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Articles 1 - 30 of 15780

Full-Text Articles in Physical Sciences and Mathematics

Substitutional And Interstitial Doping In Laco5 System For The Development Of Hard Magnetic Properties: A First Principles Study, Huseyin Ucar, Renu Choudhary, Durga Paudyal Sep 2020

Substitutional And Interstitial Doping In Laco5 System For The Development Of Hard Magnetic Properties: A First Principles Study, Huseyin Ucar, Renu Choudhary, Durga Paudyal

Ames Laboratory Accepted Manuscripts

We investigate here the changes in the electronic structure at the transition metal sites of the RE-TM5 structure (RE = Rare Earth, TM = Transition Metal) while doping the interstitial sites with nitrogen. LaCo5 compound is taken as the baseline compound owing to its critically needed intrinsic magnetic properties such as magneto-crystalline anisotropy energy (MAE) of ≈5 meV/fu [1] due to the contributions from the cobalt network. In addition, because of the lack of 4f electrons in lanthanum, complications originating from the treatment of the 4f localized electrons are absent in this compound; making it an ideal reference material to all ...


Low-Temperature Pyrolysis Of Municipal Solid Waste Components And Refuse-Derived Fuel—Process Efficiency And Fuel Properties Of Carbonized Solid Fuel, Kacper Swiechowski, Ewa Syguła, Jacek A. Koziel, Paweł Stepien, Szymon Kugler, Piotr Manczarski, Andrzej Białowiec Jun 2020

Low-Temperature Pyrolysis Of Municipal Solid Waste Components And Refuse-Derived Fuel—Process Efficiency And Fuel Properties Of Carbonized Solid Fuel, Kacper Swiechowski, Ewa Syguła, Jacek A. Koziel, Paweł Stepien, Szymon Kugler, Piotr Manczarski, Andrzej Białowiec

Agricultural and Biosystems Engineering Publications

New technologies to valorize refuse-derived fuels (RDFs) will be required in the near future due to emerging trends of (1) the cement industry’s demands for high-quality alternative fuels and (2) the decreasing calorific value of the fuels derived from municipal solid waste (MSW) and currently used in cement/incineration plants. Low-temperature pyrolysis can increase the calorific value of processed material, leading to the production of value-added carbonized solid fuel (CSF). This dataset summarizes the key properties of MSW-derived CSF. Pyrolysis experiments were completed using eight types of organic waste and their two RDF mixtures. Organic waste represented common morphological ...


Non-Equilibrium Growth Of Metal Clusters On A Layered Material: Cu On Mos2, Dapeng Jing, Ann Lii-Rosales, King C. Lai, Qiang Li, Jaeyoun Kim, Michael C. Tringides, James W. Evans, Patricia A. Thiel May 2020

Non-Equilibrium Growth Of Metal Clusters On A Layered Material: Cu On Mos2, Dapeng Jing, Ann Lii-Rosales, King C. Lai, Qiang Li, Jaeyoun Kim, Michael C. Tringides, James W. Evans, Patricia A. Thiel

Chemistry Publications

We use a variety of experimental techniques to characterize Cu clusters on bulk MoS2 formed via physical vapor deposition of Cu in ultrahigh vacuum, at temperatures ranging from 300 K to 900 K. We find that large facetted clusters grow at elevated temperatures, using high Cu exposures. The cluster size distribution is bimodal, and under some conditions, large clusters are surrounded by a denuded zone. We propose that defect-mediated nucleation, and coarsening during deposition, are both operative in this system. At 780 K, a surprising type of facetted cluster emerges, and at 900 K this type predominates: pyramidal clusters with ...


Ternary Polar Intermetallics Within The Pt/Sn/R Systems (R = La− Sm): Stannides Or Platinides?, Melissa L. Rhodehouse, Volodymyr Smetana, Chris Celania, Anja-Verena Mudring, Gerd H. Meyer May 2020

Ternary Polar Intermetallics Within The Pt/Sn/R Systems (R = La− Sm): Stannides Or Platinides?, Melissa L. Rhodehouse, Volodymyr Smetana, Chris Celania, Anja-Verena Mudring, Gerd H. Meyer

Ames Laboratory Accepted Manuscripts

Starting generally with a 4:6:3 molar ratio of Pt, Sn, and R (where R = La–Sm), with or without the application of a NaCl flux, seven ternary compounds were obtained as single crystals. The platinides Pt4Sn6R3 (R = La–Nd) crystallize with the Pt4Ge6Pr3 type of structure (oP52, Pnma, a = 27.6–27.8 Å, b = 4.59–4.64 Å, c = 9.33–9.40 Å). With R = Pr, Pt4Sn6Pr3–x (oP52, Pnma, a = 7.2863(3) Å, b = 4.4909(2) Å, c = 35.114(1) Å) is also obtained, which might be considered a ...


