Results for "Chris A. Marianetti"

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A slave mode expansion for obtaining ab-initio interatomic potentialsJan 10 2014Here we propose a new approach for performing a Taylor series expansion of the first-principles computed energy of a crystal as a function of the nuclear displacements. We enlarge the dimensionality of the existing displacement space and form new variables ... More
Structural and metal-insulator transitions in rhenium based double perovskites via orbital orderingAug 25 2017Dec 13 2017Re-based double perovskites (DPs) exhibit a complex interplay of structural and metal-insulator transitions. Here we systematically study the ground state electronic and structural properties for a family of Re-based DPs $A_2B$ReO$_6$ ($A$=Sr, Ca and ... More
Failure mechanisms of graphene under tensionApr 11 2010Recent experiments established pure graphene as the strongest material known to mankind, further invigorating the question of how graphene fails. Using density functional theory, we reveal the mechanisms of mechanical failure of pure graphene under a ... More
Applicability of DFT + U to U metal and U-Zr alloyJan 29 2016In the Letter [J. Nucl. Mater. 444, 356 (2014)] and Comment [Phys Rev B 90, 157101 (2014)], Soderlind et al. argue that 1) DFT based on GGA already models U metal and U-Zr alloy accurately, and 2) DFT + U models them worse than DFT according to results ... More
New class of planar ferroelectric Mott insulators via first principles designJun 29 2015Inorganic perovskite oxide ferroelectrics have recently generated substantial interest for photovoltaic applications; however, existing materials suffer from excessive electronic band gaps and insufficient electric polarization. The recent resurgence ... More
Compositional phase stability of correlated electron materials within DFT+DMFTMar 25 2019Predicting the compositional phase stability of strongly correlated electron materials is an outstanding challenge in condensed matter physics, requiring precise computations of total energies. In this work, we employ the density functional theory plus ... More
Chemical control of orbital polarization in artificially structured transition-metal oxides: La2NiXO6 (X=B, Al, Ga, In) from first principlesApr 26 2010Oct 06 2010The application of modern layer-by-layer growth techniques to transition-metal oxide materials raises the possibility of creating new classes of materials with rationally designed correlated electron properties. An important step toward this goal is the ... More
Covalency and the metal-insulator transition in titanate and vanadate perovskitesSep 11 2013Apr 22 2014A combination of density functional and dynamical mean-field theory is applied to the perovskites SrVO$_3$, LaTiO$_3$ and LaVO$_3$. We show that DFT+DMFT in conjunction with the standard fully localized-limit (FLL) double-counting predicts that LaTiO$_3$ ... More
Engineering Correlation Effects via Artificially Designed Oxide SuperlatticesApr 29 2013Ab initio calculations are used to predict that a superlattice composed of layers of LaTiO3 and LaNiO3 alternating along the [001] direction is a S=1 Mott insulator with large magnetic moments on the Ni sites, negligible moments on the Ti sites and a ... More
Three Dimensional Metallic and Two Dimensional Insulating Behavior in Tantalum DichalcogenidesJan 01 2014Using density functional theory with added on-site interactions (DFT+U), we study the electronic structure of bulk, monolayer, and bilayer of the layered transition-metal dichalcogenide $1T-TaS_2$. We show that a two-dimensional spin--$\frac{1}{2}$ Mott-phase ... More
A group theoretical approach to computing phonons and their interactionsApr 12 2019Here we present four independent advances which facilitate the computation of phonons and their interactions from first-principles. First, we implement a group-theoretical approach to construct the order N Taylor series of a d-dimensional crystal purely ... More
S=1/2 chains and spin-Peierls transition in TiOClJun 19 2002Dec 12 2002We study TiOCl as an example of an S=1/2 layered Mott insulator. From our analysis of new susceptibility data, combined with LDA and LDA+U band structure calculations, we conclude that orbital ordering produces quasi-one-dimensional spin chains and that ... More
