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Series

Engineering Physics

2008

Articles 1 - 9 of 9

Full-Text Articles in Physics

Emissions Scenarios In The Face Of Fossil-Fuel Peaking, Robert J. Brecha Sep 2008

Emissions Scenarios In The Face Of Fossil-Fuel Peaking, Robert J. Brecha

Physics Faculty Publications

Emissions scenarios used by the Intergovernmental Panel on Climate Change (IPCC) are based on detailed energy system models in which demographics, technology and economics are used to generate projections of future world energy consumption, and therefore, of greenhouse gas emissions. We propose in this paper that it is useful to look at a qualitative model of the energy system, backed by data from short- and medium-term trends, to gain a sense of carbon emission bounds. Here we look at what may be considered a lower bound for 21st century emissions given two assumptions: first, that extractable fossil-fuel resources follow the …

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Predicting The Hydrogen Pressure To Achieve Ultralow Friction And Diamondlike Carbon Surfaces From First Principles, Haibo Guo, Yue Qi, Xiaodong Li Jun 2008

Predicting The Hydrogen Pressure To Achieve Ultralow Friction And Diamondlike Carbon Surfaces From First Principles, Haibo Guo, Yue Qi, Xiaodong Li

Faculty Publications

Hydrogen atmosphere can significantly change the tribological behavior at diamond and diamondlike carbon (DLC) surfaces and the friction-reducing effect depends on the partial pressure of hydrogen. We combined density functional theory modeling and thermodynamic quantities to predict the equilibrium partial pressures of hydrogen at temperature T, PH2 (T), for a fully atomic hydrogen passivated diamondsurface. Above the equilibrium PH2 (T), ultralow friction can be achieved at diamond and DLC surfaces. The calculation agrees well with friction tests at various testing conditions. We also show that PH2 (T) …

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Charge Order, Dynamics, And Magnetostructural Transition In Multiferroic Lufe2o4, X. S. Xu, M. Angst, T. V. Brinzari, R. P. Hermann, J. L. Musfeldt, A. D. Christianson, D. Mandrus, B. C. Sales, S. Mcgill, J. -W. Kim, Z. Islam Jan 2008

Charge Order, Dynamics, And Magnetostructural Transition In Multiferroic Lufe2o4, X. S. Xu, M. Angst, T. V. Brinzari, R. P. Hermann, J. L. Musfeldt, A. D. Christianson, D. Mandrus, B. C. Sales, S. Mcgill, J. -W. Kim, Z. Islam

Xiaoshan Xu Papers

We investigated the series of temperature and field-driven transitions in LuFe2O4 by optical and Mossbauer spectroscopies, magnetization, and x-ray scattering in order to understand the interplay between charge, structure, and magnetism in this multiferroic material. We demonstrate that charge fluctuation has an onset well below the charge ordering transition, supporting the ‘‘order by fluctuation’’ mechanism for the development of charge order superstructure. Bragg splitting and large magneto-optical contrast suggest a low-temperature monoclinic distortion that can be driven by both temperature and magnetic field.

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Photoconductivity In Bifeo3 Thin Films, S. R. Basu, L. W. Martin, Y. H. Chu, M. Gajek, R. Ramesh, R. C. Rai, X. S. Xu, J. L. Musfeldt Jan 2008

Photoconductivity In Bifeo3 Thin Films, S. R. Basu, L. W. Martin, Y. H. Chu, M. Gajek, R. Ramesh, R. C. Rai, X. S. Xu, J. L. Musfeldt

Xiaoshan Xu Papers

The optical properties of epitaxial BiFeO3 thin films have been characterized in the visible range. Variable temperature spectra show an absorption onset near 2.17 eV, a direct gap (2.667±0.005 eV at 300 K), and charge transfer excitations at higher energy. Additionally, we report photoconductivity in BiFeO3 films under illumination from a 100 mW/cm2 white light source. A direct correlation is observed between the magnitude of the photoconductivity and postgrowth cooling pressure. Dark conductivities increased by an order of magnitude when comparing films cooled in 760 and 0.1 Torr. Large increases in photoconductivity are observed in light.

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Optical Band Gap Of Bifeo3 Grown By Molecular-Beam Epitaxy, J. F. Ihlefeld, N. J. Podraza, Z. K. Liu, R. C. Rai, X. Xu, T. Heeg, Y. B. Chen, J. Li, R. W. Collins, J. L. Musfeldt, X. Q. Pan, J. Schubert, R. Ramesh, D. G. Schlom Jan 2008

Optical Band Gap Of Bifeo3 Grown By Molecular-Beam Epitaxy, J. F. Ihlefeld, N. J. Podraza, Z. K. Liu, R. C. Rai, X. Xu, T. Heeg, Y. B. Chen, J. Li, R. W. Collins, J. L. Musfeldt, X. Q. Pan, J. Schubert, R. Ramesh, D. G. Schlom

Xiaoshan Xu Papers

BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with w rocking curve full width at half maximum values as narrow as 29 arc sec (0.008°). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74 eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films.

