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2002

Missouri University of Science and Technology

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Articles 1 - 30 of 57

Full-Text Articles in Physical Sciences and Mathematics

Invariant Sets And Inverse Limits, William Thomas Ingram Dec 2002

Invariant Sets And Inverse Limits, William Thomas Ingram

Mathematics and Statistics Faculty Research & Creative Works

In this paper we investigate the nature of inverse limits from the point of view of invariant sets. We then introduce a special class of examples of inverse limits on [0,1] using Markov bonding maps determined by members of the group of permutations on n elements. © 2002 Elsevier Science B.V. All rights reserved.

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Interactive Learning Tools: Animating Statics, Nancy Hubing, David B. Oglesby, Timothy A. Philpot, Vikas Yellamraju, Richard H. Hall, Ralph E. Flori Dec 2002

Interactive Learning Tools: Animating Statics, Nancy Hubing, David B. Oglesby, Timothy A. Philpot, Vikas Yellamraju, Richard H. Hall, Ralph E. Flori

Business and Information Technology Faculty Research & Creative Works

Computer-Based Modules for Engineering Instruction Must Be Concise, Flexible, Educational and Engaging in Order to Effectively Supplement Traditional Classroom Teaching Tools. a Computer Example that Takes More Time Than a Chalkboard Presentation is Not Likely to Be Useful in Today's Engineering Classroom. Flexible Navigation is Necessary So that the Instructor Can Quickly and Easily Respond to Student Questions. Useful Modules Must Also Improve Problem-Solving Skills or Clarify Troublesome Concepts in Order to Be Considered Worthy of Inclusion in the Limited Class Time Available. Finally, and Perhaps Most Importantly, Effective Computer-Based Modules Must Meet the Challenge of Holding the Student's Attention. …

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Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison Dec 2002

Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison

Physics Faculty Research & Creative Works

It is usually assumed that the first-Born approximation for electron-atom ionization becomes valid for the fully differential cross section at sufficiently high impact energies, at least for asymmetric collisions where the projectile suffers only a small energy loss and is scattered by a small angle. Here we investigate this assumption quantitatively for ionization of hydrogen atoms. We find that convergence of the Born approximation to the correct nonrelativistic result is generally achieved only at energies where relativistic effects start to become important. Consequently, the assumption that the Born approximation becomes valid for high energy is inaccurate, since by the time …

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Load-Sensitive Transmission Power Control In Wireless Ad-Hoc Networks, Seung Jong Park, Raghupathy Sivakumar Dec 2002

Load-Sensitive Transmission Power Control In Wireless Ad-Hoc Networks, Seung Jong Park, Raghupathy Sivakumar

Computer Science Faculty Research & Creative Works

Transmission power control in ad-hoc networks has hitherto been used only for achieving connectivity of networks. It has been implicitly assumed that the optimal throughput performance in ad-hoc networks can be achieved when using the minimum transmission power required to keep the network connected. However, in this paper we argue that such an assumption remains valid only under high node densities, which is not the characteristic of typical ad-hoc networks. Using both throughput and throughput per unit energy as the optimization criteria, we demonstrate that the optimal transmission power depends on several network characteristics such as the number of stations, …

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Electronic Structure Of Thallium Filled Skutterudites Studied By X-Ray Absorption And Mössbauer Spectroscopy, Gary J. Long, Bernard M. Mahieu, Brian C. Sales, Raphäel P. Hermann, Fernande Grandjean Dec 2002

Electronic Structure Of Thallium Filled Skutterudites Studied By X-Ray Absorption And Mössbauer Spectroscopy, Gary J. Long, Bernard M. Mahieu, Brian C. Sales, Raphäel P. Hermann, Fernande Grandjean

Chemistry Faculty Research & Creative Works

The electronic structure of the three sites in the thallium filled skutterudites was studied. Two series of thallium filled skutterudites were formed because thallium has a formal valence of +1 and iron or tin must replace some of the cobalt or antimony respectively, to maintain charge neutrality. Large atomic mean-square displacements were observed for the thallium filling atoms and it helps to produce the large thermal resistivity observed for these skutterudites.

