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Results for "Mark J Claussen"

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Science with an ngVLA: Evolved StarsOct 15 2018This chapter reviews some of the expected contributions of the ngVLA to the understanding of the late evolutionary stages of low-to-intermediate mass stars, including asymptotic giant branch (AGB) stars, post-AGB stars, and pre-planetary nebulae. Such ... More
A VLA Search for Water Masers in Six HII Regions: Tracers of Triggered Low-Mass Star FormationApr 19 2004We present a search for water maser emission at 22 GHz associated with young low-mass protostars in six HII regions -- M16, M20, NGC 2264, NGC 6357, S125, and S140. The survey was conducted with the NRAO Very Large Array from 2000 to 2002. For several ... More
MSX versus IRAS Two-Color Diagrams and the CSE-Sequence of Oxygen-Rich Late-Type StarsSep 17 2009We present MSX two-color diagrams that can be used to characterize circumstellar environments of sources with good quality MSX colors in terms of IRAS color regions for oxygen-rich stars. With these diagrams we aim to provide a new tool that can be used ... More
Astro2020: Molecular Masers as Probes of the Dynamic Atmospheres of Dying StarsMar 13 2019More than half of the dust and heavy element enrichment in galaxies originates from the winds and outflows of evolved, low-to-intermediate mass stars on the asymptotic giant branch (AGB). However, numerous details of the physics of late-stage stellar ... More
Astro2020: Unlocking the Secrets of Late-Stage Stellar Evolution and Mass Loss through Radio Wavelength ImagingMar 13 2019During the late phases of evolution, low-to-intermediate mass stars like our Sun undergo periods of extensive mass loss, returning up to 80% of their initial mass to the interstellar medium. This mass loss profoundly affects the stellar evolutionary history, ... More
Excited-state OH Mainline Masers in AU Geminorum and NML CygniJul 25 2007Excited-state OH maser emission has previously been reported in the circumstellar envelopes of only two evolved stars: the Mira star AU Geminorum and the hypergiant NML Cygni. We present Very Large Array (VLA) observations of the 1665, 1667, and excited-state ... More
Observations of the 6 Centimeter Lines of OH in Evolved (OH/IR) StarsOct 24 2006Recent observational and theoretical advances have called into question traditional OH maser pumping models in evolved (OH/IR) stars. The detection of excited-state OH lines would provide additional constraints to discriminate amongst these theoretical ... More
Time-Resolved AU-Scale Jets Traced by Masers in the IRAS 4A/B Regions of NGC1333Aug 01 2008We present results of VLBI observations of the water masers associated with IRAS 4A and IRAS 4B in the NGC 1333 star-forming region taken in four epochs over a two month period. Both objects have been classified as extremely young sources and each source ... More
Proper Motion of H2O Masers in IRAS 20050+2720 MMS1: An AU Scale Jet Associated with An Intermediate-Mass Class 0 SourceApr 01 2005We conducted a 4 epoch 3 month VLBA proper motion study of H$_2$O masers toward an intermediate-mass class 0 source IRAS 20050+2720 MMS1 (d=700 pc). From milli-arcsecond (mas) resolution VLBA images, we found two groups of H2O maser spots at the center ... More
The Detection and Characterization of cm Radio Continuum Emission from the Low-mass Protostar L1014-IRSMay 12 2007Observations by the Cores to Disk Legacy Team with the Spitzer Space Telescope have identified a low luminosity, mid-infrared source within the dense core, Lynds 1014, which was previously thought to harbor no internal source. Followup near-infrared and ... More
A Proper Motion Study of the Haro 6-10 Outflow: Evidence for a Subarcsecond BinaryMay 25 2012We present single-dish and VLBI observations of an outburst of water maser emission from the young binary system Haro 6-10. Haro 6-10 lies in the Taurus molecular cloud and contains a visible T Tauri star with an infrared companion 1.3" north. Using the ... More