Selectively Localized Wannier FunctionsJul 18 2014Since the seminal work of Marzari and Vanderbilt, maximally localized Wannier functions have become widely used as a real-space representation of the electronic structure of periodic materials. In this paper we introduce selectively localized Wannier ... More
Density functional plus dynamical mean field theory of the metal-insulator transition in early transition metal oxidesJul 24 2014Sep 24 2014The combination of density functional theory and single-site dynamical mean-field theory, using both Hartree and full continuous-time quantum Monte Carlo impurity solvers, is used to study the metal-insulator phase diagram of perovskite transition-metal ... More
First-principles prediction of redox potentials in transition-metal compounds with LDA+UJun 16 2004Jun 06 2005First-principles calculations within the Local Density Approximation (LDA) or Generalized Gradient Approximation (GGA), though very successful, are known to underestimate redox potentials, such as those at which lithium intercalates in transition metal ... More
Density Functional plus Dynamical Mean-Field Theory of the Spin-Crossover Molecule Fe(phen)$_2$(NCS)$_2$Mar 12 2015We study the spin-crossover molecule Fe(phen)$_2$(NCS)$_2$ using density functional theory (DFT) plus dynamical mean-field theory, which allows access to observables not attainable with traditional quantum chemical or electronic structure methods. The ... More
Na Induced Correlations in Na$_x$CoO$_2$May 08 2006Increasing experimental evidence is building which indicates that signatures of strong correlations are present in the Na rich region of Na$_x$CoO$_2$ (ie. $x\approx0.7$) and absent in the Na poor region (ie. $x\approx0.3$). This is unexpected given that ... More
Pressure-resistant intermediate valence in Kondo insulator SmB6Mar 07 2016Resonant x-ray emission spectroscopy (RXES) was used to determine the pressure dependence of the f-electron occupancy in the Kondo insulator SmB6. Applied pressure reduces the f-occupancy, but surprisingly, the material maintains a significant divalent ... More
A first-principles approach to nonlinear lattice dynamics: Anomalous spectra in PbTeDec 20 2013Here we introduce a new approach to compute the finite temperature lattice dynamics from first-principles via the newly developed slave mode expansion. We study PbTe where inelastic neutron scattering (INS) reveals strong signatures of nonlinearity as ... More
The Role of hybridization in NaxCoO2 and the Effect of HydrationDec 19 2003Density functional theory (DFT) within the local density approximation (LDA) is used to understand the electronic properties of Na1/3CoO2 and Na1/3CoO2(H2O)4/3, which was recently found to be superconducting1. Comparing the LDA charge density of CoO2 ... More
The low-energy ARPES and heat capacity of Na$_{0.3}$CoO$_2$: A DMFT studyDec 22 2006The cobaltates have demonstrated a wide variety complex behavior. The Na rich region of the phase diagram displays various degrees of anomalous behavior, such as Curie-Weiss behavior near a band insulator\cite{Foo:2004}, charge disproportionation\cite{Mukhamedshin:2005}, ... More
Spin-exchange-induced dimerization of an atomic 1-D systemAug 02 2012Using low-temperature scanning tunneling microscopy, we demonstrate an unambiguous 1-D system that surprisingly undergoes a CDW instability on a metallic substrate. Our ability to directly and quantitatively measure the structural distortion of this system ... More
One-Electron Physics of the ActinidesAug 08 2007We present a detailed analysis of the one-electron physics of the actinides. Various LMTO basis sets are analyzed in order to determine a robust bare Hamiltonian for the actinides. The hybridization between f- an spd- states is compared with the f-f hopping ... More
Electronic coherence in $δ$-Pu: A DMFT studyMay 12 2008A combination of Density Functional Theory and the Dynamical Mean Field theory (DMFT) is used to calculate the magnetic susceptibility, heat capacity, and the temperature dependence of the valence band photoemission spectra. The continuous-time hybridization ... More
Dynamical Mean Field Theory of Nickelate SuperlatticesApr 29 2011Apr 07 2013Dynamical mean field methods are used to calculate the phase diagram, many-body density of states, relative orbital occupancy and Fermi surface shape for a realistic model of $LaNiO_3$-based superlattices. The model is derived from density functional ... More
