Results for "J. Van Beeck"

total 196041took 0.14s
Period spacings of gravity modes in rapidly rotating magnetic stars I. Axisymmetric fossil field with poloidal and toroidal componentsMar 13 2019Context. Stellar magnetic fields are one of the candidates often invoked to explain the missing transport of angular momentum observed in the models of stellar interiors. However, the properties of an internal magnetic field and the consequences of its ... More
Period spacings of gravity modes in rapidly rotating magnetic stars I. Axisymmetric fossil field with poloidal and toroidal componentsMar 13 2019May 15 2019Context. Stellar magnetic fields are one of the candidates often invoked to explain the missing transport of angular momentum observed in the models of stellar interiors. However, the properties of an internal magnetic field and the consequences of its ... More
Multiple views of magnetism in cool starsAug 16 2012Magnetic fields are regarded as a crucial element for our understanding of stellar physics. They can be studied with a variety of methods which provide complementary - and sometimes contradictory - information about the structure, strength and dynamics ... More
Properties of simulated sunspot umbral dotsNov 26 2009Realistic 3D radiative MHD simulations reveal the magneto-convective processes underlying the formation of the photospheric fine structure of sunspots, including penumbral filaments and umbral dots. Here we provide results from a statistical analysis ... More
Dynamic masses for the close PG1159 binary SDSSJ212531.92-010745.9Dec 28 2008SDSSJ212531.92-010745.9 is the first known PG1159 star in a close binary with a late main sequence companion allowing a dynamical mass determination. The system shows flux variations with a peak-to-peak amplitude of about 0.7 mag and a period of about ... More
MHD simulations reveal crucial differences between solar and very-cool star magnetic structuresJan 20 2011We carried out 3D radiative magnetohydrodynamic simulations of the convective and magnetic structure in the surface layers (uppermost part of the convection zone and photosphere) of main-sequence stars of spectral types F3 to M2. The simulation results ... More
MHD simulations of near-surface convection in cool main-sequence starsAug 08 2014Aug 12 2014The solar photospheric magnetic field is highly structured owing to its interaction with the convective flows. Its local structure has a strong influence on the profiles of spectral lines not only by virtue of the Zeeman effect, but also through the modification ... More
Transverse component of the magnetic field in the solar photosphere observed by SunriseAug 09 2010We present the first observations of the transverse component of photospheric magnetic field acquired by the imaging magnetograph Sunrise/IMaX. Using an automated detection method, we obtain statistical properties of 4536 features with significant linear ... More
Three-dimensional simulations of near-surface convection in main-sequence stars - II. Properties of granulation and spectral linesAug 22 2013The atmospheres of cool main-sequence stars are structured by convective flows from the convective envelope that penetrate the optically thin layers and lead to structuring of the stellar atmospheres analogous to solar granulation. The flows have considerable ... More
Radial velocity observations of the 2015 Mar 20 eclipse - A benchmark Rossiter-McLaughlin curve with zero free parametersSep 02 2016Sep 05 2016On March 20, 2015, we obtained 159 spectra of the Sun as a star with the solar telescope and the FTS at the Institut f\"ur Astrophysik G\"ottingen, 76 spectra were taken during partial solar eclipse. We obtained RVs using $I_2$ as wavelength reference ... More
Towards a dynamical mass of a PG 1159 star: radial velocities and spectral analysis of SDSS J212531-010745Jan 30 2009The evolutionary scenarios which are commonly accepted for PG 1159 stars are mainly based on numerical simulations, which have to be tested and calibrated with real objects with known stellar parameters. One of the most crucial but also quite uncertain ... More
Three-dimensional simulations of near-surface convection in main-sequence stars. IV. Effect of small-scale magnetic flux concentrations on centre-to-limb variation and spectral linesMay 18 2015Magnetic fields affect the local structure of the photosphere of stars. They can considerably influence the radiative properties near the optical surface, flow velocities, and the temperature and pressure profiles. We aim at understanding qualitatively ... More