Pressure Tuning Of Structural And Magnetic Transitions In Euag4as2, Sergey L. Bud’Ko, Li Xiang, Chaowei Hu, Bing Shen, Ni Ni, Paul C. Canfield May 2020

Pressure Tuning Of Structural And Magnetic Transitions In Euag4as2, Sergey L. Bud’Ko, Li Xiang, Chaowei Hu, Bing Shen, Ni Ni, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report temperature-dependent measurements of ambient-pressure specific heat, magnetic susceptibility, anisotropic resistivity, and thermal expansion as well as in-plane resistivity under pressure up to 20.8 kbar on single crystals of EuAg4As2. Based on thermal expansion and in-plane electrical transport measurements at ambient pressure this compound has two, first-order, structural transitions in the 80–120 K temperature range. Ambient-pressure specific heat, magnetization, and thermal expansion measurements show a cascade of up to seven transitions between 8 and 16 K associated with the ordering of the Eu2+ moments. In-plane electrical transport is able to detect the more prominent of these transitions ...


Iron-Mediated Organic Matter Decomposition In Humid Soils Can Counteract Protection, Chunmei Chen, Steven J. Hall, Elizabeth Coward, Aaron Thompson May 2020

Iron-Mediated Organic Matter Decomposition In Humid Soils Can Counteract Protection, Chunmei Chen, Steven J. Hall, Elizabeth Coward, Aaron Thompson

Ecology, Evolution and Organismal Biology Publications

Soil organic matter (SOM) is correlated with reactive iron (Fe) in humid soils, but Fe also promotes SOM decomposition when oxygen (O2) becomes limited. Here we quantify Fe-mediated OM protection vs. decomposition by adding 13C dissolved organic matter (DOM) and 57FeII to soil slurries incubated under static or fluctuating O2. We find Fe uniformly protects OM only under static oxic conditions, and only when Fe and DOM are added together: de novo reactive FeIII phases suppress DOM and SOM mineralization by 35 and 47%, respectively. Conversely, adding 57FeII alone increases SOM mineralization by 8% following oxidation to 57FeIII. Under O2 ...


Magnetic Ionic Liquids As Solvents For Rna Extraction And Preservation, Chenghui Zhu, Marcelino Varona, Jared L. Anderson May 2020

Magnetic Ionic Liquids As Solvents For Rna Extraction And Preservation, Chenghui Zhu, Marcelino Varona, Jared L. Anderson

Chemistry Publications

Ribonucleic acid (RNA) is particularly sensitive to enzymatic degradation by endonucleases prior to sample analysis. In-field preservation has been a challenge for RNA sample preparation. Very recently, hydrophobic magnetic ionic liquids (MIL) have shown significant promise in the area of RNA extraction. In this study, MILs were synthesized and employed as solvents for the extraction and preservation of RNA in aqueous solution. RNA samples obtained from yeast cells were extracted and preserved by the trihexyl(tetradecyl) phosphonium tris(hexafluoroacetylaceto)cobaltate(II) ([P66614+][Co(hfacac)3–]) and trihexyl(tetradecyl) phosphonium tris(phenyltrifluoroacetylaceto)cobaltate(II) ([P66614+][Co(Phtfacac)3–]) MIL with a ...


Spectral Narrowing Accompanies Enhanced Spatial Resolution In Saturated Coherent Anti-Stokes Raman Scattering (Cars): Comparisons Of Experiment And Theory, Avinash Singh, Kalyan Santra, Xueyu Song, Jacob W. Petrich, Emily A. Smith May 2020

Spectral Narrowing Accompanies Enhanced Spatial Resolution In Saturated Coherent Anti-Stokes Raman Scattering (Cars): Comparisons Of Experiment And Theory, Avinash Singh, Kalyan Santra, Xueyu Song, Jacob W. Petrich, Emily A. Smith

Chemistry Publications

We demonstrate theoretically and confirm experimentally the mechanism by which spectral narrowing accompanies enhanced spatial resolution in a saturated coherent anti-Stokes Raman scattering (CARS) signal that is demodulated at the third harmonic (3f) of the pump modulation frequency (f). Under these modulation conditions, theory predicts a narrowing of the full width at half-maximum (FWHM) of the CARS spectrum by a factor of 2.0 with respect to that of the spectrum obtained by demodulation at the fundamental frequency. Theory also predicts an improvement of spatial resolution by a factor of 1.7. Experimentally, narrowing of the FWHM of the ...


