摘要:

Molecular order and motion in isotactic and atactic polypropylene molecules have been studied by proton magnetic resonance methods over the temperature range 77–400°K, and by x‐ray diffraction. It is shown that some motion persists at the lowest temperatures, and becomes pronounced in the temperature interval 77–110°K. This behavior is ascribed to motion of the methyl groups about the threefold axis. The resonance undergoes further narrowing near room temperature for the atactic polymer, presumably owing to rotational and translational motions of chain segments. The isotactic compound possesses a narrow resonance superposed on a broad absorption over a wide temperature range. The former, ascribed to the amorphous regions, narrows at higher temperatures than for the atactic polymer, presumably owing to constraints imposed by the crystalline regions. The chains of the isotactic compound are less mobile than in polyethylene, as shown by the resonance studies and by x‐ray diffraction comparisons of the rate of crystallization.

ISSN:0021-8979    

DOI:10.1063/1.1722964

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Measurements of the complex shear compliance (J*=J′−iJ″) of polyvinyl stearate at frequencies from 50 to 5000 cps have resulted in the discovery of several sharp resonances in the compliance as previously described. The effects of temperature and static stress normal to the direction of the dynamic shearing stress have now been studied for this material. The two principal resonances observed at 25°C were located at (1) 180 and (2) 500 cps. At successive temperatures of 30, 36, and 42°C the first resonance remained essentially unchanged, but the second resonance shifted to higher frequencies and decreased in magnitude until it virtually disappeared at 42°C. A return to 25°C and a reapplication of a slight static stress resulted in the return of the second resonance (at 525 cps). At successively increasing static stresses corresponding to compressions up to 1.8% the second resonance now decreased in magnitude and shifted to higher frequencies. The first resonance disappeared at a static compression of 0.8%. Similar effects of static stress were observed at room temperature (∼25°C) on a second set of samples of different dimensions. The reversibility of the effects of static compression were demonstrated by the second set of samples where for example, a resonance originally present at 2.8% static compression disappeared at 3.7% and reappeared when the static compression was reduced to 3.1%. The reversible nature of the effects of static stress seems to preclude the possibility of an explanation of the resonances in terms of changes in dislocation density.

ISSN:0021-8979    

DOI:10.1063/1.1722965

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The relative surface energy of a 90° domain wall in a cubic material withK1>0 (iron) has been evaluated over the range of possible wall orientations. As the plane of the wall passes through a {110} plane, the minimum‐energy configuration changes from a right‐hand to a left‐hand rotation of the atomic moments; this leads to a sharp upward cusp in the energyvsorientation curve. The calculated orientation dependence of the surface energy can be used to predict a stable wall position in an iron whisker. The prediction is in reasonable agreement with observation.

ISSN:0021-8979    

DOI:10.1063/1.1722966

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Experimental evidence is presented that magnetic writing with an electron beam is possible. The method is based on Curie‐point writing which permits local reversal of the direction of magnetization in suitable, premagnetized magnetic films by temporarily elevating the temperature above the Curie point. By utilizing the dissipation energy of a focused electron beam for this purpose, quite well‐defined traces of reversed magnetization could be recorded on MnBi films. The traces were erasable magnetically. Writing speeds corresponding to 3·104bits/sec and information densities corresponding to 105bits/cm2could be achieved in these first experiments. Considerably higher writing speeds and some increase in information density should be feasible.By means of an electron mirror micrograph of the electronically recorded magnetic trace, evidence is presented which shows that, in addition to read‐in with an electron beam, electronic read‐out of the magnetically stored information is also possible.Electronic writing of magnetic half‐tone images by controlling the size of the spots of reversed magnetization appears to be feasible also.

ISSN:0021-8979    

DOI:10.1063/1.1722967

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The diffusion of gallium into silicon has been investigated over a temperature range of 1130°C–1358°C using an open‐tube vapor‐solid diffusion technique at atmospheric pressure. Ap‐njunction method combined with incremental conductivity measurements of the diffused layer was used to determine the diffusion constant. Lower diffusivities and a somewhat higher activation energy, (&Dgr;H=95 kcal) were obtained than those reported previously.The difference is attributed to variation of diffusivity with surface concentration and is discussed on the basis of substitutional diffusion proceeding by a vacancy mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1722968

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The stability of a rapidly contracting self‐pinched discharge (fast pinch effect) is studied using three different models for the plasma dynamics: (a) the free particle model; (b) the snowplow model; (c) the shock wave model. For each model the growth in time of a small perturbation on a time‐dependent unperturbed solution of the equations of motion is obtained. It is shown that the free particle model and the shock wave model predict instabilities. The instabilities are rather mild, the instability times being of the order of the pinch time itself. The snowplow model predicts stability for the initial stages of the pinch, although instabilities probably develop later on.

ISSN:0021-8979    

DOI:10.1063/1.1722969

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Several theoretical analyses of the process of magnetization reversal in thin films by coherent rotation of the magnetization vector have been published. However, these analyses suffer from the use of questionable assumptions and from a lack of generality. This paper presents results obtained by employing an electronic digital computer to solve differential equations of greater accuracy and generality than those previously used. These results show how the optimum damping factor (which, as defined herein, differs slightly from the critical damping factor), the peak output voltage, and the reversal time vary with the magnitude and direction of a field applied to a thin ferromagnetic film with uniaxial anisotropy. The results for a particular direction of applied field show that the optimum damping factor and the peak voltage increase and the reversal time decreases with increasing magnitude of the field; and that a plot of reciprocal reversal timeversusfield magnitude is a parabola if the damping factor is always equal to its optimum value, but a hyperbola if the damping factor is a constant.

ISSN:0021-8979    

DOI:10.1063/1.1722970

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The efficiency equation for any number of thermoelectric generators thermally in series is derived. The design relationships for maximum efficiency and for maximum power transfer of a multiple stage thermoelectric generator are also given. Since the efficiencies are approximately additive, an appreciable increase in generator efficiency is anticipated by use of multiple stages.

ISSN:0021-8979    

DOI:10.1063/1.1722971

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The adiabatic elastic moduli at 25°C for single crystal alpha‐uranium are reported here as derived from measurements of high‐frequency ultrasonic wave velocities. A detailed description is given of the specimens used, and of the technique employed for obtaining small plates of proper orientation suitable for the problem. Although the specimens were small the technique of measurement produced results of relatively good precision, as evidenced by the numerous cross checks obtained. Best values of the moduli and the estimated probable errors are given.The elastic stiffness moduli in units of 1012dynes/cm2are as follows:c11=2.147 ±0.14%,c12=0.465±0.6%,c13=0.218±1.5%,c22=1.986±0.14%,c23=1.076±0.34%,c33=2.671±0.14%,c44=1.2444±0.10%,c55=0.7342±0.10%,c66=0.7433±0.10%.

ISSN:0021-8979    

DOI:10.1063/1.1722972

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The ferroelectric switching time of two BaTiO3single crystals has been measured at voltages up to 1300 v across the crystals' thicknesses, 0.108 and 0.076 mm. The switching time,ts, can be represented approximately asts=kV−32fromVequals 100 v to 1300 v applied. The shortest switching time, 7.0×10−9sec, was less than half the time taken by a dilatational wave front to traverse the crystal's thickness, 14.9×10−9sec. The results imply that ferroelectric switching in this voltage range does not involve the movement of elastic waves from one side of the crystal to the other.

ISSN:0021-8979    

DOI:10.1063/1.1722973

出版商:AIP    

年代:1958

数据来源: AIP