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Detecting Compton Reflection and a Broad Iron Line in MCG-5-23-16 with the Rossi X-ray Timing ExplorerDec 02 1997Dec 03 1997We report the detection with the Rossi X-ray Timing Explorer of a Compton reflection signature in the Seyfert galaxy MCG-5-23-16. RXTE also resolves the Fe K-alpha fluorescence line with FWHM ~48,000 km s^{-1}. This measurement provides the first independent ... More

X-ray Properties of the Central kpc of AGN and Starbursts: The Latest News from ChandraAug 30 2001The X-ray properties of 15 nearby (v<3,000 km/s) galaxies that possess AGN and/or starbursts are discussed. Two-thirds have nuclear extended emission on scales from ~0.5 to ~1.5 kpc that is either clearly associated with a nuclear outflow or morphologically ... More

The New Horizons Kuiper Belt Extended MissionJun 21 2018The central objective of the New Horizons prime mission was to make the first exploration of Pluto and its system of moons. Following that, New Horizons has been approved for its first extended mission, which has the objectives of extensively studying ... More

Overview of the New Horizons Science PayloadSep 26 2007The New Horizons mission was launched on 2006 January 19, and the spacecraft is heading for a flyby encounter with the Pluto system in the summer of 2015. The challenges associated with sending a spacecraft to Pluto in less than 10 years and performing ... More

The Carbon Monoxide Abundance in Comet 103P/Hartley during the EPOXI FlybyApr 22 2011We report the detection of several emission bands in the CO Fourth Positive Group from comet 103P/Hartley during ultraviolet spectroscopic observations from the Hubble Space Telescope (HST) on 2010 November 4 near the time of closest approach by NASA's ... More

The Positions, Colors, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005-2006Apr 29 2006May 02 2006Pluto's two small satellites, temporarily designated S/2005 P 1 and S/2005 P 2, were observed on four dates (15.1 and 18.1 May 2005, 15.7 February 2006, and 2.8 March 2006) using the Hubble Space Telescope's (HST) Advanced Camera for Surveys (ACS). Here ... More

Deconstructing NGC 7130Nov 23 2004Observations of the Seyfert 2 and starburst galaxy NGC 7130 with the Chandra X-ray Observatory illustrate that both of these phenomena contribute significantly to the galaxy's detectable X-ray emission. The active galactic nucleus (AGN) is strongly obscured, ... More

Penetrating the Deep Cover of Compton Thick Active Galactic NucleiMay 17 2006We analyze observations obtained with the Chandra X-ray Observatory of bright Compton thick active galactic nuclei (AGNs), those with column densities in excess of 1.5 x 10^{24} cm^{-2} along the lines of sight. We therefore view the powerful central ... More

Accretion and Outflow in the AGN and Starburst of NGC 5135Oct 22 2003Observations of the Seyfert 2 and starburst galaxy NGC 5135 with the Chandra X-ray Observatory demonstrate that both of these phenomena contribute significantly to its X-ray emission. We spatially isolate the active galactic nucleus (AGN) and demonstrate ... More

Discovery of Bright Variable X-ray Sources in NGC 1569 with ChandraMay 27 2003From the analysis of a ~100 ks Chandra observation of the dwarf starburst galaxy NGC 1569, we have found that the X-ray point sources, CXOU 043048.1+645050 and CXOU 043048.6+645058, showed significant time variability. During this observation, the X-ray ... More

The Far Ultraviolet Spectrum of the Io Plasma TorusOct 23 2003The spectrum of the Io plasma torus in the range 905 - 1187 A was recorded at 0.26 A resolution by the Far Ultraviolet Spectroscopic Explorer (FUSE) on 2001 January 14. Five orbits of data were obtained with the west ansa of the torus centered and tracked ... More

Automatic convexityMay 17 2001In many cases the convexity of the image of a linear map with range is $R^n$ is automatic because of the facial structure of the domain of the map. We develop a four step procedure for proving this kind of ``automatic convexity''. To make this procedure ... More

