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Multi-physics simulations using a hierarchical interchangeable software interfaceOct 12 2011We introduce a general-purpose framework for interconnecting scientific simulation programs using a homogeneous, unified software interface. Our framework is intrinsically parallel, and conveniently separates all components in memory. It performs unit ... More

Simulations of the Sunyaev-Zeldovich Effect from QuasarsAug 02 2008Quasar feedback has most likely a substantial but only partially understood impact on the formation of structure in the universe. A potential direct probe of this feedback mechanism is the Sunyaev-Zeldovich effect: energy emitted from quasar heats the ... More

The consequences of a nearby supernova on the early Solar SystemFeb 12 2018Apr 11 2018If the Sun was born in a relatively compact open cluster, it is quite likely that a massive (10MSun) star was nearby when it exploded in a supernova. The repercussions of a supernova can be rather profound, and the current Solar System may still bear ... More

The survivability of planetary systems in young and dense star clustersFeb 12 2019We perform a simulation using the Astrophysical Multipurpose Software Environment of the Orion Trapezium star cluster in which the evolution of the stars and the dynamics of planetary systems are taken into account. The initial conditions are selected ... More

The origin of interstellar asteroidal objects like 1I/2017 U1 'OumuamuaNov 09 2017May 11 2018We study the origin of the interstellar object 1I/2017 U1 'Oumuamua by juxtaposing estimates based on the observations with simulations. We speculate that objects like 'Oumuamua are formed in the debris disc as left over from the star and planet formation ... More

The radiation driven winds of rotating B[e] supergiantsMay 15 2000We have formulated the momentum equation for sectorial line driven winds from rotating stars including: (a) the oblateness of the star, (b) gravity darkening (von Zeipel effect), (c) conservation of angular momentum, (d) line driving specified by the ... More

Stellar winds near massive black holes: The case of the S-starsDec 10 2015The Galactic center provides a unique laboratory to study the interaction of a supermassive black hole (SMBH) with its gaseous and stellar environment. Simulations to determine the accretion of stellar winds from the surrounding O-stars onto the black ... More

Multi-physics simulations using a hierarchical interchangeable software interfaceApr 25 2012Sep 17 2012We introduce a general-purpose framework for interconnecting scientific simulation programs using a homogeneous, unified interface. Our framework is intrinsically parallel, and conveniently separates all component numerical modules in memory. This strict ... More

The Origin of Chaos in the Orbit of Comet 1P/HalleyJun 22 2016According to Munoz-Gutierrez et al. (2015) the orbit of comet 1P/Halley is chaotic with a surprisingly small Lyapunov time scale of order its orbital period. In this work we analyse the origin of chaos in Halley's orbit and the growth of perturbations, ... More

The influence of dense gas rings on the dynamics of a stellar disk in the Galactic centerDec 08 2015The Galactic center hosts several hundred early-type stars, about 20% of which lie in the so-called clockwise disk, while the remaining 80% do not belong to any disks. The circumnuclear ring (CNR), a ring of molecular gas that orbits the supermassive ... More

High-Performance Distributed Multi-Model / Multi-Kernel Simulations: A Case-Study in Jungle ComputingMar 01 2012High-performance scientific applications require more and more compute power. The concurrent use of multiple distributed compute resources is vital for making scientific progress. The resulting distributed system, a so-called Jungle Computing System, ... More

Formation versus destruction: the evolution of the star cluster population in galaxy mergersDec 05 2011(Abridged) Interacting galaxies are well-known for their high star formation rates and rich star cluster populations, but the rapidly changing tidal field can also efficiently destroy clusters. We use numerical simulations of merging disc galaxies to ... More

Current induced and interaction driven Dirac-point drag of massless quasi-relativistic fermionsJan 11 2016Aug 30 2016We study the quasiparticle properties of two-dimensional massless Dirac Fermions when the many-body states possess a finite momentum density in the clean limit. The lack of Galilean invariance endows the many-body states at finite momentum density with ... More

