A search for rapid optical variability in radio-quiet quasars

The detection of rapid variability on a time-scale of hours in radio-quiet quasars (RQQSOs) could be a powerful discriminator between starburst, accretion disc and relativistic jet models of these sources. This paper contains an account of a dedicated search for rapid optical variability in RQQSOs. The technique used differential photometry between the RQQSO and stars in the same field of view of the CCD. The 23 RQQSOs that were observed all have high luminosities (-27 1. The total amount of observation time was about 60 hours and these observations are part of an ongoing programme, started in September 1990, to search for rapid variability in RQQSOs. No evidence for short-term variability greater than about 0.1 magnitudes was detected in any of the 23 sources, however long-term variability was recorded for the radio-quiet quasar PG 2112+059. The finding charts are included here because they identify the RQQSO and the reference stars used in the photometry, and hence are available for use by other observers.Comment: Accepted for publication in A&AS. 10 pages, 3 figures. Figure 1 (finding charts) available by anonymous ftp from: bermuda.ucd.ie:/pub/outgoing/charts.eps.g

Hyperbolic Metamaterial Resonator-Antenna Scheme for Large, Broadband Emission Enhancement and Single Photon Collection

We model the broadband enhancement of single-photon emission from color centres in silicon carbide nanocrystals coupled to a planar hyperbolic metamaterial, HMM resonator. The design is based on positioning the single photon emitters within the HMM resonator, made of a dielectric index-matched with silicon-carbide material. The broadband response results from the successive resonance peaks of the lossy Fabry Perot structure modes arising within the high-index HMM cavity. To capture this broadband enhancement in the single photon emitters spontaneous emission, we placed a simple gold based cylindrical antenna on top of the HMM resonator. We analyzed the performance of this HMM coupled antenna structure in terms of the Purcell enhancement, quantum efficiency, collection efficiency and overall collected photon rate. For perpendicular dipole orientation relative to the interface, the HMM coupled antenna resonator leads to a significantly large spontaneous emission enhancement with Purcell factor of the order of 250 along with a very high average total collected photon rate, CPR of about 30 over a broad emission spectrum, 700 nm to 1000 nm. The peak CPR increases to about 80 at 900 nm, corresponding to the emission of silicon-carbide quantum emitters. This is a state of the art improvement considering the previous computational designs have reported a maximum average CPR of 25 across the nitrogen-vacancy centre emission spectrum, 600 nm to 800 nm with the highest value being about 40 at 650 nm

Stratigraphy and Chronology of Karst Features on Rodriguez Island, Southwestern Indian Ocean

This publication has been made available with the permission of the National Speleological Society (www.caves.org). The attached file is the published version of the article

Optimal Estimation of Interviewer Effects for Binary Response Variables through Partial Interpenetration

Estimates of sampling variance underestimate the variance of survey estimates when there are strong interviewer effects. However, interviewer effects are rarely considered in complex field surveys due to the high costs involved with adapting an interpenetrating design to produce estimates of them. This paper demonstrates how interviewer effects can be estimated by taking a sample of interviewers using the technique of partial interpenetration. The partial interpenetration approach is developed to produce cost-optimal survey designs for the estimation of the interviewer effect and population means for non-linear response variables

