bluuebunny/crossref_metadata_2025 huggingface dataset:
Strong Eddy-Current Applications of Permanent Magnets
Authors: Tendeloo K.
Published: March 2008

Small eddy-current brakes for kwh meters have a practically linear torque-speed characteristic, because the induced current increases proportionally to the low relative speed between eddy-current disk and magnetic poles.

In bigger designs a considerable reaction of the induced-current field shifts the eddy-current paths in the direction of movement, so that the electrodynamic force between current and magnetic poles deviates from the linear relation, reaches a maximum at a critical speed, and decreases asymptotically to zero at infinite speed, whereas the dissipated power becomes a maximum.

Some investigations were made into the behavior of permanent magnets with a water-cooled setup with p.m. rotor and an air-cooled device with p.m. stator, both of cylindrical shape with 11.8 in. effective diameter and an axial length of 5.5 in. and 6 in., respectively. Maximum torques of 410 ft-lb and 304 ft-lb were obtained.

Pole pieces may sometimes increase the static flux, but do not always improve the dynamic behavior.

The ideal solution might be obtained with a high-induction magnet without pole pieces, but the induction in available materials is limited by the demagnetizing effect on the free pole top.

Possible applications could be found in a retarder for heavy trucks in mountainous districts and in a flexible coupling, slipping with decreasing torque when overloaded.
Magnetic Recording Head with dc Response
Authors: Fischell R. E. , Meehan S. J.
Published: March 2008

A magnetic recording head has been developed to directly record and play back low-frequency signals, down to and including zero cps, without using amplitude, frequency, or pulse width modulation.

Two problems are encountered in dc magnetic recording. The more obvious problem is caused by the small voltage induced in the playback head when the flux changes at a very slow rate. At low frequencies, the output of a conventional playback head is proportional to the time rate of change of flux in the head; therefore, at dc the playback signal has zero amplitude. The second problem encountered in reproducing dc signals is the disappearance of the magnetic field at the gap of a ring-type head when wavelengths of considerable lengths are recorded on the tape. The magnetic field at the gap of a ring-type head becomes too small to be used when a recorded wavelength is longer than a few inches.

Combining a perpendicular head with flux sensitive playback has eliminated these two problems. A perpendicular head magnetizes the recording tape perpendicularly to the direction of tape motion, i.e., the tape is magnetized through its thickness. The pole pieces of the head are spring loaded and pressed against the tape to maintain consistent contact while the tape passes through the head. Vicalloy, in the form of a thin, homogeneous metal tape, was selected for this purpose because it contains many of the magnetic and physical characteristics desired, including a high coercive force, high remanence, and mechanical flexibility when it is rolled into a thin tape. A frequency response of dc (0 cps to 10 cps) is achieved at a tape speed of 0.027 in./sec. Pre-emphasis is not required in recording and equalization is not used during playback. Cross talk between adjacent heads in a multichannel system is below 50 db at moderate track separations.
Slow Domain Wall Motion in Homogeneous Vacuum-Deposited Iron-Nickel Films
Authors: Olmen Robert W. , Mitchell Earl N.
Published: March 2008

An experimental study has been made of slow speed domain wall velocity as a function of switching field and temperature for a “homogeneous” vacuum-deposited magnetic film using the Kerr magneto-optic technique for visual and photographic velocity measurements. The deposited film was in the form of a circle, one centimeter in diameter and about 1500 A thick with a composition of about 78% nickel and 22% iron. In the film studied, domain walls continue in motion until the film is saturated without any increase in the applied magnetic field over that necessary to just nucleate the domain. The general expression obtained for the domain wall velocity as a function of applied field H and temperature t for a contained wall is V= V0(t) exp 8.8(H −H0), where H is in oersteds and V is in cm/sec. It was also determined that the domain wall velocity increases with increasing temperature at a fixed value of the applied magnetic field. The plotted data are nonlinear but in general the velocity increases with temperature at a rate greater than the first power of the temperature but less than the square of the temperature. Observations were made over a range of wall velocities from 3.4×10−4 cm/sec to 7.6×10−2 cm/sec.
Anisotropy Field Measurements on Ni-Fe Thin Films
Authors: Alexander Rexford G.
Published: March 2008

Rotation anisotropy fields have been determined in vacuum deposited Permalloy films using pulsed external fields. The signal producing field is applied at right angles to the direction of easy magnetization, while the effective reset field is applied at a variable acute angle to the direction of easy magnetization. A special type of permeability curve is constructed using the integrated output signal. Values of the effective rotation anisotropy and the distribution of the anisotropy are determined from this curve, and are found to be related to the squareness at 90° to the easy direction.
Remagnetization Experiments in Mn1+xFe2−xO4
Authors: Matcovich T. J. , Kriessman C. J.
Published: March 2008

The remagnetization time τ has been measured as a function of external field H for a series of manganese ferrites, Mn1+xFe2−xO4. The physical properties of these compounds which enter into the domain wall model of Menyuk and Goodenough and the rotational model of Gyorgy have also been measured. It is found that α, the loss constant, is critical to the correlation of data with theory, and that neither theory can be unequivocally proved until more insight into the remagnetization process loss mechanism is acquired.
Some Observations on Evaporated Permalloy Films
Authors: Chu W. W. L. , Wolfe J. E. , Wagner B. C.
Published: March 2008