Gene and Gene-Set Analysis for Genome-Wide Association StudiesAug 19 2013Genome-wide association studies (GWAS) have identified hundreds of loci at very stringent levels of statistical significance across many different human traits. However, it is now clear that very large samples (n~10^4-10^5) are needed to find the majority ... More

Reverse mathematics of the finite downwards closed subsets of $\mathbb{N}^k$ ordered by inclusionOct 04 2016Nov 15 2016We show that the well-partial orderedness of the finite downwards closed subsets of $\mathbb{N}^k$ ,ordered by inclusion, is equivalent to the well-foundedness of the ordinal $\omega^{\omega^\omega}$. This was conjectured to be the case by Hatzikiriakou ... More

Reverse mathematics of the finite downwards closed subsets of $\mathbb{N}^k$ ordered by inclusion and adjacent Ramsey for fixed dimensionOct 04 2016Oct 04 2017We show that the well-partial orderedness of the finite downwards closed subsets of $\mathbb{N}^k$ ,ordered by inclusion, is equivalent to the well-foundedness of the ordinal $\omega^{\omega^\omega}$. This was conjectured to be the case by Hatzikiriakou ... More

Phase transition results for three Ramsey-like theoremsMar 22 2016We classify a sharp phase transition threshold for Friedman's finite adjacent Ramsey theorem. We extend the method for showing this result to two previously known classifications involving Ramsey theorem variants: the Paris--Harrington theorem and the ... More

SPHRAY: A Smoothed Particle Hydrodynamics Ray Tracer for Radiative TransferFeb 26 2008We introduce SPHRAY, a Smoothed Particle Hydrodynamics (SPH) ray tracer designed to solve the 3D, time dependent, radiative transfer (RT) equations for arbitrary density fields. The SPH nature of SPHRAY makes the incorporation of separate hydrodynamics ... More

Hadronization in Nuclei - Multidimensional StudyNov 10 2011Hadron multiplicities in semi-inclusive deep-inelastic scattering were measured on neon, krypton and xenon targets relative to deuterium at an electron-beam energy of 27.6 GeV at HERMES. These ratios were determined as a function of the virtual-photon ... More

Adjacent Ramsey theory and Higman's lemmaFeb 25 2016Feb 29 2016We show a short proof of Higman's lemma using Friedman's adjacent Ramsey theorem for pairs. This provides an alternative proof of the known upper bound for the reverse mathematical status of Higman's lemma and that of its miniaturised version.

Reverse mathematics of the finite downwards closed subsets of $\mathbb{N}^k$ ordered by inclusionOct 04 2016Oct 05 2016We show that the well-partial orderedness of the finite downwards closed subsets of $\mathbb{N}^k$ ,ordered by inclusion, is equivalent to the well-foundedness of the ordinal $\omega^{\omega^\omega}$. This was conjectured to be the case by Hatzikiriakou ... More

Monomial ideals and independence of $\mathrm{I}Σ_2$Mar 11 2016We show that a miniaturised version of Maclagan's theorem on monomial ideals is equivalent to $\mathrm{1}{-}\mathrm{Con}(\mathrm{I}\Sigma_2)$ and classify a phase transition threshold for this theorem. This work highlights the combinatorial nature of ... More

Reverse mathematics of the relativised fast growing hierarchyAug 18 2016A short note on the reverse mathematical status of the totality of the relativised fast growing hierarchy.

On $α$-largeness and the Paris-Harrington principle in $\mathrm{RCA}$ and $\mathrm{RCA}_0^{\displaystyle{*}}$Nov 28 2016We examine, within $\mathrm{RCA}$, the treatment by Ketonen and Solovay on the use of $\alpha$-largeness for giving an upper bound for the Paris-Harrington principle. We also show how to modify the arguments to work within $\mathrm{RCA}_0^{\displaystyle{*}}$. ... More

Dickson's lemma and weak Ramsey theoryDec 09 2015Oct 03 2017We explore the connections between Dickson's lemma and weak Ramsey theory. We show that a weak version of the Paris--Harrington principle for pairs in $c$ colors and miniaturized Dickson's lemma for $c$-tuples are equivalent over $\mathsf{RCA}_0^{\ast}$. ... More

