Results for "Brian W. Grefenstette"

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Measurement of the absolute Crab flux with NuSTARMar 28 2017We present results from a NuSTAR observation of the Crab made at a large off-axis angle of 1.5\degree. At these angles X-rays do not pass through the optics, but rather illuminate the detectors directly due to incomplete baffling. Due to the simplicity ... More
Evidence of Particle Acceleration in the Superbubble 30 Doradus C with NuSTARNov 29 2018We present evidence of diffuse, non-thermal X-ray emission from the superbubble 30 Doradus C (30 Dor C) using hard X-ray images and spectra from NuSTAR observations. For this analysis, we utilize data from a 200 ks targeted observation of 30 Dor C as ... More
Getting NuSTAR on target: predicting mast motionAug 04 2016The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing high energy (3-79 keV) X-ray observatory operating for four years from low Earth orbit. The X-ray detector arrays are located on the spacecraft bus with the optics modules mounted ... More
Positron clouds within thunderstormsMay 14 2015We report the observation of two isolated clouds of positrons inside an active thunderstorm. These observations were made by the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of six gamma-ray detectors, which flew on a Gulfstream ... More
NuSTAR hard X-ray observation of a sub-A class solar flareJul 15 2017Jul 18 2017We report a NuSTAR observation of a solar microflare, SOL2015-09-01T04. Although it was too faint to be observed by the GOES X-ray Sensor, we estimate the event to be an A0.1 class flare in brightness. This microflare, with only 5 counts per second per ... More
NuSTAR Detection of X-Ray Heating Events in the Quiet SunMar 22 2018The explanation of the coronal heating problem potentially lies in the existence of nanoflares, numerous small-scale heating events occuring across the whole solar disk. In this paper, we present the first imaging spectroscopy X-ray observations of three ... More
Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIAJun 19 2017Jul 12 2017NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of a microflare with NuSTAR and Hinode/XRT on 2015 April ... More
A broadband look at the old and new ULXs of NGC 6946May 08 2019Two recent observations of the nearby galaxy NGC 6946 with NuSTAR, one simultaneous with an XMM-Newton observation, provide an opportunity to examine its population of bright accreting sources from a broadband perspective. We study the three known ultraluminous ... More
Broadband X-ray Imaging and Spectroscopy of the Crab Nebula and Pulsar with NuSTARFeb 26 2015We present broadband (3 -- 78 keV) NuSTAR X-ray imaging and spectroscopy of the Crab nebula and pulsar. We show that while the phase-averaged and spatially integrated nebula + pulsar spectrum is a power-law in this energy band, spatially resolved spectroscopy ... More
NuSTAR discovery of a luminosity dependent cyclotron line energy in Vela X-1Nov 21 2013We present NuSTAR observations of Vela X-1, a persistent, yet highly variable, neutron star high-mass X-ray binary (HMXB). Two observations were taken at similar orbital phases but separated by nearly a year. They show very different 3-79 keV flux levels ... More
Non-thermal X-rays from Colliding Wind Shock Acceleration in the Massive Binary Eta CarinaeApr 19 2019Cosmic-ray acceleration has been a long-standing mystery and despite more than a century of study, we still do not have a complete census of acceleration mechanisms. The collision of strong stellar winds in massive binary systems creates powerful shocks, ... More
Reflection Spectra of the Black Hole Binary Candidate MAXI J1535-571 in the Hard State Observed by NuSTARNov 03 2017Jan 04 2018We report on a NuSTAR observation of the recently discovered bright black hole candidate MAXI J1535-571. NuSTAR observed the source on MJD 58003 (five days after the outburst was reported). The spectrum is characteristic of a black hole binary in the ... More
Locating the most energetic electrons in Cassiopeia AFeb 10 2015We present deep ($>$2.4 Ms) observations of the Cassiopeia A supernova remnant with {\it NuSTAR}, which operates in the 3--79 keV bandpass and is the first instrument capable of spatially resolving the remnant above 15 keV. We find that the emission is ... More
