Results for "Michael Cuntz"

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Simplicial arrangements with up to 27 linesAug 15 2011We compute all isomorphism classes of simplicial arrangements in the real projective plane with up to 27 lines. It turns out that Gr\"unbaums catalogue is complete up to 27 lines except for four new arrangements with 22, 23, 24, 25 lines, respectively. ... More
A bound for crystallographic arrangementsMar 01 2019A crystallographic arrangement is a set of linear hyperplanes satisfying a certain integrality property and decomposing the space into simplicial cones. Crystallographic arrangements were completely classified in a series of papers by Heckenberger and ... More
On subsequences of quiddity cycles and Nichols algebrasOct 07 2016Oct 11 2016We provide a tool to obtain local descriptions of quiddity cycles. As an application, we classify rank two affine Nichols algebras of diagonal type.
Fusion algebras with negative structure constantsApr 18 2007We introduce fusion algebras with not necessarily positive structure constants and without identity element. We prove that they are semisimple when tensored with $\mathbb{C}$ and that their characters satisfy orthogonality relations. Then we define the ... More
Fusion algebras for imprimitive complex reflection groupsOct 27 2006We prove that the Fourier matrices for the imprimitive complex reflection groups introduced by Malle define fusion algebras with not necessarily positive but integer structure constants. Hence they define Z-algebras. As a result, we obtain that all known ... More
Crystallographic arrangements: Weyl groupoids and simplicial arrangementsJun 10 2010We introduce the simple notion of a "crystallographic arrangement" and prove a one-to-one correspondence between these arrangements and the connected simply connected Cartan schemes for which the real roots are a finite root system (up to equivalence ... More
Frieze patterns as root posets and affine triangulationsJul 30 2013Jun 24 2014The entries of frieze patterns may be interpreted as coordinates of roots of a finite Weyl groupoid of rank two. We prove the existence of maximal elements in their root posets and classify those frieze patterns which can be used to build an affine simplicial ... More
A combinatorial model for tame frieze patternsNov 27 2017Jul 10 2018Let $R$ be an arbitrary subset of a commutative ring. We introduce a combinatorial model for the set of tame frieze patterns with entries in $R$ based on a notion of irreducibility of frieze patterns. When $R$ is a ring, then a frieze pattern is reducible ... More
$(22_4)$ and $(26_4)$ configurations of linesMay 02 2017We present a technique to produce arrangements of lines with nice properties. As an application, we construct $(22_4)$ and $(26_4)$ configurations of lines. Thus concerning the existence of geometric $(n_4)$ configurations, only the case $n=23$ remains ... More
Integral modular data and congruencesNov 08 2006Jun 03 2008We compute all fusion algebras with symmetric rational $S$-matrix up to dimension 12. Only two of them may be used as $S$-matrices in a modular datum: the $S$-matrices of the quantum doubles of $\mathbb{Z}/2\mathbb{Z}$ and $S_3$. Almost all of them satisfy ... More
Free, not recursively free and non rigid arrangementsJun 24 2014Jun 27 2014We construct counterexamples to Yoshinaga's conjecture that every free arrangement is either inductively free or rigid in characteristic zero. The smallest example has $13$ hyperplanes, its intersection lattice has a one dimensional moduli space, and ... More
On wild frieze patternsApr 27 2015May 06 2015In this note, among other things, we show: There are periodic wild SLk-frieze patterns whose entries are positive integers. There are non-periodic SLk-frieze patterns whose entries are positive integers. There is an SL3-frieze pattern whose entries are ... More
Combinatorial simpliciality of arrangements of hyperplanesFeb 08 2013Mar 01 2013We introduce a combinatorial characterization of simpliciality for arrangements of hyperplanes. We then give a sharp upper bound for the number of hyperplanes of such an arrangement in the projective plane over a finite field, and present some series ... More
$C^*$-algebras associated with the $ax+b$-semigroup over $\mathbb N$Nov 17 2006We present a $C^*$-algebra which is naturally associated to the $ax+b$-semigroup over $\mathbb N$. It is simple and purely infinite and can be obtained from the algebra considered by Bost and Connes by adding one unitary generator which corresponds to ... More
Supersolvable simplicial arrangementsDec 05 2017Simplicial arrangements are classical objects in discrete geometry. Their classification remains an open problem but there is a list conjectured to be complete at least for rank three. A further important class in the theory of hyperplane arrangements ... More
Free but not recursively free arrangementsFeb 17 2013We construct counterexamples to the conjecture that every free arrangement is recursively free in characteristic zero. The intersection lattice of our smallest example has a realization over a finite field which is recursively free, thus recursive freeness ... More
On root posets for noncrystallographic root systemsDec 12 2012We discuss properties of root posets for finite crystallographic root systems, and show that these properties uniquely determine root posets for the noncrystallographic dihedral types and type $H_3$, while proving that there does not exist a poset satisfying ... More
An isomorphism between the fusion algebras of $V_L^+$ and type $D^{(1)}$ level 2Sep 30 2008Oct 09 2008The fusion algebra of the vertex operator algebra $V_L^+$ for a rank 1 even lattice $L$ is explicitly shown to be isomorphic to the fusion algebra of the Kac-Moody algebra of type $D^{(1)}$ at level 2 in almost all cases.