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Superfluidity In The Solar Interior: Implications For Solar Eruptions And Climate, Oliver Manuel, Barry W. Ninham, Stig Friberg Dec 2002

Superfluidity In The Solar Interior: Implications For Solar Eruptions And Climate, Oliver Manuel, Barry W. Ninham, Stig Friberg

Chemistry Faculty Research & Creative Works

Efforts to understand unusual weather or abrupt changes in climate have been plagued by deficiencies of the standard solar model (SSM) [1]. Although it assumes that our primary source of energy began as a homogeneous ball of hydrogen (H) with a steady, well-behaved H-fusion reactor at its core, observations instead reveal a very heterogeneous, dynamic Sun. As examples, the upward acceleration and departure of H+ ions from the surface of the quiet Sun and abrupt climatic changes, including geomagnetic reversals and periodic magnetic storms that eject material from the solar surface are not explained by the SSM. The present …

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Polarized Neutron Diffraction And Mössbauer Spectral Study Of Short-Range Magnetic Correlations In The Ferrimagnetic Layered Compounds (Pph₄) [FeIiFeIii(Ox)₃] And (Nbu₄) [FeIiFeIii(Ox)₃], Simon G. Carling, Dirk W. Visser, Dimitri Hautot, Ian D. Watts, Peter Day, Jürgen Ensling, Phillip Gütlich, Gary J. Long, Fernande Grandjean Sep 2002

Polarized Neutron Diffraction And Mössbauer Spectral Study Of Short-Range Magnetic Correlations In The Ferrimagnetic Layered Compounds (Pph₄) [FeIiFeIii(Ox)₃] And (Nbu₄) [FeIiFeIii(Ox)₃], Simon G. Carling, Dirk W. Visser, Dimitri Hautot, Ian D. Watts, Peter Day, Jürgen Ensling, Phillip Gütlich, Gary J. Long, Fernande Grandjean

Chemistry Faculty Research & Creative Works

Short-range antiferromagnetic correlations have been studied in the layered compounds (PPh4) [FeIIFeIII(ox)3] and (NBu4) [FeIIFeIII(ox)3] by neutron polarization analysis and Mössbauer spectroscopy. Polarized neutron diffraction profiles obtained between 2 and 50 K on (d20-Pph4) [FeIIFeIII(ox)3] show no magnetic Bragg scattering; the lack of such scattering indicates the absence of long-range magnetic order. However, a broad asymmetric feature observed at a Q of ca. 0.8 Å-1 is attributed to two-dimensional short-range magnetic correlations, which …

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Morphologic And Magnetic Properties Of Pd₁₀₀₋ₓfeₓ Nanoparticles Prepared By Ultrasound Assisted Electrochemistry, Maribel Guzman, Jean Luc Delplancke, Gary J. Long, Jacques P. Delwiche, Marie Jeanne Hubin-Franskin, Fernande Grandjean Sep 2002

Morphologic And Magnetic Properties Of Pd₁₀₀₋ₓfeₓ Nanoparticles Prepared By Ultrasound Assisted Electrochemistry, Maribel Guzman, Jean Luc Delplancke, Gary J. Long, Jacques P. Delwiche, Marie Jeanne Hubin-Franskin, Fernande Grandjean

Chemistry Faculty Research & Creative Works

Nanopowdered alloys of Pd100-xFex, with x=4, 6, 8, and 12, have been prepared by ultrasound assisted electrochemistry. The composition of the individual particles, as determined by x-ray fluorescence, and the bulk composition, as determined by atomic absorption, are in agreement within experimental error. Transmission electron microscopy indicates that the nanopowders consist of agglomerates of small grains with a radius of approximately 5 nm, a radius which is confirmed by the broadening of the reflections in the x-ray powder diffraction patterns. X-ray fluorescence analysis of individual grains indicates a homogeneous distribution of palladium and iron throughout the …

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Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi Sep 2002

Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi

Physics Faculty Research & Creative Works

We investigate de Sitter/conformal field theory (dS/CFT) correspondence in two dimensions. We define the conserved mass of de Sitter spacetime and formulate the correspondence along the lines of the anti–de Sitter/conformal field theory duality. The asymptotic symmetry group, mass, and central charge of de Sitter spacetime are equal to those of anti–de Sitter spacetime. The entropy of two-dimensional de Sitter spacetime is evaluated by applying the Cardy formula. We calculate the boundary correlators induced by the propagation of the dilaton in two-dimensional de Sitter space. Although the dilaton is a tachyonic perturbation in the bulk, boundary conformal correlators have a …

