Axial Rod Research Articles

Circular Waveguide Backward-wave Experiments†

ABSTRACT The properties of a circular waveguide containing an axial dielectric rod of high permittivity are experimentally investigated. By use of a resonant cavity technique the propagation coefficient is determined as a function frequency for the dominant mode possessing unity azimuthal dependence. A region of backward-wave propagation is revealed in accordance with theoretical predictions made over recent years.

Properties of cylindrical waveguides containing isotropic and anisotropic media

The cut-off conditions in circular waveguide containing an axial circular rod are considered when the rod is perfectly conducting and is surrounded by dielectric material, also when the rod and the surround are comprised of dielectric material, ferrimagnetic material or plasma. The characteristic equations involve certain cylindrical functions which depend on two variables. Contours of these functions are presented for cases corresponding to modes with zero and unit azimuthal dependence. Comparison is made between the cut-off conditions for the above media, and certain relationships between these conditions and the behaviour under propagating conditions are discussed. For modes possessing zero azimuth dependence, the characteristic equation can be solved under propagating conditions using the contour graphs. As an illustration of the method, results are presented for a cylindrical waveguide containing an unmagnetised plasma rod.

Circular-waveguide backward-wave structures

The paper describes a graphical method for determining the cut-off conditions of those modes of a circular waveguide containing an axial dielectric rod which possess an azimuthal dependence of unity. Results are presented for the six modes of lowest order. It is shown that the cut-off conditions of a pair of modes such as the H1m and E1m can, under certain circumstances, coincide. This degeneracy at cut-off is shown to be associated with backward-wave propagation above cut-off. The modes with a backward-wave component are designated hybrid H1m modes, although, under certain conditions, these exhibit E-mode properties at cut-off. The propogation behaviour of the modes is investigated theoretically, special attention being given to parameters most suited to backward-wave applications. Only the mode of lowest order exhibits backward-wave properties which appear favourable for use in devices. The possible application of this mode to a backward-wave oscillator is investigated, but it is shown that with existing dielectric materials high beam voltages would be required. The application to a frequency selector is also described. The results of a study of cut-off degeneracy in other waveguide structures are given.

A PROPOSAL TO USE MICROWAVE CAVITIES TO STUDY THE SURFACE PROPERTIES OF HIGH DENSITY PLASMAS

It is suggested that the resonant properties of a cylindrical microwave cavity containing a highly conducting axial plasma rod could be used to obtain information about the dynamic properties of such a plasma. Two applications of the method are considered: an investigation of electrically exploded wires, and a study of the dynamics of the conventional z-pinch during its initial stages.

Self-induced waves in a conduit with corrugated walls. II. Experiments with air in corrugated and finned tubes

Metal bellows were found to produce a pure note when air was passed through them over a small range of velocity. An axial rod, restricting the stream to a narrow annular cross-section, was usually essential for speech, and sound was produced also by a narrow stream between the bellows and an external pipe. More powerful notes were obtained when the bellows inside the pipe were replaced by helically finned tubes. The pressure distribution in this arrangement was examined. The phase velocity of the waves inside the pipe was much less than the velocity of sound, and this effect is explained by applying the theory of wave propagation in periodic structures. The ratio of the average frequency, at which an air particle passed the protuberances, to the frequency of the sound emitted was usually about 1·6.

On Cylindrical Magnetohydrodynamic Shock Waves

If an axial rod is surrounded by an ionized gas, an expanding cylindrical shock wave can be produced by passing through the gas a current which returns along the rod. The azimuthal magnetic field of the current acts like a piston, pushing the plasma away from the rod and leaving behind a cylindrical vacuum region. The case considered is that where a uniform magnetic field parallel to the axis is initially present in the gas; in this case a transverse magnetohydrodynamic shock wave results from the current discharge. The flow is analyzed under the assumptions that the plasma is a nonviscous, nonheat-conducting, ideal gas of infinite electrical conductivity, and that the discharge current increases linearly with time. The analysis is made first on the basis of the ``snowplow'' theory of Rosenbluth, and then from a similarity solution of the full magnetohydrodynamic equations. The results of the two solutions are compared for the case γ = 7/5. It is found that the speed predicted by the snowplow theory is in very good agreement with the speed of the contact front obtained from the solution of the full equations over the entire range of shock strength, but that the snowplow speed is a good approximation to the shock speed only in the limit of strong shocks. The effect on the flow of varying the axial field is discussed.

