Results for "A. Reiners"

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Differential Rotation in F StarsOct 12 2007Differential rotation can be detected in single line profiles of stars rotating more rapidly than about $v \sin{i} = 10$ km s$^{-1}$ with the Fourier transform technique. This allows to search for differential rotation in large samples to look for correlations ... More
Monoidal categories and the Gerstenhaber bracket in Hochschild cohomologyMar 14 2014Feb 27 2015In this monograph, we extend S. Schwede's exact sequence interpretation of the Gerstenhaber bracket in Hochschild cohomology to certain exact and monoidal categories. Therefore we establish an explicit description of an isomorphism by A. Neeman and V. ... More
Spectral line lists of a nitrogen gas discharge for wavelength calibration in the range $4500-11000$cm$^{-1}$Sep 10 2015A discharge of nitrogen gas, as created in a microwave-induced plasma, exhibits a very dense molecular emission line spectrum. Emission spectra of this kind could serve as wavelength calibrators for high-resolution astrophysical spectrographs in the near-infrared, ... More
Strong dipole magnetic fields in fast rotating fully convective starsJan 25 2018M dwarfs are the most numerous stars in our Galaxy with masses between approximately 0.5 and 0.1 solar mass. Many of them show surface activity qualitatively similar to our Sun and generate flares, high X-ray fluxes, and large-scale magnetic fields. Such ... More
First signatures of strong differential rotation in A-type starsNov 14 2003We reanalyzed high quality spectra of 158 stars of spectral types A0--F1 and $v \sin{i}$ between 60 and 150 km s$^{-1}$. Using a Least Squares Deconvolution technique we extracted high $S/N$ broadening profiles and determined the loci of the Fourier transform ... More
A Volume-limited Sample of 63 M7--M9.5 Dwarfs I. Space Motion, Kinematic Age, and LithiumSep 25 2009In a volume-limited sample of 63 ultracool dwarfs of spectral type M7--M9.5, we have obtained high-resolution spectroscopy with UVES at the Very Large Telescope and HIRES at Keck Observatory. In this first paper we introduce our volume-complete sample ... More
The First Direct Measurements of Magnetic Fields on Very Low-Mass StarsOct 12 2006We present the first direct magnetic field measurements on M dwarfs cooler than spectral class M4.5. Utilizing a new method based on the effects of a field on the FeH band near 1 micron, we obtain information on whether the integrated surface magnetic ... More
Conjectures on the cohomology of the GrassmannianSep 17 2003We give a series of successively weaker conjectures on the cohomology ring of the Grassmannian, starting with the Hilbert series of a certain natural filtration.
(q,t)-analogues and GL_n(F_q)Apr 18 2008Jun 16 2009We start with a (q,t)-generalization of a binomial coefficient. It can be viewed as a polynomial in t that depends upon an integer q, with combinatorial interpretations when q is a positive integer, and algebraic interpretations when q is the order of ... More
The cyclotomic polynomial topologicallyDec 08 2010Apr 16 2012We interpret the coefficients of the cyclotomic polynomial in terms of simplicial homology.