The consequences of a nearby supernova on the early Solar SystemFeb 12 2018If the Sun was born in a relatively compact open cluster (half-mass radius ~3pc) with ~10^3 stars, it is quite likely that a massive (>10MSun) star was nearby when it exploded in a supernova. The repercussions of a supernova can be rather profound, and ... More

Slow Lévy flightsSep 04 2015Feb 04 2016Among Markovian processes, the hallmark of L\'evy flights is superdiffusion, or faster-than-Brownian dynamics. Here we show that L\'evy laws, as well as Gaussians, can also be the limit distributions of processes with long range memory that exhibit very ... More

Quantum nonlinear Hall effect induced by Berry curvature dipole in time-reversal invariant materialsAug 03 2015It is well-known that a non-vanishing Hall conductivity requires time-reversal symmetry breaking. However, in this work, we demonstrate that a Hall-like transverse current can occur in second-order response to an external electric field in a wide class ... More

Capture of exocomets and the erosion of the Oort cloud due to stellar encounters in the GalaxyOct 16 2017The Oort cloud (OC) probably formed more than 4$\,$Gyr ago and has been moving with the Sun in the Galaxy since, exposed to external influences, most prominently to the Galactic tide and passing field stars. Theories suggest that other stars might posses ... More

The origin of interstellar asteroidal objects like 1I/2017 U1Nov 09 2017With the recently discovered interstellar object 1I/2017U1 (1I/'Oumuamua) we have to realize that the Solar System is not isolated, but part of a larger environment with which we interact. We compare the kinematics of 1I/2017U1 with simulations of the ... More

Theory of Native Orientational Pinning in Quantum Hall NematicsJul 21 2013The orientation of the electron-nematic states discovered in the quantum Hall regime of GaAs $[001]$ growth-direction quantum wells is pinned by a weak native source of anisotropy. In this Letter we explain that this property, which has remained mysterious ... More

Modeling the formation and evolution of star cluster populations in galaxy simulationsFeb 04 2011(Abridged) The formation and evolution of star cluster populations are related to the galactic environment. Cluster formation is governed by processes acting on galactic scales, and star cluster disruption is driven by the tidal field. In this paper, ... More

Broken SU(4) Symmetry and The Fractional Quantum Hall Effect in GrapheneOct 06 2013Mar 28 2014We construct a variational description for incompressible ground states and charge gaps in the N = 0 LL of graphene which accounts for the 4-fold Landau level degeneracy and for the short range interactions that break the SU(4) spin-valley invariance. ... More

Landau Level Mixing and the Fractional Quantum Hall EffectFeb 15 2013Jun 24 2013We derive effective Hamiltonians for the fractional quantum Hall effect in n=0 and n=1 Landau levels that account perturbatively for Landau level mixing by electron-electron interactions. To second order in the ratio of electron-electron interaction to ... More

Exploring the Mysteries of Strong Interactions - The PANDA ExperimentJan 08 2007The physics of strong interactions is undoubtedly one of the most challenging areas of modern science. The PANDA experiment will be devoted to charmonium spectroscopy, gluonic excitations (hybrids, glueballs), open and hidden charm in nuclei, gamma-ray ... More

Physics Programme of PANDA at FAIRSep 23 2009The standard model and Quantum Chromodynamics (QCD) have undergone rigorous tests at distances much shorter than the size of a nucleon. Up to now, the predicted phenomena are reproduced rather well. However, at distances comparable to the size of a nucleon, ... More

Solving the quantum dimer and six vertex models one electric field line at a timeFeb 05 2019The nature and the very existence of the resonant plaquette valence bond state that separates the classical columnar phase and the Rokhsar and Kivelson point in the quantum dimer model remains unsettled. Here we take a different line of attack on this ... More

Molecular gas, CO, and star formation in galaxies: emergent empirical relations, feedback, and the evolution of very gas-rich systemsOct 26 2009Nov 03 2009We use time-varying models of the coupled evolution of the HI, H_2 gas phases and stars in galaxy-sized numerical simulations to: a) test for the emergence of the Kennicutt-Schmidt (K-S) and the H_2-pressure relation, b) explore a realistic H_2-regulated ... More

