1,721,062 research outputs found
The synthesis of robust broadband beamformers for equally-spaced linear arrays
No full textBroadband beamforming applied to superdirective arrays is known to be highly sensitive to transducers characteristics errors. Recently, an effective method to synthesize a robust, broadband, data-independent, filter-and-sum beamformer, which considers the probability distributions of errors, has been proposed. It considers an array with arbitrary lay-out and provides a spatial directivity pattern close to the desired one. Unfortunately, the evaluation of the cost function requires a computational load and an amount of memory that increases very quickly with the transducers and the filter coefficients. As the synthesis process requires an iterative minimization, it may become unacceptably long. In this paper, an alternative procedure for evaluating the same cost function is presented, drastically reducing such problems and without introducing any approximation. The only additional constraint is on the antenna which must be an equally-spaced linear array. This procedure makes it much easier to apply the above-mentioned synthesis method to a wide panorama of practical situations
A Computationally Efficient Procedure for the Design of Robust Broadband Beamformers
No full textBroadband beamformers using superdirective arrays are sensitive to errors in the sensor characteristics. Recently, a method that considers the probability distributions of errors to synthesize a robust optimal beamformer has been proposed. Unfortunately, the entire synthesis process may become unacceptably long due to the computational burden of the cost function. Here, we present an alternative procedure for computing the same cost function, drastically reducing such a problem
Chronic Urticaria and Celiac Disease
No full textA 4-year-old patient presented with recurrent urticaria without a clear trigger. After excluding other allergic causes, a direct link between urticaria and celiac disease was observed, a condition that affected the child who showed no gastrointestinal symptoms
A Stochastic Approach to the Synthesis of a Robust Frequency-Invariant Filter-and-Sum Beamformer
No full text
Low-Cost Acoustic Cameras for Underwater Wideband Passive Imaging
No full textThe imaging of underwater acoustic sources using passive 3-D sonar systems has many potential applications. However, to achieve both wide bandwidth and low cost, an array that is superdirective at low frequencies and aperiodic, to avoid aliasing at high frequencies, is required. To design a sparse array layout and the related filter-and-sum beamformer, a recently proposed method for airborne acoustic cameras is applied. First, the method is generalized to include position errors. Next, the method is used to demonstrate that 49 low-cost, poorly matched hydrophones are sufficient to create a square array for an underwater acoustic camera working from 500 Hz to 8.75 kHz with a side length of 1 m. Finally, the images of a simulated acoustic scenario obtained using different passive systems are compared, which reveals the advantages of the proposed design strategy
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Informazione della paziente in corso di monitoraggio ecografico della gravidanza
No full textMonduzzi Ed.,Bologna (ITALY),198
Towards fully uncalibrated room reconstruction with sound
No full textThis paper presents a novel approach for room reconstruction using unknown sound signals generated in different locations of the environment. The approach is very general, that is fully uncalibrated, i.e. the locations of microphones, sound events and room reflectors are not known a priori. We show that, even if this problem implies a highly non-linear cost function, it is still possible to provide a solution close to the global minimum. Synthetic experiments show the proposed optimization framework can achieve reasonable results even in the presence of signal noise
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