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‣ A fast electric load forecasting using adaptive neural networks

Lopes, M. L M; Lotufo, A. D P; Minussi, C. R.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 362-367
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This work presents a procedure for electric load forecasting based on adaptive multilayer feedforward neural networks trained by the Backpropagation algorithm. The neural network architecture is formulated by two parameters, the scaling and translation of the postsynaptic functions at each node, and the use of the gradient-descendent method for the adjustment in an iterative way. Besides, the neural network also uses an adaptive process based on fuzzy logic to adjust the network training rate. This methodology provides an efficient modification of the neural network that results in faster convergence and more precise results, in comparison to the conventional formulation Backpropagation algorithm. The adapting of the training rate is effectuated using the information of the global error and global error variation. After finishing the training, the neural network is capable to forecast the electric load of 24 hours ahead. To illustrate the proposed methodology it is used data from a Brazilian Electric Company. © 2003 IEEE.

‣ Involvement of alternative oxidase (AOX) in adventitious rooting of Olea europaea L. microshoots is linked to adaptive phenylpropanoid and lignin metabolism

Santos Macedo, E.; Sircar, D.; Cardoso, H.G.; Peixe, A; Arnholdt-Schmitt, B
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
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Alternative oxidase (AOX) has been proposed as a functional marker candidate in a number of events involving cell differentiation, including rooting efficiency in semi-hardwood shoot cuttings of olive (Olea europaea L.). To ascertain the general importance of AOX in olive rooting, the auxin-induced rooting process was studied in an in vitro system for microshoot propagation. Inhibition of AOX by salicylhydroxamic acid (SHAM) significantly reduced rooting efficiency. However, the inhibitor failed to exhibit any effect on the preceding calli stage. This makes the system appropriate for distinguishing dedifferentiation and de novo differentiation during root induction. Metabolite analyses of microshoots showed that total phenolics, total flavonoids and lignin contents were significantly reduced upon SHAM treatment. It was concluded that the influence of alternative respiration on root formation was associated to adaptive phenylpropanoid and lignin metabolism. Transcript profiles of two olive AOX genes (OeAOX1a and OeAOX2) were examined during the process of auxin-induced root induction. Both genes displayed stable transcript accumulation in semi-quantitative RT-PCR analysis during all experimental stages. In contrary, when the reverse primer for OeAOX2 was designed from the 3’ -UTR instead of the ORF...

‣ An Hp-Adaptive Hierarchical Formulation for the Boundary Element Method Applied to Elasticity in Two Dimensions

Pessolani,R. B. V.
Fonte: The Brazilian Society of Mechanical Sciences Publicador: The Brazilian Society of Mechanical Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2002 Português
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This paper presents an HP-Adaptive Procedure with Hierarchical formulation for the Boundary Element Method in 2-D Elasticity problems. Firstly, H, P and HP formulations are defined. Then, the hierarchical concept, which allows a substantial reduction in the dimension of equation system, is introduced. The error estimator used is based on the residual computation over each node inside an element. Finally, the HP strategy is defined and applied to two examples.

‣ Adaptive Responses Account for the β-Curve—Hormesis is Linked to Acquired Tolerance

Stebbing, A. R. D.
Fonte: International Hormesis Society Publicador: International Hormesis Society
Tipo: Artigo de Revista Científica
Publicado em /10/2003 Português
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To date there is no single shared property of the various physical and chemical agents that elicit the β-curve to account for its form, leading to the proposition that hormesis is a consequence of the nonspecificity of adaptive responses. It is argued that adaptive responses to toxic agents may be expected to follow the β-curve. Four kinds of examples are reviewed (enzyme activity, sequestration and repair, and reproductive and homeostatic responses) that corroborate this proposition. The homeostasis example (incorporating homeorhesis) is considered in more detail, using the author’s published hydroid experimental growth data, to show that both the α- and β-curves are satisfactorily explained in this way. Many consider that hormesis is merely due to regulatory overcorrections, but it is proposed that it is a consequence of adaptations of the rate-sensitive growth control mechanism (homeorhesis) to sustained levels of inhibition to which the growth control mechanism adapts. In response to low levels of inhibition, upward adjustment of preferred growth rates confers greater resistance to inhibition, with growth hormesis as a cumulative byproduct.

