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Articles 28831 - 28860 of 36694

Full-Text Articles in Physical Sciences and Mathematics

Neutron Diffraction Analysis Of Melt Spun 2:14:1 Type (Ndpr)-Fe-B Compounds With Ti And Zr Additions, Z. Chu, William B. Yelon, B. M. Ma, Z. Chen, D. N. Brown May 2002

Neutron Diffraction Analysis Of Melt Spun 2:14:1 Type (Ndpr)-Fe-B Compounds With Ti And Zr Additions, Z. Chu, William B. Yelon, B. M. Ma, Z. Chen, D. N. Brown

Physics Faculty Research & Creative Works

There has been continued technological and research interest in Nd 2Fe 14B-based compounds due to their excellent intrinsic magnetic properties [(BH) max*∼64MGOe,Ha∼73kOe]. It is found that Ti and Zr substitution in Nd 2Fe 14B leaves its magnetic properties largely unaffected. We have carried out neutron diffraction studies on Zr and Ti substituted 2:14:1 compounds. Three specimens of melt spun alloys of compositions (Nd 0.75Pr 0.25) 12Fe 80B 8, (Nd 0.75Pr 0.25) 8.4Fe 79.7Ti 4.7B 7.2 and (Nd 0.75Pr 0.25) 9.2Fe 79.2Ti 2 …

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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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Calculations On The Size Effects Of Raman Intensities Of Silicon Quantum Dots, Wei Cheng, Shang-Fen Ren May 2002

Calculations On The Size Effects Of Raman Intensities Of Silicon Quantum Dots, Wei Cheng, Shang-Fen Ren

Faculty publications – Physics

Raman intensities of Si quantum dots (QD's) with up to 11489 atoms (about 7.6 nm in diameter) for different scattering configurations are calculated. First, phonon modes in these QD's, including all vibration frequencies and vibration amplitudes, are calculated directly from the lattice-dynamic matrix by using a microscopic valence force field model combined with the group theory. Then the Raman intensities of these quantum dots are calculated by using a bond-polarizability approximation. The size effects of the Raman intensity in these QD's are discussed in detail based on these calculations. The calculations are compared with the available experimental observations. We are …

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Mechanically Milled Nanostructured (Sm,Pr) 12.5Co85.5Zr2 Magnets With Tbcu7 Structure, Hong Tang, Jian Zhou, David J. Sellmyer May 2002

Mechanically Milled Nanostructured (Sm,Pr) 12.5Co85.5Zr2 Magnets With Tbcu7 Structure, Hong Tang, Jian Zhou, David J. Sellmyer

David Sellmyer Publications

Nanostructured (Sm,Pr)(Co,Zr) magnets with the TbCu7-type structure have been synthesized by mechanically milling (Sm1-xPrx)12.5Co85.5Zr2 alloys (0≤x≤0.8) followed by appropriate annealing. Magnetic properties, structure, and microstructure have been investigated. It is found that single-phase (Sm,Pr)(Co,Zr) 7 magnets with the TbCu7 structure and with nanoscale grain size (14–19 nm) form in the whole composition range. Intrinsic coercivity Hci decreases from 20.7 to 5.6 kOe with increasing Pr content from 0 to 0.8, while energy products (BH)max shows an optimum value of 12.6 MGOe (Hciof 17.9 kOe) at …

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Fabrication And Characterization Of Co1−Xfex Alloy Nanowires, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger May 2002

Fabrication And Characterization Of Co1−Xfex Alloy Nanowires, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger

Physics Faculty Publications

Co1−xFex alloy nanowires with 40 nm diam and x=0–1.0 were fabricated by electrodeposition in nanopores of alumina templates. The crystalline structure of the nanowires is concentration dependent and shows a transition from the cobalt hexagonal-closed-packed structure (hcp) to a face-centered-cubic structure (fcc) in the concentration range 0

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Investigation Of The Magnetic Properties In Strontium–Borate Vanadate Glasses, Manford Chinkhota, Petru S. Fodor, G. D. Khattak, Lowell E. Wenger May 2002

Investigation Of The Magnetic Properties In Strontium–Borate Vanadate Glasses, Manford Chinkhota, Petru S. Fodor, G. D. Khattak, Lowell E. Wenger

