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Articles 1 - 12 of 12

Full-Text Articles in Physics

Recent Developments In Modeling Of The Stress Derivative Of Magnetization In Ferromagnetic Materials, David C. Jiles, Michael K. Devine Nov 1994

Recent Developments In Modeling Of The Stress Derivative Of Magnetization In Ferromagnetic Materials, David C. Jiles, Michael K. Devine

Ames Laboratory Publications

The effect of changing stress on the magnetization of ferromagnetic materials leads to behavior in which the magnetization may increase, or decrease, when exposed to the same stress under the same external conditions. A simple empirical law seems to govern the behavior when the magnetization begins from a major hysteresis loop. The application of the law of approach, in which the derivative of the magnetization with respect to the elastic energy supplied dM/dW is proportional to the magnetization displacement M anM, is discussed.


Frequency Dependence Of Hysteresis Curves In Conducting Magnetic Materials, David C. Jiles Nov 1994

Frequency Dependence Of Hysteresis Curves In Conducting Magnetic Materials, David C. Jiles

Ames Laboratory Publications

An extension of the hysteresis model has been developed that takes into account the effects on the hysteresis curves of eddycurrents in electrically conducting media. In the derivation presented it is assumed that the frequency of the applied field is low enough (or the thickness of the material medium small enough) that the skin effect can be ignored so that the magnetic field penetrates uniformly throughout the material. In this case, the dc hysteresis equation is extended by the addition of a classical eddy‐current‐loss term depending on (i) the rate of change of magnetization with time, (ii) the ...


Estimation Of The Free-Charge-Carrier Concentration In Fast-Ion Conducting Na2s-B2s3 Glasses From An Analysis Of The Frequency-Dependent, Ernest F. Hairetdinov, Nikolai F. Uvarov, Hitendra K. Patel, Steve W. Martin Nov 1994

Estimation Of The Free-Charge-Carrier Concentration In Fast-Ion Conducting Na2s-B2s3 Glasses From An Analysis Of The Frequency-Dependent, Ernest F. Hairetdinov, Nikolai F. Uvarov, Hitendra K. Patel, Steve W. Martin

Materials Science and Engineering Publications

ac and dc conductivities of fast-ion conducting xNa2S+(1-x)B2S3 glasses in the composition range 0.001≤x≤0.1 were analyzed using the Almond-West formula σ(ν)=σdc[1+(ν/νH)α]. The hopping frequency for free charge carriers νH, the dc conductivity σdc, and their respective activation energies were determined. The concentration of free charge carriers evaluated from the conductivities and estimated mobilities is in good agreement with the overall content of sodium cations in the glasses and it is proposed that this supports the concept of a strong and not weak electrolyte model for these ...


Band Dispersion In C60(111): An Angle-Resolved Photoemission Study, P. J. Benning, C. G. Olson, David W. Lynch, J. H. Weaver Oct 1994

Band Dispersion In C60(111): An Angle-Resolved Photoemission Study, P. J. Benning, C. G. Olson, David W. Lynch, J. H. Weaver

Physics and Astronomy Publications

Angle-resolved photoemission studies of single-crystal C60(111) films grown on GeS(001) reveal changes in valence feature line shape with emission angle and photon energy that are indicative of band dispersion. For an excitation energy (hν) of 10 eV, normal emission spectra show four sharp structures within the ∼1.1-eV-wide valence feature derived from the second highest molecular orbital (HOMO-1) of C60. For hν=8.1 eV, the 1-eV-wide HOMO-derived feature exhibits changes with emission angle mainly due to dispersion of 0.6 eV in the unoccupied bands. The distribution of electronic states underlying HOMO and HOMO-1 indicates ...


Method For Producing Strain Tolerant Multifilamentary Oxide Superconducting Wire, Douglas K. Finnemore, Theodore A. Miller, Jerome E. Ostenson, Louis A. Schwartzkopf, Steven C. Sanders Jul 1994

Method For Producing Strain Tolerant Multifilamentary Oxide Superconducting Wire, Douglas K. Finnemore, Theodore A. Miller, Jerome E. Ostenson, Louis A. Schwartzkopf, Steven C. Sanders

Iowa State University Patents

A strain tolerant multifilamentary wire capable of carrying superconducting currents is provided comprising a plurality of discontinuous filaments formed from a high temperature superconducting material. The discontinuous filaments have a length at least several orders of magnitude greater than the filament diameter and are sufficiently strong while in an amorphous state to withstand compaction. A normal metal is interposed between and binds the discontinuous filaments to form a normal metal matrix capable of withstanding heat treatment for converting the filaments to a superconducting state. The geometry of the filaments within the normal metal matrix provides substantial filament-to-filament overlap, and the ...


Monitoring Neutron Embrittlement In Nuclear Pressure Vessel Steels Using Micromagnetic Barkhausen Emissions, Levent B. Sipahi, Madhav Rao Govindaraju, David C. Jiles May 1994

Monitoring Neutron Embrittlement In Nuclear Pressure Vessel Steels Using Micromagnetic Barkhausen Emissions, Levent B. Sipahi, Madhav Rao Govindaraju, David C. Jiles

Center for Nondestructive Evaluation Publications

In nuclear power plants, neutron embrittlement of pressure vessel steels has been one of the main concerns. The use of micromagnetic Barkhausen emissions is a promising method to monitor the variations in microstructural and subsurface stress states due to their influence on these emissions. Measurements of these emissions can reveal neutron irradiationdegradation in nuclear power plant components. Samples which were irradiated at differentneutron fluences and annealed at different temperatures were obtained from three reactor surveillance programs. The results of different neutron fluences and annealing procedures showed noticeable fractional changes in the magnetic Barkhausen effect signal parameter, ΔMBE/MBE, and in ...