On the Evidence for Extreme Gravity Effects in MCG-6-30-15Jun 03 1998We examine the unusual Fe-Kalpha line profile in MCG-6-30-15 observed by ASCA during a deep minimum in the source intensity. The intense red wing and depressed blue wing of the line have been interpreted as evidence for extreme gravitational redshifts ... More

Detecting Fourier subspacesMar 24 2015Let G be a finite abelian group. We examine the discrepancy between subspaces of l^2(G) which are diagonalized in the standard basis and subspaces which are diagonalized in the dual Fourier basis. The general principle is that a Fourier subspace whose ... More

Extreme X-ray Iron Lines in Active Galactic NucleiJun 04 2002We analyze X-ray spectra of heavily obscured (N_H > 10^{24} cm^{-2}) active galaxies obtained with Chandra, concentrating on the iron K alpha fluorescence line. We measure very large equivalent widths in most cases, up to 5 keV in the most extreme example. ... More

Classical wave experiments on chaotic scatteringNov 02 2005We review recent research on the transport properties of classical waves through chaotic systems with special emphasis on microwaves and sound waves. Inasmuch as these experiments use antennas or transducers to couple waves into or out of the systems, ... More

26Al and 60Fe From Supernova ExplosionsApr 01 1995Using recently calculated yields for Type II supernovae, along with models for chemical evolution and the distribution of mass in the interstellar medium, the current abundances and spatial distributions of two key gamma-ray radioactivities, $^{26}$Al ... More

X-ray Evidence for Multiple Absorbing Structures in Seyfert GalaxiesNov 07 2004We have used X-ray spectra to measure attenuating columns in a large sample of Seyfert galaxies. Over 30 of these sources have resolved radio jets, allowing the relative orientation of the nucleus and host galaxy to be constrained. We have discovered ... More

Low-Pass Filters: Commentary on a Remark by FeynmanApr 23 2004In Feynman's lectures there is a remark about the limiting value of the impedance of an n-section ladder consisting of purely reactive elements (capacitances and inductances). The remark is that this limiting impedance $z=\lim_{n\to\infty}z_n$ has a positive ... More

Characteristic Generators and Dualization for Tail-Biting TrellisesJan 20 2011This paper focuses on dualizing tail-biting trellises, particularly KV-trellises. These trellises are based on characteristic generators, as introduced by Koetter/Vardy (2003), and may be regarded as a natural generalization of minimal conventional trellises, ... More

Variable Iron K-alpha Lines in Seyfert 1 GalaxiesAug 31 2000We find that variability of the iron K-alpha line is common in Seyfert 1 galaxies. Using data from the ASCA archive for objects that have been observed more than once during the mission, we study the time-averaged spectra from individual observations, ... More

New Horizons Upper Limits on O$_2$ in Pluto's Present Day AtmosphereJun 13 2017The surprising discovery by the Rosetta spacecraft of molecular oxygen (O$_2$) in the coma of comet 67P/Churyumov-Gerasimenko (Bieler et al. 2015) challenged our understanding of the inventory of this volatile species on and inside bodies from the Kuiper ... More

Are the Nuclei of Seyfert 2 Galaxies Viewed Face-On?Jun 11 1998We show from modeling the Fe Kalpha line in the ASCA spectra of four X-ray bright narrow emission line galaxies (Seyfert types 1.9 and 2) that two equally viable physical models can describe the observed line profile. The first is discussed by Turner ... More

A family of 2-graphs arising from two-dimensional subshiftsApr 22 2008Higher-rank graphs (or $k$-graphs) were introduced by Kumjian and Pask to provide combinatorial models for the higher-rank Cuntz-Krieger $C^*$-algebras of Robertson and Steger. Here we consider a family of finite 2-graphs whose path spaces are dynamical ... More

