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30,749 full-text articles. Page 10 of 827.

A Quadrature-Based Moment Method For Polydisperse Bubbly Flows, Jeffrey C. Heylmun, Bo Kong, Alberto Passalacqua, Rodney O. Fox 2019 Iowa State University and Ames Laboratory

A Quadrature-Based Moment Method For Polydisperse Bubbly Flows, Jeffrey C. Heylmun, Bo Kong, Alberto Passalacqua, Rodney O. Fox

Rodney O. Fox

A computational algorithm for polydisperse bubbly flow is developed by combining quadrature-based moment methods (QBMM) with an existing two-fluid solver for gas–liquid flows. Care is taken to ensure that the two-fluid model equations are hyperbolic by generalizing the kinetic model for the bubble phase proposed by Bieseuvel and Gorissen (1990). The kinetic formulation for the bubble phase includes the full suite of interphase momentum exchange terms for bubbly flow, as well as ad hoc bubble–bubble interaction terms to model the transition from isolated bubbles to regions of pure air at very high bubble-phase volume fractions. A robust numerical ...


Nematicity In The Superconducting Mixed State Of Strain Detwinned Underdoped Ba(Fe1-Xcox)(2)As-2, J. Schmidt, V. Bekeris, G. S. Lozano, M. V. Bortulé, M. Marziali Bermúdez, C. W. Hicks, Paul C. Canfield, E. Fradkin, G. Pasquini 2019 Universidad de Buenos Aires

Nematicity In The Superconducting Mixed State Of Strain Detwinned Underdoped Ba(Fe1-Xcox)(2)As-2, J. Schmidt, V. Bekeris, G. S. Lozano, M. V. Bortulé, M. Marziali Bermúdez, C. W. Hicks, Paul C. Canfield, E. Fradkin, G. Pasquini

Paul C. Canfield

Evidence of nematic effects in the mixed superconducting phase of slightly underdoped Ba(Fe1−xCox)2As2 is reported. We have found strong in-plane resistivity anisotropy for crystals in different strain conditions. For these compositions, there is no magnetic long-range order, so the description may be ascribed to the interplay between the superconducting and nematic order parameters. A piezoelectric-based apparatus is used to apply tensile or compressive strain to tune nematic domain orientation in order to examine intrinsic nematicity. Measurements are done under a rotating magnetic field, and the analysis of the angular dependence of physical quantities identifies the cases in ...


Alternative Energy Sources For Fossil Fuel Independence, Matthew Merchant 2019 The College at Brockport

Alternative Energy Sources For Fossil Fuel Independence, Matthew Merchant

Senior Honors Theses

Fossil fuel dependence has caused a massive increase in atmospheric greenhouse gas levels. These gases pollute the environment and warm the planet, resulting in climate change effects that will soon be irreversible. To prevent this, clean alternative energy sources need to be developed further and used to gain fossil fuel independence in the near future. Possible alternative energy sources to meet this goal are nuclear fission, fusion, solar, hydro, geothermal, and wind. In this paper, the results of an experiment performed to study on the relationship between a solar panel’s angle with the sun and its power production will ...


How Bright Are Fast Optical Bursts Associated With Fast Radio Bursts?, Yuan-Pei Yang, Bing Zhang, Jian-Yan Wei 2019 Yunnan University

How Bright Are Fast Optical Bursts Associated With Fast Radio Bursts?, Yuan-Pei Yang, Bing Zhang, Jian-Yan Wei

Physics & Astronomy Faculty Publications

The origin of fast radio bursts (FRBs) is still unknown. Multiwavelength observations during or shortly after the FRB phase would be essential to identify the counterpart of an FRB and to constrain its progenitor and environment. In this work, we investigate the brightness of the “fast optical bursts” (FOBs) associated with FRBs and the prospects of detecting them. We investigate several inverse Compton (IC) scattering processes that might produce an FOB, including both the one-zone and two-zone models. We also investigate the extension of the same mechanism of FRB emission to the optical band. We find that a detectable FOB ...