Estimation Of Fatigue Exposure From Magnetic Coercivity, Z. J. Chen, David C. Jiles, J. Kameda May 1994

Estimation Of Fatigue Exposure From Magnetic Coercivity, Z. J. Chen, David C. Jiles, J. Kameda

Ames Laboratory Publications

An investigation of the effects of fatigue on A533B steel under constant load amplitude is reported in this paper. It was found that the plastic strain of the sample accumulated logarithmically with the number of stress cycles after initial fatigue softening. Based on the fact that plastic strain is often linearly related to the coercivity of material, at least for small changes of H c , a phenomenological relationship has been developed and tested to correlate the number of stress cycles to this magnetic parameter. This result represents the first successful attempt to relate the fatigue exposure directly to a magnetic ...


Elastic Constants Of Bcc Cu-Al-Ni Alloys, Lluís Mañosa, M. Jurado, Antoni Planes, Jerel L. Zarestky, Thomas A. Lograsso, C. Stassis Apr 1994

Elastic Constants Of Bcc Cu-Al-Ni Alloys, Lluís Mañosa, M. Jurado, Antoni Planes, Jerel L. Zarestky, Thomas A. Lograsso, C. Stassis

Ames Laboratory Publications

We have measured the adiabatic elastic constants of two Cu-Al-Ni martensitic alloys using ultrasonic methods and we have compared the results to recent neutron-scattering experiments. It is shown that the elastic behavior of Cu-Al-Ni alloys follows the same trends exhibited by other Cu-based alloys; in particular, the TA2 long-wavelength acoustic modes are softer than all other modes.


Interface Propagation And Nucleation Phenomena For Discontinuous Poisoning Transitions In Surface-Reaction Models, James W. Evans, T. R. Ray Jan 1994

Interface Propagation And Nucleation Phenomena For Discontinuous Poisoning Transitions In Surface-Reaction Models, James W. Evans, T. R. Ray

Physics and Astronomy Publications

Here, we consider discontinuous nonequilibrium phase transitions to poisoned or ‘‘adsorbing’’ states in lattice-gas models of surface reactions. Specifically, we examine the monomer or CO-poisoning transition in the Ziff-Gulari-Barshad monomer-dimer reaction model for CO oxidation, modified to include adspecies diffusion. For CO pressures below the poisoning transition, we first characterize the propagation of and fluctuations at an interface between reactive and CO-poisoned states. Here, we utilize ideas from spatial contact models, reaction-diffusion theory, and kinetic roughening theory. Evolution is described by the Kardar-Parisi-Zhang equation, but with the nonlinearity and kinetic surface tension vanishing on approaching the transition. Next, again for ...


Anisotropy In Nucleation And Growth Of Two-Dimensional Islands During Homoepitaxy On "Hex" Reconstructed Au(100), S. Günther, E. Kopatzki, M. C. Bartelt, James W. Evans, R. J. Behm Jan 1994

Anisotropy In Nucleation And Growth Of Two-Dimensional Islands During Homoepitaxy On "Hex" Reconstructed Au(100), S. Günther, E. Kopatzki, M. C. Bartelt, James W. Evans, R. J. Behm

Physics and Astronomy Publications

We present results of a comprehensive scanning tunneling microscopy study of the nucleation and growth of Au islands on Au(100). It is shown that the reconstruction of the substrate produces strong anisotropic effects. Rate equation analysis of the experimental flux and temperature dependence of the island density suggests: (i) a critical size of i=3 for T=315−380 K, but i>3 above 400 K; and (ii) strongly anisotropic diffusion, preferentially parallel to the reconstruction rows (activation energy ∼0.2 eV). We comment on energetic and kinetic aspects of the observed island shape anisotropy.


Lattice‐Gas Model Mimicking The No+Co Reaction On Pt(100), Baoqi Meng, W. Henry Weinberg, James W. Evans Jan 1994

Lattice‐Gas Model Mimicking The No+Co Reaction On Pt(100), Baoqi Meng, W. Henry Weinberg, James W. Evans

Physics and Astronomy Publications

Various NO‐reduction reactions on Pt(100) exhibit similar dynamical behavior, presumably due to an empty site requirement for NO dissociation. This motivates analysis of a lattice‐gas model which incorporates this feature, and which here is chosen to mimic the NO+CO reaction on Pt(100): both reactants adsorb at single empty sites, NO instantaneously dissociates given an adjacent empty site (and nitrogen adatoms thus formed are immediately removed), and adjacent CO and O instantaneously react. We also include desorption of adsorbed NO and CO, but no adspecies diffusion. At lower temperatures where desorption is absent, we show that ...


Kinetics Of Restricted Solid-On-Solid Models Of Film Growth, James W. Evans, M. C. Bartelt Jan 1994

Kinetics Of Restricted Solid-On-Solid Models Of Film Growth, James W. Evans, M. C. Bartelt

Physics and Astronomy Publications

We consider the kinetics of irreversible film growth in solid-on-solid models with various restrictions on the adsorption (or growth) sites. We show how the master equations for the probabilities of subconfigurations of filled sites can be analyzed exactly to obtain coverages and spatial correlations for the first several layers. These provide an efficient framework for analysis of the early-stage growth kinetics, and indicate rapid attainment of asymptotic behavior. We illustrate the (1+1)- and (2+1)-dimensional cases for the simplest restricted solid-on-solid condition, and various modifications.