bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Dependence of the Magnetic Properties of Nickel-Iron Alloys
Authors: Clark J. J. , Fritz J. F.
Published: March 2008

The effect of temperature on the magnetic properties of six commercially available nickel-iron alloys is reported for the temperature range −60°C to +250°C. The trade names of the alloys are: Hipernik, Deltamax, Hipernik V, Supermalloy, 4-79 Mo-Permalloy, and Hymu 80.

The temperature dependence of both ac and dc magnetic properties was determined experimentally over the temperature range. Dc properties were measured by the standard ballistic testing method. At each test temperature sufficient data was taken to plot a normal magnetization curve. Remanent induction and coercive force were also determined at each temperature, these properties being measured relative to magnetizing forces in excess of 100 oersteds. Ac properties were measured by means of a modified Hay bridge, the tests being conducted at frequencies of 60, 400, and 1000 cps. At each test temperature, and for each frequency, total core loss was measured at various inductions in the range characteristic of the alloy being tested. The data presented are the average of the results of tests on six samples of each alloy.
Precipitation in a Beta-Brass-Fe Alloy
Authors: Berkowitz A. E. , Flanders P. J.
Published: March 2008

Single crystal samples of beta-brass containing 0.1% iron were annealed at 300°C and 400°C in order to develop the iron precipitate particles. At intervals during the anneals, magnetic data were obtained and analyzed in terms of the size, shape, orientation, and general magnetic behavior of the precipitate particles.

During the earliest annealing stages, superparamagnetic behavior was observed, and particle diameters were calculated from the Langevin relation. On continued annealing the magnetic properties indicated the presence of mixtures of superparamagnetic and single domain particles, and subsequently mixtures of single domain and multidomain particles.

Torque curves showed that the particles were single crystals, with iron-like magnetocrystalline anisotropy, oriented with the same crystal habit as the matrix. Single domain behavior was first observed when the particle diameters were of the order of 200 A. Elongation of the particles in the 〈111〉 directions and rotational hysteresis were noted when single domain behavior appeared. The magnetocrystalline anisotropy coefficients calculated from the torque data were reasonably close to those of iron. Maximum remanence was reached before maximum coercive force due to the much larger initial susceptibility of the superparamagnetic as compared to the multidomain particles. This was confirmed by the shapes of the hysteresis loops for the various cases.
Effect of Composition and Processing on the Activity of Some Magnetostrictive Materials
Authors: Davis C. M. , Ferebee S. F.
Published: March 2008

The dynamic magnetostrictive properties of a number of magnetic materials were determined as a function of composition and processing. The materials investigated include nickel, 2V-Permendur, a cobalt-nickel alloy, several Ni-Fe and Al-Fe alloys, and a group of ferrites represented by the formula Ni1−x−yCoxFe2+yO4 with 0.00≤x≤0.04 and 0.00≤y≤0.08. The parameters measured were: electromechanical coupling coefficient k, reversible permeability μr, dynamic magnetostrictive constant λ, Young's modulus E, and stress sensitivity λμr.

The stress sensitivity of both the Al-Fe alloys and the cobalt-substituted nickel ferrous-ferrites is sensitive to cooling rate. Ordered Al-Fe samples containing approximately 12.0% aluminum were more stress sensitive by a factor of six than were disordered samples of the same compositions. Disordering was accomplished by quenching from above the ordering temperature (approximately 600°C). When 6% of the nickel in cobalt-substituted nickel ferrite was replaced by divalent iron, the value of λμr increased by approximately 40% for quenched samples but remained relatively constant for slow-cooled samples.

The largest values of λμr observed in the Ni-Fe alloys (in excess of 106 dynes/cm2) occur in the range of 40% to 52.5% nickel. Various processing techniques were employed on the Ni-Fe alloys in this range: slow cooling, quenching, magnetic annealing, and variation in annealing temperature between 900°C and 1220°C. Such variations in processing failed to produce more than a 10% change in the value of λμr.
Superparamagnetism
Authors: Bean C. P. , Livingston J. D.
Published: March 2008

Single domain ferromagnetic particles at elevated temperatures can behave magnetically in a manner analogous to the Langevin paramagnetism of moment-bearing atoms. The main distinction is that the moment of the particle may be 105 times the atomic moment. The experimental and theoretical foundations of this effect are reviewed and indication is made of the applications of this phenomenon. Lastly, attention is drawn to some current problems in this area.
Magnetic Properties of Some Ferrite Micropowders
Authors: Berkowitz A. E. , Schuele W. J.
Published: March 2008

Micropowders of stoichiometric copper, nickel, and cobalt ferrites were prepared by low temperature (<800°C) treatment of the coprecipitated metal oxalates. The magnetic properties of each ferrite were determined as functions of particle or crystallite size in the range from 70 to >2000 A. Particle sizes were determined from x-ray line broadening and from electron micrographs.

The micropowders exhibited superparamagnetic, single domain, or multidomain behavior depending on the particle size. The critical size for single domain behavior, depending on composition, was between 300 and 700 A. In this size range, high coercive force and remanence were observed in spite of appreciable sintering of the particles in some cases. The remanence values and the magnitude and temperature dependence of the coercive force indicated that magnetocrystalline anisotropy determined the properties of the single domain particles. The magnetic properties of the very small particle size samples showed the large temperature dependence characteristic of superparamagnetism.