Quasi-simultaneous 43 and 86 GHz SiO Maser Observations and Potential Bias in the BAaDE Survey Are ResolvedAug 08 2018We observed the 43 GHz v=1, 2, and 3 and 86 GHz v=1 SiO maser transitions quasi-simultaneously for a Mira-variable-dominated sample of over 80 sources from the Bulge Asymmetries and Dynamical Evolution (BAaDE) project, using ATCA, and statistically compared ... More
Preplanetary Nebulae: An HST Imaging Survey and a New Morphological Classification SystemJul 31 2007Using the Hubble Space Telescope (HST), we have carried out a survey of candidate preplanetary nebulae (PPNs). We report here our discoveries of objects having well-resolved geometrical structures, and use the large sample of PPNs now imaged with HST ... More
Ground-State SiO Maser Emission Toward Evolved StarsMar 09 2004We have made the first unambiguous detection of vibrational ground-state maser emission from SiO toward six evolved stars. Using the Very Large Array, we simultaneously observed the v=0, J=1-0, 43.4-GHz, ground-state and the v=1, J=1-0, 43.1-GHz, first ... More
Positional Offsets Between SiO Masers in Evolved Stars and their Cross-Matched CounterpartsNov 11 2018Observations of dust-enshrouded evolved stars selected from infrared catalogs requiring high positional accuracy, like infrared spectroscopy or long baseline radio interferometric observations, often require preparational observational steps determining ... More
Proper Motion of Water Masers Near NGC1333-SVS13May 24 2001VLBA observations of water masers toward the region of NGC1333 near SVS13, the driving source for the well-known Herbig-Haro objects HH7-11, are reported. Maser emission was observed over four epochs spaced by three weeks during late 1998. SVS13 is associated ... More
High-Velocity Interstellar Bullets in IRAS05506+2414: A Very Young ProtostarFeb 08 2008We have made a serendipitous discovery of an enigmatic outflow source, IRAS 05506+2414 (hereafter IRAS 05506), as part of a multi-wavelength survey of pre-planetary nebulae (PPNs). The HST optical and near-infrared images show a bright compact central ... More
A Precise Distance to IRAS 00420+5530 via H2O Maser Parallax with the VLBAJan 05 2009We have used the VLBA to measure the annual parallax of the H2O masers in the star-forming region IRAS 00420+5530. This measurement yields a direct distance estimate of 2.17 +/- 0.05 kpc (<3%), which disagrees substantially with the standard kinematic ... More
A molecular-line study of the interstellar bullet engine IRAS 05506+2414Oct 09 2017Oct 30 2017We present interferometric and single-dish molecular line observations of the interstellar bullet-outflow source IRAS 05506+2414, whose wide-angle bullet spray is similar to the Orion BN/KL explosive outflow and likely arises from an entirely different ... More
Evidence of a Hadronic Origin for the TeV Source J1834-087Jul 13 2013We report on the discovery of compact, narrow OH line emission from the hydroxl molecule at 1720 MHz toward the extended TeV source J1834-087. The origin of this high energy emission is unknown; it could be powered by one or more candidate neutron stars ... More
The Extreme Scattering Event Toward 1741-038: H I AbsorptionAug 17 2000We report multi-epoch VLA H I absorption observations of the source 1741-038 (OT-068) before and during an extreme scattering event (ESE). Observations at four epochs, three during the ESE, were obtained. We find no changes in the equivalent width, maximum ... More
Shocked and Scorched: The Tail of a Tadpole in an Interstellar PondJan 24 2012Mar 28 2012We report multi-wavelength observations of the far-infrared source IRAS 20324+4057, including high-resolution optical imaging with HST, and ground-based near-infrared, millimeter-wave and radio observations. These data show an extended, limb-brightened, ... More