Three-dimensional simulations of near-surface convection in main-sequence stars - I. Overall structureAug 22 2013The near-surface layers of cool main-sequence stars are structured by convective flows, which are overshooting into the atmosphere. The flows and the associated spatio-temporal variations of density and temperature affect spectral line profiles and thus ... More
New Light Curves and Spectra of the close PG1159 Binary System SDSSJ212531.92-010745.9Dec 05 2007Methods to measure masses of PG1159 stars in order to test evolutionary scenarios are currently based on spectroscopic masses or asteroseismological mass determinations. SDSSJ212531.92-010745.9, a recently discovered PG1159 star in a close binary system, ... More
Three-dimensional simulations of near-surface convection in main-sequence stars. III. The structure of small-scale magnetic flux concentrationsMay 18 2015The convective envelopes of cool main-sequence stars harbour magnetic fields with a complex global and local structure. These fields affect the near-surface convection and the outer stellar atmospheres in many ways and are responsible for the observable ... More
MESA meets MURaM: Surface effects in main-sequence solar-like oscillators computed using three-dimensional radiation hydrodynamics simulationsJun 08 2016... [C]urrent stellar models predict oscillation frequencies that are systematically affected by simplified modelling of the near-surface layers. We use three-dimensional radiation hydrodynamics simulations to better model the near-surface equilibrium ... More
EXOTIME: searching for planets around pulsating subdwarf B starsMay 19 2010In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undiscovered population of substellar companions to apparently single subdwarf B stars might exist. ... More
The Rossiter-McLaughlin effect reloaded: Probing the 3D spin-orbit geometry, differential stellar rotation, and the spatially-resolved stellar spectrum of star-planet systemsJan 31 2016When a planet transits its host star, it blocks regions of the stellar surface from view; this causes a distortion of the spectral lines and a change in the line-of-sight (LOS) velocities, known as the Rossiter-McLaughlin (RM) effect. Since the LOS velocities ... More
What does Maxwell's demon want from life? When information becomes functional and physicalJul 31 2014Apr 28 2015Szilard's one-molecule engine is operated by a Maxwell's demon attempting to convert heat to work. It is argued here that when using the demon to relate information to work (Landauer's principle), the demon's goal must be regarded as an implicit assumption ... More
Almost abelian twists and AdS/CFTOct 18 2016A large class of the recently found unimodular nonabelian homogeneous Yang-Baxter deformations of the AdS_5 x S^5 superstring can be realized as sequences of noncommuting TsT transformations. I show that many of them are duals to various noncommutative ... More
Causal non-locality can arise from constrained replicationJun 02 2015Aug 31 2015The fundamental theories of physics are local theories, depending on local interactions of local variables. It is not clear if and how strictly local theories can produce non-local variables that have causal effectiveness. Yet, non-local effectiveness ... More
Single scalar cosmologyApr 17 2013Sep 27 2013The cosmology of flat FLRW universes dominated by a single scalar field is discussed. General features of the evolution of the universe and the scalar field are illustrated by specific examples. In particular the role of critical points, where the scalar ... More
On single scalar field cosmologyJan 07 2013Jan 14 2013Observations suggest, that there may be periods in the history of the universe, including the present one, in which its evolution is driven by scalar fields. This paper is concerned with the solution of the evolution equations for a spatially flat universe ... More
New supersymetries for spinning particles and black holesOct 15 1993The usual extensions of supersymmetry require the existence of a complex structure and the formulation of the theory on K\"{a}hler manifolds. It is shown, that by relaxing the constraints on the algebra of supercharges we can get new supersymmetries whenever ... More
