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Iowa State University

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2016

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Articles 1 - 30 of 56

Full-Text Articles in Physics

Enhancement Of The Superconducting Gap By Nesting In Cakfe4as4: A New High Temperature Superconductor, Daixiang Mou, Tai Kong, William R. Meier, Felix Lochner, Lin-Lin Wang, Qisheng Lin, Yun Wu, S. L. Bud’Ko, Ilya Eremin, Duane D. Johnson, Paul C. Canfield, Adam Kaminski Dec 2016

Enhancement Of The Superconducting Gap By Nesting In Cakfe4as4: A New High Temperature Superconductor, Daixiang Mou, Tai Kong, William R. Meier, Felix Lochner, Lin-Lin Wang, Qisheng Lin, Yun Wu, S. L. Bud’Ko, Ilya Eremin, Duane D. Johnson, Paul C. Canfield, Adam Kaminski

Chemistry Publications

We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe4As4. In contrast to the related CaFe2As2 compounds, CaKFe4As4 has a high Tc of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the ...


Measurements Of Double-Helicity Asymmetries In Inclusive J/Psi Production In Longitudinally Polarized P Plus P Collisions At Root S=510 Gev, Andrew Adare, Nicole Apadula, Lei Ding, John C. Hill, Nels J. Hotvedt, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Abhisek Sen, M. Shimomura, Arbin Timilsina, Shawn Whitaker, Et Al., Phenix Collaboration Dec 2016

Measurements Of Double-Helicity Asymmetries In Inclusive J/Psi Production In Longitudinally Polarized P Plus P Collisions At Root S=510 Gev, Andrew Adare, Nicole Apadula, Lei Ding, John C. Hill, Nels J. Hotvedt, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Abhisek Sen, M. Shimomura, Arbin Timilsina, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We report the double-helicity asymmetry, A(LL)(J/Psi), in inclusive J/Psi production at forward rapidity as a function of transverse momentum p(T) and rapidity |y|. The data analyzed were taken during root s = 510 GeV longitudinally polarized p + p collisions at the Relativistic Heavy Ion Collider in the 2013 run using the PHENIX detector. At this collision energy, J/Psi particles are predominantly produced through gluon-gluon scatterings, thus A(LL)(J/Psi) is sensitive to the gluon polarization inside the proton. We measured A(LL)(J/Psi) by detecting the decay daughter muon pairs mu(+)mu(-) within ...


Adsorption Of Dysprosium On The Graphite (0001) Surface: Nucleation And Growth At 300 K, Emma J. Kwolek, Huaping Lei, Ann Lii-Rosales, Mark Wallingford, Yinghui Zhou, Cai-Zhuang Wang, Michael C. Tringides, James W. Evans Dec 2016

Adsorption Of Dysprosium On The Graphite (0001) Surface: Nucleation And Growth At 300 K, Emma J. Kwolek, Huaping Lei, Ann Lii-Rosales, Mark Wallingford, Yinghui Zhou, Cai-Zhuang Wang, Michael C. Tringides, James W. Evans

Physics and Astronomy Publications

We have studied nucleation and growth of Dy islands on the basal plane of graphite at 300 K using scanning tunneling microscopy, density functional theory (DFT) in a form that includes van der Waals interactions, and analytic theory. The interaction of atomic Dy with graphite is strong, while the diffusion barrier is small. Experiment shows that at 300 K, the density of nucleated islands is close to the value predicted for homogeneous nucleation, using critical nucleus size of 1 and the DFT-derived diffusion barrier. Homogeneous nucleation is also supported by the monomodal shape of the island size distributions. Comparison with ...


