7,021 results on '"Widom A."'
Search Results
2. Vibrational Entropy and Free Energy of Solid Lithium using Covariance of Atomic Displacements Enabled by Machine Learning
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Phuthi, Mgcini Keith, Huang, Yang, Widom, Michael, and Viswanathan, Venkatasubramanian
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Condensed Matter - Materials Science ,Condensed Matter - Statistical Mechanics - Abstract
Vibrational properties of solids are key to determining stability, response and functionality. However, they are challenging to computationally predict at Ab-Initio accuracy, even for elemental systems. Ab-Initio methods for modeling atomic interactions are limited in the system sizes and simulation times that can be achieved. Due to these limitations, Machine Learning Interatomic Potentials (MLIPs) are gaining popularity and success as a faster, more scalable approach for modeling atomic interactions, potentially at Ab-Initio accuracy. Even with faster potentials, methodologies for predicting entropy, free energy and vibrational properties vary in accuracy, cost and difficulty to implement. Using the Covariance of Atomic Displacements (CAD) to predict entropy, free energy and finite-temperature phonon dispersions is a promising approach but thorough benchmarking has been hampered by the cost of Ab-Initio methods for sampling. In this work, we use a MLIP and the CAD to characterize the convergence of the predicted properties and determine optimal sampling strategies. We focus on solid lithium at zero pressure, showing that the MLIP-CAD approach reproduces experimental entropy, phonon dispersions and the martensitic transition while also comparing to more established methods.
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- 2024
3. Simulated structure and thermodynamics of decagonal Al-Co-Cu quasicrystals
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Huang, Y., Widom, M., and Mihalkovič, M.
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Condensed Matter - Materials Science - Abstract
Atomic structures of Al-Co-Cu decagonal quasicrystals (QCs) are investigated using empirical oscillating pair potentials (EOPP) in molecular dynamic (MD) simulations that we enhance by Monte Carlo (MC) swapping of chemical species and replica exchange. Predicted structures exhibit planar decagonal tilin g patterns and are periodic along the perpendicular direction. We then recalculate the energies of promising structures using first-principles density functional theory (DFT), along with energies of competing phases. We find that our $\tau$-inflated sequence of QC approximants are energetically unstable a t low temperature by at least 3 meV/atom. Extending our study to finite temperatures by calculating harmonic vibrational entropy, as well as anharmonic contributions that include chemical species swaps and tile flips, our results suggest that the quasicrystal phase is entropically stabilized at temperatur es in the range 600-800K and above. It decomposes into ordinary (though complex) crystal phases at low temperatures, including a partially disordered B2-type phase. We discuss the influence of density and composition on QC phase stability; we compare the structural differences between Co-rich and Cu-rich quasicrystals; and we analyze the role of entropy in stabilizing the quasicrystal, concluding with a discussion of the possible existence of "high entropy" quasicrystals.
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- 2024
4. First principles evaluation of phase stability in the In-Sn binary system
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Widom, Michael
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Condensed Matter - Materials Science - Abstract
The In-Sn binary alloy system exhibits several unusual features that challenge crystallographic and thermodynamic expectations. We combine first principles total energy calculation with simple thermodynamic modeling to address two key points. First, we evaluate energies along the Bain path to interpret the discontinuous transition between the phases $\alpha$-In (Pearson type tI2) and $\beta$--In$_3$Sn (also Pearson type tI2) that are identical in symmetry. Second, we demonstrate that the solid solution phases $\beta$-In$_3$Sn and $\gamma$-InSn$_4$ (Pearson type hP1) exist at high temperatures only, and they exhibit eutectoid decompositions at low temperatures.
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- 2024
5. Entropy approximations for simple fluids
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Huang, Yang and Widom, Michael
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Condensed Matter - Statistical Mechanics - Abstract
Liquid state entropy formulas based on configurational probability distributions are examined for Lennard-Jones fluids across a range temperatures and densities. These formulas are based on expansions of the entropy in series of $n$-body distribution functions. We focus on two special cases. One, which we term the ``perfect gas'' series, starts with the entropy of an ideal gas; the other, which we term the ``dense liquid series'' removes a many-body contribution from the ideal gas entropy and reallocates it among the subsequent $n$-body terms. We show that the perfect gas series is most accurate at low density, while the dense liquid series is most accurate at high density. We propose empirical interpolation methods that are capable of connecting the two series and giving consistent predictions in most situations.
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- 2023
6. Integrated Design of Aluminum-Containing High-entropy Refractory B2 Alloys with Synergy of High Strength and Ductility
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Qi, Jie, Fan, Xuesong, Hoyos, Diego Ibarra, Widom, Michael, Liaw, Peter K., and Poon, Joseph
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Condensed Matter - Materials Science ,Condensed Matter - Disordered Systems and Neural Networks - Abstract
Refractory high-entropy alloys, RHEAs, are promising high-temperature structural materials. Their large compositional space poses great design challenges for phase control and high strength-ductility synergy. The present research pioneers using integrated high-throughput machine learning with Monte Carlo simulations to effectively navigate phase-selection and mechanical-properties predictions, developing aluminum-containing RHEAs in single-phase ordered B2 alloys demonstrating both high strength and ductility. These aluminum-containing RHEAs achieve remarkable mechanical properties, including compressive yield strengths up to 1.6 GPa, fracture strains exceeding 50 percent, and significant high-temperature strength retention. They also demonstrate a tensile yield strength of 1.1 GPa with a tension ductility of 6.3 percent. Besides, we identify a valence-electron-count domain for alloy brittleness with the explanation from density-functional theory and provide crucial insights into elements' influence on atomic ordering and mechanical performance. The work sets forth a strategic blueprint for high-throughput alloy design and reveals fundamental principles that govern the mechanical properties of advanced structural alloys.
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- 2023
7. Ab-initio tensile tests applied to BCC refractory alloys
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Raghuraman, Vishnu, San, Saro, Gao, Michael C., and Widom, Michael
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Condensed Matter - Materials Science - Abstract
Refractory metals exhibit high strength at high temperature, but often lack ductility. Multiprinciple element alloys such as high entropy alloys offer the potential to improve ductility while maintaining strength, but we don't know $a-priori$ what compositions will be suitable. A number of measures have been proposed to predict the ductility of metals, notably the Pugh ratio, the Rice-Thomson D-parameter, among others. Here we examine direct $ab-initio$ simulation of deformation under tensile strain, and we apply this to a variety of Nb- and Mo-based binary alloys and to several quaternary alloy systems. Our results exhibit peak stresses for elastic deformation, beyond which defects such as lattice slip, stacking faults, transformation, and twinning, relieve the stress. The peak stress grows strongly with increasing valence electron count. Correlations are examined among several physical properties, including the above-mentioned ductility parameters., Comment: 22 pages, 13 figures, accepted for publication in Physical Review Materials
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- 2023
8. First principles residual resistivity using locally self-consistent multiple scattering method
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Raghuraman, Vishnu, Eisenbach, Markus, Widom, Michael, and Wang, Yang
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Condensed Matter - Materials Science - Abstract
The locally self-consistent multiple scattering (LSMS) method can perform efficient first-principles calculations of systems with large number of atoms. In this work, we combine the Kubo-Greenwood equation with LSMS, enabling us to calculate first-principles residual resistivity of large systems. This has been implemented in the open-source code lsms. We apply this method to selected pure elements and binary random alloys. The results compare well with experiment, and with values obtained from a first-principles effective medium technique (KKR-CPA). We discuss future applications of this method to complex systems where other methods are not applicable., Comment: 16 pages, 5 figures
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- 2023
9. Quasicrystal structure prediction: A review
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Widom, Michael and Mihalkovic, Marek
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Condensed Matter - Materials Science - Abstract
Predicting quasicrystal structures is a multifaceted problem that can involve predicting a previously unknown phase, predicting the structure of an experimentally observed phase, or predicting the thermodynamic stability of a given structure. We survey the history and current state of these prediction efforts with a focus on methods that have improved our understanding of the structure and stability of known metallic quasicrystal phases. Advances in the structural modeling of quasicrystals, along with first principles total energy calculation and statistical mechanical methods that enable the calculation of quasicrystal thermodynamic stability, are illustrated by means of cited examples of recent work.
