Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion

In this paper, we conduct an experimental investigation to study the link between the flame macroscale structure—or flame brush spatial distribution—and thermo-acoustic instabilities, in a premixed swirl-stabilized dump combustor. We operate the combustor with premixed methane–air in the range of equivalence ratio (φ) from the lean blowout limit to φ=0.75. First, we observe the different dynamic modes in this lean range as φ is raised. We also document the effect of φ on the flame macrostructure. Next, we examine the correspondence between dynamic mode transitions and changes in flame macrostructure. To do so, we modify the combustor length—by downstream truncation—without changing the underlying flow upstream. Thus, the resonant frequencies of the geometry are altered allowing for decoupling the heat release rate fluctuations and the acoustic feedback. Mean flame configurations in the modified combustor and for the same range of equivalence ratio are examined, following the same experimental protocol. It is found that not only the same sequence of flame macrostructures is observed in both combustors but also that the transitions occur at a similar set of equivalence ratio. In particular, the appearance of the flame in the outside recirculation zone (ORZ) in the long combustor—which occurs simultaneously with the onset of instability at the fundamental frequency—happens at similar φ when compared to the short combustor, but without being in latter case accompanied by a transition to thermo-acoustic instability. Then, we interrogate the flow field by analyzing the streamlines, mean, and rms velocities for the nonreacting flow and the different flame types. Finally, we focus on the transition of the flame to the ORZ in the acoustically decoupled case. Our analysis of this transition shows that it occurs gradually with an intermittent appearance of a flame in the ORZ and an increasing probability with φ. The spectral analysis of this phenomenon—we refer to as “ORZ flame flickering”—shows the presence of unsteady events occurring at two distinct low frequency ranges. A broad band at very low frequency in the range ∼(1 Hz–10 Hz) associated with the expansion and contraction of the inner recirculation zone (IRZ) and a narrow band centered around 28 Hz which is the frequency of rotation of the flame as it is advected by the ORZ flow.King Fahd University of Petroleum and Minerals (Grant R12-CE-10)King Abdullah University of Science and Technology (Grant KUS-110-010-01

Riding against the wind: a review of competition cycling aerodynamics

Aerodynamics has such a profound impact on cycling performance at the elite level that it has infiltrated almost every aspect of the sport from riding position and styles, equipment design and selection, race tactics and training regimes, governing rules and regulations to even the design of new velodromes. This paper presents a review of the aspects of aerodynamics that are critical to understanding flows around cyclists under racing conditions, and the methods used to evaluate and improve aerodynamic performance at the elite level. The fundamental flow physics of bluff body aerodynamics and the mechanisms by which the aerodynamic forces are imparted on cyclists are described. Both experimental and numerical techniques used to investigate cycling aerodynamic performance and the constraints on implementing aerodynamic saving measures at the elite level are also discussed. The review reveals that the nature of cycling flow fields are complex and multi-faceted as a result of the highly three-dimensional and variable geometry of the human form, the unsteady racing environment flow field, and the non-linear interactions that are inherent to all cycling flows. Current findings in this field have and will continue to evolve the sport of elite cycling while also posing a multitude of potentially fruitful areas of research for further gains in cycling performance

Impact of static flexion duration on the development of a neuromuscular disorder of the lumbar spine

Many occupational groups work under adverse conditions in which their spinal columns are fully flexed under load for substantial periods of time. This study was designed to determine the response of the lumbar spine to a static load of a substantial duration under a range of load magnitudes. The impact of static loads of 20, 40 and 60N were applied over 30 min flexion, 10 min rest, and 30 min flexion (for a total of one hour exposure) followed by a 7 h rest. Lumbar viscoelastic creep (laxity) and reflex electromyographic (EMG) activity were monitored over both flexion periods and the 7 h rest period. It was found that 10 min of rest was not sufficient for complete recovery of the creep developed in the first 30 min of flexion resulting in a large cumulative creep at the end of the work-rest session. Muscle activity indicated spasms during the static flexion periods and demonstrated the development of initial and delayed hyperexcitability in each of the 3 loads. Larger magnitudes of initial and delayed hyperexcitability were observed for larger loads although the differences were not statistically significant. Thus, intense periods of static flexion will result in neuromuscular disorders regardless of load magnitude. The results of the 3:1 work-rest ratio were compared with previously obtained data of a series of short static flexion periods (1:1 ratio) of the same cumulative time to determine which can best expedite the recovery of creep. Although the valuable effects of a 1:1 work-rest ratio have been documented (Sbriccoli, 2004), a 3:1 work-to-rest duration ratio was not sufficient to attenuate or prevent the development of any of the components of a neuromuscular disorder and the associated microdamage and inflammation. In conclusion, a cumulative low back disorder was elicited from exposure to two 30 min static loads spaced by a 10 min interval

Le cas de la sous-culture punk féministe américaine : vers une redéfinition de la relation dialectique "mainstream -underground" ?