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Object-Oriented Modeling And Fault Detection Of A Powder Feeder For A Laser Metal Deposition System, Robert G. Landers, Michael Gene Hilgers, Frank W. Liou, Bruce M. Mcmillin Aug 2002

Object-Oriented Modeling And Fault Detection Of A Powder Feeder For A Laser Metal Deposition System, Robert G. Landers, Michael Gene Hilgers, Frank W. Liou, Bruce M. Mcmillin

Mechanical and Aerospace Engineering Faculty Research & Creative Works

One of the most critical components of a laser metal deposition system is the powder feeder unit. Techniques are required to efficiently design and analyze these systems and to ensure fault tolerance during the operation. In this paper, a model of the powder feeder unit, based on object-oriented abstractions of it components, is developed. This model is modular in that specific components can be efficiently updated or replaced with components that perform a similar function. In addition, the model can be used for simulation allowing for efficient design and analysis. Assurance of the correctness of the powder feeder system is …

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Object-Oriented Modeling And Fauly Detection Of A Powder Feeder For A Laser Metal Deposition System, Robert G. Landers, Michael Gene Hilgers, Frank W. Liou, Bruce M. Mcmillin Aug 2002

Object-Oriented Modeling And Fauly Detection Of A Powder Feeder For A Laser Metal Deposition System, Robert G. Landers, Michael Gene Hilgers, Frank W. Liou, Bruce M. Mcmillin

Mechanical and Aerospace Engineering Faculty Research & Creative Works

One of the most critical components of a laser metal deposition system is the powder feeder unit. Techniques are required to efficiently design and analyze these systems and to ensure fault tolerance during the operation. In this paper, a model of the powder feeder unit, based on object- oriented abstractions of it components, is developed. This model is modular in that specific components can be efficiently updated or replaced with components that perform a similar function. In addition, the model can be used for simulation allowing for efficient design and analysis. Assurance of the correctness of the powder feeder system …

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Double-Logarithmic Two-Loop Self-Energy Corrections To The Lamb Shift, Ulrich D. Jentschura, I. Nandori Aug 2002

Double-Logarithmic Two-Loop Self-Energy Corrections To The Lamb Shift, Ulrich D. Jentschura, I. Nandori

Physics Faculty Research & Creative Works

Self-energy corrections involving logarithms of the parameter Z α can often be derived within a simplified approach, avoiding calculational difficulties typical of the problematic nonlogarithmic corrections (as customary in bound-state quantum electrodynamics, we denote by Z the nuclear charge number, and by α the fine-structure constant). For some logarithmic corrections, it is sufficient to consider internal properties of the electron characterized by form factors. We provide a detailed derivation of related self-energy “potentials” that give rise to the logarithmic corrections; these potentials are local in coordinate space. We focus on the double-logarithmic two-loop coefficient B62 for P states and …

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A Problematic Set Of Two-Loop Self-Energy Corrections, Ulrich D. Jentschura, Jorg Evers, Christoph H. Keitel, Krzysztof Pachucki Jul 2002

A Problematic Set Of Two-Loop Self-Energy Corrections, Ulrich D. Jentschura, Jorg Evers, Christoph H. Keitel, Krzysztof Pachucki

Physics Faculty Research & Creative Works

We investigate a specific set of two-loop self-energy corrections involving squared decay rates and point out that their interpretation is highly problematic. The corrections cannot be interpreted as radiative energy shifts in the usual sense. Some of the problematic corrections find a natural interpretation as radiative nonresonant corrections to the natural line shape. They cannot uniquely be associated with one and only one atomic level. While the problematic corrections are rather tiny when expressed in units of frequency (a few hertz for hydrogenic P levels) and do not affect the reliability of quantum electrodynamics at the current level of experimental …

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Coincident Fragment Detection In Strong Field Photoionization And Dissociation Of H₂, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Alexander Dorn, Claus Dieter Schroter, Daniel Fischer, Jose R. Crespo Lopez-Urrutia, Paul B. Neumayer, J. Deipenwisch, C. Hohr, Bernold Feuerstein, Joachim Hermann Ullrich Jul 2002

Coincident Fragment Detection In Strong Field Photoionization And Dissociation Of H₂, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Alexander Dorn, Claus Dieter Schroter, Daniel Fischer, Jose R. Crespo Lopez-Urrutia, Paul B. Neumayer, J. Deipenwisch, C. Hohr, Bernold Feuerstein, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

An investigation of the correlated electronic and nuclear motion in fragmentation of H2 in 4 x 1014 W/cm2, fs laser pulses at 795 nm was presented using the electron-ion momentum spectroscopy. The channel selective electron energy distribution indicated assumption of a new H2 ionization mechanism to interpret the differences found in the fragmentation channels. The results showed that the momentum distribution of H+ ions in the dissociation channels H(1s) + H+ + e- and 2H+ + 2e- was independent of the kinetic energy of photoelectrons.