Backward waves in waveguides containing dielectric

A method is described for determining the conditions which ensure backward-wave propagation in dielectric-loaded inhomogeneous waveguide structures. It is established that backward-wave propagation can be ensured for the hybrid H11-mode in a circular waveguide containing an axial dielectric rod whose relative permittivity exceeds approximately 9.4. The possibility of other inhomogeneous-waveguide modes exhibiting backward-wave properties is also examined.

A broad-band waveguide junction containing dielectric

A method is described for obtaining a broad-band impedance match between two joined waveguides of differing cross-section. The method involves the use of an axially mounted dielectric which partially fills the waveguide cross-section. With an appropriate choice of dielectric cross-sectional area and permittivity the electromagnetic field is mainly confined to the region of the rod. Under these conditions the waveguide cross-section may be abruptly changed without appreciable reflection. The case of two joined circular waveguides containing an axial dielectric rod is treated theoretically for H01-mode propagation. A similar configuration is studied experimentally for the H11-type mode of propagation. In both cases an appreciable reduction in reflection coefficient is demonstrated when the rod is present. The application of the principle to other waveguide crosssections is briefly mentioned.

Propagation along unbounded and bounded dielectric rods. Part 2: Propagation along a dielectric rod contained in a circular waveguide

The paper describes both approximate and exact methods for evaluating the phase-change coefficients of a circular waveguide containing an axial dielectric rod. Close correlation is found between the phase-change coefficients of this waveguide structure and those of an unbounded rod over a wide range of rod radii. The correlation enables an unambiguous classification of the modes of an unbounded rod to be made. Exact and perturbation expressions are derived for total transmitted power, power distribution and attenuation in the dielectric-rod-waveguide structure. Correlation with the attenuation coefficients of an unbounded rod is again predicted. The application of the results of the paper to ferrite devices is briefly mentioned.

Control Rod Theory for Asymmetrical Arrays and Reflected Cores

Criticality conditions suitable for hand calculations are derived for reactor control rod configurations of practical interest. Two-group diffusion theory is applied to (a) arrays of several control rods of different materials, sizes, shapes, radial, and angular location; (b) reflected cores containing a symmetric ring of similar rods, with or without an axial rod. The reduction to elementary cases is deonstrated. (auth)

The Fine Structure of the Heliozoan, Actinosphaerium nucleofilum*

SYNOPSIS.Actinosphaerium nucleofilum has been studied by light and electron microscopy. Thin sections of this organism reveal the relatively compact endoplasm to consist of numerous vacuoles and mitochondria. Scattered in the cytoplasm are dense particles, presumably ribonucleoprotein particles, endoplasmic reticulum of the rough variety and a tubular endoplasmic reticulum of the smooth variety. The many nucleido not appear to be randomly scattered in the cytoplasm but rather to be arranged in a circular pattern. Each is bounded by a double membrane envelope. A Golgi complex, consisting of isolated bodies with an ultrastructure similar to that described by others, is usually seen associated with each nucleus.The ectoplasm contains many vacuoles of varying diameter, each of which is limited by a thin membrane; vacuoles containing dense granular material, and mitochondria.The radially arranged axiopodia are extensions of the ectoplasm. The periphery is largely composed of vacuoles, some of which contain dense granules, and mitochondria. The axial rod is birefringent and consists of many fine filaments oriented parallel to the longitudinal axis of the axiopodium. The constituent filaments penetrate deep into the endoplasm where they end in the vicinity of nuclei. The fibrillar component of the axiopodia may represent contractile units.

Propagation Constants of Circular Cylindrical Waveguides Containing Ferrites

The paper describes some results of a theoretical and experimental investigation of the propagation behavior of circular cylindrical wave guides containing longitudinally magnetized ferrite rods. As long as no concentration of the RF-magnetic field in the ferrite occurs, theoretical expressions for the propagation constants can be given by applying first-order perturbation method. Faraday rotation measurements have been made between 5000 and 7600-mcs using commercially available ferrites. Reasonable agreement between theoretical and experimental results has been found for a thin axial ferrite rod in an air-filled guide in both cases of saturated and nonsaturated ferrites. Energy concentration in the ferrite determines the propagation behavior in the partially filled waveguide. This effect can be enhanced by surrounding the ferrite rod with a dielectric tube. For a given rod diameter and permittivity of the tube there is an optimum outer diameter of the tube for which the Faraday rotation becomes maximum.