Experimental study of the chemical and physical characteristics of evaporated Permalloy films have been carried out. Observations regarding chemical homogeneity, applied strains, and magnetic annealing are reported. Results showed that chemical heterogeneity could exist in such films; possible effects of heterogeneity are speculated. Longitudinal compressive strains, when applied to a magnetostrictive film, could markedly increase its magnetization reversal speed and change its preferred direction. Magnetic annealing of 75%-Ni films at 300°C in a transverse field irreversibly changed the films' preferred directions by 90°, reducing the H′ks to 3.0 oe, with maximum variations of ±0.5 oe.
Neutron Diffraction Investigations of Magnetic Phenomena in Crystalline Compounds
Authors: Wilkinson M. K.
Published: March 2008

This is the summary of a paper which discussed neutron diffraction applications and illustrated recent techniques with investigations on anhydrous iron-group dibromides and dichlorides.
On the Origin of Low Moments in Chromium-Containing Spinels
Authors: Baltzer Philip K. , Wojtowicz Peter J.
Published: March 2008

The most commonly offered interpretation of the low magnetic moments of chromium-containing spinels has relied on the existence of the Yafet and Kittel ordering scheme. The experimental evidence for angular ordering schemes on the B lattice of spinels is, however, inconclusive and contradictory. Prince, for instance, has obtained neutron diffraction data on CuCr2O4 which is consistent with, but does not uniquely determine, the Yafet-Kittel scheme. Pickart, on the other hand, has found no evidence of the angular scheme in data on (MnFe2O4)1−x+(MnCr2O4)x and (NiFe2O4)1−x+(NiCr2O4)x, although he did establish that the moment of the B lattice was lower than expected on a simple Néel picture. In this report, we present a new approach to this problem which appears to lead to a reasonable, adequate, and consistent treatment of the moment data.

It is usually supposed that the spin of the Cr3+ ion in the octahedral environment of the spinel B site is 32 giving a moment of three Bohr magnetons. A consideration of the crystal field theory pertinent to Cr3+ shows, however, that if the B site is given a sufficient tetragonal or trigonal distortion, the doublet state, having a spin of 12 and a moment of one Bohr magneton, becomes the ground state. It is known further that the B sites can be distorted from regular octahedral symmetry by the presence of Jahn-Teller distortions in neighboring sites. For example, Ni2+ and Cu2+ cause distortions when on A sites, while Cu2+ and Mn3+ cause distortions when on the B sites. The process by which the moment of an ion is reduced in this way is called “spin quenching.”

We therefore propose that the origin of the low moments in the chromites is the spin-quenching effect imposed on the Cr3+ ions by the appropriate Jahn-Teller distortions of their neighbors. We also emphasize that a macroscopically distorted phase is not required for this effect. It is only necessary that a distribution of distorting neighbors be present, sufficient in number to alter the symmetry about (and hence spin quench) at least a fraction of the chromium ions. With the aid of these hypotheses it has proved possible to explain the moment data for many chromites in a consistent way. Of particular interest are the recently studied systems, (CuFe2O4)1−x+(CuCr2O4)x and (NiFe2O4)1−x+(NiCr2O4)x.
Effect of Neutron Irradiation of the Magnetic Properties and Degree of Order of Magnetic Metal Alloys
Authors: Schindler A. I. , Salkovitz E. I. , Ansell G. S.
Published: March 2008

Sixty-cycle sine current hysteresis loops have been made on thermally treated Permalloy type material both prior to and following neutron irradiation. In all cases the hysteresis loops of the irradiated alloys resembled the constricted loops characteristic of partially ordered Ni3Fe. The effect of the sample temperature during irradiation on the magnetic properties suggests that ordering results from diffusion of vacancies.
Uniform Rotational Flux Reversal of Ferrite Toroids
Authors: Gyorgy E. M. , Hagedorn F. B.
Published: March 2008

A model is presented for the high-speed uniform rotational reversal of ferrite toroids. This model eliminates the prohibitively high demagnetizing energy usually associated with uniform rotation in toroids. Analysis of the model, to a very good approximation, leads to results identical with those obtained from uniform rotation in isotropic thin films. Experimental confirmation of a high-speed switching mode in ferrite toroids is given.
On the Magnetic Anisotropy in Manganese-Iron Spinels
Authors: Penoyer R. F. , Shafer M. W.
Published: March 2008

The magnetic anisotropy energy is measured as a function of temperature in eleven single crystal compositions corresponding to MnxFe3−xO4, where x is varied from 0.00 to 1.90. The interesting features observed are as follows.

(1) Small manganese concentrations in magnetite (x=0) are shown to decrease the temperature of the “isotropy point” known to exist in magnetite at low temperatures.

(2) An unexpected variation in the temperature dependence and magnitude of the anisotropy energy in the x=0.4 to 1.0 composition region is shown.

(3) The anisotropy energy in the composition region between x=1.0 and 1.8 is semiquantitatively shown to be related to cubic crystalline field splitting of the energy levels of ferric ions.

(4) A large planar anisotropy is measured in a crystal composition given by x = 1.90 and is discussed in terms of the expected tetragonal nature of trivalent manganese.

(5) Finally, a minute magnetic annealing effect at a temperature of 370°K has been shown to exist in a crystal composition corresponding to x=0.40 and the magnitude of this effect is shown to be dependent on the direction relative to the crystal axes of the applied magnetic field during the annealing process.
Some Crystallographic and Magnetic Properties of Square-Loop Materials in Ferrite Systems Containing Copper
Authors: Greifer Aaron P. , Croft William J.
Published: March 2008

Rectangular hysteresis loops have been found in ferrite systems containing copper during an investigation based on the proposal by Baltzer that a zero or near-zero value of the effective magnetocrystalline domain anisotropy is a necessary condition for loop squareness.