Phase Separation in Li$_x$FePO$_4$ Induced by Correlation EffectsApr 27 2004May 13 2004We report on a significant failure of LDA and GGA to reproduce the phase stability and thermodynamics of mixed-valence Li$_x$FePO$_4$ compounds. Experimentally, Li$_x$FePO$_4$ compositions ($0 \leq x \leq 1$) are known to be unstable and phase separate ... More
Electronic Structure Calculations with Dynamical Mean-Field Theory: A Spectral Density Functional ApproachNov 03 2005We present a review of the basic ideas and techniques of the spectral density functional theory which are currently used in electronic structure calculations of strongly-correlated materials where the one-electron description breaks down. We illustrate ... More
Ideal strength and phonon instability of strained monolayer materialsNov 06 2013The ideal strength of monolayer materials possessing semimetallic, semiconducting, and insulating ground states is computed using density functional theory. Here we show that, as in graphene, a soft mode occurs at the K-point in BN, graphane, and MoS$_2$, ... More
Dynamical Mean-Field Theory for Quantum ChemistryOct 15 2010Mar 03 2011The dynamical mean-field concept of approximating an unsolvable many-body problem in terms of the solution of an auxiliary quantum impurity problem, introduced to study bulk materials with a continuous energy spectrum, is here extended to molecules, i.e., ... More
Covalency, double-counting and the metal-insulator phase diagram in transition metal oxidesOct 12 2011Nov 02 2012Dynamical mean field theory calculations are used to show that for late transition-metal-oxides a critical variable for the Mott/charge-transfer transition is the number of d-electrons, which is determined by charge transfer from oxygen ions. Insulating ... More
Electronic correlations in monolayer VS$_2$Feb 26 2016The layered transition metal dichalcogenide vanadium disulfide (VS$_2$), which nominally has one electron in the $3d$ shell, is potent for strong correlation physics and is possibly another realization of an effective one-band model beyond the cuprates. ... More
Compositional phase stability of strongly correlated electron materials within DFT+$U$Nov 10 2016Predicting the compositional phase stability of strongly correlated electron materials is an outstanding challenge in condensed matter physics. In this work, we employ the DFT+U formalism to address the effects of local correlations due to transition ... More
Uniaxial Strain Tuning of Superconductivity in 2$H$-NbSe$_{2}$Mar 12 2019We explore the effect of lattice anisotropy on the charge-ordered superconductor 2H-NbSe$_{2}$. Using a novel strain apparatus, we measure the superconducting transition temperature $T_{sc}$ as a function of uniaxial strain. It is found that $T_{sc}$ ... More
Origin of Spinel Nanocheckerboards via First PrinciplesJan 14 2015Self-organizing nanocheckerboards have been experimentally fabricated in Mn-based spinels, but have not yet been explained with first principles. Using density-functional-theory, we explain the phase diagram of the $\mathrm{ZnMn_xGa_{2-x}O_4}$ system ... More
Charge transfer across transition metal oxide interfaces: emergent conductance and new electronic structureAug 01 2014Jan 02 2015We perform density functional theory plus dynamical mean field theory calculations to investi- gate internal charge transfer in an artificial superlattice composed of alternating layers of vanadate and manganite perovskite and Ruddlesden-Popper structure ... More
Influence of quantum confinement and strain on orbital polarization of four-layer LaNiO$_3$ superlattices: a DFT+DMFT studyFeb 03 2016Atomically precise superlattices involving transition metal oxides provide a unique opportunity to engineer correlated electron physics using strain (modulated by choice of substate) and quantum confinement (controlled by layer thickness). Here we use ... More
Site-selective Mott transition in rare earth nickelatesJun 13 2012A combination of density functional and dynamical mean field theory calculations are used to show that the remarkable metal-insulator transition in the rare earth nickelate perovskites arise from a site-selective Mott phase, in which the $d$-electrons ... More