Repairing Deep Neural Networks: Fix Patterns And Challenges, Md Johirul Islam, Rangeet Pan, Giang Nguyen, Hridesh Rajan May 2020

Repairing Deep Neural Networks: Fix Patterns And Challenges, Md Johirul Islam, Rangeet Pan, Giang Nguyen, Hridesh Rajan

Computer Science Publications

Significant interest in applying Deep Neural Network (DNN) has fueled the need to support engineering of software that uses DNNs. Repairing software that uses DNNs is one such unmistakable SE need where automated tools could be beneficial; however, we do not fully understand challenges to repairing and patterns that are utilized when manually repairing DNNs. What challenges should automated repair tools address? What are the repair patterns whose automation could help developers? Which repair patterns should be assigned a higher priority for building automated bug repair tools? This work presents a comprehensive study of bug fix patterns to address these ...


Ragweed And Sagebrush Pollen Can Distinguish Between Vegetation Types At Broad Spatial Scales, Hannah M. Carroll, Alan D. Wanamaker, Lynn G. Clark, Brian J. Wilsey May 2020

Ragweed And Sagebrush Pollen Can Distinguish Between Vegetation Types At Broad Spatial Scales, Hannah M. Carroll, Alan D. Wanamaker, Lynn G. Clark, Brian J. Wilsey

Ecology, Evolution and Organismal Biology Publications

Patterns of vegetation distribution at regional to subcontinental scales can inform understanding of climate. Delineating ecoregion boundaries over geologic time is complicated by the difficulty of distinguishing between prairie types at broad spatial scales using the pollen record. Pollen ratios are sometimes employed to distinguish between vegetation types, although their applicability is often limited to a geographic range. The Neotoma Paleoecology Database offers an unparalleled opportunity to synthesize a large number of pollen datasets. Ambrosia (ragweed) is a genus of mesic‐adapted species sensitive to summer moisture. Artemisia (sagebrush, wormwood, mugwort) is a genus of dry‐mesic‐adapted species resilient ...


Straggler-Resistant Distributed Matrix Computation Via Coding Theory: Removing A Bottleneck In Large-Scale Data Processing, Aditya Ramamoorthy, Anindya Bijoy Das, Li Tang May 2020

Straggler-Resistant Distributed Matrix Computation Via Coding Theory: Removing A Bottleneck In Large-Scale Data Processing, Aditya Ramamoorthy, Anindya Bijoy Das, Li Tang

Electrical and Computer Engineering Publications

The current BigData era routinely requires the processing of large scale data on massive distributed computing clusters. Such large scale clusters often suffer from the problem of "stragglers", which are defined as slow or failed nodes. The overall speed of a computational job on these clusters is typically dominated by stragglers in the absence of a sophisticated assignment of tasks to the worker nodes. In recent years, approaches based on coding theory (referred to as "coded computation") have been effectively used for straggler mitigation. Coded computation offers significant benefits for specific classes of problems such as distributed matrix computations (which ...


Impact Of Nematicity On The Relationship Between Antiferromagnetic Fluctuations And Superconductivity In Fese0.91s0.09 Under Pressure, Khusboo Rana, Li Xiang, Paul W. Wiecki, Raquel A. Ribeiro, Guilherme Gorgen Lesseux, Anna E. Böhmer, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa May 2020

Impact Of Nematicity On The Relationship Between Antiferromagnetic Fluctuations And Superconductivity In Fese0.91s0.09 Under Pressure, Khusboo Rana, Li Xiang, Paul W. Wiecki, Raquel A. Ribeiro, Guilherme Gorgen Lesseux, Anna E. Böhmer, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

The sulfur-substituted FeSe system, FeSe1−xSx, provides a versatile platform for studying the relationship among nematicity, antiferromagnetism, and superconductivity. Here, by nuclear magnetic resonance (NMR) and resistivity measurements up to 4.73 GPa on FeSe0.91S0.09, we established the pressure- (p-) temperature (T) phase diagram in which the nematic state is suppressed with pressure showing a nematic quantum phase transition (QPT) around p=0.5GPa, two superconductivity (SC) regions separated by the QPT appear, and antiferromagnetic (AFM) phase emerges above ∼3.3GPa. From the NMR results up to 2.1 GPa, AFM fluctuations are revealed to be characterized by ...


