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Results for "Richard J Martin"

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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
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
Optimal multifactor trading under proportional transaction costsApr 29 2012Proportional transaction costs present difficult theoretical problems in trading algorithm design, on account of their lack of analytical tractability. The author derives a solution of DT-NT-DT form for an arbitrary model in which the the traded asset ... More
A CDS Option MiscellanyDec 30 2011CDS options allow investors to express a view on spread volatility and obtain a wider range of payoffs than are possible with vanilla CDS. We give a detailed exposition of different types of single-name CDS option, including options with upfront protection ... More
An exactly solvable self-convolutive recurrenceMar 25 2011We consider a self-convolutive recurrence whose solution is the sequence of coefficients in the asymptotic expansion of the logarithmic derivative of the confluent hypergeometic function $U(a,b,z)$. By application of the Hilbert transform we convert this ... More
Time since maximum of Brownian motion and asymmetric Levy processesNov 02 2018Motivated by recent studies of record statistics in relation to strongly correlated time series, we consider explicitly the drawdown time of a Levy process, which is defined as the time since it last achieved its running maximum when observed over a fixed ... More
On a stochastic version of Lanchester's model of combatMay 08 2019Lanchester's model of combat has certain deficiencies in its standard form arising from the neglect of the influence of random fluctuations. Several approaches to rectify this have been proposed and various results are scattered throughout the literature. ... More
The first-passage area for drifted Brownian motion and the moments of the Airy distributionJun 14 2007An exact expression for the distribution of the area swept out by a drifted Brownian motion till its first-passage time is derived. A study of the asymptotic behaviour confirms earlier conjectures and clarifies their range of validity. The analysis also ... More
The Bravyi-Kitaev transformation for quantum computation of electronic structureAug 29 2012Quantum simulation is an important application of future quantum computers with applications in quantum chemistry, condensed matter, and beyond. Quantum simulation of fermionic systems presents a specific challenge. The Jordan-Wigner transformation allows ... More
Star Formation in the Circumnuclear Environment of NGC1068Jun 25 1998We present near-infrared emission line images of the circumnuclear ring in NGC1068. We have measured the Br_gamma fluxes in a number of star forming complexes and derived extinctions for each of these by comparison with H_alpha. We investigate the star ... More
Formation of circumbinary planets in a dead zoneJun 21 2013Circumbinary planets have been observed at orbital radii where binary perturbations may have significant effects on the gas disk structure, on planetesimal velocity dispersion, and on the coupling between turbulence and planetesimals. Here, we note that ... More
Halo Assembly Bias in Hierarchical Structure FormationMar 25 2008We investigate the origin of halo assembly bias, the dependence of halo clustering on assembly history. We relate halo assembly to peak properties measured in the Lagrangian space of the initial linear Gaussian random density field, and show how these ... More
Channels, Learning, Queueing and Remote Estimation Systems With A Utilization-Dependent ComponentMay 10 2019In this article, we survey the main models, techniques, concepts, and results centered on the design and performance evaluation of engineered systems that rely on a utilization-dependent component (UDC) whose operation may depend on its usage history ... More
Renyi entropy of the totally asymmetric exclusion processAug 01 2017Sep 28 2017The Renyi entropy is a generalisation of the Shannon entropy that is sensitive to the fine details of a probability distribution. We present results for the Renyi entropy of the totally asymmetric exclusion process (TASEP). We calculate explicitly an ... More
Soft Collinear Effective Theory for Heavy WIMP AnnihilationSep 25 2014Nov 03 2014In a large class of models for Weakly Interacting Massive Particles (WIMPs), the WIMP mass $M$ lies far above the weak scale $m_W$. This work identifies universal Sudakov-type logarithms $\sim \alpha \log^2 (2\,M/m_W)$ that spoil the naive convergence ... More
Stabilizing a Queue Subject to Action-Dependent Server PerformanceMar 01 2019We consider a discrete-time system comprising an unbounded queue that logs tasks, a non-preemptive server, and a stationary non-work-conserving scheduler. Time is uniformly divided into intervals we call epochs, within which new tasks arrive according ... More
