bluuebunny/crossref_metadata_2025_split huggingface dataset:
Instabilities in the Smooth-Anode Cylindrical Magnetron
Authors: Harris Lawrence A. 
Published: April 2005

A magnetically focused space-charge cloud of the type found in the smooth-anode magnetron is examined to determine whether a perturbation of the equilibrium condition will grow. A field analysis is carried out in which radial admittances are matched at the edge of the cloud. The solutions for the characteristic frequencies are complex, indicating that the disturbance grows with time. These instabilities occur at multiples of the Larmor frequency.
The solutions indicate that electrons oscillate with increasing swings, a process which absorbs energy. Instability therefore gives rise to some anode current even when the tube is ``cut off'' though rf power is not made available by the process.
Heat Conduction in Alloys at Low Temperatures
Authors: Estermann I. , Zimmerman J. E. 
Published: April 2005

With a view to studying the mechanism of heat conduction in low conductivity alloys, a method has been devised by which the thermal conductivity of relatively small samples (⅛- to ¼-inch diameter, 1 to 2 inches long) of various materials can be measured in the temperature regions obtainable with liquid nitrogen, liquid hydrogen, and liquid helium.
Preliminary measurements on several commercial alloys (monel, inconel, and stainless steel) gave Wiedemann-Franz ratios several times greater than the theoretical value of 2.45×10−8 watt-ohm/deg2, the deviation being greater for annealed than for cold-worked specimens. This has been interpreted in terms of appreciable lattice conduction of heat in these alloys.
Following these results, samples of an alloy of 90 percent copper 10 percent nickel were prepared with varying amounts of cold-work and with different grain sizes. Results with these samples were similar to those obtained with monel and inconel and confirm the hypothesis of lattice conduction. They also give a qualitative indication of the effectiveness of cold-work in limiting the lattice conduction of heat.
The Dielectric Properties of Ice and Snow at 3.2 Centimeters
Authors: Cumming W. A. 
Published: April 2005

A knowledge of the permittivity and loss tangent of snow and ice is essential in studying both radar echoes from snow-covered terrain and the attenuation of microwave energy through snowstorms. To provide this information, a program was carried out at the National Research Council of Canada to measure the permittivity and loss tangent of ice and snow, and also to determine the reflection coefficients of snow-covered surfaces, at a wavelength of 3.2 centimeters.
As a result of these investigations values have been obtained for the permittivity and loss tangent of snow of varying density, temperature, and water content. Theoretical values of the reflection coefficients of snow-covered surfaces, calculated from these data, are compared with the values obtained from the direct measurement of reflections from natural snow surfaces.
The Use of Radioactive Isotopes in a Study of Evaporation from Thermionic Cathodes
Authors: Leverton W. F. , Shepherd W. G. 
Published: April 2005

Radioactive tracers have been used in a study of evaporation of the alkaline earths, barium, strontium, and calcium from oxide coatings on passive nickel bases. Several percent of the total cathode Ba, Sr, and Ca leave a triple oxide cathode during processing and aging. The rates of transfer of these elements from the cathode during life tests of 118 hours at true cathode temperatures from 1175 to 1279°K obey equations of the form, logW=A−(B/T), where W is the rate of transfer in g/cm2/sec, T is the absolute temperature of the cathode, A and B are constants. The transfer of Ba from a BaO cathode obeys a similar law. The mass of Ba transferred in 118 hours of life from a triple oxide cathode at 1123°K true as 2.9×10−6g/cm2, and from a BaO cathode 1.4×10−5g/cm2. The masses of Sr and Ca transferred from a triple oxide cathode at the same temperature were 2.1×10−7 and 1.2×10−8g/cm2, respectively.
Bombardment of the anode by an electron beam during life tests decreased the quantity of Sr observed on the anode. Anode current densities of 5 to 10 ma/cm2 at electron energies of approximately 100 volts produced a fiftyfold reduction in the quantity of Sr on the anode. Experiments indicated that this decrease was not due to heating of the anode. The quantity of Ba deposited on the anode was not decreased by electron bombardment.
The very considerable transfer of Ba from the cathode during processing was greatly reduced by breaking down the carbonates and high temperature flashing the cathodes in the presence of a few mm pressure of argon gas.
A Point Focusing X-Ray Monochromator for the Study of Low Angle Diffraction
Authors: Shenfil Leon , Danielson Warren E. , DuMond Jesse W. M. 
Published: April 2005