Cyclotomic and simplicial matroidsFeb 12 2004Two naturally occurring matroids representable over Q are shown to be dual: the {\it cyclotomic matroid} $\mu_n$ represented by the $n^{th}$ roots of unity $1,\zeta,\zeta^2,...,\zeta^{n-1}$ inside the cyclotomic extension $Q(\zeta)$, and a direct sum ... More
Is it possible to detect planets around young active G and K dwarfs?Nov 14 2013Theoretical predictions suggest that the distribution of planets in very young stars could be very different to that typically observed in Gyr old systems that are the current focus of radial velocity surveys. However, the detection of planets around ... More
Invariant derivations and differential forms for reflection groupsDec 03 2016Classical invariant theory of a complex reflection group $W$ highlights three beautiful structures: -- the $W$-invariant polynomials constitute a polynomial algebra, over which -- the $W$-invariant differential forms with polynomial coefficients constitute ... More
Optimal rigidity estimates for nearly umbilical surfaces in arbitrary codimensionOct 18 2013Aug 01 2014In [dLMu05], DeLellis and M\"uller proved a quantitative version of Codazzi's theorem, namely for a smooth embedded surface $\ \Sigma \subseteq \mathbb{R}^3\ $ with area normalized to $\ {\cal H}^2(\Sigma) = 4 \pi\ $, it was shown that $\ \parallel A_\Sigma ... More
3D simulations of M star atmosphere velocities and their influence on molecular FeH linesOct 19 2009We present an investigation of the velocity fields in early to late M-type star hydrodynamic models, and we simulate their influence on FeH molecular line shapes. The M star model parameters range between log g of 3.0 - 5.0 and Teff of 2500 K and 4000 ... More
Teff and logg dependence of FeH in M-dwarfsDec 11 2008We present synthetic FeH band spectra in the z-filter range for several M-dwarf models with logg=3.0-5.0 [cgs] and Teff=2800K -3450K. Our aim is to characterize convective velocities in M-dwarfs and to give a rough estimate of the range in which 3D-atmosphere ... More
Flat-relative optimal extraction. A quick and efficient algorithm for stabilised spectrographsNov 20 2013Optimal extraction is a key step in processing the raw images of spectra as registered by two-dimensional detector arrays to a one-dimensional format. Previously reported algorithms reconstruct models for a mean one-dimensional spatial profile to assist ... More
Teff and log g dependence of velocity fields in M-starsAug 06 2009We present an investigation of velocity fields in early to late M-type hydrodynamic stellar atmosphere models. These velocities will be expressed in classical terms of micro- and macro-turbulent velocities for usage in 1D spectral synthesis. The M-star ... More
A search for star-planet interactions in chromospheric linesDec 08 2010Massive planets in very close orbits around their central stars can induce so-called star-planet interactions (SPI), which may be of magnetic or gravitational nature. In both cases, SPI can potentially cause recurring chromospheric emission on the host ... More
Evidence for Magnetic Flux Saturation in Rapidly Rotating M StarsOct 28 2008We present magnetic flux measurements in seven rapidly rotating M dwarfs. Our sample stars have X-ray and H-alpha emission indicative of saturated emission, i.e., emission at a high level independent of rotation rate. Our measurements are made using near-infrared ... More
Generalized investigation of the rotation-activity relation: Favouring rotation period instead of Rossby numberAug 26 2014Magnetic activity in Sun-like and low-mass stars causes X-ray coronal emission, which is stronger for more rapidly rotating stars. This relation is often interpreted in terms of the Rossby number, i.e., the ratio of rotation period to convective overturn ... More
The Radio Activity-Rotation Relation of Ultracool DwarfsAug 01 2011[Abridged] We present a new radio survey of about 100 late-M and L dwarfs undertaken with the VLA. The sample was chosen to explore the role of rotation in the radio activity of ultracool dwarfs. Combining the new sample with results from our previous ... More
Highly Accurate Prediction of Jobs Runtime ClassesMay 02 2016May 23 2016Separating the short jobs from the long is a known technique to improve scheduling performance. In this paper we describe a method we developed for accurately predicting the runtimes classes of the jobs to enable this separation. Our method uses the fact ... More
