ABSTRACT
Efficient automated detection of flux-transient, re-occurring flux-variable, and moving objects is increasingly important for large-scale astronomical surveys. We present braai, a ...convolutional-neural-network, deep-learning real/bogus classifier designed to separate genuine astrophysical events and objects from false positive, or bogus, detections in the data of the Zwicky Transient Facility (ZTF), a new robotic time-domain survey currently in operation at the Palomar Observatory in California, USA. Braai demonstrates a state-of-the-art performance as quantified by its low false negative and false positive rates. We describe the open-source software tools used internally at Caltech to archive and access ZTF’s alerts and light curves (kowalski
), and to label the data (zwickyverse). We also report the initial results of the classifier deployment on the Edge Tensor Processing Units that show comparable performance in terms of accuracy, but in a much more (cost-) efficient manner, which has significant implications for current and future surveys.
Hierarchical assembly models predict a population of supermassive black hole (SMBH) binaries. These are not resolvable by direct imaging but may be detectable via periodic variability (or nanohertz ...frequency gravitational waves). Following our detection of a 5.2-year periodic signal in the quasar PG 1302−102, we present a novel analysis of the optical variability of 243 500 known spectroscopically confirmed quasars using data from the Catalina Real-time Transient Survey (CRTS) to look for close (<0.1 pc) SMBH systems. Looking for a strong Keplerian periodic signal with at least 1.5 cycles over a baseline of nine years, we find a sample of 111 candidate objects. This is in conservative agreement with theoretical predictions from models of binary SMBH populations. Simulated data sets, assuming stochastic variability, also produce no equivalent candidates implying a low likelihood of spurious detections. The periodicity seen is likely attributable to either jet precession, warped accretion discs or periodic accretion associated with a close SMBH binary system. We also consider how other SMBH binary candidates in the literature appear in CRTS data and show that none of these are equivalent to the identified objects. Finally, the distribution of objects found is consistent with that expected from a gravitational-wave-driven population. This implies that circumbinary gas is present at small orbital radii and is being perturbed by the black holes. None of the sources is expected to merge within at least the next century. This study opens a new unique window to study a population of close SMBH binaries that must exist according to our current understanding of galaxy and SMBH evolution.
Highlights • Recent human clinical trial data on RNAi approaches to gene down-regulation for genetic diseases. • Overview of current anti-microRNA drugs with specific emphasis on application to ...target Hepatitis C infection. • Update on the current state of ‘exon skipping’ field for both Duchenne muscular dystrophy and spinal muscular atrophy.
The Zwicky Transient Facility (ZTF) survey generates real-time alerts for optical transients, variables, and moving objects discovered in its wide-field survey. We describe the ZTF alert stream ...distribution and processing (filtering) system. The system uses existing open-source technologies developed in industry: Kafka, a real-time streaming platform, and Avro, a binary serialization format. The technologies used in this system provide a number of advantages for the ZTF use case, including (1) built-in replication, scalability, and stream rewind for the distribution mechanism; (2) structured messages with strictly enforced schemas and dynamic typing for fast parsing; and (3) a Python-based stream processing interface that is similar to batch for a familiar and user-friendly plug-in filter system, all in a modular, primarily containerized system. The production deployment has successfully supported streaming up to 1.2 million alerts or roughly 70 GB of data per night, with each alert available to a consumer within about 10 s of alert candidate production. Data transfer rates of about 80,000 alerts/minute have been observed. In this paper, we discuss this alert distribution and processing system, the design motivations for the technology choices for the framework, performance in production, and how this system may be generally suitable for other alert stream use cases, including the upcoming Large Synoptic Survey Telescope.
