Enhanced double-mechanism creep laws for salt rocks     

Pedro A. L. P. Firme  Nuno B. Brandao  Deane Roehl  Celso Romanel 《Acta Geotechnica》2018,13(6):1329-1340

The double-mechanism creep law (DM model) is an empirical creep constitutive model widely employed in Brazilian salt rock mechanics. This model often presents good performance in steady-state creep prediction. However, transient creep is not accounted for, and whenever early creep estimates are important, the contribution of this phase might be meaningful. This work adds value by presenting two alternatives to account for transient creep in the DM model. The first alternative couples the transient function from Sandia’s multi-mechanism deformation model to the DM model steady-state creep rate (EDMT model). The second alternative couples the DM model response to Norton’s power law when the strain rate given by the latter remains lower than the one from the former (EDMP model). These models can be implemented in numerical simulators at small code extensions of the DM model implementations. Applications from previous works by the authors are revisited to validate the formulations based on experimental data. EDMT and EDMP models differ in the formulation of transient creep and, consequently, in the time of transition between the transient and the steady-state phases. Both methods were successful in treating transient creep and in simulating experimental results.  相似文献   

Embedded Behavior: Human Activities and the Construction of the Mesolithic Shellmound of Cabeço da Amoreira,Muge, Portugal     

Vera Aldeias  Nuno Bicho 《Geoarchaeology》2016,31(6):530-549

Shellmound formation processes are greatly influenced by human inputs associated with an intensive exploitation of marine and estuarine resources. The complex stratigraphy of shellmounds has been difficult to decipher and few studies have focused on the microstratigraphic record of midden formation, especially in European Mesolithic contexts. Cabeço da Amoreira is a long‐known Mesolithic shellmound located on the shores of the Muge River, a tributary of the Tagus River in central Portugal. The abundance of shellfish refuse favors an intricate and laterally variable stratigraphic succession of layers and lenses, which results in an extensive artificial mound. Here, we use micromorphological and microfacies analysis to investigate aspects pertaining to site formation, and the nature of individual anthropogenic activities at the site. This methodology allowed for a distinction between primary activities (e.g., discrete shell tossing events, trampled occupational surfaces, and activity areas), and secondary position of the sediments in intentionally raked‐up and dumped deposits. Nondepositional hiatuses and discrete geogenic sedimentation are associated with periods of abandonment. The complex superposition of events seen at Cabeço da Amoreira underlines the role of micromorphology for the identification of behavioral signatures and its relevance in deciphering shellmound adaptations.  相似文献   

Seismic analysis and strengthening of Pico Island Churches     

António Arêde  Aníbal Costa  Domingos Moreira  Nuno Neves 《Bulletin of Earthquake Engineering》2012,10(1):181-209

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Empirical seismic vulnerability analysis for masonry buildings based on school buildings survey in Iran     

Hamed Azizi-Bondarabadi  Nuno Mendes  Paulo B. Lourenço  Neda H. Sadeghi 《Bulletin of Earthquake Engineering》2016,14(11):3195-3229

School facilities in Iran, in particular masonry schools, have shown poor performance during past earthquakes and can be identified as one of the parts of the country’s infrastructure that is most vulnerable to earthquakes. Hence, in this paper a method to perform index-based damage assessment for brick masonry schools located in the province of Yazd, the central region of Iran, using a comprehensive database of school buildings, is proposed. The database was obtained from the field survey forms applied for each observed school to collect the features of and damage to the structure. The results of a vulnerability index method developed in Iran are employed as input data to obtain empirical fragility curves for the school inventory. The Macroseismic model and GNDT II level method are two empirical methods combined in this procedure. Finally, the procedure is verified using damage survey data obtained after recent earthquakes (1990 Manjil–Rudbar earthquake and 2003 Bam earthquake) that occurred in Iran.  相似文献   

Stochastic evaluation of the impact of sewer inlets’ hydraulic capacity on urban pluvial flooding     

Jo?o?P.?Leit?oEmail authorView author&#;s OrcID profile  Nuno?E.?Sim?es  Rui?Daniel?Pina  Susana?Ochoa-Rodriguez  Christian?Onof  Alfeu?Sá Marques 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(8):1907-1922