Point Island Models For Nucleation And Growth Of Supported Nanoclusters During Surface Deposition, Yong Han, Émilie Gaudry, Tiago J. Oliveira, James W. Evans Dec 2016

Point Island Models For Nucleation And Growth Of Supported Nanoclusters During Surface Deposition, Yong Han, Émilie Gaudry, Tiago J. Oliveira, James W. Evans

Physics and Astronomy Publications

Point island models (PIMs) are presented for the formation of supported nanoclusters (or islands) during deposition on flat crystalline substrates at lower submonolayer coverages. These models treat islands as occupying a single adsorption site, although carrying a label to track their size (i.e., they suppress island structure). However, they are particularly effective in describing the island size and spatial distributions. In fact, these PIMs provide fundamental insight into the key features for homogeneous nucleation and growth processes on surfaces. PIMs are also versatile being readily adapted to treat both diffusion-limited and attachment-limited growth and also a variety of other ...


Capture Zone Area Distributions For Nucleation And Growth Of Islands During Submonolayer Deposition, Yong Han, Maozhi Li, James W. Evans Dec 2016

Capture Zone Area Distributions For Nucleation And Growth Of Islands During Submonolayer Deposition, Yong Han, Maozhi Li, James W. Evans

Physics and Astronomy Publications

A fundamental evolution equation is developed to describe the distribution of areas of capture zones (CZs) associated with islands formed by homogeneous nucleation and growth during submonolayer deposition on perfect flat surfaces. This equation involves various quantities which characterize subtle spatial aspects of the nucleation process. These quantities in turn depend on the complex stochastic geometry of the CZ tessellation of the surface, and their detailed form determines the CZ area distribution (CZD) including its asymptotic features. For small CZ areas, behavior of the CZD reflects the critical island size, i. For large CZ areas, it may reflect the probability ...


Azimuthally Anisotropic Emission Of Low-Momentum Direct Photons In Au Plus Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Lei Ding, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Alexey Yu. Semenov, Abhisek Sen, M. Shimomura, C. L. Silva, Arbin Timilsina, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Dec 2016

Azimuthally Anisotropic Emission Of Low-Momentum Direct Photons In Au Plus Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Lei Ding, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Alexey Yu. Semenov, Abhisek Sen, M. Shimomura, C. L. Silva, Arbin Timilsina, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider has measured second- and third-order Fourier coefficients of the azimuthal distributions of direct photons emitted at midrapidity in Au + Au collisions at root S-NN = 200 GeV for various collision centralities. Combining two different analysis techniques, results were obtained in the transverse momentum range of 0.4 < p(T) < 4.0 GeV/c. At low p(T) the second-order coefficients, nu(2), are similar to the ones observed in hadrons. Third-order coefficients, nu(3), are nonzero and almost independent of centrality. These new results on nu(2) and nu(3), combined with previously published results on yields, are compared to model calculations that provide yields and asymmetries in the same framework. Those models are challenged to explain simultaneously the observed large yield and large azimuthal anisotropies.


Phase Field Simulations Of Plastic Strain-Induced Phase Transformations Under High Pressure And Large Shear, Mahdi Javanbakht, Valery I. Levitas Dec 2016

Phase Field Simulations Of Plastic Strain-Induced Phase Transformations Under High Pressure And Large Shear, Mahdi Javanbakht, Valery I. Levitas

Aerospace Engineering Publications

Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force ...


Spontaneous Topological Transitions Of Electromagnetic Fields In Spatially Inhomogeneous Cp-Odd Domains, Kirill Tuchin Dec 2016

Spontaneous Topological Transitions Of Electromagnetic Fields In Spatially Inhomogeneous Cp-Odd Domains, Kirill Tuchin

Physics and Astronomy Publications

Metastable CP-odd domains of the hot QCD matter are coupled to QED via the chiral anomaly. The topology of electromagnetic field in these domains is characterized by magnetic helicity. It is argued, using the Maxwell-Chern-Simons model, that spatial inhomogeneity of the domains induces spontaneous transitions of electromagnetic field between the opposite magnetic helicity states.