The Motion of Water Masers in the Pre-Planetary Nebula IRAS 16342-3814Oct 07 2008We present high angular resolution observations, using the Very Long Baseline Array (VLBA) of the NRAO, of the high-velocity water masers toward the "water-fountain" pre-planetary nebula, IRAS 16342-3814. The detailed structure of the water masers appears ... More
The Spitzer c2d Survey of Nearby Dense Cores: VI. The Protostars of Lynds Dark Nebula 1221Jul 09 2009Observations of Lynds Dark Nebula 1221 from the Spitzer Space Telescope are presented. These data show three candidate protostars towards L1221, only two of which were previously known. The infrared observations also show signatures of outflowing material, ... More
The size, luminosity and motion of the extreme carbon star IRC+10216 (CW Leonis)May 30 2012Jun 30 2012Very Large Array observations of the extreme carbon star IRC+10216 at 7 mm wavelength with 40 milli-arcsecond resolution resolve the object's radio emission, which forms an almost round uniform disk of 83 milli arcseconds diameter, corresponding to 11 ... More
High resolution radio observations of the colliding-wind binary WR140Jan 18 2005Milli-arcsecond resolution Very Long Baseline Array (VLBA) observations of the archetype WR+O star colliding-wind binary (CWB) system WR140 are presented for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in the wind-collision ... More
Radio emission from WR140Oct 07 2004Milliarcsecond resolution Very Long Baseline Array (VLBA) observations of the archetype WR+O star colliding-wind binary (CWB) system WR140 have been obtained at 23 epochs between orbital phases 0.74 to 0.97. The emission in the wind-collision region (WCR) ... More
Estimation of time delay by coherence analysisNov 16 2004Using coherence analysis (which is an extensively used method to study the correlations in frequency domain, between two simultaneously measured signals) we estimate the time delay between two signals. This method is suitable for time delay estimation ... More
Proper Motions of H2O Masers in the Water Fountain Source IRAS 19190+1102Mar 09 2010Mar 22 2010We report on the results of two epochs of Very Long Baseline Array (VLBA) observations of the 22 GHz water masers toward IRAS 19190+1102. The water maser emission from this object shows two main arc-shaped formations perpendicular to their NE-SW separation ... More
Radio continuum monitoring of the extreme carbon star IRC+10216Mar 21 2006We describe Very Large Array observations of the extreme carbon star IRC+10216 at 8.4, 14.9, and 22.5 GHz made over a two year period. We find possible variability correlated with the infrared phase and a cm- to sub-millimeter wavelength spectral index ... More
Shock-Excited Maser Emission from Supernova Remnants: G32.8-0.1, G337.8-0.1, G346.6-0.2, and the HB3/W3 ComplexMay 29 1998We present the results of VLA observations in the ground-state hydroxyl (OH) transition at 1720 MHz toward 20 supernova remnants (SNRs). We detect compact emission from four objects. For three of these objects (G32.8-0.1, G337.8-0.1, and G346.6-0.2), ... More
Towards Planetesimals in the Disk around TW Hya: 3.5 centimeter Dust EmissionJun 27 2005We present Very Large Array observations at 3.5 cm of the nearby young star TW Hya that show the emission is constant in time over weeks, months and years, and spatially resolved with peak brightness temperature ~10 K at ~0.25 (15 AU) resolution. These ... More
The OH (1720 MHz) Supernova Remnant Masers in W44: MERLIN and VLBA Polarization ObservationsMar 22 2005Full-polarization MERLIN and VLBA observations of the 1720-MHz maser emission from the OH molecule in the supernova remnant W44 are presented. Zeeman splitting has been directly resolved between right- and left-circularly polarized spectra indicating ... More