‣ An intestinal epithelial defect conferring ER stress results in inflammation involving both innate and adaptive immunity

Eri, R D; Adams, R J; Tran, T V; Tong, H; Das, I; Roche, D K; Oancea, I; Png, C W; Jeffery, P L; Radford-Smith, G L; Cook, M C; Florin, T H; McGuckin, M A
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
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We recently characterized Winnie mice carrying a missense mutation in Muc2, leading to severe endoplasmic reticulum stress in intestinal goblet cells and spontaneous colitis. In this study, we characterized the immune responses due to this intestinal epithelial dysfunction. In Winnie, there was a fourfold increase in activated dendritic cells (DCs; CD11c+ major histocompatibility complex (MHC) class IIhi) in the colonic lamina propria accompanied by decreased colonic secretion of an inhibitor of DC activation, thymic stromal lymphopoietin (TSLP). Winnie also displayed a significant increase in mRNA expression of the mucosal TH17 signature genes Il17a, IL17f, Tgfb, and Ccr6, particularly in the distal colon. Winnie mesenteric lymph node leukocytes secreted multiple TH1, TH2, and TH17 cytokines on activation, with a large increase in interleukin-17A (IL-17A) progressively with age. A major source of mucosal IL-17A in Winnie was CD4+ T lymphocytes. Loss of T and B lymphocytes in Rag1-/- × Winnie (RaW) crosses did not prevent spontaneous inflammation but did prevent progression with age in the colon but not the cecum. Adoptive transfer of naive T cells into RaW mice caused more rapid and severe colitis than in Rag1-/-, indicating that the epithelial defect results in an intestinal microenvironment conducive to T-cell activation. Thus...

‣ Adaptive IMRT using a multiobjective evolutionary algorithm integrated with a diffusion-invasion model of glioblastoma

Holdsworth, C H; Corwin, D; Stewart, R D; Rockne, R; Trister, A D; Swanson, K R; Phillips, M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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We demonstrate a patient-specific method of adaptive IMRT treatment for glioblastoma using a multi-objective evolutionary algorithm (MOEA). The MOEA generates spatially optimized dose distributions using an iterative dialog between the MOEA and a mathematical model of tumor cell proliferation, diffusion, and response. Dose distributions optimized on a weekly basis using biological metrics have the potential to substantially improve and individualize treatment outcomes. Optimized dose distributions were generated using three different decision criteria for the tumor and compared with plans utilizing standard dose of 1.8 Gy/fraction to the CTV (T2-visible MRI region plus a 2.5 cm margin). The sets of optimal dose distributions generated using the MOEA approach the Pareto front (the set of IMRT plans that delineate optimal tradeoffs amongst the clinical goals of tumor control and normal tissue sparing). MOEA optimized doses demonstrated superior performance as judged by three biological metrics according to simulated results. The predicted number of reproductively viable cells 11 weeks after 1 week of treatment was found to be the best target objective for use in the MOEA.

‣ Wavefront sensing and high resolution adaptive optics imaging in the living rodent eye.

Geng, Ying (1982 - ); Williams, David R. ; Greenberg, Kenneth P. ; Schery, Lee Anne
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xviii, 142 leaves; Illustrations:ill. (some col.)
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Thesis (Ph. D.)--University of Rochester. Institute of Optics, 2012.
Chapter 2 co-authored with Kenneth P. Greenberg and others; chapters 3-4 co-authored with Lee Anne Schery and others.; The rodent has become an increasingly valuable model for human diseases and development due to its availability for genetic manipulations. Non-invasive microscopic imaging of the rodent retina would allow tracking of retinal development, disease progression, and the efficacy of therapy in single animals. Correction of the eye’s aberrations using adaptive optics (AO) could improve the resolution of in vivo rodent retinal images, but previous attempts have been limited by the small size of its eye and the difficulty in measuring its aberrations due to poor Shack-Hartmann wavefront sensor (SHWS) spot quality. The work in this thesis describes methods developed to measure the rodent eye optics and to optimize its retinal image quality in vivo. Our first attempt was modifying a confocal fluorescence adaptive optics scanning laser ophthalmoscope (AOSLO) originally built for imaging the primate and human eye to accommodate the rat eye. Despite achieving in vivo resolution sufficient to resolve sub-cellular structures in fluorescent ganglion cells...