Reflection factorizations of Singer cyclesAug 07 2013Mar 12 2014The number of shortest factorizations into reflections for a Singer cycle in GL_n(F_q) is shown to be (q^n-1)^(n - 1). Formulas counting factorizations of any length, and counting those with reflections of fixed conjugacy classes are also given. The method ... More
CARMENES input catalogue of M dwarfs II. High-resolution imaging with FastCamAug 29 2016Aims: We search for low-mass companions of M dwarfs and characterize their multiplicity fraction with the purpose of helping in the selection of the most appropriate targets for the CARMENES exoplanet survey. Methods: We obtained high-resolution images ... More
CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOSFeb 26 2015Context. CARMENES is a stabilised, high-resolution, double-channel spectrograph at the 3.5 m Calar Alto telescope. It is optimally designed for radial-velocity surveys of M dwarfs with potentially habitable Earth-mass planets. Aims. We prepare a list ... More
CRIRES spectroscopy and empirical line-by-line identification of FeH molecular absorption in an M dwarfJul 23 2010Molecular FeH provides a large number of sharp and isolated absorption lines that can be used to measure radial velocity, rotation, or magnetic field strength with high accuracy. Our aim is to provide an FeH atlas for M-type stars in the spectral region ... More
The activity and rotation limit in the HyadesDec 08 2010We conduct a study of K to M type stars to investigate the activity and the rotation limit in the Hyades. We use a sample of 40 stars in this intermediate-age cluster (~625 Myr) to probe stellar rotation in the threshold region where stellar activity ... More
Rotation, magnetism, and metallicity of M dwarf systemsAug 17 2011Close M-dwarf binaries and higher multiples allow the investigation of rotational evolution and mean magnetic flux unbiased from scatter in inclination angle and age since the orientation of the spin axis of the components is most likely parallel and ... More
Exploring the magnetic field complexity in M dwarfs at the boundary to full convectionJan 21 2014Based on detailed spectral synthesis we carry out quantitative measurements of the strength and complexity of surface magnetic fields in the four well-known M-dwarfs GJ 388, GJ 729, GJ 285, and GJ 406 populating the mass regime around the boundary between ... More
Differential rotation in rapidly rotating F-starsSep 23 2003We obtained high quality spectra of 135 stars of spectral types F and later and derived ``overall'' broadening functions in selected wavelength regions utilizing a Least Squares Deconvolution (LSD) procedure. Precision values of the projected rotational ... More
Rapid magnetic flux variability on the flare star CN LeonisMar 08 2007We present UVES/VLT observations of the nearby flare star CN Leo covering the Wing-Ford FeH band near 1mu with high spectral resolution. Some of the FeH absorption lines in this band are magnetically sensitive and allow a measurement of the mean magnetic ... More
Detection of differential rotation in psi Cap with profile analysisJul 18 2001We report detection of differential rotation on the F5 dwarf psi Cap using line profile analysis. The Fourier transform of both FeI lambda 5775 and SiI lambda 5772 are used to obtain a projected rotational velocity of v sini = (42+-1)km/s. Modelling of ... More
A laser-lock concept to reach cm/s-precision in Doppler experiments with Fabry-Perot wavelength calibratorsAug 26 2014State-of-the-art Doppler experiments require wavelength calibration with precision at the cm/s level. A low-finesse Fabry-Perot interferometer (FPI) can provide a wavelength comb with a very large bandwidth as required for astronomical experiments, but ... More
On the possibility of detecting extrasolar planets' atmospheres with the Rossiter-McLaughlin-effectMar 12 2009The detection of extrasolar planets' atmospheres requires very demanding observations. For planets that can not be spatially separated from their host stars, i.e. the vast majority of planets, the transiting planets are the only ones allowing to probe ... More
Periodic Radio Emission from the M7 Dwarf 2MASS J13142039+1320011: Implications for the Magnetic Field TopologyJul 07 2011We present multi-epoch radio and optical observations of the M7 dwarf 2MASS J13142039+1320011. We detect a ~1 mJy source at 1.43, 4.86, 8.46 and 22.5 GHz, making it the most luminous radio emission over the widest frequency range detected from an ultracool ... More