Density functional versus spin-density functional and the choice of correlated subspace in multi-variable effective action theories of electronic structureMay 01 2015Modern extensions of density functional theory such as the density functional theory plus U and the density functional theory plus dynamical mean-field theory require choices, including selection of variable (charge vs spin density) for the density functional ... More
Computing total energies in complex materials using charge self-consistent DFT+DMFTSep 15 2014We have formulated and implemented a fully charge-self-consistent density functional theory plus dynamical mean field theory methodology which enables an efficient calculation of the total energy of realistic correlated electron systems. The density functional ... More
Total energy calculations using DFT+DMFT: computing the pressure phase diagram of the rare earth nickelatesOct 22 2013Sep 15 2014A full implementation of the $ab$ $initio$ density functional plus dynamical mean field theory (DFT+DMFT) formalism to perform total energy calculations and structural relaxations is proposed and implemented. The method is applied to the structural and ... More
Doubled strings, negative strings and null wavesAug 24 2016Nov 03 2016We revisit the fundamental string (F1) solution in the doubled formalism. We show that the wave-like solution of double field theory (DFT) corresponding to the F1/pp-wave duality pair is more properly a solution of the DFT action coupled to a doubled ... More
Orbifolds and Orientifolds as O-foldsMar 22 2019We consider quotients of string and M-theory by discrete subgroups of the U-duality group. This results in what we call O-folds, which are generalisations of orbifolds and orientifolds, and generically involve non-geometric identifications between physical ... More
Evidential Value in ANOVA Results in Favor of FabricationApr 26 2013Some scientific publications are under suspicion of fabrication of data. Since humans are bad random number generators, there might be some evidential value in favor of fabrication in the statistical results as presented in such papers. In line with Uri ... More
Open exceptional strings and D-branesApr 14 2019We study D-branes in the extended geometry appearing in exceptional field theory (or exceptional generalised geometry). Starting from the exceptional sigma model (an $E_{d(d)}$ covariant worldsheet action with extra target space coordinates), we define ... More
Evidential Value in ANOVA-Regression Results in Scientific Integrity StudiesMay 18 2014Mar 19 2015Some scientific publications are under suspicion of fabrication of data. Since humans are bad random number generators, there might be some evidential value in favor of fabrication in the statistical results as presented in such papers. In case of ANOVA-Regression ... More
The failure of DFT-based computations for a stepped-substrate-supported correlated Co wireDec 05 2013Density functional theory (DFT) has been immensely successful in its ability to predict physical properties, and, in particular, structures of condensed matter systems. Here, however, we show that DFT qualitatively fails to predict the dimerized structural ... More
Computations with finite index subgroups of $PSL_2(\mathbb Z)$ using Farey SymbolsOct 09 2007Finite index subgroups of the modular group are of great arithmetic importance. Farey symbols, introduced by Ravi Kulkarni in 1991, are a tool for working with these groups. Given such a group $\Gamma$, a Farey symbol for $\Gamma$ is a certain finite ... More
Graded Majorana spinorsJan 31 2005Mar 21 2006In many mathematical and physical contexts spinors are treated as Grassmann odd valued fields. We show that it is possible to extend the classification of reality conditions on such spinors by a new type of Majorana condition. In order to define this ... More
Simulating feedback from nuclear clusters: the impact of multiple sourcesOct 19 2015Nuclear star clusters (NCs) are found to exist in the centres of many galaxies and appear to follow scaling relations similar to those of super-massive black holes. Previous analytical work has suggested that such relations are a consequence of feedback ... More