Measurements Of Directed, Elliptic, And Triangular Flow In Cu Plus Au Collisions At Root Snn=200 Gev, Andrew Adare, N. Apadula, Sarah C. Campbell, L. Ding, John C. Hill, Nels J. Hotvedt, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, J. Perry, Timothy T. Rinn, Marzia Rosati, Abhisek Sen, A. Shaver, M. Shimomura, Arbin Timilsina, S. Whitaker, Et Al., Phenix Collaboration Nov 2016

Measurements Of Directed, Elliptic, And Triangular Flow In Cu Plus Au Collisions At Root Snn=200 Gev, Andrew Adare, N. Apadula, Sarah C. Campbell, L. Ding, John C. Hill, Nels J. Hotvedt, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, J. Perry, Timothy T. Rinn, Marzia Rosati, Abhisek Sen, A. Shaver, M. Shimomura, Arbin Timilsina, S. Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Measurements of anisotropic flow Fourier coefficients (upsilon(n)) for inclusive charged particles and identified hadrons pi(+/-), K-+/-, p, and (p) over bar produced at midrapidity in Cu + Au collisions at root s(NN) = 200 GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The particle azimuthal distributions with respect to different-order symmetry planes psi(n), for n = 1, 2, and 3 are studied as a function of transverse momentum p(T) over a broad range of collision centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three ...


Measurement Of The Higher-Order Anisotropic Flow Coefficients For Identified Hadrons In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Nov 2016

Measurement Of The Higher-Order Anisotropic Flow Coefficients For Identified Hadrons In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Measurements of the anisotropic flow coefficients v(2){Psi(2)}, v(3){Psi(3)}, v(4){Psi(4)}, and v(4){Psi(2)} for identified particles (pi(+/-), K-+/-, and p + (p) over bar) at midrapidity, obtained relative to the event planes Psi(m) at forward rapidities in Au + Au collisions at root s(NN) = 200 GeV, are presented as a function of collision centrality and particle transverse momenta p(T). The v(n) coefficients show characteristic patterns consistent with hydrodynamical expansion of the matter produced in the collisions. For each harmonic n, a modified valence quark-number N-q scaling [plotting v ...


Solution Of Population Balance Equations In Applications With Fine Particles: Mathematical Modeling And Numerical Schemes, Tan Trung Nguyen, Frédérique Laurent, Rodney O. Fox, Marc Massot Nov 2016

Solution Of Population Balance Equations In Applications With Fine Particles: Mathematical Modeling And Numerical Schemes, Tan Trung Nguyen, Frédérique Laurent, Rodney O. Fox, Marc Massot

Chemical and Biological Engineering Publications

The accurate description and robust simulation, at relatively low cost, of global quantities (e.g. number density or volume fraction) as well as the size distribution of a population of fine particles in a carrier fluid is still a major challenge for many applications. For this purpose, two types of methods are investigated for solving the population balance equation with aggregation, continuous particle size change (growth and size reduction), and nucleation: the extended quadrature method of moments (EQMOM) based on the work of Yuan et al.[52]and a hybrid method (TSM) between the sectional and moment methods, considering two ...


125te Nmr And Seebeck Effect In Bi2te3 Synthesized From Stoichiometric And Te-Rich Melts, E. M. Levin, Trevor M. Riedemann, A. Howard, Na Hyun Jo, Sergey L. Bud’Ko, Paul C. Canfield, Thomas A. Lograsso Nov 2016

125te Nmr And Seebeck Effect In Bi2te3 Synthesized From Stoichiometric And Te-Rich Melts, E. M. Levin, Trevor M. Riedemann, A. Howard, Na Hyun Jo, Sergey L. Bud’Ko, Paul C. Canfield, Thomas A. Lograsso

Materials Science and Engineering Publications

Bi2Te3 is a well-known thermoelectric material and, as a new form of quantum matter, a topological insulator. Variation of local chemical composition in Bi2Te3 results in formation of several types of atomic defects, including Bi and Te vacancies and Bi and Te antisite defects; these defects can strongly affect material functionality via generation of free electrons and/or holes. Nonuniform distribution of atomic defects produces electronic inhomogeneity, which can be detected by 125Te nuclear magnetic resonance (NMR). Here we report on 125Te NMR and Seebeck effect (heat to electrical energy conversion) for two single crystalline samples: (#1) grown from stoichiometric ...