A simplicial complex of Nichols algebrasMar 27 2015May 12 2016We translate the concept of restriction of an arrangement in terms of Hopf algebras. In consequence, every Nichols algebra gives rise to a simplicial complex decorated by Nichols algebras with restricted root systems. As applications, some of these Nichols ... More
Tits arrangements on cubic curvesNov 07 2017We classify affine rank three Tits arrangements whose roots are contained in the locus of a homogeneous cubic polynomial. We find that there exist irreducible affine Tits arrangements which are not locally spherical.
MAT-free reflection arrangementsApr 12 2019We introduce the class of MAT-free hyperplane arrangements which is based on the Multiple Addition Theorem by Abe, Barakat, Cuntz, Hoge, and Terao. We also investigate the closely related class of MAT2-free arrangements based on a recent generalization ... More
Supersolvable simplicial arrangementsDec 05 2017Jun 24 2019Simplicial arrangements are classical objects in discrete geometry. Their classification remains an open problem but there is a list conjectured to be complete at least for rank three. A further important class in the theory of hyperplane arrangements ... More
Frieze patterns over integers and other subsets of the complex numbersNov 10 2017Dec 13 2018We study (tame) frieze patterns over subsets of the complex numbers, with particular emphasis on the corresponding quiddity cycles. We provide new general transformations for quiddity cycles of frieze patterns. As one application, we present a combinatorial ... More
Coxeter and crystallographic arrangements are inductively freeNov 18 2010Using the classification of finite Weyl groupoids we prove that crystallographic arrangements, a large subclass of the class of simplicial arrangements which was recently defined, are hereditarily inductively free. In particular, all crystallographic ... More
Finite Weyl groupoidsAug 31 2010Using previous results concerning the rank two and rank three cases, all connected simply connected Cartan schemes for which the real roots form a finite irreducible root system of arbitrary rank are determined. As a consequence one obtains the list of ... More
Erratum to "C*-algebras associated with integral domains and crossed products by actions on adele spaces" by J. Cuntz and X. LiSep 16 2012We correct the K-theory computation for ring C*-algebras associated with rings of integers in number fields.
