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2003

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Articles 421 - 436 of 436

Full-Text Articles in Physical Sciences and Mathematics

Instrumentation For Studies Of Electron Emission And Charging From Insulators, C. D. Thomson, V. V. Zavyalov, John R. Dennison Jan 2003

Instrumentation For Studies Of Electron Emission And Charging From Insulators, C. D. Thomson, V. V. Zavyalov, John R. Dennison

All Physics Faculty Publications

Making measurements of electron emission properties of insulators is difficult since insulators can charge either negatively or positively under charge particle bombardment. In addition, high incident energies or high fluences can result in modification of a material’s conductivity, bulk and surface charge profile, structural makeup through bond breaking and defect creation, and emission properties. We discuss here some of the charging difficulties associated with making insulator-yield measurements and review the methods used in previous studies of electron emission from insulators. We present work undertaken by our group to make consistent and accurate measurements of the electron/ion yield properties for numerous …

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Electron Emission Properties Of Insulator Materials Pertinent To The International Space Station, C. D. Thomson, V. V. Zavyalov, John R. Dennison, Jodie Corbridge Jan 2003

Electron Emission Properties Of Insulator Materials Pertinent To The International Space Station, C. D. Thomson, V. V. Zavyalov, John R. Dennison, Jodie Corbridge

All Physics Faculty Publications

We present the results of our measurements of the electron emission properties of selected insulating and conducting materials used on the International Space Station (ISS). Utah State University (USU) has performed measurements of the electron-, ion-, and photon-induced electron emission properties of conductors for a few years, and has recently extended our capabilities to measure electron yields of insulators, allowing us to significantly expand current spacecraft material charging databases. These ISS materials data are used here to illustrate our various insulator measurement techniques that include: i) Studies of electron-induced secondary and backscattered electron yield curves using pulsed, low current electron …

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Comparison Of Classical And Charge Storage Methods For Determining Conductivity Of Thin Film Insulators, Prasanna Swaminathan, A. R. Frederickson, John R. Dennison, Alec Sim, J. Brunson, Eric Crapo Jan 2003

Comparison Of Classical And Charge Storage Methods For Determining Conductivity Of Thin Film Insulators, Prasanna Swaminathan, A. R. Frederickson, John R. Dennison, Alec Sim, J. Brunson, Eric Crapo

All Physics Faculty Publications

Conductivity of insulating materials is a key parameter to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. Classical ASTM and IEC methods to measure thin film insulator conductivity apply a constant voltage to two electrodes around the sample and measure the resulting current for tens of minutes. However, conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator. Charge decay methods expose one side of the insulator in vacuum to sequences of charged particles, light, and plasma, with a metal electrode …

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Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraftcharging, A. R. Fredrickson, John R. Dennison Jan 2003

Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraftcharging, A. R. Fredrickson, John R. Dennison

All Physics Faculty Publications

Novel methods have been developed to measure conductivity and charge storage in thin film insulating spacecraft materials subjected to space radiations. For a variety of such samples, conductivity values differ by up to 104 from values based on ASTM standards. Conductivity and charge storage properties are found to be functions of prior radiation history. A highly-charged insulator emits electrons for hours (Malter Effect) after the irradiation beam is turned off. Visible light can be used to induce emission from previously charged samples with shallow traps.

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Secondary Electron Production And Transport Mechanisms By Measurement Of Angle-Energyresolved Cross Sections Of Secondary And Backscattered Electrons, Jason Kite, John R. Dennison Jan 2003

Secondary Electron Production And Transport Mechanisms By Measurement Of Angle-Energyresolved Cross Sections Of Secondary And Backscattered Electrons, Jason Kite, John R. Dennison

All Physics Faculty Publications

The angle dependence of emitted electron spectra from a polycrystalline Au surface has been measured at several incident electron beam energies. The range of incident energies (~100 eV to 2500 eV) extends from below the first crossover energy, through Emax, to above the second crossover energy. The traditional distinction between secondary electrons (50 eV) is found to be inconsistent with our energy- and angle-resolved measurements. We suggest a more “natural” delineation occurs at the local minima of the emission spectra; this feature is studied as a function of incident energy and emission angle. This work is also supported by the …

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Lisa Data Analysis: Source Identification And Subtraction, Neil J. Cornish, Shane L. Larson Jan 2003

Lisa Data Analysis: Source Identification And Subtraction, Neil J. Cornish, Shane L. Larson

All Physics Faculty Publications

The Laser Interferometer Space Antenna will operate as an AM-FM receiver for gravitational waves. For binary systems, the source location, orientation and orbital phase are encoded in the amplitude and frequency modulation. The same modulations spread a monochromatic signal over a range of frequencies, making it difficult to identify individual sources. We present a method for detecting and subtracting individual binary signals from a data stream with many overlapping signals.

