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2002

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Articles 1 - 30 of 530

Full-Text Articles in Physics

Search For Radiative B,-Hadron Decays In Pp̅ Collisions At √S=1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Dec 2002

Search For Radiative B,-Hadron Decays In Pp̅ Collisions At √S=1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have performed a search for radiative b-hadron decays using events produced in pp̅ collisions at √s=1.8 TeV and collected by the Collider Detector at Fermilab. The decays we considered were B̅d0→K*0(→K-π+) γ, B̅s0→φ(→K+K-) γ, Λb0→ Λ(→pπ-) γ, and their charge conjugates. Two independent methods to identify photons from such decays were employed. In the first method, the photon was detected in the electromagnetic calorimeter. In the second method, the photon was identified …

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Limits On Extra Dimensions And New Particle Production In The Exclusive Photon, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Dec 2002

Limits On Extra Dimensions And New Particle Production In The Exclusive Photon, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

The exclusive γE/T signal has a small standard model cross section and is thus a channel sensitive to new physics. This signature is predicted by models with a superlight gravitino or with large extra spatial dimensions. We search for such signals at the Collider Detector at Fermilab, using 87   pb-1 of data at √s=1.8   TeV, and extract 95% C.L. limits on these processes. A limit of 221 GeV is set on the scale |F|1/2 in supersymmetric models. For 4, 6, and 8 extra dimensions, model-dependent limits on the fundamental mass scale MD of 0.55, 0.58, and …

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Viscoelasticity From A Microscopic Model Of Dislocation Dynamics, M. Christina Marchetti, Karl Saunders Dec 2002

Viscoelasticity From A Microscopic Model Of Dislocation Dynamics, M. Christina Marchetti, Karl Saunders

Physics

It is shown that the dynamics of a viscoelastic medium can be modeled as that of a two-dimensional crystal with a finite concentration of dislocations, as well as vacancy and interstitial defects. At the longest length scales the viscoelasticity is described by the simplest Maxwell model, whose shear and compressional relaxation times are obtained in terms of microscopic quantities, including the density of free dislocations. At short length scales, t bond orientational order effects become important and lead to wave vector dependent corrections to the relaxation times.

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Perturbative Calculation Of The Triply Differential Cross Section For Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, Anthony F. Starace Dec 2002

Perturbative Calculation Of The Triply Differential Cross Section For Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

Single-photon, two-electron ionization of He is analyzed, taking into account electron correlation using lowest-order perturbation theory and including all individual electron angular momenta in the final two-electron continuum. Perturbative account of electron correlation in the final state, which describes the so-called TS-1 mechanism of double photoionization, combined with a variational account of electron screening, is found to provide results for the triply differential cross section at an excess energy of 20 eV that are in excellent agreement with both absolute experimental data and results of non-perturbative calculations, for all kinematics of the process in which the TS-1 mechanism is expected …

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Search For The Production Of Single Sleptons Through R-Parity Violation In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration Dec 2002

Search For The Production Of Single Sleptons Through R-Parity Violation In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We report the first search for supersymmetric particles via s-channel production and decay of smuons or muon sneutrinos at hadronic colliders. The data for the two-muon and two-jets final states were collected by the D0 experiment and correspond to an integrated luminosity of 94 ± 5 pb-1. Assuming that R parity is violated via the single coupling λ′211, the number of candidate events is in agreement with expectation from the standard model. Exclusion contours are given in the (m0; m½) and (mΧ̅,mν planes for λ′ …

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Chaotic Free-Space Laser Communication Over Turbulent Channel, N. F. Rulkov, Mikhail Vorontsov, L. Illing Dec 2002

Chaotic Free-Space Laser Communication Over Turbulent Channel, N. F. Rulkov, Mikhail Vorontsov, L. Illing

Electro-Optics and Photonics Faculty Publications

The dynamics of errors caused by atmospheric turbulence in a self-synchronizing chaos-based communication system that stably transmits information over a ∼5  km free-space laser link is studied experimentally. Binary information is transmitted using a chaotic sequence of short-term pulses as a carrier. The information signal slightly shifts the chaotic time position of each pulse depending on the information bit. We report the results of an experimental analysis of the atmospheric turbulence in the channel and the impact of turbulence on the bit-error-rate performance of this chaos-based communication system.