An X-ray Mini-survey of Nearby Edge-on Starburst Galaxies II. The Question of Metal AbundanceNov 24 1999(abbreviated) We have undertaken an X-ray survey of a far-infrared flux limited sample of seven nearby edge-on starburst galaxies. Here, we examine the two X-ray-brightest sample members NGC 253 and M 82 in a self-consistent manner, taking account of ... More

The Discovery of Two New Satellites of PlutoJan 02 2006Pluto's first known moon, Charon, was discovered in 1978 (Christy 1978) and has a diameter about half that of Pluto (Buie 1992,Young 1994, Sicardy 2005), which makes it larger relative to its primary than any other moon in the Solar System. Previous searches ... More

Characteristics and Origin of the Quadruple System at PlutoDec 23 2005Our discovery of two new satellites of Pluto, designated S/2005 P 1 and S/2005 P 2 (henceforth, P1 and P2), combined with the constraints on the absence of more distant satellites of Pluto, reveal that Pluto and its moons comprise an unusual, highly compact, ... More

X-ray imaging of the Seyfert 2 galaxy Circinus with ChandraOct 18 2000We present results from the zeroth-order imaging of a Chandra HETGS observation of the nearby Seyfert 2 galaxy Circinus. Twelve X-ray sources were detected in the ACIS-S image of the galaxy, embedded in diffuse X-ray emission. The latter shows a prominent ... More

The triaxial ellipsoid dimensions, rotational pole, and bulk density of ESA Rosetta target asteroid (21) LutetiaMay 28 2010Jun 17 2010We seek the best size estimates of the asteroid (21) Lutetia, the direction of its spin axis, and its bulk density, assuming its shape is well described by a smooth featureless triaxial ellipsoid, and to evaluate the deviations from this assumption. Methods. ... More

New Horizons: Long-Range Kuiper Belt Targets Observed by the Hubble Space TelescopeMay 28 2014We report on Hubble Space Telescope (HST) observations of three Kuiper Belt Objects (KBOs), discovered in our dedicated ground-based search campaign, that are candidates for long-range observations from the New Horizons spacecraft: 2011 JY31, 2011 HZ102, ... More

High-resolution X-ray spectroscopy of the Seyfert 2 galaxy Circinus with ChandraOct 18 2000Results from a 60 ks Chandra HETGS observation of the nearby Seyfert 2 Circinus are presented. The spectrum shows a wealth of emission lines at both soft and hard X-rays, including lines of Ne, Mg, Si, S, Ar, Ca, and Fe, and a prominent Fe Kalpha line ... More

The nonlinear Dirac equation in Bose-Einstein condensates: I. Relativistic solitons in armchair nanoribbon optical latticesMay 28 2013Feb 15 2015We present a thorough analysis of soliton solutions to the quasi-one-dimensional nonlinear Dirac equation (NLDE) for a Bose-Einstein condensate in a honeycomb lattice with armchair geometry. Our NLDE corresponds to a quasi-one-dimensional reduction of ... More

The Seyfert-Starburst Connection in X-rays. II. Results and ImplicationsDec 01 2000We present the results of X-ray imaging and spectroscopic analysis of a sample of Seyfert 2 galaxies that contain starbursts, based on their optical and UV characteristics. These composite galaxies exhibit extended, soft, thermal X-ray emission, which ... More

Complex organic molecules in comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy): detection of ethylene glycol and formamideMay 26 2014A spectral survey in the 1 mm wavelength range was undertaken in the long-period comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy) using the 30 m telescope of the Institut de radioastronomie millim\'etrique (IRAM) in April and November-December 2013. ... More

A Search for Water Vapor Plumes on Europa using SOFIAJan 01 2019We present mid-infrared SOFIA/EXES spectroscopy of Europa, seeking direct evidence of the presence of water vapor arising from plumes venting from the surface of Europa. We place quantitatively useful upper limits on the strength of water vibrational-rotational ... More