Quenched and slowly cooled copper ferrite micropowders were prepared with similar particle sizes. The remanence and coercive force of the quenched samples were much lower than those of the slowly cooled samples. This indicated different critical sizes in these two types of copper ferrite. This could be due to the difference in either the moments or the magnetocrystalline anisotropy.
Microwave and Low-Frequency Oscillations due to Resonance Instabilities in Ferrites
Authors: Weiss M. T.
Published: March 2008

Microwave and low frequency oscillations have been observed in single crystal yttrium iron garnet disks placed in a microwave cavity with an applied dc field normal to the disk. These oscillations occur when the microwave power incident on the cavity exceeds a certain critical value in the milliwatt range. The oscillations occur as sidebands above and below the incident frequency and can also be observed as a modulation of the microwave output of the cavity.

The above phenomenon is associated with the ferromagnetic resonance instability due to the fact that the resonant frequency of a disk depends on Mz and thus on the rf magnetic field used to drive it. The combination of the disk and the resonant cavity with high power, provides the conditions necessary for relaxation oscillations to be set up.
Magnetoacoustic Resonance in Yttrium Iron Garnet
Authors: Spencer E. G. , LeCraw R. C.
Published: March 2008

Additional information is given on the conditions under which magnetoacoustic resonance is observed in polished single crystal spheres of yttrium iron garnet.
Experimental Study of the Modified Semistatic Ferrite Amplifier
Authors: Whirry Walter L. , Wang Fleur B.
Published: March 2008

A ferromagnetic parametric amplifier operating at 5930 mc is described. The imaginary component of the rf susceptibility at the signal frequency is shown to reach a negative maximum for hdc set at ferromagnetic resonance for the difference between pump and signal frequencies. The amplifier is operated both as a regenerative and super-regenerative amplifier using pulsed pump power. As a regenerative amplifier, steady-state gains of 20 db with a band width of 0.5 mc are obtained. As a super-regenerative amplifier, gains of 130 db with a band width greater than 1.5 mc are obtained. Oscillations reach their limiting value at signal outputs of 150 to 350 watts, depending upon ferrite temperature, and exhibit an initial spike. As a high gain super-regenerative amplifier, the input cw signal which doubles output average noise power is found to lie between −98 and −103 dbm.
Brittleness of Cobalt-Iron Alloys
Authors: Chen C. W. , Wiener G. W.
Published: March 2008

The brittleness of several cobalt-iron alloys has been investigated. A theoretical evaluation of the hardening mechanism of isotropic short-range order and long-range order coupled with anisotropic short-range order is made for the stoichiometric composition CoFe. The critical shearing stresses associated with the mechanisms are estimated together with that of interstitial atoms. In the absence of the effect of interstitials and other interferences, the hardening mechanisms of order may give rise to the brittleness of Co-Fe alloys. Experiments on two Co-Fe alloys with the addition of Cr or V establish the embrittling action of hydrogen at the grain boundaries.
Variation in Orientation Texture of Ultrathin Molybdenum Permalloy Tape
Authors: Koh P. K. , Lewis H. A. , Graff H. F.
Published: March 2008

It is necessary to select certain heats of molybdenum Permalloy in order to manufacture cores of ultrathin tape which have satisfactory properties for use in computer applications. In an effort to aid this selection process, quantitative pole density stereograms of {111} poles of 18 mil tapes from six production heats in both cold-rolled and annealed conditions were developed in order to reveal possible variations in texture and magnetic properties.

Cold rolling the tape developed (110)[3¯35] and (110)[33¯5] end orientations as major texture components together with a previously unnoticed cube-on-edge or (110)[001] orientation as a minor texture component whose intensity varies according to a combination of many possible processing variables.

Annealing the tape at 927°C developed (120)[001]+(210)[001]; (113)[78¯5]+(113)[785¯]; and previously unnoticed (110)[001] cube-on-edge texture components. The intensity of each individual texture component depends on the combined effect of many processing variables.

Switching coefficient, squareness of hysteresis loop (Br/Bm) and coercive force were used as magnetic parameters for evaluation of the tape cores. It was found that among other possible combinations of texture components a strong (110)[001] annealed texture component seems to associate with the highest squareness ratio and lowest coercive force of the tapes studied in the present investigation. No correlation was found between texture and switching coefficient.
Magnetic Properties of Substituted Manganese-Tin Spinels
Authors: Gilleo M. A. , Mitchell D. W.
Published: March 2008

In a Me22+Sn4+O4 spinel, Sn4+ is known to occupy octahedral sites. Therefore manganese-tin spinel, (Mn)[MnSn]O4, would be antiferromagnetic because of the strong interaction between octahedral and tetrahedral ions characteristic of magnetic spinels. The magnetic exchange interaction in a (Mn2+)-O2−-[Mn2+] linkage is of particular interest because it is known to be much weaker than is the case for Fe3+ with which Mn2+ is isoelectronic; magnetic measurements on slightly oxidized Mn-Sn spinel yield a Néel temperature of 58°K.