Competing Magnetic Interactions In The Antiferromagnetic Topological Insulator Mnbi2te4, Bing Li, J.-Q. Yan, D. Pajerowski, Elijah Gordon, Ana-Marija Nedic, Y. Sizyuk, Liqin Ke, Peter P. Orth, David Vaknin, Robert J. Mcqueeney Apr 2020

Competing Magnetic Interactions In The Antiferromagnetic Topological Insulator Mnbi2te4, Bing Li, J.-Q. Yan, D. Pajerowski, Elijah Gordon, Ana-Marija Nedic, Y. Sizyuk, Liqin Ke, Peter P. Orth, David Vaknin, Robert J. Mcqueeney

Physics and Astronomy Publications

The antiferromagnetic (AFM) compound MnBi2Te4 is suggested to be the first realization of an AFM topological insulator. We report on inelastic neutron scattering studies of the magnetic interactions in MnBi2Te4 that possess ferromagnetic triangular layers with AFM interlayer coupling. The spin waves display a large spin gap and pairwise exchange interactions within the triangular layer are long ranged and frustrated by large next-nearest neighbor AFM exchange. The degree of frustration suggests proximity to a variety of magnetic phases, potentially including skyrmion phases, which could be accessed in chemically tuned compounds or upon the application of symmetry-breaking fields.


Crystallographic Facet Selective Her Catalysis: Exemplified In Fep And Nip2 Single Crystals, Bryan Owens-Baird, Juliana P.S. Sousa, Yasmine Ziouani, Dmitri Y. Petrovykh, Nikolai A. Zarkevich, Duane D. Johnson, Yury V. Kolen'ko, Kirill Kovnir Apr 2020

Crystallographic Facet Selective Her Catalysis: Exemplified In Fep And Nip2 Single Crystals, Bryan Owens-Baird, Juliana P.S. Sousa, Yasmine Ziouani, Dmitri Y. Petrovykh, Nikolai A. Zarkevich, Duane D. Johnson, Yury V. Kolen'ko, Kirill Kovnir

Ames Laboratory Accepted Manuscripts

How the crystal structures of ordered transition-metal phosphide catalysts affect the hydrogen-evolution reaction (HER) is investigated by measuring the anisotropic catalytic activities of selected crystallographic facets on large (mm-sized) single crystals of iron-phosphide (FeP) and monoclinic nickel-diphosphide (m-NiP2). We find that different crystallographic facets exhibit distinct HER activities, in contrast to a commonly held assumption of severe surface restructuring during catalytic activity. Moreover, density-functional-theory-based computational studies show that the observed facet activity correlates well with the H-binding energy to P atoms on specific surface terminations. Direction dependent catalytic properties of two different phosphides with different transition metals, crystal structures, and ...


Ultrafast Control Of Excitonic Rashba Fine Structure By Phonon Coherence In The Metal Halide Perovskite Ch3nh3pbi3, Zhaoyu Liu, Chirag Vaswani, X. Yang, X. Zhao, Yongxin Yao, Z. Song, Di Cheng, Y. Shi, Liang Luo, Dinusha Herath Mudiyanselage, Chuankun Huang, Joong-Mok Park, Richard H. J. Kim, J. Zhao, Y. Yan, Kai-Ming Ho, Jigang Wang Apr 2020

Ultrafast Control Of Excitonic Rashba Fine Structure By Phonon Coherence In The Metal Halide Perovskite Ch3nh3pbi3, Zhaoyu Liu, Chirag Vaswani, X. Yang, X. Zhao, Yongxin Yao, Z. Song, Di Cheng, Y. Shi, Liang Luo, Dinusha Herath Mudiyanselage, Chuankun Huang, Joong-Mok Park, Richard H. J. Kim, J. Zhao, Y. Yan, Kai-Ming Ho, Jigang Wang

Ames Laboratory Accepted Manuscripts

We discover hidden Rashba fine structure in CH3NH3PbI3 and demonstrate its quantum control by vibrational coherence through symmetry-selective vibronic (electron-phonon) coupling. Above a critical threshold of a single-cycle terahertz pump field, a Raman phonon mode distinctly modulates the middle excitonic states with persistent coherence for more than ten times longer than the ones on two sides that predominately couple to infrared phonons. These vibronic quantum beats, together with first-principles modeling of phonon periodically modulated Rashba parameters, identify a threefold excitonic fine structure splitting, i.e., optically forbidden, degenerate dark states in between two bright ones with a narrow, similar to ...


Spin Dynamics In Antiferromagnetic Oxypnictides And Fluoropnictides: Lamnaso, Lamnsbo, And Bamnasf, Farhan Islam, Elijah Gordon, Pinaki Das, Yong Liu, Liquin Ke, Douglas L. Abernathy, Robert L. Mcqueeney, David Vaknin Apr 2020

Spin Dynamics In Antiferromagnetic Oxypnictides And Fluoropnictides: Lamnaso, Lamnsbo, And Bamnasf, Farhan Islam, Elijah Gordon, Pinaki Das, Yong Liu, Liquin Ke, Douglas L. Abernathy, Robert L. Mcqueeney, David Vaknin