Optical communication on CubeSats - Enabling the next era in space scienceOct 26 2018CubeSats are excellent platforms to rapidly perform simple space experiments. Several hundreds of CubeSats have already been successfully launched in the past few years and the number of announced launches grows every year. These platforms provide an ... More
3C 273 with NuSTAR: Unveiling the AGNJun 19 2015Sep 03 2015We present results from a 244\,ks \textit{NuSTAR} observation of 3C\,273 obtained during a cross-calibration campaign with the \textit{Chandra}, \textit{INTEGRAL}, \textit{Suzaku}, \textit{Swift}, and \textit{XMM-Newton} observatories. We show that the ... More
Observational Constraints of Stellar Collapse: Diagnostic Probes of Nature's Extreme Matter ExperimentMar 14 2014Supernovae are Nature's high-energy, high density laboratory experiments, reaching densities in excess of nuclear densities and temperatures above 10MeV. Astronomers have built up a suite of diagnostics to study these supernovae. If we can utilize these ... More
NuSTAR and INTEGRAL observations of a low/hard state of 1E1740.7-2942Oct 29 2013The microquasar 1E1740.7-2942, also known as the "Great Annihilator", was observed by NuSTAR in the Summer of 2012. We have analyzed in detail two observations taken ~2 weeks apart, for which we measure hard and smooth spectra typical of the low/hard ... More
NuSTAR and Swift observations of the black hole candidate XTE J1908+094 during its 2013 outburstJun 05 2015Aug 05 2015The black hole candidate XTE J1908+094 went into outburst for the first time since 2003 in October 2013. We report on an observation with the Nuclear Spectroscopic Telescope Array (NuSTAR) and monitoring observations with Swift during the outburst. NuSTAR ... More
First NuSTAR Limits on Quiet Sun Hard X-Ray Transient EventsNov 15 2017We present the first results of a search for transient hard X-ray (HXR) emission in the quiet solar corona with the \textit{Nuclear Spectroscopic Telescope Array} (\textit{NuSTAR}) satellite. While \textit{NuSTAR} was designed as an astrophysics mission, ... More
No Time for Dead Time: Timing analysis of bright black hole binaries with NuSTARSep 10 2014Timing of high-count rate sources with the NuSTAR Small Explorer Mission requires specialized analysis techniques. NuSTAR was primarily designed for spectroscopic observations of sources with relatively low count-rates rather than for timing analysis ... More
NuSTAR Observations of the Magnetar 1E 2259+586Aug 04 2014We report on new broad band spectral and temporal observations of the magnetar 1E 2259+586, which is located in the supernova remnant CTB 109. Our data were obtained simultaneously with the Nuclear Spectroscopic Telescope Array (NuSTAR) and Swift, and ... More
NuSTAR study of Hard X-Ray Morphology and Spectroscopy of PWN G21.5-0.9May 13 2014We present NuSTAR high energy X-ray observations of the pulsar wind nebula (PWN)/supernova remnant G21.5-0.9. We detect integrated emission from the nebula up to ~40 keV, and resolve individual spatial features over a broad X-ray band for the first time. ... More
The Hard X-Ray View of the Young Supernova Remnant G1.9+0.3Nov 25 2014NuSTAR observed G1.9+0.3, the youngest known supernova remnant in the Milky Way, for 350 ks and detected emission up to $\sim$30 keV. The remnant's X-ray morphology does not change significantly across the energy range from 3 to 20 keV. A combined fit ... More
The ultraluminous X-ray sources NGC 1313 X-1 and X-2: a broadband study with NuSTAR and XMM-NewtonOct 02 2013Nov 22 2013We present the results of NuSTAR and XMM-Newton observations of the two ultraluminous X-ray sources (ULX) NGC 1313 X-1 and X-2. The combined spectral bandpass of the two satellites enables us to produce the first spectrum of X-1 between 0.3 and 30 keV, ... More
The Broadband XMM-Newton and NuSTAR X-ray Spectra of Two Ultraluminous X-ray Sources in the Galaxy IC 342Jan 19 2014Nov 19 2014We present results for two Ultraluminous X-ray Sources (ULXs), IC 342 X-1 and IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by $\sim$7 days. We observe little spectral or flux variability above 1 keV between epochs, with ... More
