Liquid water uptake in unconfined Callovo Oxfordian clay-rock studied with neutron and X-ray imaging     

Stavropoulou  Eleni  Andò  Edward  Tengattini  Alessandro  Briffaut  Matthieu  Dufour  Frédéric  Atkins  Duncan  Armand  Gilles 《Acta Geotechnica》2019,14(1):19-33

The Callovo Oxfordian clay-rock (COx) is studied in France for the disposal of radioactive waste, because of its extremely low permeability. This host rock is governed by a hydromechanical coupling of high complexity. This paper presents an experimental study into the mechanisms of water uptake in small, unconfined, prismatic specimens of COx, motivated by the comprehension of cracking observed during concrete/COx interface sample preparation. Water uptake is monitored using both X-ray tomography and neutron radiography, the combination of these imaging techniques allowing material deformation and water arrival to be quantified, respectively. Given the speed of water entry and crack propagation, relatively fast imaging is required: 5-min X-ray tomographies and 10-s neutron radiographs are used. In this study, pairs of similar COx samples from the same core are tested separately with each imaging technique. Two different orientations with respect to the core are also investigated. Analysis of the resulting images yields with micro- and macro-scale insights into hydromechanical mechanisms to be obtained. This allows the cracking to be interpreted as a rapid breakdown in capillary suction (supposed large both to drying and rebound from in situ stress state) due to water arrival, which in turn causes a loss of effective stress, allowing cracks to propagate and deliver water further into the material.

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Towards realistic minimum-cost optimization of viscous fluid dampers for seismic retrofitting     

Nicolò Pollini  Oren Lavan  Oded Amir 《Bulletin of Earthquake Engineering》2016,14(3):971-998

This paper presents an effective approach for achieving minimum cost designs for seismic retrofitting using viscous fluid dampers. A new and realistic retrofitting cost function is formulated and minimized subject to constraints on inter-story drifts at the peripheries of frame structures. The components of the new cost function are related to both the topology and to the sizes of the dampers. This constitutes an important step forward towards a realistic definition of the optimal retrofitting problem. The optimization problem is first posed and solved as a mixed-integer problem. To improve the efficiency of the solution scheme, the problem is then re-formulated and solved by nonlinear programming using only continuous variables. Material interpolation techniques, that have been successfully applied in topology optimization and in multi-material optimization, play a key role in achieving practical final design solutions with a reasonable computational effort. Promising results attained for 3-D irregular frames are presented and compared with those achieved using genetic algorithms.  相似文献   

Morphotectonic analysis of Kosi River basin in Kumaun Lesser Himalaya: an evidence of neotectonics     

Charu C. Pant  Shivendra Pratap Singh 《Arabian Journal of Geosciences》2017,10(19):421

The Himalayan arc is one of the prominent sites on Earth, for ongoing research on active tectonics because of the frequent occurrence of earthquakes of low-moderate intensity that occur in various sectors of the region. The present study is an attempt to decipher the active uplift and relative tectonic activity in Kosi River basin, a part of the southern Kumaun Himalayas. Several morphotectonic parameters such as asymmetry factor (AF), hypsometric integral (HI), mountain front sinuosity (S_mf), channel sinuosity (S), and basin elongation ratio (R_e) have been calculated with an objective to compare different sub-basins in the Kosi watershed that may prove useful in deciphering of relative tectonic activity. The watershed delineation of the Kosi River basin as well as its sub-basins, and detailed drainage network has been accomplished by using the CARTOSAT-1 DEM with the help of ArcGIS 10.3 software, using TauDEM tool and Global Mapper 18. Analysis of these morphotectonic parameters reveals that although the whole of the Kosi River basin lies in the seismically active zone, but the northern part along North Almora Thrust (NAT), central part around South Almora Thrust (SAT), Ramgarh Thrust (RT), and southern part along Himalayan Frontal Thrust (HFT) are tectonically more active and undergoing neotectonic rejuvenation. The information derived would prove beneficial in identification of hazard prone areas and in planning of socio-economic development in mountainous terrain.  相似文献   

Thick self-standing bent crystals as optical elements for a Laue lens for applications in astrophysics     

Riccardo Camattari  Marco Romagnoni  Andrea Mazzolari  Gianfranco Paternò  Vincenzo Guidi  Thomas Buslaps 《Experimental Astronomy》2018,46(2):309-321

In this paper we report progresses in the realization of self-standing bent crystals, which are suitable as optical elements for Laue lenses, i.e. for optic to focus hard X-rays in the 100–1000 keV energy range. The curvature of the crystals is a key factor to enhance diffraction efficiency and energy bandpass for such an optic. In particular, two bent crystals featuring a thickness of 5 mm, made of Si and Ge respectively, were produced at the Sensor and Semiconductor Laboratory in Ferrara, Italy. The crystals were bent through the application of a carbon fibre composite. This proved to be a relatively low cost method for crystal bending, suitable for mass production. The manufactured samples were characterised via optical interferometry, and showed a fairly uniform curvature. Finally, the samples were tested exploiting hard X-ray diffraction at the ID11 facility of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. A careful analysis of the experimental data highlighted that the samples feature large energy bandpass, wide geometrical acceptance for incoming hard X-rays, and high diffraction efficiency. We therefore conclude that such self-standing crystals are good candidates as Laue lens components for astrophysics applications.  相似文献   

