摘要:

Application of the Darwin‐Prins theory to diffraction by a perfect noncentrosymmetric crystal shows that the ratio of integrated intensities for opposite faces is given by a relationship that is identical to that for a mosaic crystal.I(h,k,l)/I(h¯,k¯,l¯)=|F(h,k,l)|2/|F(h¯,k¯,l¯)|2.This result had been derived previously from the Ewald‐von Laue theory. The relationship has been verified experimentally with measurements on nearly perfect crystals of GaSb and InAs.

ISSN:0021-8979    

DOI:10.1063/1.1657956

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Interdiffusion coefficients have been measured in Au&sngbnd;Ag alloys containing 18–50 at.% Au at temperatures from 200° to 260°C and over very short penetration distances (7–35 Å). The diffusivities were determined from the rate of decay of composition modulations in vapor‐deposited films. The wavelength and amplitude of the modulations were measured by x‐ray diffraction. From the dependence of the diffusion coefficient on the wavelength of the composition modulation, it was established that it is necessary (as proposed by Hillert and by Cahn) to allow for the effect of the ``gradient energy'' on the driving force when diffusion occurs in the presence of very sharp composition gradients. The observed gradient‐energy coefficient wasK=−(2.6±0.5)×10−6erg·cm−1in agreement with a value calculated on the basis of nearest‐neighbor interactions. The interdiffusion coefficients (corrected to an infinite penetration distance) were in good agreement with an extrapolation of existing high‐temperature data obtained with conventional diffusion specimens, thus demonstrating that the vapor‐deposited film technique is capable of determining, with good precision, diffusivities of the order of 10−20cm2sec−1. This is some eight orders of magnitude smaller than those that can be measured conventionally.

ISSN:0021-8979    

DOI:10.1063/1.1657957

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Interdiffusion coefficients have been measured in Cu&sngbnd;Pd alloys containing 70–90 at.% Pd at temperatures from 355° to 440°C using films containing short wavelength composition modulations produced by evaporation. From the relative intensities of the high‐ and low‐angle satellites about the 111 Bragg peak, it was established that the composition modulations were coherent for &lgr;<28 Å (where &lgr; is the wavelength of the modulation) and were incoherent for &lgr;>38 Å. Over the range 28 to 38 Å, there was a progressive loss in coherency and this was accompanied by a twofold decrease in the diffusivity. This decrease confirms quantitatively the effect of coherency strains on diffusion predicted by Cahn. The dependence of the effective diffusion coefficient on wavelength in the coherent modulations yieldedK=−10.3×10−6erg·cm−1for the gradient‐energy coefficient.

ISSN:0021-8979    

DOI:10.1063/1.1657958

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The reflection, refraction, and transmission characteristics of a plane electromagnetic wave incident from an isotropic medium, through a moving uniaxial slab, and into another isotropic medium are studied. The conceptual equivalence of a moving medium and a stationary anisotropic one with suitably defined permittivity and permeability tensors is used for the analysis. Complete field expressions are obtained in all three regions for an arbitrary orientation of the plane of incidence and an arbitrary angle of incidence. Special cases where the plane of incidence is parallel, or perpendicular, to the direction of slab motion are considered for both an incidentEwave and an incidentHwave. Some interesting numerical results are presented for the transmission coefficient at normal incidence when the moving slab is a magnetoionic plasma subject to a strong magnetic field and when the moving slab is a uniaxial crystal.