The OH (1720 MHz) Supernova Remnant Masers in W28: MERLIN and VLBA Polarization ObservationsOct 24 2004Full-polarization MERLIN and VLBA observations of the 1720 MHz maser emission from the OH molecule in the supernova remnant W28 are presented. Zeeman splitting (|B| \approx 0.75 mG) has been directly resolved between right- and left-circularly polarized ... More
Imaging the z=0.9 Absorbing Cloud toward 1830-211Jan 15 1998We present spectroscopic imaging observations of the molecular and HI 21cm absorbing cloud at z = 0.885 toward the `Einstein ring' radio source PKS 1830-211. We derive a cloud size between 10 h^{-1} pc and 600 h^{-1} pc, and M(H_2) > 2.6x10^{4} h^{-2} ... More
The Size of the Extragalactic Source J1801-231 and the Association of Pulsar PSR B1758-23 with the Supernova Remnant W28Jul 29 2002We have used the NRAO Very Large Array (VLA) in conjunction with the Very Long Baseline Array (VLBA) Pie Town antenna as a real-time interferometer system to measure the size of the extragalactic source J1801-231 as a function of frequency from 1285 to ... More
Polarization Observations of 1720 MHz OH Masers toward the Three Supernova Remnants W28, W44, and IC443Jun 06 1997(abridged) - We present arcsecond resolution observations from the VLA of the satellite line of the hydroxyl molecule (OH) at 1720.53 MHz toward three Galactic supernova remnants: W28, W44 and IC443. All of our observations are consistent with a model ... More
The Sizes of 1720 MHz OH Masers: VLBA and MERLIN Observations of the Supernova Remnants W44 and W28Apr 12 1999We have used the NRAO Very Long Baseline Array (VLBA) to image OH(1720 MHz) masers in the supernova remnants W28 and W44 at a resolution of 40 mas. We also used MERLIN to observe the same OH(1720 MHz) masers in W44 at a resolution of 290 x 165 mas. All ... More
The Sizes of OH (1720 MHz) Supernova Remnant Masers: MERLIN and VLBA Observations of IC443Oct 02 2002MERLIN and VLBA observations of the 1720 MHz maser emission from the OH molecule in the supernova remnant IC443 are presented. Based on MERLIN data with a resolution of 160 mas, the deconvolved sizes of the maser sources are in the range 90 to 180 mas ... More
An evla and carma study of dusty disks and torii with large grains in dying starsJun 21 2011We report the results of a pilot multiwavelength survey in the radio continuum (X, Ka and Q bands, i.e., from 3.6 cm to 7 mm) carried out with the EVLA in order to confirm the presence of very large dust grains in dusty disks and torii around the central ... More
Stable 85Rb Bose-Einstein Condensates with Widely Tunable InteractionsApr 17 2000Jun 09 2000Bose-Einstein condensation has been achieved in a magnetically trapped sample of 85Rb atoms. Long-lived condensates of up to 10^4 atoms have been produced by using a magnetic-field-induced Feshbach resonance to reverse the sign of the scattering length. ... More
Magnetic Field Dependence of Ultracold Inelastic Collisions near a Feshbach ResonanceMar 14 2000May 29 2000Inelastic collision rates for ultracold $^{85}$Rb atoms in the F=2 m$_{f}$=-2 state have been measured as a function of magnetic field. Dramatic change in the vicinity of a Feshbach resonance at 155 G was observed. Similar to the elastic rate, the inelastic ... More
Understanding Mass-Loss and the late Evolution of Intermediate Mass Stars: Jets, Disks, Binarity, Dust and Magnetic FieldsMar 13 2009Almost all stars in the 1-8 Msun range evolve through the Asymptotic Giant Branch (AGB), preplanetary nebula (PPN) and planetary nebula (PN) evolutionary phases. Most stars that leave the main sequence in a Hubble time will end their lives in this way. ... More
Astrometric Positions and Proper Motions of 19 Radio StarsMar 21 2003We have used the Very Large Array, linked with the Pie Town Very Long Baseline Array antenna, to determine astrometric positions of 19 radio stars in the International Celestial Reference Frame (ICRF). The positions of these stars were directly linked ... More
