摘要:

A method has been developed for taking thermal diffusivity data at elevated temperatures with a cylindrically symmetric sample consisting of a stack of disks. An axial heater is turned on and the temperatures at three radii in the midplane are recorded as functions of time. The temperature data from the inner and outer radii are used as empirical boundary conditions, and the temperature data from the middle radius are used to obtain the thermal diffusivity. A computer has been programmed to make the calculations by the method of finite differences. Thermal diffusivity measurements have been made from 26° to 895°C on Armco iron. The values found for the thermal diffusivity by this radial method agree well with the values found by Shankset al.who used a longitudinal method with a finite rod. The radial method is particularly advantageous when samples in the form of disks, but not in the form of long rods, are available.

ISSN:0021-8979    

DOI:10.1063/1.1714485

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Crystallographic properties of the spinel systems Li0.5Ga2.5−xMnxO4(0≤x≤0.7), Li0.5Fe2.5−xMnxO4(0≤x≤0.5), and Li0.5Al2.5−xMnxO4(0≤x≤0.5) have been investigated in order to determine the effects of trivalent manganese substitution on the crystal chemistry of the ordered spinel hosts. In each system relatively small concentrations of Mn3+removed long‐range ordering of lithium ions on the octahedral sites. This loss of order was accompanied by anomalies in the dependence of lattice parameters on composition. These observations can be qualitatively interpreted by assuming that Mn3+ions tend to cluster in order to reduce the elastic energies associated with Jahn‐Teller stabilization. These effects may provide indirect evidence for lattice imperfections such as have been invoked to account for squareB‐Hhysteresis loops in ferrite materials containing Jahn‐Teller ions.

ISSN:0021-8979    

DOI:10.1063/1.1714486

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

It is shown that in ferrites exhibiting spontaneously squareB‐Hloops, reverse‐domain nucleation may occur either at a grain boundary or at a chemical inhomogeneity having a volume roughly 0.1 of a grain volume, a magnetization about 2% different from that of the parent matrix, and no static crystallographic discontinuity at the inhomogeneity‐matrix interface. It is pointed out that such chemical inhomogeneities may occur in spinels having Jahn‐Teller ions in concentrations that are too small to produce a cooperative, static distortion of the entire crystal from cubic symmetry. It is postulated that the formation of such inhomogeneities is responsible for the sharp knee in spontaneously squareB‐Hloops found in many ferrites containing Mn3+and Cu2+ions, in particular the magnesium‐manganese composition used in memory‐core ferrites.

ISSN:0021-8979    

DOI:10.1063/1.1714487

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The addition of a second component to the cesium gas phase of a thermoionic generator could increase its efficiency by reducing the work functions of the electrodes.The different possible additives were screened and hydrogen, since it appeared to be the most promising, was chosen for further study.The work function reduction of cesium‐covered nickel, molybdenum, and tungsten due to the presence of H2in the gas phase ranges from 0 to 0.5 eV. An equilibrium condition can be established between the surface and the gas phase to make the low work function surface stable at elevated temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1714488

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The work function of cesium‐covered nickel has been measured by the thermionic and photoelectric methods. A modulated light beam technique allowed the measurement of the photoelectric emission currents in the presence of thermionic currents that were 106times larger. The minimum work function of cesium‐covered nickel was determined to be 1.42±0.05 eV by the thermionic method at a nickel temperature of 530°K and a cesium reservoir temperature of 333°K. The results obtained by the photoelectric method were, on the average, 0.05 eV lower than the values determined by the thermionic method. The discrepancy is expected because of the bias introduced to both methods by local variations in work function. The agreement of the data obtained by the two methods indicates that the Richardson constant is close to the assumed value of 120 A/cm2·deg2. The work was undertaken as a first step toward the improvement of cesium‐filled thermionic generators by lowering the collector work function.

ISSN:0021-8979    

DOI:10.1063/1.1714489

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Single crystals of bismuth germanate Bi4(GeO4)3having the eulytine structure, space groupTd6, were grown. They were crucible‐free pulled from a pool of molten material produced in its own powder at 1040°C by a thermal imaging technique. The material has an index of refraction of 2.07 and transmits light between 0.4 and 6.0 &mgr;. The electro‐optic coefficientr41was determined to be 1.03·10−10cm/V. Although materials with higherr41values are known, Bi4(GeO4)3may find applications because the growth of large crystals appears possible by classical pulling techniques. A large variety of chemical substitutions are possible in the eulytine structure and might lead to improvements in the magnitude ofr41.

ISSN:0021-8979    

DOI:10.1063/1.1714490

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

This paper is concerned with the experimental determination of the arrangement of the double‐plane probes and of an upper limit of a magnetic field for valid double‐probe measurement. One of the most reliable arrangements is that of two probes facing each other and situated parallel to the field. Also, the spacing of the probes must be significantly larger than 2&lgr;D. The upper limit of the magnetic field, below which the double‐probe method remains reliable, is determined mainly by the diffusion‐controlled collecting mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1714491

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A new electrostatic probe method utilizing the triple probe is proposed in which no voltage or frequency sweep (or switching) is required. This feature enables us to determine the instantaneous values of the electron temperature (Te), as well as the electron density (ne), within a short time which is of the order of the intrinsic response time of the probe itself (⪝1&mgr;sec). Moreover, the system allows the direct display of theTevalues as well as the semidirect display of thenevalues on appropriate display units, thus permitting us to eliminate almost all procedures usually required for data processing. In view of the features mentioned, this system may be a useful diagnostic tool not only for stationary plasmas but also for rapidly varying time‐dependent plasmas of various types.This paper presents theoretical considerations for the instantaneous direct‐display system using a symmetrical triple probe. Discussions are also presented for the estimation of errors caused by the variation of ion saturation current, for the application to magnetoplasmas, and for the time and spatial resolutions. Experimental confirmation was made through the measurements of stationary magneto‐ as well as non‐magnetoplasmas. As an example of the application to time‐dependent plasmas, the electron temperature waves accompanied by the moving striations in hydrogen discharge were observed.

ISSN:0021-8979    

DOI:10.1063/1.1714492

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The thermal conductivities of both the solid sulfur and the liquid sulfur were continuously measured with an accuracy of ±1.0%. The temperature range in this experiment is from 0° to 160°C. In the temperature range from 0° to 160°C, two transition points exist; one of them is the transition point from rhombic sulfur to monoclinic sulfur at 95.5°C, and the other is the change point from monoclinic sulfur to liquid sulfur at 118.9°C. At each transition point, discontinuous and conspicuous changes in thermal conductivities can be observed by this experiment.Moreover, a new result was obtained: The thermal conductivity of monoclinic sulfur decreases with increasing temperature, although the conductivity which was obtained by Kaye's experiment increases with temperature increment.

ISSN:0021-8979    

DOI:10.1063/1.1714493

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Densities of metal films were measured using multiple beam interferometry in combination with an oscillating crystal microbalance. Film densities of Al, Au, Ag, Cr, and Cu were found to be independent of thickness within experimental accuracy of about 5% in the thickness range from 200 to 5000 Å for fixed deposition conditions. Measurements indicate that film densities were equal to bulk densities within measurement accuracy for Al, Au, Ag, and Cu for deposition at about 10−6Torr. The film density of Cr was found to be strongly dependent on oxygen partial pressure above 10−6Torr, decreasing sharply as the oxygen partial pressure increased. The effect of condensation coefficients of metal films on the optical measurements is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714494

出版商:AIP    

年代:1965

数据来源: AIP