bluuebunny/crossref_metadata_2025_split huggingface dataset:
Activation of Thermionic and Photoelectric Cathodes
Authors: Klemperer D. F. 
Published: April 2005

Thermal regeneration of an adsorptive capacity in oxidized metals and semiconductors is identified with a nonspecific tendency for oxygen atoms to bury themselves. This process, which often occurs at room temperature, leads to a positive surface potential, and the thermionic or photoelectric emission of electrons is enhanced. Photoelectric measurements which are in line with this view are presented for titanium undergoing interaction with oxygen. The emission value of the clean metal was doubled after thermally regenerating the surface at 400°C.
Activation of the electron emission of surfaces bearing thin skins of foreign oxides is ascribed to a surface configuration which is essentially similar to that of thermally regenerated metals and semiconductors. The emission from oxide-coated cathodes (thick layers of foreign oxides), is regarded as a maintained form of exoelectron emission which arises from innumerable donor centers produced during the activation process; electrons which have been emitted are replaced from the underlying metal.
Attention is finally drawn to the use of electronegative elements other than oxygen for increasing the electron emission of metal surfaces.
Theory of Noise in Magnetic Recording Tape Coated with Magnetic Particles
Authors: Mikami Itsuo 
Published: April 2005

A theoretical investigation is made on the mechanism of noise in magnetic recording tape coated with magnetic particles. It is shown that, for the tape in saturated remanence, noise does not originate from the finite size of particles, but from other factors such as finite concentration of particles, voids, aggregation of particles, and periodic imperfection. For demagnetized tape, however, those factors give a negligible noise. Hence, the origin of noise in the magnetized tape differs from that in the demagnetized one.
It is also shown that the theoretical results agree with the experiments by taking into account the fact that the true volume of single particles is smaller than the apparent volume. The theoretical signal-to-wideband-demagnetized-tape-noise ratio is independent of tape velocity and is about 56 db for the commercial audio tape of ¼-in. track width.
Heterodyne Properties of a Three-Level Quantum System
Authors: Wells Willard H. 
Published: April 2005

It is well known that a three-level system functions as a mixer for radiation at its three resonant frequencies. Here the topic is treated in detail by analogy to a three terminal-pair circuit element, one pair for each frequency. To one pair, fixed power is applied from a local oscillator, or ``pump.'' Attention is then centered on the other two pairs to determine their small-signal response and transfer characteristics. A slight generalization of the impedance concept takes account of the frequency changes and allows the results to be expressed as self-impedance at each terminal pair, and a transfer impedance between pairs. The damping effect of molecular surroundings is taken into account. The three-level maser is a special case in which the terminal pair for the idle frequency is open, and the self-impedance at the signal terminals has a negative resistive part.
Quantization of the radiation field is included by expressing quantum uncertainties in the same form as classical noise, i.e., correlation functions and power spectra. The means for doing this comes from a formalism which connects noise theory to quantum theory through the fact that the Wigner density of linear systems, such as modes of the radiation field, varies with time exactly like a classical probability density. The rules for using this technique are stated as needed without proof. The photon concept is not used.
The method is extended to include a system pumped by broad-band noise.
Determination of Twin Fault Probabilities from the Diffraction Patterns of fcc Metals and Alloys
Authors: Cohen J. B. , Wagner C. N. J. 
Published: April 2005

Twin faults may be detected from diffraction patterns of fcc metals and alloys by two existing methods: (1) from the sine coefficients of a one-dimensional Fourier series representing the peak, and (2) from the excess intensity between two peaks which are asymmetric in opposite directions, such as the 111 and 200. However, the contribution of twin faults to the particle size measured by Fourier analysis appears too large when the fault probabilities are determined by these methods.
A third technique has been developed based on the displacement of the center of gravity of a peak from the peak maximum, ΔC.G. The displacements for the 111 and 200 peaks are related to the twin fault probability β: ΔC.G. (∘2θ)111=+11β tanθ111ΔC.G. (∘2θ)200=−14.6β tanθ200. By using two peaks, such as the 111 and 200, the difficult choice of background and instrumental effects can be minimized. A comparison of the three techniques is presented.
As a consequence of the new method, it is clear that the probability of deformation stacking faults (α) should be measured from the displacements of peak maxima from those of an annealed specimen; if the C.G. is used and twin faults are present, a large error is possible.
Alternating-Current Generation with Moving Conducting Fluids
Authors: Haus H. A. 
Published: April 2005