Deconstructing the E_0 SCFT to Solve the Orbifold Paradox of the Heterotic M TheoryJun 26 2016Jun 28 2016Many heterotic orbifold models have massless twisted-sector particles with simultaneous E8_1 and E8_2 charges. In the strong-coupling M-theory dual of the heterotic string this poses a paradox: Since the E8_1 and E8_2 live at opposite ends of the x^10 ... More
Very high precision bound state spectroscopy near a $^{85}$Rb Feshbach resonanceFeb 11 2003We precisely measured the binding energy of a molecular state near the Feshbach resonance in a $^{85}$Rb Bose-Einstein condensate (BEC). Rapid magnetic field pulses induced coherent atom-molecule oscillations in the BEC. We measured the oscillation frequency ... More
An Inner Hole in the Disk around TW Hydrae Resolved in 7 Millimeter Dust EmissionApr 18 2007We present Very Large Array observations at 7 millimeters wavelength that resolve the dust emission structure in the disk around the young star TW Hydrae at the scale of the ~4 AU (~0.16") radius inner hole inferred from spectral energy distribution modeling. ... More
Controlled Collapse of a Bose-Einstein CondensateFeb 07 2001The point of instability of a Bose-Einstein Condensate (BEC) due to attractive interactions was studied. Stable 85-Rb BECs were created and then caused to collapse by slowly changing the atom-atom interaction from repulsive to attractive using a Feshbach ... More
Improved Characterization of Elastic Scattering Near a Feshbach Resonance in 85RbApr 18 2001Apr 23 2001We report extentions and corrections to the measurement of the Feshbach resonance in 85Rb cold atom collisions reported earlier [J. L. Roberts et al., Phys. Rev. Lett. 81, 5109 (1998)]. In addition to a better determination of the position of the resonance ... More
A Pilot Imaging Line Survey of RW LMi and IK Tau Using the Expanded Very large ArrayJun 29 2011We report on a pilot imaging line survey (36.0 - 37.0 GHz, with ~1 km/s spectral channels) with the Expanded Very Large Array for two asymptotic giant branch stars, RW LMi (= CIT6, which has a carbon-rich circumstellar envelope) and IK Tau (= NML Tau, ... More
VLA+PT Astrometry of 46 Radio StarsOct 31 2006We have used the Very Large Array (VLA), linked with the Pie Town Very Long Baseline Array antenna, to determine astrometric positions of 46 radio stars in the International Celestial Reference Frame (ICRF). Positions were obtained in the ICRF directly ... More
Detection of Class I Methanol (CH3OH) Maser Candidates in Supernova RemnantsDec 24 2013We have used the Karl G. Jansky Very Large Array (VLA) to search for 36 GHz and 44 GHz methanol (CH3OH) lines in a sample of 21 Galactic supernova remnants (SNRs). Mainly the regions of the SNRs with 1720 MHz OH masers were observed. Despite the limited ... More
Resonant magnetic field control of elastic scattering of cold 85RbAug 14 1998A magnetic field dependent Feshbach resonance has been observed in the elastic scattering collision rate between atoms in the F = 2, M = -2 state of 85 Rb. Changing the magnetic field by several Gauss caused the collision rate to vary by a factor of 10,000, ... More
Nongaussian fluctuations arising from finite populations: Exact results for the evolutionary Moran processSep 24 2004Feb 09 2006The appropriate description of fluctuations within the framework of evolutionary game theory is a fundamental unsolved problem in the case of finite populations. The Moran process recently introduced into this context [Nowak et al., Nature (London) 428, ... More
Desynchronizing effect of high-frequency stimulation in a generic cortical network modelMar 21 2012Transcranial Electrical Stimulation (TCES) and Deep Brain Stimulation (DBS) are two different applications of electrical current to the brain used in different areas of medicine. Both have a similar frequency dependence of their efficiency, with the most ... More