Uniformly perfect domains and convex hullsOct 10 2011Aug 01 2012Given a hyperbolic domain, the nearest point retraction is a conformally natural homotopy equivalence from the domain to the boundary of the convex core of its complement. Marden and Markovic showed that if the domain is uniformly perfect, then there ... More
A Parallel Time-Integrator for Solving the Linearized Shallow Water Equations on the Rotating SphereDec 09 2018Jan 22 2019With the stagnation of processor core performance, further reductions in the time-to-solution for geophysical fluid problems are becoming increasingly difficult with standard time integrators. Parallel-in-time exposes and exploits additional parallelism ... More
The Thurston metric on hyperbolic domains and boundaries of convex hullsFeb 09 2010Oct 04 2010We show that the nearest point retraction is a uniform quasi-isometry from the Thurston metric on a hyperbolic domain in the Riemann sphere to the boundary of the convex hull of its complement. As a corollary, one obtains explicit bounds on the quasi-isometry ... More
Mean Reversion Pays, but CostsMar 25 2011A mean-reverting financial instrument is optimally traded by buying it when it is sufficiently below the estimated `mean level' and selling it when it is above. In the presence of linear transaction costs, a large amount of value is paid away crossing ... More
Equivalent extensions of Hamilton-Jacobi-Bellman equations on hypersurfacesMar 26 2019We present a new formulation for the computation of solutions of a class of Hamilton Jacobi Bellman (HJB) equations on closed smooth surfaces of co-dimension one. For the class of equations considered in this paper, the viscosity solution of the HJB equation ... More
Renormalized volume and the volume of the convex coreFeb 17 2015Sep 01 2015We obtain upper and lower bounds on the difference between the renormalized volume and the volume of the convex core of a convex cocompact hyperbolic 3-manifold which depend on the injectivity radius of the boundary of the universal cover of the convex ... More
Electronic structure of self-assembled quantum dots: comparison between density functional theory and diffusion quantum Monte CarloMar 09 2000We have calculated the exchange, correlation, and total electronic energy of a realistic InAs self-assembled quantum dot embedded in a GaAs matrix as a function of the number of electrons in the dot. The many-body interactions have been treated using ... More
Molecular Gas and Star Formation in the CartwheelNov 23 2015Atacama Large Millimeter/submillimeter Array (ALMA) 12CO(J=1-0) observations are used to study the cold molecular ISM of the Cartwheel ring galaxy and its relation to HI and massive star formation (SF). CO moment maps find $(2.69\pm0.05)\times10^{9}$ ... More
Simple length rigidity for Kleinian surface groups and applicationsSep 08 2015We prove that a Kleinian surface groups is determined, up to conjugacy in the isometry group of $\mathbb H^3$, by its simple marked length spectrum. As a first application, we show that a discrete faithful representation of the fundamental group of a ... More
Magnetic Correlations in the Two Dimensional Anderson-Hubbard ModelSep 24 1996The two dimensional Hubbard model in the presence of diagonal and off-diagonal disorder is studied at half filling with a finite temperature quantum Monte Carlo method. Magnetic correlations as well as the electronic compressibility are calculated to ... More
Turbulent transport and its effect on the dead zone in protoplanetary discsFeb 29 2008Protostellar accretion discs have cool, dense midplanes where externally originating ionisation sources such as X-rays or cosmic rays are unable to penetrate. This suggests that for a wide range of radii, MHD turbulence can only be sustained in the surface ... More
Light, matter, and quantum randomness generation: A relativistic quantum information perspectiveOct 18 2017Apr 30 2018We study how quantum randomness generation based on unbiased measurements on a hydrogen-like atom can get compromised by virtue of the unavoidable coupling of the atom with the electromagnetic field. Concretely, we show that an adversary with access to ... More
The Pauli exclusion principle at strong coupling: Holographic matter and momentum spaceOct 04 2012For free fermions at finite density, the Pauli exclusion principle is responsible for the existence of a Fermi surface and the consequent presence of low energy spectral weight over a finite range of momenta. We investigate the extent to which this effect ... More
