Conformal Invariance, Dark Energy, and CMB Non-Gaussianity

In addition to simple scale invariance, a universe dominated by dark energy naturally gives rise to correlation functions possessing full conformal invariance. This is due to the mathematical isomorphism between the conformal group of certain 3 dimensional slices of de Sitter space and the de Sitter isometry group SO(4,1). In the standard homogeneous isotropic cosmological model in which primordial density perturbations are generated during a long vacuum energy dominated de Sitter phase, the embedding of flat spatial sections in de Sitter space induces a conformal invariant perturbation spectrum and definite prediction for the shape of the non-Gaussian CMB bispectrum. In the case in which the density fluctuations are generated instead on the de Sitter horizon, conformal invariance of the horizon embedding implies a different but also quite definite prediction for the angular correlations of CMB non-Gaussianity on the sky. Each of these forms for the bispectrum is intrinsic to the symmetries of de Sitter space and in that sense, independent of specific model assumptions. Each is different from the predictions of single field slow roll inflation models which rely on the breaking of de Sitter invariance. We propose a quantum origin for the CMB fluctuations in the scalar gravitational sector from the conformal anomaly that could give rise to these non-Gaussianities without a slow roll inflaton field, and argue that conformal invariance also leads to the expectation for the relation n_S-1=n_T between the spectral indices of the scalar and tensor power spectrum. Confirmation of this prediction or detection of non-Gaussian correlations in the CMB of one of the bispectral shape functions predicted by conformal invariance can be used both to establish the physical origins of primordial density fluctuations and distinguish between different dynamical models of cosmological vacuum dark energy.Comment: 73 pages, 9 figures. Final Version published in JCAP. New Section 4 added on linearized scalar gravitational potentials; New Section 8 added on gravitational wave tensor perturbations and relation of spectral indices n_T = n_S -1; Table of Contents added; Eqs. (3.14) and (3.15) added to clarify relationship of bispectrum plotted to CMB measurements; Some other minor modification

Optimal Control of Nonlinear Switched Systems: Computational Methods and Applications

A switched system is a dynamic system that operates by switching between different subsystems or modes. Such systems exhibit both continuous and discrete characteristics—a dual nature that makes designing effective control policies a challenging task. The purpose of this paper is to review some of the latest computational techniques for generating optimal control laws for switched systems with nonlinear dynamics and continuous inequality constraints. We discuss computational strategiesfor optimizing both the times at which a switched system switches from one mode to another (the so-called switching times) and the sequence in which a switched system operates its various possible modes (the so-called switching sequence). These strategies involve novel combinations of the control parameterization method, the timescaling transformation, and bilevel programming and binary relaxation techniques. We conclude the paper by discussing a number of switched system optimal control models arising in practical applications

LOFAR 144-MHz follow-up observations of GW170817

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 494, Issue 4, June 2020, Pages 5110–5117, ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by Advanced LIGO-Virgo. These data, with a central frequency of 144 MHz, were obtained with LOFAR, the Low-Frequency Array. The maximum elevation of the target is just 13.7 degrees when observed with LOFAR, making our observations particularly challenging to calibrate and significantly limiting the achievable sensitivity. On time-scales of 130-138 and 371-374 days after the merger event, we obtain 3$\sigma$ upper limits for the afterglow component of 6.6 and 19.5 mJy beam$^{-1}$, respectively. Using our best upper limit and previously published, contemporaneous higher-frequency radio data, we place a limit on any potential steepening of the radio spectrum between 610 and 144 MHz: the two-point spectral index $\alpha^{610}_{144} \gtrsim -2.5$. We also show that LOFAR can detect the afterglows of future binary neutron star merger events occurring at more favourable elevations.Peer reviewe

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Physician, organisational and patient characteristics explaining the use of angiotensin converting enzyme inhibitors in heart failure treatment: a multilevel study