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Mechanism For Carrier Velocity Saturation In Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris Jun 2002

Mechanism For Carrier Velocity Saturation In Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

We present a possible mechanism for the saturation of the velocity of photoinjected charge carriers in pure organic crystals, the analysis having been motivated by observations in pentacene. The mechanism is based on the strong wave vector dependence of the damping coefficient appearing in the appropriate effective mass equation. Our primary goal is to explore this mechanism in general terms rather than to apply it to a specific system such as pentacene. Our analysis is based on a Fokker-Planck equation treatment. We indicate how the damping coeffcient is related to relaxation times in usual Boltzmann equations and how it can …

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Gravity Evidence For A Larger Limpopo Belt In Southern Africa And Geodynamic Implications, Rubeni T. Ranganai, Ali Basira H. Kampunzu, Estella A. Atekwana, B. K. Paya, J. G. King, D. I. Koosimile, Edgar H. Stettler Jun 2002

Gravity Evidence For A Larger Limpopo Belt In Southern Africa And Geodynamic Implications, Rubeni T. Ranganai, Ali Basira H. Kampunzu, Estella A. Atekwana, B. K. Paya, J. G. King, D. I. Koosimile, Edgar H. Stettler

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

The Limpopo Belt of southern Africa is a Neoarchean orogenic belt located between two older Archean provinces, the Zimbabwe craton to the north and the Kaapvaal craton to the south. Previous studies considered the Limpopo Belt to be a linearly trending east-northeast belt with a width of ∼250 km and ∼600 km long. We provide evidence from gravity data constrained by seismic and geochronologic data suggesting that the Limpopo Belt is much larger than previously assumed and includes the Shashe Belt in Botswana, thus defining a southward convex orogenic arc sandwiched between the two cratons. The 2 Ga Magondi orogenic …

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Mapping The Volumetric Soil Water Content Of A California Vineyard Using High-Frequency Gpr Ground Wave Data, Susan Sharpless Hubbard, Katherine R. Grote, Yoram N. Rubin Jun 2002

Mapping The Volumetric Soil Water Content Of A California Vineyard Using High-Frequency Gpr Ground Wave Data, Susan Sharpless Hubbard, Katherine R. Grote, Yoram N. Rubin

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

An attempt was made to establish the utility of ground-penetrating radar (GPR) as a quick and noninvasive field tool for shallow soil water content estimates as a function of space and time. Initially, detailed studies of collocated data, with electromagnetic velocity estimates from GPR data compared to gravimetric measurements of water content and to soil testure were carried out. Using the procedures developed during the detailed studies, full grids of GPR data were collected over the entire site several times. Data obtained indicate that incorporation of multiple frequency GPR grids can provide high-resolution estimates of soil water content variations as …

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Differential Cross Sections And Cross-Section Ratios For The Electron-Impact Excitation Of The Neon 2p⁵3s Configuration, Murtadha A. Khakoo, James M. Wrkich, Mary Lu Larsen, G. Kleiban, Isik Kanik, Sandor Trajmar, Michael J. Brunger, P. J O Teubner, Albert Crowe, Christopher J. Fontes, Robert E H Clark, Vlado Zeman, Klaus Bartschat, Don H. Madison, Rajesh C. Srivastava, Allan Daniel Stauffer Jun 2002

Differential Cross Sections And Cross-Section Ratios For The Electron-Impact Excitation Of The Neon 2p⁵3s Configuration, Murtadha A. Khakoo, James M. Wrkich, Mary Lu Larsen, G. Kleiban, Isik Kanik, Sandor Trajmar, Michael J. Brunger, P. J O Teubner, Albert Crowe, Christopher J. Fontes, Robert E H Clark, Vlado Zeman, Klaus Bartschat, Don H. Madison, Rajesh C. Srivastava, Allan Daniel Stauffer