This dissertation seeks to analyze the complex and ambivalent relationships that exist between mainstream "dominant" culture and oppositional underground subcultures, through the study of American feminist punk subculture (notably under the form initiated by the riot grrrl networks). By confronting the views and discourses expressed by insiders of this feminist and anticapitalist subculture on the one hand, and drawing from the theoretical background of subcultural studies on the other hand, we want to examine the social function of these types of networks. How do insiders conceive their own involvement and their subcultural practices? What is the purpose of an anti-establishment underground subculture, if ever there is one? We also seek to question the concept of subversion: is it possible for a subcultural group to exert a disruptive potential in a society that apparently largely feeds on criticism of itself. We will sketch out some answers to these issues in the last part of this work by drawing some parallels between punk and feminist punk subcultures, medieval carnivalesque practices as they are described by Mikhaïl Bakhtin, and the Dionysian spirit depicted by Nietzsche.Ce travail doctoral consiste en une considération de la nature complexe et ambivalente des relations qui sont tissées entre "culture dominante "("mainstream") et sous-cultures contestataires "underground", à travers l’examen du cas de la sous-culture punk, et plus spécifiquement, du cas de la sous-culture punk féministe américaine (sous la forme du courant "riot grrrl" notamment). En nous appuyant sur les discours des actrices et acteurs de ces sphères féministes et anticapitalistes d’une part, et d’autre part sur la production théorique à laquelle ont pu donner lieu les phénomènes sous-culturels marginaux et/ou contestataires, en particulier depuis la fin des années 1970, nous souhaitons mener une réflexion sur le rôle social que peut revêtir ce genre de regroupements sociaux. De quel(s) sens leurs protagonistes investissent-t-ils leurs pratiques ? Quel peut être l’objectif d’une telle démarche, si tant est qu’il y en ait un ? Par ailleurs, il s’agit également de s’interroger sur le concept de subversion : où peut-encore se situer un éventuel potentiel disruptif, dans une société qui, comme l’ont déjà souligné beaucoup de penseurs, ainsi que beaucoup des détracteurs de cette "idéologie dominante", semble en dernière analyse assez bien s’alimenter, paradoxalement, de sa critique. Ce sont ces questionnements qui sous-tendent, dans le cadre d’une dernière partie, la mise en perspective diachronique du punk que nous proposons, en comparant cette tendance avec les réjouissances carnavalesques médiévales telles que les a décrites Mikhaïl Bakhtine, et avec l’esprit dionysiaque que Nietzsche s’est employé à cerner

Deutsche Banknoten von 1871 bis 1999 : Dokumente im Spannungsfeld von Identität, Information und Design

Die wechselvolle deutsche Geschichte des 20. Jahrhunderts spiegelt sich in den zahlreichen Banknoten wider, ausgegeben seit der Gründung des Deutschen Kaiserreiches 1871 bis zur Ausgabe der letzten DM-Serie der Bundesrepublik Deutschland 1999. Die Arbeit verfolgt das Ziel, diese Banknoten auf ihre grafischen Elemente hin zu untersuchen und Zusammenhänge zu den politischen Systemen und ihrer Selbstdarstellung aufzuzeigen, die die Banknote als einzigartiges Dokument der Geschichte im Spannungsfeld von Information, Design und Identität bestätigt. Davon ausgehend wird ein auf eine breite Zielgruppe ausgerichtetes Webformat für Videos entwickelt, die jeweils von einer deutschen Banknote ausgehend ein historisches Moment beleuchten. Die Videos würdigen die Banknote als künstlerisch und technisch hoch entwickeltes Dokument und betten sie in ihren historischen Kontext

