Results for "Martin J. Blunt"

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DeepFlow: History Matching in the Space of Deep Generative ModelsMay 14 2019The calibration of a reservoir model with observed transient data of fluid pressures and rates is a key task in obtaining a predictive model of the flow and transport behaviour of the earth's subsurface. The model calibration task, commonly referred to ... More
Reconstruction of three-dimensional porous media using generative adversarial neural networksApr 11 2017To evaluate the variability of multi-phase flow properties of porous media at the pore scale, it is necessary to acquire a number of representative samples of the void-solid structure. While modern x-ray computer tomography has made it possible to extract ... More
Conditioning of three-dimensional generative adversarial networks for pore and reservoir-scale modelsFeb 15 2018Geostatistical modeling of petrophysical properties is a key step in modern integrated oil and gas reservoir studies. Recently, generative adversarial networks (GAN) have been shown to be a successful method for generating unconditional simulations of ... More
Stochastic seismic waveform inversion using generative adversarial networks as a geological priorJun 10 2018We present an application of deep generative models in the context of partial-differential equation (PDE) constrained inverse problems. We combine a generative adversarial network (GAN) representing an a priori model that creates subsurface geological ... More
Stochastic reconstruction of an oolitic limestone by generative adversarial networksDec 07 2017Stochastic image reconstruction is a key part of modern digital rock physics and materials analysis that aims to create numerous representative samples of material micro-structures for upscaling, numerical computation of effective properties and uncertainty ... More
DeepFlow: History Matching in the Space of Deep Generative ModelsMay 14 2019Jun 12 2019The calibration of a reservoir model with observed transient data of fluid pressures and rates is a key task in obtaining a predictive model of the flow and transport behaviour of the earth's subsurface. The model calibration task, commonly referred to ... More
Generalized network modeling of capillary-dominated two-phase flowJul 10 2017Aug 28 2017We present a generalized network model for simulating capillary-dominated two-phase flow through porous media at the pore scale. Three-dimensional images of the pore space are discretized using a generalized network -- described in a companion paper ( ... More
Multimodal Functions as Flow Signatures in Complex Porous MediaJul 19 2018Aug 20 2018This study refutes the premise that the distribution of flow speeds in complex porous media can be described by a simple function such as a normal or exponential variation. In many complex porous media, including those relevant for subsurface storage ... More
Front instabilities in evaporatively dewetting nanofluidsJun 25 2008Various experimental settings that involve drying solutions or suspensions of nanoparticles -- often called nanofluids -- have recently been used to produce structured nanoparticle layers. In addition to the formation of polygonal networks and spinodal-like ... More
Topological Analysis of Foams and tetrahedral structuresOct 16 2007In this paper we characterize foams and tetrahedral structures in a unified way, by a simplified representation of both that conserves the system topology. The paper presents a workflow for an automated characterization of the topology of the void space, ... More
Modelling approaches to the dewetting of evaporating thin films of nanoparticle suspensionsJan 15 2010We review recent experiments on dewetting thin films of evaporating colloidal nanoparticle suspensions (nanofluids) and discuss several theoretical approaches to describe the ongoing processes including coupled transport and phase changes. These approaches ... More
RadVel: The Radial Velocity Modeling ToolkitJan 06 2018RadVel is an open source Python package for modeling Keplerian orbits in radial velocity (RV) time series. RadVel provides a convenient framework to fit RVs using maximum a posteriori optimization and to compute robust confidence intervals by sampling ... More
The sign problem and population dynamics in the full configuration interaction quantum Monte Carlo methodOct 25 2011Jan 28 2012The recently proposed full configuration interaction quantum Monte Carlo method allows access to essentially exact ground-state energies of systems of interacting fermions substantially larger than previously tractable without knowledge of the nodal structure ... More
Preconditioning and perturbative estimators in full configuration interaction quantum Monte CarloJan 18 2019Apr 02 2019We propose the use of preconditioning in FCIQMC which, in combination with perturbative estimators, greatly increases the efficiency of the algorithm. The use of preconditioning allows a time step close to unity to be used (without time-step errors), ... More