Data on hysteresis loop squareness of polycrystalline bodies as a function of composition, firing conditions and magnetostrictive effects are presented for the system: copper ferrite-magnesium ferrite. This system is characterized in general by large grains and long switching times. Abrupt flux changes occur in the hysteresis loop at low temperatures. Simultaneously, a decrease in the coercive force with decreasing temperature and squareness values approaching unity are observed. No crystallographic transitions were detected at low temperatures.

Magnetostrictive measurements do not unequivocally show whether anisotropy goes through zero at compositional region of maximum squareness. The saturation magnetostriction and probably the λ111 go through a minimum in this region.
Magnetic Properties of Nickel-Iron Ferrite
Authors: Menyuk N. , Dwight K.
Published: March 2008

The magnetic anisotropy of a single crystal of nickel-iron ferrite with composition Fe1.003+[Ni0.792+Fe0.363+Fe0.903+]O4 is given between 450 and 4.2°K. At high temperatures the anistropy energy has cubic symmetry, and the absolute value of the first-order anisotropy constant is a maximum at ca 200°K. Below 200°K, |K1| decreases until 10°K, at which temperature there is an abrupt transition in the anisotropy characteristics. Below 10°K the anisotropy energy contains a uniaxial term of the form Εi αi2βi2 where αi and βi are the direction cosines of the magnetization at the measuring temperature and at the annealing temperature (10°K), respectively.

This low-temperature behavior has been explained on the basis of existent theory of magnetic annealing. The model used to explain the uniaxial anisotropy term given above is shown to be consistent with the noncubic anisotropy energy obtained upon cooling the sample through 10°K in the absence of an external field. The model is also shown to lead directly to a relaxation effect which contributes a term of the form K′(α12α22+α22α32+α32α12) to the anisotropy energy above 10°K and explains the observed maximum in |K1|.
Evaluation of New High-Speed Magnetic Ferrite System for Use in Computer Components
Authors: Eichbaum Barlane R.
Published: March 2008

Present-day computer speeds are limited by the magnetic components utilized in their construction. Such components have been fabricated from square loop ferrites of the MgO·MnO·Fe2O3 system. Since such materials limit the speed at which the computers can operate, a new ferrite system, namely, the CdO·MnO·Fe2O3 system, was studied and has been proven feasible for many new high-speed applications. Some of the compositions of this new system exhibiting square hysteresis loops have switching constants as low as 0.200 oe μsec. Such materials in comparison with those of the MgO·MnO·Fe2O3 system have a much lower coercive force, require lower driving currents, and have a flux reversal or switching time which is five times as fast. These materials have been used in fast switching multipath elements and matrix switch cores. The operation of such elements is described.
Some Recent Developments in Micromagnetics at the Weizmann Institute of Science
Authors: Aharoni Amikam
Published: March 2008

Recent theoretical studies carried out in micromagnetics at this Institute are reviewed, and preliminary results are given for theoretical problems which are now under study.

The coercive force of an infinite circular cylinder is calculated as a function of the radius and of the inclination of the cylindrical axis to the applied field. For this calculation it is assumed that only the curling and the rotation in unison modes take place; and that whenever the curling is associated with a discontinuous jump, the magnetization is brought to the values tabulated by Stoner and Wohlfarth, who assumed only rotation in unison. Using the same assumptions, the rotational hysteresis loss and integral are calculated both for an aligned and for a random assembly of cylinders. The results are found to be in fair agreement with the measurements of Jacobs and Luborsky on elongated particles.

The remanence curves of a random assembly of infinite cylinders are calculated for the same model as a function of the applied field and of the radius of the cylinders.

The rotation in unison and the curling are proved to be the easiest modes for magnetization reversal in a ferromagnetic sphere. The nucleation field associated with the curling mode is calculated as a function of elongation and size for a ferromagnetic prolate spheroid. For a rather wide range of elongations this suffices as an approximation for the coercive force, which should be larger than the nucleation field but smaller than the coercive force of the infinite cylinder.

As an attempt to introduce interparticle interactions the following model is treated. A square lattice of infinite cylinders with a square cross section is assumed with all cylinders parallel to the applied field. Rotation in unison of the spins is assumed for each column of cylinders, and rotation in opposite directions but with equal magnitudes of the angle is assumed for neighboring columns. The coercive force of this model is found to be only slightly less than that given by Néel's formula which is valid for coherent rotation in a random distribution of infinite cylinders of any cross section. The dependence of the critical size and of the coercive force on the packing factor is discussed and compared with experiment.

A first approach to the study of the dependence of coercive force on imperfections is carried out by treating each of two mathematical models for a material which is infinite in all directions. The first model is a slab of finite width in which the anisotropy constant K is zero. The second one is a linear reduction of K through a slab of finite width from its constant value to zero. For both models the nucleation field is given as a function of the imperfection width. For the first model the behavior after nucleation is also discussed.
Energy Loss Resulting from Domain Wall Motion
Authors: Carr W. J.
Published: March 2008

At low frequencies the fraction of domain walls moving at a given instant is small; at higher frequencies all the walls move. Therefore, as the frequency approaches zero the eddy current constant becomes larger. The calculations of Pry and Bean are shown to pertain to the higher frequency case.