Objectives To examine temporal trends in sex and age specific incidence of self harm in children and adolescents, clinical management patterns, and risk of cause specific mortality following an index ...self harm episode at a young age.Design Population based cohort study.Setting UK Clinical Practice Research Datalink—electronic health records from 647 general practices, with practice level deprivation measured ecologically using the index of multiple deprivation. Patients from eligible English practices were linked to hospital episode statistics (HES) and Office for National Statistics (ONS) mortality records.Participants For the descriptive analytical phases we examined data pertaining to 16 912 patients aged 10-19 who harmed themselves during 2001-14. For analysis of cause specific mortality following self harm, 8638 patients eligible for HES and ONS linkage were matched by age, sex, and general practice with up to 20 unaffected children and adolescents (n=170 274).Main outcome measures In the first phase, temporal trends in sex and age specific annual incidence were examined. In the second phase, clinical management was assessed according to the likelihood of referral to mental health services and psychotropic drug prescribing. In the third phase, relative risks of all cause mortality, unnatural death (including suicide and accidental death), and fatal acute alcohol or drug poisoning were estimated as hazard ratios derived from stratified Cox proportional hazards models for the self harm cohort versus the matched unaffected comparison cohort.Results The annual incidence of self harm was observed to increase in girls (37.4 per 10 000) compared with boys (12.3 per 10 000), and a sharp 68% increase occurred among girls aged 13-16, from 45.9 per 10 000 in 2011 to 77.0 per 10 000 in 2014. Referrals within 12 months of the index self harm episode were 23% less likely for young patients registered at the most socially deprived practices, even though incidences were considerably higher in these localities. Children and adolescents who harmed themselves were approximately nine times more likely to die unnaturally during follow-up, with especially noticeable increases in risks of suicide (deprivation adjusted hazard ratio 17.5, 95% confidence interval 7.6 to 40.5) and fatal acute alcohol or drug poisoning (34.3, 10.2 to 115.7).Conclusions Gaining a better understanding of the mechanisms responsible for the recent apparent increase in the incidence of self harm among early-mid teenage girls, and coordinated initiatives to tackle health inequalities in the provision of services to distressed children and adolescents, represent urgent priorities for multiple public agencies.
The Zwicky Transient Facility: Surveys and Scheduler Bellm, Eric C.; Kulkarni, Shrinivas R.; Barlow, Tom ...
Publications of the Astronomical Society of the Pacific,
06/2019, Volume:
131, Issue:
1000
Journal Article
Peer reviewed
Open access
We present a novel algorithm for scheduling the observations of time-domain imaging surveys. Our integer linear programming approach optimizes an observing plan for an entire night by assigning ...targets to temporal blocks, enabling strict control of the number of exposures obtained per field and minimizing filter changes. A subsequent optimization step minimizes slew times between each observation. Our optimization metric self-consistently weights contributions from time-varying airmass, seeing, and sky brightness to maximize the transient discovery rate. We describe the implementation of this algorithm on the surveys of the Zwicky Transient Facility and present its on-sky performance.
Online learning-learning that involves interactions that are mediated through using digital, typically internet-based, technology-is pervasive, multi-faceted, and evolving, creating opportunities and ...challenges for educational research in the wake of the COVID-19 pandemic. In this special issue, we advance an interdisciplinary agenda for online learning research at the intersection of educational technology, educational psychology, and the learning sciences. In this first article in the issue, we define online learning including its variants, review historical and current contexts, explore its multidimensionality, and assert key issues shaping contemporary online learning. We propose five important lenses: community, engagement, pedagogy, equity, and design-based research, through which scholarly communities are creating knowledge that influences research and practice in online learning contexts. These lenses highlight points of conceptual overlap between the online and psychological learning literatures. The special issue is organized around these lenses and includes an article representing each one, complemented by commentaries that offer critical appraisal and synthesis.
Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric ...configurations of surface atoms on supported metal nanoparticles have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale is critical for understanding reactivity. Elucidation of such insights on high surface area oxide supported metal nanoparticles has been limited by less than atomic resolution typically achieved by environmental transmission electron microscopy (TEM) when operated under realistic conditions and a lack of correlated experimental measurements providing quantitative information about the distribution of exposed surface atoms under relevant reaction conditions. We overcome these limitations by correlating density functional theory predictions of adsorbate-induced surface reconstruction visually with atom-resolved imaging by in situ TEM and quantitatively with sample-averaged measurements of surface atom configurations by in situ infrared spectroscopy all at identical saturation adsorbate coverage. This is demonstrated for platinum (Pt) nanoparticle surface reconstruction induced by CO adsorption at saturation coverage and elevated (>400 K) temperature, which is relevant for the CO oxidation reaction under cold-start conditions in the catalytic convertor. Through our correlated approach, it is observed that the truncated octahedron shape adopted by bare Pt nanoparticles undergoes a reversible, facet selective reconstruction due to saturation CO coverage, where {100} facets roughen into vicinal stepped high Miller index facets, while {111} facets remain intact.