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- 2023
10. Comprehensive analysis of ordering in CoCrNi and CrNi2 alloys
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Vinícius P. Bacurau, Pedro A. F. P. Moreira, Gustavo Bertoli, Angelo F. Andreoli, Eric Mazzer, Flávio F. de Assis, Piter Gargarella, Guilherme Koga, Guilherme C. Stumpf, Santiago J. A. Figueroa, Michael Widom, Michael Kaufman, Andrea Fantin, Yifan Cao, Rodrigo Freitas, Daniel Miracle, and Francisco G. Coury
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Science - Abstract
Abstract Chemical Short-Range Order (CSRO) has attracted recent attention from many researchers, creating intense debates about its impact on material properties. The challenges lie in confirming and quantifying CSRO, as its detection proves exceptionally demanding, contributing to conflicting data in the literature regarding its true effects on mechanical properties. Our work uses high-precision calorimetric data to unambiguously prove the existence and, coupled with atomistic simulations, quantify the type of CSRO. This methodology allows us to propose a mechanism for its formation and destruction based on the heat evolution during thermal analysis and facilitates a precise identification of local ordering in CoCrNi alloys. Samples of CoCrNi (Co33Cr33Ni33) and CrNi2 (Cr33Ni66) alloys are fabricated in varying ordered states, extensively characterized via synchrotron X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy. Samples with considerably different ordered states are submitted to tensile tests with in-situ synchrotron X-ray diffraction. We demonstrate, despite inducing varied CSRO levels in CoCrNi, no significant alterations in overall mechanical behavior emerge. However, the CrNi2 alloy, which undergoes long-range ordering, experiences significant shifts in yield strength, ultimate tensile stress and ductility.
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- 2024
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11. Comprehensive analysis of ordering in CoCrNi and CrNi2 alloys
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Bacurau, Vinícius P., Moreira, Pedro A. F. P., Bertoli, Gustavo, Andreoli, Angelo F., Mazzer, Eric, de Assis, Flávio F., Gargarella, Piter, Koga, Guilherme, Stumpf, Guilherme C., Figueroa, Santiago J. A., Widom, Michael, Kaufman, Michael, Fantin, Andrea, Cao, Yifan, Freitas, Rodrigo, Miracle, Daniel, and Coury, Francisco G.
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- 2024
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12. Formation enthalpies of Al-Mn-Pd and the structure of the $i$-AlMnPd quasicrystal
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Mihalkovic, Marek and Widom, Michael
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Condensed Matter - Materials Science - Abstract
This paper reports formation enthalpies of phases in the Al-Mn-Pd ternary alloy system as calculated from first principles using electronic density functional theory. We consider all crystal structures as reported in the assessed phase diagrams of the ternary and its binary alloy subsystems (Al-Mn, Al-Pd, and Mn-Pd), as well as additional reported or hypothetical structures. Icosahedral and decagonal quasicrystalline approximants are among the structures that we predict to be stable, or nearly so. Our results suggest the need for careful experimental reexamination of phase stability in each of the alloy systems, in tandem with further efforts to refine crystallographic and ab-initio structures.
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- 2023
13. Interaction models and configurational entropies of binary MoTa and the MoNbTaW high entropy alloy
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Kim, Andrew D. and Widom, Michael
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Condensed Matter - Materials Science - Abstract
We introduce a simplified method to model the interatomic interactions of high entropy alloys based on a lookup table of cluster energies. These interactions are employed in replica exchange Monte Carlo simulations with histogram analysis to obtain thermodynamic properties across a broad temperature range. Kikuchi's Cluster Variation Method entropy formalism and high temperature series expansions are applied to directly calculate entropy from statistics on short- and long-range chemical order, and we discuss the convergence of the entropy as clusters of differing size are included.
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- 2022
14. Childhood Maltreatment and Biological Aging in Middle Adulthood: The Role of Psychiatric Symptoms
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Cathy Spatz Widom, Hang (Heather) Do, Quincy C. Miller, Magda Javakhishvili, Claire Eckstein Indik, and Daniel W. Belsky
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Anxiety ,Biological aging ,Childhood maltreatment ,Longitudinal ,Posttraumatic stress disorder ,Psychiatric disorders ,Psychiatry ,RC435-571 - Abstract
Background: Childhood maltreatment and psychiatric morbidity have each been associated with accelerated biological aging primarily through cross-sectional studies. Using data from a prospective longitudinal study of individuals with histories of childhood maltreatment and control participants followed into midlife, we tested 2 hypotheses examining whether 1) psychiatric symptoms mediate the relationship between childhood maltreatment and biological aging and 2) psychiatric symptoms of anxiety, depression, or posttraumatic stress disorder (PTSD) act in conjunction with childhood maltreatment to exacerbate the association of child maltreatment to aging. Methods: Children (ages 0–11 years) with documented histories of maltreatment and demographically matched control children were followed into adulthood (N = 607) and interviewed over several waves of the study. Depression, anxiety, and PTSD symptoms were assessed at mean ages of 29 (interview 1) and 40 (interview 2) years. Biological age was measured from blood chemistries collected later (mean age = 41 years) using the Klemera-Doubal method. Hypotheses were tested using linear regressions and path analyses. Results: Adults with documented histories of childhood maltreatment showed more symptoms of depression, PTSD, and anxiety at both interviews and more advanced biological aging, compared with control participants. PTSD symptoms at both interviews and depression and anxiety symptoms only at interview 2 predicted accelerated biological aging. There was no evidence of mediation; however, anxiety and depression moderated the relationship between childhood maltreatment and biological aging. Conclusions: These new findings reveal the shorter- and longer-term longitudinal impact of PTSD on biological aging and the amplifying effect of anxiety and depression on the relationship between child maltreatment and biological aging.
