bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wave Propagation on Helical Wires
Authors: Sollfrey William 
Published: April 2005

Previous researches on the helix have made simplifying approximations about the nature of the boundary conditions. In this paper the field equations and boundary conditions are formulated exactly. They are then solved by an expansion in powers of the ratio of the thickness of the wire to the distance between turns.
The method used consists of introducing a new coordinate system, which is such that a helical wire of circular cross section is a surface in which one coordinate is constant. Maxwell's equations and the electromagnetic boundary conditions are expressed in terms of this system. Since nonorthogonal coordinates are involved, the equations cannot be solved exactly; but a perturbation procedure may be applied as indicated above.
The result of the analysis is to show that there is a principal mode, which propagates with the free space velocity of light in the direction of the wire. The characteristics of this mode are studied, and they are compared successfully with experiment.
Electrical Properties of Selenium: I. Single Crystals
Authors: Henkels H. W. 
Published: April 2005

Crystals of hexagonal selenium have been grown in a melt. Their microstructures have been compared with those arising in vapor crystals.
The dark resistivity has been studied as a function of axis orientation, temperature, field, and time of application of a field. The thermoelectric power has been measured and attempts made to measure Hall effect. The nature of the acceptor levels has been discussed, the approximate hole densities and mobilities have been determined, and values of the activation energies obtained.
The field effects have been discussed and the phenomenon of an apparent semipermanent polarization occurring at quite low fields has been noted.
The Impedance of an Antenna over a Large Circular Screen
Authors: Storer James E. 
Published: April 2005

In the performance of antenna measurements the antenna is usually placed over a large conducting screen. The assumption is then made that the measurements are in close agreement with those that would be obtained if the screen were of infinite size. Recent experimental work, however, indicates that the finiteness of the ground screen may influence the measurements to a considerable extent.
It is therefore desirable to solve this problem theoretically in order to determine the extent of the change introduced by the use of a finite screen. This paper treats the problem of an antenna erected vertically in the center of a circular screen. An integral equation is obtained for the electric field in the plane of the screen, outside the screen. This equation is solved approximately by the use of a variational principle, and a formula is obtained for the change of antenna impedance as a function of the diameter of the screen. The formula may be used to give a simple and accurate estimate of the changes introduced by the use of a finite screen.
Arcing at Electrical Contacts on Closure. Part II. The Initiation of an Arc
Authors: Germer L. H. 
Published: April 2005

The capacity of the plates of an oscilloscope charged to 35 or 40 volts is discharged repeatedly by approaching electrodes of carbon, active silver, and inactive silver. Facts about the discharges, which are arcs of very short duration, are inferred from resulting open circuit potentials and calculated electrode separations.
The separation at the first arc varies in different experiments but corresponds on the average to a nominal electric field of 0.6×106 volts/cm for carbon or active silver and to 2×106 volts/cm for inactive silver. Each arc is initiated by a very small number of field emission electrons. The hypothesis that a single electron may perhaps be sufficient is consistent with observations at later stages of each closure when the electrodes are closer and the field much higher.
The earlier observation, that the potential across a short arc is constant and independent of current, is not true if the arc time is sufficiently short. For active silver a time comparable with 2×10−8 sec is required to establish the steady arc voltage characteristic of later stages of arcs which last longer than this. The initial time during which the potential is decreasing toward its final steady value is 100 times the transit time of a silver ion across the gap.
Enhanced Emission from Magnetron Cathodes
Authors: Jepsen Robert L. , Muller Marcel W. 
Published: April 2005

