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2019

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Articles 1 - 30 of 308

Full-Text Articles in Physics

From Critical Behavior To Catastrophic Runaways: Comparing Sheared Granular Materials With Bulk Metallic Glasses, Alan A. Long, Dmitry Denisov, Peter Schall, Todd C. Hufnagel, Xiaojun Gu, Wendelin J. Wright, Karin A. Dahmen Nov 2019

From Critical Behavior To Catastrophic Runaways: Comparing Sheared Granular Materials With Bulk Metallic Glasses, Alan A. Long, Dmitry Denisov, Peter Schall, Todd C. Hufnagel, Xiaojun Gu, Wendelin J. Wright, Karin A. Dahmen

Faculty Journal Articles

The flow of granular materials and metallic glasses is governed by strongly correlated, avalanche-like deformation. Recent comparisons focused on the scaling regimes of the small avalanches, where strong similarities were found in the two systems. Here, we investigate the regime of large avalanches by computing the temporal profile or “shape” of each one, i.e., the time derivative of the stress-time series during each avalanche. We then compare the experimental statistics and dynamics of these shapes in granular media and bulk metallic glasses. We complement the experiments with a mean-field model that predicts a critical size beyond which avalanches turn ...


Complex Oscillatory Decrease With Size In Diffusivity Of {100}-Epitaxially Supported 3d Fcc Metal Nanoclusters, King C. Lai, James W. Evans Oct 2019

Complex Oscillatory Decrease With Size In Diffusivity Of {100}-Epitaxially Supported 3d Fcc Metal Nanoclusters, King C. Lai, James W. Evans

Ames Laboratory Accepted Manuscripts

Diffusion and coalescence of supported 3D metal nanoclusters (NCs) leads to Smoluchowski Ripening (SR), a key pathway for catalyst degradation. Variation of the NC diffusion coefficient, DN, with size N (in atoms) controls SR kinetics. Traditionally, a form DN ∼ N−β was assumed consistent with mean-field analysis. However, KMC simulation of a stochastic model for diffusion of {100}-epitaxially supported fcc NCs mediated by surface diffusion reveals instead a complex oscillatory decrease of DN with N. Barriers for surface diffusion of metal atoms across and between facets, along step edges, etc., in this model are selected to accurately capture behavior ...


A Method For Automatic Detection Of Tongued And Slurred Note Transitions In Clarinet Playing, Whitney L. Coyle, Jack D. Gabriel Sep 2019

A Method For Automatic Detection Of Tongued And Slurred Note Transitions In Clarinet Playing, Whitney L. Coyle, Jack D. Gabriel

Faculty Publications

This study offers a simple method to characterize two transition types in passages of music in order to automatically distinguish slurred transitions from tongued transitions in musical settings. Data were recorded from musicians playing a clarinet with a sensor-equipped mouthpiece measuring blowing pressure in the mouth and pressure in the mouthpiece. This method allows for comparing transitions in different musical contexts, playing regimes, and between players. The method is highly reliable in automatically detecting transition types in recorded clarinet playing in both simple and more complex passages.


Obituary: Anthony Starace (1945-2019) Sep 2019

Obituary: Anthony Starace (1945-2019)

Anthony F. Starace Publications

Anthony Starace, George Holmes University Professor of physics, died Sept. 5 from complications related to pancreatitis. He was 74.

Starace was born July 24, 1945, in the Queens borough of New York City. He graduated from Stuyvesant High School and earned his bachelor’s degree from Columbia University in 1966 before moving west to the University of Chicago, where he earned his doctorate under adviser Ugo Fano in 1971. It was in Chicago that he met Katherine Fritz of Beatrice, Nebraska, his wife of 51 years.

Following a postdoctoral appointment at Imperial College London, Starace moved to Lincoln as an ...


