Showing papers by "Christopher J. Russell published in 2020"

The Parkes Pulsar Timing Array project: Second data release

Abstract: We describe 14 yr of public data from the Parkes Pulsar Timing Array (PPTA), an ongoing project that is producing precise measurements of pulse times of arrival from 26 millisecond pulsars using the 64-m Parkes radio telescope with a cadence of approximately 3 weeks in three observing bands. A comprehensive description of the pulsar observing systems employed at the telescope since 2004 is provided, including the calibration methodology and an analysis of the stability of system components. We attempt to provide full accounting of the reduction from the raw measured Stokes parameters to pulse times of arrival to aid third parties in reproducing our results. This conversion is encapsulated in a processing pipeline designed to track provenance. Our data products include pulse times of arrival for each of the pulsars along with an initial set of pulsar parameters and noise models. The calibrated pulse profiles and timing template profiles are also available. These data represent almost 21 000 h of recorded data spanning over 14 yr. After accounting for processes that induce time-correlated noise, 22 of the pulsars have weighted root-mean-square timing residuals of in at least one radio band. The data should allow end users to quickly undertake their own gravitational wave analyses, for example, without having to understand the intricacies of pulsar polarisation calibration or attain a mastery of radio frequency interference mitigation as is required when analysing raw data files.

The Parkes Pulsar Timing Array Project: Second data release

Abstract: We describe 14 years of public data from the Parkes Pulsar Timing Array (PPTA), an ongoing project that is producing precise measurements of pulse times of arrival from 26 millisecond pulsars using the 64-m Parkes radio telescope with a cadence of approximately three weeks in three observing bands. A comprehensive description of the pulsar observing systems employed at the telescope since 2004 is provided, including the calibration methodology and an analysis of the stability of system components. We attempt to provide full accounting of the reduction from the raw measured Stokes parameters to pulse times of arrival to aid third parties in reproducing our results. This conversion is encapsulated in a processing pipeline designed to track provenance. Our data products include pulse times of arrival for each of the pulsars along with an initial set of pulsar parameters and noise models. The calibrated pulse profiles and timing template profiles are also available. These data represent almost 21,000 hrs of recorded data spanning over 14 years. After accounting for processes that induce time-correlated noise, 22 of the pulsars have weighted root-mean-square timing residuals of < 1 ${\mu}$s in at least one radio band. The data should allow end users to quickly undertake their own gravitational-wave analyses (for example) without having to understand the intricacies of pulsar polarisation calibration or attain a mastery of radio-frequency interference mitigation as is required when analysing raw data files.

A pulsar-based time-scale from the International Pulsar Timing Array

Abstract: We have constructed a new time-scale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar time-scale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected time-scale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based time-scales are unlikely to contribute to the stability of the best time-scales over the next decade, but they will remain a valuable independent check on atomic time-scales. We also find that the stability of the pulsar-based time-scale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves.

Searching for gravitational-wave bursts from cosmic string cusps with the Parkes Pulsar Timing Array

Abstract: Cosmic strings are potential gravitational wave (GW) sources that can be probed by pulsar timing arrays (PTAs). In this work we develop a detection algorithm for a GW burst from a cusp on a cosmic string, and apply it to Parkes PTA data. We find four events with a false alarm probability less than 1%. However further investigation shows that all of these are likely to be spurious. As there are no convincing detections we place upper limits on the GW amplitude for different event durations. From these bounds we place limits on the cosmic string tension of G mu ~ 10^{-5}, and highlight that this bound is independent from those obtained using other techniques. We discuss the physical implications of our results and the prospect of probing cosmic strings in the era of Square Kilometre Array (SKA).