The gain of travelling-wave ferromagnetic amplifiers

The paper describes a general perturbation method for determining the gain of travelling-wave ferromagnetic amplifiers. By use of the method, the gain is determined for an amplifier employing a circular waveguide and an axial ferrite rod of small cross-section. The efficiency of such an amplifier is shown to be low, and a practical version would demand the use of larger rod cross-section and/or a slow-wave structure. Other possible waveguide configurations for amplifiers are briefly mentioned, together with certain practical aspects of construction.

Inverse Pinch Effect

In the conventional pinch effect an ionized gas is enclosed by a conducting cylinder, and a sufficiently large current passing through the gas and returning along the inner wall of the cylinder produces a magnetic field which compresses the gas into an axial filament. A device is described which produces an inverse pinch effect. Here the above conducting cylinder is replaced by an axial rod surrounded by the ionized gas. When a current passes through the gas and returns along the rod the magnetic field pushes the plasma outward, leaving a cylindrical vacuum region behind. The velocity and thickness of the expanding plasma front have been studied optically and by means of magnetic probes. Except at the highest gas densities, the velocity is in good agreement with the ``snow plow'' theory of Rosenbluth, and the thickness of the front is reasonably consistent with the ``snow plow'' model. At the higher densities it appears that diffusion of magnetic field into the plasma is significant. The advantages of the inverse pinch effect in studying plasma behavior and the idea of a magnetically stabilized inverse pinch are discussed.

Changes in the nuclear structure of bacteria, particularly during spore formation

Changes of nuclear structure in bacteria have been studied by means of the hydrochloric acid-Giemsa method which produces brilliantly stained specimens and can be carried out with almost the same ease as some of the ordinary routine staining techniques.The nuclear changes in the four spore-bearing organisms studied are outlined in Text-fig. III, to which the following numbers refer. The dumbbell bodies which are dispersed in the cells of the young growth (1) become alined in the long axis of the cell (2) where they eventually fuse into an axial nuclear cylinder (3, 4). These cells divide up into fusion cells of approximately the same length (5). The development of the ‘chromosome’ stage (1) into the fusion cell (5) is the first step in the process of sporulation. During its further development the fusion cell or spore mother cell divides twice (6, 7), with the result that it is segregated into four structures which often assume dumbbell shape. Therefore the chromatin cylinder of the individual spore mother cell seems to be equivalent to four nuclear elements one of which functions as the spore ‘chromosome’ (‘nucleus’?), whereas the remaining three disintegrate (8, 9). The ripe spore (9) representing, as it does, the smallest cell unit contains one nuclear structure only.Therefore the two main features in spore formation of bacteria appear to be (1) a fusion of the dumbbell bodies into an axial chromatin rod (‘autogamy’?), (2) a reduction partition which is reminiscent of, though not corresponding to, the more complicated phenomenon of meiosis in the higher organisms. The sporulation, as outlined in this paper, gives new proof of the important part played by the chromatinic dumbbell bodies (‘chromosomes’) in the developmental cycle of spore-bearing organisms. The fusion cell with its axial chromatin cylinder has for the first time been proved to have a progressive functional significance as a stage in a nuclear cycle. The particular mode of fusion followed by reduction partition suggests that the chromatinic dumbbell bodies may be concerned with the transmission of the hereditary characters in bacteria.

