摘要:

The inelastic scattering of fast electrons due to interband electron transitions in crystals of Li, Be, Ne, Al, and Cu is examined making use of single atom matrix elements given by Freeman. Values of the Fourier coefficientsVgandVgiof the real and imaginary part of the potential are computed for 100‐kV electrons. It is concluded that while interband transitions may account for an appreciable part of the average absorption due toVoi,Vgiis too small to account for the anomalous absorption effect observed in crystals. The result is in agreement with Yoshioka's conclusion based on the Fermi‐Thomas model.

ISSN:0021-8979    

DOI:10.1063/1.1714426

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The inelastic scattering of fast electrons due to phonon excitation is examined using a simple Einstein model. The method of analytic approximation to the atomic electron scattering factor given by Smith and Burge enables analytic expressions for the Fourier coefficients of the imaginary potential due to phonon scattering to be obtained. The Fourier coefficients are computed for several elements and reflections and the temperature dependence is examined. It is concluded that phonon scattering could account for the localization of the complex potential at the atomic positions as required to explain anomalous absorption effects, in agreement with previous results of Yoshioka and Kainuma.

ISSN:0021-8979    

DOI:10.1063/1.1714427

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Experiments have shown that some dielectric materials are electrically polarized by the passage of an intense shock wave. If the dielectric is contained between electrodes that are connected through a resistor, the shock‐induced polarization produces an electric current, which can be detected as a voltage drop across the resistor. Equations are derived which relate the magnitude of the electric current to the shock propagation characteristics and dielectric properties of the material.

ISSN:0021-8979    

DOI:10.1063/1.1714428

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The polarization produced by a shock wave has been measured for shock pressures up to 297 kbar in Plexiglas and 207 kbar in polystyrene. The polarization is produced at the shock front and undergoes relaxation after the front has passed. For both materials, Hugoniot data indicate a high‐pressure phase transition which is correlated with rapid changes in the dielectric properties of the shocked material. At the phase transition, the polarization produced at the shock front and the dielectric constant of the shocked material increase more rapidly, while the relaxation time suddenly decreases. The changes in dielectric properties at the phase transition suggest that the high‐pressure phase is more fluid.

ISSN:0021-8979    

DOI:10.1063/1.1714429

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The storage and dissipation resistance to deformation of a cohesive soil as represented by the complex modulus is obtained from stress relaxation response using the one‐sided Fourier transform. The soil response is nonlinear. An approximate method of evaluating the transform with digital computer methods is based on the use of straight line segments to form a piecewise continuous representation of the relaxation response. This allows comparison of static and dynamic response characteristics as functions of applied strain level and moisture content through the transformation from the time domain to the frequency domain. For each strain level, large and small time plateau regions of complex modulus are connected with a transition region showing an increase in modulus with increase in frequency. Complex modulus decreases with increased strain level and increased moisture content.

ISSN:0021-8979    

DOI:10.1063/1.1714430

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The existence of magnetic transitions in alloys of Fe in Au and Cu has been shown by using the Mo¨ssbauer effect. There is a significant difference in the internal‐field distribution (and hence alignment of the atomic spins) between the Cu and the Au alloys. In the former a continuous distribution exists, whereas, in the latter a unique (or very nearly unique) internal field occurs in the dilute alloys. The results for the Cu alloys are consistent with an indirect interaction of the Ruderman‐Kittel‐Yosida type of spins localized at the iron atoms. The internal‐field distribution appears to develop a minimum at zero field and a rather broad maximum which shifts gradually to higher fields with decreasing temperature. The nearly unique internal field in the dilute Au‐Fe alloys seems to exclude an explanation on the basis of a Ruderman‐Kittel‐Yosida exchange interaction. A spiral static spin density wave as the mechanism for antiferromagnetically ordering the localized spins (or ferromagnetic order for the case in which the spin density wave vector is zero) seems possible. More concentrated Au‐Fe (>16 at. % Fe) alloys show a much more rapid increase in the magnetic transition temperature than the more dilute alloys. Their behavior is ferromagnetic and can be described quite well with a nearest‐neighbor interaction using the average coordination number method suggested by Sato, Arrott, and Kikuchi. The appropriate nearest‐neighbor exchange interaction energy isJ≃2.9×10−2eV.

ISSN:0021-8979    

DOI:10.1063/1.1714431

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Extinction contours observed in silicon whiskers in the electron microscope have been studied. The details of the extinction contours depend, in general, on the orientation of the whisker and the geometry of the reflection. Several interesting diffraction effects have been observed. The intrinsic angular width of the electron beam can be determined from the extinction contours. In some cases, the extinction contours outline the cross section of the whisker, revealing directly the morphology of the whisker.

ISSN:0021-8979    

DOI:10.1063/1.1714432

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The conversion efficiency of a lumped‐parameter, explosively driven electromechanical energy converter is studied. Numerical results of the study, which show the relationship among the device parameters required for unit conversion efficiency, are presented.

ISSN:0021-8979    

DOI:10.1063/1.1714433

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Experimental studies have been made on junctions prepared by alloying indium into silicon wafers. The junctions made usingn‐type silicon, the resistivity of which ranges from 0.02 to 100 &OHgr;cm, have good Ohmic characteristics, whereas the junctions made usingp‐type silicon, in the range of resistivities from 0.05 to 50 &OHgr;cm, indicate rectifying characteristics like ordinaryp‐njunctions. From the measurement of thermoelectric voltages on recrystallized layers, electrical characteristics, and capacitance of the junctions, it has been concluded that the recrystallized layer containing indium atoms showedn‐type electrical conductivity. The carrier concentration in these layers is estimated to be about 1017cm−3near the junction side and about 1019cm−3near the indium dot.

ISSN:0021-8979    

DOI:10.1063/1.1714434

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Single crystals of ThO2were grown from molten Li2O· 2WO3solvent at 1225°–1300°C. Growth occurred primarily by solution transfer from ThO2nutrient at 1250°–1350°C to seeds in regions 20°–75° cooler. The resulting crystals, optically transparent octahedra up to 3 mm on edge, contain <500 ppm W and <50 ppm Li as major impurities. The method was also used to prepare ThO2crystals containing limited amounts of several lanthanide ions. Increased growth rates were obtained by adding 1 wt% B2O3to the Li2O· 2WO3solvent.

ISSN:0021-8979    

DOI:10.1063/1.1714435

出版商:AIP    

年代:1965

数据来源: AIP