Revealing The Nature Of Antiferroquadrupolar Ordering In Cerium Hexaboride: Ceb6, C. K. Barman, Prashant Singh, Duane Johnson, Aftab Alam 2019 Indian Institute of Technology

Revealing The Nature Of Antiferroquadrupolar Ordering In Cerium Hexaboride: Ceb6, C. K. Barman, Prashant Singh, Duane Johnson, Aftab Alam

Duane D. Johnson

The cerium hexaboride (CeB6) f-electron compound displays a rich array of low-temperature magnetic phenomena, including a “magnetically hidden” order, identified as multipolar in origin via advanced x-ray scattering. From first-principles electronic-structure results, we find that the antiferroquadrupolar(AFQ) ordering in CeB6 arises from crystal-field splitting and yields a band structure in agreement with experiments. With interactions of p electrons between Ce and B6 being small, the electronic state of CeB6 is suitably described as Ce(4f1)3+(e−)(B6)2−. The AFQ state of orbital spins is caused by an exchange interaction induced through spin-orbit interaction, which also splits the ...


Quadratic To Linear Magnetoresistance Tuning In Tmb4, Sreemanta Mitra, Jeremy Goh Swee Kang, John Shin, Jin Quan Ng, Sai Swaroop Sunku, Tai Kong, Paul C. Canfield, B. Sriram Shastry, Pinaki Sengupta, Christos Panagopoulos 2019 Nanyang Technological University

Quadratic To Linear Magnetoresistance Tuning In Tmb4, Sreemanta Mitra, Jeremy Goh Swee Kang, John Shin, Jin Quan Ng, Sai Swaroop Sunku, Tai Kong, Paul C. Canfield, B. Sriram Shastry, Pinaki Sengupta, Christos Panagopoulos

Paul C. Canfield

The change of a material's electrical resistance (R) in response to an external magnetic field (B) provides subtle information for the characterization of its electronic properties and has found applications in sensor and storage related technologies. In good metals, Boltzmann's theory predicts a quadratic growth in magnetoresistance (MR) at low B and saturation at high fields. On the other hand, a number of nonmagnetic materials with weak electronic correlation and low carrier concentration for metallicity, such as inhomogeneous conductors, semimetals, narrow gap semiconductors and topological insulators, and two dimensional electron gas, show positive, nonsaturating linear magnetoresistance (LMR). However ...


Competition Between Orthorhombic And Re-Entrant Tetragonal Phases In Underdoped Ba1-Xkxfe2as2 Probed By The Response To Controlled Disorder, Erik I. Timmons, Makariy A. Tanatar, K. Willa, S. Teknowijoyo, Kyuil Cho, M. Konczykowski, O. Cavani, Yong Liu, Thomas A. Lograsso, U. Welp, Ruslan Prozorov 2019 Iowa State University and Ames Laboratory

Competition Between Orthorhombic And Re-Entrant Tetragonal Phases In Underdoped Ba1-Xkxfe2as2 Probed By The Response To Controlled Disorder, Erik I. Timmons, Makariy A. Tanatar, K. Willa, S. Teknowijoyo, Kyuil Cho, M. Konczykowski, O. Cavani, Yong Liu, Thomas A. Lograsso, U. Welp, Ruslan Prozorov

Thomas A. Lograsso

Low-temperature (22 K) irradiation with 2.5-MeV electrons, creating point defects affecting elastic scattering, was used to study the competition between stripe C-2 and tetragonal C-4 antiferromagnetic phases which exist in a narrow doping range around x = 0.25 in hole-doped Ba1-xKxFe2As2. In nearby compositions outside of this range, at x = 0.22 and x = 0.19, the temperatures of both the concomitant orthorhombic/stripe antiferromagnetic transition T-C2 and the superconducting transition T-c are monotonically suppressed by added disorder at similar rates of about 0.1 K/mu Omega cm, as revealed through using resistivity variation as an intrinsic measure ...


Reshaping And Sintering Of 3d Fcc Metal Nanoclusters: Stochastic Atomistic Modeling With Realistic Surface Diffusion Kinetics, King C. Lai, James W. Evans 2019 Iowa State University and Ames Laboratory

Reshaping And Sintering Of 3d Fcc Metal Nanoclusters: Stochastic Atomistic Modeling With Realistic Surface Diffusion Kinetics, King C. Lai, James W. Evans

James W. Evans

Far-from-equilibrium evolution of metallic nanocluster shapes is highly sensitive to the atomistic-level details of surface diffusion for diverse local surface configurations. A stochastic model was developed incorporating realistic values for the multiple diffusion barriers (contrasting previous unrealistic generic prescriptions) based upon insights from homoepitaxial film growth. Kinetic Monte Carlo simulation then elucidates the conversion of Ag nanocubes to Wulff polyhedra mediated by nucleation of new {100}facets, the pinch-off of sufficiently elongated Ag nanorods, and key aspects of sintering for orientationally aligned Ag and Au nanoclusters. The time scale for sintering of Au nanoclusters observed in high-resolution transmission electron microscopy ...


