Showing papers by "Christopher J. Russell published in 2018"

Parkes Pulsar Timing Array constraints on ultralight scalar-field dark matter

Abstract: It is widely accepted that dark matter contributes about a quarter of the critical mass-energy density in our Universe. The nature of dark matter is currently unknown, with the mass of possible constituents spanning nearly one hundred orders of magnitude. The ultralight scalar field dark matter, consisting of extremely light bosons with m ∼ 10^(−22) eV and often called “fuzzy” dark matter, provides intriguing solutions to some challenges at sub-Galactic scales for the standard cold dark matter model. As shown by Khmelnitsky and Rubakov, such a scalar field in the Galaxy would produce an oscillating gravitational potential with nanohertz frequencies, resulting in periodic variations in the times of arrival of radio pulses from pulsars. The Parkes Pulsar Timing Array (PPTA) has been monitoring 20 millisecond pulsars at two- to three-week intervals for more than a decade. In addition to the detection of nanohertz gravitational waves, PPTA offers the opportunity for direct searches for fuzzy dark matter in an astrophysically feasible range of masses. We analyze the latest PPTA data set which includes timing observations for 26 pulsars made between 2004 and 2016. We perform a search in this data set for evidence of ultralight dark matter in the Galaxy using Bayesian and Frequentist methods. No statistically significant detection has been made. We, therefore, place upper limits on the local dark matter density. Our limits, improving on previous searches by a factor of 2 to 5, constrain the dark matter density of ultralight bosons with m ≤ 10^(−23) eV to be below 6 GeV cm^(−3) with 95% confidence in the Earth neighborhood. Finally, we discuss the prospect of probing the astrophysically favored mass range m ≳ 10^(−22) eV with next-generation pulsar timing facilities.

Risk factors for hospitalizations due to bacterial respiratory tract infections after tracheotomy

Abstract: Objective Identify characteristics associated with hospital readmission due to bacterial respiratory tract infections (bRTI) after tracheotomy. Study design Retrospective study of 8009 children 0-17 years undergoing tracheotomy from 2007 to 2013 at 48 children's hospitals in the Pediatric Health Information System database. The primary outcome was first hospital admission after tracheotomy for bRTI (ie, primary diagnosis of bRTI or a primary diagnosis of bRTI symptom and secondary diagnosis of bRTI). We used Cox-proportional hazard modeling to assess associations between patient demographic and clinical characteristics and bRTI hospital readmission. Results Median age at tracheotomy admission was 5 months (interquartile range [IQR]: 1-50 months). Thirty-six percent (n = 2899) had at least one bRTI admission. Median time-to-readmission for bRTI was 275 days (IQR: 141-530). Factors independently associated with increased risk for bRTI readmission were younger age (eg, age 2 complex chronic conditions (vs zero; aHR 1.96; 95%CI: 1.34-2.86) and discharge to home (vs post-acute care setting; aHR 1.19; 95%CI: 1.08-1.32). Trauma diagnosis at tracheotomy (aHR 0.83; 95%CI: 0.69-1) and ventilator dependency (aHR 0.88; 95%CI: 0.81-0.97) were associated with decreased risk. Conclusions Young, Hispanic children with multiple complex chronic conditions who use Medicaid insurance and are not discharged to post-acute care are at the highest risk for hospital readmission for bRTI post-tracheotomy. Future research should investigate strategies to mitigate this risk for these children.

Length of Stay and Hospital Revisit After Bacterial Tracheostomy-Associated Respiratory Tract Infection Hospitalizations.