An efficient algorithm for the calculation of reserves for non-unit linked life policiesJan 08 2014Jun 27 2014The underlying stochastic nature of the requirements for the Solvency II regulations has introduced significant challenges if the required calculations are to be performed correctly, without resorting to excessive approximations, within practical timescales. ... More
$1/f^α$ spectra in elementary cellular automata and fractal signalsOct 19 2004We systematically compute the power spectra of the one-dimensional elementary cellular automata introduced by Wolfram. On the one hand our analysis reveals that one automaton displays $1/f$ spectra though considered as trivial, and on the other hand that ... More
Cyclic dominance and biodiversity in well-mixed populationsJan 10 2008Coevolutionary dynamics is investigated in chemical catalysis, biological evolution, social and economic systems. The dynamics of these systems can be analyzed within the unifying framework of evolutionary game theory. In this Letter, we show that even ... More
The Nature of the Nuclear H2O Masers of NGC 1068: Reverberation and Evidence for a Rotating Disk GeometryApr 04 2001We report new (1995) Very Large Array observations and (1984 - 1999) Effelsberg 100m monitoring observations of the 22 GHz H2O maser spectrum of the Seyfert 2 galaxy NGC 1068. The sensitive VLA observations provide a registration of the 22 GHz continuum ... More
Investigation of topographical stability of the concave and convex Self-Organizing Map variantSep 20 2006We investigate, by a systematic numerical study, the parameter dependence of the stability of the Kohonen Self-Organizing Map and the Zheng and Greenleaf concave and convex learning with respect to different input distributions, input and output dimensions. ... More
OH (1720 MHz) Masers: A Multiwavelength Study of the Interaction between the W51C Supernova Remnant and the W51B Star Forming RegionMay 13 2013We present a comprehensive view of the W51B HII region complex and the W51C supernova remnant (SNR) using new radio observations from the VLA, VLBA, MERLIN, JCMT, and CSO along with archival data from Spitzer, ROSAT, ASCA, and Chandra. Our VLA data include ... More
Similarity based cooperation and spatial segregationApr 28 2004Jan 04 2005We analyze a cooperative game, where the cooperative act is not based on the previous behaviour of the co-player, but on the similarity between the players. This system has been studied in a mean-field description recently [A. Traulsen and H. G. Schuster, ... More
SiS in the circumstellar envelope of IRC +10126: maser and quasi-thermal emissionJun 08 2017We present new Effelsberg-100 m, ATCA, and VLA observations of rotational SiS transitions in the circumstellar envelope (CSE) of IRC +10216. Thanks to the high angular resolution achieved by the ATCA observations, we unambiguously confirm that the molecule's ... More
Improved control of delayed measured systemsOct 22 1998Jul 30 2004In this paper we address the question how the control of delayed measured chaotic systems can be improved. Both unmodified OGY control and difference control can be successfully applied only for a certain range of Lyapunov numbers depending on the delay ... More
Fixed-Connectivity MembranesDec 21 2004The statistical mechanics of flexible surfaces with internal elasticity and shape fluctuations is summarized. Phantom and self-avoiding isotropic and anisotropic membranes are discussed, with emphasis on the universal negative Poisson ratio common to ... More
Coevolutionary Dynamics: From Finite to Infinite PopulationsSep 24 2004Feb 08 2006Traditionally, frequency dependent evolutionary dynamics is described by deterministic replicator dynamics assuming implicitly infinite population sizes. Only recently have stochastic processes been introduced to study evolutionary dynamics in finite ... More
Cg in Two PagesFeb 12 2003Cg is a language for programming GPUs. This paper describes Cg briefly.