‣ Towards enhancing adaptive capacity for climate change response in South East Queensland

Smith, T.; Lynam, T.; Preston, B.; Matthews, J.; Carter, R.; Thomsen, D.; Carter, J.; Roiko, A.; Simpson, R.; Waterman, P.; Bussey, M.; Keys, N.; Stephenson, C.
Fonte: Massey University Publicador: Massey University
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
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Discussion of climate change adaptation is gaining increased prominence in sustainability policy and the academic literature. A key factor in the selection of climate adaptation initiatives is the understanding of vulnerability. However, past approaches to understanding climate change vulnerability have largely focused on assessments of exposure (e.g., change in temperature), to the exclusion of assessments of sensitivity (e.g., regions with an aging population) or adaptive capacity (e.g., the ability to implement adaptation initiatives). The authors argue that an understanding of adaptive capacity is critical to inform climate change vulnerability and to help prioritise climate change adaptation initiatives. The authors propose an approach to understand adaptive capacity, which is currently being applied in South East Queensland.; Timothy F. Smith, Timothy Lynam, Benjamin L. Preston, Julie Matthews, R. W. (Bill) Carter, Dana C. Thomsen, Jennifer Carter, Anne Roiko, Rodney Simpson, Peter Waterman, Marcus Bussey, Noni Keys & Craig Stephenson

‣ Adaptive evolution of Saccharomyces cerevisiae to generate strains with enhanced glycerol production

Kutyna, D.R.; Varela, C.; Stanley, G.A.; Borneman, A.R.; Henschke, P.A.; Chambers, P.J.
Fonte: Springer Verlag Publicador: Springer Verlag
Tipo: Artigo de Revista Científica
Publicado em //2012 Português
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The development of new wine yeast strains with improved characteristics is critical in the highly competitive wine market, which faces the demand of ever-changing consumer preferences. Although new strains can be constructed using recombinant DNA technologies, consumer concerns about genetically modified (GM) organisms strongly limit their use in food and beverage production. We have applied a non-GM approach, adaptive evolution with sulfite at alkaline pH as a selective agent, to create a stable yeast strain with enhanced glycerol production; a desirable characteristic for wine palate. A mutant isolated using this approach produced 41% more glycerol than the parental strain it was derived from, and had enhanced sulfite tolerance. Backcrossing to produce heterozygous diploids revealed that the high-glycerol phenotype is recessive, while tolerance to sulfite was partially dominant, and these traits, at least in part, segregated from each other. This work demonstrates the potential of adaptive evolution for development of novel non-GM yeast strains, and highlights the complexity of adaptive responses to sulfite selection.; D. R. Kutyna, C. Varela, G. A. Stanley, A. R. Borneman, P. A. Henschke, P. J. Chambers

‣ 2 um Narrow-band Adaptive Optics Imaging in the Arches Cluster

Blum, R. D.; Schaerer, D.; Pasquali, A.; Heydari-Malayeri, M.; Conti, P. S.; Schmutz, W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/06/2001 Português
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Canada-France-Hawaii-Telescope adaptive optics bonnette images through narrow-band filters in the $K-$band are presented for the Arches cluster. Continuum fluxes, line fluxes, and equivalent widths are derived from high angular resolution images, some near diffraction limited, for the well known massive stars in the Arches cluster. Images were obtained in the lines of \ion{He}{1} 2.06 \mic, \ion{H}{1} Br$\gamma$ (2.17 \mic), and \ion{He}{2} 2.19 \mic as well as continuum positions at 2.03 \mic, 2.14 \mic, and 2.26 \mic. In addition, fluxes are presented for \ion{H}{1} P$\alpha$ (1.87 \mic) and a nearby continuum position (1.90 \mic) from Hubble Space Telescope archival data. The 2 \mic and P$\alpha$ data reveal two new emission-line stars and three fainter candidate emission-line objects. Indications for a spectral change of one object between earlier observations in 1992/1993 and our data from 1999 are found. The ratio of \ion{He}{2} 2.19 \mic to Br$\gamma$ emission exhibits a narrow distribution among the stars, suggesting a narrow evolutionary spread centered predominantly on spectral types O4 If or Wolf-Rayet stars of the WN7 sub-type. From the approximate spectral types of the identified emission-line stars and comparisons with evolutionary models we infer a cluster age between $\sim$ 2 and 4.5 Myr.; Comment: latex...

