摘要:

The different apparatus used by some thirty investigators, who have induced double refraction in a liquid contained in the annular gap between two concentric cylinders, are examined with particular reference to the onset of turbulence. In the case where the outer cylinder alone rotates, curves are given which easily enable the critical gradients corresponding to the dimensions of the apparatus used to be found. The results of the examination are so tabulated that present and future workers in this field can quickly decide on the significance of the measurements obtained by any of the investigators. An explanation is put forward of the surprising fact that with either the inner or outer cylinder rotating measurements of double refraction apparently show no very sharp break between regions of laminar and turbulent flow. The value of making simultaneous measurements of streaming double refraction and viscosity is pointed out and the advantages of using an apparatus with rotating outer and stationary inner cylinder are briefly summarized. Mention is made of optical design.

ISSN:0021-8979    

DOI:10.1063/1.1699433

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The correlation of experimental data and the proper description of the state and history of deformation of work‐hardening materials has received much attention. An often desired objective is the plotting of a variable involving stress alone, a so‐calledeffective stress, against a variable depending on the instantaneous strain or the history of strain,effective strain. Quantities such as maximum or octahedral shearing stress and strain or better an integrated effective strain increment have been employed. Also, simple effective stress definitions have been given for anisotropic as well as isotropic metals by Dorn, by Jackson, Smith, Lankford, and by previous investigators.It is shown that the stress‐strain relations of a recent theory of plasticity provide a very convenient means of defining and studying effective stress and effective strain. The strong theoretical and practical limitations of such concepts are indicated and the calculation of specific plastic work is discussed for both isotropic and anisotropic metals.One of the major objectives of the paper is to stimulate critical experimental examination of as yet unproved assumptions in the theory of plasticity and in the correlation of experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1699434

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The known facts about nucleation phenomena in liquid metals are interpreted satisfactorily on the basis of the critical size and interfacial energy concepts. In large continuous masses nucleation is almost always catalyzed by extraneous interfaces. However, in very small droplets the probability that a catalytic inclusion is present is so much less that their minimum nucleation frequencies are reproducible and form a consistent set of values.Interfacial energies, &sgr;, between crystal nuclei and the corresponding liquids have been calculated from nucleation frequencies of small droplets on the basis of the theory of homogeneous nucleation. Energies of interfaces, &sgr;g, one atom thick and containingNatoms were calculated from the &sgr;'s. The ratio of &sgr;gto the gram atomic heat of fusion, &Dgr;Hf, was approximately 0.45 for most metals but ∼0.32 for H2O, Bi, Sb, and Ge.The effect of relative complexity of crystal structure upon the supercooling behavior of pure metals apparently is a reflection of its effect upon &Dgr;Hf.

ISSN:0021-8979    

DOI:10.1063/1.1699435

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A hot‐cathode arc in cesium vapor has been studied by the use of a plane Langmuir probe to investigate the potential distribution, electron temperature and electron density in the plasma. The range of arc currents and vapor pressures over which satisfactory probe measurements may be made are determined.In some cases it was possible to maintain the discharge with a total arc drop of less than the ionization potential of cesium (3.87 volts). Potential ``humps'' along the arc are shown to be absent, and ionization by the high energy electrons of a Maxwellian electron velocity distribution is found unsatisfactory as a possible mechanism for positive ion production in the arc. The mechanism of successive electron collisions can account for the observed ionization on the assumption that the effective lifetime in the excited state is increased by the process of the imprisonment of resonance radiation.

ISSN:0021-8979    

DOI:10.1063/1.1699436

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The allotropy of beryllium has been confirmed by employing different alloying properties of allotropic forms of metallic elements. Alloys of beryllium and gold, studied by x‐ray diffraction methods, showed that the limit of solubility of gold in beryllium is between two and three atomic percent, and practically all of it is dissolved in the &bgr;‐form. The lattice parameters of the two forms observed here are:a0=2.286A,C0=3.588A, andC0/a0=1.570 for the &agr;‐form, anda0=6.93A,C0=11.35A, andC0/a0=1.638 for the &bgr;‐form. The volume of the unit cell of the &bgr;‐form is about 29 times that of the &agr;‐form.

ISSN:0021-8979    

DOI:10.1063/1.1699437

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

WL&agr;radiation filtered through a Cu&sngbnd;Zn foil is essentially monochromatic and has the advantage over filtered CuK&agr;or MoK&agr;radiation in that theWL&agr;1line is approximately ten times as intense as theWL&agr;2line. Moreover the comparatively wide &Dgr;&lgr;‐spread (WL&agr;2−WL&agr;1) results in very sharp powder lines at those Bragg angles where the CuK&agr;doublet or MoK&agr;doublet is unresolved.

ISSN:0021-8979    

DOI:10.1063/1.1699438

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The shielding properties of the four‐foot concrete wall of the M.I.T. cyclotron have been studied, using foils for neutrons and x‐ray films for gammas. Fast neutrons were measured by counting the beta‐active products of Al27(n, p)Mg27, Fe56(n, p)Mn56, and Al27(n, &agr;)Na24reactions, thermal activation being eliminated by Cd holders. Resonance (1.44 ev) and thermal neutron distributions, measured by Cd‐In‐Cd and In, with suitable corrections, were reduced to absolute intensities by comparison with a known flux. Measurements were made with cylindrical concrete blocks fitted into a 4½″ diameter hole which extended through the concrete wall. The results indicate an attenuation factor of 8.3 per foot for the fast neutron component and 10 per foot for thermal neutrons. An estimate of the fast neutron flux above 4.5 Mev showed a transmitted intensity slightly higher than the presently accepted tolerance value when bombarding Be. The absolute thermal neutron flux was below the tolerance level. The r.m.s. distance and the diffusion length for thermal and resonance neutrons in concrete were estimated by considering the distributed source to be equivalent to a point source at the inner face of the wall. The gamma‐ray measurements were not convertible to roentgens. A mean energy of 2.7 Mev was obtained for the gamma‐radiation within the wall. The attenuation factor for total gamma‐radiation in the wall at large distances from the inner face was 5.9 per foot.

ISSN:0021-8979    

DOI:10.1063/1.1699439

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A mathematical analysis is presented which is believed to be applicable to a general class of storage tubes where signal storage is accomplished by depositing through secondary emission a charge pattern on a dielectric surface. The assumptions made to linearize and simplify the problem are outlined and plots are given of the predicted output signals for writing, reading, and cancellation operations when the input signal is a step function. Experimental evidence is presented to substantiate the analytical results.

ISSN:0021-8979    

DOI:10.1063/1.1699440

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A graphical method is derived for the analysis of microwave electron tubes, ion accelerators etc., which refers particle positions and velocities to a moving reference system. If the forces are dependent on time only, the trajectories are transformed into straight lines. For inhomogeneous fields an approximation procedure applies. To demonstrate the capabilities of this method a brief treatment of the transit time phenomena in cavity triodes is outlined.

ISSN:0021-8979    

DOI:10.1063/1.1699441

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An experimental study was made of the orienting effects of silver on sodium chloride crystallized from solution. Pronounced epitaxy was observed in the following cases: (1) On oriented films of silver with (100) and also with (111) planes parallel to the surface; and (2) on polycrystalline high purity silver sheet.

ISSN:0021-8979    

DOI:10.1063/1.1699442

出版商:AIP    

年代:1950

数据来源: AIP