The experience of older people with multimorbidity during the COVID-19 pandemic

The risk of severe COVID-19 disease is known to be higher in older individuals with multiple long-term health conditions (multimorbidity). In this briefing, we report the latest findings from the English Longitudinal Study of Ageing COVID-19 Substudy on the experiences of older people with multimorbidity during the pandemic. Not all people with multimorbidity would be classified as clinically vulnerable. We found that 35% of older individuals with multimorbidity were instructed by the NHS or their GP to shield (staying at home at all times and avoiding any face-to-face contact) on account of their vulnerability, and the majority were largely compliant with this advice. Relative to study members without multimorbidity, respondents with multimorbidity were more likely to report poor sleep quality, eating less, and being worried about not having enough food and other essentials. Unhealthy behaviours (sitting time, physical inactivity etc), poor mental health, and loneliness deteriorated considerably during the lockdown and in the two months following the lockdown. Access to medications among people with multimorbidity was not a problem, however, a fifth of individuals with multimorbidity did not have access to community health, social care services and support from other health professionals (e.g., dentist, podiatrist). When considering policies which advise people to shield or self-isolate because of their COVID-19 risk, it is important for policymakers to acknowledge that older people with multiple long-term health conditions are at higher risk of experiencing greater mental distress and worry, of engaging in unhealthy behaviours and are less likely to access health services when needed; all these factors together could potentially influence disease progression

Attacking Group Protocols by Refuting Incorrect Inductive Conjectures

Automated tools for finding attacks on flawed security protocols often fail to deal adequately with group protocols. This is because the abstractions made to improve performance on fixed 2 or 3 party protocols either preclude the modelling of group protocols all together, or permit modelling only in a fixed scenario, which can prevent attacks from being discovered. This paper describes Coral, a tool for finding counterexamples to incorrect inductive conjectures, which we have used to model protocols for both group key agreement and group key management, without any restrictions on the scenario. We will show how we used Coral to discover 6 previously unknown attacks on 3 group protocols

Nutritional management of chronic renal failure by dietitians - the South African experience

Objective: The objective of this descriptive study was to assess the practices of South African dietitians regarding the dietary treatment of patients with chronic renal failure.Subjects and design: A questionnaire was mailed to 600 randomly selected dietitians registered with the Health Professions Council of South Africa. Practices were compared to international standards for pre-dialysis, haemodialysis (HD) and peritoneal dialysis (PD) patients.Results: A 26% response rate was obtained, with only 28% of these dietitians indicating that they counsel renal patients. The majority of dietitians met the international dietary recommendations, but a substantial number deviated from them. This was especially evident in PD patients, where the deviation ranged from 20% (4 dietitians) in the case of energy and phosphate, to 55% (11 dietitians) in the case of calcium. Parameters used for the assessment of nutritional status included body mass index (45% of dietitians), serum albumin (44%), clinical examinations (43%), bioelectrical impedance (37%) and diet history (36%). Methods used to monitor dietary compliance included biochemistry, dietary history, anthropometric measurements and clinical investigation. The most frequently used approaches in the management of protein-energy malnutrition included supplemental drinks (86%) and dietary enrichment at household level (76%).Conclusion: Although the majority of dietitians met international standards for most nutrients, there was some variation and uncertainty. Ongoing education will enable South African dietitians to treat renal patients competently and with confidence.South African Journal of Clinical Nutrition Vol. 18(2) 2005: 60-6

Difficulties in Testing for Covarion-Like Properties of Sequences under the Confounding Influence of Changing Proportions of Variable Sites

The covarion (COV)-like properties of sequences are poorly described and their impact on phylogenetic analyses poorly understood. We demonstrate using simulations that, under an evolutionary model where the proportion of variable sites changes in nonadjacent lineages, log likelihood values for rates across site (RAS) and COV models become similar, making models difficult to distinguish. Further, although COV and RAS models provide a great improvement in likelihood scores over a homogeneous model with these simulated data, reconstruction accuracy of tree building is low, suggesting caution when it is suspected that proportions of variable sites differ in different evolutionary lineages. We study the performance of a recently developed contingency test that detects the presence of COV-type evolution modified for protein data. We report that if proportions of variable sites (pvar) change in a lineage-specific manner such that their distributions in different lineages become sufficiently nonoverlapping, then the contingency test can incorrectly suggest a homogeneous model. Also of concern is the possibility of different proportions of variable sites between the groups being studied. In a study of chloroplast proteins, interpretation of the test is found to be susceptible to different partitioning of taxon groups, making the test very subjective in its implementation. Extreme intergroup differences in the extent of divergence and difference in proportions of variable sites could be contributing to this effect