3,359 research outputs found

    A Bayesian framework for functional time series analysis

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    The paper introduces a general framework for statistical analysis of functional time series from a Bayesian perspective. The proposed approach, based on an extension of the popular dynamic linear model to Banach-space valued observations and states, is very flexible but also easy to implement in many cases. For many kinds of data, such as continuous functions, we show how the general theory of stochastic processes provides a convenient tool to specify priors and transition probabilities of the model. Finally, we show how standard Markov chain Monte Carlo methods for posterior simulation can be employed under consistent discretizations of the data

    An R Package for Dynamic Linear Models

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    We describe an R package focused on Bayesian analysis of dynamic linear models. The main features of the package are its flexibility to deal with a variety of constant or time-varying, univariate or multivariate models, and the numerically stable singular value decomposition-based algorithms used for filtering and smoothing. In addition to the examples of "out-of-the-box" use, we illustrate how the package can be used in advanced applications to implement a Gibbs sampler for a user-specified model.

    State Space Models in R

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    We give an overview of some of the software tools available in R, either as built- in functions or contributed packages, for the analysis of state space models. Several illustrative examples are included, covering constant and time-varying models for both univariate and multivariate time series. Maximum likelihood and Bayesian methods to obtain parameter estimates are considered.

    Absolute calibration and beam reconstruction of MITO (a ground-based instrument in the millimetric region)

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    An efficient sky data reconstruction derives from a precise characterization of the observing instrument. Here we describe the reconstruction of performances of a single-pixel 4-band photometer installed at MITO (Millimeter and Infrared Testagrigia Observatory) focal plane. The strategy of differential sky observations at millimeter wavelengths, by scanning the field of view at constant elevation wobbling the subreflector, induces a good knowledge of beam profile and beam-throw amplitude, allowing efficient data recovery. The problems that arise estimating the detectors throughput by drift scanning on planets are shown. Atmospheric transmission, monitored by skydip technique, is considered for deriving final responsivities for the 4 channels using planets as primary calibrators.Comment: 14 pages, 6 fiugres, accepted for pubblication by New Astronomy (25 March

    Peranan pendidikan dalam pembinaan kebudayaan nasional di daerah Jambi

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    Buku ini ditulis dengan tujuan untuk mengetahui faktor penghambat dan faktor pendukung pengejawantahan kebudayaan nasional yang ditransformasikan melalui pranata keluarga, pranata sekolah, pranata ekonomi , pranata agama, dan pranata politik

    An R Package for Dynamic Linear Models

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    We describe an <b>R</b> package focused on Bayesian analysis of dynamic linear models. The main features of the package are its flexibility to deal with a variety of constant or time-varying, univariate or multivariate models, and the numerically stable singular value decomposition-based algorithms used for filtering and smoothing. In addition to the examples of "out-of-the-box" use, we illustrate how the package can be used in advanced applications to implement a Gibbs sampler for a user-specified model

    Physics and modelling of generation and propagation of noise by complex sources in realistic basins

