Engineering Physics Commons^™

Comment On "Superfluid Turbulence From Quantum Kelvin Wave To Classical Kolmogorov Cascades", Jeffrey Yepez, George Vahala, Linda L. Vahala, Min Soe

Electrical & Computer Engineering Faculty Publications

No abstract provided.

Finite Element Analysis Of Ring-Shaped Emission Profile In Plasma Bullet, Yukinori Sakiyama, David B. Graves, Julien Jarrige, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

Using a one-way coupled model of neutral gas flow and plasma dynamics we report a mechanism to explain the ring-shaped emission pattern that has been observed experimentally in plasma bullets at atmospheric pressure. We solve a fluid model with the local field approximation in one-dimensional cylindrical coordinates, corresponding to a cross-section of a plasma bullet. Pulselike uniform electric field is assumed to be applied perpendicular to the simulation domain. Time and spatially resolved spectroscopic measurements support the simulation results.

Comparing Experts And Novices In Solving Electrical Circuit Problems With The Help Of Eye-Tracking, David Rosengrant, Colin Thomson, Taha Mzoughi

Faculty Articles

In order to help introductory physics students understand and learn to solve problems with circuits, we must first understand how they differ from experts. This preliminary study focuses on problem-solving dealing with electrical circuits. We investigate difficulties novices have with circuits and compare their work with those of experts. We incorporate the use of an eye-tracker to investigate any possible differences or similarities on how experts and novices solve electrical circuit problems. Our results show similarities in gaze patterns among all subjects on the components of the circuit. We further found that experts would look back at the circuit while …

Coupled Ray-Tracing And Fokker-Planck Ebw Modeling For Spherical Tokamaks, Jakub Urban, Joan Decker, Y. Peysson, Josef Preinhaelter, Gary Taylor, Linda L. Vahala, George Vahala

Electrical & Computer Engineering Faculty Publications

The AMR (Antenna—Mode-conversion—Ray-tracing) code [1, 2] has been recently coupled with the LUKE [3] Fokker-Planck code. This modeling suite is capable of complex simulations of electron Bernstein wave (EBW) emission, heating and current drive. We employ these codes to study EBW heating and current drive performance under spherical tokamak (ST) configurations—typical NSTX discharges are employed. EBW parameters, such as frequency, antenna position and direction, are varied and optimized for particular configurations and objectives. In this way, we show the versatility of EBWs.

Strain Energy And Lateral Friction Force Distributions Of Carbon Nanotubes Manipulated Into Shapes By Atomic Force Microscopy, Mark C. Strus, Roya R. Lahiji, Pablo Ares, Vincente Lopez, Arvind Raman, Ron R. Reifenberger

Other Nanotechnology Publications

The interplay between local mechanical strain energy and lateral frictional forces determines the shape of carbon nanotubes on substrates. In turn, because of its nanometer-size diameter, the shape of a carbon nanotube strongly influences its local electronic, chemical, and mechanical properties. Few, if any, methods exist for resolving the strain energy and static frictional forces along the length of a deformed nanotube supported on a substrate. We present a method using nonlinear elastic rod theory in which we compute the flexural strain energy and static frictional forces along the length of single walled carbon nanotubes (SWCNTs) manipulated into various shapes …

Analysis On Strategies Of Liners Against The Global Financial Crisis, Feng Chen

World Maritime University Dissertations

No abstract provided.

Thermodynamic Stability Of Transition States In Nanosystems, Alexander Umantsev

Chemistry and Physics Faculty Working Papers

We present a theory which shows that, in a closed system of fixed volume capable of undergoing a phase transition, the transition state can be thermodynamically stable against the bulk phases if a certain material parameters criterion is fulfilled. In a small system below the critical size the transition state turns into a globally stable phase that can be observed experimentally. This effect is analogous to stabilization of icosahedral structures in clusters of certain sizes and energies. Stabilization of the transition state in small systems of limited resources allows us to conjecture that, in the case of a melting/freezing transition …

Pressure-Driven Transport Of Particles Through A Converging-Diverging Microchannel, Ye Ai, Sang W. Joo, Yingtao Jiang, Xiangchun Xuan, Shizhi Qian