Imaging Propagative Exciton Polaritons In Atomically Thin Wse2 Waveguides, F. Hu, Y. Luan, Jacob Speltz, D. Zhong, C. H. Liu, J. Yan, D. G. Mandrus, X. Xu, Zhe Fei Sep 2019

Imaging Propagative Exciton Polaritons In Atomically Thin Wse2 Waveguides, F. Hu, Y. Luan, Jacob Speltz, D. Zhong, C. H. Liu, J. Yan, D. G. Mandrus, X. Xu, Zhe Fei

Ames Laboratory Accepted Manuscripts

The exciton polariton (EP) is a half-light and half-matter quasiparticle that is promising for exploring both fundamental quantum phenomena as well as photonic applications. Van der Waals materials, such as transition-metal dichalcogenide (TMD), emerge as a promising nanophotonics platform due to its support of long propagative EPs even at room temperature. However, real-space studies have been limited to bulk crystal waveguides with a thickness no less than 60 nm. Here we report the nano-optical imaging of the transverse-electric EPs in WSe2 nanoflakes down to a few atomic layers, which can be turned on and off by tuning the polarization state ...


Stormtime Thermospheric Neutral Winds Obtained From A Data Assimilation Model, Ludger Scherliess Sep 2019

Stormtime Thermospheric Neutral Winds Obtained From A Data Assimilation Model, Ludger Scherliess

Funded Research Records

No abstract provided.


9th Annual Postdoctoral Science Symposium, University Of Texas Md Anderson Cancer Center Postdoctoral Association Sep 2019

9th Annual Postdoctoral Science Symposium, University Of Texas Md Anderson Cancer Center Postdoctoral Association

MD Anderson Cancer Center Postdoctoral Association Annual Postdoctoral Science Symposium Abstracts

The mission of the Annual Postdoctoral Science Symposium (APSS) is to provide a platform for talented postdoctoral fellows throughout the Texas Medical Center to present their work to a wider audience. The MD Anderson Postdoctoral Association convened its inaugural Annual Postdoctoral Science Symposium (APSS) on August 4, 2011.

The APSS provides a professional venue for postdoctoral scientists to develop, clarify, and refine their research as a result of formal reviews and critiques of faculty and other postdoctoral scientists. Additionally, attendees discuss current research on a broad range of subjects while promoting academic interactions and enrichment and developing new collaborations.


Predicting Complex Relaxation Processes In Metallic Glass, Yang Sun, Si-Xu Peng, Qun Yang, Feng Zhang, Meng-Hao Yang, Cai-Zhuang Wang, Kai-Ming Ho, Hai-Bin Yu Sep 2019

Predicting Complex Relaxation Processes In Metallic Glass, Yang Sun, Si-Xu Peng, Qun Yang, Feng Zhang, Meng-Hao Yang, Cai-Zhuang Wang, Kai-Ming Ho, Hai-Bin Yu

Ames Laboratory Accepted Manuscripts

Relaxation processes significantly influence the properties of glass materials. However, understanding their specific origins is difficult; even more challenging is to forecast them theoretically. In this study, using microseconds molecular dynamics simulations together with an accurate many-body interaction potential, we predict that an Al90Sm10 metallic glass would have complex relaxation behaviors: In addition to the main (α) relaxation, the glass (i) shows a pronounced secondary (β) relaxation at cryogenic temperatures and (ii) exhibits an anomalous relaxation process (α2) accompanying α relaxation. Both of the predictions are verified by experiments. Computational simulations reveal the microscopic origins of relaxation processes: while the ...


Force Oscillations Distort Avalanche Shapes, Louis W. Mcfaul, Wendelin J. Wright, Jordan Sickle, Karin A. Dahmen Sep 2019

Force Oscillations Distort Avalanche Shapes, Louis W. Mcfaul, Wendelin J. Wright, Jordan Sickle, Karin A. Dahmen

Faculty Journal Articles

Contradictory scaling behavior in experiments testing the principle of universality may be due to external oscillations. Thus, the effect of damped oscillatory external forces on slip avalanches in slowly deformed solids is simulated using a mean-field model. Akin to a resonance effect, oscillatory driving forces change the dynamics of avalanches with durations close to the oscillation period. This problem can be avoided by tuning mechanical resonance frequencies away from the range of the inverse avalanche durations. The results provide critical guidance for experimental tests for universality and a quantitative understanding of avalanche dynamics under a wide range of driving conditions.


