherical particle size can be computed.

ISSN:0021-8979    

DOI:10.1063/1.1698243

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The lower limit of size of biological objects which can be photographed with the electron microscope, by the aid of shadow‐casting, is shown to depend upon the smoothness of substrate upon which they can be mounted, and upon the continuity of structure of the thin films with which they are shadowed. Numerous attempts to improve the existing deficiencies are reported, both with respect to producing smoother substrate films, and to producing films for shadow‐casting of high efficiency and continuity of structure.No success has been encountered in producing a usable substrate film perceptibly smoother than the collodion and Formvar films commonly used. It is found that the best shadow‐casting material for this type of film is uranium or uranium oxide.Verification has been obtained of the severe granulation of gold films previously used in the pre‐shadowed replica process, when subjected to the electron current of a biased‐beam electron gun. Attempts to reduce the granulation to a satisfactory level have failed. Various methods of preparing pre‐shadowed replicas are reported. The factors affecting the tenacity of evaporated films to glass surfaces are discussed. It is found that elements which oxidize readily are relatively adherent to glass, while the elements gold, palladium, platinum, and rhodium are not. Uranium sulfide can be used as a pre‐shadowed replica material, but only with some uncertainty, owing to its chemical instability. It has been found that a palladium‐platinum mixture is the most satisfactory material for use in the pre‐shadowed replica technique, and that films of this mixture in a thickness of about 6A produce adequate shadows in which there is no sign of granulation. The surface of clean glass is again found to have the smoothest structure of any material known, with practically no sharp discontinuities in elevation as great as 10A.An appendix is given, in which technical details of shadow‐casting and replica production are described.

ISSN:0021-8979    

DOI:10.1063/1.1698244

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A simple numerical‐graphical method for the calculation of stresses in plastic zones adjacent to boundaries of arbitrary shape is outlined, applicable to problems of plane plastic flow in ideally plastic materials. For illustration, the method is applied to determine the stresses in plastic zones near elliptic free boundaries. The yield load of a tensile bar containing elliptic notches is obtained for a series of notches of varying sharpness. Some related problems are discussed briefly.

ISSN:0021-8979    

DOI:10.1063/1.1698224

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698225

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Heat transfer inside sweat‐cooled metals is analyzed and formulas showing the temperature distributions along the length of a sweat‐cooled bar and across a sweat‐cooled hollow cylinder are derived.

ISSN:0021-8979    

DOI:10.1063/1.1698226

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698228

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698229

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698230

出版商:AIP    

年代:1949

数据来源: AIP