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We derive and numerically validate a low-order oscillator model to capture the stochastic dynamics of a prototypical thermoacoustic system (a Rijke tube) undergoing a subcritical Hopf bifurcation in the presence of additive noise. We find that on the fixed-point branch before the bifurcation, the system is dominated by the first duct mode, and the Fokker-Planck solution for the first Galerkin mode can adequately predict the stochastic dynamics of the overall system. We also find that this analytical framework predicts well the dominant mode on the limit-cycle branch, but underperforms in the hysteretic bistable zone where the role of nonlinearities is more pronounced. Besides offering new insights into stochastic thermoacoustic behavior, this study shows that an analytical framework based on the Fokker-Planck equation can facilitate the early detection of thermoacoustic instabilities in a Rijke-tube model subjected to noise.
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We numerically explore the two-dimensional, incompressible, isothermal flow through a wavy channel, with a focus on how the channel geometry affects the routes to chaos at Reynolds numbers between 150 and 1000. We find that (i) the period-doubling route arises in a symmetric channel, (ii) the Ruelle-Takens-Newhouse route arises in an asymmetric channel, and (iii) the type-II intermittency route arises in both asymmetric and semiwavy channels. We also find that the flow through the semiwavy channel evolves from a quasiperiodic torus to an unstable invariant set (chaotic saddle), before eventually settling on a period-1 limit-cycle attractor. This study reveals that laminar channel flow at elevated Reynolds numbers can exhibit a variety of nonlinear dynamics. Specifically, it highlights how breaking the symmetry of a wavy channel can not only influence the critical Reynolds number at which chaos emerges, but also diversify the types of bifurcation encountered en route to chaos itself.
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Nader Karimi, Larry K. B. Li, Manosh C. Paul, Mohammad Hossein Doranehgard and Freshteh Sotoudeh introduce the RSC Advances themed issue on Advances in Sustainable Hydrogen Energy.
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Reservoir computing is a powerful tool for forecasting turbulence because its simple architecture has the computational efficiency to handle high-dimensional systems. Its implementation, however, often requires full state-vector measurements and knowledge of the system nonlinearities. We use nonlinear projector functions to expand the system measurements to a high dimensional space and then feed them to a reservoir to obtain forecasts. We demonstrate the application of such reservoir computing networks on spatiotemporally chaotic systems, which model several features of turbulence. We show that using radial basis functions as nonlinear projectors enables complex system nonlinearities to be captured robustly even with only partial observations and without knowing the governing equations. Finally, we show that when measurements are sparse or incomplete and noisy, such that even the governing equations become inaccurate, our networks can still produce reasonably accurate forecasts, thus paving the way towards model-free forecasting of practical turbulent systems.
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We numerically explore the quenching and amplification of self-excited thermoacoustic oscillations in two nonidentical Rijke tubes interacting via time-delay and dissipative coupling. On applying either type of coupling separately, we find that the presence of nonidentical heater powers can shrink the regions of amplitude death in both oscillators, while producing new regions of amplitude amplification in the weaker oscillator. We find that the magnitude of amplitude amplification grows with the heater power mismatch and with the total power input. These effects are also present when both types of coupling are applied simultaneously. This study highlights the critical role that nonidentical thermal loads can play in determining the amplitude response of coupled thermoacoustic systems, facilitating the design of control strategies for coupled oscillatorlike devices such as gas turbines.
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Background: PRECISE-DYAD is an observational cohort study of mother-child dyads running in urban and rural communities in The Gambia and Kenya. The cohort is being followed for two years and includes uncomplicated pregnancies and those that suffered pregnancy hypertension, fetal growth restriction, preterm birth, and/or stillbirth. Methods: The PRECISE-DYAD study will follow up ~4200 women and their children recruited into the original PRECISE study. The study will add to the detailed pregnancy information and samples in PRECISE, collecting additional biological samples and clinical information on both the maternal and child health.Women will be asked about both their and their child's health, their diets as well as undertaking a basic cardiology assessment. Using a case-control approach, some mothers will be asked about their mental health, their experiences of care during labour in the healthcare facility. In a sub-group, data on financial expenditure during antenatal, intrapartum, and postnatal periods will also be collected. Child development will be assessed using a range of tools, including neurodevelopment assessments, and evaluating their home environment and quality of life. In the event developmental milestones are not met, additional assessments to assess vision and their risk of autism spectrum disorders will be conducted. Finally, a personal environmental exposure model for the full cohort will be created based on air and water quality data, combined with geographical, demographic, and behavioural variables. Conclusions: The PRECISE-DYAD study will provide a greater epidemiological and mechanistic understanding of health and disease pathways in two sub-Saharan African countries, following healthy and complicated pregnancies. We are seeking additional funding to maintain this cohort and to gain an understanding of the effects of pregnancies outcome on longer-term health trajectories in mothers and their children.