C*-algebras associated with integral domains and crossed products by actions on adele spacesJun 26 2009We compute the K-theory for C*-algebras naturally associated with rings of integers in number fields. The main ingredient is a duality theorem for arbitrary global fields. It allows us to identify the crossed product arising from affine transformations ... More
K-theory for ring C*-algebras attached to function fieldsNov 26 2009We compute the K-theory of ring C*-algebras for polynomial rings over finite fields. The key ingredient is a duality theorem which we had obtained in a previous paper. It allows us to show that the K-theory of these algebras has a ring structure and to ... More
The Regular C*-algebra of an Integral DomainJul 09 2008To each integral domain R with finite quotients we associate a purely infinite simple C*-algebra in a very natural way. Its stabilization can be identified with the crossed product of the algebra of continuous functions on the "finite adele space" corresponding ... More
On the Tits cone of a Weyl groupoidMar 26 2018We translate the axioms of a Weyl groupoid with (not necessarily finite) root system in terms of arrangements. The result is a correspondence between Weyl groupoids permitting a root system and Tits arrangements satisfying an integrality condition which ... More
Simplicial arrangements on convex conesMay 29 2015We introduce the notion of a Tits arrangement on a convex open cone as a special case of (infinite) simplicial arrangements. Such an object carries a simplicial structure similar to the geometric representation of Coxeter groups. The standard constructions ... More
Arrangements of ideal type are inductively freeNov 23 2017Jan 31 2019Extending earlier work by Sommers and Tymoczko, in 2016 Abe, Barakat, Cuntz, Hoge, and Terao established that each arrangement of ideal type $\mathcal{A}_\mathcal{I}$ stemming from an ideal $\mathcal{I}$ in the set of positive roots of a reduced root ... More
Non-recursive freeness and non-rigidity of plane arrangementsOct 13 2014In the category of free arrangements, inductively and recursively free arrangements are important. In particular, in the former, Terao's open problem asking whether freeness depends only on combinatorics is true. A long standing problem whether all free ... More
The freeness of ideal subarrangements of Weyl arrangementsApr 30 2013May 20 2014A Weyl arrangement is the arrangement defined by the root system of a finite Weyl group. When a set of positive roots is an ideal in the root poset, we call the corresponding arrangement an ideal subarrangement. Our main theorem asserts that any ideal ... More
Strongly symmetric smooth toric varietiesAug 09 2011We investigate toric varieties defined by arrangements of hyperplanes and call them strongly symmetric. The smoothness of such a toric variety translates to the fact that the arrangement is crystallographic. As a result, we obtain a complete classification ... More
Bivariant $K$-theory and the Weyl algebraJan 22 2004Jul 19 2004We introduce a new version $kk^{\rm alg}$ of bivariant $K$-theory that is defined on the category of all locally convex algebras. A motivating example is the Weyl algebra $W$, i.e. the algebra generated by two elements satisfying the Heisenberg commutation ... More
S-Type and P-Type Habitability in Stellar Binary Systems: A Comprehensive Approach. II. Elliptical OrbitsSep 12 2014Nov 26 2014In the first paper of this series, a comprehensive approach has been provided for the study of S-type and P-type habitable regions in stellar binary systems, which was, however, restricted to circular orbits of the stellar components. Fortunately, a modest ... More
S-Type and P-Type Habitability in Stellar Binary Systems: A Comprehensive Approach. I. Method and ApplicationsMar 26 2013Oct 25 2013A comprehensive approach is provided to the study of both S-type and P-type habitability in stellar binary systems, which in principle can also be expanded to systems of higher order. P-type orbits occur when the planet orbits both binary components, ... More
C*-algebras associated with algebraic actionsSep 23 2015Dec 03 2015This is a survey of work in which the author was involved in recent years. We consider C*-algebras constructed from representations of one or several algebraic endomorphisms of a compact abelian group - or, dually, of a discrete abelian group. In our ... More
Semigroup C*-algebras and toric varietiesMar 21 2017Let S be a finitely generated subsemigroup of Z^2. We derive a general formula for the K-theory of the left regular C*-algebra for S.
Quillen's work on the foundations of cyclic cohomologyFeb 27 2012We give a survey of Quillen's contributions, apart from the very first joint paper with Loday, to the area of cyclic homology.
Non-commutative Simplicial Complexes and the Baum-Connes ConjectureMar 30 2001We associate a non-commutative $C^*$-algebra with any locally finite simplicial complex. We determine the $K$-theory of these algebras and show that they can be used to obtain a conceptual explanation for the Baum-Connes conjecture.