A one-dimensional, small-amplitude analysis is presented of alternating-current generation by a stationary electromagnetic circuit coupling to waves in a moving, perfectly conducting fluid. In a uniform applied dc magnetic field the waves in the fluid are either compressional waves if the time-average velocity v̄0 is transverse to the dc magnetic field, or Alfvén waves if it is along the dc magnetic field. It is shown that, for velocities v0 greater than the velocity of propagation c of the compressional or Alfvén waves, self-excited oscillations may be produced in a resistively loaded coil coupling to the fluid. In a traveling-wave circuit and in a resistively loaded distributed circuit coupling to the fluid, growing waves are found which result from a transformation of the fluid energy into electromagnetic energy. There is a close analogy between these power-generation mechanisms and those employed in microwave electron-beam tubes.
The results of two- and three-dimensional analyses are summarized in order to show that the phenomena predicted by the simplified one-dimensional analysis occur in less idealized geometries. Possible applications are briefly discussed with reference to ac power generation by using combustion gases or a flow of a high-temperature plasma.
Increase in Dielectric Constant during Switching in Barium Titanate and Triglycine Sulfate
Authors: Fatuzzo Ennio 
Published: April 2005

The increase in dielectric constant and losses during switching was measured in barium titanate and triglycine sulfate (TGS) at frequencies up to 2 Gc. These measurements revealed the presence of two relaxations, one at low frequencies (described by Landauer, Young, and Drougard) and a new one at higher frequencies. The relaxation frequency of this new relaxation is 100 Mc in the case of triglycine sulfate and higher than 2 Gc in the case of BaTiO3. The value of Δε′ at the relaxation frequency is 2 for triglycine sulfate and 1.2 for BaTiO3.
A model which explains the experimental facts is given. The increase in dielectric constant and losses is attributed to oscillations of the ``side'' walls of the ferroelectric domains in the case of the high frequency relaxation. The low-frequency relaxation is believed to be due to oscillations of ``front'' walls of the newly formed domains.
Electrical Conductivity of Cesium-Seeded Atmospheric Pressure Plasmas near Thermal Equilibrium
Authors: Harris Lawson P. 
Published: April 2005

Measurements have been made of the electrical conductivities of gaseous mixtures formed by the addition of small fractions of cesium vapor to nitrogen, helium, neon, or argon. The mixtures were maintained near thermal equilibrium at temperatures in the 1500°–2000°K range and a total pressure of one atmosphere. The cesium vapor pressures ranged over two decades, from 0.1 to 10 Torr.
The apparatus consists, in essence, of two heated zones connected by a slow flow. The first zone is a low-temperature (200°–400°C) oven where the body-gas flow picks up the cesium vapor. The second zone is a small electrically heated furnace (1250°–1850°C) containing a diode test section.
The principal measurements taken were the seeding temperature, furnace temperature, and voltages and currents in the test section.
The results exhibit variations with temperature, seeding pressure, and gas species that correlate reasonably well with simple theory and values for electron collision frequencies and cross sections taken from the literature.
Hypervelocity Impact of Radioactive Projectiles into Stainless Steel and Aluminum
Authors: Rolsten R. F. , Schmitt R. A. 
Published: April 2005

Radioactive, cylindrical, steel projectiles were explosively accelerated into plates of stainless steel and aluminum. The amounts of radioisotopes Fe59 and Cr51 in the projectile prior to acceleration and in the crater in plate were measured in order to determine the fraction of the original projectile remaining in the crater.
Impact experiments with steel plates showed that 3.4 to 7.8% of the original projectile remained in the crater of the steel plate; 3.6 to 7.5% of the original projectile remained in the crater of the aluminum plate. Data on any given crater, obtained by the measurement of both Fe59 and Cr51, are in good concordance. The fraction of the projectile remaining in the crater is independent of the impact velocity over the range of 12 000 to 14 900 ft/sec (3600 to 4540 m/sec).
Improved Thermionic Emitter Using Uniaxially Oriented Tungsten
Authors: Weissman Ira , Kinter M. L. 
Published: April 2005