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We use a low-order oscillator model to investigate the mutual synchronization of a thermoacoustic system consisting of two turbulent lean-premixed combustors coupled via a cross-talk tube. The model consists of two Van der Pol (VDP) oscillators coupled via dissipative and time-delay terms. We show that, despite its simplicity, the model can reproduce many of the synchronization phenomena observed experimentally, such as amplitude death, desynchronization (quasiperiodicity), synchronization (phase locking), and nonlinear energy pumping from a limit-cycle mode to a damped mode. This study shows that the mutual synchronization dynamics of a turbulent thermoacoustic system can be reproduced with just a simple coupled VDP model. This suggests that such a model could be used to identify new strategies for quenching limit-cycle oscillations in turbulent thermoacoustic systems, such as gas turbines and rocket engines.
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OBJECTIVES: To evaluate community-based health workers' ability to identify cases of hypertension in pregnancy, safely deliver methyldopa and magnesium sulphate and make referrals when appropriate. STUDY DESIGN: This was part of Nigeria Community-Level Interventions for Pre-eclampsia (CLIP) cluster randomized controlled trial (NCT01911494). Community-based Health Workers (CHW) recruited pregnant women from five Local Government Areas (clusters) and used mobile health aid for clinical assessment of pre-eclampsia. MAIN OUTCOME MEASURES: The primary outcome was the number of adverse events that occurred after the administration of magnesium sulphate and/or methyldopa to pregnant women by CHWs. FINDINGS: Of 8790 women receiving mobile health-guided care, community-based health workers in Nigeria provided 309 women with hypertension (4.2% of delivered women), and safely administered 142 doses of intramuscular magnesium sulphate. Community Heath Extension Workers (CHEWs) and nurses gave fifty-two and sixty-seven doses of intramuscular magnesium sulphate respectively, twenty-three doses were given by other health care workers (midwives, community health officers, health assistants). The high rate of administration by nurses can be explained by turf protection as well as their seniority within the health system. Also, CHEWs and nurses gave 124 doses of oral methyldopa and 126 urgent referrals were completed. There were no complications related to administration of treatment or referral. INTERPRETATION: These findings demonstrate the ability of community-based health workers to safely administer methyldopa and intramuscular magnesium sulphate. The use of task-sharing, therefore, could drastically reduce the three delays (triage, transport and treatment) associated with high maternal mortality and morbidity in rural communities in low- and middle-income countries.
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Antihypertenseurs/usage thérapeutique , Compétence clinique , Services de santé communautaires/normes , Pré-éclampsie/prévention et contrôle , Adolescent , Adulte , Antihypertenseurs/administration et posologie , Référenciation , Femelle , Humains , Sulfate de magnésium/administration et posologie , Sulfate de magnésium/usage thérapeutique , Méthyldopa/effets indésirables , Méthyldopa/usage thérapeutique , Adulte d'âge moyen , Nigeria , Grossesse , Jeune adulteRÉSUMÉ
In less-resourced settings, adverse pregnancy outcome rates are unacceptably high. To effect improvement, we need accurate epidemiological data about rates of death and morbidity, as well as social determinants of health and processes of care, and from each country (or region) to contextualise strategies. The PRECISE database is a unique core infrastructure of a generic, unified data collection platform. It is built on previous work in data harmonisation, outcome and data field standardisation, open-access software (District Health Information System 2 and the Baobab Laboratory Information Management System), and clinical research networks. The database contains globally-recommended indicators included in Health Management Information System recording and reporting forms. It comprises key outcomes (maternal and perinatal death), life-saving interventions (Human Immunodeficiency Virus testing, blood pressure measurement, iron therapy, uterotonic use after delivery, postpartum maternal assessment within 48 h of birth, and newborn resuscitation, immediate skin-to-skin contact, and immediate drying), and an additional 17 core administrative variables for the mother and babies. In addition, the database has a suite of additional modules for 'deep phenotyping' based on established tools. These include social determinants of health (including socioeconomic status, nutrition and the environment), maternal co-morbidities, mental health, violence against women and health systems. The database has the potential to enable future high-quality epidemiological research integrated with clinical care and discovery bioscience.