Catalytic Conversion In Nanoporous Materials: Concentration Oscillations And Spatial Correlations Due To Inhibited Transport And Intermolecular Interactions, Andrés García, James W. Evans Nov 2016

Catalytic Conversion In Nanoporous Materials: Concentration Oscillations And Spatial Correlations Due To Inhibited Transport And Intermolecular Interactions, Andrés García, James W. Evans

Physics and Astronomy Publications

We show that steady-state catalytic conversion in nanoporous materials can occur in a quasi-counter-diffusion mode with the reactant (product) concentration strongly decaying (growing) into the pore, but also with oscillations in the total concentration. These oscillations reflect the response of the fluid to the transition from an extended to a confined environment near the pore opening. We focus on the regime of strongly inhibited transport in narrow pores corresponding to single-file diffusion. Here, limited penetration of the reactant into the pores and the associated low reaction yield is impacted by strong spatial correlations induced by both reaction (non-equilibrium correlations) and ...


Half-Metallic Co-Based Quaternary Heusler Alloys For Spintronics: Defect- And Pressure-Induced Transitions And Properties, Enamullah, D. D. Johnson, K. G. Suresh, Aftab Alam Nov 2016

Half-Metallic Co-Based Quaternary Heusler Alloys For Spintronics: Defect- And Pressure-Induced Transitions And Properties, Enamullah, D. D. Johnson, K. G. Suresh, Aftab Alam

Ames Laboratory Publications

Heusler compounds offer potential as spintronic devices due to their spin polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin polarization in a single manifold. Yet, Heuslers often exhibit intrinsic disorder that degrades its half-metallicity and spin polarization. Using density-functional theory, we analyze the electronic and magnetic properties of equiatomic Heusler (L21) CoMnCrAl and CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder (thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained for a limited range. Antisite ...


Big Area Additive Manufacturing Of High Performance Bonded Ndfeb Magnets, Li Ling, Angelica Tirado, I. C. Nlebedim, Orlando Rios, Brian Post, Vlastimil Kunc, R. R. Lowden, Edgar Lara-Curzio, Magnet Applications, Inc., Thomas A. Lograsso, M. Parans Paranthaman Oct 2016

Big Area Additive Manufacturing Of High Performance Bonded Ndfeb Magnets, Li Ling, Angelica Tirado, I. C. Nlebedim, Orlando Rios, Brian Post, Vlastimil Kunc, R. R. Lowden, Edgar Lara-Curzio, Magnet Applications, Inc., Thomas A. Lograsso, M. Parans Paranthaman

Ames Laboratory Publications

Additive manufacturing allows for the production of complex parts with minimum material waste, offering an effective technique for fabricating permanent magnets which frequently involve critical rare earth elements. In this report, we demonstrate a novel method - Big Area Additive Manufacturing (BAAM) - to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm3, and the room temperature magnetic properties ...


Comparison Of S-Adsorption On (111) And (100) Facets Of Cu Nanoclusters, Jeffrey S. Boschen, Jiyoung Lee, Theresa L. Windus, James W. Evans, Patricia A. Thiel, Da-Jiang Liu Oct 2016

Comparison Of S-Adsorption On (111) And (100) Facets Of Cu Nanoclusters, Jeffrey S. Boschen, Jiyoung Lee, Theresa L. Windus, James W. Evans, Patricia A. Thiel, Da-Jiang Liu

Physics and Astronomy Publications

In order to gain insight into the nature of chemical bonding of sulfur atoms on coinage metal surfaces, we compare the adsorption energy and structural parameters for sulfur at four-fold hollow (4fh) sites on (100) facets and at three-fold hollow (3fh) sites on (111) facets of Cu nanoclusters. Consistent results are obtained from localized atomic orbital and plane-wave based density functional theory using the same functionals. PBE and its hybrid counterpart (PBE0 or HSE06) also give similar results. 4fh sites are preferred over 3fh sites with stronger bonding by ∼0.6 eV for nanocluster sizes above ∼280 atoms. However, for ...


