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2002

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Articles 181 - 210 of 530

Full-Text Articles in Physics

Magnetoresistance Study In Thin Zig Zag Nife Wires, J. L. Tsai, S.F. Lee, Y.D. Yao, C. Yu, Sy_Hwang Liou May 2002

Magnetoresistance Study In Thin Zig Zag Nife Wires, J. L. Tsai, S.F. Lee, Y.D. Yao, C. Yu, Sy_Hwang Liou

Sy-Hwang Liou Publications

Thickness dependence on the domain wall resistivity of zig zag thin permalloy wires was studied from 10 to 300 K. The maximum domain wall resistivity was obtained in wire with 100-nm-film thickness. The multidomain state resistivity was 14.29 µΩ cm, while single-domain state resistivity was 14.36 µΩ cm at 10 K. The ratio of domain wall magnetoresistance was measured to be 0.034%, 0.112%, and 0.258%, and the magnetic field where the domain wall started to switch was measured as –70, –40, and +80 Oe for wires with thicknesses of 20, 40, and 100 nm, respectively, at 250 K. Domain wall …

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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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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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Magnetization Reversal Of Elliptical Co/Cu/Co Pseudo-Spin Valve Dots, Ngocnga Dao, Scott L. Whittenburg, Y. Hao, Leszek M. Malkinski, Jian Qing Wang, C. A. Ross May 2002

Magnetization Reversal Of Elliptical Co/Cu/Co Pseudo-Spin Valve Dots, Ngocnga Dao, Scott L. Whittenburg, Y. Hao, Leszek M. Malkinski, Jian Qing Wang, C. A. Ross

Chemistry and Biochemistry Faculty Publications

We present our recent simulated results on Cr (5 nm)/ Cu (5 nm)/ Co (5 nm)/ Cu (3 nm)/ Co (2 nm) pseudo-spin valve dots. The simulated results agree qualitatively with the experimental results. Three different sizes of elliptical dots, and were simulated. Our simulations show that in these types of dots magnetization reversal occurs by the formation of domain walls: for and for No domain wall was observed in the reversal of the dots. For such dots, the simulated loops show a small two-step reversal pattern with the thin upper layer partially reversing followed by complete reversal of both …

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The Finite-Temperature Densities Of States For Half-Metallic Ferromagnets, Ralph Skomski, Peter A. Dowben May 2002

The Finite-Temperature Densities Of States For Half-Metallic Ferromagnets, Ralph Skomski, Peter A. Dowben

Peter Dowben Publications

A unitary spinor transformation is used to show that the spin-down density of states (DOS) of half-metallic ferromagnets becomes nonzero at finite temperatures. In a strict sense, this thermally activated spin mixing means that half-metallic ferromagnetism is limited to zero temperature. Similar effects are created by crystal imperfections, interfaces, and surfaces. The calculations, which imply that the finite-temperature resistivity of an individual spin channel is never infinite, are used to discuss recent experimental work on half-metallic oxides and Heusler-type alloys.

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Structure And Magnetic Properties Of Sputtered (Nd,Dy)(Fe,Co,Nb,B) 5.5/M (M = Feco,Co) Multilayer Magnets, W. Liu, Z.D. Zhang, J. Ping Liu, Xingzhong Li, X.K. Sun, David J. Sellmyer May 2002

Structure And Magnetic Properties Of Sputtered (Nd,Dy)(Fe,Co,Nb,B) 5.5/M (M = Feco,Co) Multilayer Magnets, W. Liu, Z.D. Zhang, J. Ping Liu, Xingzhong Li, X.K. Sun, David J. Sellmyer

David Sellmyer Publications

The magnetic properties of nanocomposite multilayer magnets of the (Nd,Dy)(Fe,Co,Nb,B) 5.5/M (M = Co,FeCo) on Ti-buffered Si substrates have been investigated. X-ray diffraction results reveal that the Nd2Fe14B-type phase in almost all the films is randomly oriented. Different thickness x (nm) for Co layers and y (nm) for FeCo layers were adopted in the multilayers. It is found that high remanence is achieved in the nanocomposite multilayer films consisting of the Nd2Fe14B-type phase and soft magnetic phase for Co with 6≥x≥4 and for FeCo with 10≥y≥6. The …