A point focusing x-ray monochromator was designed and constructed for low angle scattering studies. The anastigmatic point focus is achieved by means of two cylindrically bent quartz crystals whose focal circles are mutually perpendicular. The beam, emanating from the copper target of an x-ray tube, is reflected in succession, first from the crystal defining the horizontal focal circle, and second from the crystal defining the vertical focal circle following which it comes to a monochromatic point focus of wavelength 1.537A (CuKα1). The sample to be studied is placed between the second crystal and the point focus, and the scattered beam is detected by means of a photographic film placed at the point focus, at right angles to the undeviated beam, the latter being suppressed by means of an absorber, or allowed to pass through a hole in the film.
Mathematical analysis, in which a ray was traced through the two-crystal system, revealed correctly the shape and size of the point focus, and the possibility of reducing the latter in size by stopping down the beam emerging from the target.
Latex Particle Size Determination Using Diffraction Peaks Obtained with the Point Focusing X-Ray Monochromator
Authors: Danielson Warren E. , Shenfil Leon , DuMond Jesse W. M. 
Published: April 2005

We describe the results of experiments we have made, using the point focusing monochromator as the primary tool, to determine the particle size of latex spheres. The suitability of the instrument for this particular study is described and the experimental data obtained are tabulated, these data coming from our experiments with three physically distinct samples of Dow latex. We attempt to make a critical interpretation of the data by considering separately several possible space arrangements which the latex spheres might assume when the water, which is initially the suspending fluid, is evaporated. Corrections for the finite size and shape of the ``point'' focus are described. The absence of a significant difference in the mean particle sizes of the three samples considered is established.
The data from all three samples is combined to yield a mean particle diameter under an external pressure of one atmosphere of 2687.5A with a statistical standard deviation of 1.2A and a fixed (systematic) error estimated to be not more than ±7A.
The Decay and Recovery of the Pulsed Emission of Oxide-Coated Cathodes
Authors: Matheson R. M. , Nergaard L. S. 
Published: April 2005

The decay and recovery of the pulsed emission of cathodes consisting of BaO on nickel are studied. The emission of the cathodes is measured in diodes of cylindrical geometry having water-cooled copper anodes spaced 0.019 inch from the cathode.
Most of the diodes show a decay of anode current when first put in pulse operation. Decays of 2–50 percent are observed during 150-μs pulses. The decay tends to disappear when the tubes are aged under pulse conditions. The peak current is a linearly decreasing function of the logarithm of the duty cycle, even when there is no perceptible decay during the pulses. The rate of decrease is independent of the pulse repetition rate and decreases with cathode temperature.
Current-voltage characteristics during the pulse and recovery periods are obtained by short sampling pulses. A comparison of these characteristics with computed ideal characteristics does not discriminate unambiguously between a variation of emission and a variation of internal cathode impedance as a source of current decay. Studies to separate the contributions of these effects are in progress.
Radiation from a Dielectric Wave Guide
Authors: Whitmer Robert M. 
Published: April 2005

The radiation from an infinite dielectric slab fed by a line source has been calculated from a branch-cut integral. The modal efficiency of the device as a wave guide is defined as the ratio of the power propagated in a mode to the sum of the modal and radiated powers. For a range of the parameters such that only one mode can be propagated, the modal efficiency has been plotted numerically. Except for extreme values of the parameters, the efficiency runs around 80 percent to 90 percent.
The slab form is not one likely to be used in practice, but the efficiency of a cylinder would be expected to have about the same value.
A Lower Bound and Other Properties of the Mean-Square Error of Linear Measurement Systems
Authors: Hammond Joseph L. 
Published: April 2005