Laser Angle-Resolved Photoemission As A Probe Of Initial State K(Z) Dispersion, Final-State Band Gaps, And Spin Texture Of Dirac States In The Bi2te3 Topological Insulator, Minna Arrala, Hasnain Hafiz, Daixiang Mou, Yun Wu, Rui Jiang, Trevor Riedemann, Thomas A. Lograsso, Bernardo Barbiellini, Adam Kaminski, Arun Bansil, Matti Lindroos Oct 2016

Laser Angle-Resolved Photoemission As A Probe Of Initial State K(Z) Dispersion, Final-State Band Gaps, And Spin Texture Of Dirac States In The Bi2te3 Topological Insulator, Minna Arrala, Hasnain Hafiz, Daixiang Mou, Yun Wu, Rui Jiang, Trevor Riedemann, Thomas A. Lograsso, Bernardo Barbiellini, Adam Kaminski, Arun Bansil, Matti Lindroos

Ames Laboratory Publications

We have obtained angle-resolved photoemission spectroscopy (ARPES) spectra from single crystals of the topological insulator material Bi2Te3 using a tunable laser spectrometer. The spectra were collected for 11 different photon energies ranging from 5.57 to 6.70 eV for incident light polarized linearly along two different in-plane directions. Parallel first-principles, fully relativistic computations of photointensities were carried out using the experimental geometry within the framework of the one-step model of photoemission. A reasonable overall accord between theory and experiment is used to gain insight into how properties of the initial- and final-state band structures as well as those of ...


Origin Of Magnetic Anisotropy In Doped Ce2co17 Alloys, Liqin Ke, D. A. Kukusta, Duane D. Johnson Oct 2016

Origin Of Magnetic Anisotropy In Doped Ce2co17 Alloys, Liqin Ke, D. A. Kukusta, Duane D. Johnson

Ames Laboratory Publications

Magnetocrystalline anisotropy (MCA) in doped Ce2Co17 and other competing structures was investigated using density functional theory. We confirmed that the MCA contribution from dumbbell Co sites is very negative. Replacing Co dumbbell atoms with a pair of Fe or Mn atoms greatly enhance the uniaxial anisotropy, which agrees quantitatively with experiment, and this enhancement arises from electronic-structure features near the Fermi level, mostly associated with dumbbell sites. With Co dumbbell atoms replaced by other elements, the variation of anisotropy is generally a collective effect and contributions from other sublattices may change significantly. Moreover, we found that Zr doping promotes the ...


Energy Gap Evolution Across The Superconductivity Dome In Single Crystals Of (Ba1−Xkx)Fe2as2, Kyuil Cho, Marcin Kończykowski, Serafim Teknowijoyo, Makariy A. Tanatar, Yong Liu, Thomas A. Lograsso, Warren E. Straszheim, Vivek Mishra, Saurabh Maiti, Peter J. Hirschfeld, Ruslan Prozorov Sep 2016

Energy Gap Evolution Across The Superconductivity Dome In Single Crystals Of (Ba1−Xkx)Fe2as2, Kyuil Cho, Marcin Kończykowski, Serafim Teknowijoyo, Makariy A. Tanatar, Yong Liu, Thomas A. Lograsso, Warren E. Straszheim, Vivek Mishra, Saurabh Maiti, Peter J. Hirschfeld, Ruslan Prozorov

Ames Laboratory Publications

The mechanism of unconventional superconductivity in iron-based superconductors (IBSs) is one of the most intriguing questions in current materials research. Among non-oxide IBSs, (Ba1−xKx)Fe2As2 has been intensively studied because of its high superconducting transition temperature and fascinating evolution of the superconducting gap structure from being fully isotropic at optimal doping (x ≈ 0.4) to becoming nodal at x > 0.8. Although this marked evolution was identified in several independent experiments, there are no details of the gap evolution to date because of the lack of high-quality single crystals covering the entire K-doping range of the superconducting dome. We ...