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Studies Of Breakdown In A Pressurized Rf Cavity, M. Bastaninejad, A. A. Elmustafa, C. M. Ankenbrandt, A. Moretti, M. Popovic, K. Yonehara, D. M. Kaplan, M. Alsharo'a, P. M. Hanlet, R. P. Johnson, M. Kuchnir, D. Newsham, D. V. Rose, C. Thoma, D. R. Welch Jan 2008

Studies Of Breakdown In A Pressurized Rf Cavity, M. Bastaninejad, A. A. Elmustafa, C. M. Ankenbrandt, A. Moretti, M. Popovic, K. Yonehara, D. M. Kaplan, M. Alsharo'a, P. M. Hanlet, R. P. Johnson, M. Kuchnir, D. Newsham, D. V. Rose, C. Thoma, D. R. Welch

Mechanical & Aerospace Engineering Faculty Publications

Microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 805 MHz RF cavity experiments [1] have been used to investigate the mechanism of RF breakdown [2]. The images show evidence for melting and boiling in small regions of ∼10 micron diameter on tungsten, molybdenum, and beryllium electrode surfaces. In these experiments, the dense hydrogen gas in the cavity prevents electrons or ions from being accelerated to high enough energy to participate in the breakdown process so that the only important variables are the fields and the metallic surfaces. The distributions of breakdown remnants on the electrode surfaces …

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Advances On Elic Design Studies, S. A. Bogacz, P. Chevtsov, Ya. Derbenev, P. Evtushenko, G. Krafft, A. Hutton, R. Li, L. Merminga, J. Musson, B. Yunn, Y. Zhang, H. Sayed Jan 2008

Advances On Elic Design Studies, S. A. Bogacz, P. Chevtsov, Ya. Derbenev, P. Evtushenko, G. Krafft, A. Hutton, R. Li, L. Merminga, J. Musson, B. Yunn, Y. Zhang, H. Sayed

Physics Faculty Publications

An electron-ion collider of a center-of-mass energy up to 90 GeV at luminosity up to 1035 cm-2s-1 with both beams highly polarized is essential for exploring the new QCD frontier of strong color fields in nuclear and precisely imaging the sea-quarks and gluons in the nucleon. A conceptual design of a ring-ring collider based on CEBAF (ELIC) with energies up to 9 GeV for electrons/positrons and up to 225 GeV for protons and 100 GeV/u for ions has been proposed to fulfill the science desire and to serve as the next step for CEBAF after the …

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Combinatorial Investigation Of Magnetostriction In Fe-Fa And Fe-Ga-Al, Jason R. Hattrick-Simpers, Dwight Hunter, Corneliu M. Craciunescu, Kyu Sung Jang, Makoto Murakami, James Cullen, Manfred Wuttig, Ichiro Takeuchi, Samuel E. Lofland, Leonid Bendersky, Noble Woo, Robert Bruce Vandover, Toshiya Takahashi, Yasubumi Furuya Jan 2008

Combinatorial Investigation Of Magnetostriction In Fe-Fa And Fe-Ga-Al, Jason R. Hattrick-Simpers, Dwight Hunter, Corneliu M. Craciunescu, Kyu Sung Jang, Makoto Murakami, James Cullen, Manfred Wuttig, Ichiro Takeuchi, Samuel E. Lofland, Leonid Bendersky, Noble Woo, Robert Bruce Vandover, Toshiya Takahashi, Yasubumi Furuya

Faculty Publications

A high-throughput high-sensitivity optical technique for measuringmagnetostriction of thin-film composition-spread samples has been developed. It determines the magnetostriction by measuring the induced deflection of micromachined cantilever unimorph samples. Magnetostrictionmeasurements have been performed on as-deposited Fe–Ga and Fe–Ga–Al thin-film composition spreads. The thin-film Fe–Ga spreads display a similar compositional variation of magnetostriction as bulk. A previously undiscovered peak in magnetostriction at low Ga content was also observed and attributed to a maximum in the magnetocrystalline anisotropy. Magnetostrictive mapping of the Fe–Ga–Al ternary system reveals the possibility of substituting up to 8at.%Al in Fe70Ga30 without significant degradation of magnetostriction.

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Performance Comparison Of Pb(Zr0.52Ti0.48)O3-Only And Pb(Zr0.52Ti0.48)O3-On-Silicon Resonators, Hengky Chandrahalim, Sunil A. Bhave, Ronald G. Polcawich, Jeff Pulskamp, Dan Judy, Roger Kaul, Madan Dubey Jan 2008

Performance Comparison Of Pb(Zr0.52Ti0.48)O3-Only And Pb(Zr0.52Ti0.48)O3-On-Silicon Resonators, Hengky Chandrahalim, Sunil A. Bhave, Ronald G. Polcawich, Jeff Pulskamp, Dan Judy, Roger Kaul, Madan Dubey

Faculty Publications

This paper provides a quantitative comparison and explores the design space of lead zirconium titanate (PZT)–only and PZT-on-silicon length-extensional mode resonators for incorporation into radio frequency microelectromechanical system filters and oscillators. We experimentally measured the correlation of motional impedance (RX) and quality factor (Q) with the resonators’ silicon layer thickness (tSi). For identical lateral dimensions and PZT-layer thicknesses (tPZT), the PZT-on-silicon resonator has higher resonant frequency (fC), higher Q (5100 versus 140), lower RX (51 Ω versus 205 Ω), and better linearity [third-order input intercept …

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