1,720,998 research outputs found
Optimal design of reinforcement of masonry arches = Progetto ottimo di rinforzi di archi in muratura
Full text linkThe preservation of Italian architectural heritage is of crucial importance and requires ongoing interventions to ensure its structural integrity.
Masonry constructions are designed to withstand gravitational loads through their geometric configuration; however, they are susceptible to instabilities induced by slight changes of the loading distribution. The recent seismic events highlighted this weak mechanical behavior of masonry structures and thus the need for strengthening interventions. One of the commonly used methods for strengthening masonry structures is the application of tensile reinforcements, which constraint the kinematics of the masonry system and consequently increase the collapse load. Nevertheless, as evidenced by recent seismic events, current strengthening techniques have demonstrated ineffective in preserving masonry constructions and, in some cases, have even contributed to induce unpredicted collapse mechanisms.
In order to bridge the gap between structural safety and preservation, innovative strengthening materials such as Fiber Reinforced Cementitious Matrix composites (FRCM), have been developed and are increasingly being used due to their greater compatibility with the substrates they are intended to reinforce. However, experimental results have demonstrated that the presence of reinforcement significantly modifies the structural behavior of masonry, leading to different collapse modes such as crushing or sliding between joints.
Therefore, a key purpose of this thesis is to develop a design procedure for “optimal” reinforcement interventions for masonry arches that increase the collapse multiplier without excessively constraining the structural system. This approach allows for limiting the extent of strengthening interventions while preserving the typical mechanical behavior of masonry arches.
In the framework of the non-standard limit analysis for dry masonry systems, an optimization algorithm is implemented to design the optimal reinforcement by defining the collapse load multiplier and the related mechanism. In particular, the limit analysis problem with a non-associative flow rule involves the solution of the nonlinear programming (NLP) as a sequence of linear programming problems (LP). Then, this algorithm is enhanced with additional constraint equations in the linear programming problem to take into account the inserted reinforcement. A first solution considered is the use of elastic reinforcements capable to limit the opening at the interface endpoints at the extrados or the intrados where the reinforcement is applied, inhibiting a hinge to occur on the opposite side of the interface. A second option is employing elastic perfectly plastic reinforcements that give the structure some degree of ductility, since after the yielding limit the reinforcement is capable to freely deform. The implemented algorithm is then validated through numerical simulations
A New algorithm for unsupervised global and local color correction
No full textIn this work we present a new algorithm for digital images unsupervised enhancement with simultaneous global and local effects, called ACE for Automatic Color Equalization. It is based on a computational model of the human visual system that merges the two basic “Gray World” and “White Patch” global equalization mechanisms. Inspired by some adaptation mechanisms of the human vision, it realizes a local filtering effect by taking into account the color spatial distribution in the image. Like the human visual system, ACE is able to “adapt” to widely varying lighting conditions and to extract visual information from the environment efficaciously. It has shown promising results in achieving different equalization tasks, e.g. performing color and lightness constancy, realizing image dynamic data driven stretching, controlling the contrast. Characteristics, tests and results are presented
A multiscale framework for spatial gamut mapping
No full textImage reproduction devices, such as displays or printers, can reproduce only a limited set of colors, denoted the color gamut. The gamut depends on both theoretical and technical limitations. Reproduction device gamuts are significantly different from acquisition device gamuts. These facts raise the problem of reproducing similar color images across different devices. This is
well known as the gamut mapping problem. Gamut mapping algorithms have been developed mainly using colorimetric pixel-wise
principles, without considering the spatial properties of the image.
The recently proposed multilevel gamut mapping approach takes spatial properties into account and has been demonstrated to
outperform spatially invariant approaches. However, they have some important drawbacks. To analyze these drawbacks, we build a common framework that encompasses at least two important previous multilevel gamut mapping algorithms. Then, when the causes of the drawbacks are understood, we solve the typical problem of possible hue shifts. Next, we design appropriate operators and functions to strongly reduce both haloing and possible undesired over compression. We use challenging synthetic images, as well as real photographs, to practically show that the improvements give the expected results
Local linear LUT method for spatial colour-correction algorithm speed-up
No full textThere is a class of nonlinear filtering algorithms for digital colour enhancement, characterised by data-driven local effects and high computational cost. A new method called LLL (local linear look-up table (LUT)) is presented, which speeds up these filters without losing their local effect. Usually, classic LUT-based methods are global whereas the approach presented here uses the principles of LUT transformation in a local way. The main idea of this method is to apply the colour-enhancement algorithm to a small sub-sampled version of the input image and to use a modified look-up table technique to maintain the local filtering effect of the colour-enhancement algorithm. The method increases the speed of colour-filtering algorithms, reducing the number of pixels involved in the computation by sub-sampling the input image. To overcome possible loss of detail due to sub-sampling, an optional, additional stage to maintain high-frequency content is shown. LLL with two of these filters, the Brownian Retinex implementation and the automatic colour equalisation algorithm, are tested. Results, comparison and conclusions are presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
From Retinex to Automatic Color Equalization : issues in developing a new algorithm for unsupervised color equalization
No full textIn this work we present a comparison between two color equalization algorithms: Retinex, the famous model due to Land and McCann and ACE, a new algorithm, recently presented by the authors. These two algorithms share a common approach to color equalization but different computational models. The paper
introduces the two models focusing on differences and common points. An analysis of their computational characteristics
illustrates the way Retinex approach has influenced ACE structure and which aspects of the first algorithm have been modified in the second one and how. Their interesting equalization properties, like lightness and color constancy, image dynamic stretching,
global and local filtering, data driven dequantization are qualitatively and quantitatively presented and compared, together with their ability to mimic the human visual system
ACE: an Automatic Color Equalization Algorithm
No full textIn this work we present a new algorithm for digital images unsupervised enhancement, called ACE for Automatic Color Equalization. It is based on a new computational approach that merges the "Gray World" and "White Patch" equalization mechanisms, while taking into account the spatial distribution of color information. Inspired by some adaptation mechanisms of the human visual system, ACE is able to adapt to widely varying lighting conditions, and to extract visual information from the environment efficaciously. ACE has shown promising results in solving the color constancy problem and performing an image dynamic data driven stretching. Tests and results are presented
Perceptually inspired HDR images tone mapping with color correction
No full textIn this paper we present a novel Tone Mapping Operator (TMO) for High Dynamic Range (HDR) images. Starting from an algorithm for low dynamic range image enhancement and color correction called ACE (Automatic Color Enhancement); we keep its differential and local behavior, introducing new features to correctly handle the high variation of HDR images. In particular, we add a non-linear local regulator able to automatically tune the algorithm parameters on image variations. In this way, the algorithm behavior changes according to local variations. Moreover, a key setting feature has been added to control the output appearance; it automatically proposes an appropriate key value for the final spatial invariant display mapping. The proposed method performs the spatial variant filtering using only one parameter that tunes output detail visibility versus overall contrast. We propose a default setting that guarantees a good solution in most cases. Test, results and comparison are presented
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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