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In 1849, Hippolyte Fizeau determined the speed of light in a famous experiment. The idea was to measure the time taken for a pulse of light to travel between an intense light source and a mirror about 8 km away. A rotating cogwhee...
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In 1849, Hippolyte Fizeau determined the speed of light in a famous experiment. The idea was to measure the time taken for a pulse of light to travel between an intense light source and a mirror about 8 km away. A rotating cogwheel with 720 notches, that could be rotated at a variable speed, was used to chop the light beam and determine the flight time. In 2017, physicists and technicians of the University of Mons in Belgium reproduced the experiment with modern devices to allow members of the public to measure the speed of light themselves. The light source used was a low power laser, and the cogwheel was replaced by an electrically driven chopper, but the general spirit of Fizeau's experiment was preserved. The exhibition was organised in the belfry of Mons, a baroque-style building classified as a UNESCO World Heritage site. The solutions found for the main problems encountered are presented here to help colleagues intending to reproduce the experiment.
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The systematic observation of damage caused by recent Italian earthquakes has highlighted the high seismic vulnerability of belfries, the inner part of bell towers. In this study, the authors propose a simplified methodology for s...
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The systematic observation of damage caused by recent Italian earthquakes has highlighted the high seismic vulnerability of belfries, the inner part of bell towers. In this study, the authors propose a simplified methodology for safety checks of belfries that is usable for risk analysis at territorial level for the whole bell tower, according to the method proposed by the Italian Directive of October 12,2007, Guidelines for the Evaluation and the Reduction of the Seismic Vulnerability of Cultural Heritage. The new mechanical method takes into account the possible activation of two different collapse mechanisms, connected to combined actions of compression and bending or shear action, supposing different static schemes in relation to the real belfry configuration. The seismic force at the base of the belfry is calculated also considering the influence of the second mode of vibration through a correction factor obtained by spectral analyses on several bell towers damaged by the 1976 Friuli earthquake. A validation of the proposed approach has been shown for two belfries damaged by the 2002 Molise earthquake and by the 2009 Abruzzi earthquakes, to highlight the reliability of the method in comparison to the simplified approach proposed in the literature.
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? 2022In this work, the overall structure of the proposed “belfry-typed” absorber sensor is composed of four layers, from bottom to top are Si substrate, Au layer, SiO2 dielectric layer and the top “belfry-typed” graphene laye...
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? 2022In this work, the overall structure of the proposed “belfry-typed” absorber sensor is composed of four layers, from bottom to top are Si substrate, Au layer, SiO2 dielectric layer and the top “belfry-typed” graphene layer, respectively. Among them, the design of the “bell tower” pattern is inspired by the common bell tower building in daily life. Compared with the previous absorber based on frequency superposition method, the patterned graphene structure greatly simplifies the actual processing steps. By using FDTD to simulation, it is found that the structure has two perfect resonance absorption modes with absorption rates of 99.92% and 99.88% at 7578 nm and 8635 nm. Considering that the special surface plasmon tunability of graphene, the two-mode regulation can be achieved by controlling Fermi energy, relaxation times and structural geometry parameters. Moreover, the refractive index sensitivity of the device was discussed. The three basic parameters evaluating the performance of sensor are 1477.5 nm/RIU of sensitivity, 25.47 of FOM and 123.4 of quality factor. Finally, the specific circumstance of the absorber applied in actual life such as in aqueous solution, 10%, 20%, 25%, 60% glucose solution and 30%, 50% sugar solution was simulated and discussed. These results suggest that the proposed absorber has high refractive index sensitivity and high response speed, with which the absorber has high application value in photoelectric detection, switching and imaging.
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In recent years, a millennia-long oak tree-ring width chronology, consisting of 3194 samples from 387 locations, was developed in the Czech Republic. Despite the collection of such a huge dataset, the replication in the 19th Centu...
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In recent years, a millennia-long oak tree-ring width chronology, consisting of 3194 samples from 387 locations, was developed in the Czech Republic. Despite the collection of such a huge dataset, the replication in the 19th Century was very low and the natural oak distribution in the Czech Republic was insufficiently covered by recent samples, especially inWestern Bohemia. This study aimed to remove these weaknesses, which have limited the paleoclimatic potential of this dataset, and to determine the number of sapwood rings, which is crucial for dendrochronological dating. Therefore, newrecent samples were randomly collected at numerous sawmills along the Czech-German border. The historical material was usually sampled using a Pressler borer from church belfry constructions traditionally made from oak. In total, 252 recent and 90 historical tree-ring width series were incorporated into the chronology. The newly built chronology cumulatively consists of 3536 series, which covers the continuous period of A. D. 352-2014. The resulting tree-ring width record shows robust signal strength and homogeneous coverage of the territory. We show that the number of sapwood rings is constant over time. Therefore, we recommend using an estimate of 5-24 sapwood rings for a more precise dating of historical wood findings in the Czech Republic.
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The experimental characterization of historical bell towers and wall belfries can provide important information for the calibration of numerical models as well as to implement proper restoration strategies. Within this framework, ...
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The experimental characterization of historical bell towers and wall belfries can provide important information for the calibration of numerical models as well as to implement proper restoration strategies. Within this framework, the presented study is concerned with the experimental dynamic assessment of an ancient belfry dating back to 1537. The structure is part of the "SantaMaria in Aracoeli Church" (Rome, Italy), an important heritage construction placed on the summit of the Capitoline Hill, close to the building that hosts the Major's office. Several field tests have been conducted using accelerometers, and records obtained under different dynamic loading scenarios have been examined. Moreover, experimental accelerations have been elaborated to estimate the most important modal features of the structure and to validate a finite element model. Field tests have confirmed that severe vibrations are induced when the bells swing, and thus a slight reduction of the swing angle has been suggested in order to provide an immediate and inexpensive benefit to the structure. A new set of field tests demonstrates that the new swing angle is sufficient to reduce the induced vibrations while preserving the original sound.
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The safeguard of historical heritage cannot disregard a rational assessment of the seismic vulnerability of the assets, especially in areas as Italy where high exposure and hazard may lead to significant risk. In this context, whi...
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The safeguard of historical heritage cannot disregard a rational assessment of the seismic vulnerability of the assets, especially in areas as Italy where high exposure and hazard may lead to significant risk. In this context, while established empirical methods based on observed damage after earthquakes are available for some constructional typologies as churches and palaces, large-scale approaches for masonry bell towers aimed at defining a vulnerability ranking for prioritisation of intervention are still missing or not sufficiently validated.In this paper, a novel simplified vulnerability model is formulated through sensitivity-informed parameter reduction of a more detailed mechanics-based assessment methodology. The framework is based on (a) a parametric representation of the bell tower, (b) a mechanical model providing a measure of collapse, (c) a vulnerability definition based on the measure of collapse. The variation ranges of the input parameters are calibrated against the results of the surveys carried out in the historical centre of Naples. A global sensitivity analysis is then used to identify the most important parameters governing the vulnerability of the structure and remove the least influential parameters. Vulnerability models based on different amount of input data are finally proposed, and their accuracy is assessed comparatively with the original mechanical model. The results show that good accuracy can be obtained by using six geometrical and typological parameters, while further increase in the quality of the prediction may be achieved with the introduction of additional information regarding materials and constructional features, which can only be acquired by means of more detailed surveys on-site.
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