The Seyfert-Starburst Connection in X-rays. I. The DataDec 01 2000We analyze X-ray spectra and images of a sample of Seyfert 2 galaxies that unambiguously contain starbursts, based on their optical and UV characteristics. Although all sample members contain active galactic nuclei (AGNs), supermassive black holes or ... More

SN 1987A - Presupernova Evolution and the Progenitor StarMay 20 1997Ten years later, astronomers are still puzzled by the stellar evolution that produced SN 1987A --- a blue supergiant. In single star models, the new OPAL opacities make blue solutions more difficult to achieve, though still possible for certain choices ... More

Global Albedos of Pluto and Charon from LORRI New Horizons ObservationsApr 20 2016The exploration of the Pluto-Charon system by the New Horizons spacecraft represent the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the Solar System's "Third Zone" within the ... More

A recipe for free-energy functionals of polarizable molecular fluidsFeb 13 2014Classical density-functional theory is the most direct approach to equilibrium structures and free energies of inhomogeneous liquids, but requires the construction of an approximate free-energy functional for each liquid of interest. We present a general ... More

The Neutron Star and Black Hole Initial Mass FunctionOct 26 1995Using recently calculated models for massive stellar evolution and supernovae coupled to a model for Galactic chemical evolution, neutron star and black hole birth functions (number of neutron stars and black holes as a function of their mass) are determined ... More

Interstellar Pickup Ion Observations to 38 AUOct 14 2017We provide the first direct observations of interstellar H+ and He+ pickup ions in the solar wind from 22 AU to 38 AU. We use the Vasyliunas and Siscoe model functional form to quantify the pickup ion distributions, and while the fit parameters generally ... More

X-Ray Evidence for Multiple Absorbing Structures in Seyfert NucleiNov 01 2005We have discovered a correlation between the X-ray absorbing column densities within Seyfert galaxies and the relative alignment between the central engines and their host galactic disks. This correlation carries several implications for Seyfert unification ... More

Locally nonconical convexityMay 19 2000There is a hierarchy of structure conditions for convex sets. In this paper we study a recently defined [3, 8, 9] condition called locally nonconical convexity (abbreviated LNC). Is is easy to show that every strictly convex set is LNC, as are half-spaces ... More

Galactic Chemical Evolution: Hydrogen Through ZincNov 01 1994Using the output from a grid of 60 Type II supernova models (Woosley \& Weaver 1994) of varying mass (11 $\ltaprx$ M/M\sun $\ltaprx$ 40) and metallicity (0, 10$^{-4}$, 0.01, 0.1, and 1 Z\sol), the chemical evolution of 76 stable isotopes, from hydrogen ... More

On the formation location of Uranus and Neptune as constrained by dynamical and chemical models of cometsApr 26 2011The D/H enrichment observed in Saturn's satellite Enceladus is remarkably similar to the values observed in the nearly-isotropic comets. Given the predicted strong variation of D/H with heliocentric distance in the solar nebula, this observation links ... More

A computationally efficacious free-energy functional for studies of inhomogeneous liquid waterDec 06 2011Jul 26 2012We present an accurate equation of state for water based on a simple microscopic Hamiltonian, with only four parameters that are well-constrained by bulk experimental data. With one additional parameter for the range of interaction, this model yields ... More

An X-ray and Optical Investigation of the Starburst-driven Superwind in the Galaxy Merger Arp 299Dec 16 1998We present a detailed investigation of the X-ray and optical properties of the starburst-merger system Arp299 (NGC 3690, Mrk 171), with an emphasis on its spectacular gaseous nebula. We analyse \rosat and \asca X-ray data and optical spectra and narrow-band ... More

Very Extended X-ray and H-alpha Emission in M82: Implications for the Superwind PhenomenonApr 18 1999We discuss the properties and implications of a 3.7x0.9 kpc region of spatially-coincident X-ray and H-alpha emission about 11.6 kpc to the north of the galaxy M82 previously discussed by Devine and Bally (1999). The PSPC X-ray spectrum is fit by thermal ... More