Physics Faculty Research & Creative Works

Electron-impact differential cross-section measurements for the excitation of the 2p53s configuration of Ne are reported. The Ne cross sections are obtained using experimental differential cross sections for the electron-impact excitation of the n = 2 levels of atomic hydrogen [Khakoo et al., Phys. Rev. A 61, 012701-1 (1999)], and existing experimental helium differential cross-section measurements, as calibration standards. These calibration measurements were made using the method of gas mixtures (Ne and H followed by Ne and He), in which the gas beam profiles of the mixed gases are found to be the same within our experimental errors. We …

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Magnetic And Neutron Diffraction Studies On Prmnsb₂, Satish K. Malik, Zili Chu, Amish G. Joshi, Jinbo Yang, William B. Yelon, Qingsheng Cai, William Joseph James, Kishore Kamaraju May 2002

Magnetic And Neutron Diffraction Studies On Prmnsb₂, Satish K. Malik, Zili Chu, Amish G. Joshi, Jinbo Yang, William B. Yelon, Qingsheng Cai, William Joseph James, Kishore Kamaraju

Physics Faculty Research & Creative Works

Magnetic and neutron diffraction studies have been carried out on PrMnSb2. Magnetization data in the temperature range of 5-400 K show two magnetic transitions: one at ∼175 K attributed to the antiferromagnetic ordering of the Mn moments, and the other at ∼35 K possibly due to the antiferromagnetic ordering of the Pr moments. The magnetization-field isotherms at various temperatures are consistent with the above. Neutron diffraction data obtained at various temperatures can be fitted with a nearly antiferromagnetically coupled Mn moment of ∼3μB at 70 K. At 10 K, moments both on Mn (∼3.5μB) and …

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Structure And Magnetic Properties Of The Mnbi Low Temperature Phase, Jinbo Yang, William B. Yelon, William Joseph James, Qingsheng Cai, Samit Roy, Naushad Ali May 2002

Structure And Magnetic Properties Of The Mnbi Low Temperature Phase, Jinbo Yang, William B. Yelon, William Joseph James, Qingsheng Cai, Samit Roy, Naushad Ali

Physics Faculty Research & Creative Works

High purity MnBi low temperature phase has been prepared and analyzed using magnetic measurements and neutron diffraction. The low-temperature phase of the MnBi alloy has a coercivity μ0iHc of 2.0 T at 400 K, and exhibits a positive temperature coefficient from 0 to at least 400 K. The neutron data refinement indicated that the Mn atom changes its spin direction from c axis above room temperature to nearly perpendicular to the c axis at 50 K. A canted magnetic structure has been observed below 200 K. The anisotropy field increases with increasing temperature which gives rise to …

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Observation Of Novel Disordered Rhombohedral R₂Fe₁₇ (R=Rare Earth) Based Compounds, William B. Yelon, William Joseph James, Jinbo Yang, Kishore Kamaraju, Qingsheng Cai, Zili Chu, Satish K. Malik May 2002

Observation Of Novel Disordered Rhombohedral R₂Fe₁₇ (R=Rare Earth) Based Compounds, William B. Yelon, William Joseph James, Jinbo Yang, Kishore Kamaraju, Qingsheng Cai, Zili Chu, Satish K. Malik

Physics Faculty Research & Creative Works

A recent study of (SmGd)Fe 14Si3 showed an anomalous x-ray diffraction pattern [P. C. Ezekwenna, G. K. Marasinghe, J.-H. Nam, W. J. James, W. B. Yelon, M. Ellouze, and Ph. I'Héritier, J. Appl. Phys. 87, 6716 (2000)]. Although all observed peaks could be indexed to the rhombohedral 2:17 phase (R-3m) many lines were strongly reduced in intensity. Subsequently, the same phenomenon was seen in neutron diffraction patterns from Nd2-xDysFe17-ySiy alloys and conventional refinement using the rhombohedral phase left significant residuals. Fourier mapping revealed additional density along the c-axis chains of Fe dumbbells …

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Possible Ordering Of Ru And Cu In The Charge-Reservoir Of Magneto-Superconductor Rusr₂Gdcu₂O₈ (Ru-1212): Magnetic, Transport, And Tem Microstructural Studies, V. P. S. Awana, S. Ichihara, J. Nakamura, M. Karppinen, H. Yamauchi, Jinbo Yang, William B. Yelon, William Joseph James, Satish K. Malik May 2002

