摘要:

The study of wet biological tissuesin situusing the electron microscope was made possible by modifying existing replica techniques and developing a new wet replication method. The shortcomings of existing replica techniques are discussed and the modifications necessitated are described.Replicas of wet tissues were produced in extremely thin polystyrene films which could be observed directly in the electron microscope; however, superior results were obtained by preparing silica replicas from the replicated polystyrene films. A modified two‐replica silica method proved satisfactory but the three‐replica silica method developed was preferable. Electron micrographs of wet wood fiber surfaces used to illustrate these techniques reveal new data concerning submicroscopic cell wall structure.The problem of interpreting replicas of partially degraded and disorganized materials is illustrated and discussed briefly.

ISSN:0021-8979    

DOI:10.1063/1.1699576

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

In recent years reports have appeared from various ionospheric observatories concerning the appearance of a third magneto‐ionic component or a so‐calledztrace. The phenomenon has also been called magneto‐ionic triple splitting. After having recorded a number of such triple splits at the new Kiruna observatory, we became very interested in the problem as a whole. The entire matter was examined theoretically and as a result it has been possible to show that strong coupling often exists between the ordinary andzcomponents as a critical level. It has further been possible to show that thezwave becomes strongly excited when the collisional frequencyvapproaches the critical collisional frequencyvcof Appleton and Builder. Whenvis larger thanvctheoecho rapidly disappears and only thezandxcomponents remain (ifvcis sufficiently small,i.e.at very high latitudes). A useful expression for the transmission coefficient of theo —zwave has been derived.

ISSN:0021-8979    

DOI:10.1063/1.1699577

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Equations are developed for the transmission of a plane elastic wave through a plate at oblique incidence with unequal fluid medium on each side of the plate. The plate transmitting both the dilatation and shear wave is reduced to a simple equivalent circuit with impedances which are functions of the incidence angle.

ISSN:0021-8979    

DOI:10.1063/1.1699578

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Nine heavy lubricating oils, four light lubricating oils, three aircraft engine fuels, one diesel fuel, and distilled water were tested for their air solubility and for the rate of solution and evolution of air when equilibrium is disturbed. The technique consisted of shaking of a container partly filled with liquid and taking accurate pressure measurements of the air above the liquid. Since air in solution exerts no pressure, the variation of pressure during and after the agitation furnished information on the amount of air that went into or came out of solution and their time rates. The solution was considered to have reached equilibrium when further shaking no longer changed the air content of the liquid.A wide variation exists in the solubility constants and rates, but the rate of evolution was always found to be proportional to the supersaturation, and the rate of solution to the undersaturation, under otherwise similar conditions. At room temperature the air solubility constant for distilled water is 1.84 percent, for a gasoline approximately 20 percent, and for (light and heavy) lubricating oils approximately 10 percent. The ``half‐life'' for evolution on the other hand was 3.86 sec. for distilled water, 0.13–0.24 sec. for gasoline, 3.6–7.6 sec. for light, and 11.6–51.4 sec. for heavy lubricating oils.The investigation gave some insight into the phenomenon of cavitation which is still largely shrouded in mystery.

ISSN:0021-8979    

DOI:10.1063/1.1699579

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A method has been proposed to measure self‐diffusion in metals by measurement of the contact conductance of an interface between two metallic spheres or hemispheres. By combining Kuczynski's equation for self‐diffusion with Bowden and Tabor's equation for the contact conductance between two metallic spheres a relationship has been obtained between contact conductance and the time of heating of the spheres. Thus by measurement of junction conductance as a function of time of heating, for different temperatures, diffusion coefficients and the heat of self‐diffusion can be evaluated in the normal manner. A similar relationship has been obtained for two spheres or hemispheres initially pressed together to give a known contact conductance before heating.

ISSN:0021-8979    

DOI:10.1063/1.1699580

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

In conical flows the velocity, pressure, and density do not vary on lines through the vertex of the cone. In this paper it is shown that for interferograms of general conical flows &dgr;(y, z)/z=f(y/z), whereyandzare any set of Cartesian coordinates with origin at the image of the vertex of the cone, and &dgr; is the fringe shift aty, z. Thus, for strictly conical flow, a graph of &dgr;(y, z)/z versus y/zshould be a single curve. This suggests a test for approximate conicity that requires very little computation. This test is applied to interferograms obtained from a number of approximately axisymmetric flows at various Mach numbers about cone‐cylinders in free flight. Plotted fringe shift data from the region near the nose fall into a narrow band, an indication of approximate conicity. They also closely check the corresponding theoretical fringe shift curve calculated for Taylor‐Maccoll flow.

ISSN:0021-8979    

DOI:10.1063/1.1699581

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

IfNcollinear antennas are individually center driven, the only transmission line in the neutral plane is the one for a central unit ifNis odd. Since lines that are not in a neutral plane constitute antennas, such an array is not practically useful.For a single driven unit with symmetrical, parasitic, collinear elements, the driving transmission line is in the neutral plane and may be replaced by an equivalent generator and terminal‐zone network. An array with two parasites is analyzed. Since the currents in the halves of the three units are not alike, three simultaneous integral equations occur. By making reasonable assumptions these are reduced to the single equation of the isolated antenna but with a different kernel. Approximate expressions are obtained for the currents and for the mutual and self‐impedances of the elements.The collinear antenna with outer elements driven from the central one by phase‐reversing stubs is studied. For three elements components of the currents in the several possible modes are obtained with different degrees of approximation. The in‐phase currents in the antennas are greatest, and are obtained with considerable accuracy. The currents in the outer units are not symmetrical, but with elements of length &lgr;/2 the odd components of the currents are shown to be negligible.

ISSN:0021-8979    

DOI:10.1063/1.1699582

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

This paper considers the radial and vertical oscillations of a synchro‐cyclotron beam. It is found that various oscillations of substantially constant or increasing amplitude may occur in certain regions of the field, in which there are angular or other asymmetries, though only one possible oscillation (that atn≃⅕) can occur in a field that is cylindrically and vertically symmetric. The conditions for the various oscillations, and their behavior, are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1699583

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

If, in a multiply‐connected elastic solid, discontinuities are permitted across a stationary barrier in either the strain or its first derivatives or both, dislocations of a more general type than encountered in classical theory are possible. A number of these more general dislocations have been obtained for states of plane and anti‐plane strain in a hollow right circular cylinder when the surface of discontinuity is a single stationary plane barrier. Some of the dislocations found possess the characteristic that although the strain is continuous across the barrier the displacement discontinuity isnotone which would be possible in a rigid body. Examination of the conditions for the uniqueness of solution of the boundary value problems of elasticity reveals that when dislocations of the more general type are admitted appropriate data must be given at each point on the specified barrier in addition to the usual information.

ISSN:0021-8979    

DOI:10.1063/1.1699584

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The impedance of an atmospheric pressure d.c. arc was measured at 1000 mc/sec. by means of a coaxial line and standing wave detector. The reactance and resistance of the arc, an essentially lumped load at the end of the line, increase with length of arc. The resistance decreases with increasing current and is approximately the same as the d.c. ``resistance.'' The reactance is capacitive and nearly independent of current. Air, argon, and helium were studied at currents from 1–4 amp. d.c. arc current.

ISSN:0021-8979    

DOI:10.1063/1.1699585

出版商:AIP    

年代:1950

数据来源: AIP