In recent years, the meaning of successful living has moved from extending lifetime to improving the quality of aging, mainly in terms of high cognitive and physical functioning together with avoiding diseases. In healthy elderly, falls represent an alarming accident both in terms of number of events and the consequent decrease in the quality of life. Stability control is a key approach for studying the genesis of falls, for detecting the event and trying to develop methodologies to prevent it. Wearable sensors have proved to be very useful in monitoring and analyzing the stability of subjects. Within this manuscript, a review of the approaches proposed in the literature for fall risk assessment, fall prevention and fall detection in healthy elderly is provided. The review has been carried out by using the most adopted publication databases and by defining a search strategy based on keywords and boolean algebra constructs. The analysis aims at evaluating the state of the art of such kind of monitoring, both in terms of most adopted sensor technologies and of their location on the human body. The review has been extended to both dynamic and static analyses. In order to provide a useful tool for researchers involved in this field, the manuscript also focuses on the tests conducted in the analyzed studies, mainly in terms of characteristics of the population involved and of the tasks used. Finally, the main trends related to sensor typology, sensor location and tasks have been identified.

Microwave imaging (MWI) represents a well-known tool for quantitatively retrieving unknown objects in a nondestructive way. Microwave radiation is non-ionizing, which suggests that MWI can be also attractive for medical diagnostics applications. This work proposes a novel MWI multi-frequency technique, which combines compressive sensing (CS) with the well-known distorted Born iterative method (DBIM). CS strategies are emerging as a promising tool in MWI applications, which can improve reconstruction quality and/or reduce the number of data samples. The proposed approach is based on iterative shrinkage thresholding algorithm (ISTA), which has been modified to include an automatic and adaptive selection of multithreshold values. This adaptive multi-threshold ISTA (AMTISTA) implementation is applied in reconstruction of two-dimensional (2-D) numerical heterogeneous breast phantoms, where it outerperforms the standard thresholding implementation. We show that our approach is also successful in three-dimensional (3-D) simulations of a realistic imaging experiment, despite the mismatch between the data and our algorithm's forward model. These results suggest that the proposed algorithm is a promising tool for medical MWI applications.

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Ground penetrating radar (GPR) technology for underground exploration consists in the transmission of an electromagnetic signal in the ground for sensing the presence of buried objects. While monostatic or bistatic configurations are usually adopted, a limited number of multistatic GPR systems have been proposed in the scientific literature. In this manuscript, we investigate the recovery performance of a specific and unconventional contactless multistatic GPR system, designed at the Georgia Institute of Technology for the subsurface imaging of anti-tank and anti-personnel plastic mines. In particular, for the first time, tomographic approaches are tested against this experimental multistatic GPR system, while most GPR processing in the scientific literature processes multi-monostatic experimental data sets. Firstly, by mimicking the system at hand, an accurate theoretical as well as numerical analysis is performed in order to estimate the data information content and the performance achievable. Two different tomographic linear approaches are adopted, i.e. the linear sampling method (LSM) and the Born approximation (BA) method, this latter enhanced by means of the compressive sensing (CS) theoretical framework. Then, the experimental data provided by the Georgia Institute of Technology are processed by means of a multi-frequency CS and BA-based method, thus generating very accurate 3D maps of the investigated underground scenario. Index Terms-ground penetrating radar (GPR), inverse scattering (IS) problem, microwave tomography, plastic landmine detection, linear sampling method (LSM), Born approximation (BA), compressive sensing (CS), sparse recovery. I. INTRODUCTIONROUND-PENETRATING radar (GPR) represents a powerful technology able to investigate in a non-invasive and non-destructive way non-accessible scenarios, as witnessed by the numerous and different applications, which include demining, lunar explorations, archaeology, geology, and civil engineering [1].GPR technology is usually adopted for subsurface imaging

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