Polytechnic University of Milan

About: Polytechnic University of Milan is a education organization based out in Milan, Italy. It is known for research contribution in the topics: Finite element method & Population. The organization has 18231 authors who have published 58416 publications receiving 1229711 citations. The organization is also known as: PoliMi & L-NESS.

Video Denoising, Deblocking, and Enhancement Through Separable 4-D Nonlocal Spatiotemporal Transforms

Abstract: We propose a powerful video filtering algorithm that exploits temporal and spatial redundancy characterizing natural video sequences. The algorithm implements the paradigm of nonlocal grouping and collaborative filtering, where a higher dimensional transform-domain representation of the observations is leveraged to enforce sparsity, and thus regularize the data: 3-D spatiotemporal volumes are constructed by tracking blocks along trajectories defined by the motion vectors. Mutually similar volumes are then grouped together by stacking them along an additional fourth dimension, thus producing a 4-D structure, termed group, where different types of data correlation exist along the different dimensions: local correlation along the two dimensions of the blocks, temporal correlation along the motion trajectories, and nonlocal spatial correlation (i.e., self-similarity) along the fourth dimension of the group. Collaborative filtering is then realized by transforming each group through a decorrelating 4-D separable transform and then by shrinkage and inverse transformation. In this way, the collaborative filtering provides estimates for each volume stacked in the group, which are then returned and adaptively aggregated to their original positions in the video. The proposed filtering procedure addresses several video processing applications, such as denoising, deblocking, and enhancement of both grayscale and color data. Experimental results prove the effectiveness of our method in terms of both subjective and objective visual quality, and show that it outperforms the state of the art in video denoising.

Space geodesy: Subsidence and flooding in New Orleans

Abstract: A subsidence map of the city offers insight into the failure of the levees during Hurricane Katrina.

A unified high-level Petri net formalism for time-critical systems

Abstract: The authors introduce a high-level Petri net formalism-environment/relationship (ER) nets-which can be used to specify control, function, and timing issues. In particular, they discuss how time can be modeled via ER nets by providing a suitable axiomatization. They use ER nets to define a time notation that is shown to generalize most time Petri-net-based formalisms which appeared in the literature. They discuss how ER nets can be used in a specification support environment for a time-critical system and, in particular, the kind of analysis supported. >

A review of self-healing concrete for damage management of structures

Abstract: The increasing concern for safety and sustainability of structures is calling for the development of smart self-healing materials and preventive repair methods. The appearance of small cracks (<300 µm in width) in concrete is almost unavoidable, not necessarily causing a risk of collapse for the structure, but surely impairing its functionality, accelerating its degradation, and diminishing its service life and sustainability. This review provides the state-of-the-art of recent developments of self-healing concrete, covering autogenous or intrinsic healing of traditional concrete followed by stimulated autogenous healing via use of mineral additives, crystalline admixtures or (superabsorbent) polymers, and subsequently autonomous self-healing mechanisms, i.e. via, application of micro-, macro-, or vascular encapsulated polymers, minerals, or bacteria. The (stimulated) autogenous mechanisms are generally limited to healing crack widths of about 100–150 µm. In contrast, most autonomous self-healing mechanisms can heal cracks of 300 µm, even sometimes up to more than 1 mm, and usually act faster. After explaining the basic concept for each self-healing technique, the most recent advances are collected, explaining the progress and current limitations, to provide insights toward the future developments. This review addresses the research needs required to remove hindrances that limit market penetration of self-healing concrete technologies.

Reduced Kinetic Schemes of Complex Reaction Systems: Fossil and Biomass‐Derived Transportation Fuels

Abstract: The kinetic modeling of the pyrolysis and combustion of liquid transportation fuels is a very complex task for two different reasons: the challenging characterization of the complex mixture of several hydrocarbon isomers and the complexity of the oxidation mechanisms of large hydrocarbon and oxygenated molecules. While surrogate mixtures of reference components allow to tackle the first difficulty, the complex behavior of the oxidation mechanisms is mostly overcome by reducing the total number of involved species by adopting a lumping approach. After a first investigation of the different liquid fuels (gasoline, kerosene, and diesel fuels), a short discussion on the lumping techniques allows to highlight the advantages of this approach. The lumped POLIMI pyrolysis and oxidation mechanism of hydrocarbon and oxygenated fuels is then used for generating several skeletal mechanisms for typical surrogate mixtures, moving from pure n-heptane up to heavy diesel fuels. These skeletal models are simply reduced with a reaction flux analysis, and they involve between 100 and 200 species. While these sizes already allow detailed computational fluid dynamics (CFD) calculations in internal combustion engines, further reduction phases are necessary when the interest is toward more complex CFD computations. To maintain the standard structure of the skeletal mechanisms, successive reduction phases are not considered. Moreover, new regulations pushed toward a greater use of renewable fuels. For these reasons, the skeletal models are also extended to biogasolines including methanol, ethanol, and n-butanol. Similarly, skeletal models of diesel and biodiesel fuels, including methyl esters, are also provided. Several comparisons with experimental data and complete validations in the operating range of internal combustion engines are also reported. The whole set of comparisons with experimental data obtained in a wide range of conditions not only validate the reduced models of specific transportation fuels but also the complete kinetic scheme POLIMI_1404.