129 research outputs found
Seismic Station Installations and Their Impact on the Recorded Signals and Derived Quantities
The role of local geology in controlling ground motion has long been acknowledged.
Consequently, increasing attention is paid to the assessment of the geophysical properties
of the soils at the seismic stations, which impact the station recordings and a series
of related quantities, particularly those referring to seismic hazard estimates. Not the
same level of attention is commonly dedicated to the seismic station installation, to the
point that it is generally believed that housings and shelters containing seismic instruments
are of no interest, because they can only affect frequencies well above the engineering
range of interest. Using examples from seismometric and accelerometric
stations, we describe the (1) housing, (2) foundation, and (3) pillar effects on the seismic
records. We propose a simple working scheme to identify the existence of potential
installation-related issues and to assess the frequency fidelity range of response of
a seismic station to ground motion. Our scheme is developed mostly on ambient noise
recordings and, thus, surface waves. The hope is that, besides the parameters that start
to be routinely introduced in the seismic archives (VS30, soil classes, etc.), the assessment
of the maximum reliable frequency, under which no soilâstructure interaction is
expected, also becomes a mandatory information. In our experience, for some installation
sites, the maximum reliable frequency can even be less than a very few hert
An FDD-based modal parameter-less proportional flexibility-resembling matrix for response-only damage detection
Modal flexibility-based methods are effective tools for vibration-based structural damage detection, including in the output-only case. These methods are typically characterized by two stages: first, the modal parameters are identified, thus obtaining a certain number of modes; second, these modal parameters are used to assemble the modal flexibility matrix. This paper proposes a method for estimating a matrix that approximates a proportional flexibility matrix, termed proportional flexibility-resembling (PFR) matrix, and shows that this matrix can be used for damage detection and localization purposes. This matrix is obtained through signal processing operations to be executed after applying the first steps of the frequency-domain decomposition (FDD) technique-i.e., after the singular value decomposition of the spectral density matrix. The defining aspect of the PFR matrix is that, differently from the traditional formulation of modal flexibility and proportional flexibility matrices, it can be assembled without the need of an explicit identification of the modal parameters. In fact, the matrix is estimated by processing all first singular vectors and also all first singular values in a selected frequency range. In the proposed method, the typical two stage approach of traditional modal flexibility methods is avoided, and the intervention of an operator is limited to setting the values of a few parameters in the initial phase of the process. Numerical simulations and experimental data from a testbed structure were used to show the effectiveness of the proposed approach, and the analyses were performed by considering structures with different damage scenarios and damping properties
Potential instability of gas hydrates along the chilean margin due to ocean warming
In the last few years, interest in the offshore Chilean margin has increased rapidly due to the presence of gas hydrates. We have modelled the gas hydrate stability zone off Chilean shores (from 33\ub0 S to 46\ub0 S) using a steady state approach to evaluate the effects of climate change on gas hydrate stability. Present day conditions were modelled using published literature and compared with available measurements. Then, we simulated the effects of climate change on gas hydrate stability in 50 and 100 years on the basis of Intergovernmental Panel on Climate Change and National Aeronautics and Space Administration forecasts. An increase in temperature might cause the dissociation of gas hydrate that could strongly affect gas hydrate stability. Moreover, we found that the high seismicity of this area could have a strong effect on gas hydrate stability. Clearly, the Chilean margin should be considered as a natural laboratory for understanding the relationship between gas hydrate systems and complex natural phenomena, such as climate change, slope stability and earthquakes
Detection of a slow-flow component in contrast-enhanced ultrasound of the synovia for the differential diagnosis of arthritis
Contrast Enhanced Ultrasound (CEUS) is a sensitive imaging technique to assess tissue vascularity, that can be useful in the quantification of different perfusion patterns. This can particularly important in the early detection and differentiation of different types of arthritis. A Gamma-variate can accurately quantify synovial perfusion and it is flexible enough to describe many heterogeneous patterns. However, in some cases the heterogeneity of the kinetics can be such that even the Gamma model does not properly describe the curve, especially in presence of recirculation or of an additional slowflow component. In this work we apply to CEUS data both the Gamma-variate and the single compartment recirculation model (SCR) which takes explicitly into account an additional component of slow flow. The models are solved within a Bayesian framework. We also employed the perfusion estimates obtained with SCR to train a support vector machine classifier to distinguish different types of arthritis. When dividing the patients into two groups (rheumatoid arthritis and polyarticular RA-like psoriatic arthritis vs. other arthritis types), the slow component amplitude was significantly different across groups: mean values of a1 and its variability were statistically higher in RA and RA-like patients (131% increase in mean, p = 0.035 and 73% increase in standard deviation, p = 0.049 respectively). The SVM classifier achieved a balanced accuracy of 89%, with a sensitivity of 100% and a specificity of 78%. © 2017 SPIE