Early-time observations of Type Ia supernovae (SNe Ia) are essential to constrain the properties of their progenitors. In this paper, we present high-quality light curves of 127 SNe Ia discovered by ...the Zwicky Transient Facility (ZTF) in 2018. We describe our method to perform forced point-spread function photometry, which can be applied to other types of extragalactic transients. With a planned cadence of six observations per night (three g + three r), all of the 127 SNe Ia are detected in both g and r bands more than 10 days (in the rest frame) prior to the epoch of g-band maximum light. The redshifts of these objects range from z = 0.0181 to 0.165; the median redshift is 0.074. Among the 127 SNe, 50 are detected at least 14 days prior to maximum light (in the rest frame), with a subset of nine objects being detected more than 17 days before g-band peak. This is the largest sample of young SNe Ia collected to date; it can be used to study the shape and color evolution of the rising light curves in unprecedented detail. We discuss six peculiar events in this sample: one 02cx-like event ZTF18abclfee (SN 2018crl), one Ia-CSM SN ZTF18aaykjei (SN 2018cxk), and four objects with possible super-Chandrasekhar mass progenitors: ZTF18abhpgje (SN 2018eul), ZTF18abdpvnd (SN 2018dvf), ZTF18aawpcel (SN 2018cir), and ZTF18abddmrf (SN 2018dsx).
The COVID-19 pandemic has adversely affected population mental health. We aimed to assess temporal trends in primary care-recorded common mental illness, episodes of self-harm, psychotropic ...medication prescribing, and general practitioner (GP) referrals to mental health services during the COVID-19 emergency in the UK.
We did a population-based cohort study using primary care electronic health records from general practices registered on the UK Clinical Practice Research Datalink (CPRD). We included patient records from Jan 1, 2010, to Sept 10, 2020, to establish long-term trends and patterns of seasonality, but focused primarily on the period January, 2019–September, 2020. We extracted data on clinical codes entered into patient records to estimate the incidence of depression and anxiety disorders, self-harm, prescriptions for antidepressants and benzodiazepines, and GP referrals to mental health services, and assessed event rates of all psychotropic prescriptions and self-harm. We used mean-dispersion negative binomial regression models to predict expected monthly incidence and overall event rates, which were then compared with observed rates to assess the percentage reduction in incidence and event rates after March, 2020. We also stratified analyses by sex, age group, and practice-level Index of Multiple Deprivation quintiles.
We identified 14 210 507 patients from 1697 UK general practices registered in the CPRD databases. In April, 2020, compared with expected rates, the incidence of primary care-recorded depression had reduced by 43·0% (95% CI 38·3–47·4), anxiety disorders by 47·8% (44·3–51·2), and first antidepressant prescribing by 36·4% (33·9–38·8) in English general practices. Reductions in first diagnoses of depression and anxiety disorders were largest for adults of working age (18–44 and 45–64 years) and for patients registered at practices in more deprived areas. The incidence of self-harm was 37·6% (34·8–40·3%) lower than expected in April, 2020, and the reduction was greatest for women and individuals aged younger than 45 years. By September, 2020, rates of incident depression, anxiety disorder, and self-harm were similar to expected levels. In Northern Ireland, Scotland, and Wales, rates of incident depression and anxiety disorder remained around a third lower than expected to September, 2020. In April, 2020, the rate of referral to mental health services was less than a quarter of the expected rate for the time of year (75·3% reduction 74·0–76·4).
Consequences of the considerable reductions in primary care-recorded mental illness and self-harm could include more patients subsequently presenting with greater severity of mental illness and increasing incidence of non-fatal self-harm and suicide. Addressing the effects of future lockdowns and longer-term impacts of economic instability on mental health should be prioritised.
National Institute for Health Research and Medical Research Council.
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