It also is pointed out that the hysteresis loss should not be the lower limit of the loss vs frequency curve as usually measured.
Effect of crystalline orientation on parallel and perpendicular exchange biases in FePt∕FeMn multilayers
Authors: Phuoc Nguyen N. , Suzuki Takao
Published: March 2008

A systematic study of parallel and perpendicular exchange biases in FePt∕FeMn multilayers epitaxially deposited onto MgO(100), MgO(110), and MgO(111) substrates by ion beam sputter-deposition system was performed. The ratio of parallel and perpendicular exchange biases is not only strongly dependent on crystalline orientation but also on the thickness of FePt layers. The result suggests that the spin structure at the interface in multilayer thin films may not be the same as that of the antiferromagnetic bulk.
Magnetotransport and magnetic properties of weak ferromagnetic semiconductors: Ca doped LaCrO3
Authors: Alvarez G. A. , Wang X. L. , Peleckis G. , Dou S. X. , Zhu J. G. , Lin Z. W.
Published: March 2008

We report the magnetic and magnetotransport properties of Ca doped La1−xCaxCrO3 (x=0, 0.1, 0.2, and 0.3). Both the magnetic and transport properties are very sensitive to Ca substitution. The Néel temperature TN decreases substantially with increasing calcium doping concentration from 290to160K. A weak ferromagnetic state with large coercive fields of up to 3T is present for the Ca doped LaCrO3. The temperature dependence of the resistivity shows that all the Ca doped compounds are semiconducting and their resistivities decrease with increasing Ca for low doping levels. The resistivity curves show thermally activated behavior and a variable range hopping behavior at high temperatures. The magnetotransport measurements show a negative magnetoresistance. Furthermore, an anomalous peak was observed in the field dependence of magnetoresistance for the LCCO materials.
A comparative study of alternating write-current-induced pole tip protrusion in perpendicular and longitudinal recording heads
Authors: Song Suping , Pan Tao , Fang Dori , Stoev Kroum , Ho Michael , Mao Sining
Published: March 2008

This paper presents a comparative study of alternating write-current-induced pole tip protrusions (WPTP) in perpendicular magnetic recording (PMR) and longitudinal magnetic recording (LMR) heads during writing operation. Both finite element modeling and experimental measurements were performed for this study. The results show that the writer resistance and inductance as well as the WPTP of PMR heads are all substantially lower than those of LMR heads within the write-current frequency range under consideration. It is found that the WPTP of a LMR head is mainly attributed to the eddy-current-induced Joule heating in yoke, whereas for a PMR head, the contribution to the WPTP from the Joule heating generated in write coils is comparable to that induced in yoke.
The effects of room temperature aging upon the magnetic properties of Ba-hexaferrite films grown on 6H-SiC substrates
Authors: Chen Z. , Cai Zhuhua , Yang Aria , Ziemer Katherine S. , Vittoria Carmine , Harris V. G.
Published: March 2008

The successes of making acceptable magnetic properties BaM films by different techniques based on pulsed laser deposition were reported in the past years. The key was to introduce a proper buffer layer to promote two dimensional growths on these semiconductor material substrates. After years, we go back to characterize these samples made by different processings. The purpose of this experiment is to explore the role of the buffer layers especially with the time dependence and thus demonstrate our film suitable for the potential future application. These samples are characterized by scanning electron microscopy, x-ray diffraction, and vibrating sample magnetometry comparing to characteristics of the as deposited films.
Design and implementation of antihandshaking position control for a voice coil motor
Authors: Lin Shir-Kuan , Wang Chao-Min , Wang Shyh-Jier
Published: March 2008

This paper deals with the position control of the voice coil motor (VCM) with handshaking. A disturbance observer is proposed to estimate the low-frequency handshaking disturbance, so that a handshaking-robust controller can be constructed. While a handshaking stabilizer can compensate for the vibration of the whole lens set, a robust controller is still required to precisely hold the autofocusing lens by rejecting the handshaking disturbance. To meet the request of miniaturization, the control is implemented on a field programmable gate array chip.
The hard magnetic properties and microstructure evolution of the multilayer [NdFeBNbCu∕FeBSi]⋅n thin films
Authors: Chiriac H. , Grigoras M. , Lupu N. , Urse M. , Buta V.
Published: March 2008

The influence of the thickness of constituent layers and annealing conditions for multilayer [NdFeBNbCu∕FeBSi]⋅n thin films on the magnetic properties and microstructure is reported. The Nb–Cu combination inhibits the grain growth and promotes the formation of nucleation sites. The FeSiB layer insertion leads to a slight increase in the Curie temperature and to a rectangular hysteresis loop. As compared to Ta∕NdFeBNbCu (540nm)∕Ta single layer, the Ta∕[NdFeBNbCu(180nm)∕FeBSi(15nm)]⋅3∕Ta multilayer nanocomposite films exhibit very good magnetic properties such as squareness Mr∕Ms of about 0.92, maximum energy product of about 397kJ∕m3, and an increase in the Curie temperature of about 17°C due to stratification by using FeBSi film as space layer.
Evaluation of performance and magnetic characteristics of a radial-radial flux compound-structure permanent-magnet synchronous machine used for hybrid electric vehicle
Authors: Zheng Ping , Liu Ranran , Shen Lin , Li Lina , Fan Weiguang , Wu Qian , Zhao Jing
Published: March 2008