Case Studies of Habitable Trojan Planets in the System of HD 23079Apr 15 2011We investigate the possibility of habitable Trojan planets in the HD 23079 star-planet system. This system consists of a solar-type star and a Jupiter-type planet, which orbits the star near the outer edge of the stellar habitable zone in an orbit of ... More
Application of the Titius-Bode Rule to the 55 Cancri System: Tentative Prediction of a Possibly Habitable PlanetJul 25 2011Jan 06 2012Following the notion that the Titius-Bode rule (TBR) may also be applicable to some extra-solar planetary systems, although this number could be relatively small, it is applied to 55 Cancri, which is a G-type main-sequence star currently known to host ... More
Cyclic Theory and the Bivariant Chern-Connes CharacterMar 31 2001We give a survey of cyclic homology/cohomology theory including a detailed discussion of cyclic theories for various classes of topological algebras. We show how to associate cyclic classes with Fredholm modules and $K$-theory classes and how to construct ... More
Can Planets Exist in the Habitable Zone of 55~Cancri?Feb 25 2019The aim of our study is to explore the possible existence of Earth-mass planets in the habitable zone of 55~Cancri, an effort pursued based on detailed orbital stability simulations. This star is known to possess (at least) five planets with masses ranging ... More
Weyl groupoids with at most three objectsMay 13 2008We adapt the generalization of root systems of the second author and H. Yamane to the terminology of category theory. We introduce Cartan schemes, associated root systems and Weyl groupoids. After some preliminary general results, we completely classify ... More
C*-algebras associated with endomorphisms and polymorphisms of compact abelian groupsFeb 27 2012Jun 10 2012A surjective endomorphism or, more generally, a polymorphism in the sense of \cite{SV}, of a compact abelian group $H$ induces a transformation of $L^2(H)$. We study the C*-algebra generated by this operator together with the algebra of continuous functions ... More
BinHab: A Numerical Tool for the Calculation of S/P-Type Habitable Zones in Binary SystemsSep 11 2014The aim of this contribution is to introduce the numerical tool BinHab, a publicly accessible code, available at The University of Texas at Arlington, that allows the calculation of S-type and P-type habitable zones of general binary systems.
Fitting Formulas for Determining the Existence of S-type and P-type Habitable Zones in Binary Systems: First ResultsSep 23 2016Sep 27 2016We present initial work about attaining fitting formulas for the quick determination of the existence of S-type and P-type habitable zones in binary systems. Following previous work, we calculate the limits of the climatological habitable zone in binary ... More
Reflection groupoids of rank two and Cluster algebras of type $A$Nov 16 2009We extend the classification of finite Weyl groupoids of rank two. Then we generalize these Weyl groupoids to `reflection groupoids' by admitting non-integral entries of the Cartan matrices. This leads to the unexpected observation that the spectrum of ... More
Algebraic K-theory and locally convex algebrasMar 21 2005We consider functors from the category of locally convex algebras to abelian groups and prove invariance under smooth homotopies for weakly J-stable algebras, where J is a harmonic operator ideal. This applies in particular to negative algebraic K-theory. ... More
Witt Vector Rings and the Relative de Rham Witt ComplexOct 20 2014Jun 23 2015In this paper we develop a novel approach to Witt vector rings and to the (relative) de Rham Witt complex. We do this in the generality of arbitrary commutative algebras and arbitrary truncation sets. In our construction of Witt vector rings the ring ... More
Fitting Formulae and Constraints for the Existence of S-type and P-type Habitable ZonesOct 09 2017We derive fitting formulae for the quick determination of the existence of S-type and P-type habitable zones in binary systems. Based on previous work, we consider the limits of the climatological habitable zone in binary systems (which sensitively depend ... More
UV Habitability of Possible Exomoons in Observed F-star Planetary SystemsMar 09 2015In the present study we explore the astrobiological significance of F-type stars of spectral type between F5 V and F9.5 V, which possess Jupiter-type planets within or close to their climatological habitable zones. These planets, or at least a subset ... More
An alternative to Witt vectorsNov 12 2013Dec 18 2013The ring of Witt vectors associated to a ring R is a classical tool in algebra. We introduce a ring C(R) which is more easily constructed and which is isomorphic to the ring of Witt vectors W(R) for a perfect F_p-algebra R. It is obtained as the completion ... More
S-Type and P-Type Habitability in Stellar Binary Systems: A Comprehensive Approach III. Results for Mars, Earth, and super-Earth PlanetsJan 31 2019In Paper I and II, a comprehensive approach was utilized for the calculation of S-type and P-type habitable regions in stellar binary systems for both circular and elliptical orbits of the binary components. It considered a joint constraint including ... More
