摘要:

The growth of crystals from the melt in oriented, crosslinked polyethylene was studied by x‐ray diffraction and birefringence as a function of orientation. It was found that for samples elongated more than about 200%, the crystals grow with theircaxes parallel to the stretching direction. At elongations less than 200%, there is a rather abrupt transition to a mode of growth in which thebaxis is perpendicular to the stretching direction with a tendency for theaaxis to be aligned parallel to this direction. An interpretation is made in terms of the folded‐chain concept of crystal structure.

ISSN:0021-8979    

DOI:10.1063/1.1777074

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The swelling of elastomers in solvents is a useful method for determining the effective crosslinking of the polymeric structure. However, it is now shown that this method may be applied satisfactorily to highly filled polymers. A unique method has been devised for the accurate measurement of the swelling ratio of the gel phase of the filled polymers. The method is based on the observation that the binder‐filler bond, for most filler particles, releases on swelling. The binder around the particle swells, leaving a hollow pocket which becomes filled with solvent. Corrections for this ``waste'' solvent lead to the equations from which the swelling of the polymer can be calculated. Experimental verification is given for several filled systems.

ISSN:0021-8979    

DOI:10.1063/1.1777075

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Alfve´n and Spitzer have obtained an expression for the drift velocity of a charged particle in an inhomogeneous magnetic field. The result is correct to first order in the ratio of the drift velocity to the particle velocity. We have presented here a class of fields for which the drift velocity may be calculated exactly.

ISSN:0021-8979    

DOI:10.1063/1.1777076

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A method is presented for the approximate estimation of mobility ratiob=&mgr;n/&mgr;pfrom the Hall constant measurements taken in the vicinity of the intrinsic region and in this region itself. It is based on the discussion of a formula giving the Hall constant of a nondegenerate semiconductor at the exhaustion. Examples of these determinations are given; the results obtained show reasonable agreement with others' estimations.

ISSN:0021-8979    

DOI:10.1063/1.1777077

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The origin of the excess and hump current in Esaki diodes is described in terms of discrete defect energy levels in the forbidden band. The hump current results from equi‐energy transitions of electrons which originate in a defect level in thenside and tunnel to the valence band on thepside. Impurity conduction is required for appreciable hump currents. The position of the hump locates the defect level if the Fermi level is known for thenside. The excess current is explained in terms of energy dissipating transitions in which electrons start from a defect location within the junction, tunnel to a virtual state in a localized defect in thepregion, and drop to the valence band by impact recombination. A crude derivation by the WKB method relates the logarithm of the excess current to the bias voltage where the proportionality factor contains the square root of the effective mass of the electron. From current‐voltage curves for diodes fabricated from germanium, silicon, and gallium arsenide, the effective electron masses are estimated as 0.01, 0.1, and 0.05m, respectively. Defect levels in germanium are estimated at 0.06 and 0.24 ev below the conduction band; levels in silicon are located at 0.04 and 0.42 ev; and in gallium arsenide 0.12 and 0.5 ev below the conduction band. The simultaneous existence of two defect levels can give rise to two distinct slopes of the logIvsVcurve which have been observed in silicon and gallium arsenide diodes following irradiation with 2 Mev electrons.

ISSN:0021-8979    

DOI:10.1063/1.1777078

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The statistical distribution of phosphor crystals in the solid dielectric material of a practical electroluminescent lamp influences the observed characteristics of the lamp. Calculation on the basis of a very simple model shows that maximum efficiency is favored by high phosphor concentration, fine particles, and thick phosphor layers; the slope and intercept of the usual brightness voltage plots are affected by the same variables. Measurements on electroluminescent lamps with these variations are in substantial agreement with the predictions.

ISSN:0021-8979    

DOI:10.1063/1.1777079

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Energy dissipation in solids is important in both transient and steady‐state measurements. The results of such measurements can be associated with a distribution of relaxation times provided the material is linear. In the present work, general relations are derived for the attenuation factor, phase factor, and specific dissipation function 1/Qpertaining to transmission of small amplitude stress waves in a material describable by a distribution of relaxation times. Next, a specific, physically realizable relaxation time distribution is used to obtain a creep function and to relate transient creep and frequency response measurements. Curves of 1/Qvs frequency are calculated with a digital computer and show a region approximately proportional to frequency at sufficiently low relative frequencies, a region of virtual frequency independence, and a final region proportional to inverse frequency at high relative frequency. The relation of the present work to other treatments of creep and internal friction is discussed, and the applicability is examined of the analytic and numeric results to creep measurements on metals and rocks, to low‐frequency wave transmission in the earth, to other damping results for the earth as a whole, and to higher‐frequency wave transmission and vibration results for geophysical and other solids. Good agreement between theory and experiment is found for frequency regions where adequate data are available, indicating that all the damping phenomena considered may be well described by a linear theory in the range of very small strain.

ISSN:0021-8979    

DOI:10.1063/1.1777080

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

An analysis of the published measurements of breakdown voltage for various gap lengths for uniform and approximately uniform fields shows that the results may be represented by the breakdown equationV=Cx&agr;and that the values of &agr; lie in the range 0.1 to 1.1 with a mode of 0.7. A theory is developed which leads both to a breakdown equation of the same form and to a general expression to account for the range of values of &agr;. This expression is confirmed for gaps up to 0.075 cm by direct experiment. The development is based on the postulate that an electron beam is emitted from the cathode, diverges, and bombards the anode to cause breakdown when a critical power flux is reached. The factorCis shown to include the critical power flux and to be related to both field and electrode separation. In support of the theory, the radii of craters produced on the anode are measured and shown to be related to the radius of an electron beam at the anode. Calculation shows the current carried by the beam to be of the order of 10−4amp. Values of the critical power flux obtained from the equationV=Cx&agr;and from anode crater data, respectively, agree within a factor of 1.5 and are of the order of 108w cm−2. To explain the observed phenomena, a multiple electron beam system is proposed.

ISSN:0021-8979    

DOI:10.1063/1.1777081

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Low‐frequency noise measurements have been made throughout the entire useful bias range of germanium and GaAs Esaki diodes. Evidence is presented in agreement with Esaki and Yajima that a near square‐law relationship exists between the mean‐square, short‐circuit noise current and excess current for bias voltages beyond the valley voltage in germanium diodes. Attempts to find a like relationship in GaAs were not conclusive. Measurements of the noise within the negative‐resistance regions of the diodes showed a nearly continuous exponential relationship between excess noise and bias for the germanium units and a similar plot was obtained for the GaAs diodes, except a well‐defined peak in the noise current was found at about 0.2 v forward bias. The evidence that the results indicate a rather continuous distribution of allowed states in the forbidden band of the germanium samples and a possible localized maximum in these states in the GaAs samples is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1777082

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A quantitative treatment of the photographic process is carried out, modeled on the Gurney Mott theory. This is extended by taking account of the distribution of photolytic silver during and after the exposure. Applications of the theory are made to some simple types of sensitizing. The most important physical parameter of a photographic grain seems to be the number of electron traps.

ISSN:0021-8979    

DOI:10.1063/1.1777083

出版商:AIP    

年代:1961

数据来源: AIP