A breed of compound-structure permanent-magnet synchronous machine (CS-PMSM) is used for power-split hybrid electric vehicles (HEVs). It can help to fulfill both the speed and torque control of the internal combustion engine and, thus, realize the optimum operation of the HEV. In this paper, a radial-radial flux CS-PMSM, which is integrated by two machines radially [one stator machine (SM) and one double-rotor machine (DRM)], is designed and investigated. The machine performance is evaluated with finite-element method (FEM) and satisfactory results are obtained. The back electromotive force curves of the two machines are somewhat similar to sinusoidal ones; the average torques both meet the requirements; and due to the adoption of skewed slots, the cogging torques and torque ripples are quite small. The inductance parameter is calculated with a phasor diagram based two-dimensional FEM and the magnetic saturation and cross-magnetization effect are discussed. It is concluded that the SM is slightly saturated with no or little cross-magnetization phenomenon, whereas the DRM has deep-degree magnetic saturation and the cross-magnetization effect is notable.
Directionally negative friction: A method for enhanced sampling of rare event kinetics
Authors: MacFadyen James , Wereszczynski Jeff , Andricioaei Ioan
Published: March 2008

A method exploiting the properties of an artificial (nonphysical) Langevin dynamics with a negative frictional coefficient along a suitable manifold and positive friction in the perpendicular directions is presented for the enhanced calculation of time-correlation functions for rare event problems. Exact time-correlation functions that describe the kinetics of the transitions for the all-positive, physical system can be calculated by reweighting the generated trajectories according to stochastic path integral treatment involving a functional weight based on an Onsager–Machlup action functional. The method is tested on a prototypical multidimensional model system featuring the main elements of conformational space characteristic of complex condensed matter systems. Using the present method, accurate estimates of rate constants require at least three order of magnitudes fewer trajectories than regular Langevin dynamics. The method is particularly useful in calculating kinetic properties in the context of multidimensional energy landscapes that are characteristic of complex systems such as proteins and nucleic acids.
Transmission electron microscopy study of the intermixing of Fe–Pt multilayers
Authors: Kaiser T. , Sigle W. , Goll D. , Goo N. H. , Srot V. , van Aken P. A. , Detemple E. , Jäger W.
Published: March 2008

Multilayers composed of 5×(6.4nmFe∕5.6nmPt) were annealed at temperatures up to 735°C. The intermixing was analyzed by analytical and high-resolution transmission electron microscopy. Intermixing and full ordering to the L10 structure was completed after annealing at 735°C. The temperature dependence of intermixing is best described by a three-step process including diffusion through diluted alloys during initial intermixing (400–500°C), diffusion through L12-ordered alloys (around 600°C), and diffusion in the final L10-ordered film above 700°C.
NIMROD resistive magnetohydrodynamic simulations of spheromak physics
Authors: Hooper E. B. , Cohen B. I. , McLean H. S. , Wood R. D. , Romero-Talamás C. A. , Sovinec C. R.
Published: March 2008

The physics of spheromak plasmas is addressed by time-dependent, three-dimensional, resistive magnetohydrodynamic simulations with the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. Included in some detail are the formation of a spheromak driven electrostatically by a coaxial plasma gun with a flux-conserver geometry and power systems that accurately model the sustained spheromak physics experiment [R. D. Wood et al., Nucl. Fusion 45, 1582 (2005)]. The controlled decay of the spheromak plasma over several milliseconds is also modeled as the programmable current and voltage relax, resulting in simulations of entire experimental pulses. Reconnection phenomena and the effects of current profile evolution on the growth of symmetry-breaking toroidal modes are diagnosed; these in turn affect the quality of magnetic surfaces and the energy confinement. The sensitivity of the simulation results addresses variations in both physical and numerical parameters, including spatial resolution. There are significant points of agreement between the simulations and the observed experimental behavior, e.g., in the evolution of the magnetics and the sensitivity of the energy confinement to the presence of symmetry-breaking magnetic fluctuations.
A unified density-functional treatment of dynamical, nondynamical, and dispersion correlations. II. Thermochemical and kinetic benchmarks
Authors: Johnson Erin R. , Becke Axel D.
Published: March 2008

In a previous work [J. Chem. Phys. 127, 124108 (2007)] we introduced an exact-exchange-based density-functional methodology incorporating dynamical, nondynamical, and dispersion correlations, called DF07. In this work, the performance of the DF07 method is assessed on a variety of thermochemical and kinetic benchmark data including ionization potentials, electron affinities, proton affinities, isomerization energies, bond dissociation enthalpies, and barrier heights of radical reactions. DF07 gives uniform accuracy over all our benchmark data without any refitting of parameters. The importance of the exact-exchange character of DF07 is highlighted through comparison with a three-parameter hybrid meta-generalized-gradient-approximation functional.
Linear and nonlinear optical properties of Si nanocrystals in SiO2 deposited by plasma-enhanced chemical-vapor deposition
Authors: Hernández S. , Pellegrino P. , Martínez A. , Lebour Y. , Garrido B. , Spano R. , Cazzanelli M. , Daldosso N. , Pavesi L. , Jordana E. , Fedeli J. M.
Published: March 2008