X-ray emission from Seyfert 2 galaxies with optical polarized broad linesJun 04 2000We analyze the 0.5-10 keV spectra of six Seyfert 2 galaxies observed with the X-ray satellite ASCA: Mrk 3, Mrk 348, Mrk 1210, Mrk 477, NGC 7212, and Was 49b. These galaxies were selected based on their possession of optical polarized broad lines. In the ... More

Possible X-ray diagnostic for jet/disk dominance in Type 1 AGNApr 12 2007Using Rossi X-ray Timing Explorer Seyfert 1 and 1.2 data spanning 9 years, we study correlations between X-ray spectral features. The sample consists of 350 time-resolved spectra from 12 Seyfert 1 and 1.2 galaxies. Each spectrum is fitted to a model with ... More

New Constraints on Additional Satellites of the Pluto SystemNov 30 2005May 23 2006Observations of Pluto and its solar-tidal stability zone were made using the Advanced Camera for Surveys' (ACS) Wide Field Channel (WFC) on the Hubble Space Telescope on UT 2005 May 15 and UT 2005 May 18. Two small satellites of Pluto, provisionally designated ... More

Ultraviolet and visible photometry of asteroid (21) Lutetia using the Hubble Space TelescopeDec 23 2009Jul 06 2010The asteroid (21) Lutetia is the target of a planned close encounter by the Rosetta spacecraft in July 2010. To prepare for that flyby, Lutetia has been extensively observed by a variety of astronomical facilities. We used the Hubble Space Telescope (HST) ... More

Haze in Pluto's AtmosphereFeb 24 2017Feb 28 2017Haze in Pluto's atmosphere was detected in images by both the Long Range Reconnaissance Imager (LORRI) and the Multispectral Visible Imaging Camera (MVIC) on New Horizons. LORRI observed haze up to altitudes of at least 200 km above Pluto's surface at ... More

Spectral Analysis of the Accretion Flow in NGC 1052 with SuzakuMar 20 2009We present an analysis of the 101 ks, 2007 Suzaku spectrum of the LINER galaxy NGC 1052. The 0.5-10 keV continuum is well-modeled by a power-law modified by Galactic and intrinsic absorption, and it exhibits a soft, thermal emission component below 1 ... More

High-Precision Orbit Fitting and Uncertainty Analysis of (486958) 2014 MU69May 06 2018NASA's New Horizons spacecraft will conduct a close flyby of the cold classical Kuiper Belt Object (KBO) designated (486958) 2014 MU69 on January 1, 2019. At a heliocentric distance of 44 AU, "MU69" will be the most distant object ever visited by a spacecraft. ... More

Detection of CO and HCN in Pluto's atmosphere with ALMAJun 10 2016Oct 13 2016Observations of the Pluto-Charon system, acquired with the ALMA interferometer on June 12-13, 2015, have yielded a detection of the CO(3-2) and HCN(4-3) rotational transitions from Pluto, providing a strong confirmation of the presence of CO, and the ... More

α7 nicotinic acetylcholine receptor signaling modulates ovine fetal brain astrocytes transcriptome in response to endotoxin: comparison to microglia, implications for prenatal stress and development of autism spectrum disorderDec 17 2018Dec 31 2018Neuroinflammation in utero may result in lifelong neurological disabilities. Astrocytes play a pivotal role, but the mechanisms are poorly understood. No early postnatal treatment strategies exist to enhance neuroprotective potential of astrocytes. We ... More

Alpha7 nicotinic acetylcholine receptor signaling modulates ovine fetal brain astrocytes transcriptome in response to endotoxinDec 17 2018Apr 09 2019Neuroinflammation in utero may result in lifelong neurological disabilities. Astrocytes play a pivotal role, but the mechanisms are poorly understood. No early postnatal treatment strategies exist to enhance neuroprotective potential of astrocytes. We ... More