Preconditioning and perturbative estimators in full configuration interaction quantum Monte CarloJan 18 2019We propose the use of preconditioning in FCIQMC which, in combination with perturbative estimators, greatly increases the efficiency of the algorithm. The use of preconditioning allows a time step close to unity to be used (without time-step errors), ... More
Density matrix quantum Monte CarloMar 20 2013Apr 26 2014We present a quantum Monte Carlo method capable of sampling the full density matrix of a many-particle system at finite temperature. This allows arbitrary reduced density matrix elements and expectation values of complicated non-local observables to be ... More
Interaction Picture Density Matrix Quantum Monte CarloJun 09 2015Oct 14 2015The recently developed density matrix quantum Monte Carlo (DMQMC) algorithm stochastically samples the N -body thermal density matrix and hence provides access to exact properties of many-particle quantum systems at arbitrary temperatures. We demonstrate ... More
Semi-stochastic full configuration interaction quantum Monte Carlo: developments and applicationFeb 17 2015Apr 29 2015We expand upon the recent semi-stochastic adaptation to full configuration interaction quantum Monte Carlo (FCIQMC). We present an alternate method for generating the deterministic space without a priori knowledge of the wave function and present stochastic ... More
An efficient and accurate perturbative correction to initiator full configuration interaction quantum Monte CarloApr 25 2018Jun 12 2018We present a perturbative correction within initiator full configuration interaction quantum Monte Carlo (i-FCIQMC). In the existing i-FCIQMC algorithm, a significant number of spawned walkers are discarded due to the initiator criteria. Here we show ... More
Excited-state diffusion Monte Carlo calculations: a simple and efficient two-determinant ansatzAug 28 2018Dec 10 2018We perform excited-state variational Monte Carlo and diffusion Monte Carlo calculations using a simple and efficient wave function ansatz. This ansatz follows the recent variation-after-response formalism, accurately approximating a configuration interaction ... More
Charge-transfer excited states: Seeking a balanced and efficient wave function ansatz in variational Monte CarloJul 28 2017Sep 27 2017We present a simple and efficient wave function ansatz for the treatment of excited charge-transfer states in real-space quantum Monte Carlo methods. Using the recently-introduced variation-after-response method [J. Chem. Phys. 145, 081103 (2016)], this ... More
Accurate exchange-correlation energies for the warm dense electron gasFeb 16 2016Sep 10 2016Density matrix quantum Monte Carlo (DMQMC) is used to sample exact-on-average $N$-body density matrices for uniform electron gas systems of up to 10$^{124}$ matrix elements via a stochastic solution of the Bloch equation. The results of these calculations ... More
Broken symmetry and the variation of critical properties in the phase behaviour of supramolecular rhombus tilingsJan 25 2012The degree of randomness, or partial order, present in two-dimensional supramolecular arrays of isophthalate tetracarboxylic acids is shown to vary due to subtle chemical changes such as the choice of solvent or small differences in molecular dimensions. ... More
Open-source development experiences in scientific software: the HANDE quantum Monte Carlo projectJul 21 2014Nov 14 2015The HANDE quantum Monte Carlo project offers accessible stochastic algorithms for general use for scientists in the field of quantum chemistry. HANDE is an ambitious and general high-performance code developed by a geographically-dispersed team with a ... More
Orbits for the Impatient: A Bayesian Rejection Sampling Method for Quickly Fitting the Orbits of Long-Period ExoplanetsMar 30 2017We describe a Bayesian rejection sampling algorithm designed to efficiently compute posterior distributions of orbital elements for data covering short fractions of long-period exoplanet orbits. Our implementation of this method, Orbits for the Impatient ... More
Discovery of a White Dwarf Companion to HD 159062May 15 2019We report on the discovery of a white dwarf companion to the nearby late G dwarf star, HD 159062. The companion is detected in 14 years of precise radial velocity (RV) data, and in high-resolution imaging observations. RVs of HD 159062 from 2003-2018 ... More
Theory & observations of the PWN-SNR complexSep 06 2014Feb 10 2015In this work, we study theoretical and observational issues about pulsars (PSRs), pulsar wind nebulae (PWNe) and supernova remnants (SNRs). In particular, the spectral modeling of young PWNe and the X-ray analysis of SNRs with magnetars comparing their ... More