OBJECTIVE: Heart failure treatment in general practice is not concordant with guideline recommendations. Insight into the key determinants at different levels is needed in order to improve care. The aim was to assess the influence of physician, organisational and patient characteristics on the treatment of chronic heart failure with angiotensin converting enzyme (ACE) inhibitors in primary care. METHODS: Physician and organisational data were collected by means of a questionnaire. Patient and treatment data were extracted from electronic medical records. Multilevel analysis was used to assess the effect of physician, organisational and patient factors on the treatment with ACE inhibitors in terms of prescription rate and dosage. RESULTS: Data from 735 randomly selected heart failure patients were extracted from the medical records of 95 general practitioners (GPs). Patients who visited a cardiologist or an outpatient heart failure clinic were more likely to receive an ACE inhibitor. In addition, relatively young patients, male patients and patients already using a diuretic were more likely to receive an ACE inhibitor. Furthermore, male patients and patients with concomitant hypertension were more likely to receive a higher dose of ACE inhibitor. GP characteristics did not determine whether CHF patients received ACE inhibitor treatment. CONCLUSION: The differences in ACE inhibitor prescribing seem to be linked more to patient than physician characteristics. Interventions to improve the quality of care should therefore focus on the treatment of specific patient groups. Specialised care, particularly through outpatient clinics, could lead to improvement in the use of ACE inhibitors

An educational programme for peer review groups to improve treatment of chronic heart failure and diabetes mellitus type 2 in general practice

Rationale, aims and objectives Peer review groups are considered helpful for quality improvement in primary care. An interactive educational programme for small peer groups was developed, focusing on the implementation of newly developed treatment guidelines. The aim is to evaluate the effect of the programme on adherence to treatment guidelines in general practice. Methods A cluster randomized trial using a balanced incomplete block design was used; one arm received a programme on treatment of chronic heart failure (CHF), the other on hypertension treatment in diabetes mellitus type 2 (T2DM). A random sample of 10 CHF and 10 T2DM patients per GP was drawn, for whom data were extracted from electronic patient records 1 years before and 6 months after the intervention. The outcomes were prescribing of ACE inhibitors, and antihypertensive treatment in T2DM. The effect was analysed separately for both programmes using multilevel regression models. Results All 27 peer review groups in one region in the Netherlands were randomized, of which 16 participated. No significant effects were observed in the CHF group or in the T2DM group. The opportunity for change was limited, as only 53% of the CHF patients and 60% of the T2DM patients had a contact with their GP between the intervention and follow-up measurement. Conclusion The peer review programme was not successful for changing the treatment of chronic patients, although the programme focused on dealing with barriers perceived by the participants. Not all problems perceived can be solved in a peer group discussion

Physician, organizational, and patient factors associated with suboptimal blood pressure mManagement in Type 2 diabetic patients in primary care

OBJECTIVE - To assess the quality of hypertension care in patients with type 2 diabetes in general practice and identify physician, organizational, and patient factors associated with sub-optimal care. RESEARCH DESIGN AND METHODS - Data from 895 randomly selected diabetic patients were extracted from the electronic medical records of 95 general practitioners. Physician and organizational characteristics were collected with a questionnaire. We conducted a multilevel analysis to identify associations with blood pressure registration, hypertension treatment, and achievement of target blood pressure levels. RESULTS - For 652 patients (73%), a blood pressure measurement was recorded in the last year. Of these patients, 132 (20%) reached a target level of 135/85 mmHg. In total, 595 patients were classified as having hypertension, of whom 192 received no treatment (32%), 193 received an ACE inbibitor (32%), and 210 received other antihypertensives. Patients visiting a diabetes facility, referred to a specialist, with a female general practitioner, or with a general practitioner with < less-than-or-equal-to >10 years work experience had better recordings of their blood pressure. Suboptimal treatment was higher in older patients and smoking patients. Treatment was better in patients with coronary comorbidity, hyperlipidemia, or those referred to a specialist. Not achieving the blood pressure target was related to older age of the patients CONCLUSIONS - Hypertension management of type 2 diabetic patients in primary care is suboptimal. Characteristics of general practitioners as well as additional care provided by a diabetes facility or a specialist are associated with better processes of care, but blood pressure outcomes are not as clearly related to these factors