Search results for "Geophysics"

Volume change characteristics of fine-grained soils due to sequential thermo-mechanical stresses

2019

Know-how of volume change characteristics, VCC, of the fine-grained soils, exposed to thermal stresses, is essential for design of various thermo-active structures. These stresses are known to induce excess pore-water pressure, Δu θ , in the saturated state of such soils, which in turn affects their compression and shear strength characteristics. In this context, through several experimental studies, the effect of thermo-mechanical stress-path, the over-consolidation ratio (OCR) and degree of saturation on VCC (viz., thermally induced volumetric strain, ε vθ , compression and re-compression indices, c c and c r ) of the fine-grained soils has been demonstrated by earlier researchers. Howeve…

Nonstationary flow surface theory for modeling the viscoplastic behaviors of soils

2016

Abstract This paper presents a three-dimensional elastic viscoplastic model that can describe the time-dependent behaviors of soft clays. The constitutive model is formulated based on the nonstationary flow surface theory and incorporates new developments, including (i) an improved definition of the nonstationary flow surface that is capable of capturing the stress–strain behaviors under different loading paths, (ii) a unique stress–strain—viscoplastic-strain-rate equation that is able to explicitly describe the nonstationary flow surface, and (iii) a final stable state concept that identifies the final equilibrium state at the end of creep and stress relaxation, which is also used to simpl…

Chronology for the Cueva Victoria fossil site (SE Spain): Evidence for Early Pleistocene Afro-Iberian dispersals

2014

Cueva Victoria has provided remains of more than 90 species of fossil vertebrates, including a hominin phalanx, and the only specimens of the African cercopithecid Theropithecus oswaldi in Europe. To constrain the age of the vertebrate remains we used paleomagnetism, vertebrate biostratigraphy and (230)Th/U dating. Normal polarity was identified in the non-fossiliferous lowest and highest stratigraphic units (red clay and capping flowstones) while reverse polarity was found in the intermediate stratigraphic unit (fossiliferous breccia). A lower polarity change occurred during the deposition of the decalcification clay, when the cave was closed and karstification was active. A second polarit…

Beaches in Valencian Coast

2018

The main factors that determined the Valencian beaches characteristics are the configuration of relief structures; fluvial sediment supply; low tidal range; the predominance of low energy waves; scarcity of big storms; longshore littoral drift; and human action. There is a significant prevalence of sandy beaches. Nevertheless, both at the northern part of the Gulf of Valencia and in the structural segment, between the Cape Sant Antoni and Alicante city, pebble and gravel beaches are predominant. Most of the Valencian beaches have experienced significant morphological changes during the last decades due to the human interventions -voluntary or involuntary- in the coastal system. The implemen…

Impact of sedimentology and diagenesis on the petrophysical properties of a tight oolitic carbonate reservoir. The case of the Oolithe Blanche Format…

2013

18 pages; International audience; The Oolithe Blanche Formation was studied in three quarries, located at the south-eastern edge of the Paris Basin (France). Heterogeneities in reservoir properties were assessed through a sedimentological, diagenetic and petrophysical study. The relationships between depositional settings, diagenesis and petrophysical properties were analysed using detailed petrographic studies, image analysis, Nano CTscans and petrophysical measurements. The carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso- and macroporosity. Early cementation vs. early compaction processes (mainly g…

Optimization and Inversion

2009

Ensemble reconstruction constraints on the global carbon cycle sensitivity to climate

2010

The processes controlling the carbon flux and carbon storage of the atmosphere, ocean and terrestrial biosphere are temperature sensitive and are likely to provide a positive feedback leading to amplified anthropogenic warming. Owing to this feedback, at timescales ranging from interannual to the 20-100-kyr cycles of Earth's orbital variations, warming of the climate system causes a net release of CO(2) into the atmosphere; this in turn amplifies warming. But the magnitude of the climate sensitivity of the global carbon cycle (termed gamma), and thus of its positive feedback strength, is under debate, giving rise to large uncertainties in global warming projections. Here we quantify the med…

In-situ high spatial resolution LA-MC-ICPMS 230Th/U dating enables detection of small-scale age inversions in speleothems

2017

Abstract We present an in-situ method for Th and U isotope measurements by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) to determine possible age inversions of stalagmites, using a 213 nm Nd:YAG laser connected to an MC-ICPMS. Due to the low ion beam intensity of 230 Th (20–120 counts per second, cps), we carefully optimized the operating parameters to get highest possible ion beam intensities, i.e., laser fluence (25 J cm −2 ), spot size (110 μm), pulse repetition rate (20 Hz), scan speed (4 μm s −1 ), integration time (1000 s), and He and Ar gas flow (∼0.9 L min −1 and ∼0.6 L min −1 respectively). A precision (2 relative standard error, 2RSE) o…

Predicting gully occurrence at watershed scale: Comparing topographic indices and multivariate statistical models

2020

In this study, the ability of five topographic indices to predict the gully trajectories observed in two adjacent watersheds located in Sicily (Italy) was evaluated. Two of these indices, named MSPI and MTWI, as far as we know, have never been employed to this aim. They were obtained by multiplying the stream power index (SPI) and the topographic wetness index (TWI), respectively, by the convergence index (CI). The predictive ability of the topographic indices was measured by using both cut-off independent (AUC: area under the receiver operating characteristic curve) and dependent statistics (Cohen's kappa index κ, sensitivity, specificity). These statistics were calculated also for 100 MAR…

Total absorption spectroscopy of fission fragments relevant for reactor antineutrino spectra

2016

International audience; The accurate determination of reactor antineutrino spectra remains a very active research topic for which new methods of study have emerged in recent years. Indeed, following the long-recognized reactor anomaly (measured antineutrino deficit in short baseline reactor experiments when compared with spectral predictions), the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have recently demonstrated the existence of spectral distortions in their measurements with respect to the same predictions. These spectral predictions were obtained through the conversion of integral beta-energy spectra obtained at the ILL research reactor. Several s…