Abstract: OBJECTIVES: To identify factors associated with longer length of stay (LOS) and higher 30-day hospital revisit rates for children hospitalized with bacterial tracheostomy–associated respiratory tract infections (bTARTIs). METHODS: This was a multicenter, retrospective cohort study using administrative data from the Pediatric Health Information System database between 2007 and 2014 of patients 30 days to 17 years old with a principal discharge diagnosis of bTARTI or a principal discharge diagnosis of bTARTI symptoms with a secondary diagnosis of bTARTI. Primary outcomes of LOS (in days) and 30-day all-cause revisit rates (inpatient, observation, or emergency department visit) were analyzed by using a 3-level hierarchical regression model (discharges within patients within hospital). RESULTS: We included 3715 unique patients and 7355 discharges. The median LOS was 4 days (interquartile range: 3–8 days), and the 30-day revisit rate was 30.5%. Compared with children 1 to 4 years old, children aged 30 days to 12 months had both longer LOS (adjusted length of stay [aLOS] = +0.9 days; 95% confidence interval [CI]: 0.6 to 1.3) and increased hospital revisit risk (adjusted odds ratio [aOR] = 1.5; 95% CI: 1.3 to 1.7). Other factors associated with longer LOS included public insurance (aLOS = +0.5 days; 95% CI: 0.2 to 0.8), 3 or more complex chronic conditions (CCCs), mechanical ventilation (acute or chronic), and empirical anti- Pseudomonas aeruginosa antibiotics (aLOS = +0.6 days; 95% CI: 0.3 to 0.9). Other factors associated with 30-day revisit included 4 or more CCCs (aOR = 1.3; 95% CI: 1.1 to 1.6) and chronic ventilator dependency (aOR = 1.1; 95% CI: 1.0 to 1.3). CONCLUSIONS: Ventilator-dependent patients

Search for a radio pulsar in the remnant of supernova 1987A

Abstract: We have observed the remnant of supernova SN 1987A (SNR 1987A), located in the Large Magellanic Cloud (LMC) to search for periodic and/or transient radio emission with the Parkes 64 m-diameter radio telescope. We found no evidence of a radio pulsar in our periodicity search and derived 8 sigma upper bounds on the flux density of any such source of 31 mu Jy at 1.4 GHz and 21 mu Jy at 3 GHz. Four candidate transient events were detected with greater than 7 sigma significance, with dispersion measures (DMs) in the range 150-840 cm(-3) pc. For two of them, we found a second pulse at slightly lower significance. However, we cannot at present conclude that any of these are associated with a pulsar in SNR1987A. As a check on the system, we also observed PSR B0540-69, a young pulsar that also lies in the LMC. We found eight giant pulses at the DM of this pulsar. We discuss the implications of these results for models of the supernova remnant, neutron star formation, and pulsar evolution.

Factors Associated With Length of Stay and 30-Day Revisits in Pediatric Acute Pancreatitis.

Abstract: Objective The objective of the study was to identify factors associated with length of stay (LOS) and 30-day hospital revisit for patients hospitalized with acute pancreatitis (AP). Method Multicenter, retrospective cohort study using the Pediatric Health Information System database. Multilevel linear and logistic regression was used to identify factors independently associated with the primary outcome variables of LOS and 30-day hospital revisit in children aged 1 and 18 years discharged with a primary discharge diagnosis of AP from participating hospitals between 2008 and 2013. Results For the 7693 discharges, median LOS was 4 days (interquartile range 3-7 days) and 30-day revisit rate 17.6% (n = 1356). Discharges were primarily girls (55%), Caucasian (46%), and 6 years old or older (85%). On multilevel regression, factors independently associated with both longer LOS and higher revisit odds included malignant and gastrointestinal complex chronic conditions (CCCs) and total parenteral nutrition use while hospitalized. Male gender was associated with both lower LOS (adjusted length of stay = -0.6 days, 95% confidence interval [CI] = -0.8 to -0.4) and decreased revisit odds (aOR 0.85; 95% CI = 0.74 to 0.97). Hispanic ethnicity was associated with increased LOS (adjusted length of stay = +0.8 days, 95% CI = +0.5 to +1.1), but no change in revisit odds. Conclusions Certain demographic and clinical factors, including gender, ethnicity, and type of CCC, were independently associated with LOS and risk of 30-day hospital revisit for pediatric AP. Children with malignant and gastrointestinal CCCs who require total parenteral nutrition are at highest risk for both longer LOS and hospital revisit when admitted with AP. These patient populations may benefit from intensive care coordination when hospitalized for AP.