Modelling and control of a high redundancy actuator

The high redundancy actuation concept is a completely new approach to fault tolerance, and it is important to appreciate that it provides a transformation of the characteristics of actuators so that the actuation performance (capability) degrades slowly rather than suddenly failing, even though individual elements themselves fail. This paper aims to demonstrate the viability of the concept by showing that a highly redundant actuator, comprising a relatively large number of actuation elements, can be controlled in such a way that faults in individual elements are inherently accommodated, although some degradation in overall performance will inevitably be found. The paper introduces the notion of fault-tolerant systems and the highly redundant actuator concept. Then a model for a two by two configuration with electro-mechanical actuation elements is derived. Two classical control approaches are then considered based on frequency domain techniques. Finally simulation results under a number of faults show the viability of the approach for fault accommodation without re-configuratio

Motion of Inertial Observers Through Negative Energy

Recent research has indicated that negative energy fluxes due to quantum coherence effects obey uncertainty principle-type inequalities of the form |\Delta E|\,{\Delta \tau} \lprox 1\,. Here $|\Delta E|$ is the magnitude of the negative energy which is transmitted on a timescale $\Delta \tau$. Our main focus in this paper is on negative energy fluxes which are produced by the motion of observers through static negative energy regions. We find that although a quantum inequality appears to be satisfied for radially moving geodesic observers in two and four-dimensional black hole spacetimes, an observer orbiting close to a black hole will see a constant negative energy flux. In addition, we show that inertial observers moving slowly through the Casimir vacuum can achieve arbitrarily large violations of the inequality. It seems likely that, in general, these types of negative energy fluxes are not constrained by inequalities on the magnitude and duration of the flux. We construct a model of a non-gravitational stress-energy detector, which is rapidly switched on and off, and discuss the strengths and weaknesses of such a detector.Comment: 18pp + 1 figure(not included, available on request), in LATEX, TUPT-93-

Cold Feedback in Cooling-Flow Galaxy Clusters

We put forward an alternative view to the Bondi-driven feedback between heating and cooling of the intra-cluster medium (ICM) in cooling flow galaxies and clusters. We adopt the popular view that the heating is due to an active galactic nucleus (AGN), i.e. a central black hole accreting mass and launching jets and/or winds. We propose that the feedback occurs with the entire cool inner region (5-30 kpc). A moderate cooling flow does exist here, and non-linear over-dense blobs of gas cool fast and are removed from the ICM before experiencing the next major AGN heating event. Some of these blobs may not accrete on the central black hole, but may form stars and cold molecular clouds. We discuss the conditions under which the dense blobs may cool to low temperatures and feed the black hole.Comment: 6 pages, no figures, to appear in the Proceedings of "Heating vs. Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching (Germany

Efficacy of psychological therapies in people with inflammatory bowel disease: a systematic review and meta-analysis