Un modelo de simulaci\uf3n de sistemas de engorda de bovinos a pastoreo
A simulation model of beef cattle fattening systems based on grazing
pastures was developed. The objective was to evaluate different pasture
options under different management strategies, types of beef cattle,
stocking densities, supplementation strategies and input prices. This
model was structured based on a program, whose main module drives
management input and generates result files. The dynamic section uses
biological subroutines to solve equations simulating biological
processes, the most important being the metabolizable energy intake and
live weight change. Pasture growth and nutritive value were simulated
empirically from the interpolation of monthly data of pasture growth
and digestibility of different pasture types. The model also calculates
processes related to pasture management, forage conservation and
bioeconomic aspects. The physical grazing experiment, carried out
during the 1979-1980 seasons was utilized to validate the animal
sub-system, A coefficient of determination higher than 95% was obtained
when simulated and real values measured in the respective experiments
were correlated by regression analysis, verifying the non existence of
bias in the estimations. The root mean square error (RMSE) was smaller
than 6%, suggesting that this model is realistic and has a high degree
of precision.Se elabor\uf3 un modelo de simulaci\uf3n de sistemas de
producci\uf3n de carne basado en utilizaci\uf3n de pasturas, cuyo
objetivo fue evaluar diferentes alternativas pratenses bajo distintas
modalidades de manejo, tipos de bovinos, densidades de carga,
estrategias de suplementaci\uf3n y precios de insumos. El modelo se
estructur\uf3 sobre la base de un programa computacional, cuyo
m\uf3dulo principal maneja archivos de datos de manejo y genera
archivos de resultados. La secci\uf3n din\ue1mica est\ue1
estructurada en subrutinas orientadas a resolver ecuaciones que simulan
los procesos biol\uf3gicos, siendo los m\ue1s importantes el
consumo de energ\ueda metabolizable y el cambio de peso vivo. El
crecimiento y valor nutritivo de los pastizales fue simulado
emp\uedricamente a partir de la interpolaci\uf3n de datos mensuales
de tasas de crecimiento y digestibilidad de diferentes tipo de
pasturas. El modelo tambi\ue9n calcula los procesos relacionados con
el manejo del pastoreo, conservaci\uf3n de forrajes y aspectos
bioecon\uf3micos. Para la validaci\uf3n del subsistema animal, se
utilizaron los datos de peso vivo de toretes Hereford obtenidos de los
experimentos f\uedsicos de pastoreo realizados durante la temporada
1979-1980. Al relacionar mediante un an\ue1lisis de regresi\uf3n
los valores simulados con los medidos en los experimentos, se obtuvo un
coeficiente de determinaci\uf3n superior al 95%, confirm\ue1ndose
la inexistencia de sesgo en la estimaci\uf3n. La ra\uedz del error
cuadr\ue1tico medio (RMSE) no super\uf3 el 6%, lo que
indicar\ueda que este modelo es realista y tiene un alto grado de
precisi\uf3n
La ricostruzione dello scuotimento del terremoto del Garda del 2004 (ML=5.2)
Il terremoto di magnitudo ML=5.2 che nel 2004 ha colpito il lato
occidentale del Lago di Garda (Nord Italia) viene modellato sia
nellâapprossimazione di sorgente puntiforme sia mediante simulazioni
da sorgente estesa, al fine di investigare lâanisotropia del campo
di risentimento osservata tra 5 e 15 km di distanza epicentrale. Il
confronto con le osservazioni viene effettuato in termini intensitĂ
macrosismica IMCS osservata, considerando i soli comuni localizzati
su roccia (o formazione «rigida») fino a 40 km dallâepicentro; un
ulteriore confronto fra simulazioni e osservazioni viene effettuato
utilizzando i dati registrati dalla stazione accelerometrica di Vallio
Terme (GVD), localizzata a 13.3 km dallâepicentro, appartenente alla
rete nazionale (RAN).
Le simulazioni piĂč semplici utilizzano una sorgente puntiforme
ed equazioni predittive empiriche in termini di intensitĂ . Le modellazioni
a faglia estesa riproducono il campo di scuotimento in termini
di valori di picco dello scuotimento, successivamente convertiti in
intensitĂ attraverso relazioni empiriche. Nonostante la moderata
magnitudo dellâevento, le simulazioni a faglia estesa, che richiedono
lâassunzione di ipotesi plausibili sia sulla geometria della sorgente
che sulle proprietĂ di attenuazione del mezzo di propagazione, sono
in grado di confermare lâanisotropia osservata della distribuzione di
intensitĂ a scala regionale (30Ă30 km2). Inoltre, poichĂ© la distribuzione
delle intensitĂ presenta anche eterogeneitĂ a scala locale (di
dimensione inferiore a 3 km), probabilmente dovute ad effetti geologici
e geomorfologici, oppure ad effetti di interazione terreno-struttura,
nella seconda parte del lavoro vengono presentati alcuni esempi
di misure di rumore sismico e di misure di frequenza propria
degli edifici
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