Response Formalism within Full Configuration Interaction Quantum Monte Carlo: Static Properties and Electrical ResponseMay 10 2018Jun 15 2018We formulate a general, arbitrary-order stochastic response formalism within the Full Configuration Interaction Quantum Monte Carlo framework. This modified stochastic dynamic allows for the exact response properties of correlated multireference electronic ... More
Krylov-projected quantum Monte CarloSep 08 2014Jun 03 2015We present an approach to the calculation of arbitrary spectral, thermal and excited state properties within the full configuration interaction quantum Monte Carlo framework. This is achieved via an unbiased projection of the Hamiltonian eigenvalue problem ... More
Analysis of a New Space-Time Parallel Multigrid Algorithm for Parabolic ProblemsNov 03 2014We present and analyze a new space-time parallel multigrid method for parabolic equations. The method is based on arbitrarily high order discontinuous Galerkin discretizations in time, and a finite element discretization in space. The key ingredient of ... More
Discovery of a White Dwarf Companion to HD 159062May 15 2019May 17 2019We report on the discovery of a white dwarf companion to the nearby late G dwarf star, HD 159062. The companion is detected in 14 years of precise radial velocity (RV) data, and in high-resolution imaging observations. RVs of HD 159062 from 2003-2018 ... More
Gravity as a Gauge Theory of TranslationsJul 16 2009The Poincar\'e group can be interpreted as the group of isometries of a minkowskian space. This point of view suggests to consider the group of isometries of a given space as the suitable group to construct a gauge theory of gravity. We extend these ideas ... More
Analysis of a Time Multigrid Algorithm for DG-Discretizations in TimeSep 18 2014Sep 30 2014We present and analyze for a scalar linear evolution model problem a time multigrid algorithm for DG-discretizations in time. We derive asymptotically optimized parameters for the smoother, and also an asymptotically sharp convergence estimate for the ... More
Non-linear biases, stochastically-sampled effective Hamiltonians and spectral functions in quantum Monte Carlo methodsJun 07 2018Jul 23 2018In this article we study examples of systematic biases that can occur in quantum Monte Carlo methods due to the accumulation of non-linear expectation values, and approaches by which these errors can be corrected. We begin with a study of the Krylov-projected ... More
Density matrices in full configuration interaction quantum Monte Carlo: Excited states, transition dipole moments and parallel distributionApr 04 2017Jun 16 2017We present developments in the calculation of reduced density matrices (RDMs) in the full configuration interaction quantum Monte Carlo (FCIQMC) method. An efficient scheme is described to allow storage of RDMs across distributed memory, thereby allowing ... More
The HANDE-QMC project: open-source stochastic quantum chemistry from the ground state upNov 28 2018Dec 04 2018Building on the success of Quantum Monte Carlo techniques such as diffusion Monte Carlo, alternative stochastic approaches to solve electronic structure problems have emerged over the last decade. The full configuration interaction quantum Monte Carlo ... More
Supercomputing and Ap starsMay 06 1998Certain problems in the field of stellar atmospheres, polarized radiative transfer and magnetic field diagnostics cannot be addressed by means of traditional sequential programming techniques because CPU times become prohibitive on even the fastest single ... More
Nuclear Physics and Lattice QCDSep 15 2005Lattice QCD is progressing toward being able to impact our understanding of nuclei and nuclear processes. I discuss areas of nuclear physics that are becoming possible to explore with lattice QCD, the techniques that are currently available and the status ... More
K_L -> pi pi e e in Chiral Perturbation TheoryAug 11 1999The rare decay K_L -> pi pi e e that has recently been observed by KTeV is analyzed in chiral perturbation theory at the one-loop level.
The Two-Nucleon Sector with Effective Field TheoryMay 04 1999I present the results obtained for several observables in the two-nucleon sector using effective field theory with KSW power-counting and dimensional regularization. In addition to the phase shifts for nucleon-nucleon scattering, several deuteron observables ... More
Including PionsApr 17 1998Recent progress in using effective field theory to describe systems with two nucleons is discussed with particular emphasis placed on the inclusion of pions. Inconsistencies arising in Weinberg's power counting are demonstrated with two concrete examples. ... More
Magnetic Moment of the $Λ_c$, $Ξ_{c1}^+$ and $Ξ_{c1}^0$Jan 27 1994The magnetic moment of the $\Lambda_c$, $\Xi_{c1}^+$ and $\Xi_{c1}^0$ vanish when the charm quark mass is taken to infinity because the light degrees of freedom are in a spin zero configuration. The heavy quark spin-symmetry violating contribution from ... More
Nuclei from QCD : Strategy, Challenges and StatusDec 30 2005I describe progress that is being made toward calculating the properties and interactions of nuclei from QCD.