‣ Each H^{1/2}-stable projection yields convergence and quasi-optimality of adaptive FEM with inhomogeneous Dirichlet data in R^d

Aurada, Markus; Feischl, Michael; Kemetmüller, Josef; Page, Marcus; Praetorius, Dirk
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/06/2013 Português
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We consider the solution of second order elliptic PDEs in $\R^d$ with inhomogeneous Dirichlet data by means of an $h$-adaptive FEM with fixed polynomial order $p\in\N$. As model example serves the Poisson equation with mixed Dirichlet-Neumann boundary conditions, where the inhomogeneous Dirichlet data are discretized by use of an $H^{1/2}$-stable projection, for instance, the $L^2$-projection for $p=1$ or the Scott-Zhang projection for general $p\ge1$. For error estimation, we use a residual error estimator which includes the Dirichlet data oscillations. We prove that each $H^{1/2}$-stable projection yields convergence of the adaptive algorithm even with quasi-optimal convergence rate. Numerical experiments with the $L^2$- and Scott-Zhang projection conclude the work.; Comment: 37 pages, 8 figures

‣ The Geometry of r-adaptive meshes generated using Optimal Transport Methods

Budd, C. J.; Russell, R. D.; Walsh, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/09/2014 Português
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The principles of mesh equidistribution and alignment play a fundamental role in the design of adaptive methods, and a metric tensor M and mesh metric are useful theoretical tools for understanding a methods level of mesh alignment, or anisotropy. We consider a mesh redistribution method based on the Monge-Ampere equation, which combines equidistribution of a given scalar density function with optimal transport. It does not involve explicit use of a metric tensor M, although such a tensor must exist for the method, and an interesting question to ask is whether or not the alignment produced by the metric gives an anisotropic mesh. For model problems with a linear feature and with a radially symmetric feature, we derive the exact form of the metric M, which involves expressions for its eigenvalues and eigenvectors. The eigenvectors are shown to be orthogonal and tangential to the feature, and the ratio of the eigenvalues (corresponding to the level of anisotropy) is shown to depend, both locally and globally, on the value of the density function and the amount of curvature. We thereby demonstrate how the optimal transport method produces an anisotropic mesh along a given feature while equidistributing a suitably chosen scalar density function. Numerical results are given to verify these results and to demonstrate how the analysis is useful for problems involving more complex features...

‣ Locally Adaptive Frames in the Roto-Translation Group and their Applications in Medical Imaging

Duits, R.; Janssen, M. H. J.; Hannink, J.; Sanguinetti, G. R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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Locally adaptive differential frames (gauge frames) are a well-known effective tool in image analysis, used in differential invariants and PDE-flows. However, at complex structures such as crossings or junctions, these frames are not well-defined. Therefore, we generalize the notion of gauge frames on images to gauge frames on data representations $U:\mathbb{R}^{d} \rtimes S^{d-1} \to \mathbb{R}$ defined on the extended space of positions and orientations, embedded as a Lie group quotient in the roto-translation group $SE(d)$, $d=2,3$. This allows to define multiple frames per position, one per orientation. We compute these frames via exponential curve fits in the extended data representations in $SE(d)$. These curve fits minimize first or second order variational problems which are solved by spectral decomposition of, respectively, a structure tensor or Hessian of data on $SE(d)$. We include these gauge frames in differential invariants and crossing preserving PDE-flows acting on extended data representation $U$ and we show their advantage compared to the standard left-invariant frame on $SE(d)$. Applications include crossing-preserving filtering and improved segmentations of the vascular tree in retinal images, and new 3D extensions of coherence-enhancing diffusion via invertible orientation scores.

‣ The First Laser Guide Star Adaptive Optics Observations of the Galactic Center: Sgr A*'s Infrared Color and the Extended Red Emission in its Vicinity

Ghez, A. M.; Hornstein, S. D.; Lu, J.; Bouchez, A.; Mignant, D. Le; van Dam, M. A.; Wizinowich, P.; Matthews, K.; Morris, M.; Becklin, E. E.; Campbell, R. D.; Chin, J. C. Y.; Hartman, S. K.; Johansson, E. M.; Lafon, R. E.; Stomski, P. J.; Summers, D. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/08/2005 Português
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(Abridged) We present the first Laser Guide Star Adaptive Optics (LGS-AO) observations of the Galactic center. LGS-AO has dramatically improved the quality, robustness, and versatility with which high angular resolution infrared images of the Galactic center can be obtained with the W. M. Keck II 10-meter telescope. Specifically, Strehl ratios of 0.7 and 0.3 at L'[3.8 micron] and K'[2.1 micron], respectively, are achieved in these LGS-AO images. During our observations, the infrared counterpart to the central supermassive black hole, Sgr A*-IR, showed significant infrared intensity variations, with observed L' magnitudes ranging from 12.6 to 14.5 mag. The faintest end of our L' detections, 1.3 mJy (dereddened), is the lowest level of emission yet observed for this source by a factor of 3. No significant variation in the location of SgrA*-IR is detected as a function of either wavelength or intensity. Near a peak in its intensity, we obtained the first measurement of SgrA*-IR's K'-L' color (3.0 +- 0.2 mag, observed), which corresponds to an intrinsic spectral index of -0.5 +- 0.3. This is significantly bluer than other recent infrared measurements. Because our measurement was taken at a time when Sgr A* was ~6 times brighter in the infrared than the other measurements...