On the kinematic age of brown dwarfs: Radial velocities and space motions of 43 nearby L dwarfsJan 12 2010We present radial velocity measurements of a sample of L0-L8 dwarfs observed with VLT/UVES and Keck/HIRES. We combine these measurements with distance and proper motion from the literature to determine space motions for 43 of our targets. We identify ... More
A high resolution spectral atlas of brown dwarfsJul 18 2007We present a UVES/VLT high resolution atlas of three L dwarfs and one T dwarf system, spectral classes at which most of the objects are brown dwarfs. Our atlas covers the optical region from H$\alpha$ up to the near infrared at 1 $\mu$m. We present spectral ... More
Investigation of transit-selected exoplanet candidates from the MACHO surveyApr 11 2007Context: Planets outside our solar system transiting their host star, i. e. those with an orbital inclination near 90 degree, are of special interest to derive physical properties of extrasolar planets. With the knowledge of the host star's physical parameters, ... More
Observations of Cool-Star Magnetic FieldsMar 01 2012Cool stars like the Sun harbor convection zones capable of producing substantial surface magnetic fields leading to stellar magnetic activity. The influence of stellar parameters like rotation, radius, and age on cool-star magnetism, and the importance ... More
The effects of inclination, gravity darkening and differential rotation on absorption profiles of fast rotatorsJun 24 2003Mechanisms influencing absorption line profiles of fast rotating stars can be sorted into two groups; (i) intrinsic variations sensitive to temperature and pressure, and (ii) global effects common to all spectral lines. I present a detailed study on the ... More
Rotation- and temperature-dependence of stellar latitudinal differential rotationSep 14 2005Sep 30 2005More than 600 high resolution spectra of stars with spectral type F and later were obtained in order to search for signatures of differential rotation in line profiles. In 147 stars, the rotation law could be measured, 28 of them are found to be differentially ... More
Homological epimorphisms, recollements and Hochschild cohomology - with a conjecture by Snashall-Solberg in viewNov 04 2014Jun 02 2016We show that recollements of module categories give rise to homomorphisms between the associated Hochschild cohomology algebras which preserve the strict Gerstenhaber structure, i.e., the cup product, the graded Lie bracket and the squaring map. We review ... More
Equivariant Bifurcation and Absolute Irreducibility in $\R^8$ A contribution to the Ize conjectureOct 08 2012Sep 06 2013M. Field [5] refers to an unpublished work by J. Ize for a result that loss of stability through an absolutely irreducible representation of a compact Lie group leads to bifurcation of steady states. The main ingredient of the proof is the hypotheses, ... More
Magnetic Fields in Low-mass Stars: An Overview of Observational BiasesOct 22 2013Stellar magnetic dynamos are driven by rotation, rapidly rotating stars produce stronger magnetic fields than slowly rotating stars do. The Zeeman effect is the most important indicator of magnetic fields, but Zeeman broadening must be disentangled from ... More
Evidence for accretion in a nearby, young brown dwarfAug 24 2009We report on the discovery of the young, nearby, brown dwarf 2MASS J0041353$-$562112. The object has a spectral type of M7.5, it shows Li absorption and signatures of accretion, which implies that it still has a disk and suggests an age below 10 Myr. ... More
A Hybrid Channel Model based on WINNER for Vehicle-to-X ApplicationJan 22 2016V2V and V2I channel modeling became recently more of interest. To provide realistic radio channels either expensive measurements or complex ray tracing simulations are mostly used. Stochastic channel models are of low complexity but do not offer that ... 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
The Narrowest M-dwarf Line Profiles and the Rotation-Activity Connection at Very Slow RotationFeb 23 2007The rotation-activity connection explains stellar activity in terms of rotation and convective overturn time. It is well established in stars of spectral types F--K and in M-type stars of young clusters. It is not established in field M-dwarfs, because ... More
Magnetic Fields on Cool StarsDec 06 2010Magnetic fields are an important ingredient to cool star physics, and there is great interest in measuring fields and their geometry in order to understand stellar dynamos and their influence on star formation and stellar evolution. During the last few ... More
