Design of high-area-ratio nozzle contours using circular arcs

A method using circular arcs to generate the divergence contour in a supersonic nozzle is presented. Comparison of the arc-based geometry with existing nozzle contours demonstrated that an average decrease in axial length of 7.5% can be expected when the arc-based design method is applied to a core stage nozzle. Two arc-based and conventional nozzles were evaluated numerically across the pressure operating range of a core stage engine to compare calculated thrust and separation characteristics with existing data. The length-weighted thrust coefficient was increased by 0.3–1.8% in the arc-based design in both configurations. Separated flow characteristics were compared using contours of Mach number and static pressure distributions, which suggested equivalent side loading in the arc-based nozzle at separated flow conditions. The result indicates that a geometric advantage independent of thrust may be achieved when the arc-based method is applied to high-area-ratio nozzle contour design

Computational simulation of an altitude adaptive nozzle concept

A computational analysis of an annular converging-diverging (CD) and an altitude adaptive expansion-deflection (ED) nozzle is presented. Numerical results were generated using a 2D axisymmetric, pressure-coupled solver in conjunction with the Spalart-Allmaras turbulence closure model and second order spatial discretisation schemes. Results were recorded over a theoretical altitude range and compared to experimental static pressure readings and schlieren images. The correlation between numerical and experimental static pressure values was high for all cases. Comparison of schlieren imagery outlined the large variety of flow regions within the ED nozzle flow field. The interactions between these regions were highly sensitive to turbulence and reinforced that conventional inviscid analytical techniques are unable to accurately describe behaviour within the ED nozzle flow field. The results highlight the salient effect of viscous effects within the ED nozzle flow field and justify a continued approach utilising computational fluid dynamics to increase understanding of the ED nozzle concept

Suppressing restricted shock separation in a subscale rocket nozzle using contour geometry

The use of a thrust-optimized contour (TOC) for the supersonic nozzle in a rocket engine will inherently maximize the propulsive efficiency and payload capacity of the entire launch system. A TOC can be approximated using a skewed parabola, commonly referred to as a thrust-optimized parabola (TOP), and the TOP contour can be manipulated to avoid undesirable flow separation during low-altitude operation by increasing the static wall pressure at the expense of thrust (approximately 0.1 0.2%). For this reason, a TOP design is often used in nozzles with a high area ratio, such as those used in the Vulcain and Vulcain 2 corestage engines, and suggests that ensuring full-flowing operation at low-altitude conditions can be considered a nozzle design requirement. Unfortunately, any thrust-optimized nozzle may excite an undesirable shift between a free shock separation (FSS) and restricted shock separation (RSS) mode during engine startup and shutdown. The shift between an FSS and an RSS flowregimewas first noticed during operation of the high-area-ratio J2-S engine, and the RSS condition consequently was deemed responsible for inducing high structural loading to the nozzle walls. However, it was later found that the highest levels of side loading were, in fact, caused by the transition process to and from the RSS flow condition, as opposed to the RSS phenomenon itself. Because the precise flow mechanisms that drive the transition to and from the RSS condition are still not fully understood, the structural loading that occurs as a result of RSS appears to currently be accepted as a design consideration in core-stage rocket nozzles. A nozzle contour that was capable of suppressing the RSS flow condition itself would inherently prevent the transition to and from RSS and, therefore, decrease the structural loading that occurs during these transition phases. For a net benefit to be realized, the resulting nozzle must produce an equal or greater thrust coefficient compared to the existing design, as well as avoid flow separation during low-altitude operation. In this paper, a set of equivalent thrust-optimized nozzle contours have been produced using an arc-based design method to determine if the suppression of RSS could be achieved by manipulating the contour geometry. The subscale Volvo S1 TOP nozzle that was designed by Volvo Aero Corporation (now GKN Aerospace Engine Systems) was selected as the test case due to the availability of experimental data that captures the transition from FSS to RSS and to ensure that a positive result may be applicable to a full-scale rocket engine, because this nozzle has been shown to possess equivalent flow characteristics to the core-stage Vulcain engine nozzle

Diagnostic accuracy of OCTA and OCT for myopic choroidal neovascularisation: a systematic review and meta-analysis