Background There is increasing evidence for an influence of the gut–brain axis on the natural history of inflammatory bowel disease (IBD). Psychological therapies could, therefore, have beneficial effects in individuals with IBD, but data are conflicting. We aimed to update our previous systematic review and meta-analysis to assess whether the inclusion of more randomised controlled trials (RCTs) showed any beneficial effects and whether these effects varied by treatment modality. Methods In this systematic review and meta-analysis, we searched MEDLINE, Embase, Embase Classic, PsychINFO, and the Cochrane Central Register of Controlled Trials from Jan 1, 2016, to April 30, 2023, for RCTs published in any language recruiting individuals aged 16 years or older with IBD that compared psychological therapy with a control intervention or treatment as usual. We pooled dichotomous data to obtain relative risks (RR) with 95% CIs of inducing remission in people with active disease or of relapse in people with quiescent disease at final follow-up. We pooled continuous data to estimate standardised mean differences (SMD) with 95% CIs in disease activity indices, anxiety scores, depression scores, stress scores, and quality-of-life scores at completion of therapy and at final follow-up. We pooled all data using a random-effects model. Trials were analysed separately according to whether they recruited people with clinically active IBD or predominantly individuals whose disease was quiescent. We conducted subgroup analyses by mode of therapy and according to whether trials recruited selected groups of people with IBD. We used the Cochrane risk of bias tool to assess bias at the study level and assessed funnel plots using the Egger test. We assessed heterogeneity using the I2 statistic. Findings The updated literature search identified a total of 469 new records, 11 of which met eligibility criteria. 14 studies were included from our previous meta-analysis published in 2017. In total, 25 RCTs were eligible for this meta-analysis, all of which were at high risk of bias. Only four RCTs recruited patients with active IBD; there were insufficient data for meta-analysis of remission, disease activity indices, depression scores, and stress scores. In patients with active IBD, psychological therapy had no benefit compared with control for anxiety scores at completion of therapy (two RCTs; 79 people; SMD –1·04, 95% CI –2·46 to 0·39), but did have significant benefit for quality-of-life scores at completion of therapy (four RCTs; 309 people; 0·68, 0·09 to 1·26), although heterogeneity between studies was high (I2=82%). In individuals with quiescent IBD, RR of relapse of disease activity was not reduced with psychological therapy (ten RCTs; 861 people; RR 0·83, 95% CI 0·62 to 1·12), with moderate heterogeneity (I2=60%), and the funnel plot suggested evidence of publication bias or other small study effects (Egger test p=0·046). For people with quiescent IBD at completion of therapy, there was no difference in disease activity indices between psychological therapy and control (13 RCTs; 1015 people; SMD –0·01, 95% CI –0·13 to 0·12; I2=0%). Anxiety scores (13 RCTs; 1088 people; –0·23, –0·36 to –0·09; 18%), depression scores (15 RCTs; 1189 people; –0·26, –0·38 to –0·15; 2%), and stress scores (11 RCTs; 813 people; –0·22, –0·42 to –0·03; 47%) were significantly lower, and quality-of-life scores (16 RCTs; 1080 people; 0·31, 0·16 to 0·46; 30%) were significantly higher, with psychological therapy versus control at treatment completion. Statistically significant benefits persisted up to final follow-up for depression scores (12 RCTs; 856 people; –0·16, –0·30 to –0·03; 0%). Effects were strongest in RCTs of third-wave therapies and in RCTs that recruited people with impaired psychological health, fatigue, or reduced quality of life at baseline. Interpretation Psychological therapies have beneficial, short-term effects on anxiety, depression, stress, and quality-of-life scores, but not on disease activity. Further RCTs in selected groups are needed to establish the place for such therapies in IBD care

A Diagnosis of Irritable Bowel Syndrome Using Rome IV Criteria and Limited Investigations is Durable in Secondary Care

Background & Aims Irritable bowel syndrome (IBS) is a positive diagnosis, made using symptom-based criteria and limited, judicious, investigation. However, this may lead to uncertainty on the part of clinicians regarding potential for a missed diagnosis of organic gastrointestinal disease. Few studies have examined durability of a diagnosis of IBS, and none have used the current gold standard to diagnose IBS, the Rome IV criteria. Methods We collected complete symptom data from 373 well-characterized adults meeting Rome IV criteria for IBS referred to a single UK clinic between September 2016 and March 2020. All patients underwent relatively standardized work-up to exclude relevant organic disease before diagnosis. We followed these individuals up to December 2022, assessing rates of rereferral, reinvestigation, and missed organic gastrointestinal disease. Results During a mean follow-up of 4.2 years per patient (total follow-up in all patients, 1565 years), 62 (16.6%) patients were rereferred. Of these, 35 (56.5%) were rereferred for IBS and 27 (43.5%) for other gastrointestinal symptoms. Among the 35 rereferred with IBS this was caused by a change in symptoms in only 5 (14.3%). Reinvestigation was undertaken in 21 (60.0%) of 35 rereferred with IBS and 22 (81.5%) of 27 rereferred with other symptoms (P = .12). Only 4 (9.3% of those reinvestigated and 1.1% of the entire cohort) new cases of relevant organic disease, which may have been responsible for IBS symptoms at baseline, were identified (1 case of chronic calcific pancreatitis among those rereferred with IBS and 1 case each of inflammatory bowel disease–unclassified, moderate bile acid diarrhea, and small bowel obstruction among those rereferred with other gastrointestinal symptoms). Conclusions Despite rereferral for gastrointestinal symptoms among 1 in 6 patients overall, with almost 10% rereferred with ongoing IBS symptoms, and substantial reinvestigation rates, missed organic gastrointestinal disease occurred in only 1%. A diagnosis of Rome IV IBS after limited investigation is safe and durable

Novel symptom clusters predict disease impact and healthcare utilisation in inflammatory bowel disease: Prospective longitudinal follow-up study