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Exact Nucleation Modes In Arrays Of Magnetic Particles, Ralph Skomski May 2002

Exact Nucleation Modes In Arrays Of Magnetic Particles, Ralph Skomski

Ralph Skomski Publications

Magnetization reversal in arrays of magnetic nanoparticles with perpendicular anisotropy is investigated. Aside from domain-wall propagation effects, the reversal involves two main aspects: the nucleation behavior of individual particles and interparticle interactions. Due to magnetostatic self-interaction effects, the interparticle interaction cannot be reduced to a stray-field correction to the external field. Exact nucleation fields and explicit stray-field and self-interaction contributions are obtained for rings of equidistant dots. An exact treatment of self-interactions in various structurally inhomogeneous but rotationally symmetric wire, sphere, and thin-film nanostructures leads to renormalization of the uniaxial anisotropy. Finally, an approximate method to calculate nucleation fields is …

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Spin Blockade Effects In Chromium Oxide Intergrain Magnetoresistance, Andrei Sokolov, C.S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin May 2002

Spin Blockade Effects In Chromium Oxide Intergrain Magnetoresistance, Andrei Sokolov, C.S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin

Peter Dowben Publications

CrO2 thin films with crystallites of a significant size permit investigation of the thin intergrain conduction between a limited numbers of crystals. Phoemission techniques reveal that the CrO2 films are covered by a 1–2-nm-thick Cr2O3 insulating barrier. The electronic band gap of the surface electrons is 3.4 eV at low temperatures, decreases sharply down to 2.8 eV at ambient. Electric transport though a few junctions in series shows a remarkable zero-bias anomaly, interpreted in terms of blockade effects. We show that the magnetoresistance is governed by low-bias blockade in these junctions. © 2002 American Institute …

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Exchange-Controlled Magnetic Anisotropy, Ralph Skomski May 2002

Exchange-Controlled Magnetic Anisotropy, Ralph Skomski

Ralph Skomski Publications

The magnetocrystalline anisotropy of 5f transition-metal atoms (actinides) is investigated. A simple model Hamiltonian reproduces the observed huge low-temperature anisotropy of cubic actinide compounds such as US and predicts the temperature dependence of the anisotropy. The dominance of the spin–orbit and crystal–field interactions means that the magnitude of the anisotropy is limited only by interatomic exchange. One consequence is that cubic and uniaxial 4f magnets have similar magnitudes of the anisotropy and similar temperatures dependencies.

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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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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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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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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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Structure And Superconductivity Of Dy (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤ 0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon May 2002

Structure And Superconductivity Of Dy (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤ 0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon

Physics Faculty Research & Creative Works

Structural and superconducting properties of single-phase La-substituted compounds of the formula Dy(Ba 2-yLay)Cu3Oz (0.0≤y≤0.5) have been investigated by neutron diffraction, electrical resistivity, and magnetization measurements. The compound DyBa 2Cu3O7-δ (orthorhombic, space group Pmmm) exhibits superconductivity with transition temperature, T c, of about 90 K. Rietveld analysis of the neutron diffraction data on La containing compounds reveals that the orthorhombicity decreases with increasing La concentration and the compounds become tetragonal for higher La content. The overall oxygen content increases as divalent Ba is replaced by trivalent La and approximately compensates for …

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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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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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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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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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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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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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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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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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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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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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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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Residential Radon Exposure And Lung Cancer: Variation In Risk Estimates Using Alternative Exposure Scenarios, R. William Field, Brian J. Smith, Daniel J. Steck, Charles F. Lynch May 2002

Residential Radon Exposure And Lung Cancer: Variation In Risk Estimates Using Alternative Exposure Scenarios, R. William Field, Brian J. Smith, Daniel J. Steck, Charles F. Lynch

Physics Faculty Publications

The most direct way to derive risk estimates for residential radon progeny exposure is through epidemiologic studies that examine the association between residential radon exposure and lung cancer. However, the National Research Council concluded that the inconsistency among prior residential radon case-control studies was largely a consequence of errors in radon dosimetry. This paper examines the impact of applying various epidemiologic dosimetry models for radon exposure assessment using a common data set from the Iowa Radon Lung Cancer Study (IRLCS). The IRLCS uniquely combined enhanced dosimetric techniques, individual mobility assessment, and expert histologic review to examine the relationship between cumulative …

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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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