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He Ii Reverberation In Active Galactic Nucleus Spectra, Mark C. Bottorff, Jack A. Baldwin, Gary J. Ferland, Jason W. Ferguson, Kirk T. Korista Dec 2002

He Ii Reverberation In Active Galactic Nucleus Spectra, Mark C. Bottorff, Jack A. Baldwin, Gary J. Ferland, Jason W. Ferguson, Kirk T. Korista

Physics and Astronomy Faculty Publications

This paper compares the observed reverberation response lags and the intensity ratios of the broad-line region (BLR) emission lines He II λ1640, He II λ4686, and C IV λ1549 with predictions. Published observations indicate that the He II λ1640 lag is 3 times shorter than the lags of He II λ4686 or C IV λ1549. Diverse models, however, do not reproduce this observation. Extensive improved numerical simulations of the hydrogenic isoelectronic sequence emission show that the He II spectrum remains especially simple, even in the central regions of a luminous quasar. Line trapping never builds up a significant population of …

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Two-Photon Bremsstrahlung Processes In Atoms: Polarization Effects And Analytic Results For The Coulomb Potential, A. A. Krylovetskiĭ, N. L. Manakov, S. I. Marmo, Anthony F. Starace Dec 2002

Two-Photon Bremsstrahlung Processes In Atoms: Polarization Effects And Analytic Results For The Coulomb Potential, A. A. Krylovetskiĭ, N. L. Manakov, S. I. Marmo, Anthony F. Starace

Anthony F. Starace Publications

The partial wave analysis of two-photon free–free (bremsstrahlung) electron transition cross sections during scattering by a static potential U(r), as well as by an atom with a nonzero angular momentum, is carried out. The dipole interaction with radiation is taken into account in the second order of perturbation theory for the general case of elliptic polarization of photons. The polarization and angular dependences of the twophoton potential scattering amplitude is presented as a combination of the scalar product of electron momenta and photon polarization vectors and five atomic parameters containing Legendre polynomials of the scattering angle as …

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Search For Minimal Supergravity In Single-Electron Events With Jets And Large Missing Transverse Energy In Pp̅ Collisions At √S =1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration Dec 2002

Search For Minimal Supergravity In Single-Electron Events With Jets And Large Missing Transverse Energy In Pp̅ Collisions At √S =1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We describe a search for evidence of minimal supergravity (MSUGRA) in 92.7 pb-1 of data collected with the DØ detector at the Fermilab Tevatron pp̅ collider at√s =1.8 TeV. Events with a single electron, four or more jets, and large missing transverse energy were used in this search. The major backgrounds are from W +jets, misidentified multijet, tt̅, and WW production. We observe no excess above the expected number of background events in our data. A new limit in terms of MSUGRA model parameters is obtained.

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Magnetic Properties Of Er2mn3si5, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, A. V. Morozkin, Z. Chu, William B. Yelon, S. K. Malik, Y. Yamamoto, H. Hori Dec 2002

Magnetic Properties Of Er2mn3si5, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, A. V. Morozkin, Z. Chu, William B. Yelon, S. K. Malik, Y. Yamamoto, H. Hori

Physics Faculty Research & Creative Works

Magnetization measurements have been carried out on the Er2Mn3Si5 compound (tetragonal Sc2Fe3Si5-type, space group P4/mnc) in the temperature range 1.8-300 K. There is a crossover from a room temperature paramagnetic phase to a ferromagnetic phase at 75 K (TC1). A second magnetic transition is observed at 11.5 K (TC2). The magnetic susceptibility in the paramagnetic region, above 100 K, follows simple Curie-Weiss type behavior. The magnetization does not saturate at 2 K even in applied fields of 7 T. Neutron diffraction data collected at 300 …

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Controlling Laser High-Order Harmonic Generation Using Weak Counter-Propagating Light, Sergei Leonidovich Voronov Dec 2002

Controlling Laser High-Order Harmonic Generation Using Weak Counter-Propagating Light, Sergei Leonidovich Voronov

Theses and Dissertations

Laser high-order harmonic generation in the presence of relatively weak interfering light is investigated. The interfering pulses intersect the primary harmonic-generating laser pulse at the laser focus. The interfering light creates a standing intensity and phase modulation on the field, which disrupts microscopic phase matching and shuts down local high harmonic production. Suppression of the 23rd harmonic (by two orders of magnitude) is observed when a counter-propagating interfering pulse of light is introduced. A sequence of counter-propagating pulses can be used to shut down harmonic production in out-of-phase zones of the generating volume to achieve quasi phase matching. Harmonic emission …

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Isotropization In Brane Gas Cosmology, Scott Watson, Robert H. Brandenberger Dec 2002

