1,720,957 research outputs found
Two Problems in Control Theory and Applications to Economics
Full text linkThe thesis is composed by two dierent parts, which are not related each other. The rst part is devoted to study a class of optimal control problems, where the state equation is an ordinary dierential equation with delay in the control variable. This class of problems arises in economic applications, in particular in optimal advertising problems. The control problem is embedded in a suitable Hilbert space and the associated Hamilton-Jacobi-Bellman
(HJB) equation considered in this space. It is proved that the value function is continuous with respect to a weak norm and that it solves in the viscosity sense the associated HJB equation. The main result is the proof of a directional C1-regularity result for the value function. This result represents the starting point to dene a feedback map in classical sense going towards a verication theorem yielding optimal feedback controls for the problem. In the second part of the thesis, the techniques of the Malliavin Calculus are applied to a stochastic dierential equation whose coecients depend on a control process, in particular in the special case of Markovian controls. It is calculated the stochastic derivative of the stochastic dierential equation and it is proved that the Malliavin matrix is strictly positive, assuring the results of existence and regularity of densities for the controlled process.The thesis is composed by two dierent parts, which are not related each other. The rst part is devoted to study a class of optimal control problems, where the state equation is an ordinary dierential equation with delay in the control variable. This class of problems arises in economic applications, in particular in optimal advertising problems. The control problem is embedded in a suitable Hilbert space and the associated Hamilton-Jacobi-Bellman
(HJB) equation considered in this space. It is proved that the value function is continuous with respect to a weak norm and that it solves in the viscosity sense the associated HJB equation. The main result is the proof of a directional C1-regularity result for the value function. This result represents the starting point to dene a feedback map in classical sense going towards a verication theorem yielding optimal feedback controls for the problem. In the second part of the thesis, the techniques of the Malliavin Calculus are applied to a stochastic dierential equation whose coecients depend on a control process, in particular in the special case of Markovian controls. It is calculated the stochastic derivative of the stochastic dierential equation and it is proved that the Malliavin matrix is strictly positive, assuring the results of existence and regularity of densities for the controlled process.LUISS PhD Thesi
A parametric study of the term structure dynamics
No full textWe present an analysis of the dynamics of the term structure of interest rates based on the study of the time evolution of the parameters of a variation of the Nelson–Siegel model. The results show that it is extremely difficult to find a relation between the evolution of the term structure and the behavior of macroeconomic variables different from the official interest rate
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
Irreversible investment with fixed adjustment costs: a stochastic impulse control approach
No full textWe consider an optimal stochastic impulse control problem over an infinite time horizon motivated by a model of irreversible investment choices with fixed adjustment costs. By employing techniques of viscosity solutions and relying on semiconvexity arguments, we prove that the value function is a classical solution to the associated quasi-variational inequality. This enables us to characterize the structure of the continuation and action regions and construct an optimal control. Finally, we focus on the linear case, discussing, by a numerical analysis, the sensitivity of the solution with respect to the relevant parameters of the problem
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
Dynamic programming for optimal control problems with delays in the control variable
Full text linkWe study a class of optimal control problems with state constraint, where the state equation is a differential equation with delays in the control variable. This class of problems arises in some economic applications, in particular in optimal advertising problems. The optimal control problem is embedded in a suitable Hilbert space, and the associated Hamilton-Jacobi-Bellman (HJB) equation is considered in this space. It is proved that the value function is continuous with respect to a weak norm and that it solves in the viscosity sense the associated HJB equation. The main results are the proof of a directional C1-regularity for the value function and the feedback characterization of optimal controls. © 2014 Society for Industrial and Applied Mathematics
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
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