bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Speed Microwave Switching of Semiconductors
Authors: Garver R. V. , Spencer E. G. , LeCraw R. C. 
Published: April 2005

The high-speed microwave semiconductor switch, employing an n-type germanium diode, has been further investigated to determine the ultimate switching speed. Data are presented which show that pulse rise and decay times are as fast as 3 mμsec. This limit is imposed by the capacitances and inductances of the equipment and is not intrinsic to the germanium diode. The ultimate rise and decay times are determined by relaxation processes in the germanium, and are expected to be faster than 1 mμsec.
Two switching pulses of variable spacing in time were employed to show that there are no essential residual processes in the germanium following the application of a pulse. Since there is then no measured dead time of switching, the pulse-repetition rate is limited by the rise times and decay times.
Measurements have been made on a series of semiconductor switches using different concentrations of donors. As the concentration is decreased, avalanche breakdown occurs at higher negative voltages which allows switching of higher microwave powers. Successful operation has been obtained with microwave powers as high as one watt impinging upon the semiconductor switch. In general, rise and decay times tend to increase as donors decrease. Thus, rise times and decay times of 10 mμsec were obtained at one watt of microwave power.
Simple Geometric Model for the Effect of Porosity on Material Constants
Authors: Euler Ferdinand 
Published: April 2005

The effect of porosity on several material constants can be described by three types of empirical functions. One of these features linear increase from zero to unity of the relative bulk material constant when the relative density increases from π/6 to 1. An almost identical function results from application of a theoretical model with the following properties.
(1) The porous compact is divided into two systems: first, isolated pores in a continuous solid matrix; second, solid grains mixed with continuous voids.
(2) The geometry of both systems is assumed to be a cubic array of equal spheres. With this simplification, the relative bulk material constants of each system are calculated as functions of the relative density. The equations obtained are valid for those material constants which are ratios of corresponding fluxes and forces in the sense defined by Maxwell (e.g., the electric conductivity).
(3) Weight factors for the presence of either system are introduced.
(4) The weight factor for the system of isolated pores is assumed equal to the relative bulk material constant of the total compact for all values of relative density.
The implications of this model to the mechanism of sintering are discussed.
Lifetime in Pulled Silicon Crystals
Authors: Bittmann C. A. , Bemski G. 
Published: April 2005

Lifetime data of 46 pulled silicon crystals are interpreted in terms of the Shockley-Read recombination theory. The data are consistent with the theory under the assumption of a single recombination level and a constant concentration of recombination centers, independent of the resistivity of the crystals. However, it is not possible to distinguish between two possibilities as to the location of the recombination level in the lower or the upper half of the energy gap by this type of experiment.
The energy levels thus obtained are at 0.17 ev from the valence band or 0.20 ev from the conduction band in p-type silicon and at 0.22 ev from the valence band or 0.25 ev from the conduction band in n-type silicon.
Maser Oscillators
Authors: Helmer J. C. 
Published: April 2005

Two maser oscillators have been constructed and operated. The behavior of one maser has been observed under various operating conditions by comparing it with the second maser which is used as a reference standard. The expeimental setup is shown and experimental results are given. The frequency-pulling effects of the beam and the oscillation amplitude as a function of cavity-tuning are compared with the theoretically expected behavior. It is shown that the simple behavior predicted by theory exists only for oscillation frequencies which are well removed from line center.
The theoretical curves are obtained from a new analysis which includes the velocity distribution in the beam. A comparison is made between the velocity-distributed and uni-velocity theories. It is shown that the introduction of the velocity distribution drops the maximum beam efficiency from 1 to 0.76 and causes a region of stability to appear in the beam frequency-pulling function.
Rectification Properties of Metal-Silicon Contacts
Authors: Wurst E. C. , Borneman E. H. 
Published: April 2005