Numerical determination of partial spectrum of Hermitian matrices using a Lanczos method with selective reorthogonalizationNov 06 2012We introduce a new algorithm for finding the eigenvalues and eigenvectors of Hermitian matrices within a specified region, based upon the LANSO algorithm of Parlett and Scott. It uses selective reorthogonalization to avoid the duplication of eigenpairs ... More
On Triangulating Dynamic Graphical ModelsOct 19 2012This paper introduces new methodology to triangulate dynamic Bayesian networks (DBNs) and dynamic graphical models (DGMs). While most methods to triangulate such networks use some form of constrained elimination scheme based on properties of the underlying ... More
Non-Minimal Triangulations for Mixed Stochastic/Deterministic Graphical ModelsJun 27 2012We observe that certain large-clique graph triangulations can be useful to reduce both computational and space requirements when making queries on mixed stochastic/deterministic graphical models. We demonstrate that many of these large-clique triangulations ... More
What is the origin of the soft excess in AGN?Sep 08 2006Sep 28 2006We investigate the nature of the soft excess below 1 keV observed in AGN. We use the XMM-Newton data of the low redshift, optically bright quasar, PG 1211+143, and we compare it with the Narrow Line Seyfert 1 galaxy, 1H 0707-495, which has one of the ... More
Bounds on the convergence of Ritz values from Krylov subspaces to interior eigenvalues of Hermitean matricesOct 13 2011We consider bounds on the convergence of Ritz values from a sequence of Krylov subspaces to interior eigenvalues of Hermitean matrices. These bounds are useful in regions of low spectral density, for example near voids in the spectrum, as is required ... More
Growth of brightest cluster galaxies via mergers since z = 1Jul 05 2013Hierarchical assembly within clusters of galaxies is tied directly to the evolution of the Brightest Cluster Galaxies (BCGs), which dominate the stellar light in the centres of rich clusters. In this paper we investigate the number of mergers onto BCGs ... More
Valuations and Metrics on Partially Ordered SetsMar 16 2009We extend the definitions of upper and lower valuations on partially ordered sets, and consider the metrics they induce, in particular the metrics available (or not) based on the logarithms of such valuations. Motivating applications in computational ... More
One Monopole with k SingularitiesSep 27 2010We present all charge one monopole solutions of the Bogomolny equation with k prescribed Dirac singularities for the gauge groups U(2), SO(3), or SU(2). We analyze these solutions comparing them to the previously known expressions for the cases of one ... More
Singular Monopoles from Cheshire BowsOct 05 2010Singular monopoles are nonabelian monopoles with prescribed Dirac-type singularities. All of them are delivered by the Nahm's construction. In practice, however, the effectiveness of the latter is limited to the cases of one or two singularities. We present ... More
Efficiently Inferring Pairwise Subtree Prune-and-Regraft Adjacencies between Phylogenetic TreesJun 28 2016We develop a time-optimal O(mn^2)-time algorithm for the problem of constructing the subtree prune-regraft (SPR) graph on a collection of m phylogenetic trees with n leaves. This improves on the previous bound of O(mn^3). Such graphs are used to better ... More
Black hole thermodynamics, stringy dualities and double field theoryAug 16 2016Aug 24 2016We discuss black hole thermodynamics in the manifestly duality invariant formalism of double field theory (DFT). We reformulate and prove the first law of black hole thermodynamics in DFT, using the covariant phase space approach. After splitting the ... More
The Exceptional Sigma ModelFeb 01 2018We detail the construction of the exceptional sigma model, which describes a string propagating in the "extended spacetime" of exceptional field theory. This is to U-duality as the doubled sigma model is to T-duality. Symmetry specifies the Weyl-invariant ... More
Submillimetre surveys: The prospects for HerschelJun 22 2009Using the observed submillimetre source counts, from 250-1200 microns (including the most recent 250, 350 and 500 micron counts from BLAST), we present a model capable of reproducing these results, which is used as a basis to make predictions for upcoming ... More
Foundations of Black Hole Accretion Disk TheoryApr 28 2011Jan 21 2013This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal ... More