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Search For Resonance Decays To Lepton+Jet At Desy Hera And Limits On Leptoquarks, S. Chekanov, M. Derrick, D. Krakauer, J. H. Loizides, S. Magill, B. Musgrave, 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, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan Jan 2003

Search For Resonance Decays To Lepton+Jet At Desy Hera And Limits On Leptoquarks, S. Chekanov, M. Derrick, D. Krakauer, J. H. Loizides, S. Magill, B. Musgrave, 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, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan

Faculty Publications

A search for narrow-width resonances that decay into electron+jet or neutrino+jet has been performed with the ZEUS detector at the DESY ep collider HERA operating at center-of-mass energies of 300 and 318 GeV. An integrated e+p luminosity of 114.8 pb-1 and e-p luminosity of 16.7 pb-1 were used. No evidence for any resonance was found. Limits were derived on the Yukawa coupling λ as a function of the mass of a hypothetical resonance that has arbitrary decay branching ratios into eq or vq. These limits also apply to squarks predicted by R-parity-violating supersymmetry. Limits for the production of leptoquarks described …

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Measurement Of Proton-Dissociative Diffractive Photoproduction Of Vector Mesons At Large Momentum Transfer At Hera: The Zeus Collaboration, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, 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, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan, D. Bartsch Jan 2003

Measurement Of Proton-Dissociative Diffractive Photoproduction Of Vector Mesons At Large Momentum Transfer At Hera: The Zeus Collaboration, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, 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, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan, D. Bartsch

Faculty Publications

Diffractive photoproduction of vector mesons, γp → VY, where Y is a proton-dissociative system, has been measured in e+p interactions with the ZEUS detector at HERA using an integrated luminosity of 25 pb-1. The differential cross section, dσ/dt, is presented for 1.2 < -t < 12 GeV2, where t is the square of the four-momentum transferred to the vector meson. The data span the range in photon-proton centre-of-mass energy, W, from 80 GeV to 120 GeV. The t distributions are well fit by a power law, dσ/dt ∝ (-t)-n. The slope of the effective Pomeron trajectory, measured from the W dependence of the ρ0 and φ cross sections in bins of t, is consistent with zero. The ratios dσγp→φY/dt to dσγp→ρ0Y/dt and dσγp→J/ψY/dt to dσγp→ρ0Y/dt increase with increasing -t. Decay-angle analyses for ρ0, φ and J/ψ mesons have been carried out. For the ρ0 and φ mesons, contributions from single and double helicity flip are observed. The results are compared to expectations of theoretical models.

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Measurement Of The Stochasticity Of Low-Latitude Geomagnetic Temporal Variations, Mark Anthony Reynolds, James A. Wanliss Jan 2003

Measurement Of The Stochasticity Of Low-Latitude Geomagnetic Temporal Variations, Mark Anthony Reynolds, James A. Wanliss

Publications

Ground magnetometer measurements of total magnetic field strength from 6 stations at low latitudes were analyzed using power spectrum and Hurst range scaling techniques. The Hurst exponents for most of these time-series were near 0.5, which indicates stochasticity, with the highest latitude stations exhibiting some persistence with Hurst exponents greater than 0.6. Although no definite correlations are evident, the relative increase of the Hurst exponent with latitude suggests the possibility that the underlying dynamics of the magnetosphere change with latitude. This result may help quantify the dynamics of the inner magnetosphere itself without the direct presence of the solar wind …

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The Local-Time Variation Of The Quiet Plasmasphere: Geosynchronous Observations And Kinetic Theory, Mark Anthony Reynolds, G. Ganguli, Y-J Su, M.F. Thomsen Jan 2003

The Local-Time Variation Of The Quiet Plasmasphere: Geosynchronous Observations And Kinetic Theory, Mark Anthony Reynolds, G. Ganguli, Y-J Su, M.F. Thomsen

Publications

The quiet-time structure of the plasmaspheric density was investigated using observations of the Los Alamos geosynchronous satellites, and these observations were compared with theoretical predictions of the quasi-static localtime variation by a kinetic model. It was found that the coupling to the ionosphere (via the local-time variation of the exobase) played a key role in determining the density structure at 6.6 RE. The kinetic model predicts that most of the local-time variation at geosynchronous orbit is due to the variation of the exobase parameters. During quiet times, when the convection electric field is dominated by the corotation field, the effects …

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Optimal Entanglement Generation From Quantum Operations, Matthew S. Leifer, L. Henderson, N. Linden Jan 2003

Optimal Entanglement Generation From Quantum Operations, Matthew S. Leifer, L. Henderson, N. Linden

Mathematics, Physics, and Computer Science Faculty Articles and Research

We consider how much entanglement can be produced by a nonlocal two-qubit unitary operation, UAB—the entangling capacity of UAB. For a single application of UAB , with no ancillas, we find the entangling capacity and show that it generally helps to act with UAB on an entangled state. Allowing ancillas, we present numerical results from which we can conclude, quite generally, that allowing initial entanglement typically increases the optimal capacity in this case as well. Next, we show that allowing collective processing does not increase the entangling capacity if initial entanglement is allowed.