NuSTAR observations of X-ray bursts from the magnetar 1E 1048.1-5937Jun 12 2014We report the detection of eight bright X-ray bursts from the 6.5-s magnetar 1E 1048.1-5937, during a 2013 July observation campaign with the Nuclear Spectroscopic Telescope Array (NuSTAR). We study the morphological and spectral properties of these bursts ... More
NuSTAR Observations of the Bullet Cluster: Constraints on Inverse Compton EmissionMar 11 2014The search for diffuse non-thermal inverse Compton (IC) emission from galaxy clusters at hard X-ray energies has been undertaken with many instruments, with most detections being either of low significance or controversial. Background and contamination ... More
Sagittarius A* High Energy X-ray Flare Properties During NuSTAR Monitoring of the Galactic Center from 2012 to 2015May 22 2017Understanding the origin of the flaring activity from the Galactic center supermassive black hole, Sagittarius A*, is a major scientific goal of the NuSTAR Galactic plane survey campaign. We report on the data obtained between July 2012 and April 2015, ... More
First hard X-ray detection of the non-thermal emission around the Arches cluster: morphology and spectral studies with NuSTARDec 10 2013The Arches cluster is a young, densely packed massive star cluster in our Galaxy that shows a high level of star formation activity. The nature of the extended non-thermal X-ray emission around the cluster remains unclear. The observed bright Fe K_alpha ... More
Evidence of Significant Energy Input in the Late Phase of a Solar Flare from NuSTAR X-Ray ObservationsJan 26 2017We present observations of the occulted active region AR12222 during the third {\em NuSTAR} solar campaign on 2014 December 11, with concurrent {\em SDO/}AIA and {\em FOXSI-2} sounding rocket observations. The active region produced a medium size solar ... More
NuSTAR observations of magnetar 1E 1841-045Oct 23 2013Nov 19 2013We report new spectral and temporal observations of the magnetar 1E 1841-045 in the Kes 73 supernova remnant obtained with the Nuclear Spectroscopic Telescope Array (NuSTAR). Combined with new Swift and archival XMM-Newton and Chandra observations, the ... More
The Reflection Component from Cygnus X-1 in the Soft State Measured by NuSTAR and SuzakuOct 14 2013The black hole binary Cygnus X-1 was observed in late-2012 with the Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku, providing spectral coverage over the ~1-300 keV range. The source was in the soft state with a multi-temperature blackbody, ... More
The First Focused Hard X-ray Images of the Sun with NuSTARMay 31 2016We present results from the the first campaign of dedicated solar observations undertaken by the \textit{Nuclear Spectroscopic Telescope ARray} ({\em NuSTAR}) hard X-ray telescope. Designed as an astrophysics mission, {\em NuSTAR} nonetheless has the ... More
Category-Theoretic Quantitative Compositional Distributional Models of Natural Language SemanticsNov 06 2013This thesis is about the problem of compositionality in distributional semantics. Distributional semantics presupposes that the meanings of words are a function of their occurrences in textual contexts. It models words as distributions over these contexts ... More
Towards a Formal Distributional Semantics: Simulating Logical Calculi with TensorsApr 22 2013Apr 28 2013The development of compositional distributional models of semantics reconciling the empirical aspects of distributional semantics with the compositional aspects of formal semantics is a popular topic in the contemporary literature. This paper seeks to ... More
NuSTAR detection of hard X-ray phase lags from the accreting pulsar GS 0834-430Jul 26 2013The NuSTAR hard X-ray telescope observed the transient Be/X-ray binary GS 0834-430 during its 2012 outburst - the first active state of this system observed in the past 19 years. We performed timing and spectral analysis, and measured the X-ray spectrum ... More
The smooth cyclotron line in Her X-1 as seen with NuSTARSep 20 2013Her X-1, one of the brightest and best studied X-ray binaries, shows a cyclotron resonant scattering feature (CRSF) near 37 keV. This makes it an ideal target for detailed study with the Nuclear Spectroscopic Telescope Array (NuSTAR), taking advantage ... More