Emission from most practical electron sources is nonuniform over the emitting area. Ordinary metallic surfaces are polycrystalline and their emission comes from many different small crystal facets whose work functions can vary over a wide range of values. As an example, the range of work functions of tungsten goes from a low of 4.3 eV for the (116) face to a high of 5.9 eV for the (110) face. Substantially improved uniformity of work function and current density would result if the entire emitting surface contained only a single-crystal plane. The use of a single crystal as a means of obtaining such a surface is costly and wasteful since its unique bulk properties are superfluous and do not in any way contribute towards the improved performance. Even more important, using a single crystal inherently limits one to planar geometries.
Many polycrystalline materials of arbitrary shape, among them the refractory metals, when prepared by chemical vapor deposition can be made to exhibit a high degree of uniaxial crystal orientation with their preferred axis centered about the direction of growth. Given proper treatment after deposition, the surface of such materials predominantly consists of a single-crystal plane.
In this paper, X-ray, optical, and thermionic-emission measurements are described which were made on vapor-deposited tungsten prepared by the hydrogen reduction of tungsten hexafluoride. By comparing volt-ampere characteristics of high-vacuum diodes, one of which contains a conventional tungsten filament and the other a chemically vapor deposited one, of identical dimensions, it is found that there is an expected improvement in emission uniformity due to the uniaxial grain orientation in the latter.
By a similar comparison of cesium-neutralized energy-converter diodes, it is shown that the improved surface uniformity results in significantly improved power quadrant characteristics.
Work Hardening and Dislocation Arrangement of fcc Single Crystals. II. Electron Microscope Transmission Studies of Ni–Co Single Crystals and Relation to Work-Hardening Theory
Authors: Mader Siegfried , Seeger Alfred , Thieringer Hans-Martin 
Published: April 2005

The dislocation arrangement in the primary glide plane of deformed Ni–Co crystals of different compositions and stacking fault energies was investigated by the transmission electron microscope technique. The thin foils were found to contain mainly dislocations of the primary glide system close to the edge orientation. Very few screw dislocations were observed; they were presumably lost during the preparation. Straight dislocations in 〈110〉 directions, presumably Lomer-Cottrell dislocations, were found in particular at intermediate and low stacking fault energies. The dislocation density shows local variations so that ``dislocation braids'' can be discerned from the background. For Ni+40% Co, the dislocation densities and arrangements are compared with slip line results obtained from the same crystals. These results are found to be compatible with the so-called glide-zone model and the geometrical interpretation of the slip-line pattern based on it.
The final section deals with the dynamic aspect of plastic deformation and with the theory of work hardening by long-range stresses. It is shown that the experimental observations fit this theory. Some objections that have been raised against the theory are discussed and met.
A Low-Density Plasma for Molecular Ion Dissociation
Authors: Stirling W. L. , Matlock O. D. , Hoy H. C. , Meece V. J. 
Published: April 2005

A hydrogen arc has been developed which produces a low-density plasma column. The electrodes of the arc discharge are geometrically arranged such that the plasma drifts through a hole in the arc anode along a flux tube of the confining magnetic field.
A differentially-pumped vacuum system was constructed which achieved a base pressure of 2.5×10−10 Torr in the inner liner region while at liquid-nitrogen temperature. A density of about 1010 particles cm−3 can be achieved in the plasma column contained in the inner liner region, down field from the arc chamber, with a gas flow of 2 cm3 min−1 into the arc chamber. At this flow, the pressure in the inner liner rises to 3×10−9 Torr. The ion-to-neutral density ratio under these conditions is about 30 to 1 in the inner liner region.
Optical Properties of Powders. Part I. Optical Absorption Coefficients and the Absolute Value of the Diffuse Reflectance. Part II. Properties of Luminescent Powders
Authors: Melamed N. T. 
Published: April 2005