The Effect of the Cosmic Web on Cluster Weak Lensing Mass EstimatesMay 23 2000Mar 08 2001In modern hierarchical theories of structure formation, rich clusters of galaxies form at the vertices of a weblike distribution of matter, with filaments emanating from them to large distances and with smaller objects forming and draining in along these ... More
MARVIN: An Open Machine Learning Corpus and Environment for Automated Machine Learning Primitive Annotation and ExecutionAug 11 2018In this demo paper, we introduce the DARPA D3M program for automatic machine learning (ML) and JPL's MARVIN tool that provides an environment to locate, annotate, and execute machine learning primitives for use in ML pipelines. MARVIN is a web-based application ... More
Performance and Reliability Implications of Two Dimensional Shading in Monolithic Thin Film Photovoltaic ModulesMar 18 2013We analyze the problem of partial shading in monolithically integrated thin film photovoltaic (TFPV) modules, and explore how the shape and size of the shadows dictate their performance and reliability. We focus on the aspects of shading problem unique ... More
The Birthplaces of Gamma-Ray BurstsMar 14 2007We use population synthesis to construct distributions of gamma-ray bursts (GRBs) for different proposed progenitor models. We use a description of star formation that takes into account the evolution of metallicity with redshift and galaxy mass, the ... More
Dynamical effects of the long bar in the Milky WayAug 04 2008Nov 10 2008We examine the dynamical effects on disk stars of a "long bar" in the Milky Way by inserting a triaxial rotating bar into an axisymmetric disk+bulge+dark halo potential and integrating 3-D orbits of 104 tracer stars over a period of 2 Gyr. The long bar ... More
Non-Fermi liquid fixed points and anomalous Landau damping in a quantum critical metalAug 08 2018Nov 28 2018We present a functional renormalization group calculation of the properties of a quantum critical metal in $d=2$ spatial dimensions. Our theory describes a general class of Pomeranchuk instabilities with $N_b$ flavors of boson. At small $N_b$ we find ... More
Efficient estimation of Banach parameters in semiparametric modelsApr 25 2005Consider a semiparametric model with a Euclidean parameter and an infinite-dimensional parameter, to be called a Banach parameter. Assume: (a) There exists an efficient estimator of the Euclidean parameter. (b) When the value of the Euclidean parameter ... More
Efficiently Inferring Pairwise Subtree Prune-and-Regraft Adjacencies between Phylogenetic TreesJun 28 2016Nov 08 2016We develop a time-optimal $O(mn^2)$-time algorithm for the problem of constructing the subtree prune-regraft (SPR) graph on a collection of $m$ phylogenetic trees with $n$ leaves. This improves on the previous bound of $O(mn^3)$. Such graphs are used ... More
Implications for unified schemes from submillimetre and far-infrared follow-up of radio-selected samplesDec 20 2004We extend our previous analysis which used generalized luminosity functions (GLFs) to predict the number of quasars and galaxies in low-radio-frequency-selected samples as a function of redshift, radio luminosity, narrow-emission-line luminosity and type ... More
Non-Fermi-liquid behavior and anomalous suppression of Landau damping in layered metals close to ferromagnetismOct 09 2014Feb 12 2015We analyse the low-energy physics of nearly ferromagnetic metals in two spatial dimensions using the functional renormalization group technique. We find a new low-energy fixed point, at which the fermionic (electron-like) excitations are non-Fermi-liquid ... More
Geometry and fluxes of SL(5) exceptional field theoryDec 01 2014Mar 26 2015We use a geometric approach to construct a flux formulation for the SL(5) U-duality manifest exceptional field theory. The resulting formalism is well-suited for studying gauged supergravities with geometric and non-geometric fluxes. Here we describe ... More
Type II strings are ExceptionalDec 19 2017Feb 06 2018We construct the exceptional sigma model: a two-dimensional sigma model coupled to a supergravity background in a manifestly (formally) $E_{D(D)}$-covariant manner. This formulation of the background is provided by Exceptional Field Theory (EFT), which ... More