NuSTAR discovery of a 3.76-second transient magnetar near Sagittarius A*May 08 2013May 15 2013We report the discovery of 3.76-s pulsations from a new burst source near Sgr A* observed by the NuSTAR Observatory. The strong signal from SGR J1745-29 presents a complex pulse profile modulated with pulsed fraction 27+/-3 % in the 3-10 keV band. Two ... More
The Formation of Stellar Cusps in Galactic NucleiMay 12 2012The dynamics of galactic nuclei can be affected by several mechanisms. Among these are stellar evolution, stellar collisions, mass segregation, and tidal disruptions of stars due to the central black hole. In this presentation I will address how each ... More
Measurement of the Total Charm Cross Section by Electron-Positron Annihilation at Energies Between 3.97-4.26 GeVJan 07 2008Jan 28 2008Using the CLEO-c detector, we have measured the charm hadronic cross sections for $e^{+}e^{-}$ annihilations at a total of thirteen center-of-mass energies between 3.97 and 4.26 GeV. Observed cross sections for the production of $D\bar{D}$, $D^{*}\bar{D}$, ... More
The distribution of radioactive $^{44}$Ti in Cassiopeia ADec 08 2016The distribution of elements produced in the inner-most layers of a supernova explosion is a key diagnostic for studying the collapse of massive stars. Here we present the results of a 2.4 Ms \textit{NuSTAR} observing campaign aimed at studying the supernova ... More
Spectral and temporal properties of the ultra-luminous X-ray pulsar in M82 from 15 years of Chandra observations and analysis of the pulsed emission using NuSTARJul 21 2015Dec 16 2015The recent discovery by Bachetti et al. (2014) of a pulsar in M82 that can reach luminosities of up to 10^40 ergs s^-1, a factor of ~100 the Eddington luminosity for a 1.4 Msol compact object, poses a challenge for accretion physics. In order to better ... More
The Nuclear Spectroscopic Telescope Array (NuSTAR)Aug 07 2010The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing hard X-ray (5 -- 80 keV) telescope to orbit. NuSTAR will offer a factor 50 -- 100 sensitivity improvement compared to previous collimated ... More
A Compositional Distributional Semantics, Two Concrete Constructions, and some Experimental EvaluationsMay 09 2011Jun 07 2011We provide an overview of the hybrid compositional distributional model of meaning, developed in Coecke et al. (arXiv:1003.4394v1 [cs.CL]), which is based on the categorical methods also applied to the analysis of information flow in quantum protocols. ... More
Transforming Wikipedia into an Ontology-based Information Retrieval Search Engine for Local Experts using a Third-Party TaxonomyNov 04 2015May 30 2016Wikipedia is widely used for finding general information about a wide variety of topics. Its vocation is not to provide local information. For example, it provides plot, cast, and production information about a given movie, but not showing times in your ... More
Learning Explanatory Rules from Noisy DataNov 13 2017Jan 25 2018Artificial Neural Networks are powerful function approximators capable of modelling solutions to a wide variety of problems, both supervised and unsupervised. As their size and expressivity increases, so too does the variance of the model, yielding a ... More
Experimental Support for a Categorical Compositional Distributional Model of MeaningJun 20 2011Modelling compositional meaning for sentences using empirical distributional methods has been a challenge for computational linguists. We implement the abstract categorical model of Coecke et al. (arXiv:1003.4394v1 [cs.CL]) using data from the BNC and ... More
Experimenting with Transitive Verbs in a DisCoCatJul 15 2011Jul 23 2011Formal and distributional semantic models offer complementary benefits in modeling meaning. The categorical compositional distributional (DisCoCat) model of meaning of Coecke et al. (arXiv:1003.4394v1 [cs.CL]) combines aspected of both to provide a general ... More
NuSTAR Hard X-ray Survey of the Galactic Center Region I: Hard X-ray Morphology and Spectroscopy of the Diffuse EmissionOct 15 2015We present the first sub-arcminute images of the Galactic Center above 10 keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR J17456-2901 into non-thermal X-ray filaments, molecular clouds, point sources and a previously unknown central ... More
NuSTAR Hard X-ray Survey of the Galactic Center Region II: X-ray Point SourcesMay 12 2016We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3-79 keV) X-ray point sources in a 0.6 deg^2 region around Sgr A* with a total exposure of 1.7 Ms, and 7 sources ... More