Physics Faculty Publications

To further elucidate the nature of the valence state of V ions in vanadate glasses,magnetic susceptibility measurements in the temperature range of 5 to 300 K have been performed on a series of vanadium–strontium–borate (V2O5+SrO+B2O3) oxide glasses with V2O5 concentrations greater than 50 mol %. The magnetic susceptibility for these oxide glasses is found to consist of a temperature-independentparamagnetic contribution arising from V2O5 and a Curie–Weiss temperature-dependent contribution associated with magnetic V4+ ions being present in concentrations between 2% and 10% of the total V concentration. The negative Curie–Weiss temperatures in the range of 0 to −2.8 K indicate a …

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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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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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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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Predictions And Observations In Theories With Varying Couplings, Christian Armendariz-Picon May 2002

Predictions And Observations In Theories With Varying Couplings, Christian Armendariz-Picon

Physics - All Scholarship

We consider a toy universe containing conventional matter and an additional real scalar field, and discuss how the requirements of gauge and diffeomorphism invariance essentially single out a particular set of theories which might describe such a world at low energies. In these theories, fermion masses and g-factors, as well as the electromagnetic coupling turn to be scalar field dependent; fermion charges and the gravitational coupling might be assumed to be constant. We then proceed to study the impact of a time variation of the scalar field on measurements of atomic spectra at high redshifts. Light propagation is not affected …

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A Class Of Boron-Rich Solid-State Neutron Detectors, B. W. Robertson, Shireen Adenwalla, A. Harken, P. Welsch, Jennifer I. Brand, Peter A. Dowben, J.P. Claassen May 2002

A Class Of Boron-Rich Solid-State Neutron Detectors, B. W. Robertson, Shireen Adenwalla, A. Harken, P. Welsch, Jennifer I. Brand, Peter A. Dowben, J.P. Claassen

Peter Dowben Publications

Real-time solid-state neutron detectors have been fabricated from semiconducting boron–carbon alloys, deposited by plasma-enhanced chemical vapor deposition. Single neutrons were detected and signals induced by gamma rays were determined to be insignificant. The source gas closo-1,2-dicarbadodecaborane (ortho-carborane) was used to fabricate the boron–carbon alloys with only the natural isotopic abundance of 10B. Devices made of thicker boron–carbon alloy layers enriched in 10B could lead to increased detection efficiency and active diodes could use the inherent micron scale spatial resolution, increasing the range of possible applications. © 2002 American Institute of Physics. [DOI: 10.1063/1.1477942]

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Search For Leptoquark Pairs Decaying Into Νν + Jets In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration May 2002

Search For Leptoquark Pairs Decaying Into Νν + Jets In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We present the results of a search for leptoquark (LQ) pairs in (85.2 ± 3.7) pb-1 of pp̅ collider data collected by the D0 experiment at the Fermilab Tevatron. We observe no evidence for leptoquark production and set a limit on σ(pp̅→ LQ L̅Q̅→ νν + jets) as a function of the mass of the leptoquark (mLQ). Assuming the decay LQ → νq, we exclude scalar leptoquarks for mLQ< 98 GeV/c2, and vector leptoquarks for mLQ < 200 GeV/c2 and coupling which produces the minimum cross section, at a 95% confidence …

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Threshold-Related Enhancement Of The High-Energy Plateau In Above-Threshold Detachment, Bogdan Borca, M.V. Frolov, N.L. Manakov, Anthony F. Starace May 2002

Threshold-Related Enhancement Of The High-Energy Plateau In Above-Threshold Detachment, Bogdan Borca, M.V. Frolov, N.L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

We present nonperturbative theoretical results showing a resonant-like enhancement of above-threshold detachment spectra in the region of the high-energy plateau as the laser intensity sweeps across channel thresholds. This enhancement has a pure quantum origin stemming from well-known threshold phenomena in multichannel problems whose features are clearly demonstrated in our numerical results. Similar well-known anomalies at neutral atom thresholds are expected to explain experimentally observed resonant-like enhancements of above-threshold ionization spectra.

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Threshold-Related Effects In High-Order Harmonic Generation, Bogdan Borca, Anthony F. Starace, A. V. Flegel, M. V. Frolov, N. L. Manakov May 2002

Threshold-Related Effects In High-Order Harmonic Generation, Bogdan Borca, Anthony F. Starace, A. V. Flegel, M. V. Frolov, N. L. Manakov

Department of Physics and Astronomy: Faculty Publications

We present exact ab initio quantum results for harmonic generation (HG) by a weakly bound electron interacting with a strong monochromatic laser field. The analytic structure of the HG amplitude resulting from the multiphoton detachment thresholds is demonstrated. Our numerical results show that the HG spectrum is sensitive primarily to the distance in energy from the thresholds, thereby opening new possibilities for control of HG.

