1,721,057 research outputs found
Dynamic characterization of an all-FRP pultruded construction
No full textAll-FRP (Fiber Reinforced Polymer) structures made of pultruded structural elements are common in many countries, while their dynamic characterization is by far less uncommon. We focus on the evaluation of the dynamic features of a pavilion entirely built with pultruded FRP elements, with the only exception of the steel bolts used for connections. The all-FRP construction, located at the IUAV University Campus (Venice, Italy) was realized after a specific call for architectural design and required complex and dedicated calculation from a structural point of view. As for any new construction, the numerical finite element model was first produced and then compared with the experimental results, acquired once the structure was completed. This implies that the validation of the numerical model could be performed only a posteriori. The experimental dynamic characterization of the structure was performed according to the principles of the operational modal analysis, that is exploiting ambient microtremors as excitation for the structure. The same technique was exploited to assess the dynamic behaviour of foundation subsoil. The comparison between the experimental and the model turns out to be interesting, because the dynamic characteristics of all FRP constructions are still widely unknown in the current literature
A simple but effective cellular automaton for earthquakes
No full textThe physics of fractures, which forms the basis of seismic faulting, is not very amenable to simple deterministic differential equations. For this reason a different approach, aimed at reproducing the statistical mechanical properties of earthquakes, has attracted progressively increasing interest. A variety of models have been presented but there seems to be little that can be done to ascertain the merits and defects of each. We set the clock back and attempt to derive a dynamically evolving automation that is as simple as possible and that incorporates all the basic ingredients and includes strain diffusion, a process often disregarded in simple models in spite of its crucial importance. Our automaton is based on a homogeneous grid of cells and its rupturing is controlled by a generalized local threshold. The automation also considers local dissipation of energy and time-dependent strain applications. This simple model is capable of reproducing earthquake dynamics, including the effects due to transient loads such as those imposed by elastic waves, with an efficiency superior to that of the most complicated automata and with less stringent assumptions
Implementing cellular automata models for earthquakes on parallel computers
No full textCellular automata models require simulations on both large grids, to avoid border effects, and on a large number of realizations, to study the system properties under stationary. Implementing the cellular automata codes on parallel computers would appear as an ideal solution. Unfortunately, the cellular automata models which are appropriate for earthquakes can only be partially parallelized because they have an intrinsically sequential component. Under extensive modeling using MPI on CRAY T3 and Origin 8300 supercomputers we show that a substantial speed-up can nevertheless be achieved by coarsening the system and making a few mild assumptions on the logical flow of the interactions among macrocells
What criticality in cellular automata models of earthquakes?
No full textSix different 2-D prototype cellular automata models are developed to analyse the main variants of the massless automata proposed so far to reproduce earthquake physics. The analysis aims at identifying the existence of features common to these models, if any. The different model variants were studied with regard to: (1) initial grid configuration, homogeneous or random heterogenous; (2) loading function, random or uniform; (3) local dissipation; (4) local redistribution. As a first general result, it is found that the model exhibit critically over a very restricted range of spatial scales, much smaller than that imposed by the geometrical dimensions of the grid alone. The latter, in contrast, governs the initial transient dynamics, which exhibits much larger events. As a second general result, the foreshocks are found to increase systematically in both rate of occurrence and size prior to main shocks, with a simultaneous progressive deficit of small events. This, in turn, implies an increase in correlation length and a 'precursor' decrease in the b-value. As a third general result, the presence of foreshocks in cellular automata and the difficulties in detecting them in real earthquakes still only give a limited applicability of the present cellular automata models to the real world. As a final general result, periodic recurrence of main shocks is found only for locally dissipative models
Passive imaging in nondiffuse acoustic wavefields