Area contacts of twenty different metals were made on n and p silicon. The contacts were applied by the use of jet plating techniques, with the exception of alkali metal contacts which were pressure contact or mercury amalgam contact. A qualitative correlation is shown to exist between the work function of the metals and the rectification of these metals on n and p silicon. I–V characteristics taken on eleven of these metal-silicon contacts lend further support to this picture. Consideration of a quantitative work function model is made difficult due to the many errors and interpretations involved in using metal work function values.
Transistor structures were made and studied for several of the metal-silicon contacts. From analysis of this transistor data it is found that an excess current three orders of magnitude greater than theory predicts, must be present in the diodes made from these metals. This excess current is not adequately explained by any presently known mechanism.
Solar Radiation and Atmospheric Attenuation at 6-Millimeter Wavelength
Authors: Whitehurst Robert N. , Copeland Jack , Mitchell F. H. 
Published: April 2005

A microwave radiometer of the Dicke type for the 6-mm wavelength range has been built and operated to measure radiation from the sun and attenuation in the earth's atmosphere. The total vertical attenuation in the earth's atmosphere on four clear summer days averages 1.2 db. It is presumably due principally to oxygen, since the 6-mm wavelength is well up on one wing of the 5-mm absorption line. The quoted values are in agreement with a line-width constant of 0.02 cm−1. Attenuation in clouds is highly variable. An additional 1 db above the fair-weather value is typical for a thin overcast.
Measurements during the summer of 1956 indicate an effective solar temperature of about 4500°K. This value is appreciably lower than temperatures reported at 7.5 and 8.5 mm, and it favors a model of the lower chromosphere which assumes temperatures well below the optical surface value of 5700°K.
Magnetic Induction and Coercive Force Data on Members of the Series BaAlxFe12−xO19 and Related Oxides
Authors: Van Uitert L. G. 
Published: April 2005

Oxides having the magnetoplumbite structure and a wide range of magnetic properties have been examined. The magnetic saturations of the compositions MIIFe12O19 can be lowered by replacing part of the iron with the ions Al3+, Ga3+, Mn3+, Cr3+, and Ge3+ amongst others. MII in the above formula can be Ba2+, Sr2+, or Pb2+. Calcium can replace these ions in part. Even the samples with magnetic saturations below 200 gauss can be prepared as crystallographically oriented compacts. Contrary to its behavior in ferrites, Ga3+ does not appear to occupy tetrahedral sites in the magnetoplumbite structure.
Evidence is presented for the occurrence of points of magnetic compensation in the BaAlxFe12−xO19 series. As the aluminum contents of the materials increase toward such a point, the ratio 2K/I (where K is the magnetocrystalline anisotropy constant and I is the saturation magnetization) also increases. As a consequence the ferromagnetic resonance frequencies associated with the materials move to higher frequencies, and extremely high coercive forces are realized.
Magnesium-Copper-Manganese-Aluminum Ferrites for Microwave Applications
Authors: Van Uitert L. G. 
Published: April 2005

Magnesium-manganese-aluminum ferrites prepared by dry pressing techniques are usually fired in the temperature range between 1350 and 1400°C for extended periods of time to obtain samples having high relative densities. When about ten percent of the magnesium in such a system is replaced by copper, as in the series Mg0.9Cu0.1AlxFe1.75−x Mn0.04O4±, it is possible to obtain samples with high relative densities and dc resistivities by firing in the 1250 to 1300°C range. Such materials are suitable for microwave applications.
The preparation of ferrites of this type is discussed and data presented on the saturation inductions, Curie temperatures, densities, and dc resistivities.
Electrical Resistivity of Cyclohexane as a Function of Temperature and Water Concentration
Authors: Staudhammer Peter , Seyer William F. 
Published: April 2005

An equation relating the potential applied to and the current flowing in a liquid dielectric has been derived. The theoretical equation predicts that beyond a certain threshold potential the current is independent of the applied potential and is proportional to the number of ions produced per unit volume per unit time.
Measurements of the number of ions produced in cyclohexane as a function of temperature and water concentration were made. It was found that in the pure state about 200 ions/cm3-sec were produced, while in the water saturated cyclohexane at 50°C about 1.6×105 ions per cm3 per sec were produced. It was concluded that the conductance in the pure state was due to ionization by cosmic radiation.
When the cyclohexane was saturated with water, a large increase in the conductivity was observed as the cyclohexane passed through the freezing point. This behavior corresponds to an increase in the dielectric constant as noted by Seyer and Barrow.
Electric Strength and Liquid Structure
Authors: Lewis T. J. 
Published: April 2005

