Results for "Brian W. Grefenstette"

total 71287took 0.21s
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
Observational Artifacts of NuSTAR: Ghost Rays and Stray LightNov 07 2017The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, flies two conical approximation Wolter-I mirrors at the end of a 10.15m mast. The optics are coated with multilayers of Pt/C and W/Si that operate from 3--80 keV. Since the optical ... 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
Joint X-ray, EUV and UV Observations of a Small MicroflareDec 21 2018Jun 29 2019We present the first joint observation of a small microflare in X-rays with the Nuclear Spectroscopic Telescope ARray (NuSTAR), UV with the Interface Region Imaging Spectrograph (IRIS) and EUV with the Solar Dynamics Observatory/Atmospheric Imaging Assembly ... 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
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
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
High-Energy X-ray Imaging of the Pulsar Wind Nebula MSH~15-52: Constraints on Particle Acceleration and TransportAug 01 2014We present the first images of the pulsar wind nebula (PWN) MSH 15-52 in the hard X-ray band (>8 keV), as measured with the Nuclear Spectroscopic Telescope Array (NuSTAR). Overall, the morphology of the PWN as measured by NuSTAR in the 3-7 keV band is ... More
Spectral calibration and modeling of the NuSTAR CdZnTe pixel detectorsSep 02 2011Sep 05 2011The Nuclear Spectroscopic Telescope Array (NuSTAR) will be the first space mission to focus in the hard X-ray (5-80 keV) band. The NuSTAR instrument carries two co-aligned grazing incidence hard X-ray telescopes. Each NuSTAR focal plane consists of four ... 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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
A Spatially Resolved Study of the Synchrotron Emission and Titanium in Tycho's Supernova Remnant with NuSTARApr 27 2015Oct 28 2015We report results from deep observations (~750 ks) of Tycho's supernova remnant (SNR) with NuSTAR. Using these data, we produce narrow-band images over several energy bands to identify the regions producing the hardest X-rays and to search for radioactive ... More
Calibration of the NuSTAR High Energy Focusing X-ray TelescopeApr 07 2015Sep 03 2015We present the calibration of the \textit{Nuclear Spectroscopic Telescope Array} (\nustar) X-ray satellite. We used the Crab as the primary effective area calibrator and constructed a piece-wise linear spline function to modify the vignetting response. ... More
A Hard X-Ray Power-Law Spectral Cutoff in Centaurus X-4Mar 26 2014Oct 16 2014The low-mass X-ray binary Cen X-4 is the brightest and closest (<1.2 kpc) quiescent neutron star transient. Previous 0.5-10 keV X-ray observations of Cen X-4 in quiescence identified two spectral components: soft thermal emission from the neutron star ... 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
Characterizing X-ray and Radio emission in the Black Hole X-Ray Binary V404 Cygni during QuiescenceJul 14 2015Mar 01 2016We present results from multi-wavelength simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cyg in quiescence. Our coverage with NuSTAR provides the very first opportunity to study the X-ray spectrum of V404 Cyg at energies ... More
NuSTAR detection of high-energy X-ray emission and rapid variability from Sagittarius A* flaresMar 04 2014Mar 11 2014Sagittarius A* harbors the supermassive black hole that lies at the dynamical center of our Galaxy. Sagittarius A* spends most of its time in a low luminosity emission state but flares frequently in the infrared and X-ray, increasing up to a few hundred ... 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
Multiple Conceptual Coherences in the Speed Tutorial: Micro-processes of Local StabilityAug 19 2010Researchers working within knowledge-in-pieces traditions have often employed observational approaches to investigate micro-processes of learning. There is growing evidence from this line of work that students' intuitive thinking about physical phenomena ... 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
NuSTAR results and future plans for magnetar and rotation-powered pulsar observationsFeb 05 2014The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing hard X-ray mission in orbit and operates in the 3-79 keV range. NuSTAR's sensitivity is roughly two orders of magnitude better than previous missions in this energy band thanks to ... 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
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
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
Corpus-based Method for Automatic Identification of Support Verbs for NominalizationsMar 09 1995Nominalization is a highly productive phenomena in most languages. The process of nominalization ejects a verb from its syntactic role into a nominal position. The original verb is often replaced by a semantically emptied support verb (e.g., "make a proposal"). ... 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
Evidence for a Variable Ultrafast Outflow in the Newly Discovered Ultraluminous Pulsar NGC 300 ULX-1Mar 06 2018Jun 18 2018Ultraluminous pulsars are a definite proof that persistent super-Eddington accretion occurs in nature. They support the scenario according to which most Ultraluminous X-ray Sources (ULXs) are super-Eddington accretors of stellar mass rather than sub-Eddington ... 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
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
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
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
Improving the Prompt Electromagnetic Energy Component of Jet Energy Resolution with pi0 Fitting in High Granularity Electromagnetic CalorimetersMar 12 2012We investigate improving the hadronic jet energy resolution using mass-constrained fits of pi0 decays using high granularity electromagnetic calorimeters. Single pi0 studies have indicated a large potential for improvement in the energy resolution of ... More
An extension of Hecke's converse theoremFeb 22 1995Associated to a newform $f(z)$ is a Dirichlet series $L_f(s)$ with functional equation and Euler product. Hecke showed that if the Dirichlet series $F(s)$ has a functional equation of the appropriate form, then $F(s)=L_f(s)$ for some holomorphic newform ... More
Population III star formation in a Lambda CDM universe, I: The effect of formation redshift and environment on protostellar accretion rateJul 02 2006Sep 15 2006(abridged) We perform 12 extremely high resolution adaptive mesh refinement cosmological hydrodynamic simulations of Population III star formation in a Lambda CDM universe, varying the box size and large-scale structure, to understand systematic effects ... More