Spectral response and contact of the unitary Fermi gasFeb 22 2019May 24 2019We measure radiofrequency (rf) spectra of the homogeneous unitary Fermi gas at temperatures ranging from the Boltzmann regime through quantum degeneracy and across the superfluid transition. For all temperatures, a single spectral peak is observed. Its ... More
Probabilistic Analysis of Linear Programming DecodingFeb 02 2007Mar 10 2008We initiate the probabilistic analysis of linear programming (LP) decoding of low-density parity-check (LDPC) codes. Specifically, we show that for a random LDPC code ensemble, the linear programming decoder of Feldman et al. succeeds in correcting a ... More
Compressive and Adaptive Millimeter-wave SARFeb 06 2014We apply adaptive sensing techniques to the problem of locating sparse metallic scatterers using high-resolution, frequency modulated continuous wave W-band RADAR. Using a single detector, a frequency stepped source, and a lateral translation stage, inverse ... More
Non-Equilibrium Large N Yukawa Dynamics: marching through the Landau poleAug 13 2001The non-equilibrium dynamics of a Yukawa theory with N fermions coupled to a scalar field is studied in the large N limit with the goal of comparing the dynamics predicted from the renormalization group improved effective potential to that obtained including ... More
On the ionisation fraction in protoplanetary disks III. The effect of X-ray flares on gas-phase chemistryMay 11 2006Context. Recent observations of the X-ray emission from T Tauri stars in the Orion nebula have shown that they undergo frequent outbursts in their X-ray luminosity. These X-ray flares are characterised by increases in luminosity by two orders of magnitude, ... More
On the Ionisation Fraction in Protoplanetary Disks I: Comparing Different Reaction NetworksSep 19 2005Nov 09 2005We calculate the ionisation fraction in protostellar disk models using a number of different chemical reaction networks, including gas-phase and gas-grain reaction schemes. The disk models we consider are conventional alpha-disks, which include viscous ... More
On the Ionisation Fraction in Protoplanetary Disks II: The Effect of Turbulent Mixing on Gas--phase ChemistrySep 19 2005We calculate the ionisation fraction in protostellar disk models using two different gas-phase chemical networks, and examine the effect of turbulent mixing by modelling the diffusion of chemical species vertically through the disk. The aim is to determine ... More
Spectral response and contact of the unitary Fermi gasFeb 22 2019We measure radiofrequency (rf) spectra of the homogeneous unitary Fermi gas at temperatures ranging from the Boltzmann regime through quantum degeneracy and across the superfluid transition. For all temperatures, a single spectral peak is observed. Its ... More
Boiling a Unitary Fermi LiquidNov 01 2018Jan 20 2019We study the thermal evolution of a highly spin-imbalanced, homogeneous Fermi gas with unitarity limited interactions, from a Fermi liquid of polarons at low temperatures to a classical Boltzmann gas at high temperatures. Radio-frequency spectroscopy ... More
Measuring the phase velocity of twisted wavefrontsOct 17 2018Traditionally one defines the speed of a wave as a property of the medium. Recent studies in photonics have challenged this idea, indicating that spatial shaping of the optical wavefront has can alter the arrival time of single photons when compared to ... More
Quantum teleportation over 100 km of fiber using highly-efficient superconducting nanowire single photon detectorsOct 02 2015Quantum teleportation is an essential quantum operation by which we can transfer an unknown quantum state to a remote location with the help of quantum entanglement and classical communication. Since the first experimental demonstrations using photonic ... More
Single-photon source characterization with infrared-sensitive superconducting single-photon detectorsJul 28 2006Single-photon sources and detectors are key enabling technologies in quantum information processing. Nanowire-based superconducting single-photon detectors (SSPDs) offer single-photon detection from the visible well into the infrared with low dark counts, ... More
Capacity Planning for Cluster Tools in the Semiconductor IndustryMay 03 2016This paper proposes a new model for Cluster-tools with two load locks. Cluster-tools are widely used to automate single wafer processing in semiconductor industry. The load locks are the entry points into the vacuum of the Cluster-tool's mainframe. Usually ... More
Polarization and Strong Infra-Red Activity in Compressed Solid HydrogenSep 25 1998Under a pressure of ~150 GPa solid molecular hydrogen undergoes a phase transition accompanied by a dramatic rise in infra-red absorption in the vibron frequency range. We use the Berry's phase approach to calculate the electric polarization in several ... More