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- 2024
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15. Analysis of ab-initio total energies obtained by different DFT implementations
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Raghuraman, Vishnu, Wang, Yang, and Widom, Michael
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Condensed Matter - Materials Science - Abstract
Ab-initio crystal structure prediction depends on accurate calculation of the energies of competing structures. Many DFT codes are available that utilize different approaches to solve the Kohn-Sham equation. We evaluate the consistency of three software packages (WIEN2k, VASP and MuST) that utilize three different methods (FL-APW, plane-wave pseudopotential and the KKR-Green's Function methods) by comparing the relative total energies obtained for a set of BCC and FCC binary metallic alloys. We focus on the impact of choices such as muffin-tin $vs.$ full-potential, angular momentum cutoff and other important KKR parameters. Different alloy systems prove more or less sensitive to these choices, and we explain the differences through study of the angular variation of their potentials. Our results can provide guidance in the application of KKR as a total energy method for structure prediction., Comment: 18 pages, 9 figures
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- 2022
16. Vibrational entropy of crystalline solids from covariance of atomic displacements
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Huang, Yang and Widom, Michael
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Condensed Matter - Statistical Mechanics ,Condensed Matter - Materials Science - Abstract
The vibrational entropy of a solid at finite temperature is investigated from the perspective of information theory. Ab initio molecular dynamics (AIMD) simulations generate ensembles of atomic configurations at finite temperature from which we obtain the $N$-body distribution of atomic displacements, $\rho_N$. We calculate the information-theoretic entropy from the expectation value of $\ln{\rho_N}$. At a first level of approximation, treating individual atomic displacements independently, our method may be applied using Debye-Waller B-factors, allowing diffraction experiments to obtain an upper bound on the thermodynamic entropy. At the next level of approximation we correct the overestimation through inclusion of displacement covariances. We apply this approach to elemental body-centered cubic sodium and face-centered cubic aluminum, showing good agreement with experimental values above the Debye temperatures of the metals. Below the Debye temperatures we extract an effective vibrational density of states from eigenvalues of the covariance matrix, and then evaluate the entropy quantum mechanically, again yielding good agreement with experiment down to low temperatures. Our method readily generalizes to complex solids, as we demonstrate for a high entropy alloy. Further, our method applies in cases where the quasiharmonic approximation fails, as we demonstrate by calculating the HCP/BCC transition in Ti.
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- 2022
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17. Domain Walls in the Heisenberg-Ising Spin-1/2 Chain
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Saenz, Axel, Tracy, Craig A., and Widom, Harold
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Mathematics - Probability ,Mathematical Physics ,60K35 - Abstract
In this paper we obtain formulas for the distribution of the left-most up-spin in the Heisenberg-Ising spin-1/2 chain with anisotropy parameter $\Delta$, also known as the XXZ spin-1/2 chain, on the one-dimensional lattice $\mathbb{Z}$ with domain wall initial conditions. We use the Bethe Ansatz to solve the Schr$\"o$dinger equation and a recent antisymmetrization identity of Cantini, Colomo, and Pronko (arXiv:1906.07636) to simplify the marginal distribution of the left-most up-spin. In the $\Delta=0$ case, the distribution $F_2$ arises. In the $\Delta \neq 0$ case, we propose a conjectural series expansion type formula based on a saddle point analysis. The conjectural formula turns out to be a Fredholm series expansion in the $\Delta \rightarrow 0$ limit and recovers the result for $\Delta = 0$., Comment: 41 pages, 4 figures. Version 2 corrects a typo in notation for equation (98)
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- 2022
18. Nonlinear deformation and elasticity of BCC refractory metals and alloys
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Raghuraman, Vishnu, Widom, Michael, and Gao, Michael C.
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Condensed Matter - Materials Science - Abstract
Application of isotropic pressure or uniaxial strain alters the elastic properties of materials; sufficiently large strains can drive structural transformations. Linear elasticity describes stability against infinitesimal strains, while nonlinear elasticity describes the response to finite deformations. It was previously shown that uniaxial strain along [100] drives refractory metals and alloys towards mechanical instabilities. These include an extensional instability, and a symmetry-breaking orthorhombic distortion caused by a Jahn-Teller-Peierls instability that splays the cubic lattice vectors. Here, we analyze these transitions in depth. Eigenvalues and eigenvectors of the Wallace tensor identify and classify linear instabilities in the presence of strain. We show that both instabilities are discontinuous, leading to discrete jumps in the lattice parameters. We provide physical intuition for the instabilities by analyzing the changes in first principles energy, stress, bond lengths and angles upon application of strain. Electronic band structure calculations show differential occupation of bonding and anti-bonding orbitals, driven by the changing bond lengths and leading to the structural transformations. Strain thresholds for these instabilities depend on the valence electron count., Comment: 31 pages, 17 figures, 1 table, accepted to Physical Review Materials
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- 2022
19. Childhood Maltreatment and Biological Aging in Middle Adulthood: The Role of Psychiatric Symptoms
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Widom, Cathy Spatz, Do, Hang (Heather), Miller, Quincy C., Javakhishvili, Magda, Eckstein Indik, Claire, and Belsky, Daniel W.
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- 2024
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20. Quantity, size distribution, and sources of leaf-level particulate matter from a major steel plant in SW Ohio: Implications for the spatial footprint of an emitter
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Khodadadi, Maral, Widom, Elisabeth, and Krekeler, Mark
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- 2024
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21. Factors influencing adult cognitive appraisals of childhood sexual abuse
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Miller, Quincy C. and Widom, Cathy Spatz
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- 2024
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22. Formation enthalpies of Al–Mn–Pd and the structure of the i-AlMnPd quasicrystal
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Mihalkovič, Marek and Widom, Michael
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- 2023
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23. Simulated structure and thermodynamics of decagonal Al-Co-Cu quasicrystals
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Yang Huang, Michael Widom, and M. Mihalkovič
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Physics ,QC1-999 - Abstract
Atomic structures of Al-Co-Cu decagonal quasicrystals (dQCs) are investigated using empirical oscillating pair potentials (EOPP) in molecular dynamic (MD) simulations that we enhance by Monte Carlo (MC) swapping of chemical species and replica exchange. Predicted structures exhibit planar decagonal tiling patterns and are periodic along the perpendicular direction. We then recalculate the energies of promising structures using first-principles density functional theory (DFT), along with energies of competing phases. We find that our τ-inflated sequence of QC approximants (QCAs) are energetically unstable at low temperature by at least 3 meV/atom. Extending our study to finite temperatures by calculating harmonic vibrational entropy, as well as anharmonic contributions that include chemical species swaps and tile flips, our results suggest that the quasicrystal phase is entropically stabilized at temperatures in the range 600-800 K and above. It decomposes into ordinary (though complex) crystal phases at low temperatures, including a partially disordered B2-type phase. We discuss the influence of density and composition on QC phase stability; we compare the structural differences between Co-rich and Cu-rich quasicrystals; and we analyze the role of entropy in stabilizing the quasicrystal, concluding with a discussion of the possible existence of “high entropy” quasicrystals.