At the Bottom of the Main Sequence: Activity and magnetic fields beyond the threshold to complete convectionDec 14 2007Dec 18 2007The bottom of the main sequence hosts objects with fundamentally different properties. At masses of about 0.3 M$_{\odot}$, stars become fully convective and at about 0.08 M$_{\odot}$ the hydrogen-burning main sequence ends; less massive objects are brown ... More
Ultra-Cool and Extra-Vigorous: Rotation and Activity in M and L dwarfsOct 29 2007The study of rotation and activity in low-mass stars or brown dwarfs of spectral classes M and L has seen enormous progress during the last years. I summarize the results from different works that measured activity, rotation, and sometimes magnetic fields. ... More
Calibrating models of ultralow-mass starsOct 17 2005Evolutionary and atmospheric models have become available for young ultralow-mass objects. These models are being used to determine fundamental parameters from observational properties. TiO bands are used to determine effective temperatures in ultralow-mass ... More
Activity-induced radial velocity jitter in a flaring M dwarfMar 15 2009We investigate the effect of stellar activity and flares on short-term radial velocity measurements in the mid-M flare star CN Leo. Radial velocity variations are calculated from 181 UVES spectra obtained during three nights. We searched for spectral ... More
On the SNR Variability in Noisy Compressed SensingDec 12 2016Mar 15 2017Compressed sensing (CS) is a sampling paradigm that allows to simultaneously measure and compress signals that are sparse or compressible in some domain. The choice of a sensing matrix that carries out the measurement has a defining impact on the system ... More
Magnetic field observations of low-mass starsJan 13 2009Direct measurements of magnetic fields in low-mass stars of spectral class M have become available during the last years. This contribution summarizes the data available on direct magnetic measurements in M dwarfs from Zeeman analysis in integrated and ... More
Exact sequences, Hochschild cohomology, and the Lie module structure over the $M$-relative centerJul 09 2014Jan 29 2016In this article, we present actions by central elements on Hochschild cohomology groups with arbitrary bimodule coefficients, as well as an interpretation of these actions in terms of exact sequences. Since our construction utilises the monoidal structure ... More
Simple Mechanisms For Agents With ComplementsMar 25 2016Sep 02 2016We study the efficiency of simple auctions in the presence of complements. [DMSW15] introduced the single-bid auction, and showed that it has a price of anarchy (PoA) of $O(\log m)$ for complement-free (i.e., subadditive) valuations. Prior to our work, ... More
CARMENES input catalogue of M dwarfs: III. Rotation and activity from high-resolution spectroscopic observationsFeb 06 2018CARMENES is a spectrograph for radial velocity surveys of M dwarfs with the aim of detecting Earth-mass planets orbiting in the habitable zones of their host stars. To ensure an optimal use of the CARMENES Guaranteed Time Observations, in this paper we ... More
The CARMENES search for exoplanets around M dwarfs - Photospheric parameters of target stars from high-resolution spectroscopyFeb 08 2018The new CARMENES instrument comprises two high-resolution and high-stability spectrographs that are used to search for habitable planets around M dwarfs in the visible and near-infrared regime via the Doppler technique. Characterising our target sample ... More
The CARMENES search for exoplanets around M dwarfs: Wing asymmetries of H$α$, Na I D, and He I linesJan 31 2018Stellar activity is ubiquitously encountered in M dwarfs and often characterised by the H$\alpha$ line. In the most active M dwarfs, H$\alpha$ is found in emission, sometimes with a complex line profile. Previous studies have reported extended wings and ... More
Magnetic fields in M-dwarfs: quantitative results from detailed spectral synthesis in FeH linesDec 07 2010Strong surface magnetic fields are ubiquitously found in M-dwarfs with mean intensities on the order of few thousand Gauss-three orders of magnitude higher than the mean surface magnetic field of the Sun. These fields and their interaction with photospheric ... More
Detection of strong activity in the eclipsing binary brown dwarf 2MASSJ05352184-0546085 - A possible explanation for the temperature reversalNov 04 2007We show high resolution spectra of the eclipsing brown dwarf binary 2MASSJ05352184-0546085 taken at the two opposite radial velocity maxima. Comparisons of the TiO bands to model and template spectra are fully consistent with the temperatures previously ... More
