摘要:

The distribution of electrical potential in a conduit carrying an axially symmetrical flow through an homogeneous magnetic field, which is perpendicular to the flow, is analyzed. It is shown that it is possible to eliminate the difficulties arising from induced currents in electromagnetic determinations of the velocity distribution by measuring the potential gradient ∂&psgr;/∂y(ybeing ⊥Hand ⊥v) along a diameter bisecting the angle between theHaxis and theYaxis. The knowledge of the distribution of (∂&psgr;/∂y)45°at a known discharge through the conduit determines the velocity distributionv=f(r).

ISSN:0021-8979    

DOI:10.1063/1.1721654

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

By means of the vector calculus, it is proved that the magnitude, orientation, and location of the resultant dipole of a system of sources and sinks inside a finite volume conductor is given by an integration over the bounding surface. The method is applied to finding the ``heart vector,'' or the resultant dipole moment of the human heart. The theory was checked in two‐ and three‐dimensional electrolytic tank models of the human thorax.

ISSN:0021-8979    

DOI:10.1063/1.1721655

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Breakdown field strengths have been measured in air and hydrogen at pressures of the order of 1 micron Hg and frequencies from 25 to 90 Mc/sec between flat metal electrodes at separations from 1 to 4 cm. By suddenly applying a high voltage and then lowering it slowly an upper breakdown curve has been observed. This new curve can be combined with the lower breakdown curve and cut‐off frequency such as reported previously by the Guttons, and by Gill and von Engel to form the boundaries of a breakdown region in the frequency‐field strength domain.The simple secondary electron resonance theories developed by Danielsson and Gill and von Engel have been extended by the semi‐empirical determination of minimum and maximum limiting values of the electron‐emission phase angle, a minimum limiting value of electron arrival energy, and a ratio between electron arrival and emission velocities.

ISSN:0021-8979    

DOI:10.1063/1.1721656

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Switching or triggering in certain nonlinear circuits having two stable states is studied in graphic detail. The minimum and maximum pulse requirements are discussed and some of the general ideas of bistability considered. A convenient technique for studying the response of circuits, apparently in slow motion, is described.

ISSN:0021-8979    

DOI:10.1063/1.1721657

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The qualitative explanation by Loeb of the constancy of the amplification factor with increasing corona currents with coaxial cylindrical electrodes used, as in conventional Geiger counters, is placed on a quantitative basis. As anticipated, it is shown that it is the screening action of the space charge which is responsible for the constancy and the stability of the average discharge current. The fluctuations superposed on the constant current, previously reported by us, are explained as a response of the system having a definite resonance frequency to the statistical fluctuations of the photoelectric current. The theoretical predictions are confirmed by experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1721658

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The problem of focusing long electron beams by means of magnetic or electric fields which vary periodically along the beam is considered. Four specific cases are discussed: periodic fields of the axially symmetric and quadrupole type with either electric or magnetic fields employed. The equations of motion are written and solutions obtained which show beam trajectories corresponding to essentially parallel flow. Under certain specified conditions only small ripples are present. Actual trajectories as plotted by the analog computer are shown and charts and equations are presented to aid in the design of practical periodic focusing systems.

ISSN:0021-8979    

DOI:10.1063/1.1721659

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A method is described for constructing germanium high‐voltage diodes, utilizing 15‐mil germanium spheres instead of the usual flat wafer. The spheres are produced within a few minutes in quantities of several hundred thousand or more by blowing molten high‐purity germanium from a graphite crucible. The spherical pellets can be annealed, ground, etched, and assembled into diodes by techniques easily adaptable to automatic mass production. The assembled diode uses a sphere‐plane contact rather than the conventional whisker contact. Peak back‐voltages in the range 50–100 volts are easily obtainable. Series‐assembled units for higher voltages are easily made.

ISSN:0021-8979    

DOI:10.1063/1.1721660

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Part I is a description of some of the factors involved in the recovery by pure zinc single crystals at 35°C of the ability to creep following plastic deformation. The following observations were made: (1) Complete recovery of the ability to show an initial instantaneous plastic extension occurs much less readily than recovery of the ability to show transient creep. (2) Once the quasi‐viscous creep stage is reached no recovery of transient creep occurs when the load is partially or completely removed for two minutes, but removal of only 6 percent of the load for 100 minutes permits partial recovery of transient creep at the full load. A 300 minute ``rest'' at 91.5 percent of the full load resulted in complete recovery of the transient creep at full load, even though creep occurred at the reduced stress. (3) The recovery of quasi‐viscous creep at a reduced stress after exposure to a higher stress was also investigated. The recovery was slower, the larger the initial load. (4) The rate of the time‐dependent contraction of zinc crystals on removal of the load probably follows a power law in the time. There is also an instantaneous nonelastic contraction which is about ten times larger than the elastic contraction.These results show that the role of thermal fluctuations in activating the units of flow is very different from the role of the stress. The applications of the Eyring rate equation to quasi‐viscous creep which have been made in the past are, therefore, not valid. A variable activation energy must be postulated in order to account for the kinetics of creep and recovery. These results are interpreted in terms of the dislocation theory of plastic flow.In Part II a phenomenon is described in which pure zinc single crystals are consistently found to become temporarily hardened by annealing in vacuum above 200–260°C. The hardness thus introduced can be removed by straining the crystal and then allowing it to stand at temperatures below 200°C. The crystal is in this way returned to its normal plastic state. The hardening is not removed by electropolishing the crystal, so is not a surface phenomenon. Though similar to Orowan's thermal hardening effect, it differs by requiring a much higher temperature and by not requiring the addition of impurities.

ISSN:0021-8979    

DOI:10.1063/1.1721661

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Germanium metal, both single crystalline and polycrystalline, is frequently found to contain sharp fluctuations in impurity concentration. These are superimposed on the gradual variations expected as the result of ordinary segregation processes.A rather simple technique for detecting fluctuations of this kind has been developed. It is more sensitive than resistivity scanning and does not involve the use of radioactive tracers. This technique has been applied to a number of samples. The origin, value, and elimination of these fluctuations are discussed briefly.

ISSN:0021-8979    

DOI:10.1063/1.1721662

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The resistance experienced by a curved and elongated small particle is studied by the method of velocity perturbations. The fundamental equations determining the perturbations are derived from the equations of Oseen. The particle is curved in such a way that the axis of the particle is formed by an arc of circle. The opening angle may vary to exhibit various shapes from a straight ellipsoid to a closed ring. Results illustrate the circumstances under which manifests the cooperation between the different parts of the particle. Apart from this pure hydrodynamical interest, the problem has applications to long chain molecules in solution and to suspensions of swimming organisms. It demonstrates the effect of skew shape by taking for the chain molecule a model in the form of a variable‐curved ellipsoid instead of a sphere or a cluster of spherical symmetry, as the coordination of the chain links, even in the case of free rotation, leads initially to configurations of variable skewness generally obscured under the averaging processes by current theories.

ISSN:0021-8979    

DOI:10.1063/1.1721663

出版商:AIP    

年代:1954

数据来源: AIP