Application of Wave Propagation to Pyroshock Analysis

Pyroshocks are high frequency transients due to pyrotechnic devices used in aerospace engineering in order to deploy solar arrays and antennae, separate subsystems from the spacecraft or separate the spacecraft itself from the base stage booster; their prediction is usually complex and very time consuming.The aim of this article is to investigate on the application of the analysis of transmission of waves in elastic media in order to predict the dynamic response to pyroshocks. The work is completed by numerical examples, related to components of common use in the aerospace engineering field, showing the comparison between results obtained by using both MSC-NASTRAN and this novel application of wave propagation analysis

Earthen plasters stabilized through sustainable additives: An experimental campaign

The earthen architecture widely spread in many countries of Europe, America, Asia, Africa, testifies to a particular material and immaterial culture. Nevertheless, it is a fragile heritage, which needs continuous maintenance. To encourage the preservation of such evidence of building techniques, an experimental campaign aimed at the development and evaluation of the performances of protective earthen plasters was undertaken. The durability of the plasters was improved through the addition of different additives, some of them traditional (such as lime and gypsum) and others innovative (geopolymers, enzymes), and resulting from industrial wastes (cement kiln dust). These additives have been selected considering low production costs and a reduced environmental impact, to improve the sustainability of the interventions. The performances of the earthen plasters in terms of efficacy (resistance to water erosion, water absorption, drilling, thermo-hygrometric cycles) and compatibility (changes in color and water vapor permeability) have been evaluated. Good performances were obtained by the different mixtures and, in particular, by those stabilized with gypsum. The results of this experimentation could find a useful application in the preservation of both ancient and new earthen built heritage

Stabilization of earthen plasters: Exchange of knowledge and experiences between Italy and Morocco

The preservation of earthen architectural heritage and earthen contemporary architecture asks for the experimentation and the development of proper materials and intervention techniques in order to prevent decays which may compromise the conservation of earthen heritage over time. This research program, thanks to a bilateral cooperation between the CNRST-UCA and CNR-ICVBC, aims to design and test earth-based plasters stabilized with traditional products (gypsum or lime), in order to acquire information necessary to develop more durable earthen mixtures to be applied both on existing and new buildings. The experimental campaign intends to assess the capacity of these stabilized plasters to guarantee an appropriate protection of earthen walls. The plasters have been tested at first in laboratory, then they have been applied on an earthen building in the outskirts of Marrakesh. The performances of the on site plasters are still under study and will not be presented in this paper

Whale sharks as oceanic nurseries for Golden Trevally

The Golden Trevally, Gnathanodon speciosus, is a large predatory fish with an extremely broad tropical Indo-Pacific distribution that crosses many biogeographical boundaries. Both published information and freely available imagery suggest that small juvenile G. speciosus are often associated with whale sharks, Rhincodon typus; an association that could explain the unusually widespread distribution of G. speciosus, and suggests a novel nursery relationship. The possibility of such an association has the potential to reshape our understanding of the ecological roles played by long-range migrants such as R. typus and other megafauna, our understanding of the full extent of their conservation value, and how we manage both members of the relationship

Novelty detection across a small population of real structures: A negative selection approach

Vibration-based Structural Health Monitoring (SHM), exploits a variety of approaches for novelty detection. In particular, many data-based methods try to recognise patterns by exploiting analogies with the human body's natural defences at a cellular level. These algorithms fall within the Artificial Immune System (AIS) class and can be chosen, according to their peculiarities, to solve specific problems in diverse application areas. This study investigates the damage-detection process in different operational conditions, obtained by applying structural modifications to a laboratory-scale aeroplane, which follows the geometric features of the GARTEUR benchmark project. Damage identification is performed by exploiting the Negative Selection Algorithm (NSA), already applied by some of the authors on numerically-simulated case studies, and chosen for its capability of self/non-self discrimination under varying operational or environmental conditions. The research is expanded by using sparse autoencoders for feature dimensionality reduction. The method is applied to an experimental dataset acquired via Scanning Laser Doppler Vibrometer (SLDV) measurements, to identify consistent damage-sensitive features from the frequency response functions, and to obtain a reliable fault-detection performance

Active crustal extension and strain accumulation from GPS data in the Molise region (central-southern Apennines, Italy)

In this paper, we report new GPS measurements which indicate active NE-SW extension and strain accumulation in the Molise region (Apennines, Italy). The GPS observations were collected during campaigns on benchmarks of the dense IGM95 network (average distance 20 km), spanning a maximum observation interval of 13 years, and have been integrated with measurements from the available permanent GPS sites. Considering the differential motion of the GPS sites, located on the Tyrrhenian and Adriatic coasts, we can evaluate a 4-5 mm/yr extension accommodated across this part of the Apennines. The velocity field exhibits clusters of sites with homogeneous velocity vectors, outlining two main divergence areas, both characterized by the largest velocity gradients: one near Venafro and the other near Isernia where two primary active faults and several historical earthquakes have been documented. These results suggest that an active extension in this part of the Apennines can be currently distributed between the two faults systems associated with the largest earthquakes of this region