Cathoristic logic: A modal logic of incompatible propositionsNov 26 2014Cathoristic logic is a multi-modal logic where negation is replaced by a novel operator allowing the expression of incompatible sentences. We present the syntax and semantics of the logic including complete proof rules, and establish a number of results ... More
Investigation of the Role of Elastic Unitarity in High-Energy Scattering: Gribov's Theorem and the Froissart BoundMar 27 2001We re-examine V. Gribov's theorem of 1960 according to which the total cross-section cannot approach a finite non-zero limit with, at the same time, a diffraction peak having a finite slope. We are very close to proving by an explicit counter-example ... More
Sparse group lasso and high dimensional multinomial classificationMay 06 2012Feb 06 2013The sparse group lasso optimization problem is solved using a coordinate gradient descent algorithm. The algorithm is applicable to a broad class of convex loss functions. Convergence of the algorithm is established, and the algorithm is used to investigate ... More
Internet Protocol Version 6: Dead or Alive?Aug 17 2018Internet Protocol (IP) is the narrow waist of multilayered Internet protocol stack which defines the rules for data sent across networks. IPv4 is the fourth version of IP and first commercially available for deployment set by ARPANET in 1983 which is ... More
Jahn-Teller Distortion and Ferromagnetism in the Dilute Magnetic Semiconductors GaN:MnNov 16 2004Using first-principles total-energy methods, we investigate Jahn-Teller distortions in III-V dilute magnetic semiconductors, GaAs:Mn and GaN:Mn in the cubic zinc blende structure. The results for an isolated Mn impurity on a Ga site show that there is ... More
Modeling Dual Pathways for the Metazoan Spindle Assembly CheckpointOct 28 2006Using computational modelling, we investigate mechanisms of signal transduction focusing on the spindle assembly checkpoint where a single unattached kinetochore is able to signal to prevent cell cycle progression. This inhibitory signal switches off ... More
$Ω_c$ and other charmed baryons revisitedApr 10 1995The mass of the $\Omega^0_c$ baryon with quark content (ssc) is computed in a potential model whose parameters have been determined in 1981 by fitting the spectrum of heavy mesons. It is found in perfect agreement with a recent measurement at the CERN ... More
First principles study of the adsorption of C60 on Si(111)Oct 31 2000The adsorption of C60 on Si(111) has been studied by means of first-principles density functional calculations. A 2x2 adatom surface reconstruction was used to simulate the terraces of the 7x7 reconstruction. The structure of several possible adsorption ... More
Tomography and state reconstruction with superconducting single-photon detectorsJun 22 2012Sep 06 2012We perform quantum state reconstruction of coherent and thermal states with a detector which has an enhanced multiphoton response. The detector is based on superconducting nanowires, where the bias current sets the dependence of the click probability ... More
Sparse and compositionally robust inference of microbial ecological networksAug 18 2014Feb 14 201516S-ribosomal sequencing and other metagonomic techniques provide snapshots of microbial communities, revealing phylogeny and the abundances of microbial populations across diverse ecosystems. While changes in microbial community structure are demonstrably ... More
Two and Three-body Contacts in the Unitary Bose GasAug 15 2016In many-body systems governed by pairwise contact interactions, a wide range of observables is linked by a single parameter, the two-body contact, which quantifies two-particle correlations. This profound insight has transformed our understanding of strongly ... More
Splay nematic phaseJun 26 2018Nov 13 2018Different liquid crystalline phases with long-range orientational but not positional order, so-called nematic phases, are scarce. It rarely occurs that a new nematic phase is discovered and such event is inevitably accompanied by a great interest. Here, ... More
The X-ray Spectrum of the z=6.30 QSO SDSS J1030+0524Jun 24 2004We present a deep XMM-Newton observation of the z=6.30 QSO SDSS J1030+0524, the second most distant quasar currently known. The data contain sufficient counts for spectral analysis, demonstrating the ability of XMM-Newton to measure X-ray spectral shapes ... More
Generalising rate heterogeneity across sites in statistical phylogeneticsFeb 20 2017May 02 2019Phylogenetics uses alignments of molecular sequence data to learn about evolutionary trees relating species. Along branches, sequence evolution is modelled using a continuous-time Markov process characterised by an instantaneous rate matrix. Early models ... More