The formation of planets in circumbinary disksOct 17 2012We examine the formation of planets around binary stars in light of the recently discovered systems Kepler 16, 34 and 35. We conduct hydrodynamical simulations of self gravitating disks around binary systems. The selected binary and disk parameters are ... More

Deviations from the Schmidt-Kennicutt relations during early galaxy evolutionMay 19 2010We utilize detailed time-varying models of the coupled evolution of stars and the HI, H_2, and CO-bright H_2 gas phases in galaxy-sized numerical simulations to explore the evolution of gas-rich and/or metal-poor systems, expected to be numerous in the ... More

Non-Local Transport Mediated by Spin-SupercurrentsAug 05 2014In thin film ferromagnets with perfect easy-plane anisotropy, the component of total spin perpendicular to the easy plane is a good quantum number and the corresponding spin supercurrent can flow without dissipation. In this Letter we explain how spin ... More

SU(3) and SU(4) singlet quantum Hall states at $ν=2/3$Jun 08 2015Sep 28 2015We report on an exact diagonalization study of fractional quantum Hall states at filling factor $\nu=2/3$ in a system with a four-fold degenerate $n$=0 Landau level and SU(4) symmetric Coulomb interactions. Our investigation reveals previously unidentified ... More

Composite fermion duality for half-filled multicomponent Landau LevelsSep 27 2016We study the interplay of particle-hole symmetry and fermion-vortex duality in multicomponent half-filled Landau levels, such as quantum Hall gallium arsenide bilayers and graphene. For the $\nu{=}1/2{+}1/2$ bilayer, we show that particle-hole-symmetric ... More

Density, spin, and pairing instabilities in polarized ultracold Fermi gasesJan 13 2012We study the influence of population imbalance on the pairing, spin, and density instabilities of a two component ideal Fermi gas after a sudden quench of interactions near a Feshbach resonance. Over a large region of parameters the pairing instability ... More

Detecting gene innovations for phenotypic diversity across multiple genomesDec 16 2012Gene innovation is a key mechanism on the evolution and phenotypic diversity of life forms. There is a need for tools able to study gene innovation across an increasingly large number of genomic sequences to maximally capitalise our understanding of biological ... More

Stoner Instability of the Composite Fermi SeaFeb 06 2018We study two-component electrons in the lowest Landau level at total filling factor $\nu_T=1/2$ with anisotropic mass tensors and principal axes rotated by $\pi/2$ as realized in Aluminum Arsenide (AlAs) quantum wells. Combining exact diagonalization ... More

On "finitary" Ramsey's theoremAug 09 2015Jul 05 2016We examine a version of Ramsey's theorem based on Tao, Gaspar and Kohlenbach's "finitary" infinite pigeonhole principle.We will show that the "finitary" infinite Ramsey's theorem naturally gives rise to statements at the level of the infinite Ramsey's ... More

The strength of SCT soundnessSep 26 2017In this paper we continue the study, from Frittaion, Steila and Yokoyama (2017), on size-change termination in the context of Reverse Mathematics. We analyze the soundness of the SCT method. In particular, we prove that the statement "any program which ... More

Intermediate-mass black holes in globular clusters: observations and simulationsJan 29 2015The study of intermediate-mass black holes (IMBHs) is a young and promising field of research. Formed by runaway collisions of massive stars in young and dense stellar clusters, intermediate-mass black holes could still be present in the centers of globular ... More

N-body Integrators with Individual Time Steps from Hierarchical SplittingMay 25 2012We review the implementation of individual particle time-stepping for N-body dynamics. We present a class of integrators derived from second order Hamiltonian splitting. In contrast to the usual implementation of individual time-stepping, these integrators ... More

Multi-scale and multi-domain computational astrophysicsFeb 19 2014Astronomical phenomena are governed by processes on all spatial and temporal scales, ranging from days to the age of the Universe (13.8,Gyr) as well as from km size up to the size of the Universe. This enormous range in scales is contrived, but as long ... More

