bluuebunny/crossref_metadata_2025_split huggingface dataset:
Likelihood Detection with a Multiple-Markov Process
Authors: Potter D. S. , Leedham C. D. 
Published: April 2005

The problem of signal detection in the presence of noise has received considerable attention in the literature. The problem is approached historically by minimization of a signal-to-noise ratio. This formulation utilizes the properties of the process under consideration in terms of the frequency content as expressed by the correlation function and/or the power spectral density. The integral equations that evolve have, as their solution, the impulse response or the Fourier transform of the optimum processing device. With this approach, the statistics of the process do not enter the mechanism of solution explicity.
An alternative approach to the problem is to consider the statistics expressed in terms of the distribution function, explicitly. In general, a process with a frequency distribution that is other than white will yield a likelihood ratio in a form that is complicated algebraically. The linear prediction possible with processes that exhibit mth-order Markovian properties allows a solution, however, and this solution embodies both the statistical and the correlation properties explicitly. For the special case of Gaussian statistics, the equivalence with other techniques is demonstrated.
Microwave Generation in Pulsed Ferrites
Authors: Shaw H. J. , Elliott B. J. , Harker K. J. , Karp A. 
Published: April 2005

A pulsed magnetic field applied to a magnetically saturated ferrite sample is capable of initiating a coherent precession and of translating upward both the frequency and energy associated with this precession. A coupled circuit resonance can then extract energy from the system at a desired frequency. For large precession amplitude the rise of the pulsed magnetic field up to the bias field level must be nonadiabatic; the precession buildup is described by computer calculations. To avoid destructive effects of spin-wave buildup, the total risetime of the pulsed magnetic field must be less than a threshold value which depends on the precession angle; this threshold is determined from computer calculations of transient spin-wave growth. Operation within this time allows the precession angle to appreciably exceed the usual steady-state precession threshold set by spin-wave instabilities.
In experiments performed with YIG spheres mounted in an integral circuit element containing a tunable X-band slot resonator and a pulsed field coil, providing pulsed magnetic fields rising beyond 3 kG in approximately 1 nsec, energy in the range of hundreds of W·nsec has been generated over the X-band frequency range, with pulse widths of the order of 1 nsec. The output pulses have good interpulse phase coherence and are studied in detail using a sampling oscilloscope to observe the instantaneous rf waveforms.
Temperature Stabilization of Unsaturated Microwave Ferrite Devices
Authors: Stern E. , Ince W. J. 
Published: April 2005

A technique utilizing a composite magnetic series circuit is described wherein the flux density of unsaturated microwave ferrite is maintained constant in spite of large changes in microwave ferrite saturation magnetization, coercive force, and hysteresis loop shape. The composite circuit consists of a driver, a flux limiter, and a microwave ferrite. The driver supplies the necessary mmf to maintain constant flux level in the circuit throughout the temperature range. The flux limiter, a particularly stable ferrite material, establishes the constant flux level. The driver and flux limiter may lie outside the microwave region and may in consequence possess indifferent microwave properties.
A simple design procedure is described for determining the driver and flux limiter dimensions. Special attention is given to the effects of air gaps and leakage fluxes which tend to reduce the effectiveness of the technique.
A remanence phase shifter is described which suffers a 16% loss of phase shift as a result of an 80°C rise of temperature. By the application of composite circuit techniques, the temperature sensitivity was reduced to less than 2½% over the same temperature range.
Constant-Phase Electrically Controllable rf Attenuator using Permalloy Films at Resonance
Authors: Ngo D. T. 
Published: April 2005