Analysis Of The London Penetration Depth In Ni-Doped Cakfe4 As4, D. Torsello, Kyuil Cho, Kamal R. Joshi, Sunil Ghimire, G. A. Ummarino, Naufer Nusran, Makariy A. Tanatar, William R. Meier, Mingyu Xu, Sergey L. Bud’Ko, Paul C. Canfield, G. Ghigo, Ruslan Prozorov Sep 2019

Analysis Of The London Penetration Depth In Ni-Doped Cakfe4 As4, D. Torsello, Kyuil Cho, Kamal R. Joshi, Sunil Ghimire, G. A. Ummarino, Naufer Nusran, Makariy A. Tanatar, William R. Meier, Mingyu Xu, Sergey L. Bud’Ko, Paul C. Canfield, G. Ghigo, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

We report combined experimental and theoretical analysis of superconductivity in CaK(Fe1−xNix)4As4 (CaK1144) for x=0, 0.017, and 0.034. To obtain the superfluid density ρ=[1+ΔλL(T)/λL(0)]−2, the temperature dependence of the London penetration depth ΔλL(T) was measured by using a tunnel-diode resonator (TDR) and the results agreed with the microwave coplanar resonator (MWR) with the small differences accounted for by considering a three orders of magnitude higher frequency of MWR. The absolute value of λL(T≪Tc)≈λL(0) was measured by using MWR, λL(5K)≈170±20 nm, which ...


Slowing Down Of Spin Glass Correlation Length Growth: Simulations Meet Experiments, Qiang Zhai, V. Martin-Mayor, Deborah L. Schlagel, Gregory G. Kenning, Raymond L. Orbach Sep 2019

Slowing Down Of Spin Glass Correlation Length Growth: Simulations Meet Experiments, Qiang Zhai, V. Martin-Mayor, Deborah L. Schlagel, Gregory G. Kenning, Raymond L. Orbach

Ames Laboratory Accepted Manuscripts

The growth of the spin glass correlation length has been measured as a function of the waiting time tw on a single crystal of CuMn (6 at. %), reaching values ξ∼150 nm, larger than any other glassy correlation length measured to date. We find an aging rate dlntw/dlnξ larger than found in previous measurements, which evinces a dynamic slowing down as ξ grows. Our measured aging rate is compared with simulation results by the Janus Collaboration. After critical effects are taken into account, we find excellent agreement with the Janus data.


Multiple Ferromagnetic Transitions And Structural Distortion In The Van Der Waals Ferromagnet Vi3 At Ambient And Finite Pressures, Elena Gati, Yuji Inagaki, Tai Kong, Robert J. Cava, Yuji Furukawa, Paul C. Canfield, Sergey L. Bud’Ko Sep 2019

Multiple Ferromagnetic Transitions And Structural Distortion In The Van Der Waals Ferromagnet Vi3 At Ambient And Finite Pressures, Elena Gati, Yuji Inagaki, Tai Kong, Robert J. Cava, Yuji Furukawa, Paul C. Canfield, Sergey L. Bud’Ko

Ames Laboratory Accepted Manuscripts

We present a combined study of zero-field (51) V and I-127 NMR at ambient pressure and specific heat and magnetization measurements under pressure up to 2.08 GPa on bulk single crystals of the van der Waals ferromagnet VI3. At ambient pressure, our results consistently demonstrate that VI3 undergoes a structural transition at T-s approximate to 78 K, followed by two subsequent ferromagnetic transitions at T-FM1 approximate to 50 K and T-FM2 approximate to 36 K upon cooling. At lowest temperature (T < T-FM2), two magnetically ordered V sites exist, whereas only one magnetically ordered V site is observed for T-FM1 < T < T-FM2. Whereas T-FM1 is almost unaffected by external pressure, T-FM2 is highly responsive to pressure and merges with the T-FM1 line at p 0.6 GPa. At even higher pressures (p approximate to 1.25 GPa), the T-FM2 line merges with the structural transition at T-s which becomes moderately suppressed with p for p < 1.25 GPa. Taken together, our data point toward a complex magnetic structure and an interesting interplay of magnetic and structural degrees of freedom in VI3.


