摘要:

The torsion of a thin‐walled cylinder is studied using the low‐temperature or visco‐plastic limit of Hart’s state variable theory for the inelastic behavior of metals. For values of the shear stress lower than the ’’hardness’’ of the material, reversible elongation is found to accompany the recoverable twist. For shear stress exceeding the hardness there are, in addition, a permanent twist and elongation. These predictions agree qualitatively with existing experiments. Detailed quantitative results, for several loading histories, are obtained for nickel.

ISSN:0021-8979    

DOI:10.1063/1.327674

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An electrostatic potential well was produced by injecting positive zinc ions into a hollow cathode. The apparatus consisted of two concentric spherical electrodes with the inner wire‐mesh electrode being 91% transparent. Ion current pulses as high as 40 mA were injected by a vacuum‐arc source located between the spheres. The outer sphere was biased at 4 kV and the inner sphere from 0 to −1.5 kV so that the ions would circulate between the spheres and be drawn toward the inner sphere. Current pulses lasted up to 20 &mgr;s and during the current pulses, potential wells of up to 200 V were formed by the accumulation of ions within the inner electrode. The well profile was computed from the deflection of a 2‐nA swept electron beam. The deflection was measured with a many‐slotted circumferential detector which intercepted the beam after it traversed the space‐charge region. Each profile was calculated from data recorded during a single 2‐&mgr;s sweep of the probing beam.

ISSN:0021-8979    

DOI:10.1063/1.327675

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A thermionic cathode reflex discharge and the plasma it produces are studied. It is found that extremely quiescent plasmas can be produced when the electron‐loss rate due to classical diffusion is equal to the ion‐loss rate. Particle and power balances for the quiescent plasma are obtained, and the average electron energy loss per ion produced is determined.

ISSN:0021-8979    

DOI:10.1063/1.327676

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This paper presents an investigation of cross focusing of two Gaussian EM beams (of frequencies &ohgr;1and &ohgr;2) propagating in the extraordinary mode in a collisionless magnetoplasma and the excitation of an upper hybrid beam at the difference frequency &Dgr;&ohgr;=&ohgr;1–&ohgr;2. The effect of changing the strength of the static magnetic field on cross‐focusing of the two pump waves is significant; the power of the upper hybrid beam also depends on the magnetic field.

ISSN:0021-8979    

DOI:10.1063/1.327677

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A large number of GaAs substrates GaAlAs double‐heterostructure (DH) wafers, and high‐radiance GaAlAs DH light‐emitting diodes (LEDS) were evaluated using transmission cathodoluminescence (TCL). We show that only epitaxial wafers with a high defect density as revealed by TCL readily develop dark line defects (DLDs) with current injection, optical excitation, or electron beam excitation. Furthermore, in agreement with the previous work, the electron‐beam‐induced DLDs originate at dislocations and their growth requires minority‐carrier injection. Based on these results, it is inferred that TCL can serve as a nondestructive screening technique for the selection of materials that produces a high yield of reliable LEDs.

ISSN:0021-8979    

DOI:10.1063/1.327678

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Lindhard’s dielectric theory of energy loss is applied to the stopping of energetic ions in solids. The Lindhard formalism, in combination with the local density approximation and the concept of effective charge, is used to calculate the stopping powers of heavy ions in many targets and over a wide range of projectile energies. Theoretically calculated stopping powers are compared with available experimental data.

ISSN:0021-8979    

DOI:10.1063/1.327679

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A theoretical model is presented which accounts for the electroepitaxial growth kinetics and composition of multicomponent compounds in terms of mass transport in the liquid and phase diagram relationships. The mass transport in the interface is dominated by electromigration in the absence of convection and by diffusion in the presence of convection. The composition of the solid is controlled by the Peltier effect at the growth interface and by the diffusion and mobility constants of the solute components and the growth velocity (current density). Thus, for a given solution composition, the composition of the solid can be varied by varying the current density. For a given current density the composition remains constant even in the case of relatively thick epitaxial layers. All aspects of the model were found to be in good agreement with the growth and composition characteristics of Gax−1AlxAs layers.

ISSN:0021-8979    

DOI:10.1063/1.327680

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A clean surface of LaB6(210) exhibits the low work function of 2.2±0.1 eV at room temperature. This is lower than those of the (100), (110), and (111) surfaces. Similarly to the (100) surface, La atoms exist in a (1×1) ordered structure at the outermost layer of the (210) clean surface. The value of the low work function of LaB6has been discussed on the basis of those data together with the Lang‐Kohn theory. The changes of the (210) surface with oxygen chemisorption are more analogous to those of the (110) surface than the (100) and (111) surface. Work function changes from 2.2 to 3.1 eV with oxygen exposure and saturates above ∼15 L; the periodicity of the surface‐atomic lattice disappears almost completely.

ISSN:0021-8979    

DOI:10.1063/1.327681

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We demonstrate that Ti implanted into &agr;‐Fe (with ∼60 appm C impurity) getters C (along with a lesser amount of N) upon postimplantation annealing and precipitates as TiC. The microstructure of the TiC precipitates is examined with TEM for annealing temperatures up to 860 °C. The precipitate size evolution is discussed in terms of growth, ripening, and dissolution processes. The precipitate size increases with anneal temperature for 1 h anneals. At 700 °C no change in precipitate size is observed for anneal times up to 16 h. At 800 °C, an increase in size is observed for increasing anneal times between 1–64 h, while at 860 °C this increase is thought to occur prior to 1 h and the precipitates are observed to decrease with increasing anneal times between 1 and 4 h. At 800–860 °C, the precipitates have a disk‐like shape, and their orientation in the &agr;‐Fe matrix can be used to identify two types of interfacial area with different degrees of coherency. The implications of the observed microstructure for studies of trapping of embrittling impurities in &agr;‐Fe and for modifying the surface mechanical properties are discussed.

ISSN:0021-8979    

DOI:10.1063/1.327727

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The Snoek peak figures and peak heights on impure iron were investigated in various ranges of strain amplitude. The Snoek peak heights &Dgr;−&Dgr;bdecreases as strain amplitude increases, and the amount of decrease is related to the amount of plastic strain damping. There is failure of superposition at high amplitude and at Snoek peak site, probably due to microstrain.

ISSN:0021-8979    

DOI:10.1063/1.327728

出版商:AIP    

年代:1980

数据来源: AIP