Detecting Planets Around Very Low Mass Stars with the Radial Velocity MethodAug 31 2009Dec 11 2009The detection of planets around very low-mass stars with the radial velocity method is hampered by the fact that these stars are very faint at optical wavelengths where the most high-precision spectrometers operate. We investigate the precision that can ... More
Fiber polytopes for the projections between cyclic polytopesDec 17 1997The cyclic polytope $C(n,d)$ is the convex hull of any $n$ points on the moment curve ${(t,t^2,...,t^d):t \in \reals}$ in $\reals^d$. For $d' >d$, we consider the fiber polytope (in the sense of Billera and Sturmfels) associated to the natural projection ... More
Modelling the molecular Zeeman effect in M-dwarfs: methods and first resultsAug 15 2010We present first quantitative results of the surface magnetic field measurements in selected M-dwarfs based on detailed spectra synthesis conducted simultaneously in atomic and molecular lines of the FeH Wing-Ford $F^4\,\Delta-X^4\,\Delta$ transitions. ... More
From solar-like to anti-solar differential rotation in cool starsNov 13 2013Stellar differential rotation can be separated into two main regimes: solar-like when the equator rotates faster than the poles and anti-solar when the polar regions rotate faster than the equator. We investigate the transition between these two regimes ... More
Strong latitudinal shear in the shallow convection zone of a rapidly rotating A-starDec 09 2004We have derived the mean broadening profile of the star V102 in the region of the open cluster IC4665 from high resolution spectroscopy. At a projected equatorial rotation velocity of vsini = (105 +- 12)km/s we find strong deviation from classical rotation. ... More
A search for star-planet interactions in the upsilon Andromedae system at X-ray and optical wavelengthsOct 27 2010Feb 08 2011Close-in, giant planets are expected to influence their host stars via tidal or magnetic interaction. But are these effects strong enough in suitable targets known so far to be observed with today's instrumentation? The upsilon And system, an F8V star ... More
Capture and release of a conditional state of a cavity QED system by quantum feedbackFeb 12 2002Detection of a single photon escaping an optical cavity QED system prepares a non-classical state of the electromagnetic field. The evolution of the state can be modified by changing the drive of the cavity. For the appropriate feedback, the conditional ... More
What controls the large-scale magnetic fields of M dwarfs?Sep 24 2013Observations of active M dwarfs show a broad variety of large-scale magnetic fields encompassing dipole-dominated and multipolar geometries. We detail the analogy between some anelastic dynamo simulations and spectropolarimetric observations of 23 M stars. ... More
Multiwavelength observations of a giant flare on CN Leonis I. The chromosphere as seen in the optical spectraJul 13 2008Flares on dM stars contain plasmas at very different temperatures and thus affect a wide wavelength range in the electromagnetic spectrum. While the coronal properties of flares are studied best in X-rays, the chromosphere of the star is observed best ... More
Time evolution and squeezing of the field amplitude in cavity QEDDec 18 2000We present the conditional time evolution of the electromagnetic field produced by a cavity QED system in the strongly coupled regime. We obtain the conditional evolution through a wave-particle correlation function that measures the time evolution of ... More
Mechanically Reinforced MgB2 Wires and Tapes with High Transport CurrentsApr 29 2002In this contribution, different concepts for mechanically reinforced MgB2 wires with high transport currents are presented and characterised. It is shown that the achieved critical transport currents depend strongly on the conductor concept, the choice ... More
Can stellar activity make a planet seem misaligned?Jul 11 2016Several studies have shown that the occultation of stellar active regions by the transiting planet can generate anomalies in the high-precision transit light curves, and these anomalies may lead to an inaccurate estimate of the planetary parameters (e.g., ... More