The optical properties of powders are determined for the case of particles, large compared with the wave-length of light. The solution for the diffusion of light in a quasi-infinitely thick powder is applied to relate certain measurements obtained on powders with the corresponding properties of the bulk material.
In Part I, the diffuse reflectance R of a powder is first derived in general form in terms of the parameters of the individual particle, taking into account both internal and external scattering. Parameters are then obtained for a model for randomly shaped particles, and used to relate the diffuse reflectance to the optical absorption coefficient, the index of refraction, and the particle diameter. The relationship is compared with measurements on materials of different refractive indices.
Part II deals with applications to luminescent powders, the calculation of the characteristics of emission in the presence of optical absorption, and the calculation of cascade transfer yields.
Ferromagnetic Resonance in Thin Films with Perpendicular Fields at Radio Frequencies
Authors: Hasty Turner E. 
Published: April 2005

Ferromagnetic resonance absorption in thin Permalloy films has been studied at frequencies from 1 to 50 Mc with the steady magnetic field applied perpendicular to the plane of the film. This technique provides a direct means of measuring the saturation magnetization since the rf resonance absorption occurs when the applied field is equal to 4πM+Hk. The main problem with this experiment is that of keeping the film oriented so that at least parts of it are exactly perpendicular to the applied field. A misorientation of 20 sec causes the precession frequency at H = 4πM+Hk to shift from zero to 90 Mc. This problem was overcome by using a cross modulation field.
The width of the absorption line at 2 Mc for a typical film was 22 Oe. The linewidth increased with frequency until a maximum width of 65 Oe was observed at 15 Mc. As the frequency was increased past this, the linewidth began to decrease and a number of subsidiary absorption peaks began to appear below the main line. This behavior is attributed to the roughness of the film surface.
Spin-Wave Resonance in Films Magnetized Parallel to the Surface
Authors: Wolf Peter 
Published: April 2005

A theoretical analysis is presented for spin-wave resonance in thin ferromagnetic films magnetized in the plane of the film by a dc field. It is shown that, at very high frequencies, a spin-wave resonance spectrum occurs if a suitable surface anisotropy is present.
The analysis is based on the Landau—Lifshitz equation and Maxwell's equations. Both surfaces of the film are assumed to possess uniaxial surface anisotropies of equal magnitude with the axes normal to the plane of the film. Magnetization precession is excited by a weak rf field applied in the plane of the film but perpendicular to the dc field and equal at both surfaces of the film.
The boundary conditions for the magnetization1 are different for the oscillating component Mn normal to the film and the component Mp in the plane of the film. The component Mn is influenced by the surface anisotropy and, therefore, more or less pinned at the surfaces. However, the surface anisotropy has no influence on the component Mp, and accordingly, the derivative of Mp with respect to the normal direction vanishes at the surfaces. To fulfil these and the electromagnetic boundary conditions, three linearly independent wave solutions of the Landau—Lifshitz equation and Maxwell's equations are required.
The amplitude of the spin-wave modes and their spacing depends not only on the surface anisotropy constant Ks but also on the frequency ω of the rf field. At frequencies ω, much smaller than 4πMγ the precessional cone is very flat with Mn&lt;&lt;Mp. In this case the influence of the surface anisotropy is weakened and the rf field can strongly excite only one spin-wave mode, the slightly disturbed uniform precession. The other modes are weak. At frequencies equal to or higher than 4πMγ, the cone of precession becomes nearly circular with Mn ≈ Mp, and the pinning action of the surface anisotropy increases correspondingly. At these higher frequencies, two modes are excited strongly.
Theoretical absorption curves for Permalloy films with 4πMγ ≈ 2π·30 Gc are calculated for two frequencies and a range of thicknesses. For the surface anisotropy constant a value of 1 erg/cm2 is chosen. At 10 Gc only one strongly excited mode is predicted. At 30 Gc two modes have large amplitudes. The amplitude of one mode increases with increasing film thickness, whereas the amplitude of the other mode remains approximately constant. This theoretical result is similar to the experimental findings of Chen and Morrish2 at 24 Gc which, however, the authors explained in terms of stratified layers within the film.
Effect of Hydrogenation on the Paramagnetic Resonance of Gd in Pd and Pd-Rich Alloys
Authors: Shaltiel D. 
Published: April 2005