Finite Weyl groupoids of rank threeDec 01 2009We continue our study of Cartan schemes and their Weyl groupoids. The results in this paper provide an algorithm to determine connected simply connected Cartan schemes of rank three, where the real roots form a finite irreducible root system. The algorithm ... More
Weyl groupoids of rank two and continued fractionsJul 01 2008A relationship between continued fractions and Weyl groupoids of Cartan schemes of rank two is found. This allows to decide easily if a given Cartan scheme of rank two admits a finite root system. We obtain obstructions and sharp bounds for the entries ... More
Atmospheric Heating and Wind Acceleration: Results for Cool Evolved Stars based on Proposed ProcessesJun 24 2014Jun 26 2014A chromosphere is a universal attribute of stars of spectral type later than ~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae binaries) show extended and highly turbulent chromospheres, which develop into slow massive winds. The ... More
About Exobiology: The Case for Dwarf K StarsJun 30 2016One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special ... More
A New Version of Reimers' law of Mass Loss Based on a Physical ApproachJul 26 2005We present a new semi-empirical relation for the mass loss of cool stellar winds, which so far has frequently been described by "Reimers' law". Originally, this relation was based solely on dimensional scaling arguments without any physical interpretation. ... More
A critical test of empirical mass loss formulae applied to individual giants and supergiantsFeb 06 2007To test our new, improved Reimers-type mass-loss relation, given by Schroder & Cuntz in 2005 (ApJL 630, L73), we take a look at the best studied galactic giants and supergiants - particularly those with spatially resolved circumstellar shells and winds, ... More
Generation of Longitudinal Flux Tube Waves in Theoretical Main-Sequence Stars: Effects of Model ParametersSep 21 2010Context. Continued investigation of the linkage between magneto-acoustic energy generation in stellar convective zones and the energy dissipation and radiative emission in outer stellar atmospheres in stars of different activity levels. Aims. We compute ... More
Planet-Induced Emission Enhancements in HD 179949: Results from McDonald ObservationsFeb 16 2012We monitored the Ca II H and K lines of HD 179949, a notable star in the southern hemisphere, to observe and confirm previously identified planet induced emission (PIE) as an effect of star-planet interaction. We obtained high resolution spectra (R ~ ... More
Orbital Stability of Planets in Binary Systems: A New Look at Old ResultsDec 19 2007Feb 15 2008About half of all known stellar systems with Sun-like stars consist of two or more stars, significantly affecting the orbital stability of any planet in these systems. This observational evidence has prompted a large array of theoretical research, including ... More
Orbital Stability of Earth-Type Planets in Binary SystemsDec 19 2007About half of all known stellar systems with Sun-like stars consist of two or more stars, significantly affecting the orbital stability of any planet in these systems. Here we study the onset of instability for an Earth-type planet that is part of a binary ... More
Solar Magnetic Flux Tube Simulations with Time-Dependent IonizationAug 07 2012In the present work we expand the study of time-dependent ionization previously identified to be of pivotal importance for acoustic waves in solar magnetic flux tube simulations. We focus on longitudinal tube waves (LTW) known to be an important heating ... More
Exocomets in the 47 UMa System: Theoretical Simulations including Water TransportOct 23 2018Motivated by ongoing discoveries of features (most likely) attributable to exocomets in various systems, this study examines the dynamics of possible comets around 47 UMa. Based on the assumption that most systems hosting planets should also harbor leftovers ... More
Case Studies of Exocomets in the System of HD 10180Nov 08 2017The aim of our study is to investigate the dynamics of possible comets in the HD 10180 system. This investigation is motivated by the discovery of exocomets in various systems, especially $\beta$ Pictoris, as well as in at least ten other systems. Detailed ... More
On the Dynamics of Comets in Extrasolar Planetary SystemsMar 16 2019Since very recently, we acquired knowledge on the existence of comets in extrasolar planetary systems. The formation of comets together with planets around host stars now seems evident. As stars are often born in clusters of interstellar clouds, the interaction ... More
On the K-theory of crossed products by automorphic semigroup actionsMay 24 2012Let P be a semigroup that admits an embedding into a group G. Assume that the embedding satisfies a certain Toeplitz condition and that the Baum-Connes conjecture holds for G. We prove a formula describing the K- theory of the reduced crossed product ... More