Population III Star Formation in a Lambda WDM UniverseFeb 14 2006Jun 05 2006In this paper we examine aspects of primordial star formation in a gravitino warm dark matter universe with a cosmological constant. We compare a set of simulations using a single cosmological realization but with a wide range of warm dark matter particle ... More
Classical Hadrodynamics: A New Approach to Ultrarelativistic Heavy-Ion CollisionsJun 28 1994We discuss a new approach to ultrarelativistic heavy-ion collisions based on classical hadrodynamics for extended nucleons, corresponding to nucleons of finite size interacting with massive meson fields. This new theory provides a natural covariant microscopic ... 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
Particle-Production Mechanism in Relativistic Heavy-Ion CollisionsJun 28 1994We discuss the production of particles in relativistic heavy-ion collisions through the mechanism of massive bremsstrahlung, in which massive mesons are emitted during rapid nucleon acceleration. This mechanism is described within the framework of classical ... More
On the limit cycle for the 1/r^2 potential in momentum spaceMar 08 2005The renormalization of the attractive 1/r^2 potential has recently been studied using a variety of regulators. In particular, it was shown that renormalization with a square well in position space allows multiple solutions for the depth of the square ... More
Genetically Improved BarraCUDAMay 28 2015BarraCUDA is a C program which uses the BWA algorithm in parallel with nVidia CUDA to align short next generation DNA sequences against a reference genome. The genetically improved (GI) code is up to three times faster on short paired end reads from The ... More
Population III star formation in a Lambda CDM universe, II: Effects of a photodissociating backgroundJun 29 2007Sep 28 2007We examine aspects of primordial star formation in the presence of a molecular hydrogen-dissociating ultraviolet background. We compare a set of AMR hydrodynamic cosmological simulations using a single cosmological realization but with a range of ultraviolet ... More
Universally Coupled Massive GravityMar 11 2005Jul 14 2007We derive Einstein's equations from a linear theory in flat space-time using free-field gauge invariance and universal coupling. The gravitational potential can be either covariant or contravariant and of almost any density weight. We adapt these results ... More
A Compact Circumstellar Shell as the Source of High--velocity Features in SN 2011feMay 19 2015High--velocity features (HVF), especially of Ca II, are frequently seen in Type Ia supernovae observed prior to B-band maximum (Bmax). These HVF start at more than 25,000 km/s in the days after first light, and slow to about 18,000 km/s near Bmax. To ... 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
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
Luminous Dark MatterAug 11 2010Jan 13 2011We propose a dark matter model in which the signal in direct detection experiments arises from electromagnetic, not nuclear, energy deposition. This can provide a novel explanation for DAMA while avoiding many direct detection constraints. The dark matter ... 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
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
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
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
"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
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
Population III Star Formation In Large Cosmological Simulations I. Halo Temporal and Physical EnvironmentJun 19 2013We present a semi-analytic, computationally inexpensive model to identify halos capable of forming a Population III star in cosmological simulations across a wide range of times and environments. This allows for a much more complete and representative ... 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
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
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
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
Non-cancellation of electroweak logarithms in high-energy scatteringSep 05 2014Dec 09 2014We study electroweak Sudakov corrections in high energy scattering, and the cancellation between real and virtual Sudakov corrections. Numerical results are given for the case of heavy quark production by gluon collisions involving the rates $gg \to t ... More
Magnon Splitting Induced by Charge Transfer in the Three-Orbital Hubbard ModelNov 14 2017Jun 11 2018Understanding spin excitations and their connection to unconventional superconductivity have remained a central issue since the discovery of the cuprates. Direct measurement of the dynamical spin structure factor in the parent compounds can provide key ... More
Spin Dephasing as a Probe of Mode Temperature, Motional State Distributions, and Heating Rates in a 2D Ion CrystalJan 03 2014We employ spin-dependent optical dipole forces to characterize the transverse center-of-mass (COM) motional mode of a two-dimensional Wigner crystal of hundreds of $^9$Be$^+$. By comparing the measured spin dephasing produced by the spin-dependent force ... More
Simulating Quantum Magnetism with Correlated Non-Neutral Ion PlasmasMar 01 2013By employing forces that depend on the internal electronic state (or spin) of an atomic ion, the Coulomb potential energy of a strongly coupled array of ions can be modified in a spin-dependent way to mimic effective quantum spin Hamiltonians. Both ferromagnetic ... More
Testing that a Local Optimum of the Likelihood is Globally Optimum using Reparameterized EmbeddingsMay 31 2019Many mathematical imaging problems are posed as non-convex optimization problems. When numerically tractable global optimization procedures are not available, one is often interested in testing ex post facto whether or not a locally convergent algorithm ... More
A Deep X-ray View of the Synchrotron-Dominated Supernova Remnant G330.2+1.0Feb 08 2018We present moderately deep (125 ks) {\it XMM-Newton} observations of supernova remnant G330.2$+$1.0. This remnant is one of only a few known that fall into "synchrotron-dominated" category, with the emission almost entirely dominated by a nonthermal continuum. ... More
A Direct Detection of Gas Accretion: The Lyman Limit System in 3C 232Feb 26 2010Apr 22 2010The gas added and removed from galaxies over cosmic time greatly affects their stellar populations and star formation rates. QSO absorption studies in close QSO/galaxy pairs create a unique opportunity to study the physical conditions and kinematics of ... More
The Insignificance of Global Reheating in the Abell 1068 Cluster: X-Ray AnalysisOct 01 2003We report on a Chandra observation of the massive, medium redshift (z=0.1386) cooling flow cluster Abell 1068. We detect a clear temperature gradient in the X-ray emitting gas from kT ~ 5 keV in the outer part of the cluster down to roughly 2 keV in the ... More