Mechanical Engineering Faculty Research

Pressure-driven transport of particles through a symmetric converging-diverging microchannel is studied by solving a coupled nonlinear system, which is composed of the Navier–Stokes and continuity equations using the arbitrary Lagrangian–Eulerian finite-element technique. The predicted particle translation is in good agreement with existing experimental observations. The effects of pressure gradient, particle size, channel geometry, and a particle’s initial location on the particle transport are investigated. The pressure gradient has no effect on the ratio of the translational velocity of particles through a converging-diverging channel to that in the upstream straight channel. Particles are generally accelerated in the converging region and then …

Electron Multipactor: Theory Review, Comparison And Modeling Of Mitigation Techniques In Icepic, Neil G. Rogers

Theses and Dissertations

Mitigation approaches for single surface multipactor at dielectric windows are investigated using Particle-In-Cell (PIC) simulations. Initially baseline susceptibility diagrams are constructed analytically and compared with self-consistent, dynamic system trajectories. The power deposited on the surface of a dielectric window in an HPM system is considered using three different methods and the results of PIC simulations. Geometric mitigation is then considered by varying the window orientation with respect to the HPM electric held. Small angular deviations, less than 20 degrees, from the nominal case of normal incidence show dramatic changes in the susceptibility diagram. A materials approach to mitigation is then …

Optical Properties And Magnetochromism In Multiferroic Bifeo3, X. S. Xu, T. V. Brinzari, S. Lee, Y. H. Chu, L. W. Martin, A. Kumar, S. Mcgill, R. C. Rai, R. Ramesh, V. Gopalan, S. W. Cheong, J. L. Musfeldt

Xiaoshan Xu Papers

In order to investigate spin-charge coupling in multiferroic oxides, we measured the optical properties of BiFeO₃. Although the direct 300 K charge gap is observed at 2.67 eV, absorption onset actually occurs at much lower energy with Fe³⁺ excitations at 1.41 and 1.90 eV. Temperature and magnetic-field-induced spectral changes reveal complex interactions between on-site crystal-field and magnetic excitations in the form of magnon sidebands. We employ the sensitivity of these magnon sidebands to map out the magnetic-fieldtemperature phase diagram which demonstrates optical evidence for spin spiral quenching above 20 T and suggests a spin domain reorientation near …

Magnon Sidebands And Spin-Charge Coupling In Bismuth Ferrite Probed By Nonlinear Optical Spectroscopy, M. O. Ramirez, A. Kumar, S. A. Denev, N. J. Podraza, X. S. Xu, R. C. Rai, Y. H. Chu, J. Seidel, L. W. Martin, S. -Y. Yang, E. Saiz, J. F. Ihlefeld, S. Lee, J. Klug, S. W. Cheong, M. J. Bedzyk, O. Auciello, D. G. Schlom, R. Ramesh, J. Orenstein, J. L. Musfeldt, V. Gopalan

Xiaoshan Xu Papers

The interplay between spin waves (magnons) and electronic structure in materials leads to the creation of additional bands associated with electronic energy levels which are called magnon sidebands. The large difference in the energy scales between magnons (meV) and electronic levels (eV) makes this direct interaction weak and hence makes magnon sidebands difficult to probe. Linear light absorption and scattering techniques at low temperatures are traditionally used to probe these sidebands. Here we show that optical secondharmonic generation, as the lowest-order nonlinear process, can successfully probe the magnon sidebands at room temperature and up to 723 K in bismuth ferrite, …

Anisotropic Magnetoresistance And Planar Hall Effect In Epitaxial Films Of La0.7Ca0.3Mno3, N. Naftalis, Y. Bason, J. Hoffman, X. Hong, C. H. Ahn, L. Klein

Xia Hong Publications

We measured the anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) in a [001] oriented epitaxial thin film of La_0.7Ca_0.3MnO₃ (LCMO) as a function of magnetic field, temperature, and current direction relative to the crystal axes. We find that both AMR and PHE in LCMO depend strongly on the current orientation relative to the crystal axes, and we demonstrate the applicability of AMR and PHE equations based on a fourth order magnetoresistance tensor consistent with the film symmetry.