Emergence Of A Potent Multidrug Efflux Pump Variant That Enhances Campylobacter Resistance To Multiple Antibiotics, Hong Yao, Zhangqi Shen, Yang Wang, Fengru Deng, Dejun Liu, Gaowa Naren, Lei Dai, Chih-Chia Su, Bing Wang, Shaolin Wang, Congming Wu, Edward W. Yu, Qijing Zhang, Jianzhong Shen Sep 2016

Emergence Of A Potent Multidrug Efflux Pump Variant That Enhances Campylobacter Resistance To Multiple Antibiotics, Hong Yao, Zhangqi Shen, Yang Wang, Fengru Deng, Dejun Liu, Gaowa Naren, Lei Dai, Chih-Chia Su, Bing Wang, Shaolin Wang, Congming Wu, Edward W. Yu, Qijing Zhang, Jianzhong Shen

Veterinary Microbiology and Preventive Medicine Publications

Bacterial antibiotic efflux pumps are key players in antibiotic resistance. Although their role in conferring multidrug resistance is well documented, the emergence of “super” efflux pump variants that enhance bacterial resistance to multiple drugs has not been reported. Here, we describe the emergence of a resistance-enhancing variant (named RE-CmeABC) of the predominant efflux pump CmeABC in Campylobacter, a major zoonotic pathogen whose resistance to antibiotics is considered a serious antibiotic resistance threat in the United States. Compared to the previously characterized CmeABC transporters, RE-CmeABC is much more potent in conferring Campylobacter resistance to antibiotics, which was shown by increased MICs ...


Asymmetric Mass Acquisition In Labi: Topological Semimetal Candidate, Yun Wu, Tai Kong, Lin-Lin Wang, Duane D. Johnson, Daixiang Mou, Lunan Huang, Benjamin Schrunk, Sergey L. Bud'ko, Paul C. Canfield, Adam Kaminski Aug 2016

Asymmetric Mass Acquisition In Labi: Topological Semimetal Candidate, Yun Wu, Tai Kong, Lin-Lin Wang, Duane D. Johnson, Daixiang Mou, Lunan Huang, Benjamin Schrunk, Sergey L. Bud'ko, Paul C. Canfield, Adam Kaminski

Ames Laboratory Publications

We use our high resolution He-lamp-based, tunable laser-based angle-resolved photoemission spectroscopy measurements and density functional theory calculations to study the electronic properties of LaBi, a binary system that was proposed to be a member of a new family of topological semimetals. Both bulk and surface bands are present in the spectra. The dispersion of the surface state is highly unusual. It resembles a Dirac cone, but upon closer inspection we can clearly detect an energy gap. The bottom band follows roughly a parabolic dispersion. The dispersion of the top band remains very linear, “V” -shape like, with the tip approaching ...


Prediction Of Blood Back Spatter From A Gunshot In Bloodstain Pattern Analysis, P. M. Comiskey, A. L. Yarin, S. Kim, Daniel Attinger Aug 2016

Prediction Of Blood Back Spatter From A Gunshot In Bloodstain Pattern Analysis, P. M. Comiskey, A. L. Yarin, S. Kim, Daniel Attinger

Mechanical Engineering Publications

A theoretical model for predicting and interpreting blood-spatter patterns resulting from a gunshot wound is proposed. The physical process generating a backward spatter of blood is linked to the Rayleigh-Taylor instability of blood accelerated toward the surrounding air, allowing the determination of the initial distribution of drop sizes and velocities. Then the motion of many drops in air is considered with governing equations accounting for gravity and air drag. Based on these equations, a numerical solution is obtained. It predicts the atomization process, the trajectories of the back-spatter drops of blood from the wound to the ground, the impact angle ...


Metallic Layer-By-Layer Photonic Crystals For Linearly-Polarized Thermal Emission And Thermophotovoltaic Device Including Same, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant Jul 2016

Metallic Layer-By-Layer Photonic Crystals For Linearly-Polarized Thermal Emission And Thermophotovoltaic Device Including Same, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant

Iowa State University Patents

Metallic thermal emitters consisting of two layers of differently structured nickel gratings on a homogeneous nickel layer are fabricated by soft lithography and studied for polarized thermal radiation. A thermal emitter in combination with a sub-wavelength grating shows a high extinction ratio, with a maximum value close to 5, in a wide mid-infrared range from 3.2 to 7.8 μm, as well as high emissivity up to 0.65 at a wavelength of 3.7 μm. All measurements show good agreement with theoretical predictions. Numerical simulations reveal that a high electric field exists within the localized air space surrounded ...


