196,604 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
Design of superdirective planar arrays with sparse aperiodic layouts for processing broadband signals via 3-D beamforming
No full textChronic 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
Analisi informativa: un approccio orientato alla pragmatica
No full text2005 Crocco C., Aureli M., “Analisi informativa: un approccio orientato alla pragmatica”, in F. Albano Leoni e R. Giordano (eds.), Italiano Parlato. Analisi di un dialogo, pp. 213-229, Napoli, Liguori Editore
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
Recursive segmentation based on higher order statistics in thermal imaging pedestrian detection
No full textAutomatic pedestrian detection based on thermal imaging is currently performed in two steps. The segmentation step subdivides the image into multiple regions of interest (ROIs) discarding background regions, while the classification step discriminates pedestrians from non pedestrians in each candidate ROI. In this paper a computationally inexpensive new method is proposed for the segmentation step, which recursively subdivides the image into smaller and smaller rectangular ROIs until a candidate pedestrian is identified. ROI boundaries are found on the base of an adaptive threshold updated at each step of the algorithm, while threshold tuning relies on higher order statistics of gray level histograms. Tests performed on OTCBVS database demonstrate significant improvement over a recent literature method in terms of accuracy and efficiency of segmentation
On the design of a microwave imaging system to monitor thermal ablation of liver tumors
No full textThermal ablation treatment of cancer is increasingly adopted in the clinical practice, being minimally invasive and highly specific. However, a significant drawback of the technique is the lack of effective imaging modalities for monitoring the changes undergoing in the thermally treated tissue. In this respect, microwave imaging has been proposed as a possible candidate, owing to its portability, low-cost, non-ionizing nature, and capability to detect changes in dielectric properties of tissues induced by the temperature. The goal of this paper is to provide the guidelines for the design of a microwave imaging system for thermal ablation monitoring of liver tumors. To this end, an analytical study is performed to determine the proper working conditions, in terms of frequency band and matching medium. Then, three antipodal Vivaldi antennas on different dielectric substrates are designed and numerically assessed. Among those antennas, the Vivaldi antenna on RT/duroid 6010LM substrate proved to be the most suitable choice. The results of this study pave the way to an experimental assessment of microwave imaging as a modality to monitor thermal ablation treatments
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