Modelling for robust feedback control of fluid flows

This paper addresses the problem of designing low-order and linear robust feedback controllers that provide a priori guarantees with respect to stability and performance when applied to a fluid flow. This is challenging, since whilst many flows are governed by a set of nonlinear, partial differential–algebraic equations (the Navier–Stokes equations), the majority of established control system design assumes models of much greater simplicity, in that they are: firstly, linear; secondly, described by ordinary differential equations (ODEs); and thirdly, finite-dimensional. With this in mind, we present a set of techniques that enables the disparity between such models and the underlying flow system to be quantified in a fashion that informs the subsequent design of feedback flow controllers, specifically those based on the H∞ loop-shaping approach. Highlights include the application of a model refinement technique as a means of obtaining low-order models with an associated bound that quantifies the closed-loop degradation incurred by using such finite-dimensional approximations of the underlying flow. In addition, we demonstrate how the influence of the nonlinearity of the flow can be attenuated by a linear feedback controller that employs high loop gain over a select frequency range, and offer an explanation for this in terms of Landahl’s theory of sheared turbulence. To illustrate the application of these techniques, an H∞ loop-shaping controller is designed and applied to the problem of reducing perturbation wall shear stress in plane channel flow. Direct numerical simulation (DNS) results demonstrate robust attenuation of the perturbation shear stresses across a wide range of Reynolds numbers with a single linear controller

A Period of Controlled Elevation of IOP (CEI) Produces the Specific Gene Expression Responses and Focal Injury Pattern of Experimental Rat Glaucoma

PURPOSE: We determine if several hours of controlled elevation of IOP (CEI) will produce the optic nerve head (ONH) gene expression changes and optic nerve (ON) damage pattern associated with early experimental glaucoma in rats. METHODS: The anterior chambers of anesthetized rats were cannulated and connected to a reservoir to elevate IOP. Physiologic parameters were monitored. Following CEI at various recovery times, ON cross-sections were graded for axonal injury. Anterior ONHs were collected at 0 hours to 10 days following CEI and RNA extracted for quantitative PCR measurement of selected messages. The functional impact of CEI was assessed by electroretinography (ERG). RESULTS: During CEI, mean arterial pressure (99 ± 6 mm Hg) and other physiologic parameters remained stable. An 8-hour CEI at 60 mm Hg produced significant focal axonal degeneration 10 days after exposure, with superior lesions in 83% of ON. Message analysis in CEI ONH demonstrated expression responses previously identified in minimally injured ONH following chronic IOP elevation, as well as their sequential patterns. Anesthesia with cannulation at 20 mm Hg did not alter these message levels. Electroretinographic A- and B-waves, following a significant reduction at 2 days after CEI, were fully recovered at 2 weeks, while peak scotopic threshold response (pSTR) remained mildly but significantly depressed. CONCLUSIONS: A single CEI reproduces ONH message changes and patterns of ON injury previously observed with chronic IOP elevation. Controlled elevation of IOP can allow detailed determination of ONH cellular and functional responses to an injurious IOP insult and provide a platform for developing future therapeutic interventions

Research ethics in an unethical world: the politics and morality of engaged research

This article explores ethical dilemmas in researching the world of work. Recent contributions to WES have highlighted challenges for engaged research. Based on the emancipatory epistemologies of Bourdieu, Gramsci and Burawoy, the authors examine moral challenges in workplace fieldwork, question the assumptions of mainstream ethics discourses and seek to identify an alternative approach. Instead of an ethics premised on a priori, universal precepts that treasures academic neutrality, this article recognises a morality that responds to the social context of research with participation and commitment. The reflection in this study is based on fieldwork conducted in the former Soviet Union. Transformation societies present challenges to participatory ethnography but simultaneously provide considerable opportunities for developing an ethics of truth. An approach that can guide engaged researchers through social conflict’s ‘messy’ reality should hinge on loyalty to the emancipation struggles of those engaged in it

Environmental screening tools for assessment of infrastructure plans based on biodiversity preservation and global warming (PEIT, Spain).

Most Strategic Environmental Assessment (SEA) research has been concerned with SEA as a procedure, and there have been relatively few developments and tests of analytical methodologies. The first stage of the SEA is the ‘screening’, which is the process whereby a decision is taken on whether or not SEA is required for a particular programme or plan. The effectiveness of screening and SEA procedures will depend on how well the assessment fits into the planning from the early stages of the decision-making process. However, it is difficult to prepare the environmental screening for an infrastructure plan involving a whole country. To be useful, such methodologies must be fast and simple. We have developed two screening tools which would make it possible to estimate promptly the overall impact an infrastructure plan might have on biodiversity and global warming for a whole country, in order to generate planning alternatives, and to determine whether or not SEA is required for a particular infrastructure plan

Relationship between the magnitude of intraocular pressure during an episode of acute elevation and retinal damage four weeks later in rats