What Effective Field Theory May Contribute to the Blast ProgramJul 07 1998Recent progress in using effective field theory to describe two nucleon systems is reviewed.
Estimating the Tail Index by using Model AveragingOct 22 2014Oct 29 2014The ideas of model averaging are used to find weights in peak-over-threshold problems using a possible range of thresholds. A range of the largest observations are chosen and considered as possible thresholds, each time performing estimation. Weights ... More
The efficiency of the likelihood ratio to choose between a t-distribution and a normal distributionMay 08 2015A decision must often be made between heavy-tailed and Gaussian errors for a regression or a time series model, and the t-distribution is frequently used when it is assumed that the errors are heavy-tailed distributed. The performance of the likelihood ... More
The performance of univariate goodness-of-fit tests for normality based on the empirical characteristic function in large samplesMay 20 2016Jun 01 2016An empirical power comparison is made between two tests based on the empirical characteristic function and some of the best performing tests for normality. A simple normality test based on the empirical characteristic function calculated in a single point ... More
Competition between finite-size effects and dipole-dipole interactions in few-atom systemsJun 30 2016In this paper, we study the competition between finite-size effects (i.e. discernibility of particles) and dipole-dipole interactions in few-atom systems coupled to the electromagnetic field in vacuum. We consider two hallmarks of cooperative effects, ... More
The spectrum of a vertex model and related spin one chain sitting in a genus five curveJun 05 2017We derive the transfer matrix eigenvalues of a three-state vertex model whose weights are based on a $\mathrm{R}$-matrix not of difference form with spectral parameters lying on a genus five curve. We have shown that the basic building blocks for both ... More
Integrable Vertex Models with General TwistsDec 21 2005We review recent progress towards the solution of exactly solved isotropic vertex models with arbitrary toroidal boundary conditions. Quantum space transformations make it possible the diagonalization of the corresponding transfer matrices by means of ... More
Algebraic Bethe ansatz for a class of coupled asymmetric six-vertex free-fermion modelMar 18 2003We present an algebraic Bethe ansatz for certain submanifolds of the bilayer vertex models proposed by Shiroishi and Wadati as coupled asymmetric six-vertex free-fermion models. A peculiar feature of our formulation is the presence of a diagonal monodromy ... More
The excitations of the sympletic integrable models and their applicationsDec 09 2000The Bethe ansatz equations of the fundamental Sp(2N) integrable model are solved by a peculiar configuration of roots leading us to determine the nature of the excitations. They consist of N elementary generalized spinons and N-1 composite excitations ... More
On the parafermionic scattering of an integrable Heisenberg model with impurityFeb 21 1994We have studied the massive parafermionic sector of an integrable spin-$s$ chain with an impurity of spin-$s^{'}$ in presence of a magnetic field. The effect of the impurity is encoded in a computable parafermionic impurity scattering amplitude and its ... More
An Integrable Nineteen Vertex Model Lying on a HypersurfaceOct 24 2014We have found a family of solvable nineteen vertex model with statistical configurations invariant by the time reversal symmetry within a systematic study of the respective Yang-Baxter relation. The Boltzmann weights sit on a degree seven algebraic threefold ... More
On the integrability of the SU(N) Hubbard modelOct 05 1997We exhibit explicitly the intertwiner operator for the monodromy matrices of the recent proposed SU(N) Hubbard model [5]. This produces a new family of non-additive R-matrices and generalizes an earlier result by Shastry [2].