Ecological constraint mapping: understanding uutcome-limiting bottlenecks for improved environmental decision-making in marine and coastal environments

Despite genuine attempts, the history of marine and coastal ecosystem management is littered with examples of poor environmental, social and financial outcomes. Marine ecosystems are largely populated by species with open populations, and feature ecological processes that are driven by multiple, interwoven, dynamic causes and effects. This complexity limits the acquisition of relevant knowledge of habitat characteristics, species utilisation and ecosystem dynamics. The consequence of this lack of knowledge is uncertainty about the link between action taken and outcome achieved. Such uncertainty risks misdirected human and financial investment, and sometimes may even lead to perverse outcomes. Technological advances offer new data acquisition opportunities, but the diversity and complexity of the biological and ecological information needed to reduce uncertainty means the increase in knowledge will be slow unless it is undertaken in a structured and focussed way. We introduce “Ecological Constraint Mapping” – an approach that takes a “supply chain” point of view and focusses on identifying the principal factors that constrain life-history outcomes (success/productivity/resilience/fitness) for marine and coastal species, and ultimately the quality and resilience of the ecosystems they are components of, and the life-history supporting processes and values ecosystems provide. By providing a framework for the efficient development of actionable knowledge, Ecological Constraint Mapping can facilitate a move from paradigm-based to knowledge-informed decision-making on ecological issues. It is suitable for developing optimal solutions to a wide range of conservation and management problems, providing an organised framework that aligns with current perspectives on the complex nature of marine and coastal systems

10 Hz GPS seismology for moderate magnitude earthquakes: the case of the Mw 6.3 L’Aquila (Central Italy) event

The 2009 April 6th Mw 6.3 L'Aquila destructive earthquake was successfully recorded by closely spaced 10-Hz and 1-Hz recording GPS receivers and strong motion accelerometers located above or close to the 50° dipping activated fault. We retrieved both static and dynamic displacements from Very High-Rate GPS (VHRGPS) recordings by using Precise Point Positioning kinematic analysis. We compared the GPS positions time series with the closest displacement time series obtained by doubly-integrating strong motion data, first, to assess the GPS capability to detect the first seismic arrivals (P waves) and, secondly, to evaluate the accelerometers capability to detect co-seismic offsets up to ~45 s after the earthquake occurrence. By comparing seismic and VHRGPS frequency contents, we inferred that GPS sampling rates greater than 2.5 Hz (i.e. 5 or 10 Hz) are required in the near-field of moderate magnitude events to provide “alias-free” solutions of coseismic dynamic displacements. Finally, we assessed the consistency of the dynamic VHRGPS results as a constraint on the kinematic rupture history of the mainshock. These results suggested that the high-rate sampling GPS sites in the near field can be as useful as strong motion station for earthquake source studies

Coseismic and initial postseismic slip of the 2009 Mw 6.3 l’Aquila earthquake, Italy, from GPS measurements

Here we report the preliminary results of GPS data inversions for coseismic and initial afterslip distributions of the Mw 6.3 2009 April 6 L’Aquila earthquake. Coseismic displacements of continuous and survey-style GPS sites, show that the earthquake ruptured a planar SW-dipping normal fault with ∼0.6 m average slip and an estimated moment of 3.9 × 1018 Nm. Geodetic data agree with the seismological and geological information pointing out the Paganica fault, as the causative structure of the main shock. The position of the hypocentre relative to the coseismic slip distribution supports the seismological evidence of southeastward rupture directivity. These results also point out that the main coseismic asperity probably ended downdip of the Paganica village at a depth of few kilometres in agreement with the small (1–10 cm) observed surface breaks. Time-dependent post-seismic displacements have been modelled with an exponential function. The average value of the estimated characteristic times for near-field sites in the hanging-wall of the fault is 23.9 ± 5.4 d. The comparison between coseismic slip and post-seismic displacements for the first 60 d after the main shock, shows that afterslip occurred at the edges of the main coseismic asperity with a maximum estimated slip of ∼25 cm and an equivalent seismic moment of 6.5 × 1017 Nm. The activation of the Paganica fault, spatially intermediate between the previously recognized main active fault systems, suggests that strain accumulation in the central Apennines may be simultaneously active on distinct parallel fault systems.Published1539–15461.1. TTC - Monitoraggio sismico del territorio nazionale1.9. Rete GPS nazionaleJCR Journalrestricte