The central purpose of this paper is to establish a lower bound on the mean-square error of linear, noisy, dissipative measurement systems designed to measure a constant quantity. A lower bound on mean-square error is determined to be (2kTA)/t, where k is Boltzmann's constant, T is the absolute system temperature, t is the time consumed by the measurement, and A is a parameter of the measurement system closely related to its driving point immittance. This lower bound shows, among other things, that a nonzero measurement interval is required to obtain a useful estimate of the quantity being measured.
The lower bound is arrived at by considering a logical structure for linear noisy measurement systems and mathematical expressions derived for the mean-square error of such systems. The key step in establishing the lower bound is the consideration of the unavoidable random perturbation at the system input due to the generalized Nyquist noise discussed earlier by Callen and Welton. Use of the general lower bound is illustrated by establishing more specific lower bounds for two classes of systems, namely, current measuring galvanometers and thermal detectors. In these cases the lower bounds are consistent with minimum values for the mean-square error of such systems as previously reported in the literature by McCombie.
Piezoelectric Optical-Maser Modulator
Authors: Johnson L. F. , Kahng D. 
Published: April 2005

An optical-maser modulator employing a transparent piezoelectric medium is described. The device is based on multiple interference in transmission or reflection, the intensity in the interference pattern being modulated by a change in thickness of the piezoelectric plate. Using barium titanate it is shown that 80% modulation and 20-Mc bandwidths are readily attainable. A sacrifice of modulation to 10% permits bandwidths ∼200 Mc. A slight modification allows the device to operate purely as a phase modulator.
In addition, an optical-maser modulator employing a grating ruled on a piezoelectric medium is described. Spatial modulation is brought about by a change in grating constant via the piezoelectric effect. As a communication device in conjunction with an optical maser operating at 0.7μ, 10% modulation and a bandwidth ∼10 Mc can be obtained using barium titanate driven near the fundamental resonance frequency.
Color Centers and the Flow Stress of LiF Single Crystals
Authors: Nadeau John S. 
Published: April 2005

Lithium fluoride crystals were exposed to cobalt-60 gamma radiation at 300° and 78°K. Changes of the flow stress and of the optical absorption were measured in an effort to relate the hardening to identifiable color centers.
In crystals irradiated at 300°K there was found to be a good correlation between the flow stress and the concentration of F centers. The magnitude of the hardening, however, suggested that it was caused by interstitial defects. Comparison of the hardening produced by additive coloring with that produced by irradiation indicated that the hardening defects were interstitial fluorines. This direct relation between interstitials and F centers supports a Varley type of mechanism for F-center production in the bulk crystal. Some limited experiments with NaCl and KCl showed qualitatively the same behavior and suggest that the same F-center production mechanism may occur in them.
Irradiation of LiF at 78°K produced stable trapped-hole centers and pulse annealing experiments showed that the Vk center (self-trapped hole) contributed to the hardness at low temperatures. A sharp decrease of flow stress was observed at about 110°K where the paramagnetic resonance experiments of Kanzig and the optical measurements of Wiegand and Smoluchowski indicate disappearance of the Vk center.
Velocities and Densities of Dislocations in Germanium and Other Semiconductor Crystals
Authors: Chaudhuri A. R. , Patel J. R. , Rubin L. G. 
Published: April 2005

The average velocities of dislocations have been measured in four semiconductor crystals-silicon, germanium, gallium antimonide, and indium antimonide. The range of measured velocities was between 10−6 and 2×10−1 cm/sec. The dislocation velocities in these crystals are relatively insensitive to stress when compared to LiF or Si-Fe. The effect of temperature, in the range 0.5 to 0.8TM, on the velocities at various constant stresses was measured and the activation energies for the dislocation velocities were obtained in each of the crystals. No marked dependence of activation energy as a function of the applied stress was obtained.
The effect of strain on the dislocation densities was measured as a function of orientation, temperature, and strain rate. It was found that even in initially dislocation-free crystals, dislocations were generated at quite low stresses. From direct measurements of etch pits and dislocation velocities it was possible to estimate the fraction of mobile dislocations. Under certain conditions the percentage of mobile dislocations was as low as 3 to 8%.
Interactions between the Corona Discharge and a Zinc Oxide Electrode
Authors: Elder Tait 
Published: April 2005