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Higher-Order Evaluation Of The Critical Temperature For Interacting Homogeneous Dilute Bose Gases, Frederico F. F. De Souza Cruz, Marcus Pinto, Rudnei O. Ramos, Paulo Sena May 2002

Higher-Order Evaluation Of The Critical Temperature For Interacting Homogeneous Dilute Bose Gases, Frederico F. F. De Souza Cruz, Marcus Pinto, Rudnei O. Ramos, Paulo Sena

Dartmouth Scholarship

We use the nonperturbative linear δ expansion method to evaluate analytically the coefficients c1 and c''2 that appear in the expansion for the transition temperature for a dilute, homogeneous, three-dimensional Bose gas given by Tc=T0(1+c1an1/3+[c′2ln(an1/3)+c''2]a2n2/3+O(a3n)), where T0 is the result for an ideal gas, a is the s-wave scattering length, and n is the number density. In a previous work the same method has been used to evaluate c1 to order δ2 with the result c1=3.06. Here, we push the calculation to the next two orders obtaining c1=2.45 at order δ3 and c1=1.48 at order δ4. Analyzing the topology …

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Humidity And Temperature Boundaries For Biofilm Formation In Yucca Mountain, Terry Ann Else, Penny S. Amy, James Jay, Amy J. Smiecinski May 2002

Humidity And Temperature Boundaries For Biofilm Formation In Yucca Mountain, Terry Ann Else, Penny S. Amy, James Jay, Amy J. Smiecinski

Publications (YM)

To determine the long-term success of the recommended Yucca Mountain high-level nuclear waste repository, studies of bacterial colonization and biofilm development are needed. Bacteria involved in microbially-influenced corrosion and degradation are known to form biofilms with the potential to impact the integrity of repository packaging and structural materials. Temperature and humidity are environmental factors that can greatly affect biofilm formation. Therefore, it is necessary to determine the temperature and humidity conditions that affect biofilm formation. Microcosms, which simulated the repository environment of Yucca Mountain, were placed at temperatures ranging from 30° C to 70° C and in relative humidities ranging …

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Measurement Of B-Meson Lifetimes Using Fully Reconstructed B Decays Produced, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration May 2002

Measurement Of B-Meson Lifetimes Using Fully Reconstructed B Decays Produced, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present an improved measurement of b-meson lifetimes using fully reconstructed B-decays produced in pp̅ collisions at √s =1.8 TeV, using 114 pb-1 of data collected at the Collider Detector at Fermilab. We obtain τ (B+)=1.636±0.058(stat) ±0.025(syst) ps, τ (B0)=1.497±0.073(stat) ±0.032(syst) ps and for the lifetime ratio τ (B+)/(B0)=1.093±0.066(stat) ±0.028(syst).

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Effect Of Implanted Metal Impurities On Superconducting Tungsten Films, Betty A. Young, T. Saab, Blas Cabrera, A. J. Miller, P. L. Brink, J. P. Castle May 2002

Effect Of Implanted Metal Impurities On Superconducting Tungsten Films, Betty A. Young, T. Saab, Blas Cabrera, A. J. Miller, P. L. Brink, J. P. Castle

Physics

The superconducting transition temperature of more than 30 thin-film tungsten samples was measured using a dilution refrigerator. The samples were fabricated using a 99.999% pure tungsten target and a dc magnetron sputtering system. Individual films were then doped with metal impurity ions using an accurate ion implantation technique. The effect of the metal–ion doping on the superconducting transition temperature was measured for samples with superconducting transitions in the range of 40–150 mK. Magnetic dopant species including Ni, Co, and Fe resulted in suppressed values of the tungsten Tc. The suppression was linear with increasing dopant concentration, for concentrations …

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Deep Hole Traps In N-Gan Films Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, Z-Q. Fang, David C. Look, Richard J. Molnar, A. V. Osinsky May 2002

Deep Hole Traps In N-Gan Films Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, Z-Q. Fang, David C. Look, Richard J. Molnar, A. V. Osinsky

Physics Faculty Publications

Concentrations of deep hole traps were measured in a set of hydride vapor phase epitaxy grown samples with thicknesses varying from 2.6 to 68 μm. Results were obtained from low temperature capacitance–voltage measurements before and after illumination and from deep level transient spectroscopy measurements with optical injection (ODLTS). The former revealed the presence of high densities (∼1015 to 1016 cm−3) of hole traps whose concentration decreased with sample thickness in a manner similar to that found for the dislocation density. Capacitance versus temperature measurements in the dark and after illumination suggested that these traps form a …

