Aaron D. Johnson
A5000175769- Pulsars and Gravitational Waves Research
- Cosmology and Gravitation Theories
- Geophysics and Gravity Measurements
- Radio Astronomy Observations and Technology
- Gamma-ray bursts and supernovae
- Communication in Education and Healthcare
- Black Holes and Theoretical Physics
- Astrophysical Phenomena and Observations
- Renal cell carcinoma treatment
- Renal and related cancers
- Work-Family Balance Challenges
- Astronomical Observations and Instrumentation
- Computational Physics and Python Applications
- Astrophysics and Cosmic Phenomena
- Public Relations and Crisis Communication
- Galaxies: Formation, Evolution, Phenomena
- Media Influence and Health
- Seismology and Earthquake Studies
- Genetic and Kidney Cyst Diseases
- Job Satisfaction and Organizational Behavior
- Superconducting and THz Device Technology
- Participatory Visual Research Methods
- Gaussian Processes and Bayesian Inference
- Atomic and Subatomic Physics Research
- Molecular Biology Techniques and Applications
California Institute of Technology
2023-2024
University of Wisconsin–Milwaukee
2021-2024
Campbell Collaboration
2023
Montgomery College
2021-2022
University of Arkansas at Fayetteville
2017-2019
National Institutes of Health
2007-2008
National Cancer Institute
2007-2008
Center for Cancer Research
2007-2008
Harvard University
2006
West Virginia University
2002-2004
Abstract We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by North American Nanohertz Observatory Gravitational Waves. The correlations follow Hellings–Downs pattern expected gravitational-wave background. presence such background with power-law spectrum favored over model only independent noises Bayes factor in excess 10 14 , and this same an uncorrelated common factors 200–1000, depending on...
Abstract The 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) shows positive evidence presence of a low-frequency gravitational-wave (GW) background. In this paper, we investigate potential cosmological interpretations signal, specifically cosmic inflation, scalar-induced GWs, first-order phase transitions, strings, and domain walls. We find that, with exception stable strings field theory origin, all these models can...
We searched for an isotropic stochastic gravitational wave background in the second data release of International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing campaigns North America, Europe, and Australia. In our reference search power law strain spectrum form $h_c = A(f/1\,\mathrm{yr}^{-1})^{\alpha}$, we found strong evidence spectrally-similar low-frequency process amplitude $A 3.8^{+6.3}_{-2.5}\times10^{-15}$ spectral index $\alpha -0.5 \pm 0.5$,...
The NANOGrav 15-year data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such gravitational waves, here we analyze signal as coming from population supermassive black hole (SMBH) binaries distributed throughout Universe. We show that astrophysically motivated models SMBH binary populations are able to reproduce both amplitude and shape observed spectrum. multiple model variations GWB spectrum at our current...
Abstract We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15 yr data set North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is a pulsar array (PTA) experiment that sensitive to low-frequency gravitational waves (GWs). This NANOGrav’s fifth public release, including both “narrowband” “wideband” time-of-arrival (TOA) measurements corresponding models. have added 21 MSPs extended our baselines by 3 yr, now spanning nearly...
Pulsar timing arrays (PTAs) are galactic-scale gravitational wave detectors. Each individual arm, composed of a millisecond pulsar, radio telescope, and kiloparsecs-long path, differs in its properties but, aggregate, can be used to extract low-frequency (GW) signals. We present noise sensitivity analysis accompany the NANOGrav 15-year data release associated papers, along with an in-depth introduction PTA models. As first step our analysis, we characterize each pulsar set three types white...
Abstract Evidence for a low-frequency stochastic gravitational-wave background has recently been reported based on analyses of pulsar timing array data. The most likely source such is population supermassive black hole binaries, the loudest which may be individually detected in these data sets. Here we present search individual binaries NANOGrav 15 yr set. We introduce several new techniques, enhance efficiency and modeling accuracy analysis. uncovered weak evidence two candidate signals,...
Abstract The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence the presence of an isotropic nanohertz gravitational-wave background (GWB) in its 15 yr data set. However, if GWB is produced by a population inspiraling supermassive black hole binary (SMBHB) systems, then predicted to be anisotropic, depending on distribution these systems local Universe and statistical properties SMBHB population. In this work, we search anisotropy using multiple...
ABSTRACT The International Pulsar Timing Array 2nd data release is the combination of sets from worldwide collaborations. In this study, we search for continuous waves: gravitational wave signals produced by individual supermassive black hole binaries in local universe. We consider on circular orbits and neglect evolution orbital frequency over observational span. find no evidence such set sky averaged 95 per cent upper limits their amplitude h95. most sensitive 10 nHz with h95 = 9.1 ×...
Abstract The NANOGrav 15 yr data provide compelling evidence for a stochastic gravitational-wave (GW) background at nanohertz frequencies. simplest model-independent approach to characterizing the frequency spectrum of this signal consists simple power-law fit involving two parameters: an amplitude A and spectral index γ . In Letter, we consider next logical step beyond minimal model, allowing running (i.e., logarithmic dependence) index, <mml:math...