When the initial equality of the sublattice magnetizations of Mn2+ ions in octahedral and tetrahedral sites is upset by substitution of nonmagnetic, divalent ions, Mg2+ and Zn2+, for Mn2+, spontaneous magnetization appears. The Néel temperature is decreased by these substitutions largely as a consequence of the smaller number of interactions between the reduced number of Mn2+ ions in the two different sites. For equal substitutions for Mn2+ in Mn2SnO4, the moment changes more rapidly in the case of Mg2+ than Zn2+. The moment depends upon the size of the substituent ion because, in this case, the ions involved are spherical and of the same valence. A smaller size of these substituent ions leads to a greater predominance of occupation of the octahedral sites because substitution there increases the Madelung potential both by reduction of lattice constant and increase of oxygen parameter. The sequence, Mg2+, Zn2+, Mn2+, of increasing ionic sizes corresponds to that of increasing lattice constants, 8.60 8.67, 8.88 A, of the respective tin spinels. Substitution of Ge4+ for Sn4+ takes place principally in tetrahedral sites because of the very small size of Ge4+.

Similarly, spontaneous magnetization appears with oxidation of Mn2SnO4. The resultant oxidized manganese ions (presumably Mn3+) are of the same average valence, though of smaller size, than the octahedral ions and, therefore, also appear in octahedral sites. Because Sn4+ is rejected to maintain valence balance, the octahedral sublattice magnetization is increased by oxidation.
Effect of Impurities on the Temperature Dependence of the (110) [001] Texture in Silicon-Iron
Authors: May J. E. , Turnbull D.
Published: March 2008

Effects of impurities on the formation of the strong (110)[001] texture in silicon-iron were studied. It was observed that the temperature range in which the (110)[001] texture forms can be increased by varying the type and amount of impurity. The temperature at which the (110)[001] texture forms is proposed to be determined by the solubility of the impurity. The authors also propose that the strong (110)[001] texture develops in silicon-iron because (110)[001] grains possess lower free energy even at the increased temperatures than grains in other orientations.
Progress in Ultrathin Mo-Permalloy Tapes with Square Hysteresis Loops
Authors: Littmann Martin F. , Ward Chester E.
Published: March 2008

Commercial production of ultrathin cold-rolled tapes of 4-79 Mo-Permalloy has been accompanied by research on melting, processing, and annealing procedures leading to improved quality control. A wide range of magnetic properties with pulse magnetization is available by selection of tape thickness and final annealing temperature of the cores.

The effect of reduced thickness is a generally higher coercivity and increased squareness. The switching coefficient is lowest for 18 mil tape, but at drives below about 0.25 oe the switching time is not less than for 14 mil because of the higher coercive force.

With increasing temperature of the final anneal, both squareness (measured by static Br/Bm ratio) and coercive force decrease. The decrease in coercive force is accompanied also by a decrease in the switching coefficient until a minimum value of the switching coefficient is reached after which it decreases with further decrease in coercive force. This point of minimum switching coefficient appears to be related to a crystal structure in which the grains extend through the sheet thickness with minimum lateral growth. Data illustrative of the uniformity of static and dynamic magnetic properties between lots of material with present technology are given.
Test of Spin-Wave Theory with Precision Magnetization Measurements
Authors: Foner S. , Thompson E. D.
Published: March 2008

Magnetic moment measurements of single crystal nickel, made from 4.2° to 290°K in a uniform magnetizing field applied along principal crystallographic directions, are presented. The precision of the measurements permits accurate comparison with predictions of spin-wave theory. At low temperatures (less than 150°K) Δσ ∝ T1.5±0.1 in agreement with spin-wave theory. Deviations from the T1.5 law, observed at high temperatures, are much larger than predicted by high-order terms of spin-wave theory. Possible sources for the effect, including temperature variation of g value and/or exchange constant, are summarized. Estimates of exchange constant are given.
Electromagnetic Support Arrangement with Three-Dimensional Control. I. Theoretical
Authors: Jenkins A. W. , Parker Hermon M.
Published: March 2008

The original electromagnetic support developed in the late 1930's is a one-dimensional system. Servoed control is obtained in one direction and only inherent stability due to the field shape is obtained in the lateral directions. In this paper the more general problem of a three-dimensionally controlled support is treated theoretically. By virtue of making certain assumptions which seem reasonably close to practical feasibility two basic three-dimensional support schemes have been devised, in which ideally the three mutually perpendicular forces are uncoupled. The two arrangements are described and the theory is applied to predict support performance and to predict the amount of coupling to be expected due to deviations from the ideal system.
Flux Instrument for Rapid Comparison of Crystal Anisotropies
Authors: Cole R. W. , Honeycutt C. R.
Published: March 2008

A rotating disk instrument for rapid comparison of crystal anisotropies is described. In it a circular disk rotates in a magnetic field parallel to the place of the disk. Because of crystal anisotropy the magnetization I makes an angle θ with the magnetic intensity H. Some instruments, called torque magnetometers or magnetic torquemeters, measure the torque per unit volume, HI sinθ. In this instrument the disk rotates at 1800 rpm with its axis perpendicular to H.