A constant-phase, electrically controllable attenuator using Permalloy films has been investigated both analytically and experimentally. The well known behavior of the permeability as a function of bias field near resonance is utilized. The permeability of a Permalloy film can be expressed as μ=μ1−jμ2. In a film-loaded strip line, the attenuation constant is strongly affected by μ2 while the phase constant depends on the magnitude and sign of μ1. Controllable attenuation with net zero phase change can be realized with the following arrangement: Two film strips, identical in properties and geometry are used in a strip line and both are biased at H0, the resonance bias field, resulting in a maximum attenuation and zero phase shift. Super-imposed is a control field of opposite polarity on the two film strips. If the control field is set at ΔH, then the net bias field is H0−ΔH on one film strip and H0+ΔH on the other, yielding a permeability, −|μ1|−j|μ2| on one and +|μ1|−j|μ2| on the other. As a result, the phase change due to the reactive permeability components cancel each other out and only the attenuation due to the loss component remains.
Such an attenuator has been built and tested successfully over a frequency range from 1 to 3 Gc/sec.
An Integrating Type of Electronic Hysteresigraph
Authors: De Mott E. G. 
Published: April 2005

An electronic hysteresigraph, which integrates without recourse to electromechanical means and is free of drift, has been developed. In operation, a search coil surrounds the magnetic specimen to be tested, and the specimen is then subjected to a change in externally applied magnetic field strength. The time integral of the potential induced in the search coil is a measure of the magnetic flux change in the specimen. The induced potential is applied to a solid-state voltage-to-frequency converter which produces a series of output pulses, the number of which is proportional to ∫edt. These pulses are summed on a digital counter to give a measure of the flux change. A digital-to-analog converter then provides a dc output which drives the Y axis of an X-Y recorder.
A signal proportional to the applied magnetic field strength is simultaneously fed to the X axis of the recorder and a continuous B vs H plot is obtained. This is a real-time mode as the response of the various measuring elements is practically instantaneous.
In considering the integrator, it is interesting to note that absolute accuracy traceability in calibrating the voltage-to-freqency converter is referred directly to the volt, as represented by the standard cell, and to the second, as represented by a crystal-controlled time base. This is in contrast to the generally used secondary standards of mutual inductance and current shunt millivolt drop.
Magnetic Film with Helical Anisotropy
Authors: Thompson D. A. , Finzi L. A. , Chang H. , Albert P. 
Published: April 2005

A helical anisotropy film is characterized by the induced anisotropy of the form K sin2[π(z)−2πz/d], where K is the anisotropy constant, θ is the magnetization orientation, z is the coordinate along the direction of film thickness, and d is the film thickness.
It has been predicted by solving Euler's equation that for film thickness greater than the critical value 2π(A/K)½ (A=exchange constant), stable states may occur in which the magnetization orientation θ follows approximately the helical variation of the easy axis. The magnetic characteristics of a helical film can be clearly demonstrated by the M-H loops of the top or bottom layers, as obtainable with a Kerr magneto-optic apparatus. The transitions from a saturated state to a helical state and from one helical state to another result in multiple-threshold M-H loops.
Nonmagnetostrictive Permalloy films have been electroplated onto a slowly rotating substrate in the presence of a dc orienting field. Samples of 3 μ or more thickness show the helical anisotropy characteristics while a sample of less than 0.5-μ thickness behaves as a uniaxial film. Furthermore, control samples of each thickness have also been electroplated on a stationary substrate. They only show the usual uniaxial anisotropy property.
Effect of Magnetostatic Interactions on the Real and Imaginary Parts of the Transverse Biased Permeability in Thin Ni-Fe Films
Authors: Oredson H. N. 
Published: April 2005

It has been found that the rapid fall off of μ′ (the imaginary part of the permeability) on the low-field side of μ′ vs HT is due to the formation of locking domains, and that in this region the probability density function is not proportional to μ′.
This fall off can be predicted from μ (the real part of the permeability) by assuming that the fall off in μ is due entirely to the effects of locking domains. When this is done, and Δ90, the inhomogeneity in anisotropy magnitude, is determined from the corrected probability density curves the relationship arc sin Δ90=4α90 is found nearly to hold, but a coefficient of 5 gives a better fit to the data. It is suggested that the 5 comes from anisotropies of order higher than 2 due to higher-order interactions. These interactions are responsible for triaxial anisotropy introduced by etching a polycrystalline film into small triangles, and for higher-order anisotropies found by etching small rectangles.
A theoretical expression for the permeability has been found as μ−1=HT−H̄K+Mdπ−1[2A/(HT−H̄K)M]−12[δHb/(1.64)8(HT−H̄K)]2,where HT is the transverse bias field, H̄T is the average anisotropy field, M is the saturation magnetization, d is the film thickness, A is the exchange constant, and δHb is the inhomogeneity in the magnitude of the anisotropy, defined as Δ90 H̄K. This expression gives a very good fit to the data.
Magneto-Optical Properties of Materials Containing Divalent Europium
Authors: Suits J. C. , Argyle B. E. , Freiser M. J. 
Published: April 2005