ISSN:0021-8979    

DOI:10.1063/1.1657959

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

We have examined the particles emitted radially by dc arcs drawn in a vacuum ambient on cathodes of several elements, as well as the axial (through‐anode) ion flux from a copper cathode. The axial results for copper agree grossly with the radial copper results. Significant quantities of multiply charged ions were seen for all elements examined. All arc volt‐ampere characteristics were positive in the range of currents observed: 30 to 250 A. We drew the following conclusions (normalizing energy in units of ion energy/ion charge): (1) The energy distributions for the various ions are similar, peaking at potentials well above the arc voltage. (2) The fraction of ions that are singly charged tends to increase with increasing arc current. (3) For a given element, as the degree of ionization increases the location of the ion‐energy distribution peak shifts to lower energies. (4) For a given degree of ionization, the location of the peak tends toward higher energies for elements with greater arc voltages. (5) The location of the peak shifts toward lower energies as the arc current increases. A possible mechanism for the production of ions with energies corresponding to potentials greater than the anode potential lies in the theory of a potential peak near the cathode.

ISSN:0021-8979    

DOI:10.1063/1.1657960

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Experimental data are presented on the currents induced in organic liquids by injection from a tunnel cathode. The injection level was varied over a wide range resulting in almost no space‐charge limitation to almost complete space‐charge limitation. Results were different from that usually observed in solids, in that at low fields, the steady‐state current was proportional toV2, while at high fields the current was proportional toV.By proper choice of electrode spacing and applied voltage, space‐charge‐limited current transients as low as 10−11A/cm2and 5 sec transit times were observed. A smooth transition between the electrode‐limited and the space‐charge limited regimes was achieved by varying the junction voltage that varied the injection level.

ISSN:0021-8979    

DOI:10.1063/1.1657961

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The relative resistance change of a properly seasoned manganin coil was measured at the center of the region of indifference for the bismuth II‐III, thallium II‐III, and barium I‐II phase transformations in a hydrostatic system. The equilibrium pressures for these transformations were obtained from the relative resistance change of manganin which was calibrated with pressure by means of the mercury L‐I and bismuth I‐II transition pressures. Equilibrium pressures corrected to 25°C of 26.861±0.042, 36.569±0.153, and 56.273±0.521 kbar were determined for the bismuth II‐III, thallium II‐III, and barium I‐II phase transformations, respectively. Only the barium I‐II point deviated from the presently accepted high pressure scale. On the basis of the manganin pressure gauge, either the presently accepted value of the barium I‐II point is too high by about 2.5 kbar or the pressure coefficient of manganin resistance changes sharply between 37 and 59 kbar. A two‐point quadratic calibration curve was satisfactory for pressures to 37 kbar.

ISSN:0021-8979    

DOI:10.1063/1.1657962

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Tantalum may be converted from a type I to a type II superconductor when small amounts of interstitial impurities are present. The resistance of type I and type II wire specimens was measured in a transverse magnetic field during the superconducting to normal transition. It was found that for both types carrying a transport current, the resistance for the major portion of the transition region is a function of the Lorentz force acting on the normal domains of the intermediate state or on the flux filaments of the mixed state. The effects of strain and impurity were also studied and were interpreted in terms of their influence in retarding the motion or pinning of normal domains in the material.

ISSN:0021-8979    

DOI:10.1063/1.1657963

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The equations for the terminal characteristics of a composite superconductor are formulated taking into account heat transfer to a coolant, interface thermal contact resistance, and the size of the superconductor itself. The nonlinear heat‐transfer characteristics of liquid helium are also taken into account in an approximate manner. The general relationship for stability is derived in terms of dimensionless parameters involving the size and characteristics of the substrate and the superconductor and the heat‐transfer coefficients at the interfaces between the superconductor and the substrate, and between the substrate and the coolant. It is also concluded that if the superconducting strands are smaller than a characteristic size, one would espect that flux jumps should disappear.

ISSN:0021-8979    

DOI:10.1063/1.1657964

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A technique is described for determining optimum, minimum volume shapes for uniform current density superconducting solenoids. The calculations include the effects of the dependence of current density upon the peak field at the coil winding and lead to coils which are significantly longer than those predicted by previous, field‐independent optimization techniques.

ISSN:0021-8979    

DOI:10.1063/1.1657965

出版商:AIP    

年代:1969

数据来源: AIP