摘要:

The dipolar interactions in a two sublattice ferrimagnet are shown to give rise to magnetostatic modes associated with the exchange resonance frequency. The shift in these modes due to retardation effects is calculated. The exchange resonance frequency is shown to depend on the size of the sample when dipolar and retardation effects are included.

ISSN:0021-8979    

DOI:10.1063/1.1659167

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The theory of the motion of a cleavage crack created by wedging open the ends of a double cantilevered crystal at a constant rate has been investigated. The results are presented for use in analysis of experimental studies of fracture dynamics in lithium fluoride reported in Part II of this series. A solution of the quasistatic equations of motion of the crack including kinetic energy effects has been found from which the dynamic fracture surface energies may be deduced for a propagating crack of this geometry by observations of either the time dependence of the crack length or the profile of the fracture opening near its tip. The detailed configurations of dislocations accompanying the tip of a moving crack in alkali halides have been calculated using dislocation dynamics and continuum elasticity theory. The plastic deformation contribution to the effective fracture surface energy has been determined and some of its consequences worked out.

ISSN:0021-8979    

DOI:10.1063/1.1659168

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The dynamics of cleavage of long slender single crystals of LiF has been observed with high‐speed cine´‐photography in order to measure the surface energy and the dislocation processes in a propagating semiplastic crack. The fracture surface energy deduced from these observations could be separated into two parts, a reversible thermodynamic surface energy and a contribution due to dissipative plastic deformation, using the theoretical analysis given in Part I of this series. A specific reversible surface energy of 480±50 erg/cm2was obtained and the plastic contribution was found to persist to fracture velocities > 104cm/sec. Dislocation mechanisms of dissipation persisting to very high crack velocities and to temperatures as low as 90°K were deduced from studies of etch‐pit patterns and atomic step structures on the cleaved surfaces. The atomic step structures were observed by imaging in the electron microscope replicas of eptiaxial metal deposits grown from the vapor at the step sites. The plastic flow processes were found to be consistent with the theory of Part I and the observed magnitude of the plastic contribution to the surface energy.

ISSN:0021-8979    

DOI:10.1063/1.1659169

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The equation of motion for cracks which are subjected to stress pulses is derived by the Lagrangian method. An asymptotic solution is used to determine terminal crack velocity. The time in which essentially constant velocity will be reached is determined. The equation is further used to formulate a dynamic stability criterion. In addition to a critical stress a critical time of stress duration is of importance. Critical time and critical stress can be combined to a critical action. From this principle, a number of conclusions are derived which are used to explain a number of experimental facts for which a theoretical explanation was lacking hitherto.

ISSN:0021-8979    

DOI:10.1063/1.1659170

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Porous metal wafers and thin films were produced by selectively etching the rod phase of the directionally solidified eutectics NiAl&sngbnd;Cr and NiAl&sngbnd;Mo and by a two‐state replication process, respectively. The 0.5‐&mgr;‐diam holes were uniform in size and distribution with densities as high as 8.5×107holes/cm2. The flow properties of these porous membranes were tested using three liquids of different viscosity and were found to be in agreement with Poisseuille's law.

ISSN:0021-8979    

DOI:10.1063/1.1659171

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

This paper describes some materials problems involved in the preparation of lithium‐drifted germanium gamma‐ray detectors. A preliminary study shows some decided differences between the characteristics of the original starting material and the characteristics of the material after various fabrication procedures.

ISSN:0021-8979    

DOI:10.1063/1.1659172

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The xeroradiographic properties of selenium have been investigated using a typical medical x‐ray spectrum. The influence of applied field was found to be very important in determining the surface potential discharge rate for both positively and negatively charged selenium. The x‐ray energy absorbed per surface charge neutralized varied from 39 to 2.2 eV as the applied field increased from 104to 2.4×105V/cm. No effect of thickness on the discharge properties of evaporated selenium layers up to 530‐&mgr;m thick was observed.

ISSN:0021-8979    

DOI:10.1063/1.1659173

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A transition from an initial emission‐limited current to a steady‐state space‐charge‐limited current has been observed in evaporated films of amorphous selenium. A simple model of this transition has been developed which can be used to illustrate the trapping dynamics and estimate the free carrier range.

ISSN:0021-8979    

DOI:10.1063/1.1659174

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A floating double probe operating at radio frequencies in the MHz range has been developed to the point where measurements of sheath capacitance and resistance yield values for plasma ionization density and electron temperature with an accuracy of ≈8% and ≈16%, respectively. The experimental technique used supersedes previous methods in that it enables sheath capacities as low as 10−2pF to be measured. The analysis of the results has been extended to cover the important nonplanar (cylindrical) sheath case. As a result of these two developments, the technique is now applicable to small diameter probes which are essential for measurements in most gas discharge plasmas. The performance of the probes has been checked over a range of plasma densities and working frequencies and has been found to give results which are in good agreement with microwave cavity and dc probe measurements. This type of measurement has various advantages over the usual dc probe methods in terms of complete isolation, but it is expected that its main application will be in situations where the use of the dc probe is suspect due to probe surface contamination effects.

ISSN:0021-8979    

DOI:10.1063/1.1659175

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The coupling of an incident microwave signal in a Tonks‐Dattner resonance to discrete low‐frequency modes in a plasma column is presented both theoretically and experimentally. The necessary conditions that the incident power and frequency had to meet in order to excite these modes are also explained and experimentally tested.

ISSN:0021-8979    

DOI:10.1063/1.1659176

出版商:AIP    

年代:1970

数据来源: AIP