No full textA main property of diffuse acoustic wavefields is that, taken any two points, each of them can be seen as the source of waves and the other as the recording station. This property is shown to follow simply from array azimuthal selectivity and Huygens principle in a locally isotropic wavefield. Without time reversal, this property holds approximately also in anisotropic azimuthally uniform wavefields, implying much looser constraints for undistorted passive imaging than those required by a diffuse field. A notable example is the seismic noise field, which is generally nondiffuse, but is found to be compatible with a finite aperture anisotropic uniform wavefield. The theoretical predictions were confirmed by an experiment on seismic noise in the mainland of Venice, Italy. © 2008 The American Physical Society
Resonance versus Shape of Sedimentary Basins
No full textSediment-filled basins are of interest both in exploration geophysics and in earthquake
seismology in assessing their potential to amplify ground shaking. By means of numerical
models, we present a number of dimensionless ratios between the main resonance
frequencies that can be measured on the top of the basins and their geometry and
mechanical properties, under the hypothesis of rigid bedrock. These resonance frequency
ratios depend largely on the aspect ratio of the basins, whereas the mechanical properties
of the sediments (specifically, the Poisson’s coefficient) do not substantially affect the horizontal
resonance frequency ratios. We discuss whether the modal frequencies measured
on real basins can be used to extract information about the basins themselves and whether
the theoretical expected modal sequence can be used to design experimental surveys
aimed at assessing the dynamic behavior of basins
Performance of Different ANNs in Microtremor H/V Peak Classification
No full textThe microtremor horizontal-to-vertical (H/V) technique is extensively used to both assess the seismic amplification potential of soils and, in combination with other surface wave-based techniques, to reconstruct the near-surface seismic stratigraphy. The H/V peak frequencies are traditionally interpreted in terms of soil resonances, and, in this case, they are assigned a “stratigraphic origin.” However, not all H/V peaks mark subsoil resonances, and some of them have “anthropic” or “artefactual” origin. Recognizing the nature of H/V peaks should be mandatory before any stratigraphic interpretation. Nonetheless, this problem is not given the attention it deserves. Because this classification is not easy to achieve using standard statistical techniques, we decided to train two supervised neural networks: a traditional artificial neural network using a set of input values extracted from the individual (horizontal and vertical) microtremor spectra and a convolutional neural network working on images of the microtremor spectra. The nets were trained on an Italian dataset and tested on a U.S. dataset, collected by different operators and with different instruments. Both the nets achieved a classification accuracy of ∼90%; however, the convolutional one showed a greater generalization capability compared to the traditional one. Such machine learning algorithms can be useful tools to discriminate the origin of H/V peaks, complementing the traditional SESAME guidelines, which do not go into much detail on this topic
N,N,N-Tris(tert-butoxycarbonyl)-L-arginine: five isoforms whose obtainment depends on procedure and a scrupulous NMR confirmation of their structures.
No full textL-arginine is often covalently linked to delivery systems for increasing their transfection activity and reducing toxicity and its basic nitrogen atoms need protection for example with tert-butoxycarbonyl group. Following three reported protocols which assured the goal of obtaining the widely cited αN,ωN,ω’N-tris(tert-butyloxycarbonyl)-L-arginine, surprisingly we achieved also other four isoforms (Figure 1). With the first selected procedure [1] αN,ωN,ω’N-Tris(tert-butyloxycarbonyl)-L-arginine was never obtained. The second one [2] provided the desired compound but as a mixture of geometric isomers E/Z while the third [3] protocol led to a single very pure isoform in high yield but with an unreported symmetrical structure. Since BOC protection is transient this discovery would seem of poor interest but results obtained from following investigations about the behavior of each one of the isoforms obtained in the esterification reactions of our interest shown that their reactivity depends on their structure. With this work we reported a detailed description of this unexpected results and the NMR investigation performed with particular care for double bonds geometry and position which confirmed the structures.
[1] H. Konno, K. Kubo, H. Makabe, E. Toshiro, N. Hinoda, K. Nosakaa, K: Akaji, Tetrahedron 63, 9502 (2007) doi:10.1016/j.tet.2007.06.082
[2] J. Izdebski, T. Gers, D. Kunce, P. Markovsky, J. Pept. Sci. 11, 60 (2005) doi: 10.1002/psc.585
[3] M. A. Jones, A. D. Hislop, J. S. Snaith, Org. Biomol. Chem. 4, 3769 (2006) doi: 10.1039/b611170
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