Suppression of thermoacoustic instabilities in a swirl combustor through microjet air injection

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 85-87).Thermoacoustic or combustion instability, a positive feedback loop coupling heat release rate and acoustic oscillations in a combustor, is one of the greatest challenges currently facing the development of new gas turbine systems for propulsion and power generation. Traditional gas turbine designs have bypassed the problem of combustion instability by designing non-premixed combustors around a fixed operating point. Increasing trends toward lower emissions and greater fuel flexibility have placed more emphasis on developing lean-premixed combustors that are stable over a range of operating conditions. This thesis explores two aspects of combustion instability in the context of a swirl-stabilized, lean-premixed combustor: the role of the major coherent flow structures, and the potential for using secondary air injection to passively suppress combustion instability. Microjets inject air into the combustion chamber in the flame anchoring zone. These microjet injectors attempt to modify the flow field so as to break the feedback mechanism between the chamber acoustics and the heat release rate. Eight microjet injector configurations are studied. Flow is injected axially into the outer recirculation zone or radially into the inner recirculation zone. The injectors inject air with either no swirl, the same swirl direction as the main air flow, or the opposite swirl direction as the main air flow. Chamber acoustics are measured using sensitive microphones. The flame and flow field are interrogated using high-speed imaging and stereoscopic particle image velocimetry. The bulk of this work was conducted for lean propane/air flames, slightly above the lean blowoff limit. Two modes of instability were examined: the 1/4 wave mode at 40 Hz, and the 3/4 wave mode at 105 Hz. Without microjet injection, the combustor transitions directly from the 1/4 wave mode instability to the 3/4 wave mode instability as the equivalence ratio is increased above 0.58. Counter-swirling radial microjets injecting air into the inner recirculation zone increased the lower limit of the 3/4 wave mode to an equivalence ratio of 0.62 and reduced the amplitude of the 1/4 wave mode, effectively creating a stable operating regime for equivalence ratios between the two modes. Microjet injector tests indicate that the inner recirculation zone has a dominant role in the dynamic stabilization of the flame. This observation is confirmed by stereoscopic PIV measurements that reveal periodic formation and collapse of the vortex breakdown bubble in the 3/4 wave mode and vortex shedding in the inner recirculation zone in the 1/4 wave mode.by Zachary Alexander LaBry.S.M

Description of day case costs and tariffs of cataract surgery from a sample of nine European countries

The project IMPACT-HTA has received funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement No. 779312.Background: The lack of transparency in the methodology of unit cost estimation and the usage of confidential or undisclosed information prevents cost comparisons and makes the transferability of the results across countries difficult. The objective of this article is to compare the methodologies used in the estimation of the cost of a day case cataract extirpation that are described in the official and publicly available sources and to study how these translate into different unit cost estimates. Methods: A literature review was conducted to identify the main sources of unit costs of cataract extirpation. A semistructured questionnaire to obtain information on national costing methodologies was developed and sent to consortium partners in nine European countries. Additionally, publicly available sources of unit cost of cataract surgery in those countries included in the European Healthcare and Social Cost Database (EU HCSCD) were analysed. Results: The findings showed a considerable diversity across countries on unit costs varying from 432.5€ in Poland (minor degree of severity) to 3411.96€ in Portugal (major degree of severity). In addition, differences were found in the year of cost publication and on the level of detail of different types of cataract surgery. The unit of activity were Diagnosis-Related Groups in all countries except Slovenia. All unit costs include direct costs and variable overheads (except Germany where nursing costs are financed separately). Differences were identified in the type of fixed overheads included in unit costs. Methodological documents explaining the identification, measurement and evaluation of resources included in the unit costs, as well as use of appropriate cost drivers are publicly available only in England, Portugal and Sweden. Conclusions: We can conclude that while unit costs of cataract extirpation are publicly available, the information on methodological aspects is scarce. This appears to pose a significant problem for cross-country comparisons of costs and transferability of results from one country to another.European Commission 77931

Reducción gradual de dosis frente a deprescripción abrupta de antipsicóticos en pacientes con demencia: una revisión sistemática