Evolution Of Structural, Magnetic, And Transport Properties In Mnbi2−X Sbx Te4, Jiaqiang Yan, Satoshi Okamoto, Michael A. Mcguire, Andrew F. May, Robert J. Mcqueeney, Brian C. Sales Sep 2019

Evolution Of Structural, Magnetic, And Transport Properties In Mnbi2−X Sbx Te4, Jiaqiang Yan, Satoshi Okamoto, Michael A. Mcguire, Andrew F. May, Robert J. Mcqueeney, Brian C. Sales

Ames Laboratory Accepted Manuscripts

Here we report the evolution of structural, magnetic, and transport properties in MnBi2−xSbxTe4(0≤x≤2) single crystals. MnSb2Te4, isostructural to MnBi2Te4, is successfully synthesized in single-crystal form. Magnetic measurements suggest an antiferromagnetic order below TN=19K for MnSb2Te4 with the magnetic moments aligned along the crystallographic c axis. With increasing Sb content in MnBi2−xSbxTe4, the a-lattice parameter decreases linearly following Vegard's law, while the c-lattice parameter shows little compositional dependence. The contraction along a is caused by the reduction of the Mn-Te-Mn bond angle, while the Mn-Te bond length remains nearly constant. The antiferromagnetic ordering temperature ...


Correlations Between Short- And Long-Time Relaxation In Colloidal Supercooled Liquids And Glasses, Chandan K. Mishra, Xiaoguang Ma, Piotr Habdas, Kevin B. Aptowicz, A. G. Yodh Aug 2019

Correlations Between Short- And Long-Time Relaxation In Colloidal Supercooled Liquids And Glasses, Chandan K. Mishra, Xiaoguang Ma, Piotr Habdas, Kevin B. Aptowicz, A. G. Yodh

Physics

Spatiotemporal dynamics of short- and long-time structural relaxation are measured experimentally as a function of packing fraction, φ, in quasi-two-dimensional colloidal supercooled liquids and glasses. The relaxation times associated with long-time dynamic heterogeneity and short-time intracage motion are found to be strongly correlated and to grow by orders of magnitude with increasing φ toward dynamic arrest. We find that clusters of fast particles on the two timescales often overlap, and, interestingly, the distribution of minimum-spatial-separation between closest nonoverlapping clusters across the two timescales is revealed to be exponential with a decay length that increases with φ. In total, the experimental ...


Tunneling Anisotropic Magnetoresistance In Ferroelectric Tunnel Junctions, Artem Alexandrov, M. Ye. Zhuravlev, Evgeny Y. Tsymbal Aug 2019

Tunneling Anisotropic Magnetoresistance In Ferroelectric Tunnel Junctions, Artem Alexandrov, M. Ye. Zhuravlev, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Using a simple quantum-mechanical model, we explore a tunneling anisotropic magnetoresistance (TAMR) effect in ferroelectric tunnel junctions (FTJs) with a ferromagnetic electrode and a ferroelectric barrier layer, where spontaneous polarization gives rise to the Rashba and Dresselhaus spin-orbit coupling (SOC). For realistic parameters of the model, we predict sizable TAMR measurable experimentally. For asymmetric FTJs, whose electrodes have different work functions, the built-in electric field affects the SOC parameters and leads to TAMR being dependent on the ferroelectric polarization direction. The SOC change with polarization switching affects tunneling conductance, revealing an alternative mechanism of tunneling electroresistance. These results demonstrate alternative ...


Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi Aug 2019

Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi

Aerospace Engineering Publications

Elastocaloric cooling, which exploits the latent heat released and absorbed as stress-induced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in non-vapor-compression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hysteresis. Here, we report on creating high-performance low-hysteresis elastocaloric cooling materials via additive manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are found to be beneficial to elastocaloric performances when they are combined with the binary Ti-Ni compound in nanocomposite configurations. The resulting microstructure gives rise ...