Mechanisms Of Enhanced Thermal Stability Of Polarization In Lead-Free (Bi 1/2na 1/2) 0.94ba 0.06tio 3/Zno Ceramic Composites, Zhongming Fan, Lin Zhou, Tae-Hoon Kim, Ji Zhang, Shan-Tao Zhang, Xiaoli Tan 2019 Iowa State University

Mechanisms Of Enhanced Thermal Stability Of Polarization In Lead-Free (Bi 1/2na 1/2) 0.94ba 0.06tio 3/Zno Ceramic Composites, Zhongming Fan, Lin Zhou, Tae-Hoon Kim, Ji Zhang, Shan-Tao Zhang, Xiaoli Tan

Xiaoli Tan

(Bi 1/2Na 1/2)TiO 3-based solid solutions, one of the major systems of lead-free piezoelectric ceramics, exhibit a low thermal depolarization temperature ( T d~100°C). It was reported that by incorporating 30 mol% ZnO particles to form a ceramic composite of (Bi 1/2Na 1/2) 0.94Ba 0.06TiO 3/ZnO, the depolarization process can be shifted up to ~250 °C. In the present work, a variety of advanced transmission electron microscopy techniques, including in situ heating, annular bright-field, high-angle annular dark-field, geometric phase analysis, energy-dispersive spectrum and electron energy-loss spectroscopy, are employed to investigate the ...


Equatorial Disturbance Dynamo Vertical Plasma Drifts Over Jicamarca: Bi‐Monthly And Solar Cycle Dependence, Luis Navarro Dominguez, Bela G. Fejer, Ludger Scherliess 2019 Utah State University

Equatorial Disturbance Dynamo Vertical Plasma Drifts Over Jicamarca: Bi‐Monthly And Solar Cycle Dependence, Luis Navarro Dominguez, Bela G. Fejer, Ludger Scherliess

All Physics Faculty Publications

We use extensive incoherent scatter radar observations from the Jicamarca Radio Observatory to study the local time and bi‐monthly dependence of the equatorial disturbance dynamo vertical plasma drifts on solar flux and geomagnetic activity. We show that the daytime disturbance drifts have generally small magnitudes with largest values before noon and an apparent annual variation. Near dusk, they are downward throughout the year with largest values during the equinoxes and smallest during June solstice. These downward drifts increase strongly with solar flux, and shift to later local times. They also increase with increasing geomagnetically active conditions with no apparent ...


Hcp: A Matlab Package To Create Beautiful Heatmaps With Richly Annotated Covariates, Manuela Salvucci, Jochen HM Prehn 2019 Royal College of Surgeons in Ireland

Hcp: A Matlab Package To Create Beautiful Heatmaps With Richly Annotated Covariates, Manuela Salvucci, Jochen Hm Prehn

Physiology and Medical Physics Articles

HCP (HeatmapCovariatePlot) provides a simple high level application programming interface (API) to design elaborated visualizations in a modular fashion. The user can select which elements to include, covariate row annotations and/or heatmaps, by invoking the AddCovariateRow or the AddHeatmap methods. Elements can be vertically stacked and also grouped in functionally related sub-blocks encapsulated by the AddSubBlock method to adjust the figure layout. The plotting options in HCP are chosen sensibly to create production-quality out-of-the-box visualizations in most use-case. HCP features several plotting options to adjust the plot aesthetics to cater for the user preferences in terms of colormaps, labelling ...