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Thermoelectric Cooling At Cryogenic Temperatures, S. R. Harutyunyan, V. H. Vardanyan, A. S. Kuzanyan, V. R. Nikoghosyan, S. Kunii, K. S. Wood, Armen Gulian Jan 2003

Thermoelectric Cooling At Cryogenic Temperatures, S. R. Harutyunyan, V. H. Vardanyan, A. S. Kuzanyan, V. R. Nikoghosyan, S. Kunii, K. S. Wood, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

Experimental results demonstrating Peltier cooling below 10 K are reported, using crystals of the thermoelectric cerium hexaboride (CeB6). Direct measurements of the Peltier cooling showed δT up to ∼0.2 K in magnitude at T∼4–5 K. All three kinetic parameters: resistivity (ρ), heat conductivity (k), and Seebeck coefficient (S), characterizing the thermoelectric figure of merit ZT=S2T/ρk, were measured, giving high-confidence results.

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Atomic Structure, Binding Energy, And Magnetic Properties Of Iron Atoms Supported On A Polyaromatic Hydrocarbon, L. Senapati, S. K. Nayak, B. K. Rao, P. Jena Jan 2003

Atomic Structure, Binding Energy, And Magnetic Properties Of Iron Atoms Supported On A Polyaromatic Hydrocarbon, L. Senapati, S. K. Nayak, B. K. Rao, P. Jena

Physics Publications

The atomic structure, energetics, and properties of gas-phase cluster complexes containing coronene (C24H12) molecule and up to two iron atoms are studied for the first time using density functional theory and generalized gradient approximation for exchange and correlation. The geometries of the neutral and cationic iron–coronene complexes are optimized without symmetry constraint and by examining the possibility that iron atoms could occupy various sites via individual π or bridging interactions. In both neutral and cationic complexes a single Fe atom is found to preferentially occupy the on-top site above the outer ring, while two Fe atoms dimerize and reside on …

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Superfluorescence Polarization: Signature Of Collisional Redistribution, A. Kumarakrishnan, S. Chudasama, Xianming Han Jan 2003

Superfluorescence Polarization: Signature Of Collisional Redistribution, A. Kumarakrishnan, S. Chudasama, Xianming Han

Scholarship and Professional Work - LAS

We have studied effects of magnetic sublevel degeneracy on the polarization of superfluorescent pulses generated on the Ca 4s4p1P1–3d4s1D2 transition at 5.5μm. These pulses were generated from a cell of length 50 cm by optically pumping calcium vapor on the 4s21S0–4s4p1P1 transition in the presence of Ar gas. The axis of ellipticity of superfluorescence (SF) polarization is oriented parallel to the axis of the pump-laser polarization at large detunings, and undergoes an abrupt rotation through 90° for detunings close to resonance. The distribution of populations in the magnetic sublevels of the 1P1 state can be estimated using a simple model …

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Spontaneous Magnetization Generated By Spin, Pulsating, And Planar Combustion Synthesis, Karen S. Martirosyan, J. R. Claycomb, G. Gogoshin, R. A. Yarbrough, J. H. Miller Jr., D. Luss Jan 2003

Spontaneous Magnetization Generated By Spin, Pulsating, And Planar Combustion Synthesis, Karen S. Martirosyan, J. R. Claycomb, G. Gogoshin, R. A. Yarbrough, J. H. Miller Jr., D. Luss

Physics and Astronomy Faculty Publications and Presentations

The motion of the high temperature front during combustion synthesis of ferrite materials generates residual magnetization in cylindrical product samples. The combustion wave created a current density of up to 10 A/cm2, which influenced the magnetization distribution. The measured peak magnetic field intensity was up to 8 mT. Qualitatively different magnetic field maps were generated in ferrite samples synthesized by different combustion modes. The average magnetization vector generated by either planar or pulsating combustion was oriented at a smaller angle with respect to the pellet axis ~f<45°! than those generated by spin combustion ~60°

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Mode-Cleaning And Injection Optics Of The Gravitational-Wave Detector Geo600, S. Goßler, M. M. Casey, A. Grant, H. Grote, Volker Quetschke Jan 2003

Mode-Cleaning And Injection Optics Of The Gravitational-Wave Detector Geo600, S. Goßler, M. M. Casey, A. Grant, H. Grote, Volker Quetschke

Physics and Astronomy Faculty Publications and Presentations

The British–German interferometric gravitational-wave detector GEO600 uses two high-finesse triangular ring cavities of 8 m optical pathlength each, as an optical mode-cleaning system. The modecleaner system is housed in an ultrahigh-vacuum environment to avoid contamination of the optics and to minimize both the influence of refractive index variations of the air and acoustic coupling to the optics. To isolate the cavities from seismic noise, all optical components are suspended as double pendulums. These pendulums are damped at their resonance frequencies at the upper pendulum stage with magnet-coil actuators. A suspended reaction mass supports three coils matching magnets bonded onto the …

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