Background Predicting adverse disease outcomes and high-volume users of healthcare amongst patients with inflammatory bowel disease (IBD) is difficult. Aims The aim of this study is to use latent class analysis to create novel clusters of patients and to assess whether these predict outcomes during 6.5 years of longitudinal follow-up. Methods Baseline demographic features, disease activity indices, anxiety, depression, and somatoform symptom-reporting scores were recorded for 692 adults. Faecal calprotectin (FC) was analysed at baseline in 348 (50.3%) patients (<250 mcg/g defined biochemical remission). Using baseline gastrointestinal and psychological symptoms, latent class analysis identified specific patient clusters. Rates of glucocorticosteroid prescription or flare, escalation, hospitalisation, or intestinal resection were compared between clusters using multivariate Cox regression. Results A three-cluster model was the optimum solution; 132 (19.1%) patients had below-average gastrointestinal and psychological symptoms (cluster 1), 352 (50.9%) had average levels of gastrointestinal and psychological symptoms (cluster 2), and 208 (30.1%) had the highest levels of both gastrointestinal and psychological symptoms (cluster 3). Compared with cluster 1, cluster 3 had significantly increased risk of flare or glucocorticosteroid prescription (hazard ratio (HR): 2.13; 95% confidence interval (CI): 1.46–3.10), escalation (HR: 1.92; 95% CI: 1.34–2.76), a composite of escalation, hospitalisation, or intestinal resection (HR: 2.05; 95% CI: 1.45–2.88), or any of the endpoints of interest (HR: 2.06; 95% CI: 1.45–2.93). Healthcare utilisation was highest in cluster 3. Conclusions Novel model-based clusters identify patients with IBD at higher risk of adverse disease outcomes who are high-volume users of healthcare

Utility of irritable bowel syndrome subtypes and most troublesome symptom in predicting disease impact and burden

Background Little is known about the characteristics of individuals with irritable bowel syndrome (IBS) according to stool subtype or the most troublesome symptom reported by the individual, or whether these are useful in predicting the impact of IBS. Methods We collected demographic, gastrointestinal, and psychological symptoms, healthcare usage and direct healthcare costs, impact on work and activities of daily living, and quality of life data from individuals with Rome IV-defined IBS. Key Results We recruited 752 people with Rome IV IBS. Individuals with IBS-D reported a poorer disease-specific quality of life than those with IBS-C or IBS-M (mean (SD) IBS-QOL 45.3 (23.0) for IBS-D, vs. 52.3 (19.9) for IBS-C, vs. 49.4 (22.0) for IBS-M, p = 0.005). Mean (SD) IBS-QOL scores were also lower amongst those who reported diarrhea (44.8 (22.3)) or urgency (44.6 (22.3)) as their most troublesome symptom, compared with those reporting abdominal pain (52.2 (22.9)), constipation (49.5 (21.8)), or abdominal bloating or distension (50.4 (21.3)). However, there were no differences in mean EQ-5D scores, IBS severity, levels of anxiety, depression, somatoform symptom-reporting, or gastrointestinal symptom-specific anxiety. Direct healthcare costs of IBS were similar across all subtypes and all most troublesome symptom groups, although some differences in work productivity and social leisure activities were detected. Conclusions and Inferences There appears to be limited variation in the characteristics of individuals with Rome IV IBS based on both stool subtypes and most troublesome symptom reported, suggesting that gastrointestinal symptoms alone have limited ability to predict disease impact and burden

Skin health in northern Australia

Achieving healthy skin requires the prevention of infectious diseases that affect the skin. Prevention activities range from environmental health improvements to address inequities in living situations, through to community-wide treatment programs to reduce transmission and improve skin health. In this paper we discuss the pathogens that cause and conditions that arise when skin is infected, the burden of disease in northern Australia, and some of the current research underway to address this high burden, which predominantly affects remote-living Aboriginal and Torres Strait Islander children and families

Of Bounces, Branes and Bounds

Some recent studies have considered a Randall-Sundrum-like brane world evolving in the background of an anti-de Sitter Reissner-Nordstrom black hole. For this scenario, it has been shown that, when the bulk charge is non-vanishing, a singularity-free ``bounce'' universe will always be obtained. However, for the physically relevant case of a de Sitter brane world, we have recently argued that, from a holographic (c-theorem) perspective, such brane worlds may not be physically viable. In the current paper, we reconsider the validity of such models by appealing to the so-called ``causal entropy bound''. In this framework, a paradoxical outcome is obtained: these brane worlds are indeed holographically viable, provided that the bulk charge is not too small. We go on to argue that this new finding is likely the more reliable one.Comment: 15 pages, Revtex; references added and very minor change

On the chirality of quark modes

A model for the QCD vacuum based on a domainlike structured background gluon field with definite duality attributed to the domains has been shown elsewhere to give confinement of static quarks, a reasonable value for the topological susceptibility and indications that chiral symmetry is spontaneously broken. In this paper we study in detail the eigenvalue problem for the Dirac operator in such a gluon mean field. A study of the local chirality parameter shows that the lowest nonzero eigenmodes possess a definite mean chirality correlated with the duality of a given domain. A probability distribution of the local chirality qualitatively reproduces histograms seen in lattice simulations.Comment: RevTeX4, 5 figures, 14 page