摘要:

An earlier theory for the rate law&psgr;(t)=&bgr; ln(1+t/&tgr;)for strain, orq(t)=b−1 ln(1+t/&tgr;)for chemisorption, is extended to cover a law for creep in materials which has been of interest recently, and takes the form&psgr;(t)=(&bgr;/&ngr;)[(1+t/&tgr;)&ngr;−1]. The theory is formal in that it utilises only general concepts such as probability of success and attempt frequency.

ISSN:0021-8979    

DOI:10.1063/1.1728939

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

It is proposed that differences between the thermal expansion of the macroscopic and crystal lattice volumes of crystalline polymers might be attributed to thermal generation of new substitutional sites. Consideration of the molecular arrangements suggests that vacancies can be generated within the lamellae at molecular folds and ends and at any point along some helical molecules. Part of the displaced molecule can be transported by point defects to the crystal surface where new sites are formed. Analysis of the available data for polyethylene shows the concentration of new sites (&Dgr;n/n) to be 2.2×10−2at 100°C with an energy of creation of 0.2 eV and an entropy of creation of 5.3×10−4eV/°K per site. It is pointed out that the phenomenon could account for the so‐called glass transitions and is, therefore, closely related to the ``amorphous'' relaxations observed in crystalline polymers. The need for additional experiments is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1728940

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The classical scattering for repulsive potentials is treated approximately by a matching method. The matching potential is a cut‐off potential which matches the value and the slope of the actual potential at the distance of closest approach. The method is thought to be successfully applicable to interatomic potentials of the screened Coulomb type. Comparison is made with machine results for an exponentially screened Coulomb potential. The differential cross section and the stopping power are compared for various energies. The agreement in the differential cross section is fair except for very low energy transfers. The stopping powers agree over a wide energy range with an error of only a few percent. Further comparison is made with another approximation given by Lehman and Shapiro.

ISSN:0021-8979    

DOI:10.1063/1.1728941

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An experiment is described that enables the statistical stability of the Preisach diagram for interacting ferromagnetic particles to be tested. The samples used were of &ggr;—Fe2O3dispersed in a nonferromagnetic matrix to a nominal packing density of 20% by volume. Both oriented and nonoriented samples were examined. In every case the diagram was found to be stable over most of the area bounded by the major remanence loop. The region of departure from stability occurred at the higher levels of remanent intensity. A method of calculating the diagrams using only dc measurements is given. They are then used to predict accurately the ascending remanence curve after ac demagnetization for each sample. Finally, it is shown how the experimental ascending and descending remanence curves, which could not be explained by Wohlfarth's relations [J. Appl. Phys.29, 595 (1958)] based on noninteracting particles, can be completely described in terms of the Preisach diagram.

ISSN:0021-8979    

DOI:10.1063/1.1728942

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A new theoretical approach to the problem of describing the nonlinear behavior of non‐Newtonian materials is presented. The theory is based upon the assumption that the nonlinear characteristics can be associated with some structural change of the material, and that reaction kinetics can be applied to this breakdown. The theory allows treatment of time‐dependent (thixotropic) materials, and in a limiting form (equilibrium) can be applied to time‐independent materials. The theory has been applied to a variety of materials, including polymer latex solutions, polyethylene polymer melts, and a heavy thixotropic mineral oil. The results are gratifying.

ISSN:0021-8979    

DOI:10.1063/1.1728943

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Time‐resolved free‐space microwave measurements are used to study the loss mechanisms in the afterglow of an intense He discharge between 100 and 1000 &mgr;. The method of evaluation is developed in detail and the results of the measurements and their accuracy are given. Some of the problems and limitations of the microwave method are discussed; in particular, plots of the field pattern between the horns are presented indicating that a reasonable interpretation in terms of an integrated path length is possible.

ISSN:0021-8979    

DOI:10.1063/1.1728944

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The five independent elastic constants of hexagonal CaMg2have been determined by the ultrasonic pulse‐echo technique over the temperature range, 100–300°K. In keeping with normal metallic behavior, the measured elastic constants do not fit the Cauchy relations. The degree of elastic isotropy is high, particularly so with respect to compressive or tensile strains. The compressibility of the compound is slightly less than the average of the compressibilities of the constituent elements. This compressibility behavior is reasonable on the basis of the small negative heat and volume of formation of the compound.

ISSN:0021-8979    

DOI:10.1063/1.1728945

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A dislocation interaction in fcc crystals is considered which yields a barrier dislocation extended in the glide direction. The barrier consists of a high‐energy stacking fault bounded by two partial dislocations. The barrier stability is discussed in relation to both work hardening and quench hardening.

ISSN:0021-8979    

DOI:10.1063/1.1728946

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

It is shown that there is an error in Schroeder's calculation of the electronic thermal conductivity due to circulating currents in a two‐phase material. With reasonable values for the properties of the two phases, quantitative agreement between the predictions of the model and the experimental data of Cosgrove, McHugh, and Tiller is obtained for both the electronic thermal conductivity and the Seebeck coefficient.

ISSN:0021-8979    

DOI:10.1063/1.1728947

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

This paper presents a simple physical and mathematical model and experimental support of the manner in which magnetic flux penetrates into a high‐field superconductor. Based on this model a new device using high‐field superconductors in their bulk form called a superconducting magnetic flux compressor is proposed. Present theory suggests that magnetic field strengths approaching the critical field strength of a high‐field superconductor (> 100 kOe) should be attainable using the apparatus and techniques described. It was found experimentally with the particular high‐field superconductors tested that compressed field strengths of 15 kOe could be achieved. Beyond this value anomalous magnetic flux jumping occurred that limited the field strengths obtainable. The characteristic conditions under which magnetic flux jumping is found are discussed. The experimental results also suggest that heat is generated when a high‐field superconductor is exposed to an alternating magnetic field well below the critical field strength.

ISSN:0021-8979    

DOI:10.1063/1.1728948

出版商:AIP    

年代:1962

数据来源: AIP