Finite Temperature StringsOct 02 1992These are lecture notes for the 1992 Erice Workshop on String Quantum Gravity and Physics at the Planck Energy Scale. In this talk a review of earlier work on finite temperature strings was presented. Several topics were covered, including the canonical ... More
Obstructions to QuantizationSep 10 1998Quantization is not a straightforward proposition, as shown by Groenewold's and Van Hove's discovery, more than fifty years ago, of an "obstruction" to quantization. Their "no-go theorems" assert that it is impossible to consistently quantize every classical ... More
On quantizing semisimple basic algebrasDec 18 2000Nov 15 2001We show that there is a consistent polynomial quantization of the coordinate ring of a basic nilpotent coadjoint orbit of a semisimple Lie group. We also show, at least in the case of a nilpotent orbit in sl(2,R)*, that any such quantization is essentially ... More
Anomalous Spectral Types and Intrinsic Colors of Young StarsJul 12 2016We highlight differences in spectral types and intrinsic colors observed in pre-main sequence (pre-MS) stars. Spectral types of pre-MS stars are wavelength-dependent, with near-infrared spectra being 3-5 spectral sub-classes later than the spectral types ... More
Sleep, Neuroengineering and DynamicsDec 30 2013Modeling of consciousness-related phenomena and neuroengineering are fields that are rapidly growing together. We review recent approaches and developments and point out some promising directions of future research: Understanding the dynamics of consciousness ... More
The phase response of the cortical slow oscillationDec 30 2013Cortical slow oscillations occur in the mammalian brain during deep sleep and have been shown to contribute to memory consolidation, an effect that can be enhanced by electrical stimulation. As the precise underlying working mechanisms are not known it ... More
Azimuthal di-hadron correlations in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV from STARJun 20 2006We present the centrality dependence of the azimuthal angle correlation shapes between a trigger and associated charged hadrons in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV from the STAR experiment. The away-side structure is significantly modified ... More
A Balloon-borne Large Aperture Submillimeter TelescopeDec 14 2000A new generation of sub-orbital platforms will be operational in the next few years. These new telescopes will operate from airborne and balloon-borne platforms where the atmosphere is transparent enough to allow sensitive measurements to be made in the ... More
On the Groenewold-Van Hove problem for R^{2n}Sep 16 1998Oct 19 1998We discuss the Groenewold-Van Hove problem for R^{2n}, and completely solve it when n = 1. We rigorously show that there exists an obstruction to quantizing the Poisson algebra of polynomials on R^{2n}, thereby filling a gap in Groenewold's original proof ... More
On a Full Quantization of the TorusJul 31 1995I exhibit a prequantization of the torus which is actually a ``full'' quantization in the sense that a certain complete set of classical observables is irreducibly represented. Thus in this instance there is no Groenewold-Van Hove obstruction to quantization. ... More
Coevolutionary dynamics in large, but finite populationsJul 11 2006Coevolving and competing species or game-theoretic strategies exhibit rich and complex dynamics for which a general theoretical framework based on finite populations is still lacking. Recently, an explicit mean-field description in the form of a Fokker-Planck ... More
Stochastic differential equations for evolutionary dynamics with demographic noise and mutationsMar 15 2012We present a general framework to describe the evolutionary dynamics of an arbitrary number of types in finite populations based on stochastic differential equations (SDE). For large, but finite populations this allows to include demographic noise without ... More
Asymptotic Level Density of the Elastic Net Self-Organizing Feature MapSep 20 2006Whileas the Kohonen Self Organizing Map shows an asymptotic level density following a power law with a magnification exponent 2/3, it would be desired to have an exponent 1 in order to provide optimal mapping in the sense of information theory. In this ... More
The OMC-1 molecular hydrogen outflow as a fragmented stellar wind bubbleNov 07 1996We present new images of the OMC-1 molecular hydrogen outflow, made using long-slit spectroscopy in order to accurately subtract the underlying continuum emission. These images reveal an extremely clumpy, quasi-spherical inner shell that breaks up at ... More
A model for dynamical evolution of science in spaceJul 31 2014How does the topological space of science emerge? Inspired by the concept of maps of science, i.e. mapping scientific topics to a scientific space, we ask which topological structure a dynamical process of authors collaborating and publishing papers can ... More
Hard X-ray Emission from the NGC 5044 GroupFeb 04 2011Observations made with the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) to constrain the hard X-ray emission in the NGC 5044 group are reported here. Modeling a combined PCA and ROSAT position sensitive proportional counter (PSPC) ... More
On quantizing semisimple basic algebras II: The general caseAug 22 2002We prove that there is no consistent polynomial quantization of the coordinate ring of a basic non-nilpotent coadjoint orbit of a semisimple Lie group.