Existing theories of the static magnetron do not predict violation of the Hull cut-off condition or cathode bombardment. Measurements made at anode voltages and magnetic fields much larger than those used by earlier investigators revealed violations of the Hull cut-off condition considerably more pronounced than those previously reported, and much greater amounts of cathode bombardment. When sufficient cathode bombardment takes place, emission may be enhanced (through secondary emission) by a factor of ∼103 over the thermionic value. When enhanced emission occurs in magnetrons employing pure metal cathodes, it is found that maximum current limits exist for each magnetic field. These limits form a maximum current boundary on a voltage-current plot. The maximum current boundary depends on secondary emission properties of the cathode surface and on geometry. Experimental observations on enhanced emission, cathode bombardment, the maximum current boundary, and flow of anode current in violation of the Hull cut-off condition are combined into a self-consistent picture in static magnetrons employing pure metal cathodes. Although cathode bombardment and flow of anode current are still unexplained, their existence can account for the observed enhanced emission and maximum current boundary. In this it is unnecessary to endow the cathodes with anomalous thermionic or secondary emission properties.
The process causing cathode bombardment, enhanced emission, and flow of anode current in violation of the Hull cut-off condition is believed to be an electronic interaction which occurs almost entirely in the relatively dense region of space charge surrounding the cathode. The significant factors influencing the interaction appear to be applied electric and magnetic fields, space charge density, and thickness of the space charge sheath. The basic problem of electronic interaction in the static magnetron is partially defined. It is expected that when a realistic solution to this problem exists, including a correct account of cathode bombardment, the occurrence of enhanced emission would be automatically predicted.
Heat Transfer in Isotropic Turbulence
Authors: Corrsin Stanley 
Published: April 2005

The postulated problem of heat transfer in a stationary isotropic turbulence under constant small temperature gradient is examined from both Lagrangian and Eulerian points of view. By combination of Taylor's ``diffusion by continuous movements'' and a new temperature fluctuation equation somewhat like the wellknown turbulent energy equation, it is possible to obtain (1) an expression for the turbulent heat transfer coefficient which depends only on velocity field, and (2) an approximate expression for the corresponding correlation coefficient which depends only on velocity field and fluid physical properties.
A preliminary result is given for ``turbulent Prandtl Number'' in a homogeneous shear flow in terms of the shear and heat transfer correlation coefficients.
The Collapse and Rebound of a Gas Bubble
Authors: Trilling Leon 
Published: April 2005

The velocity and pressure field in a slightly compressible liquid resulting from the collapse of a spherical bubble is computed as a function of the pressure at the bubble wall, using the acoustic approximation. The results are accurate as long as the liquid velocities are small compared to the sonic velocity in the liquid; they agree with the results previously obtained by C. Herring.
The following bubble model is then investigated. The bubble is supposed filled with inviscid perfect non-conducting gas; special emphasis is given to the gas motion which involves a series of shock waves. A fraction of the energy of compression is thus degraded so that the radius of the bubble after the first rebound is somewhat less than the original radius. The pressure variation at the bubble wall is virtually the same as if the gas were compressed uniformly and isentropically.
A Vertical Shaft for the Production of Thick Artificial Clouds and for the Study of Precipitation Mechanics
Authors: Gunn Ross 
Published: April 2005

Progress in cloud physics has been seriously limited because of the impossibility of conducting controlled cloud experiments on a sufficiently large scale. To meet the requirements, a laboratory has been built in which thick artificial expansion type clouds may be produced under controlled and measurable conditions.
A mine shaft 0.210 kilometer deep and 2.2×2.2 meters in cross section has been sealed and adapted to the production of thick artificial clouds. The shaft and its principal auxiliaries necessary for the study of some of the basic problems of clouds and precipitation are described. Dense, thick clouds completely filling the shaft are now being produced on a routine basis. Some preliminary illustrative data are presented.
Mechanism for Self-Diffusion in Graphite
Authors: Dienes G. J. 
Published: April 2005