Sewer inlet structures are vital components of urban drainage systems and their operational conditions can largely affect the overall performance of the system. However, their hydraulic behaviour and the way in which it is affected by clogging is often overlooked in urban drainage models, thus leading to misrepresentation of system performance and, in particular, of flooding occurrence. In the present paper, a novel methodology is proposed to stochastically model stormwater urban drainage systems, taking the impact of sewer inlet operational conditions (e.g. clogging due to debris accumulation) on urban pluvial flooding into account. The proposed methodology comprises three main steps: (i) identification of sewer inlets most prone to clogging based upon a spatial analysis of their proximity to trees and evaluation of sewer inlet locations; (ii) Monte Carlo simulation of the capacity of inlets prone to clogging and subsequent simulation of flooding for each sewer inlet capacity scenario, and (iii) delineation of stochastic flood hazard maps. The proposed methodology was demonstrated using as case study design storms as well as two real storm events observed in the city of Coimbra (Portugal), which reportedly led to flooding in different areas of the catchment. The results show that sewer inlet capacity can indeed have a large impact on the occurrence of urban pluvial flooding and that it is essential to account for variations in sewer inlet capacity in urban drainage models. Overall, the stochastic methodology proposed in this study constitutes a useful tool for dealing with uncertainties in sewer inlet operational conditions and, as compared to more traditional deterministic approaches, it allows a more comprehensive assessment of urban pluvial flood hazard, which in turn enables better-informed flood risk assessment and management decisions.  相似文献   

A multi-arc approach for chaotic orbit determination problems     

Daniele Serra  Federica Spoto  Andrea Milani 《Celestial Mechanics and Dynamical Astronomy》2018,130(11):75

Chaotic dynamical systems are characterized by the existence of a predictability horizon, connected to the notion of Lyapunov time, beyond which predictions of the state of the system are meaningless. In order to study the main features of orbit determination in the presence of chaos, Spoto and Milani (Celest Mech Dyn Astron 124:295–309, 2016) applied the classical least-squares fit and differential correction algorithm to determine a chaotic orbit and a dynamical parameter of a simple discrete system—Chirikov standard map (cf. Chirikov in Phys Rep 52:263, 1979)—with observations distributed beyond the predictability horizon. They found a time limit beyond which numerical calculations are affected by numerical instability: the computability horizon. In this article, we aim at pushing forward such inherent obstacle to numerical calculations in chaotic orbit determination by applying the classical and the constrained multi-arc method (cf. Alessi et al. in Mon Not R Astron Soc 423:2270–2278, 2012) to the same dynamical system. These strategies entail the determination of an orbit when observations are grouped in separate observed arcs. For each arc, a set of initial conditions is determined and, in the case of the constrained multi-arc method, all subsequent arcs are constrained to belong to the same trajectory. We show that the use of these techniques in place of the standard least-squares method has significant advantages: Not only can we perform accurate numerical calculations well beyond the computability horizon, in particular, the constrained multi-arc strategy improves considerably the determination of the dynamical parameter.  相似文献   

    

Jean Serra 《Mathematical Geology》1987,19(4):349-355

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New constraints on neutrino masses from cosmology     

Alessandro Melchiorri  Scott Dodelson  Paolo Serra  Ane Slosar 《New Astronomy Reviews》2006,50(11-12):1020

By combining data from cosmic microwave background (CMB) experiments (including the recent WMAP third year results), large scale structure (LSS) and Lyman-α forest observations, we derive upper limits on the sum of neutrino masses of Σm_ν < 0.17 eV at 95% c.l. We then constrain the hypothesis of a fourth, sterile, massive neutrino. For the third massless +1 massive neutrino case we bound the mass of the sterile neutrino to m_s < 0.26 eV at 95% c.l. These results exclude at high significance the sterile neutrino hypothesis as an explanation of the LSND anomaly. We then generalize the analysis to account for active neutrino masses which tightens the limit to m_s < 0.23 eV and the possibility that the sterile abundance is not thermal. In the latter case, the constraints in the (mass, density) plane are non-trivial. For a mass of >1 eV or <0.05 eV the cosmological energy density in sterile neutrinos is always constrained to be ω_ν < 0.003 at 95% c.l. However, for a sterile neutrino mass of 0.25 eV, ω_ν can be as large as 0.01.  相似文献   