The changes in I sinθ, the component of the magnetization perpendicular to H, induce an emf in pickup coils, which are placed with their common axis perpendicular to the axis of the rotating disk and perpendicular to H. If the pickup coils are spherical, as in the similar instrument built by Siegel, the ratio of the flux through the coil to the magnetic moment of the specimen can be accurately calculated. Without such an absolute calibration the flux instrument is nevertheless convenient for rapidly comparing the disks of oriented polycrystalline silicon-iron with a single crystal disk of the same dimensions. The standard deviation between percent orientations (relative torque peaks) determined with this flux magnetometer and a conventional torque magnetometer is 3%. The emf from the pickup coils is integrated electronically and displayed on an oscilloscope.
Domain Pattern Movements in Silicon-Iron Observed by Electron Mirror Microscopy
Authors: Mayer Ludwig
Published: March 2008

Recent results of the application of electron mirror microscopy for magnetic investigations are reported. It is shown that electron mirror microscopy reveals magnetic domain patterns not only in magnetic materials with a uniaxial direction of easy magnetization but also in materials with several directions of easy magnetization exhibiting basically flux closure domain configurations. On silicon-iron specimens three types of domain manifestation were observed. In two types normal components of the magnetic fields above the entire extension of the domains, weak as they may be, permit the observation. In cases where no such magnetic field components exist, domain walls proper can be observed if magnetic fields are applied. This possibility probably stems from an unsymmetry of the magnetic field above domain walls when a magnetic field is applied. Movements in the domain patterns and domain wall motions can be observed instantaneously because electron mirror microscopy is unhampered by time delays inherent in the Bitter technique. This electronic observation method is also applicable at temperatures at which conventional methods fail. Motion pictures photographed directly from the viewing screen of the electron mirror microscope portray quite adequately the domain patterns set in motion by applied magnetic fields.
Rotational Hysteresis in Thin Films
Authors: Mayfield J. R.
Published: March 2008

Rotational losses in films of nickel-iron have been studied over a wide range of frequencies and applied fields by measuring the torque exerted on the films by a rotating magnetic field. Rotational frequencies from 10 cps to 1 mc and field intensities from zero to 100 oe were used with films ranging in nickel content from 70% to 90% and in thickness from 400 A to 12 000 A.

For applied fields less than 2K/M, the observed losses agree well with the theory of rotational hysteresis in materials with uniaxial anisotropy. When combined with standard torque or hysteresis loop data, these losses yield information regarding the uniformity of the effective anisotropy within the sample. In fields considerably greater than 2K/M the loss per cycle for any given sample is found to be independent of the rotational frequency. According to the analysis of Gilbert and Kelly, in which the high-field losses are proportional to the intrinsic damping parameter, these experimental results imply an inverse frequency dependence of the damping parameter. However, correlations between the high-field and the low-field losses, as well as the results of certain auxiliary experiments indicate that the high-field losses are of essentially the same origin as the low-field losses and are not a measure of the intrinsic rotational damping.
Structural and Magnetic Properties of Permalloy Films
Authors: Lloyd J. C. , Smith R. S.
Published: March 2008

The wall motion coercive force Hc and the rotational coercive force Hr of thin electroplated nickel-iron films are studied as a function of film roughness. Three types of roughness are considered : the first, periodic with a wavelength large compared to a domain wall width and an amplitude small compared with the film thickness; the second, of the order of size of a domain wall; and the third, a substrate roughness that is large compared to the film thickness.

H c was found to be related to film thickness according to Hc = CsD+n. This observation was predicted by Néel, except that his assumption of a form of roughness only of the first kind led to a single value for n of −43. Electron micrographs showed that roughness of the second kind increased with film thickness, indicating that n depends on this factor. Roughness of the third kind, as introduced by unidirectional polishing, results in an increase of Cs, while n and Hr are not affected. This third type of roughness was observed to orient the easy magnetic axis parallel to the polishing grooves.
Magnetic Annealing of Yttrium Iron Garnet
Authors: Calhoun B. A.
Published: March 2008

At −195°C the hysteresis loops of certain yttrium iron garnet cores are strongly affected by a large magnetic field applied as the cores are cooled from room temperature. In order for this magnetic annealing effect to occur, the dc resistivity at room temperature must be less than 109 ohm-cm. The hysteresis loops, permeability and pulse response of these cores have been measured at −195°. The magnetic behavior of the annealed cores at this temperature can be explained qualitatively by assuming that the domain walls do not move under the influence of magnetic fields less than a critical value.
Temperature-Dependent Lag in Polycrystalline Yttrium-Iron Garnet
Authors: Epstein D. J. , Frackiewicz B.
Published: March 2008

Certain samples of polycrystalline yttrium-iron garnet are characterized by a room-temperature permeability spectrum having two regions of dispersion, one at microwaves, the other at rf frequency. The former dispersion is identified as gyromagnetic in origin. The rf dispersion, which exhibits a temperature-activated shift to lower frequency with decreasing temperature, appears due to an electron-diffusion controlled domain-wall relaxation. The activation energy for the process is 0.38 ev.
Some Electrical and Magnetic Properties of Garnets
Authors: Anderson Elmer E.
Published: March 2008

Polycrystalline specimens have been prepared of yttrium-iron garnet (YIG) and substituted garnets of the forms 3Y2O3·(5−x)Fe2O3·xGa2O3 and (3−x)Y2O3·xR2O3·5Fe2O3, where R represents a rare earth element. Measurements have been made of lattice constants, magnetic moments, dc conductivity, permittivity, and permeability. The permeability and magnetic losses were measured from dc to 2 kMc. Density has a large effect on the low-frequency initial permeability; values varied from 14 to 170 for the YIG samples studied. Nominal room temperature properties of YIG are: a = 12.374±0.005 A; μi′/μ0∼70 at 1 Mc, ∼10 at  100 Mc, ∼1 at 1 kMc; ρ = 1010 ohm-cm; ε′/ε0∼12 at 20 Mc; μβ = 6.8 Bohr magnetons per formula weight. Gallium substitution increased the conductivity but decreased the other quantities measured. Rare earth substitutions had significant effects on the magnetic moments but produced only slight changes in the other quantities. The permeability spectrum of dysprosium-substituted YIG clearly shows a domain wall absorption peak at 400 kc and a spin-resonance absorption at 400 Mc.
Some Magnetic Properties of the Chromium (III) Halides at 4.2°K
Authors: Hansen Wilford N.
Published: March 2008