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Santé infantile , Santé maternelle , Maladies du placenta , Collecte de données , Femelle , Humains , Nourrisson , Nouveau-né , Grossesse , Prise en charge prénatale , EnregistrementsRÉSUMÉ
Low-emissions can-annular gas turbines are prone to develop low-frequency self-excited thermoacoustic oscillations. Such oscillations arise from the coupling between adjacent combustors and can increase wear and thermal stresses. In this experimental study, we explore the mutual synchronization of two thermoacoustic oscillators (i.e., two model combustors) interacting via dissipative and time-delayed coupling, as introduced via a cross-talk section. Unlike most previous studies, our study makes use of a turbulent lean-premixed flame in each combustor, bringing the system configuration closer to that of practical gas turbines. Using stationary and transient measurements, we examine the effect of the cross-talk diameter and length so as to gain insight into the effect of dissipative and time-delayed coupling. We find that strengthening the dissipative coupling promotes mutual synchronization, but that weakening the dissipative coupling leads to weakly coupled or desynchronized oscillations. On operating the two combustors at different conditions, we find a significant reduction in their overall oscillation amplitude for some coupling conditions. On varying the combustor length and examining the transient response, we find elaborate changes in the pressure-heat-release-rate coupling, spontaneous mode transitions between coupled thermoacoustic modes, and the emergence of a rhomboid structure in the phase plane owing to the coexistence of in-phase and out-of-phase synchronization. In the combustion community, these two types of synchronization are known to be associated with push-push modes and push-pull modes. These findings offer new insight into the mutual synchronization of low-frequency, self-excited thermoacoustic oscillations in can-annular gas turbines, paving the way for the development of improved control strategies.
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We present a framework for performing input-output system identification near a Hopf bifurcation using data from only the fixed-point branch, prior to the Hopf point itself. The framework models the system with a van der Pol-type equation perturbed by additive noise, and identifies the system parameters via the corresponding Fokker-Planck equation. We demonstrate the framework on a prototypical thermoacoustic oscillator (a flame-driven Rijke tube) undergoing a supercritical Hopf bifurcation. We find that the framework can accurately predict the properties of the Hopf bifurcation and the limit cycle beyond it. This study constitutes an experimental demonstration of system identification on a reacting flow using only prebifurcation data, opening up pathways to the development of early warning indicators for nonlinear dynamical systems near a Hopf bifurcation.
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We experimentally investigate the nonlinear dynamics of a thermoacoustically self-excited aero-engine combustion system featuring a turbulent swirling liquid-fueled diffusion flame in a variable-length combustor. We focus on the steady-state dynamics via simultaneous measurements of the acoustic pressure in the combustor and the heat release rate (HRR) from the flame. When the combustor length is increased following the onset of thermoacoustic instability, we find that the pressure signal transitions from a period-1 limit cycle to chaos, whereas the HRR signal remains chaotic owing to the presence of an intrinsic hydrodynamic mode in the flame. When the hydrodynamic mode is filtered out of the data, we find that the pressure and HRR signals are in generalized synchronization. However, when the hydrodynamic mode is retained in the data, we find that the pressure and HRR signals are either weakly phase synchronized or desynchronized. This study has two main contributions: (i) it shows that a liquid-fueled diffusion-flame combustor can exhibit dynamics as complex as those of its gaseous-fueled premixed-flame counterparts and (ii) it highlights the need to be exceptionally careful when selecting a diagnostic signal from which to calculate nonlinear measures of self-excited thermoacoustic oscillations, because our experiments show that the pressure and HRR signals can be desynchronized by the presence of a hydrodynamic mode in the flame at a frequency different from that of the dominant thermoacoustic mode.