Late Pleistocene raised beaches of coastal Estremadura,central Portugal     

Michael M. Benedetti  Jonathan A. Haws  Caroline L. Funk  J. Michael Daniels  Patrick A. Hesp  Nuno F. Bicho  Thomas A. Minckley  Brooks B. Ellwood  Steven L. Forman 《Quaternary Science Reviews》2009,28(27-28):3428-3447

We present new stratigraphic, sedimentological, and chronological data for a suite of tectonically raised beaches dating to Marine Isotope Stages 5, 4, and 3 along the Estremadura coast of west-central Portugal. The beach deposits are found in association with ancient tidal channels and coastal dunes, pollen bearing mud and peat, and Middle Paleolithic archaeological sites that confirm occupation of the coastal zone by Neanderthal populations. The significance of these deposits is discussed in terms of the archaeological record, the tectonic and geomorphic evolution of the coast, and correlation with reconstructions of global climate and eustatic sea-level change. Direct correlation between the Estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits (which are near or beyond the limit of radiocarbon dating). Evidence from multiple sites dated by AMS radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea-level changes along this coast during Marine Isotope Stage 3. Two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka, recording a rise in relative sea level around the time of Heinrich Event 4 at 39 ka. Depending on assumptions about eustatic sea level at the time they were deposited, we estimate that these beaches have been uplifted at rates of 0.4–4.3 mm yr^?1 by the combined effects of tectonic, halokinetic, and isostatic processes. Uplift rates of 1–2 mm yr^?1 are likely if the beaches represent sea level stands at roughly 40 m below modern, as suggested by recent eustatic sea level reconstructions. Evidence from coastal bluffs and the interior of the study area indicates extensive colluvial, fluvial, and aeolian sedimentation beginning around 31 ka and continuing into the Holocene. These geomorphic adjustments are related to concomitant changes in climate and sea level, providing context that improves our understanding of Late Pleistocene landscape change and human occupation on the western Iberian margin.  相似文献   

European dry spell length distributions, years 1951–2000     

C. Serra  M.D. Martínez  X. Lana  A. Burgueño 《Theoretical and Applied Climatology》2013,114(3-4):531-551

Daily precipitation records of 267 European rain gauges are considered to obtain dry spell length (DSL) series along the second half of the twentieth century. A dry spell consists of consecutive days with daily rain amount below a given threshold, R ₀. Four DSL series are obtained for R ₀ values equal to 0.1, 1.0, 5.0, and 10.0 mm/day, and their empirical distributions are properly fitted to different statistical models: Pearson type III (PE3), Weibull (WEI), generalised Pareto, (GPA) and lognormal distributions. The parameters of every model are estimated by L-moments, and the goodness of fit is assessed by quantifying discrepancies between empirical and theoretical distributions in the L-skewness–kurtosis diagrams. The most common best-fitting model is PE3, especially for 0.1 and 1.0 mm/day. Nevertheless, a few stations in southern Europe are better modelled by the WEI distribution. For 5.0 and 10.0 mm/day, the spatial distribution of the best-fitting model is more heterogeneous than for the lowest thresholds. While PE3 is still the preferred model for Western Europe, some DSL series are better fitted to WEI or GPA models. Maps of DSL average and standard deviation and expected lengths for return periods of 2, 5, 10, 25, and 50 years show some common features. Whereas for thresholds of 0.1 and 1.0 mm/day, a N–S gradient is detected, especially in Mediterranean areas; for 5.0 and 10.0 mm/day, a NW–SE gradient is observed in the Iberian Peninsula and a SW–NE gradient in the Scandinavian Peninsula. Then, the vicinity to Atlantic and Arctic Oceans and the Mediterranean Sea, as well as orographic features, are more determining factors than the latitude in patterns associated with the highest R ₀ thresholds. Finally, a regional frequency analysis based on a clustering algorithm is attempted for the four thresholds R ₀, with the PE3 model as the parent distribution for the largest clusters.  相似文献