摘要:

The potentiometer circuit designed for measuring minute variations in small resistances developed by P. W. Bridgman has been used to measure the effect of tension, applied in a direction parallel to that of the current, on the resistance of iron single crystals (elastoresistance). Correction for strain permitted the calculation of the more informative physical characteristic, the elastoresistivity. In order to obtain at least an indication of the expected anisotropy of elastoresistivity, two single crystals of different orientations were investigated. Deformation temperatures of +30° and −78°C were used to observe the effect of temperature on the (relative) elastoresistivity. The increase in &Dgr;&rgr;/&rgr; with decreasing temperature was larger than anticipated. The elastoresistivity and elastoresistance showed considerable anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.1728867

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The sizes of particles prepared in mercury with diameters less than about 3000 Å were determined by electron microscope examination, analysis of the magnetization curve, calculation from the temperature dependence of magnetic remanence, tin adsorption, and analysis of their growth kinetics. The results of the various methods were found to be in reasonable agreement.

ISSN:0021-8979    

DOI:10.1063/1.1728868

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A theory for the scattering of light from a film of a polymer possessing randomly correlated oriented fluctuations of anisotropic elements is presented. The case for the film possessing both density and orientation fluctuations is considered. It is shown that one can separate these contributions from measurements obtained using polarized light. The consequences of non‐randomly correlated fluctuations are qualitatively considered.

ISSN:0021-8979    

DOI:10.1063/1.1728869

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Measurements of the internal friction in pure Al and two aluminium alloys with 2 and 2.95 wt % Cu were made using a torsional pendulum. With solution‐treated and quenched alloys a weak internal friction peak (peak I) was obtained at the same temperature range at which grain boundary relaxation occurred in pure Al. The peaks disappeared after a few minutes of aging due to the blocking of grain boundary relaxation on precipitation. The activation energyHcorresponding to this peak is 32±1 kcal/mole for both the 2 and 2.95% alloys. A grain boundary peak also appeared in furance‐cooled 2% alloy withH= 31±1 kcal/mole, but instead of a peak an inflexion point appeared in 2.95% alloy. For pure Al,H= 32.4 kcal/mole was obtained. Due to re‐solution of the precipitates at higher temperatures another strong internal friction peak (peak II) appeared a few degrees below the solubility temperatures for both the alloys. The position of the peak is insensitive to the frequency of measurements but the peak height decreases on increasing the frequency. From the rigidity modulus measurements the solubility temperatures for the 2 and 2.95 wt % Cu in Al are obtained and are found to be in good agreement with previous results. An internal friction peak due to Zener relaxation, however, has not been observed in these alloys.

ISSN:0021-8979    

DOI:10.1063/1.1728870

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The thermoelectric figure of meritTzof a semiconductor is calculated as a function of the width of the conduction band. It is found thatTzapproaches zero as the bandwidth goes to zero. The existence of an optimum bandwidth is established; however, the magnitude cannot be ascertained on the basis of the simple model used here.

ISSN:0021-8979    

DOI:10.1063/1.1728871

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The slowing down of an energetic particle in a random assembly of scattering centers is discussed. Certain averages for physically interesting quantities can be calculated in a very general form, including unequal masses of scattering and slowing down particles. The averages refer to quantities such as the total distance traveled (L) and the vector distance to the final positions (xi) and powers thereof. Two assumptions simplify the evaluation of the general results considerably: (&agr;) The mean free path &lgr; is a simple power of the energyE: &lgr;(E)∼E&mgr;; (&bgr;) the distributiong(E; &egr;) of energies &egr; after one collision with initial energyEdoes not change its shape withE:Eg(E; &egr;)=&kgr;(&egr;/E). A special distribution of this kind is the hard core distribution. Under assumptions &agr;and&bgr; all calculations are reduced to the evaluation of an integral like ∫&kgr;(&eegr;)&eegr;&mgr;d&eegr;. For equal masses and the hard core distribution, one can easily calculate averages of any power ofLand obtain the distribution function ofL, this being proportional toL1/&mgr;exp(−L/&lgr;). Under the assumption &bgr;alone, with arbitrary &lgr;(E), results are given for special distributions and equal masses (including the hard core distribution). The evaluation of the averages now requires simple integrals over &lgr; for linear averages and double integrals for quadratic averages with known integral kernels. For unequal masses, approximations are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1728872

