1,721,055 research outputs found
Direct inversion from partial-boundary data in electrical impedance tomography
Get PDFIn electrical impedance tomography (EIT) one wants to image the conductivity distribution of a body from current and voltage measurements carried out on its boundary. In this paper we consider the underlying mathematical model, the inverse conductivity problem, in two dimensions and under the realistic assumption that only a part of the boundary is accessible to measurements. In this framework our data are modeled as a partial Neumann-to-Dirichlet map (ND map). We compare this data to the full-boundary ND map and prove that the error depends linearly on the size of the missing part of the boundary. The same linear dependence is further proved for the difference of the reconstructed conductivities - from partial and full boundary data. The reconstruction is based on a truncated and linearized D-bar method. Auxiliary results include an extrapolation method to estimate the full-boundary data from the measured one, an approximation of the complex geometrical optics solutions computed directly from the ND map as well as an approximate scattering transform for reconstructing the conductivity. Numerical verification of the convergence results and reconstructions are presented for simulated test cases
PROPAGATION AND RECOVERY OF SINGULARITIES IN THE INVERSE CONDUCTIVITY PROBLEM
Get PDFThe ill-posedness of Calderon's inverse conductivity problem, responsible for the poor spatial resolution of electrical impedance tomography (EIT), has been an impetus for the development of hybrid imaging techniques, which compensate for this lack of resolution by coupling with a second type of physical wave, typically modeled by a hyperbolic PDE. We show in two dimensions how, using EIT data alone, to use propagation of singularities for complex principal-type PDEs to efficiently detect interior jumps and other singularities of the conductivity. Analysis of variants of the CGO solutions of Astala and Paivarinta (Ann. Math. (2) 163: 1 (2006), 265-299) allows us to exploit a complex principal-type geometry underlying the problem and show that the leading term in a Born series is an invertible nonlinear generalized Radon transform of the conductivity. The wave front set of all higher-order terms can be characterized, and, under a prior, some refined descriptions are possible. We present numerics to show that this approach is effective for detecting inclusions within inclusions.Peer reviewe
SAT solution for the networked economy
No full textDiplomityössä oli pyrkimyksenä arvioida SIM-korttiohjelmistojen menestymisen mahdollisuuksia nykypäivän ohjelmistomarkkinassa.
SIM-kortti on älykortti, jota käytetään matkapuhelinliittymän tilaajan yksilöllisen GSM-verkkoavaimen tallentamiseen.
SIM-kortti on myös mikrotietokone, joka mahdollistaa SAT nimellä kulkevien ohjelmien ajon kortilla.
SAT-sovelluskehityksestä ovat perinteisesti vastanneet verkko-operaattorit sekä SIM-korttivalmistajat.
Maailmassa on kuitenkin myös muutamia pieniä SAT-kehitykseen erikoistuneita yrityksiä, kuten tässä diplomityössä käsitelty case-yritys.
Perinteisesti nämä pienet SAT-kehitykseen erikoistuneet yritykset ovat toimineet verkko-operaattoreiden ja SIM-korttivalmistajien alihankkijoina.
Diplomityön tarkoituksena olikin selvittää, olisiko verkkoliiketoimintamallein mahdollista löytää uusia myynnin kanavia SAT-kehitykseen erikoistuneille yrityksille.
Työn tavoitteiden saavuttamiseksi SIM-ohjelmistomarkkina analysoitiin käyttäen kahta eri teoreettista mallia, Porterin viiden voiman mallia ja verkkoliiketoimintamallia.
Porterin viiden voiman mallin avulla arvioitiin SIM-korttiohjelmistoyrityksen toimintaympäristö.
Verkkoliiketoimintamallilla pyrittiin arvioimaan SIM-korttiohjelmistoyrityksen yhteistyömahdollisuudet liiketoiminta-ympäristön muiden yritysten kanssa.
Kahdesta yllämainitusta mallista tehdyt johtopäätökset koottiin yhdeksi malliksi, jota sovellettiin diplomityön case-yrityksen analyysiin.
Malli osoitti, että SAT-kehittäjien tulisi pyrkiä pois perinteisestä alihankkijan roolista ja lisätä yhteistyötä esimerkiksi IT-kokonaisratkaisuja tuottavien yritysten kanssa.
Case-yrityksen analyysistä saadut tarkemmat tulokset tukivat näitä yleisiä johtopäätöksiä, ja case-yritykselle arvioitiinkin soveliaammaksi keskittää voimat esimerkiksi Identity Management järjestelmien (IdM) osakokonaisuuksien toimittamiseen kuin jatkaa perinteistä mallia verkko-operaattoreiden ja SIM-korttivalmistajien alihankkijana
Finland at CERN: Working for the next 100 years of solutions
No full textProfessor of Industrial Mathematics, University of Helsink
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Random tree besov priors – towards fractal imaging
No full textWe propose alternatives to Bayesian prior distributions that are frequently used in the study of inverse problems. Our aim is to construct priors that have similar good edge-preserving properties as total variation or Mumford-Shah priors but correspond to well-defined infinite-dimensional random variables, and can be approximated by finite-dimensional random vari-ables. We introduce a new wavelet-based model, where the non-zero coefficients are chosen in a systematic way so that prior draws have certain fractal behaviour. We show that realisations of this new prior take values in Besov spaces and have singularities only on a small set τ with a certain Hausdorff dimension. We also introduce an efficient algorithm for calculating the MAP estimator, arising from the the new prior, in the denoising problem.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Statistic
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