The mechanism for self-diffusion in single crystals of graphite has been examined theoretically. Calculations for vacancy and direct interchange mechanisms are based on atomic interactions within the graphite hexagonal layers. These interactions are obtained from the known systematic change of carbon-carbon bond strength with interatomic distance. In order to be able to calculate the energy of formation of an interstitial carbon atom, a potential function has been devised to account for interaction between the planes. This potential function consists of two terms, a van der Waals' attraction and an exponential type repulsion. The adjustable constants have been evaluated from known physical data. The interplanar cohesive energy of graphite is calculated to be 4.36 kcal/mole.
Comparison of the total activation energies for self-diffusion via vacancies, direct interchange, and interstitial atoms indicates that direct interchange is the preferred mechanism. The activation energy for self-diffusion by means of direct interchange is estimated to be 90 kcal/mole. The present theoretical treatment is not applicable to diffusion along grain boundaries or pores.
Studies of Self-Diffusion in Graphite Using C-14 Tracer
Authors: Feldman M. H. , Goeddel W. V. , Dienes G. J. , Gossen W. 
Published: April 2005

Self-diffusion in graphite was measured over the temperature range from 1835°C to 2370°C by observing the penetration of C-14 tracer initially applied to one end of a graphite rod.
The experimental data were found to be in agreement with a diffusion mechanism consisting of concurrent volume and grain boundary processes. Activation energies for both processes (EV and EB) could not be uniquely obtained from the data, however. An independent determination of either is required in order to evaluate the other. On the basis of recent theoretical work, EV may be taken to be 90 kcal/mole. From the present experiments and the above value of EV, the activation energy for grain boundary diffusion, EB, is calculated to be 75.4 kcal/mole.
Bariated Tungsten Emitters
Authors: Hughes Ray C. , Coppola Patrick P. 
Published: April 2005

Thermionic emitters consisting of barium oxide dispersed throughout a body of porous tungsten can be successfully made if suitable compounds of barium are employed as the source of the oxide. Compounds such as the carbonate, which can oxidize tungsten and react to form Ba3WO6: 3BaCO3+W→Ba3WO6+3CO,are unsuitable. However, if by various means, BaO is dispersed in tungsten, reaction occurs at operating temperature of the cathode to slowly generate free barium: 6BaO+W→Ba3WO6+3Ba, which diffuses to the surface and lowers the work function.
Cathodes consisting of approximately 5 percent of BaO in W are capable of supplying continuous emission in excess of 100 amp/cm2, give equivalent dc and pulsed emission, and are highly resistant to damage by arcing, temporary poor vacuum, ion bombardment, and high temperatures.
Emission current of approximately 8 amp/cm2 was obtained at an operating temperature of 1000°C from a typical cathode of this type. The life of this cathode, at 1100°C, was in excess of 650 hours. Constants of the Richardson equation for a relatively inactive cathode were φ=1.56 ev, A=0.6 amp/cm2/deg2.
The Scattering of Radio Waves by Meteorological Particles
Authors: Labrum N. R. 
Published: April 2005

The scattering of electromagnetic waves by clouds of small spheroidal obstacles is considered from a theoretical standpoint. Numerical data are obtained for the case of clouds composed of partly melted ice particles. These results are applied to the interpretation of ``bright band'' radar echoes from meteorological formations.
It is also shown that these echoes may contain a component with polarization at right angles to that of the transmitted beam. It is suggested that this property could be utilized in certain cases to provide additional information as to the nature of the scattering particles.
On the Accumulation of Errors in the Numerical Solution of Differential Equations
Authors: Papoulis A. 
Published: April 2005

The following gives a method for the evaluation of errors in the numerical solution of systems of differential equations.
Under certain assumptions the errors can be obtained by finding the difference r(x) between the computed solution y(x) passing through the given initial point, and the solution Y(x) passing through a neighboring point—that is, by solving the same equations repeatedly with different initial conditions.
Unsteady-State Separation Performance of Cascades. I
Authors: Montroll Elliott W. , Newell Gordon F. 
Published: April 2005