Parkes Transient Events. I. Database of Single Pulses, Initial Results, and Missing Fast Radio Bursts

Abstract: A large number of observations from the Parkes 64\\,m-diameter radio telescope, recorded with high time resolution, are publicly available. We have re-processed all of the observations obtained during the first four years (from 1997 to 2001) of the Parkes Multibeam receiver system in order to identify transient events and have built a database that records the 568,736,756 pulse candidates generated during this search. We have discovered a new fast radio burst (FRB), FRB~010305, with a dispersion measure of 350$\\pm$5\\,\\,cm$^{-3}\\,$pc and explored why so few FRBs have been discovered in data prior to 2001. After accounting for the dispersion smearing across the channel bandwidth and the sky regions surveyed, the number of FRBs is found to be consistent with model predictions. We also present five single pulse candidates from unknown sources, but with Galactic dispersion measures. We extract a diverse range of sources from the database, which can be used, for example, as a training set of data for new software being developed to search for FRBs in the presence of radio frequency interference.

Parkes transient events: I. Database of single pulses, initial results and missing FRBs

Abstract: A large number of observations from the Parkes 64\,m-diameter radio telescope, recorded with high time resolution, are publicly available. We have re-processed all of the observations obtained during the first four years (from 1997 to 2001) of the Parkes Multibeam receiver system in order to identify transient events and have built a database that records the 568,736,756 pulse candidates generated during this search. We have discovered a new fast radio burst (FRB), FRB~010305, with a dispersion measure of 350$\pm$5\,\,cm$^{-3}\,$pc and explored why so few FRBs have been discovered in data prior to 2001. After accounting for the dispersion smearing across the channel bandwidth and the sky regions surveyed, the number of FRBs is found to be consistent with model predictions. We also present five single pulse candidates from unknown sources, but with Galactic dispersion measures. We extract a diverse range of sources from the database, which can be used, for example, as a training set of data for new software being developed to search for FRBs in the presence of radio frequency interference.

Applying saliency-map analysis in searches for pulsars and fast radio bursts

Abstract: Context. We investigate the use of saliency-map analysis to aid in searches for transient signals, such as fast radio bursts and individual pulses from radio pulsars.Aims. Our aim is to demonstrate that saliency maps provide the means to understand predictions from machine learning algorithms and can be implemented in pipelines used to search for transient events.Methods. We implemented a new deep learning methodology to predict whether any segment of the data contains a transient event. The algorithm was trained using real and simulated data sets. We demonstrate that the algorithm is able to identify such events. The output results are visually analysed via the use of saliency maps.Results. We find that saliency maps can produce an enhanced image of any transient feature without the need for de-dispersion or removal of radio frequency interference. The maps can be used to understand which features in the image were used in making the machine learning decision and to visualise the transient event. Even though the algorithm reported here was developed to demonstrate saliency-map analysis, we have detected a single burst event, in archival data, with dispersion measure of 41 cm−3 pc that is not associated with any currently known pulsar.

Technology-Dependent Pediatric Inpatients at Children's Versus Nonchildren's Hospitals.

Abstract: BACKGROUND AND OBJECTIVE: Technology-dependent children (TDC) are admitted to both children’s hospitals (CHs) and nonchildren’s hospitals (NCHs), where there may be fewer pediatric-specific specialists or resources. Our objective was to compare the characteristics of TDC admitted to CHs versus NCHs. METHODS: This was a multicenter, retrospective study using the 2012 Kids’ Inpatient Database. We included patients aged 0 to 18 years with a tracheostomy, gastrostomy, and/or ventricular shunt. We excluded those who died, were transferred into or out of the hospital, had a length of stay (LOS) that was an extreme outlier, or had missing data for key variables. We compared patient and hospital characteristics across CH versus NCH using χ2 tests and LOS and cost using generalized linear models. RESULTS: In the final sample of 64 521 discharges, 55% of discharges of TDC were from NCHs. A larger proportion of those from CHs had higher disease severity (55% vs 49%; P CONCLUSIONS: Because the majority of TDC are hospitalized at NCHs, future research on TDC should incorporate NCH settings. Further studies should investigate if some may benefit from regionalization of care or earlier transfer to a CH.