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- 2024
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24. An investigation of high entropy alloy conductivity using first-principles calculations
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Raghuraman, Vishnu, Wang, Yang, and Widom, Michael
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Condensed Matter - Materials Science - Abstract
The Kubo-Greenwood equation, in combination with the first-principles Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) can be used to calculate the DC residual resistivity of random alloys at T = 0 K. We implemented this method in a multiple scattering theory based ab initio package, MuST, and applied it to the ab initio study of the residual resistivity of the high entropy alloy Al$_x$CoCrFeNi as a function of $x$. The calculated resistivities are compared with experimental data. We also predict the residual resistivity of refractory high entropy alloy MoNbTaV$_x$W. The calculated resistivity trends are also explained using theoretical arguments., Comment: 18 pages, 9 figures (not including Supplementary Material). The article has been submitted to Applied Physics Letters
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- 2021
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25. From childhood maltreatment to intimate partner violence perpetration: A prospective longitudinal examination of the roles of executive functioning and self-esteem
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Díaz-Faes, Diego A. and Widom, Cathy Spatz
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- 2024
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26. Publisher Correction: Optimization of Parylene C and Parylene N thin films for use in cellular co-culture and tissue barrier models
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Gholizadeh, Shayan, Lincoln, Daniela M., Allahyari, Zahra, Widom, Louis P., Carter, Robert N., and Gaborski, Thomas R.
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- 2023
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27. Optimization of Parylene C and Parylene N thin films for use in cellular co-culture and tissue barrier models
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Gholizadeh, Shayan, Lincoln, Daniela M., Allahyari, Zahra, Widom, Louis P., Carter, Robert N., and Gaborski, Thomas R.
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- 2023
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28. How Atomic Bonding Plays the Hardness Behavior in the Al–Co–Cr–Cu–Fe–Ni High Entropy Family
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Andrea Fantin, Giovanni O. Lepore, Michael Widom, Sergey Kasatikov, and Anna M. Manzoni
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hardness ,high entropy alloys ,local lattice distortions ,Monte Carlo molecular dynamics ,short-range order ,Materials of engineering and construction. Mechanics of materials ,TA401-492 - Abstract
A systematic study on a face‐centered cubic‐based compositionally complex alloy system Al–Co–Cr–Cu–Fe–Ni in its single‐phase state is carried out, where a mother senary compound Al8Co17Cr17Cu8Fe17Ni33 and five of its suballoys, obtained by removing one element at a time, are investigated and exhaustively analyzed determining the contribution of each alloying element in the solid solution. The senary and the quinaries are compared using experimental techniques including X‐ray absorption spectroscopy, X‐ray diffraction, transmission electron microscopy, and first principles hybrid Monte Carlo/molecular dynamics simulations. Chemical short‐range order and bond length distances have been determined both at the experimental and computational level. Electronic structure and local atomic distortions up to 5.2 Å have been correlated to the microhardness values. A linear regression model connecting hardness with local lattice distortions is presented.
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- 2024
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29. The impact of chemical short-range order on the thermophysical properties of medium- and high-entropy alloys
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Angelo F. Andreoli, Andrea Fantin, Sergey Kasatikov, Vinícius P. Bacurau, Michael Widom, Piter Gargarella, Eric M. Mazzer, Thomas G. Woodcock, Kornelius Nielsch, and Francisco G. Coury
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High-entropy alloys ,Chemical short-range order ,Dilatometry ,Differential scanning calorimetry ,Order-disorder effects ,Materials of engineering and construction. Mechanics of materials ,TA401-492 - Abstract
The unusual behavior observed in the coefficient of thermal expansion and specific heat capacity of CrFeNi, CoCrNi, and CoCrFeNi medium/high-entropy alloys is commonly referred to as the K-state effect. It is shown to be independent of the Curie temperature, as demonstrated by temperature-dependent magnetic moment measurements. CoCrFeNi alloy is chosen for detailed characterization; potential reasons for the K-state effect such as texture, recrystallization, and second-phase precipitation are ruled out. An examination of the electronic structure indicates the formation of a pseudo-gap in the Density of States, which suggests a specific chemical interaction between Ni and Cr atoms upon alloying. Hybrid Monte Carlo/Molecular Dynamic (MC/MD) simulations indicate the presence of non-negligible chemical short-range order (CSRO). Local lattice distortions are shown to be negligible, although deviations around Cr and Ni elements from those expected in a fully disordered structure are experimentally observed by X-ray absorption spectroscopy. The determined bonding distances are in good agreement with MC/MD calculations. A mechanism is proposed to explain the anomalies and calorimetric experiments and their results are used to validate the mechanism.
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- 2024
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30. Ab-initio free energies of liquid metal alloys: application to the phase diagrams of Li-Na and K-Na
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Huang, Yang, Widom, Michael, and Gao, Michael C.
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Condensed Matter - Materials Science ,Condensed Matter - Statistical Mechanics - Abstract
Comparison of free energies between different phases and different compositions underlies the prediction of alloy phase diagrams. To allow direct comparison, consistent reference points for the energies or enthalpies are required, and the entropy must be placed on an absolute scale, yielding absolute free energies. Here we derive absolute free energies of liquids from ab-initio molecular dynamics (AIMD) by combining the directly simulated enthalpies with an entropy derived from simulated densities and pair correlation functions. As an example of the power of this method we calculate the phase diagrams of two binary alkali metal alloys, Li-Na and K-Na, revealing a critical point and liquid-liquid phase separation in the former case, and a deep eutectic in the latter. Good agreement with experimental data demonstrates the power of this simple method.
- Published
- 2021
31. The impact of chemical short-range order on the thermophysical properties of medium- and high-entropy alloys
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Andreoli, Angelo F., Fantin, Andrea, Kasatikov, Sergey, Bacurau, Vinícius P., Widom, Michael, Gargarella, Piter, Mazzer, Eric M., Woodcock, Thomas G., Nielsch, Kornelius, and Coury, Francisco G.
