Volume 18, Issue 10, 01 October 1947
Index of content:
18(1947); http://dx.doi.org/10.1063/1.1697559View Description Hide Description
When a charged particle approaches a region of uniform magnetic field its trajectory is affected by the fringing field. Compensation for the effect of the fringing field may in some cases be achieved by the use of virtual field boundaries which are outwardly displaced from the actual boundaries. A definition of the virtual boundary in terms of the effect of the fringing field upon the trajectories is formulated. A procedure for calculating the displacement d of the virtual from the actual field boundary is given using the methods previously developed for calculating ion trajectories in non‐uniform magnetic fields. Using this procedure several values of the displacement for various magnet dimensions and conditions have been calculated. A method of altering the geometry of sector‐type mass spectrometers to correct for the effects of the fringing fields is proposed. It is shown that the angular and spatial separations of the individual ion trajectories in an ion beam of small angular spread as it approaches a uniform field region through a fringing field are approximately the same as for the ideal case wherein the magnet field changes discontinuously at the boundary.
18(1947); http://dx.doi.org/10.1063/1.1697560View Description Hide Description
This paper considers the theory of band‐pass wave‐guide filters formed by cascading rectangular cavities separated by quarter guide wave‐lengths. Formulas for resonant frequency, loaded Q, and insertion loss in the pass band are derived for a single stage using matrix theory and are in a form suitable for design purposes.
The general theory of ``n'' stages is worked out using matrix algebra, and it is shown that the insertion loss and phase shift of ``n'' stages are given by:,where Tn(x) and Un(x) are the first and rationalized second kind Tschebyscheff polynomials.
The specific design procedure is outlined including the design of a finite thickness inductive aperture.
18(1947); http://dx.doi.org/10.1063/1.1697561View Description Hide Description
A method is devised for computing the properties of a complex microwavenetwork in terms of the properties of the circuit elements which in combination form the network. It is particularly suited to machine computation of the properties of circuits of such complexity that simpler, more direct methods fail. It is also applicable to low frequency networks. The elements of such networks may be regarded as interconnected by transmission lines of zero length. A numerical example is used to illustrate the method.
18(1947); http://dx.doi.org/10.1063/1.1697562View Description Hide Description
The paper is concerned primarily with the electron guns employed in electron microscopy.
The position of the image of the cathode, the magnification, and the divergence of the beam leaving the anode are calculated for a three‐electrode electron gun with plane electrodes and circular apertures both for zero and battery bias. The simplifying assumption is made that the electrostatic lenses are thin. The results are compared with the experiments of Johannson. The extension of the results to the gun used in the transmission electron microscope is considered with the aid of electrolytic trough measurements. The case of a gun biased by a cathode resistor is also discussed.
On the One‐Dimensional Theory of Steady Compressible Fluid Flow in Ducts with Friction and Heat Addition18(1947); http://dx.doi.org/10.1063/1.1697563View Description Hide Description
Steady, diabatic (non‐adiabatic), frictional, variable‐area flow of a compressible fluid is treated in differential form on the basis of the one‐dimensional approximation. The basic equations are first stated in terms of pressure, temperature, density, and velocity of the fluid. Considerable simplification and unification of the equations is then achieved by choosing the square of the local Mach number as one of the variables to describe the flow.
The transformed system of equations thus obtained is first examined with regard to the existence of a solution. It is shown that, in general, a solution exists whose calculation requires knowledge only of the variation with position of any three of the dependent variables of the system. The direction of change of the flow variables can be obtained directly from the transformedequations without integration. As examples of this application of the equations, the direction of change of the flow variables is determined for two special flows.
In the particular case when the local Mach numberM=1, a special condition must be satisfied by the flow if a solution is to exist. This condition restricts the joint rate of variation of heating, friction, and area at M=1. Further analysis indicates that when a solution exists at this point it is not necessarily unique.
Finally, it is shown that the physical phenomenon of choking, which is known to occur in certain simple flow situations, is related to restrictions imposed on the variables by the form of the transformedequations. The phenomenon of choking is thus given a more general significance in that the transformedequations apply to a more general type of flow than has hitherto been treated.
18(1947); http://dx.doi.org/10.1063/1.1697564View Description Hide Description
In electron microscopic studies of Fischer‐Tropsch catalysts, an interesting phenomenon was observed in cobaltmetalpowder reduced from cobaltous oxide. The oxide particles sintered into larger smooth droplets of cobalt that were aggregated into thin hexagonal‐shaped platelets. X‐ray diffraction analysis showed the presence of the hexagonal crystal phase of cobalt. A possible explanation is that the aggregates are formed by forces similar to those operating in normal crystal formation, but of reduced magnitude insufficient to destroy the identity of the component particles.
18(1947); http://dx.doi.org/10.1063/1.1697565View Description Hide Description
The water‐repellent nature of glass surfaces treated with different silicones is examined by means of contact‐angle measurements. Results are given showing the effect of various concentrations of silicones, types of glass, temperature of heat treatment, length of time of heat treatment, and surface roughness on the water contact angles. Silicones containing the methyl and phenyl group show good heat stability at temperatures of 500°C for short periods of time.
18(1947); http://dx.doi.org/10.1063/1.1697566View Description Hide Description
An apparatus for the observation of the Kerr electro‐optic effect in liquids and polymers using microsecond electrical pulses, is presented and evaluated. This method offers a convenient way of studying internal motions and molecular configurations of polymeric material with a minimum of heating usually accompanying these observations. Electrical pulses of from 1‐ to 1000‐microsecond width, 60–1000 p.p.s., at amplitudes up to 5000 volts are generated by conventional methods. These pulses are used to orient low molecular weight and polymeric materials placed between the plates of a condenser. The circular polarization induced in the polarized light passing between the plates actuates a photo‐multiplier tube in order that the light pulses may be studied with an oscillograph.
Curves of Kerr constant versus temperature at temperatures to −80°C are compared with the literature. Oscillograms showing the response of several liquids and polymers are shown. Oscillograms showing an interesting difference between orientation and relaxation time are presented, as are oscillograms showing clearly both orientation and distortion polarization simultaneously.
18(1947); http://dx.doi.org/10.1063/1.1697567View Description Hide Description
Simultaneous photographs, taken in two perpendicular directions, have been obtained of long sparks in various gases at 1‐atmosphere pressure. The experiments were undertaken in order to decide whether the localized afterglows, noticed as long streaks in rotating mirrorspark photographs, were caused by some discharge mechanism or by purely geometrical effects resulting from the tortuous nature of the spark channels. The results show that the second explanation is not feasible. Some qualitative interpretations of the effects are given.
18(1947); http://dx.doi.org/10.1063/1.1697568View Description Hide Description
- LETTERS TO THE EDITOR
18(1947); http://dx.doi.org/10.1063/1.1697569View Description Hide Description
18(1947); http://dx.doi.org/10.1063/1.1697570View Description Hide Description