This paper concerns the exact solution of the nonlinear differential equations which describe the time dependent behavior of multistage cascade separating processes for separation of two very similar molecular species. The Rayleigh separation law is postulated for each stage.
The main questions of interest in the nonstationary operation of cascades involve (a) their behavior while the concentration of the required component is being built up to the desired value; (b) the behavior of the cascade during the transition from one stationary mode of operation to another; and (c) the manner in which local concentration fluctuations are propagated through the cascade. We have derived analytical expressions that are suitable for the discussion of all of these points in square cascades. The cases of finite, half infinite, and infinite cascades are considered with and without product withdrawal.
A brief discussion of the linearization of a class of nonlinear second-order partial differential equations is given in Appendix I.
Space-Charge-Limited Currents between Inclined Plane Electrodes
Authors: Ivey Henry F. 
Published: April 2005

The method of attack devised by Walker has been applied to the problem of current flow between inclined plane electrodes. It is assumed that the initial velocities of emission are negligible. Solutions for the potential distribution, the space-charge characteristic (``perveance''), the particle trajectories, and the transit time in such diodes under conditions of complete space-charge limitation are given. The trajectories and transit time have also been determined for the space-charge-free case. The results are presented in both graphical and tabular form. In most cases the solutions are given for angles between the electrodes as great as 180°.
For an angle between the electrodes of approximately 118° the transit time in the space-charge-free case is equal to that for complete space charge limitation. The effect of accidental electrode tilt on the perveance of a diode, which presumably has parallel electrodes, has also been investigated. A rectangular electrode whose width is 1.24 times the interelectrode spacing is relatively insensitive to tilt about a line passing through its center and parallel to its side. A disk-shaped electrode is insensitive to tilt about any axis passing through its center if its diameter is 1.42 times the interelectrode spacing.
Phenomena Associated with the Flight of Ultra-Speed Pellets. Part III. General Features of Luminosity
Authors: Rinehart John S. , Allen William A. , White W. C. 
Published: April 2005

Ultra-speed pellets of the lighter metals such as aluminum and magnesium generate intensely luminous trails when fired through air. A pronounced characteristic of the luminous trails is the intermittent manner in which the light is emitted. This effect has also been observed in meteors and in studies of conventional shaped charges. Photographs indicate that flashing is caused by yawing of the pellet.
The brilliant flashes of light are associated with the ablation and subsequent burning of material from the pellet. There is evidence that the material is removed from the pellet in the form of small droplets.
The brightness, luminous output, and temperature of the trail generated by an aluminum pellet have been measured. The brightness is approximately 25,000 lamberts, the luminous output is 30,000 lumen-seconds, and the color temperature is 2900°K.
Study of Imperfections of Crystal Structure in Polycrystalline Materials: Low Carbon Alloy and Silicon Ferrite
Authors: Slade J. J. , Weissmann Sigmund 
Published: April 2005

The technique of the new x-ray double spectrometer method as described in a former paper1 is applied to the study of angular misalignment of crystal structure in alloys.
To obtain a better statistical evaluation of the x-ray intensity data the method is extended to include arrays of spots on the Debye-Scherrer lines at high elevations. A complete mathematical discussion of the photometric transformation of the crystallite rocking curves is presented.
The specimens investigated include a low carbon alloy annealed at 850°C and three silicon ferrite samples annealed at 980°, 1100°, and 1200°C.
The quantitative data obtained disclose a significant dependence of crystal perfection on annealing temperature, and demonstrate clearly that the angular misalignment of the coherently reflecting regions within the grains decreases with annealing temperature provided this temperature is not excessive.
Valuable information regarding the influence of cold rolling on the subsequent annealing process is obtained. Thus, the extent of partial recrystallization of the silicon ferrite is deduced from the statistical data, and the differential grain size between the surface layers and the interior of the specimen is revealed through the study of the diffraction effects with radiation of different wavelengths.
A mechanism of grain bending during plastic deformation is suggested and a relationship between magnetic properties, annealing temperature, and crystal perfection of the silicon ferrite is pointed out.
Deformation and Fracturing of Thick-Walled Steel Cylinders under Explosive Attack
Authors: Pearson John , Rinehart John S. 
Published: April 2005

