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UCL University College London Eprints (334,440 recursos)
UCL Eprints collects the work of UCL researchers and makes it freely available over the web, helping the worldwide scholarly community to discover UCL research. Institutional repositories like UCL Eprints complement the traditional academic publishing and scholarly communications processes. They raise the visibility of research and help to maximise its impact. UCL researchers are encouraged to deposit a copy of each journal article, conference paper, working paper, and any other research output, in the UCL Eprints at the earliest opportunity, ensuring that their research reaches as wide an audience as possible.

Mostrando recursos 141 - 160 de 333,856

141. Heuristic parameter-choice rules for convex variational regularization based on error estimates - Jin, B; Lorenz, DA
In this paper, we are interested in heuristic parameter-choice rules for general convex variational regularization which are based on error estimates. Two such rules are derived and generalize those from quadratic regularization, namely, the Hanke-Raus rule and quasi-optimality criterion. A posteriori error estimates are shown for the Hanke-Raus rule, and convergence for both rules is also discussed. Numerical results for both rules are presented to illustrate their applicability. © 2010 Society for Industrial and Applied Mathematics.

142. Numerical estimation of the Robin coefficient in a stationary diffusion equation - Jin, B; Zou, J
A finite-element method is proposed for the nonlinear inverse problem of estimating the Robin coefficient in a stationary diffusion equation from boundary measurements of the solution and the heat flux. The inverse problem is formulated as an output least squares optimization problem with an appropriate regularization, then the finite-element method is employed to discretize the nonlinear optimization system. Mathematical properties of both the continuous and the discrete optimization problems are investigated. The conjugate gradient method is employed to solve the optimization problem, and an efficient preconditioner via the Sobolev inner product is also suggested. Numerical results for several two-dimensional problems...

143. Function spaces and optimal currents in impedance tomography - Jin, B; Maass, P; Khan, T; Pidcock, M
The main objective of this paper is to compare analytically as well as numerically different approaches for obtaining optimal input currents in impedance tomography. Following the approaches described in, e.g. [Cheney and Isaacson, IEEE Trans. Biomed. Eng. 39: 852 860, 1992, Isaacson, IEEE Trans. Med. Imag. 5: 91 95, 1986, Ito and Kunisch, SIAM J. Contr. Optim. 33: 643 666., 1995, Knowles, An optimal current functional for electrical impedance tomography, 2004], we aim at constructing input currents j, which contain the most information about the difference between the unknown physical conductivity σ* and a given approximation σ 0. The differences...

144. Hierarchical Bayesian inference for Ill-posed problems via variational method - Jin, B; Zou, J
This paper investigates a novel approximate Bayesian inference procedure for numerically solving inverse problems. A hierarchical formulation which determines automatically the regularization parameter and the noise level together with the inverse solution is adopted. The framework is of variational type, and it can deliver the inverse solution and regularization parameter together with their uncertainties calibrated. It approximates the posteriori probability distribution by separable distributions based on Kullback-Leibler divergence. Two approximations are derived within the framework, and some theoretical properties, e.g. variance estimate and consistency, are also provided. Algorithms for their efficient numerical realization are described, and their convergence properties are...

145. R47H TREM2 variant increases risk of typical early-onset Alzheimer's disease but not of prion or frontotemporal dementia. - Slattery, CF; Beck, JA; Harper, L; Adamson, G; Abdi, Z; Uphill, J; Campbell, T; Druyeh, R; Mahoney, CJ; Rohrer, JD; Kenny, J; Lowe, J; Leung, KK; Barnes, J; Clegg, SL; Blair, M; Nicholas, JM; Guerreiro, RJ; Rowe, JB; Ponto, C; Zerr, I; Kretzschmar, H; Gambetti, P; Crutch, SJ; Warren, JD; Rossor, MN; Fox, NC; Collinge, J; Schott, JM; Mead, S
Rare TREM2 variants are significant risk factors for Alzheimer's disease (AD).

