293 research outputs found
On the constrained mock-Chebyshev least-squares
The algebraic polynomial interpolation on uniformly distributed nodes is
affected by the Runge phenomenon, also when the function to be interpolated is
analytic. Among all techniques that have been proposed to defeat this
phenomenon, there is the mock-Chebyshev interpolation which is an interpolation
made on a subset of the given nodes whose elements mimic as well as possible
the Chebyshev-Lobatto points. In this work we use the simultaneous
approximation theory to combine the previous technique with a polynomial
regression in order to increase the accuracy of the approximation of a given
analytic function. We give indications on how to select the degree of the
simultaneous regression in order to obtain polynomial approximant good in the
uniform norm and provide a sufficient condition to improve, in that norm, the
accuracy of the mock-Chebyshev interpolation with a simultaneous regression.
Numerical results are provided.Comment: 17 pages, 9 figure
Adjustment curves for binary responses associated to stochastic processes
Functional Data, Random Multiplicative Cascade, Adjustment Curve, Stochastic Process
Pharmacological blockade of the WNT-beta-catenin signaling: a possible first-in-kind DMOAD.
International audienc
Polynomial approximation of derivatives by the constrained mock-Chebyshev least squares operator
The constrained mock-Chebyshev least squares operator is a linear
approximation operator based on an equispaced grid of points. Like other
polynomial or rational approximation methods, it was recently introduced in
order to defeat the Runge phenomenon that occurs when using polynomial
interpolation on large sets of equally spaced points. The idea is to improve
the mock-Chebyshev subset interpolation, where the considered function is
interpolated only on a proper subset of the uniform grid, formed by nodes that
mimic the behavior of Chebyshev--Lobatto nodes. In the mock-Chebyshev subset
interpolation all remaining nodes are discarded, while in the constrained
mock-Chebyshev least squares interpolation they are used in a simultaneous
regression, with the aim to further improving the accuracy of the approximation
provided by the mock-Chebyshev subset interpolation. The goal of this paper is
two-fold. We discuss some theoretical aspects of the constrained mock-Chebyshev
least squares operator and present new results. In particular, we introduce
explicit representations of the error and its derivatives. Moreover, for a
sufficiently smooth function in , we present a method for
approximating the successive derivatives of at a point , based
on the constrained mock-Chebyshev least squares operator and provide estimates
for these approximations. Numerical tests demonstrate the effectiveness of the
proposed method.Comment: 17 pages, 23 figure
Culture expansion in low-glucose conditions preserves chondrocyte differentiation and enhances their subsequent capacity to form cartilage tissue in three-dimensional culture.
Culture conditions that preserve a stable chondrocyte phenotype are desirable in cell-based cartilage repair to maximize efficacy and clinical outcome. This study investigates whether low-glucose conditions will preserve the chondrocyte phenotype during culture expansion. Articular chondrocytes were culture-expanded in media supplemented with either low (1 mM) or high (10 mM) glucose. The metabolic phenotype, reactive oxygen species generation, and mRNA expression of markers of differentiation or catabolism were assessed by reverse-transcription quantitative polymerase chain reaction after four population doublings (PDs) and subsequent tissue formation capacity determined using pellet cultures. Continuous monolayer culture was used to determine the population doubling limit. After expansion in monolayer for four PDs, chondrocytes expanded in low-glucose conditions exhibited higher expression of the differentiation markers SOX9 and COL2A1 and reduced expression of the catabolic metalloproteinase matrix metallopeptidase 13. When chondrocytes expanded in low glucose were cultured in micropellets, they consistently generated more cartilaginous extracellular matrix than those expanded in high glucose, as evaluated by wet weight, sulfated glycosaminoglycan content, and hydroxyproline assay for collagen content. The same pattern was observed whether high or low glucose was used during the pellet culture. During expansion, chondrocytes in high-glucose generated 50% more reactive oxygen species than low-glucose conditions, despite a lower dependence on oxidative phosphorylation for energy. Furthermore low-glucose cells exhibited >30% increased population doubling limit. These data suggests that low-glucose expansion conditions better preserve the expression of differentiation markers by chondrocytes and enhance their subsequent capacity to form cartilage in vitro. Therefore, low glucose levels should be considered for the expansion of chondrocytes intended for tissue engineering applications.This study was funded by the Medical Research Council/Engineering and Physical Sciences Research Council (EPSRC) discipline bridging initiative grant PPA026, EPSRC Platform Grant EP/E046975/1; Human Frontier Science Program Grant RGP0025/2009-C and Arthritis Research U.K. grants 19654 and 19344
Product integration rules by the constrained mock-Chebyshev least squares operator
In this paper we consider the problem of the approximation of definite integrals on finite intervals for integrand functions showing some kind of "pathological" behavior, e.g. "nearly" singular functions, highly oscillating functions, weakly singular functions, etc. In particular, we introduce and study a product rule based on equally spaced nodes and on the constrained mock-Chebyshev least squares operator. Like other polynomial or rational approximation methods, this operator was recently introduced in order to defeat the Runge phenomenon that occurs when using polynomial interpolation on large sets of equally spaced points. Unlike methods based on piecewise approximation functions, mainly used in the case of equally spaced nodes, our product rule offers a high efficiency, with performances slightly lower than those of global methods based on orthogonal polynomials in the same spaces of functions. We study the convergence of the product rule and provide error estimates in subspaces of continuous functions. We test the effectiveness of the formula by means of several examples, which confirm the theoretical estimates
Activation of WNT and BMP signaling in adult human articular cartilage following mechanical injury
Peer reviewedPublisher PD
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