Magnetization curves for CrF3, CrBr3, and CrI3 at 4.2°K have been determined for fields up to 16 kilogauss. CrF3 exhibits hysteresis with a remanent moment of 0.04 Bohr magneton, and a saturation moment of ca 0.1. CrF3 is evidently ferrimagnetic. CrBr3 exhibits no hysteresis, and below 350 gauss the magnetization is strictly linear with field. CrI3 exhibits pronounced hysteresis not fully developed at 16 kilogauss. The expected saturation moment of 3 Bohr magnetons is compatible with the curves for CrBr3 and CrI3.
Anisotropy of Superparamagnetic Particles as Measured by Torque and Resonance
Authors: Livingston J. D. , Bean C. P.
Published: March 2008

Simple statistical reasoning has been applied to the case of an assembly of crystallographically aligned superparamagnetic particles at a given field and temperature. The apparent magnetocrystalline anisotropy as measured both by torque and resonance has been deduced for the cases of uniaxial and cubic anisotropies. Certain features of recent experimental results on precipitated cobalt particles can be explained, including the observation that, at high temperatures, the anisotropy measured by resonance is greater than that measured by torque.
Stoner-Wohlfarth Calculation on Particle with Both Magnetocrystalline and Shape Anisotropy
Authors: Johnson Clark E. , Brown William Fuller
Published: March 2008

Previously, it had been assumed that the presence of a minimum of magnetocrystalline anisotropy energy along the long axis of an acicular single-domain particle would increase the coercive force. A theoretical calculation using the Stoner-Wohlfarth model with a magnetocrystalline energy term indicates this is not always true.

For an acicular polycrystalline single-domain particle with cubic magnetocrystalline anisotropy, it is assumed that the crystallites are ordered with the [111] direction parallel to the long axis, and the other directions randomly oriented around this [111] direction.

Carrying out the Stoner-Wohlfarth calculation with various ratios of magnetocrystalline anisotropy to shape anisotropy shows the presence of certain stable states of magnetization which are inaccessible by merely traversing the hysteresis loop. Also, the coercive force of a random agglomerate is related in a complex way to the anisotropy ratio (ratio of crystalline to shape anistropy constants), becoming zero for large values of the anistropy ratio. “Butterfly” hysteresis loops also appear for a wide range of anisotropy ratios.
Millimicrosecond Magnetic Switching and Storage Element
Authors: Meier Donal A.
Published: March 2008

A magnetic rod suitable for performing the logical switching and storage functions required in a digital computer has been developed. The magnetic element consists of a silver-coated glass rod upon which is electroplated a Fe-Ni alloy several thousand angstroms thick.

A single element for a coincident-current memory requiring two inputs, an inhibit winding, and a sense winding would consist of four separate single layer concentric solenoids wound over the magnetic rod. Memory matrices, each consisting of many solenoids, can be stacked and simultaneously threaded with the rod. The switching speed of the element operating in a coincident-current mode is approximately 70 mμsec. The output voltage generated across a ten-turn sense winding is 200 to 500 mv depending upon the alloy thickness.

The rod is also suitable as a multi-input logical switch. Separate inhibiting windings wound over the rod perform the NOR function of its input literals. A total of thirty separate inhibiting windings have been demonstrated in the laboratory. Satisfactory operation in the 2- to 5-Mc range using transistors in conjunction with the rod has been shown to be practical.

Continuous plating and testing in conjunction with automatic machine winding techniques make the rod appear economically attractive in digital computer applications.
Remarks on Magnetically Dilute Systems
Authors: Sato H. , Arrott A. , Kikuchi R.
Published: March 2008

Because of the inadequacies of previous treatments of the magnetic properties of magnetically dilute systems when used to interpret experimental results, a re-examination of the problem starting from a simple model is made. The treatments of the problem discussed here using an Ising model show that a Curie or a Néel temperature does not appear until a finite concentration of magnetic atoms is obtained if the atomic distribution is random. This concentration depends on the coordination number of the lattice and on the range of interaction, but not on the strength of the interaction. The results given here for nearest neighbor interactions describe the general behavior observed in magnetically dilute solutions. Such things as anomalously high values of “effective magnetic moments” per magnetic atom and its concentration dependence, curvature in inverse susceptibility against temperature plots, and parasitic paramagnetism in the weakly ferromagnetic alloys, etc., are reasonably well explained. When the system has antiferromagnetic interactions, it is found that the inverse susceptibility shows a complicated temperature dependence varying with concentration and that the existence of a maximum in the susceptibility does not necessarily mean the onset of antiferromagnetism. Special references are made to iron in gold and chromium and to manganese in copper.
Analysis of power spectral density of random Landau-Lifshitz-Slonczewski dynamics by using stochastic processes on graphs
Authors: Mayergoyz Isaak D. , Serpico Claudio , Bertotti Giorgio , Bonin Roberto , d’Aquino Massimiliano
Published: March 2008