Background/Objectives: The purpose of this project was to systematically review and meta-analyse studies assessing the diagnostic accuracy of optical coherence tomography angiography (OCTA) and optical coherence tomography (OCT) for myopic choroidal neovascularisation (mCNV). Fluorescein angiography (FA) was accepted as the reference standard. Methods: PUBMED and EMBASE were searched from inception to March 2021 for studies evaluating the test accuracy of OCTA and/or OCT for diagnosing mCNV. The Preferred Reporting Items for Systematic Reviews and Meta-analyses of Diagnostic Test Accuracy Studies guideline was followed, and the Grading of Recommendations, Assessment, Development and Evaluation approach was used to frame clinical recommendations. Pooled estimates of test accuracy were obtained using a bivariate model. Results: Of 410 studies assessed for eligibility, 3 studies were identified that compared OCTA to FA and 3 studies were identified that compared spectral domain (SD) OCT to FA. All studies had at least one major methodological flaw leading to an overall high risk of bias. On meta-analysis, the pooled sensitivity of OCTA was 0.89 (95% CI 0.78–0.94) and pooled specificity was 0.93 (95% CI 0.79–0.98). The pooled sensitivity of SD-OCT was 0.99 (95% CI 0.91–1.00). Due to uncertainty in individual studies, the pooled specificity of SD-OCT could not be estimated. Conclusions: OCTA can reliably diagnose mCNV in clinically suspected patients, however, SD-OCT may not reliably establish a positive diagnosis of mCNV. Future large, prospective studies with improvements in conduct and reporting are needed to strengthen these clinical recommendations

The Secrets of African Managerial Success

Summary Summary It has become customary to despair at the quality of African public sector management, and to attribute the problem to an inhospitable social and political context. Yet we can discover success stories even in the usual sector in which failure is most prevalent. By looking at these cases we can attempt to discover the ‘secret of success’ and thus some indications about how to deal with less successful cases. This article attempts to do this by looking at the life and career histories of four prominent Kenyan officials who were able to endow success on many enterprises that they led. It concludes that the way in which they were able to maintain the autonomy of their organisations was by establishing effective links with the political leadership; it explains how their commitment to good administration derived from and was reinforced by a strong sense of professional vocation; how their capacity to raise resources was reinforced by their ability to maintain the support of donor agencies; how they sought effective methods of balancing Africanisation against the need to retain expatriate staff; and how their willingness to take risks depended upon their ability to make a good living outside the state service if need be. Resumé Resumé Les Secrets du Succès du Management africain Il est devenu courant de désespérer de la qualité du management du secteur publique africain, et d'attribuer le problème à un contexte politique et social défavorable. Pourtant on peut trouver des succès même dans le secteur rural, où normalement l'échec est le plus fréquent. En analysant ces cas, nous pouvons essayer de découvrir les ‘secrets du succès’ et ainsi trouver quelques indications sur la manière de résoudre ceux qui ont moins réussi. Cet article se propose de présenter cette analyse en s'appuyant sur un exposé de la vie et la carrière de quatre important officiels du Kenya, qui ont mené au succès bien des projets qu'ils ont dirigés. Il analyse la manière dont ils ont réussi à maintenir l'autonomie de leurs organisations en établissant des liens efficaces avec les dirigeants politiques; aussi comment leur engagement pour une bonne administration provenait et était renforcée par un sentiment profond de vocation professionelle; comment leur aptitude à augmenter les resources a été renforcée par leur compétence dans le maintien de leur soutien Ils ont recherché des méthodes effectives pour équilibrer l'africanisation et le besoin de conserver le personnel étrange; Ils ont aussi recherché comment le fait qu'ils étaient disposés à prendre des risques dépendait de leur aptitude à gagner leur vie en dehors de leur fonction publique si cela était nécessaire

Genetic Diversity of PCR-Positive, Culture-Negative and Culture-Positive Mycobacterium ulcerans Isolated from Buruli Ulcer Patients in Ghana.

Culture of Mycobacterium ulcerans from Buruli ulcer patients has very low sensitivity. Thus confirmation of M. ulcerans infection is primarily based on PCR directed against IS2404. In this study we compare the genotypes obtained by variable number of tandem repeat analysis of DNA from IS2404-PCR positive cultures with that obtained from IS2404 positive, culture-negative tissue. A significantly greater genetic heterogeneity was found among culture-negative samples compared with that found in cultured strains but a single genotype is over-represented in both sample sets. This study provides evidence that both the focal location of bacteria in a lesion as well as differences in the ability to culture a particular genotype may underlie the low sensitivity of culture. Though preliminary, data from this work also suggests that mycobacteria previously associated with fish disease (M. pseudoshottsii) may be pathogenic for humans