Linear and nonlinear optical properties of silicon suboxide SiOx films deposited by plasma-enhanced chemical-vapor deposition have been studied for different Si excesses up to 24at.%. The layers have been fully characterized with respect to their atomic composition and the structure of the Si precipitates. Linear refractive index and extinction coefficient have been determined in the whole visible range, enabling to estimate the optical bandgap as a function of the Si nanocrystal size. Nonlinear optical properties have been evaluated by the z-scan technique for two different excitations: at 0.80eV in the nanosecond regime and at 1.50eV in the femtosecond regime. Under nanosecond excitation conditions, the nonlinear process is ruled by thermal effects, showing large values of both nonlinear refractive index (n2∼−10−8cm2∕W) and nonlinear absorption coefficient (β∼10−6cm∕W). Under femtosecond excitation conditions, a smaller nonlinear refractive index is found (n2∼10−12cm2∕W), typical of nonlinearities arising from electronic response. The contribution per nanocrystal to the electronic third-order nonlinear susceptibility increases as the size of the Si nanoparticles is reduced, due to the appearance of electronic transitions between discrete levels induced by quantum confinement.
Multiscale structures in relativistic pair plasmas
Authors: Iqbal M. , Berezhiani V. I. , Yoshida Z.
Published: March 2008

The steady-state solution of a pair plasma with relativistic thermal velocity of the constituent particles (electrons and positrons) is investigated. The relaxed state can be written as a superposition of three Beltrami fields. Generally, the associated scale parameters could be a complex conjugate pair and a real one. It is shown that at higher thermal energies, all the scale parameters become real. It is also observed that one component gets a large scale (system size) while the other two components appear with small scale of the order of the skin depth at relativistic temperature.
High quantum efficiency two color type-II InAs∕GaSb n-i-p-p-i-n photodiodes
Authors: Delaunay Pierre-Yves , Nguyen Binh-Minh , Hoffman Darin , Hood Andrew , Huang Edward Kwei-Wei , Razeghi Manijeh , Tidrow Meimei Z.
Published: March 2008

A n-i-p-p-i-n photodiode based on type-II InAs∕GaSb superlattice was grown on a GaSb substrate. The two channels, with respective 50% of responsivity cutoff wavelengths at 7.7 and 10μm, presented quantum efficiencies (QEs) of 47% and 39% at 77K. The devices can be operated as two diodes for simultaneous detection or as a single n-i-p-p-i-n detector for sequential detection. In the latter configuration, the QEs at 5.3 and 8.5μm were measured as high as 40% and 39% at 77K. The optical cross-talk between the two channels could be reduced from 0.36 to 0.08 by applying a 50mV bias.
The proximity effect of the regrowth interface on two-dimensional electron density in strained Si
Authors: Liu J. , Lu T. M. , Kim J. , Lai K. , Tsui D. C. , Xie Y. H.
Published: March 2008

We studied the density of two-dimensional electron gas (2DEG) in Si∕SiGe heterostructures as a function of the distance between the substrate-epilayer interface and the 2DEG layer. The 2DEG sheet density was observed to change from 2.2×1011to3.5×1011cm−2. Theoretical simulations are shown to be consistent with the experimental results within experimental errors. The slight deviations of the experimental results possibly come from temperature variation of the Sb dopant source during the growth of the Sb doping layer.
Magnetotransport and dielectric properties of perovskite ruthenate and titanate thin films
Authors: Hao J. H. , Wang Z. H. , Gao J.
Published: March 2008

Perovskite thin films of conductive ferromagnetic SrRuO3 and incipient ferroelectric SrTiO3 were epitaxially grown by laser molecular beam technique. The magnetotransport properties of ferromagnetic films were measured by applying the magnetic field within a wide temperature range. We have observed magnetization hysteresis and significant anisotropic magnetotransport behaviors of thin films. The low-frequency dielectric properties of SrTiO3 films were studied. It is found that the microstructures and strain in films may strongly affect the magnetotransport and dielectric properties of perovskite oxides.
Linear and nonlinear optical properties of BiFeO3
Authors: Kumar Amit , Rai Ram C. , Podraza Nikolas J. , Denev Sava , Ramirez Mariola , Chu Ying-Hao , Martin Lane W. , Ihlefeld Jon , Heeg T. , Schubert J. , Schlom Darrell G. , Orenstein J. , Ramesh R. , Collins Robert W. , Musfeldt Janice L. , Gopalan Venkatraman
Published: March 2008

Using spectroscopic ellipsometry, the room temperature refractive index and absorption versus wavelength of the ferroelectric antiferromagnet bismuth ferrite, BiFeO3, are reported. The material has a direct band gap at 442nm wavelength (2.81eV). Using optical second harmonic generation, the nonlinear optical coefficients were determined to be d15∕d22=0.20±0.01, d31∕d22=0.35±0.02, d33∕d22=−11.4±0.20, and ∣d22∣=298.4±6.1pm∕V at a fundamental wavelength of 800nm.
Measuring reversible photomechanical switching rates for a molecule at a surface
Authors: Comstock Matthew J. , Levy Niv , Cho Jongweon , Berbil-Bautista Luis , Crommie Michael F. , Poulsen Daniel A. , Fréchet Jean M. J.
Published: March 2008

We have used single-molecule-resolved scanning tunneling microscopy to measure the photomechanical switching rates of azobenzene-derived molecules at a gold surface during exposure to UV and visible light. This enables the direct determination of both the forward and reverse photoswitching cross sections for surface-mounted molecules at different wavelengths. In a dramatic departure from molecular behavior in solution-based environments, visible light does not efficiently reverse the reaction for azobenzene-derived molecules at a gold surface.
The effect of boron diffusions on the defect density and recombination at the (111) silicon-silicon oxide interface
Authors: Jin H. , Jellett W. E. , Chun Z. , Weber K. J. , Blakers A. W. , Smith P. J.
Published: March 2008