Josephson Plasma Resonance in Tl$_2$Ba$_2$CaCu$_2$O$_8$ in a Magnetic Field Measured using THz SpectroscopyAug 15 2001We report the first measurements of the $c$-axis Josephson Plasma Resonance (JPR) in Tl$_2$Ba$_2$CaCu$_2$O$_8$ as a function of temperature with and without a $c$-axis magnetic field using terahertz time-domain spectroscopy in transmission. The JPR is ... 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
Metal-Insulator transitions in generalized Hubbard modelsDec 20 1999We study the Mott transition in Hubbard models with a degenerate band on different 3-dimensional lattices. While for a non-degenerate band only the half-filled system may exhibit a Mott transition, with degeneracy there can be a transition for any integer ... More
Coupled regularization with multiple data discrepanciesNov 30 2017We consider a class of regularization methods for inverse problems where a coupled regularization is employed for the simultaneous reconstruction of data from multiple sources. Applications for such a setting can be found in multi-spectral or multi-modality ... More
Polarization and localization in insulators: generating function approachNov 02 1999Mar 28 2000We develop the theory and practical expressions for the full quantum-mechanical distribution of the intrinsic macroscopic polarization of an insulator in terms of the ground state wavefunction. The central quantity is a cumulant generating function which ... More
An introduction to pressure metrics on higher Teichmüller spacesJul 14 2015Sep 09 2016We discuss how one uses the thermodynamic formalism to produce metrics on higher Teichm\"uller spaces. Our higher Teichm\"uller spaces will be spaces of Anosov representations of a word-hyperbolic group into a semi-simple Lie group. We begin by discussing ... More
Coupling and Harnack inequalities for Sierpinski carpetsOct 01 1993Uniform Harnack inequalities for harmonic functions on the pre- and graphical Sierpinski carpets are proved using a probabilistic coupling argument. Various results follow from this, including the construction of Brownian motion on Sierpinski carpets ... More
An introduction to pressure metrics on higher Teichmüller spacesJul 14 2015Aug 14 2017We discuss how one uses the thermodynamic formalism to produce metrics on higher Teichm\"uller spaces. Our higher Teichm\"uller spaces will be spaces of Anosov representations of a word-hyperbolic group into a semi-simple Lie group. We begin by discussing ... More
Exchange-Correlation Hole in Polarized Insulators: Implications for the Microscopic Functional Theory of DielectricsSep 05 1997We present a simple and direct proof that the exchange-correlation hole, and therefore the exchange-correlation energy, in a polarized insulator is not determined by the bulk density alone. It is uniquely characterized by the density and the macroscopic ... More
Optimal radiotherapy treatment planning using minimum entropy modelsMay 26 2011We study the problem of finding an optimal radiotherapy treatment plan. A time-dependent Boltzmann particle transport model is used to model the interaction between radiative particles with tissue. This model allows for the modeling of inhomogeneities ... More
Penalized estimation in large-scale generalized linear array modelsOct 12 2015Sep 02 2016Large-scale generalized linear array models (GLAMs) can be challenging to fit. Computation and storage of its tensor product design matrix can be impossible due to time and memory constraints, and previously considered design matrix free algorithms do ... More
Performance Improvements for Nuclear Reaction Network IntegrationJan 22 2014Mar 03 2014Aims: The aim of this work is to compare the performance of three reaction network integration methods used in stellar nucleosynthesis calculations. These are the Gear's backward differentiation method, Wagoner's method (a 2nd-order Runge-Kutta method), ... More
Coupled regularization with multiple data discrepanciesNov 30 2017Mar 22 2018We consider a class of regularization methods for inverse problems where a coupled regularization is employed for the simultaneous reconstruction of data from multiple sources. Applications for such a setting can be found in multi-spectral or multi-modality ... More
The lateral transhipment problem with a-priori routes, and a lot sizing applicationDec 23 2015We propose exact solution approaches for a lateral transhipment problem which, given a pre-specified sequence of customers, seeks an optimal inventory redistribution plan considering travel costs and profits dependent on inventory levels. Trip-duration ... More
Domain Wall Dominated UniversesAug 05 1999Sep 08 1999We consider a cosmogony with a dark matter component consisting of a network of frustrated domain walls. Such a network provides a solid dark matter component with $p=-(2/3)\rho $ that remains unclustered on small scales and with $\Omega_{\rm dw}\approx ... More
