Forward-looking sonar image compression by integrating keypoint clustering and morphological skeleton

Forward-Looking Sonar (FLS) is one of the most effective devices for underwater exploration which provides high-resolution images that can be used for several tasks in marine research, oceanographic, and deep-sea exploration. The limitation of current underwater acoustic channels does not allow transmitting these images in real-time, therefore image compression is required. Since acoustic images are characterized by speckle noise, an important challenge, in this area, is how to perform the compression while preserving relevant information. In this paper, a novel lossy forward-looking acoustic image compression method based on the combination between keypoint clustering and Morphological Skeleton (MS) is proposed. Keypoints are extracted by using A-KAZE feature extractor, while Density-Based Spatial Clustering of Application with Noise (DBSCAN) is used to find keypoint clusters representing a region-of-interest (ROI). Then, MS is executed to compact the ROI. The rest of the image is down-sampled and quantized through K-Means Clustering and represented via colour indexing. Finally, the information is compressed by using Brotli data compression. The experimental results on real FLS images demonstrate that our method achieves good outcomes in terms of quality metrics and compression ratio.

     

The Acute Toxicity of Mineral Fibres: A Systematic In Vitro Study Using Different THP-1 Macrophage Phenotypes

Alveolar macrophages are the first line of defence against detrimental inhaled stimuli. To date, no comparative data have been obtained on the inflammatory response induced by different carcinogenic mineral fibres in the three main macrophage phenotypes: M0 (non-activated), M1 (pro-inflammatory) and M2 (alternatively activated). To gain new insights into the different toxicity mechanisms of carcinogenic mineral fibres, the acute effects of fibrous erionite, crocidolite and chrysotile in the three phenotypes obtained by THP-1 monocyte differentiation were investigated. The three mineral fibres apparently act by different toxicity mechanisms. Crocidolite seems to exert its toxic effects mostly as a result of its biodurability, ROS and cytokine production and DNA damage. Chrysotile, due to its low biodurability, displays toxic effects related to the release of toxic metals and the production of ROS and cytokines. Other mechanisms are involved in explaining the toxicity of biodurable fibrous erionite, which induces lower ROS and toxic metal release but exhibits a cation-exchange capacity able to alter the intracellular homeostasis of important cations. Concerning the differences among the three macrophage phenotypes, similar behaviour in the production of pro-inflammatory mediators was observed. The M2 phenotype, although known as a cell type recruited to mitigate the inflammatory state, in the case of asbestos fibres and erionite, serves to support the process by supplying pro-inflammatory mediators.     

Sub-Solidus Synthesis and Microwave Dielectric Characterization of Plagioclase Feldspars

Na _x Ca_{1− x} Al_{2− x} Si_{2+ x} O₈ plagioclase solid solutions (0≤ x ≤1) were synthesized under sub-solidus conditions using a solid-state reaction technique. The plagioclase formation and the sintering temperature decreased with an increase in x from the anorthite (CaAl₂Si₂O₈; x =0) to the albite (NaAlSi₃O₈; x =1).
Microwave (MW) dielectric measurements revealed that slow-cooled ( P 1 ) anorthite exhibited higher Q × f values than fast-cooled ( I 1 ) anorthite. Slow cooling also considerably improved the Q × f values of the sodium-rich Na _x Ca_{1− x} Al_{2− x} Si_{2+ x} O₈ solid solutions (0.8≤ x ≤1), where the highest Q × f value of 17 600 GHz was obtained for slow-cooled Na_0.8Ca_0.2Al_1.2Si_2.8O₈. The temperature coefficient of resonant frequency (τ_f) approached zero for 0.8≤ x ≤1.     

Static crack extension prediction in aluminium alloy at low temperature

The evaluation of the crack initiation and crack extension under different environmental conditions is very important for many engineering applications. Several crack extension criteria have been proposed in the last decades, but each criterion can be employed only for particular materials, loading configurations, environmental conditions. In the present paper, the R-criterion (minimum extension of the core plastic zone) is modified in order to take into account the temperature dependence. The modified criterion is herein employed to predict the crack path and the crack extension force for an edge-cracked finite plate under tension, by using a simplified procedure to determine the stress-intensity factor (SIF) for different initial crack configurations. Then, results concerning some experimental tests performed on edge-cracked aluminium alloy sheet specimens at different temperatures are reported. Finally, the theoretical results are compared (in terms of crack extension force and crack path) with the experimental data.     

Discharge pulses of hydroelectric dams and their effects in the downstream limnological conditions: a case study in a large tropical river (SE Brazil)