Societies and Academies

LEEDS. Philosophical and Literary Society, June 19.—J. Ewles: A torsion magnetometer. A new instrument for laboratory use based on the principle that the couple required to hold a magnet of moment M at right angles to a field H is MH. Magnetic forces are removed by balancing against the torsion in a phosphor bronze strip supporting the ‘needle.’ All the experiments usually performed with both the deflection and vibration magnetometers may be performed with this instrument.—F. A. Long: Note on the behaviour of a neon-tube under heavy discharge. When using a neon (‘Osglim’) lamp in parallel with the coils of an electromagnet, the discharge through the lamp on breaking the current was of bright bluish-violet colour instead of the usual pink glow, and included two or more flashes. An examination of current voltage during the discharge shows that at the commencement a current of several amperes passes, while the voltage falls much lower than the usual extinction value.—C. W. Shoppee: On the possibility of ring-chain valency tautomerism and of a type of mobile-hydrogen tautomerism analogous to the Wagner-Meerwein re-arrangement. Part 5: Pina-colic electron displacement as an explanation of various intramolecular transformations. A discussion and an attempted correlation of various intramolecular transformations on the basis of tautomeric change. The general mechanism proposed gives a satisfactory explanation of many known changes, and where divergences occur between theory and fact, reinvestigation confirms the theoretical prediction.—L. R. Johnson and A. Wormall: Potassium thiocyan-ate and the diastatic action of saliva and plant-diastases. Potassium thiocyanate exerts an activating influence on the diastatic action of human saliva, and this effect is significant, even with concentrations of the salt which may be present in the saliva. The thiocyanate appears to accelerate the first stages only in the hydrolysis of starch, and the rate of formation of reducing sugars is not markedly increased. The stimulating effect of this salt on the germination of potatoes and barley is discussed in relation to its influence on diastatic action.—R. G. S. Hudson and F. W. Anderson: On the Lower Carboniferous corals. Hettonia fallax, gen. et sp. n. The genus Hettonia, a member of the Clisiophyllidse, is characterised by a solid central column built of an axial rod surrounded by tabular thickening. Hettonia fattax, the only species as yet described, is remarkable in that it possesses a distinct gerontic stage in which there is no cohrmella, and therefore simulates Can-inia. In addition, dedifferentiation is a common occurrence in this species. Certain new and un-described structures are recognised in the ephebic stage of the corallite, and are attributed to calicular gemination. The prototheca and part of the brephic structure are built while the young corallite is still attached to the parent individual, and remain there after separation of the young form.—Lorna I. Scott and Ada B. Whitworth: A structural peculiarity of the exodermis of the root of Pelargonium. In the root of Pelargonium the hypodermal cells develop a convex band of thickening, which runs round each cell on the radial and transverse walls. At maturity, the bands consist of lignified cellulose, with traces of silica, and show characteristic optical properties, which disappear on treatment with cellulose solvents. —W. Garstang and Margery I. Platt: On the asym-rmetry and closure of the endostyle in Gyclosalpa pinnata. The authors describe from sections the structure of the closed endostyle of Gyclosalpa pinnata. They confirm the absence of the left marginal band, and confirm it as due to the development of an interlocking mechanism by which the endostyle is firmly closed as a tube. The missing band, however, is present at both extremities with normal relations. The endostyle possesses a posterior growing point (cf. larval Amphioxus).

Brief Notes on the Structure and Development of Spirochæta anodontæ Keysselitz

ABSTRACT Much uncertainty still prevails as to the structure and biological relationships of the spirochætes. Earlier observers —not altogether influenced perhaps by a desire to prove their affinities with the hæmoflagellates—equipped them with an undulating membrane and a complicated nuclear apparatus, the existence of which is very problematical; and much controversy has existed as to their mode of division, longitudinal or transverse. The very claim of the organisms found in Mollusca, as well as that of the smaller spirochætes, to be called by this name, depending as it must on their relationship to Sp. plicatilis Ehrenberg, the type-species, is not very firmly established, since the structure of the latter—a system of large waves, each broken by smaller undulations superposed on them, with a central axial rod and a series of dots, regarded as nuclei—is markedly different from that of the later additions to the genus. It is desirable, therefore, to record any observations which may tend to throw light on the morphology and life-history of these organisms.

The Kinship of Ascidians and Vertebrates

ABSTRACT In 1867 Kowalevsky published, in the transactions of the Imperial Academy of St. Petersburg, some observations which are more profoundly interesting than anything of the kind which has appeared of late years, since, if correct, they indicate distinctly a bridge over the chasm, supposed to separate Vertebrates from all other animals. They prove the existence of a bicavitary structure, of a neural tube and a visceral tube, separated by an axial cartilaginous rod, in the early stages of development of Ascidians, an arrangement previously believed to be essentially characteristic of Vertebrates.