Gravitational waves and massless particle fieldsJun 07 1999Jun 09 1999These notes address the planar gravitational wave solutions of general relativity in empty space-time, and analyze the motion of test particles in the gravitational wave field. Next we consider related solutions of the Einstein equations for the gravitational ... More
Commuting difference operators with applications to orthogonal polynomials in several variablesApr 03 1996Elementary properties of the Koornwinder-Macdonald multivariable Askey-Wilson polynomials are discussed. Studied are the orthogonality, the difference equations, the recurrence relations, and the orthonormalization constants for these polynomials. Essential ... More
Commuting difference operators with polynomial eigenfunctionsJun 07 1993We present explicit generators of an algebra of commuting difference operators with trigonometric coefficients. The operators are simultaneously diagonalized by recently discovered q-polynomials (viz. Koornwinder's multivariable generalization of the ... More
A hybrid constraint programming and semidefinite programming approach for the stable set problemFeb 25 2003This work presents a hybrid approach to solve the maximum stable set problem, using constraint and semidefinite programming. The approach consists of two steps: subproblem generation and subproblem solution. First we rank the variable domain values, based ... More
Almost abelian twists and AdS/CFTOct 18 2016Oct 31 2016A large class of the recently found unimodular nonabelian homogeneous Yang-Baxter deformations of the AdS_5 x S^5 superstring can be realized as sequences of noncommuting TsT transformations. I show that many of them are duals to various noncommutative ... More
Dynamical Space-Time and Gravitational WavesNov 04 2016According to General Relativity gravity is the result of the interaction between matter and space-time geometry. In this interaction space-time geometry itself is dynamical: it can store and transport energy and momentum in the form of gravitational waves. ... More
Modelling recorded crime: a full search for cointegrated modelsApr 29 2008Oct 30 2008A modelgenerator is developed that searches for cointegrated models among a potentially large group of candidate models. The generator employs the first step of the Engle-Granger procedure and orders cointegrated models according to the information criterions ... More
Asymptotics of multivariate orthogonal polynomials with hyperoctahedral symmetryDec 29 2004We present a formula describing the asymptotics of a class of multivariate orthogonal polynomials with hyperoctahedral symmetry as the degree tends to infinity. The polynomials under consideration are characterized by a factorized weight function satisfying ... 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
Killing-Yano tensors and generalized supersymmetries in black-hole and monopole geometriesSep 23 1994New kinds of supersymmetry arise in supersymmetric $\sg$-models describing the motion of spinning point-particles in classical backgrounds, for example black-holes, or the dynamics of monopoles. Their geometric origin is the existence of Killing-Yano ... More
Relations between some analytic representations of one-loop scalar integralsAug 04 1994We compare several parametrized analytic expressions for an arbitrary off-shell one-loop $n$-point function in scalar field theory in $D$-dimensional space-time, and show their equivalence both directly and through path-integral methods.
Relativistic Dynamics of Spin in Strong External FieldsMar 23 1993The dynamics of relativistic spinning particles in strong external electromagnetic or gravitational fields is discussed. Spin-orbit coupling is shown to affect such relativistic phenomena as time-dilation and perihelion shift. Possible applications include ... More
Propagators and Path IntegralsAug 25 1995Nov 01 1995Path-integral expressions for one-particle propagators in scalar and fermionic field theories are derived, for arbitrary mass. This establishes a direct connection between field theory and specific classical point-particle models. The role of world-line ... More
Multivariable continuous Hahn and Wilson polynomials related to integrable difference systemsJul 19 1995Multivariable generalizations of the continuous Hahn and Wilson polynomials are introduced as eigenfunctions of rational Ruijsenaars type difference systems with an external field.