Dynamical Dark Energy or Simply Cosmic Curvature?Feb 26 2007Jul 27 2007We show that the assumption of a flat universe induces critically large errors in reconstructing the dark energy equation of state at z>~0.9 even if the true cosmic curvature is very small, O(1%) or less. The spuriously reconstructed w(z) shows a range ... More
Five-brane actions in double field theoryDec 05 2017Mar 25 2018We construct an action for NSNS 5-branes which is manifestly covariant under O(d,d). This is done by doubling $d$ of the spacetime coordinates which appear in the worldvolume action. By formulating the DBI part of the action in a manner similar to a "gauged ... More
Uncertainties in Supernova Yields I: 1D ExplosionsDec 22 2006Theoretical nucleosynthetic yields from supernovae are sensitive to both the details of the progenitor star and the explosion calculation. We attempt to comprehensively identify the sources of uncertainties in these yields. In this paper we concentrate ... More
Conditional Random Field Autoencoders for Unsupervised Structured PredictionNov 05 2014Nov 10 2014We introduce a framework for unsupervised learning of structured predictors with overlapping, global features. Each input's latent representation is predicted conditional on the observable data using a feature-rich conditional random field. Then a reconstruction ... More
A study of spectral and timing properties of Cyg X-1 based on a large sample of pointed RXTE observationsNov 26 2010We study a large sample of RXTE PCA/HEXTE observations of Cyg X-1. We characterize the spectra by soft and hard X-ray colours (which define the spectral states), and fit them with a physical model of hybrid, thermal/non-thermal Comptonization. We then ... More
Weak lensing surveys and the intrinsic correlation of galaxy ellipticitiesMay 18 2000We explore the possibility that an intrinsic correlation between galaxy ellipticities arising during the galaxy formation process may account for part of the shear signal recently reported by several groups engaged in weak lensing surveys. Using high ... More
Improved Transition-Based Parsing by Modeling Characters instead of Words with LSTMsAug 04 2015Aug 11 2015We present extensions to a continuous-state dependency parsing method that makes it applicable to morphologically rich languages. Starting with a high-performance transition-based parser that uses long short-term memory (LSTM) recurrent neural networks ... More
Semiparametrically Efficient Estimation of Constrained Euclidean ParametersAug 14 2015Consider a quite arbitrary (semi)parametric model with a Euclidean parameter of interest and assume that an asymptotically (semi)parametrically efficient estimator of it is given. If the parameter of interest is known to lie on a general surface (image ... More
Segmental Recurrent Neural NetworksNov 18 2015Mar 01 2016We introduce segmental recurrent neural networks (SRNNs) which define, given an input sequence, a joint probability distribution over segmentations of the input and labelings of the segments. Representations of the input segments (i.e., contiguous subsequences ... More
Possible topologically non-trivial superconducting order parameter in type-II Weyl semimetal T_d-MoTe_2Apr 18 2017MoTe_2, with the orthorhombic T_d phase, is a new type (type-II) of Weyl semimetal, where the Weyl Fermions emerge at the boundary between electron and hole pockets. Non-saturating magnetoresistance (MR), and superconductivity were also observed in T_d-MoTe_2. ... More
Hundredfold Enhancement of Light Emission via Defect Control in Monolayer Transition-Metal DichalcogenidesApr 30 2018Two dimensional (2D) transition-metal dichalcogenide (TMD) based semiconductors have generated intense recent interest due to their novel optical and electronic properties, and potential for applications. In this work, we characterize the atomic and electronic ... More
Introspection LearningFeb 27 2019Traditional reinforcement learning agents learn from experience, past or present, gained through interaction with their environment. Our approach synthesizes experience, without requiring an agent to interact with their environment, by asking the policy ... More
The Exceptional Sigma ModelFeb 01 2018Apr 11 2018We detail the construction of the exceptional sigma model, which describes a string propagating in the "extended spacetime" of exceptional field theory. This is to U-duality as the doubled sigma model is to T-duality. Symmetry specifies the Weyl-invariant ... More