The thermodynamic Bethe ansatz for deformed W$A_{N-1}$ conformal field theoriesJan 16 1992We propose and investigate the thermodynamic Bethe ansatz equations for the minimal $W_p^N$ models~(associated with the $A_{N-1}$ Lie algebra) perturbed by the least~($Z_N$ invariant) primary field $\Phi_N$. Our results reproduce the expected ultraviolet ... More
Frederick William Gehring, Life and MathematicsNov 28 2016Frederick William Gehring was a hugely influential mathematician who spent most of his career at the University of Michigan. Gehring's major research contributions were to Geometric Function Theory, particularly in higher dimensions $\IR^n$, $n\geq 3$. ... More
Harmonic degree 1 maps are diffeomorphisms: Lewy's theorem for curved metricsOct 17 2013In 1936 H. Lewy showed that the Jacobian determinant of a harmonic homeomorphism between planar domains does not vanish and thus the map is a diffeomorphism. This built on the earlier existence results of Rad\'o and Kneser. R. Shoen and S.T. Yau generalised ... More
Random Lattices, Punctured Tori and the Teichmüller distributionJul 29 2018The moduli space of lattices of $\mathbb{C}$ is a Riemann surface of finite hyperbolic area with the square lattice as an origin. We select a lattice from the induced uniform distribution and calculate the statistics of the Teichm\"uller distance to the ... More
Two-qubit entangling gates between distant atomic qubits in a latticeMar 06 2017Jun 06 2017Arrays of qubits encoded in the ground-state manifold of neutral atoms trapped in optical (or magnetic) lattices appear to be a promising platform for the realization of a scalable quantum computer. Two-qubit conditional gates between nearest-neighbor ... More
Limits on Kaluza-Klein Models from COBE ResultsJul 05 1995The large-angular-scale anisotropy of the cosmic microwave background radiation in multidimensional cosmological models (Kaluza-Klein models) is studied. Limits on parameters of the models imposed by the experimental data are obtained. It is shown that ... More
Orthospectra of Geodesic Laminations and Dilogarithm Identities on Moduli SpaceMar 04 2009Given a measured lamination on a finite area hyperbolic surface we consider a natural measure Mon the real line obtained by taking the push-forward of the volume measure of the unit tangent bundle of the surface under an intersection function associated ... More
Saddlepoint methods in portfolio theoryDec 30 2011We discuss the use of saddlepoint methods in the analysis of portfolios, with particular reference to credit portfolios. The objective is to proceed from a model of the loss distribution, given through probabilities, correlations and the like, to an analytical ... More
pi+ pi+, K+ K+ and B B InteractionsOct 02 2008The most recent calculations of pi+ pi+ and K+ K+ scattering by the NPLQCD collaboration using domain-wall valence quarks on staggered MILC configurations are presented. In addition, a quenched calculation of the potentials between two B-mesons is discussed. ... More
The Delta-Delta Intermediate State in 1S0 Nucleon-Nucleon Scattering From Effective Field TheoryNov 12 1996We examine the role of the Delta-Delta intermediate state in low energy NN scattering using effective field theory. Theories both with and without pions are discussed. They are regulated with dimensional regularization and MSbar subtraction. We find that ... More
Nuclear Physics from Lattice QCDOct 26 2011I review recent progress in the development of Lattice QCD into a calculational tool for nuclear physics. Lattice QCD is currently the only known way of solving QCD in the low-energy regime, and it promises to provide a solid foundation for the structure ... More
Effective Field Theory in Nuclear PhysicsJul 11 2000I review recent developments in the application of effective field theory to nuclear physics. Emphasis is placed on precision two-body calculations and efforts to formulate the nuclear shell model in terms of an effective field theory.
Universal trading under proportional transaction costsMar 21 2016The theory of optimal trading under proportional transaction costs has been considered from a variety of perspectives. In this paper, we show that all the results can be interpreted using a universal law, illustrating the results in trading algorithm ... More
Discussion: Latent variable graphical model selection via convex optimizationNov 05 2012Discussion of "Latent variable graphical model selection via convex optimization" by Venkat Chandrasekaran, Pablo A. Parrilo and Alan S. Willsky [arXiv:1008.1290].
Baryon and lepton number violating effective operators in a non-universal extension of the Standard ModelDec 01 2014It is well known that non-abelian Yang-Mills theories present non-trivial minima of the action, the so-called instantons. In the context of electroweak theories these instanton solutions may induce violations of baryon and lepton number of the form $\Delta ... More
Integrability of the odd eight-vertex model with symmetric weightsNov 08 2017In this paper we investigate the integrability properties of a two-state vertex model on the square lattice whose microstates at a vertex has always an odd number of incoming or outcoming arrows. This model was named odd eight-vertex model by Wu and Kunz ... More
Integrable mixed vertex models from braid-monoid algebraMar 04 1999We use the braid-monoid algebra to construct integrable mixed vertex models. The transfer matrix of a mixed SU(N) model is diagonalized by nested Bethe ansatz approach.