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- 2024
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32. PMS2CL interference leading to erroneous identification of a pathogenic PMS2 variant in Black patients
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Jacqueline Cappadocia, Lisa B. Aiello, Michael J. Kelley, Bryson W. Katona, Kara N. Maxwell, Anurag Verma, Ph.D., Shefali S. Verma, Ph.D., Yuki Bradford, M.S., Ashlei Brock, Stephanie DerOhannessian, Scott Dudek, M.S., Joseph Dunn, Theodore Drivas, M.D., Ph.D., Ned Haubein, Khadijah Hu-Sain, Renae Judy, Ashley Kloter, Yi-An Ko, Meghan Livingstone, Linda Morrel, Colleen Morse, M.S., Afiya Poindexter, Marjorie Risman, M.S., Teo Tran, Fred Vadivieso, JoEllen Weaver, Daniel J. Rader, M.D., Marylyn D. Ritchie, Ph.D., Michael D. Feldman, M.D., Ph.D., Christina Beechert, Caitlin Forsythe, M.S., Erin D. Fuller, Zhenhua Gu, M.S., Michael Lattari, Alexander Lopez, M.S., John D. Overton, Ph.D., Maria Sotiropoulos Padilla, M.S., Manasi Pradhan, M.S., Kia Manoochehri, B.S., Thomas D. Schleicher, M.S., Louis Widom, Sarah E. Wolf, M.S., Ricardo H. Ulloa, B.S., Amelia Averitt, Ph.D., Nilanjana Banerjee, Ph.D., Michael Cantor, M.D., Dadong Li, Ph.D., Sameer Malhotra, M.D., Deepika Sharma, MHI, Jeffrey Staples, Ph.D., Xiaodong Bai, Ph.D., Suganthi Balasubramanian, Ph.D., Suying Bao, Ph.D., Boris Boutkov, Ph.D., Siying Chen, Ph.D., Gisu Eom, B.S., Lukas Habegger, Ph.D., Alicia Hawes, B.S., Shareef Khalid, Olga Krasheninina, M.S., Rouel Lanche, B.S., Adam J. Mansfield, B.A., Evan K. Maxwell, Ph.D., George Mitra, B.A., Mona Nafde, M.S., Sean O’Keeffe, Ph.D., Max Orelus, B.B.A., Razvan Panea, Ph.D., Tommy Polanco, B.A., Ayesha Rasool, M.S., Jeffrey G. Reid, Ph.D., William Salerno, Ph.D., Jeffrey C. Staples, Ph.D., Kathie Sun, Ph.D., Goncalo Abecasis, D.Phil., Joshua Backman, Ph.D., Amy Damask, Ph.D., Lee Dobbyn, Ph.D., Manuel Allen Revez Ferreira, Ph.D., Arkopravo Ghosh, M.S., Christopher Gillies, Ph.D., Lauren Gurski, B.S., Eric Jorgenson, Ph.D., Hyun Min Kang, Ph.D., Michael Kessler, Ph.D., Jack Kosmicki, Ph.D., Alexander Li, Ph.D., Nan Lin, Ph.D., Daren Liu, M.S., Adam Locke, Ph.D., Jonathan Marchini, Ph.D., Anthony Marcketta, M.S., Joelle Mbatchou, Ph.D., Arden Moscati, Ph.D., Charles Paulding, Ph.D., Carlo Sidore, Ph.D., Eli Stahl, Ph.D., Kyoko Watanabe, Ph.D., Bin Ye, Ph.D., Blair Zhang, Ph.D., Andrey Ziyatdinov, Ph.D., Ariane Ayer, B.S., Aysegul Guvenek, Ph.D., George Hindy, Ph.D., Giovanni Coppola, M.D., Jan Freudenberg, M.D., Jonas Bovijn, M.D., Katherine Siminovitch, M.D., Kavita Praveen, Ph.D., Luca A. Lotta, M.D., Manav Kapoor, Ph.D., Mary Haas, Ph.D., Moeen Riaz, Ph.D., Niek Verweij, Ph.D., Olukayode Sosina, Ph.D., Parsa Akbari, Ph.D., Priyanka Nakka, Ph.D., Sahar Gelfman, Ph.D., Sujit Gokhale, B.E., Tanima De, Ph.D., Veera Rajagopal, Ph.D., Alan Shuldiner, M.D., Gannie Tzoneva, Ph.D., Juan Rodriguez-Flores, Ph.D., Esteban Chen, M.S., Marcus B. Jones, Ph.D., Michelle G. LeBlanc, Ph.D., Jason Mighty, Ph.D., Lyndon J. Mitnaul, Ph.D., Nirupama Nishtala, Ph.D., Nadia Rana, Ph.D., Jaimee Hernandez, Goncalo Abecasis, PhD, Aris Baras, M.D., Andrew Deubler, Aris Economides, Ph.D., and Luca A. Lotta, M.D., Ph.D.
- Subjects
PMS2 ,germline genetic testing ,Lynch syndrome ,PMS2CL ,pseudogene interference ,Genetics ,QH426-470 ,Medicine - Abstract
This study investigates the frequency of a clinically reported variant in PMS2, NM_000535.7:c.2523G>A p.(W841∗), from next-generation sequencing studies in 2 racially diverse cohorts. We identified clinical reports of the PMS2 c.2523G>A p.(W841∗) variant in the National Precision Oncology Program’s somatic testing database (n = 25,168). We determined frequency of the variant in germline exome sequencing from the Penn Medicine BioBank (n = 44,256) and in gnomAD. The PMS2 c.2523G>A p.(W841∗) was identified as a homozygous variant on tumor testing in an adult patient of self-identified Black race/ethnicity with no evidence of constitutional mismatch repair deficiency. The variant was clinically reported on 35 total tumor and liquid biopsy tests (0.1%), and all individuals with the variant were of self-identified Black race/ethnicity (0.6% of n = 5787). In individuals of African genetic ancestry (AFR), the variant's germline frequency was reported to be 0.2% and 1.3% in the Penn Medicine BioBank (PMBB) and gnomAD, respectively. The variant cannot be found in any individuals of European genetic ancestry (EUR) from either of the databases. The variant is found in a region of PMS2 with 100% homology to the PMS2CL pseudogene. PMS2 c.2523G>A p.(W841∗), when identified, is typically an African-ancestry-specific PMS2CL pseudogene variant, which should be recognized to prevent misdiagnosis of Lynch syndrome in Blacks.
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- 2024
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33. Edge Dislocations Can Control Yield Strength in Refractory Body-Centered-Cubic High Entropy Alloys
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Maresca, Francesco, Lee, Chanho, Feng, Rui, Chou, Yi, Ungar, Tamas, Widom, Michael, An, Ke, Poplawsky, John, Chou, Yi-Chia, Liaw, Peter, and Curtin, William
- Subjects
Condensed Matter - Materials Science - Abstract
Energy efficiency is motivating the search for new high-temperature metals. Some new body-centered-cubic random multicomponent "high entropy alloys (HEAs)" based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional strengths at high temperatures but the physical origins of this outstanding behavior are not known. Here we show, using integrated neutron-diffraction (ND), high-resolution transmission electron microscopy (HRTEM), and theory, that the high strength and strength retention of a NbTaVTi alloy and a new high-strength/low-density CrMoNbV alloy are attributable to edge dislocations. This is surprising because plastic-flow in BCC elemental metals and dilute alloys is universally accepted to be controlled by screw dislocations. We use the insight and theory to perform a computationally-guided search over $10^7$ BCC HEAs and identify over $10^6$ possible ultra-strong high-temperature alloy compositions for future exploration.