A variety of relatively transparent materials containing Eu+ + have become available, thus enabling a study to be made of the magneto-optical properties of the Eu+ + ion in widely different environments. The following materials are reviewed: Eu2SiO4 (orthorhombic structure with a ferromagnetic Curie temperature Tc of 7°K), dilute Eu+ + in CaF2 (fluorite structure), EuF2 (fluorite structure, Tc≈0), EuO−Al2O3−B2O3 glasses (Tc=0), EuSe (NaCl structure, Tc=7°K), and EuO (NaCl structure, Tc=69°K).
We discuss the magneto-optical properties of the ``nonmagnetic'' materials (CaF2: Eu+ +, EuF2, Eu glasses) in terms of an intra-atomic 4f7→4f65d transition. Using this transition, calculation of the Faraday and Cotton-Mouton birefringence in EuF2 gives reasonable agreement with experiment. The magneto-optical properties of the ``magnetic materials'' (Eu chalcogenides) are discussed in terms of an interatomic (4f7) (4f7) → (4f6) (4f75d) transition. This transition gives reasonable agreement with the observed magnitudes of the magnetic absorption edge shifts in EuSe and EuO.
Thermal Properties of Spin-Wave Impurity States
Authors: Wolfram T. , Hall W. 
Published: April 2005

The effect of dilute magnetic impurities on the thermal properties of an ideal simple cubic spin ½ Heisenberg ferromagnet has been investigated. It is shown that for a small ratio ε of impurity—host to host—host exchange low-lying ``s-type'' virtual spin-wave states result which cause a large density of states to occur at low energies. These low-energy states lead to an accumulation of spin disorder at and near the impurity site. Consequently the impurity magnetization decreases far more rapidly than that of the host. This effect is accompanied by a large increase in the low-temperature spin-wave specific heat. Analytic solutions to the Green's function equations are calculated for temperatures near T = 0 and near T = Tc, the Curie temperature. Self-consistent numerical solutions are presented for both the magnetization and spin-wave specific heat as a function of temperature. For small ε the impurity magnetization is approximated by the Brillouin function mI=μβ tanh [(μβH+6J′〈S1z〉)/kT],where J′ is the host-impurity exchange and 〈S1z〉 is the thermal average for the impurity nearest-neighbor spins. 〈S1z〉 is found to be depressed from the bulk value by an amount which increases with temperature and is about 0.84 of the bulk value as T→Tc.
A detailed account of these calculations will be published elsewhere.
Properties of Thin Films of High-Permeability Alloys
Authors: Flur B. L. , Griest A. J. 
Published: April 2005

A number of commercially available high-permeability nickel-iron-base alloys with low values of coercive force, magnetostriction, and crystalline anisotropy are of potential interest as materials for thin-film memory elements. Because of their compositional complexity, however, films of these alloys are not easily prepared by vacuum deposition. By use of bias sputtering, thin films of Mumetal, Conetic AA, Supermalloy, and 4–79 Permalloy have been successfully prepared. The effects of substrate temperature (100°–400°C) and film thickness (500–1000 Å) on the properties of wall-motion threshold H0, anisotropy field Hk0, dispersion α90, skew β, magnetostriction, and sheet resistivity have been experimentally determined.
In general, for the same thickness and substrate temperature, the high-permeability alloys show lower H0 and Hk0 than the binary 81% Ni-19% Fe alloy. The data show that the reduction is most pronounced in the molybdenum-containing alloys, less so in Conetic AA, and least in Mumetal. Molybdenum additions appear to be the most effective in inhibiting the rate of increase of dispersion with increasing H0/Hk0 ratio; e.g., a Supermalloy film was deposited with H0/Hk0=0.9 Oe/0.4 Oe and α90=4.5°.
Reduced Manganese Moment in Manganese Chromite
Authors: Dwight K. , Menyuk N. , Feinleib J. , Wold A. 
Published: April 2005