Thermodynamics And Historical Relevance Of A Jetting Thermometer Made Of Chinese Zisha Ceramic, Vincent Lee, Daniel Attinger Jul 2016

Thermodynamics And Historical Relevance Of A Jetting Thermometer Made Of Chinese Zisha Ceramic, Vincent Lee, Daniel Attinger

Mechanical Engineering Publications

Following a recent trend of scientific studies on artwork, we study here the thermodynamics of a thermometer made of zisha ceramic, related to the Chinese tea culture. The thermometer represents a boy who “urinates” shortly after hot water is poured onto his head. Long jetting distance is said to indicate that the water temperature is hot enough to brew tea. Here, a thermodynamic model describes the jetting phenomenon of that pee-pee boy. The study demonstrates how thermal expansion of an interior air pocket causes jetting. A thermodynamic potential is shown to define maximum jetting velocity. Seven optimization criteria to maximize ...


Ferromagnetic Quantum Critical Point Avoided By The Appearance Of Another Magnetic Phase In Lacrge3 Under Pressure, Valentin Taufour, Udhara S. Kaluarachchi, Rustem Khasanov, Manh Cuong Nguyen, Zurab Guguchia, Pabitra Kumar Biswas, Pietro Bonfà, Roberto De Renzi, Xiao Lin, Stella K. Kim, Eun Deok Mun, Hyunsoo Kim, Yuji Furukawa, Cai-Zhuang Wang, Kai-Ming Ho, Sergey L. Bud'ko, Paul C. Canfield Jul 2016

Ferromagnetic Quantum Critical Point Avoided By The Appearance Of Another Magnetic Phase In Lacrge3 Under Pressure, Valentin Taufour, Udhara S. Kaluarachchi, Rustem Khasanov, Manh Cuong Nguyen, Zurab Guguchia, Pabitra Kumar Biswas, Pietro Bonfà, Roberto De Renzi, Xiao Lin, Stella K. Kim, Eun Deok Mun, Hyunsoo Kim, Yuji Furukawa, Cai-Zhuang Wang, Kai-Ming Ho, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

The temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q=0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 ...


Itinerant And Localized Magnetization Dynamics In Antiferromagnetic Ho, L. Rettig, C. Dornes, N. Thielemann-Kühn, Helmholtz-Zentrum Berlin Für Materialien Und Energie Gmbh, H. Zabel, Deborah L. Schlagel, Thomas A. Lograsso, M. Chollet, A. Robert, M. Sikorski, S. Song, J. M. Glownia, S. L. Johnson, U. Staub Jun 2016

Itinerant And Localized Magnetization Dynamics In Antiferromagnetic Ho, L. Rettig, C. Dornes, N. Thielemann-Kühn, Helmholtz-Zentrum Berlin Für Materialien Und Energie Gmbh, H. Zabel, Deborah L. Schlagel, Thomas A. Lograsso, M. Chollet, A. Robert, M. Sikorski, S. Song, J. M. Glownia, S. L. Johnson, U. Staub

Ames Laboratory Publications

Using femtosecond time-resolved resonant magnetic x-ray diffraction at the Ho L 3 absorption edge, we investigate the demagnetization dynamics in antiferromagnetically ordered metallic Ho after femtosecond optical excitation. Tuning the x-ray energy to the electric dipole ( E 1 , 2 p → 5 d ) or quadrupole ( E 2 , 2 p → 4 f ) transition allows us to selectively and independently study the spin dynamics of the itinerant 5 d and localized 4 f electronic subsystems via the suppression of the magnetic (2 1 3 − τ ) satellite peak. We find demagnetization time scales very similar to ferromagnetic 4 f systems, suggesting that the loss ...