The NuSTAR Hard X-ray Survey of the Norma Arm RegionFeb 28 2017We present a catalog of hard X-ray sources in a square-degree region surveyed by NuSTAR in the direction of the Norma spiral arm. This survey has a total exposure time of 1.7 Ms, and typical and maximum exposure depths of 50 ks and 1 Ms, respectively. ... More
Mean values of L-functions and symmetryDec 13 1999Recently Katz and Sarnak introduced the idea of a symmetry group attached to a family of L-functions, and they gave strong evidence that the symmetry group governs many properties of the distribution of zeros of the L-functions. We consider the mean-values ... More
Ambiguity in the Determination of the Free Energy for a Model of the Circle MapAug 09 2006We consider a simple model to describe the widths of the mode locked intervals for the critical circle map. Using two different partitions of the rational numbers, based on Farey series and Farey tree levels respectively, we calculate the free energy ... More
Slightly Bimetric GravitationJan 16 2001Aug 16 2007The inclusion of a flat metric tensor in gravitation permits the formulation of a gravitational stress-energy tensor and the formal derivation of general relativity from a linear theory in flat spacetime. Building on the works of Kraichnan and Deser, ... More
Interactional processes for stabilizing conceptual coherences in physicsMay 24 2012Research in student knowledge and learning of science has typically focused on explaining conceptual change. Recent research, however, documents the great degree to which student thinking is dynamic and context-sensitive, implicitly calling for explanations ... More
A Solution to the Strong CP Problem with Gauge-Mediated Supersymmetry BreakingFeb 03 1998Apr 29 1998We demonstrate that a certain class of low scale supersymmetric ``Nelson-Barr'' type models can solve the strong and supersymmetric CP problems while at the same time generating sufficient weak CP violation in the $K^{0}-\bar{K}^{0}$ system. In order ... More
A Deep Learning Framework for Single-Sided Sound Speed Inversion in Medical UltrasoundSep 30 2018Dec 10 2018Objective: Ultrasound elastography is gaining traction as an accessible and useful diagnostic tool for such things as cancer detection and differentiation and thyroid disease diagnostics. Unfortunately, state of the art shear wave imaging techniques, ... More
Partitions of 2^ω and completely ultrametrizable spacesJun 05 2014We prove that, for every n, the topological space {\omega}_n^{\omega} (where {\omega}_n has the discrete topology) can be partitioned into {\omega}_n copies of the Baire space. Using this fact, the authors then prove two new theorems about completely ... More
Authentication with Distortion CriteriaMar 12 2005Mar 16 2005In a variety of applications, there is a need to authenticate content that has experienced legitimate editing in addition to potential tampering attacks. We develop one formulation of this problem based on a strict notion of security, and characterize ... More
A rapidly spinning supermassive black hole at the centre of NGC 1365Feb 27 2013Broad X-ray emission lines from neutral and partially ionized iron observed in active galaxies have been interpreted as fluorescence produced by the reflection of hard X-rays off the inner edge of an accretion disk. In this model, line broadening and ... More
K-Athena: a performance portable structured grid finite volume magnetohydrodynamics codeMay 10 2019Large scale simulations are a key pillar of modern research and require ever increasing computational resources. Different novel manycore architectures have emerged in recent years on the way towards the exascale era. Performance portability is required ... More
X-Ray Polarimetry with the Polarization Spectroscopic Telescope Array (PolSTAR)Oct 28 2015This paper describes the Polarization Spectroscopic Telescope Array (PolSTAR), a mission proposed to NASA's 2014 Small Explorer (SMEX) announcement of opportunity. PolSTAR measures the linear polarization of 3-50 keV (requirement; goal: 2.5-70 keV) X-rays ... More
"Not not bad" is not "bad": A distributional account of negationJun 10 2013With the increasing empirical success of distributional models of compositional semantics, it is timely to consider the types of textual logic that such models are capable of capturing. In this paper, we address shortcomings in the ability of current ... More