The net magnetization, magnetic susceptibility, 55Mn nuclear magnetic resonance, and neutron-diffraction properties of MnCr2O4 have been reinvestigated. Our results are in general agreement with earlier findings. The neutron-diffraction pattern of MnCr2O4 evidences appreciable deviation from a pure spiral configuration. Furthermore, the susceptibility data indicate that the Mn+ + ions possess a reduced magnetic moment of about 4.3μB, rather than the previously assumed value of 5.0μB. Given the hypothesis of an admixture of quartet states with quenched orbital momentum into the 6S free-ion ground state, the reduced value of the 55Mn hyperfine field observed in manganese chromite is consistent with this low value for the manganese moment.
The interpretation of the NMR result in terms of a ferrimagnetic spiral ground-state spin configuration remains essentially unchanged, a manganese cone angle of about 61° being indicated. The use of 4.3μB for the Mn+ + moment improves the agreement between the theoretical and observed neutron-diffraction patterns, but the best fit is still obtained with a much smaller value for this cone angle, namely 33°. Within the spiral model, the observed magnetic-diffraction intensities are incompatible with the larger cone angle; the NMR findings are incompatible with the smaller. Other discrepancies are also discussed.
Internal Magnetic Field Analysis and Synthesis for Prescribed Magnetoelastic Delay Characteristics
Authors: Auld B. A. , Strauss W. 
Published: April 2005

A systematic procedure is given for synthesizing the internal magnetic field required to realize prescribed magnetoelastic delay characteristics. The method is based on the expression Tr = (2/c) {y+ω[γHi′(y, He)]−1} for the transit time of magnetoelastic waves in ferromagnetic insulators. Here Hi′(y, He) is the gradient of the internal magnetic field at the turning point, and He is the external magnetic field. Some necessary conditions for physical realizability are discussed and a delay-bandwidth invariant is demonstrated. Field distributions are obtained having the characteristics: (a) ∂Tr/∂ω = 0, independent of ω at specified Hi(0, He), and (b) ∂Tr/∂ω = 0, independent of Hi(0, He) at specified ω. The last case is used as a basis for evaluating the bandwidth capabilities of magnetoelastic variable delay lines. Limitations on the bandwidth, delay variation, and delay distortion are discussed.
Realization of a desired internal magnetic field is greatly simplified by a method for determining the field from measurements of the transit time Tr(ω, He) of magnetoelastic pulses and the separation Sm(ω, He) in magnetic field between adjacent standing-wave modes. The relation Hi′ = ωSm/πc gives y = Φ(ω/γ, He) = (c/2)[Tr−2π/γSm] in terms of measurable quantities; inversion of the function Φ at constant He recovers the internal field in the form ω/γ = Hi(y, He). This method has been applied to data from an yttrium iron garnet rod immersed in a steady, uniform, axial field He; a comparison of the measured results with existing theory is presented.
Influence of Statistical Time Lags upon Electric Breakdown in Electronegative Gases
Authors: Crowe Robert W. 
Published: April 2005

Measurement of the electric strength of SF6 and a number of other electronegative gases has provided direct evidence that an unusually long statistical time lag is associated with the breakdown process in such gases under certain experimental conditions. For example, time lags in excess of one minute have been reported for the breakdown of SF6. The reason for the difference in breakdown behavior of such gases, when compared with the behavior of the more common gases, is not well understood.
The intent in writing this paper was not merely to verify the fact that the time required for breakdown is completely random, although evidence of this plays an important role in the theories and equations developed here. The paper represents an attempt to provide an explanation of the role that these statistical time lags can often play in yielding misleading experimental values of the electric breakdown voltage, when measured under certain standard test conditions. A number of cases are discussed and evaluated by combining accurate experimental data with theories involving the occurance of random events. It is concluded that the ``apparent'' value of the electric breakdown voltage in electronegative gases ought to be strongly dependent upon the mean statistical time lag, the nature of voltage application, and the electrode configuration. The experimentally observed appearance of field emission from the cathode surface at voltages considerably in excess of the threshold value, can be used to derive theoretical relationships which indicate that rather significant ``apparent'' deviations from Paschen's law are to be expected under certain experimental conditions. The latter inconsistency and the method of avoiding it are described in the paper.
Frictional Electrification of Belts of Insulating Materials. II. Relation between Charge Density and Work Done Against Friction
Authors: Cunningham R. G. 
Published: April 2005