‣ Imaging the Cool Hypergiant NML Cygni's Dusty Circumstellar Envelope with Adaptive Optics

Schuster, M. T.; Marengo, M.; Hora, J. L.; Fazio, G. G.; Humphreys, R. M.; Gehrz, R. D.; Hinz, P. M.; Kenworthy, M. A.; Hoffmann, W. F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/04/2009 Português
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We present sub-arcsec angular resolution, high-Strehl ratio mid-IR adaptive optics images of the powerful OH/IR source and cool hypergiant NML Cyg at 8.8, 9.8 and 11.7 um. These images reveal once more the complexity in the dusty envelope surrounding this star. We spatially resolve the physical structures (radius ~0.14", ~240 AU adopting a distance of 1.74 kpc) responsible for NML Cyg's deep 10 um silicate dust absorption feature. We also detect an asymmetric excess, at separations of ~0.3" to 0.5" (~520 to 870 AU), NW from the star. The colors of this excess are consistent with thermal emission of hot, optically thin dust. This excess is oriented in the direction of the Cyg OB2 stellar association, and is likely due to the disruption of NML Cyg's dusty wind with the near-UV radiation flux from the massive hot stars within Cyg OB2. This interaction was predicted in our previous paper (Schuster et al. 2006), to explain the geometry of an inverted photo-dissociation region observed at optical wavelengths.; Comment: Accepted for publication on The Astrophysical Journal

‣ Extinction controlled Adaptive Mask Coronagraph Lyot and Phase Mask dual concept for wide extinction area

Bourget, P.; Schuhler, N.; Mawet, D.; Haguenauer, P.; Girard, J.; Gonte, F.
Fonte: Society of Photo-Optical Instrumentation Engineers (SPIE) Publicador: Society of Photo-Optical Instrumentation Engineers (SPIE)
Tipo: Book Section; PeerReviewed Formato: application/pdf
Publicado em 13/09/2012 Português
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A dual coronagraph based on the Adaptive Mask concept is presented in this paper. A Lyot coronagraph with a variable diameter occulting disk and a nulling stellar coronagraph based on the Adaptive Phase Mask concept using polarization interferometry are presented in this work. Observations on sky and numerical simulations show the usefulness of the proposed method to optimize the nulling efficiency of the coronagraphs. In the case of the phase mask, the active control system will correct for the detrimental effects of image instabilities on the destructive interference (low-order aberrations such as tip-tilt and focus). The phase mask adaptability both in size, phase and amplitude also compensate for manufacturing errors of the mask itself, and potentially for chromatic effects. Liquid-crystal properties are used to provide variable transmission of an annulus around the phase mask, but also to achieve the achromatic π phase shift in the core of the PSF by rotating the polarization by 180°.A compressed mercury (Hg) drop is used as an occulting disk for the Lyot mask, its size control offers an adaptation to the seeing conditions and provides an optimization of the Tip-tilt correction.

‣ Clarifying our View of Star Formation in Massive Young Clusters with Adaptive Optics

Lu, Jessica R.; Clarkson, Will; McCrady, Nate; Ghez, Andrea M.; Morris, Mark R.; Stolte, Andrea; Yelda, Sylvana; Do, Tuan
Fonte: Astronomical Society of the Pacific Publicador: Astronomical Society of the Pacific
Tipo: Book Section; PeerReviewed Formato: application/pdf
Publicado em //2011 Português
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Observations of massive (> 10^4 M_⊙), young (<10 Myr) star clusters within our Galaxy allow us to fully sample the upper end of the initial mass function within a single star formation event. Such clusters also reside in a range of environments including the Galactic disk, the Galactic center region, and immediately surrounding the supermassive black hole in our Galactic nucleus. However, studies of these clusters are limited by crowding in the dense cores, strong and variable visible extinction, and confusion between cluster members and contaminating field stars. Using Keck laser-guided adaptive optics observations, we obtain high-resolution images and high-precision proper motions to both identify individual cluster members and investigate the kinematic properties of such clusters. As we build up complete proper motion data sets for several massive young clusters, our multi-color near-infrared photometry will yield precise mass functions that can be compared to search for environmental dependencies.