146. Altered body schema processing in frontotemporal dementia with C9ORF72 mutations - Downey, LE; Fletcher, PD; Golden, HL; Mahoney, CJ; Agustus, JL; Schott, JM; Rohrer, JD; Rossor, MN; Crutch, SJ; Warren, JD; Beck, J; Mead, S
Background: Mutations in C9ORF72 are an important cause of frontotemporal dementia (FTD) and motor neuron disease. Accumulating evidence suggests that FTD associated with C9ORF72 mutations (C9ORF72-FTD) is distinguished clinically by early prominent neuropsychiatric features that might collectively reflect deranged body schema processing. However, the pathophysiology of C9ORF72-FTD has not been elucidated. Methods: We undertook a detailed neurophysiological investigation of five patients with C9ORF72-FTD, in relation to patients with FTD occurring sporadically and on the basis of mutations in the microtubule-associated protein tau gene and healthy older individuals. We designed or adapted behavioural tasks systematically to assess aspects of somatosensory body...

147. Sparsity reconstruction in electrical impedance tomography: An experimental evaluation - Gehre, M; Kluth, T; Jin, B; Maass, P; Lipponen, A; Seppnen, A; Kaipio, JP
We investigate the potential of sparsity constraints in the electrical impedance tomography (EIT) inverse problem of inferring the distributed conductivity based on boundary potential measurements. In sparsity reconstruction, inhomogeneities of the conductivity are a priori assumed to be sparse with respect to a certain basis. This prior information is incorporated into a Tikhonov-type functional by including a sparsity-promoting -penalty term. The functional is minimized with an iterative soft shrinkage-type algorithm. In this paper, the feasibility of the sparsity reconstruction approach is evaluated by experimental data from water tank measurements. The reconstructions are computed both with sparsity constraints and with a...

148. A new choice rule for regularization parameters in Tikhonov regularization - Ito, K; Jin, B; Zou, J
This article proposes and analyses a novel heuristic rule for choosing regularization parameters in Tikhonov regularization for inverse problems. The existence of solutions to the regularization parameter equation is shown, and a variational characterization of the inverse solution is provided. Some a posteriori error estimates of the approximate solutions to the inverse problem are also established. An iterative algorithm is suggested for the efficient numerical realization of the new choice rule, which is shown to have a practically desirable monotone convergence. Numerical experiments for both mildly and severely ill-posed benchmark inverse problems with various regularizing functionals of Tikhonov type, e.g....

149. Sparsity regularization for parameter identification problems - Jin, B; Maass, P
The investigation of regularization schemes with sparsity promoting penalty terms has been one of the dominant topics in the field of inverse problems over the last years, and Tikhonov functionals with ℓ-penalty terms for 1 p 2 have been studied extensively. The first investigations focused on regularization properties of the minimizers of such functionals with linear operators and on iteration schemes for approximating the minimizers. These results were quickly transferred to nonlinear operator equations, including nonsmooth operators and more general function space settings. The latest results on regularization properties additionally assume a sparse representation of the true solution as well...

150. Iterative parameter choice by discrepancy principle - Jin, B; Zhao, Y; Zou, J
This work is concerned with the numerical implementation of the discrepancy principle for nonsmooth Tikhonov regularization for linear inverse problems. First, some theoretical properties of the solutions to the discrepancy equation, i.e., uniqueness and upper bounds, are discussed. Then, the idea of Padé approximation is exploited for designing model functions with model parameters iteratively updated. Two algorithms are proposed for its efficient numerical realization, i.e., a two-parameter algorithm based on model functions and a quasi-Newton method, and their convergence properties are briefly discussed. Numerical results for four nonsmooth models are presented to demonstrate the accuracy of the principle and to...

151. Gradient-based estimation of Manning's friction coefficient from noisy data - Calo, VM; Collier, N; Gehre, M; Jin, B; Radwan, H; Santillana, M
We study the numerical recovery of Manning's roughness coefficient for the diffusive wave approximation of the shallow water equation. We describe a conjugate gradient method for the numerical inversion. Numerical results for one-dimensional models are presented to illustrate the feasibility of the approach. Also we provide a proof of the differentiability of the weak form with respect to the coefficient as well as the continuity and boundedness of the linearized operator under reasonable assumptions using the maximal parabolic regularity theory. © 2012 Elsevier B.V. All rights reserved.