Ames Laboratory Accepted Manuscripts

Inelastic neutron scattering (INS) from polycrystalline antiferromagnetic LaMnAsO, LaMnSbO, and BaMnAsF are analyzed using a J(1)-J(2)-J(c) Heisenberg model in the framework of the linear spin-wave theory. All three systems show clear evidence that the nearest- and next-nearest-neighbor interactions within the Mn square lattice layer (J(1) and J(2)) are both antiferromagnetic (AFM). However, for all compounds studied the competing interactions have a ratio of 2J(2)/J(1) < 1, which favors the square lattice checkerboard AFM structure over the stripe AFM structure. The interplane coupling Jc in all three systems is on the order of similar to 3 x 10(-4)J(1), rendering the magnetic properties of these systems with quasi-two-dimensional character. The substitution of Sb for As significantly lowers the in-plane exchange coupling, which is also reflected in the decrease of the Neel temperature, T-N. Although BaMnAsF shares the same MnAs sheets as LaMnAsO, their J(1) and J(2) values are substantially different. Using density functional theory, we calculate exchange parameters J(ij) to rationalize the differences among these systems.


Sediment Controls Dynamic Behavior Of A Cordilleran Ice Stream At The Last Glacial Maximum, Ellen A. Cowan, Sarah D. Zellers, Juliane Müller, Maureen H. Walczak, Lindsay L. Worthington, Beth E. Caissie, Wesley A. Clary, John M. Jaeger, Sean P. S. Gulick, Jacob W. Pratt, Alan C. Mix, Stewart J. Fallon Apr 2020

Sediment Controls Dynamic Behavior Of A Cordilleran Ice Stream At The Last Glacial Maximum, Ellen A. Cowan, Sarah D. Zellers, Juliane Müller, Maureen H. Walczak, Lindsay L. Worthington, Beth E. Caissie, Wesley A. Clary, John M. Jaeger, Sean P. S. Gulick, Jacob W. Pratt, Alan C. Mix, Stewart J. Fallon

Geological and Atmospheric Sciences Publications

The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow ...


Single-Atom-Layer Traps In A Solid Electrolyte For Lithium Batteries, Feng Zhu, Md Shafiqul Islam, Lin Zhou, Zhenqi Gu, Ting Liu, Xinchao Wang, Jun Luo, Ce-Wen Nan, Yifei Mo, Cheng Ma Apr 2020

Single-Atom-Layer Traps In A Solid Electrolyte For Lithium Batteries, Feng Zhu, Md Shafiqul Islam, Lin Zhou, Zhenqi Gu, Ting Liu, Xinchao Wang, Jun Luo, Ce-Wen Nan, Yifei Mo, Cheng Ma

Ames Laboratory Accepted Manuscripts

In order to fully understand the lithium-ion transport mechanism in solid electrolytes for batteries, not only the periodic lattice but also the non-periodic features that disrupt the ideal periodicity must be comprehensively studied. At present only a limited number of non-periodic features such as point defects and grain boundaries are considered in mechanistic studies. Here, we discover an additional type of non-periodic feature that significantly influences ionic transport; this feature is termed a “single-atom-layer trap” (SALT). In a prototype solid electrolyte Li0.33La0.56TiO3, the single-atom-layer defects that form closed loops, i.e., SALTs, are found ubiquitous by atomic-resolution electron ...


Effective Dispersion Of Mgo Nanostructure On Biochar Support As A Basic Catalyst For Glucose Isomerization, Season S. Chen, Yang Cao, Daniel C.W. Tsang, Jean-Philippe Tessonnier, Jin Shang, Deyi Hou, Zhengtao Shen, Shicheng Zhang, Yong Sik Ok, Kevin C.-W. Wu Apr 2020

Effective Dispersion Of Mgo Nanostructure On Biochar Support As A Basic Catalyst For Glucose Isomerization, Season S. Chen, Yang Cao, Daniel C.W. Tsang, Jean-Philippe Tessonnier, Jin Shang, Deyi Hou, Zhengtao Shen, Shicheng Zhang, Yong Sik Ok, Kevin C.-W. Wu

Chemical and Biological Engineering Publications

Glucose isomerization to fructose is one of the most important reactions in the field of biomass valorization. We demonstrate wood waste valorization with MgCl2 salt to synthesize an environment-friendly catalyst (i.e., MgO-biochar), which exhibits effective glucose-to-fructose isomerization with over 30% fructose yield and 80% selectivity at only 100 °C for 30 min in water as a green medium. This study highlights that one-step synthesis can effectively disperse and tether MgO nanostructures to the biochar matrix, which displays a significant reduction of Mg leaching compared to MgO-biochars produced by two-step synthesis and pure MgO. The MgCl2 acts as a porogen ...