A technique for computing the autocorrelation function and power spectral density of stochastic Landau-Lifshitz-Slonczewski dynamics is presented. This technique is based on the mathematical machinery of stochastic processes on graphs.
Detection of air-gap eccentricity and broken-rotor bar conditions in a squirrel-cage induction motor using the radial flux sensor
Authors: Hwang Don-Ha , Han Sang-Bo , Woo Byung-Chul , Sun Jong-Ho , Kang Dong-Sik , Kim Byung-Kuk , Cho Youn-Hyun
Published: March 2008

A new method for detecting eccentricity and broken rotor bar conditions in a squirrel-cage induction motor is proposed. Air-gap flux variation analysis is done using search coils, which are inserted at stator slots. Using this method, the leakage flux in radial direction can be directly detected. Using finite element method, the air-gap flux variation is accurately modeled and analyzed. From the results of the simulation, a motor under normal condition shows maximum magnetic flux density of 1.3T. On the other hand, the eccentric air-gap condition displays about 1.1T at 60° and 1.6T at 240°. A difference of flux density is 0.5T in the abnormal condition, whereas no difference is detected in the normal motor. In the broken rotor bar conditions, the flux densities at 65° and 155° are about 0.4 T and 0.8T, respectively. These simulation results are coincided with those of experiment. Consequently, the measurement of the magnetic flux at air gap is one of effective ways to discriminate the faulted conditions of the eccentricity and broken rotor bars.
Automatic generation of active coordinates for quantum dynamics calculations: Application to the dynamics of benzene photochemistry
Authors: Lasorne Benjamin , Sicilia Fabrizio , Bearpark Michael J. , Robb Michael A. , Worth Graham A. , Blancafort Lluìs
Published: March 2008

A new practical method to generate a subspace of active coordinates for quantum dynamics calculations is presented. These reduced coordinates are obtained as the normal modes of an analytical quadratic representation of the energy difference between excited and ground states within the complete active space self-consistent field method. At the Franck-Condon point, the largest negative eigenvalues of this Hessian correspond to the photoactive modes: those that reduce the energy difference and lead to the conical intersection; eigenvalues close to 0 correspond to bath modes, while modes with large positive eigenvalues are photoinactive vibrations, which increase the energy difference. The efficacy of quantum dynamics run in the subspace of the photoactive modes is illustrated with the photochemistry of benzene, where theoretical simulations are designed to assist optimal control experiments.
Initial experiments on the shock-ignition inertial confinement fusion concept
Authors: Theobald W. , Betti R. , Stoeckl C. , Anderson K. S. , Delettrez J. A. , Glebov V. Yu. , Goncharov V. N. , Marshall F. J. , Maywar D. N. , McCrory R. L. , Meyerhofer D. D. , Radha P. B. , Sangster T. C. , Seka W. , Shvarts D. , Smalyuk V. A. , Solodov A. A. , Yaakobi B. , Zhou C. D. , Frenje J. A. , Li C. K. , Séguin F. H. , Petrasso R. D. , Perkins L. J.
Published: March 2008

Shock ignition is a two-step inertial confinement fusion concept where a strong shock wave is launched at the end of the laser pulse to ignite the compressed core of a low-velocity implosion. Initial shock-ignition technique experiments were performed at the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using 40-μm-thick, 0.9-mm-diam, warm surrogate plastic shells filled with deuterium gas. The experiments showed a significant improvement in the performance of low-adiabat, low-velocity implosions compared to conventional “hot-spot” implosions. High areal densities with average values exceeding ∼0.2g∕cm2 and peak areal densities above 0.3g∕cm2 were measured, which is in good agreement with one-dimensional hydrodynamical simulation predictions. Shock-ignition technique implosions with cryogenic deuterium and deuterium-tritium ice shells produced areal densities close to the 1D prediction and achieved up to 12% of the predicted 1D fusion yield.
Dynamics of molecular exchange between aligning adsorbed film of liquid crystal and the bulk
Authors: Guo Rui , Reznikov Yuriy , Slyusarenko Kostyantyn , Kumar Satyendra
Published: March 2008

The liquid crystal (LC) originally filled in thin cells is replaced by a different LC having a drastically different pretilt angle. The mechanism of desorption/adsorption of LC molecules from/on the adsorbed LC film at the substrate changes the composition of the adsorbed layer and thus the pretilt angle. The time dependence of molecular pretilt angle at solid surfaces of homogeneously aligned LC cells is measured. The characteristic molecular exchange time depends on the coefficients of desorption of the first LC. The results presented here provide an important insight into the molecular exchange between solid surface and bulk fluid.
Compressible or incompressible blend of interacting monodisperse star and linear polymers near a surface
Authors: Batman Richard , Gujrati P. D.
Published: March 2008

