Hyperspectral Unmixing Overview: Geometrical, Statistical, and Sparse Regression-Based Approaches

Imaging spectrometers measure electromagnetic energy scattered in their instantaneous field view in hundreds or thousands of spectral channels with higher spectral resolution than multispectral cameras. Imaging spectrometers are therefore often referred to as hyperspectral cameras (HSCs). Higher spectral resolution enables material identification via spectroscopic analysis, which facilitates countless applications that require identifying materials in scenarios unsuitable for classical spectroscopic analysis. Due to low spatial resolution of HSCs, microscopic material mixing, and multiple scattering, spectra measured by HSCs are mixtures of spectra of materials in a scene. Thus, accurate estimation requires unmixing. Pixels are assumed to be mixtures of a few materials, called endmembers. Unmixing involves estimating all or some of: the number of endmembers, their spectral signatures, and their abundances at each pixel. Unmixing is a challenging, ill-posed inverse problem because of model inaccuracies, observation noise, environmental conditions, endmember variability, and data set size. Researchers have devised and investigated many models searching for robust, stable, tractable, and accurate unmixing algorithms. This paper presents an overview of unmixing methods from the time of Keshava and Mustard's unmixing tutorial [1] to the present. Mixing models are first discussed. Signal-subspace, geometrical, statistical, sparsity-based, and spatial-contextual unmixing algorithms are described. Mathematical problems and potential solutions are described. Algorithm characteristics are illustrated experimentally.Comment: This work has been accepted for publication in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensin

Log-Gaussian processes for AI-assisted TAS experiments

To understand the origins of materials properties, neutron scattering experiments at three-axes spectrometers (TAS) investigate magnetic and lattice excitations in a sample by measuring intensity distributions in its momentum (Q) and energy (E) space. The high demand and limited availability of beam time for TAS experiments however raise the natural question whether we can improve their efficiency or make better use of the experimenter's time. In fact, using TAS, there are a number of scientific questions that require searching for signals of interest in a particular region of Q-E space, but when done manually, it is time consuming and inefficient since the measurement points may be placed in uninformative regions such as the background. Active learning is a promising general machine learning approach that allows to iteratively detect informative regions of signal autonomously, i.e., without human interference, thus avoiding unnecessary measurements and speeding up the experiment. In addition, the autonomous mode allows experimenters to focus on other relevant tasks in the meantime. The approach that we describe in this article exploits log-Gaussian processes which, due to the log transformation, have the largest approximation uncertainties in regions of signal. Maximizing uncertainty as an acquisition function hence directly yields locations for informative measurements. We demonstrate the benefits of our approach on outcomes of a real neutron experiment at the thermal TAS EIGER (PSI) as well as on results of a benchmark in a synthetic setting including numerous different excitations.Comment: Main: 22 pages, 5 figures | Extended Data: 8 figures | Supplementary Information: 5 pages, 2 figure

EXTERNAL CORPORATE GOVERNANCE MECHANISMS: MERGERS AND ACQUISITIONS ON THE BRAZILIAN MARKET

The research aims to answer the following question: What is the effectiveness of mergers and acquisitions in the Brazilian market as external corporate governance mechanism? The main objective of the study is to verify if mergers and acquisitions operations in Brazilian market may act as an external mechanism of corporate governance, replacing managers and, as a consequence of changes in management, improving financial performance. The study is exploratory, qualitative in its approach, supported by documentary research on secondary data concerning an intentional sample of Brazilian companies aiming to identify the effect of M&A operations on the corporate governance structure of the acquired firm and on its financial results. Data obtained on the website of the Brazilian Securities and Exchange Commission (CVM), related to Brazilian M&A operations in the period 2005-2010, were analyzed. Although M&A operations in Brazil were found to have disciplinary nature in our sample of firms in the studied period, our results are inconclusive regarding the effectiveness of these transactions and external governance mechanisms

Long-term evaluation of patient satisfaction and quality of life in pectus excavatum repair

Abstract Background: The aim of our study was to evaluate long-term patient satisfaction and quality-of-life improvement in grown-up patients treated for pectus excavatum with the Nuss procedure in the pediatric age, searching for correlation between preoperative characteristics and long-term outcomes. Methods: At first, we performed a retrospective analysis of pediatric patients undergoing the Nuss procedure in a 5-year period. We administered, at least 5 years after bar removal, a single-step questionnaire to focus on the assessment of patient satisfaction with operative results. Results: Most patients stated general health and exercise tolerance were improved after the operation. High levels of overall satisfaction were reported after Nuss repair, with 95.6% of patients being either satisfied or very satisfied. Overall, 87.0% of patients stated they would have the operation again. The high overall satisfaction after surgery was not correlated with the deformity severity and the presence of physical symptoms before correction. Conclusions: Patients expressed high levels of satisfaction in terms of self-image and quality of life. Improvement in cosmetic appearance and health in general translated in most patients in an improvement of social life. The degree of postoperative pain after the Nuss procedure is the overriding factor in the patient’s perception of the quality of the postoperative course