Tracing the Evolution of High Redshift Galaxies Using Stellar AbundancesDec 02 2013Sep 25 2015This paper presents the first results from a model for chemical evolution that can be applied to N-body cosmological simulations and quantitatively compared to measured stellar abundances from large astronomical surveys. This model convolves the chemical ... More
Discovering Discrete Latent Topics with Neural Variational InferenceJun 01 2017May 21 2018Topic models have been widely explored as probabilistic generative models of documents. Traditional inference methods have sought closed-form derivations for updating the models, however as the expressiveness of these models grows, so does the difficulty ... More
Investigating the Role of Prior Disambiguation in Deep-learning Compositional Models of MeaningNov 15 2014This paper aims to explore the effect of prior disambiguation on neural network- based compositional models, with the hope that better semantic representations for text compounds can be produced. We disambiguate the input word vectors before they are ... More
Lambek vs. Lambek: Functorial Vector Space Semantics and String Diagrams for Lambek CalculusFeb 02 2013The Distributional Compositional Categorical (DisCoCat) model is a mathematical framework that provides compositional semantics for meanings of natural language sentences. It consists of a computational procedure for constructing meanings of sentences, ... More
Exploring impulsive solar magnetic energy release and particle acceleration with focused hard X-ray imaging spectroscopyJan 03 2017How impulsive magnetic energy release leads to solar eruptions and how those eruptions are energized and evolve are vital unsolved problems in Heliophysics. The standard model for solar eruptions summarizes our current understanding of these events. Magnetic ... More
As a matter of force - Systematic biases in idealized turbulence simulationsMar 14 2018May 06 2018Many astrophysical systems encompass very large dynamical ranges in space and time, which are not accessible by direct numerical simulations. Thus, idealized subvolumes are often used to study small-scale effects including the dynamics of turbulence. ... More
The unusual quadruple system HD 91962 with a "planetary" architectureApr 24 2015The young nearby solar-type star HD 91962 is a rare quadruple system where three companions revolve around the main component with periods of 170.3 days, 8.85 years, and 205 years. The two outer orbits are nearly co-planar, and all orbits have small eccentricities. ... More
Strange metallicity in the doped Hubbard modelJun 21 2018Jan 16 2019Strange or bad metallic transport, defined by its incompatibility with conventional quasiparticle pictures, is a theme common to strongly correlated materials and ubiquitous in many high temperature superconductors. The Hubbard model represents a minimal ... More
Triggering and Delivery Algorithms for AGN FeedbackMar 11 2016We compare several common sub-grid implementations of AGN feedback, focusing on the effects of different triggering mechanisms and the differences between thermal and kinetic feedback. Our main result is that pure thermal feedback that is centrally injected ... More
The Chemical Composition of Praesepe (M44)Aug 15 2013Star clusters have long been used to illuminate both stellar evolution and Galactic evolution. They also hold clues to the chemical and nucleosynthetic processes throughout the history of the Galaxy. We have taken high signal-to-noise, high-resolution ... More
Networks: An Economic PerspectiveAug 29 2016We discuss social network analysis from the perspective of economics. We organize the presentaion around the theme of externalities: the effects that one's behavior has on others' well-being. Externalities underlie the interdependencies that make networks ... More
Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a ClusterAug 19 2006We construct a simple model for radioisotopic enrichment of the protosolar nebula by injection from a nearby supernova, based on the inverse square law for ejecta dispersion. We find that the presolar radioisotopes abundances (i.e., in solar masses) demand ... More