A Proof of Solomon's RuleJun 19 2007We put forward a proof of Solomon's rule, in terms of matrices, for multiplication in the descent algebra of the symmetric group. Our proof exploits the graphs that we can obtain from all the subsets of the set of transpositions, $\{(i,i+1)\}_{i=1}^{n-1}$. ... More
Diagonalization of an Integrable Discretization of the Repulsive Delta Bose Gas on the CircleApr 13 2006We introduce an integrable lattice discretization of the quantum system of n bosonic particles on a ring interacting pairwise via repulsive delta potentials. The corresponding (finite-dimensional) spectral problem of the integrable lattice model is solved ... More
Scattering theory of discrete (pseudo) Laplacians on a Weyl chamberDec 31 2004To a crystallographic root system we associate a system of multivariate orthogonal polynomials diagonalizing an integrable system of discrete pseudo Laplacians on the Weyl chamber. We develop the time-dependent scattering theory for these discrete pseudo ... 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
Unimodular jordanian deformations of integrable superstringsApr 18 2019May 17 2019We find new homogeneous r matrices containing supercharges, and give examples of backgrounds associated with their corresponding Yang-Baxter deformed superstrings. We obtain these r matrices and backgrounds as special scaling limits of recently found ... More
Introduction to the thermodynamic Bethe ansatzJun 09 2016Jul 24 2016We give a pedagogical introduction to the thermodynamic Bethe ansatz, a method that allows us to describe the thermodynamics of integrable models whose spectrum is found via the (asymptotic) Bethe ansatz. We set the stage by deriving the Fermi-Dirac distribution ... More
The Brandeis Dice Problem and Statistical MechanicsAug 28 2014Jaynes invented the Brandeis Dice Problem as a simple illustration of the MaxEnt (Maximum Entropy) procedure that he had demonstrated to work so well in Statistical Mechanics. I construct here two alternative solutions to his toy problem. One, like Jaynes' ... More
Parameter estimation of a Levy copula of a discretely observed bivariate compound Poisson process with an application to operational risk modellingDec 01 2012A method is developed to estimate the parameters of a Levy copula of a discretely observed bivariate compound Poisson process without knowledge of common shocks. The method is tested in a small sample simulation study. Also, the method is applied to a ... More
The Jordanian deformation of su(2) and Clebsch-Gordan coefficientsSep 01 1997Representation theory for the Jordanian quantum algebra U=U_h(sl(2)) is developed using a nonlinear relation between its generators and those of sl(2). Closed form expressions are given for the action of the generators of U on the basis vectors of finite ... More
Completing the Standard Model with right-handed neutrinos and Z'Jun 10 2015In this lecture I review the most relevant modifications of the Standard Model of particle physics that result from inclusion of right-handed neutrinos and a new neutral gauge boson Z'.
Killing-Yano tensors, non-standard supersymmetries and an index theoremOct 11 1999The existence of Killing-Yano tensors on space-times can be probed by spinning particles. Specifically, Dirac particles possess new fermionic constants of motion corresponding to non-standard supersymmetries on the particle worldline. A geometrical duality ... More
Fermions and world-line supersymmetryDec 11 1995The world-line path-integral representation of fermion propagators is discussed. Particular attention is paid to the representation of $\gamma_5$, which is connected to the realization of manifest world-line supersymmetry.
Kaehler manifolds and supersymmetrySep 09 2003Supersymmetric field theories of scalars and fermions in 4-D space-time can be cast in the formalism of Kaehler geometry. In these lectures I review Kaehler geometry and its application to the construction and analysis of supersymmetric models on Kaehler ... More
Cyclotron motion in a gravitational-wave backgroundJun 29 1999We examine the motion of a relativistic charged particle in a constant magnetic field perturbed by gravitational waves incident along the direction of the magnetic field. We apply a generalized energy conservation law to compute the variations of the ... More
Stability and mass of point particlesSep 19 1997Feb 06 1998In this paper we consider classical point particles in full interaction with an arbitrary number of dynamical scalar and (abelian) vector fields. It is shown that the requirement of stability ---vanishing self-force--- is sufficient to remove the well-known ... More
Supersymmetry and the Geometry of Taub-NUTSep 23 1994The supersymmetric extension of Taub-NUT space admits 4 standard supersymmetries plus several additional non-standard ones. The geometrical origin of these symmetries is traced. The result has applications to fermion modes in gravitational instantons ... More