The NANOGrav 15-year data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such gravitational waves, here we analyze signal as coming from population supermassive black hole (SMBH) binaries distributed throughout Universe. We show that astrophysically motivated models SMBH binary populations are able to reproduce both amplitude and shape observed spectrum. multiple model variations GWB spectrum at our current...
Pulsar timing array collaborations, such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), are seeking to detect nanohertz gravitational waves emitted by supermassive black hole binaries formed in aftermath of galaxy mergers. We have searched continuous from individual circular using NANOGrav's recent 12.5-year data set. created new methods accurately model uncertainties on pulsar distances our analysis, and we implemented techniques account a common red noise...
Abstract Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more metric theories of gravity can have additional modes, produce different interpulsar correlations. In this work, search the NANOGrav set quadrupolar HD scalar-transverse (ST) We find that are best fit to no significant...
Abstract We present the results of a Bayesian search for gravitational wave (GW) memory in NANOGrav 12.5 yr data set. find no convincing evidence any signals this Bayes factor 2.8 favor model that includes signal and common spatially uncorrelated red noise (CURN) compared to including only CURN. However, further investigation shows disproportionate amount support comes from three dubious pulsars. Using more flexible red-noise these pulsars reduces 1.3. Having found compelling evidence, we go...
Pulsar timing arrays (PTAs) use an array of millisecond pulsars to search for gravitational waves in the nanohertz regime pulse time arrival data. This paper presents rigorous tests PTA methods, examining their consistency across relevant parameter space. We discuss updates 15-year isotropic gravitational-wave background analyses and corresponding code representations. Descriptions internal structure flagship algorithms enterprise ptmcmcsampler are given facilitate understanding likelihood...
Upgrades beyond the current second generation of ground-based gravitational wave detectors will allow them to observe tens thousands neutron star and black hole binaries. Given typical minute-to-hour duration signals in detector frequency band, a number overlap time-frequency plane resulting nonzero cross-correlation. We examine source confusion arising from overlapping whose tracks cross. Adopting median observed merger rate $100$ Gpc$^{-3}$yr$^{-1}$, each binary signal overlaps with an...
In recent years nonverbal immediacy has received considerable attention from researchers concerned with instructional communication, interpersonal and organizational communication. Unfortunately, the instruments used to measure in these contexts sometimes have been problematic terms of their reliability estimates. This research attempted overcome this problem, or failing that, identify cause(s) reduced reliability. The resulted a scale high when as either self‐report an other‐report measure....
No AccessJournal of UrologyAdult Urology1 Jul 2008Feasibility and Outcomes Repeat Partial Nephrectomyis accompanied byCpG Hypermethylation the UCHL1 Gene Promoter is Associated With Pathogenesis Poor Prognosis in Renal Cell CarcinomaAntisense Attenuation p21 Sensitizes Kidney Cancer to Apoptosis Response Conventional DNA Damaging Chemotherapy Enhancement Phospho-p53A Pilot Trial Vascular Targeted Photodynamic Therapy for Tissue Aaron Johnson, Sunil Sudarshan, Jack Liu, W. Marston Linehan,...
An isotropic stochastic background of nanohertz gravitational waves creates excess residual power in pulsar-timing-array datasets, with characteristic inter-pulsar correlations described by the Hellings-Downs function. These appear as nondiagonal terms noise covariance matrix, which must be inverted to obtain likelihood. Searches for background, require many likelihood evaluations, are therefore quite computationally expensive. We propose a more efficient method: we first compute approximate...
Patients with von Hippel-Lindau disease may require repeat partial nephrectomies to avoid the need for renal replacement therapy. We evaluated outcomes in patients who underwent third or fourth on same kidney, which we call salvage nephrectomy.We retrospectively reviewed charts of surgery at National Cancer Institute from 1999 2006. identified 11 13 whom nephrectomy was performed. Surgical were assessed by preservation as well intraoperative and postoperative complications. Functional...
The Darboux transformation between ordinary differential equations is a 19th century technique that has seen wide use in quantum theory for producing exactly solvable potentials the Schr\"odinger equation with specific spectral properties. In this paper we show same appears black hole theory, relating, instance, Zerilli and Regge-Wheeler axial polar Schwarzschild perturbations. reveals these two to be isospectral, well known result whose method been repeatedly reintroduced under different...
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence the presence of an isotropic nanohertz gravitational wave background (GWB) in its 15 yr dataset. However, if GWB is produced by a population inspiraling supermassive black hole binary (SMBHB) systems, then predicted to be anisotropic, depending on distribution these systems local Universe and statistical properties SMBHB population. In this work, we search anisotropy using multiple methods bases...
Abstract The cosmic merger history of supermassive black hole binaries (SMBHBs) is expected to produce a low-frequency gravitational wave background (GWB). Here we investigate how signs the discrete nature this GWB can manifest in pulsar timing arrays (PTAs) through excursions from, and breaks in, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mi>GW</mml:mi> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> <mml:mo...