Information weighted sampling for detecting rare items in finite populations with a focus on securityOct 22 2013Frequently one has to search within a finite population for a single particular individual or item with a rare characteristic. Whether an item possesses the characteristic can only be determined by close inspection. The availability of additional information ... More
A novel approach for using programming exercises in electromagnetism courseworkJul 01 2017While there exists a significant number of web interactives for introductory physics, students are almost never shown the computer code that generates these interactives even when the physics parts of these programs are relatively simple. Building off ... More
A Game-Centered, Interactive Approach for Using Programming Exercises in Introductory PhysicsJan 07 2017Jun 01 2017Incorporating computer programming exercises in introductory physics is a delicate task that involves a number of choices that may have a strong affect on student learning. We present an approach that speaks to a number of common concerns that arise when ... More
Improved bridge constructs for stochastic differential equationsSep 30 2015Apr 25 2016We consider the task of generating discrete-time realisations of a nonlinear multivariate diffusion process satisfying an It\^o stochastic differential equation conditional on an observation taken at a fixed future time-point. Such realisations are typically ... More
The Impact of Hydrodynamic Mixing on Supernova ProgenitorsJul 05 2005Recent multidimensional hydrodynamic simulations have demonstrated the importance of hydrodynamic motions in the convective boundary and radiative regions of stars to transport of energy, momentum, and composition. The impact of these processes increases ... More
Near threshold rotational excitation of molecular ions by electron-impactAug 07 2006New cross sections for the rotational excitation of H$_3^+$ by electrons are calculated {\it ab initio} at low impact energies. The validity of the adiabatic-nuclei-rotation (ANR) approximation, combined with $R$-matrix wavefunctions, is assessed by comparison ... More
Gravitational Wave Emission From Core-Collapse of Massive StarsJun 06 2001Sep 25 2001We derive estimates for the characteristics of gravitational radiation from stellar collapse, using recent models of the core-collapse of Chandrasekhar mass white dwarfs (accretion induced collapse), core-collapse supernovae and collapsars, and the collapse ... More
Evaporation of a Kerr black hole by emission of scalar and higher spin particlesJan 13 1998Jul 20 1998We study the evolution of an evaporating rotating black hole, described by the Kerr metric, which is emitting either solely massless scalar particles or a mixture of massless scalar and nonzero spin particles. Allowing the hole to radiate scalar particles ... More
Chemodynamical analysis of bulge stars for simulated disc galaxiesSep 24 2009We analyse the kinematics and chemistry of the bulge stars of two simulated disc galaxies using our chemodynamical galaxy evolution code GCD+. First we compare stars that are born inside the galaxy with those that are born outside the galaxy and are accreted ... More
Population-Based Reversible Jump Markov Chain Monte CarloNov 01 2007In this paper we present an extension of population-based Markov chain Monte Carlo (MCMC) to the trans-dimensional case. One of the main challenges in MCMC-based inference is that of simulating from high and trans-dimensional target measures. In such ... More
Helical Strands in the Jet-like Narrow Line Region of ESO 428-G14Aug 08 1996We present HST/WFPC2 images of the narrow line region (NLR) of the Seyfert 2 galaxy ESO 428-G14 (0714-2914, M4-1). The NLR consists of many individual, thin strands, which are very closely related to the radio jet and produce a highly complex yet ordered ... More
An O(D,D) Invariant Hamiltonian Action for the SuperstringAug 22 2013Feb 11 2014We construct O(D,D) invariant actions for the bosonic string and RNS superstring, using Hamiltonian methods and ideas from double field theory. In this framework the doubled coordinates of double field theory appear as coordinates on phase space and T-duality ... More