Possible Ordering Of Ru And Cu In The Charge-Reservoir Of Magneto-Superconductor Rusr₂Gdcu₂O₈ (Ru-1212): Magnetic, Transport, And Tem Microstructural Studies, V. P. S. Awana, S. Ichihara, J. Nakamura, M. Karppinen, H. Yamauchi, Jinbo Yang, William B. Yelon, William Joseph James, Satish K. Malik

Physics Faculty Research & Creative Works

Magnetization vs temperature behavior of RuSr2GdCu2O8-δ (Ru-1212) measured in an field of 5 Oe, shows a clear branching of zero-field-cooled (ZFC) and field-cooled (FC) curves around 140 K, a cusp at 135 K, and a diamagnetic transition around 20 K (in the ZFC branch). The cusp at 135 K is due to the antiferromagnetic ordering of the Ru moments. The magnetization-field isotherms, below 50 K, show a nonlinear contribution from a ferromagnetic component. The resistance vs temperature behavior of the compound, in applied fields of 0, 3, and 7 T, confirms that the sample is …

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Magnetic And Mössbauer Studies On Oxygen Deficient Perovskite, La₀.₆Sr₀.₄Feo3-Δ, Jinbo Yang, William B. Yelon, William Joseph James, X.-D. Zhou, Yixiang Xie, Harlan U. Anderson, Zili Chu May 2002

Magnetic And Mössbauer Studies On Oxygen Deficient Perovskite, La₀.₆Sr₀.₄Feo3-Δ, Jinbo Yang, William B. Yelon, William Joseph James, X.-D. Zhou, Yixiang Xie, Harlan U. Anderson, Zili Chu

Physics Faculty Research & Creative Works

Samples of La0.6Sr0.4Fe3-δ with varying oxygen vacancy contents were prepared by heating them in different gas flows. Magnetization measurement showed that samples with low oxygen vacancies have a magnetic ordering temperature in the range of 300-325 K while those with 9%-12% oxygen vacancies have a magnetic ordering temperature of 800 K and higher. Mössbauer spectra at 300 K exhibit paramagnetic or weak magnetic characteristics for the N2, O2, and air-quenched samples, whereas an average hyperfine field of 52 T is found for the CO/CO2 reduced samples. The heat treatment in …

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Magnetic Properties Of Iron-Rich Mixed Rare-Earth Sm₂-ₓtbₓfe17-YSiY Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, William Joseph James, Ph. I'Héritier May 2002

Magnetic Properties Of Iron-Rich Mixed Rare-Earth Sm₂-ₓtbₓfe17-YSiY Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, William Joseph James, Ph. I'Héritier

Physics Faculty Research & Creative Works

A series of Sm2-xTbxFe17-ySiy solid solutions with x = 0, 1, and 1.5 and y = 1, 2, and 3 were prepared by induction melting stoichiometric amounts of high purity elements. The x-ray diffraction data confirm that the postannealed samples are 2:17 intermetallics of the R3 space group. The lattice parameters and the unit cell volumes were calculated using a modified Rietveld program. The fitted intensities showed behavior related to a disordered rhombohedral structure as inferred from neutron data. It was observed that for a particular y, the unit cell volume decreased almost …

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Gpr Monitoring Of Volumetric Water Content In Soils Applied To Highway Construction And Maintenance, Katherine R. Grote, Susan Sharpless Hubbard, Yoram N. Rubin May 2002

Gpr Monitoring Of Volumetric Water Content In Soils Applied To Highway Construction And Maintenance, Katherine R. Grote, Susan Sharpless Hubbard, Yoram N. Rubin

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

An overview is given on two experiments, a controlled pit study and a transportation application in subasphalt soils. Both experiments show that common-offset ground-penetrating radar (GPR) reflection data can be used to estimate θv to a high degree of accuracy. The methodology developed in these two experiments provides a technique for obtaining quick, noninvasive, accurate, and high-resolution estimates of θv.

