ISSN:0021-8979    

DOI:10.1063/1.1707361

出版商:AIP    

年代:1944

数据来源: AIP

摘要:

The cyclotron is in process of a metamorphosis from an academic luxury for nuclear physicists to an indispensable tool for applied science and industry. Tracer experiments with induced radioactivities have become invaluable for basic studies in other sciences and as a guide to engineering development in many industries. The radioactivities and neutron radiations themselves are being put to use in industry and in medicine on an ever increasing scale. The time is near when the use of the cyclotron as a production unit may even outweigh its further scientific usefulness. Cyclotron physicists, well aware of this trend, are eager to push the development of the instrument to engineering perfection. To further this effort, this paper evaluates available information which may aid in improving the efficiency, reliability, and output and in determining most economical sizes and designs of cyclotrons for large scale applications.

ISSN:0021-8979    

DOI:10.1063/1.1707364

出版商:AIP    

年代:1944

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1707362

出版商:AIP    

年代:1944

数据来源: AIP

摘要:

An experiment has been designed to check a previously proposed equivalence of the effects of changes in strain rate and in temperature upon the stress‐strain relation in metals. It is found that this equivalence is valid for the typical steels investigated. The behavior of these steels at very high rates of deformation may, therefore, be obtained by tests at moderate rates of deformation performed at low temperatures. The results of such tests are described. Aside from changing the isothermal stress‐strain relation, an increase of strain rate tends to change the conditions from isothermal to adiabatic. It is found that at low temperatures, the adiabatic stress‐strain relation in the plastic range is radically different from the isothermal, having an initial negative rather than a positive slope. This initial negative slope renders unstable homogeneous plastic deformation.

ISSN:0021-8979    

DOI:10.1063/1.1707363

出版商:AIP    

年代:1944

数据来源: AIP

摘要:

This paper deals with considerations concerning the reduction in amplitude of unwanted vibrations of machinery parts through the use of materials of high damping capacity. The problem is to reconcile the requirement for high damping with that for high mechanical quality (strength, fatigue resistance, etc.). Two ways are suggested: (1) the use of a material whose decrement generally is low but rises rapidly as the stress increases; (2) the use of a material whose damping capacity is low but rises to high peaks in certain frequency ranges. It is shown by numerical computation in two instances, namely, turbine blade vibrations and crankshaft oscillations in engines, how the suggested methods would work out in practice.

ISSN:0021-8979    

DOI:10.1063/1.1707365

出版商:AIP    

年代:1944

数据来源: AIP

摘要:

Investigations have been made of the various factors considered to influence the sensitivity of the microradiographic method for the examination of alloys. Both target element and applied voltage influenced the results. Radiographs are shown to demonstrate the effect; an explanation is given in terms of the x‐ray emission curves and the absorption differential curves for the phases of the radiographed alloy. Target‐specimen distance was an important factor for uncollimated rays, particularly for distances of less than 6 in. with minute inhomogeneities or with low values for the absorption differential. The size of inhomogeneity, lower limit of absorption differential, and upper limit of magnification were also studied. For investigation of the distribution of elements in inhomogeneities, it was concluded that, contrary to previous reports, both target element and applied voltage must be carefully chosen after a study of the absorption differential curves. The optimum voltage range is usually 2.5 to 3.5 times the excitation potential.

ISSN:0021-8979    

DOI:10.1063/1.1707366

出版商:AIP    

年代:1944

数据来源: AIP

摘要:

This paper presents: (1) a comparison between several approximate theoretical formulas for the input impedance of cylindrical antennas in the light of available experimental evidence; and (2) a discussion of the local capacitance in the vicinity of the input terminals, mathematical difficulties created by its presence, and methods of overcoming these difficulties. No exact solution of the antenna problem is available at present and so far it is impossible to set definite limits for errors which may be involved in various approximations. For this reason in appraising these approximations one is forced to rely on one's judgment and on experimental evidence. It is hoped that this paper will aid in correlating theory and experiment to the advantage of both.

ISSN:0021-8979    

DOI:10.1063/1.1707367

出版商:AIP    

年代:1944

数据来源: AIP

摘要:

An alternative formula for the input impedance of a cylindrical antenna is derived from Halle´n's integral equation. It is shown that the introduction of a variable parameterZ(z) in place of Halle´n's &OHgr;=log (4l2/a2) modifies the numerical results considerably, and leads to much better agreement with experimental evidence.

ISSN:0021-8979    

DOI:10.1063/1.1707368

出版商:AIP    

年代:1944

数据来源: AIP

摘要:

Combined torsion and tension of thin‐walled tubes constitutes one of the few testing arrangements in which a fairly general state of uniform stress can be realized without too great experimental difficulties. A manner of representing graphically the results of such tests is used to discuss, in geometrical terms, some stress‐strain relations of the mathematical theory of plasticity. It is shown that the theories of B. de Saint‐Venant, M. Le´vy, and R. v. Mises lead to physically unacceptable conclusions unless the material is supposed to be rigid as long as the stresses have not reached the yield limit. The predictions of the theories of L. Prandtl, E. Reuss, H. Hencky, and A. Na´dai are compared with the results of experiments on mild steel; the possible effects of viscosity and strain hardening are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1707369

出版商:AIP    

年代:1944

数据来源: AIP

摘要:

Part I. General problems of technique arising in three‐dimensional photoelastic analysis by means of the frozen stress pattern method are discussed. These include suggestions for loading, slicing, improvement of boundary visibility, a discussion of time stresses, and methods for the determination of the fringe order and fringe value in a model with a static or frozen stress pattern. A number of instructive three‐dimensional stress patterns are shown. Part II. Stress concentration factors for shafts with ratios ofr/dequal to 0.0666, 0.323, and 0.164 are determined,rbeing the radius of the hole,Dthe diameter of the shaft, andd=D−2r. Part III. A relation is established between two‐ and three‐dimensional factors of stress concentration for a range ofr/dwhich does not exceed 0.5, which is believed to cover the most practical cases. It is shown that the three‐dimensional factors are somewhat greater than the two‐dimensional factors for the same ratio ofr/d.

ISSN:0021-8979    

DOI:10.1063/1.1707370

出版商:AIP    

年代:1944

数据来源: AIP