Topological States In A15 Superconductors, Minsung Kim, Cai-Zhuang Wang, Kai-Ming Ho 2019 Iowa State University and Ames Laboratory

Topological States In A15 Superconductors, Minsung Kim, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

Superconductors with the A15 structure are prototypical type-II s-wave superconductors which have generated considerable interest in early superconducting material history. However, the topological nature of the electronic structure remains unnoticed so far. Here, using first-principles band structure calculations based on density-functional theory, we show that the A15 superconductors (Ta3Sb, Ta3Sn, and Ta3Pb) have nontrivial band topology in the bulk electronic band structures, leading to the formation of topological surface states near the Fermi energy. Due to the bulk superconductivity, the proximity effect in the topological surface states would induce topological superconductivity even without heterostructure of a topological insulator and an ...


A Quadrature-Based Moment Method For Polydisperse Bubbly Flows, Jeffrey C. Heylmun, Bo Kong, Alberto Passalacqua, Rodney O. Fox 2019 Iowa State University and Ames Laboratory

A Quadrature-Based Moment Method For Polydisperse Bubbly Flows, Jeffrey C. Heylmun, Bo Kong, Alberto Passalacqua, Rodney O. Fox

Chemical and Biological Engineering Publications

A computational algorithm for polydisperse bubbly flow is developed by combining quadrature-based moment methods (QBMM) with an existing two-fluid solver for gas–liquid flows. Care is taken to ensure that the two-fluid model equations are hyperbolic by generalizing the kinetic model for the bubble phase proposed by Bieseuvel and Gorissen (1990). The kinetic formulation for the bubble phase includes the full suite of interphase momentum exchange terms for bubbly flow, as well as ad hoc bubble–bubble interaction terms to model the transition from isolated bubbles to regions of pure air at very high bubble-phase volume fractions. A robust numerical ...


Blandford-Znajek Process In Vacuo And Its Holographic Dual, Ted Jacobson, Maria J. Rodriguez 2019 University of Maryland

Blandford-Znajek Process In Vacuo And Its Holographic Dual, Ted Jacobson, Maria J. Rodriguez

All Physics Faculty Presentations

Blandford and Znajek discovered a process by which a spinning black hole can transfer rotational energy to a plasma, offering a mechanism for energy and jet emissions from quasars. Here we describe a version of this mechanism that operates with only vacuum electromagnetic fields outside the black hole. The setting, which is not astrophysically realistic, involves either a cylindrical black hole or one that lives in 2+1 spacetime dimensions, and the field is given in simple, closed form for a wide class of metrics. For asymptotically anti–de Sitter black holes in 2+1 dimensions, the holographic dual of ...


Magnetic Fluctuations In The Itinerant Ferromagnet Lacrge3 Studied By 139la Nmr, K. Rana, H. Kotegawa, R. R. Ullah, J. S. Harvey, Sergey L. Bud’ko, Paul C. Canfield, H. Tou, V. Taufour, Yuji Furukawa 2019 Iowa State University and Ames Laboratory

Magnetic Fluctuations In The Itinerant Ferromagnet Lacrge3 Studied By 139la Nmr, K. Rana, H. Kotegawa, R. R. Ullah, J. S. Harvey, Sergey L. Bud’Ko, Paul C. Canfield, H. Tou, V. Taufour, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

LaCrGe3 is an itinerant ferromagnet with a Curie temperature of T C = 85 K and exhibits an avoided ferromagnetic quantum critical point under pressure through a modulated antiferromagnetic phase as well as tricritical wing structure in its temperature-pressure-magnetic field ( T – p – H) phase diagram. In order to understand the static and dynamical magnetic properties of LaCrGe3 , we carried out 139 La nuclear magnetic resonance (NMR) measurements. Based on the analysis of NMR data, using the self-consistent-renormalization (SCR) theory, the spin fluctuations in the paramagnetic state are revealed to be isotropic ferromagnetic and three dimensional (3D) in nature. Furthermore, the system ...


Superconductivity In The Van Der Waals Layered Compound Ps2, Yan-Ling Li, Elissaios Stavrou, Qiang Zhu, Samantha M. Clarke, Yunguo Li, Hong-Mei Huang 2019 Jiangsu Normal University

Superconductivity In The Van Der Waals Layered Compound Ps2, Yan-Ling Li, Elissaios Stavrou, Qiang Zhu, Samantha M. Clarke, Yunguo Li, Hong-Mei Huang

Physics & Astronomy Faculty Publications

van der Waals (vdW) layered compounds provided a fruitful research platform for the realization of superconductivity. However, a vdW layered superconductor with a high transition temperature (Tc) at ambient conditions is still rare. Here, using variable-composition evolutionary structure predictions, we systematically explored the stable compounds in the P-S system up to 20 GPa. Opposed to the complex stoichiometries at ambient conditions, only one compound, PS2, is predicted to be thermodynamically stable above 8 GPa. Strikingly, PS2 is a vdW layered material isostructural to 3R−MoS2 exhibiting a predicted Tc of around 11 K at ambient pressure, both in the bulk ...