Transport spin polarisation in SrRuO3 measured through Point Contact Andreev reflectionAug 02 2002Nov 05 2002We report a study in which Andreev reflection using a Nb point contact is used to measure the transport spin polarisation of the 4d itinerant ferromagnet SrRuO3. By performing the study in high quality thin films with residual resistivities less than ... More
What controls the magnetic geometry of M dwarfs?Dec 01 2012Context: observations of rapidly rotating M dwarfs show a broad variety of large-scale magnetic fields encompassing dipole-dominated and multipolar geometries. In dynamo models, the relative importance of inertia in the force balance -- quantified by ... More
Spreading of EGF Receptor Activity into EGF-free Regions and Molecular Therapies of CancerMar 18 2008The primary activation of the epidermal growth factor receptor (EGFR) has become a prominent target for molecular therapies against several forms of cancer. But despite considerable progress during the last years, many of its aspects remain poorly understood. ... More
Differential posets and Smith normal formsNov 12 2008We conjecture a strong property for the up and down maps U and D in an r-differential poset: DU+tI and UD+tI have Smith normal forms over Z[t]. In particular, this would determine the integral structure of the maps U, D, UD, DU, including their ranks ... More
Representation stability for cohomology of configuration spaces in $\mathbf{R}^d$May 15 2015Dec 11 2015This paper studies representation stability in the sense of Church and Farb for representations of the symmetric group $S_n$ on the cohomology of the configuration space of $n$ ordered points in $\mathbf{R}^d$. This cohomology is known to vanish outside ... More
Improved orbital solution and masses for the very low-mass multiple system LHS 1070Mar 05 2008Jun 04 2008We present a refined orbital solution for the components A, B, and C of the nearby late-M type multiple system LHS 1070. By combining astrometric datapoints from NACO/VLT, CIAO/SUBARU, and PUEO/CFHT, as well as a radial velocity measurement from the newly ... More
The lattice of closure relations of a posetSep 17 1994In this paper we show that the set of closure relations on a finite poset P forms a supersolvable lattice, as suggested by Rota. Furthermore this lattice is dually isomorphic to the lattice of closed sets in a convex geometry (in the sense of Edelman ... More
A Monte Carlo study of surface sputtering by dual and rotated ion beamsSep 27 2011Several, recently proposed methods of surface manufacturing based on ion beam sputtering, which involve dual beam setups, sequential application of ion beams from different directions, or sample rotation, are studied with the method of kinetic Monte Carlo ... More
Weyl group $q$-Kreweras numbers and cyclic sievingMay 30 2016The paper concerns a definition for $q$-Kreweras numbers for finite Weyl groups $W$, refining the $q$-Catalan numbers for $W$, and arising from work of the second author. We give explicit formulas in all types for the $q$-Kreweras numbers. In the classical ... More
Wavepacket-current <--> supercurrent conversion in closed N/S/N circuitsSep 26 2000The rise and decay in space and time of a supercurrent in a superconductor between two normal current leads connected to a reservoir is computed with the help of quasiparticle wavepackets which suffer Andreev scattering in the interfaces between the normal ... More
A universal coefficient theorem for Gauss's LemmaSep 27 2012Oct 24 2012We prove a version of Gauss's Lemma. It recursively constructs polynomials {c_k} for k=0,1,...,m+n, in Z[a_i,A_i,b_j,B_j] for i=0,...,m, and j=0,1,...,n, having degree at most (m+n choose m) in each of the four variable sets, such that whenever {A_i},{B_j},{C_k} ... More
Estimation of Radio Channel Parameters in Case of an Unknown TransmitterDec 11 2015This paper investigates the estimation of radio channel parameters from receiver data, whereby the transmitter is fully unknown. We use a multipath model to describe the radio channel between transmitter and receiver. According to this model, we discuss ... More
A Volume-limited Sample of 63 M7-M9.5 Dwarfs II. Activity, magnetism, and the fade of the rotation-dominated dynamoDec 21 2009In a volume-limited sample of 63 ultracool dwarfs of spectral type M7-M9.5, we have obtained high-resolution spectroscopy with UVES at the Very Large Telescope and HIRES at Keck Observatory. In this second paper, we present projected rotation velocities, ... More
P-partitions revisitedJun 30 2011Feb 15 2012We compare a traditional and non-traditional view on the subject of P-partitions, leading to formulas counting linear extensions of certain posets.