Deformations of Calogero-Moser SystemsOct 18 1993Recent results are surveyed pertaining to the complete integrability of some novel n-particle models in dimension one. These models generalize the Calogero-Moser systems related to classical root systems. Quantization leads to difference operators instead ... More
Sharpness of the percolation transition in the two-dimensional contact processJul 16 2009Jan 07 2011For ordinary (independent) percolation on a large class of lattices it is well known that below the critical percolation parameter $p_c$ the cluster size distribution has exponential decay and that power-law behavior of this distribution can only occur ... More
Approximate zero-one laws and sharpness of the percolation transition in a class of models including two-dimensional Ising percolationSep 24 2008One of the most well-known classical results for site percolation on the square lattice is the equation $p_c+p_c^*=1$. In words, this equation means that for all values $\neq p_c$ of the parameter $p$, the following holds: either a.s. there is an infinite ... More
The Domino EffectJan 07 2004The physics of a row of toppling dominoes is discussed. In particular the forces between the falling dominoes are analyzed and with this knowledge, the effect of friction has been incorporated. A set of limiting situations is discussed in detail, such ... More
How the symbol grounding of living organisms can be realized in artificial agentsMar 17 2015A system with artificial intelligence usually relies on symbol manipulation, at least partly and implicitly. However, the interpretation of the symbols - what they represent and what they are about - is ultimately left to humans, as designers and users ... More
How unusual was autumn 2006 in Europe?Nov 23 2007The temperatures in large parts of Europe have been record high during the meteorological autumn of 2006. Compared to 1961-1990, the 2m temperature was more than three degrees Celsius above normal from the North side of the Alps to southern Norway. This ... More
Cosmic scalar fields with flat potentialJun 26 2002The dynamics of cosmic scalar fields with flat potential is studied. Their contribution to the expansion rate of the universe is analyzed, and their behaviour in a simple model of phase transitions is discussed.
Gravitational Waves and Black Holes: an Introduction to General RelativityApr 15 1997In these lectures general relativity is outlined as the classical field theory of gravity, emphasizing physical phenomena rather than mathematical formalism. Dynamical solutions representing traveling waves as well as stationary fields like those of black ... More
BRST Field Theory of Relativistic ParticlesFeb 07 1992A generalization of BRST field theory is presented, based on wave operators for the fields constructed out of, but different from the BRST operator. We discuss their quantization, gauge fixing and the derivation of propagators. We show, that the generalized ... More
Gauge-covariant extensions of Killing tensors and conservation lawsAug 01 2014In classical and quantum mechanical systems on manifolds with gauge-field fluxes, constants of motion are constructed from gauge-covariant extensions of Killing vectors and tensors. This construction can be carried out using a manifestly covariant procedure, ... More
Worldine deviations and epicyclesJan 14 2002In general relativity, only relative acceleration has an observer-independend meaning: curvature and non-gravitational forces determine the rate at which world lines of test bodies diverge or converge. We derive the equations governing both in the conventional ... More
Domain boundaries, Goldstone bosons and gravitational wavesMar 13 1995The dynamical behaviour of domain boundaries between different realizations of the vacuum of scalar fields with spontaneously broken phases is investigated. They correspond to zero-modes of the Goldstone fields, moving with the speed of light, and turn ... More
The alldifferent Constraint: A SurveyMay 08 2001The constraint of difference is known to the constraint programming community since Lauriere introduced Alice in 1978. Since then, several solving strategies have been designed for this constraint. In this paper we give both a practical overview and an ... More
Comment on "Observation of Spin Injection at a Ferromagnet-Semiconductor Interface, by P.R. Hammar et alJan 13 2000In a recent Letter Hammar et al. claim the observation of injection of a spin-polarized current in a two-dimensional electron gas (2DEG). This is an important observation, since, despite considerable effort of several groups, all attempts to realize spin-injection ... More
On the Equilibrium Configuration of the BC-type Ruijsenaars-Schneider SystemOct 04 2004It is shown that the ground-state equilibrium configurations of the trigonometric BC-type Ruijsenaars-Schneider systems are given by the zeros of Askey-Wilson polynomials.