Isotropization In Brane Gas Cosmology, Scott Watson, Robert H. Brandenberger

Physics - All Scholarship

Brane Gas Cosmology (BGC) is an approach to unifying string theory and cosmology in which matter is described by a gas of strings and branes in a dilaton gravity background. The Universe is assumed to start out with all spatial dimensions compact and small. It has previously been shown that in this context, in the approximation of neglecting inhomogeneities and anisotropies, there is a dynamical mechanism which allows only three spatial dimensions to become large. However, previous studies do not lead to any conclusions concerning the isotropy or anisotropy of these three large spatial dimensions. Here, we generalize the equations …

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Biaxial Strain-Modified Valence And Conduction Band Offsets Of Zinc-Blende Gan, Gap, Gaas, Inn, Inp, And Inas, And Optical Bowing Of Strained Epitaxial Ingan Alloys, Gus L. W. Hart, P. R. C. Kent, Alex Zunger Dec 2002

Biaxial Strain-Modified Valence And Conduction Band Offsets Of Zinc-Blende Gan, Gap, Gaas, Inn, Inp, And Inas, And Optical Bowing Of Strained Epitaxial Ingan Alloys, Gus L. W. Hart, P. R. C. Kent, Alex Zunger

Faculty Publications

Using density-functional calculations, we obtain the (001) biaxial strain dependence of the valence and conduction band energies of GaN, GaP, GaAs, InN, InP, and InAs. The results are fit to a convenient-to-use polynomial and the fits provided in tabular form. Using the calculated biaxial deformation potentials in large supercell empirical psuedopotential calculations, we demonstrate that epitaxial strain reduces the InGaN alloy bowing coefficient compared to relaxed bulk alloys.

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High-Energy Ball Milling Of Polymers, Jabari Robinson Dec 2002

High-Energy Ball Milling Of Polymers, Jabari Robinson

Electronic Dissertations and Theses

With metallic materials, the mechanism of milling is generally regarded as a combination of fracturing and cold-welding of powder particles. The same general mechanism is expected to apply polymers, but some aspects of the mechanism may be different for polymers due their chainlike molecular nature, lower moduli, and higher sensitivity to temperature. In spite of some potential problems some researchers have recently demonstrated that milling can be used to produce polymers and blends with acceptable mechanical properties. C. Bai and associates used high-energy ball milling at three temperatures on poly (ethylene terephthalate) and produced favorable results. Spontak et. al. cryogenically …

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Effects Of Germanium On The Electronic Transport Mechanism In Co20 (Cu-XGeX)80 Nanogranular Ribbons, J. He, Z. D. Zhang, J. Ping Liu, David J. Sellmyer Dec 2002

Effects Of Germanium On The Electronic Transport Mechanism In Co20 (Cu-XGeX)80 Nanogranular Ribbons, J. He, Z. D. Zhang, J. Ping Liu, David J. Sellmyer

David Sellmyer Publications

The dependency of giant magnetoresistance (GMR) on the nonmagnetic matrix in nanogranular Co20 (Cu1-xGex)80 ribbons was studied. When the matrix Cu is substituted with semiconductor Ge, the magnetoresistance transitioned from negative to positive at low temperatures. The positive GMR effect is closely related to the quantity of Co/Co3Ge2/Co junctionlike configurations. This result provides evidence for the competition between two types of electronic transport mechanisms in the magnetic granular ribbons: (i) electronic spin-dependent scattering, inducing a negative magnetoresistance and (ii) Coulomb blockade of the electronic tunneling, inducing a positive magnetoresistance.

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Poiseuille Advection Of Chemical Reaction Fronts: Eikonal Approximation, R. S. Spangler, Boyd F. Edwards, J. Chem Dec 2002

Poiseuille Advection Of Chemical Reaction Fronts: Eikonal Approximation, R. S. Spangler, Boyd F. Edwards, J. Chem

All Physics Faculty Publications

An eikonal equation including fluid advection is derived from the cubic reaction-diffusion-advection equation, and is used to investigate the speeds and shapes of chemical reaction fronts subject to Poiseuille flow between parallel plates. Although the eikonal equation is usually regarded as valid when the front thickness is small compared to the radius of curvature of the front and to the size of the system, it is also found to be valid when the reaction front is thick with respect to the gap width. This new regime of applicability of the eikonal equation is consistent with its derivation, which requires only …