Fractal and Multifractal Analysis of the Rise of Oxygen in Earth's Early AtmosphereFeb 13 2014Jun 09 2015The rise of oxygen in Earth's atmosphere that occurred 2.4 to 2.2 billion years ago is known as the Earth's Great Oxidation, and its impact on the development of life on Earth has been profound. Thereafter, the increase in Earth's oxygen level persisted, ... More
Habitability of Earth-type Planets and Moons in the Kepler-16 SystemJan 11 2012Feb 22 2012We demonstrate that habitable Earth-mass planets and moons can exist in the Kepler-16 system, known to host a Saturn-mass planet around a stellar binary, by investigating their orbital stability in the standard and extended habitable zone (HZ). We find ... More
Climatological and UV-based Habitability of Possible Exomoons in F-star SystemsMar 09 2015Dec 06 2016We explore the astrobiological significance of F-type stars of spectral type between F5 V and F9.5 V, which possess Jupiter-type planets within or close to their climatological habitable zones. These planets, or at least a subset of those, may also possess ... More
The Stability of the Suggested Planet in the nu Octantis System: A Numerical and Statistical StudyJan 11 2012We provide a detailed theoretical study aimed at the observational finding about the nu Octantis binary system that indicates the possible existence of a Jupiter-type planet in this system. If a prograde planetary orbit is assumed, it has earlier been ... More
C*-algebras of Toeplitz type associated with algebraic number fieldsMay 26 2011Jun 10 2012We associate with the ring $R$ of algebraic integers in a number field a C*-algebra $\cT[R]$. It is an extension of the ring C*-algebra $\cA[R]$ studied previously by the first named author in collaboration with X.Li. In contrast to $\cA[R]$, it is functorial ... More
Acoustic wave propagation in the solar atmosphere. IV Nonadiabatic wave excitation with frequency spectraMar 17 1997We study the response of the solar atmosphere to excitations by large amplitude acoustic waves with radiation damping now included. Monochromatic adiabatic waves, due to unbalanced heating, generate continuously rising chromospheric temperature plateaus ... More
Study of Resonances for the Restricted 3-Body ProblemMay 04 2012Our aim is to identify and classify mean-motion resonances (MMRs) for the coplanar circular restricted three-body problem (CR3BP) for mass ratios between 0.10 and 0.50. Our methods include the maximum Lyapunov exponent, which is used as an indicator for ... More
On the K-theory of the C*-algebra generated by the left regular representation of an Ore semigroupJan 23 2012May 25 2013We compute the K-theory of C*-algebras generated by the left regular representation of left Ore semigroups satisfying certain regularity conditions. Our result describes the K-theory of these semigroup C*-algebras in terms of the K-theory for the reduced ... More
On the Possibility of Habitable Moons in the System of HD 23079: Results from Orbital Stability StudiesApr 03 2013Apr 08 2013The aim of our study is to investigate the possibility of habitable moons orbiting the giant planet HD 23079b, a Jupiter-mass planet, which follows a low-eccentricity orbit in the outer region of HD 23079's habitable zone. We show that HD 23079b is able ... More
Astrobiological Effects of F, G, K and M Main-Sequence StarsDec 19 2007Feb 15 2008We focus on the astrobiological effects of photospheric radiation produced by main-sequence stars of spectral types F, G, K, and M. The photospheric radiation is represented by using realistic spectra, taking into account millions or hundred of millions ... More
The habitability of super-Earths in Gliese 581May 25 2007Oct 12 2007Aims: The planetary system around the M star Gliese 581 consists of a hot Neptune (Gl 581b) and two super-Earths (Gl 581c and Gl 581d). The habitability of this system with respect to the super-Earths is investigated following a concept that studies the ... More
Biological Damage due to Photospheric, Chromospheric and Flare Radiation in the Environments of Main-Sequence StarsNov 10 2009We explore the biological damage initiated in the environments of F, G, K, and M-type main-sequence stars due to photospheric, chromospheric and flare radiation. The amount of chromospheric radiation is, in a statistical sense, directly coupled to the ... More
Habitability of the Goldilocks Planet Gliese 581g: Results from Geodynamic ModelsFeb 18 2011Feb 22 2011Aims: In 2010, detailed observations have been published that seem to indicate another super-Earth planet in the system of Gliese 581 located in the midst of the stellar climatological habitable zone. The mass of the planet, known as Gl 581g, has been ... More
Habitability of Super-Earths: Gliese 581c and 581dDec 19 2007Feb 19 2008The unexpected diversity of exoplanets includes a growing number of super-Earth planets, i.e., exoplanets with masses smaller than 10 Earth masses. Unlike the larger exoplanets previously found, these smaller planets are more likely to have a similar ... More
