摘要:

The distribution of column lengthsp(n)/Ncin a powder sample is given by the following combinations of the coefficients of the Fourier series expansion of the x‐ray diffraction line shape:p(n)/Nc=(2An−An+1−An−1)/A0−A1).

ISSN:0021-8979    

DOI:10.1063/1.1729586

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Curves of thermal expansion parallel and perpendicular to the polar axis are shown for poled barium titanate and lead titanate zirconate ceramics. Anistropy is remarkably higher in the latter due to greater alignment by 90° switching during poling. The anisotropy disappears after heating through the Curie point, and is also virtually eliminated within a given temperature range below the Curie point after exposure to a temperature only slightly above this range. The contraction in the polar direction upon first heating is due largely to a decrease in the alignment of domains originally reoriented by 90° during poling. The reversible expansion on repeated heating is due to a combination of domain anisotropy and a reversible increase in nonpolar alignment during heating. The pyroelectric effect is also greatly reduced in subsequent heating, although piezoelectric constants are reduced only slightly. The pyroelectric effect is found to be largely primary in both barium titanate and lead titanate zirconate ceramics. The increase in nonpolar 90° domain alignment on second heating of the lead titanate zirconate causes the primary and secondary pyroelectricity to be of opposite sign near room temperature.

ISSN:0021-8979    

DOI:10.1063/1.1729587

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Lattice parameters and distribution coefficients for the Bi2Te3‐Bi2Se3pseudobinary alloy system have been determined for several compositions across the phase diagram. Theclattice constant (based on a hexagonal lattice) shows deviation from Vegard's law between 33% Bi2Se3and pure Bi2Se3with maximum deviation at 67% Bi2Se3. Thermal energy gap as a function of composition shows a maximum near 33% Bi2Se3and a minimum near 67% Bi2Se3. It is postulated that at least two sets of energy band minima are present in this alloy system.

ISSN:0021-8979    

DOI:10.1063/1.1729588

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An experimental method is presented, for the study of glow discharges, that can provide data suitable for analysis in terms of the diffusion of a ternary mixture. Particular emphasis is given to the constriction of flow discharges in neon with increasing gas density. It is found that quantitative estimates of the onset of this phenomenon are now possible.

ISSN:0021-8979    

DOI:10.1063/1.1729589

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Low‐energy electron diffraction patterns obtained from Ge(100) and Ge(111) clean surfaces are described and analyzed. The Ge(100) surface structure is the same as that observed with Si (100) surfaces. Parameters for the atom sites are reported. Structural units for both Ge and Si (111) clean surfaces are strongly suggested by the data reported for these surfaces. They have an atom defect of about 25% in the top layer. A wide variety of such structures can be proposed and three of them appear to have been observed. The importance of long‐range order on the density of semiconductor chemical ``surface states'' is emphasized and surface bands are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1729590

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The effects of pressure and temperature on the O&sngbnd;Ge and I&sngbnd;Ge surface reaction systems were studied by means of low‐energy electron‐diffraction with single‐crystal (100) and (111) surfaces. The results are very similar to those reported for silicon, but have a displacement to lower temperatures of about 350°C. On both surfaces the oxide films are amorphous, but well‐crystallized two‐dimensional iodide structures were obtained and the transitions to the iodides are ``reconstructive.'' The slopes for all four transitions from the ``clean'' surfaces correspond to energies of about 55 kcal/mole. Clustering phenomena are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1729591

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Strong magnetic fields are useful in work with high velocity charged particles by virtue of their ability to rotate the particle momentum vector. The degree of usefulness is measured by the extent to which the desired rotations can be produced at the proper positions in the field. It is frequently necessary to inject charged particles into magnetic fields at points remote from these proper positions, in which case the injection parameters which enable the particles to reach these positions must be specified. For the production of gyromagnetic radiation in axially symmetric magnetostatic fields the proper positions correspond to the high field regions near the symmetry axis. The present introductory study is concerned with delineating approximate injection parameter ranges which allow the particles to attain the regions of high magnetic field strength in the field whose axial variation is bell‐shaped. The single‐particle model is adopted, and the results of both qualitative and quantitative investigations are presented.A general formulation of the axially symmetric, magnetostatic field, forbidden‐zone theory is given and the useful concept of the paraxial forbidden zones is introduced. This theory is then applied to obtain qualitative answers to the injection problem for the bell‐shaped field for both zero and nonzero values of the angular momentum constant. Quantitative relations for the zero angular momentum constant case are obtained using the bell‐shaped field paraxial trajectories. A discussion of the limitations of the approximations employed is included.

ISSN:0021-8979    

DOI:10.1063/1.1729592

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The magnetic field in the vicinity of the center of a magnet gap is analyzed. In measuring an angle by means of a Hall cell in the magnetic field of the gap, the inhomogeneity of the magnetic field due to the influence of the edge of the gap leads to an error. The maximum error of the Hall voltage due to this cause is shown to be (5/16)Ww2/R3, whereWis gap spacing,Ris magnet face radius, andwis Hall cell width in direction across whichVHis measured.

ISSN:0021-8979    

DOI:10.1063/1.1729593

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A particular solution of the linearized Boltzmann equation, applicable to longitudinal oscillations of a one‐dimensional plasma without collisions, is constructed. It has the properties that (i) the Vlasov dispersion relation (1) is satisfied rigorously; (ii) that for large values of time, the perturbation decays as 1/t½; and (iii) that the solution may be singular at some points. The solution is not included in the theories of Van Kampen or Landau because of (iii), but it is in no sense a general solution of the initial value problem. The frequency at which damping is slowest is approximately twenty‐five percent above the plasma frequency.

ISSN:0021-8979    

DOI:10.1063/1.1729594

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The rf spectrum of a gaseous discharge in a strong magnetic field is measured with the aid of a fixed frequency receiver by sweeping the magnetic field by approximately two percent. Source of radiation and receiving equipment are described. The following results were obtained: (1) A series of emission lines around the cyclotron frequency. (2) An emission at a frequency which increases with increasing magnetic field strength and decreases with increasing external voltage. (3) A strong resonance when both frequencies coincide: the intensity increases by a factor of 100 and more.The frequency spectrum is discussed in terms of a simple theory, which accounts for local space‐charge fields. Their spatial distribution is inferred from the frequency behavior of the emission lines. Finally, a mechanism is suggested which classifies the resonance effect as an energy transfer from a longitudinal plasma mode into e.m. radiation.

ISSN:0021-8979    

DOI:10.1063/1.1729595

出版商:AIP    

年代:1963

数据来源: AIP