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The lung is a specialized barrier organ that must tightly regulate interstitial fluid clearance and prevent infection in order to maintain effective gas exchange. Lymphatic vessels are important for these functions in other organs, but their roles in the lung have not been fully defined. In the present study, we addressed how the lymphatic vasculature participates in lung homeostasis. Studies using mice carrying a lymphatic reporter allele revealeded that, in contrast to other organs, lung lymphatic collecting vessels lack smooth muscle cells entirely, suggesting that forward lymph flow is highly dependent on movement and changes in pressure associated with respiration. Functional studies using CLEC2-deficient mice in which lymph flow is impaired due to loss of lympho-venous hemostasis or using inducible lung-specific ablation of lymphatic endothelial cells in a lung transplant model revealeded that loss of lymphatic function leads to an inflammatory state characterized by the formation of tertiary lymphoid organs (TLOs). In addition, impaired lymphatic flow in mice resulteds in hypoxia and features of lung injury that resemble emphysema. These findings reveal both a lung-specific mechanism of lymphatic physiology and a lung-specific consequence of lymphatic dysfunction that may contribute to chronic lung diseases that arise in association with TLO formation.
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Cellules endothéliales , Lectines de type C/déficit , Alvéoles pulmonaires , Emphysème pulmonaire , Structures lymphoïdes tertiaires , Animaux , Cellules endothéliales/immunologie , Cellules endothéliales/anatomopathologie , Lectines de type C/immunologie , Souris , Alvéoles pulmonaires/immunologie , Alvéoles pulmonaires/traumatismes , Alvéoles pulmonaires/anatomopathologie , Emphysème pulmonaire/génétique , Emphysème pulmonaire/immunologie , Emphysème pulmonaire/anatomopathologie , Structures lymphoïdes tertiaires/immunologie , Structures lymphoïdes tertiaires/anatomopathologieRÉSUMÉ
The fullPIERS model is a risk prediction model developed to predict adverse maternal outcomes within 48â¯h for women admitted with pre-eclampsia. External validation of the model is required before implementation for clinical use. We assessed the temporal and external validity of the fullPIERS model in high income settings using five cohorts collected between 2003 and 2016, from tertiary hospitals in Canada, the United States of America, Finland and the United Kingdom. The cohorts were grouped into three datasets for assessing the primary external, and temporal validity, and broader transportability of the model. The predicted risks of developing an adverse maternal outcome were calculated using the model equation and model performance was evaluated based on discrimination, calibration, and stratification. Our study included a total of 2429 women, with an adverse maternal outcome rate of 6.7%, 6.6%, and 7.0% in the primary external, temporal, and combined (broader) validation cohorts, respectively. The model had good discrimination in all datasets: 0.81 (95%CI 0.75-0.86), 0.82 (95%CI 0.76-0.87), and 0.75 (95%CI 0.71-0.80) for the primary external, temporal, and broader validation datasets, respectively. Calibration was best for the temporal cohort but poor in the broader validation dataset. The likelihood ratios estimated to rule in adverse maternal outcomes were high at a cut-off of ≥30% in all datasets. The fullPIERS model is temporally and externally valid and will be useful in the management of women with pre-eclampsia in high income settings although model recalibration is required to improve performance, specifically in the broader healthcare settings.
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Modèles biologiques , Pré-éclampsie/diagnostic , Issue de la grossesse/épidémiologie , Adulte , Femelle , Âge gestationnel , Humains , Modèles logistiques , Valeur prédictive des tests , Grossesse , Études prospectives , Appréciation des risques/méthodesRÉSUMÉ
We experimentally investigate the synchronization dynamics of a self-excited thermoacoustic system forced beyond its phase-locked state. The system consists of a laminar premixed flame in a tube combustor subjected to periodic acoustic forcing. On increasing the forcing amplitude above that required for phase locking, we find that the system can transition out of phase locking and into chaos, which is consistent with the Afraimovich-Shilnikov theorem for the breakdown of a phase-locked torus. However, we also find some unexpected behavior, most notably the emergence of a strange nonchaotic attractor (SNA) before the onset of chaos. We verify the existence of the SNA and chaotic attractor by examining the correlation dimension, the autocorrelation function, the power-law scaling in the Fourier amplitude spectrum, the permutation entropy in a pseudoperiodic surrogate test, and the permutation spectrum. In summary, this study explores the SNA and chaotic dynamics of a thermoacoustic system forced beyond its phase-locked state, opening up new pathways for the development of alternative strategies to control self-excited thermoacoustic oscillations in combustion devices such as gas turbines and rocket engines.