The Basal Chromospheric Mg II h+k Flux of Evolved Stars: Probing the Energy Dissipation of Giant ChromospheresFeb 23 2011Mar 01 2011Of a total of 177 cool G, K, and M giants and supergiants, we measured the Mg II h+k line emission of extended chromospheres in high-resolution (LWR) IUE spectra by using the IUE final data archive at STScI, and derived the respective stellar surface ... More
The Advection of Supergranules by Large-Scale FlowsMar 22 2010We produce a 10-day series of simulated Doppler images at a 15-minute cadence that reproduces the spatial and temporal characteristics seen in the SOHO/MDI Doppler data. Our simulated data contains a spectrum of cellular flows with but two necessary components ... More
Weak completions, bornologies and rigid cohomologyDec 20 2017Let $V$ be a complete discrete valuation ring with residue field $k$ of positive characteristic and with fraction field $K$ of characteristic 0. We clarify the analysis behind the Monsky--Washnitzer completion of a commutative $V$-algebra using completions ... More
Nonarchimedean bornologies, cyclic homology and rigid cohomologyAug 01 2017Let $V$ be a complete discrete valuation ring with residue field $k$ and with fraction field $K$ of characteristic 0. We clarify the analysis behind the Monsky--Washnitzer completion of a commutative $V$-algebra using spectral radius estimates for bounded ... More
The Instability Transition for the Restricted 3-Body Problem. III. The Lyapunov Exponent CriterionJun 24 2011We establish a criterion for the stability of planetary orbits in stellar binary systems by using Lyapunov exponents and power spectra for the special case of the circular restricted 3-body problem (CR3BP). The centerpiece of our method is the concept ... More
Astrobiology in the Environments of Main-Sequence Stars: Effects of Photospheric RadiationDec 19 2007We explore if carbon-based macromolecules (such as DNA) in the environments of stars other than the Sun are able to survive the effects of photospheric stellar radiation, such as UV-C. Therefore, we focus on main-sequence stars of spectral types F, G, ... More
An algorithm for quantifying dependence in multivariate data setsJul 04 2012Sep 27 2012We describe an algorithm to quantify dependence in a multivariate data set. The algorithm is able to identify any linear and non-linear dependence in the data set by performing a hypothesis test for two variables being independent. As a result we obtain ... More
Logic Programming with Graph Automorphism: Integrating naut with Prolog (Tool Description)Jul 17 2016Aug 01 2016This paper presents the plnauty~library, a Prolog interface to the nauty graph-automorphism tool. Adding the capabilities of nauty to Prolog combines the strength of the "generate and prune" approach that is commonly used in logic programming and constraint ... More
Slow Steady-Shear of Plastic Bead RaftsOct 12 2004Experimental measurements of the response of a two dimensional system of plastic beads subjected to steady shear are reported. The beads float at the surface of a fluid substrate and are subjected to a slow, steady-shear in a Couette geometry. The flow ... More
Asymmetric response of a jammed plastic bead raftMay 18 2006Fluctuation-dissipation relations have received significant attention as a potential method for defining an effective temperature in nonequilibrium systems. The successful development of an effective temperature would be an important step in the application ... More
Examples of nonpolygonal limit shapes in i.i.d. first-passage percolation and infinite coexistence in spatial growth modelsSep 13 2010Mar 13 2013We construct an edge-weight distribution for i.i.d. first-passage percolation on $\mathbb{Z}^2$ whose limit shape is not a polygon and whose extreme points are arbitrarily dense in the boundary. Consequently, the associated Richardson-type growth model ... More
Group analysis of differential equations and generalized functionsDec 28 1999We present an extension of the methods of classical Lie group analysis of differential equations to equations involving generalized functions (in particular: distributions). A suitable framework for such a generalization is provided by Colombeau's theory ... More
What the characters of irreducible subrepresentations of Jordan cells can tell us about LCFTJul 22 2013Jan 04 2014In this article, we review some aspects of logarithmic conformal field theories which can be inferred from the characters of irreducible submodules of indecomposable modules. We will mainly consider the W(2,2p-1,2p-1,2p-1) series of triplet algebras and ... More
Interface dynamics in discrete forward-backward diffusion equationsApr 05 2013We study the motion of phase interfaces in a diffusive lattice equation with bistable nonlinearity and derive a free boundary problem with hysteresis to describe the macroscopic evolution in the parabolic scaling limit. The first part of the paper deals ... More