Design Optimization Of Superconducting Parallel-Bar Cavities, Subashini De Silva, Jean R. Delayen

Physics Faculty Publications

The parallel-bar structure is a new superconducting geometry whose features and properties may have significant advantages over conventional superconducting deflecting and crabbing cavities for a number of applications. Jefferson Lab is in need for a 499 MHz, 11 GeV rf separator as part of its 12 GeV upgrade program. We report on design optimization studies performed todate for this and other applications.

Options For An 11 Gev Rf Beam Separator For The Jefferson Lab Cebaf Upgrade, Jean R. Delayen, M. Spata, H. Wang

Physics Faculty Publications

The CEBAF accelerator at Jefferson Lab has had, since first demonstration in 1996, the ability to deliver a 5-pass electron beam to experimental halls (A, B, and C) simultaneously. This capability is provided by a set of three, room temperature 499 MHz rf separators in the 5th pass beamline. The separator cavity is a two-rod, two-cell TEM mode type resonator, which has high shunt impedance. The 12 GeV baseline design does not preserve the capability of separating the 5th pass, 11 GeV beam for the 3 existing halls. Several options for restoring this capability, including extension of the present room …

A New Tem-Type Deflecting And Crabbing Rf Structure, Jean R. Delayen, H. Wang

Physics Faculty Publications

A new type of rf structure for the deflection and crabbing of particle bunches is introduced. It is comprised of a number of parallel TEM-resonant lines operating in opposite phase from each other. One of its main advantages is its compactness compared to conventional crabbing cavities operating in the TM110 mode, thus allowing low frequency designs. The properties and characteristics of this type of structure are presented.

Measurement Of Direct Fₒ(980) Photoproduction On The Proton, K. P. Adhikari, H. Bagdasaryan, S. Bültmann, S. L. Careccia, K. V. Dharmawardane, G. E. Dodge, N. Kalantarians, A. Klein, A.V. Klimenko, S. E. Kuhn, J. Lanchiet, M. R. Niroula, J. Zhang

Physics Faculty Publications

We report on the results of the first measurement of exclusive f₀(980) meson photoproduction on protons for E_γ = 3.0–3.8  GeV and −t = 0.4–1.0  GeV² . Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The resonance was detected via its decay in the π⁺π⁻ channel by performing a partial wave analysis of the reaction γp→pπ⁺π⁻ . Clear evidence of the f₀(980) meson was found in the interference between P and S waves at M _π+π− ∼1  GeV. The S -wave differential …

High-Mobility Few-Layer Graphene Field Effect Transistors Fabricated On Epitaxial Ferroelectric Gate Oxides, X. Hong, A. Posadas, K. Zou, C. H. Ahn, J. Zhu

Xia Hong Publications

The carrier mobility μ of few-layer graphene (FLG) field-effect transistors increases tenfold when the SiO₂ substrate is replaced by single-crystal epitaxial Pb(Zr_0.2Ti_0:8)O₃ (PZT). In the electron-only regime of the FLG, μ reaches 7 X 10⁴ cm² / Vs at 300 K for n = 2.4 X 10¹²=cm², 70% of the intrinsic limit set by longitudinal acoustic (LA) phonons; it increases to 1.4 X 10⁵ cm² / Vs at low temperature. The temperature-dependent resistivity p(T) reveals a clear signature of LA phonon scattering, yielding …

Quantum Scattering Time And Its Implications On Scattering Sources In Graphene, X. Hong, K. Zou, J. Zhu

Xia Hong Publications

We determine the quantum scattering time T_q in six graphene samples with mobility of 4 400<μ <17 000 cm² /V s over a wide range of carrier density (1.2<n<6X10¹²/cm2). T_q derived from Shubnikov–de Haas oscillation ranges ~25–74 fs, corresponding to a single-particle level broadening of 4.5–13 meV. The ratio of the transport to quantum scattering time T_t /T_q spans 1.5–5.1 in these samples, which can be quantitatively understood combining scattering from short-ranged centers and charged impurities located within 2 nm of the graphene sheet. Our results suggest that charges residing on the SiO …