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INTRODUÇÃO: o aparelho funcional é uma forma eficaz de tratar as más oclusões de Classe II esqueléticas em crianças e adolescentes. Um protocolo de avanço mandibular progressivo de 12 meses já demonstrou ser capaz de aumentar o crescimento condilar e melhorar o prognatismo mandibular utilizando o aparelho de Herbst. OBJETIVO: relatar o caso clínico (apresentado como um dos requisitos para aprovação no Exame de Ortodontia para Filiação ao Royal College of Surgeons de Edimburgo*) de uma menina chinesa de 11 anos de idade, com 11mm de sobressaliência, tratada na Fase I da terapia de modificação do crescimento, ao longo de 12 meses, utilizando o aparelho Twin Block com um expansor palatal Hyrax e um extrabucal de puxada alta, em um protocolo de avanço mandibular progressivo, seguido pela Fase II da terapia, com um aparelho Edgewise pré-ajustado.
INTRODUCTION: Functional appliances are an effective way of treating skeletal Class II malocclusion in children and adolescents. A 12 month step-wise mandibular advancement protocol has been proved to enhance the condylar growth and improve the mandibular prognathism using Herbst appliance. OBJECTIVES: The following case report documented a 11 year-old Chinese girl with 11 mm overjet treated by a Phase I 12-month growth modification therapy using Twin Block appliance with Hyrax palatal expander and high pull headgear in a step-wise mandibular advancement protocol followed by a Phase II preadjusted Edgewise appliance therapy. This is one of the cases submitted for the Membership of Orthodontics Examination of the Royal College of Surgeons of Edinburgh.
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Humains , Femelle , Enfant , Malocclusion de classe II , Thérapie myofonctionnelle , Appareils orthodontiques amovibles , OrthèsesRÉSUMÉ
Fixed functional appliance is an effective way of treating skeletal Class II malocclusion in children and adolescents. The following case report documented a 13-year-old boy with 15 mm overjet treated by a phase I 12-month growth modification therapy using Herbst appliance with Hyrax palatal expander and high pull headgear in a stepwise mandibular advancement protocol followed by a phase II pre-adjusted edgewise appliance therapy. It is one of the cases submitted for the Membership of Orthodontics Examination of the Royal College of Surgeons of Edinburgh.
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Céphalométrie , Malocclusion de classe II , Appareils de traction extraorale , Humains , Malocclusion de classe II/thérapie , Appareils orthodontiques fonctionnels , Surocclusion/thérapieRÉSUMÉ
OBJECTIVES: The aim of this study was to compare the effectiveness of using Ping On ointment and using petroleum jelly in the treatment of temporomandibular joint (TMJ) and masticatory muscle pain, in order to establish the true efficacy of Ping On ointment. METHODS: In this randomized, double-blinded, placebo-controlled trial, 55 subjects with TMJ and/or masticatory pain (Group I patients according to the Research Diagnostic Criteria for Temporomandibular Disorder (RDC/TMD) received Ping On ointment for 4 weeks, or placebo for 4 weeks. Subjects were evaluated with standard measures of efficacy: pain intensity measured by visual analogue scale and maximal comfortable mandibular opening, at baseline and again after 4 weeks of treatment. RESULTS: Ping On ointment significantly reduced the symptoms of painful TMJs and/or masticatory muscles. Maximal comfortable mandibular opening also improved in the Ping On ointment group compared with the placebo, but was not clinically significant. CONCLUSIONS: This preliminary study suggests that topical application of Ping On ointment may be considered for further investigation as a potential first-line treatment modality, before prescribing analgesics, for the management of TMDs. It is topically applied, safe, reversible, and effective in managing TMDs and masticatory muscle pain.
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Médicaments issus de plantes chinoises/usage thérapeutique , Muscles masticateurs/effets des médicaments et des substances chimiques , Douleur/traitement médicamenteux , Troubles de l'articulation temporomandibulaire/traitement médicamenteux , Articulation temporomandibulaire/effets des médicaments et des substances chimiques , Administration par voie topique , Adulte , Médicaments issus de plantes chinoises/administration et posologie , Médicaments issus de plantes chinoises/pharmacologie , Femelle , Humains , Mâle , Adulte d'âge moyen , OnguentsRÉSUMÉ
A 15 year and 1 month old Chinese female with palatally impacted upper left canine was successfully treated with an upper removable appliance with a magnet incorporated to provide orthodontic traction force. This case report indicates the possibility of using magnetic force as a safe, effective and comfortable way for orthodontic traction.