Magnetoelectric Effect At The Ni/Hfo2 Interface Induced By Ferroelectric Polarization, Qiong Yang, Lingling Tao, Zhen Jiang, Yichun Zhou, Evgeny Tsymbal, Vitaly Alexandrov Aug 2019

Magnetoelectric Effect At The Ni/Hfo2 Interface Induced By Ferroelectric Polarization, Qiong Yang, Lingling Tao, Zhen Jiang, Yichun Zhou, Evgeny Tsymbal, Vitaly Alexandrov

Evgeny Tsymbal Publications

Driven by the technological importance of the recently discovered ferroelectric HfO2, we explore a magnetoelectric effect at the HfO2-based ferroelectric-ferromagnetic interface. Using density-functionaltheory calculations of the Ni/HfO2/Ni (001) heterostructure as a model system, we predict a stable and sizable ferroelectric polarization in a few-nm-thick HfO2 layer. For the Ni/HfO2 interface with opposite polarization directions (pointing to or away from the interface), we find a sizable difference in the interfacial Ni—O bonding, resulting in dissimilar degrees of depletion of the electron density around the interface. The latter affects the relative population ...


Experimental Realization Of An Extreme-Parameter Omnidirectional Cloak, Bin Zheng, Yihao Yang, Zheping Shao, Qinghui Yan, Nian-Hai Shen, Lian Shen, Huaping Wang, Erping Li, Costas M. Soukoulis, Hongsheng Chen Aug 2019

Experimental Realization Of An Extreme-Parameter Omnidirectional Cloak, Bin Zheng, Yihao Yang, Zheping Shao, Qinghui Yan, Nian-Hai Shen, Lian Shen, Huaping Wang, Erping Li, Costas M. Soukoulis, Hongsheng Chen

Ames Laboratory Accepted Manuscripts

An ideal transformation-based omnidirectional cloak always relies on metamaterials with extreme parameters, which were previously thought to be too difficult to realize. For such a reason, in previous experimental proposals of invisibility cloaks, the extreme parameters requirements are usually abandoned, leading to inherent scattering. Here, we report on the first experimental demonstration of an omnidirectional cloak that satisfies the extreme parameters requirement, which can hide objects in a homogenous background. Instead of using resonant metamaterials that usually involve unavoidable absorptive loss, the extreme parameters are achieved using a nonresonant metamaterial comprising arrays of subwavelength metallic channels manufactured with 3D metal ...


Mechanical Resonances Of Mobile Impurities In A One-Dimensional Quantum Fluid, Thomas L. Schmidt, Giacomo Dolcetto, Christopher J. Pedder, Karyn Le Hur, Peter Orth Aug 2019

Mechanical Resonances Of Mobile Impurities In A One-Dimensional Quantum Fluid, Thomas L. Schmidt, Giacomo Dolcetto, Christopher J. Pedder, Karyn Le Hur, Peter Orth

Ames Laboratory Accepted Manuscripts

We study a one-dimensional interacting quantum liquid hosting a pair of mobile impurities causing backscattering. We determine the effective retarded interaction between the two impurities mediated by the liquid. We show that for strong backscattering this interaction gives rise to resonances and antiresonances in the finite-frequency mobility of the impurity pair. At the antiresonances, the two impurities remain at rest even when driven by a (small) external force. At the resonances, their synchronous motion follows the external drive in phase and reaches maximum amplitude. Using a perturbative renormalization group analysis in quantum tunneling across the impurities, we study the range ...