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The following work treats Kottler's saltus problem of diffraction of electromagnetic waves emitted by a Hertzian oscillator source and the analogous Kirchhoff's scalar problem of waves emitted by a point source. The medium is a homogeneous isotropic dielectric. In the vector case a new exact solution of the basic integrals is presented, at axial points only, (a) behind a circular aperture in a ``black'' screen, and (b) behind its complementary ``black'' disk. The relative time‐averaged intensity of energy flow is plotted for the disk only. It is shown that the scalar theory predicts considerably larger values than the electromagnetic theory for identical geometrical dispositions.

ISSN:0021-8979    

DOI:10.1063/1.1728873

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The semiphenomenological transport equations that are commonly used in the theory of semiconductors have been rewritten in variables appropriate to the discussion of an illuminated isothermal semiconductor in which the band gap is a linear function of one of the position coordinates. It has been found necessary to neglect those terms in the transport equations that arise from variations in mobility and effective mass. The first section considers electrical conduction in a uniformly doped specimen under weak illumination; deviations from Ohm's law were found to be small. In the second section, the potential distribution in a highly illuminated sample of such material, both with and without a junction present, is found. The major contribution to the total potential is the same as that found earlier by Tauc. These results are then used to determine the best geometry for a solar‐energy converter in which such materials are used, and to calculate the efficiency of this converter as a function of illumination. The greatest efficiency possible was found to be 43%.

ISSN:0021-8979    

DOI:10.1063/1.1728874

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The possibility of trapping significant quantities of point defects during growth of a crystal is considered. Calculations are based on the well‐established theory of growth from the vapor on vicinal surfaces and the results are applied approximately to more complex cases. Concentrations of point defects, either above or below equilibrium, can be trapped under some conditions. In most cases the effect is insignificant. The crucial characteristic of a growth condition is defined by the dimensionless parameterDv/RdwhereDvis the bulk diffusion coefficient for point defects (vacancies),Ris the growth rate, anddis the ``effective thickness'' of the surface. The value ofdis about 1 atom layer in most cases, but may be greater at solid‐melt interfaces. Large supersaturations of point defects may be trapped ifDv/Rdis small. For very large values ofDv/Rd, subsaturation concentrations of vacancies may be trapped. Growth trapping accounts for the loss of dislocations from metal whisker crystals during growth and may support a simple explanation of some substructure formation during solidification of pure single crystals.

ISSN:0021-8979    

DOI:10.1063/1.1728875

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A theory of evaporation of a monolayer is here presented in which the evaporation of individual atoms, without interaction, is treated by statistical methods and in which the effect of interactions between atoms when the coverage is finite is treated by the thermodynamic reasoning developed by Langmuir. By combining these two approaches an expression is obtained which has, formally, only one adjustable constant, namely, the binding energy at zero coverage. The types of interactions taken into account are (following Langmuir): (a) finite size of surface atoms, and (b) dipole repulsion. Values of dipole moment are derived from thermionic emission. Assumptions have to be made regarding the partition functions relating to a surface atom. On the assumption that the only energy states available to a surface atom are those of translation parallel to the surface, agreement within the spread of currently available data for thorium on tungsten is obtained by using a binding energy at zero coverage of 7.61 ev. More precise data are required for determination of whether there must be some other and more complete specification of the partition functions for surface atoms.

ISSN:0021-8979    

DOI:10.1063/1.1728876

出版商:AIP    

年代:1962

数据来源: AIP