Bethe ansatz solution of the $Osp(1|2n)$ invariant spin chainFeb 22 1995We have applied the analytical Bethe ansatz approach in order to solve the $Osp(1|2n)$ invariant magnet. By using the Bethe ansatz equations we have calculated the ground state energy and the low-lying dispersion relation. The finite size properties indicate ... More
RG flows and resonance scattering amplitudesNov 02 1992We review recent progresses in the study of factorized resonance scattering S-matrices. The resonance amplitudes are introduced through a suitable analytical continuation of the ADE Toda S-matrices. By using the thermodynamic Bethe ansatz approach we ... More
Renormalization group trajectories from resonance factorized S-matricesMay 12 1992We propose and investigate a large class of models possessing resonance factorized S-matrices. The associated Casimir energy describes a rich pattern of renormalization group trajectories related to flows in the coset models based on the simply laced ... More
The Theory of Quasiconformal Mappings in Higher Dimensions, INov 04 2013We present a survey of the many and various elements of the modern higher-dimensional theory of quasiconformal mappings and their wide and varied application. It is unified (and limited) by the theme of the author's interests. Thus we will discuss the ... More
Random Ideal Hyperbolic Quadrilaterals, the Cross Ratio Distribution and Punctured ToriJul 17 2018Earlier work introduced a geometrically natural probability measure on the group of all M\"obius transformations of the hyperbolic plane so as to be able to study "random" groups of M\"obius transformations, and in particular random two-generator groups. ... More
The tension equation with holomorphic coefficients, harmonic mappings and rigidityOct 17 2013The tension equation for a mapping $f:{\mathbb C}\to {\mathbb C}$ is the nonlinear second order equation \[ \Delta f +\varphi(f) f_z f_{\bar z} = 0\] Solutions are "harmonic" mappings. Here we give a complete description of the solution space of mappings ... More
The Geometry and Arithmetic of Kleinian GroupsNov 11 2013In this article we survey and describe various aspects of the geometry and arithmetic of Kleinian groups - discrete nonelementary groups of isometries of hyperbolic $3$-space. In particular we make a detailed study of two-generator groups and discuss ... More
The Solar Neighborhood. XXXIII. Parallax Results from the CTIOPI 0.9m Program: Trigonometric Parallaxes of Nearby Low-Mass Active and Young SystemsJan 02 2014We present basic observational data and association membership analysis for 45 young and active low-mass stellar systems from the ongoing RECONS photometry and astrometry program at the Cerro Tololo Inter-American Observatory. Most of these systems have ... More
HNCO abundances in galaxies: Tracing the evolutionary state of starburstsDec 19 2008The chemistry in the central regions of galaxies is expected to be strongly influenced by their nuclear activity. To find the best tracers of nuclear activity is of key importance to understand the processes taking place in the most obscured regions of ... More
Photodissociation chemistry footprints in the Starburst galaxy NGC 253Nov 13 2009We report the first detection of PDR molecular tracers, namely HOC+, and CO+, and confirm the detection of the also PDR tracer HCO towards the starburst galaxy NGC 253, claimed to be mainly dominated by shock heating and in an earlier stage of evolution ... More
A new Algorithm Based on Factorization for Heterogeneous Domain DecompositionSep 12 2014Often computational models are too expensive to be solved in the entire domain of simulation, and a cheaper model would suffice away from the main zone of interest. We present for the concrete example of an evolution problem of advection reaction diffusion ... More
Estimation of the shape parameter of a generalized Pareto distribution based on a transformation to Pareto distributed variablesOct 29 2012Dec 14 2012Random variables of the generalized Pareto distribution, can be transformed to that of the Pareto distribution. Explicit expressions exist for the maximum likelihood estimators of the parameters of the Pareto distribution. The performance of the estimation ... More
Hadronic Interactions with lattice QCDOct 12 2010I describe recent progress toward calculating hadronic interactions with Lattice QCD.