Tests have been conducted on annealed heavy-walled cylinders of low carbon (1020) steel internally loaded by explosive charges. The purpose of these tests was to obtain basic information on the manner and type of fracturing and plastic flow obtained by extremely high pressures acting for short durations. It was observed that all of the cylinders tended to fracture in long fragments in the same basic pattern, but with variations because of wall thickness and manner of loading. Experimental results indicate that the radial cleavage type of fracture is initiated within the cylinder wall and propagated to the surface, while the shear type fracture associated with the inner portion of the cylinder wall appears as an independent energy relieving process.
Microstructure analysis of the cylinder fragments shows a definite relationship between the type of fracture and the amount of distortion of the grain boundary. Considerable shock twinning is present in the cylinder fragments, and the grain structure near the inner surface shows severe distortion and flow. Strain measurements indicate that considerable plastic strain occurs during the explosive loading and cleavage fractures were always observed to occur in association with considerable plastic deformation.
Contribution to the Theory of the Silicon Carbide Contact
Authors: Holm Else 
Published: April 2005

1. The high limiting contact voltage of 40 to 50 volts in contacts between silicon carbide members (single crystals of the black-green variety) is explained on the basis of the known temperature-voltage relation.
2. Practically clean silicon carbide possesses a superficial layer which functions as a potential hill for the electrons. Because of its thinness the hill is penetrable for the electric current by means of the tunnel effect. The tunnel resistance per unit area was investigated with terminal areas of the order of 2 mm2. Being constant at small voltages, it drops down through some orders of magnitude within the voltage range of 0.5 to 5 volts, showing that the work function for emission of electrons into the barrier material from the adjacent metal is of the order of 3 electron volts. From the amount of the tunnel resistance it is concluded that the thickness of the potential hill is of the order of 10 to 20 Angstrom units. The simultaneity of applied voltage and tunnel current is demonstrated.
Eddy-Currents in Solid Cylindrical Cores Having Non-Uniform Permeability
Authors: Aspden Harold 
Published: April 2005

A method of estimating magnetization losses due to eddy-currents in solid cylindrical cores of ferromagnetic material is given. The conception of complex permeability is introduced to show the effects which hysteresis has upon the degree of flux penetration. A formula is given for the effective permeability which should be used in the classical treatment in which nonlinearities have been ignored.
An arbitrary case in which the permeability changes across the core section is considered and the solution is extended to a core which is homogeneous, but whose permeability changes with the degree of magnetization. In this way errors due to a nonlinear B-H curve are reduced and the complex permeability notation is shown to lead to a more reasonable Steinmetz relationship.
The eddy-current anomaly is mentioned and it is noted that the theory developed is suited to a consideration of the anomaly as explained in terms of time-lag effects.
The Radiation Resistance of Resonant Transmission Lines
Authors: Chipman R. A. , Carr E. F. , Hoy N. A. , Yurko M. 
Published: April 2005

For resonant sections of a transmission line consisting of parallel silver rods extending vertically above a metal ground plane, the resonance curves of input admittance as a function of line length have been drawn by a synchronized recording meter apparatus, and the effective total resistance of each resonant line calculated. This has been done for frequencies between 300 Mcps and 1400 Mcps, for resonant line lengths up to several wavelengths, for line sections with both open-circuit and short-circuit termination at the top, and in each case with and without a large metal pipe shielding the test line. Radiation resistance is obtained as the difference between the resistance calculations for any one resonant line section unshielded and shielded.
With a probable error of about 5 percent the radiation resistance is found to be proportional to the square of the frequency, and to be independent of line length and of whether the top termination is an open circuit or a short circuit. The absolute values agree reasonably well with the theory of Storer and King [Proc. Inst. Radio Engrs. 39, 1408 (1951)] and disagree conclusively with some predictions of earlier theories.