Flux Growth Of Phosphide And Arsenide Crystals, Jian Wang, Philip Yox, Kirill Kovnir Apr 2020

Flux Growth Of Phosphide And Arsenide Crystals, Jian Wang, Philip Yox, Kirill Kovnir

Ames Laboratory Accepted Manuscripts

Flux crystal growth has been widely applied to explore new phases and grow crystals of emerging materials. To accommodate the needs of high-quality single crystals, the flux crystal growth should be reliable, controllable, and predictable. The selections of suitable flux and growth conditions remain empirical due to the lack of systematic investigation especially for reactions, which involve highly volatile components, such as P and As. Considering the flux elements, often the system in question is a quaternary or a higher multinary system, which drastically increases complexity. In this manuscript, on the examples of flux growth of phosphides and arsenides, guidelines ...


Manipulating Magnetism In The Topological Semimetal Eucd2as2, Na Hyun Jo, Brinda Kuthanazhi, Yun Wu, Erik I. Timmons, Tae-Hoon Kim, Lin Zhou, Lin-Lin Wang, Benjamin G. Ueland, Andriy Palasyuk, Dominic H. Ryan, Robert J. Mcqueeney, Kyungchan Lee, Benjamin Schrunk, Anton A. Burkov, Ruslan Prozorov, Sergey L. Bud’Ko, Adam Kaminski, Paul C. Canfield Apr 2020

Manipulating Magnetism In The Topological Semimetal Eucd2as2, Na Hyun Jo, Brinda Kuthanazhi, Yun Wu, Erik I. Timmons, Tae-Hoon Kim, Lin Zhou, Lin-Lin Wang, Benjamin G. Ueland, Andriy Palasyuk, Dominic H. Ryan, Robert J. Mcqueeney, Kyungchan Lee, Benjamin Schrunk, Anton A. Burkov, Ruslan Prozorov, Sergey L. Bud’Ko, Adam Kaminski, Paul C. Canfield

Physics and Astronomy Publications

EuCd2As2 is a magnetic semimetal that has the potential of manifesting nontrivial electronic states, depending on its low temperature magnetic ordering. Here, we report the successful synthesis of single crystals of EuCd2As2 that order ferromagnetically or antiferromagnetically depending on the level of band filling, thus allowing for the use of magnetism to tune the topological properties within the same host. We explored their physical properties via magnetization, electrical transport, heat capacity, and angle-resolved photoemission spectroscopy measurements and conclude that EuCd2As2 is an excellent, tunable system for exploring the interplay of magnetic ordering and topology.


Competing Pairing Interactions Responsible For The Large Upper Critical Field In A Stoichiometric Iron-Based Superconductor Cakfe4as4, Matthew Bristow, William Knafo, Pascal Reiss, William R. Meier, Paul C. Canfield, Stephen J. Blundell, Amalia I. Coldea Apr 2020

Competing Pairing Interactions Responsible For The Large Upper Critical Field In A Stoichiometric Iron-Based Superconductor Cakfe4as4, Matthew Bristow, William Knafo, Pascal Reiss, William R. Meier, Paul C. Canfield, Stephen J. Blundell, Amalia I. Coldea

Physics and Astronomy Publications

The upper critical field of multiband superconductors is an important quantity that can reveal details about the nature of the superconducting pairing. Here we experimentally map out the complete upper-critical-field phase diagram of a stoichiometric superconductor, CaKFe4As4, up to 90T for different orientations of the magnetic field and at temperatures down to 4.2K. The upper critical fields are extremely large, reaching values close to ∼3Tc at the lowest temperature, and the anisotropy decreases dramatically with temperature, leading to essentially isotropic superconductivity at 4.2K. We find that the temperature dependence of the upper critical field can be well described ...


Light-Driven Raman Coherence As A Nonthermal Route To Ultrafast Topology Switching In A Dirac Semimetal, Chirag Vaswani, Lin-Lin Wang, Dinusha Herath Mudiyanselage, Q. Li, P. M. Lozano, G. D. Gu, Di Cheng, Boqun Song, Liang Luo, Richard H.J. Kim, Chuankun Huang, Zhiyan Liu, M. Mootz, I. E. Perakis, Yongxin Yao, Kai-Ming Ho, Jigang Wang Apr 2020

Light-Driven Raman Coherence As A Nonthermal Route To Ultrafast Topology Switching In A Dirac Semimetal, Chirag Vaswani, Lin-Lin Wang, Dinusha Herath Mudiyanselage, Q. Li, P. M. Lozano, G. D. Gu, Di Cheng, Boqun Song, Liang Luo, Richard H.J. Kim, Chuankun Huang, Zhiyan Liu, M. Mootz, I. E. Perakis, Yongxin Yao, Kai-Ming Ho, Jigang Wang

Ames Laboratory Accepted Manuscripts

A grand challenge underlies the entire field of topology-enabled quantum logic and information science: how to establish topological control principles driven by quantum coherence and understand the time dependence of such periodic driving. Here we demonstrate a few-cycle THz-pulse-induced phase transition in a Dirac semimetal ZrTe5 that is periodically driven by vibrational coherence due to excitation of the lowest Raman active mode. Above a critical THz-pump field threshold, there emerges a long-lived metastable phase, approximately 100 ps, with unique Raman phonon-assisted topological switching dynamics absent for optical pumping. The switching also manifests itself by distinct features: nonthermal spectral shape, relaxation ...