Quantum State Detection Via EliminationMay 28 1999We present the view of quantum algorithms as a search-theoretic problem. We show that the Fourier transform, used to solve the Abelian hidden subgroup problem, is an example of an efficient elimination observable which eliminates a constant fraction of ... More
Simulation of the electron-phonon interaction in infinite dimensionsMar 14 1994The electron-phonon interaction corresponding to the Holstein model (with Coulomb repulsion) is simulated in infinite dimensions using a novel quantum Monte Carlo algorithm. The thermodynamic phase diagram includes commensurate charge-density-wave phases, ... More
Phantom maps and chromatic phantom mapsNov 05 1998In the first part, we determine conditions on spectra X and Y under which either every map from X to Y is phantom, or no nonzero maps are. We also address the question of whether such all or nothing behaviour is preserved when X is replaced with V smash ... More
Some remarks on singularities in quantum cosmologyMay 13 1996Nov 27 1996We discuss to what extent classical singularities persist upon quantization in two simple cosmological models.
The Eagle's EGGs: fertile or sterile?Feb 01 2002We present a deep, high spatial resolution (0.35 arcsec FWHM), near-infrared (1-2.5 micron) imaging survey of the Eagle Nebula, M16, made with the VLT, centred on the famous elephant trunks. We compare these data with the existing HST optical images to ... More
Quillen model structures for relative homological algebraNov 26 2000Jul 19 2013An important example of a model category is the category of unbounded chain complexes of R-modules, which has as its homotopy category the derived category of the ring R. This example shows that traditional homological algebra is encompassed by Quillen's ... More
Practical and Robust Stenciled Shadow Volumes for Hardware-Accelerated RenderingJan 06 2003Twenty-five years ago, Crow published the shadow volume approach for determining shadowed regions in a scene. A decade ago, Heidmann described a hardware-accelerated stencil buffer-based shadow volume algorithm. Unfortunately hardware-accelerated stenciled ... More
The Statistical Mechanics of MembranesFeb 02 2000The fluctuations of two-dimensional extended objects membranes is a rich and exciting field with many solid results and a wide range of open issues. We review the distinct universality classes of membranes, determined by the local order, and the associated ... More
The Origin of the 4.5 micron Excess from Dwarf GalaxiesApr 26 2009Dwarf galaxies tend to have redder [3.6 micron] - [4.5 micron] Spitzer broadband colors than spirals. To investigate this effect, for a large sample of dwarf galaxies we combine Spitzer fluxes with data at other wavelengths and compare to population synthesis ... More
Counterion Condensation in Strong, Flexible PolyelectrolytesDec 24 1996We present results of molecular dynamics simulations of strong, flexible polyelectrolyte chains in solution with added salt. The effect of added salt on the polyelectrolyte chain structure is fully treated for the first time as a function of polymer density. ... More
Thermal Fluctuations at Second Order Phase TransitionsJul 12 1993We construct a new coarse-grained effective potential which enables us to estimate the probabilities of thermal fluctuations above an arbitrary threshold at different length scales.
Bordism Groups of Immersions and Classes Represented by Self-IntersectionsApr 07 2005We prove a geometrical version of Herbert's theorem by considering the self-intersection immersions of a self-transverse immersion up to bordism. This generalises Herbert's theorem to additional cohomology theories and gives a commutative diagram in the ... More
Convex Hulls of Random Walks: Large-Deviation PropertiesJan 05 2015We study the convex hull of the set of points visited by a two-dimensional random walker of T discrete time steps. Two natural observables that characterize the convex hull in two dimensions are its perimeter L and area A. While the mean perimeter <L> ... More
On the Fundamental Characteristics of Ultra-Dense Small Cell NetworksOct 15 2017In order to cope with the forecasted 1000x increase in wireless capacity demands by 2030, network operators will aggressively densify their network infrastructure to reuse the spectrum as much as possible. However, it is important to realise that these ... More
Charge and the topology of spacetimeMay 19 1999Sep 02 1999A new class of electrically charged wormholes is described in which the outer two sphere is not spanned by a compact coorientable hypersurface. These wormholes can therefore display net electric charge from the source free Maxwell's equation. This extends ... More
Eternal acceleration from M-theoryFeb 10 2006Mar 22 2006The dimensional reduction of $D$-dimensional spacetimes arising in string/M-theory, to the conformal Einstein frame, may give rise to cosmologies with accelerated expansion. Through a complete analysis of the dynamics of doubly warped product spacetimes, ... More