257 research outputs found
Closed-Loop Control of a Piezo-Fluidic Amplifier
Fluidic valves based on the Coand\u{a} effect are increasingly being
considered for use in aerodynamic flow control applications. A limiting factor
is their variation in switching time, which often precludes their use. The
purpose of this paper is to demonstrate the closed-loop control of a recently
developed, novel piezo-fluidic valve that reduces response time uncertainty at
the expense of operating bandwidth. Use is made of the fact that a fluidic jet
responds to a piezo tone by deflecting away from its steady state position. A
control signal used to vary this deflection is amplitude modulated onto the
piezo tone. Using only a pressure measurement from one of the device output
channels, an output-based LQG regulator was designed to follow a desired
reference deflection, achieving control of a 90 m/s jet. Finally, the
controller's performance in terms of disturbance rejection and response time
predictability is demonstrated.Comment: 31 pages, 23 figures. Published in AIAA Journal, 4th May 202
Structure and Phase Transitions of Metastable Hexagonal Uranium Thin Films
We report a simple technique for the synthesis of uniaxially textured,
metastable hexagonal close-packed-like uranium thin films with thicknesses
between 175-2800 \r{A}. The initial structure and texture of the layers have
been studied via X-ray diffraction and reflectivity and the time-dependent
transitions of the samples into various orientations of orthorhombic
-U have been mapped by similar techniques. The final crystallographic
orientations of each system and the timescales on which the transitions occur
are found to depend on the lattice parameters of the original layer. The
absence of the -U (001) orientation in the transition products
suggests that the transitions in these layers are mediated by mechanisms other
than the [110] transverse acoustic phonon mode previously suggested for the
cubic -U(110) to hcp-U(00.1) to -U(001) displacive phase
transition. Alternative transition pathways are discussed
Beam-Steering Performance of Flat Luneburg Lens at 60 GHz for Future Wireless Communications
The beam-steering capabilities of a simplified flat Luneburg lens are reported at 60 GHz. The design of the lens is first described, using transformation electromagnetics, before discussion of the fabrication of the lens using casting of ceramic composites. The simulated beam-steering performance is shown, demonstrating that the lens, with only six layers and a highest permittivity of 12, achieves scan angles of ±30° with gains of at least 18 dBi over a bandwidth from 57 to 66 GHz. To verify the simulations and further demonstrate the broadband nature of the lens, raw high definition video was transmitted over a wireless link at scan angles up to 36°
Re-evaluation of the near infrared spectra of mitochondrial cytochrome c oxidase: Implications for non invasive in vivo monitoring of tissues
We re-determined the near infrared (NIR) spectral signatures (650-980 nm) of the different cytochrome c oxidase redox centres, in the process separating them into their component species. We confirm that the primary contributor to the oxidase NIR spectrum between 700 and 980 nm is cupric CuA, which in the beef heart enzyme has a maximum at 835 nm. The 655 nm band characterises the fully oxidised haem a3/CuBbinuclear centre; it is bleached either when one or more electrons are added to the binuclear centre or when the latter is modified by ligands. The resulting 'perturbed' binuclear centre is also characterised by a previously unreported broad 715-920 nm band. The NIR spectra of certain stable liganded species (formate and CO), and the unstable oxygen reaction compounds P and F, are similar, suggesting that the latter may resemble the stable species electronically. Oxidoreduction of haem a makes no contribution either to the 835 nm maximum or the 715 nm band. Our results confirm the ability of NIRS to monitor the CuAcentre of cytochrome oxidase activity in vivo, although noting some difficulties in precise quantitative interpretations in the presence of perturbations of the haem a3/CuBbinuclear centre
Analysis of Granular Flow in a Pebble-Bed Nuclear Reactor
Pebble-bed nuclear reactor technology, which is currently being revived
around the world, raises fundamental questions about dense granular flow in
silos. A typical reactor core is composed of graphite fuel pebbles, which drain
very slowly in a continuous refueling process. Pebble flow is poorly understood
and not easily accessible to experiments, and yet it has a major impact on
reactor physics. To address this problem, we perform full-scale,
discrete-element simulations in realistic geometries, with up to 440,000
frictional, viscoelastic 6cm-diameter spheres draining in a cylindrical vessel
of diameter 3.5m and height 10m with bottom funnels angled at 30 degrees or 60
degrees. We also simulate a bidisperse core with a dynamic central column of
smaller graphite moderator pebbles and show that little mixing occurs down to a
1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local
ordering and porosity (from Voronoi volumes), the residence-time distribution,
and the effects of wall friction and discuss implications for reactor design
and the basic physics of granular flow.Comment: 18 pages, 21 figure
A Bayesian approach to analyzing phenotype microarray data enables estimation of microbial growth parameters
Biolog phenotype microarrays enable simultaneous, high throughput analysis of cell cultures in different environments. The output is high-density time-course data showing redox curves (approximating growth) for each experimental condition. The software provided with the Omnilog incubator/reader summarizes each time-course as a single datum, so most of the information is not used. However, the time courses can be extremely varied and often contain detailed qualitative (shape of curve) and quantitative (values of parameters) information. We present a novel, Bayesian approach to estimating parameters from Phenotype Microarray data, fitting growth models using Markov Chain Monte Carlo methods to enable high throughput estimation of important information, including length of lag phase, maximal ``growth'' rate and maximum output. We find that the Baranyi model for microbial growth is useful for fitting Biolog data. Moreover, we introduce a new growth model that allows for diauxic growth with a lag phase, which is particularly useful where Phenotype Microarrays have been applied to cells grown in complex mixtures of substrates, for example in industrial or biotechnological applications, such as worts in brewing. Our approach provides more useful information from Biolog data than existing, competing methods, and allows for valuable comparisons between data series and across different models
Effects of improved home heating on asthma in community dwelling children: randomised controlled trial
Objective To assess whether non-polluting, more effective home heating (heat pump, wood pellet burner, flued gas) has a positive effect on the health of children with asthma
Parmodulins Inhibit Thrombus Formation Without Inducing Endothelial Injury Caused by Vorapaxar
Protease-activated receptor-1 (PAR1) couples the coagulation cascade to platelet activation during myocardial infarction and to endothelial inflammation during sepsis. This receptor demonstrates marked signaling bias. Its activation by thrombin stimulates prothrombotic and proinflammatory signaling, whereas its activation by activated protein C (APC) stimulates cytoprotective and antiinflammatory signaling. A challenge in developing PAR1-targeted therapies is to inhibit detrimental signaling while sparing beneficial pathways. We now characterize a novel class of structurally unrelated small-molecule PAR1 antagonists, termed parmodulins, and compare the activity of these compounds to previously characterized compounds that act at the PAR1 ligand–binding site. We find that parmodulins target the cytoplasmic face of PAR1 without modifying the ligand-binding site, blocking signaling through Gαq but not Gα13 in vitro and thrombus formation in vivo. In endothelium, parmodulins inhibit prothrombotic and proinflammatory signaling without blocking APC-mediated pathways or inducing endothelial injury. In contrast, orthosteric PAR1 antagonists such as vorapaxar inhibit all signaling downstream of PAR1. Furthermore, exposure of endothelial cells to nanomolar concentrations of vorapaxar induces endothelial cell barrier dysfunction and apoptosis. These studies demonstrate how functionally selective antagonism can be achieved by targeting the cytoplasmic face of a G-protein–coupled receptor to selectively block pathologic signaling while preserving cytoprotective pathways
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