Dark Matter Annihilation and Primordial Star FormationJul 24 2008We investigate the effects of weakly-interacting massive particle (WIMP) dark matter annihilation on the formation of Population III.1 stars, which are theorized to form from the collapse of gas cores at the centers of dark matter minihalos. We consider ... More
A Convolutional Neural Network for Modelling SentencesApr 08 2014The ability to accurately represent sentences is central to language understanding. We describe a convolutional architecture dubbed the Dynamic Convolutional Neural Network (DCNN) that we adopt for the semantic modelling of sentences. The network uses ... More
Factoring Hecke polynomials modulo a primeNov 15 1998Let T^{N,chi}_{p,k}(x) be the characteristic polynomial of the Hecke operator T_p acting on the space of cusp forms S_k(N,chi). We describe the factorization of T^{N,chi}_{p,k}(x) mod l as k varies, and we explicitly calculate those factorizations for ... More
The Extreme Scattering Event Toward PKS 1741-038: VLBI ImagesOct 18 1999Jan 20 2000(Abridged) We report multi-epoch VLBI observations of the source PKS 1741-038 as it underwent an extreme scattering event. Observations at four epochs were obtained, and images were produced at three of these. During the event the source consisted of ... More
A Synoptic, Multiwavelength Analysis of a Large Quasar SampleDec 19 2005We present variability and multi-wavelength photometric information for the 933 known quasars in the QUEST Variability Survey. These quasars are grouped into variable and non-variable populations based on measured variability confidence levels. In a time-limited ... More
Zero Sound Attenuation near the Quantum Limit in Normal Liquid 3He close to the Superfluid TransitionOct 01 2002The zero sound attenuation of normal liquid 3He has been studied over a range of temperatures from slightly above the superfluid transition temperature, Tc, to approximately 10 mK at the constant pressures of 1 bar and 5 bar. Using longitudinal LiNbO3 ... More
An optimal choice of Dirichlet polynomials for the Nyman-Beurling criterionNov 22 2012We give a conditional result on the constant in the B\'aez-Duarte reformulation of the Nyman-Beurling criterion for the Riemann Hypothesis. We show that assuming the Riemann hypothesis and that $\sum_{\rho}\frac{1}{|\zeta'(\rho)|^2}\ll T^{3/2-\delta}$, ... More
Autocorrelation of ratios of L-functionsNov 05 2007Dec 05 2007We give a new heuristic for all of the main terms in the quotient of products of L-functions averaged over a family. These conjectures generalize the recent conjectures for mean values of L-functions. Comparison is made to the analogous quantities for ... More
Fragmentation in Dusty Low-Metallicity Star Forming HalosSep 16 2013The first stars in the universe, termed Population III, are thought to have been very massive compared to the stars that form in the present epoch. As feedback from the first generation of stars altered the contents of the interstellar medium, the universe ... More
Protostellar Feedback Processes and the Mass of the First StarsAug 18 2010We review theoretical models of Population III.1 star formation, focusing on the protostellar feedback processes that are expected to terminate accretion and thus set the mass of these stars. We discuss how dark matter annihilation may modify this standard ... More
Cost-benefit Analysis of Visualization in Virtual EnvironmentsFeb 25 2018Feb 28 2018Visualization and virtual environments (VEs) have been two interconnected parallel strands in visual computing for decades. Some VEs have been purposely developed for visualization applications, while many visualization applications are exemplary showcases ... More
Palindromic random trigonometric polynomialsDec 09 2008We show that if a real trigonometric polynomial has few real roots, then the trigonometric polynomial obtained by writing the coefficients in reverse order must have many real roots. This is used to show that a class of random trigonometric polynomials ... More
The Formation of Population III Binaries from Cosmological Initial ConditionsJul 16 2009Previous high resolution cosmological simulations predict the first stars to appear in the early universe to be very massive and to form in isolation. Here we discuss a cosmological simulation in which the central 50 solar mass clump breaks up into two ... More