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Exclusion Limits On The Wimp-Nucleon Cross Section From The Cryogenic Dark Matter Search, D. Abrams, D. S. Akerib, M. S. Armel-Funkhouser, L. Baudis, D. A. Bauer, A. Bolozdynya, P. L. Brink, R. Bunker, B. Cabrera, D. O. Caldwell, J. P. Castle, C. L. Chang, R. M. Clarke, M. B. Crisler, R. Dixon, D. Driscoll, S. Eichblatt, R. J. Gaitskell, S. R. Golwala, E. E. Haller, J. Hellmig, D. Holmgren, M. E. Huber, S. Kamat, A. Lu, V. Mandic, J. M. Martinis, P. Meunier, S. W. Nam, H. Nelson, T. A. Perera, M. C. Perillo Isaac, W. Rau, R. R. Ross, T. Saab, B. Sadoulet, J. Sander, R. W. Schnee, T. Shutt, A. Smith, A. H. Sonnenschein, A. L. Spadafora, G. Wang, S. Yellin, Betty A. Young Dec 2002

Exclusion Limits On The Wimp-Nucleon Cross Section From The Cryogenic Dark Matter Search, D. Abrams, D. S. Akerib, M. S. Armel-Funkhouser, L. Baudis, D. A. Bauer, A. Bolozdynya, P. L. Brink, R. Bunker, B. Cabrera, D. O. Caldwell, J. P. Castle, C. L. Chang, R. M. Clarke, M. B. Crisler, R. Dixon, D. Driscoll, S. Eichblatt, R. J. Gaitskell, S. R. Golwala, E. E. Haller, J. Hellmig, D. Holmgren, M. E. Huber, S. Kamat, A. Lu, V. Mandic, J. M. Martinis, P. Meunier, S. W. Nam, H. Nelson, T. A. Perera, M. C. Perillo Isaac, W. Rau, R. R. Ross, T. Saab, B. Sadoulet, J. Sander, R. W. Schnee, T. Shutt, A. Smith, A. H. Sonnenschein, A. L. Spadafora, G. Wang, S. Yellin, Betty A. Young

Physics

The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.9% efficiency, and surface events are rejected with >95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to ∼10%. Results of …

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Si Doping Of High-Al-Mole Fraction Alxga1-Xn Alloys With Rf Plasma-Induced Molecular-Beam-Epitaxy, Jeonghyun Hwang, William J. Schaff, Lester F. Eastman, Shawn T. Bradley, Leonard J. Brillson, David C. Look, J. Wu, Wladek Walukiewicz, Madalina Furis, Alexander N. Cartwright Dec 2002

Si Doping Of High-Al-Mole Fraction Alxga1-Xn Alloys With Rf Plasma-Induced Molecular-Beam-Epitaxy, Jeonghyun Hwang, William J. Schaff, Lester F. Eastman, Shawn T. Bradley, Leonard J. Brillson, David C. Look, J. Wu, Wladek Walukiewicz, Madalina Furis, Alexander N. Cartwright

Physics Faculty Publications

Very high levels of n-type doping of AlxGa1−xN alloys were recently achieved by rf plasma-induced molecular-beam epitaxy on sapphire substrates and Si as a dopant. Electron concentrations were obtained up to 1.25×1020 cm−3 when the Al mole fraction was 50%, and 8.5×1019 cm−3 electrons were measured even when the Al mole fraction was 80%. Other material properties were determined by optical absorption, photoluminescence, cathodoluminescence, x-ray diffraction, and atomic force microscopy measurements and high optical and morphological qualities were shown.

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Recombination Of Excitons Bound To Oxygen And Silicon Donors In Freestanding Gan, A. Wysmolek, K. P. Korona, R. Stepniewski, J. M. Baranowsky, J. Bloniarz, M. Potemski, R. L. Jones, David C. Look, J. Kuhl, S. S. Park, S. K. Lee Dec 2002

Recombination Of Excitons Bound To Oxygen And Silicon Donors In Freestanding Gan, A. Wysmolek, K. P. Korona, R. Stepniewski, J. M. Baranowsky, J. Bloniarz, M. Potemski, R. L. Jones, David C. Look, J. Kuhl, S. S. Park, S. K. Lee

Physics Faculty Publications

The neutral donor bound exciton recombination processes in freestanding GaN have been studied. The photoluminescence spectrum shows emission lines related to silicon and oxygen donors. Time-resolved luminescence allows us to correlate the principal donor bound exciton lines with their two-electron satellites. The magnetic field splitting of the two-electron lines is well described by the theory of the hydrogen atom in a magnetic field. For the oxygen donor a 1.5 meV chemical shift and a 30.8 meV effective Rydberg have been evaluated. Two-electron satellites involving excitations to the 2p and 2s donor states are separated by an energy of 1.0 and …

