摘要:

The wear resistance of single crystals of sapphire was determined as a function of crystallographic orientation with respect to plane of wear and rubbing direction. Distinct anisotropy was found. Evidence of plastic flow at the wear surface on both basal and prismatic slip systems was obtained. In bulk deformation tests, these systems do not become operative until a temperature of 1000°C is reached for basal slip, 1800°C for prismatic slip. The resistance against wear correlates in a qualitative way with the relative ease of operation of the two slip systems involved. When the orientation is such that both basal and prismatic slip are blocked, a brittle type of wear occurs that is characterized by conchoidal fracture. All results confirm that plastic flow during rubbing is a governing factor in, if not an integral part of, the wear process for even such a hard material as sapphire.

ISSN:0021-8979    

DOI:10.1063/1.1728269

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Magnetization reversal at an angle to the easy direction has been studied on Permalloy films with different values of coercive forceHcand anisotropy fieldHK. The hysteresis properties show that ``inverted'' films (Hc>HK) do not represent a special case, but that every film exhibits inversion in a certain sector of field direction. In the inversion sector, two critical field values are observed. The corresponding Bitter patterns make it evident that the lower critical field is due to a partial rotation process which is accompanied by a splitting of the film into many fine domains, whilst the higher one is due to wall motion. The observed processes can be understood qualitatively if the dispersion of the local values of the anisotropy field and anisotropy direction, as well as the internal exchange and stray field coupling are taken into account.

ISSN:0021-8979    

DOI:10.1063/1.1728270

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The specific heat of an assembly of independent superparamagnetic particles has been calculated with the methods of statistical mechanics. The cases of isotropic particles in an applied field and anisotropic particles in the absence of a field have been considered. The specific heat calculated is temperature dependent and is of the order ofkper particle at low temperatures. A smaller contribution varying linearly with temperature can also appear, thereby affecting the linear temperature coefficient of specific heat usually associated with the electronic specific heat. Conditions are discussed under which these effects should be experimentally observable.

ISSN:0021-8979    

DOI:10.1063/1.1728271

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Under electron bombardment at 40°C, two fluorescence bands in the near infrared are observed in many CdS crystals. The bands are at about 8500 A and 1.05&mgr;. The 8500‐A band is reduced in intensity by electron bombardment at 100 and 275 Kev and by exposure to x radiation. The 1.05−&mgr;band is not greatly affected by these irradiations. Heat treatment for ½ hr at 200°C partially restores the 8500‐A band. The effect is interpreted as a redistribution of electrons over the existing defects. The defect responsible for the 8500‐A band is believed to be copper in a particular ionization state. The 1.05−&mgr;band is observed to appear after heat treatment at 200°C if it is not present originally. This fact makes the origin of this latter band uncertain.

ISSN:0021-8979    

DOI:10.1063/1.1728272

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A detailed experimental investigation of the influence of the specimen geometry on the transverse magnetoresistance has been made. Differentiation between the bulk properties and the geometrical contributions has been accomplished. It was found that the enhancement of the magnetoresistance effect in rectangular elements is due to the Hall effect rather than to its absence and that the bulk property has anH2relationship while the geometry effect is linear withHand inversely proportional to the length‐to‐width ratio.

ISSN:0021-8979    

DOI:10.1063/1.1728273

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The usefulness of a new representation of the relaxation spectrum for elasticoviscous liquids is discussed, and an idealized form of this spectrum is used to interpret experimental results concerning polymer solutions.

ISSN:0021-8979    

DOI:10.1063/1.1728274

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The calculations of Chasmar and Stratton [R. P. Chasmar and R. Stratton, J. Electronic and Control7, 52 (1959)] for the determination of the maximum thermoelectric figure of merit are extended for the case of acoustical scattering. Graphical data are presented for the determination of the material parameter, the optimum values of several quantities, and the degradation of the figure of merit for nonoptimum conditions. The variations of the Seebeck coefficient and the electrical conductivity computed from exact statistics are compared with experimental results for several alloys of thermoelectric interest. Good agreement is found except for high electrical conductivities. Other anomalies are noted.

ISSN:0021-8979    

DOI:10.1063/1.1728275

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

By use of experimental data from a large number of free flight impact tests involving diffraction grating measurement of strain, a detailed and very close experimental verification is given for the G. I. Taylor theory of dislocations in polycrystalline annealed aluminum. Applying the finite amplitude wave theory, with a theoretical parabolic stress‐strain curve obtained from dislocation theory, experimental and theoretical correlations within approximately 1% are obtained for the velocities of strain propagation, maximum strain, largest distance of penetration of maximum strain, dynamic stress levels in the first diameter, time of contact, coefficient of restitution, mushrooming in the first diameter, and an energy balance before and after impact. Variations in the plastic wave development and dynamic stress behavior below the Karman critical velocity are considered theoretically and experimentally in terms of a difference in the initial elastic reflection behavior below the critical velocity. Plastic deformation is found to be independent of strain rate, even at experimentally determined values of 2000 in./in./sec. Initial shock fronts exceeding the dilatational velocity are experimentally identified near the impact face. The subsequent development of dispersive plastic wave fronts following the passage of the initial shock, also are found to be in accordance with predictions based upon dislocation theory. The equipartition of energy in the vicinity of the impact face has been found to be related to the reflection behavior of these initial shock fronts at the lateral surface of the rod.

ISSN:0021-8979    

DOI:10.1063/1.1728276

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The theoretical power output of a ruby laser is examined under certain idealized operating conditions, and it is found that there are two principal regions of operation. These are the regions of strong oscillation characterized by the conditionp&tgr;2/A»h&ngr;13/&sgr;13and the region of saturation in whichp&tgr;3/A»h&ngr;13/&sgr;13. Herep/Ais the ``pumping'' illumination within the absorption band of ruby, &tgr;2is a charactersitic relaxation time of fluorescence in ruby, &tgr;3is a characteristic thermal relaxation time from the excitedUband, &ngr;13is the pumping frequency, and &sgr;13is the cross section for interaction between pumping radiation and Cr3+ions in ruby. Efficiency of operation is examined under two limiting conditions.

ISSN:0021-8979    

DOI:10.1063/1.1728277

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Birefringence techniques which emphasize the difference in stress on each side of a slip plane having edge dislocations of one sign are described. The principal stresses due to edge dislocations in a glide band are found to be parallel and perpendicular to the Burgers vector. The opposite stressed regions on both sides of a slip plane produce opposite retardations in the phase of light passing through the slip plane. When this light is retarded in phase by an amount equal to the advancement from the compressive region (or advanced by an amount equal to the retardation from the tensive region), a birefringence band forms which is, for instance, dark on the compressive side, light on the tensive side in a background having an intensity halfway between these two shades. These asymmetrically shaded birefringence bands are observed when viewed both normal and parallel to the Burgers vector and this is shown to be a direct consequence of the edge dislocations in the slip planes and to be independent of screws. The asymmetry of the band permits a determination of the sign of the dislocations in the slip plane and the apparent position of its source. The magnitude of the principal stress parallel to the Burgers vector was computed from the measured retardations and found to be in good agreement with that computed from the dislocation stress fields.

ISSN:0021-8979    

DOI:10.1063/1.1728278

出版商:AIP    

年代:1961

数据来源: AIP