Diameter of reduced wordsJun 25 2009Oct 07 2011For finite reflection groups of types A and B, we determine the diameter of the graph whose vertices are reduced words for the longest element and whose edges are braid relations. This is deduced from a more general theorem that applies to supersolvable ... More
Plyades: A Python Library for Space Mission DesignJul 01 2016Plyades: A Python Library for Space Mission Design Designing a space mission is a computation-heavy task. Software tools that conduct the necessary numerical simulations and optimizations are therefore indispensable. The usability of existing software, ... More
Dynamical Transitions in a Dragged Growing Polymer ChainJul 22 2016We extend the Rouse model of polymer dynamics to situations of non-stationary chain growth. For a dragged polymer chain of length $N(t) = t^\alpha$, we find two transitions in conformational dynamics. At $\alpha= 1/2$, the propagation of tension and the ... More
Implementation of the Hierarchical Reference Theory for simple one-component fluidsDec 03 2001Apr 12 2002Combining renormalization group theoretical ideas with the integral equation approach to fluid structure and thermodynamics, the Hierarchical Reference Theory is known to be successful even in the vicinity of the critical point and for sub-critical temperatures. ... More
Semigroups Generated by Elliptic Operators in Non-Divergence Form on $C_0(/omega)$Oct 08 2010Given a bounded domain in the Euclidean space satisfying the uniform outer cone condition, we show that a uniformly elliptic operator of second order with continuous second order coefficients generates a holomorphic semigroup on the space of all continuous ... More
The First High-Resolution Spectra of 1.3 L SubdwarfsDec 06 2005We present the first high-resolution (R ~ 31,000) spectra of the cool sdL 2MASS0532, and what was originally identified as an early-type L subdwarf (sdL) LSR1610-0040. Our work, in combination with contemporaneous work by Cushing and Vacca, makes it clear ... More
Altair's inclination from line profile analysisAug 10 2004We present a detailed spectroscopic study of line broadening in the A7IV-V star Altair. In a wavelength region covering 690AA we reconstruct the overall broadening profile taking into account more than 650 spectral lines. From the broadening profile we ... More
Influence of the Preparation Process on Microstructure, Critical Current Density and Tc of MgB2 Powder-In-Tube WiresOct 28 2002MgB2 wires and tapes suffer from a limitation of the transport current densities, especially at low field, due to an unsufficient thermal stabilization caused by hot spots from a non-homogeneous microstructure, the presence of secondary phases and voids. ... More
Cyclic sieving of noncrossing partitions for complex reflection groupsJan 27 2007Mar 30 2009We prove an instance of the cyclic sieving phenomenon, occurring in the context of noncrossing parititions for well-generated complex reflection groups.
Hopf Algebras in CombinatoricsSep 30 2014Aug 22 2016These notes -- originating from a one-semester class by their second author at the University of Minnesota -- survey some of the most important Hopf algebras appearing in combinatorics. After introducing coalgebras, bialgebras and Hopf algebras in general, ... More
The Göttingen Solar Radial Velocity Project: Sub-m/s Doppler precision from FTS observations of the Sun as a starMar 01 2016Radial velocity observations of stars are entering the sub-m/s domain revealing fundamental barriers for Doppler precision experiments. Observations of the Sun as a star can easily overcome the m/s photon limit but face other obstacles. We introduce the ... More