We consider a lattice model of a mixture of repulsive, attractive, or neutral monodisperse star (species A) and linear (species B) polymers with a third monomeric species C, which may represent free volume. The mixture is next to a hard, infinite plate whose interactions with A and C can be attractive, repulsive, or neutral. These two interactions are the only parameters necessary to specify the effect of the surface on all three components. We numerically study monomer density profiles using the method of Gujrati and Chhajer that has already been previously applied to study polydisperse and monodisperse linear-linear blends next to surfaces. The resulting density profiles always show an enrichment of linear polymers in the immediate vicinity of the surface due to entropic repulsion of the star core. However, the integrated surface excess of star monomers is sometimes positive, indicating an overall enrichment of stars. This excess increases with the number of star arms only up to a certain critical number and decreases thereafter. The critical arm number increases with compressibility (bulk concentration of C). The method of Gujrati and Chhajer is computationally ultrafast and can be carried out on a personal computer (PC), even in the incompressible case, when simulations are unfeasible. Calculations of density profiles usually take less than 20min on PCs.
Observations of the collapse of asymmetrically driven convergent shocks
Authors: Rygg J. R. , Frenje J. A. , Li C. K. , Séguin F. H. , Petrasso R. D. , Marshall F. J. , Delettrez J. A. , Knauer J. P. , Meyerhofer D. D. , Stoeckl C.
Published: March 2008

The collapse of strong convergent shocks in spherical geometry is observed using measurements of induced nuclear production and x-ray emission. Precise and absolute measurements of the timing and yield of nuclear production induced by the collapse of laser-driven shocks give the same results when shocks are launched by uniform (<2%rms) or nonuniform (up to 32% rms) laser illumination. The observation was repeated for both low-mode (dominated by spherical harmonic modes ℓ=1–2) and high-mode (ℓ=31–500) drive asymmetries. For low-mode nonuniform drive, the center of collapse as observed through x-ray emission shifts away from target center toward the direction of low intensity. The x-ray emission brightness is seen to drop precipitously with larger low-mode drive asymmetry, in stark contrast to the drive-uniformity insensitivity of nuclear yields at the time of shock collapse.
Room temperature photoluminescence at 4.5μm from InAsN
Authors: Zhuang Q. , Godenir A. M. R. , Krier A. , Lai K. T. , Haywood S. K.
Published: March 2008

Nitrogen incorporation in InAsN epilayers grown by radio-frequency plasma-assisted molecular beam epitaxy was investigated as a function of growth conditions. Reduced growth rate, growth temperature, and arsenic flux significantly enhance the nitrogen incorporation. Optimal growth conditions allowed us to obtain high quality InAsN with nitrogen composition of up to 2.5%. The epilayers exhibit intense 4K photoluminescence (PL) with double-peak features, which were attributed to free carrier recombination and localized carrier recombination. Strong room temperature PL emission up to a wavelength of 4.5μm is obtained.
Perturbation of the Wigner equation in inner product C*-modules
Authors: Chmieliński Jacek , Ilišević Dijana , Moslehian Mohammad Sal , Sadeghi Ghadir
Published: March 2008

Let A be a C*-algebra and B be a von Neumann algebra that both act on a Hilbert space H. Let M and N be inner product modules over A and B, respectively. Under certain assumptions, we show that for each mapping f:M→N satisfying ‖∣⟨f(x),f(y)⟩∣−∣⟨x,y⟩∣‖⩽φ(x,y) (x,y∊M), where φ is a control function, there exists a solution I:M→N of the Wigner equation ∣⟨I(x),I(y)⟩∣=∣⟨x,y⟩∣ (x,y∊M) such that ‖f(x)−I(x)‖⩽φ(x,x) (x∊M).
Sudden disruption of the cross-tail current in the magnetotail
Authors: Ma Z. W.
Published: March 2008

A Hall magnetohydrodynamic simulation is used to study current dynamic processes with realistic magnetotail geometry. The simulation results indicate that sudden disruption of cross-tail current at the near Earth region inside 15RE is triggered by fast magnetic reconnection with the reconnection rate ∼0.15. The cross-tail current density exhibits an impulsive intensification in the late growth phase. The magnitude of the current increases more than one order within a few minutes. After the reconnection onset, the cross-tail current is suddenly disrupted in a few Alfvén times, which is in good agreement with that from the satellite observations. Associated with the current disruption, the tail-like geometry becomes a dipolarlike structure with an impulsive enhancement of the magnetic field Bz. Large increases of the electric field and Earthward bulk flow in this simulation are observed immediately after the reconnection onset.
Heterodyne polarization coherent anti-Stokes Raman scattering microscopy
Authors: Lu Fake , Zheng Wei , Huang Zhiwei
Published: March 2008

We develop a heterodyne-detected polarization coherent anti-Stokes Raman scattering (HP-CARS) microscopy for high sensitive and high contrast molecular vibration imaging. The HP-CARS technique, which utilizes interference of the weak resonant CARS signal and the relatively intense local oscillator field generated simultaneously within the same focal excitation volume of the sample for optical heterodyne detection, yields an approximately sevenfold improvement in vibrational contrast compared with local oscillator CARS, while exhibiting a 12-fold amplification of the resonant signal compared with P-CARS. We demonstrate this method by imaging both 4.69μm polystyrene beads and unstained human epithelial cells in aqueous environments.
Planar high-Tc superconducting quantum interference device gradiometer for simultaneous measurements of two magnetic field gradients
Authors: Steppke A. , Becker C. , Grosse V. , Dörrer L. , Schmidl F. , Seidel P. , Djupmyr M. , Albrecht J.
Published: March 2008

