摘要:

The effect of various variables, such as type of stress, stress magnitude, duration of stressing, and environment on the initiation and development of crazing in linear polymers is discussed. The basic nature of crazing is investigated in some detail for polystyrene specimens by means of the light microscope, the electron microscope and the x‐ray spectrometer. The results of these observations and their bearing on the fundamental group structure of polystyrene molecules is presented.The relationship between crazing and orientation is discussed, as well as the effect of both of these factors on the mechanical properties. The experimental results are compared, wherever possible, with the previously reported data of other investigators. A short discussion is then given of a theory of crazing from the point of view of the molecular structure of the material.

ISSN:0021-8979    

DOI:10.1063/1.1699546

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The differential equation defining the relation between temperature and distance in that portion of a vacuum tube filament which is cooled by both conduction and radiation is formulated. This equation has been solved by numerical integration; the results are presented as a set of universal curves in a form convenient for use in vacuum tube design. The calculations agree well with some experimental measurements which were made to verify the theory.

ISSN:0021-8979    

DOI:10.1063/1.1699547

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The spread of electron beams caused by space‐charge forces is discussed. Under certain conditions ions formed from the residual gas may be trapped in the beam. An equilibrium condition may be established in which the electron and ion densities are equal, and then space‐charge forces will be neutralized. Under these conditions high current densities may be produced at low voltages. A theory of ion trapping is discussed, and the equilibrium condition is formulated.Experimental data are presented which were obtained by the application of microsecond pulses to the beam. This technique is described, and its advantages and possibilities are mentioned. Data are given on beam spread as a function of current, voltage and pressure. Data on the improvement due to ion trapping are included. An increase of current density by a factor of 30 was observed with the structures tested. Results are included on ion build‐up time as a function of pressure, and on beam noise and stability in the presence of trapped ions.

ISSN:0021-8979    

DOI:10.1063/1.1699548

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Tube‐shaped samples were stretched in a direction parallel to the tube axis and at the same time inflated to cause a tangential extension. In this way 600 percent axial and 300 percent tangential elongation could be attained simultaneously. The stresses were calculated from the pressure in the tube and the dynamometer readings.The results are plotted as axial stress‐strain curves at different tangential elongations ranging from 0–300 percent.The curve for a higher tangential elongation lies at higher stresses than that for a lower tangential elongation; the differences are however larger than the theory predicts.At 600 percent axial elongation stress relaxation was measured at different tangential elongations. It appears that the relaxation constant is independent of the tangential elongation.

ISSN:0021-8979    

DOI:10.1063/1.1699549

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

In a previous paper, we reached a consideration that the endurance limit of a material should be determined by the amount of the mean stress in a certain area around a point, instead of the stress at the point, and the extent of the area is determined for several kind of metals, by using the results of tension‐compression fatigue tests.In this paper, the extent of area where the mean value of stress to be taken, is determined for a mild steel in another way, viz., by a torsion fatigue test, and we reached the conclusion that the extent of area chiefly depends on the kind of metal and independent of the course of the experiment.

ISSN:0021-8979    

DOI:10.1063/1.1699550

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The axial and radial components of the magnetic field of a plane circular loop are expressed in terms of cylindrical coordinates. The expressions involve two integrals which are related to certain of the complete elliptic integrals. Tables of values of these integrals are presented. Interpolation in these tables facilitates rapid calculation of the field components.

ISSN:0021-8979    

DOI:10.1063/1.1699551

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Investigation of oxide‐coated cathodes has been made to determine the effect on electron emission of varying the proportions of emitting oxides. The results show that maximum electron emission under saturation conditions is obtained from a solid solution containing strontium oxide (SrO) and barium oxide (BaO) in an approximate molecular ratio of 7 to 3.These results also indicate that maximum size of the co‐precipitated alkaline‐earth carbonate particle occurs at the same molecular ratio as that giving maximum electron emission from the oxides.When the saturation emission obtained with a square‐wave voltage pulse was measured, the current pulse as observed on a synchroscope was also a square wave and showed no measurable decay characteristic for a pulse duration time of 10 microseconds.

ISSN:0021-8979    

DOI:10.1063/1.1699552

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

In this paper the applicability of non‐radiating surface waves for transmission lines is investigated. Two types of waves are considered. The first one, originally studied by A. Sommerfeld, is guided by a cylindrical conductor of finite conductivity. Although this wave type has (under comparable conditions) much lower attenuation than the waves in coaxial cables or rigid wave guides, its practical application is restricted by the fact that the extension of the field is very large. Efficient excitation and undisturbed propagation of this wave mode are feasible only for very high frequencies. The other wave type considered in this paper has not been treated in the literature. It is guided by a conductor which is coated with a dielectric layer or the surface of which is otherwise modified; for example, by being threaded. The field of this wave type has a structure similar to that of Sommerfeld's wave, but the extension of the field can be controlled by the surface modification. Thus low loss transmission lines on the basis of this wave type become feasible for frequencies above 100 megacycles. The information necessary for the design of such lines is given and the agreement between the theoretically expected transmission losses and the measured transmission losses is checked.

ISSN:0021-8979    

DOI:10.1063/1.1699553

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Control area, or the integrated error for a step function input, has been used as a measure of control system performance. For systems described by&thgr;0(s)&thgr;i(s)=e−sTd(&tgr;1s+1)(&tgr;2s+1)…(&tgr;ms+1)(T1s+1)(T2s+1)…(Tns+1), it is proved that the control area isA=Td+i=1n Ti−i=1m&tgr;i. A simple method of evaluation is presented and some limitations of the control area criterion are mentioned.

ISSN:0021-8979    

DOI:10.1063/1.1699554

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A new electron microscope of greatly simplified design has been constructed. The instrument has a resolution of 100 Angstroms, yet is small enough to be mounted on a desk or laboratory table. Magnetic lenses are energized by permanent magnets. An accelerating voltage of 50 kilovolts is varied over a narrow range to provide means of focus. Images may be photographed on 2×2 plates. Plates may be changed in a minute, and specimens in fifteen seconds. Direct magnifications of 1500, 3000 and 6000 are possible depending on pole pieces used. Photographic images may be enlarged up to ten times. The instrument is free of x‐radiation and completely interlocked and provided with shorting devices for protection from high voltage.

ISSN:0021-8979    

DOI:10.1063/1.1699555

出版商:AIP    

年代:1950

数据来源: AIP