Recent work on the electric strength of pure hydrocarbon liquids has shown that the strength is probably determined by the amount of energy lost by conduction electrons exciting molecular vibrations by collisions while moving under the applied field through the liquid. The strength can then be determined in terms of a mean free path for the collisions involved. The present paper attempts to show that the liquid structure, i.e., the molecular arrangements in the liquid phase, is also influencing the strength, and this is illustrated by measurements of the temperature effect on the strength of some n-paraffins, the molecules of which are known to pack with their long axes parallel producing a degree of anisotropy.
Distinct breaks in the electric strength vs temperature characteristics are found, even when density changes are accounted for, and these occur at temperatures which are in very good agreement with similar breaks in the characteristics of other properties such as density, viscosity, and heat capacity. These breaks have already been associated with changes in liquid structure from quasi-crystallinity to molecular libration (245°K) and from molecular libration to free rotation (288–353°K). If molecular orientation takes place in the applied field then the electron energy loss will be different in the three liquid ``phases'' and would account for the observed transitions in the breakdown characteristics.
Hydrodynamic Theory for the Flow of a Viscoelastic Fluid
Authors: Pao Yoh-Han 
Published: April 2005

A hydrodynamic theory for the flow of a viscoelastic fluid is formulated and applied. The viscoelasticity is specified in terms of the conventional and well-known relaxation and retardation spectra. Time dependent recoverable strains are defined with respect to convected rotating coordinate axes. The theory is linear to the extent that these strains are small although the over-all displacement gradients of the fluid may be large. The theory is applied to two-dimensional steady-state simple shear flow to predict the variation of the apparent viscosity and the steady-state elastic compliance with shear rate. Pressure flow through a pipe of circular cross section has also been treated.
Previous work of a similar nature is reviewed.
Space Charge Effects in Beam-Type Magnetrons
Authors: Gould Roy W. 
Published: April 2005

A theoretical treatment of space charge effects in beam-type magnetron amplifiers and oscillators is given. It is assumed that the beam is relatively thin and that the magnetic field is large. The ``cyclotron waves'' are not treated. A space charge parameter appears in this theory of magnetron-type traveling-wave interaction in a manner which is analogous to the manner in which QC appears in ordinary traveling-wave interaction. A distinctive feature of the space charge waves in the magnetron case is that one increases along the beam and the other decreases along the beam. A simple physical explanation of this effect is given.
This theory is then used to determine the starting conditions of an M-type backward wave oscillator. It is found that when the tube is long in space charge wavelengths there is an appreciable reduction of starting current. When the space charge parameter approaches zero, the solutions found here reduce to the usual two-wave solutions.
Magnetostriction of Aluminum-Iron Single Crystals in the Region of 6 to 30 Atomic Percent Aluminum
Authors: Hall R. C. 
Published: April 2005

The spontaneous saturation magnetostriction and the forced magnetostriction were measured on slowly cooled single crystals of the ferromagnetic aluminum-iron alloys in the composition range from 6 to 30 atomic percent aluminum. The value of the first constant of spontaneous saturation magnetostriction at 6 atomic percent aluminum is similar to that at 6 atomic percent silicon in iron. At compositions containing larger amounts of aluminum, the first constant becomes very large; however, near 30% aluminum the constant drops and approaches zero. The second constant of spontaneous saturation magnetrostriction is negative below 17% aluminum, reaches a maximum near Fe3Al, and drops near 30% aluminum.
Values of the isotropic forced-magnetostriction constant below 25 atomic percent aluminum were found to be slightly higher than that for iron but less than that for silicon iron. Above 25% aluminum the isotropic constant became very large. The anisotropic forced-magnetostriction constants were the largest for the single crystal having 29.6% aluminum; a good fit of the experimental data to the calculated curve was found for this alloy.
Resonance Absorption of Neutrons by Thorium Cylinders
Authors: Davis Monte V. 
Published: April 2005