A combination of electron paramagnetic resonance (EPR) and minority carrier lifetime measurements is used to unambiguously demonstrate that the presence of a B diffusion layer at the surface of oxidized Si (111) wafers causes a significant increase in the interface defect density as well as interface recombination, compared to undiffused surfaces. EPR measurements show a nearly three-fold increase in the Pb center density, while the lifetime measurements indicate an increase in surface recombination activity by a factor of more than two, for B diffused samples with a sheet resistance of ∼250Ω∕◻◻.
The Geography of Internet Adoption by Independent Retailers in the Netherlands
Authors: Weltevreden Jesse W J , Atzema Oedzge A L C , Frenken Koen , de Kruif Karlijn , van Oort Frank G
Published: March 2008

So far, the literature on Internet adoption by retailers has paid little attention to spatial variables. Using data on approximately 12 000 independent retailers, we investigate the geographical diffusion of Internet strategies in the Netherlands. In particular, we examine to what extent Internet adoption differs among shopping centers, cities, and regions, while accounting for organizational variables. Results suggest that independent retailers at city and village centers are more likely to adopt information-only and online sales strategies than independents located at shopping centers at the bottom of the retail hierarchy. Furthermore, independent retailers in large(r) cities have a higher probability of adopting the Internet than their counterparts in small(er) cities. On the regional level, the likelihood of Internet adoption is higher for independent retailers in core regions than for independents in the periphery. Thus, geography seems to matter for Internet adoption by independent retailers.
Distance-Measure Impacts on the Calculation of Transport Service Areas Using GIS
Authors: Gutiérrez Javier , García-Palomares Juan Carlos
Published: March 2008

Access coverage is important in public transit planning, as this is the means by which service is provided to riders. In fact the proximity of demand (population and employment) to stops or stations on the network to a great extent explains its greater or lesser usage by potential users. Coverage of service areas can be delineated by GIS through the creation of buffers around transit facilities based on Euclidean (straight-line) distance. A second method is based on calculations of distances along a street network (network distance). The choice of the distance calculation method affects significantly the final results in terms of population covered. This paper assesses the overestimation of the straight-line-distance method, which is the most widely used in coverage analysis, by comparing it with that of network distances. It investigates systematically the factors influencing this overestimation, such as the density of stops or stations, the coverage distance thresholds and the characteristics of the area analysed (street-network design, barriers, and population distribution in the neighbourhood of the bus stop or station). Finally, it concludes that the network-distance method provides systematically better estimates of transit ridership than the Euclidean distance method.
A Discrete-Choice Approach to Modeling Social Influence on Individual Decision Making
Authors: Páez Antonio , Scott Darren M , Volz Erik
Published: March 2008

Individual decision making is commonly studied using discrete choice models. Models of this type are applied extensively to the study of travel behavior, residential location, and employment decisions, among other topics of interest. A notable characteristic of the underlying economic theory is the assumption that individuals seek to maximize utility on the basis of their personal attributes and the attributes of the alternatives available to them. This approach ignores the interrelated nature of decision making in social situations—in other words, the role that social structures play in shaping behavior. In this paper we describe a multinomial discrete choice approach to analyzing individual behavior in social situations where position in a social network may encourage or discourage different courses of action. By means of a simulation example, we explore some properties of the model, in particular the effect of network topology.
Foucault's Spatial Combat
Authors: Johnson Peter
Published: March 2008

Many diverse spatial features within Foucault's historical studies have been analysed productively within Anglophone human geography. Although much of this work has tended to focus on Foucault's mid to later projects, especially around issues of health, surveillance, governmentality, and sexuality, his earlier archaeological studies have also produced fruitful avenues of research. Concentrating on the latter, and taking up Elden's notion of Foucault's use of space as a tool of analysis, I explore how Foucault's intense study of modern literature, particularly Roussel and Blanchot, contributes to underlying modes of spatialisation that drive his study of the history of clinical medicine, as well as the complex explanation of his archaeological approach. Following Deleuze, I argue that these spatialisations are both the instrument and the object of his studies. They generate devices and tactics for dismantling established methods of analysis and manifest the powerful, multiple effects of discourse, whilst remaining meticulously at the level of description.
Rapid Detection of Person Information in a Naturalistic Scene
Authors: Fletcher-Watson Sue , Findlay John M , Leekam Susan R , Benson Valerie
Published: March 2008

A preferential-looking paradigm was used to investigate how gaze is distributed in naturalistic scenes. Two scenes were presented side by side: one contained a single person (person-present) and one did not (person-absent). Eye movements were recorded, the principal measures being the time spent looking at each region of the scenes, and the latency and location of the first fixation within each trial. We studied gaze patterns during free viewing, and also in a task requiring gender discrimination of the human figure depicted. Results indicated a strong bias towards looking to the person-present scene. This bias was present on the first fixation after image presentation, confirming previous findings of ultra-rapid processing of complex information. Faces attracted disproportionately many fixations, the preference emerging in the first fixation and becoming stronger in the following ones. These biases were exaggerated in the gender-discrimination task. A tendency to look at the object being fixated by the person in the scene was shown to be strongest at a slightly later point in the gaze sequence. We conclude that human bodies and faces are subject to special perceptual processing when presented as part of a naturalistic scene.
Cyanuric Chloride: an Efficient Catalyst for Ring Opening of Epoxides with Thiols Under Solvent-Free Conditions
Authors: Bandgar Babasaheb P. , Joshi Neeta S. , Kamble Vinod T. , Sawant Sanjay S.
Published: March 2008