In a negative point-to-plane corona discharge in air, mutual interactions are observed between the electrode and the discharge when the anode is a film composed of zinc oxide incorporated in a resin binder. The current carried by the corona discharge increases by more than fivefold as the zinc oxide becomes negatively charged. When the electrostatic charge on the zinc oxide surface is dissipated by light the current falls to the value which is observed when a metal conductor replaces the zinc oxide resin film electrode in an identical geometry.
Another feature of the discharge interaction is that the zinc oxide resin films are able to accept and retain over 109 electronic charges per square centimeter of excess negative electrostatic charge despite the fact that the bulk conductivity of the films measured electrodynamically either before or after corona charging is often greater than 10−11 Ω−1 cm−1. Selected single crystals of zinc oxide have also been observed to accept and retain electrostatic charge for several seconds after exposure to the negative corona discharge, while concurrent measurements show that the conductivity of the crystals remains unchanged at 10−2 Ω−1 cm−1 throughout the experimental treatment. In both cases the charge can be dissipated by less than 1014 photons/cm2 of actinic light. It was thus possible to make Xerographic prints on single zinc oxide crystals. No effects comparable to these are observed with a positive corona discharge.
The paper is primarily experimental in scope. Support is introduced for the hypothesis that the effect of negative ions of the corona discharge on the zinc oxide resin film surface is the creation of small isolated charged regions, presumably the result of the ``blocking contact'' made with the zinc oxide surface by individual negative ions from the discharge. These regions behave as islands of high resistivity which can accept and retain electrostatic charge even when immersed in a relatively conducting sea of unaltered film material. The anomalous, or unexpectedly high, corona current is then attributed to an increase in conductivity of the corona gap resulting from additional ionization of the air near the charged zinc oxide resin film surface. This ionization is caused by localized high potential gradients in the vicinity of excess negative charges isolated on these islands, and the dissipation of these charges by light thus produces the observed photosensitive decrease in corona current. A comparison is made between the resistive island model and the model which constrains the pigment resin film to behave as a homogeneous insulator after electrostatic charging.
Characteristics of p-i-n Junctions Produced by Ion-Drift Techniques in Silicon
Authors: Mayer J. W. 
Published: April 2005

p-i-n junctions were fabricated by ion-drift techniques using lithium in p-type silicon. Highly compensated intrinsic regions from 0.1 to 5.0 mm were obtained. At temperatures between 120° and 200°C, the space charge of thermally generated carriers in the intrinsic region distorted the lithium ion distribution, producing linear graded junctions whose gradients were between 1011 and 1014 atoms/cm3/cm. Room-temperature capacitance measurements were used to determine the impurity distribution. Agreement was found between calculated and measured values of the impurity gradient. Precipitation of lithium ions in the intrinsic region was not observed.
The increase of the direct current under reverse junction potential as a function of the increased width of the depletion region permitted measurement of the diffusion and depletion-region-generated current components. The value of the diffusion current component at any temperature was proportional to the resistivity of the p-type silicon. The depletion-region-generated component was proportional to the width of the depletion region.
Energy Density Distribution in a Polished Cylinder of Laser Material
Authors: Sooy W. R. , Stitch M. L. 
Published: April 2005