Applying saliency-map analysis in searches for pulsars and fast radio bursts

Abstract: To investigate the use of saliency-map analysis to aid in searches for transient signals, such as fast radio bursts and individual pulses from radio pulsars. We aim to demonstrate that saliency maps provide the means to understand predictions from machine learning algorithms and can be implemented in piplines used to search for transient events. We have implemented a new deep learning methodology to predict whether or not any segment of the data contains a transient event. The algorithm has been trained using real and simulated data sets. We demonstrate that the algorithm is able to identify such events. The output results are visually analysed via the use of saliency maps. We find that saliency maps can produce an enhanced image of any transient feature without the need for de-dispersion or removal of radio frequency interference. Such maps can be used to understand which features in the image were used in making the machine learning decision and to visualise the transient event. Even though the algorithm reported here was developed to demonstrate saliency-map analysis, we have detected, in archival data, a single burst event with dispersion measure of $41$\,cm$^{-3}$pc that is not associated with any currently known pulsar.

Variations in Care for Breastfed Infants Admitted to US Children’s Hospitals: A Multicenter Survey of Inpatient Providers

Abstract: BACKGROUND: Studies have revealed an association between hospitalization of breastfed infants and weaning posthospitalization. It is unknown what steps inpatient providers at children’s hospitals are currently taking to support breastfeeding mothers of hospitalized infants, their comfort providing breastfeeding counseling, and what training they receive. METHODS: We conducted a multicenter survey study of pediatric providers who care for infants hospitalized at 3 urban, tertiary-care children’s hospitals over a 12-month period. A convenience sample of nurses, residents, and attending physicians agreed to participate. Participants completed a 24-question questionnaire addressing provider practices, comfort with breastfeeding counseling, and previous breastfeeding education. Data were summarized as medians (interquartile ranges) and frequencies (percentages). Kruskal-Wallis and χ2 tests were used to compare between provider types. RESULTS: A total of 361 out of 1097 (33%) eligible providers completed the survey: 133 (21%) nurses, 166 (45%) residents, and 62 (63%) attending physicians. Provider practices varied by provider type. We observed a general trend that providers do not routinely review breastfeeding techniques, directly observe feeds, or use standardized breastfeeding assessment tools. Residents and attending physicians were more likely than nurses to feel comfortable with breastfeeding counseling (P = .02). Residents were more likely than nurses and attending physicians to have received breastfeeding education in the last 3 years (P CONCLUSIONS: Practices, comfort, and previous education varied by provider type. There was a general pattern that providers do not routinely perform certain practices. Further studies are needed to determine if inpatient provider practices affect weaning posthospitalization and if inpatient quality improvement initiatives will help mothers continue breastfeeding posthospitalization.

Top Articles in Pediatric Hospital Medicine: July 2019 to June 2020.

Abstract: The last academic year has been filled with discussions of inequality, overuse, and a chance to reflect on our own biases within medicine. As a field, we took a momentous step forward with the first set of physicians qualifying and sitting for the Pediatric Hospital Medicine (PHM) Subspecialty Boards. This event, however, was embroiled with concerns around gender disparities and inequity, sparking petitions signed by thousands of physicians, and calls for accountability and transparency within our systems. Fast forward 4 months and the world was turned upside down in the face of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Pediatric hospitalists in locations like New York City converted pediatric units to adult units, precepted internal medicine residents, and within a period of weeks organized the Pediatric Overflow Planning Contingency Response Network. Finally, police violence, killings, and protests have brought systemic racism to the forefront as a public health crisis. We care for children regardless of their cultural backgrounds, gender orientation, and socioeconomic status (SES); as such, we as a community have the chance to play a critical role in instigating change for addressing and uprooting systemic racism. In this context, we have reviewed with a critical lens articles published from July 2019 through June 2020 to winnow down the expanse of literature over this past 12 months into the Top Articles for PHM (an annual presentation at the PHM conference). In undertaking this endeavor, we reviewed 11 925 articles from 19 journals (Table 1). We conducted this review in 3 steps, detailed in Fig 1. In the first step, we reviewed article titles and eliminated articles on the basis of a series of questions to broadly …