The integrated effective resonance neutron absorption cross section of thorium-232 cylinders has been experimentally investigated by danger coefficient measurements in the Hanford Test Pile. The results were interpreted to yield the effective resonance integral as a function of the surface-to-mass ratio of the thorium cylinders. The experiments were extended to determine the Doppler coefficients resulting from heating the thorium in a constant neutron energy spectrum in the reactor.
After correction for 1/v neutron absorption, the effective resonance integral can be approximated as a function of the surface-to-mass ratio by ∫ (σa0)effdE′E′=6.11[1+5.0SM(1−0.87SM)]. The value assigned to the Doppler coefficient of the volume absorption of the effective resonance integral is 1A∂A∂T=(2.3±0.2)10−4/∘C. The results are compared to similar measurements on uranium.
Structure and Characteristics of Silicon Carbide Light-Emitting Junctions
Authors: Patrick Lyle 
Published: April 2005

Current-voltage characteristics of SiC p-n junctions have been measured on light-emitting samples prepared in such a way as to minimize leakage at the periphery and through ``blue spots.'' The characteristics of such junctions are found to be very different from those previously reported. We deduce from the characteristics that these junctions have a p-n*-n structure rather than a p-n structure. The high resistivity n* layer is essential for the observed light-emission. This layer, together with the blue spots which short circuit the p-n* junction, determines the form of the reverse characteristic. Two portions of the reverse characteristic take their form from space-charge-limited currents in the n* layer.
A theory is given of the forward characteristic of the p-n*-n structure and compared with the experimental I-V curve. The theory permits one to obtain a value of the thermal energy gap from a forward characteristic at a single temperature. From a fit of our data the energy gap is found to be 2.83±0.1 ev at room temperature.
Results of some experiments on crystal growing are presented and an explanation of the manner of growth of light-emitting junctions is suggested.
Luminescent Gas Flow Visualization for Low Density Wind Tunnels
Authors: Kunkel W. B. , Hurlbut F. C. 
Published: April 2005

At static pressures below a few millimeters of mercury the optical thickness of wind tunnel gas streams becomes insufficient for conventional flow visualization techniques in aerodynamic testing. In the University of California low density wind tunnel, where the free stream static pressure is of the order of one-tenth of one millimeter of mercury, use has been made of various gaseous afterglow phenomena in the visualization of low density flows. The present paper describes the successful application of afterglows in flows of nitrogen, air, argon, and helium.
On the basis of recent tests the range of practicability of the enriched air glow technique was found to extend from Mach 2 to Mach 4. The argon and helium glows were found to be useful in the range Mach 1.3 to Mach 2. Discussion of the ranges of applicability and of other aspects of the observed glows is supported by representative glow photographs.
Studies of Molecular Scattering at the Solid Surface
Authors: Hurlbut F. C. 
Published: April 2005

Experimental studies of molecular scattering at the gas-surface interface are described in which molecular beams of N2 were scattered at surfaces of steel, aluminum, and glass. Polar surveys of the issuing molecule flux indicate the scattering to be well represented by a cosine distribution in most cases. A moderate deviation from such a distribution was observed in the case of the glass-N2 interaction.
It is shown how measurements of scattering at the surface may be used to derive values of the momentum transfer coefficient, f(s), in a rarefied gas flow where s is defined as the ratio of the mass speed of the flow to the most probable thermal speed of the molecules. In order to complete the calculation where scattering information alone is available from experiment, assumptions must be made relating to the energy exchange at the surface. In the case of the present calculation, where a surface interaction model was formed in part from the glass -N2 scattering data, two extremal assumptions relating to the energy exchange lead to values of f(s) of approximately 0.97 at s=0.1.
Magnetization Reversal in Thin Films at Low Fields
Authors: Conger R. L. , Essig F. C. 
Published: April 2005