Filling dependence of the Mott transition in the degenerate Hubbard modelMay 25 1999Describing the doped Fullerenes using a generalized Hubbard model, we study the Mott transition for different integer fillings of the t_1u band. We use the opening of the energy-gap E_g as a criterion for the transition. E_g is calculated as a function ... More
Quantum Monte Carlo calculations for integer-doped FulleridesApr 06 1998The doped Fullerides can be well described by a Hubbard model, which comprises the partly filled, threefold-degenerate t_1u orbital and the on-site Coulomb interaction U. The orbital degeneracy is known to shift the critical ratio U_c/W for the Mott-Hubbard ... More
Optimization of Gutzwiller Wavefunctions in Quantum Monte CarloMar 04 1999Gutzwiller functions are popular variational wavefunctions for correlated electrons in Hubbard models. Following the variational principle, we are interested in the Gutzwiller parameters that minimize e.g. the expectation value of the energy. Rewriting ... More
An improved bound for Sullivan's convex hull theoremJul 14 2014Sep 22 2015Sullivan showed that there exists $K_0$ such that if $\Omega\subset \hat{\mathbb{C}}$ is a simply connected hyperbolic domain, then there exists a conformally natural $K_0$-quasiconformal map from $\Omega$ to the boundary ${\rm Dome}(\Omega)$ of the convex ... More
Exponential Integrators with Parallel-in-Time Rational Approximations for the Shallow-Water Equations on the Rotating SphereMay 16 2018Feb 02 2019High-performance computing trends towards many-core systems are expected to continue over the next decade. As a result, parallel-in-time methods, mathematical formulations which exploit additional degrees of parallelism in the time dimension, have gained ... More
Nanowire photonic crystal waveguides for single-atom trapping and strong light-matter interactionsFeb 05 2014We present a comprehensive study of dispersion-engineered nanowire photonic crystal waveguides suitable for experiments in quantum optics and atomic physics with optically trapped atoms. Detailed design methodology and specifications are provided, as ... More
Fixed-node DMC for Fermions on a lattice: Application to the doped FulleridesAug 11 1998Fullerides are crystals made from C60 molecules. When doped with alkali metals the valence electrons of the alkali atoms are transfered to the C60 molecules. We show how to set up a model Hamiltonian to describe the correlated hopping of these electrons ... More
Mott Transition in Degenerate Hubbard Models: Application to Doped FullerenesAug 23 1996The Mott-Hubbard transition is studied for a Hubbard model with orbital degeneracy N, using a diffusion Monte-Carlo method. Based on general arguments, we conjecture that the Mott-Hubbard transition takes place for U/W \propto \sqrt{N}, where U is the ... More
Ab Initio Quantum Chemistry using the Density Matrix Renormalization GroupAug 11 1998In this paper we describe how the density matrix renormalization group (DMRG) can be used for quantum chemical calculations for molecules, as an alternative to traditional methods, such as configuration interaction or coupled cluster approaches. As a ... More
Complete Analysis of Baryon Magnetic Moments in 1/N_cApr 19 2004Apr 21 2004We generate a complete basis of magnetic moment operators for the N_c = 3 ground-state baryons in the 1/N_c expansion, and compute and tabulate all associated matrix elements. We then compare to previous results derived in the literature and predict additional ... More
Stochastic turbulence modeling in RANS simulations via Multilevel Monte CarloNov 01 2018A multilevel Monte Carlo (MLMC) method for quantifying model-form uncertainties associated with the Reynolds-Averaged Navier-Stokes (RANS) simulations is presented. Two, high-dimensional, stochastic extensions of the RANS equations are considered to demonstrate ... More
Screening, Coulomb pseudopotential, and superconductivity in alkali-doped FullerenesFeb 17 1999We study the static screening in a Hubbard-like model using quantum Monte Carlo. We find that the random phase approximation is surprisingly accurate almost up to the Mott transition. We argue that in alkali-doped Fullerenes the Coulomb pseudopotential ... More
Mott-Hubbard insulators for systems with orbital degeneracyJan 21 1997We study how the electron hopping reduces the Mott-Hubbard band gap in the limit of a large Coulomb interaction U and as a function of the orbital degeneracy N. The results support the conclusion that the hopping contribution grows as roughly \sqrt{N}W, ... More
Hyperon Radiative Decays in the 1/N_c ExpansionApr 29 2004Using a recent calculation of transition magnetic moments in the 1/N_c expansion and a calculation showing the suppression of E2/M1 by powers of N_c, we compute the widths for the radiative decays Sigma^* --> Sigma gamma, Sigma^* --> Lambda gamma, and ... More
