241 research outputs found
The influence of piezoceramic stack location on nonlinear behavior of langevin transducers
Power ultrasonic applications such as cutting, welding, and sonochemistry often use Langevin transducers to generate power ultrasound. Traditionally, it has been proposed that the piezoceramic stack of a Langevin transducer should be located in the nodal plane of the longitudinal mode of vibration, ensuring that the piezoceramic elements are positioned under a uniform stress during transducer operation, maximizing element efficiency and minimizing piezoceramic aging. However, this general design rule is often partially broken during the design phase if features such as a support flange or multiple piezoceramic stacks are incorporated into the transducer architecture. Meanwhile, it has also been well documented in the literature that power ultrasonic devices driven at high excitation levels exhibit nonlinear behaviors similar to those observed in Duffing-type systems, such as resonant frequency shifts, the jump phenomenon, and hysteretic regions. This study investigates three Langevin transducers with different piezoceramic stack locations by characterizing their linear and nonlinear vibrational responses to understand how the stack location influences nonlinear behavior
A numerical solution for addressing the overturning phenomena of heritage assets
Historical heritage represent a crucial aspect for societies and therefore it should be preserved from natural disasters such as earthquake. Base isolation systems are widely used to mitigate the horizontal effects of strong ground motions on important buildings and bridges, but there are also interesting applications on statues. However, such systems are characterized by properties that are quite different from the ones that belong to traditional civil structures. For this reason, national and international regulations are not exhaustive and actual dynamics of the system should be studied through numerical and experimental methods. Starting from analytical formulations, the paper investigates the sliding and rocking motion in details, being the typical one of statues under seismic loads. The presented numerical model describes the problem and is an alternative to the analytical formulation to perform several analyses automatically. In addition, it allows running parametric analyses to assess the influence of various parameters, such as eccentricity, stiffness, mass, geometric ratios, etc. Future work is geared to validate the numerical model trough performing experimental tests on shaking table
Experimental Investigation of the Static and Dynamic behaviors of 3D-Printed Shell Structures
Over the last years, several optimization strategies were conducted to find the optimal shape minimizing internal stress or total weight (volume) of shell structures. In recent times, this structure typology gained a great importance among researchers and the scientific community for the renowed interest in the form-findind optimization of column-free space solution for large span roofing constructions. In the present paper, a form-finding of a shallow grid shells was introduced basing on the multy-body rope approach (MRA) for the definitions of vault shapes and different hole percentage. In order to obtain an experimental validation, a physical model was reproduced at the laboratory scale performing ad hoc measurements to compare the observed respect to the simulated behaviour. A 3D printing procedure based on the Fuse Deposition Modeling (FDM) technique in polylactide (PLA) material was used to realise form-works of the cement based blocks of the scaled prototype. Several static and dynamic load configurations are investigated, collecting into a sensitivity analysis the parameters which mainly affect the structural behaviour. To simulate earthquake ground motion an assigned frequency range as dynamic input to the structure was provided by a shaking table. Finally, some preliminary considerations of the dynamic response of the model were provided testing the robustness of the form-finding approach when horizontal load are taken into account
Integrated platform to assess seismic resilience at the community level
Due to the increasing frequency of disastrous events, the challenge of creating large-scale simulation models has become of major significance. Indeed, several simulation strategies and methodologies have been recently developed to explore the response of communities to natural disasters. Such models can support decision-makers during emergency operations allowing to create a global view of the emergency identifying consequences. An integrated platform that implements a community hybrid model with real-time simulation capabilities is presented in this paper. The platform's goal is to assess seismic resilience and vulnerability of critical infrastructures (e.g., built environment, power grid, socio-technical network) at the urban level, taking into account their interdependencies. Finally, different seismic scenarios have been applied to a large-scale virtual city model. The platform proved to be effective to analyze the emergency and could be used to implement countermeasures that improve community response and overall resilience
Valutazione dellâesposizione a sostanze chimiche: il ruolo del monitoraggio biologico in lavoratori esposti a TCE.