‣ Adaptive pacing, cognitive behaviour therapy, graded exercise, and specialist medical care for chronic fatigue syndrome: a cost-effectiveness analysis

McCrone, Paul R.; Sharpe, Michael; Chalder, Trudie; Knapp, Martin; Johnson, Anthony L.; Goldsmith, Kimberley A.; White, Peter D.
Fonte: PLoS ONE Publicador: PLoS ONE
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //2012 Português
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Background The PACE trial compared the effectiveness of adding adaptive pacing therapy (APT), cognitive behaviour therapy (CBT), or graded exercise therapy (GET), to specialist medical care (SMC) for patients with chronic fatigue syndrome. This paper reports the relative cost-effectiveness of these treatments in terms of quality adjusted life years (QALYs) and improvements in fatigue and physical function. Methods Resource use was measured and costs calculated. Healthcare and societal costs (healthcare plus lost production and unpaid informal care) were combined with QALYs gained, and changes in fatigue and disability; incremental cost-effectiveness ratios (ICERs) were computed. Results SMC patients had significantly lower healthcare costs than those receiving APT, CBT and GET. If society is willing to value a QALY at £30,000 there is a 62.7% likelihood that CBT is the most cost-effective therapy, a 26.8% likelihood that GET is most cost effective, 2.6% that APT is most cost-effective and 7.9% that SMC alone is most cost-effective. Compared to SMC alone, the incremental healthcare cost per QALY was £18,374 for CBT, £23,615 for GET and £55,235 for APT. From a societal perspective CBT has a 59.5% likelihood of being the most cost-effective...

‣ Model reference adaptive control for mobile robots in trajectory tracking using radial basis function neural networks

Rossomando,F. G.; Soria,C.; Patiño,D.; Carelli,R.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2011 Português
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This paper propose an Model Reference Adaptive Control (MRAC) for mobile robots for which stability conditions and performance evaluation are given. The proposed control structure combines a feedback linearization model, based on a kinematics nominal model, and a direct neural network-based adaptive dynamics control. The architecture of the dynamic control is based on radial basis functions neural networks (RBF-NN) to construct the MRAC controller. The parameters of the adaptive dynamic controller are adjusted according to a law derived using Lyapunov stability theory and the centers of the RBF are adapted using the supervised algorithm. The resulting MRAC controller is efficient and robust in the sense that it succeeds to achieve a good tracking performance with a small computational effort. Stability result for the adaptive neuro-control system is given. It is proved that control errors are ultimately bounded as a function of the approximation error of the RBF-NN. Experimental results showing the practical feasibility and performance of the proposed approach to mobile robotics are given.

‣ Voltage stability enhancement using an adaptive hysteresis controlled variable speed wind turbine driven EESG with MPPT

Jeevajothi,R; Devaraj,D
Fonte: Journal of Energy in Southern Africa Publicador: Journal of Energy in Southern Africa
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2014 Português
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This paper investigates the enhancement in voltage stability achieved while connecting a variable speed wind turbine (VSWT) driven electrically excited synchronous generator (EESG) into power systems. The wind energy conversion system (WECS) uses an AC-DC-AC converter system with an uncontrolled rectifier, maximum power point tracking (MPPT) controlled dc-dc boost converter and adaptive hysteresis controlled voltage source converter (VSC). The MPPT controller senses the rectified voltage (VDC) and traces the maximum power point to effectively maximize the output power. With MPPT and adaptive hysteresis band current control in VSC, the DC link voltage is maintained constant under variable wind speeds and transient grid currents.The effectiveness of the proposed WECS in enhancing voltage stability is analysed on a standard IEEE 5 bus system, which includes examining the voltage magnitude, voltage collapse and reactive power injected by the systems. Simulation results show that the proposed WECS has the potential to improve the long-term voltage stability of the grid by injecting reactive power. The performance of this scheme is compared with a fixed speed squirrel cage induction generator (SCIG), a variable speed doubly-fed induction generator (DFIG) and a variable speed permanent magnet synchronous generator (PMSG).