2,4,6-Trichloro-1,3,5-triazine-catalyzed convenient and efficient ring opening of epoxides with thiols under solvent-free conditions is described. Short reaction time, mild reaction conditions, inexpensive and readily available catalyst, and excellent yields of products are attractive features of this methodology.
Synthesis, Structure, and Antibacterial Activity of Novel 5-Arylpyrazole Derivatives
Authors: Liu Xin-Hua , Lv Peng-Cheng , Li Bo , Zhu Hai-Liang , Song Bao-An
Published: March 2008

A series of novel 1-(acetyl,carboxamide,carbothioamide)substituted-5-(substituted-phenyl)-3-methy-4,5-dihydropyrazole derivatives have been synthesized and characterized by 1H NMR, IR, ESI-MS, and elemental analysis. Compounds 6h and 6q were further characterized by single crystal X-ray structural analysis. All of the compounds have been screened for their antibacterial potential in vitro against Bacillus subtilis ATCC 6633, Escherichia coli ATCC 35218, Pseudomonas fluorescens ATCC 13525, and Staphylococcus aureus ATCC 6538. Among the tested compounds, some of them display significant activity against the tested strains, and compounds 5ac and 6h show potent activity with a minimum inhibitory concentration value of 1.562 μg mL–1 against B. subtilis ATCC 6633, which is comparable to the positive control penicillin. Structure–effect relationships are also discussed based on the experimental data.
The Reactivity of Diorganotellurium Oxides Towards Phenol and o-Nitrophenol. Hypervalent and Secondary Bonding of Four Different Product Classes
Authors: Beckmann Jens , Bolsinger Jens , Duthie Andrew
Published: March 2008

The reaction of the diorganotellurium oxides R2TeO (R = Ph, p-MeOC6H4, p-Me2NC6H4) with phenol and o-nitrophenol produces diorganotellurium hydroxy phenolates, R2Te(OH)OPh (1, R = Ph; 2, R = p-MeOC6H4; 3, R = p-Me2NC6H4), diorganotellurium bis(phenolates) R2Te(OPh)2 (4, R = Ph; 5, R = p-MeOC6H4; 6, R = p-Me2NC6H4), tetraorganoditelluroxane bis(o-nitrophenolates), (R′O)R2TeOTeR2(OR′) (7, R = p-MeOC6H4; 8, R = p-Me2NC6H4; R′ = o-NO2C6H4), and a hexaphenyltritelluroxane bis(o-nitrophenolate) (R′O)Ph2TeOTePh2OTePh2(OR′) (9, R′ = o-NO2C6H4), respectively. The redistribution reactions of R2Te(OPh)2 (4, R = Ph; 5, R = p-MeOC6H4; 6, R = p-Me2NC6H4) with the corresponding diorganotellurium oxides R2TeO and diorganotellurium dichlorides R2TeCl2 (R = Ph, p-MeOC6H4, p-Me2NC6H4) give rise to the formation of moisture sensitive tetraorganoditelluroxane bis(phenolates) (PhO)R2TeOTeR2(OPh) (10, R = Ph; 11, R = p-MeOC6H4; 12, R = p-Me2NC6H4) and diorganotellurium chloro phenolates, R2Te(Cl)OPh (13, R = Ph; 14, R = p-MeOC6H4; 15, R = p-Me2NC6H4), respectively. The reaction of the diorganotellurium oxides R2TeO with the corresponding diorganotellurium dichlorides R2TeCl2 (R = Ph, p-MeOC6H4, p-Me2NC6H4) affords tetraorganoditelluroxane dichlorides ClR2TeOTeR2Cl (16, R = Ph; 17, R = p-MeOC6H4; 18, R = p-Me2NC6H4) as air-stable solid materials. The reactivity of 1–18 can be rationalized by the kinetic lability of the Te–O and Te–Cl bonds. Compounds 1–18 have been characterized by solution and solid-state 125Te NMR spectroscopy and 2, 4, 6, 7, 9, 17, and 18 have also been analyzed by X-ray crystallography.
ATP-dependent activation of p21
WAF1/CIP1
-associated Cdk2 by Cdc6
Authors: Kan Qiuming , Jinno Shigeki , Yamamoto Hanako , Kobayashi Kohei , Okayama Hiroto
Published: March 2008

When cells progressing in mid-S phase are damaged with a base-modifying chemical, they arrest in S phase long after the CHK1 checkpoint signal fades out, partly because of p53-mediated long-lasting induction of the cyclin-dependent kinase inhibitor p21
WAF1/CIP1
. We have recently found that enforced expression of Cdc6, the assembler of prereplicative complexes, markedly advances recovery from the prolonged S-phase arrest and reactivation of Cdk2 despite the presence of a high level of induced p21. Here, we report that Cdc6 protein can activate p21-associated Cdk2 in an ATP-dependent manner
in vitro
. Consistently, Cdc6 mutated for ATPase or a putative cyclin binding motif is no longer able to activate the Cdk2
in vitro
or promote reinitiation of S-phase progression and reactivation of Cdk2
in vivo
. These results reveal the never anticipated function of Cdc6 and redefine its role in the control of S-phase progression in mammalian cells.