For large values of work done against friction, the charge density on an insulating belt slipping on a metal roller exponentially approaches a limiting value. This limiting value increases as the pressure between the belt and roller is increased.
A triboelectric series can be formed for the two belt materials and the two roller materials used in these experiments. The positions of the rollers in this series are qualitatively related to their contact potential differences.
Temperature Variation of the Magnetization Curve of Superparamagnetic Alloys
Authors: Kneller E. , Wolff M. , Egger E. 
Published: April 2005

Thermodynamical considerations suggest that in precipitation alloys there will, in general, be a gradual transition of composition between precipitate and matrix over at least a few atom layers. Since the Curie temperature of solutions is a continuous function of composition, this implies that the magnetically effective volume of ferromagnetic precipitates in a nonferromagnetic matrix depends on temperature. This interface effect may be rather large, especially for small particles.
It is shown that characteristic deviations of the magnetic behavior of superparamagnetic alloys from that predicted by current theory of superparamagnetism, which assumes temperature-independent particle volumes, can be explained quantitatively by the interface effect. In particular, a corresponding analysis of initial susceptibility data taken on 2 Fe-24 Ni-74 Cu as aged at 873°K yields for the interface thickness Δρ of spherical precipitates, in the size range between 19 and 45 Å in radius, the value Δρ≃12.3 Å.
It is suggested that the analysis of magnetic data, as outlined in this paper, may be utilized to determine concentration profiles of precipitates in suitable alloy systems.
Optical Inhomogeneities in Gallium Arsenide
Authors: Drougard M. E. 
Published: April 2005

Slices of pulled, n-type gallium arsenide crystals containing the growth axis have been examined in transmission using an infrared image converter. Under conditions of parallel illumination some samples exhibit a pattern of alternating dark and bright lines, whose spacing is sometimes equal to the length of crystal pulled during a rotation of the crucible and generally smaller. The visibility of these growth striations is shown to be due to periodic variations of the real part of the refractive index, arising from periodic variations of the width of the optical energy gap or of the free-carrier concentration. In very highly doped samples the band-gap changes are associated with a varying Burstein shift, largely compensated by a corresponding shrinking of the gap. In undoped crystals contaminated by silicon, carbon, or aluminum the band-gap changes can be ascribed to an alloy effect.
Other inhomogeneities seen in transmission include strains (using polarized light), p-n and n-n junctions, a mottled appearance in boat-grown crystals and unidentified defects in epitaxially deposited layers.
Space-Charge Polarization in Glass Films
Authors: Snow E. H. , Dumesnil M. E. 
Published: April 2005

It is shown that electrical polarization effects in glass films can be conveniently studied using a metal-glass-silicon dioxide-silicon double-layer capacitor. The buildup of a polarization in the glass layer under the application of a voltage at elevated temperatures can be detected from the resulting shift ΔV in the capacitance-voltage characteristic. Equations are derived on the basis of a simple model which gives ΔV as a function of time, temperature, applied voltage, and the glass and oxide thicknesses.
Experimental data for a lead borosilicate glass are presented and shown to be in excellent agreement with this model. The time constant for polarization of the glass has an activation energy of 1.05 eV and is of the order of weeks at room temperature and minutes at 100°C. The diffusion coefficient calculated from this time constant is in agreement with that for lead in glasses of similar composition and hence it is concluded that in this glass the major mobile ion is Pb++.
Additional long-term polarization effects are observed when the metal is biased positively and these are related to the diffusion of sodium contaminant out of the glass layer into the underlying silicon dioxide.