Generalized Near Horizon Extreme Binary Black Hole Geometry, Jacob Ciafre, Shahar Hadar, Erin Rickenbach, Maria J. Rodriguez Aug 2019

Generalized Near Horizon Extreme Binary Black Hole Geometry, Jacob Ciafre, Shahar Hadar, Erin Rickenbach, Maria J. Rodriguez

All Physics Faculty Publications

We present a new vacuum solution of Einstein’s equations describing the near horizon region of two neutral, extreme (zero-temperature), corotating, nonidentical Kerr black holes. The metric is stationary, asymptotically near horizon extremal Kerr (NHEK), and contains a localized massless strut along the symmetry axis between the black holes. In the deep infrared, it flows to two separate throats which we call “pierced-NHEK” geometries: each throat is NHEK pierced by a conical singularity. We find that in spite of the presence of the strut for the pierced-NHEK geometries the isometry group SL(2,R)×U(1) is restored. We find ...


Loop Currents And Anomalous Hall Effect From Time-Reversal Symmetry-Breaking Superconductivity On The Honeycomb Lattice, P.M.R. Brydon, D.S.L. Abergel, Daniel Agterberg, Victor M. Yakovenko Aug 2019

Loop Currents And Anomalous Hall Effect From Time-Reversal Symmetry-Breaking Superconductivity On The Honeycomb Lattice, P.M.R. Brydon, D.S.L. Abergel, Daniel Agterberg, Victor M. Yakovenko

Physics Faculty Articles

We study a tight-binding model on the honeycomb lattice of chiral d-wave superconductivity that breaks time-reversal symmetry. Because of its nontrivial sublattice structure, we show that it is possible to construct a gauge-invariant time-reversal-odd bilinear of the pairing potential. The existence of this bilinear reflects the sublattice polarization of the pairing state. We show that it generates persistent loop current correlations around each lattice site and opens a topological mass gap at the Dirac points, resembling Haldane’s model of the anomalous quantum Hall effect. In addition to the usual chiral d-wave edge states, there also exist electronlike ...


Probing The Direct Factor For Superconductivity In Fese-Based Superconductors By Raman Scattering, Animin Zhang, Xiaoli Ma, Yimeng Wang, Shanshan Sun, Bin Lei, Hechang Lei, Xianhui Chen, Xiaoqun Wang, Changfeng Chen, Qingming Zhang Aug 2019

Probing The Direct Factor For Superconductivity In Fese-Based Superconductors By Raman Scattering, Animin Zhang, Xiaoli Ma, Yimeng Wang, Shanshan Sun, Bin Lei, Hechang Lei, Xianhui Chen, Xiaoqun Wang, Changfeng Chen, Qingming Zhang

Physics & Astronomy Faculty Publications

The FeSe-based superconductors exhibit a wide range of critical temperature Tcunder a variety of material and physical conditions, but extensive studies to date have yet to produce a consensus view on the underlying mechanism. Here we report on a systematic Raman-scattering work on intercalated FeSe superconductors Lix(NH3)yFe2Se2 and (Li,Fe)OHFeSe compared to pristine FeSe. All three crystals show an anomalous power-law temperature dependence of phonon linewidths, deviating from the standard anharmonic behavior. This intriguing phenomenon is attributed to electron-phonon coupling effects enhanced by electron correlation, as evidenced by the evolution of the A1g Raman mode. Meanwhile, an ...


Extensive Soot Compaction By Cloud Processing From Laboratory And Field Observations, Janarjan Bhandari, Swarup China, Kamal Kant Chandrakar, Greg Kinney, Will Cantrell, Raymond Shaw, Lynn Mazzoleni, Giulia Girotto, Noopur Sharma, Kyle Gorkowski, Stefania Gilardoni, Stefano Decesari, Maria Cristina Facchini, Nicola Zanca, Giulia Pavese, Francesco Esposito, Manvendra K Dubey, Allison C Aiken, Rajan K Chakrabarty, Hans Moosmüller, Timothy B Onasch, Rahul A Zaveri, Barbara V Scarnato, Paulo Fialho, Claudio Mazzoleni Aug 2019