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Depth-Dependent Investigation Of Defects And Impurity Doping In Gan/Sapphire Using Scanning Electron Microscopy And Cathodoluminescence Spectroscopy, X. L. Sun, S. H. Goss, L. J. Brillson, David C. Look, Richard J. Molnar May 2002

Depth-Dependent Investigation Of Defects And Impurity Doping In Gan/Sapphire Using Scanning Electron Microscopy And Cathodoluminescence Spectroscopy, X. L. Sun, S. H. Goss, L. J. Brillson, David C. Look, Richard J. Molnar

Physics Faculty Publications

Cathodoluminescence (CL) imaging and temperature-dependent cathodoluminescence spectroscopy (CLS) have been used to probe the spatial distribution and energies of electronic defects near GaN/Al2O3 interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy imaging, CLS, and CL imaging show systematic variations in defect emissions with a wide range of HVPE GaN/sapphire electronic properties. These data, along with electrochemical capacitance–voltage profiling and secondary ion mass spectrometry provide a consistent picture of near-interface doping by O out-diffusion from Al2O3 into GaN over hundreds of nanometers. Low-temperature CL spectra exhibit a new donor level …

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Energetic Particles From Three-Dimensional Magnetic Reconnection Events In The Swarthmore Spheromak Experiment, Michael R. Brown, C. D. Cothran, Matthew J. Landreman , '03, David J. Schlossberg , '01 May 2002

Energetic Particles From Three-Dimensional Magnetic Reconnection Events In The Swarthmore Spheromak Experiment, Michael R. Brown, C. D. Cothran, Matthew J. Landreman , '03, David J. Schlossberg , '01

Physics & Astronomy Faculty Works

Measurements are presented from the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] showing a population of superthermal, super-Alfvénic ions with Ē≅90 eV and Emax⩾200 eV accelerated by reconnection activity in three-dimensional magnetic structures. These energetic ions are temporally and spatially correlated with three-dimensional magnetic reconnection events (measured with a 3D probe array) and are accelerated along the X-line normal to the local 2D plane of reconnection. In a typical SSX discharge, the peak reconnection electromotive force ℰ=vBL⩽(105 m/s)(0.05 T)(0.1 m)=500 V consistent with our observations. In addition, test particle simulations using magnetohydrodynamic (MHD) data from …

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Preferential Orientation Of Short Chain Vapor Deposited Polyaniline Thin Films On Gold, B. Xu, Jaewu Choi, Peter A. Dowben May 2002

Preferential Orientation Of Short Chain Vapor Deposited Polyaniline Thin Films On Gold, B. Xu, Jaewu Choi, Peter A. Dowben

Peter Dowben Publications

Vapor deposited short chain polyaniline thin films were studied using angle-resolved photoemission spectroscopy. Films grown on two different substrates, oxidized Si surfaces and Au, show distinctly different properties. Some indication of preferential molecular orientation was observed for ultrathin films deposited on Au substrates, but not on the Si substrates with the native oxide surface. Clear indication of metallic character was observed for some of the polyaniline ultrathin films, consistent with recent theory suggesting that alignment of chains parallel with a metal substrate enhance metallicity.

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Zero-Bias Anomaly In Cro2 Junctions, Andrei Sokolov, C.-S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, H.-K. Jeong, T. Komesu, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin May 2002

Zero-Bias Anomaly In Cro2 Junctions, Andrei Sokolov, C.-S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, H.-K. Jeong, T. Komesu, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin

Peter Dowben Publications

CrO2thin films, with crystallites of several microns size, provide the opportunity for the investigation of the intergrain tunneling between a few crystals separated by a 1-2 nm thick Cr2O3 film. A pronounced zero-bias anomaly of the conductance is found at low temperatures. Combined photoemission and inverse photoemission temperature-dependent studies confirm the occurrence of Coulomb blockade. For the strong-tunneling case (R2), the magnetoresistance decreases strongly with bias. For the weak-tunneling case (R>>RQ), the magnetoresistance decreases by a factor two with increasing bias, as predicted by a co-tunneling model.