Paramagnetic resonance of Gd in Pd and rare-earth-doped Pd has been reported recently.1,2 It was shown that a strong interaction with a long range exists between the conduction electrons and the spin part of the localized rare-earth ions. This was exhibited via the g shift of the Gd in pure Pd, with respect to its ionic value, e.g., g = 1.992±0.001, and the additional shift of the resonance when additional rare-earth impurities were alloyed into the Pd. The interaction and its range are attributed to the high density of states of the unfilled d band of the Pd. In Pd-Ag alloys the Gd g value shifts continuously toward its ionic g value with the increase of the silver content. This shift has the same behavior as the decrease of susceptibility with the increase of Ag concentration.1 For 40% Pd 60% Ag the g shift, as well as the susceptibility, are almost zero. These results confirm the above statement.
When Pd is hydrogenated the g value of Gd changes from 1.88 for the pure sample to 2.00 for a sample with H:Pd ratio of 50%. Thus hydrogenation shifts the g of Gd back to its ionic value. Alloying rare-earth impurities into Pd broadens the Gd line but produces no g shift in the hydrogenated samples. These results show that the interaction between the Gd localized moment and the conduction electrons is largely suppressed. This is expected from the fact that hydrogen reduces the anomalously high susceptibility of Pd.
The Gd resonance in mixed α and β phases (H/Pd from 5% to 60%) shows two lines: one at g ≈ 2.00, the other at g ≈ 1.90 corresponding to the lines in the separated β and α phase, respectively. The line intensities are roughly proportional to the amount of each phase present. This result contradicts Mott's hypothesis that the linear decrease of the Pd susceptibility with the increase of the hydrogen concentration is caused by filling the holes in the Pd d band with the hydrogen electrons.3 If Mott's hypothesis were correct, a continuous shift of the Gd g value, as in the case of Pd-Ag alloys, would be expected. We, therefore, conclude that the linear decrease of the susceptibility with hydrogen content is due to the proportion of the α and β palladium.
The additional increase of the linewidth in β palladium with increase of Gd or other rare-earth concentration is mostly accounted for by dipole-dipole broadening. Even with signal-to-noise ratios of 2000:1 only one line was observed. Despite the fact that powdered samples were used, the shape closely approximates a Lorenzian line. Therefore, we have assumed that all the seven ΔM = ±1 transition lines of the Gd 8S7/2 state are included in this line. The extrapolated linewidth for zero Gd concentration was 80 G. This gives an estimated upper limit for the zero field splitting of Gd in β palladium of 5 10−4 cm−1.
Influence of Particle Size on the Coercive Force of Barium Ferrite Powders
Authors: Tenzer R. K. 
Published: April 2005

The influence of milling on the intrinsic coercive force (Hci) of different ferrite powders has been studied recently by several investigators. These have ascribed changes of coercive force to dislocations which are introduced through milling and are removed through subsequent annealing.
In our own studies of barium ferrite powders we relate the changes of Hci to changes in particle size. This interpretation is supported by experimental data and electron micrographs. The large particles of barium ferrite material (calcined at 1300°C) change during ball milling from predominantly multidomain size (several microns) to nearly superparamagnetic size (0.02–0.5 microns). Accordingly, coercive force increases at first and then decreases as milling is extended.
Annealing of ball milled material between 800° and 1100°C results in slight sintering. Since the sintering reduces the number of nearly superparamagnetic particles, considerable increases in coercive force occur.
These interpretations are further supported by the temperature dependence of the coercive force. After short milling, when multidomain particles are still predominant, Hci decreases as temperature of powder is lowered. After extended milling, however, this effect changes sign which is attributed to thermal fluctuations of the magnetization in nearly superparamagnetic particles.