PURPOSE: To determine relationship between the magnitude of intraocular pressure (IOP) during a fixed-duration episode of acute elevation and the loss of retinal function and structure 4 weeks later in rats. METHODS: Unilateral elevation of IOP (105 minutes) was achieved manometrically in adult Brown Norway rats (9 groups; n = 4 to 8 each, 10-100 mm Hg and sham control). Full-field ERGs were recorded simultaneously from treated and control eyes 4 weeks after IOP elevation. Scotopic ERG stimuli were white flashes (-6.04 to 2.72 log cd.s.m(-2)). Photopic ERGs were recorded (1.22 to 2.72 log cd.s.m(-2)) after 15 min of light adaptation (150 cd/m(2)). Relative amplitude (treated/control, %) of ERG components versus IOP was described with a cummulative normal function. Retinal ganglion cell (RGC) layer density was determined post mortem by histology. RESULTS: All ERG components failed to recover completely normal amplitudes by 4 weeks after the insult if IOP was 70 mmHg or greater during the episode. There was no ERG recovery at all if IOP was 100 mmHg. Outer retinal (photoreceptor) function demonstrated the least sensitivity to prior acute IOP elevation. ERG components reflecting inner retinal function were correlated with post mortem RGC layer density. CONCLUSIONS: Retinal function recovers after IOP normalization, such that it requires a level of acute IOP elevation approximately 10 mmHg higher to cause a pattern of permanent dysfunction similar to that observed during the acute event. There is a 'threshold' for permanent retinal functional loss in the rat at an IOP between 60 and 70 mmHg if sustained for 105 minutes or more

Inverse Association between trans Isomeric and Long-Chain Polyunsaturated Fatty Acids in Pregnant Women and Their Newborns: Data from Three European Countries

Background: trans unsaturated fatty acids are thought to interfere with essential fatty acid metabolism. To extend our knowledge of this phenomenon, we investigated the relationship between trans isomeric and long-chain polyunsaturated fatty acids (LCPUFA) in mothers during pregnancy and in their infants at birth. Methods: Fatty acid composition of erythrocyte phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was determined in Spanish (n = 120), German (n = 78) and Hungarian (n = 43) women at the 20th and 30th week of gestation, at delivery and in their newborns. Results: At the 20th week of gestation, the sum of trans fatty acids in PE was significantly (p < 0.01) lower in Hungarian [0.73 (0.51), % wt/wt, median (IQR)] than in Spanish [1.42 (1.36)] and German [1.30 (1.21)] women. Docosahexaenoic acid (DHA) values in PE were significantly (p < 0.01) higher in Hungarian {[}5.65 (2.09)] than in Spanish [4.37 (2.60)] or German [4.39 (3.3.2)] women. The sum of trans fatty acids significantly inversely correlated to DHA in PCs in Spanish (r = -0.37, p < 0.001), German (n = -0.77, p < 0.001) and Hungarian (r = -0.35, p < 0.05) women, and in PEs in Spanish (r = -0.67, p < 0.001) and German (r = -0.71, p < 0.001), but not in Hungarian (r = -0.02) women. Significant inverse correlations were seen between trans fatty acids and DHA in PEs at the 30th week of gestation (n = 241, r = -0.52, p < 0.001), at delivery (n = 241, r = -0.40, p < 0.001) and in cord lipids (n = 218, r = -0.28, p < 0.001). Conclusion: Because humans cannot synthesize trans isomeric fatty acids, the data obtained in the present study support the concept that high maternal trans isomeric fatty acid intake may interfere with the availability of LCPUFA both for the mother and the fetus. Copyright (C) 2011 S. Karger AG, Base

Phylogenomics of non-model ciliates based on transcriptomic analyses

© The Author(s) 2015. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited. The attached file is the published version of the article

Autoimmune and autoinflammatory mechanisms in uveitis

The eye, as currently viewed, is neither immunologically ignorant nor sequestered from the systemic environment. The eye utilises distinct immunoregulatory mechanisms to preserve tissue and cellular function in the face of immune-mediated insult; clinically, inflammation following such an insult is termed uveitis. The intra-ocular inflammation in uveitis may be clinically obvious as a result of infection (e.g. toxoplasma, herpes), but in the main infection, if any, remains covert. We now recognise that healthy tissues including the retina have regulatory mechanisms imparted by control of myeloid cells through receptors (e.g. CD200R) and soluble inhibitory factors (e.g. alpha-MSH), regulation of the blood retinal barrier, and active immune surveillance. Once homoeostasis has been disrupted and inflammation ensues, the mechanisms to regulate inflammation, including T cell apoptosis, generation of Treg cells, and myeloid cell suppression in situ, are less successful. Why inflammation becomes persistent remains unknown, but extrapolating from animal models, possibilities include differential trafficking of T cells from the retina, residency of CD8(+) T cells, and alterations of myeloid cell phenotype and function. Translating lessons learned from animal models to humans has been helped by system biology approaches and informatics, which suggest that diseased animals and people share similar changes in T cell phenotypes and monocyte function to date. Together the data infer a possible cryptic infectious drive in uveitis that unlocks and drives persistent autoimmune responses, or promotes further innate immune responses. Thus there may be many mechanisms in common with those observed in autoinflammatory disorders

Azimuthal Anisotropy of Photon and Charged Particle Emission in Pb+Pb Collisions at 158 A GeV/c

The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in Pb + Pb collisions at 158 A GeV/c in the WA98 experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.Comment: 8 pages and 6 figures. The manuscript has undergone a major revision. The unwanted correlations were enhanced in the random subdivision method used in the earlier version. The present version uses the more established method of division into subevents separated in rapidity to minimise short range correlations. The observed results for charged particles are in agreement with results from the other experiments. The observed anisotropy in photons is explained using flow results of pions and the correlations arising due to the decay of the neutral pion