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- 2020
34. Cluster variation method analysis of correlations and entropy in BCC solid solutions
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Hoffman, Nathaniel and Widom, Michael
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Condensed Matter - Materials Science - Abstract
Solid solutions occur when multiple chemical species share sites of a common crystal lattice. Although the single site occupation is random, chemical interaction preferences bias the occupation probabilities of neighboring sites, and this bias reduced the entropy of mixing below its ideal value. Sufficiently strong bias leads to symmetry-breaking phase transitions. We apply the cluster variation method to explore solid solutions on body centered cubic lattices in the context of two specific compounds that exhibit opposite ordering trends. Employing density functional theory to model the energetics, we show that CuZn exhibits an order-disorder transition to the CsCl prototype structure, while AlLi instead takes the NaTl prototype structure, and we evaluate their temperature-dependent order parameters, correlations and entropies., Comment: 13 pages, 8 figures
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- 2020
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35. An averaged cluster approach to including chemical short range order in KKR-CPA
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Raghuraman, Vishnu, Wang, Yang, and Widom, Michael
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Condensed Matter - Materials Science - Abstract
The single-site Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) ignores short range ordering present in disordered metallic systems. In this paper, we establish a new technique to fix this shortcoming by embedding an averaged cluster that displays chemical short range order (SRO). The degree of SRO can be tuned by externally defined order parameters. This averaged cluster can be embedded in the single site CPA medium, or a self-consistently obtained effective medium that contains SRO information. The validity of this method is demonstrated by applying it to two alloy systems - the CuZn body centered cubic (BCC) solid solution, and AlCrTiV, a four-element BCC high entropy alloy. A comparison between the non-self-consistent and self-consistent modes is also provided for the two above mentioned systems. We make the code available on the internet. Planned extensions to this work are discussed., Comment: 9 pages, 7 figures; minor revisions based on reviewer comments; added a section on self-consistent CA-CPA
- Published
- 2020
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36. Deciphering the sources and processes feeding young monogenetic volcanoes from the Michoacán Guanajuato Volcanic Field (Mexico): A study case of El Astillero and El Pedregal
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Larrea, Patricia, Widom, Elisabeth, Siebe, Claus, Salinas, Sergio, and Kuentz, Dave
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- 2023
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37. Optimization of Parylene C and Parylene N thin films for use in cellular co-culture and tissue barrier models
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Shayan Gholizadeh, Daniela M. Lincoln, Zahra Allahyari, Louis P. Widom, Robert N. Carter, and Thomas R. Gaborski
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Medicine ,Science - Abstract
Abstract Parylene has been used widely used as a coating on medical devices. It has also been used to fabricate thin films and porous membranes upon which to grow cells. Porous membranes are integral components of in vitro tissue barrier and co-culture models, and their interaction with cells and tissues affects the performance and physiological relevance of these model systems. Parylene C and Parylene N are two biocompatible Parylene variants with potential for use in these models, but their effect on cellular behavior is not as well understood as more commonly used cell culture substrates, such as tissue culture treated polystyrene and glass. Here, we use a simple approach for benchtop oxygen plasma treatment and investigate the changes in cell spreading and extracellular matrix deposition as well as the physical and chemical changes in material surface properties. Our results support and build on previous findings of positive effects of plasma treatment on Parylene biocompatibility while showing a more pronounced improvement for Parylene C compared to Parylene N. We measured relatively minor changes in surface roughness following plasma treatments, but significant changes in oxygen concentration at the surface persisted for 7 days and was likely the dominant factor in improving cellular behavior. Overall, this study offers facile and relatively low-cost plasma treatment protocols that provide persistent improvements in cell-substrate interactions on Parylene that match and exceed tissue culture polystyrene.
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- 2023
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38. Spontaneous formation of thermodynamically stable Al--Cu--Fe icosahedral quasicrystal from realistic atomistic simulations
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Mihalkovic, Marek and Widom, Michael
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Condensed Matter - Materials Science - Abstract
Icosahedral quasicrystals spontaneously form from the melt in simulations of Al--Cu--Fe alloys. We model the interatomic interactions using oscillating pair potentials tuned to the specific alloy system based on a database of density functional theory (DFT)-derived energies and forces. Favored interatomic separations align with the geometry of icosahedral motifs that overlap to create face-centered icosahedral order on a hierarchy of length scales. Molecular dynamics simulations, supplemented with Monte Carlo steps to swap chemical species, efficiently sample the configuration space of our models, which reach up to 9846 atoms. Exchanging temperatures of independent trajectories (replica exchange) allows us to achieve thermal equilibrium at low temperatures. By optimizing structure and composition we create structures whose DFT energies reach to within $\sim$2 meV/atom of the energies of competing crystal phases. Free energies obtained by adding contributions due to harmonic and anharmonic vibrations, chemical substitution disorder, phasons, and electronic excitations, show that the quasicrystal becomes stable against competing phases at temperatures above 600K. The average structure can be described succinctly as a cut through atomic surfaces in six-dimensional space that reveal specific patterns of preferred chemical occupancy. Atomic surface regions of mixed chemical occupation demonstrate the proliferation of phason fluctuations, which can be observed in real space through the formation, dissolution and reformation of large scale icosahedral motifs -- a picture that is hidden from diffraction refinements due to averaging over the disorder and consequent loss of information concerning occupancy correlations.
- Published
- 2019
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39. Formation of Graphene atop a Si adlayer on the C-face of SiC
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Li, Jun, Wang, Qingxiao, He, Guowei, Widom, Michael, Nemec, Lydia, Blum, Volker, Kim, Moon, Rinke, Patrick, and Feenstra, Randall M.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
The structure of the SiC(000-1) surface, the C-face of the {0001} SiC surfaces, is studied as a function of temperature and of pressure in a gaseous environment of disilane (Si2H6). Various surface reconstructions are observed, both with and without the presence of an overlying graphene layer (which spontaneously forms at sufficiently high temperatures). Based on cross-sectional scanning transmission electron microscopy measurements, the interface structure that forms in the presence of the graphene is found to contain 1.4 - 1.7 monolayers (ML) of Si, a somewhat counter-intuitive result since, when the graphene forms, the system is actually under C-rich conditions. Using ab initio thermodynamics, it is demonstrated that there exists a class of Si-rich surfaces containing about 1.3 ML of Si that are stable on the surface (even under C-rich conditions) at temperatures above about 400 K. The structures that thus form consist of Si adatoms atop a Si adlayer on the C-face of SiC, with or without the presence of overlying graphene., Comment: 19 pages with 8 figures, along with 6 pages of Supplemental Material; v2 adds refs. 56,59-62 all being prior work, along with several paragraphs in the Discussion or Summary sections of the manuscript discussing this prior work; v3 corrects several typographical errors
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- 2019
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40. First Principles Study of Electronic Structure and Fermi Surface in Rare-earth Filled Skutterudites RPt4Ge12
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Pascut, Gheorghe Lucian, Widom, Michael, Haule, Kristjan, and Quader, Khandker F.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Other Condensed Matter - Abstract
Experiments on rare-earth filled skutterudites demonstrate an intriguing array of thermodynamic, transport and superconducting properties, and bring to fore theoretical challenges posed by f-electron systems. First principle calculations based density functional theory and its extensions for strongly correlated systems such as the Hubbard U correction, provide valuable information about electronic structure that can be used to understand experiments. We present a comprehensive study of the electronic structure and Fermi surface of a series of rare earth filled skutterudites, RPt4Ge12 (where R = La, Ce, Pr), aimed at shedding light on: consequences of progressive increase of f-orbital occupancy in the series; the effects of the Hubbard parameter U; the Fermi surfaces, band structures and densities of states. The calculated Fermi surfaces may be relevant to the question of multi-band versus single-band superconductivity. Computed densities of states qualitatively explain the available resonant photoemission spectroscopy experiments, and (together with available specific heat measurements) provide estimates of the effective masses. We also show the existence of pseudogaps in the total density of states which may be relevant for the thermoelectric properties of these systems., Comment: 17 pages, 11 figures
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- 2019
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41. Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe$_2$
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Lüpke, Felix, Waters, Dacen, de la Barrera, Sergio C., Widom, Michael, Mandrus, David G., Yan, Jiaqiang, Feenstra, Randall M., and Hunt, Benjamin M.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
The quantum spin Hall (QSH) state was recently demonstrated in monolayers of the transition metal dichalcogenide 1T'-WTe$_2$ and is characterized by a band gap in the two-dimensional (2D) interior and helical one-dimensional (1D) edge states. Inducing superconductivity in the helical edge states would result in a 1D topological superconductor, a highly sought-after state of matter. In the present study, we use a novel dry-transfer flip technique to place atomically-thin layers of WTe$_2$ on a van der Waals superconductor, NbSe$_2$. Using scanning tunneling microscopy and spectroscopy (STM/STS), we demonstrate atomically clean surfaces and interfaces and the presence of a proximity-induced superconducting gap in the WTe$_2$ for thicknesses from a monolayer up to 7 crystalline layers. At the edge of the WTe$_2$ monolayer, we show that the superconducting gap coexists with the characteristic spectroscopic signature of the QSH edge state. Taken together, these observations provide conclusive evidence for proximity-induced superconductivity in the QSH edge state in WTe$_2$, a crucial step towards realizing 1D topological superconductivity and Majorana bound states in this van der Waals material platform.
