Generazione e caratterizzazione dinamica di potenziali ottici mediante un dispositivo a microspecchi

In questa tesi si tratta della caratterizzazione dinamica dei potenziali ottici che possono essere ottenuti mediante un dispositivo a microspecchi (DMD), che sarà utilizzato in esperimenti con atomi freddi. Lo studio della superfluidità nei condensati di Bose-Einstein, e del fenomeno ad essa strettamente collegato della formazione di vortici, è uno filoni di ricerca più sviluppati nell'ambito della fisica degli atomi freddi. Gli apparati sperimentali fanno uso di complessi sistemi di generazione di potenziali ottici variabili nel tempo. Un dispositivo a microspecchi consiste di una matrice di specchi, ciascuno dei quali può essere controllato da un attuatore elettromeccanico; questo dispositivo consente quindi di modulare la radiazione luminosa che esso riflette, variandola anche nel tempo. È possibile quindi utilizzare tale dispositivo per produrre un potenziale ottico variabile nel tempo. Il lavoro sperimentale svolto per questa tesi comprende misure di tempi di commutazione e fedeltà delle immagini generate utilizzando un dispositivo a microspecchi, e lo sviluppo di un codice di controllo che, mediante un algoritmo PID, consenta di ridurre le distorsioni indotte dal sistema ottico

Should We Cry over the Spilt Milk? Market Power and Structural Change along Dairy Supply Chains in EU Countries

A “first-pass” test on a set of monthly prices index series from 2000 to 2015 was applied to detect market power exertion in the dairy value chain of 25 EU countries. Due to econometric and theoretical restrictions, the test yielded conclusive findings only in 11 over 25 EU Countries. Such results show that in Austria, Portugal, Slovakia, Hungary and Croatia, the downstream sector exerts market power. Other EU countries (Spain, UK, Denmark, Czech Republic, Bulgaria and Sweden) are characterised by perfectly competitive dairy chains. These results were consistent with the findings of previous studies based on structural and mark-up models. Results of the market power test in the subsample of 11 countries have been related to various structural characteristics of the dairy chains. Market power exertion is negatively related to the average farm size. Such variable may be seen as a proxy of the degree of supply concentration provided by Producers Organizations (POs) to increase the bargaining power of the farm sector along the food chain. To test such a hypothesis, comparable data on supply concentration by POs across EU Countries are necessary. On the other hand, the structural change, represented by the increase of average farm size over time and the concentration rate in higher classes (above 250,000 € of Standard Output) is almost unrelated to the perfectly competitive conduct along EU dairy chains

SGP-dec:A Scaled Gradient Projection method for2D and 3D images deconvolution

SGP-dec is a Matlab package for the deconvolution of 2D and 3D images corrupted by Poisson noise. Following amaximum likelihood approach, SGP-dec computes a deconvolved image by early stopping an iterative method for the minimization of the generalized Kullback-Lieibler divergence. The iterative minimization method implemented by SGP-dec is a Scaled Gradient Projection (SGP) algorithm that can be considered an acceleration of the Expectation Maximization method, also known as Richardson-Lucy method. The main feature of the SGP algorithm consists in the combination of non-expensivediagonally scaled gradient directions with adaptive Barzilai-Borwein steplength rules specially designed for thesedirections; global convergence properties are ensured by exploiting a line-search strategy (monotone or nonmonotone)along the feasible direction.The algorithm SGP is provided to be used as iterative regularization method; this means that a regularized reconstruction can be obtained by early stopping the SGP sequence. Several early stopping strategies can be selected, basedon different criteria: maximum number of iterations, distance of successive iterations or function values, discrepancyprinciple; the user must choose a stopping criterion and fixsuited values for the parameters involved by the chosen criterion

SGP-IDL: a Scaled Gradient Projection method for image deconvolution in an Interactive Data Language environment

An Interactive Data Language (IDL) package for the single and multiple deconvolution of 2D images corrupted by Poisson noise, with the optional inclusion of a boundary effect correction. Following a maximum likelihood approach, SGP-IDL computes a deconvolved image by early stopping of the scaled gradient projection (SGP) algorithm for the solution of the optimization problem coming from the minimization of the generalized Kullback-Leibler divergence between the computed image and the observed image. The algorithms have been implemented also for Graphic Processing Units (GPUs)