Few-Body Lattice CalculationsNov 10 2006I discuss the recent progress toward computing few-body observables using numerical lattice techniques. The focus is overwhelmingly on the latest results from lattice QCD calculations. I present preliminary results from a lattice calculation of the central ... More
$Λ(1405)$ Contribution to Kaon-Nucleon Scattering Lengths In Chiral Perturbation TheoryApr 18 1994We examine the role of the $\Lambda(1405)$ in kaon-nucleon scattering lengths using chiral perturbation theory. The leading nonanalytic SU(3) corrections reduce the coupling of the $\Lambda (1405)$ to $KN$ compared to $\Sigma\pi$. S-wave $K^-p$ scattering ... More
Nuclear Physics from QCD : The Anticipated Impact of Exa-Scale ComputingDec 04 2010I discuss highlights in the progress that is being made toward calculating processes of importance in nuclear physics from QCD using high performance computing. As exa-scale computing resources are expected to become available around 2017, I present current ... More
Discovery of Diffuse X-ray Emission in 47 TucApr 10 1995We present the results of a search for diffuse x-ray sources in a 65 ksec ROSAT PSPC exposure of 47 Tuc. There is faint, soft emission on the NE side of the cluster at a distance of 6 arcmin from the core. The location of this emission along the direction ... More
Sharp thresholds for high-dimensional and noisy recovery of sparsityMay 30 2006The problem of consistently estimating the sparsity pattern of a vector $\betastar \in \real^\mdim$ based on observations contaminated by noise arises in various contexts, including subset selection in regression, structure estimation in graphical models, ... More
Zeeman Doppler maps: the true and the spuriousApr 23 2016Oct 06 2016Numerical models of atomic diffusion in magnetic atmospheres of ApBp stars predict abundance structures that differ from the empirical abundance maps derived with (Zeeman) Doppler mapping (ZDM). Whereas both equilibrium abundance stratification calculations ... More
Integrable three-state vertex models with weights lying on genus five curvesMar 16 2013We investigate the Yang-Baxter algebra for $\mathrm{U}(1)$ invariant three-state vertex models whose Boltzmann weights configurations break explicitly the parity-time reversal symmetry. We uncover two families of regular Lax operators with nineteen non-null ... More
The two-dimensional O(3) nonlinear $σ$-model at finite temperatureFeb 13 1992We present a direct derivation of the thermodynamic integral equations of the O(3) nonlinear $\sigma$-model in two dimensions.
Exact solution of the simplest super-orthosymplectic invariant magnetOct 10 1994We present the exact solution of the $Osp(1|2)$ invariant magnet by the Bethe ansatz approach. The associated Bethe ansatz equation exhibit a new feature by presenting an explicit and distinct phase behaviour in even and odd sectors of the theory. The ... More
The role of virtual photons in quantum tunnelingDec 14 2018Quantum tunneling, a phenomenon which has no counterpart in classical physics, is the quantum-mechanical process by which a microscopic particle can transition through a potential barrier even when the energy of the incident particle is lower than the ... More
Simulated Coevolution in a Mutating EcologyOct 26 1999Mar 08 2000The bit-string Penna Model is used to simulate the competition between an asexual parthenogenetic and a sexual population sharing the same environment. A new-born of either population can mutate and become a part of the other with some probability. In ... More
Stochastic approximation with cone-contractive operators: Sharp $\ell_\infty$-bounds for $Q$-learningMay 15 2019Motivated by the study of $Q$-learning algorithms in reinforcement learning, we study a class of stochastic approximation procedures based on operators that satisfy monotonicity and quasi-contractivity conditions with respect to an underlying cone. We ... More
SUSY and Dark Matter Constraints from the LHCMay 05 2006The ability of the LHC to make statements about the dark matter problem is considered, with a specific focus on supersymmetry. After reviewing the current strategies for supersymmetry searches at the LHC (in both CMS and ATLAS), some key ATLAS studies ... More
On an early paper of Maryam MirzakhaniSep 21 2017Oct 17 2017Maryam Mirzakhani, the first female (and first Iranian) Fields Medalist, passed away on July 14, 2017 at the age of 40. This short note remembers her 1996 article in the Bulletin of the Institute of Combinatorics and its Applications and her early years ... More
A weighted least squares procedure to approximate least absolute deviation estimation in time series with specific reference to infinite variance unit root problemsOct 08 2012A weighted regression procedure is proposed for regression type problems where the innovations are heavy-tailed. This method approximates the least absolute regression method in large samples, and the main advantage will be if the sample is large and ... More