The concept of a setMay 11 2009Metaphysical interpretations of set theory are either inconsistent or incoherent. The uses of sets in mathematics actually involve three distinct kinds of collections (surveyable, definite, and heuristic), which are governed by three different kinds of ... More

Quantum graphs as quantum relationsJun 12 2015Dec 27 2015The "noncommutative graphs" which arise in quantum error correction are a special case of the quantum relations introduced in [N. Weaver, Quantum relations, Mem. Amer. Math. Soc. 215 (2012), v-vi, 81-140]. We use this perspective to interpret the Knill-Laflamme ... More

Reasoning about constructive conceptsDec 28 2011Dec 12 2013We find that second order quantification is problematic when a quantified concept variable is supposed to function predicatively. This issue is analyzed and it is shown that a constructive interpretation of the falling under relation suffices to resolve ... More

Intuitionism and the liar paradoxApr 13 2010The concept of informal mathematical proof considered in intuitionism is apparently vulnerable to a version of the liar paradox. However, a careful reevaluation of this concept reveals a subtle error whose correction blocks the contradiction. This leads ... More

Predicativity beyond Gamma_0Sep 11 2005May 11 2009We reevaluate the claim that predicative reasoning (given the natural numbers) is limited by the Feferman-Schutte ordinal Gamma_0. First we comprehensively criticize the arguments that have been offered in support of this position. Then we analyze predicativism ... More

The semantic conception of proofDec 28 2011Dec 12 2013We analyze the informal semantic conception of proof and axiomatize the proof relation and the provability operator. A self referential propositional calculus which admits provable liar type sentences is introduced and proven consistent. We also investigate ... More

Sub-Riemannian metrics for quantum Heisenberg manifoldsJan 05 1998Every Heisenberg manifold has a natural "sub-Riemannian" metric with interesting properties. We describe the corresponding noncommutative metric structure for Rieffel's quantum Heisenberg manifolds.

The Local Lifting Problem for $D_4$Jun 12 2017Jun 23 2017For a prime $p$, a cyclic-by-$p$ group $G$ and a $G$-extension $L|K$ of complete discrete valuation fields of characteristic $p$ with algebraically closed residue field, the local lifting problem asks whether the extension $L|K$ lifts to characteristic ... More

Set theory and C*-algebrasApr 09 2006We survey the use of extra-set-theoretic hypotheses, mainly the continuum hypothesis, in the C*-algebra literature. The Calkin algebra emerges as a basic object of interest.

Tracing the Bipolar Outflow from Orion Source ISep 16 2009Using CARMA, we imaged the 87 GHz SiO v=0 J=2-1 line toward Orion-KL with 0.45 arcsec angular resolution. The maps indicate that radio source I drives a bipolar outflow into the surrounding molecular cloud along a NE--SW axis, in agreement with the model ... More

Quantum relationsMay 03 2010We define a "quantum relation" on a von Neumann algebra M \subset B(H) to be a weak* closed operator bimodule over its commutant M'. Although this definition is framed in terms of a particular representation of M, it is effectively representation independent. ... More

On the unique predual problem for Lipschitz spacesNov 06 2016Nov 09 2016For any metric space X, the predual of Lip(X) is unique. If X has finite diameter or is complete and convex --- in particular, if it is a Banach space --- then the predual of Lip_0(X) is unique.

The Kadison-Singer problem in discrepancy theorySep 07 2002We give a combinatorial form of the Kadison-Singer problem, a famous problem in C*-algebra. This combinatorial problem, which has several minor variations, is a discrepancy question about vectors in C^n. Some partial results can be easily deduced from ... More

The Kadison-Singer problem in discrepancy theory, IIMar 11 2013We apply Srivastava's spectral sparsification technique to a vector balancing version of the Kadison-Singer problem. The result is a one-sided version of the conjectured solution.