- Published
- 2019
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42. Disentangling contact and ensemble epistasis in a riboswitch
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Wonderlick, Daria R., Widom, Julia R., and Harms, Michael J.
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- 2023
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43. Dynamics of zero-point energy and two-slit phenomena for photons
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Widom, A., Swain, J., Srivastava, Y. N., Blasone, M., and Vitiello, G.
- Subjects
Quantum Physics - Abstract
An earlier forward and backward in time formalism developed by us to discuss non-relativistic electron diffraction is generalized to the relativistic case and here applied to photons. We show how naturally the zero-point energy emerges in the Planck black-body spectrum once symmetric in time motion - inherent in the Maxwell equations - is invoked for photons. Then, a detailed study is made of two-slit experiments for photons and some novel phenomena, amenable to experiments, are proposed, that arise due to the spin of the photon., Comment: 10 pages. arXiv admin note: text overlap with arXiv:1510.06272
- Published
- 2018
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44. Domain Walls in the Heisenberg-Ising Spin- Chain
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Saenz, Axel, Tracy, Craig A., Widom, Harold, Gohberg, Israel, Founding Editor, Ball, Joseph A., Series Editor, Böttcher, Albrecht, Series Editor, Dym, Harry, Series Editor, Langer, Heinz, Series Editor, Tretter, Christiane, Series Editor, Basor, Estelle, editor, Ehrhardt, Torsten, editor, and Tracy, Craig A., editor
- Published
- 2022
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45. Longterm Consequences of Childhood Maltreatment
- Author
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Widom, Cathy Spatz, Korbin, Jill E., Series Editor, and Krugman, Richard D., Series Editor
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- 2022
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46. “PMS2CL interference leading to erroneous identification of a pathogenic PMS2 variant in Black Patients”
- Author
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Cappadocia, Jacqueline, primary, Aiello, Lisa B., additional, Kelley, Michael J., additional, Katona, Bryson W., additional, Maxwell, Kara N., additional, Verma, Anurag, additional, Verma, Shefali S., additional, Bradford, Yuki, additional, Brock, Ashlei, additional, DerOhannessian, Stephanie, additional, Dudek, Scott, additional, Dunn, Joseph, additional, Drivas, Theodore, additional, Haubein, Ned, additional, Hu-Sain, Khadijah, additional, Judy, Renae, additional, Kloter, Ashley, additional, Ko, Yi-An, additional, Livingstone, Meghan, additional, Morrel, Linda, additional, Morse, Colleen, additional, Poindexter, Afiya, additional, Risman, Marjorie, additional, Tran, Teo, additional, Vadivieso, Fred, additional, Weaver, JoEllen, additional, Rader, Daniel J., additional, Ritchie, Marylyn D., additional, Feldman, Michael D., additional, Beechert, Christina, additional, Forsythe, Caitlin, additional, Fuller, Erin D., additional, Gu, Zhenhua, additional, Lattari, Michael, additional, Lopez, Alexander, additional, Overton, John D., additional, Padilla, Maria Sotiropoulos, additional, Pradhan, Manasi, additional, Manoochehri, Kia, additional, Schleicher, Thomas D., additional, Widom, Louis, additional, Wolf, Sarah E., additional, Ulloa, Ricardo H., additional, Averitt, Amelia, additional, Banerjee, Nilanjana, additional, Cantor, Michael, additional, Li, Dadong, additional, Malhotra, Sameer, additional, Sharma, Deepika, additional, Staples, Jeffrey, additional, Bai, Xiaodong, additional, Balasubramanian, Suganthi, additional, Bao, Suying, additional, Boutkov, Boris, additional, Chen, Siying, additional, Eom, Gisu, additional, Habegger, Lukas, additional, Hawes, Alicia, additional, Khalid, Shareef, additional, Krasheninina, Olga, additional, Lanche, Rouel, additional, Mansfield, Adam J., additional, Maxwell, Evan K., additional, Mitra, George, additional, Nafde, Mona, additional, O’Keeffe, Sean, additional, Panea, Razvan, additional, Polanco, Tommy, additional, Rasool, Ayesha, additional, Reid, Jeffrey G., additional, Salerno, William, additional, Staples, Jeffrey C., additional, Sun, Kathie, additional, Abecasis, Goncalo, additional, Backman, Joshua, additional, Damask, Amy, additional, Dobbyn, Lee, additional, Revez Ferreira, Manuel Allen, additional, Ghosh, Arkopravo, additional, Gillies, Christopher, additional, Gurski, Lauren, additional, Jorgenson, Eric, additional, Kang, Hyun Min, additional, Kessler, Michael, additional, Kosmicki, Jack, additional, Li, Alexander, additional, Lin, Nan, additional, Liu, Daren, additional, Locke, Adam, additional, Marchini, Jonathan, additional, Marcketta, Anthony, additional, Mbatchou, Joelle, additional, Moscati, Arden, additional, Paulding, Charles, additional, Sidore, Carlo, additional, Stahl, Eli, additional, Watanabe, Kyoko, additional, Ye, Bin, additional, Zhang, Blair, additional, Ziyatdinov, Andrey, additional, Ayer, Ariane, additional, Guvenek, Aysegul, additional, Hindy, George, additional, Coppola, Giovanni, additional, Freudenberg, Jan, additional, Bovijn, Jonas, additional, Siminovitch, Katherine, additional, Praveen, Kavita, additional, Lotta, Luca A., additional, Kapoor, Manav, additional, Haas, Mary, additional, Riaz, Moeen, additional, Verweij, Niek, additional, Sosina, Olukayode, additional, Akbari, Parsa, additional, Nakka, Priyanka, additional, Gelfman, Sahar, additional, Gokhale, Sujit, additional, De, Tanima, additional, Rajagopal, Veera, additional, Shuldiner, Alan, additional, Tzoneva, Gannie, additional, Rodriguez-Flores, Juan, additional, Chen, Esteban, additional, Jones, Marcus B., additional, LeBlanc, Michelle G., additional, Mighty, Jason, additional, Mitnaul, Lyndon J., additional, Nishtala, Nirupama, additional, Rana, Nadia, additional, Hernandez, Jaimee, additional, Baras, Aris, additional, Deubler, Andrew, additional, and Economides, Aris, additional
- Published
- 2024