A calculation of the flux distribution inside a smooth-walled laser cylinder is made for two limiting assumptions about the nature of the incident pumping flux. The idealized case of a line source at one focus of an elliptical reflector producing a convergent cylindrical wavefront at the other focus leads in the expected way to a singularity at the center of the crystal, and for sufficiently large values of the product of the doping concentration and diameter, the flux density goes through a minimum before increasing. This corresponds to the relatively rare physical situation in which the laser crystal is much larger than the pump source and both are very small compared to the reflector.
A much more realistic assumption of isotropic flux distribution cannot be integrated in closed form and required a machine calculation. This reveals that the distribution is strongly dependent on doping, and that for light doping the flux density in the central region is approximately three-fold higher than in the peripheral regions. This is used as a hypothesis to explain low observed laser efficiencies by postulating that for typical operation the central region is undergoing laser action while the more voluminous peripheral region is absorbing pump energy and converting it to fluorescence. Some experimental evidence to support this hypothesis is obtained by measurements of the inversion, averaged over the whole crystal, by means of absorptivity measurements. It has been shown that laser action commences while the crystal is still, on the average, absorbing.
High-Temperature Steady-State Creep Rate in Single-Crystal MgO
Authors: Cummerow R. L. 
Published: April 2005

Steady-state, three-point bending deflection rate measurements on single-crystal MgO samples in the temperature range of 1450°–1700°C show that creep is a thermally activated process without an unique activation energy. The measured energies range from 3.5 to about 7 eV. This range of energies can be explained in terms of self-diffusion data if it is assumed that the creep rate is limited by self-diffusion. Small deviations from stoichiometry are shown to be very important in controlling the creep rate as they are in all ionic or electron transport processes. Understanding and control of these deviations are necessary to obtain a quantitative understanding of either steady-state creep or diffusion.
The variation of creep rate with stress can be described by a power law with an exponent varying from 4 to 7. This range of exponent lends some support to the theory based on edge dislocation climb over barriers as the rate limiting step. On the other hand, such barriers have not been observed in single crystals of MgO and other substances, so that some other mechanism in which diffusion is rate limiting may be operating.
The creep rate is apparently independent of subgrain structure, precipitates observed at room temperature, surface roughness, spectroscopically determined impurity content, the valence state of the iron impurity, and dislocation strain pattern after bending.
Crystallinity and Electronic Properties of Evaporated CdS Films
Authors: Dresner J. , Shallcross F. V. 
Published: April 2005

The effect of several processing methods on the crystallinity and electronic properties of evaporated CdS films has been investigated. Diffusion of Cu or Ag at temperatures above 450°C has yielded films composed of crystals of controllable size ranging from 10−5 to 1 cm in diameter. The electron mobility depends strongly on the reorientation of the crystallites but is only slightly affected by their size. The best films obtained have shown mobilities for photogenerated carriers of 300 cm2V−1 sec−1, characteristic of the bulk crystal. Typical values of the total trap density are in the range of 1019 to 1021 cm−3, compared to 1014 to 1016 in single crystals. The resistivity of the high mobility films can be controlled by the addition of Cl or Ga at the proper stage of the processing.
In the photoconductive films, the mobility may vary with the illumination level by an order of magnitude. In films processed at temperatures above 400°C, a model of conducting crystallites separated by thin insulating barriers is insufficient account for the observed results.
Mechanism of High-Power-Density Electron Beam Penetration in Metal
Authors: Schwarz Helmut 
Published: April 2005

Electron beams of approximately 2 kW power and acceleration voltages in the range about 100 kV are focused on metal surfaces in spots of 15 to 250 μ so that maximum power densities of more than 1013 W/m2 can be achieved.
Such electrons penetrate several orders of magnitude deeper into the solid or liquid materials than the classical penetration depth of 100 keV electrons would allow for. A high-speed movie (2500 frames per second) of the process shows that the surface is closed by a liquid film most of the time and that it only ruptures during very short intervals. The temperatures at the surface and in the interior of the welds have been determined during the process, experimentally and theoretically, respectively. Also, the dislocation of the metal within the weld has been studied with an electron-probe x-ray microanalyzer and with radio-active tracing. Measurements of mass density show that it decreases after the material has been affected by the electron beam.
In the discussion, a tentative explanation of the effect is offered.