Unimodular jordanian deformations of integrable superstringsApr 18 2019We find new homogeneous r matrices containing supercharges, and give examples of backgrounds associated with their corresponding Yang-Baxter deformed superstrings. We obtain these r matrices and backgrounds as special scaling limits of recently found ... More
Neutrinos, a window on new physicsDec 13 2014This paper reviews some aspects of the physics of neutrinos, in particular neutrino masses and the issue of Dirac versus Majorana neutrinos. The see-saw mechanism is described and it is argued that the Majorana nature of neutrinos can be tested by measuring ... More
D = 1 supergravity and quantum cosmologyJul 27 2017Using a D = 1 supergravity framework I construct a super-Friedmann equation for an isotropic and homogenous universe including dynamical scalar fields. In the context of quantum theory this becomes an equation for a wave-function of the universe of spinorial ... More
Testing approximate normality of an estimator using the estimated MSE and bias with an application to the shape parameter of the generalized Pareto distributionOct 08 2012Nov 21 2012Often it is not easy to choose between estimators, based on the estimated MSE and bias using simulation studies. Normality in small samples and a variance of the estimator, which is correct and easy to calculate using a single sample, give the added advantage ... More
Remarks on the Zeros of the Associated Legendre Functions with Integral DegreeFeb 09 2007We present some formulas for the computation of the zeros of the integral-degree associated Legendre functions with respect to the order.
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
Extensive fitness and human cooperationMar 16 2015Sep 10 2015Evolution depends on the fitness of organisms, the expected rate of reproducing. Directly getting offspring is the most basic form of fitness, but fitness can also be increased indirectly by helping genetically related individuals (such as kin) to increase ... More
Active causation and the origin of meaningOct 08 2013May 25 2014Purpose and meaning are necessary concepts for understanding mind and culture, but appear to be absent from the physical world and are not part of the explanatory framework of the natural sciences. Understanding how meaning (in the broad sense of the ... More
Spinning bodies in General RelativityApr 16 2015Nov 17 2015A covariant hamiltonian formalism for the dynamics of compact spinning bodies in curved space-time in the test-particle limit is described. The construction allows a large class of hamiltonians accounting for specific properties and interactions of spinning ... More
Covariant hamiltonian dynamicsDec 20 2006Dec 28 2006We discuss the covariant formulation of the dynamics of particles with abelian and non-abelian gauge charges in external fields. Using this formulation we develop an algorithm for the construction of constants of motion, which makes use of a generalization ... More
Cosmological Higgs fieldsJul 07 2002Sep 24 2002We present a time-dependent solution to the coupled Einstein-Higgs equations for general Higgs-type potentials in the context of flat FRW cosmological models. Possible implications are discussed.
Particles, fluids and vorticesJul 18 2001Classical particle mechanics on curved spaces is related to the flow of ideal fluids, by a dual interpretation of the Hamilton-Jacobi equation. As in second quantization, the procedure relates the description of a system with a finite number of degrees ... More
D = 1 Supergravity and Spinning ParticlesOct 05 1995Nov 30 1995In this paper I review the multiplet calculus of $N = 1$, $D = 1$ local supersymmetry with applications to the construction of models for spinning particles in background fields, and models with space-time supersymmetry. New features include a non-linear ... More
The gravitational field of a light waveAug 07 2008According to the classical Einstein-Maxwell theory of gravity and electromagnetism, a light-wave traveling in empty space-time is accompanied by a gravitational field of the pp-type. Therefore point masses are scattered by a light wave, even if they carry ... More
Aspects of BRST QuantizationJan 16 2002BRST-methods provide elegant and powerful tools for the construction and analysis of constrained systems, including models of particles, strings and fields. These lectures provide an elementary introduction to the ideas, illustrated with some important ... 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
The relativistic Calogero model in an external fieldSep 07 1995Sep 13 1995Recent results are surveyed regarding the spectrum and eigenfunctions of the inverse square Calogero model with harmonic confinement and its relativistic analogue.