Operator algebras associated with the Klein-Gordon position representation in relativistic quantum mechanicsSep 07 2002We initiate a mathematically rigorous study of Klein-Gordon position operators in single-particle relativistic quantum mechanics. Although not self-adjoint, these operators have real spectrum and enjoy a limited form of spectral decomposition. The associated ... More

New Horizons Constraints on Charon's Present Day AtmosphereAug 24 2016We report on a variety of standard techniques used by New Horizons including a solar ultraviolet occultation, ultraviolet airglow observations, and high-phase look-back particulate search imaging to search for an atmosphere around Pluto's large moon Charon ... More

Structure of the photo-catalytically active surface of SrTiO3Aug 05 2015A major goal of energy research is to use visible light to cleave water directly, without an applied voltage, into hydrogen and oxygen. Since the initial reports of the ultraviolet (UV) activity of TiO2 and SrTiO3 in the 1970s, researchers have pursued ... More

Is set theory indispensable?May 11 2009Although Zermelo-Fraenkel set theory (ZFC) is generally accepted as the appropriate foundation for modern mathematics, proof theorists have known for decades that virtually all mainstream mathematics can actually be formalized in much weaker systems which ... More

Hilbert bimodules with involutionAug 23 1999We examine Hilbert bimodules which possess a (generally unbounded) involution. Topics considered include a linking algebra representation, duality, locality, and the role of these bimodules in noncommutative differential geometry.

Truth and the liar paradoxDec 28 2011We analyze the informal notion of truth and conclude that it can be formalized in essentially two distinct ways: constructively, in terms of provability, or classically, as a hierarchy of concepts which satisfy Tarski's biconditional in limited settings. ... More

Mathematical conceptualismSep 11 2005Sep 12 2005This is an explanation and defense of "mathematical conceptualism" for a general mathematical and philosophical audience. I make a case that it is cogent, rigorous, attractive, and better suited to ordinary mathematical practice than all other foundational ... More

Set theory and cyclic vectorsFeb 25 2002Let H be a separable, infinite dimensional Hilbert space and let S be a countable subset of H. Then most positive operators on H have the property that every nonzero vector in the span of S is cyclic, in the sense that the set of operators in the positive ... More

Quantum graphs as quantum relationsJun 12 2015Jun 28 2017The "noncommutative graphs" which arise in quantum error correction are a special case of the quantum relations introduced in [N. Weaver, Quantum relations, Mem. Amer. Math. Soc. 215 (2012), v-vi, 81-140]. We use this perspective to interpret the Knill-Laflamme ... More

Classical curves via one-vertex mapsJan 08 2012Jul 16 2012One-vertex maps (a type of dessin d'enfant) give a uniform characterization of certain well-known algebraic curves, including those of Klein, Wiman, Accola-Maclachlan and Kulkarni. The characterization depends on a new classification of one-vertex (dually, ... More

A prime C*-algebra that is not primitiveJun 28 2001Jul 06 2001We construct a non-separable C*-algebra that is prime but not primitive.

A counterexample to a conjecture of Akemann and AndersonMay 22 2001Akemann and Anderson made a conjecture about ``paving'' projections in finite dimensional matrix algebras which, if true, would settle the well-known Kadison-Singer problem. We falsify their conjecture by an explicit seqence of counterexamples.

Paradoxes of rational agency and formal systems that verify their own soundnessDec 12 2013Dec 21 2013We consider extensions of Peano arithmetic which include an assertibility predicate. Any such system which is arithmetically sound effectively verifies its own soundness. This leads to the resolution of a range of paradoxes involving rational agents who ... More

Kinds of conceptsDec 28 2011The central focus is on clarifying the distinction between sets and proper classes. To this end we identify several categories of concepts (surveyable, definite, indefinite), and we attribute the classical set theoretic paradoxes to a failure to appreciate ... More

Constructive truth and circularityMay 11 2009Apr 13 2010We propose a constructive interpretation of truth which resolves the standard semantic paradoxes.