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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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Electronic-Structure Modifications Induced By Surface Segregation In La0.65Pb0.35Mno3 Thin Films, C.N. Borca, B. Xu, T. Komesu, H.-K. Jeong, M.T. Liu, Sy_Hwang Liou, Shane Stadler, Y. Idzerda, Peter A. Dowben Dec 2002

Electronic-Structure Modifications Induced By Surface Segregation In La0.65Pb0.35Mno3 Thin Films, C.N. Borca, B. Xu, T. Komesu, H.-K. Jeong, M.T. Liu, Sy_Hwang Liou, Shane Stadler, Y. Idzerda, Peter A. Dowben

Peter Dowben Publications

Using spin-polarized inverse photoemission and X-ray absorption spectroscopy techniques, we show that the electronic structure of La0.65Pb0.35MnO3 thin films depends on the composition at the surface. With a gentle annealing procedure, the surface provides a maximum of 80% spin asymmetry at 0.5 eV above the Fermi level in spite of extensive Pb segregation. A heavily annealed (restructured) surface exhibits a reduced surface "ordering" temperature of 240 K (compared to the approximately 335 K bulk value) as well as a reduced spin asymmetry value of 40% at 0.5 eV above Fermi energy.

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N Coupled Nonlinear Schrödinger Equations: Special Set And Applications To N=3, Foek T. Hioe Dec 2002

N Coupled Nonlinear Schrödinger Equations: Special Set And Applications To N=3, Foek T. Hioe

Physics Faculty/Staff Publications

Analytic solutions for a special set of N coupled nonlinear Schrödinger equations characterized by 2N interaction types are presented for N = 1–3. They provide an overview of the important role played by nonlinear couplings

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Two-Dimensional Imaging Of Neutral Alkali Atom Samples Using Surface Ionization, Katharina Gillen-Christandl, Gregory P. Lafyatis, Andrei Modoran, Tung-Hsiu Shih Dec 2002

Two-Dimensional Imaging Of Neutral Alkali Atom Samples Using Surface Ionization, Katharina Gillen-Christandl, Gregory P. Lafyatis, Andrei Modoran, Tung-Hsiu Shih

Physics

We describe the design and characterization of a high resolution, high efficiency detector for two-dimensional imaging of neutral atoms. Incident atoms are surface-ionized by a tungsten-coated hot ribbon and the resulting ions are accelerated into a microchannel plate detector with a phosphor screen output. With this design we can detect individual alkali and other low ionization potential atoms and molecules with a spatial resolution of ∼ 20 μm. We find backgrounds on the order of 30 Hz over an active detection region of 20 mm2, a time response of ⩽ 1/30 s, and a detection efficiency of …

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Properties Of Hadronic Final States In Diffractive Deep Inelastic Ep Scattering At Desy Hera, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli Dec 2002

Properties Of Hadronic Final States In Diffractive Deep Inelastic Ep Scattering At Desy Hera, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli

Faculty Publications

Characteristics of the hadronic final state of diffractive deep inelastic scattering events ep→eXp were studied in the kinematic range 4X35GeV, 4

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Power Scaling Feasibility Of Chromium-Doped Ii-Vi Laser Sources And The Demonstration Of A Chromium-Doped Zinc Selenide Face-Cooled Disk Laser, Jason B. Mckay Dec 2002

Power Scaling Feasibility Of Chromium-Doped Ii-Vi Laser Sources And The Demonstration Of A Chromium-Doped Zinc Selenide Face-Cooled Disk Laser, Jason B. Mckay

Theses and Dissertations

Tunable lasers in the 2-4 µm wavelength range are needed for Air Force sensor applications. Chromium-doped II-VI materials are a promising class of laser material for tunable operation in this wavelength range, but until recently had not produced enough output power to meet application requirements. This dissertation investigates Cr2+:II-VI material properties and potential laser designs, then experimentally demonstrates and analyzes the performance of a Cr2+:ZnSe disk laser design that can produce sufficient output power. Cr2+:II-VI laser materials are found to be susceptible to overheating and thermal lensing, but are otherwise satisfactory laser materials. The …