Phase Field Approach With Anisotropic Interface Energy And Interface Stresses: Large Strain Formulation, Valery I. Levitas, James A. Warren Jun 2016

Phase Field Approach With Anisotropic Interface Energy And Interface Stresses: Large Strain Formulation, Valery I. Levitas, James A. Warren

Aerospace Engineering Publications

A thermodynamically consistent, large-strain, multi-phase field approach (with consequent interface stresses) is generalized for the case with anisotropic interface (gradient) energy (e.g. an energy density that depends both on the magnitude and direction of the gradients in the phase fields). Such a generalization, if done in the “usual” manner, yields a theory that can be shown to be manifestly unphysical. These theories consider the gradient energy as anisotropic in the deformed configuration, and, due to this supposition, several fundamental contradictions arise. First, the Cauchy stress tensor is non-symmetric and, consequently, violates the moment of momentum principle, in essence the ...


Field-Temperature Phase Diagram And Entropy Landscape Of Ceausb2, Lishan Zhao, Edward A. Yelland, Jan A. Bruin, Ilya Sheikin, Paul C. Canfield, Veronika Fritsch, Hideaki Sakai, Andrew P. Mackenzie, Clifford W. Hicks May 2016

Field-Temperature Phase Diagram And Entropy Landscape Of Ceausb2, Lishan Zhao, Edward A. Yelland, Jan A. Bruin, Ilya Sheikin, Paul C. Canfield, Veronika Fritsch, Hideaki Sakai, Andrew P. Mackenzie, Clifford W. Hicks

Ames Laboratory Publications

We report a field-temperature phase diagram and an entropy map for the heavy-fermion compound CeAuSb2. CeAuSb2 orders antiferromagnetically below TN=6.6 K and has two metamagnetic transitions, at 2.8 and 5.6 T. The locations of the critical end points of the metamagnetic transitions, which may play a strong role in the putative quantum criticality of CeAuSb2 and related compounds, are identified. The entropy map reveals an apparent entropy balance with Fermi-liquid behavior, implying that above the Néel transition the Ce moments are incorporated into the Fermi liquid. High-field data showing that the magnetic behavior is remarkably anisotropic ...


Excitation Of Chandrasekhar-Kendall Photons In Quark Gluon Plasma By Propagating Ultrarelativistic Quarks, Kirill Tuchin May 2016

Excitation Of Chandrasekhar-Kendall Photons In Quark Gluon Plasma By Propagating Ultrarelativistic Quarks, Kirill Tuchin

Physics and Astronomy Publications

A quark propagating through the quark gluon plasma and scattering off the thermal gluons can radiate photons in states with definite angular momentum and magnetic helicity. These states, known as the Chandrasekhar-Kendall states, are eigenstates of the curl operator and have a nontrivial topology. I compute the spectrum of these states in the ultrarelativistic limit and study its properties.


Isotope Effect On Electron-Phonon Interaction In Multiband Superconductor Mgb2, Adam Kaminski, Daixiang Mou, Paul C. Canfield, Serguei Budko, Lunan Huang, Valentin Taufour, Yun Wu, Soham Manni Apr 2016

Isotope Effect On Electron-Phonon Interaction In Multiband Superconductor Mgb2, Adam Kaminski, Daixiang Mou, Paul C. Canfield, Serguei Budko, Lunan Huang, Valentin Taufour, Yun Wu, Soham Manni

Ames Laboratory Datasets

We investigate the effect of isotope substitution on electron-phonon interaction in multi-band superconductor MgB$_2$ using tunable laser based Angle Resolved Photoemission Spectroscopy. The kink structure around 70 meV in Sigma band, which is caused by electron coupling to E_2g phonon mode, is shifted to higher binding energy by ~3.5 meV in Mg^10B2. The changes of the kink energy reported here suggest that the anharmonicity of the E2g phonon in MgB2 is very small, which reopens the debate about the unusually small isotope coefficient in this material. These results are the benchmark for investigation of isotope effect in ...