1,721,036 research outputs found
Lamé and ZK: spectral analysis and unique continuation
Full text linkThe bulk of this thesis focuses on two fields that are being deeply investigated both by the mathematical and physical community, namely spectral theory and unique continuation. Both these theories are extremely rich and nowadays represent inclusive terms covering a wide variety of branches of physics and mathematics. More precisely, the first one, in its general meaning, includes theories which extend the eigenvalues analysis for square matrices to a much broader class of mathematical characters, for instance, due to their relevance in quantum interpretation, to unbounded operators in Hilbert space. The second one is concerned with the search for classes of functions for which the vanishing in a region ensures the vanishing in a larger one, roughly speaking it is the issue to find the correct analogue of harmonic functions for which the Liouville theorem guarantees the stated rigidity.
The structure of this document is roughly the following. The main body of work of this thesis is contained in the first two parts, in which the aforementioned themes are analyzed, specifically spectral properties for the non self-adjoint perturbed Lamé operator of elasticity and unique continuation for Zakharov-Kuznetzov dispersive equation are objects of our investigation. Each part contains an introductory chapter which endeavors to give an overview of the problem in exam and to clarify why it is worthy of attention. Moreover a time-based analysis, involving also the recent developments of these matters, is provided in the same chapters. At times the discussion is chosen to be informal in order to convey the basic underlying ideas. The concise statements together with their proofs, employing the necessary rigor lacking in the introductions, are given in the following chapters.
The third part is slightly different, it is not concerned with achieved results but it involves a future possible project that we would like to deepen. More precisely the prospect presented takes place in the field of inverse problems in elasticity. The possibility to re-adapt some useful tools earned to address the problems described in the first two parts has played a relevant role to motivate solidly this future investigation
Identification in structural vector autoregressive models with structural changes
Full text linkAn increasing strand of the literature uses structural changes and different
heteroskedasticity regimes found in the data constructively to improve the
identification of structural parameters in Structural Vector Autoregressions
(SVAR). A standard assumption in this literature is that the reduced form
unconditional covariance matrix of the system varies while the structural
parameters remain constant. Under this condition it is possible to identify
the SVAR without the need to resort to theory-driven restrictions. With
macroeconomic data, the hypothesis that the structural parameters are
invariant to breaks is untenable. This paper investigates the identification
issues that arise in SVARs when structural breaks occurring at known dates affect both the reduced form covariance matrix and the structural
parameters. The knowledge that different heteroskedasticity regimes
characterize the data is combined with theory-driven restrictions giving
rise to new necessary and sufficient local identification rank conditions
which generalize the ones which apply for SVARs with constant parameters.
This approach opens interesting possibilities for practitioners. An
empirical illustration shows the usefulness of the suggested identification strategy by focusing on a small monetary policy SVAR of the U.S. economy. Two heteroskedasticity regimes are found to characterize the data before andafter the 1980s and this information is combined with economic reasoning to identify the effect of monetary policy shocks on output and inflatio
Testing the purchasing power parity through I(2) cointegration techniques
No full textThis paper contributes to the empirical literature on the purchasing power parity (PPP) over the post-Bretton Woods period by providing a time-series based interpretation of the controversial evidence characterizing the dynamics of real exchange rates. It is shown that the persistence of deviations from the PPP between a set of European countries and the United States may be empirically attributed to the presence of I(2) stochastic trends in prices using Consumer Price Indices. Interestingly, the slow adjustment towards the equilibrium can be modelled through 'integral-proportional' equilibrium correction models and this evidence can be partly reconciled with theories where the inflation rate reduces the markup of profit-maximizing firms acting on imperfectly competitive markets
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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