Impact-induced differentiation in icy bodiesJul 05 2016By the time icy objects grow to about the mass of Europa and silicate bodies grow to approximately lunar mass, a large high-speed impact can generate an intact melt region that allows the dense material to gravitationally segregate, forming a large density ... More
Asymptotic Spectrum of Kerr Black Holes in the Small Angular Momentum LimitSep 23 2010Sep 24 2010We study analytically the highly damped quasinormal modes of Kerr black holes in the small angular momentum limit. To check the previous analytic calculations in the literature, which use a combination of radial and tortoise coordinates, we reproduce ... More
Effects of an Additional Conduction Band on Singlet-Antiferromagnet Competition in the Periodic Anderson ModelJan 31 2017May 23 2017The competition between antiferromagnetic (AF) order and singlet formation is a central phenomenon of the Kondo and Periodic Anderson Hamiltonians, and of the heavy fermion materials they describe. In this paper, we explore the effects of an additional ... More
Multi-messenger Bayesian parameter inference of a binary neutron-star mergerDec 12 2018The combined detection of a binary neutron-star merger in both gravitational waves (GWs) and electromagnetic (EM) radiation spanning the entire spectrum -- GW170817 / AT2017gfo / GRB170817A -- marks a breakthrough in the field of multi-messenger astronomy. ... More
A Simple Model for r-Process Scatter and Halo EvolutionMar 06 2001Recent observations of heavy elements produced by rapid neutron capture (r-process) in the halo have shown a striking and unexpected behavior: within a single star, the relative abundances of r-process elements heavier than Eu are the same as the same ... More
Measuring the Coronal Properties of IC4329A with NuSTARDec 12 2013We present an analysis of a ~160 ks NuSTAR observation of the nearby bright Seyfert galaxy IC4329A. The high-quality broadband spectrum enables us to separate the effects of distant reflection from the direct coronal continuum, and to therefore accurately ... More
NuSTAR and Suzaku observations of the hard state in Cygnus X-1: locating the inner accretion diskMay 29 2015We present simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR ) and Suzaku observations of the X-ray binary Cygnus X-1 in the hard state. This is the first time this state has been observed in Cyg X-1 with NuSTAR, which enables us to study the ... More
The Broad-band X-ray Spectrum of IC 4329A from a Joint NuSTAR/Suzaku ObservationApr 29 2014We have obtained a deep, simultaneous observation of the bright, nearby Seyfert galaxy IC 4329A with Suzaku and NuSTAR. Through a detailed spectral analysis, we are able to robustly separate the continuum, absorption and distant reflection components ... More
An Extremely Luminous and Variable Ultraluminous X-ray Source in the Outskirts of Circinus Observed with NuSTAROct 09 2013Following a serendipitous detection with the NuSTAR observatory, we present a multi-epoch spectral and temporal analysis of an extreme ultraluminous X-ray source (ULX) located in the outskirts of the Circinus galaxy, hereafter Circinus ULX5, including ... More
New Constraints on the Black Hole Low/Hard State Inner Accretion Flow with NuSTARNov 07 2014We report on an observation of the Galactic black hole candidate GRS 1739-278 during its 2014 outburst, obtained with NuSTAR. The source was captured at the peak of a rising "low/hard" state, at a flux of ~0.3 Crab. A broad, skewed iron line and disk ... More
Broadband X-ray Spectra of the Ultraluminous X-ray Source Holmberg IX X-1 observed with NuSTAR, XMM-Newton and SuzakuFeb 12 2014Jul 14 2014We present results from the coordinated broadband X-ray observations of the extreme ultraluminous X-ray source Holmberg IX X-1 performed by NuSTAR, XMM-Newton and Suzaku in late 2012. These observations provide the first high-quality spectra of Holmberg ... More
A NuSTAR observation of the center of the Coma ClusterNov 06 2014Jan 12 2015We present the results of a 55ks NuSTAR observation of the core of the Coma Cluster. The global spectrum can be explained by thermal gas emission, with a conservative 90% upper limit to non-thermal inverse Compton (IC) emission of $5.1 \times 10^{-12}$ ... More