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Temporal Variation Of Seismic B-Values Beneath Northeastern Japan Island Arc, Aimin Cao, Stephen S. Gao May 2002

Temporal Variation Of Seismic B-Values Beneath Northeastern Japan Island Arc, Aimin Cao, Stephen S. Gao

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

Analysis of a high quality seismic catalog reveals that the average of seismic b-values in the crust beneath most part of northeastern Japan island arc decreased from 0.86 between 1984 and 1990, to 0.73 between 1991 and 1995. The two areas with the largest decrease are found to be in the same areas where the coupling between the North American and the Pacific plates is the highest, as suggested by a recent geodetic study. In the same time period, the annual seismic moment release increased by 10 times. In addition, there seems to be a corresponding increase in volcanic activities …

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The Relationship Between Magnetic Interactions And Near Neighbor Interatomic Distances In The Transition Metal Sublattice Of R(Mn/Fe)₆A₆(R=Nd Or Sm, A=Ge Or Sn), G. K. Marasinghe, J. Han, William Joseph James, William B. Yelon, Naushad Ali May 2002

The Relationship Between Magnetic Interactions And Near Neighbor Interatomic Distances In The Transition Metal Sublattice Of R(Mn/Fe)₆A₆(R=Nd Or Sm, A=Ge Or Sn), G. K. Marasinghe, J. Han, William Joseph James, William B. Yelon, Naushad Ali

Chemistry Faculty Research & Creative Works

The magnetic and crystallographic structures of R(Fe/Mn)6A6 (R=Nd or Sm and A = Ge or Sn) intermetallics have been investigated using x-ray and neutron diffraction techniques and superconducting quantum interference device magnetic measurements. For both stannides (A = Sn) and germanides (A = Ge), the lattice contracts with increasing iron content. In the case of the stannides, substitution of manganese by iron enhances the saturation magnetization and Curie temperature at low iron concentrations (x ≤2 ) suggesting the presence of an extremely rare occurrence, positive coupling between iron and manganese magnetic moments. In contrast, the magnetic properties …

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Saturation Of Charge Carrier Velocity With Increasing Electric Fields: Theoretical Investigations For Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris May 2002

Saturation Of Charge Carrier Velocity With Increasing Electric Fields: Theoretical Investigations For Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

Should one expect injected charge carrier velocities to saturate as the applied electric field is increased simply because of the nonparabolicity of bands? Does the apparent saturation observed in recent experiments in hydrocarbon crystals signify, as supposed in some current interpretations of the data, that the carrier motion is coherent or bandlike and that the disappearance of the saturation at higher temperatures is indicative of a crossover from coherent to incoherent motion? These questions are addressed with the help of general theoretical investigations involving Drude-like considerations, quantum kinetic equations, and a Fokker-Planck analysis.

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Mantle Discontinuities Beneath Southern Africa, Stephen S. Gao, Paul G. Silver, Kelly H. Liu, Kaapvaal Seismic Group May 2002

Mantle Discontinuities Beneath Southern Africa, Stephen S. Gao, Paul G. Silver, Kelly H. Liu, Kaapvaal Seismic Group

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

Seismic velocity discontinuities within the top 1000 km of the Earth beneath southern Africa are imaged by stacking about 1300 source-normalized broadband seismograms recorded by the Southern African Seismic Experiment. The Moho, 410, and 660 kilometer discontinuities are clearly detected. The mean mantle transition zone thickness is 245 km, essentially the same as the global average, suggesting that the transition zone is not anomalously warm. Thus, the lower-mantle 'African Superplume' beneath our study area has no discernible effect on transition zone temperature and is consequently confined to the lower mantle. Variations in transition zone thickness appear to be related to …

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Orbital Ordering In Paramagnetic Lamno₃ And Kcuf₃, Julia E. Medvedeva, Michael A. Korotin, Vladimir I. Anisimov, Arthur J. Freeman May 2002

Orbital Ordering In Paramagnetic Lamno₃ And Kcuf₃, Julia E. Medvedeva, Michael A. Korotin, Vladimir I. Anisimov, Arthur J. Freeman

Physics Faculty Research & Creative Works

Ab initio studies of the stability of orbital ordering, its coupling to magnetic structure and its possible origins (electron-phonon and/or electron-electron interactions) are reported for two perovskite systems, LaMnO3 and KCuF3. We present an average spin state calculational scheme that allowed us to treat a paramagnetic state and to succesfully describe the experimental magnetic or orbital phase diagram of both LaMnO3 and KCuF3 in crystal structures when the Jahn-Teller distortions are neglected. Hence, we conclude that the orbital ordering in both compounds is purely electronic in origin.

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