Here, we present a planar superconducting quantum interference device (SQUID) structure consisting of four SQUIDs connected to antenna structures for simultaneous measurements of two magnetic field components. Using YBa2Cu3O7−x thin film technology, we are able to prepare gradiometer structures on strontium titanate (SrTiO3) tetracrystals containing two crossing 30° grain boundaries. This allows the production of four SQUID loops onto one substrate which can fulfill the high demands of symmetry inside the antenna structures. In our arrangement, the SQUID loops can act as independent field sensors which allow a measurement of two independent magnetic field gradient components.
Modeling Cities in 3D: A Cellular Automaton Approach
Authors: Benguigui Lucien , Czamanski Daniel , Roth Rafael
Published: March 2008

This paper presents a quasi-3D cellular automaton (CA) simulation model of cities. A 2D CA model includes a cell attribute that represents building height information. Dynamic processes are depicted using four parameters: initial building coverage, interaction with adjacent neighborhood, inertia, and noise. These parameters can assume simple economic interpretation. Some combinations of values of the parameters result in cities that experience paths of convergent growth. Some values lead to cities that experience phase transitions. We suggest a typology of resulting urban patterns and note the emergence of spatial clusters of high-rise buildings.
The Effect of Categorisation on Sensitivity to Second-Order Relations in Novel Objects
Authors: Nishimura Mayu , Maurer Daphne
Published: March 2008

Adults appear to be more sensitive to configural information, including second-order relations (the spacing of features), in faces than in other objects. Superior processing of second-order relations in faces may arise from our experience of identifying faces at the individual level of categorisation (eg Bob versus John) but other objects at the basic level of categorisation (eg table versus chair; Gauthier and Tarr, 1997 Vision Research37 1673–1682). We simulated this learning difference with novel stimuli (comprised of blobs) by having two groups view the same stimuli but learn to identify the objects only at the basic level (based on the number of constituent blobs) or at both the basic level and individual level (based on the spacing, or second-order relations, of the blobs) of categorisation. Results from two experiments showed that, after training, observers in the individual-level training group were more sensitive to the second-order relations in novel exemplars of the learned category than observers in the basic-level training group. This is the first demonstration of specific improvement in sensitivity to second-order relations after training with non-face stimuli. The findings are consistent with the hypothesis that adults are more sensitive to second-order relations in faces than in other objects, at least in part, because they have more experience identifying faces at the individual level of categorisation.
Recognition Properties of Flavin Analogues with Bile Acid-Based Receptors: Role of Steric Effects in Hydrogen Bond Based Molecular Recognition
Authors: Chattopadhyay Prosenjit , Nagpal Rekha , Pandey Pramod S.
Published: March 2008

The recognition properties of 7,8-dimethyl flavin analogues by bile acid-based receptors that contain 2,6-diaminopyridine and the dioctylamide of 2,6-diaminopyridine in CHCl3 were determined. The results show that the bile acid-based receptors bind 7,8-dimethyl flavin analogues less effectively as compared to 7,8-unsubstituted flavins reported earlier, which is contrary to the known fact that the association constants increase with increasing electron-donating capacity of the substituents at the 7 and 8 positions of the flavin analogues.
Ruthenium(II) Complexes of Chelating Ligands Containing Benzoxazole and Benzothiazole Subunits: Synthesis, X-Ray Crystallography, Spectroscopy, and Electrochemistry
Authors: Richardson Chris , Keene F. Richard , Steel Peter J.
Published: March 2008

Bis(2,2′-bipyridyl)ruthenium(ii) complexes of four chelating ligands that contain benzoxazole or benzothiazole rings have been prepared and characterized by NMR spectroscopy, visible absorption spectroscopy, electrochemical measurements and, in two cases, by X-ray crystallography. The incorporation of these ring systems has a marked effect on the electronic properties of the resulting complexes.
Correlation and path coefficient analysis in sugarcane
Authors: Tyagi Anand Prakash , Lal Praduman
Published: March 2008

Correlation and path coefficient analysis was undertaken among agronomic and bio-chemical characters of importance in sugarcane. Correlation between agronomic characters revealed positive and significant (P = 0.01) correlation between plant volume and number of millable stalks (0.874), plant volume and weight per stalk (0.812), plant volume and weight of millable stalks (0.962), plant volume and stalk thickness (0.842), number of millable stalks and weight of millable stalks (0.889) and other agronomic characters. There was a non-significant but positive correlation between number of millable stalks refractrometer brix (0.05), number of millable stalks and stalk height (0.285) and other characters. In case of bio-chemical characters, positive and significant (P = 0.01) correlation was recorded between Pure Obtainable Cane Sugar (POCS) and pol (0.901), POCS and purity (0.763) and pol and purity (0.780). Negative but non-significant correlation was observed between POCS and fibre. Correlation studies indicate that for sugarcane yield plant volume, plant height, number of millable stalks per stool, stalk thickness and weight of millable stalks are the most important characters. However, for biochemical characters POCS, pol and purity are the most important characters. Path coefficient analysis in the case of agronomic characters showed revealed that the weight of millable stalks was the most important character with the highest direct effect on sugarcane yield followed by stalk height, number of millable stalks and stalk thickness among agronomic traits. In bio-chemical characters highest direct effect was on percent POCS followed by percent purity and percent fibre. In nutshell correlation and path coefficient analysis in present study suggests that clones or varieties with high plant volume, plant height, and other agronomic characters should be used in hybridization programme.