The escape of ionising radiation from high-redshift dwarf galaxiesApr 18 2011The UV escape fraction from high-redshift galaxies plays a key role in models of cosmic reionisation. Because it is currently not possible to deduce the escape fractions during the epoch of reionisation from observations, we have to rely on numerical ... More

A connected component-based method for efficiently integrating multiscale $N$-body systemsJul 26 2014We present a novel method for efficient direct integration of gravitational N-body systems with a large variation in characteristic time scales. The method is based on a recursive and adaptive partitioning of the system based on the connected components ... More

Diagnostics of the molecular component of PDRs with mechanical heating. II: line intensities and ratiosMar 27 2014CO observations in active galactic nuclei and star-bursts reveal high kinetic temperatures. Those environments are thought to be very turbulent due to dynamic phenomena such as outflows and high supernova rates. We investigate the effect of mechanical ... More

Changes in orientation and shape of protoplanetary discs moving through an ambient mediumJul 04 2017Misalignments between the orbital planes of planets and the equatorial planes of their host stars have been observed in our solar system, in transiting exoplanets, and in the orbital planes of debris discs. We present a mechanism that causes such a spin-orbit ... More

Dickson's lemma and weak Ramsey theoryDec 09 2015We explore the connections between Dickson's lemma and weak Ramsey theory.

Vacuum Predictions and Measurements for an Internal Pellet TargetJan 04 2007Measurements with low Z targets at internal experiments typically imply a gas load which deteriorates the ring vacuum. Future experiments need reliable estimates for the expected vacuum conditions in order to design 4-pi detectors closely surrounding ... More

SO(5) symmetry in the quantum Hall effect in grapheneJun 09 2014Dec 22 2014Electrons in graphene have four flavors associated with low-energy spin and valley degrees of freedom. The fractional quantum Hall effect in graphene is dominated by long-range Coulomb interactions which are invariant under rotations in spin-valley space. ... More

Modelling Mechanical Heating in Star-Forming Galaxies: CO and 13CO Line Ratios as Sensitive ProbesSep 08 2016We apply photo-dissociation region (PDR) molecular line emission models, that have varying degrees of enhanced mechanical heating rates, to the gaseous component of simulations of star-forming galaxies taken from the literature. Snapshots of these simulations ... More

Incorporating the molecular gas phase in galaxy-size numerical simulations: first applications in dwarf galaxiesMar 21 2006We present models of the evolution of the gaseous and stellar content of galaxies incorporating the formation of H_2 out of HI gas as part of such a model. We do so by formulating a subgrid model for gas clouds that uses well-known cloud scaling relations ... More

Disc truncation in embedded star clusters: Dynamical encounters versus face-on accretionJun 21 2017Observations indicate that the dispersal of protoplanetary discs in star clusters occurs on time scales of about 5 Myr. Several processes are thought to be responsible for this disc dispersal. Here we compare two of these processes: dynamical encounters ... More

Characterising face-on accretion onto and the subsequent contraction of protoplanetary discsFeb 14 2017Observations indicate that stars generally lose their protoplanetary discs on a timescale of about 5 Myr. Which mechanisms are responsible for the disc dissipation is still debated. Here we investigate the movement through an ambient medium as a possible ... More

Gone with the wind: the impact of wind mass transfer on the orbital evolution of AGB binary systemsMay 08 2018In low-mass binary systems, mass transfer is likely to occur via a slow and dense stellar wind when one of the stars is in the AGB phase. Observations show that many binaries that have undergone AGB mass transfer have orbital periods of 1-10 yr, at odds ... More

Face-on accretion onto a protoplanetary discJul 04 2016Globular clusters (GCs) are known to harbor multiple stellar populations. To explain these observations Bastian et al. suggested a scenario in which a second population is formed by the accretion of enriched material onto the low-mass stars in the initial ... More

Invariant form of spin-transfer switching conditionJun 24 2009We derive an invariant form of the current-induced switching condition in spin-transfer devices and show that for energy minima and maxima the "switching ability" of the current is determined by the spin torque divergence. In contrast, energy saddle points ... More