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Coexistence Of Ferromagnetic And Glassy States In Mechanically Milled Gdal2, C. Stark, P. M. Shand, T. M. Pekarek, D. Williams, R. Brown, Lanping Yue, Diandra Leslie-Pelecky Dec 2002

Coexistence Of Ferromagnetic And Glassy States In Mechanically Milled Gdal2, C. Stark, P. M. Shand, T. M. Pekarek, D. Williams, R. Brown, Lanping Yue, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Measurements of DC susceptibility, AC susceptibility, and AC susceptibility with an applied DC bias field were performed on mechanically milled GdAl2. A paramagnetic phase exists above a temperature T ≈ 140 K. However, there are significant deviations from the Curie-Weiss Law in this temperature regime, suggesting multiple magnetic components. Fits to the high temperature data show that two Curie-Weiss terms represent the data quite well. Below 140 K one of these magnetic components becomes ferromagnetic as indicated by a shoulder in the AC susceptibility and DC susceptibility data. This ferromagnetic component is suppressed by the application of sufficiently …

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Quiet Time Variability Of The Geosynchronous Magnetic Field And Its Response To The Solar Wind, Jeff Sanny, J. A. Tapia, D. G. Sibeck, M. B. Moldwin Dec 2002

Quiet Time Variability Of The Geosynchronous Magnetic Field And Its Response To The Solar Wind, Jeff Sanny, J. A. Tapia, D. G. Sibeck, M. B. Moldwin

Physics Faculty Works

We present a survey of the variability of the geosynchronous magnetic field strength on the dayside using observations by the GOES satellites over a period exceeding 4 years. Only intervals of reduced geomagnetic activity, as defined by Dst > −20 nT, were considered in this study. The magnetic field strength data were filtered with a passband of 1.7 mHz to 17 mHz (1–10 minutes), a process that eliminates the diurnal variation of the field strength and the effects of most of the higher frequency (>17 mHz) ultralow-frequency (ULF) waves. The geosynchronous field strength appears to exhibit the greatest variability in …

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Investigation Of The Corrosion Of Steel By Lead-Bismuth Eutectic (Lbe) Using Scanning Electron Microscopy And X-Ray Photoelectron Spectroscopy, Daniel Koury Dec 2002

Investigation Of The Corrosion Of Steel By Lead-Bismuth Eutectic (Lbe) Using Scanning Electron Microscopy And X-Ray Photoelectron Spectroscopy, Daniel Koury

UNLV Theses, Dissertations, Professional Papers, and Capstones

Lead Bismuth Eutectic (LBE) has been proposed for use in programs for accelerator transmutation of waste. LBE is the leading candidate material as a spallation target and an option for the sub-critical blanket coolant. The corrosion of 316 and 316L stainless steels by LBE has been studied using UNLV's facilities for Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). We have compared exposed and unexposed samples and studied the differences. Some amount of surface contamination is present on the samples and has been removed by ionbeam etching. The unexposed samples reveal typical stainless steel characteristics: a chromium oxide passivation …

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Mobility And Immobility Of Mid-Ocean Ridges And Their Implications To Mantle Dynamics, Me Kamwaya Nov 2002

Mobility And Immobility Of Mid-Ocean Ridges And Their Implications To Mantle Dynamics, Me Kamwaya

Tanzania Journal of Science

In the past two decades, the mobility of mid-ocean ridges relative to the mantle (absolute migration) have been correlated with major observable features, such as, spreading asymmetry and asymmetry in the abundance of seamounts. The mobility of mid-ocean ridges is also thought to be an important factor that influences the diversity of ridge-crest basalts. However, the mobility of mid-ocean ridges have not yet been defined and mapped. The absolute migration of global mid-ocean ridges since 85 Ma has been computed and mapped. Global mid-ocean ridges have migrated extensively at varying velocities during that period. Presently, the fast-migrating ridges are the …

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Searches For Excited Fermions In Ep Collisions At Hera, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli Nov 2002

Searches For Excited Fermions In Ep Collisions At Hera, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli

Faculty Publications

Searches in ep collisions for heavy excited fermions have been performed with the ZEUS detector at HERA. Excited states of electrons and quarks have been searched for in e+ p collisions at a centre-of-mass energy of 300 GeV using an integrated luminosity of 47.7 pb-1. Excited electrons have been sought via the decays e± → eγ, e± → eZ and e± → vW. Excited quarks have been sought via the decays q± → qγ and q± → qW. A search for excited neutrinos decaying via v± → vγ, v± → vZ and v± → eW is presented using e-p collisions …

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