Coastal aquifer response to extreme storm events in Emilia‐Romagna,Italy          下载免费PDF全文

Beatrice M.S. Giambastiani  Nicolò Colombani  Nicolas Greggio  Marco Antonellini  Micòl Mastrocicco 《水文研究》2017,31(8):1613-1621

With global warming and sea level rise, many coastal systems will experience increased levels of inundation and storm flooding, especially along sandy lowland coastal areas, such as the Northern Adriatic coast (Italy). Understanding how extreme events may directly affect groundwater hydrology in shallow unconfined coastal aquifers is important to assess coastal vulnerability and quantify freshwater resources. This study investigates shallow coastal aquifer response to storm events. The transitory and permanent effects of storm waves are evaluated through the real time monitoring of groundwater and soil parameters, in order to characterize both the saturated and unsaturated portions of the coastal aquifer of Ravenna and Ferrara (southern Po Delta, Italy). Results highlight a general increase in hydraulic head and soil moisture, along with a decrease in groundwater salinity and pore water salinity due to rainfall infiltration during the 2 days storm event. The only exceptions are represented by the observation wells in proximity to the coastline (within 100 m), which recorded a temporary increase in soil and water salinity caused by the exceptional high waves, which persist on top of the dune crest during the storm event. This generates a saline plume that infiltrates through the vadose zone down to the saturated portion of the aquifer causing a temporary disappearance of the freshwater lens generally present, although limited in size, below the coastal dunes. Despite the high hydraulic conductivity, the aquifer system does not quickly recover the pre‐storm equilibrium and the storm effects are evident in groundwater and soil parameters after 10 days past the storm overwash recess.  相似文献   

New class of regular and well behaved exact solutions in general relativity     

Neeraj Pant  R. N. Mehta  Mamta Joshi Pant 《Astrophysics and Space Science》2010,330(2):353-359

We present a new class of spherically symmetric regular and well behaved solutions of the general relativistic field equations in isotropic coordinates. These solutions describe perfect fluid balls with positively finite central pressure and positively finite central density; their ratio is less than one and causality condition is obeyed at the centre. The solutions of this class, the outmarch of pressure, density pressure-density ratio and the ratio of sound speed to light is monotonically decreasing. Keeping in view of well behaved nature in terms of central red shift and surface red shift and by assuming the surface density ρ _b =2×10¹⁴ g/cm³, we constructed a Neutral star model for k=2, resulting into maximum mass ≈6.36M _Θ, linear dimension ≈48.08 km, surface red shift ≈1.132 and central red shift ≈17.1314.  相似文献   

Spectroscopic analysis of the candidate β Cephei star σ Cas: Atmospheric characterization and line-profile variability     

G. Catanzaro  R. Ventura  F. Ferrara  L. Paternò 《New Astronomy》2010,15(1):39-45

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Fluid‐induced breakdown of monazite in medium‐grade metasedimentary rocks of the Pontremoli basement (Northern Apennines,Italy)          下载免费PDF全文

D. Lo Pò  R. Braga  H.‐J. Massonne  G. Molli  A. Montanini  T. Theye 《Journal of Metamorphic Geology》2016,34(1):63-84

The last (decompression) stages of the metamorphic evolution can modify monazite microstructure and composition, making it difficult to link monazite dates with pressure and temperature conditions. Monazite and its breakdown products under fluid‐present conditions were studied in micaschist recovered from the cuttings of the Pontremoli1 well, Tuscany. Coronitic microstructures around monazite consist of concentric zones of apatite + Th‐silicate, allanite and epidote. The chemistry and microstructure of the monazite grains, which preserve a wide range of chemical dates ranging from Upper Carboniferous to Tertiary times, suggest that this mineral underwent a fluid‐mediated coupled dissolution–reprecipitation and crystallization processes. Consideration of the chemical zoning (major and selected trace elements) in garnet, its inclusion mineralogy (including xenotime), monazite breakdown products and phase diagram modelling allow the reaction history among accessory minerals to be linked with the reconstructed P–T evolution. The partial dissolution and replacement by rare earth element‐accessory minerals (apatite–allanite–epidote) occurred during a fluid‐present decompression at 510 ± 35 °C. These conditions represent the last stage of a metamorphic history consisting of a thermal metamorphic peak at 575 °C and 7 kbar, followed by the peak pressure stage occurring at 520 °C and 8 kbar. An anticlockwise P–T path or two clockwise P–T loops can fit the above P–T constraints. The former path may be related to a context of late Variscan strike‐slip‐dominated exhumation with minor Tertiary (Alpine‐related) reworking and fluid infiltration, while the latter requires an Oligocene–Miocene fluid‐present tectono‐metamorphic overprint on the Variscan paragenesis.  相似文献   

Anisotropic charged analogue of Heintzmann’s solution     

N. Pradhan  Neeraj Pant 《Astrophysics and Space Science》2015,356(1):67-74

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Modeling quasar central engine as a relativistic radiating star     

Ksh. Newton Singh  Neeraj Pant 《Astrophysics and Space Science》2015,355(1):171-177

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