Extensive Soot Compaction By Cloud Processing From Laboratory And Field Observations, Janarjan Bhandari, Swarup China, Kamal Kant Chandrakar, Greg Kinney, Will Cantrell, Raymond Shaw, Lynn Mazzoleni, Giulia Girotto, Noopur Sharma, Kyle Gorkowski, Stefania Gilardoni, Stefano Decesari, Maria Cristina Facchini, Nicola Zanca, Giulia Pavese, Francesco Esposito, Manvendra K Dubey, Allison C Aiken, Rajan K Chakrabarty, Hans Moosmüller, Timothy B Onasch, Rahul A Zaveri, Barbara V Scarnato, Paulo Fialho, Claudio Mazzoleni

Michigan Tech Publications

Soot particles form during combustion of carbonaceous materials and impact climate and air quality. When freshly emitted, they are typically fractal-like aggregates. After atmospheric aging, they can act as cloud condensation nuclei, and water condensation or evaporation restructure them to more compact aggregates, affecting their optical, aerodynamic, and surface properties. Here we survey the morphology of ambient soot particles from various locations and different environmental and aging conditions. We used electron microscopy and show extensive soot compaction after cloud processing. We further performed laboratory experiments to simulate atmospheric cloud processing under controlled conditions. We find that soot particles sampled after ...


Yang-Mills Sources For Biconformal Gravity, Walter Davis Muhwezi Aug 2019

Yang-Mills Sources For Biconformal Gravity, Walter Davis Muhwezi

Physics Capstone Project

We present a gauge formulation of Yang-Mills matter sources for Biconformal gravity. Biconformal gravity is a 2n-dimensional conformal gauge theory with a curvature linear action that has been shown to reproduce scale invariant general relativity on the cotangent bundle of n-dimensional space time. We present a generalization of Yang-Mills theories in biconformal space and show that the field equations with sources reduce the Yang-Mills sector to n-dimensional Yang-Mills theory in curved spacetime. We compute the restrictive conditions on the energy-momentum tensor required by the gravitational field equations.


Hyperfine Splitting In Muonium: Accuracy Of The Theoretical Prediction, Michael I. Eides Aug 2019

Hyperfine Splitting In Muonium: Accuracy Of The Theoretical Prediction, Michael I. Eides

Physics and Astronomy Faculty Publications

In the last twenty years, the theory of hyperfine splitting in muonium developed without any experimental input. Finally, this situation is changing and a new experiment on measuring hyperfine splitting in muonium is now in progress at J-PARC. The goal of the MuSEUM experiment is to improve by an order of magnitude experimental accuracy of the hyperfine splitting and muon-electron mass ratio. Uncertainty of the theoretical prediction for hyperfine splitting will be crucial for comparison between the forthcoming experimental data and the theory in search of a possible new physics. In the current literature estimates of the error bars of ...


An Effective Electric Dipole Model For Voltage-Induced Gating Mechanism Of Lysenin, Eric Krueger, Daniel Fologea Aug 2019

An Effective Electric Dipole Model For Voltage-Induced Gating Mechanism Of Lysenin, Eric Krueger, Daniel Fologea

Physics Faculty Publications and Presentations

Lysenin is a pore-forming toxin, which self-inserts open channels into sphingomyelin containing membranes and is known to be voltage regulated. The mechanistic details of its voltage gating mechanism, however, remains elusive despite much recent efforts. Here, we have employed a novel combination of experimental and computational techniques to examine a model for voltage gating, that is based on the existence of an “effective electric dipole” inspired by recent reported structures of lysenin. We support this mechanism by the observations that (i) the charge-reversal and neutralization substitutions in lysenin result in changing its electrical gating properties by modifying the strength of ...


Self-Consistent Two-Gap Description Of Mgb2 Superconductor, Hyunsoo Kim, Kyuil Cho, Makariy A. Tanatar, Valentin Taufour, Stella K. Kim, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir G. Kogan, Ruslan Prozorov Aug 2019

Self-Consistent Two-Gap Description Of Mgb2 Superconductor, Hyunsoo Kim, Kyuil Cho, Makariy A. Tanatar, Valentin Taufour, Stella K. Kim, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir G. Kogan, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

A self-consistent two-gap γ -model is used to quantitatively describe several thermodynamic properties of MgB 2 superconductor. The superconducting coupling matrix, νij , was obtained from the fitting of the superfluid density in the entire superconducting temperature range. Using this input, temperature-dependent superconducting gaps, specific heat, and upper critical fields were calculated with no adjustable parameters and compared with the experimental data as well as with the first-principles calculations. The observed agreement between fit and data shows that γ -model provides adequate quantitative description of the two-gap superconductivity in MgB 2 and may serve as a relatively simple and versatile self-consistent ...