A systematic review of techniques and interventions for improving adherence to inclusion and exclusion criteria during enrolment into randomised controlled trials

<p>Abstract</p> <p>Background</p> <p>Enrolment of patients into a randomised controlled trial (RCT) in violation of key inclusion or exclusion criteria, may lead to excess avoidable harm. The purpose of this paper was to systematically identify and review techniques and interventions proven to prevent or avoid inappropriate enrolment of patients into RCTs.</p> <p>Methods</p> <p>EMBASE, MEDLINE, Cochrane Database of Systematic Reviews, Cochrane Methodology Register, online abstract repositories, and conference websites were searched. Experts were contacted and bibliographies of retrieved papers hand-searched. The search cut-off date was 31 August 2009.</p> <p>Results</p> <p>No primary publications were found. We identified one study in the grey literature (conference abstracts and presentations) reporting the results of an evaluation of the effectiveness of an intervention designed to prevent or avoid inappropriate enrolment of patients into an RCT. In the context of a multicentre trial, use of a dummy enrolment run-in phase was shown to reduce enrolment errors significantly (<it>P </it>< 0.001), from 16.1% during the run-in phase to < 1% after trial initiation.</p> <p>Conclusions</p> <p>Our systematic search yielded only one technique or intervention shown to improve adherence to eligibility criteria during enrolment into RCTs. Given the potential harm involved in recruiting patients into a clinical trial in violation of key eligibility criteria, future research is needed to better inform those conducting clinical trials of how best to prevent enrolment errors</p

Determinants of response to a parent questionnaire about development and behaviour in 3 year olds: European multicentre study of congenital toxoplasmosis.

Background: We aimed to determine how response to a parent-completed postal questionnaire measuring development, behaviour, impairment, and parental concerns and anxiety, varies in different European centres. Methods: Prospective cohort study of 3 year old children, with and without congenital toxoplasmosis, who were identified by prenatal or neonatal screening for toxoplasmosis in 11 centres in 7 countries. Parents were mailed a questionnaire that comprised all or part of existing validated tools. We determined the effect of characteristics of the centre and child on response, age at questionnaire completion, and response to child drawing tasks. Results: The questionnaire took 21 minutes to complete on average. 67% (714/1058) of parents responded. Few parents (60/1058) refused to participate. The strongest determinants of response were the score for organisational attributes of the study centre (such as direct involvement in follow up and access to an address register), and infection with congenital toxoplasmosis. Age at completion was associated with study centre, presence of neurological abnormalities in early infancy, and duration of prenatal treatment. Completion rates for individual questions exceeded 92% except for child completed drawings of a man (70%), which were completed more by girls, older children, and in certain centres. Conclusion: Differences in response across European centres were predominantly related to the organisation of follow up and access to correct addresses. The questionnaire was acceptable in all six countries and offers a low cost tool for assessing development, behaviour, and parental concerns and anxiety, in multinational studies

Thalamic inputs to dorsomedial striatum are involved in inhibitory control: evidence from the five-choice serial reaction time task in rats

Rationale Corticostriatal circuits are widely implicated in the top-down control of attention including inhibitory control and behavioural flexibility. However, recent neurophysiological evidence also suggests a role for thalamic inputs to striatum in behaviours related to salient, reward-paired cues. Objectives Here, we used designer receptors exclusively activated by designer drugs (DREADDs) to investigate the role of parafascicular (Pf) thalamic inputs to the dorsomedial striatum (DMS) using the five-choice serial reaction time task (5CSRTT) in rats. Methods The 5CSRTT requires sustained attention in order to detect spatially and temporally distributed visual cues and provides measures of inhibitory control related to impulsivity (premature responses) and compulsivity (perseverative responses). Rats underwent bilateral Pf injections of the DREADD vector, AAV2-CaMKIIa-HA-hM4D(Gi)-IRES-mCitrine. The DREADD agonist, clozapine N-oxide (CNO; 1 μl bilateral; 3 μM) or vehicle, was injected into DMS 1 h before behavioural testing. Task parameters were manipulated to increase attention load or reduce stimulus predictability respectively. Results We found that inhibition of the Pf-DMS projection significantly increased perseverative responses when stimulus predictability was reduced but had no effect on premature responses or response accuracy, even under increased attentional load. Control experiments showed no effects on locomotor activity in an open field. Conclusions These results complement previous lesion work in which the DMS and orbitofrontal cortex were similarly implicated in perseverative responses and suggest a specific role for thalamostriatal inputs in inhibitory control