Lâobiettivo di questo studio era esaminare i profili di un gruppo di lavoratori di un reparto di manutenzione di unâindustria aeronautica espostio a tricloroetilene (TCE) dopo il 2001/59/ce ed il DL n. 197 06/14/2002, e di verificare lâutilitĂ e la validitĂ del monitoraggio biologico come fattore determinante per la sicurezza degli operatori
5S-IGS rDNA in wind-pollinated trees (Fagus L.) encapsulates 55 million years of reticulate evolution and hybrid origins of modern species
Standard models of plant speciation assume strictly dichotomous genealogies in which a species, the ancestor, is replaced by two offspring species. The reality in windâpollinated trees with long evolutionary histories is more complex: species evolve from other species through isolation when genetic drift exceeds gene flow; lineage mixing can give rise to new species (hybrid taxa such as nothospecies and allopolyploids). The multiâcopy, potentially multiâlocus 5S rDNA is one of few gene regions conserving signal from dichotomous and reticulate evolutionary processes down to the level of intraâgenomic recombination. Therefore, it can provide unique insights into the dynamic speciation processes of lineages that diversified tens of millions of years ago. Here, we provide the first highâthroughput sequencing (HTS) of the 5S intergenic spacers (5SâIGS) for a lineage of windâpollinated subtropical to temperate trees, the Fagus crenata â F. sylvatica s.l. lineage, and its distant relative F. japonica. The observed 4963 unique 5SâIGS variants reflect a complex history of hybrid origins, lineage sorting, mixing via secondary gene flow, and intraâgenomic competition between two or more paralogousâhomoeologous 5S rDNA lineages. We show that modern species are genetic mosaics and represent a striking case of ongoing reticulate evolution during the past 55 million years
The BOOMERANG North America Instrument: a balloon-borne bolometric radiometer optimized for measurements of cosmic background radiation anisotropies from 0.3 to 4 degrees
We describe the BOOMERANG North America (BNA) instrument, a balloon-borne
bolometric radiometer designed to map the Cosmic Microwave Background (CMB)
radiation with 0.3 deg resolution over a significant portion of the sky. This
receiver employs new technologies in bolometers, readout electronics,
millimeter-wave optics and filters, cryogenics, scan and attitude
reconstruction. All these subsystems are described in detail in this paper. The
system has been fully calibrated in flight using a variety of techniques which
are described and compared. It has been able to obtain a measurement of the
first peak in the CMB angular power spectrum in a single balloon flight, few
hours long, and was a prototype of the BOOMERANG Long Duration Balloon (BLDB)
experiment.Comment: 40 pages, 22 figures, submitted to Ap
Benznidazole Therapy Modulates Interferon-Îł and M2 Muscarinic Receptor Autoantibody Responses in Trypanosoma cruzi-Infected Children
OBJECTIVE: The presence of autoantibodies with adrenergic and cholinergic activity, capable of triggering neurotransmitter receptor-mediated effects, has been associated with pathogenesis in T. cruzi-infected hosts. The goal of this study was to investigate the production of anti-M2 muscarinic receptor autoantibodies (Anti-M2R AAbs) as well as the IFN-Îł profile in children at the early stage of Chagas disease, and to examine whether trypanocidal chemotherapy with benzonidazole (BZ) could modify both response patterns. METHODS: This study comprised 30 T. cruzi-infected children (mean age: 13.8 years) and 19 uninfected controls (mean age: 12.7 years). Infected patients were treated with BZ and followed-up. Blood samples collected at diagnosis-T0, end of treatment-T1, and six months later-T2 were analysed by ELISA for detection of Anti-M2R AAbs and circulating levels of IFN-Îł. RESULTS: At T0, anti-M2R AAbs were demonstrated in 56.7% of T. cruzi-infected patients, whereas uninfected controls were 100% negative. The average age of Anti-M2R AAbs(+) patients was higher than that from negative population. Infected children also displayed significantly stronger serum IFN-Îł responses than controls. Upon BZ treatment, a significant linear decreasing trend in Anti-M2R AAb reactivity was recorded throughout the follow-up, with 29.7-88.1% decrease at T2. IFN-Îł circulating levels also declined by T2. CONCLUSION: Anti-M2R AAbs and IFN-Îł raise early during chagasic infection in children and are downmodulated by BZ therapy. These findings reinforce the usefulness of early BZ treatment not only to eliminate the parasite but also to reduce potentially pathogenic immune responses
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