Constraints on Natural MNS Parameters from |U_e3|Dec 16 2003May 04 2004The MNS matrix structure emerging as a result of recent neutrino measurements strongly suggests two large mixing angles (solar and atmospheric) and one small angle (|U_e3| << 1). Especially when combined with the neutrino mass hierarchy, these values ... More
A presentation for the symplectic blob algebraAug 10 2018The symplectic blob algebra $b_n$ ($n \in \mathbb{N}$) is a finite dimensional algebra defined by a multiplication rule on a basis of certain diagrams. The rank $r(n)$ of $b_n$ is not known in general, but $r(n)/n$ grows unboundedly with $n$. For each ... More
On the parallelization of stellar evolution codesNov 22 2018Multidimensional nucleosynthesis studies with hundreds of nuclei linked through thousands of nuclear processes are still computationally prohibitive. To date, most nucleosynthesis studies rely either on hydrostatic/hydrodynamic simulations in spherical ... More
Sensitivity analysis for dose deposition in radiotherapy via a Fokker-Planck modelOct 21 2014In this paper we study the sensitivities of electron dose calculations with respect to the stopping power and the transport coefficients. We focus on the application to radiotherapy simulations. We use a Fokker-Planck approximation to the Boltzmann transport ... More
Actions of higher-rank lattices on free groupsApr 19 2010Apr 13 2011If $G$ is a semisimple Lie group of real rank at least 2 and $\Gamma$ is an irreducible lattice in $G$, then every homomorphism from $\Gamma$ to the outer automorphism group of a finitely generated free group has finite image.
An asymptotic multipartite Kühn-Osthus theoremApr 11 2016In this paper we prove an asymptotic multipartite version of a well-known theorem of K\"uhn and Osthus by establishing, for any graph $H$ with chromatic number $r$, the asymptotic multipartite minimum degree threshold which ensures that a large $r$-partite ... More
Screening of a point charge: a fixed-node diffusion Monte Carlo studyApr 19 1999We study the static screening in a Hubbard-like model using fixed-node diffusion Monte Carlo. We find that the random phase approximation is surprisingly accurate even for metallic systems close to the Mott transition. As a specific application we discuss ... More
Dielectric screening in doped FulleridesApr 07 1998For conventional superconductors the electron-electron interaction is strongly reduced by retardation effects, making the formation of Cooper pairs possible. In the alkali-doped Fullerides, however, there are no strong retardation effects. But dielectric ... More
On quasi-heredity and cell module homomorphisms in the symplectic blob algebraJul 18 2017This paper reports key advances in the study of the representation theory of the symplectic blob algebra. For suitable specialisations of the parameters we construct four large families of homomorphisms between cell modules. We hence find a large family ... More
Symplectormophism groups of non-compact manifolds, orbifold balls, and a space of LagrangiansMay 31 2013We establish connections between contact isometry groups of certain contact manifolds and compactly supported symplectomorphism groups of their symplectizations. We apply these results to investigate the space of symplectic embeddings of balls with a ... More
Convergence of Finite Element Methods for Singular Stochastic ControlNov 20 2017Jun 07 2018A numerical method is proposed for a class of stochastic control problems including singular behavior. This method solves an infinite-dimensional linear program equivalent to the stochastic control problem using a finite element type approximation, which ... More
Machine Learning of Algebraic Stress Models using Deterministic Symbolic RegressionMay 18 2019A novel deterministic symbolic regression method SpaRTA (Sparse Regression of Turbulent Stress Anisotropy) is introduced to infer algebraic stress models for the closure of RANS equations directly from high-fidelity LES or DNS data. The models are written ... More
An asymptotic multipartite Kühn-Osthus theoremApr 11 2016Jul 13 2017In this paper we prove an asymptotic multipartite version of a well-known theorem of K\"uhn and Osthus by establishing, for any graph $H$ with chromatic number $r$, the asymptotic multipartite minimum degree threshold which ensures that a large $r$-partite ... More
Interdependent Security with Strategic Agents and Cascades of InfectionFeb 26 2015We investigate cascades in networks consisting of strategic agents with interdependent security. We assume that the strategic agents have choices between i) investing in protecting themselves, ii) purchasing insurance to transfer (some) risks, and iii) ... More