A statistical theory of magnetization reversal in thin films for reversing fields less than the anisotropy field is presented in which it is assumed that reversal takes place by domain wall motion. The number of moving domain walls is determined by a simple statistical model which allows for the random nucleation of walls as the reversing field increases. Experimental data are presented in support of this theory.
Two equations for the velocity of a domain wall in a thin film are presented; these arise since two alternative forms of the equation of motion of the magnetization vector are considered.
Retardation Effects Caused by Ferrite Sample Size on the Frequency Shift of a Resonant Cavity
Authors: Tompkins J. E. , Spencer E. G. 
Published: April 2005

Using perturbation theory, expressions are derived for the frequency shift of a circularly polarized resonant microwave cavity upon insertion of a ferrite sample small compared with the wavelength. Retardation effects are considered in deriving the rf field h2 internal to the sample. By integrating h1·h2dv (where h1 is the applied rf field) over the sample volume, a closed-form expression is obtained for the cavity frequency shift. The theory is applied to the magnetic resonance in ferrites. The calculated magnetic resonance line shape is found to remain symmetrical as the sample size is increased. Retardation effect, thus, does not explain the asymmetry of the resonance lines which have been observed for polycrystalline ferrite. Results of the theory are also compared with measurements on a single crystal of ferrite having the rather large maximum permeability loss term of 100. Theoretical and measured values are in close agreement.
The theory is also compared with the somewhat different results of other recent theoretical treatments, in which an approximate expression for an effective magnetic dipole moment for the sample was computed, rather than integrating the internal rf fields over the volume of the sample.
Apparatus for the Measurement of Shear Modulus and Internal Friction between 4.2 and 100°K
Authors: Sinnott K. M. 
Published: April 2005

An apparatus has been constructed to measure the shear modulus and logarithmic decrement of polymers from 4.2 to 100°K. The apparatus consists of a small torsion pendulum suspended on a rigid support at the bottom of a large glass Dewar vessel. After cooling to 4.2°K with liquid helium, the pendulum warms up at an initial rate of 0.1° per minute. Torsional oscillations of the pendulum are excited electrically and recorded photographically. The estimated accuracy of the modulus and logarithmic decrement is ±5.0%.
Measurements of the shear modulus and logarithmic decrement have been made, from 4.2 to 100°K, on a series of tetrafluoroethylene-hexafluoropropylene copolymers.
Adiabatic Elastic Moduli of Single Crystal Alpha-Uranium
Authors: Fisher E. S. , McSkimin H. J. 
Published: April 2005

The adiabatic elastic moduli at 25°C for single crystal alpha-uranium are reported here as derived from measurements of high-frequency ultrasonic wave velocities. A detailed description is given of the specimens used, and of the technique employed for obtaining small plates of proper orientation suitable for the problem. Although the specimens were small the technique of measurement produced results of relatively good precision, as evidenced by the numerous cross checks obtained. Best values of the moduli and the estimated probable errors are given.
The elastic stiffness moduli in units of 1012 dynes/cm2 are as follows: c11=2.147 ±0.14%,c12=0.465±0.6%,c13=0.218±1.5%,c22=1.986±0.14%,c23=1.076±0.34%,c33=2.671±0.14%,c44=1.2444±0.10%,c55=0.7342±0.10%,c66=0.7433±0.10%.
Effect of Torsional Stress on the Electrode Potential of Copper
Authors: Nobe Ken , Seyer William F. 
Published: April 2005

The emf of a galvanic cell which consisted of a stressed metal electrode and an unstressed metal electrode was measured. The experimental data showed that for low torsional stresses there was a parabolic relationship between the emf and the torsional stress.
It was observed that the stressed electrode was more anodic with respect to the unstressed reference electrode in agreement with the majority of the previous investigations.
Experimental data of emf and torsional stresses for B & S gauge 12, 14, and 16 hard-drawn copper wires are presented.