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    The need to develop more accurate numerical tools for the propagation of noise in underwater environments is driven by the continuous increase of human activity in the sea and coastal areas. Noise has been shown to be dangerous to marine wildlife, and steps should be taken soon to mitigate it. Knowing that the primary sources of noise pollution at sea are marine propellers, one of the problems is assessing how the noise generated interacts with the environment, since up to now, the main focus was the characterization of the acoustic signature in the near field or, alternatively, the propagation of simplified acoustic sources in sea-like domains. The work conducted in this thesis assesses the modelling of complex acoustic sources and the propagation of acoustic pressure in realistic domains. A propagation model based on the solution of the acoustic wave equation in the time and space domain is implemented and used in conjunction with the Ffowcs Williams and Hawkings (FW-H) to analyze the possible patterns occurring in the underwater environment. Specifically, we analyzed the noise radiated by a marine propeller in a canal, focusing on the effects of the boundaries on the acoustic field and, secondly, the consequence of a rotating body placed underneath a free surface. We defined a new methodology called Full Acoustic Analogy (FAA) to achieve these results. This methodology aims to overcome some intrinsic limitations of the known Acoustic Analogies. The study presented here attempts to bridge the gap between noise characterization and its propagation by introducing a new methodology for evaluating flow-induced noise in a realistic environment. The propagation model developed, which used the finite-difference-time-domain method, has been compared against benchmark cases (monopole source propagating in classical waveguides) for which an analytical solution is available, and it provides accurate results of the acoustic field. Furthermore, a second analysis is conducted on two classical waveguides: the Ideal one and the Pekeris one. The solution of the wave equation in time and physical space enables the implementation of different sources, such as dipole and quadrupole; therefore, we analyzed the acoustic response of the Pekeris waveguide. The results show that the propagation of the acoustic pressure is strongly affected by the directivity pattern of the source. This was the first step in evaluating the capabilities of the solution of the acoustic equation in the presence of sources characterized by complex directivity since our ultimate goal is to evaluate the noise emitted by a propeller. In the second part, the FAA analogy is introduced, and we describe how the acoustic pressure obtained with the FW-H equation is used as a source term in the propagation model. After the validation of the new proposed methodology in an unbounded homogeneous domain, we investigate the propagation of the linear part of the noise generated by a naval propeller within a canal. Local maxima and minima of the acoustic fields arise from the interaction between the noise source and the environment; in particular, they derive from the superposition of direct and reflected waves. Moreover, a rotating body placed underneath a free surface generates a peculiar asymmetry of the acoustic field associated with the interaction between the acoustic waves and the free surface.The need to develop more accurate numerical tools for the propagation of noise in underwater environments is driven by the continuous increase of human activity in the sea and coastal areas. Noise has been shown to be dangerous to marine wildlife, and steps should be taken soon to mitigate it. Knowing that the primary sources of noise pollution at sea are marine propellers, one of the problems is assessing how the noise generated interacts with the environment, since up to now, the main focus was the characterization of the acoustic signature in the near field or, alternatively, the propagation of simplified acoustic sources in sea-like domains. The work conducted in this thesis assesses the modelling of complex acoustic sources and the propagation of acoustic pressure in realistic domains. A propagation model based on the solution of the acoustic wave equation in the time and space domain is implemented and used in conjunction with the Ffowcs Williams and Hawkings (FW-H) to analyze the possible patterns occurring in the underwater environment. Specifically, we analyzed the noise radiated by a marine propeller in a canal, focusing on the effects of the boundaries on the acoustic field and, secondly, the consequence of a rotating body placed underneath a free surface. We defined a new methodology called Full Acoustic Analogy (FAA) to achieve these results. This methodology aims to overcome some intrinsic limitations of the known Acoustic Analogies. The study presented here attempts to bridge the gap between noise characterization and its propagation by introducing a new methodology for evaluating flow-induced noise in a realistic environment. The propagation model developed, which used the finite-difference-time-domain method, has been compared against benchmark cases (monopole source propagating in classical waveguides) for which an analytical solution is available, and it provides accurate results of the acoustic field. Furthermore, a second analysis is conducted on two classical waveguides: the Ideal one and the Pekeris one. The solution of the wave equation in time and physical space enables the implementation of different sources, such as dipole and quadrupole; therefore, we analyzed the acoustic response of the Pekeris waveguide. The results show that the propagation of the acoustic pressure is strongly affected by the directivity pattern of the source. This was the first step in evaluating the capabilities of the solution of the acoustic equation in the presence of sources characterized by complex directivity since our ultimate goal is to evaluate the noise emitted by a propeller. In the second part, the FAA analogy is introduced, and we describe how the acoustic pressure obtained with the FW-H equation is used as a source term in the propagation model. After the validation of the new proposed methodology in an unbounded homogeneous domain, we investigate the propagation of the linear part of the noise generated by a naval propeller within a canal. Local maxima and minima of the acoustic fields arise from the interaction between the noise source and the environment; in particular, they derive from the superposition of direct and reflected waves. Moreover, a rotating body placed underneath a free surface generates a peculiar asymmetry of the acoustic field associated with the interaction between the acoustic waves and the free surface

    Transition to a greener fashion:how and why main brands are moving towardsa more sustainable business

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    The fashion industry has long been identified as a main driver of systemic environmental damage. Especially for so-called “fast fashion” giants that operate on a strategic model based on both overproduction and overconsumption. As environmental concerns become ever more relevant in public discourse, several key corporate players have taken steps to reduce their environmental impact and make their supply chains more sustainable. In order to investigate on this matter, we readapt existing research frameworks to measure the economic and sustainability performance, and their correlation, of eight-company sample selected among the great fast-fashion “giants” and evaluate their commitment to sustainability issues

    Looking at Berlin, Ending up on Capitol Hill

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