Localized Singlets And Ferromagnetic Fluctuations In The Dilute Magnetic Topological Insulator Sn0.95mn0.05te, David Vaknin, Santanu Pakhira, Deborah L. Schlagel, Farhan Islam, Jianhua Zhang, D. M. Pajerowski, Cai-Zhuang Wang, David C. Johnston, Robert J. Mcqueeney Apr 2020

Localized Singlets And Ferromagnetic Fluctuations In The Dilute Magnetic Topological Insulator Sn0.95mn0.05te, David Vaknin, Santanu Pakhira, Deborah L. Schlagel, Farhan Islam, Jianhua Zhang, D. M. Pajerowski, Cai-Zhuang Wang, David C. Johnston, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

The development of long-range ferromagnetic (FM) order in dilute magnetic topological insulators can induce dissipationless electronic surface transport via the quantum anomalous Hall effect. We measure the magnetic excitations in a prototypical magnetic topological crystalline insulator, Sn0.95Mn0.05Te, using inelastic neutron scattering. Neutron diffraction and magnetization data indicate that our Sn0.95Mn0.05Te sample has no FM long-range order above a temperature of 2 K. However, we observe slow, collective FM fluctuations (<70μeV), indicating proximity to FM order. We also find a series of sharp peaks originating from local excitations of antiferromagnetically (AF) coupled and isolated Mn-Mn dimers with JAF=460μeV. The simultaneous presence of collective and localized components in the magnetic spectra highlight different roles for substituted Mn ions, with competition between FM order and the formation of AF-coupled Mn-Mn dimers.


A Syringe-Based Biosensor To Rapidly Detect Low Levels Of Escherichia Coli (Ecor13) In Drinking Water Using Engineered Bacteriophages, Troy C. Hinkley, Spencer Garing, Paras Jain, John Williford, Anne-Laure M. Le Ny, Kevin P. Nichols, Joseph E. Peters, Joey N. Talbert, Sam R. Nugen Mar 2020

A Syringe-Based Biosensor To Rapidly Detect Low Levels Of Escherichia Coli (Ecor13) In Drinking Water Using Engineered Bacteriophages, Troy C. Hinkley, Spencer Garing, Paras Jain, John Williford, Anne-Laure M. Le Ny, Kevin P. Nichols, Joseph E. Peters, Joey N. Talbert, Sam R. Nugen

Food Science and Human Nutrition Publications

A sanitized drinking water supply is an unconditional requirement for public health and the overall prosperity of humanity. Potential microbial and chemical contaminants of drinking water have been identified by a joint effort between the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF), who together establish guidelines that define, in part, that the presence of Escherichia coli (E. coli) in drinking water is an indication of inadequate sanitation and a significant health risk. As E. coli is a nearly ubiquitous resident of mammalian gastrointestinal tracts, no detectable counts in 100 mL of drinking water is the ...


Observations Show That Wind Farms Substantially Modify The Atmospheric Boundary Layer Thermal Stratification Transition In The Early Evening, Daniel A. Rajewski, Eugene S. Takle, Andy Vanloocke, Samantha L. Purdy Mar 2020

Observations Show That Wind Farms Substantially Modify The Atmospheric Boundary Layer Thermal Stratification Transition In The Early Evening, Daniel A. Rajewski, Eugene S. Takle, Andy Vanloocke, Samantha L. Purdy

Agronomy Publications

Single wind turbines and large wind farms modify local scales of atmospheric boundary layer (ABL) turbulence through different mechanisms dependent on location within the wind farm. These changes in turbulence scales would most likely have notable influence on surface fluxes and microclimate during the afternoon and early evening stability transition. Profiles of Richardson number and shear and buoyancy from 1‐Hz tall tower measurements in and near a wind farm in an agricultural landscape were used to quantify departures in stability characteristics during the fallow seasons. A single turbine wake decoupled turbulent connection between the surface and above the wind ...