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Dust Emission From Active Galactic Nuclei, Maia Nenkova, Željko Ivezić, Moshe Elitzur May 2002

Dust Emission From Active Galactic Nuclei, Maia Nenkova, Željko Ivezić, Moshe Elitzur

Physics and Astronomy Faculty Publications

Unified schemes of active galactic nuclei require an obscuring dusty torus around the central source, giving rise to a Seyfert 1 line spectrum for pole-on viewing and Seyfert 2 characteristics in edge-on sources. Although the observed IR is in broad agreement with this scheme, the behavior of the 10 μm silicate feature and the width of the far-IR emission peak remained serious problems in all previous modeling efforts. We show that these problems find a natural explanation if the dust is contained in approximately five to 10 clouds along radial rays through the torus. The spectral energy distributions of …

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Nonlinear Dynamics Of Mode-Locking Optical Fiber Ring Lasers, Kristin M. Spaulding, Darryl H. Yong, Arnold D. Kim, J Nathan Kutz May 2002

Nonlinear Dynamics Of Mode-Locking Optical Fiber Ring Lasers, Kristin M. Spaulding, Darryl H. Yong, Arnold D. Kim, J Nathan Kutz

All HMC Faculty Publications and Research

We consider a model of a mode-locked fiber ring laser for which the evolution of a propagating pulse in a birefringent optical fiber is periodically perturbed by rotation of the polarization state owing to the presence of a passive polarizer. The stable modes of operation of this laser that correspond to pulse trains with uniform amplitudes are fully classified. Four parameters, i.e., polarization, phase, amplitude, and chirp, are essential for an understanding of the resultant pulse-train uniformity. A reduced set of four coupled nonlinear differential equations that describe the leading-order pulse dynamics is found by use of the variational nature …

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The Blazhko Effect Of The Rr Lyrae Star Gv Andromedae, Kevin M. Lee, Edward G. Schmidt, Shawn T. Langan May 2002

The Blazhko Effect Of The Rr Lyrae Star Gv Andromedae, Kevin M. Lee, Edward G. Schmidt, Shawn T. Langan

Edward Schmidt Publications

We have obtained 462 new V and R observations of the RR Lyrae star GV Andromedae. Our data set is consistent with a primary period of 0.528092 days; however, the light curve of GV And cannot be well described by a single period. We conclude that GV And demonstrates the Blazhko effect with a Blazhko period of approximately 32 days.

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Zero-Bias Anomaly In Cro2 Junctions, Andrei Sokolov, C.-S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, H.-K. Jeong, T. Komesu, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin May 2002

Zero-Bias Anomaly In Cro2 Junctions, Andrei Sokolov, C.-S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, H.-K. Jeong, T. Komesu, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin

Sy-Hwang Liou Publications

CrO2 thin films, with crystallites of several microns size, provide the opportunity for the investigation of the intergrain tunneling between a few crystals separated by a 1-2 nm thick Cr2O3 film. A pronounced zero-bias anomaly of the conductance is found at low temperatures. Combined photoemission and inverse photoemission temperature-dependent studies confirm the occurrence of Coulomb blockade. For the strong-tunneling case (R2), the magnetoresistance decreases strongly with bias. For the weak-tunneling case (R>>RQ), the magnetoresistance decreases by a factor two with increasing bias, as predicted by a co-tunneling model.

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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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Search For Single-Top-Quark Production In Pp̅ Collisions At √S =1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration May 2002

Search For Single-Top-Quark Production In Pp̅ Collisions At √S =1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We search for standard model single-top-quark production in the W-gluon fusion and W* channels using 106 pb-1 of data from pp̅ collisions at √s =1.8 TeV collected with the Collider Detector at Fermilab. We set an upper limit at 95% confidence level (C.L.) on the combined W-gluon fusion and W* single-top cross section of 14 pb, roughly six times larger than the standard model prediction. Separate 95% C.L. upper limits in the W-gluon fusion and W* channels are also determined and are found to be 13 and 18 pb, respectively.

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Photoexcitation Of A Dipole-Forbidden Resonance In Helium, B. Krassig, E. P. Kanter, S. H. Southworth, Renaud Guillemin, Oliver Hemmers, Dennis W. Lindle, R. Wehlitz, N. L. S. Martin May 2002

Photoexcitation Of A Dipole-Forbidden Resonance In Helium, B. Krassig, E. P. Kanter, S. H. Southworth, Renaud Guillemin, Oliver Hemmers, Dennis W. Lindle, R. Wehlitz, N. L. S. Martin

Environmental Studies Faculty Publications

We have observed photoexcitation of the dipole-forbidden 1s21S0→2p21D2 resonance in helium by measuring the nondipolar forward-backward asymmetry of photoelectron angular distributions in the 2ℓ2ℓ′ autoionizing region. By exploiting the electric dipole-quadrupole interference in the excitation of both the 2s2p1P1 and 2p21D2 levels, we have observed the quadrupole resonance in photoabsorption and extracted its Fano line shape parameters and the relative phase of the 1sEp and 1sEd continua. We find the quadrupole line profile index q2 to be markedly different from theoretical expectations.

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