Objective: To synthesize the available evidence on antipsychotic gradual dose reduction or abrupt deprescription in the older people population with dementia. Methods: A systematic review of intervention studies. PubMed, Embase, Web of Science-Core Collection, Cochrane Library, Scopus, MEDLINE(Ovid), and PsycINFO databases were consulted. Articles were eligible for inclusion if they were intervention studies (randomized or quasi-experimental trials) evaluating the effectiveness of dose reduction or complete withdrawal antipsychotic deprescribing strategies in people with dementia. The screening process, data extraction, data analysis and bias risk assessment were performed by two independent reviewers and any discrepancies were triangulated with a third reviewer. Results: Eight clinical trials were ultimately included in the systematic review, two of which were quasi experimental. Over 60% of participants came from nursing or care homes. There is evidence of several strategies for deprescribing antipsychotics. Five studies used an abrupt withdrawal schedule and three studies used a gradual dose reduction. Deprescription through abrupt and gradual withdrawal schedules showed no significant differences in the management of behavioral symptoms, although abrupt withdrawals showed significantly higher rates of relapse and/or adverse events. Conclusion: Deprescribing antipsychotics is feasible in those people with dementia, and it is associated with benefits in terms of survival, and with potential improved outcomes in the management and relapse of behavioral and psychological symptoms of dementia. It seems reasonable that tapering off antipsychotic medication should be assessed after 12 weeks of treatment or when behavioural symptoms are under control.Objetivo: Sintetizar la evidencia disponible sobre la reducción gradual de la dosis de antipsicóticos o su deprescripción abrupta en personas mayores con demencia. Métodos: Revisión sistemática de estudios de intervención. Se consultaron las bases de datos PubMed, Embase, Web of Science-Core Collection, Cochrane Library, Scopus, MEDLINE (Ovid) y PsycINFO. Se incluyeron estudios (ensayos aleatorios o cuasiexperimentales) que evaluaban la efectividad de estrategias de deprescripción de antipsicóticos de reducción de dosis o abstinencia completa. Dos revisores independientes, triangulando por un tercer revisor realizaron el proceso de selección, extracción y análisis de datos, y evaluación del riesgo de sesgo. Resultados: Se incluyeron 8 ensayos clínicos en la revisión sistemática, dos de los cuales fueron cuasi experimentales. Más del 60% de los participantes procedían de residencias de personas ancianas. Existe evidencia de varias estrategias para deprescribir antipsicóticos. Cinco estudios utilizaron un calendario de retiro abrupto y tres estudios utilizaron una reducción gradual de la dosis. La deprescripción mediante esquemas de retiro abrupto y gradual no mostró diferencias significativas en el manejo de los síntomas conductuales, y mostraron tasas significativamente más altas de recaída y/o eventos adversos. Conclusión: La deprescripción de antipsicóticos es factible en personas con demencia, y se asocia a beneficios en términos de supervivencia y con posibles mejoras en el manejo y la recaída de los síntomas conductuales y psicológicos de la demencia. Parece razonable que la reducción gradual de la medicación antipsicótica se evalúe después de 12 semanas de tratamiento o cuando los síntomas conductuales estén bajo control

INES: Interactive tool for construction and extrapolation of partitioned survival models

Background INES (INteractive model for Extrapolation of Survival and cost) provides an open-access tool powered by R that implements three-state partitioned survival models (PSM). This article describes the properties of the tool, and the situations where INES may or may not be suitable. Methods INES is designed to be used by investigators or healthcare professionals who have a good grasp of the principles of economic evaluation and understand the strengths and weaknesses of partitioned survival models, but are not sufficiently familiar with a statistical package such as Excel or R to be able to construct and test a de-novo PSM themselves. INES is delivered to the user via a batch file. Once downloaded to the user’s hard drive, it interacts with the user via a portable version of R with web interactivity built in Shiny. INES requires absolutely no knowledge of R and the user does not need to have R or any of its dependences installed. Hence the user will deal with a standalone Shiny app. Inputs (digitalized survival curves, unit costs, posology, hazard ratios, discount rate) can be uploaded from a template spreadsheet. Results The INES application provides a seamlessly integrated package for estimating a set of parametric hazard functions for progression free and overall survival, selecting an appropriate function from this menu, and applying this as an input to a PSM to calculate mean costs and quality-adjusted life years. Examples are given that may serve as a tutorial. Conclusion INES offers a rapid, flexible, robust and transparent tool for parametric survival analysis and calculating a PSM that can be used in many different contexts