Direct Photorelease Of Alcohols From Boron-Alkylated Bodipy Photocages, Julie A. Peterson, Logan J. Fischer, Elizabeth J. Gehrmann, Pradeep Shrestha, Ding Yuan, Chamari S. Wijesooriya, Emily A. Smith, Arthur H. Winter Mar 2020

Direct Photorelease Of Alcohols From Boron-Alkylated Bodipy Photocages, Julie A. Peterson, Logan J. Fischer, Elizabeth J. Gehrmann, Pradeep Shrestha, Ding Yuan, Chamari S. Wijesooriya, Emily A. Smith, Arthur H. Winter

Chemistry Publications

BODIPY photocages allow release of substrates us-ing visible light irradiation. They have the drawback of requiring reasonably good leaving groups for photorelease. Photorelease of alcohols is often accomplished by attachment with carbonate linkages, which upon photorelease liberate CO2 and gen-erate the alcohol. Here, we show that boron-alkylated BODIPY photocages are capable of directly photoreleasing both aliphatic alcohols and phenols upon irradiation via photocleavage of ether linkages. Direct photorelease of a hydroxycoumarin dye was demonstrated in living HeLa cells.


Evaluating Lignin Valorization Via Pyrolysis And Vapor-Phase Hydrodeoxygenation For Production Of Aromatics And Alkenes, Alireza Saraeian, Alvina Aui, Yu Gao, Mark M. Wright, Marcus Foston, Brent H. Shanks Mar 2020

Evaluating Lignin Valorization Via Pyrolysis And Vapor-Phase Hydrodeoxygenation For Production Of Aromatics And Alkenes, Alireza Saraeian, Alvina Aui, Yu Gao, Mark M. Wright, Marcus Foston, Brent H. Shanks

Chemical and Biological Engineering Publications

Lignin valorization to chemicals is an important component of creating economically viable biofuels production from lignocellulosic biomass. Any such strategy should aim at producing chemicals used at scales that can appropriately match lignin availability. Herein, a combined pyrolysis and low-pressure hydrodeoxygenation (HDO) process configuration is proposed to achieve total oxygen removal and obtain hydrocarbon (aromatic and alkene) products. This approach is tested for its robustness for lignin feedstocks obtained from a variety of sources and extracted using different procedures. The experimental results demonstrate that regardless of the lignin source, the HDO process using a MoO3 catalyst was able to funnel ...


Ac And Dc Differential Bridge Structure Suitable For Electrochemical Interfacial Capacitance Biosensing Applications, Sara Neshani, Charles K. A. Nyamekye, Scott Melvin, Emily A. Smith, Degang J. Chen, Nathan Neihart Mar 2020

Ac And Dc Differential Bridge Structure Suitable For Electrochemical Interfacial Capacitance Biosensing Applications, Sara Neshani, Charles K. A. Nyamekye, Scott Melvin, Emily A. Smith, Degang J. Chen, Nathan Neihart

Electrical and Computer Engineering Publications

This paper presents a capacitive differential bridge structure with both AC and DC excitation and balancing capability for low cost electrode-solution interfacial capacitance biosensing applications. The proposed series RC balancing structure offers higher sensitivity, lower susceptibility to common-mode interferences, and drift control. To evaluate the bridge performance in practice, possible effects of initial bridge imbalance due to component mismatches are investigated considering the required resolution of the balancing networks, sensitivity, and linearity. This evaluation is also a guideline to designing the balancing networks, balancing algorithm and the proceeding readout interface circuitry. The proposed series RC bridge structure is implemented along ...


Coherent Band-Edge Oscillations And Dynamic Longitudinal-Optical Phonon Mode Splitting As Evidence For Polarons In Perovskites, Zhaoyu Liu, Chirag Vaswani, Liang Luo, Di Cheng, X. Yang, Xin Zhao, Yongxin Yao, Z. Song, R. Brenes, R. J. H. Kim, J. Jean, V. Bulović, Y. Yan, Kai-Ming Ho, Jigang Wang Mar 2020

Coherent Band-Edge Oscillations And Dynamic Longitudinal-Optical Phonon Mode Splitting As Evidence For Polarons In Perovskites, Zhaoyu Liu, Chirag Vaswani, Liang Luo, Di Cheng, X. Yang, Xin Zhao, Yongxin Yao, Z. Song, R. Brenes, R. J. H. Kim, J. Jean, V. Bulović, Y. Yan, Kai-Ming Ho, Jigang Wang

Ames Laboratory Accepted Manuscripts

The coherence of collective modes, such as phonons and polarons, and their modulation of electronic states is long sought in complex systems, which is a crosscutting issue in photovoltaics and quantum electronics. In photovoltaic cells and lasers based on metal halide perovskites, the presence of polarons, i.e., photocarriers dressed by the macroscopic motion of charged lattice, assisted by terahertz (THz) longitudinal-optical (LO) phonons, has been intensely studied yet is still debated. This may be key for explaining the remarkable properties of the perovskite materials, e.g., defect tolerance, long charge lifetimes, and diffusion lengths. Here we use the intense ...