Erratum: "Imaging The Three‐Dimensional Orientation And Rotational Mobility Of Fluorescent Emitters Using The Tri‐Spot Point Spread Function", Oumeng Zhang, Jin Lu, Tianben Ding, Matthew D. Lew Aug 2019

Erratum: "Imaging The Three‐Dimensional Orientation And Rotational Mobility Of Fluorescent Emitters Using The Tri‐Spot Point Spread Function", Oumeng Zhang, Jin Lu, Tianben Ding, Matthew D. Lew

Electrical & Systems Engineering Publications and Presentations

In the original paper, a calibration error exists in the image-formation model used to analyze experimental images taken by our microscope, causing a bias in the orientation measurements in Figs. 2 and 3. The updated measurements are shown in Fig. E1. We have also updated the supplementary material for the original article to discuss the revised PSF model and estimation algorithms (supplementary material 2) and show the revised model and measurements (Figs. S1, S3, S7, S8, and S10–S13).


Monitoring Ambient Laboratory Conditions With A Raspberry Pi, Joshua Boman Aug 2019

Monitoring Ambient Laboratory Conditions With A Raspberry Pi, Joshua Boman

Physics Capstone Project

Precise experimental devices and measurements can be sensitive to changing physical conditions in the lab. The purpose of this research was to develop a standardized computer automated package to monitor and record changes in laboratory conditions, including ambient temperature, atmospheric pressure, relative humidity, light intensity, motion, and power outages. The computer-interfaced device was based around an inexpensive Raspberry Pi microcomputer and commercially available sensors. The Raspberry Pi uploads the sensor data to a file used by LabVIEW to further analyze, plot and display the calibrated sensor data in real time and trigger alarms. This capability allows the Material Physics Research ...


Picosecond Time-Resolved Dynamics Of Energy Transfer Between Gan And The Various Excited States Of Eu3+ Ions, Ruoqiao Wei, Brandon Mitchell, Dolf Timmerman, Tom Gregorkiewicz, Wanxin Zhu, Jun Tatebayashi, Shuhei Ichikawa, Yasufumi Fujiwara, Volkmar Dierolf Aug 2019

Picosecond Time-Resolved Dynamics Of Energy Transfer Between Gan And The Various Excited States Of Eu3+ Ions, Ruoqiao Wei, Brandon Mitchell, Dolf Timmerman, Tom Gregorkiewicz, Wanxin Zhu, Jun Tatebayashi, Shuhei Ichikawa, Yasufumi Fujiwara, Volkmar Dierolf

Physics

To elucidate the energy transfer and reexcitation processes in Eu-doped GaN layers that are used in recently developed, highly efficient red light-emitting diodes, a systematic series of photoluminescence and time-resolved photoluminescence (TR-PL) measurements was performed. Critical insights on how “slow” Eu processes (∼µs) can compete against fast semiconductor processes (∼ps) are revealed using TR-PL with a high temporal resolution, as it is found that the initial energy transfer from GaN to the Eu3+ ions takes place rapidly, on a timescale of <100 ps. Below band-gap resonant excitation was used to identify the states into which the energy transfer occurs. For the most efficient Eu defect complexes, this transfer dominantly occurs directly into the 5 D0 state of Eu3+. Less efficient complexes also exhibit transfer into the 5 D2 state, the emission of which can be detected using photoluminescence at low temperature, indicating the importance of the excitation pathway on device efficiency. Under high excitation intensity, reexcitation can also occur, leading to a redistribution of population into the 5 D2, 5 D1, or 5 D0 states.