Axiomatizing mathematical conceptualism in third order arithmeticMay 11 2009We review the philosophical framework of mathematical conceptualism as an alternative to set-theoretic foundations and show how mainstream mathematics can be developed on this basis. The paper includes an explicit axiomatization of the basic principles ... More

A "quantum" Ramsey theorem for operator systemsJan 03 2016Jan 13 2016Let V be a linear subspace of M_n(C) which contains the identity matrix and is stable under the formation of Hermitian adjoints. We prove that if n is sufficiently large then there exists a rank k orthogonal projection P such that dim(PVP) = 1 or k^2. ... More

Analysis in J_2Sep 11 2005Sep 12 2005This is an expository paper in which I explain how core mathematics, particularly abstract analysis, can be developed within a concrete countable set J_2 (the second set in Jensen's constructible hierarchy). The implication, well-known to proof theorists ... More

Lipschitz algebras and derivations II: exterior differentiationJul 17 1998Basic aspects of differential geometry can be extended to various non-classical settings: Lipschitz manifolds, rectifiable sets, sub-Riemannian manifolds, Banach manifolds, Weiner space, etc. Although the constructions differ, in each of these cases one ... More

Optomechanics with a polarization non-degenerate cavityJun 22 2016Experiments in the field of optomechanics do not yet fully exploit the photon polarization degree of freedom. Here experimental results for an optomechanical interaction in a polarization nondegenerate system are presented and schemes are proposed for ... More

The Puzzling Detection of X-rays From Pluto by ChandraOct 25 2016Using Chandra ACIS-S, we have obtained imaging Xray spectrophotometry of the Pluto system in support of the New Horizons flyby on 14 July 2015. 174 ksec of observations were obtained on 4 visits in Feb 2014 to Aug 2015. We measured a net signal of 6.8 ... More

X-ray Emission from the Prototypical LINER Galaxy NGC 1052Feb 18 1999We examine the 0.1 to 10.0 keV X-ray spectrum of the bright nuclear LINER galaxy NGC 1052, one of two elliptical galaxies known to contain a luminous H2O maser. The observed 2.0-10.0 keV spectrum is unusually flat (photon index Gamma~0.2) and best described ... More

Ambiguities in fits to the complex X-ray spectra of starburst galaxiesMar 02 2000Spectral fits to X-ray data from both NGC 253 and M 82 provide ambiguous results. The so-called ``best fit'' results depend on the instrument with which the data were obtained and obviously on the choice of spectral model composition. We show that different ... More

Probes of Jet-Disk-Coupling in AGN from Combined VLBI and X-Ray ObservationsJul 09 2004The formation of powerful extragalactic jets is not well understood at present as well as the associated key question:``What makes an AGN radio loud?''. Here we discuss how the combination of VLBI and X-ray spectroscopic observations allows the inter-relation ... More

The Obscuring Starburst of NGC 6221 and Implications for the Hard X-ray BackgroundApr 18 2001We present NGC 6221 as a case study of ``X-ray loud composite galaxies,'' which appear similar to starbursts at optical wavelengths and resemble traditional active galactic nuclei in X-rays. The net optical spectrum of NGC 6221 is properly characterized ... More

Overview of initial results from the reconnaissance flyby of a Kuiper Belt planetesimal: 2014 MU69Jan 09 2019Jan 24 2019The centerpiece objective of the NASA New Horizons first Kuiper Extended Mission (KEM-1) was the close flyby of the Kuiper Belt Object KBO) 2014 MU69, nicknamed Ultima Thule. On 1 Jan 2019 this flyby culminated, making the first close observations of ... More

Global Albedos of Pluto and Charon from LORRI New Horizons ObservationsApr 20 2016Jan 09 2017The exploration of the Pluto-Charon system by the New Horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the Solar System's "Third Zone" of distant ... More

Spicing up continuum solvation models with SaLSA: the spherically-averaged liquid susceptibility ansatzOct 08 2014Continuum solvation models enable electronic structure calculations of systems in liquid environments, but because of the large number of empirical parameters, they are limited to the class of systems in their fit set (typically organic molecules). Here, ... More