On certain multiple Bailey, Rogers and Dougall type summation formulasDec 25 1997A multidimensional generalization of Bailey's very-well-poised bilateral basic hypergeometric ${}_6\psi_6$ summation formula and its Dougall type ${}_5H_5$ hypergeometric degeneration for $q\to 1$ is studied. The multiple Bailey sum amounts to an extension ... More
Simulations of the solar near-surface layers with the CO5BOLD, MURaM, and Stagger codesJan 05 2012Radiative hydrodynamic simulations of solar and stellar surface convection have become an important tool for exploring the structure and gas dynamics in the envelopes and atmospheres of late-type stars and for improving our understanding of the formation ... More
Spectral variability of photospheric radiation due to faculae I: The Sun and Sun-like starsMay 12 2017Context. Stellar spectral variability on timescales of a day and longer, arising from magnetic surface features such as dark spots and bright faculae, is an important noise source when characterising extra-solar planets. Current 1D models of faculae do ... More
Domino MagnificationJan 03 2013Jan 28 2013The conditions are investigated under which a row of increasing dominoes is able to keep tumbling over. The analysis is restricted to the simplest case of frictionless dominoes that only can topple not slide. The model is scale invariant, i.e. dominoes ... More
Reply to "Comment on 'Generalization of the Kohn-Sham system that can represent arbitrary one-electron density matrices'"May 09 2017Aug 21 2017Our paper [Phys. Rev. A 93, 052512 (2016)], proposing a novel form of single determinant wave function that admits non-idempotent 1-electron density matrices, has recently received a Comment [Phys. Rev. A ??, 0????? (2017)] suggesting a number of flaws: ... More
Auto-oscillation threshold, narrow spectral lines, and line jitter in spin-torque oscillators based on MgO magnetic tunnel junctionsOct 06 2008We demonstrate spin torque induced auto-oscillation in MgO-based magnetic tunnel junctions. At the generation threshold, we observe a strong line narrowing down to 6 MHz at 300K and a dramatic increase in oscillator power, yielding spectrally pure oscillations ... More
Generalization of the Kohn-Sham system that can represent arbitary one electron density matricesDec 07 2015May 17 2016Density functional theory is currently the most widely applied method in electronic structure theory. The Kohn-Sham method, based on a fictitious system of non-interacting particles, is the work horse of the theory. The particular form of the Kohn-Sham ... More
Aspects of Multi-Dimensional Modelling of Substellar AtmospheresDec 14 2010Theoretical arguments and observations suggest that the atmospheres of Brown Dwarfs and planets are very dynamic on chemical and on physical time scales. The modelling of such substellar atmospheres has, hence, been much more demanding than initially ... More
Modeling of Physical Network SystemsOct 16 2015Conservation laws and balance equations for physical network systems typically can be described with the aid of the incidence matrix of a directed graph, and an associated symmetric Laplacian matrix. Some basic examples are discussed, and the extension ... More
Dynamical stripe correlations and the spin fluctuations in cuprate superconductorsFeb 06 1997It is conjectured that the anomalous spin dynamics observed in the normal state of cuprate superconductors might find its origin in a nearly ordered spin system which is kept in motion by thermally meandering charged domain walls. `Temperature sets the ... More
Constructing Dualities from Quantum State ManifoldsSep 02 2015The thesis develops a systematic procedure to construct semi-classical gravitational duals from quantum state manifolds. Though the systems investigated are simple quantum mechanical systems without gauge symmetry many familiar concepts from the conventional ... More
The 16O(e,e'pp)14C reaction to discrete final statesDec 16 2003Differential cross sections for exclusive 16O(e,e'pp)14C processes are computed within a distorted-wave framework which includes central short-range correlations and intermediate \Delta+ excitations. The cross sections are compared to high-resolution ... More
Quantum Statistical Physics of Glasses at Low TemperaturesSep 21 2009Dec 19 2009We present a quantum statistical analysis of a microscopic mean-field model of structural glasses at low temperatures. The model can be thought of as arising from a random Born von Karman expansion of the full interaction potential. The problem is reduced ... More