To address daily fluctuations in electricity demands, the quantities of water passing through the turbines of hydropower plants can vary significantly (up to fourfold) during a 24‐h cycle. This study evaluates the effects of hourly variations in water discharges on the limnological conditions observed in two below‐dam river stretches. The study reservoirs, Capivara and Taquaruçu, are the 9th and 10th reservoirs in a cascade of dams in the Paranapanema River in south‐east Brazil. The reservoirs exhibit different trophic conditions, water retention times, thermal regimes and spillway positions. Capivara Reservoir is deeper, meso‐eutrophic, with a high water retention time and hypolimnetic discharges (32 m) varying between 500 and 1400 m³ s^?1. In contrast, Taquaruçu Reservoir is relatively shallow, oligo‐mesotrophic, and has a low retention time, with water discharges varying between 500 and 2000 m³ s^?1. Its turbine water intake zone also is more superficial (7 m). For two periods of the year, winter and summer, profiles of limnological measurements were developed in the lacustrine (above‐dam site) zones of the reservoirs, as well as in the downstream river stretches (below‐dam site). In both cases, the sampling was carried out at 4‐h intervals over a complete nictemeral cycle. The results demonstrated that the reservoir operating regime (water discharge variations) promoted significant differences in the conditions of the river below the dams, especially for water velocity, turbidity, and nutrient and suspended solids concentrations. The reservoir physical characteristics, including depth, thermal stratification and outlet structure, are also key factors influencing the limnology and water quality at the below‐dam sampling sites. In the case of Capivara Reservoir, for example, the low dissolved oxygen concentration (<5.0 mg L^?1) in its bottom water layer was transferred to the downstream river stretches during the summer. These study results demonstrated that it is important to continue such investigations as a means of verifying whether or not these high‐amplitude/low‐frequency variations could negatively affect the downstream river biota.     

Reconfigurable Coprocessor for Multimedia Application Domain

A new reconfigurable architectural template is presented. Such a template is composed of coarse-grained and fine-grained reconfigurable datapath and control to obtain performances at custom designed chip level. To show the adaptability/performance of such architectural template, the architecture has been customized (i.e. datapath and control features of the template have been properly sized) for multimedia application domain. To evaluate complexity and maximum clock frequency of the proposed architecture, it has been synthesized using Synopsys Design Compiler on a standard-cell 0.18 μ m technology. Estimated number of transistors is 335 K, while maximum allowable frequency is 460 MHz. Performances have been evaluated comparing the number of clock cycles and the processing time required to process application domain dominant kernels with commercial devices: we obtained up to 95% reduction with respect to ARM and up to 94% reduction with respect to TMS320C5510 in terms of clock cycles. Salvatore M. Carta (1997 Electronic Eng. Master. 2002 Electronics and Computer Science PhD) joined the Department of Electrical and Electronics Engineering of the University of Cagliari, Italy in 1998 as PhD student. From 2005 he has been assistant professor in Department of Mathematics and Computer Science of the University of Cagliari. His research interests focus mainly on architectures, software and tools for embedded and portable computing, with particular emphasis on: languages, architectures and compilers for reconfigurable and parallel computing; Networks-on-chip; Operating systems for multiprocessor-systems-on-chip; low power real-time scheduling algorithms. Danilo Pani (2002 Electronic Eng. Master, 2006 Electronics and Computer Science PhD) joined the Department of Electrical and Electronics engineering of the University of Cagliari, Italy in 2002 as Electronics and Computer Science PhD student. His primary research interests are in the area of Digital Signal Processing architectures and systems, Biomedical Engineering, Reconfigurable Systems and Cooperative VLSI architectures for distributed computing. Luigi Raffo (1989 Master, 1994 Electronics and Computer Science PhD) joined Department of Electrical and Electronics Engineering of the University of Cagliari, Italy in 1994 as assistant professor. From 1998 he has been professor of Digital System Design, Integrated Systems Architectures and Microelectronics at the same Department. His research activity is mainly in the design of low-power analog and digital architectures/chips. He has been project manager of many local and international projects. He is author of more than 50 international papers in the field.     

Stochastic gradient-adaptive complex-valued nonlinear neural adaptive filters with a gradient-adaptive step size.

A class of variable step-size learning algorithms for complex-valued nonlinear adaptive finite impulse response (FIR) filters is proposed. To achieve this, first a general complex-valued nonlinear gradient-descent (CNGD) algorithm with a fully complex nonlinear activation function is derived. To improve the convergence and robustness of CNGD, we further introduce a gradient-adaptive step size to give a class of variable step-size CNGD (VSCNGD) algorithms. The analysis and simulations show the proposed class of algorithms exhibiting fast convergence and being able to track nonlinear and nonstationary complex-valued signals. To support the derivation, an analysis of stability and computational complexity of the proposed algorithms is provided. Simulations on colored, nonlinear, and real-world complex-valued signals support the analysis.     

Code Normalization for Self-Mutating Malware

Next-generation malware will adopt self-mutation to circumvent current malware detection techniques. The authors propose a strategy based on code normalization that reduces different instances of the same malware into a common form that can enable accurate detection.     

Equivalences and optimizations in an expressive XSLT subset

XML is the standard data interchange format and XSLT is the W3C proposed standard for transforming and restructuring XML documents. It turns out that XSLT has very powerful query capabilities as well. Hovewer, due to its complex syntax and lack of formal specification, it is not a trivial task to decide whether two XSLT stylesheets yield the same result, even if for an XSLT subset. We isolate such fragment, powerful enough for expressing several interesting queries and for manipulating XML documents and show how to translate them into queries expressed in a properly extended version of TAX, a powerful XML query algebra, for which we provide a collection of equivalence rules. It is then possible to reason about XSLT equivalences, by translating XSLT stylesheets into XTAX expressions and then statically verifying their equivalence, by means of the mentioned equivalence rules.