Interaction corrections to the polarization function of grapheneJun 15 2012Sep 18 2012The first-order interaction correction to the irreducible polarization function of pristine graphene is studied at arbitrary relation between momentum and frequency. The results are used to calculate the dielectric function and the dynamical conductivity ... More

Diagnostics of the Molecular Component of PDRs with Mechanical HeatingMar 22 2012Context. Multitransition CO observations of galaxy centers have revealed that significant fractions of the dense circumnuclear gas have high kinetic temperatures, which are hard to explain by pure photon excitation, but may be caused by dissipation of ... More

Anomalous stabilization in a spin-transfer system at high spin polarizationJun 24 2009Switching diagrams of nanoscale ferromagnets driven by a spin-transfer torque are studied in the macrospin approximation. We consider a disk-shaped free layer with in-plane easy axis and external magnetic field directed in-plane at 90 degrees to that ... More

The Astrophysical Multipurpose Software EnvironmentJul 11 2013We present the open source Astrophysical Multi-purpose Software Environment (AMUSE, www.amusecode.org), a component library for performing astrophysical simulations involving different physical domains and scales. It couples existing codes within a Python ... More

Constraining cloud parameters using high density gas tracers in galaxiesSep 08 2016Far-infrared molecular emission is an important tool used to understand the excitation mechanisms of the gas in the inter-stellar medium of star-forming galaxies. In the present work, we model the emission from rotational transitions with critical densities ... More

Star Formation in the vicinity of Nuclear Black Holes: Young Stellar Objects close to Sgr A*Jul 31 2014It is often assumed that the strong gravitational field of a super-massive black hole disrupts an adjacent molecular cloud preventing classical star formation in the deep potential well of the black hole. Yet, young stars have been observed across the ... More

Young Stellar Objects close to Sgr A*Nov 19 2013We aim at modelling small groups of young stars such as IRS 13N, 0.1 pc away from Sgr A*, which is suggested to contain a few embedded massive young stellar objects. We perform hydrodynamical simulations to follow the evolution of molecular clumps orbiting ... More

The evolution of embedded star clustersNov 03 2011We study the evolution of embedded clusters. The equations of motion of the stars in the cluster are solved by direct N-body integration while taking the effects of stellar evolution and the hydrodynamics of the natal gas content into account. The gravity ... More

How rapidly do supermassive black hole "seeds" grow at early times?Mar 29 2007We investigate the physical conditions for the growth of intermediate mass seed black holes assumed to have formed from remnants of the first generation of massive stars. We follow the collapse of high-sigma halos with Tvir > 1e4 K using cosmological, ... More

Periodic bursts of Star Formation in Irregular GalaxiesApr 07 2004We present N-body/SPH simulations of the evolution of an isolated dwarf galaxy including a detailed model for the ISM, star formation and stellar feedback. Depending on the strength of the feedback, the modelled dwarf galaxy shows periodic or quasi-periodic ... More

Density Estimators in Particle Hydrodynamics: DTFE versus regular SPHMar 04 2003Mar 06 2003We present the results of a study confronting density maps reconstructed by the Delaunay Tessellation Field Estimator (DTFE) and by regular SPH kernel-based techniques. The comparison between the two methods clearly demonstrates the superior performance ... More

Interaction-Enhanced Coherence Between Two-Dimensional Dirac LayersMar 16 2012We estimate the strength of interaction-enhanced coherence between two graphene or topological insulator surface-state layers by solving imaginary-axis gap equations in the random phase approximation. Using a self-consistent treatment of dynamic screening ... More

Logarithmic singularities and quantum oscillations in magnetically doped topological insulatorsNov 29 2017Apr 16 2018We report magnetotransport measurements on magnetically doped (Bi,Sb)$_2$Te$_3$ films grown by molecular beam epitaxy. In Hallbar devices, logarithmic dependence on temperature and bias voltage are obseved in both the longitudinal and anomalous Hall resistance. ... More