Dynamical Spacetime Symmetry, Benjamin Lovelady, James Thomas Wheeler 2019 Utah State University

Dynamical Spacetime Symmetry, Benjamin Lovelady, James Thomas Wheeler

Benjamin Lovelady

According to the Coleman-Mandula theorem, any gauge theory of gravity combined with an internal symmetry based on a Lie group must take the form of a direct product in order to be consistent with basic assumptions of quantum field theory. However, we show that an alternative gauging of a simple group can lead dynamically to a spacetime with compact internal symmetry. The biconformal gauging of the conformal symmetry of n-dimensional Euclidean space doubles the dimension to give a symplectic manifold. Examining one of the Lagrangian submanifolds in the flat case, we find that in addition to the expected SO(n ...


Crystal Growth And Magnetic Structure Of Mnbi2 Te 4, J.-Q. Yan, Q. Zhang, T. Heitmann, Zengle Huang, K. Y. Chen, J.-G. Cheng, Weida Wu, David Vaknin, B. C. Sales, Robert J. McQueeney 2019 Oak Ridge National Laboratory

Crystal Growth And Magnetic Structure Of Mnbi2 Te 4, J.-Q. Yan, Q. Zhang, T. Heitmann, Zengle Huang, K. Y. Chen, J.-G. Cheng, Weida Wu, David Vaknin, B. C. Sales, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

Millimeter-sized MnBi2Te4 single crystals are grown out of a Bi-Te flux and characterized using magnetic, transport, scanning tunneling microscopy, and spectroscopy measurements. The magnetic structure of MnBi2Te4 below TN is determined by powder and single-crystal neutron diffraction measurements. Below TN = 24 K, Mn2+ moments order ferromagnetically in the ab plane but antiferromagnetically along the crystallographic c axis. The ordered moment is 4.04(13)μB/Mn at 10 K and aligned along the crystallographic c axis in an A-type antiferromagnetic order. Below TN, the electrical resistivity drops upon cooling or when going across the metamagnetic transition in increasing magnetic fields ...


Removal Versus Ablation In Krf Dry Laser Cleaning Of Polystyrene Particles From Silicon, Sergey I. Kudryashov, Susan D. Allen 2019 Florida State University

Removal Versus Ablation In Krf Dry Laser Cleaning Of Polystyrene Particles From Silicon, Sergey I. Kudryashov, Susan D. Allen

Susan D. Allen

Direct absorption and melting of 0.2, 0.5 and 1.1 μm polystyrene particles on a Si substrate irradiated by 248 nm excimer laser radiation was found to contribute to their dry laser removal via a "hopping" mechanism at cleaning thresholds of 0.05, 0.1, and 0.16 J/cm 2, respectively. Ablation of these particles, which starts near the beginning of substrate deceleration at fluences above 0.4-0.5 J/cm 2, suppresses particle removal due to ablative recoil momentum. At fluences above a second cleaning threshold of 0.7 J/cm 2 particles are completely evaporated ...


Photoacoustic Study Of Krf Laser Heating Of Si: Implications For Laser Particle Removal, Sergey I. Kudryashov, Susan D. Allen 2019 Florida State University

Photoacoustic Study Of Krf Laser Heating Of Si: Implications For Laser Particle Removal, Sergey I. Kudryashov, Susan D. Allen

Susan D. Allen

A photoacoustic study of KrF laser heating of Si has revealed that the dominant mechanism of acoustic generation is thermoacoustic with a considerable contribution from the concentration-deformation mechanism at laser fluences below the Si melting threshold of 0.5 J/cm 2. Upon Si melting the contraction of the molten material contributes significantly to acoustic generation. At fluences above 1.4 J/cm 2 laser ablation of the molten layer enhances the amplitude of the compression pulse and diminishes that of the rarefaction pulse. The results of photoacoustic measurements allow optimization of experimental conditions for dry laser particle removal.

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