Absence Of Spin Liquid Behavior In Nd3ga5sio14 Using Magneto-Optical Spectroscopy, X. S. Xu, T. V. Brinzari, S. Mcgill, H. D. Zhou, C. R. Wiebe, J. L. Musfeldt

Xiaoshan Xu Papers

We measured the low-lying crystal field levels of Nd³⁺ in Nd₃Ga₅SiO₁₄ via magneto-optical spectroscopy and employed the extracted energies, magnetic moments, and symmetries to analyze the magnetic properties and test the spin liquid candidacy of this material. The exchange interaction is surprisingly small, a discovery that places severe constraints on models used to describe the ground state of this system. Further, it demonstrates the value of local-probe photophysical techniques for rare-earthcontaining materials where bulk property measurements can be skewed by low-lying electronic structure.

The Effect Of Copt Crystallinity And Grain Texturing On Properties Of Exchange-Coupled Fe/Copt Systems, H. Oguchi, A. Zambano, M. Yu, Jason R. Hattrick-Simpers, D. Banerjee, Y. Liu, Z. L. Wang, J. P. Liu, S. E. Lofland, D. Josell, I. Takeuchi

Faculty Publications

The effect of the crystallinity and the grain texturing of CoPt hard layers on exchange coupled Fe/CoPt soft/hard magnetic systems was studied using gradient thickness multilayer thin films. We have studied the hard layer structures by transmission electron microscopy and x-ray diffraction, and characterized the exchange coupling interaction through magnetization loops obtained by the magneto-optical Kerr effect measurement. We found that exchange coupling strongly depends on the crystalline characteristics of the CoPt hard layer. There is correlation between the mixture of different grain orientations of the CoPt hard layer and coupling efficiency. In particular, interlayer coupling is enhanced when there …

The Adaptability Of Langmuir Probes To The Pico-Satellite Regime, Andrew Jay Auman

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The purpose of this thesis is to investigate whether it is feasible to use Langmuir probes on pico-satellites flying in low Earth orbit over mid- to low-latitude geographic regions. Following chapters on the expected ionospheric conditions and an overview of Langmuir probe theory, a chapter addressing the difficulties involved with pico-satellite Langmuir probes is presented. Also, the necessary satellite-to-probe surface area requirements in order to achieve confidence in pico-satellite Langmuir probe data, for the orbital regions of interest to this thesis, are stated.

Biomarker Identification For Prostate Cancer Using An Efficient Feature Selection Algorithm, Vamsi Krishnam Raju Mantena

Electrical & Computer Engineering Theses & Dissertations

In recent years, there has been an increased interest in using protein mass spectrometry to identify biomarkers that discriminate diseased from healthy individuals. A biomarker is a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathological processes, or pharmacological responses to a therapeutic intervention. Identifying biomarkers will be an important step towards disease characterization and patient management. One challenge of biomarker identification is how to handle the high dimensional mass spectral data. In this thesis, we applied an efficient feature selection algorithm to mass spectrometry data obtained from prostate tissue samples to identify prostate …

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 …

Raman Studies Of 1,3,5,7 Cyclooctatetraene At High Pressure, Martin Galley, Ed Romano, Sergey Tkachev, Michael Pravica

Undergraduate Research Opportunities Program (UROP)

We performed Raman spectroscopic studies of 1,3,5,7-cyclooctatetraene at elevated pressures up to 10 GPa with the aim of examining possible planarization of the molecule and further studying two prior-discovered phases of the solid with pressure. The Raman excitation source was a Krypton-ion laser operating at 674.1 nm (give wavelength).

1,3,5,7 Cyclooctatetraene has an octagonal formation however it is not aromatic or anti-aromatic (not a subject to the 4n+2 Huckel’s rule) [1]. As a result, its adopts a somewhat reactive tub shape. Upon the addition or removal of one to two electrons under ambient conditions, the molecule planarizes and becomes aromatic …

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, P_H2 (T), for a fully atomic hydrogen passivated diamondsurface. Above the equilibrium P_H2 (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 P_H2 (T) …

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.

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.

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 …

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.

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 …