152. Chronos: A NIR spectroscopic galaxy survey. From the formation of galaxies to the peak of activity - Cropper, MS; Cropper, M

153. A two-stage method for inverse medium scattering - Ito, K; Jin, B; Zou, J
We present a novel numerical method to the time-harmonic inverse medium scattering problem of recovering the refractive index from noisy near-field scattered data. The approach consists of two stages, one pruning step of detecting the scatterer support, and one resolution enhancing step with nonsmooth mixed regularization. The first step is strictly direct and of sampling type, and it faithfully detects the scatterer support. The second step is an innovative application of nonsmooth mixed regularization, and it accurately resolves the scatterer size as well as intensities. The nonsmooth model can be efficiently solved by a semi-smooth Newton-type method. Numerical results for...

154. Novel microdeletion in LOR causing autosomal dominant Loricrin keratoderma. - Kinsler, VA; Drury, S; Khan, A; Waelchli, R; Rukaite, G; Barnicoat, A; Lench, N; Harper, JI; O'Shaughnessy, RF
An eight year-old girl presented with generalized xerosis and scaling without erythema, mild palmo-plantar keratoderma (PPK) with acral fissuring, and moderate global developmental delay with microcephaly. She was born as a collodion baby, as were her three siblings and her Father, all of whom shared the cutaneous findings, but without neurological abnormality. Mother was unaffected. Peripheral blood DNA was sequenced using a Nextera (Illumina(®) ) next generation sequencing custom-designed targeted capture panel of clinically relevant published Dermatology genes, including known ichthyosis and PPK genes. A DNA library was prepared using fragmentation, tagging and targeted amplification, before sequencing on an ABI...

155. Roles of the constituent chains of botulinum neurotoxin type A in the blockade of neuromuscular transmission in mice - Wadsworth, JDF; Shone, CC; Melling, J; Dolly, JO

156. All my mates have got it, so it must be okay”: Constructing a Richer Understanding of Privacy Concerns—An Exploratory Focus Group Study - Morton, AJ
The measurement of peoples’ privacy concern has traditionally focused on their general level of privacy concern (e.g. Westin), or on organisations’ information handling practices (e.g. CFIP and IUIPC). A richer approach to the construction of peoples’ privacy concerns is proposed in which the level of an individual’s privacy concern about a technology service—consisting of a technology platform and providing organisation—is constructed from: (1) their innate level of privacy concern; (2) absence, or inadequate implementation, of the attributes of a technology service the individual considers important (e.g. online security mechanisms, privacy policy, etc.); and (3) environmental cues (e.g. friends’ advice and...

157. Nicotine patch preloading for smoking cessation (the preloading trial): study protocol for a randomized controlled trial - Lindson-Hawley, N; Coleman, T; Docherty, G; Hajek, P; Lewis, S; Lycett, D; McEwen, A; McRobbie, H; Munafo, MR; Parrott, S; Aveyard, P

158. Clinical features and pharmacotherapy of childhood monoamine neurotransmitter disorders - Ng, J; Kurian, MA; Heales, SJR
Childhood neurotransmitter disorders are increasingly recognised as an expanding group of inherited neurometabolic syndromes. They are caused by disturbance in synthesis, metabolism, and homeostasis of the monoamine neurotransmitters, including the catecholamines (dopamine, norepinephrine, and epinephrine) and serotonin. Disturbances in monoamine neurotransmission will lead to neurological symptoms that often overlap with clinical features of other childhood neurological disorders (such as hypoxic ischaemic encephalopathy, cerebral palsy, other movement disorders, and paroxysmal conditions); consequently, neurotransmitter disorders are frequently misdiagnosed. The diagnosis of neurotransmitter disorders is made through detailed clinical assessment, analysis of cerebrospinal fluid neurotransmitters, and further supportive diagnostic investigations. Early and accurate...

159. Laser ultrasonic microscopy - Sharples, SD; Clark, M; Smith, RJ; Ellwood, RJ; Li, W; Somekh, MG

160. Determination of the acoustoelastic coefficient for surface acoustic waves using dynamic acoustoelastography: An alternative to static strain - Ellwood, R; Stratoudaki, T; Sharples, SD; Clark, M; Somekh, MG


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