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47. Band Structure Theory of the BCC to HCP Burgers Distortion
- Author
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Feng, Bojun and Widom, Michael
- Subjects
Condensed Matter - Materials Science - Abstract
The Burgers distortion is a two-stage transition between body centered cubic (BCC) and hexagonal close-packed (HCP) structures. Refractory metal elements from the Sc and Ti columns of the periodic table (BCC/HCP elements) form BCC structures at high temperatures but transition to HCP at low temperatures via the Burgers distortion. Elements of the V and Cr columns, in contrast, remain BCC at all temperatures. The energy landscape of BCC/HCP elements exhibits an alternating slide instability, while the normal BCC elements remain stable as BCC structures. This instability is verified by the presence of unstable elastic constants and vibrational modes for BCC/HCP elements, while those elastic constants and modes are stable in BCC elements. We show that a pseudogap opening in the density of states at the Fermi level drives the Burgers distortion in BCC/HCP elements, suggesting the transition is of the Jahn-Teller-Peierls type. The pseudogap lies below the Fermi level for regular BCC elements in the V and Cr columns of the periodic table. The wave vector $k_S$ when the gap opens relates to the reciprocal lattice vector G=(1 $\frac{1}{2}$ $\frac{1}{2}$) of the distorted BCC structure as $k_S$=$\frac{1}{2}$G. BCC binary alloys containing both BCC/HCP and BCC elements exhibit a similar instability but stabilize part way through the BCC to HCP transition.
- Published
- 2018
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48. Temperature-dependent conformations of exciton-coupled Cy3 dimers in double-stranded DNA
- Author
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Kringle, Loni, Sawaya, Nicolas P. D., Widom, Julia, Adams, Carson, Raymer, Michael G., Aspuru-Guzik, Alán, and Marcus, Andrew H.
- Subjects
Physics - Chemical Physics ,Quantum Physics - Abstract
Understanding the properties of electronically interacting molecular chromophores, which involve internally coupled electronic-vibrational motions, is important to the spectroscopy of many biologically relevant systems. Here we apply linear absorption, circular dichroism (CD), and two-dimensional fluorescence spectroscopy (2DFS) to study the polarized collective excitations of excitonically coupled cyanine dimers (Cy3)2 that are rigidly positioned within the opposing sugar-phosphate backbones of the double-stranded region of a double-stranded (ss) - single-stranded (ss) DNA fork construct. We show that the exciton-coupling strength of the (Cy3)2-DNA construct can be systematically varied with temperature below the ds - ss DNA denaturation transition. We interpret spectroscopic measurements in terms of the Holstein vibronic dimer model, from which we obtain information about the local conformation of the (Cy3)2 dimer, as well as the degree of static disorder experienced by the Cy3 monomer and the (Cy3)2 dimer probe locally within their respective DNA duplex environments. The properties of the (Cy3)2-DNA construct we determine suggest that it may be employed as a useful model system to test fundamental concepts of protein-DNA interactions, and the role of electronic-vibrational coherence in electronic energy migration within exciton-coupled bio-molecular arrays.
- Published
- 2018
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- View/download PDF
49. Barium isotope evidence of a fluid-metasomatized mantle component in the source of Azores OIB
- Author
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Yu, Hui-Min, Nan, Xiao-Yun, Wu, Fei, Widom, Elisabeth, Li, Wang-Ye, Kuentz, David, and Huang, Fang
- Published
- 2022
- Full Text
- View/download PDF
50. Search for magnetic monopoles with the MoEDAL forward trapping detector in 2.11 fb$^{-1}$ of 13 TeV proton-proton collisions at the LHC
- Author
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MoEDAL Collaboration, Acharya, B., Alexandre, J., Baines, S., Benes, P., Bergmann, B., Bernabéu, J., Bevan, A., Branzas, H., Campbell, M., Caramete, L., Cecchini, S., de Montigny, M., De Roeck, A., Ellis, J. R., Fairbairn, M., Felea, D., Frank, M., Frekers, D., Garcia, C., Hays, J., Hirt, A. M., Janecek, J., Kim, D. -W., Kinoshita, K., Korzenev, A., Lacarrère, D. H., Lee, S. C., Leroy, C., Levi, G., Lionti, A., Mamuzic, J., Margiotta, A., Mauri, N., Mavromatos, N. E., Mermod, P., Mitsou, V. A., Orava, R., Ostrovskiy, I., Parker, B., Patrizii, L., Păvălaş, G. E., Pinfold, J. L., Popa, V., Pozzato, M., Pospisil, S., Rajantie, A., de Austri, R. Ruiz, Sahnoun, Z., Sakellariadou, M., Santra, A., Sarkar, S., Semenoff, G., Shaa, A., Sirri, G., Sliwa, K., Soluk, R., Spurio, M., Srivastava, Y. N., Suk, M., Swain, J., Tenti, M., Togo, V., Tuszyński, J. A., Vento, V., Vives, O., Vykydal, Z., Widom, A., Willems, G., Yoon, J. H., and Zgura, I. S.
- Subjects
High Energy Physics - Experiment ,High Energy Physics - Phenomenology - Abstract
We update our previous search for trapped magnetic monopoles in LHC Run 2 using nearly six times more integrated luminosity and including additional models for the interpretation of the data. The MoEDAL forward trapping detector, comprising 222~kg of aluminium samples, was exposed to 2.11~fb$^{-1}$ of 13 TeV proton-proton collisions near the LHCb interaction point and analysed by searching for induced persistent currents after passage through a superconducting magnetometer. Magnetic charges equal to the Dirac charge or above are excluded in all samples. The results are interpreted in Drell-Yan production models for monopoles with spins 0, 1/2 and 1: in addition to standard point-like couplings, we also consider couplings with momentum-dependent form factors. The search provides the best current laboratory constraints for monopoles with magnetic charges ranging from two to five times the Dirac charge., Comment: 8 pages, 5 figures, 1 table, accepted for publication in Phys. Lett. B
- Published
- 2017
- Full Text
- View/download PDF
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